|
ScienceWeek
SCIENCEWEEK
ScienceWeek - July 12, 2002 Vol. 6 Number 28
An Online Research Digest Published Weekly Since 1997
--------------------------------------------------
As is your sort of mind, so is your sort of search:
You will find what you desire.
-- Robert Browning (1812-1889)
--------------------------------------------------
=-=-=-=-=-=-=-=-=
Section 1
=-=-=-=-=-=-=-=-=
1. History of Chemistry: Chemical Dynamics and Chain Reactions
2. On Astrophysical Jets
3. On Measuring Spacetime
4. On the Evolution of Color Vision
5. On Computations by Biological Systems
6. On Prokaryotic Diversity
7. On Functional Synthetic Oligomers
8. Current Problems in Crystal Engineering
9. On the Causes of Rising Sea-Level
10. On the Therapeutic Cloning Debate in Europe
11. On Hemorrhagic Fever Viruses as Biological Weapons
12. On Congestive Heart Failure
13. In Focus:Dinosaurs, Dragons, and Dwarfs: The Evolution of
Maximal Body Size
14. New Books
15. ScienceWeek Notices and Subscription Information
=-=-=-=-=-=-=-=-=
Section 2
=-=-=-=-=-=-=-=-=
1. HISTORY OF CHEMISTRY: CHEMICAL DYNAMICS AND CHAIN REACTIONS
In this context, the term "chain reaction" refers to a series of
reactions in which the product of each step is a reagent for the
next step, the overall process thus continuing with explosive
rapidity. Improved understanding of chain reactions led to
better methods of plastics formation, and the analogous nuclear
chain reaction led to the nuclear bomb and controlled nuclear
energy. In general, A chemical chain reaction proceeds by a
sequence subdivided into three stages: (a) Initiation, in which
a reactive intermediate, which may be an atom, an ion, or a
neutral molecular fragment, is formed, usually through the
action of an agent such as light, heat, or a catalyst. (b)
Propagation, whereby the intermediate reacts with the original
reactants, producing stable products and another intermediate,
whether of the same or different kind; the new intermediate
reacts as before, so a repetitive cycle begins. (c) Termination,
which may be natural, as when all the reactants have been
consumed or the containing vessel causes the chain carriers to
recombine as fast as they are formed, but more often is induced
intentionally by introduction of substances called inhibitors or
antioxidants.
Nikolay Semenov (1896-1986), discussed below, developed the
theory of "branched chain reactions". Branched chain reactions
are a form of chain reaction in which the number of chain
carriers increases in each propagation. As a result the reaction
accelerates extremely rapidly, sometimes being completed in less
than 1 millisecond.
J. van Houten (St. Michael's College, US) discusses chemical
dynamics and chain reactions, the author making the following
points:
1) The post-World War II era saw a remarkable increase in
interest in chemical dynamics and the mechanisms of fast
chemical reactions. In part, that interest can be attributed to
research on fuels and munitions in the years leading up to and
during the war. There also were many peaceful applications
derived from better understanding of combustion processes in
internal combustion engines, jet engines, and high explosives.
Furthermore, technological advances in the first half of the
20th century had made it possible to study ever-faster reactions
in ever-more detail.
2) In 1901 Jacobus van't Hoff (1852-1911) received the first
Nobel Prize for "the discovery of the laws of chemical
dynamics," and van't Hoff and the 1903 Nobel Laureate Svante
Arrhenius (1859-1927) were responsible for the concept that
molecules must collide with sufficient energy if they are to
react. However, the dynamic behavior of many reactions could not
be explained by the laws that van't Hoff had proposed. For
example, phosphorus was known to glow in air (hence the term
phosphorescence) but not in pure oxygen or in atmospheres with
reduced oxygen partial pressure (2).
3) Photo-initiated reactions presented another paradox early in
the 20th century -- the concept that a single photon could
initiate a reaction in a single molecule was accepted in
accordance with Planck's theory, however the ability of a single
photon to initiate the reaction of literally millions of
molecules did not seem to make sense. In 1913 Max Bodenstein
(1871-1942) had first advanced the concept of reactive
intermediates as part of a chain reaction mechanism. Bodenstein
managed to obtain an empirical fit to the kinetics of the
reaction H(sub2) + Br(sub2) --> 2HBr, and he found that iodine
hindered the reaction. However, he could not find a correlation
between the free energy and the kinetics of the reaction (3).
Ten years later Christiansen and Kramers postulated that chain
reactions might be initiated thermally as well as by light and,
furthermore, if two or more reactive intermediates were produced
then the reaction could branch, resulting in an explosion.
4) Christiansen and Kramers did not pursue their research on
chain reactions, and investigations of the reaction of
phosphorus vapor with oxygen were taken up in 1926 by two
scientists, Chariton and Valta, working at the Leningrad
Physico-Technical Institute headed by Nikolay Semenov
(1896-1986). They showed that the reaction of phosphorus vapor
with oxygen did, indeed, depend on the pressure of the gases,
with an explosion occurring only at intermediate pressures, and
with no reaction at very high or very low pressures. Bodenstein,
who was considered to be the world's authority on chemical
dynamics at the time, stated that the results were
incomprehensible and must be wrong. However, the simple fact
that the experimental results were incomprehensible using the
available models of the time did not mean that the results were
wrong. Semenov explained the results by showing that chain
reactions lead to explosions when the chain branches, thereby
increasing the concentration of the reactive intermediates and,
consequently, the rate of the reaction. Furthermore, Semenov
developed the mathematical relations that showed why the rate of
branching, and hence the rate of the reaction, was facilitated
at intermediate pressures but not at higher or lower pressures.
Semenov received the Nobel Prize in Chemistry in 1956.
References (abridged):
1. Nobel e-Museum-Chemistry 1956 (with links to Prize
Presentation and Biography pages),
http://www.nobel.se/chemistry/'laureates/1956/index.html
2. See Keiter, R. L.; Gamage, C. P., J. Chem. Educ. 2001, 78,
908 for a discussion of this phenomenon and a demonstration
involving the reaction between white phosphorus and oxygen.
3. Stock, J. T. ACS National Meeting, Chicago, August 2001, HIST
47.
J. Chem Educ. 2002 79:414
Web Links: chemical chain reactions
ScienceWeek http://www.scienceweek.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
2. ON ASTROPHYSICAL JETS
In this context, the term "poloidal magnetic field" refers to a
magnetic field generated by an electric current flowing in a
ring. (A "toroidal magnetic field" is an electric field
generated by a current flowing in a solenoid round a torus.)
Mario Livio (Space Telescope Science Institute, US) discusses
astrophysical jets, the author making the following points:
1) Although a wide variety of astrophysical objects produce
powerful jets, we still lack a comprehensive theory of their
formation. In our Galaxy, young stellar objects, massive X-ray
binaries, black hole X-ray transients, symbiotic stars,
supersoft X-ray sources and even some planetary nebulae are all
accreting systems that produce jets. Among extragalactic
sources, powerful jets are observed in active galactic nuclei
(accreting, supermassive black holes) and are thought to exist
in -ray bursts (which possibly involve accreting, stellar-mass
black holes).
2) Despite the ubiquity of jets, there is no generally accepted
theory for the mechanism of their acceleration and alignment.
Early attempts to explain this collimation involved nozzles
(similar to rocket exhausts), in which an adiabatic flow
propagating in a medium with decreasing pressure first converges
and then diverges as it accelerates to supersonic speed. Another
idea was that the collimating agents are funnels that are formed
at the centres of dense tori. Radiation pressure on
electron–positron pairs, on resonance lines, or on dust, have
been suggested to accelerate jets in some of the systems
mentioned above.
3) The main problem of these early models is that they do not
work for all classes of astrophysical jets. For example,
although the power emitted by the central source approaches the
critical Eddington luminosity (at which radiation pressure
exactly balances gravity) in supersoft X-ray sources, this is
not true for most other classes of objects. The drag caused by
radiation limits the attainable speeds to values below those
observed in other (ultrarelativistic) jets. Similarly, dense
tori with narrow axisymmetric funnels, which were once assumed
to exist around black holes, were later shown to be unstable to
non-axisymmetric instabilities that could destroy them on a
dynamic timescale. An important question, therefore, is whether
a universal mechanism of acceleration and collimation that
operates in all classes can be found? At the present time, the
most promising universal mechanism for jet acceleration and
collimation relies on an accretion disc threaded by a poloidal,
large-scale magnetic field.(1-4)
References (abridged):
1. Mirabel, I. F. & Rodriguez, L. F. Nature 392, 673–676 (1998).
2. Wilms, J. et al. Mon. Notices R. Astron. Soc. 328, L27–L31
(2001).
3. Celotti, A. & Blandford, R. D. in Black Holes in Binaries and
Galactic Nuclei: Diagnostics, Demography and Formation (eds
Kaper, L. et al.) 206–215 Springer, Berlin, 2001).
4. Livio, M. in Probing the Physics of Active Galactic Nuclei by
Multiwavelength Monitoring (eds Peterson, B. M. et al.) 225–248
(ASP, San Francisco, 2001).
Nature 2002 417:125
Web Links: astrophysical jets
Related Background:
BLACK HOLES, MAGNETIC FIELDS, AND RELATIVISTIC JETS
1) S. Koide et al (Toyama University, JP) discuss black holes,
the authors making the following points:
1) Relativistic jets have now been discovered in several
different classes of astrophysical objects, including active
galactic nuclei, microquasars, and gamma ray bursts. A rapidly
spinning black hole may exist at the center of each of these
objects, and energetic reactions that occur near the hole may be
responsible for the jets. One of the most promising processes
for producing relativistic jets is the extraction of rotational
energy from a spinning (Kerr) black hole. One method of
extraction is the "Penrose process", which uses fission of a
particle near the black hole to extract the black hole
rotational energy. However, this process may not be applicable
to most astrophysical objects, because the particle fission must
occur near the black hole, and the relative velocity of the
particles produced by the fission should be near the speed of
light. On the other hand, Blandford and Znajek (1977)
demonstrated that a large-scale magnetic field around a Kerr
black hole also could extract rotational energy. They assumed a
magnetic force-free condition, which corresponds to an extremely
strong magnetic field or an extremely low inertia plasma case.
2) The authors report that using numerical simulations, they
modeled the general relativistic magnetohydrodynamic behavior of
a plasma flowing into a rapidly rotating black hole in a
large-scale magnetic field. The results demonstrate that a
torsional Alfven wave is generated by the rotational dragging of
space near the black hole. The wave transports energy along the
magnetic field lines outward, causing the total energy of the
plasma near the hole to decrease to negative values. When this
negative energy plasma enters the black hole horizon, the
rotational energy of the black hole decreases. Through this
process, the energy of the spinning black hole is extracted
magnetically, and this process may be applicable to the
formation of relativistic jets.
Science 2002 295:1688
References (abridged):
1. T. J. Pearson, et al., Nature 290, 365 (1981)
2. J. A. Biretta, W. B. Sparks, F. Macchetto, Astrophys. J. 520,
621 (1999)
3. I. F. Mirabel and L. F. Rodriguez, Nature 371, 46 (1994)
4. S. J. Tingay, et al., Nature 374, 141 (1995)
5. S. R. Kulkarni, et al., Nature 398, 389 (1999)
Notes:
In this context, a "jet" is a long thin linear feature of bright
emission extending from a compact object. Jets are very common
at radio wavelengths, but have also been observed in optical and
x-ray emissions. A "relativistic jet" is a jet moving at close
to the speed of light.
A "Kerr black hole" has angular momentum but no charge (i.e., a
rotating black hole with no charge).
In general, an "Alfven wave" is a disturbance transmitted
through a plasma (a fully ionized gas) in the presence of a
magnetic field. The direction of propagation is parallel to the
mean magnetic field, with the plasma particles vibrating at
right angles to this direction. The speed of propagation, the
"Alfven speed", depends on the magnetic field strength and
plasma density. Such waves are a type of magnetohydrodynamic
wave, and they have been directly observed in solar wind
high-speed streams from the Sun and in planetary magnetospheres.
The boundary of a black hole is called the "event horizon"
(black hole horizon), because any event within the boundary is
invisible outside, the invisibility resulting from the fact that
no radiation can escape to be detected.
Some galaxies are known to have very "active" central regions
from which enormous amounts of energy are emitted each second,
and it is believed that these "active galactic nuclei" are
probably powered by accretion of matter into a supermassive
black hole of 10^(6) to 10^(9) solar-masses. Astronomers have
recently discovered that many active galactic nuclei eject
clouds of ionized gas with velocities of up to 10 percent of the
speed of light over a wide range of angles, in contrast to the
previously known collimated jets. These mass outflows are
considered to be intriguing because they provide information
about the dynamical forces (such as radiation and wind pressure)
near an active supermassive black hole.
Quasars (quasi-stellar objects) are extremely luminous sources
radiating energy over the entire spectrum from x-rays to radio
waves, and which are apparently the oldest and most distant
objects in the universe. They are believed to involve massive
black holes. Microquasars are quasars of apparent stellar mass.
Gamma ray bursts are intense flashes of gamma rays detected at
energies up to 10^(6) electronvolts. They were discovered by US
Air Force satellites in 1967 but not declassified until 1973.
The detection of these bursts averages about 1 per day, and
measurements indicate the distribution of bursts is isotropic,
i.e., they are uniformly distributed across the sky. The current
consensus is that gamma ray bursts are produced by the merger of
two neutron stars, and up to this point, the bursts that have
been noted apparently originate outside our own galaxy.
Related background:
PLASMA JETS IN ACTIVE GALACTIC NUCLEI
A.P. Lobanov and J.A. Zensus (Max Planck Institute for Radio
Astronomy Bonn, DE) discuss plasma jets in active galactic
nuclei. One of the most intriguing features observed in active
galactic nuclei is highly collimated and relativistic plasma
outflows (jets) that originate in the immediate vicinity of the
center of activity and propagate at distances of up to several
megaparsecs (1 parsec = 3.26 light years). Observations of jets
in active galactic nuclei probe the behavior of extremely
relativistic matter in the Universe and provide a unique and
remote "laboratory" for studying the most powerful cosmic
phenomena such as supermassive black holes and extragalactic
accretion disks. The quasar 3C273 is one of the closest and most
luminous and best studied active galactic nuclei, with a
prominent relativistic outflow observed in the x-ray, optical,
and radio wave bands. The relativistic jet observed in this
quasar is one-sided, with no signs of emission on the counterjet
side at dynamic ranges of up to 16,000:1. This is evidence for
strong relativistic boosting in an intrinsically double-sided
outflow powered by an accretion disk around a black hole. The
enhanced emission features (jet components) identified in the
jet on scales of up to approximately 20 milli-arc seconds are
moving at apparent speeds exceeding the speed of light by
factors of 5 to 8. These jet components may result from the
flares observed in this quasar in the optical and radio
wavelengths and also reflect the precession of the jet axis. The
structure and kinematics of such outflows are typically
explained in terms of shock waves and Kelvin-Helmholtz
instability.
Science 2001 294:128
ScienceWeek http://www.scienceweek.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
3. ON MEASURING SPACETIME
The general theory of relativity essentially derives its origin
from the need to extend the space and time concepts of the
special theory of relativity from the domain of electric and
magnetic phenomena to all of physics, and particularly to the
theory of gravitation. According to general relativity,
space-time is curved, and this curvature is equivalent to the
presence of a gravitational field. Far from being rigid and
homogeneous, the general-relativistic space-time continuum of
the theory has geometric properties that vary from point to
point and that are affected by local physical processes.
Space-time ceases to be a scaffolding for the dynamics of nature
and becomes an integral part of the dynamic process. Not only
are the properties of space and time subject to scientific
investigation, to study by means of experiments, but specific
properties, such as the amount of curvature in a particular
location at a specified time, are measurable with physical
instruments.
Max Tegmark (University of Pennsylvania, US) discusses
spacetime, the author making the following points:
1) Traditionally, space was merely a three-dimensional (3D)
static stage where the cosmic drama played out over time.
Einstein's theory of general relativity (1) replaced this
concept with 4D spacetime, a dynamic geometric entity with a
life of its own, capable of expanding, fluctuating, and even
curving into black holes. Now, the focus of research is
increasingly shifting from the cosmic actors to the stage
itself. Triggered by progress in detector, space, and computer
technology, an avalanche of astronomical data is revolutionizing
our ability to measure the spacetime we inhabit on scales
ranging from the cosmic horizon down to the event horizons of
suspected black holes, using photons and astronomical objects as
test particles.
2) According to general relativity theory, spacetime is what
mathematicians call a manifold, characterized by a topology and
a metric. The topology gives the global structure, and we can
ask: Is space infinite in all directions or multiply connected,
like say a hypersphere or doughnut, so that traveling in a
straight line could in principle bring you back home -- from the
other direction? The metric determines the local shape of
spacetime (i.e., the distances and time intervals we measure)
and is mathematically specified by a 4 × 4 matrix at each point
in spacetime.
3) General relativity theory consists of two parts, each
providing a tool for measuring the metric. The first part of
general relativity theory states that, in the absence of
nongravitational forces, test particles (objects not heavy
enough to have a noticeable effect on the metric) move along
geodesics in spacetime, in generalized straight lines, so the
observed motions of photons and astronomical objects allow the
metric to be reconstructed. The author refers to this as
geometric measurements of the metric. The second part of general
relativity theory states that the curvature of spacetime
(expressions involving the metric and its first two derivatives)
is related to its matter content -- in most cosmological
situations simply the density and pressure, but sometimes also
bulk motions and stress energy. The author refers to such
measurements of the metric as indirect, because they assume the
validity of the Einstein field equations of general relativity
theory.
4) The current consensus in the cosmological community is that
spacetime is extremely smooth, homogeneous, and isotropic
(translationally and rotationally invariant) on large (
approximately 10^(23) to 10^(26) m) scales, with small
fluctuations that have grown over time to form objects like
galaxies and stars on smaller scales. Cosmic microwave
background observations (2) have shown that space is almost
isotropic on the scale of our cosmic horizon (approximately
10^(26) m), with the metric fluctuating by only about one part
in 10^(5) from one direction to another; combining this with the
so-called cosmological principle (the assumption that there is
nothing special about our vantage point) implies that space is
homogeneous as well. 3D maps of the galaxy and quasar
distribution give more direct evidence for large-scale
homogeneity.(4,5)
References (abridged):
1. A. Einstein, Relativity: The Special and the General Theory
(Random House, New York, 1920).
2. The cosmic microwave background (CMB) is the oldest light
around, emanating from the hot opaque hydrogen plasma that
filled the universe during its first 400,000 years. An
up-to-date review is available from M. White and J. Cohn,
http://arxiv.org/abs/astro-ph/0203120 (2002).
4. C. M. Will, Theory & Experiment in Gravitational Physics
(Cambridge Univ. Press, Cambridge, 1993).
5. C. M. Will, http://arxiv.org/abs/gr-qc/9811036 (1998).
Science 2002 296:1427
Web Links: general relativity theory
Related Background:
1905: EINSTEIN'S ANNUS MIRABILIS
"By the spring of 1905, the 26-year-old Einstein had decided
that physicists were 'out of [their] depth'. From calculations
based on Planck's radiation law, Einstein drew the astounding
'general conclusion' that light can be a particle and a wave,
and in fact both at once, a wave/particle duality. Therefore the
electromagnetic world-picture could not succeed, because
Lorentz's theory could represent radiation, or light, only as a
wave, and so could never provide a way to explain how the
electron's mass is generated by its own radiation. Whereas
Planck had discovered certain peculiarities about the energy of
radiation, Einstein set out to explore the structure of
radiation itself. Einstein's particles of light differed
fundamentally from Newton's in ways that even he did not yet
fully realize. Around the third week of May 1905, Einstein sent
his friend Habicht what are surely some of the greatest
understatements in the history of science. He wrote that he had
only some 'inconsequential babble' for his friend, whom he
lambasted for neither writing nor visiting him during Easter:
'So what are you up to, you frozen whale, you smoked, dried,
canned piece of soul... I promise you four papers.' The first
paper is the light quantum paper that Einstein referred to as
'very revolutionary'. The second suggested a means to measure
the size of atoms using diffusion and viscosity of liquids. The
third one explored Brownian motion using methods of the
molecular theory of heat. 'The fourth paper is only a draft at
this point, and is an electrodynamics of moving bodies which
employs a modification of the theory of space and time; the
purely kinematic part of this paper will surely interest you.'
What is so incredible about this outburst of creativity is that
by late May two papers were completed and the third was in draft
form." [Editor's note: The fourth paper, the so-called
relativity paper, was completed a few weeks later in June 1905.]
Arthur I. Miller: _Einstein, Picasso: Space, Time, and the
Beauty That Causes Havoc_. Basic Books, New York 2001, p.189
Related Background:
COSMOLOGY: COSMOLOGICAL THEORIES
James Peebles (P. James E. Peebles) (1935- ), is a distinguished
senior cosmologist whose work has been of great influence in the
field for many decades. Among other contributions, in 1965,
Peebles, in collaboration with Robert Dicke, predicted that a
background radiation should be detectable as a remnant of the
Big Bang. Peebles also calculated that the amount of helium
present in the Universe as a consequence of the Big Bang should
be 25 to 30 percent, a figure that agrees with current
observations. Peebles is also the author of several advanced
texts that defined the subject of cosmology for a generation of
astronomers. In a recent essay, Peebles confronts current
theories in cosmology and makes the following points:
1) Peebles suggests that cosmologists have firmly established
the foundations of their field, gathering over the past 70 years
abundant evidence that the Universe is expanding and cooling:
... ... a) The light from distant galaxies is shifted toward the
red, as it should be if space is expanding and galaxies are
pulled away from one another.
... ... b) A sea of thermal radiation fills space, as it should
if space was previously denser and hotter.
... ... c) The Universe contains large amounts of deuterium and
helium, as it should if temperatures were once much higher.
... ... d) Galaxies billions of years ago look distinctly
younger, as they should if they are close to the time when no
galaxies existed.
... ... e) The curvature of space-time seems to be related to
the material content of the Universe, as it should be if the
Universe is expanding according to the predictions of Einstein's
gravity theory -- the general theory of relativity.
The author points out that the idea that the Universe is
expanding and cooling is the essence of the Big Bang theory, and
the author states: "You will notice I have said nothing about an
'explosion' -- the Big Bang theory describes how our Universe is
evolving, not how it began."
2) Peebles points out that we do not know what the Universe was
doing before it was expanding. A leading theory, "*inflation",
is an attractive addition to the framework of cosmology, but it
lacks support from various other parts of the framework, and
such support is precisely what cosmologists are now seeking. If
measurements in progress agree with the unique signatures of
inflation, then such measurements will be counted as a
persuasive argument for inflation theory. "But until that time,
I would not settle any bets on whether inflation really
happened. I am not criticizing the theory; I simply mean that
this is brave, pioneering work still to be tested."
3) Concerning the current use of the "*cosmological constant" as
an explanatory concept in understanding the evidence for an
accelerating Universe, Peebles states: "The evidence is
impressive, but I am still uneasy about details of the case for
the cosmological constant, including possible contradictions
with the evolution of galaxies and their spatial distribution.
The theory of the accelerating Universe is a work in progress. I
admire the architecture, but I would not want to move in just
yet."
4) Peebles concludes: "Over time, inflation, *quintessence, and
other concepts now under debate either will be solidly
integrated into the central framework or will be abandoned and
replaced by something better. In a sense, we are working
ourselves out of a job. But the Universe is a complicated place,
to put it mildly, and it is silly to think we will run out of
productive lines of research anytime soon. Confusion is a sign
that we are doing something right: it is the fertile commotion
of a construction site."
Scientific American January 2001
Text Notes:
... ... *inflation: The inflationary model, first proposed by
Alan Guth in 1980, proposes that quantum fluctuations in the
time period 10^(-35) to 10^(-32) seconds after time zero were
quickly amplified into large density variations during the
"inflationary" 10^(50) expansion of the universe in that time
frame.
... ... *cosmological constant: See following report.
... ... *quintessence: See following report.
Related Background:
ON QUINTESSENCE AND THE EVOLUTION OF THE COSMOLOGICAL CONSTANT
In cosmology, the "cosmological constant" is a mathematical term
introduced by Einstein into the equations of general relativity,
the purpose to obtain a solution of the equations corresponding
to a "static universe". The term describes a pressure (if
positive) or a tension (if negative) which can cause the
Universe to expand or contract even in the absence of any
matter. In other words, the cosmological constant represents an
effective "vacuum energy". When the expansion of the Universe
was discovered, Einstein apparently began to regard the
introduction of this term as a mistake, and he described the
cosmological constant as the "greatest mistake of my life". But
the term has reappeared as the proposed source of apparent
accelerated cosmic expansion.
P.J.E. Peebles (Princeton University, US) presents a short
review of current ideas concerning the cosmological constant,
the author making the following points: 1) Contrary to
expectations, the evidence is that the Universe is expanding at
approximately twice the velocity required to overcome the
gravitational pull of all the matter the Universe contains. The
implication of this is that in the past the greater density of
mass in the Universe gravitationally slowed the expansion, while
in the future the expansion rate will be close to constant or
perhaps increasing under the influence of a new type of matter
that some call "quintessence". 2) Quintessence began as
Einstein's cosmological constant, Lambda. It has negative
gravitational mass: its gravity pushes things apart. 3) Particle
physicists later adopted Einstein's Lambda as a good model for
the gravitational effect of the *active vacuum of quantum
physics, although the idea is at odds with the small value of
Lambda indicated by cosmology. 4) Theoretical cosmologists have
noted that as the Universe expands and cools, Lambda tends to
decrease. As the Universe cools, *symmetries among forces are
broken, particles acquire masses, and these processes tend to
release an analogue of *latent heat. The vacuum energy density
accordingly decreases, and with it the value of Lambda. Perhaps
an enormous Lambda drove an early rapid expansion that smoothed
the primeval chaos to make the near uniform Universe we see
today, with a decrease in Lambda over time to its current value.
This is the cosmological *inflation concept. 5) The author
suggests that the recent great advances in detectors,
telescopes, and observatories on the ground and in space have
given us a rough picture of what happened as our Universe
evolved from a dense, hot, and perhaps quite simple early state
to its present complexity. Observations in progress are filling
in the details, and that in turn is driving intense debate on
how the behavior of our Universe can be understood within
fundamental physics.
Nature 1999 398:25
Text Notes:
... ... *active vacuum of quantum physics: This refers to the
idea that the vacuum state in quantum mechanics has a zero-point
energy (minimum energy) which gives rise to vacuum fluctuations,
so the vacuum state does not mean a state of nothing, but is
instead an active state.
... ... *symmetries among forces are broken: If a theory or
process does not change when certain operations are performed on
it, the theory or process is said to possess a symmetry with
respect to those operations. For example, a circle remains
unchanged under rotation or reflection, and a circle therefore
has rotational and reflection symmetry. The term "symmetry
breaking" refers to the deviation from exact symmetry exhibited
by many physical systems, and in general, symmetry breaking
encompasses both "explicit" symmetry breaking and "spontaneous"
symmetry breaking. Explicit symmetry breaking is a phenomenon in
which a system is not quite, but almost, the same for two
configurations related by exact symmetry. Spontaneous symmetry
breaking refers to a situation in which the solution of a set of
physical equations fails to exhibit a symmetry possessed by the
equations themselves.
... ... *latent heat: In general, this is the quantity of heat
absorbed or released when a substance changes its physical phase
(e.g., solid to liquid) at constant temperature.
... ... *inflation concept: The inflationary model, first
proposed by Alan *Guth in 1980, proposes that quantum
fluctuations in the time period 10^(-35) to 10^(-32) seconds
after time zero were quickly amplified into large density
variations during the "inflationary" 10^(50) expansion of the
universe in that time frame.
ScienceWeek http://www.scienceweek.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
4. ON THE EVOLUTION OF COLOR VISION
In the vertebrate eye, "rod cells" (rods) are one of the two
main types of light-sensitive cells found in the retina. Rods
provide monochromatic vision in dim light and are found chiefly
in the periphery of the retina. "Cone cells" (cones) are the
receptor cells responsible for color vision. Apart from their
ability to discriminate wavelengths of light, the two receptors
differ markedly in sensitivity: a rod can respond to a single
photon, whereas more than 100 photons are required to activate a
cone.
Color vision, the ability to discriminate light on the basis of
wavelength composition, is found in humans, in other primates,
and in certain species of birds, fishes, reptiles, and insects.
These animals have visual receptors that respond differentially
to the various wavelengths of visible light. Each type of
receptor is especially sensitive to light of a particular
wavelength composition. Evidence indicates that primates,
including humans, possess three classes of cone photoreceptors
that differ in the photopigments they contain and in their
neural connections. In humans, two of these, the R and G cones,
are sensitive to all wavelengths of the visible spectrum from
380 to 700 nanometers. The B cones, whose sensitivity peaks at
about 440 nm, are not appreciably excited by wavelengths longer
than 540 nm. The perception of blueness and yellowness depends
upon the level of excitation of B cones in relation to that of R
and G cones. No two wavelengths of light can produce equal
excitations in all three kinds of cones. It follows that,
provided they are sufficiently different to be discriminable, no
two wavelengths can give rise to identical sensations.
Kit Wolf (University of Newcastle upon Tyne, UK) discusses the
evolution of color vision, the author making the following
points:
1) Most mammals are dichromats and can only distinguish between
two dimensions of color: bright versus dark and blue versus
yellow [1] . In contrast, humans are trichromats, our extra
class of photoreceptor enabling us to discriminate between reds
and greens which would otherwise appear identical. However, this
ostensibly modest improvement in our visual capabilities has
hidden costs: the increased sparsity of each type-specific cone
matrix may theoretically reduce visual spatial acuity, and
colour-anomalous ('color-blind') humans, whose visual world is
akin to that of dichromats, can sometimes see features
camouflaged by red–green patterns that trichromats cannot detect
[2] . Nonetheless, trichromacy is highly conserved in those few
primate species that have evolved it. Of over 3,200 old-world
monkeys and apes surveyed, inherited color-anomalous vision has
only ever been found in three closely related individuals [3,4]
, though on an evolutionary timescale such transmissible
deficits are likely to have arisen spontaneously many times
over. What tips the evolutionary balance so decisively in favour
of trichromats?
2) Several explanations for the evolution of color vision have
been put forward [5] . Color might serve as a cue for object
recognition; animals may use color to assess the health of other
members of their species; and color could aid image
segmentation. But the hypothesis that has attracted the most
attention is that trichromacy evolved as an aid to frugivory
(the eating of fruits) . This notion is particularly attractive,
as many fruits gradually turn yellow, red or orange during
ripening. These colours are strikingly visible to trichromats,
but dichromats have difficulty distinguishing them from a
dappled background of green leaves [5]. Furthermore, fruit is an
important component of most modern primate diets, and fossil and
physiological evidence suggests that this was also true of early
primates. Párraga et al. [2002] have recently demonstrated that
the spatial characteristics of human red–green vision are better
matched to scenes containing fruit than they are to natural
scenes chosen at random.
3) In summary: Trichromatic vision may have evolved as an aid to
frugivory. This hypothesis is supported by the recent
demonstration that the spatial characteristics of pictures
containing fruit are particularly well matched to the abilities
of the human visual system.
References (abridged):
1. Jacobs G.H. (1993) The distribution and nature of colour
vision among the mammals. Biol. Rev., 68:413-471.
2. Morgan M.J., Adam A. and Mollon J.D. (1992) Dichromates
detect color-camouflaged objects that are not detected by
trichromates. Proc. Roy. Soc. Lond. Series B-Biol. Sci.,
248:291-295.
3. Jacobs G.H. and Williams G.A. (2001) The prevalence of
defective color vision in Old World monkeys and apes. Color Res.
Appl., 26:S123-S127.
4. Onishi A., Koike S., Ida M., Imai H., Shichida Y., Takenaka
O., Hanazawa A., Konatsu H., Mikami A. and Goto S. et al. (1999)
Vision-Dichromatism in macaque monkeys. Nature, 402:139-140.
5. Mollon J.D. (1989) 'Tho' she kneel'd in that place where they
grew..'-the uses and origins of primate colour vision. J. Exp.
Biol., 146:21-38.
Current Biology 2002 12:R253
Web Links: color vision
ScienceWeek http://www.scienceweek.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
5. ON COMPUTATIONS BY BIOLOGICAL SYSTEMS
Mark J. Schnitzer (Bell Laboratories, US) discusses computations
by biological systems, the author making the following points:
1) When can a physical system be said to perform a computation?
In the broadest sense, every physical system performs a
computation by realizing a solution to the dynamic equations
that govern its physical behavior. However, physical computing
is more interesting in the narrower domain in which a set of
physical variables represents the values of another set of
mathematical ones. A physical variable might be a voltage within
a digital computer, the height of a stack of poker chips, or a
chemical concentration in a biological cell. These variables are
then dynamically transformed by physical processes, in a way
that represents algorithmic manipulation of the mathematical
variables.
2) For physical computing systems that are also biological, it
is often fruitful to view the organism as the 'user' of the
computation. Natural selection has created many species in which
individual survival rests on effective, often remarkable,
computations performed by the organism's own physiology. For
example, many bats locate insect prey by emitting ultrasonic
pulses and detecting the echoes. By detecting small Doppler
shifts in the frequency of the returning pulses, the bat's
nervous system can discern acoustic 'texture' and so distinguish
prey from inanimate objects. Such elegant calculations suggest
some of the selection pressures that may have shaped the
underlying computational mechanisms, and can help to guide
future research.
3) Further understanding of such computations would come from a
knowledge of how acoustic variables are represented in the bat
brain, of the mathematical algorithms that describe the
transformation of these variables, of the biophysical mechanisms
by which the transformations are performed, and of the
computational errors that these mechanisms introduce in the
presence of noise. These issues also concern natural selection.
Algorithms should facilitate competent, or even near-optimal,
computation. Theoretical engineering tools can help us to
appreciate constraints on biological designs and to evaluate
computational performance in relation to physical limits.
Furthermore, because computations are carried out using
biological molecules and cells, the physical properties of this
hardware must also have constrained natural selection.(1-5)
References:
1. Carew, T. Behavioral Neurobiology (Sinauer, Sunderland,
Massachusetts, 2000).
2. von Neumann, J. The Computer and the Brain 2nd edn (Yale
Univ. Press, New Haven, Connecticut, 1958).
3. Koch, C. Biophysics of Computation (Oxford Univ. Press,
Oxford, 1999).
4. Weiner, N. Cybernetics 2nd edn (MIT Press, Cambridge,
Massachusetts, 1961).
5. Wandell, B. A. Foundations of Vision (Sinauer, Sunderland,
Massachusetts, 1995).
Nature 2002 416:683
Web Links: cybernetics
ScienceWeek http://www.scienceweek.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
6. ON PROKARYOTIC DIVERSITY
V. Torsvik et al (University of Bergen, NO) discuss prokaryotic
diversity, the authors making the following points:
1) Microscopic prokaryotic organisms are a largely unnoticed
part of Earth's biota. They constitute the domains Archaea and
Bacteria and consist of possibly millions of different species.
Prokaryotic diversity is a product of about 3.8 billion years of
evolution -- 2 billion years longer than that of eukaryotic
organisms, and is probably the reason for their extraordinary
diversity and habitat range. The prokaryotes are a crucial
component of the biosphere because they catalyze processes
sustaining all life on Earth and are thus the engines for the
biogeochemical cycles. However, only approximately 4500 species
have been characterized, leaving most of the diversity of
prokaryotes unexplored.
2) Traditionally, the unit of diversity is the species, but we
do not know whether any naturally occurring entity of
prokaryotic species exists, and a variety of definitions for the
concept are used for these organisms. First, the "phylophenetic"
definition circumscribes the species as a "monophyletic and
genomically coherent cluster of individual organisms that show a
high degree of overall similarity in many independent
characteristics, and is diagnosable by a discriminative
phenotypic property" (1). Second, a species can be defined as an
assemblage of strains sharing 70% or more DNA homology (2).
Third, in an ecological definition, the species and niche
concept are linked, and thus a species consists of the organisms
occupying the same niche (3). Thus, diversity can be defined as
the number of prokaryotic species and their relative abundance
in a community, or as the amount and distribution of information
in a community (4).
3) Diversity estimates for natural bacterial communities have
traditionally depended on cultivable species, but results from
the use of molecular techniques to measure diversity suggest
that reliance on culture has led to a longstanding underestimate
of bacterial diversity. DNA and RNA analyses imply prokaryotic
diversity far greater than was predicted, and are beginning to
hint at the role of bacterial and viral diversity in global
ecological cycles. For instance, most investigations of
prokaryotic diversity relate to surface environments, but recent
research suggests that the biota extend deep into Earth's crust,
and that the majority of prokaryotic organisms might occur in
the oceanic and terrestrial subsurface. The total carbon biomass
in subsurface terrestrial microorganisms has been estimated to
equal that of all terrestrial and marine plants, and may be the
largest constituent of the entire Earth biomass (5).
4) In summary: There are probably millions of species in the
microorganismal domains Bacteria and Archaea (the prokaryotes),
and we are only just beginning to work out the basic principles
governing their distribution and abundance in natural
environments. One characteristic that has become clear is that
prokaryote diversity in aquatic environments is orders of
magnitude less than in sediments and soils. Hypotheses and
models explaining such differences are under development and are
beginning to offer promising insights into the mechanisms
governing prokaryote diversity and ecosystem function.
References (abridged):
1. R. Rosell-Mora and R. Amann, FEMS Microbiol. Rev. 25, 39
(2001)
2. R. R. Colwell, R. A. Clayton, B. A. Ortiz-Conde, D. Jacobs,
E. Russek-Cohen, in Microbial Diversity and Ecosystem Function,
D. Allsopp, R. R. Colwell, D. L. Hawksworth, Eds. (CAB
International, Wallingford, UK, 1995), pp. 3-15.
3. T. F. Thingstad, Limnol. Oceanogr. 45, 1320 (2000)
4. R. M. Atlas, in Advances in Microbial Ecology, K. C.
Marshall, Ed. (Plenum, New York, 1984), vol. 7, pp. 1-47.
5. W. B. Whitman, D. C. Coleman, W. J. Wiebe, Proc. Natl. Acad.
Sci. U.S.A. 95, 6578 (1998)
Science 2002 296:1064
Web Links: prokaryotic diversity
ScienceWeek http://www.scienceweek.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
7. ON FUNCTIONAL SYNTHETIC OLIGOMERS
E.A. Archer and M.J. Krische (University of Texas, US) discuss
functional synthetic oligomers, the authors making the following
points:
1) The capability of defining structure carries with it the
potential to engineer functionality. As demonstrated by
naturally occurring macromolecules, the precise control of
structure confers exceptional mechanical properties (e.g.,
arachnid silk fibers),(1,2) remarkable catalytic functions
(e.g., cytochrome-p450),(3) and high-density information storage
capabilities (e.g., CD-ROM technology approximately 10^(8)
bits/cm^(2) versus DNA approximately 10^(21) bits/cm^(3)).(4) As
insight into the relationship between biomacromolecular
structure and function broadens, so does the capacity of
humankind to address the design of conformationally distinct,
functional synthetic oligomers endowed with properties that may
complement or even exceed their natural counterparts. Progress
toward these goals is underscored by the design of unnatural
oligomers possessing therapeutically relevant biological
activities.(5)
2) The development of increasingly sophisticated functional
synthetic oligomers and polymers will require reliable methods
for the control of their secondary and tertiary structure.
However, few rational approaches to the directed organization of
synthetic oligomers and polymers have been forthcoming. To date,
the vast majority of assembly strategies exploit global aspects
of structure, for example, the formation of phase-separated and
liquid-crystalline domains via solvophobically and sterically
driven assembly of block copolymers, dendronized polymers, and
dendritic macromolecules. In comparison to solvophobic forces,
hydrogen bond interactions possess greater strength and
directionality. Consequently, hydrogen bonds may be utilized to
enforce more localized order. Moreover, the recurrent structure
of oligomers and polymers makes such systems well suited to the
periodic presentation of hydrogen bond donor/acceptor sites.
3) To address the assembly of molecular strands, the authors
have introduced a molecular casting strategy whereby the
supramolecular connectivities of monomeric molecular components
are used to define structural parameters for the design of
related oligomers encoded with predefined modes of assembly.
This strategy has been successfully applied to the design of
high-affinity dimeric duplex oligomers based on the
2-amino-4,6-dichlorotriazine hydrogen-bonding motif.
4) The authors now report an investigation of a homologous
series of oligomers via NMR spectroscopy, vapor pressure
osmometry, isothermal titration calorimetry, and
cross-hybridization experiments involving the analysis of
dye-labeled strands via thin-layer chromatography. The authors
suggest their data give insight into the structural and
interactional features of the oligomers required for
high-affinity, high-specificity binding and define a platform
for the design of second-generation systems and related duplex
strands for use in nanoscale assembly.
References (abridged):
1. Qu, Y.; Payne, S. C.; Apkarian, R. P.; Conticello, V. P. J.
Am. Chem. Soc. 2000, 122, 5014.
2. For a review, see: Deming, T. J. Adv. Mater. 1997, 9, 299.
3. For a review, see: Loew, G. H.; Harris, D. L. Chem. Rev.
2000, 100, 407.
4. Martin, P. J. In Photochromism. Introduction to Molecular
Electronics; Petty, M. C., Bryce, M. R., Bloor, D., Eds.; Oxford
University Press: New York, 1995; pp 114-117.
5. For selected examples, see: (a) Smith, A. B., III; Keenan, T.
P.; Holcomb, R. C.; Sprengeler, P. A.; Guzman, M. C.; Wood, J.
L.; Carroll, P. J.; Hirschmann, R. J. Am. Chem. Soc. 1992, 114,
10672. (b) Zuckerman, R. N.; Martin, E. J.; Spellmeyer, D. C.;
Stauber, G. B.; Shoemaker, K. R.; Kerr, J. M.; Figliozzi, G. M.;
Goff, D. A.; Siani, M. A.; Simon, R. J.; Banville, S. C.; Brown,
E. G.; Wang, L.; Richter, L. S.; Moos, W. H. J. Med. Chem. 1994,
37, 2678. (c) Werder, M.; Hauser, H.; Abele, S.; Seebach, D.
Helv. Chim. Acta 1999, 10, 1774. (d) Hamuro, Y.; Schneider, J.
P.; DeGrado, W. F. J. Am. Chem. Soc. 1999, 121, 12200. (e)
Porter, E. A.; Wang, X.; Lee, H.-S.; Weisblum, B.; Gellman, S.
H. Nature 2000, 404, 565.
J. Am. Chem. Soc. 2002 124:5074
Web Links: synthetic oligomers
ScienceWeek http://www.scienceweek.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
8. CURRENT PROBLEMS IN CRYSTAL ENGINEERING
S.E. Gibson et al (King's College London, UK) discuss crystal
engineering, the authors making the following points:
1) Crystal engineering is a science that aims to both predict
and control solid-state architecture: connectivity, mutual
orientations, and symmetry.(1-5) Successful crystal engineering
has implications in the fabrication of nonlinear optical
materials (for which crystal polarity is a prerequisite),
polymorph control, control of solid-state reactivity, and the
design of composite materials. These goals have largely yet to
be realized. However, the identification and prediction of
recognizable, recurring solid-state packing motifs are a
reality.(3) In cases where such motifs can be isolated from
other interactions of importance, the reproducibility of these
motifs, and hence their predictive value, increases.(5) Thus the
predominance of the strongly hydrogen-bonded carboxylic acid
dimer allows the design of numerous networks and topologies.
Similarly, many general rules can be laid down about crystal
packing within a wide variety of organic and metallo-organic
systems.(4) More specific generalizations may often be made as
well, as demonstrated by Etter (1990).
2) The introduction of polarity into solid-state systems is of
particular interest in the design of nonlinear optical
materials. While this is generally possible to engineer given a
chiral molecule (resolved chiral compounds must crystallize in
polar space groups in the absence of disorder), it is of much
greater economy to be able to engineer polar and/or chiral
solid-state structures from achiral or racemic building blocks.
The occurrence of bulk crystal chirality (and its spontaneous
resolution) in the absence of molecular chirality is much more
haphazard, however, and often limited to very specific compounds.
3) The authors report a study in crystal engineering that brings
together highly stereoselective molecular and crystal synthesis
allowing the preparation and control of a range of resolved,
chiral solid-state compounds.
References (abridged):
1. Desiraju, G. Angew. Chem., Int. Ed. Engl. 1995, 34, 2311.
2. Braga, D.; Maini, L.; Grepioni, F. Angew. Chem., Int. Ed.
1998, 37, 2240-2242.
3. Thalladi, V. R.; Goud, B. S.; Hoy, V. J.; Allen, F. H.;
Howard, J. A. K.; Desiraju, G. R. Chem. Commun. 1996, 401-402.
4. Braga, D.; Grepioni, F.; Desiraju, G. R. Chem. Rev. 1998, 98,
1375.
5. Desiraju, G. R. In The Crystal As a Supramolecular Entity;
Lehn, J. M., Ed.; John Wiley & Sons: Chichester, 1996; Vol. 2.
J. Am. Chem. Soc. 2002 124:5109
Web Links: crystal engineering
Related Background:
ON CRYSTAL POLYMORPHISM
C.A. Mitchell et al (Eli Lilly & Co., US) discuss crystal
polymorphism, the authors making the following points:
1) In this context, the term "polymorphism" refers to the
ability of a molecule to adopt different crystal forms. Crystal
polymorphism reflects the delicate balance of forces responsible
for guiding molecular organization in the solid state. Though
often viewed as an annoyance, this phenomenon represents an
opportunity to examine subtle structure-property relationships
and the relationship between molecular conformation and crystal
packing. An elucidation of polymorphism promises molecular-level
control of crystallization and improvement in crystal structure
design and prediction.
2) Polymorphism also has considerable technological significance
owing to the dependence of crystal properties on solid-state
structure. For example, the discovery and characterization of
the polymorphs of a drug are important for evaluation of shelf
stability (against transformations to other polymorphs) and
bioavailability of the final pharmaceutical product. Polymorph
screening is a particularly important component of drug
development processes because of patent protection of new
crystal forms, regulations that require polymorph identification
and characterization, and the need for strict monitoring and
recording of process conditions to achieve controlled and
reproducible crystallization outcomes.
3) Despite decades of polymorphism studies, prediction of all
possible polymorphs of a given substance remains difficult.
Furthermore, it is impossible to guarantee that all experimental
parameters that could lead to the discovery of unknown forms
have been exhausted or that polymorphs produced through an
ostensibly reliable process will not disappear at a later time.
J. Am. Chem. Soc. 2001 123:10830
Related Background:
ON THE PREDICTION OF CRYSTAL STRUCTURE
J. Pillardy et al (Cornell University, US) discuss crystal
structure prediction, the authors making the following points:
1) Crystal structure prediction is one of the most challenging
and important problems in theoretical and applied crystal
chemistry. It plays an extremely important role in fields in
which the rational design of new organic solids is involved
(e.g., pharmaceuticals, explosives, pigments, photosensitive and
optoelectronic materials, etc.), and it is also of significance
in solving problems of crystal polymorphism.
2) Despite much effort by many research groups during the past
20 years, the general problem of crystal structure prediction is
far from being solved. Generally, the term "crystal structure
prediction" is understood to refer to a search for the most
thermodynamically and kinetically favorable crystal structures
for a given molecular composition without using any experimental
information. (In many cases, however, experimental data are
included implicitly in the force field or taken into
consideration by conducting the search in the most common
crystal space groups).
3) Unfortunately, no theoretical methods capable of taking into
account the kinetic factors (conditions of nucleation and
growth, nature of solvent, etc.) have been developed. Therefore,
crystal structure prediction is currently based solely on
thermodynamic considerations coupled with the assumption that
the structure observed experimentally corresponds to the global
minimum of the free energy. However, free energy is not a
function of geometrical coordinates of a single crystal
structure. Therefore, the traditional approach to crystal
structure prediction assumes that the free energy of a crystal
can be approximated by its potential energy (which can be
computed easily), with the lowest minima corresponding to the
structures observed experimentally. In both theory and practice,
this is a far from satisfactory compromise.
Proc. Nat. Acad. Sci. 2001 98:12351
ScienceWeek http://www.scienceweek.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
9. ON THE CAUSES OF RISING SEA-LEVEL
M.F. Meier and J.M. Wahr (University of Colorado, US) discuss
rising sea level, the authors making the following points:
1) The gradual rise of sea level is one of the most troubling
aspects of global change, especially because it is likely to
accelerate in the future as global warming progresses.
Understanding the linkage between warming climate and sea-level
rise therefore is important and has been the subject of much
study (e.g., refs. 1-5). Two processes are involved: an increase
of the mass of water in the oceans (the eustatic component),
derived largely from the melting of ice on land, and an increase
of the volume of the ocean without change in mass (the steric
component), largely caused by the thermal expansion of ocean
water. Neither of these components is understood fully, and
observations are not sufficient yet to develop a precise
assessment of the causes of present-day sea-level rise let alone
a projection of future rise. In fact many of the analyses
produce conflicting results.
2) Societal and economic impacts of sea-level rise are evident
already, and the consequences of continued rise are substantial
(2). Beach erosion and shoreline retreat affect valuable real
estate in developed nations and the livelihood of many
waterfront communities in developing countries. Shoreline
retreat may pinch out coastal wetlands against developed areas,
or the wetlands may be harmed irreversibly if the rate of
sea-level rise exceeds the rate at which the biota can adapt.
Rising sea level can influence the rate of salt-water incursion
into coastal aquifers, expansion of the salt-water wedge in
estuaries, and the probability of damage from storm surges along
coastlines. More than 100 million people live within 1 mile of
the mean sea level, and the problem is especially urgent and
serious for the low-lying small island nations of the world.
3) Most published values for global sea-level rise are based on
tide-gage data provided by the Permanent Service for Sea Level,
adjusted in various ways to account for the nonrepresentative
sampling of gage locations and local rates of uplift or
depression of the land caused by the ongoing postglacial rebound
(also called glacial isostatic adjustment). These adjusted
observations and the estimated component causes of sea-level
change during the 20th century were summarized in the scientific
assessments of the Intergovernmental Panel on Climate Change
(IPCC; refs. 4 and 5). The problem of understanding current
sea-level rise is obvious from the numbers: the central value of
the "observed" rise is twice the central value of the sum of the
estimated components, and the central value of the sum of the
components is less than the minimum estimate of the observed
rise. An additional complication is that the tide-gage
observations show no statistically valid acceleration during the
20th century, but observations of ocean warming (and thus
thermal expansion of ocean water) and glacier wastage (causing
transfer of water from land to sea) clearly implies acceleration
during the 20th century (5). To resolve these contradictions, we
can investigate the measurement of global sea level, the
observations of the climate-related processes that may affect
sea level, and the "signature" of eustatic or steric changes of
the ocean on the rotation of the Earth.
4) The important question is this: Do we understand the causes
of sea-level rise in the 20th century well enough to make
confident projections for its course in the 21st century?
Clearly, we still have a problem here. Munk(6) has invoked some
powerful arguments to clarify the issue, but as he states, the
enigma is not resolved yet.
References (abridged):
1. Revelle, R. R. (1990) Sea Level Change (Natl. Acad. Press,
Washington, DC).
2. Douglas, B. C. , Kearney, M. S. & Leatherman, S. P. (2001)
Sea Level Rise; History and Consequences (Academic, San Diego).
3. Warrick, R. A. & Oerlemans, J. (1990) in Climate Assessment:
The Intergovernmental Panel on Climate Change Assessment, eds.
Houghton, J. T., Jenkins, G. J. & Ephraums, J. J. (Cambridge
Univ. Press, New York), pp. 257-281.
4. Warrick, R. A. , Le Provost, C. , Meier, M. F. , Oerlemans,
J. & Woodworth, P. A. (1996) in Climate Change 1995: The Science
of Climate Change, eds. Houghton, J. T., Meira Filho, L. G.,
Callander, B. A., Harris, N., Kattenberg, A. & Maskell, K.
(Cambridge Univ. Press, New York), pp. 359-405.
5. Church, J. A. , Gregory, J. M. , Huybrechts, P. , Kuhn, M. ,
Lambeck, K. , Nhuan, M. T. , Qin, P. & Woodworth, P. L. (2001)
Climate Change: The Scientific Basis (Cambridge Univ. Press, New
York), pp. 501-555.
6. Munk, W. (2002) Proc. Natl. Acad. Sci. USA 99, 6550-6555
Proc. Nat. Acad. Sci. 2002 99:6524
Web Links: rising sea level
Related Background:
GLOBAL WARMING, SEA-LEVEL RISE, AND LOSS OF COASTAL WETLANDS
J.P. Donnelly and M.D. Bertness (Brown University, US) discuss
sea-level rise and coastal wetlands, the authors making the
following points:
1) Recent studies indicate that both climate warming and
increases in the rate of sea-level rise in New England over the
last 150 years are unprecedented in at least the last 1000
years. The possibility that emission of greenhouse gases is
influencing and will continue to influence global climate and
potentially sea-level rise has prompted considerable research
into the possible implications for plant and animal communities.
2) The distribution of New England salt marsh communities is
intrinsically linked to the magnitude, frequency, and duration
of tidal inundation. Cordgrass (Spartina alterniflora)
exclusively inhabits the frequently flooded lower elevations,
whereas a mosaic of marsh hay (Spartina patens), spike grass
(Distichlis spicata), and black rush (Juncus gerardi) typically
dominate higher elevations.
3) The authors report that monitoring plant zonal boundaries in
two New England salt marshes revealed that low-marsh cordgrass
rapidly moved landward at the expense of higher-marsh species
between 1995 and 1998. Plant macrofossils from sediment cores
across modern plant community boundaries provided a 2500-year
record of marsh community composition and documented the
migration of cordgrass into the high marsh. Isotope dating
revealed that the initiation of cordgrass migration occurred in
the late 19th century and continued through the 20th century.
The timing of the initiation of cordgrass migration is
coincident with an acceleration in the rate of sea-level rise
recorded by the New York tide gauge.
4) The authors suggest these results indicate that increased
flooding associated with accelerating rates of sea-level rise
has stressed high-marsh communities and promoted landward
migration of cordgrass. If current rates of sea-level rise
continue or increase slightly over the next century, New England
salt marshes will be dominated by cordgrass. If climate warming
causes sea- level rise rates to increase significantly over the
next century, these cordgrass dominated marshes will likely
drown, resulting in extensive losses of coastal wetlands.
Proc. Nat. Acad. Sci. 2001 98:14218
ScienceWeek http://www.scienceweek.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
10. ON THE THERAPEUTIC CLONING DEBATE IN EUROPE
Kathinka Evers (International Council for Science, NO) discusses
therapeutic cloning, the author making the following points:
1) Although recent advances in stem-cell research hold promise
for therapeutic use, this promise has been accompanied by
social, political, economic, legal, religious, and ethical
questions. These questions have touched a raw nerve, and
numerous laws and regulations have been implemented or are being
considered in order to control the use and spread of this new
technology. The legal situation is particularly complex in
Europe, where each country is governed through both national
legislation and the international European legislation passed by
the European Union. Since there are deep social and political
disparities among countries within the union that stem in part
from cultural and religious differences, it is not surprising
that a patchwork of legislation and regulation is emerging.
These legislative and regulatory initiatives address two main
ethical questions. First, does the production or use of human
embryos in research threaten human dignity? And second, might
therapeutic cloning lead to a commercialization of human eggs or
embryos?
2) The debate over the production or use of embryos in research
can be reframed to highlight the ethical issues if it is posed
in the following form: To what extent do human embryos and
fetuses in their early stages have the right to protection? It
is a fundamental tenet in many European cultures that humans
shall not be treated merely as the means to an end but also as
ends in themselves. If the rights accorded to humans after birth
are also valid for unborn humans, from what stage of development
are these rights accorded?
3) The vigor with which this problem is debated varies from
country to country. In countries in which religion has a strong
influence on political decision making, such as Italy, Germany,
Norway, Argentina, and the United States, the moral status of
the human sperm, egg, or fetus is at the center of the debate.
If a fertilized egg is conceded moral status, conducting
experiments on this egg becomes more morally problematic than if
it were not conceded any such status in its own right. A focus
on human dignity reveals a basic conflict: the mother's dignity
(especially her right to ultimate authority over her own body)
stands opposed to that of the fertilized egg (in terms of its
right to develop into a person). The dignity of the adult human
(male or female) also conflicts with what is alleged in some
countries to be the right of the sperm or unfertilized egg not
to be prevented from fertilizing or being fertilized by the use
of contraception.
4) In summary: If stem-cell research were allowed to develop
further, advances in this field could ensure the treatment of
numerous human diseases, such as Parkinson's disease,
Alzheimer's disease, multiple sclerosis, heart disease,
diabetes, and leukemia. A bank of stem-cell lines is currently
being developed in Sweden. On the other hand, it is clear that
the need to regulate the use of knowledge increases in
proportion to the effect that knowledge has on society. With
respect to human cloning, we need international rules that
protect all people from potential abuse in all countries equally
(with special emphasis on and awareness of people in an
economically, politically, or environmentally disadvantaged
position). To achieve such protection, this regulation must
cover research and its applications in every region,
independently of whether it is privately or publicly funded. In
order for such a regulation to be more than yet another eloquent
and toothless declaration, the rules must be backed up by an
internationally representative body with the mandate to issue
sanctions. A substantial challenge will be to prevent abuse and
ensure protection without thereby hindering the science from
developing sufficiently to fulfill its promise.(1-5)
References (abridged):
1. Der Nationale Ethikrat. Stellungnahme zum import menschlicher
embryonaler stammzellen. (Accessed April 23, 2002, at
http://www.nationalerethikrat.de/mitteilung20dez01.htm)
2. Stamceller. Olso, Norway: Bioteknologinemnda — the Norwegian
Biotechnology Advisory Board. (Accessed April 12, 2002, at
http://www.bion.no/tema/stamceller.shtml.)
3. Terapeutisk kloning forskningsfeltet og etiske dilemmare.
Report from the open hearing on December 14, 2000, in Oslo,
Norway. Norway: Ole Johan Borge, 2000:18-9.
4. Petitnicolas C, Perez M. Les enjeux du clonage thérapeutique.
(Marc Peschanski quote.) Le Figaro. January 19-20, 2002.
(Accessed April 12, 2002, at http://www.inserm.fr.)
5. Opinion on the preliminary draft revision of the laws on
bioethics. No. 67. January 18, 2001. Paris: Comité Consultantif
National d'Ethique, 2001. (Accessed April 12, 2002, at
http://www.comite-ethique.fr/english/start.htm) Vetenskapsrådet
— the Swedish Research Council. The Swedish Research Council's
guidelines for research — ethical review of human stem-cell
research. (Accessed April 23, 2002, at
http://www.vr.se/medicin/index.asp?id=44&dok_id=1014)
New Engl. J. Med. 2002 346:1579
Web Links: cloning debate
ScienceWeek http://www.scienceweek.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
11. ON HEMORRHAGIC FEVER VIRUSES AS BIOLOGICAL WEAPONS
The term "hemorrhagic fever" refers to a syndrome that occurs in
perhaps 20 to 40% of infections by a number of different viruses
of the families Arenaviridae (Lassa fever, Bolivian hemorrhagic
fever, Argentinean hemorrhagic fever), Bunyaviridae
(Crimean-Congo hemorrhagic fever), Flaviviridae (Dengue
hemorrhagic fever, Omsk hemorrhagic fever), Filoviridae (Ebola
fever, Marburg virus disease), etc. Some types of hemorrhagic
fever are tick-borne, others mosquito-borne, and some seem to be
zoonoses (animal diseases transmittable to humans). Clinical
manifestations are high fever, scattered petechiae,
gastrointestinal tract and other organ bleeding, hypotension,
and shock. Kidney damage may be severe, especially in Korean
hemorrhagic fever and neurologic signs may appear, especially in
the Argentinean-Bolivian types. Five types of hemorrhagic fever
are transmissible person-to-person: Bolivian hemorrhagic fever,
Lassa fever, Ebola fever, Marburg virus disease, and
Crimean-Congo hemorrhagic fever.
L. Borio et al (Johns Hopkins University, US) discuss
hemorrhagic fever viruses, the authors making the following
points:
1) Hemorrhagic fever viruses have been weaponized by the former
Soviet Union, Russia, and the United States.(13-15) There are
reports that yellow fever may have been weaponized by North
Korea.(14) The former Soviet Union and Russia produced large
quantities of Marburg, Ebola, Lassa, and New World arenaviruses
(specifically, Junin and Machupo) until 1992.(13, 15) Soviet
Union researchers quantified the aerosol infectivity of Marburg
virus for monkeys, determining that no more than a few virions
are required to cause infection.(16) Yellow fever and Rift
Valley fever viruses were developed as weapons by the US
offensive biological weapons program prior to its termination in
1969.(14) The Japanese terrorist cult Aum Shinrikyo
unsuccessfully attempted to obtain Ebola virus as part of an
effort to create biological weapons.(17)
2) Several studies have demonstrated successful infection of
nonhuman primates by aerosol preparations of Ebola, Marburg,
Lassa, and New World arenaviruses. Arguments asserting that the
absence of effective antiviral therapy and vaccines would make
these viruses too dangerous to develop as weapons are not
supported by the historical record.
3) In 1999, the Centers for Disease Control and Prevention (CDC)
classified the hemorrhagic fever viruses as category A bioweapon
agents, based on the potential to cause widespread illness and
death, ease of dissemination or person-to-person transmission,
potential for major public health impact, and requirement of
special action for public health preparedness.
4) In nature, hemorrhagic fever viruses reside in animal hosts
or arthropod vectors. The natural reservoir of filoviruses is
unknown. Humans are infected incidentally, acquiring the disease
by the bite of an infected arthropod, via aerosol generated from
infected rodent excreta, or by direct contact with infected
animal carcasses. With the exception of Rift Valley fever and
the diseases caused by flaviviruses (yellow fever, Omsk
hemorrhagic fever, and Kyasanur Forest disease), which are not
transmissible from person to person, infected humans can spread
the disease to close contacts, which may result in community
outbreaks and nosocomial infections. Limited knowledge exists
about transmission because outbreaks of these diseases are
sporadic and unpredicted and often occur in areas without
adequate medical and public health infrastructure. Outbreaks are
usually well under way or have subsided by the time data
gathering begins. The risks associated with various modes of
transmission are not well defined because most persons who
acquire these infections have a history of multiple contacts by
multiple modes. Infections acquired percutaneously are
associated with the shortest incubation period and highest
mortality. Person-to-person airborne transmission appears to be
rare but cannot be ruled out.
References (abridged):
13. Alibek K, Handelman S. Biohazard: The Chilling True Story of
the Largest Covert Biological Weapons Program in the World, Told
From the Inside by the Man Who Ran It. New York, NY: Random
House; 1999.
14. Center for Nonproliferation Studies. Chemical and biological
weapons: possession and programs past and present. November
2000. Available at:
http://cns.miis.edu/research/cbw/possess.htm (Accessed January
10, 2002).
15. Miller J, Engelberg S, Broad WJ. Germs: Biological Weapons
and America's Secret War. Waterville, Me: GK Hall; 2002.
16. Bazhutin NB, Belanov EF, Spiridonov VA, et al. The effect of
the methods for producing an experimental Marburg virus
infection on the characteristics of the course of the disease in
green monkeys [in Russian]. Vopr Virusol. 1992;37:153-156.
17. Global Proliferation of Weapons of Mass Destruction:
Hearings Before the Permanent Subcommittee on Investigations of
the Committee on Governmental Affairs, United States Senate,
104th Cong, 1st-2nd Sess (1996).
J. Am. Med. Assoc. 2002 287:2391
Web Links: hemorrhagic fever
ScienceWeek http://www.scienceweek.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
12. ON CONGESTIVE HEART FAILURE
J.A. Towbin and N.E. Bowles (Baylor College of Medicine, US)
discuss congestive heart failure, the authors making the
following points:
1) Cardiomyopathies are disorders affecting heart muscle that
usually result in inadequate pumping of the heart. They are the
most common cause of heart failure and each year kill more than
10,000 people in the US. In recent years, there have been
breakthroughs in understanding the molecular mechanisms involved
in this group of conditions, with knowledge of the genetic basis
for cardiomyopathies perhaps seeing the largest advance,
enabling clinicians to devise improved diagnostic strategies and
preparing the stage for new therapies.
2) Congestive heart failure resulting from cardiomyopathy is a
serious malady and a principal cause of death and disability in
children and adults. This disorder is the most common disease
that leads to heart transplant, with an associated healthcare
cost in the United States of roughly US$200 million per year(1).
Cardiomyopathies are classified into four forms: dilated,
hypertrophic, restrictive and arrhythmogenic right ventricular
dysplasia/cardiomyopathy. Restrictive cardiomyopathy is the
rarest form, accounting for only 5% of the total(2), but has the
worst prognosis and poorest therapeutic options of all the
cardiomyopathies(3). Arrhythmogenic right ventricular dysplasia
is a complex arrhythmogenic disorder associated with
cardiomyopathy and characterized by gradual loss of myocytes and
replacement by fatty and fibrous tissue(4). In Italy the
prevalence has been reported as 1:5,000 people, accounting for
20% of sudden deaths in young adults(5) and 25% of cardiac
sudden deaths among athletes; the incidence and prevalence are
unknown in the US.
3) Dilated cardiomyopathy is the most common cause of congestive
heart failure, affecting 40 people in every 100,000 of the
population. Depending on the diagnostic criteria used, the
annual incidence varies from 5 to 8 cases in a population of
100,000; the true incidence is probably underestimated by these
numbers, as many asymptomatic cases go unrecognized.
4) Idiopathic dilated cardiomyopathy is characterized by an
increased ventricular chamber size and reduced pumping of the
heart (that is, reduced contractility) in the absence of
coronary artery disease, valvular abnormalities or pericardial
disease. Backflow through the mitral valves and abnormal heart
rhythms are common. Clinical features include common symptoms of
congestive heart failure such as shortness of breath, easy
fatigability, inability to tolerate physical exertion, fainting,
light headedness, sweating at rest, and sudden death. Other
signs are increased heart rate and an enlarged liver.
References (abridged):
1. O'Connell, J. B. & Bristow, M. R. Economic impact of heart
failure in the United States: time for a different approach. J.
Heart Lung Transplant 13, S107-S112 (1994).
2. Richardson, P. et al. Report of the 1995 World Health
Organization/International Society and Federation of Cardiology
Task Force on the definition and classification of
cardiomyopathies. Circulation 93, 841-842 (1996).
3. Kushwaha, S. S., Fallon, J. T. & Fuster, V. Restrictive
cardiomyopathy. N. Engl. J. Med. 336, 267-276 (1997).
4. Corrado, D. et al. Spectrum of clinicopathologic
manifestations of arrhythmogenic right ventricular
cardiomyopathy/dysplasia: a multicenter study. J. Am. Coll.
Cardiol. 30, 1512-1520 (1997).
5. Thiene, G., Nava, A., Corrado, D., Rossi, L. & Pennelli, N.
Right ventricular cardiomyopathy and sudden death in young
people. N. Engl. J. Med. 318, 129-133 (1988).
Nature 2002 415:227
Web Links: congestive heart failure
ScienceWeek http://www.scienceweek.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
13. IN FOCUS: DINOSAURS, DRAGONS, AND DWARFS: THE EVOLUTION OF
MAXIMAL BODY SIZE
G.P. Burness et al (University of California Los Angeles, US)
discuss the evolution of maximal body size, the authors making
the following points:
1) The size and taxonomic affiliation of the largest locally
present species ("top species") of terrestrial vertebrate vary
greatly among faunas, raising many unsolved questions. Why are
the top species on continents bigger than those on even the
largest islands, bigger in turn than those on small islands? Why
are the top mammals marsupials on Australia but placentals on
the other continents? Why is the world's largest extant lizard
(the Komodo dragon) native to a modest-sized Indonesian island,
of all unlikely places? Why is the top herbivore larger than the
top carnivore at most sites? Why were the largest dinosaurs
bigger than any modern terrestrial species?
2) A useful starting point is the observation of Marquet and
Taper (1998), based on three data sets (Great Basin
mountaintops, Sea of Cortez islands, and the continents), that
the size of a landmass's top mammal increases with the
landmass's area. To explain this pattern, they noted that
populations numbering less than some minimum number of
individuals are at high risk of extinction, but larger
individuals require more food and hence larger home ranges, thus
only large landmasses can support at least the necessary minimum
number of individuals of larger-bodied species. If this
reasoning were correct, one might expect body size of the top
species also to depend on other correlates of food requirements
and population densities, such as trophic level and metabolic
rate. Hence the authors assembled a data set consisting of the
top terrestrial herbivores and carnivores on 25 oceanic islands
and the 5 continents to test 3 quantitative predictions:
a) Within a trophic level, body mass of the top species will
increase with land area, with a slope predictable from the slope
of the relation between body mass and home range area.
b) For a given land area, the top herbivore will be larger than
the top carnivore by a factor predictable from the greater
amounts of food available to herbivores than to carnivores.
c) Within a trophic level and for a given area of landmass, top
species that are ectotherms will be larger than ones that are
endotherms, by a factor predictable from ectotherms' lower food
requirements.
3) The authors point out that on reflection, one can think of
other factors likely to perturb these predictions, such as
environmental productivity, over-water dispersal, evolutionary
times required for body size changes, and changing landmass area
with geological time. Indeed, the database of the authors does
suggest effects of these other factors. The authors point out
they propose their three predictions not because they expect
them always to be correct, but because they expect them to
describe broad patterns that must be understood in order to be
able to detect and interpret deviations from those patterns.
Proc. Nat. Acad. Sci. 2001 98:14518
Web Links: evolution of body size
ScienceWeek http://www.scienceweek.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
14. NEW BOOKS
Astrotomography: Indirect Imaging Methods in Observational
Astronomy. H.M.J. Boffin, D. Steeghs, J. Cuypers, eds. Lecture
Notes in Physics 573. Springer-Verlag, New York, 2001. $86.00
(434 pp.). ISBN 3540422137
Deep Fields. S. Cristiani,A. Renzini, R. E. Williams, eds. ESO
Astrophysics Symposia. Proc. wksp., Garching, Germany, Oct.
2000. Springer-Verlag, New York, 2001. $39.95 (379 pp.). ISBN
3540427996
First Steps in the Origin of Life in the Universe. J.
Chela-Flores, T. Owen, F. Raulin, eds. Proc. conf., Trieste,
Italy, Sept. 2000. Kluwer Academic, Norwell, Mass., 2001.
$120.00 (428 pp.). ISBN 1402000774
Gamma-Ray Bursts in the Afterglow Era. E. Costa, F. Frontera, J.
Hjorth, eds. ESO Astrophysics Symposia. Proc. wksp., Rome,
Italy, Oct. 2000. Springer-Verlag, New York, 2001. $39.95 (459
pp.). ISBN 3540427716
Astrophysics. A. Peraiah. Cambridge U. Press, New York, 2002.
$110.00, $40.00 paper (480 pp.). ISBN 0521770017
Physics of Neutron Star Interiors. D. Blaschke, N. K.
Glendenning, A. Sedrakian, eds. Lecture Notes in Physics 578.
Proc. wksp., Trento, Italy, June-July, 2000. Springer-Verlag,
New York, 2001. $99.00 (509 pp.). ISBN 3540423400
The Search for Life in the Universe. 3rd edition. D. Goldsmith,
T. Owen. University Science Books, Sausalito, Calif., 2001
[1992]. $62.50 (573 pp.). ISBN 1891389165
Stellar Physics. Vol. 2: Stellar Evolution and Stability. G. S.
Bisnovatyi-Kogan (translated from Russian by A. Y. Blinov, M.
Romanova). Astronomy and Astrophysics Library. Springer-Verlag,
New York, 2002. $89.95 (381 pp.). ISBN 3540669876
X-Ray Astronomy: Stellar Endpoints, AGN, and the Diffuse X-ray
Background. N. E. White, G. Malaguti, G. G. C. Palumbo, eds. A1P
Conference Proceedings 599. Proc. conf., Bologna, Italy, Sept.
1999. A1P, Melville, N.Y, 2001. $260.00 (1041 pp.). ISBN
0735400431
Astrobiology: The Quest for the Condi tions of Life. G. Homeck,
C. Baumstark-Khan, eds. Springer-Verlag, New York, 2002. $54.95
(411 pp.). ISBN 3540421017
Galaxies and Cosmology. 2nd edition. F. Combes, P. Boisse,A.
Mazure,A. Blanchard (translated from French by M. Seymour).
Astronomy and Astrophysics Library. Springer-Verlag, New York,
2002 [1995]. $64.00 (444 pp.). ISBN 3540419276
Hamiltonian Field Theory in the Radiating Regime. P. T.
Chrusciel, J. Jezierski, J. Kijowski. Lecture Notes in Physics
m70. Springer-Verlag, New York, 2002. $39.00 (172 pp.). ISBN
3540428844
An Introduction to Mathematical Cosmology. 2nd edition. J. N.
Islam. Cambridge U. Press, New York, 2002 [1992]. $90.00,
$33.00 paper (248 pp.). ISBN 0521496500, ISBN 0521499739 paper
Phase Transitions in the Early Universe: Theory and
Observations. H. J. De Vega, I. M. Khalatnikov, N. G. Sanchez,
eds. NATO Science Series, Series II: Mathematics, Physics and
Chemistry 40. Proc. course, Erice, Sicily, Italy, Dec. 2000.
Kluwer Academic, Norwell, Mass., 2001. $189.00 (593 pp.). ISBN
1402000561
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
NOTICES
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
In the text, the affiliation following the names of authors in
sources with more than one author is the affiliation of the lead
author.
ScienceWeek copyright extends only to material originated by
ScienceWeek. Other copyrights may obtain for other material.
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:
Information concerning subscriptions is available at:
http://www.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) 1997-2002 SCIENCE-WEEK
All Rights Reserved
US Library of Congress ISSN 1529-1472
---------------------------------------------
ScienceWeek/Spectrum Press Inc.
3023 N. Clark Street #109
Chicago, 60657-5205 IL, USA.
---------------------------------------------
-----end file
|