ScienceWeek

SCIENCE-WEEK

A Weekly Email Digest of the News of Science

A journal devoted to the improvement of communication
between the scientific disciplines, and between scientists,
science educators, and science policy-makers.

April 6, 2001 -- Vol. 5 Number 14

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A paradox is truth standing on its head to
attract attention.
-- Nicholas Falletta

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=-=-=-=-=-=-=-=-=
Section 1
=-=-=-=-=-=-=-=-=

Contents of this Issue (Full reports in Section 2):

1. ORIGIN OF LIFE:
DIFFERENTIAL ADSORPTION OF NUCLEIC ACID BASES
The idea that the adsorption of organic substances onto inorganic
surfaces might have been involved in the origin of life on Earth
was discussed 50 years ago by the crystallographer J.D. Bernal
(1901-1971). More recently, in 1982, the chemist A.G. Cairns-
Smith suggested that life developed from crystals, with life
originating from replication of clay crystals. Researchers now
report they have determined the equilibrium adsorption isotherms
for the nucleic acid purine and pyrimidine bases dissolved in
water on the surface of crystalline graphite. The markedly
different adsorption behavior of the bases comprises an elution
series: guanine > adenine > hypoxanthine > thymine > cytosine >
uracil. The authors propose that such differential properties
were relevant to the prebiotic chemistry of the bases, and may
have influenced the composition of the primordial genetic
architecture.
(S.J. Sowerby et al: Proc. Natl. Acad. Sci. US 30 Jan 01 98:820)

2. MEDICAL BIOLOGY:
RESULTS OF TRANSPLANTATION THERAPY IN PARKINSON'S DISEASE
In recent years, many researchers have expressed hope that
transplantation cell therapy would prove effective in the
treatment of Parkinson's disease. A new report, however, suggests
there is much work yet to be done. Researchers have now conducted
a double-blind, sham-surgery-controlled trial of implantation of
embryonic dopamine neurons in patients with severe Parkinson's
disease in order to determine whether the implanted neurons
survived and led to improvement in the symptoms and signs of
Parkinson's disease and to examine the effect of age on the
efficacy of implantation. The authors report that transplants of
embryonic dopamine neurons survive in the putamen of patients
with Parkinson's disease, regardless of age. Transplantation had
some benefits in patients 60 years old and younger, but not in
older patients. The occurrence of late post-treatment impairment
of voluntary movement (dystonia and dyskinesia) indicates that
the surgical technique may need further refinement.
(C.R. Freed et al: New England J. Med. 8 Mar 01 344:710)

3. MEDICAL BIOLOGY: ON CHEMOKINES AND BREAST CANCER METASTASIS
Researchers report that the chemokine receptors CXCR4 and CCR7
are highly expressed in human breast cancer cells, malignant
breast tumors, and metastases, and that the known ligands of
these receptors exhibit peak levels of expression in organs
representing the first destination of breast cancer metastasis.
In breast cancer cells, signaling via CXCR4 and CCR7 mediates
actin polymerization and pseudopodia formation, and subsequently
induces chemotactic and invasive responses. In vivo, neutralizing
the interactions of the ligands of these chemokine receptors
significantly impairs metastasis of breast cancer cells to
regional lymph nodes and lung. Malignant melanoma, which has a
similar metastatic pattern as breast cancer but also a high
incidence of skin metastasis, shows high expression levels of the
chemokine receptor CCR10 in addition to CXCR4 and CCR7. The
authors suggest their findings indicate that chemokines and their
receptors have a critical role in determining the metastatic
destination of tumor cells.
(A. Mueller et al: Nature 1 Mar 01 410:50)

4. PARTICLE PHYSICS: ON MUONS AND PRECESSION
The particle now called the "muon" was discovered in 1936 by Carl
Anderson (1905-1991), who discovered the particle while studying
cosmic rays. The muon is a negatively-charged lepton similar to
the electron except that its mass is approximately 207 times the
electron mass. The muon has a average lifetime of 2.2
microseconds, and decays into an electron, a neutrino, and an
antineutrino. Researchers report the latest result of a study of
the behavior of muons in a magnetic field. The measurement of the
magnetic moment of the positive muon has an uncertainty of only
one part per billion, three times better than the existing value.
Moreover, the result deviates in a small but important way from
the predictions of the standard model. At this level of
precision, the behavior of the muon becomes sensitive to the
existence of new heavy particles, such as those required by
supersymmetry, and the measurements take on a special theoretical
importance. (Frank Wilczek: Nature 1 Mar 01 410:28)

5. PLANETARY SCIENCE:
ON BIOSIGNATURES IN THE MARTIAN METEORITE ALH84001
Researchers report magnetite crystals in the Martian meteorite
ALH84001 to be both chemically and physically identical to
terrestrial, biogenically precipitated, intracellular magnetites
produced by magnetotactic bacteria. Specifically, both magnetite
populations are single domain and chemically pure crystals, and
exhibit a unique crystal form the authors call "truncated hexa-
octahedral". The authors suggest that unless there is an unknown
and unexplained inorganic process on Mars that is conspicuously
absent on the Earth and forms truncated hexa-octahedral
magnetites, these magnetite crystals in the Martian meteorite
ALH84001 were likely produced by a biogenic process and
constitute evidence of the oldest life yet found. In a contiguous
paper, researchers report the presence of magnetite crystal
chains in the ALH84001 meteorite is incompatible with a
nonbiological origin.
(K.L. Thomas-Keprta et al:
Proc. Natl. Acad. Sci. US 27 Feb 01 98:2164)
(E.I. Friedmann et al: 
Proc. Natl. Acad. Sci. US 27 Feb 01 98:2176)

6. PHYSICAL CHEMISTRY:
DYNAMIC BEHAVIOR OF WATER IN SOLVATION SHELLS
Two reports advancing our understanding of the physical chemistry
of aqueous solutions have appeared, one report on the dynamics of
hydration shells, and the other report of the dynamics of water
autoionization. In one laboratory researchers report the direct
measurement of the dynamics of water molecules in the solvation
shell of an ion in aqueous solution. The evidence indicates the
hydrogen-bond dynamics of water molecules solvating a chloride,
bromide, or iodide anion is slow compared with pure liquid water,
suggesting that the aqueous solvation shells of these ions are
rigid. This rigidity can play an important role in the overall
dynamics of chemical reactions in aqueous solution. Another
laboratory group reports they have revealed the autoionization
mechanism of water with an ab initio molecular dynamics model.
The authors report they identify the rare fluctuations in
solvation energies that destabilize an oxygen-hydrogen bond.
(M.F. Kropman and H.J. Bakker: Science 16 Mar 01 291:2118)
(P.L. Geissler et al: Science 16 Mar 01 291:2121)

7. IN FOCUS: 1905: EINSTEIN'S ANNUS MIRABILIS

8. FROM THE SCIENCEWEEK ARCHIVE:
CONTROL OF INFECTIOUS DISEASES 1900-1999


=-=-=-=-=-=-=-=-=
Section 2
=-=-=-=-=-=-=-=-=

1. ORIGIN OF LIFE:
DIFFERENTIAL ADSORPTION OF NUCLEIC ACID BASES
     The idea that the adsorption of organic substances onto
inorganic surfaces might have been involved in the origin of life
on Earth was discussed 50 years ago by the crystallographer J.D.
Bernal (1901-1971). More recently, in 1982, the chemist A.G.
Cairns-Smith suggested that life developed from crystals, with
life originating from replication of clay crystals. In the
Cairns-Smith model, life began through the influence of natural
selection on the growth of inorganic crystals, with clay
structures the first carriers of genetic information. Replication
occurred by the accidental detachment of layers in the clay
lattice, the layers serving as nuclei for the growth of new
daughter molecules. Later, organic chemicals were incorporated
into the structure of the replicating crystallites, and
competition favored those systems that were more adaptable
because they used organic molecules to carry out their functions.
Nucleic acids (RNA and DNA) then evolved, taking over as the
basic information repository making up the genes of the organism,
and under the pressure of natural selection, the original clay-
mineral component was dispensed with entirely.
     In general, the term "RNA world hypothesis" refers to the
concept that RNA nucleotide sequences with catalytic and
self-replicating capabilities predated catalytic protein systems
in prebiological epochs. It is believed, however, that the
nucleotides constituting RNA were scarce on early Earth, so that
RNA-based life must have acquired the ability to synthesize RNA
nucleotides from simpler and more readily available precursors
such as sugars and nucleic acid bases. Apparently plausible
prebiotic synthesis routes have been proposed for sugars, sugar
phosphates, and the four RNA bases, but the coupling of these
molecules into nucleotides, specifically pyrimidine nucleotides,
poses a challenge to the RNA world hypothesis.
... ... S.J. Sowerby et al (4 authors at 2 installations, SE DE)
present a study of the adsorption of nucleic acid bases on
crystalline graphite, the authors making the following points:
     1) The authors point out that the purine and pyrimidine
bases, the coding elements of nucleic acids, are products of
supposed prebiotic chemistries that invoked cyanide and have been
synthesized in reactions that also yield amino acids. The
apparent prebiotic availability of these compounds supports the
RNA World hypothesis for the origin of life on Earth, which
proposes that the first living system consisted of one or more
polymers of catalytic RNA capable of self-replication that
subsequently evolved the ability to encode more versatile peptide
catalysts. RNA can act as both information carrier and catalyst,
and in the laboratory, RNA can be coerced into various catalytic
functions through directed Darwinian evolution (directed natural
selection).
     2) The authors point out that the adsorption of organic
molecules has long been considered a relevant prebiotic process.
The purine and pyrimidine bases adsorb spontaneously from aqueous
media onto inorganic solids and have been observed on the
surfaces of graphite, MoS(sub2), crystalline gold, and clays.
Scanning probe microscopy studies have shown that the nucleotide
bases are planar-arranged on these surfaces like jigsaw puzzle
pieces, and are stabilized by van der Waals interactions with the
underlying surface and by hydrogen bonds between adjacent
molecules, a configuration originally postulated in 1987 on the
basis of thermodynamic measurements made at the mercury-water
interface. The hydrogen bonds between the bases are drawn from a
discrete set of possible interactions, including those of Watson-
Crick pairing found in nucleic acids. The monolayers can be
likened to nucleic acid molecules because the sugar-phosphate
scaffold also supports the arrangement of bases. Each position in
the scaffold can be mapped to the next by a simple translation
operation, which resembles a major property of the underlying
crystal.
     3) The authors report they have determined the equilibrium
adsorption isotherms for the nucleic acid purine and pyrimidine
bases dissolved in water on the surface of crystalline graphite.
The markedly different adsorption behavior of the bases comprises
an elution series: guanine > adenine > hypoxanthine > thymine >
cytosine > uracil. The authors propose that such differential
properties were relevant to the prebiotic chemistry of the bases,
and may have influenced the composition of the primordial genetic
architecture.
-----------
S.J. Sowerby et al: Differential adsorption of nucleic acid
bases: Relevance to the origin of life.
(Proc. Natl. Acad. Sci. US 30 Jan 01 98:820)
-------------------
Summary by SCIENCE-WEEK http://scienceweek.com 6Apr01
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
ORIGIN OF LIFE: PRODUCTION OF PEPTIDES ON INORGANIC SURFACES
The primordial process responsible for the activation of amino
acids and the formation of peptides under primordial conditions
is one of the great riddles of the origin of life. ... ... Huber
and Wachterschauser (Technische Universitat Munchen, DE) now
report that in experiments modeling volcanic or hydrothermal
settings, amino acids were converted into their peptides by use
of coprecipitated (Ni,Fe)S and CO in conjunction with H(sub2)S
(or CH(sub3)SH) as a catalyst and condensation agent at 100
degrees centigrade and pH 7 to 10 under anaerobic aqueous
conditions. The amino acids involved in the experiments were
phenylalanine, tyrosine, and glycine. The authors suggest their
results demonstrate that amino acids can be activated under
geochemically relevant conditions, and that the results support a
thermophilic origin of life with a primordial surface metabolism
on transition metal sulfide minerals. They further suggest that a
continuously recycling library of peptides was generated on the
surfaces of a library of (Fe,Ni)S structures, and that the
results raise the possibility that CO and Ni had a much greater
role in the primordial metabolism than in any of the known extant
metabolisms. They point out that all known extant organisms are
found in habitats with low activities of CO and Ni, and they
suggest this could explain why organisms resorted to the
formation of CO from CO(sub2) and to the elimination of nickel
from many enzymes.
QY: Gunter Wachterschauser, Tal 29, D-80331 Munchen, DE.
(Science 31 Jul 98 281:670) (Science-Week 28 Aug 98)
-------------------
Related Background:
ORIGIN OF LIFE: THE PRESENT STATUS OF CHEMICAL THEORY
The essential question involved in the origin of what we call
life is how can order arise from disorder? At the present time,
this question is approached on two fronts: 1) study of the
principal features of self-organizing systems, systems in which
order does arise from disorder, systems in which order is indeed
demanded from disorder on thermodynamic grounds; and 2) study of
the detailed chemistry of such systems, the chemistry of
organization and the chemistry of components. In the case of
components, it is essential that appropriate self-organizing
components exist in the first place if they are to become self-
organized, and such candidate components are thus the focus of
much chemical research in this area. In 1953, the chemist Stanley
Miller reported what soon became a famous experiment. To water
under a gas mixture of methane, ammonia, and hydrogen, he added
an electrical discharge. After one week of continuous electrical
discharge, he found that a number of important biological
molecules, including amino acids, had been formed. Miller
proposed his experiment as a model for the conditions under which
the essential compounds necessary for life originated . The
Miller experiment was a watershed, and it began a new era of
experimentation and analysis of possible primordial components.
Coupled with this, were the new important discoveries by
astrophysicists of the presence of organic molecules in the
interstellar medium and in meteorites. In a review of origin of
life theories, P. Radetsky (Univ. of California Santa Cruz, US)
points out that the Miller theory is no longer the consensus
theory, that contemporary geologists believe the primordial
atmosphere consisted primarily of carbon dioxide and nitrogen,
which are less reactive than the gases in the Miller experiment,
and that the field is currently embroiled in controversy fueled
for the most part by an absence of hard fact.
QY: Peter Radetsky, Univ. of California Santa Cruz 408-429-4008
(Earth February 1988) (Science-Week 2 Jan 98)
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
BIOCHEMICAL EVOLUTION: POLYMERIZATION ON MINERAL SURFACES
J. Smith (University of Chicago, US) proposes a conceptual
framework for consideration of the origins of replicating
biopolymers. Although extended Darwinian natural selection
coupled with Mendel-Watson-Crick genetic inheritance/mutation
provides a plausible framework for integrating the patchy
paleontological record with the increasingly complex biochemical
zoo of the present Earth, the actual chemical beginning of "life"
still poses major challenges. How could the first replicating and
energy-supplying molecules have been assembled from simpler
materials that were undoubtedly available on the early proto-
continents? Catalysis at mineral surfaces might generate
replicating biopolymers from simple chemicals supplied by
meteorites, volcanic gases, and photochemical gas reactions. But
many ideas are implausible in detail because the proposed mineral
surfaces strongly prefer water and other ionic species to organic
ones. The molecular sieve silicalite (Union Carbide; = Al-free
Mobil ZSM-5 zeolite) has a 3-dimensional 10-ring channel system
whose electrically neutral silicon-oxide surface strongly adsorbs
organic species over water, and the ZSM-5 type zeolite mutinaite
has recently been found in Antarctica. The author proposes that
zeolites with similar structures may have existed on the surface
of Earth during its life-origin phase, and that polymer migration
along weathered silicic surfaces of micrometer-wide channels of
feldspars might have led to assembly of replicating catalytic
biomolecules and perhaps primitive cellular organisms. The author
suggests that weakly metamorphosed Archaean rocks might retain
microscopic clues to the proposed mineral adsorbent/catalysts,
and that other frameworks are also possible, including ones with
laevo/dextro one-dimensional channels.
QY: Joseph V. Smith: smith@geol.uchicago.edu
(Proc. Natl. Acad. Sci. US 31 Mar 98 95:3370)
(Science-Week 8 May 98)
For more information: http://scienceweek.com/swfr.htm

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=

2. MEDICAL BIOLOGY:
RESULTS OF TRANSPLANTATION THERAPY IN PARKINSON'S DISEASE
     Parkinson's disease (also called Parkinson disease) is a
slowly progressive degenerative central nervous system disorder,
characterized by decreased movement, muscular rigidity, resting
tremor, and postural instability.
     The disease was first described by James Parkinson (1755-
1824) in 1817 and is now known to be associated with degeneration
of one or more specific regions of the brain (dopaminergic neuron
groups such as the *substantia nigra) and resultant loss of
*neural projections to several important brain centers.
     Dopaminergic neurons are nerve cells that use dopamine as a
*neurotransmitter substance. Dopamine is found in several major
areas of the brain, and it is the degeneration of so-called
dopamine neurons that is apparently involved in Parkinson's
disease.
     One must distinguish "parkinsonism" from Parkinson's
disease. Parkinsonism is a syndrome (a complex of symptoms; in
this context, a complex of various movement symptoms) that may be
caused by Parkinson's disease, but which may also be caused by
infectious, vascular, pharmacological, toxic, metabolic,
structural, and various degenerative disorders. In other words,
not every individual with parkinsonism has Parkinson's disease.
The major differentiating characteristic is the response to the
drug "*levodopa", which is converted by the body into dopamine.
Individuals with parkinsonism who respond to levodopa treatment
receive a diagnosis of Parkinson's disease.
     At the present time, Parkinson's disease is the 4th most
common neurodegenerative disease of the elderly. It affects
approximately 1 percent of people older than 65 years, and 0.4
percent of people between 40 and 65 years.
     In recent years, many researchers have expressed hope that
transplantation cell therapy would prove effective in the
treatment of this disease. A new report, however, suggests there
is much work yet to be done.
... ... C.R. Freed et al (12 authors at 5 installations, US)
present a study of transplantation cell therapy in the treatment
of Parkinson's disease, the authors making the following points:
     1) The authors point out that after several years of
treatment with levodopa and other drugs, motor disturbances
ranging from decreased spontaneous movement (bradykinesia) to
excessive muscular movements (hyperkinesia) develop in many
patients with Parkinson's disease. No drug therapy has eliminated
these disturbances. However, the implantation of embryonic
dopamine neurons into the brain may improve motor control, and
the authors and others have reported that transplanted dopamine
neurons survive, and that patients may have progressive clinical
improvement over a period of three to four years. All these
studies were "unblinded", and the number of patients in each
study was small.
     2) The authors report they have now conducted a double-
blind, sham-surgery-controlled trial of implantation of embryonic
dopamine neurons in patients with severe Parkinson's disease in
order to determine whether the implanted neurons survived and led
to improvement in the symptoms and signs of Parkinson's disease
and to examine the effect of age on the efficacy of implantation.
The study involved 40 patients, 34 to 75 years of age, who had
severe Parkinson's disease (average duration of disease 14
years), the patients randomly assigned to receive a transplant of
nerve cells or undergo only sham surgery. All patients were
followed in a double-blind manner for one year. In the transplant
recipients, cultured midbrain (mesencephalic) tissue from four
embryos were implanted into the *putamen bilaterally. In the
patients who underwent sham surgery, holes were drilled in the
skull but the external membrane covering the brain (the "dura")
was not penetrated.
     3) The authors report that transplants of embryonic dopamine
neurons survive in the putamen of patients with Parkinson's
disease, regardless of age. Transplantation had some benefits in
patients 60 years old and younger, but not in older patients. The
occurrence of late post-treatment impairment of voluntary
movement (dystonia and dyskinesia) indicates that the surgical
technique may need further refinement.
... ... In a commentary on the above work (headlined as a journal
"editorial"), G.D. Fischbach and G.M. McKhannn (National
Institutes of Health, US) make the following points:
     1) The authors (Fischbach and McKhann) suggest that to reach
a consensus about therapies involving the implantation of tissue
or cells in Parkinson's disease, we must learn more about the
circuits within the *basal ganglia and their extrinsic
connections. Transplanted dopaminergic neurons are said to
"innervate" targets in the putamen, but this term is used
loosely, since precise measures of synaptic function are not
available. We do not know how dopamine affects the firing of
individual neurons or the function of particular circuits.
     2) The authors (Fischbach and McKhann) suggest it is
unlikely, for both practical and biological reasons, that
transplantation of fragments of embryonic tissue will be the
therapy of the future. In the present study, tissue from the
midbrain of four embryos was injected on each side of the brain
in each patient. Parkinson's disease is not a rare disorder:
estimates of prevalence in the US range between 700,000 and 1
million. The number of fetuses required would be staggering, even
if only a small proportion of the patients were to receive
transplants. Moreover, heterogeneity within tissue fragments is a
major barrier to reproducibility.
     3) The authors (Fischbach and McKhann) state: "*Immortalized
cell lines are our best hope for the development of cells as
realistic and reliable therapeutic agents. The use of cell lines
derived from pluripotent human fetal or embryonic *stem cells
poses profound ethical questions." Finally, the authors conclude:
"The brain is a most complex structure, so incremental results on
the way to cures are to be welcomed rather than dismissed as less
than perfect."
-----------
C.R. Freed et al: Transplantation of embryonic dopamine neurons
for severe Parkinson's disease.
(New England J. Med. 8 Mar 01 344:710)
QY: Curt R. Freed: curt.freed@uchsc.edu
-----------
G.D. Fischbach and G.M. McKhann: Cell therapy for Parkinson's
disease.
(New England J. Med. 8 Mar 01 344:765)
QY: Gerald D. Fischbach: National Institute of Neurological
Diseases and Stroke, Bethesda, MD 20892 (US).
-----------
Text Notes:
... ... *substantia nigra: A large cell mass at the base of the
brain that receives input from a number of cortical and
subcortical structures ("cortical" refers to cerebral cortex).
... ... *neural projections: In this context, the term
"projection" refers to arrays of nerve fibers originating in one
location and transmitting activity to one or more other
locations.
... ... *neurotransmitter substance: Neurotransmitters are
chemical substances released at the terminals of nerve axons in
response to the propagation of an impulse to the end of that
axon. The neurotransmitter substance diffuses into the synapse,
the junction between the presynaptic nerve ending and the
postsynaptic neuron, and at the membrane of the postsynaptic
neuron the transmitter substance interacts with a receptor.
Depending on the type of receptor, the result may be an
excitatory or an inhibitory effect on the postsynaptic nerve
cell.
... ... *levodopa: (L-dopa) The biologically active form
of "dopa", which is converted into dopamine. Dopamine = 3,4-
dihydroxyphenylethylamine. Dopa = 3,4-dihydroxypheynylalanine.
... ... *putamen: One of the 3 major clusters of nerve cells
("nuclei") that make up the *basal ganglia.
... ... *basal ganglia: The term "basal ganglia" refers to a
group of nuclei lying deep in the subcortical white matter of the
frontal lobes, these nuclei involved in the organization of motor
behavior. In this context, a "nucleus" is a cluster of nerve
cells.
... ... *Immortalized cell lines: Immortalized cell lines are
tissue culture cells with unlimited replicative capacity. Such
cell lines can be maintained in the laboratory to serve as an
effectively unlimited reservoir of new cells, in contrast to
cells from fetal tissue, whose supply is limited.
... ... *stem cells: In general, "stem cells" are precursor
cells, cells that have not yet differentiated into specialized
cells. The early embryo consists mostly of stem cells. A
"totipotent stem cell" is a stem cell that has the capacity to
differentiate into any kind of tissue cell; a "pluripotent stem
cell" is a stem cell that has the capacity to differentiate into
several different kinds of tissue cell.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 6Apr01
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
ON NEW SURGICAL APPROACHES TO PARKINSON'S DISEASE
... Pat Phillips (_J. Amer. Med. Assoc._) reviews current work on
surgical approaches to the disease presented at a recent (July
1999) international congress, the author making the following
points:
     1) Deep brain stimulation and cell transplantation are new
techniques of great interest to clinicians involved in the
surgical treatment of patients with Parkinson's disease,
particularly in the treatment of those patients in more advanced
stages of the disease. Apparently, one factor responsible for the
resurgence of interest in surgical treatment is the limited
success of medical therapy with the drug levodopa. Other factors
are safer and more accurate surgical techniques, improvements in
microelectrode recording techniques during surgery, and advances
in neuroimaging (i.e., imaging of gross brain structures), all of
which combine to allow surgeons to reach their targets with
greater accuracy and less likelihood of adverse effects.
     2) Concerning deep brain stimulation, at specialized centers
in Europe and North America, high-frequency deep brain
stimulation of 3 different targets in the brain has been the
focus of an apparently promising surgical approach. The targets
are the *subthalamic nucleus, the globus pallidus internus, and
the ventral intermediate nucleus. The procedure involves
implanting an electrode deep into one of the 3 target areas using
a *stereotactic technique and microelectrode guidance. The
microelectrodes provide recordings of local neuron activity that
enable the neurosurgeon to detect typical electrical activity
patterns of cell group targets or of adjacent structures to be
avoided.
     3) Concerning *cell transplantation, fetal cell
transplantation has been performed worldwide on approximately 360
patients in 17 clinical centers, and preliminary evidence
apparently indicates that the procedure can be done safely,
reliably, and reproducibly. However, this approach has been
limited because of societal concern about the use of fetal
tissue, and because of technical surgical issues, including
identification of the best target area for transplantation. Some
neurosurgeons believe it is unlikely that fetal tissue
transplantation will ever by performed outside of a small number
of clinical installations, and that instead fetal tissue
transplantation is likely to serve as the standard for assessment
of protocols using non-fetal tissue transplantation. Researchers
are currently experimenting with a variety of non-fetal cells for
use in transplantation. Retinal cells, for example, secrete
dopamine and neurotrophic factors, and are candidates for
transplantation research.
-----------
Pat Phillips: New surgical approaches to Parkinson disease.
(J. Amer. Med. Assoc. 22/29 Sep 99 282:1117)
QY: QY: Pat Phillips [jama@ama-assn.org]
-----------
Text Notes:
... ... *substantia nigra: See main report.
... ... *neural projections: See main report.
... ... *neurotransmitter substance: See main report.
... ... *levodopa: See main report.
... ... *subthalamic nucleus, the globus pallidus internus, and
the ventral intermediate nucleus: In this context, a "nucleus" is
a cluster of nerve cells in the brain. The term "basal ganglia"
refers to a group of nuclei lying deep in the subcortical white
matter of the frontal lobes, these nuclei involved in the
organization of motor behavior. The globus pallidus is one of the
major components of the basal ganglia, and the subthalamic
nucleus is often considered to be part of this group. The ventral
intermediate nucleus is a nucleus in the thalamus, a major
subcortical assembly of nuclei, and the ventral intermediate
nucleus is also involved in the modulation of motor control. In
general, the "modulation" of motor control in the nervous system,
like the modulation of the motions of a complex machine, depends
in a major way on feedback control circuits. In the human nervous
system, the motor control feedback loops are widespread in the
brain, involving a number of major structures, and dysfunctions
in any local parts of the various loops can have serious
consequences.
... ... *stereotactic technique: A stereotaxic device is a rigid
metal coordinate frame into which the head of a patient is fixed
so that microscale positioning of electrodes at any particular
coordinate position can be effected without displacement caused
by movement of the patient.
... ... *cell transplantation: In general, the cell
transplantation procedures in this context are at the present
time concerned with the transplantation of cells that secrete
dopamine, the objective to increase the working concentration of
dopamine in relevant structures. The transplanted cells are thus
drug delivery vehicles rather than replacements for dysfunctional
neurons. Fetal cell transplantation, however, offers the
possibility of transplantation of primitive cells (stem cells)
that will differentiate into working new neurons that supplant
defective adult neurons.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 22Oct99
For more information: http://scienceweek.com/swfr.htm

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=

3. MEDICAL BIOLOGY: ON CHEMOKINES AND BREAST CANCER METASTASIS
     Although the term "metastasis" is usually used in connection
with the spread of cancer, the term actually refers to the spread
of any disease from an original location to other tissues.
Concerning cancer, what is important is that malignant cells have
the ability to invade healthy body tissues with very little of
the restrictions that normally constrain non-malignant cells.
Following a nearby invasion, a number of malignant cells may
detach from the initial ("primary") tumor and invade a body
cavity (e.g., abdominal or thoracic) or enter the blood or lymph
system. This latter condition can lead to widespread metastasis,
with those malignant cells that survive in the blood or lymph
invading adjacent body tissues and establishing secondary tumors.
In the final stage of metastasis, the secondary tumors become
vascularized, with new networks of blood vessels providing
nutrients for the further growth of these secondary tumors. 
(Any macroscopic new tissue, whether resulting from repairing a
wound, normal growth, or tumors, requires a blood supply, with
blood vessel growth in tumors initiated by chemical triggers
called "tumor angiogenesis factors".) In all stages of
metastasis, malignant cells must resist the antitumor defenses of
the body in order to survive.
     A common popular misconception is that migration of tumor
cells is a late development in the history of a tumor. On the
contrary, almost from inception, a tumor may shed cells into the
circulation. From animal models, it is estimated that a 1-
centimeter tumor sheds more than 1 million cells a day into the
venous circulation. In animals, circulating tumor cells usually
die as a result of intravascular trauma: the longer a tumor cell
spends in the circulation, the greater the chance of its death.
The probability that a circulating tumor cell will become a
metastatic tumor is estimated to be less than 10^(-6).
     Experiments suggest that metastasis is not a random event,
and that the primary tumor may regulate the growth of metastatic
tumors, and removal of the primary tumor often results in
accelerated growth of the metastases.
     The term "cytokine" refers to any substance that promotes
cell growth and cell division. As a promoter of cell growth and
division, a cytokine acts as a messenger to cells, and the
transmission of the message requires a binding of the cytokine 
molecule to a cytokine-specific receptor on the cell surface.
"Chemokines" are a type of cytokine, the chemokines in general
comprising several groups of polypeptides with molecular weights
in the range 8 to 10 kilodaltons. The chemokines are chemokinetic
and chemotactic, normally stimulating white blood cell
(leukocyte) attraction and movement.
     The G-proteins are a family of signal-coupling proteins that
act as intermediaries between activated cell  receptors and
effectors, for example, the transduction of hormonal signals from
the cell surface to the cell interior. The G-protein is
apparently embedded in the cell membrane with parts exposed on
the outside surface and inside surface. The outside moiety is
activated by the first messenger, and the inside moiety activates
the second messenger, the G-protein thus acting as a
trans-membrane signal transducer.
     Endothelial cells are flat cells forming a layer lining
blood vessels, lymphatic vessels, the heart, etc., and when
migrating tumor cells circulate in blood or lymph, they must
adhere to endothelial cells before they can pass through the
walls of blood or lymph vessels and into the adjacent tissues.
The interaction of migrating tumor cells and endothelial cells is
thus of considerable importance in metastasis. So-called
"adhesion molecules" are molecules expressed on the surface of a
cell that mediate the adhesion of the cell to other cells or
to the extracellular matrix. Adhesion molecules bind to receptors
that are classed collectively as "integrins".
     In general, "hematopoietic cells" (hemopoietic cells) are
any cells involved in the formation of blood cells.
     In this context, a "growth factor" is any specific substance
that must be present in a culture medium for multiplication of
the cultured cells to occur. Certain growth factors have been
identified as cytokine proteins (peptide hormones) that stimulate
the growth and division of target cells by binding to cell
membrane receptors. "Transforming growth factors" are cytokine
growth factors that produce in target cells some of the growth
characteristics of cancer cells.
     The term "actin" refers to a family of ubiquitous structural
proteins present in all cells with a nucleus (eukaryote cells),
and the term "cytoskeleton" refers to the quasi-rigid matrix that
among other things determines cell shape. Both actin and the
cytoskeleton are of considerable importance in the production and
movements of pseudopods, the protoplasmic extensions involved in
the amoeba-like movements of migrating cells.
... ... A. Mueller et al (14 authors at 6 installations, US, DE,
MX) report new evidence of the involvement of chemokine receptors
in breast cancer metastasis, the authors making the following
points:
     1) The authors point out that metastasis is the result of
several sequential steps and represents a highly organized, non-
random, and organ-selective process. Although various molecules
have been implicated in the metastasis of breast cancer, the
precise mechanisms determining the directional migration and
invasion of tumor cells into specific organs remains to be
established. 
     2) The authors point out that through their interaction with
G-protein coupled receptors, the secreted proteins called
chemokines induce cytoskeletal rearrangement, firm adhesion to
endothelial cells, and directional migration. Chemokines act in a
coordinated fashion with cell surface proteins, including
integrins, to direct the specific homing of various subsets of
hematopoietic cells to specific anatomical sites. Breast cancer
is characterized by a distinct metastatic pattern involving the
regional lymph nodes, bone marrow, lung, and liver, with tumor
cell migration and metastasis sharing many similarities with
leukocyte trafficking, which is critically regulated by
chemokines and their receptors.
     3) The authors report that the chemokine receptors CXCR4 and
CCR7 are highly expressed in human breast cancer cells, malignant
breast tumors, and metastases, and that the known ligands of
these receptors exhibit peak levels of expression in organs
representing the first destination of breast cancer metastasis.
In breast cancer cells, signaling via CXCR4 and CCR7 mediates
actin polymerization and pseudopodia formation, and subsequently
induces chemotactic and invasive responses. In vivo, neutralizing
the interactions of the ligands of these chemokine receptors
significantly impairs metastasis of breast cancer cells to
regional lymph nodes and lung. Malignant melanoma, which has a
similar metastatic pattern as breast cancer but also a high
incidence of skin metastasis, shows high expression levels of the
chemokine receptor CCR10 in addition to CXCR4 and CCR7. The
authors suggest their findings indicate that chemokines and their
receptors have a critical role in determining the metastatic
destination of tumor cells.
     4) The authors conclude: "Our findings are probably not
unique to breast cancer. Other tumor entities of hematopoietic
and non-hematopoietic origin... express functionally active
chemokine receptors that mediate tumor cell migration in vitro.
Our results in breast cancer and malignant melanoma suggest that
malignant cells, in general, express distinct and non-random
patterns of chemokine receptors... Currently, intense efforts are
underway to identify small-molecule antagonists for many
chemokine receptors. We propose that small molecule antagonists
of chemokine receptors... may be useful to interfere with tumor
progression and metastasis in tumor patients."
... ... In a commentary on the above report, Lance A. Liotta
(National Institutes of Health, US) makes the following points:
     1) It was already recognized in the 19th century that
secondary tumors are seeded by cells released from the original
tumor, the seeding cells ferried around the body in the lymphatic
and blood circulations. Autopsies have revealed that some organs
have large numbers of secondary tumors, while other organs have
relatively few. The basis for this bias has been a puzzle,
because the pattern cannot be explained simply by differences in
blood and lymph flow in different organs.
     2) The author points out that three major theories have been
proposed to explain the bias of metastases towards certain
organs, but animals studies have failed to reveal which theory is
correct. The three theories are as follows:
... ... a) Tumor cells leave the blood and lymphatic systems to
the same extent at all organs, but multiply only in those organs
that have the appropriate growth factors.
... ... b) The endothelial cells that line blood vessels in
target organs express adhesion molecules that cause circulating
tumor cells to stop circulating and invade those organs.
... ... c) The chemokine theory holds that organ-specific
attractant molecules enter the circulation, stimulating the
migrating tumor cells to invade the walls of blood vessels and
enter the organs.
     The author (Liotta) points out that there is evidence to
support all three theories, but the mediator molecules -- whether
they be growth factors, adhesion molecules, or chemoattractants
-- have remained unknown. "Now, however, Mueller et al have
identified chemoattractants in target organs and chemoattractant
receptors on tumor cells, providing molecular support for the
chemoattraction theory. Moreover, [they] have shown that they can
block metastasis in animals by blocking the receptors."
-----------
A. Mueller et al: Involvement of chemokine receptors in breast
cancer metastasis.
(Nature 1 Mar 01 410:50)
QY: Albert Zlotnik: azlotnik@eosbiotech.com
-----------
Lance A. Liotta: An attractive force in metastasis.
(Nature 1 Mar 01 410:24)
QY: Lance A. Liotta: lance@helix.nih.gov
-------------------
Summary by SCIENCE-WEEK http://scienceweek.com 6Apr01
For more information: http://scienceweek.com/swfr.htm

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=

4. PARTICLE PHYSICS: ON MUONS AND PRECESSION
     In this context, the term "magnetic moment" refers to the
ratio between the maximum torque exerted on a moving charge in a
magnetic field and the strength of that field. If the charge is
spinning, in addition to the magnetic moment associated with the
translocation movement of the charge, there is also a spin
magnetic moment associated with the rotation.
     The term "precession" refers to a form of motion that occurs
when a torque is applied to a spinning (rotating) body in such a
manner that the torque changes the axis of rotation.
     "Cosmic rays" are high-energy particles falling on the Earth
from space, the particles traveling at velocities close to the
velocity of light. So-called "primary cosmic rays" consist of the
nuclei of the most abundant elements, plus electrons, positrons,
neutrinos, and gamma-ray photons. The particles energies are
enormous, ranging from 10^(8) to 10^(20) electron volts, and as
these particles enter the atmosphere of Earth they collide with
oxygen and nitrogen nuclei to produce "secondary cosmic rays".
These secondary cosmic rays consist of elementary particles,
including muons, and gamma-ray photons. A single high-energy
primary particle can produce a large shower of secondary
particles. Before the advent of high-energy accelerators, cosmic
rays were the only source for the study of high-energy particles.
Cosmic rays were discovered by V.F. Hess (1883-1964) during a
balloon flight in 1912, and it is now generally believed that
almost all cosmic rays with energies less than 10^(18) electron
volts originate from within our Galaxy.
     The term "lepton" refers to a class of elementary particles.
Although they are affected by electromagnetic and gravitational
forces, apart from that they are involved only with weak
interactions, acted upon by weak forces but not by strong forces.
The leptons include the electron, the muon, the tau lepton, and
their associated neutrinos. The "weak force" occurs between
leptons (particles without internal structure, e.g., electrons,
muons, neutrinos) and hadrons (particles with internal structure,
e.g., neutrons and protons); In general, the weak force is
responsible for radioactivity.
     The term "quark" refers to a hypothetical fundamental
particle, having charges whose magnitudes are one-third or
two-thirds of the electron charge, and from which the elementary
particles may in theory be constructed.
     In quantum mechanics, "spin" is the intrinsic angular
momentum of a subatomic particle. Spin states are quantized,
multiples of h/2ã, where h = Planck's constant, and each particle
is characterized by a quantum spin number which is the multiple
factor. All subatomic particles can be classified as one of two
types: "fermions" are particles with half-integer values of spin,
and "bosons" are particles with integer values of spin. Leptons
are fermions.
     The "Z boson" is an electrically neutral elementary
particle, discovered in 1983, which is believed to mediate weak
interactions. The "W boson", also discovered in 1983, is of two
types, positively charged or negatively charged, and like the Z
boson it mediates weak interactions.
     The particle now called the "muon" was discovered in 1936 by
Carl Anderson (1905-1991), who discovered the particle while
studying cosmic rays. The muon is a negatively-charged lepton
similar to the electron except that its mass is approximately 207
times the electron mass. The muon has a average lifetime of 2.2
microseconds, and decays into an electron, a neutrino, and an
antineutrino. "Mesons" are a class of elementary particles
involved in strong interactions in the atomic nucleus. Muons were
originally called "mu-mesons" because they were thought to be
mesons, but that idea was eventually abandoned, and muons are now
recognized as leptons. Similar to the electron, which has an
associated positive particle called the "positron", there exists
a positively charged muon.
      The term "virtual particles" refers to particles whose
duration of existence and non-existence is of the order of
quantum fluctuations. Such particles, for example, are considered
to be exchanged between two interacting charged particles. In
another sense, a virtual particle can be considered as the
traveling mass equivalent of a traveling energy perturbation in a
field.
     The term "quantum vacuum" refers to the fact that in quantum
mechanics the vacuum state has a non-zero energy produced by
quantum fluctuations, these quantum fluctuations expressed in the
transient existence of virtual particles.
     In this context, the term "supersymmetry" refers to a
theoretical approach in particle physics in which a special
theoretical symmetry exists between fermions and bosons. In
general, supersymmetry provides a connection between the known
elementary particles of matter (quarks and leptons, which are all
fermions) and the particles that convey the fundamental forces
(which are all bosons). By demonstrating that one type of
particle is in effect a different facet of the other type,
supersymmetry effectively reduces the number of basic types of
particle from two to one. In supersymmetry, every particle has a
sypersymmetric partner: for example, each electron has an s-
electron or "selectron" partner; each muon has an s-muon or
"smuon" partner.
     In this context, the term "standard model" refers to the
combination of two theories of particle physics into a single
framework to describe all interactions of subatomic particles
(except those interactions due to gravity). The two components of
the standard model are "electroweak theory" which describes
interactions via the electromagnetic and weak forces, and quantum
chromodynamics, which is the current theory of the "strong
nuclear force".
... ... Frank Wilczek (Massachusetts Institute of Technology, US)
presents a commentary on recent research on the muon, the author
making the following points:
     1) The author points out that a large team of researchers at
Brookhaven National Laboratory (US) (H. Brown et al:
http://xxx.lanl.gov/abs/hep-ex/0102017) have reported the latest
result of a study of the behavior of muons in a magnetic field.
The measurement of the magnetic moment of the positive muon has
an uncertainty of only one part per billion, three times better
than the existing value. Moreover, the result deviates in a small
but important way from the predictions of the standard model. At
this level of precision, the behavior of the muon becomes
sensitive to the existence of new heavy particles, such as those
required by supersymmetry, and the measurements take on a special
theoretical importance.
     2) In 1948, Julian Schwinger (1918-1994) calculated that the
interaction of electrons with virtual photons modifies their
magnetic moment in a way that quantitatively explains the
experimentally determined magnetic moment of the electron.
Richard Feynman (1918-1988) generalized the calculation, and
using these techniques coupled with the standard model, magnetic
moments can be calculated with extraordinary precision. This also
holds for muons, which are more convenient to study than
electrons because the magnetic moment of the muon is considerably
more sensitive to the effects of heavy particles. The strength of
the magnetic moment of the muon can be measured in a high-quality
magnetic field by monitoring how rapidly it precesses. But to
reach the precision of the Brookhaven experiment requires the
world's largest superconducting magnet and measurements from
billions of muons. The experiment is a tour de force of modern
experimental technique, with the character of the result best
conveyed by providing the numerical value of the measurement: The
new measured value of the magnetic moment of the muon is
2.0023318319 (+- 0000000013).
     3) The above is an experimental value, and the author points
out that theorists have also worked hard to achieve this level of
accuracy. The calculations of theorists must include not only the
effects of virtual photons, but also more complex effects that
arise because the properties of the virtual photons are
themselves modified by interactions with virtual electrons,
muons, tau leptons, and quarks. Also, the small effects of the
virtual versions of much heavier particles (e.g., W and Z bosons)
come into play. With everything considered, there is a mismatch
between theory and experiment of approximately 4 parts per
billion. The most plausible explanations of the discrepancy
(excluding computational or experimental error, or a statistical
fluke) involve adding to the standard model rather than
discarding it. Indeed the simplest explanation is that there is
some new species of virtual particle that has been left out of
the theoretical calculations because its analogue in the real
world is very heavy and unstable and has so far escaped detection
in particle accelerators.
-----------
Frank Wilczek: Precision precession
(Nature 1 Mar 01 410:28)
QY: Frank Wilczek: wilczek@mit.edu
-------------------
Summary by SCIENCE-WEEK http://scienceweek.com 6Apr01
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
PARTICLE PHYSICS: THE SEARCH FOR THE HIGGS BOSON
     The current "Standard Model" in particle physics is
essentially a combination of two theories into a single framework
to describe all interactions of subatomic particles, except those
interactions due to gravity. The two theories are a)
"*electroweak theory", which describes interactions via the
electromagnetic force and the "*nuclear weak force", and b)
*quantum chromodynamics, which is the theory of the *strong
nuclear force. Both of these theories describe the interactions
between particles in terms of the exchange of intermediate
"messenger" particles that have one unit of intrinsic angular
momentum ("spin"). In addition to these force-carrying particles,
the Standard Model encompasses two families of subatomic
particles that comprise matter and that have spins of one-half
unit. These particles are the *quarks and the *leptons, of which
there are 6 varieties ("flavors") of each, related in pairs in
three "generations" of increasing mass. Ordinary matter is built
from the lightest generation; heavier types of quark and lepton
have been discovered in studies of high-energy particle
interactions.
     According to current physics, all particles in nature are
either fermions or bosons, with fermions (always elementary
particles) having half-integer spin (spin-states characterized by
half-integer multiples of Planck's constant divided by 2ã), and
bosons (all other particles) having integer spin (spin-states
characterized by integer multiples of Planck's constant divided
by 2ã). In general, bosons are particles that obey *Bose-Einstein
statistics, and they include photons, *pi mesons, all nuclei
having an even number of particles, and all particles with
integer or zero spin.
     In theory, there are 6 types of quarks, the so-called "top
quark" the most massive and with an electric charge of +2/3. In
1995, two independent groups reported they had found the top
quark, and they established the mass of the top quark as
approximately 176 billion electron volts (176 Gev).
     The "Z particle" is an electrically neutral carrier of the
weak nuclear force that acts upon all known subatomic particles.
The mass of the Z particle (93 GeV) is approximately 100 times
the mass of the proton, and it has a lifetime of only 10^(-25)
seconds. The Z particle is essentially the neutral partner of the
related electrically-charged "W particle". The W particle has
either positive or negative charge, both with a mass of 83 GeV.
Direct evidence for both Z and W particles was obtained in 1983.
     In general, the "Higgs particle" (named after Peter Higgs,
who proposed the particle in 1964, is the carrier of an all-
pervading fundamental field ("Higgs field") hypothesized to endow
elementary particles with mass via interactions of the field with
the elementary particles. The idea is that the variety of masses
of elementary particles arises because the different particles
have different strengths of interaction with the Higgs field. The
Higgs field is without direction (scalar), and the Higgs
particle, which "carries" the Higgs field (the particle
corresponding to perturbations in the Higgs field), is a spin-
zero particle with a non-zero mass. Since it is spin-zero, the
Higgs particle is thus a boson, and so it called the "Higgs
boson."
... ... M. Riordan et al (Stanford Linear Accelerator Center, US)
present a review on current research on the Higgs boson, the
authors making the following points:
     1) The authors point out that a critical requirement of the
Standard Model is a means to endow elementary particles with the
property of mass. According to the Higgs mechanism, particle
masses are the result of an invisible energy field (Higgs field)
that permeates space and confers inertia upon most elementary
particles. Without such an all-pervasive ethereal medium, the
elementary particles would remain forever massless like the
photon -- "racing about at light speed and never coalescing into
galaxies, stars, planets, and people."
     2) According to the wave-particle duality of quantum
mechanics, the Higgs field should become manifest as a spinless
particle called the "Higgs boson", which corresponds to
disturbances in the field. Searches for this object have occurred
at ever higher energies since the late 1970s, and possible
evidence for its existence was recently obtained at the European
Center for Particle Physics (CERN). New searches are about to
begin on the recently upgraded Tevatron collider at the Fermi
National Accelerator Laboratory (US).
     3) The authors point out that the evidence so far indicates
that the Higgs boson is a very massive particle, heavier than all
known elementary particles except possibly the top quark. There
are indications of the direct production of a Higgs boson near
115 Gev, a mass-energy which would be in a agreement with recent
indirect evidence that such a particle should have a mass less
than approximately twice that of the Z particle.
     4) The authors conclude: "The advanced linear electron-
positron colliders now being designed in Germany, Japan, and the
United States are ideally suited for detailed studies of such a
relatively light Higgs boson."
-----------
M. Riordan et al: The search for the Higgs boson.
(Science 12 Jan 00 291:259)
QY: Michael Riordan: michael@slac.stanford.edu
-----------
Text Notes:
... ... *electroweak theory: In 1979, Sheldon Glashow, Abdus
Salam, and Steven Weinberg shared the Nobel Prize in Physics for
their formulation of electroweak theory, which is essentially the
mathematical unification of the electromagnetic force and the
nuclear weak force.
... ... *nuclear weak force: The nuclear weak interactions are
the interactions involved in radioactive decay.
... ... *quantum chromodynamics: Quantum chromodynamics (QCD) is
a theory that describes the strong interaction (strong nuclear
force) in terms of quarks and antiquarks and the exchange of
massless "gluons" between them. The "chromo-" in chromodynamics
derives from the use of designated "color" attributes of quarks,
the various "colors" labels for various quark properties.
... ... *strong nuclear force: The current view among nuclear
physicists is as follows: each nucleus contains a population of
protons and neutrons, collectively known as nucleons, as well as
a host of other particles that bind the nucleons together. Each
nucleon, in turn, is made up of three quarks bound by what is
called the strong nuclear force.
... ... *quarks: A quark is a hypothetical fundamental particle,
having charges whose magnitudes are one-third or two-thirds of
the electron charge, and from which the elementary particles may
in theory be constructed.
... ... *leptons: A class of elementary particles. Although they
are affected by electromagnetic and gravitational forces, apart
from that they are involved only with weak interactions, acted
upon by weak forces but not by strong forces, as opposed to
quarks, which are acted upon by strong forces but not by weak
forces. One further difference between leptons and quarks is that
leptons can be isolated as single particles, whereas quarks
apparently cannot. The leptons include the electron, the muon,
the tau, and their associated neutrinos. The mass of the tau is
approximately 3484 times the mass of the electron; the mass of
the muon is intermediate.
... ... *Bose-Einstein statistics: Bose-Einstein statistics is
the statistical mechanics of a system of indistinguishable
particles for which there is no restriction on the number of
particles that may simultaneously exist in the same quantum
energy state. Particles that obey Bose-Einstein statistics are
called "bosons".
... ... *pi mesons: (pions) Pi mesons are subatomic particles
with masses approximately 270 times the mass of the electron.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 26Jan01
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
PHYSICS: ON THE STANDARD MODEL AND A UNIFIED PHYSICS
In particle physics, the "Standard Model" is a theoretical
framework whose basic idea is that all the visible matter in the
universe can be described in terms of the elementary particles
leptons and quarks and the forces acting between them. Leptons
are a class of point-like fundamental particles showing no
internal structure and no involvement with the strong forces.
Electrons and neutrinos are among the particles classified as
leptons. The strong force (nuclear strong force) is one of the
four fundamental forces: the gravitational force, the
electromagnetic force, the nuclear strong force, and the nuclear
weak force (see below), with the strong force approximately 100
times stronger than the electromagnetic force. A quark is a
hypothetical fundamental particle, having charges whose
magnitudes are one-third or two-thirds of the electron charge,
and from which the elementary particles may in theory be
constructed. At the present time, ongoing experimental projects
in particle physics are expected to permit a completion of the
Standard Model, but a unified theory of all forces known to
physics is not yet in sight.
... ... Steven Weinberg (University of Texas Austin, US) presents
the following considerations concerning the Standard Model and
current attempts to achieve a unified physics:
     1) In physics, the greatest advances of the past have been
steps involving unification: a) the unification of terrestrial
and celestial mechanics by Isaac Newton (1642-1727) in the 17th
century; b) the unification of optics with the theories of
electricity and magnetism by James Clerk Maxwell (1831-1879) in
the 19th century; c) the unification of space-time geometry and
the theory of gravitation by Albert Einstein (1879-1955) in the
years 1905 to 1916; d) the unification of chemistry and atomic
physics by quantum mechanics in the 1920s.
     2) Our current theory of elementary particles and forces,
known as the Standard Model of particle physics, has achieved a
unification of electromagnetism with the weak interactions, the
forces responsible for the change of neutrons and protons into
each other in radioactive processes and in the stars. The
Standard Model also gives a separate by similar description of
the strong interactions, the forces that hold quarks together
inside protons and neutrons, and that hold protons and neutrons
together inside atomic nuclei. We have ideas about how the theory
of strong interactions can be unified with the theory of weak and
electromagnetic interactions, but the approach may only work if
gravity is included, and the inclusion of gravity presents
serious theoretical difficulties.
     3) The Standard Model is a quantum field theory. Its basic
ingredients are fields, including the electric and magnetic
fields of 19th century electrodynamics. Perturbations in these
fields carry energy and momentum from place to place, and quantum
mechanics indicates these perturbations come in bundles, or
quanta, which are recognized in the laboratory as elementary
particles. For example the quantum of the electromagnetic field
is the photon. The Standard Model includes a field for each type
of elementary particle that has been observed in high-energy
physics laboratories.
     4) The Standard Model is a quantum field theory of a special
kind, one that is "renormalizable". This term goes back to the
1940s, when physicists were learning how to use the first quantum
field theories to calculate small shifts of atomic energy levels.
They found that calculations using quantum field theory kept
producing infinite quantities, a situation which usually
indicates a theory is badly flawed or is being pushed beyond its
limits of validity. Eventually, physicists discovered a way to
deal with the infinite quantities by absorbing them into a
redefinition, or "renormalization", of just a few physical
constants, such as the charge and mass of the electron.
     5) Although the profoundest advances in fundamental physics
tend to occur when the principles of different types of theories
are reconciled within a single new framework, we do not yet know
what guiding principle underlies the unification of quantum field
theory, as embodied in the Standard Model, with general
relativity. The quantum nature of space and time must be dealt
with in a unified theory. At the shortest distance scales, space
may be replaced by a continually reconnecting structure of
*strings and membranes -- or by something stranger still.
     6) The author suggests it is impossible to state when these
problems will be overcome. "They may be solved in a preprint put
out tomorrow by some young theorist. They may not be solved by
2050, or even 2150. But when they are solved... we will not have
any trouble in recognizing the truth of the fundamental unified
theory. The test will be whether the theory successfully accounts
for the measured values of the physical constants of the Standard
Model, along with whatever effects beyond the Standard Model may
have been discovered by then."
-----------
Steven Weinberg: A unified physics by 2050?
(Scientific American December 1999)
QY: Steven Weinberg, University of Texas Austin 512-471-3434.
-----------
Text Notes:
... ... *strings and membranes: See background material below.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 14Jan00
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
ON FIELD THEORY IN PHYSICS
In physics, a field is an entity that acts as intermediary in
interactions between particles, and which is distributed over
part or all of space, and whose properties are functions of space
coordinates, and except for static fields, also functions of
time. There is also a quantum-mechanical analog of this entity,
in which the function of space and time is replaced by an
operator at each point in space-time. ... ... Roman Jackiw
reviews present theoretical work in the theory of elementary
particles and forces, and the author makes the following points:
1) Present-day theory for fundamental processes (i.e.,
descriptions of elementary particles and forces) is phenomenally
successful. Experimental data confirms theoretical prediction,
and where accurate calculation and experiments are attainable,
agreement is achieved to 6 or 7 figures. Two examples: a) The
helium atom ground state energy (*Rydbergs) is experimentally
measured as -5.8071394 and theoretically calculated as
-5.8071380. b) The muon magnetic dipole moment is experimentally
measured as 2.00233184600 and theoretically calculated as
2.00233183478. 2) The theoretical structure within which this
success has been achieved is *local field theory, which offers a
wide variety of applications, and which provides a model for
fundamental physical reality as described by our theories of
*strong, electroweak, and gravitational processes. No other
framework exists in which one can calculate so many phenomena
with such ease and accuracy. 3) But is spite of these successes,
today there is little confidence that field theory will advance
our understanding of nature at its fundamental workings beyond
what has already been achieved. Although in principle all
observed phenomena can be explained by present-day field theory,
these accounts are still imperfect, requiring ad hoc inputs.
Moreover, because of conceptual and technical obstacles,
classical gravity theory has not been integrated into the
*quantum field description of nongravitational forces:
*quantizing the *metric tensor of Einstein's theory produces a
quantum field theory beset by infinities that apparently cannot
be controlled. 4) These shortcomings are actually symptoms of a
deeper lack of understanding concerning *symmetry and symmetry
breaking... Physicists are happy in the belief that Nature in its
fundamental workings is essentially simple, but observed physical
phenomena rarely exhibit overwhelming regularity. Therefore, at
the very same time that we construct a physical theory with
intrinsic symmetry, we must find a way to break the symmetry in
physical consequences of the model. 5) These problems have
produced a theoretical impasse for over two decades, and in the
absence of new experiments to channel theoretical speculation,
some physicists have concluded that it will not be possible to
make progress on these questions within field theory, and they
have turned to a new structure, "*string theory". In field
theory, the quantized excitations are point particles with point
interactions, and this gives rise to the infinities. In string
theory, the excitations are extended objects -- strings -- with
nonlocal interactions; there are no infinities in string theory,
and that enormous defect of field theory is absent. 6) Yet in
spite of its positive features, until now string theory has
provided a framework rather than a definite structure, and a
precise derivation of the *Standard Model has yet to be given.
The author concludes: "On previous occasions when it appeared
that quantum field theory was incapable of advancing our
understanding of fundamental physics, new ideas and new
approaches to the subject dispelled the pessimism. Today we do
not know whether the impasse within field theory is due to a
failure of imagination or whether indeed we have to present
fundamental physical laws in a new framework, thereby replacing
the field theoretic one, which has served us well for over 100
years."
-----------
Roman Jackiw (Massachusetts Institute of Technology, US)
Field theory: Why have some physicists abandoned it?
(Proc. Natl. Acad. Sci. US 27 Oct 98 95:12776)
QY: Roman Jackiw, Mass. Inst. of Technology 617-253-1000.
-----------
Text Notes:
... ... *Rydbergs: A unit of energy used in atomic physics,
value = 13.605698 electronvolts.
... ... *local field theory: In this context, "locality" is the
condition that two events at spatially separated locations are
entirely independent of each other, provided that the time
interval between the events is less than that required for a
light signal to travel from one location to the other. For
example, the quantum mechanical wave function is a "local" field.
... ... *strong, electroweak, and gravitational processes: The
fundamental forces comprise the gravitational force, the
electromagnetic force, the nuclear strong force, and the nuclear
weak force. The "electroweak" interactions are a unification of
the electromagnetic and nuclear weak interactions, and are
described by the Weinberg-Salam theory (sometimes called "quantum
flavordynamics"; also called the Glashow-Weinberg-Salam theory).
... ... *quantum field description: In general, a quantum field
theory is a quantum mechanical theory applied to systems having
an infinite number of *degrees of freedom.
... ... *degrees of freedom: In general, the number of
independent parameters required to specify the configuration of a
system.
... ... *quantizing: In experimental physics, a quantized
variable is a variable taking only discrete multiple values of a
quantum mechanical constant. In theoretical physics, "quantizing"
means the consistent application of certain rules that lead from
classical to quantum mechanics. In general, "quantization" is a
transition from a classical theory or a classical quantity to a
quantum theory or the corresponding quantity in quantum
mechanics.
... ... *metric tensor: The mathematical statement (involving a
set of quantities) that describes the deviation of the Pythagoras
theorem in a curved space.
... ... *symmetry and symmetry breaking: If a theory or process
does not change when certain operations are performed on it, the
theory or process is said to possess a symmetry with respect to
those operations. For example, a circle remains unchanged under
rotation or reflection, and a circle therefore has rotational and
reflection symmetry. The term "symmetry breaking" refers to the
deviation from exact symmetry exhibited by many physical systems,
and in general, symmetry breaking encompasses both "explicit"
symmetry breaking and "spontaneous" symmetry breaking. Explicit
symmetry breaking is a phenomenon in which a system is not quite,
but almost, the same for two configurations related by exact
symmetry. Spontaneous symmetry breaking refers to a situation in
which the solution of a set of physical equations fails to
exhibit a symmetry possessed by the equations themselves.
... ... *string theory: In particle physics, string theory is a
theory of elementary particles based on the idea that the
fundamental entities are not point-like particles but finite
lines (strings), or closed loops formed by strings, the strings
one-dimensional curves with zero thickness and lengths (or loop
diameters) of the order of the Planck length of 10^(-35) meters. 
... ... *Standard Model: See main report.
-------------------
Summary & Notes by SCIENCE-WEEK  4Dec98
-------------------
Related Background:
THEORETICAL PHYSICS: ON STRING THEORY
... ... B.R. Greene et al present a short review of recent
developments in string theory and make the following points: 1)
Particle physics has spent much of this century grappling with
one basic question in various forms: What are the fundamental
*degrees of freedom needed to describe nature, and what are the
laws that govern their dynamics. 2) The current "Standard Model"
of particle physics -- which is nearly 25 years old and which has
much experimental evidence in its favor -- involves 6 *quarks, 6
*leptons, 4 *forces, and the as yet unobserved *Higgs boson. But
this model contains internal indications that it too may be just
another step along the path of uncovering the truly fundamental
degrees of freedom. The Standard Model is valid to distances as
small as 10^(-16) cm, and there is some evidence that the next
level of structure will be detected only at a distance scale of
the order of 10^(-32) cm, which is far beyond our abilities to
measure in the laboratory. 3) A related important issue concerns
the unification of general relativity and quantum mechanics. A
serious problem arises when general relativity is extrapolated to
small distance scales of the order of 10^(-32) cm where quantum
effects must be taken into account: the relevant theoretical
equations produce uncontrollable divergences, and the history of
particle physics suggests this is an indication of a new physics
occurring at these distance scales. 4) String theory offers hope
of addressing both of these issues. There is only one known way
to cure the divergence problem in the quantum-mechanical
expansion of general relativity, and that is to model the
particles in the theory not as points but as one-dimensional
loops of "string". Every consistent such string model necessarily
contains a special kind of particle -- the "*graviton" --  whose
long-distance interactions are described by general relativity.
So in a sense, string theory predicts gravity. 5) An exciting new
frontier was opened during the past few years with the discovery
of "string duality", which predicts equivalences among various
different physical systems. This discovery has its roots in the
properties of "supersymmetry", a novel type of symmetry that all
consistent string theories possess. Briefly, supersymmetry
relates properties of two basic types of particles -- bosons and
*fermions -- which cannot be related by ordinary symmetry. There
is a current belief that supersymmetry will play a role in the
structure of particle physics beyond the Standard Model. One of
the important achievements of string duality has been the
determination of the behavior of the 5 consistent string theories
when interactions become strong. All the consistent string
theories are apparently related to each other, and to an
elaboration known as "membrane theory" (M-theory). String duality
has produced hope that there may be only one possible string-
theoretic model of the universe, and that it may be possible to
eventually predict such features as particle masses and
interaction strengths directly from such a theory. The authors
conclude: "Development has been rapid on many fronts since string
duality was introduced. We may be seeing glimpses of the
underlying principle manifested in these new results. The
challenging task that lies ahead is to discover that principle
and thereby find what may well be the truly fundamental degrees
of freedom in our universe."
-----------
B.R. Greene et al (3 authors at 3 installations, US)
String theory.
(Proc. Natl. Acad. Sci. US 15 Sep 98 95:11039)
QY: David R. Morrison 
-----------
Text Notes:
... ... *degrees of freedom: See previous report.
... ... *quarks: See previous report.
... ... *leptons: A class of elementary particles. Although they
are affected by electromagnetic and gravitational forces, apart
from that they are involved only with weak interactions, acted
upon by weak forces but not by strong forces, as opposed to
quarks, which are acted upon by strong forces but not by weak
forces. One further difference between leptons and quarks is that
leptons can be isolated as single particles, whereas quarks
apparently cannot. The leptons include the electron, the muon,
the tau, and their associated neutrinos. The mass of the tau is
approximately 3484 times the mass of the electron; the mass of
the muon is intermediate.
... ... *forces: See previous report (fundamental forces).
... ... *Higgs boson: Higgs fields (named after Peter W. Higgs,
University of Edinburgh, UK) constitute a set of fundamental
theoretical fields that induce spontaneous symmetry breaking. In 
general, spontaneous symmetry breaking occurs in systems whose
underlying symmetry state is unstable. A Higgs particle is
associated with a Higgs field in the same way that a photon is
associated with the electromagnetic field. Higgs bosons are
massive mesons whose existence is predicted by certain theories.
Mesons are apparently composed of quark and anti-quark pairs;
they are produced by various high-energy interactions and decay
into stable particles.
... ... *graviton: Several quantum field theories consistent with
both quantum mechanics and special relativity postulate that the
gravitational force between two quantum domain particles is
generated by the exchange of an intermediate particle called a
graviton.
... ... *fermions: Fermions (electrons, protons, neutrons) are
particles that obey the Pauli exclusion principle: i.e., no two
fermions of the same kind can occupy the same quantum state.
-------------------
Summary & Notes by SCIENCE-WEEK  16Oct98
-------------------
Related Background:
ON RECENT DEVELOPMENTS IN SUPERSTRING THEORY
Bose-Einstein statistics is the statistical mechanics of a system
of indistinguishable particles for which there is no restriction
on the number of particles that may simultaneously exist in the
same quantum energy state. Bosons are particles that obey Bose-
Einstein statistics, and they include photons, pi mesons, all
nuclei having an even number of particles, and all particles with
integer spin. Fermions (electrons, protons, neutrons) are
particles that obey the Pauli exclusion principle: i.e., no two
fermions of the same kind can occupy the same quantum state.
In particle physics, string theory is a theory of elementary
particles based on the idea that the fundamental entities are not
point-like particles but finite lines (strings), or closed loops
formed by strings, the strings one-dimensional curves with zero
thickness and lengths (or loop diameters) of the order of the
Planck length of 10^(-35) meters. The fundamental forces comprise
the gravitational force, the electromagnetic force, the nuclear
strong force, and the nuclear weak force, and the "grand unified
theories" are theories that aim to provide a mathematical frame-
work in which the electromagnetic forces, strong forces, and weak
forces emerge as parts of a single unified force, with the three
forces related by symmetry. Supersymmetry is an aspect of an
extension of the grand unified theories, an attempt to unify all
the four fundamental forces, i.e., linking gravitation to the
electromagnetic force, the strong force, and the weak force
through a supersymmetry scheme, and superstrings are strings in
this scheme that obey supersymmetry. ... ... John H. Schwarz
(California Institute of Technology, US) presents a brief
overview of some of the advances in understanding super-
string theory that have been achieved in the last few years.
String theories that have a symmetry relating bosons and
fermions, called "supersymmetry", are called "superstring"
theories. Major advances in understanding of the physical world
have been achieved during the past century by focusing on
apparent contradictions between well-established theoretical
structures. In each case the reconciliation required a better
theory, often involving radical new concepts and striking
experimental predictions. Four major advances of this type were
the discoveries of special relativity, quantum mechanics, general
relativity, and quantum field theory. This was quite an
achievement for one century, but there is one fundamental
contradiction that still needs to be resolved, namely the clash
between general relativity and quantum field theory. Many
theoretical physicists are convinced that superstring theory will
provide the answer.
QY: John H. Schwarz, Calif. Inst. of Technology 818-395-6811.
(Proc. Natl. Acad. Sci. US 17 Mar 98)
(Science-Week 10 Apr 98)
-------------------
Related Background:
ON THE EVOLUTION OF STRING THEORY TO MEMBRANE THEORY
... Membrane theory (M-theory) is a recent extension of string
theory in which the fundamental physical entities are considered
as surfaces in a many-dimensional space (membranes) rather than
as lines or loop elements (open or closed strings). Given all of
the above, some caution is necessary: the translation of a highly
abstract mathematical model of physical reality into
non-mathematical language is often an exercise of limited
usefulness, and in this case in particular, we are presenting
only the ghost of the theoretical scheme. String theory was
originally invented in the 1960s as a theory of the strong force,
became overshadowed by the strong force theory of gluons and
quarks, then had a revival in the 1980s -- but with the history
more dependent on new work than on fashion. ... ... M. Duff
(Texas A & M Univ., US), who is active in string theory and
membrane theory, in a review of various aspects of the history
and essentials of string theory and membrane theory, suggests
that future historians may judge the 20th century as "a time when
theorists were like children playing on the seashore, diverting
themselves with the smoother pebbles or prettier shells of
superstrings, while the great ocean of M-theory lay undiscovered
before them."
QY: Michael J. Duff, Texas A & M Univ. 409-847-9451.
(Scientific American February 1998) (Science-Week 23 Jan 98)
For more information: http://scienceweek.com/swfr.htm

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=

5. PLANETARY SCIENCE:
ON BIOSIGNATURES IN A MARTIAN METEORITE ALH84001
     On August 6, 1996, a team of scientists, a group headed by
David Mckay at the US National Aeronautics and Space
Administration (NASA), held a press conference to announce they
had found evidence of former life on Mars in a Martian meteorite.
The meteorite was part of a collection made in 1984 at Allan
Hills in Antarctica and has the name ALH84001 [*Note #1]. About
the size of a potato, this meteorite weighs 1.9 kilograms. Its
Martian origin was first recognized in 1993, and the material of
the meteorite has been dated as crystallized 4.5 billion years
ago, with the meteorite ejected from Mars 14.4 million years ago,
and the meteorite resident in Antarctic ice for 13,000 years. The
meteorite consists largely of orthopyroxenite, which is an
*igneous rock comparable to *basalt.
     The 1996 claim of evidence of former life in this meteorite
was based on apparent fossilized "nannobacteria" [see related
background material below], and was not widely accepted by either
the paleobiology community or by other scientific groups at NASA.
From the beginning, it has been known that carbonate globules
found in this meteorite have dark margins of abundant tiny
crystals of the form of iron oxide known as "magnetite".
Comparable magnetite crystals are produced by some bacteria
(e.g., Magnetospirillum magnetotacticum), which apparently use
them for orientation within Earth's magnetic field. The crystals
of these bacteria are similar to the magnetic crystals of the
ALH84001 meteorite, and the McKay group has been claiming for
several years that these magnetite crystals are further evidence
of former life in the meteorite.
     Now two contiguous reports of analyses of these magnetite
crystals have appeared, one report from the McKay group and the
other report from another group, both reports concluding that the
crystals are of biological origin.
... ... K.L. Thomas-Keprta et al (10 authors at 6 installations,
US CA) present an analysis of a subpopulation of magnetite
[Fe(sub3)O(sub4)] present in abundance within the iron-rich rims
of the carbonate globules considered previously to be the fossil
remains of Martian microbes. The authors make the following
points:
     1) The authors report these Martian magnetites to be both
chemically and physically identical to terrestrial, biogenically
precipitated, intracellular magnetites produced by magnetotactic
bacteria (strain MV-1). Specifically, both magnetite populations
are single [magnetic] domain and chemically pure crystals, and
exhibit a unique crystal form the authors call "truncated hexa-
octahedral".
     2) The authors point out there are no known reports of
inorganic processes to explain the observation of truncated hexa-
octahedral magnetites in a terrestrial sample, and that in
bacteria of strain MV-1 their presence is likely a product of
natural selection. Unless there is an unknown and unexplained
inorganic process on Mars that is conspicuously absent on the
Earth and forms truncated hexa-octahedral magnetites, the authors
suggest that these magnetite crystals in the Martian meteorite
ALH84001 were likely produced by a biogenic process, and that
these crystals are Martian magnetofossils and constitute evidence
of the oldest life yet found.
... ... E.I. Friedmann et al (4 authors at 4 installations, US ES
DE) present an analysis of chains of magnetite crystals in the
meteorite ALH84001, the authors making the following points:
     1) The authors report the presence of magnetite crystal
chains in the meteorite is demonstrated by high-power stereo
*backscattered scanning electron microscopy. Five characteristics
of such chains (uniform crystal size and shape within chains,
gaps between crystals, orientation of elongated crystals along
the chain axis, flexibility of chains, and a halo that is a
possible remnant of a membrane around chains), observed or
inferred to be present in magnetotactic bacteria but incompatible
with a nonbiological origin, are shown to be present.
     2) The authors conclude: "We suggest the following scenario:
First, decomposed remains of dead magnetobacteria suspended in a
carbonate-rich fluid penetrated fissures of ALH84001, already
crushed by previous asteroid impact... Second, evaporation of the
liquid led to the deposition of pancake-shaped carbonate
globules, and magnetite crystals and chain fragments were
deposited in the periphery of the carbonate discs, perhaps
through the mechanism for ring deposition of particles dispersed
in liquid drops."
-----------
[Editor's note: The response of the astrobiology and paleobiology
communities to these reports has for the most part apparently
been skepticism. Indeed, it is difficult to support an
interpretation of a biological origin of the Martian magnetite
crystals on the primary grounds that no contrary evidence for
such inorganic crystal formation yet exists. Future research will
demonstrate whether or not such crystals can be formed by
nonbiological processes. The same is true of the apparent
magnetite "chains" in the meteorite. Commenting several years ago
on the controversy concerning claims of fossils of former life in
the Martian meteorite ALH84001, Malcolm Walter said: "What we are
observing is the messy business of science in action at the
frontiers of knowledge. In many ways, there is nothing unusual
about it, except that it is happening in a very public way." In
addition, there is the old adage that has been stated and
restated in many forms: "Extraordinary claims require
extraordinary evidence." As one paleobiologist recently remarked,
perhaps no one will be satisfied until a Martian meteorite is
found to contain a clamshell.]
-----------
K.L. Thomas-Keprta et al: Truncated hexa-octahedral magnetite
crystals in ALH84001: Presumptive biosignatures.
(Proc. Natl. Acad. Sci. US 27 Feb 01 98:2164)
QY: Kathie L. Thomas-Keprta: kthomas@ems.jsc.nasa.gov
-----------
E.I. Friedmann et al: Chains of magnetite crystals in the
meteorite ALH84001: Evidence of biological origin.
(Proc. Natl. Acad. Sci. US 27 Feb 01 98:2176)
QY: E. Imre Friedmann: friedmann@gal.arc.nasa.gov
-----------
Malcolm Walter: _The Search for Life on Mars_
(Perseus Books, New York 1999, p.91)
QY: Malcolm Walter: Macquarie University, Sydney AU.
-----------
Text Notes:
... ... *Note #1: The number of meteorites found in Antarctica is
as great as in the rest of the world combined: a) dark-colored
rocks are readily visible in the Antarctic ice-cap; b) the ice
sheet concentrates moveable rocks in small areas.
... ... *igneous rock: Igneous rocks are rocks that have
congealed from a molten mass.
... ... *basalt: Basalt is a dark gray to black igneous rock of
volcanic origin that cools rapidly. It is found as basement
rock on land, and on sea floor spreading from mid-ocean ridges.
... ... *backscattered: In general, in this context,
"backscattering" is the deflection of radiation by scattering
processes through angles greater than 90 degrees with respect to
the original angle of travel.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 6Apr01
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
PLANETARY SCIENCE:
EVIDENCE SUPPORTING POSSIBILITY OF LOW-TEMPERATURE LIFE-BEARING
METEORITES
In 1984, a 1.9 kilogram meteorite the size of a potato
(designated ALH84001) was found in Antarctica, and because of its
chemical composition the consensus is that this meteorite (and a
dozen similar meteorites) originated from the planet Mars. The
basis for the consensus is the detailed quantitative
correspondence of the trapped gases in the meteorites to Martian
atmospheric gases, and the specific distributions of oxygen
isotopes. In 1996 a group of researchers, D. McKay et al
(National Aeronautics and Space Administration Johnson Space
Center, US; Stanford University, US) reported they had concluded
that unusual characteristics of the meteorite ALH84001 can be
most reasonably interpreted as vestiges of ancient Martian
bacterial life. In particular, the authors noted the presence of
tubules 20 to 40 nanometers in diameter (called by some
"nannobacteria" or "nanobacteria"), and they proposed these
structures were fossilized bacteria or parts of microorganisms.
The report was first delivered at a press conference in August
1996 (published as a paper 9 days later) and provoked
considerable media attention and controversy when it appeared.
The controversy has continued, with many biologists objecting to
the interpretation of the rock data, and in particular objecting
to the idea of "bacteria" 20 to 40 nanometers in diameter.
... ... B.P. Weiss et al (7 authors at 3 installations, US CA)
present the results of analysis of images of the magnetic field
of the Martian meteorite ALH84001, the authors making the
following points:
     1) The authors point out that large-body impacts are the
only known natural processes capable of ejecting a rock from
Mars. It has been suggested that some rocks could be ejected
without being shocked and heated, and laboratory experiments have
produced chipped fragments of only lightly shocked material
moving at approximately 20 percent of Martian escape velocity,
and thermal conductivity calculations demonstrate that passage
through Earth's atmosphere will not heat the interior of
meteorites larger than 0.3 centimeters above 100 degrees
centigrade.
     2) The authors report that ultra-high resolution
magnetometer images of the magnetic field of meteorite ALH84001
reveal a spatially heterogeneous pattern of magnetization
associated with fractures and rock fragments. Heating the
meteorite to 40 degrees centigrade reduces the intensity of some
magnetic features, indicating that the interior of the rock has
not been above this temperature since before its ejection from
the surface of Mars.
     3) The authors report their results thus indicate that major
impact events are capable of moving rocks from the surface of
Mars to the surface of Earth without subjecting them to
temperatures high enough to cause thermal sterilization of
eukarya or bacteria. Dynamic simulations of Martian impact events
indicate that materials can be launched into a wide variety of
orbits. The authors suggest that although most of the
approximately 1 ton of Martian rocks that are believed to land on
Earth each year have spent several million years in space, one in
10^(7) of the arriving rocks will have made the journey in less
than a year, and that every million years, approximately 10 rocks
larger than 100 grams are estimated to be transferred in just 2
to 3 years of travel time. It has been estimated that bacterial
spores, as well as microorganisms within rocks, can survive in
deep space for more than 5 years. Thus, the authors suggest,
their results indicate that it may not be necessary to protect
Earth's present biosphere by quarantining rocks retrieved by a
Mars sample return mission, since conditions have been
appropriate to allow low-temperature rocks -- and, if present,
microorganisms -- from Mars to be transported to Earth throughout
most of geological time.
     4) In summary, the authors state: "[Our] data support the
hypothesis that meteorites could transfer life between planets in
the Solar System."
-----------
B.P. Weiss et al: A low temperature transfer of ALH84001 from
Mars to Earth.
(Science 27 Oct 00 290:791)
QY: Benjamin P. Weiss: bweiss@gps.caltech.edu
-------------------
Summary by SCIENCE-WEEK http://scienceweek.com 10Nov00
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
THE MARTIAN METEORITE MICROBES CONTROVERSY: AN UPDATE
... ... Allan Treiman (National Aeronautics and Space
Administration, US) presents a review and update of the ALH84001
meteorite controversy, the author making the following points: 1)
Early hopes for a fast resolution of the controversy concerning
meteorite ALH84001 have evaporated: no agreement has emerged on
whether or not the meteorite ever contained Martian life. 2)
There is no disagreement that ALH84001 formed on Mars
approximately 4.5 billion years ago, that the meteorite was
probably ejected into space approximately 16 million years ago by
an asteroid impact, that the meteorite fell in Antarctica 13,000
years ago, and that the meteorite remained in Antarctica until
found on the ice in 1984. 3) ALH84001 is an igneous rock (i.e., a
rock congealed from a molten mass) that apparently crystallized
slowly from molten lava and which contains globules of carbonate
minerals scattered along fractures. All the evidence for life is
in the carbonate globules or their rims. 4) The 4 lines of
evidence originally proposed by the McKay group were a) the
presence in the meteorite of carbon compounds (polycyclic
aromatic hydrocarbons) suggestive of decayed organic matter; b)
the presence in the meteorite of unusual small crystals of
magnetite (an iron oxide) matching identical crystals believed to
be produced only by Earth bacteria; c) the presence in the
meteorite of apparently incompatible minerals (e.g., iron-sulfide
and iron-oxide) close together whose proximity would suggest
organic action if the rock were from Earth; and d) the presence
in the meteorite of bacteria-shaped formations. 5) The author
[Treiman] suggests that a) The polycyclic aromatic hydrocarbons
may or may not be Martian, and if they are, they may or may not
be related to life. b) The magnetite crystals are indeed Martian,
but there is evidence that some of these crystals formed without
life and the origin of the others remains unclear. c) The mineral
associations in the carbonate globules do not prove life, but
also do not exclude it. d) The bacteria-shaped objects in
ALH84001 are not fossil bacteria but could be fossils of bacteria
fragments. (McKay's group now agrees that the objects are too
small to be fossil microbes.) 6) The author concludes: "McKay's
original hypothesis (as expressed in the 1996 paper) depended on
all four lines of evidence working together... The evidence has
not been verified, so the hypothesis has not succeeded... Despite
world attention, significant spending, and the work of the best
laboratories on Earth, the question [of life on Mars] is
unresolved."
-----------
Allan Treiman: Microbes in a Martian meteorite?
(Sky & Telescope April 1999) (ScienceWeek 21 May 99)
QY: Allan Treiman: treiman@lpi.jsc.nasa.gov
-------------------
Related Background:
EVIDENCE THAT MARTIAN METEORITE AMINO ACIDS ARE CONTAMINANTS
As the subunits that compose protein polymers in living systems,
the detection of certain amino acids in a material is often
interpreted as indicating a possible biological origin. The
meteorite ALH84001, along with a number of other discovered
meteorites, has a composition that suggests it was apparently
ejected from the surface of Mars, and during the past year it has
been proposed that microanalysis of this meteorite indicates the
possible presence of bio-organics and biogenic fossils. This
proposal, however, has met with considerable controversy, and the
controversy is still in full force. ... ... Bada et al (4 authors
at 3 installations, US) now report that the amino acids present
in a sample of the ALH84001 meteorite appear to be terrestrial in
origin and similar to those found in the ice where the meteorite
was discovered, although the possibility remains that minute
amounts of endogenous amino acids are preserved in the meteorite.
The authors suggest that radiocarbon studies (cf. contiguous
report: Jull et al, Science 279:366 1998), coupled with their own
amino acid results, indicate that major and minor organic
constituents in the Martian meteorites are contaminants.
QY: Jeffrey L. Bada: jbada@ucsd.edu
(Science 16 Jan 98) (ScienceWeek 30 Jan 98)
For more information: http://scienceweek.com/swfr.htm

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=

6. PHYSICAL CHEMISTRY:
DYNAMIC BEHAVIOR OF WATER IN SOLVATION SHELLS
     In general, a solute dissolves in a solvent when the
interaction energy between the solvent and solute components is
greater than the interaction energy between the solute components
themselves. In solution, solvent molecules surround each solvent
component in a "solvation shell" whose lifetime is short or long
depending on interactants and conditions.
     Water is an excellent solvent because of its highly polar
character and hydrogen-bonding possibilities, which produce
relatively high interaction energies with ions and polar solutes.
When water is a solvent in a system, the solvation shell is
called the "hydration shell", and the character and history of
this shell are of great importance in molecular considerations of
reactions in both biological and non-biological systems.
Consider, for example, the permeation of ions through biological
membranes. What role does the ion hydration shell play in
differential ion permeability through membranes? Are ions
stripped of their hydration shells and then resolvated in the ion
channels? Definitive answers to these questions are not yet
apparent.
     In general, with reference to water, the term
"autoionization" refers to the ability of water to behave both as
an acid (a proton donor) and a base (a proton acceptor). The
general schema for this behavior is that expressed by a reaction
equation in which 2 water molecules on one side of the equation
are in equilibrium with a hydrated hydronium ion [H(sub3)O(+)]
and a hydrated hydroxide ion [OH(-)] on the other side of the
equation. At 25 degrees centigrade, the concentration of
hydronium ion in pure water is 1.0 x 10^(-7) moles per liter, and
the concentration of hydroxide ions is the same, producing the
14-unit logarithmic pH scale in which the pH of pure water is 7.
     In general, the term "nonlinear spectroscopy" refers to the
study of energy levels not normally accessible with ordinary
optical spectroscopy, the technique involving the use of
nonlinear effects such as multi-photon absorption and ionization.
     In general, "ab initio" (from first principles) calculations
utilize experimental data on atomic systems to facilitate the
adjustment of parameters. The excellent performance of ab initio
techniques distinguishes them from their predecessors, the
"semiempirical" methods, with the quantitative predictions of ab
initio techniques usually falling within experimental error when
comparisons are made to experimental measurements.
     Two reports advancing our understanding of the physical
chemistry of aqueous solutions have now appeared, one report on
the dynamics of hydration shells, and the other report of the
dynamics of water autoionization.
... ... M.F. Kropman and H.J. Bakker (FOM Institute AMOLF, NL)
present a report on the direct measurement of the dynamics of
water molecules in the solvation shell of an ion in aqueous
solution. The authors report the hydrogen-bond dynamics of water
molecules solvating a chloride, bromide, or iodide anion is slow
compared with pure liquid water, indicating that the aqueous
solvation shells of these ions are rigid. The authors suggest
this rigidity can play an important role in the overall dynamics
of chemical reactions in aqueous solution. The experiments were
performed with femtosecond mid-infrared nonlinear spectroscopy,
since this technique allows the spectral response of the water
molecules in the solvation shell to be distinguished clearly from
that of the other water molecules in the solution.
... ... P.L Geissler et al (5 authors at 3 installations, US DE)
present a report on autoionization in liquid water, the authors
making the following points:
     1) The authors point out that the dissociation of the water
molecule in liquid water is the fundamental event in acid-base
chemistry, determining the pH of water. Because of the short time
scales and microscopic length scales involved, the dynamics of
this autoionization have not been directly probed by experiment.
     2) The authors report they have revealed the autoionization
mechanism with an ab initio molecular dynamics model. The authors
report they identify the rare fluctuations in solvation energies
that destabilize an oxygen-hydrogen bond. Through the transfer of
protons along a hydrogen-bond "wire", the nascent ions separate
by 3 or more neighbors. If the hydrogen-bond wire connecting the
two ions is subsequently broken, a metastable charge-separated
state occurs, and the ions may then diffuse to large separations.
If, however, the hydrogen-bond wire remains unbroken, the ions
recombine rapidly. Because of the concomitant large electric
fields, the transient ionic species produced by these dynamics
may provide an experimentally detectable signal.
     3) The authors conclude that the dynamics of both electric
fields and hydrogen bonding play important roles in the
autoionization mechanism. Rare electric field fluctuations drive
the dissociation of oxygen-hydrogen bonds, and ions produced in
this manner usually recombine quickly because the solvation
fluctuation vanishes within tens of femtoseconds. But when such a
fluctuation is coincident with breaking of the hydrogen-bond wire
(a process normally occurring approximately once every
picosecond), rapid recombination is then not possible. It is with
this coincidence of events that the system crosses a transition
state. The authors suggest this scenario implies the existence of
many short-lived hydronium and hydroxide ions in water, and that
the decay of this transient population over approximately 100
femtoseconds should be observable.
-----------
M.F. Kropman and H.J. Bakker: Dynamics of water molecules in
aqueous solvation shells.
(Science 16 Mar 01 291:2118)
QY: H.J. Bakker: bakker@amolf.nl
-----------
P.L. Geissler et al: Autoionization in liquid water.
(Science 16 Mar 01 291:2121)
QY: David Chandler: chandler@cchem.berkeley.edu
-------------------
Summary by SCIENCE-WEEK http://scienceweek.com 6Apr01
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
ON WATER AND THE STRUCTURES OF BIOLOGICAL MOLECULES
A prominent consideration in the minds of biologists who work at
the level of cells and molecules is that water is the most
prevalent chemical substance in all biological systems, and that
interactions of water with other biological molecules,
particularly with biological macromolecules, are not clearly
understood but are probably of considerable significance.
... ... M. Gerstein and M. Levitt present a review of some
aspects of the physical chemistry of water and an account of
their own computer simulations of biological macromolecules in
aqueous solutions. The authors make the following points: 1) At
the present time it is possible to model proteins and their
associated water molecules on a desktop computer in a few days.
Researchers have now simulated the aqueous structures of more
than 50 proteins and nucleic acids. 2) A single water molecule
has an essentially tetrahedral geometry, with an oxygen atom at
the center of the tetrahedron, hydrogen atoms at 2 of the 4
corners, and clouds of negative charges at the other 2 corners.
Reflecting the tetrahedral geometry of water, each molecule in
liquid water often forms 4 hydrogen bonds: 2 hydrogen bonds
between its hydrogens and the oxygen atoms of 2 other water
molecules, and 2 hydrogen bonds between its oxygen atom and the
hydrogens of other water molecules. The necessity of maintaining
a tetrahedral hydrogen-bonded structure gives water an "open"
loosely packed structure compared with that of most other liquids
[*Note #1]. 3) Present computer simulations are able to reproduce
quantitatively many of the bulk properties of water, such as its
average structure, rate of diffusion, and *heat of vaporization.
4) Biological molecules such as proteins and DNA contain both
hydrophilic and hydrophobic parts arranged in long chains. The 3-
dimensional structures of these molecules are determined by the
way these chains fold into more compact arrangements in which
hydrophilic groups are on the surface where they can interact
with water and hydrophobic groups are buried in the interior away
from water. These local macromolecule solubility considerations
were formulated in 1959 by Walter Kauzman as a "hydrophobic
effect" crucial for protein folding. 4) There are 3 types of
water molecules that must be considered in a computer model of a
biological molecule in aqueous solution: a) the ordered water
surrounding and strongly interacting with the macromolecule; b)
the bulk water beyond the ordered water; and, c) any water
molecules that may be buried within the macromolecule. 5)
Computer simulations of DNA in water have revealed that water
molecules are able to interact with nearly every part of the
double helix of DNA, including the nucleotide base pairs that
constitute the genetic code. In contrast, water is not able to
penetrate deeply into the structure of proteins, whose
hydrophobic regions are arranged on the inside into a close-
fitting core [*Note #2].
-----------
M. Gerstein and M. Levitt (2 installations, US)
Simulating water and the molecules of life.
(Scientific American November 1998)
QY: Mark Gerstein, Yale University, 203-432-4771.
-----------
Text Notes:
... ... *Note #1: In hydrated crystal structures, water molecules
generally donate two hydrogen bonds but may accept either one or
two. When water molecules are 3-coordinated (rather than 4-
coordinated as discussed by the authors in their review), the
geometry can be planar or pyramidal. But examples are known of
coordination as low as 2 and as large as 7.
... ... *heat of vaporization: The quantity of energy required to
evaporate 1 mole (or a unit mass) of a liquid at constant
pressure and temperature.
... ... *Note #2: Concerning the interaction of water molecules
with biological molecules, water molecules hydrogen-bonded to the
functional groups of biological molecules are apparently linked
in chains into extended networks, and some researchers have
suggested the *polarizability of these networks provides a 
mechanism for long-range recognition between biological molecules
in aqueous solution.
... ... *polarizability: The electric dipole moment induced in a
system (such as an atom or molecule) by an electric field of unit
strength.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 13Nov98
For more information: http://scienceweek.com/swfr.htm

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7. IN FOCUS: 1905: EINSTEIN'S ANNUS MIRABILIS
"By the spring of 1905, the 26-year-old Einstein had decided that
physicists were 'out of [their] depth'. From calculations based
on Planck's radiation law, Einstein drew the astounding 'general
conclusion' that light can be a particle and a wave, and in fact
both at once, a wave/particle duality. Therefore the
electromagnetic world-picture could not succeed, because
Lorentz's theory could represent radiation, or light, only as a
wave, and so could never provide a way to explain how the
electron's mass is generated by its own radiation. Whereas Planck
had discovered certain peculiarities about the energy of
radiation, Einstein set out to explore the structure of radiation
itself. Einstein's particles of light differed fundamentally from
Newton's in ways that even he did not yet fully realize. Around
the third week of May 1905, Einstein sent his friend Habicht what
are surely some of the greatest understatements in the history of
science. He wrote that he had only some 'inconsequential babble'
for his friend, whom he lambasted for neither writing nor
visiting him during Easter: 'So what are you up to, you frozen
whale, you smoked, dried, canned piece of soul... I promise you
four papers.' The first paper is the light quantum paper that
Einstein referred to as 'very revolutionary'. The second
suggested a means to measure the size of atoms using diffusion
and viscosity of liquids. The third one explored Brownian motion
using methods of the molecular theory of heat. 'The fourth paper
is only a draft at this point, and is an electrodynamics of
moving bodies which employs a modification of the theory of space
and time; the purely kinematic part of this paper will surely
interest you.' What is so incredible about this outburst of
creativity is that by late May two papers were completed and the
third was in draft form." [Editor's note: The fourth paper, the
so-called relativity paper, was completed a few weeks later in
June 1905.]
-----------
Arthur I. Miller: _Einstein, Picasso: Space, Time, and the Beauty
That Causes Havoc_
(Basic Books, New York 2001, p.189)

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8. FROM THE SCIENCEWEEK ARCHIVE:
CONTROL OF INFECTIOUS DISEASES 1900-1999
The first US civilian whose life was saved by penicillin died in
June 1999 at the age of 90 years. The story is as follows: In
March 1942, a 33-year-old woman was hospitalized for a month with
a life-threatening streptococcal infection at a New Haven,
Connecticut hospital. She was delirious, and her temperature
reached almost 107 degrees fahrenheit (41 degrees centigrade).
Treatments with sulfa drugs, blood transfusions, and surgery had
no effect. As a last resort, her doctors injected her with a
minuscule amount of an obscure experimental drug called
penicillin. Her hospital chart, now at the Smithsonian
Institution, indicates a sharp overnight drop in temperature, and
apparently by the next day she was no longer delirious. The woman
survived to marry, raise a family, and meet Alexander Fleming
(1881-1955), the scientist who discovered penicillin [*Note #1].
In 1945, Fleming was awarded the Nobel Prize for Physiology and
Medicine, along with Ernst Chain and Howard Florey, who helped
develop penicillin into a widely available medical product.
... ... The US Centers for Disease Control and Prevention, in a
recent review of the control of infectious diseases in the 20th
century, makes the following points:
     1) Deaths from infectious diseases have declined markedly in
the US during the 20th century. This decline contributed to a
sharp drop in infant and child mortality, and to the 29.2-year
increase in life expectancy.
     2) In 1900, 30.4 percent of all deaths occurred among
children less than 5 years of age; in 1997, deaths in this group
were only 1.4 percent of the total.
     3) In 1900, the 3 leading causes of death were a) pneumonia,
b) tuberculosis, c) diarrhea and inflammation of the intestinal
tract (enteritis). These 3 causes, together with diphtheria,
caused one-third of all deaths. Of these deaths, 40 percent were
among children less than 5 years of age. In 1997, heart disease
and cancers accounted for 54.7 percent of all deaths, with 4.5
percent attributable to pneumonia, influenza, and human immune
deficiency virus (HIV) infection.
     4) Despite this overall progress, one of the most
devastating epidemics in human history occurred during the 20th
century: the 1918 influenza epidemic that resulted in 20 million
deaths, including 500,000 in the US, in less than 1 year -- more
than have died in as short a time during any war or famine in the
world. HIV infection, first recognized in 1981, has caused a
pandemic that is still in progress, affecting 33 million people
and causing an estimated 13.9 million deaths. These epidemics
illustrate the volatility of infectious diseases death rates and
unpredictability of disease emergence.
-----------
CDC Morbidity and Mortality Weekly Report: Control of Infectious
Diseases, 1900-1999.
(MMWR 1999 48:621) (J. Amer. Med. Assoc. 15 Sep 99 282:1029)
QY: National Center for Environmental Health, Centers for Disease
Control and Prevention, Atlanta, GA 30333 US.
-----------
Text Notes:
... ... *Note #1: The story of Fleming's discovery of penicillin
is a classic tale of serendipity. In 1928, shortly after he was
appointed professor of bacteriology at the University of London,
Fleming left a culture of staphylococcus germs uncovered for some
days. He was finished working with the culture, and he was about
to discard the culture dish when he noticed that several specks
of mold had fallen into it, and that around every mold speck the
bacterial colony had dissolved away for a short distance. The
clear space surrounding each speck indicated that bacteria had
died and no new growth had invaded the area. The physicist John
Tyndall (1820-1893), who among other things did much research
with ordinary dust, had briefly noted a similar observation 50
years earlier. Fleming isolated the mold and eventually
identified it as Penicillium notatum, a mold closely related to
the common variety often found growing on stale bread. Fleming
decided that the mold liberated some compound that inhibited
bacterial growth, and he labelled the substance "penicillin". In
a lecture many years later, Fleming spoke of his accidental
discovery of penicillin: "I have been trying to point out that in
our lives chance may have an astonishing influence and, if I may
offer advice to the young laboratory worker, it would be this --
never to neglect an extraordinary appearance or happening. It may
be -- usually is, in fact -- a false alarm that leads to nothing,
but it may on the other hand be the clue provided by fate to lead
you to some important advance."
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 24Sep99
For more information: http://scienceweek.com/swfr.htm


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