ScienceWeek

From the Editors of ScienceWeek:
We are in deep sadness over the tragic events in New York of
September 11, 2001. The poet Byron once wrote of "the madmen
who have made men mad by their contagion; conquerors and kings,
founders of sects and systems." Deranged minds filled with
hatred are capable of causing great misery among civilized
peoples. "Furor arma ministrat," ("Madness supplies the arms")
wrote Virgil more than 2000 years ago. Civilization will
prevail, but with still another scar on its face. We transmit
this issue of ScienceWeek as it was prepared prior to last
Tuesday.
---------------------------------------------------------------

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.

September 14, 2001 -- Vol. 5 Number 37

-----------------------------------------------

One of the symptoms of approaching nervous
breakdown is the belief that one's work is
terribly important.
-- Bertrand Russell (1872-1970)

-----------------------------------------------

This issue of ScienceWeek is dedicated to the
memory of Karen E. Wetterhahn (1949-1997)
(cf. Report #14 this issue).

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

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

1. Cometary Origin of Earth's Biosphere
2. Neural AND Gates in Barn Owls
3. Salaries of US Chemists
4. A New Sea-Floor Venting System
5. Zeolites
6. Environmental Influences on Nucleic Acid Structure
7. Microcircuitry in the Cerebral Cortex
8. System Control in the Adaptive Immune System
9. Synapses in the Nervous and Immune Systems
10. A Classic Antibiotic Out of Production
11. Gene Numbers and the Sizes of Genomes
12. Malignant Glioma
13. In Focus: On Fundamental Theory in Physics
14. SW Archive: Wetterhahn Poisoning Case
15. Sources

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

1. COMETARY ORIGIN OF EARTH'S BIOSPHERE
     Composed of ice and dust, comets are relatively small
objects in orbit around the Sun. They are believed to exist in
large numbers in regions beyond the planets (the *Oort Cloud and
the *Kuiper Belt), where they are perturbed by the gravitational
influence of passing stars into new orbits that bring them into
the inner Solar System. When a comet is far from the Sun, its
nucleus is frozen solid and shines only by reflected light; as
the nucleus nears the Sun, its temperature increases and it
releases gas and dust.
     Like certain meteorites, comets are apparently vestiges of
the origin of the Solar System, with comets believed to be icy
*planetesimal remainders from the formation of the outer planets.
The total population of the Oort Cloud and Kuiper belt may be
10^(12) objects, with a combined mass greater than the Earth. The
main component of cometary ice is apparently frozen water, plus
some methane, carbon monoxide, and carbon dioxide. Also detected
in comets are formaldehyde, hydrogen cyanide, and methyl cyanide.
All of these molecules, detected by spectroscopy, are also found
in interstellar nebulae similar to the original "solar nebula"
(see below) from which the Sun was formed.
     The current consensus view of the origin of the Solar System
proposes that its formation began with the gravitational collapse
of part of an interstellar cloud of gas and dust, the cloud with
an initial mass only 10 to 20 percent larger than the present
mass of the Sun and approximately spherical in shape. As the
cloud revolved about the Galactic center, its collapse caused it
to rotate, the speed of rotation increasing as the cloud
contracted, the increase in accordance with the conservation of
angular momentum. As the cloud contracted, it flattened to form a
disk around a central condensation, this configuration called the
"solar nebula". As gas and dust were pulled in toward the central
condensation, potential energy was converted to kinetic energy
and the temperature of the material rose until ultimately the
temperature became great enough in the interior of the
condensation for nuclear reactions to begin and give birth to a
star -- our Sun. Meanwhile, the material of the rotating disk
collided, coalesced, and gradually formed larger and larger
objects by accretion.
... ... Armand H. Delsemme (University of Toledo, US) discusses
evidence concerning a possible cometary origin of the Earth's
biosphere. The proposed scenario for the formation and evolution
of Earth and its biosphere is as follows: The process began with
the settling of dust in the accretionary disk of the protosolar
system. The dusk accreted into ever larger pieces, eventually
forming a hot but dry rock (the proto-Earth) after 40 million
years. When the Solar System was merely 50 million years old, a
grazing collision between the proto-Earth and a Mars-sized body
resulted in the formation of the Moon and the loss of all
volatiles and water that had been brought by an early cometary
bombardment. The heavy cometary bombardment continued for at
least the next 600 million years, with comets bringing water,
atmospheric gases, and prebiotic organic molecules to Earth. Some
of the oldest known sedimentary rocks (which indicate the
presence of water) were formed when the Earth was merely 800
million years old. Earth's current biosphere is rich in the
elements present in interstellar dust and comets, suggesting a
cometary origin. The proportions of the various elements in
living organisms and cosmic sources are remarkably similar,
except for that of calcium, which is present in higher organisms,
and phosphorus, which is present in all organisms. Calcium and
phosphorus are not present in comets.
-----------
AS 2001 89:439
-----------
Notes:
... ... *Oort Cloud: The Oort cloud is an apparent spherical
shell of comets 10,000 to 100,000 astronomical units (AU) from
the Sun and the proposed source of comets that orbit the Sun. The
cloud is at the extreme edge of the Sun's influence, halfway to
the nearest star, and it is believed that when the cloud is
perturbed by passing stars, comets may be sent into a solar
orbit. The size and structure of the Oort cloud have been deduced
from statistical studies of the orbits of comets; there is no
direct evidence for the cloud's existence. Approximately 900
comets are known. The cloud is named after Jan Hendrik Oort
(1900-1992). Oort first proposed the existence of the cloud in
1950. In 1927, Oort calculated the mass and size of the Galaxy,
and the distance of the Sun from its center, from the observed
movements of the stars around the center.
... ... *Kuiper Belt: In 1951 the astronomer Gerard P. Kuiper
(1905-1973) postulated the existence of a belt of objects beyond
the orbit of Pluto. Both the existence and nature of the objects
were matters of speculation for decades, until finally in 1992
Jewitt and Luu identified the first Kuiper object. The current
estimate is that as many as 10^(8) objects larger than 10
kilometers in diameter may exist in what is called the "Kuiper
belt", a disc that hugs the plane of the planetary system and
lies between 35 and 1000 *AU from the Sun. Observations to date 
have yielded some 55 trans-Neptune bodies with radii on the order
of 100 km or larger, and Pluto is considered by some astronomers
to be a member of this population.
... ... *planetesimal: Planetesimals are bodies with dimensions
of 10^(-3) to 10^(3) meters that are believed to form planets by
a process of accretion. The term "accretion" refers to an
aggregation, an increase in the mass of a body by the addition of
smaller bodies that collide and adhere to it, provided the
relative velocities are low enough for coalescence. As the mass
of the agglomerate increases, so does the rate of accretion, and
this accretion process is believed to generally occur in the form
of a disk. A stellar accretion disk is a swarm of dust grains
that evolve into planetesimals and then planets.
-----------
SCIENCE-WEEK 14 Sep 2001 http://scienceweek.com

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

2. NEURAL "AND GATES" IN BARN OWLS
     In this context, a "logic operation" is an operation
performed on quantities (operands) that can be assigned a truth
value, the value either "true" or "false". A "truth table" is a
table of values that describes a particular logic operation.
     An AND operation is a logic operation combining two
statements in such a way that the outcome is true only if both
statements are true, otherwise the outcome is false.
     In this context, the term "gate" refers to a logic gate. In
general, a "logic gate" is a device, usually electronic, that is
used to control the flow of signals in a computer by performing
logic operations on its input, with two or more inputs to the
gate and only one output. The term "AND gate" refers to a logic
gate whose output is high only when all inputs are high,
otherwise the output is low. The AND gate thus performs the AND
operation on its inputs and has the same truth table as the AND
operation.
... ... Charles Day (Physics Today) discusses neural AND gates in
nervous systems.
     1) In a landmark paper in 1943, W. McCulloch and W. Pitts
proved theoretically that a network of integrating neurons can
perform any computational operation, including multiplication,
and their formalism underlies artificial neural networks
currently used to predict weather or stock prices. For some time,
however, researchers have suspected that individual neurons can
multiply. Like an AND gate, a multiplicative neuron fires only
when all its neurons are positive. An additive neuron, in
contrast, is more like an OR gate, firing whenever the total sum
of inputs is above a certain threshold, even if some inputs are
negative.
     2) Now Pena and Konishi (2001) provide evidence for neural
multiplication, uncovering the neural mechanism by which barn
owls combine time-difference and intensity cues to locate sound
sources. This experiment not only bolsters the case that some
neurons are more than simple adding machines, but also adds a
final and physiological touch to the model of Stern and Colburn
(1978), which proposed to explain how humans localize sound.
     3) In general, owls, humans, and other two-eared creatures
locate sound sources by exploiting differences in the signals
detected at each ear. A sound coming from the right, for example,
will reach the right ear before the left ear, and will be less
intense in the left ear because the sound has been partially
absorbed by the head. The barn owl's ear openings are not at the
same level, and this asymmetry heightens the barn owl's ability
to localize sound, especially in the vertical dimension. Even in
total darkness, an owl can find and snatch a mouse off the
ground.
     4) Earlier experiments of Konishi involved equipping owls
with tiny loudspeakers placed in their ears, and manipulating
sound arrival time and intensity differences to trick an owl into
believing a sound comes from a direction chosen by the
experimenter. Whenever an owl hears a sound, it turns its head to
face the source. In the earlier experiments, induction coils
fixed to the owl's head and coupled to an external magnetic field
recorded the direction of the owl's gaze.
     5) In the current experiments, owls were anesthetized,
fitted with loudspeakers, and microelectrodes used to make
recordings from individual space-specific neurons in the owl's
nervous system. Analysis of the data revealed these neurons to be
performing multiplication operations, although the cellular
mechanism involved is not clear. The quantitative properties of
the logic operation are similar to those derived theoretically in
1978 by Stern and Colburn.
-----------
PT 2001 June
SCI 2001 292:249
-----------
SCIENCE-WEEK 14 Sep 2001 http://scienceweek.com
-------------------
Related Background:
ON THE ACCURACY OF SOUND LOCALIZATION IN AN INSECT
Humans use at least two different strategies to localize the
horizontal position of sound sources, depending on the
frequencies in the stimulus. For frequencies below 3000 hertz,
interaural time differences are used to localize the source;
above these frequencies, interaural intensity differences are
used as cues. The longest interaural time differences in humans,
which are produced by sounds arising directly lateral to one ear,
are on the order of only 700 microseconds (the width of the head
divided by the speed of sound in air). Experiments, however,
demonstrate that humans can actually detect interaural time
differences as small as 10 microseconds, and this sensitivity
translates into an accuracy for sound localization of
approximately 1 degree.
     The term "parasitoid" refers to organisms, especially
insects, that introduce their eggs into another animal, the eggs
hatching and larvae developing in a slow and controlled manner
using the resources of the host without killing it. At
maturation, the parasitoid emerges and usually does cause the
death of the host.
... ... A.C. Mason et al (3 authors at Cornell University, US)
present a report of hyperacute directional hearing in a
microscale insect auditory system, the authors making the
following points:
     1) The authors point out that the physics of sound
propagation imposes fundamental constraints on sound
localization: for a given frequency, the smaller the receiver,
the smaller the available cues. Thus, the creation of nanoscale
acoustic microphones with directional sensitivity is very
difficult. The fly Ormia ochracea possesses an unusual "ear" that
largely overcomes these physical constraints, and attempts to
exploit principles derived from O. ochracea for improved hearing
aids are now in progress.
     2) The authors point out that O. ochracea (Diptera:
Tachinidae) is a parasitoid fly, with egg-laying (gravid) female
flies locating their hosts, male crickets, by homing in on the
loud and persistent songs of the crickets. Because of its small
body size (less than 1 centimeter in any aspect), this fly must
deal with extremely small interaural difference cues to guide
directional hearing. The calling song of the host cricket is an
amplitude-modulated 5000 hertz tone (6.8 centimeter wavelength).
The distance between the eardrums of the fly is approximately 0.5
millimeters, which means that 5 kilohertz sound waves are not
diffracted by the body of the fly and generate no interaural
intensity difference (indeed, none can me measured). The
interaural time difference is frequency independent and depends
only on the speed of sound and the distance between the two ears.
The maximal interaural time difference in this fly at 90 degrees
azimuth is 1.5 microseconds and decreases to zero for a sound
source on the midline axis. This minuscule interaural time
difference is the only physical cue available for computation of
source direction. Nevertheless, this fly can reliably localize
cricket song both in nature and in the laboratory.
     3) The authors report experiments that demonstrate that O.
ochracea can behaviorally localize a salient sound source with a
precision equal to that of humans. Despite its small size and
minuscule interaural cues, the fly localizes sound sources to
within 2 degrees azimuth. As the eardrums of the fly are less
than 0.5 millimeters apart, localization cues are of the order of
50 nanoseconds. Directional information is represented in the
fly's auditory system by the relative timing of receptor
responses in the two ears, and low-jitter, phasic receptor
responses are pooled to achieve hyperacute time-coding.
     4) The authors suggest that the principle evolutionary
innovation responsible for the ability of this fly to overcome
its unfavorable auditory physics is a pair of anatomically and
functionally couple eardrums. The mechanical resonance of the
fly's peripheral auditory apparatus in a directional sound field
transforms the minuscule time delay in the free field into two
cues that can used by its nervous system: a) the interaural time
delay between the eardrums is increased from a maximum of 1.5
microseconds to approximately 55 microseconds; b) the vibration
amplitude difference between the two eardrums is as much as 10
decibels for sound sources at 45 to 90 degrees azimuth. Thus,
minute interaural time differences in the sound field are
converted by eardrum mechanics to interaural differences that are
process by the nervous system.
     5) The authors suggest these results demonstrate that
nanoscale/microscale directional microphones patterned after the
fly O. ochracea have the potential for highly accurate
directional sensitivity independent of the size of the
microphones. In the fly itself this performance is dependent on a
newly discovered set of specific coding strategies employed by
the fly's nervous system.
-----------
NAT 2001 410:686
SW 2001 18 May
-----------
SCIENCE-WEEK 14 Sep 2001 http://scienceweek.com
-------------------
Related Background:
ELECTROPHYSIOLOGICAL DEVELOPMENT OF AUDITORY HAIR CELLS
Evolution has resulted in the development of an array of
remarkable sensory systems in living organisms, but perhaps the
most exquisitely designed sensory systems are the mammalian
visual and auditory systems. Whereas the visual system is
constructed to respond with high sensitivity to input photons,
the structure of the auditory system has as its function the
detection and analysis of the mechanical vibrations produced by
sound waves. The sensory receptors in the mammalian auditory
system are the so-called "hair cells" of the *cochlea, cells with
extensions ("hairs"; *stereocilia) that respond to mechanical
vibrations of a surrounding fluid, the cells arranged in a
flexible sheet, and the physical properties of the sheet of cells
and their surroundings such that sounds of differing frequencies
produce maximum mechanical input at differing loci on the sheet,
the result a topological representation of the frequency spectrum
of input sound waves. The auditory hair cells are essentially
energy transducers, transducing mechanical energy into electrical
energy, and this electrical energy in turn exciting associated
nerve cells to produce a topological signal pattern conveyed to
the central nervous system for analysis. The electrical behavior
of sensory and nerve cells is dependent on the specifics of
various *ion channels in their *plasma membranes, and one
important question concerns the changes that take place in the
various cellular ion channels during *cell differentiation.
... ... Kros et al (3 authors at 3 installations, UK DE) now
present evidence for the development changes that occur in *inner
hair cells. The authors report that in mice, responses to sound
can first be recorded from the auditory nerve and observed
behaviorally from 10 to 12 days after birth, and that these
responses mature rapidly over the next 4 days. Before this time,
mouse inner hair cells have slow voltage responses and fire
spontaneous and evoked action potentials. During development of
auditory responsiveness, a large fast potassium conductance is
expressed, greatly speeding up the membrane time constant and
preventing action potentials. This change in potassium channel
expression turns the inner hair cell from a regenerative spiking
pacemaker into a high-frequency signal transducer.
-----------
NAT 1998 394:281
SW 7 Aug 98
-----------
Notes:
... ... *cochlea: The cochlea is essentially a canal in bone,
differing in morphology among the mammals. The human cochlea is a
cone-shaped cavity in the temporal bone, forming one of the
divisions of the labyrinth (internal ear), and consists of a
spiral canal that contains various structures, in particular the
spiral organ of Corti, which contains the auditory hair cells.
... ... *stereocilia: Nonmotile cilia. In this context, they
extend from hair cells, and when they are mechanically bent by
hydrodynamic waves, an electrical change in the hair cells is
produced.
... ... *ion channels: Ion channels are protein channels in cell
membranes that allow ions to pass from extracellular solution to
intracellular solution and vice versa. Most ion channels are
selective, allowing only certain ions to pass, and an individual
cell has ion channels with various ion selectivities. The
selectivity of an ion channel can be "gated", the channel
effectively opened or closed, and ion channels are said to
*voltage-gated or *ligand-gated, depending on how the change in
selectivity is provoked.
... ... *plasma membranes: This is the membrane that separates
living cells from their environment, consisting of lipid bilayer
and associated proteins, the ensemble approximately 75 to 100
angstroms in thickness. Similar membranes are also found within a
cell surrounding various organelles.
... ... *cell differentiation: This refers to the developmental
specialization of cells exhibited by changes in morphology,
biochemistry, function, etc.
... ... *inner hair cells: Sensory hair cells are present in
several sensory systems, including the auditory system, the
vestibular system, and in taste buds. There are two groups of
auditory hair cells in the cochlea, labelled "inner" and "outer"
hair cells according to their anatomical position.
... ... *voltage-gated: Refers to opening or closing of an ion
channel by changes in the electrical potential across the
membrane.
... ... *ligand-gated: Refers to opening and closing of an ion
channel by interactions between ligands and membrane receptors. 
-----------
SCIENCE-WEEK 14 Sep 2001 http://scienceweek.com
-------------------
Related Background:
LOCALIZATION OF SOUND BY EARLY-BLIND HUMAN SUBJECTS
There are currently two experimentally-based views concerning the
question of whether blind persons develop capacities of their
remaining senses that exceed those of sighted individuals. One
view proposes that blind individuals are severely impaired
because vision is so essential in the development of spatial
concepts. The second view proposes that compensation occurs
through the remaining senses, allowing blind individuals to
develop an accurate concept of space. ... ... N. Lessard et al
report a study of 3-dimensional spatial mapping by early-blind
individuals with or without residual vision. Four groups were
tested: totally blind subjects (n = 8); blind subjects with
residual vision in the peripheral field (n = 3); normally sighted
but blindfolded controls (n = 7); sighted controls (n = 29).
Subjects were asked to localize a sound source in the horizontal
plane, the sounds delivered randomly through 16 loudspeakers
mounted on a semicircular perimeter. Subjects were tested under
monaural and binaural listening conditions. The authors report
the following: 1) early-blind subjects can map the auditory
environment with equal or better accuracy than sighted subjects;
2) Unlike sighted subjects, early-blind subjects can correctly
localize sounds monaurally; 3) blind individuals with residual
peripheral vision localized sounds less precisely than sighted or
totally blind subjects, confirming that compensation varies
according to the etiology and extent of blindness. The authors
suggest their results resolve a long-standing controversy by
providing behavioral evidence that totally blind individuals have
better auditory ability than sighted subjects, enabling them to
compensate for their loss of vision.
-----------
NAT 1998 395:278
SW 1998 9 Oct
-----------
SCIENCE-WEEK 14 Sep 2001 http://scienceweek.com

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

3. SALARIES OF US CHEMISTS
Michael Heylin (CEN) discusses new data concerning salaries of US
chemists. The current employment situation for chemists is
apparently the best in more than a decade. Unemployment is down
sharply from last year, and fewer chemists are in part-time or
postdoctoral positions. The median salary for all chemists
responding to the survey of the American Chemical Society is
$73,000. For PhD chemists as a group, the median salary is
$82,200. For chemists with master's degrees, the median salary is
$65,000, and for chemists with bachelor's degrees, the median
salary is $55,000. The unemployment rate among chemists is at 1.5
percent. Concerning PhDs, the median salary in industry is
$90,200, in government $84,800, and in academia $63,000. The
improvements for the chemistry profession came as the longest and
strongest economic expansion in US history began to expire. The
boom started in 1993 and generated 15 million more jobs
nationally to bring the civilian domestic work-force to 142
million people. The boom caused the strongest national employment
market since 1969, and dropped the overall unemployment rate from
7.8 percent in March 1992 to 4.3 percent in March 2001. Of the
working chemists responding to the survey, 84.3 percent are
white, 11.4 percent Asian, 2.5 percent Hispanic, 1.8 percent
black, 0.3 percent American Indian, and 24.8 percent women. Of
all US chemists, 79.8 percent are native-born Americans.
-----------
CEN 2001 20 Aug
-----------
SCIENCE-WEEK 14 Sep 2001 http://scienceweek.com

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

4. A NEW SEA-FLOOR VENTING SYSTEM
     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.
     The term "lithosphere" refers to the outer layer of the
Earth, comprising the crust and upper mantle, and extending to a
depth of 50 to 70 kilometers. The traditional view of tectonics
(changes in the structure of the Earth's crust) is that the
lithosphere consists of a strong brittle layer overlying a weak
ductile layer. "Plate tectonics" is the current consensus theory
that the Earth's lithosphere is broken into fairly rigid plates,
seven or eight major plates and many smaller plates, and that
convection within the underlying less rigid "asthenosphere"
causes the plates (and the associated continents and crust) to
move relative to each other.
     "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.
     A "mid-ocean ridge" is a long linear elevated volcanic
structure often lying along the middle of the ocean floor,
tending to occupy central positions as a consequence of the
oceans forming by symmetrical spreading of two lithosphere plates
from the ridge site. In extent, an oceanic ridge is usually 1000
to 4000 kilometers wide and rising 2 to 3 kilometers above the
flanking basins.
... ... D.S. Kelley et al (University of Washington, US) discuss
current investigations of hydrothermal vents. Evidence is growing
that hydrothermal venting occurs not only along mid-ocean ridges
but also on old regions of the oceanic crust away from spreading
centers. The authors report the discovery of an extensive
hydrothermal field at 30 degrees North near the eastern
intersection of the Mid-Atlantic Ridge and the Atlantis fracture
zone. The vent field (named "Lost City") is distinctly different
from all other known sea-floor hydrothermal fields in that it is
located on 1.5-million-year-old crust, nearly 15 kilometers from
the spreading axis, and may be driven by the heat of exothermic
serpentinization reactions between sea water and mantle rocks. It
is located on a dome-like massif and is dominated by steep-sided
carbonate chimneys, rather than by the sulfide structures typical
of "black smoker" hydrothermal fields. The vent fluids are
relatively cool (40 to 75 degrees Celsius) and alkaline (pH 9 to
9.8), supporting dense microbial communities that include
anaerobic thermophiles. Because the geological characteristics of
the Atlantis massif are similar to numerous areas of old crust
along the Mid-Atlantic, Indian, and Arctic ridges, the authors
suggest these results indicate that a much larger portion of the
oceanic crust may support hydrothermal activity and microbial
life than previously thought.
-----------
NAT 2001 412 145
-----------
SCIENCE-WEEK 14 Sep 2001 http://scienceweek.com
-------------------
Related Background:
ON THE PUZZLES OF HYPERTHERMOPHILES
... 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.
-----------
PNAS 2000 97:12961
-----------
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.
-----------
SW 2001 19 Jan
-----------
SCIENCE-WEEK 14 Sep 2001 http://scienceweek.com

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

5. ZEOLITES
X. Rozanska et al (Eindhoven University of Technology, NL)
discuss zeolites and reaction selectivity. Zeolites are natural
or synthetic silicon oxide crystals composed of a network of
SiO(sub4) tetrahedral units that link together by sharing oxygen
atoms. The potential energy surface of the zeolite Si-O-Si angles
is rather flat, which explains the large variety of accessible
micropore structures that can be formed by zeolites. With their
well-defined microporous structures, zeolites are interesting
agents for separation purposes. Moreover, their mechanical and
thermal properties have given them an important position in
heterogeneous catalysis. In addition, zeolite-catalyzed reactions
often display high product-selectivity, the selectivity based on
the zeolite microporous structure producing various consequences
in the course of a reaction. Concerning reactant selectivity, for
example, since the zeolite micropore channels have a well-defined
diameter, reactants larger than this diameter cannot enter the
micropores in order to react, and reactants smaller than the
micropore will be the only reactants involved in the reaction.
Once a reactant molecule has adsorbed within the zeolite mouth,
it must diffuse toward the reactions sites, and this diffusion
can be highly dependent on the size and shape of the zeolite
micropores as well as on the size of the reactants or products.
After reaction has occurred the products must diffuse away from
the micropores. These selective properties are not only valid in
the case of zeolite catalysts, but also in the case of zeolite
molecular sieves.
-----------
JACS 2001 123:7655
-----------
SCIENCE-WEEK 14 Sep 2001 http://scienceweek.com

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

6. ENVIRONMENTAL INFLUENCES ON NUCLEIC ACID STRUCTURE
D. Hamelberg et al (Georgia State University, US) discuss the
influences of environment on the structures of nucleic acids.
Such influences are of fundamental importance to the interactions
of nucleic acids with proteins, other cellular components, drugs,
as well as to DNA packaging in viral particles. Although it has
been recognized that ions are required for the formation of
stable nucleic acid structures, the direct influence of ion
interactions on sequence-specific nucleic acid conformation and
dynamics is still debated. Two limiting models have been proposed
to explain the origins of DNA conformational heterogeneity and
the roles of cations. The traditional "base-clash model" assumes
that DNA duplexes have sequence-dependent conformations that are
not significantly influenced by the local positions or
fluctuations of ions. The alternative "electrostatic model"
proposes that the local positions and transient fluctuations of
ions impact DNA conformation and dynamics, primarily through
asymmetric neutralization of phosphate charges. In this model
cations would have a strong influence on time-dependent
conformation. These two limiting models are somewhat difficult to
test by experiment because they both predict similar average
structures that agree with experimental results. However, their
molecular explanations for a variety of conformational states are
different.
-----------
JACS 123:7745
-----------
SCIENCE-WEEK 14 Sep 2001 http://scienceweek.com

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

7. MICROCIRCUITRY IN THE CEREBRAL CORTEX
     The cerebral cortex is a thin surface layering of nerve
cells of the brain, the region only  several millimeters thick
but covering all of the brain surface. This is the part of the
central nervous system most intimately involved with the
so-called "higher faculties", although the cortex operates in
concert with other parts of the brain. The structure is primitive
in lower mammals, and is found progressively more pronounced and
with greater surface area in primates and man.
... ... J. Kozloski et al (Columbia University, US) discuss the
microcircuitry of the mammalian cerebral cortex, a tissue of
apparently impenetrable complexity. The cortical microcircuit,
i.e., the intra- and interlaminar connections within a local
neocortical region, is still largely unknown, although its
characterization is essential to any theory of cortical function.
The search for rules governing the cortical microcircuit has
revealed wide diversities of neurons, columnar and horizontal
connectivity, and distinct interlaminar and long-range
projections (output connections). Connections from other cortical
neurons can be precise, targeting specific postsynaptic
locations. However, connectivity rules among excitatory cells,
which constitute the vast majority of cortical neurons, remain
unclear. Some studies indicate that excitatory neurons are weakly
interconnected in probabilistic patterns, so that specificity can
be found only at the statistical level. At the same time, because
the number of different classes of neocortical neurons is still
unknown and could approach several hundreds, any apparent lack of
target specificity might result from heterogeneous sampling.
Also, physiological studies indicate remarkable circuit
specificity. The authors used an optical probing technique to
detect postsynaptic targets of neurons in brain slices, and then
chose targets for dual recordings. By imaging hundreds of neurons
simultaneously, while electrically stimulating a trigger cell,
the authors optically detected the "follower" neurons connected
to it. The authors suggest their data reveal precisely organized
microcircuits.
-----------
SCI 2001 293:868
-----------
SCIENCE-WEEK 14 Sep 2001 http://scienceweek.com
-------------------
Related Background:
OPTICAL PROBING OF NEURONAL CIRCUITS
     Since the functioning of any nervous system depends on the
interconnections of nerve cells, one of the important objectives
of neurobiological research is the characterization of neuronal
circuitry. But in nerve cell systems containing thousands or
millions of nerve cells and their interconnections, this is no
easy task, and in most nervous systems, the detailed circuits are
as yet unknown, even when the nature of the computation carried
out by particular circuits is evident.
     A direct approach to deciphering neuronal circuits is their
reconstruction with electron microscopy, but this has been
achieved only for the nervous system of the *nematode worm
Caenorhabditis elegans, which nervous system consists of 302
neurons exhibiting a stereotyped connectivity from animal to
animal. For most organisms, electron microscopic reconstructions
of entire circuits are impractical because of the high number of
neurons present and the laboriousness of serial reconstruction
from thin slices of tissue.
     Another approach to identify circuits involves intracellular
recordings from connected cells. and this has been done
extensively in invertebrates. In vertebrate preparations, dual
recordings of randomly chosen neurons in *brain slices have been
combined with anatomical reconstruction to identify *synaptic
contacts. But this approach suffers from the problem that the
probability that randomly chosen neurons are connected is low.
This, and the large number of neuronal types, makes testing of
possible connections and sequential examination of circuits
impractical.
... ... Z.A. Peterlin et al (5 authors at Columbia University,
US) now report a method using calcium imaging that allows rapid
identification of neuronal connections. The method consists of
stimulating one neuron (the "trigger neuron") while imaging a
population of nerve cells to detect which other neurons
("follower neurons") are activated by the trigger. By using a
bulk-loaded fluorescent calcium indicator in slices of mouse
visual cortex, the authors report they have demonstrated that
neurons that display *somatic calcium transients time-locked to
the spikes of a trigger neuron are directly connected to the
trigger neuron. The bulk-loaded fluorescent calcium indicator was
fura-2 acetoxymethyl ester, a previously established calcium
indicator in nerve cells. The authors suggest this technique
could be applied to reconstruct and assay circuits in the
mammalian central nervous system.
-----------
PNAS 2000 97:3619
-----------
Notes:
... ... *nematode worm: An abundant and ubiquitous phylum of
unsegmented roundworms.
... ... *brain slices: "Brain slices" are exactly that, the brain
removed from the animal and a thin slice of a particular region
prepared in an appropriate solution for electrophysiological
recording of nerve cell activity.
... ... *synaptic contacts: The junction between the terminal of
the axon of one neuron and another neuron is called a "synapse".
... ... *somatic calcium transients: The main part of the nerve
cell, the central part from which projections arise, is called
the "soma". When a nerve cell is activated, the permeability of
the surface membrane to various ions undergoes transient changes.
If, for example, the permeability of the surface membrane to
calcium ion undergoes a transient increase, the result is a
transient calcium ion current, increasing the intracellular
concentration of calcium. In this context, a transient increase
of intracellular calcium ion produces fluorescence of a calcium
ion indicator.
-----------
SW 2000 9 Jun
-----------
SCIENCE-WEEK 14 Sep 2001 http://scienceweek.com

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

8. SYSTEM CONTROL IN THE ADAPTIVE IMMUNE SYSTEM
Ronald H. Germain (National Institutes of Health, US) discusses
systems-analytic aspects of the adaptive immune system. Operation
of a relatively strict set of rules would seem necessary to
ensure well-controlled behavior by such a complex system,
resulting in a very mechanistic interpretation of most
immunological experiments: input X directly and reliably causes a
cell to generate output A under a given initial condition.
However, as one dissects the immune system at finer and finer
levels of resolution, there is actually a decreasing
predictability in the behavior of any particular unit of function
(e.g., a gene or a cell). A major challenge is thus understanding
what endows the overall ensemble with both sensitivity and global
reliability despite variations in the concentration, initial
state, local behavior, or precise number of the participating
components. Emerging evidence suggests that these properties
arise from a combination of 1) small alterations in the
probabilistic behavior of a biochemical pathway, a cell, or a
collection of cells; 2) the amplification of these induced
changes by positive-feedback loops and/or exponential cell
growth; 3) the action of counter-regulatory controls that
modulate these potentially unidirectional explosive processes;
and 4) the summation of individual topographically dispersed
cellular responses subject to these local control mechanisms.
-----------
SCI 2001 293:240
-----------
SCIENCE-WEEK 14 Sep 2001 http://scienceweek.com

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

9. SYNAPSES IN THE NERVOUS AND IMMUNE SYSTEMS
A. Trautmann and E. Vivier (CNRS, FR) discuss similarities
between the nervous system and the immune system, two systems
that share a number of unique features. These systems are both
composed of complex networks of primary and accessory cells that
are in constant communication with each other. In both systems, a
record of the encounter of a primary cell with a stimulus is
preserved, such that upon reencountering the stimulus, the system
remembers it and responds accordingly. Transmembrane signaling
through surface receptors of both neurons and lymphocytes is
regulated by the clustering of these receptors with each other
and with other molecules. In both systems, information is
transferred at points of contact between cells, the points of
contact called "synapses". Although synapses in the nervous and
immune systems are clearly different, they have in common a
number of molecules that are required for synapse formation and
operation. For example, major histocompatibility complex
proteins, which are key players in the immune system, are also
involved in the formation of the nervous system. Now new evidence
by A.A. Khan et al (2001) indicates that agrin, a well-
characterized glycoprotein in neuromuscular junctions, is also
present in the immune system. Khan et al propose that immune-cell
agrin may participate in the clustering of antigen-specific T-
cell receptors and accessory costimulatory molecules at the
immune synapse between T cells and antigen-presenting cells.
-----------
SCI 2001 292:1667,1681
-----------
SCIENCE-WEEK 14 Sep 2001 http://scienceweek.com

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

10. A CLASSIC ANTIBIOTIC OUT OF PRODUCTION
Spectinomycin is an antibiotic produced by the fungus
Streptomyces spectabilis. The drug is an aminocyclitol (related
to aminoglycosides), acting selectively to inhibit protein
synthesis in gram-negative bacteria by binding to and acting on
the 30s ribosome subunit. While the drug is effective against a
number of gram-negative bacterial species, it is generally
inferior to other drugs to which such microbes are susceptible.
Its sole current application in the US is in the single-dose
treatment of gonorrhea caused by beta-lactamase-producing
gonococci or in the treatment of gonorrhea occurring in
individuals hypersensitive to penicillin. The US Centers for
Disease Control now reports that in April 2001, Pharmacia
Corporation announced it was discontinuing US production of
spectinomycin (Trobicin) because of low sales volume, and
remaining spectinomycin inventory will expire on June 30, 2001.
No other pharmaceutical company manufactures or sells
spectinomycin in the US. This antibiotic is recommended for
patients infected with Neisseria gonorrhoeae who have
contraindications to the antibiotics cephalosporin and
fluoroquinolones. Patients in this contraindication category
include 1) pregnant women with documented cephalosporin allergies
(fluoroquinolones are contraindicated in pregnancy); and 2)
patients with documented cephalosporin allergies who acquired
gonorrhea infection in areas where fluoroquinolone-resistant N.
gonorrhoeae is endemic (e.g., Asia, Hawaii, and other Pacific
islands).
-----------
MMWR 2001 50:470
JAMA 2001 286:40
-----------
SCIENCE-WEEK 14 Sep 2001 http://scienceweek.com

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

11. GENE NUMBERS AND THE SIZES OF GENOMES
V. Walbot and D.A. Petrov (Stanford University, US) discuss the
sizes of genomes. Complete sequencing of higher eukaryote genomes
has brought the surprise that despite hundreds of millions of
years of evolutionary separation and strikingly different sizes
and body plans, diverse organisms contain nearly the same number
of genes, e.g., approximately 30,000 genes for humans, 13,600 for
the fruit fly Drosophila melanogaster, 18,400 for the nematode
worm Caenorhabditis elegans, and 26,000 for the flowering plant
Arabidopsis thaliana. In contrast to the modest variation in gene
number, eukaryotic genome size varies over 5 orders of magnitude,
a paradoxical feature that was noted long before genes were
cloned. Even within a single species, that of maize (Zea mays),
for example, genome size varies 50 percent. Furthermore,
variation in genome size does not follow any taxonomic logic:
large genomes are found in some "simple" eukaryotic algae and
small genomes are found in advanced organisms. Nor does genome
size correlate with lifespan: both the ephemeral annual plant
Arabidopsis and the long-lived peach tree have tiny genomes. Now
that we know that higher eukaryotes encode approximately the same
number of genes, noncoding DNA must explain the diversity of
genome sizes. Indeed, a majority of the 3000 megabase human
genome is composed of inactive retrotransposons and other
noncoding repetitive sequences, whereas the 100 megabase genomes
of Drosophila, C. elegans, and Arabidopsis contain only a low
percentage of such sequences.
-----------
PNAS 2001 98:8163
-----------
SCIENCE-WEEK 14 Sep 2001 http://scienceweek.com

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

12. MALIGNANT GLIOMA
E.A. Maher et al (Dana-Farber Cancer Institute, US) discuss
malignant glioma. Malignant brain tumors strike deep into the
psyche of those receiving and those delivering the diagnosis.
Malignant gliomas, the most common subtype of primary brain
tumors, are aggressive, highly invasive, and neurologically
destructive tumors considered to be among the deadliest of human
cancers. In its most aggressive manifestation, glioblastoma,
median survival ranges from 9 to 12 months, despite maximum
treatment efforts -- a statistical fact that has changed little
over several decades of technological advances in neurosurgery,
radiation therapy, and clinical trials of conventional and novel
therapeutics. Over the same time period, there has been an
explosion of knowledge in cancer biology and basic science
discovery that has fueled meaningful progress in the treatment of
many common human cancers, including those of the breast, lung,
and prostate. It is perplexing that therapies used effectively in
the treatment of these solid tumors are overwhelmingly
ineffective in the treatment of glioblastoma, perhaps reflecting
the eccentric biology and cellular origin of this neoplasm. To
date, only one new agent has been documented to have modest
activity against intermediate grade gliomas, whereas no effective
agents have emerged for the treatment of glioblastoma, despite 20
years of enrolling patients in clinical trials.
-----------
GD 2001 15:1311
-----------
SCIENCE-WEEK 14 Sep 2001 http://scienceweek.com

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

13. IN FOCUS: ON FUNDAMENTAL THEORY IN PHYSICS
[Editor's note: Here are three views of fundamental theory in
physics, two views concerning the Standard Model, and one view
concerning the Theory of Everything. Both Steven Weinberg and
Robert B. Laughlin are Nobel Laureates in physics.]
----------------------------------------------
"In a sense, the Standard Model has achieved the goals that
science has traditionally set. Finally, for the first time in
history, we have a complete description of how our physical world
works. There are no puzzles or conflicts between theory and
experiment. It is the underlying physical theory for all of
chemistry, the behavior of matter, the behavior of stars, and all
that we see. [But] that does not in any way imply that doing
science has ended, because the equations still need to be solved
for many systems, and unexpected properties emerge for complex
systems. Once we had the Standard Model, we could ask new
questions about the Universe as a whole, and we could inquire why
the Standard Model took one form and not another. Many questions
that were philosophical or entirely speculative have recently
become normal research topics in physics, astrophysics, and
cosmology... An interesting perspective on physics beyond the
domain of the Standard Model is provided by asking about the
relative status of experiment and theory as a field progresses.
Particle physics began as a field about a century ago; one could
date it to the discovery of the electron, or perhaps a few years
later to the use of particle beams, which allowed us to learn the
atom had a nucleus. From then until the discovery of the Standard
Model in the early 1970s, experiment was ahead of theory -- there
were many unexpected discoveries and essentially no successful
predictions. Once the Standard Model was written, it explained
many puzzles and made many dramatic and successful predictions.
There were no experimental surprises for over two decades -- all
results either had been clearly predicted or at least were
anticipated. Once we go beyond the domain of the Standard Model,
the situation is mixed. Today theory and experiment are again
making progress together, as they did throughout most of the
history of physics. But the situation is different in an
important way from that of the century before the Standard Model,
because now the Standard Model provides a framework that allows
new kinds of questions to be formulated."
-----------
Gordon Kane: _Supersymmetry: Squarks, Photinos, and the Unveiling
of the Ultimate Laws of Nature_
(Perseus Publishing, Cambridge MA 2000, p.35,39)
http://www.amazon.com/exec/obidos/ASIN/0738204892/scienceweek
-----------
SCIENCE-WEEK 14 Sep 2001 http://scienceweek.com
-------------------
Related Background:
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."
-----------
SA 1999 December
SW 2000 14 Jan
-----------
SCIENCE-WEEK 14 Sep 2001 http://scienceweek.com
-------------------
Related Background:
THEORETICAL PHYSICS: ON THE THEORY OF EVERYTHING
... R.B. Laughlin and D. Pines (2 installations, US) present
a provocative commentary on current fundamental theory in
physics, the authors making the following points:
     1) The term "Theory of Everything" refers to the ultimate
theory of the Universe, a set of equations capable of describing
all phenomena that have been observed, or that will ever be
observed. It is the modern incarnation of the reductionist idea
of the ancient Greeks, an approach to the natural world that has
been extremely successful and which for many people is the
central paradigm of physics. A special case of this idea is the
general wavefunction equation of nonrelativistic quantum
mechanics, which describes the everyday world in terms of known
quantities: the charge and mass of the electron, the charges and
masses of the atomic nuclei, and Planck's constant. Less
immediate things in the Universe, such as the planet Jupiter,
nuclear fission, the Sun, or the isotopic abundances of elements
in space are not described by this equation, because important
variables such as gravity and nuclear interactions are missing.
But concerning everyday people-scale phenomena, this equation is
for all practical purposes the Theory of Everything for our
everyday world.
     2) The authors suggest, however, that examining the Theory
of Everything, it becomes obvious that it is not even remotely a
theory of every thing. We know the equation is correct because it
has been solved accurately for small numbers of particles
(isolated atoms and small molecules) and found to agree in minute
detail with experiment. But it cannot be solved accurately when
the number of particles exceeds approximately 10. The authors
suggest that no computer existing, or that will ever exist, can
break this barrier -- it is a "catastrophe of dimension": If the
amount of computer memory required to represent the quantum
wavefunction of one particle is N, then the amount of computer
memory required to represent the wavefunction of k particles is
N^(k). Although it is possible to perform approximate
calculations for larger systems, and such calculations have in
many cases been valuable, the schemes for approximating are not
first-principles deductions, they are rather art keyed to
experiment. These approximate approaches thus tend to be the
least reliable precisely when reliability is most needed, i.e.,
when experimental information is scarce, the physical behavior
has no precedent, and the key questions have not yet been
identified.
     3) A variety of physical phenomena easily observed in the
laboratory (e.g., the *quantum Hall effect, *superfluid helium,
*Josephson effect) permit measurements of exact quantities that
cannot be deduced by direct calculation from the present Theory
of Everything, for exact results cannot be predicted by
approximate calculations. The authors suggest this point is still
not understood by many professional physicists, who find it
easier to believe that a deductive link exists, and has only to
be discovered, than to face the truth that there is no link. But
the absence of a link is true nonetheless, and not denied by the
reliability of such experiments: The important consideration is
that experiments concerning these physical phenomena work because
there are higher organizing principles in nature that make them
work.
     4) Concerning Big Bang cosmology and attempts to develop
fundamental theory from considerations and observations of the
early Universe, the authors suggest that no one familiar with
violent high-temperature phenomena would dare to infer anything
about the equations of quantum mechanics by studying explosions,
for explosions are unstable and quite unpredictable from one
experiment to the next. The authors suggest that the assumption
that the early Universe should be exempt from this problem, and
that a Theory of Everything can be inferred from observations of
the early Universe, is not justified by anything except wishful
thinking. It could very well turn out that the Big Bang is the
ultimate emergent phenomenon, "for it is impossible to miss the
similarity between the large-scale structure recently discovered
in the density of galaxies and the structure of styrofoam,
popcorn, or puffed cereals."
     5) The authors suggest that the fact that the essential role
played by higher organizing principles in determining emergent
behavior continues to be disavowed by so many physical scientists
is a poignant comment on the nature of modern science. To solid-
state physicists and chemists, who are schooled in quantum
mechanics and deal with it every day in the context of
unpredictable electronic phenomena such as that exhibited by
*Kondo insulators or *cuprate superconductivity, the existence of
these organizing principles in emergent behavior is so obvious
that it is a commonplace not discussed in polite company. But to
other scientists, the idea is considered dangerous and ludicrous,
since it is fundamentally at odds with the reductionist beliefs
central to much of physics. But, the authors suggest, the safety
that comes from acknowledging only the facts one likes is
fundamentally incompatible with science, and sooner or later this
attitude "must be swept away by the forces of history".
     6) The authors point out that for the biologist, evolution
and emergence are part of daily life. For many physicists, on the
other hand, the transition from a reductionist approach may not
be easy, but should, in the long run, prove highly satisfying.
Living with emergence means, among other things, focusing on what
experiment tells us about candidate scenarios for the way a given
system might behave before attempting to explore the consequences
of any specific model. This contrasts sharply with the imperative
of reductionism, which requires us never to use experimental
observations in the formulation of theory, as the objective of
reductionism is to construct a deductive path from the ultimate
equations to the experiment without "cheating". But this is
unreasonable when the behavior in question is emergent, for the
higher organizing principles -- the core physical ideas on which
the model is based -- would have to be deduced from the
underlying equations, and in general this is impossible.
Repudiation of this physically unreasonable constraint is the
first step down the road to fundamental discovery.
     7) The authors conclude: "The central task of theoretical
physics in our time is no longer to write down the ultimate
equations but rather to catalogue and understand emergent
behavior in its many guises, including potentially life itself.
We call this physics of the next century the study of complex
adaptive matter. For better or worse we are now witnessing a
transition from the science of the past, so intimately linked to
reductionism, to the study of complex adaptive matter, firmly
based in experiment, with its hope for providing a jumping-off
point for new discoveries, new concepts, and new wisdom."
-----------
PNAS 2000 97:28
-----------
Notes:
... ... *quantum Hall effect: In classical physics, the Hall
effect is the development of a transverse voltage across a
current-carrying conductor in a magnetic field, the voltage being
perpendicular to both the  direction of the current and the
direction of the magnetic field. In quantum physics, there are
two other Hall effects, an integer charge quantum Hall effect,
and a fractional charge quantum Hall effect, these quantum Hall
effects being observed at extremely low temperatures (a few
degrees Kelvin) and extremely intense magnetic fields (at least
several tesla). Both quantum Hall effects were first noted in the
1980s, and the fractional quantum Hall effect, although
experimentally observed, has not been theoretically resolved. In
1982, R.B. Laughlin (one of the authors of the paper reviewed in
the present report) postulated the theoretical existence of
quasi-particle excitations with fractional charge e/3, where e is
the conventional electronic charge, the quasi-particle being the
statistical result of the collective motion of many electrons. R.
de-Picciotto et al (1997) apparently demonstrated unambiguously
the existence of quasi-particles with fractional charge as
predicted by Laughlin's theory. 
... ... *superfluid helium: In general, a "superfluid" is a fluid
that flows without any resistance. "Superconductivity" is
sometimes considered as a special case of superfluidity in which
the "fluid" components (electrons) are charged. But more
conventionally, superfluidity is considered a property of liquid
helium at extremely low temperatures, a property that enables
liquid helium to flow without friction. Both helium isotopes
(sup4)He (the common isotope, often denoted as helium-4) and
(sup3)He (the rare isotope, often denoted as helium-3) possess
superfluidity under special circumstances.
... ... *Josephson effect: In general, any of the phenomena that
occur at sufficiently low temperatures when a current flows
through a thin insulating layer between two superconducting
substances. Such phenomena were predicted theoretically by B.D.
Josephson in 1962. Josephson was 22 years of age when he made his
theoretical discovery; he received the Nobel Prize in Physics in
1973.
... ... *Kondo insulators: An insulator exhibiting the Kondo
effect. The Kondo effect is a large anomalous increase in the
resistance of certain dilute alloys of magnetic materials in
nonmagnetic hosts as the temperature is lowered. In general, the
Kondo effect occurs when an impurity atom with an unpaired
electron is placed in a metal, producing an interaction of
localized electrons with delocalized electrons.
... ... *cuprate superconductivity: In general, high-temperature
superconductivity exhibited by certain copper alloys. The
accepted theory of ordinary low-temperature superconductivity
is the Bardeen-Cooper-Schrieffer theory (1957). At the present
time, a successful theory of high-temperature superconductivity
has not been developed, in spite of a great deal of effort. J.G.
Bednorz and K.A. Mueller shared the Nobel Prize in Physics in
1987 for their discovery of high-temperature superconductivity in
a ceramic oxide (lanthanum-barium-copper) alloy at 30 degrees
kelvin, at that time the highest superconductivity temperature
ever observed.
-----------
SW 2000 25 Feb
-----------
SCIENCE-WEEK 14 Sep 2001 http://scienceweek.com

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

14. SW ARCHIVE:
WETTERHAHN LABORATORY POISONING CASE: FINAL MEDICAL REPORT
In the spring of 1997, the science community, and in particular
the chemistry community, was saddened to learn of the tragic
death of Karen E. Wetterhahn, age 48, a professor of chemistry
(Dartmouth College, US) and a noted researcher on the effects of
heavy metals in biological systems. Wetterhahn died of
dimethylmercury poisoning as the result of the accidental
spillage of a few drops of the chemical on her latex glove-
covered hand. The accident occurred on August 14, 1996, and the
poisoning produced progressive destruction of Wetterhahn's
nervous system, until she finally died 10 months later. Before
she lapsed into a vegetative state, Karen Wetterhahn requested
that her case be presented to the general medical community, to
scientists working with mercury, and to toxicologists, in the
hope of improving the recognition, treatment, and prevention of
future cases of mercury poisoning. The full medical case report
of the illness, death, and autopsy of Karen E. Wetterhahn has now
been published. Nierenberg et al (9 authors at 2 installations,
US), the authors of the report, make the following points: 1)
Dimethylmercury is lethal at a dose of approximately 400 mg of
mercury (equivalent to a few drops, or approximately 5 mg per
kilogram of body weight. It is classified as a "supertoxic"
chemical. 2) Records suggest that Wetterhahn handled dimethyl-
mercury on only one day, while wearing latex gloves and working
under a ventilated hood designed to prevent exposure to chemical
fumes. She had delayed but ultimately fatal neurotoxic effects
similar to those caused by methylmercury compounds, and this case
illustrates the potent toxicity of dimethylmercury and the need
for additional safety precautions if it is to be used in any
scientific research. 2) Five months after the accident, on
January 20, 1997, Wetterhahn was admitted to the university
medical center with a 5 day history of progressive deterioration
in balance, gait, and speech. She had lost 15 lb over a period of
2 months, and had experienced several brief episodes of nausea,
diarrhea, and abdominal discomfort. 3) Wetterhahn recalled that
in August 1996, while transferring liquid dimethylmercury from a
container to a capillary tube, she spilled several drops from the
tip of the pipette onto the back of her gloved hand. She reported
that she had cleaned up the spill and then removed the protective
gloves. (The date of the accident was established from her
notebooks and other laboratory data to be August 14, 1996.) 4) On
February 6th, 22 days after the first neurologic symptoms
developed (and 176 days after exposure), Wetterhahn became
unresponsive to all visual, verbal, and light-touch stimuli. 5)
The authors report they could find only 3 previously reported
cases of poisoning with dimethylmercury, all of which were fatal,
and that equally bleak outcomes had been reported in patients
with severe methylmercury poisoning. In view of the dismal
prognosis, and after more than 3 months of aggressive treatment
and support, Wetterhahn's advance directives were followed, and
she died peacefully on June 8, 1998, 298 days after exposure. 6)
Some anatomical findings from the autopsy report: "The cortex of
the cerebral hemispheres was diffusely thinned, to 3 mm. The
visual cortex around the calcarine fissure was grossly gliotic,
as was the superior surface of the superior temporal gyri. The
cerebellum showed diffuse atrophy of both vermal and hemispheric
folia. Microscopical study showed extensive neuronal loss and
gliosis bilaterally within the primary visual and auditory
cortices, with milder loss of neurons and gliosis in the motor
and sensory cortices. There was widespread loss of cerebellar
granular-cell neurons, Purkinje cells, and basket-cell neurons,
with evidence of loss of parallel fibers in the molecular
layer... An extensive high mercury content was found in the
frontal lobe and visual cortex, liver, and kidney cortex. The
mercury content of the brain was approximately 6 times that of
whole blood at the time of death... 7) The authors conclude:
"Dimethylmercury appears to be so dangerous that scientists
should use less toxic mercury compounds whenever possible. Since
dimethylmercury is a "supertoxic" chemical that can quickly
permeate common latex gloves and form a toxic vapor after a
spill, its synthesis, transportation, and use by scientists
should be kept to a minimum, and it should be handled only with
extreme caution and with the use of rigorous protective
measures."
-----------
NEJM 1998 338:1672
SW 1998 26 Jun
-----------
SCIENCE-WEEK 14 Sep 2001 http://scienceweek.com
-------------------
Related Background:
DEATH OF PROMINENT CHEMIST PROMPTS CALL FOR CHANGE IN NMR METHODS
The international chemistry community was shocked recently by the
death of Karen E. Wetterhahn, age 48, Professor of Chemistry at
Dartmouth College (US). Wetterhahn was a well-known authority
on the effects of heavy metals on biological systems. Ten months
ago, in the course of calibrating a nuclear magnetic resonance
(NMR) apparatus with the standard dimethylmercury, Wetterhahn
accidentally spilled a few drops of the substance on her latex-
covered hand. Unexpectedly, the substance penetrated the glove,
and within a few months the first neurological symptoms of
mercury poisoning appeared. She died on June 8th. John Winn, head
of the Dartmouth Chemistry Department, and others, have now
called for the chemical community to establish an NMR standard
safer than dimethylmercury.
-----------
CEN 1997 16 Jun
SW 1997 26 Jun
-----------
SCIENCE-WEEK 14 Sep 2001 http://scienceweek.com

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

15. SOURCES:
AS: Amer. Scientist; CEN: Chem. & Eng. News; GD: Genes & Dev.;
GR: Genome Res.; JACS: J. Amer. Chem. Soc.; JAMA: J. Amer. Med.
Assoc.; JCE: J. Chem. Educ.; MMWR: CDC Morbidity and Mortality
Weekly Report; NAT: Nature; NATM: Nature Medicine; NEJM: New
Engl. J. Med.; NYT: New York Times; NYR: New York Review; PNAS:
Proc. Natl. Acad. Sci.; PRL: Phys. Rev. Lett.; PT: Physics Today;
SA: Scientific American; SCI: Science; SW: ScienceWeek; TS: The
Scientist.

In the text, the affiliation following the author's name is the
affiliation of the lead author. The indication (na) signifies no
known research affiliation.

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

NOTICES
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=

CHANGE OF EMAIL ADDRESS:
If at any time you need to change the Email address at which you
receive SW, please send the information to:
request@scienceweek.com

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

SCIENCE-WEEK SUBSCRIPTIONS:
Complete subscription information is available at:
http://scienceweek.com/subinfo.htm

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

We welcome comments, suggestions, and criticisms from our
subscribers. Public letters relevant to any report are also
welcome. Editorial contact: editors@scienceweek.com

Editor/Publisher: Dan Agin
Managing Editor: Claire Haller
Associate Editor: Joan Oliner

Copyright (c) 1997-2001 SCIENCE-WEEK/Spectrum Press Inc.
All Rights Reserved
US Library of Congress ISSN 1529-1472

---------------------------------------------
ScienceWeek is published by Spectrum Press Inc.,
3023 N. Clark Street #109, Chicago, 60657-5205 IL, USA.
---------------------------------------------
-----end file