ScienceWeek

SCIENCE-WEEK

A Weekly Email Digest of the News of Science

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

August 17, 2001 -- Vol. 5 Number 33

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It takes a long time to understand nothing.
-- Edward Dahlberg (1900-1977)

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Section 1
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Contents of this Issue (Full reports in Section 2):

1. Life Without Photosynthesis
2. Turbulent Heat Flow
3. Intermolecular Disulfide Bonds and Prion Diseases
4. Origin of the Asteroid Belt
5. Nature of Earth's Mantle
6. Organismic Control of Evolution
7. Defining Diseases in the Genomics Era
8. AIDS - First 20 Years
9. Prevalence of Atrial Fibrillation in Adults
10. Cell Culture Forensics
11. Comparing Plant and Animal Diseases
12. Efficacy of Surgery for Temporal Lobe Epilepsy
13. In Focus: On Forensics
14. SW Archive: History of Physics: The Neutrino
15. Sources

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Section 2
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1. LIFE WITHOUT PHOTOSYNTHESIS
     From the standpoint of chemistry, photosynthesis can be
defined as the reductive carboxylation of organic substrates
carried on by chlorophyll-containing biological cells capable of
using light as their energy source. Fully oxidized carbon atoms
in the form of carbon dioxide are covalently linked ("fixed") to
organic acceptor molecules and are subsequently reduced and
rearranged into sugars and other organic molecules, with light
energy used to drive the fixation and provide the reducing power.
In a more general sense, the term "photosynthesis" refers to any
harvesting of radiant energy by a living system for use in the
synthesis of various compounds, with recognition that
photosynthesis by non-terrestrial living systems, if such systems
exist, may be quite different than photosynthesis on Earth.
     Jupiter's satellite system consists of at least 16 moons,
the four largest of which are called the Galilean moons, since
they were discovered by Galileo Galilei (1564-1642). They are Io,
Europa, Ganymede, and Callisto, in order of their orbital
distance from Jupiter. Europa, which is slightly smaller than
Earth's moon, has a thick icy crust, and may also have a liquid
water mantle beneath this crust. Very few craters are present on
Europa, which suggests an active surface that renews itself and
thus erases craters as fast as they form from impacts. The
surface also shows numerous lines about 30 kilometers wide and
1000 kilometers long, and these have been interpreted to be
breaks in the crust where water from below has refrozen. The
possible existence of a liquid water mantle beneath the ice on
Europa is of great interest to planetary scientists, since such a
mantle might contain life forms.
     C.F. Chyba and K.P. Hand (Stanford University, US) discuss
the possibility of life without photosynthesis on Jupiter's moon
Europa. Recent planetary exploration has demonstrated that oceans
of liquid water appear to be common in our Solar System. Galileo
spacecraft measurements of induced magnetic fields suggest that
Jupiter's large icy moons -- Europa, Ganymede, and Callisto -- 
all harbor salty oceans beneath the surface ice, which is of
great interest for extraterrestrial biology because life as we
know it requires liquid water.
     But life also requires energy, and life that does not
harvest sunlight directly obtains that energy from chemical
disequilibrium in the environment. On Earth, photosynthesis,
coupled with organic carbon burial, has produced oxidizing
surface conditions that provide chemical disequilibria for living
systems to exploit. Sunlight cannot, however, penetrate
kilometers of ice. The chemical energy available in the form of
disequilibrium concentrations of redox reactants is therefore
substantially less, raising the possibility of entropic death for
subsurface oceans.
     However, because non-photosynthetic sources of molecular
oxygen and other oxidants are available even to subsurface
oceans, entropic death may be avoided. Photosynthesis is nearly
impossible in Europa's oceans, but radiation processing of
Europa's ice and liquid water might nevertheless provide chemical
disequilibrium for life in Europa's ocean, with potassium-40
decay via gamma or beta emission decomposing water and leading to
oxygen and hydrogen production.
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SCI 2001 292:2026
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SCIENCE-WEEK 17 Aug 2001 http://scienceweek.com
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Related Background:
ASTROBIOLOGY: ON THE SEARCH FOR LIFE ON EUROPA
     It is an irony that although the term "living system" is
widely used in science, the term has no consensus definition.
Instead, there are many definitions: physiological, biochemical,
genetic, metabolic, thermodynamic, and so on. One might think the
question of the definition of "life" is only of philosophical
significance, but if you are designing a robot to search for
"life" on another astronomical body, precisely what is the robot
to search for? At the present time, the answer to this question
is not at all clear.
     Concerning definitions, the various definitions of "life"
currently in use can in general be summarized as follows:
     1) The physiological definition defines a living system as a
system that performs various functions such as eating,
metabolizing, excreting, breathing, moving, growing, reproducing,
and being responsive to external stimuli.
     2) The biochemical definition defines a living system as a
system that contains reproducible hereditary information coded in
nucleic acids and that metabolizes by controlling the rate of
chemical reactions with protein catalysts (enzymes).
     3) The genetic definition defines a living system as a
system capable of evolution by natural selection.
     4) The metabolic definition defines a living system as a
system with a definite boundary, the system continually
exchanging some of its materials with its surroundings, but the
exchange not altering the general properties of the system, at
least over some period of time.
     5) The thermodynamic definition defines a living system as
an open system manifesting a local increase in order (decrease in
entropy) at the expense of a larger decrease in order outside the
system.
     Of course, physical scientists can immediately think of many
"non-living" physical systems that can be described by one or
more of the above definitions, but biologists are fully aware of
such counter-examples and admit the ambiguities of all the
definitions. Research on Earth-bound living systems goes on,
ambiguity or no ambiguity, but when the focus is a search for
living systems elsewhere, the ambiguities become critical...
... ... C.F. Chyba and C.B. Phillips (Stanford University, US)
present a commentary on the search for life on Europa, the
authors making the following points:
     1) The authors point out that no broadly accepted definition
of life exists, and that most proposed definitions face severe
objections. Nevertheless, one working definition of life has
become influential in the "origin-of-life" community, the
definition that life is a self-sustained chemical system capable
of undergoing Darwinian evolution. The idea that the origin of
life is the same as the origin of evolution is a popular
corollary. The authors (Chyba and Phillips) suggest, however,
that such a definition is unlikely to prove useful to a remote
_in situ_ search for life. In a search for extraterrestrial life
in our Solar System, we instead fall back on a less ambitious
notion -- "life as we know it", meaning life based on a liquid
water solvent, a suite of biogenic elements (most particularly
carbon), and a source of free energy. The authors state: "The
availability of these on a given world would suggest life to be
possible, so that further exploration may be warranted."
     2) The authors point out that only once before have we
conducted a robotic search for extraterrestrial life. The Viking
spacecraft carried three experiments to search for life in
Martian soil samples, the experiments as designed implicitly
adopting a metabolic definition by searching for chemical changes
associated with metabolism. But instead of finding unambiguous
evidence of Martian biology, Viking appears to have encountered
unanticipated non-biological oxidant chemistry. The Viking gas
chromatograph mass spectrometer failed to find any organic
molecules in the Martian soil at the parts-per-billion or parts-
per-million level. The instrumentation provided a de facto search
for life that implicitly assumed a biochemical definition: no
(detected) organics, no life. In effect, a metabolic search for
life that yielded some ambiguously positive results was undercut
by the negative results of a search based on biochemistry.
     3) The authors suggest that with the benefit of 25 years
hindsight, there are a number of lessons to be learned from the
Viking experience in the search for life on Europa. a) If payload
limits permit, a remote search for life should use experiments
that assume contrasting definitions of life. b) If only one life-
detection experiment can be flown, the biochemical definition
should probably be primary. c) It is crucial to establish the
geological and chemical context within which biological
experiments will be conducted. Had the presence of the Martian
oxidants already been demonstrated, different biology experiments
would have been flown on Viking. d) Life detection experiments
should provide valuable information even if they fail to find
life. e) Nevertheless, exploration often cannot be hypothesis-
testing: much of what we do in planetary missions is simply
exploration.
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PNAS 2001 98:801
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SCIENCE-WEEK 9 Mar 2001 http://scienceweek.com
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Related Background:
CELL BIOLOGY: LIFE IN EXTREME ENVIRONMENTS
In this context, the term "extremophiles" refers to organisms,
both *prokaryotes and eukaryotes, that live at the relative
extreme of some parameter, e.g., temperature, pressure, acidity,
salinity, etc. Such organisms have been an increasing focus of
research since the 1960s, and intensive study of these organisms
has provided important insights into a number of biological
problems at several levels of biological organization, and has
also yielded some important applications.
... ... L.J. Rothschild and R.L. Mancinelli (NASA Ames Research
Center, US) present a review of current research on
extremophiles, the authors making the following points concerning
the various types of extremophiles:
     1) All biological organisms must either live within certain
conditions, or guard against the environment in order to maintain
these conditions intracellularly: a) In nearly all cases, the
water within a biological system must be liquified. Liquid water
is apparently the _sine qua non_ of life on Earth. b) Life
requires an input of energy, but an organism must also be able to
control energy flow. c) Redox chemistry is apparently universal
in living organisms; any condition that shuts down redox
chemistry is usually lethal. d) Since life is based on organic
chemistry, conditions in general must be such that organic
chemistry is allowed to operate.
     2) The authors point out that extremes of temperature create
challenges to biological organisms, from the structural
devastation produced by ice crystals at one extreme to the
denaturation of biomolecules at the other extreme. The solubility
of gases in water is correlated with temperature, creating
problems at high temperatures for aquatic organisms requiring
oxygen or carbon dioxide. Temperatures approaching 100 degrees
centigrade normally denature proteins and nucleic acids and
increase the fluidity of membranes to lethal levels. Chlorophyll
degrades above 75 degrees centigrade, excluding photosynthesis.
However, despite these restraints, thermal preferences of
biological organisms range from hyperthermophilic (maximum growth
at greater than 80 degrees centigrade) to psychrophilic (maximum
growth at less than 15 degrees centigrade). The most
hyperthermophilic organism, an *archaean prokaryote named
Pyrolobus fumarii, grows at temperatures up to 113 degrees
centigrade. Certain enzymes have high activity up to 142 degrees
centigrade. There are thermophiles among a number of groups of
prokaryotes; in contrast, the upper limit for eukaryotes is
apparently approximately 60 degrees centigrade. Concerning low
temperatures, representatives of all major taxa inhabit
environments with temperatures below 0 degrees centigrade. The
lowest recorded temperatures for active microbial communities is
approximately -18 degrees centigrade. The *nematode worm
Panagrolaimus davidi can apparently withstand the freezing of all
body water, a unique exception to the rule that frozen
intracellular water is lethal.
     3) Concerning the effects of other extremes, the authors
point out the following:
... ... a) The bacterium D. radiodurans is famous for its ability
to withstand radiation up to 20 *kilo-grays of gamma radiation
and UV radiation up to doses of 1000 joules per square meter.
... ... b) The deep sea floor (approximately 11,000 meters) of
the north Pacific Mariana trench harbors organisms that can grow
at standard temperature and pressure, but the trench has also
yielded obligatory "piezophiles" that can grow at 70 to 80
megapascals, but not below 50 megapascals.
... ... c) Organisms that can tolerate extreme desiccation enter
"anhydrobiosis", a state characterized by little intracellular
water and no metabolic activity. Organisms that can become
anhydrobiotic and survive include bacteria, yeast, fungi, plants,
insects, *tardigrades, *mycophagous nematodes, and the shrimp
Artemis salina. Tardigrades can survive vacuum desiccation.
... ... d) Concerning salinity, there are numerous species of
"halophiles", and some archaea, *cyanobacteria, and the green
alga Dunaliella salina can withstand periods in saturated sodium
chloride.
... ... e) Concerning pH, the red alga Cyanidium caldarium grows
at a pH as low as 0.5, although its growth optimum is pH 2 to 3.
The green alga Dunaliella acidophila can survive pH 0, with a
sharp growth maximum at pH 1. There are also various fungi that
grow near pH 0. The organism Ferroplasma acidarmanus has been
described growing at pH 0 in acid mine drainage in Iron Mountain,
California, the organism apparently thriving in a brew of
sulfuric acid and high levels of copper, arsenic, cadmium, and
zinc, with only a cell membrane and no cell wall. Various
archaea, bacteria, *protists, and *rotifers have been described
growing at pH 10.5.
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NAT 2001 409:1092
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Text Notes:
... ... *prokaryotes and eukaryotes: In general, prokaryotes are
unicellular organisms lacking a membrane-bound cell nucleus;
eukaryotes are unicellular or multicellular organisms in which
cells do contain a membrane=bound nucleus.
... ... *kilo-grays: 1 gray (Gy) = 1 joule of radiation energy
absorbed per kilogram of tissue. 1 rad = 0.01 Gy = 100 ergs per
gram of tissue. An example of magnitude significance: The entire
human body can probably absorb a single dose of up to 2 grays
without death. But as the whole body dose approaches 4.5 grays,
the death rate is approximately 50 percent. In general, the
effect of radiation on biological systems depends on total dose
and dose rate, with biological effects differing according to the
type of radiation. The sievert (Sv) equals the amount
of energy absorbed by a tissue or substance adjusted by a quality
factor to account for the biologic effects of different types of
radiation. For x-rays and gamma rays, the sievert equals the
gray. The approximate average total whole-body environmental
radiation from all ordinary sources of a human in the US is less
than 2 millisieverts per year.
... ... *archaean prokaryote: In current biotaxonomy, the
prokaryotes are divided into two groups, Archaea and Bacteria,
the groups differing primarily in certain biochemical attributes.
... ... *nematode worm: An abundant and ubiquitous phylum of
unsegmented roundworms.
... ... *tardigrades: An order of minute aquatic arthropods.
... ... *mycophagous nematodes: In general, nematodes that feed
on fungi.
... ... *cyanobacteria: A phylum of bacteria characterized by
blue-green (cyan) photosynthetic pigments, abundant in a variety
of habitats, particularly in fresh water and soil. Cyanobacteria
are responsible for generating a large portion of the free oxygen
in the Earth's atmosphere. They apparently produced stromatolite
limestone deposits, as well as the bulk of modern petroleum
deposits. (Stromatolites are laminated calcareous microbial
fossil deposits formed principally by cyanobacteria and algae.)
... ... *protists: (Proctista) One of the phylogenetic kingdoms,
this category is defined mostly by exclusion and contains all the
eukaryotic nucleated organisms that cannot be classified as
animal, plant, or fungus. Protists include protozoans, algae,
kelps, slime molds, and many obscure eukaryotes.
... ... *rotifers: An abundant and widespread phylum of
microscopic multicellular animals the size of large protozoa but
at the "organ" level of organization.
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SCIENCE-WEEK http://scienceweek.com 20Apr01
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Related Background:
BIOCHEMISTRY: ON THE PUZZLES OF HYPERTHERMOPHILES
     In this context, the term "geothermal" refers to the escape
of heat from the interior of the Earth into the Earth's surface,
and the term "hydrothermal" refers to hot solutions rising from 
cooling molten rock (magma). "Hydrothermal vents" are hot springs
occurring in volcanic regions of the ocean floor. The heavy-metal
ions and hydrogen sulfide dissolved in the overheated vent fluid
precipitate as metal sulfides as soon as contact with seawater
cools the fluid. This reaction produces the characteristic
underwater black "smoke" plume, with a vent "smoker chimney"
building up from precipitated materials, mostly gypsum and
sulfides.
     "Plate tectonics" is the modern theory that unifies many of
the features and characteristics of continental drift and sea
floor spreading into a coherent model. Continental drift is the
slow movement of the Earth's land masses, a shifting across the
underlying molten material. Sea-floor spreading is the process
whereby sea floor is continuously created as the crustal plates
move apart, and continuously destroyed where the plates push
against each other. The term "mid-ocean(ic) ridge" refers to a
topographic feature of a tectonic spreading center between
diverging oceanic plates. New crustal material is formed by
upswelling magma (molten material from which rock forms) as the
plates diverge.
     In general, bacteria have adapted to a wide range of
temperatures, with the range of temperature over which optimal
growth can occur in any one species spanning approximately 20
degrees centigrade; the range over which any growth at all takes
place usually spans approximately 40 to 50 degrees centigrade.
     Bacteria that grow at temperatures of less than 15 degrees
centigrade are called "psychrophiles". Obligate psychrophiles,
which have been isolated from Arctic and Antarctic ocean waters
and sediments, have optimum growth temperatures of approximately
10 degrees centigrade and do not survive if exposed to 20 degrees
centigrade.
     The term "mesophilic bacteria" refers to those bacteria in
which optimum growth occurs between 20 and 45 degrees centigrade;
such bacteria can usually grow in or survive temperatures between
10 and 50 degrees centigrade, and all animal pathogens are in
this group.
     So-called "thermophilic bacteria" are the only organisms
that can grow at temperatures higher than 60 degrees centigrade.
Such temperatures are encountered in rotting compost piles, hot
springs, and oceanic geothermal vents. In the runoff of a hot
spring, various thermophiles are found near the source where the
temperature has fallen to approximately 70 degrees centigrade. An
example is the species Thermus aquaticus, which has an optimum
temperature for growth of 70 degrees centigrade, and a maximum
temperature for growth of 79 degrees centigrade.
     In the mid-1980s, researchers discovered bacteria in
nutrient-rich, extremely hot hydrothermal vents in the deep sea
floor. For example, the bacteria in the genus Pyrodictium thrive
in the temperature range 80 to 110 degrees centigrade,
temperatures at which the water remains liquid only because of
the extremely high pressure.
... ... R.A. Zierenberg et al (3 authors at 3 installations, US)
present a review of current research on life in extreme
environments such as hydrothermal vents, the authors making the
following points concerning current puzzles in this area:
     1) The authors point out that eruption of volcanic rocks at
mid-ocean ridges is the major mechanism by which heat is lost
from the interior of the Earth. Approximately one-third of the
heat is removed from the sea-floor spreading centers by
convective circulation of sea water, and the magnitude of this
heat loss requires that the entire volume of the oceans
circulates through the mid-ocean ridges in approximately 10
million years. Seawater interaction with volcanic rocks at near
400 degrees centigrade results in substantial chemical flux and
makes an important contribution to buffering the composition of
some elements in sea water. Sea-floor hydrothermal vents support
ecosystems with enormous biomass and productivity compared with
that observed elsewhere in the deep oceans. What is the energy
source that fuels these oases of life and what adaptations allow
them to exist in these extreme environments?
     2) Although there is a potential abundance of chemical
energy at hydrothermal vents, deep-sea hydrothermal biological
communities have had to adapt to extreme conditions to exploit
this resource. Of particular interest are the hyperthermophiles,
which are defined as microorganisms able to grow at 90 degrees
centigrade and above. Approximately 20 different types of such
organisms are now known. They have been found both within the
walls of black smoker chimneys and where the hydrothermal vent
fluids mix with the surrounding seawater. Classifications of the
hyperthermophiles has provided new insights into the evolution
and the origin of life. All but two of the hyperthermophilic
genera are classified by *ribosomal RNA analysis as "Archaea"
(formerly Archaebacteria), which are the second domain of
prokaryotic life, in addition to the bacteria. By these
phylogenetic analyses, the hyperthermophilic archaea types and
the two hyperthermophilic bacteria types are the most slowly
evolving within their domains, suggesting that life may have
first evolved when the Earth was much hotter than it is now. Such
a thesis is very controversial, the thesis suggesting that extant
life forms are largely the result of temperature adaptations to
lower (below hyperthermophilic) temperatures.
     3) Evolution gives no clue, however, as to how life can
thrive near and above 100 degrees centigrade. Most microbes, and
all *eukaryotic cells, cannot survive at temperatures much above
50 degrees centigrade because of the general instability of
biological molecules. The 3-dimensional structure of most enzymes
and other proteins are lost at temperatures much above 70 degrees
centigrade, and the double-helical structure of DNA has a
comparable lack of stability in _in vitro_ studies. There are
also a wide variety of ubiquitous metabolites that are rapidly
hydrolyzed at temperatures above 90 degrees centigrade. How do
hyperthermophilic cells circumvent these problems?
     4) Although there are some examples of modified pathways and
unusual enzymes in hyperthermophiles, in general the biochemistry
of these organisms closely resembles that of the mesophilic
world. Yet, most enzymes from hyperthermophiles are extremely
stable at high temperatures, showing optimal catalytic activity
above 100 degrees centigrade with virtually no activity at
ambient temperature. These enzymes contain exactly the same 20
amino acids as enzymes from conventional organisms, so why are
they so stable? Sequence comparisons of analogous proteins from
hyperthermophilic and conventional organisms are essentially
identical, so the enormous amount of sequence information now
becoming available will be of little use in elucidating
stabilizing mechanisms. Comparisons must be made at the level of
3-dimensional structures, yet even then, there are no gross
structural differences between hyperthermophilic proteins and
their mesophilic counterparts, and both forms are stabilized by
the same noncovalent interactions. The number and extent of such
interactions is generally only slightly higher in the
hyperthermophilic versions, so extended protein stability at 100
degrees centigrade appears to be the result of very subtle,
synergistic, and cooperative intramolecular interactions.
Moreover, different types of hyperthermophilic proteins seem to
have unique solutions to the problem. A general mechanism by
which any conventional protein could be made stable and
functional at temperatures above 100 degrees centigrade may not
be forthcoming.
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PNAS 2000 97:12961
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Text Notes:
... ... *ribosomal RNA: A ribosome (not to be confused with
riboZYME) is a small particle, a complex of various ribonucleic
acid component subunits and proteins that functions as the site
of protein synthesis. The tripartite kingdom proposal (Archaea,
Bacteria, Eukarya) of Woese and others is primarily based on gene
sequence analysis of particular ribosomal RNA fractions.
... ... *eukaryotic cells: In general, a eukaryotic cell is any
biological cell containing internal membrane-bound organelles
such as a nucleus.
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SCIENCE-WEEK http://scienceweek.com 19Jan01

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2. TURBULENT HEAT FLOW
     Leo P. Kadanoff (University of Chicago, US) discusses
turbulent heat flow. Rayleigh-Benard systems are enclosed fluids
heated from below and cooled from above. Usually, as a fluid is
heated, it will become less dense. At the lowest heating rates,
there is no motion. Then, as the heating rate is increased, one
observes successively a steady motion, a periodic oscillation,
and a chaotic domain. At yet higher heating rates, one finds
turbulent motion in which the fluid swirls in highly-structured
but never-repeating patterns.
     At least four strategies will isolate features of turbulent
flow for scientific study: a) Look for the qualitative geometry
of characteristic structures recurring in the flow. b) Analyze
fluctuations, looking for characteristic probability
distributions. c) Obtain quantitative characterizations of the
average flows. d) Measure and study the space and time dependence
of velocities and other observables. In each case the attempt is
to isolate elements of the flow that are open to prediction,
replication, and comparison among different systems.
     The author concludes: "In recent years, there has been much
discussion of complexity in physical systems. At one time, many
people believed that the study of complexity could give rise to a
new science. In this science, as in others, there would have been
general laws, with specific situations being understandable as
the inevitable working out of these laws of nature. Up to now, we
have not found any such laws."
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PT 2001 August
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SCIENCE-WEEK 17 Aug 2001 http://scienceweek.com

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3. INTERMOLECULAR DISULFIDE BONDS AND PRION DISEASES
     Prions are a class of poorly understood proteins implicated
in a number of exotic human neurological diseases and in some
common animal diseases such as sheep scrapie and bovine
spongiform encephalopathy in cattle ("mad cow disease").
Spongiform encephalopathies are a type of brain disease found in
humans and animals and are characterized by macroscopic vacancies
produced by the disease process (the brain has a sponge-like
appearance). What is remarkable about prions is that they behave
as infectious agents, but they are 100 times smaller than viruses
and their mechanism of replication is unclear. One human disease
in which prions have been strongly implicated is Creutzfeldt-
Jakob disease (CJD), which appears to have a genetic basis in
about 15% of the cases. All the prion diseases are apparently
associated with the accumulation in the brain of an abnormal
protease-resistant isoform of the prion protein. In other words,
an abnormal variant of the normal prion protein is somehow copied
or produced by the disease process, which can be initiated by
introducing infectious prion into the system.
     E. Welker et al (Cornell University, US) discuss possible
chemical reactions involved in prion conformation changes.
Transmissible spongiform encephalopathies are fatal
neurodegenerative diseases characterized by vacuolation of brain
tissue and deposition of amyloid fibrils. These diseases are
unusual in that they have long incubation times and low
infectivities, and may be infectious, sporadic, or inherited.
     Even more remarkably, these diseases do not result from
typical pathogens such as bacteria and viruses; rather, the key
event is apparently the conversion of a protein (the prion
protein PrP) from its normal (cellular) isoform to an abnormal
"scrapie" isoform. Although the structures of the cellular
isoform for several species have been well characterized by NMR,
structural data on the scrapie isoform are scarce; however it is
generally believed that the prion protein conversion is purely
conformational and involves no chemical reactions.
     There is indeed ample experimental evidence for a
conformation change. However, the authors argue that prion
protein conversion may also involve a covalent reaction of the
sole intramolecular disulfide bond of the cellular prion.
Specifically, the available biochemical data are consistent with
the hypothesis that infectious prions are composed of scrapie
prion polymers linked by intermolecular disulfide bonds. Thus,
the prion protein conversion may involve not only a
conformational transition but also a thiol/disulfide exchange
reaction between the terminal thiolate of such a scrapie prion
polymer and the disulfide bond of a normal prion monomer.
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PNAS 2001 98:4334
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4. ORIGIN OF THE ASTEROID BELT
     The current nebula theory of planet formation proposes that
star-planet systems begin as a contracting cloud of gas and dust
that flattens into a rotating disk. The center of this cloud
becomes the star, and the planets eventually form in the disk of
the nebula. In the inner part of the nebula, the hottest part,
only high density minerals can form solid grains. The outer
regions are cooler, and in those regions icy materials of lower
density are formed. Planets grow from these solid materials,
beginning as dust grains, which grow by condensation and
accretion into planetesimals that range from a few centimeters to
a few kilometers in diameter. These planetesimals settle into a
thin plane around the star and accumulate into larger bodies, the
largest of which grow the fastest and eventually become
protoplanets.
     Once the star becomes a luminous object, the remaining
nebula is cleared as the star's radiation and the stellar-wind
(powerful streams of charged particles from the star's surface)
push the remnants out of the system. Thus ends the phase of
planet-building. As might be expected, the above theory is also
the current view of the history of our own solar system. Since
the details of disk formation, and the physical properties of
protoplanetary disks, can be modelled by quantitative theory, the
general idea is to investigate such disks that are apparent
around stars to test the theoretical models. There is no way to
do that with our own solar system, because the protoplanetary
disk is long gone. One needs young stars.
     Asteroids (also called "minor planets") are small rocky
objects, most of which orbit the Sun in a belt between the orbits
of Mars and Jupiter. A few asteroids follow orbits that bring
them into the inner Solar System, and several asteroids
occasionally pass within a few tens of millions of miles of
Earth. Some asteroids are located in the orbit of Jupiter, and
some asteroids have been detected as far away as the orbit of
Saturn.
     The term "asteroid belt" refers to the zone between the
orbits of Mars and Jupiter that contains the majority of
asteroids, the belt essentially with boundaries of 1.7 and 4.0
astronomical units. It is estimated that collisions between
asteroids in the asteroid belt occur at velocities of
approximately 5 kilometers per second.
     Concerning asteroids in general, approximately 200 of these
objects are more than 100 kilometers (60 miles) in diameter, and
more than 2000 asteroids are more than 10 kilometers in diameter.
There are believed to be approximately half a million asteroids
with diameters greater than 1 kilometer. The consensus view is
that asteroids are composed of material that failed to build a
planet at a distance of 2.8 *astronomical units (AU) from the
Sun, perhaps due to the influence of massive Jupiter just outside
the asteroid belt. Until recently, the shapes and surface
features of asteroids were a matter of conjecture; during the
past decade, however, significant direct observations of
asteroids have been relayed back to Earth from spacecraft.
     Derek C. Richardson (University of Maryland, US) discusses a
new hypothesis of the origin of the asteroid belt. A common
misconception is that asteroids are the remains of a large planet
that mysteriously exploded long ago. However, at the present time
there is hardly enough material in the asteroid belt to make a
small moon, let alone a planet, so the consensus is that
something must have happened that either prevented the formation
of a planet between Mars and Jupiter or that cleared out most of
the material that accumulated there. Most astronomers consider
that Jupiter was involved, since it is the largest and therefore
the most gravitationally influential planet. But exactly what
happened is a matter of debate, since presently Jupiter affects
only a few narrow regions of the asteroid belt.
     J.E. Chambers and G.W. Wetherill (Meteorit. Planet. Sci.
2001 36:381) have now proposed a new hypothesis that describes
what may have happened. The essential idea is that there may once
have been Earth-sized planets in the asteroid belt, but a
combination of complex dynamics and chance events resulted in
most of the material being removed. The proposal is that Jupiter
grew rapidly enough to eventually perturb the asteroidal planets,
with perturbations caused by resonances between the orbits of the
giant planet and the young asteroidal planets. In this situation,
a resonance would arise when the orbital periods of two bodies
are whole-number ratios of each other. The Chambers-Wetherill
model is based on numerical simulations, and these simulations
apparently indicate that interactions between embryo planets and
Jupiter would cause more than 90 percent of the mass in the
asteroid belt to be cleared in less than a few hundred million
years.
-----------
NAT 2001 411:899
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Text Notes:
     *astronomical units: (AU) 1 AU = the mean distance from
the Sun to the Earth = approximately 93 million miles, and
exactly 149,597,870 kilometers.
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SCIENCE-WEEK 17 Aug 2001 http://scienceweek.com

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5. NATURE OF EARTH'S MANTLE
     Studies of seismic wave velocities have been central to our
understanding of the structure of the deep interior of the Earth.
The center of the Earth, located below 2900 kilometers, comprises
the "core", which is divided into two parts. The "outer core" is
believed to be composed of molten metallic iron alloyed with
nickel and some light elements such as oxygen, hydrogen, carbon,
or sulfur. In contrast, the "inner core", which extends from 5155
kilometers to the Earth's center, is probably composed of solid
iron-nickel metal with significantly lesser amounts of light
components. Overlying the core is the "mantle", divided into
"upper mantle" and "lower mantle" by a zone of rapid increase in
density and seismic wave velocity at approximately 700 kilometers
depth. The so-called "crust", the outermost solid layer of the
Earth, represents less than 1 percent of the Earth's volume and
varies in thickness from approximately 5 kilometers beneath the
oceans to approximately 60 kilometers beneath continental
mountain chains. The term "lithosphere" refers to the upper
(oceanic and continental) layer of the solid Earth, the
lithosphere comprising all crustal rocks and the brittle part of
the uppermost mantle. At the high temperatures that exist beneath
the lithosphere, the mantle is apparently slowly deforming, its
flow associated with "plate tectonics".
     Catherine McCammon (University of Bayreuth, DE) discusses
current research on Earth's mantle. Seismological studies
indicate that a boundary at 660 kilometers divides the transition
zone from the lower mantle, but in the absence of direct samples
from this region, the nature of the boundary has remained
unclear. In particular, the nature of convection -- whether such
convection involves the whole mantle or is layered with a
boundary at 660 kilometers -- remains unknown. The possibility
that diamonds may contain tiny inclusions of lower mantle
material was recognized in 1984 by B.H. Scott et al, but it
required another decade for more convincing evidence for such
inclusions to be found. Similar evidence has now been reported
from at least 12 localities on 5 continents, and the inclusions
provide insights into the 660-kilometer boundary and, more
generally, into mantle chemistry, diamond formation, and mantle
dynamics. The mineral ferropericlase accounts for more than half
of the inclusions described thus far; other inclusions consist of
enstatite and calcium silicate.
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SCI 2001 293:813
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6. ORGANISMIC CONTROL OF EVOLUTION
     Marina Chicurel (_Science_) discusses the ability of
organisms to have some control over their own evolution. With
roots dating back to Charles Darwin in the mid-1850s, the
question of whether organisms harbor systems for adjusting their
own rate of evolution remains open. Recent experiments suggest
that organisms have mechanisms of speeding their evolution by
boosting their genetic variability, and the idea is generating
increasing excitement among a group of cell and molecular
biologists. Within the past 2 years, for example, researchers
have revealed molecular clues that could help explain apparent
increases in genetic variability not only in bacteria but in
eukaryotes as well. However, a number of evolutionary biologists
are attempting to reduce this enthusiasm. Although the critics
say the new molecular findings are intriguing, they question
their origins and role in evolution. Specifically, these
biologists say it is uncertain whether these processes were
selected for their ability to generate variability in the first
place. Nor is it clear whether these processes accelerate long-
term evolution. Because most mutations are harmful, increased
variability may often be costly to individuals and species.
According to one evolutionary biologist, "it is hard to see how
selection would directly favor a process that generated random
variation or even one that just preserved it."
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SCI 2001 292:1824
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SCIENCE-WEEK 17 Aug 2001 http://scienceweek.com
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Related Background:
NEW DATA SUGGESTS IMPORTANCE OF MUTATION RATE VARIABILITY
There is a growing consensus that at least in bacteria mutation
rates within a species can be highly variable, and that this
variability is itself subjected to Darwinian selection. Two
related reports appeared this week, one involving mathematical
modeling [F. Taddei et al (University of Paris, FR; University of
Sussex, UK], and the other experimental observations of
populations of the bacterium E. coli [P. D. Sniegowski et al
(University of Pennsylvania, US; Michigan State University US)].
Both groups provide support for the idea that high mutation rates
may play an important role in adaptive evolution. In an essay
reviewing this work, E. Richard Moxon (University of Oxford, UK)
and David S. Thaler (Rockefeller University, US) claim a broader
implication, and state, "The generation of variation is itself
under genetic control, allowing a reflectivity -- an
informational feedback -- on the mechanisms by which diversity is
generated in biological evolution."
-----------
NAT 1997 12 June
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SCIENCE-WEEK 19 Jun 2001 http://scienceweek.com

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7. DEFINING DISEASES IN THE GENOMICS ERA
     L.K.F. Temple et al (University of Toronto, CA) discuss
concepts of disease in the genomics era. The human genome
sequence will dramatically alter how we define, prevent, and
treat disease. As more and more genetic variations among
individuals are discovered, there will be a rush to label many of
these variations as disease-associated. The authors suggest we
need to define the term "disease" so that it incorporates our
expanding genetic knowledge, taking into account the possible
risks and adverse consequences associated with certain genetic
variations, while acknowledging that a definition of disease
cannot be based solely on one genetic abnormality. The authors
point out that the human genetic sequence is likely to reveal
many harmless genetic variations that will turn out not to be
associated with disease. Disease is a fluid concept influenced by
societal and cultural attitudes that change with time and in
response to new scientific and medical discoveries. Until we
resolve questions about polymorphisms, incomplete penetrance of
genetic mutations, and the contribution of environmental factors
to disease etiology, we will not be able to assess the
probability of adverse consequences associated with a particular
gene abnormality. Until a mutation is demonstrated to involve a
defined risk of developing adverse consequences, individuals
carrying that mutation should not be considered diseased.
-----------
SCI 2001 293:807
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SCIENCE-WEEK 17 Aug 2001 http://scienceweek.com

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8. AIDS - FIRST 20 YEARS
     Kent A. Sepkowitz (Sloan-Kettering Cancer Center, US)
discusses the first 20 years of AIDS. The disease now known as
acquired immunodeficiency syndrome was first reported 20 years
ago (June 5, 1981) in the _Morbidity and Mortality Weekly Report_
of the Centers for Disease Control under the quiet title
"Pneumocystis pneumonia -- Los Angeles". The description was not
the lead article; that distinction went to a report of dengue
infections in vacationers returning to the US from the Caribbean.
Not even the most pessimistic reader could have anticipated the
scope and scale the epidemic would assume two decades later. By
December 2000, 21.8 million people worldwide had died of the
disease, including more Americans (438,795) than died in World
War I and World War II combined. During the 1990s, the disease
was transformed for many patients in industrialized nations from
a predictably fatal infection to a chronic condition requiring
daily medication and occasional visits to the doctor's office.
But the epidemic currently threatens to spin completely out of
control in many of the world's poorest nations, and improved
control of HIV infection in the next decade looms as a daunting
task. An effective vaccine is not imminent, and most governments
are unlikely to initiate frank public discussion about sexual
intercourse and injection-drug use, despite the glaring need.
Nonetheless, patients and health care workers alike should find
solace and inspiration in the remarkable achievements of the past
20 years. Not so long ago, the hope that a cause of AIDS would be
found and that effective therapies for the disease would be
developed seemed as unlikely as global control of the disease
seems today.
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NEJM 2001 344:1764
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SCIENCE-WEEK 17 Aug 2001 http://scienceweek.com

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9. PREVALENCE OF ATRIAL FIBRILLATION IN ADULTS
     The cardiac "atrium" is the upper chamber of each half of
the heart, and "atrial fibrillation" is a heart condition marked
by rapid and arrhythmic contractions of the atria, which causes
the lower chambers (ventricles) to beat irregularly at a rate of
130 to 150 per minute. A.S. Go et al discuss the prevalence of
diagnosed atrial fibrillation in adults. Atrial fibrillation is
the most common clinically significant cardiac arrythmia. It is
also a potent risk factor for ischemic stroke, increasing the
risk of stroke 5-fold and accounting for approximately 15 percent
of all strokes in the US. Symptomatic atrial fibrillation may
also reduce quality of life, functional status, and cardiac
performance. The prevalence of atrial fibrillation increases
substantially with age. In general, atrial fibrillation is
associated with higher medical costs and increased risk of death. 
The authors report a study to estimate the prevalence of atrial
fibrillation, with US national projections of the number of
persons with atrial fibrillation through the year 2050. The
authors report their results confirm that atrial fibrillation is
common among older adults. The number of patients with atrial
fibrillation is likely to increase 2- to 5-fold during the next
50 years, reflecting the growing proportion of elderly
individuals.
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JAMA 2001 285:2370
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SCIENCE-WEEK 17 Aug 2001 http://scienceweek.com

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10. CELL CULTURE FORENSICS
     Stephen J. O'Brien (National Cancer Institute, US) discusses
the problem of cell line contamination. Genomics, proteomics,
vaccinology, transgenics, stem cells -- advances in all these
areas critically depend on tissue culture, the ability to
cultivate an organism's living cells in plastic dishes.
Nutritional trial and error for decades of painstaking cell
gardening laid the groundwork for the several thousand human
primary cell explants and immortal tumor lines available in
modern biotechnology. Now, the 50-year-old problem of cell line
misidentification from cell contamination, mislabeling, or, in
some cases, conscious deceit, has a brand new tool for cell and
individual validation, a composite short tandem repeat (also
called genomic microsatellite) genotype signature. The new
advances, the latest in cell identification technologies,
represent the most advanced and powerful forensic approach to
dispense with the embarrassing, expensive, and maddening cell
contamination that occurs in biomedical laboratories. The extent
of inadvertent cell line contamination is enormous. During the
1970s and 1980s, as many as one in three cell lines deposited in
cell culture repositories were imposters, one cell line
overtaking or masquerading as another.
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PNAS 2001 98:7656
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SCIENCE-WEEK 17 Aug 2001 http://scienceweek.com

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11. COMPARING PLANT AND ANIMAL DISEASES
     B.J. Staskawicz et al discuss comparisons between plant and
animal diseases. The ability of pathogenic microorganisms to harm
both animal and plant hosts has been documented since the initial
demonstration in the 1870s that microbes were causal agents of
disease. Since the initial discoveries by R. Koch in 1876 that
Bacillus anthracis caused anthrax and by T.J. Burrill in 1878
that Erwinia amylovora caused fire blight in pears, knowledge of
animal and plant diseases has increased enormously. Today, the
genomes of the most animal and plant pathogens have been or will
be sequenced, and the molecular basis of pathogenicity is
beginning to be elucidated. Furthermore, several model plant and
animal host genomes are fully sequenced, and basic discoveries
made in the post-genomic era will fuel the quest for development
of new strategies for disease control. In the past 5 years,
observations have revealed that bacterial pathogens share common
strategies to infect and colonize plant and animal hosts. One
strategy is the ability to deliver effector proteins into their
respective host cells to mimic, suppress, or modulate host
defense signaling pathways and to enhance pathogen fitness. On
the host side, plants and animals have both evolved sophisticated
surveillance mechanisms to recognize various bacterial pathogens.
Plants recognize distinct effectors from pathogenic bacteria,
whereas animals recognize conserved molecular patterns such as
those derived from lipopolysaccharide or peptidoglycan. The
discovery that surveillance proteins in diverse hosts share
common protein signatures that perform similar functions has
provoked ideas concerning how these resistance mechanisms
evolved.
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SCI 2001 292:2285
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SCIENCE-WEEK 17 Aug 2001 http://scienceweek.com
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Related Background:
EVIDENCE OF A VIRUS SWITCHING HOSTS FROM PLANT TO VERTEBRATE
On occasion, viruses are transmitted to a host species that they
have not previously infected or that they rarely infect, and
several of these atypical interspecies transmission events (host-
switching events) have led to disease outbreaks in this century.
The mixing of viral genomes can occur via recombination, and this
has been linked to severe disease outbreaks, and in some cases
may involve host-switching. To date, however, there is no
evidence reported of recombination between viruses that infect
hosts from different kingdoms: e.g., no evidence of vertebrate-
infecting viruses recombining with plant-infecting viruses. Two
known vertebrate viruses of the circovirus family (Porcine
circovirus and Psittacine beak and feather disease circovirus)
are similar in many ways to certain plant-infecting nanoviruses.
Circoviruses and nanoviruses are both small icosahedral particles
17 to 22 nanometers in diameter, with small circular single-
stranded DNA genomes. The genomes of circoviruses are about 2
kilobases long, whereas nanovirus genomes are about 1 kilobases
long. M.J. Gibbs and G.F. Weiller (AU) now provide genome
analytical evidence indicating that circoviruses evolved from a
nanovirus, that a nanovirus DNA was transferred from a plant to a
vertebrate, that the transferred DNA maintained the ability to
replicate and was therefore a type of virus, and that the
transfer was a host-switch. The authors speculate that this host-
switch occurred when a vertebrate was exposed to sap from an
infected plant.
-----------
PNAS 1999 6 Jul
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SCIENCE-WEEK 23 Jul 1999 http://scienceweek.com
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Related Background:
HUMAN IMMUNE SYSTEM LINKAGE TO A PLANT DEFENSE SYSTEM
Interstitial tissue is a general term for tissue forming
interstices in an organ or tissue, and "glioma" is a general term
for any neoplasm deriving from one of the various types of cells
that form the interstitial tissue of brain, spinal cord, pineal
gland, posterior pituitary gland, or retina. Glioblastoma
multiforme is a type of glioma that occurs most frequently in the
adult brain. ... ... Szyperski et al (4 authors at Institute for
Molecular Biology and Biophysics Zurich, CH) report that a human
glioma pathogenesis-related protein (GliPR), which is highly
expressed in the brain tumor glioblastoma multiforme (which
arises from brain immune cells), shows 35% amino acid sequence
identity with a tomato pathogenesis-related protein (P14a), which
has an important role for the plant defense system. The authors
compared the molecular structure of both proteins in the folded
state and identified a common partially solvent-exposed spatial
cluster of 4 amino acid residues, this cluster apparently
conserved in all known plant pathogenesis related proteins of a
particular type (called Type 1). The authors suggest their data
indicate a common active site for the human and plant proteins
and a functional link between the human immune system and a plant
defense system. In an analysis of possible evolutionary linkages,
the authors further suggest that the human immune and plant
defensive proteins considered here arose from a common ancestor
that evolved into a large pathogenesis-related protein
superfamily that includes the human protein (GliPR), plant
pathogenesis-related proteins of Type 1, mammalian sperm-coating
proteins, allergens of insect venoms, and snake or lizard
toxins -- the superfamily thus appearing in the 3 kingdoms of
animals, plants, and fungi. Although all these proteins exhibit
alignment of their amino acid sequences with the human glioma
protein, the underlying mechanism for the action of these
proteins is unknown. The authors suggest it is possible all the
proteins of this superfamily operate according to the same
molecular mechanism.
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PNAS 1998 3 Mar
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SCIENCE-WEEK 27 Mar 1998 http://scienceweek.com

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12. EFFICACY OF SURGERY FOR TEMPORAL LOBE EPILEPSY
     Hypersynchronous discharge of groups of neurons in the brain
can produce the motor symptoms of seizure activity if these
neurons are directly or indirectly connected to the part of the
brain controlling peripheral muscle tissue. When seizures are a
chronic syndrome, a diagnosis of "epilepsy" is usually made, but
it is important to understand that the term "epilepsy" refers to
chronic seizures produced by any cause, e.g., trauma, infection,
genetic dysfunction, neuroactive drugs, etc. Thus epilepsy is not
a unitary disease; it rather a label for a collection of
symptoms.
     S. Wiebe et al (University of Western Ontario, CA) report a
randomized controlled trial of surgery for temporal epilepsy.
Randomized trials of surgery for epilepsy have not previously
been conducted because of the difficulties involved in designing
and implementing feasible studies, and the lack of data
supporting the therapeutic usefulness of surgery has precluded
making strong recommendations for patients with epilepsy.
     The authors conducted a randomized controlled trial to
assess the efficacy and safety of surgery for temporal-lobe
epilepsy. 80 patients with temporal-lobe epilepsy were randomly
assigned to surgery (40 patients; surgical group) or treatment
with antiepileptic drugs for one year (40 patients; medical
group). Evaluations were made after one year, and the results
demonstrate that in temporal-lobe epilepsy surgery is superior to
prolonged medical therapy, and that randomized trials of surgery
for epilepsy are feasible and appear to yield precise estimates
of treatment effects.
     In a commentary on this report, Jerome Engel Jr. (University
of California Los Angeles, US) points out that approximately one-
third of people in the US with epilepsy have seizures that cannot
be controlled by anti-epileptic drugs. As many as one-quarter to
one-half of these people are potential candidates for surgical
treatment, yet a 1990 survey revealed that only 1500 therapeutic
surgical procedures for epilepsy were performed in the US in that
year, and that the rate of use of surgery for epilepsy was
equally low in other industrialized countries.
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NEJM 2001 345:311,365
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SCIENCE-WEEK 17 Aug 2001 http://scienceweek.com
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Related Background:
BRAIN PLASTICITY IN CHILDREN AFTER HEMISPHERECTOMY
Epilepsy is a term unhappily applied to several dozen different
seizure disorders, their commonality being central nervous system
seizures rather than identical pathological processes causing the
seizures. From a neurophysiological standpoint, a seizure is the
end result of a massive discharge of nerve cells, often the motor
neuron pathways that activate muscle cells. Seizures can be
produced by various central nervous system infections, metabolic
disturbances, toxic agents, cerebral oxygen deficiency, expanding
brain lesions, cerebral trauma, cerebral hemorrhage, and so on.
In general, any physiological event or series of events that
produces a wide disruption of central nervous system activity has
the potential for production of seizures of one sort or another.
Most patients who for reasons known (symptomatic epilepsies) or
unknown (idiopathic epilepsies) are chronically subjected to
seizures can be helped with various pharmacological agents such
as phenytoin or cloneazepam, but 10% to 20% of patients have
seizures that cannot be managed by drugs. If the seizures are due
to a specific damaged locus in the brain (the "epileptic focus"),
the recourse for these patients, if the locus can be determined,
is surgery. What is done is to completely remove the epileptic
focus, sometimes an area no larger than a small coin, and if the
surgery is successful the cure is immediate and permanent. There
are cases, however, in which the affected part of the brain is
quite large, the seizures completely unmanageable, and the only
recourse is radical surgery. Since severe chronic epilepsy due to
brain lesions is usually first diagnosed in young children, it is
such children who are the usual patients in radical brain surgery
for epilepsy. The most radical and fairly common procedure is
hemispherectomy, removal of an entire half of the brain, and the
most remarkable aspect of this is that when the surgical
procedure is successful, not only are the seizures eliminated,
but the child can function as well or almost as well as any other
child. It is an example of a phenomenon well-known to
neurobiologists called "brain plasticity", the ability of the
brain to recover the function of a damaged or removed region by
assignment of the function to an undamaged location. The language
area of the brain, for example, is often considered to be fixed
on the left side of the brain by genetics, but in truth it is not
so fixed, and if the left side of the brain is removed at an
early age, the right side of the brain will quickly develop a
language center and there will be little functional impairment.
In a recent publication, Eileen P.G. Vining (Johns Hopkins
University, Baltimore MD US) reports the progress of 54 children
who underwent hemispherectomy for recurrent severe epileptic
seizures. The majority of the patients were seizure-free
following surgery, no longer needed drugs, and many of the
patients are now in school. One of the most significant facts
about the human brain is that its histological development
continues at least until adolescence, and the dynamism of this
histological development is what is responsible for its
remarkable plasticity.
-----------
Pediatrics August 1997
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SCIENCE-WEEK 22 Aug 1997 http://scienceweek.com

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13. IN FOCUS: ON FORENSICS
"Many trace the work of forensic pathology -- the medicolegal
investigation of death -- to the ancient Greeks who, circa 380
BC, began dissecting various animal carcasses and applying their
findings -- at times absurdly -- to humans. Greek physicians did
perform the rare human dissection. But Hippocratic writings
express a deep disdain for the business, even as they named it:
_autopsy_. Despite strange implications of self-examination, the
term has resisted 2000 years of scientific lobbying to replace it
with the more logical _necropsy_. The Egyptians, meanwhile,
suffered no such Hippocratic qualms. Historic accounts of anatomy
and pathology classes at the Museum of Alexandria in the 3rd and
4th century BC describe not only autopsies but also the live
dissection of criminals 'for the study, even while they breathed,
of those parts which Nature had before concealed.' Among the
Greek and Egyptian observations were descriptions of death's
first known clocks: _rigor mortis_, or postmortem stiffening, and
_algor mortis_, body cooling. Unlike their 19th century
counterparts, who would chart the stiffening and cooling with
hour-by-hour muscle testing and body-core thermometers, the
ancients were satisfied with the postmortem touch test that
homicide detectives still use today: warm and not stiff -- not
dead more than a couple hours; warm and stiff -- dead between a
couple hours and a half day; cold and stiff -- dead between a
half day and two days; cold and not stiff -- dead more than two
days... History records the first known application of medical
knowledge to death investigation in 44 BC. Summoned to examine
the body of Julius Caesar, the Roman physician Antistius
announced that he knew which of the would-be emperor's 23 stab
wounds had proved fatal. By clocking death to a particular blow,
Antistius thwarted the plot by which the Roman senators had hoped
to avoid any _one_ of them standing trial for murder. In the end,
history tells us, they all paid with their lives. Antistius's
historic death determination, however dubious it may have been,
marked the beginning of the pathologist's role as expert witness
to murder. In fact, it gave us the term _forensic_, Latin for 
'before the forum', which is where Antistius made his fateful
declaration."
-----------
Jessica Snyder Sachs: _Corpse: Nature, Forensics, and the
Struggle to Pinpoint Time of Death_.
(Perseus Publishing, Cambridge MA, 2001, p.11)
(To be published November 2001)
http://www.amazon.com/exec/obidos/ASIN/073820336X/scienceweek
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SCIENCE-WEEK 17 Aug 2001 http://scienceweek.com

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14. SW ARCHIVE: HISTORY OF PHYSICS: THE NEUTRINO
     The history of particle physics during the first 30 years of
the 20th century is an excellent example of the intimate
interplay between theory and experiment. One of the central
problems in the physics of matter during this period was to
understand the emissions of radioactive substances first
discovered in 1896 by Henri Becquerel (1852-1908). Spontaneous
radioactive decay is essentially a spontaneous transmutation of
an unstable atomic nucleus (nuclide) A into nuclide B, with
nuclide A initially in a higher energy state and losing energy to
transmute into the "daughter" nuclide B. During the early years
of particle physics, the energy loss was considered to be
accomplished by emission of one of three types, depending on the
nature of nuclide A: positively charged alpha particles (helium
nuclei), negatively charged beta particles (electrons), or
neutral gamma rays (high energy electromagnetic radiation). Since
the energies of decaying nuclides and daughter nuclides are fixed
according to nuclide identity, one would expect the observed
energies of the 3 types of particles to also be fixed for each
species of decaying nuclide. During the period before 1927, this
was known to be true for alpha particles and gamma rays, but
there was intense controversy about whether it was true for beta
particles. Indeed, some early experiments indicated that it was
not true for beta particles, and this posed a problem, since
conservation laws require an accounting for all the energy and
the numbers for beta decay did not add up. The controversy
continued for nearly 30 years, particularly among
experimentalists who disagreed concerning experimental methods
and interpretations of experimental results, until finally in the
late 1920s it was conclusively demonstrated by experiment that
during the beta-decay process high-speed electrons of various
energies are emitted with a continuous beta-emission energy
distribution spectrum (i.e., a plot of the number of electrons
vs. energy of these electrons) over the range of energies.
     Given the experimental evidence of a continuous beta-decay
spectrum, theoreticians tackled the problem of accounting for
beta decay without violating conservation laws. In 1930, 
Wolfgang Pauli (1900-1958) proposed that when a beta particle was
emitted, another particle, without charge, and perhaps without
mass, was also emitted, and that this second particle carried off
the missing energy. Enrico Fermi (1901-1954) suggested the
particle carrying the missing energy be called "neutrino", which
is Italian for "little neutral one", and in 1934 Fermi
incorporated the neutrino into his theory of beta decay.
     Most theoretical and experimental physicists immediately
accepted the proposed existence of the neutrino as the best
solution to an important puzzle, but it was not until 1956 that
Frederick Reines (1918-1998) and Clyde Cowan (1919-1974) managed
to finally obtain experimental evidence for the existence of the
elusive neutrino by means of experiments involving emission beams
from a fission reactor. Enrico Fermi received the Nobel Prize in
Physics in 1938; Wolfgang Pauli received the Nobel Prize in
Physics in 1945; and Frederick Reines received the Nobel Prize in
Physics in 1995. (Clyde Cowan was not eligible for the Nobel
Prize at the time it was awarded to Reines, since the Nobel Prize
is not awarded posthumously.) 
... ... Allan Franklin (University of Colorado Boulder, US)
presents an essay on the history of beta decay and the neutrino
1900-1930. The author points out there were two major responses
to the establishment of the continuous energy spectrum of beta
decay. One idea, favored by Niels Bohr (1885-1962), was that
energy might not be conserved in beta decay. But work on the
*Compton effect provided evidence against this view. The second
major response was Pauli's "desperate way out", Pauli suggesting
that a very light, neutral particle was also emitted in the beta
decay. Pauli originally called this particle the "neutron", but
Fermi christened the particle the "neutrino" and quickly
incorporated the neutrino into a successful theory of beta decay.
During the next few decades, Fermi's theory was strongly
supported by experimental observations, and that success provided
most physicists with sufficient evidence for the existence of the
neutrino. As stated by Frederick Reines, for 26 years before the
existence of the neutrino was experimentally demonstrated, "the
[Fermi] theory was so attractive in its explanation of beta decay
that belief in the neutrino as a 'real' entity was general."
-----------
Editor's note: Although modern views of beta decay and the
neutrino (see related background material below) are more complex
than the views held in the early years of the 20th century, a
remarkable group of early experimental and theoretical particle
physicists (only some of whom are mentioned in this SW brief)
provided the foundation that still supports our understanding of
the atomic nucleus and radioactive decay.
-----------
PT 2000 February
-----------
Text Notes:
... ... *Compton effect: (Compton scattering) In general, the
reduction in the energy of high energy photons when the photons
are scattered by free electrons, the electrons thereby gaining
energy, with total energy conserved. The effect was discovered in
1923 by A.H. Compton (1892-1962). Compton received the Nobel
Prize in Physics in 1927.
-------------------
SCIENCE-WEEK http://scienceweek.com 5May00
-------------------
Related Background:
ON NEUTRINO OSCILLATIONS
The fundamental particles of 20th century physics came into
existence as theoretical constructions designed to explain
certain specific experimental observations. In some cases, the
existence of a particular particle has been verified by direct
experiment; in other cases, the required verification experiments
are extremely difficult to accomplish, and the particles related
to these experiments have remained theoretical constructions.
The neutrino was first theoretically postulated by Wolfgang Pauli
(1900-1958) in 1930 in order to maintain the conservation of
energy principle in the analysis of the results of certain *beta-
decay experiments. The Pauli neutrino was a particle with no
charge and zero rest mass. Experimentally, the particle was
tentatively identified by F. Reines and C. Cowan in 1953 and more
definitely in 1956. Neutrinos are "leptons", which are a group of
point-like particles with *spin of 1/2 that are not affected by
so-called "*strong interactions" and that are not constructed of
*quarks. In the *Standard Model in particle physics, there are 6
particle types categorized as leptons: the electron, the *muon,
the massive *tau lepton, and a neutrino associated with each of
these (denoted as 3 neutrino "flavors" or "generations"). 
Neutrinos are produced in great numbers by the Sun, but they
almost never interact with atoms, and an estimated 10^(12) solar
neutrinos flow through our bodies each second without any
consequence. Measurements of solar neutrinos, however, have
produced a mystery: the neutrino density measured by detectors is
approximately one-third that expected from theoretical
calculations of solar neutrino emission. Two kinds of solutions
have been proposed to resolve this mystery, one solution
involving revisions to the theory of stellar structure, and the
other solution involving revisions to nuclear particle theory. In
the latter case, the proposal is that the neutrino may oscillate
among the 3 different flavors (states), with the result that
neutrino detectors detect only one flavor or one-third of the
solar emission. The existence of such neutrino oscillation would
have important implications, since it has been believed that
neutrinos, like photons, have zero mass. But theory indicates
that if neutrinos oscillate they must have mass, and neutrinos
are so numerous that even an extremely small mass would
theoretically be sufficient to affect the future of the Universe
as a whole. The question of neutrino oscillation, therefore, is a
critical problem affecting a good deal of fundamental physics and
cosmology, and there is recent evidence interpreted to indicate
that such oscillation does indeed occur and that neutrinos do
indeed have nonzero mass.
... ... K. Kaneyuki and K. Scholberg (2 installations, JP US)
present a detailed review of current research concerning neutrino
oscillations, the authors making the following points:
     1) The basic strategy for measuring neutrino oscillations is
simple. Given a source of neutrinos, either natural or
artificial, one allows the neutrinos to propagate for a known
distance, and then one obtains as much quantitative information
as possible concerning their energy and flavor. If the amount of
a given flavor, as a function of energy and distance, is that
expected from the quantum mechanical predictions arising from the
oscillation hypothesis, then neutrino oscillation has been
discovered.
     2) Three neutrino sources are currently used in research:
The Sun, atmospheric *cosmic-ray showers, and particle
accelerators. At present, the clearest neutrino oscillation
evidence from atmospheric neutrinos comes from the "Super-
Kamiokande" experiment, which observes neutrino interactions by
detecting *Cherenkov (Cerenkov) radiation. The Super-Kamiokande
experiment has been built and operated by a collaboration of
approximately 130 scientists from Japan and the US, the project
headed by Y. Totsuka (University of Tokyo, JP). The apparatus
consists of 50 kilotons of ultrapure water housed approximately
one kilometer underground in the Kamioka mine in Japan. The
detector consists of 2 concentric cylinders 40 meters high and
with an outer radius of 20 meters. The inner cylinder contains
11,146 inward-facing photomultiplier tubes, each 50 centimeters
in diameter. These photomultiplier tubes detect Cherenkov
radiation from particle interactions inside the inner cylinder
(which contains the ultrapure water). The outer cylinder has 1885
20-centimeter-diameter photomultiplier tubes facing outward to
check for non-neutrino related Cherenkov radiation from entering
charged particles (cosmic-ray muons and radioactivity). Super-
Kamiokande began operation on April 1, 1996.
     3) The essential basis of the Super-Kamiokande experiment is
as follows: When a high-energy cosmic-ray particle (e.g., a
proton) hits an atomic nucleus in the upper atmosphere, the
collision produces a shower of secondary particles. Some of these
particles decay to other particles, some of which are neutrinos.
Most of the charged particles produced in the shower lose energy
as they move through the atmosphere and into the Earth's surface.
Neutrinos, however, because of their extremely small rate of
interaction, pass through the atmosphere and the ground, the vast
majority penetrating to the other side of the Earth. But a few
neutrinos do interact (e.g., with the ultrapure water in the
Super-Kamiokande reservoir), and the Super-Kamiokande apparatus
can detect the interaction of approximately 8 neutrinos per day
in its inner volume.
     4) The authors conclude: "These are exciting times for
neutrino physics, and for elementary particle physics as a whole.
The atmospheric neutrino data fit the neutrino-oscillation
hypothesis beautifully, and this verification that at least some
neutrinos have mass is an enormous step forward: It is the first
clear indication of physics beyond the Standard Model."
-----------
AS 1999 87:222
-----------
Text Notes:
... ... *beta-decay: A type of interaction in which an unstable
atomic nucleus changes into a nucleus of the same mass number but
different proton number. The change involves the conversion of a
neutron into a proton with the emission of an electron and an
electron *antineutrino, or of a proton into a neutron with the
emission of a positron and an electron neutrino. The electrons or
positrons emitted are called "beta particles". (Positrons are
electron antiparticles. See *antineutrino.)
... ... *antineutrino: An antiparticle (antimatter) is a
subatomic particle that has the same mass as another particle and
equal but opposite values of some other property or properties.
For example, the antiparticle of the electron is the positron. An
antineutrino, the antiparticle to the neutrino, has zero mass,
*spin 1/2, and positive helicity. There are 2 antineutrinos, one
associated with the electron and one associated with the *muon.
... ... *spin: 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.
... ... *strong interactions: According to the *Standard Model,
the fundamental forces comprise the gravitational force, the
electromagnetic force, the nuclear strong force, and the nuclear
weak 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.
... ... *Standard Model: 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.
... ... *muon: The 3 leptons (electron, muon, tau) differ from
each other only in mass. The muon is 200 times more massive than
the electron.
... ... *tau: (tauon) The mass of the tau particle is 3560 times
the mass of the electron.
... ... *cosmic-ray: Cosmic rays are highly energetic particles
moving at close to the speed of light and continuously bombarding
the Earth's atmosphere from all directions. The energies of the
particles are enormous and range from 10^(8) to over 10^(19)
electronvolts.
... ... *Cherenkov (Cerenkov) radiation: Discovered in 1934 by
Cerenkov (1904-1990), Cerenkov radiation is electromagnetic
radiation, usually bluish light, emitted by a beam of high-energy
charged particles passing through a transparent medium at a speed
greater than the speed of light in that medium. The radiation is
essentially a shock wave, the effect analogous to that of a sonic
boom.
-------------------
SCIENCE-WEEK http://scienceweek.com 25Jun99

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

15. SOURCES:
AGP:      Archives of General Psychiatry
APL:      Applied Physics Letters
AS:       American Scientist
CEN:      Chemical & Engineering News
GD:       Genes & Development
GR:       Genome Research
ICAR:     Icarus
JAAD:     Journal of the American Academy of Dermatology
JACS      Journal of the American Chemical Society
JAMA:     Journal of the American Medical Association
JCE:      Journal of Chemical Education
NAT:      Nature
NEJM:     New England Journal of Medicine
NYT:      New York Times
PNAS:     Proceedings of the National Academy of Sciences
PRL:      Physical Review Letters
PT:       Physics Today
SA:       Scientific American
SCI:      Science
SK:       Skeptic
SW:       ScienceWeek
TB:       The Biochemist
TS:       The Scientist

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