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ScienceWeek
SCIENCE-WEEK
A Weekly Email Digest of the News of Science
A journal devoted to the improvement of communication
between the scientific disciplines, and between scientists,
science educators, and science policy-makers.
November 24, 2000 -- Vol. 4 Number 47
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Science comes from the knowing that you want to know.
-- Eli Siegel
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Section 1
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Contents of this Issue (Full reports in Section 2):
1. ASTROPHYSICS:
COSMIC BACKGROUND RADIATION AND COSMOLOGICAL MODELS
Recent measurements of temperature variation in the cosmic
microwave background reveal distinctive patterns in these
fluctuations, patterns which depend on the details and
composition of the Universe, and cosmologists are beginning to
interpret these patterns through detailed statistical studies.
The results are in accord with the expectations of inflation -- a
nearly "flat" Universe, which can be described as a small piece
of an enormous hypersphere -- and in accord with independent
estimates of various quantities such as the density of dark
matter.
2. GEOPHYSICS:
SEISMIC TOMOGRAPHY AND MANTLE DYNAMICS
Seismic tomography has resulted in breakthrough advances in the
last two decades, revealing fundamental geodynamical processes
throughout the Earth's mantle and core. Convective circulation of
the entire mantle is taking place, with subducted oceanic
lithosphere sinking into the lower mantle, overcoming the
resistance to penetration provided by the phase boundary near
650-kilometer depth that separates the upper and lower mantle.
Continued advances in seismic tomography, geodynamic modeling,
and high-pressure-high-temperature mineral physics will be needed
to fully quantify the complex dynamics of our planet's interior.
3. PHYSICAL CHEMISTRY:
VIBRATIONAL MOTIONS AND REACTIVITY
The control of chemical reaction rates by vibrational excitation
has been a long-sought goal in chemistry. There has also been
much interest in determining the amount of excitation in the
vibrational modes of the products, which provides a signature of
the path by which the reaction occurs. New work demonstrates that
quantum theoretical calculations, which in the past decade have
achieved remarkable accuracy for 3-atom reactions involving 3-
dimensions, have progressed to the point where it is now possible
to accurately predict energy disposal in 4-atom reactions
involving six dimensions.
4. CELL BIOLOGY:
PLANT CELL WALLS AND EXPANSINS
The plant cell wall is an important structure that determines
cell shape, glues cells together, provides essential mechanical
strength and rigidity, and acts as a critical barrier against
pathogens. Secreted by growing cells, the primary wall is a
polymeric network of crystalline cellulose microfibrils embedded
in a hydrophilic matrix of hemicellulose and pectins. It has
recently become apparent that during growth, plant cells secrete
a protein called "expansin", a protein that unlocks the network
of cell wall polysaccharides, permitting turgor-driven cell
enlargement.
5. PALEOBIOLOGY:
CULTIVATION OF A 250-MILLION YEAR OLD BACTERIUM
There have been claims of cultivatable bacterial spores found in
various ancient materials, including rocks millions of years old,
but for most of these claims there has been considerable doubt
about the origin of the cultivated bacteria. In 1995, researchers
reported the revival and identification of bacterial spores in 25
to 40 million year old amber, the spores obtained from a bee
preserved in the amber, and because of the care taken to avoid
contamination of the sample, this finding is currently accepted
as valid. Now researchers report the isolation and growth of a
previously unrecognized spore-forming bacterium from a brine
inclusion within a 250-million-year-old salt crystal.
6. MEDICAL BIOLOGY:
SMOKING PREVALENCE AMONG ADULTS IN THE US 1998
In 1998 in the US, an estimated 47.2 million adults (24.1 percent
of the adult population), comprising 24.8 million men (26.4
percent) and 22.4 million women (22.0 percent) were current
smokers. Current smoking prevalence was lowest among persons with
at least 16 years of education (11.3 percent) and highest among
persons with 9 to 11 years of education (36.8 percent). Smoking
prevalence was higher among persons living below the poverty
level (32.3 percent) than among those living at or above the
poverty level (23.5 percent). A comprehensive approach to tobacco
control is not yet in place.
7. IN FOCUS: SCIENCE VERSUS DOGMA
8. FROM THE SCIENCEWEEK ARCHIVE:
GRADUATE STUDENT STRESS: A PROPOSAL IN THE WAKE OF A TRAGEDY
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Section 2
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1. ASTROPHYSICS:
COSMIC BACKGROUND RADIATION AND COSMOLOGICAL MODELS
The central problem of cosmology is to provide a self-
consistent view of the past, present, and future of the Universe
that takes into account not only concepts and observations in
astrophysics but also concepts and observations in all of
physics, particularly those in particle physics and quantum
physics. Thus, a cosmological model is a conceptual edifice built
with the bricks of fundamental physics, and as physics changes,
and observations change, so do the acceptable models. Can there
be a "final theory" in cosmology? Probably not until there is a
"final physics", a physics in which all new observations are
without surprises. We are certainly not there yet; in fact, the
objective is so distant, there is perhaps not even a glimmer of a
shadow in the murky mist. But as the astrophysicist Edwin Hubble
said, "The search will continue. The urge is older than history.
It is not satisfied and it will not be oppressed."
Contemporary cosmology distinguishes two kinds of matter,
"ordinary matter" and "dark matter". In general, a baryon is a
nuclear particle (e.g., a proton) built from 3 quarks
(fundamental particles that combine to make up protons, neutrons,
and mesons), and so-called "ordinary matter" is baryonic. In this
context, the term "dark matter" refers to material whose presence
can be inferred from its effects on the motions of stars and
galaxies, but which cannot be seen directly because it emits
little or no radiation. It is believed that as much as 90 percent
of the mass in the Universe may exist as some form or dark
matter, although the proposed percentage of dark matter varies
widely with different cosmological models.
The major current cosmological models propose a "Big Bang",
an initial explosive origin of the Universe at a time zero. 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, and that these density variations
eventually led to the formation of galaxies and clusters of
galaxies.
What is known as the "cosmic microwave background radiation"
was discovered accidentally in 1964, when A.A. Penzius and R.
Wilson, measuring noise that might interfere with satellite
communications, noted a mysterious signal that was soon
interpreted to be the microwave background radiation originating
in the Big Bang. In 1978, Penzius and Wilson received the Nobel
Prize in Physics for this discovery. The cosmic microwave
background is black-body radiation (the emission radiation of a
perfect absorber of radiation) at a present temperature of 2.73
degrees Kelvin, and has an almost equal intensity in all
directions in space. The deviations from isotropic intensity,
however, are of extreme importance in theoretical cosmology.
Central to current cosmological considerations are the
distinctions between the geometries of a "flat" (uncurved;
infinite in both extent and lifetime), "closed" (spherical;
finite in both extent and lifetime), and "open" (*hyperbolic;
infinite and expanding forever) Universe. An important quantity
is the Omega parameter, defined as the ratio of the density of
matter (or energy) in the Universe to the theoretical density
required for flatness. An Omega with a value of greater than 1
implies a closed Universe; a value less than 1 implies an open
Universe; a value equal to 1 implies a flat Universe. The problem
for the past 60 years has thus been to obtain an estimate of the
mass density of the Universe from observations. The current
standard conception is that the geometry of the Universe is flat.
... ... Craig J. Hogan (University of Washington Seattle, US)
presents a commentary on current research in cosmology, the
author making the following points:
1) Recent measurements of temperature variation in the
cosmic microwave background reveal distinctive patterns in these
fluctuations, patterns which depend on the details and
composition of the Universe, and cosmologists are beginning to
interpret these patterns through detailed statistical studies.
The results are in accord with the expectations of inflation -- a
nearly "flat" Universe, which can be described as a small piece
of an enormous *hypersphere -- and in accord with independent
estimates of various quantities such as the density of dark
matter.
2) Nevertheless, there are several unexpected and possibly
important discrepancies. The sharpest and most interesting
discrepancy is the estimate of the density of ordinary (baryonic)
matter in the Universe: the new data suggest that the mean number
of neutrons and protons per unit volume is greater than was
thought.
3) The author concludes: "Exploration of this discrepancy
might lead to something really new -- perhaps a simple
reinterpretation of data on abundances, or perhaps a new
ingredient not yet included in the standard cosmological model."
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Craig J. Hogan: Cosmic discord.
(Nature 2 Nov 00 408:47)
QY: Craig J. Hogan: hogan@astro.washington.edu
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Text Notes:
... ... *hypersphere: If one considers a circle (2-dimensional),
a sphere (3-dimensional), the term "hypersphere" refers to the
subsequent members of the series, where the number of dimensions
is >= 4. A hypersphere is thus defined as the set of n-tuples of
points [x(sub1), x(sub2), ..., x(subn)] such that
x(sub1)^(2) + x(sub2)^(2) + ... + x(subn)^(2) = R^(2) where R is
the radius of the hypersphere.
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Summary & Notes by SCIENCE-WEEK http://scienceweek.com 24Nov00
For more information: http://scienceweek.com/swfr.htm
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Related Background:
COSMOLOGY: EXPECTATIONS IN THE NEXT CENTURY OF RESEARCH
Cosmology is one of the grand sciences, a domain of research
whose results have enormous intellectual consequences, at least
for people who care about what they are and where they are.
Martin Rees (Cambridge University, UK) presents an essay on the
near-future research expectations of cosmologists, the author
making the following points:
1) Astronomers still do not know what the Universe is made
of. Observable radiation-emitting objects -- such as stars,
*quasars, and galaxies -- apparently constitute only a small
fraction of the matter in the Universe. The vast bulk of matter
is dark and unaccounted for, and most cosmologists believe this
dark matter is composed of weakly interacting particles left over
from the *Big Bang. But dark matter could be something more
exotic. "Whatever the case, it is clear that galaxies, stars and
planets are a mere afterthought in a Cosmos dominated by quite
different stuff." The author suggests that intensive searches for
dark matter, mainly via sensitive underground experiments
designed to detect elusive subatomic particles, will continue in
the coming decade, and that within the next decade both the
amount and nature of dark matter will be clarified.
2) The author suggests that research in the near-future is
also likely to focus on the evolution of the large-scale
structure of the Universe. The current view is that ever since
the Big Bang, gravity has been amplifying inhomogeneities,
building up structures and enhancing temperature contrasts -- "a
prerequisite for the emergence of the complexity that lies around
us now and of which we're a part." The author suggests that
astronomers are now learning more about the 10 billion year
process of Cosmic evolution by creating virtual universes on
computers, and that in the coming years researchers will be able
to simulate the history of the Universe with ever improving
realism and then compare the results with astronomical
observations.
3) The author suggests that the great mystery for
cosmologists is the series of events that occurred less than 1
millisecond after the Big Bang, when the Universe was
extraordinarily small, hot, and dense. "The laws of physics with
which we are familiar offer little firm guidance for explaining
what happened during this critical period." To solve this
problem, it will necessary to improve and refine current
observations in order to understand the characteristics of the
Universe when it was only one second old: its expansion rate, the
size of its density fluctuations, and its proportions of ordinary
atoms, dark matter, and radiation.
4) The author suggests the following Cosmic timeline for the
evolution of the Universe from the Big Bang to the present:
... ... a) 10^(-43) seconds after the Big Bang: the *Quantum
Gravity Era.
... ... b) 10^(-36) seconds after the Big Bang: Probable *Era of
Inflation.
... ... c) 10^(-5) seconds after the Big Bang: Formation of
protons and neutrons from *quarks.
... ... d) 3 minutes after the Big Bang: Synthesis of atomic
nuclei.
... ... e) 300,000 years after the Big Bang: First atoms form.
... ... f) 1 billion years after the Big Bang: Appearance of
first stars, galaxies, and quasars.
... ... g) 10 to 15 billion years after the Big Bang: Appearance
of modern galaxies.
5) The author concludes: "How did a hot amorphous fireball
evolve, over 10 to 15 billion years, into our complex Cosmos of
galaxies, stars, and planets? How did atoms assemble -- here on
Earth and perhaps on other worlds -- into living beings intricate
enough to ponder their own origins? These questions are a
challenge for the new millennium. Answering them may well be an
unending quest."
-----------
Martin Rees: Exploring our Universe and others.
(Scientific American December 1999)
QY: Martin Rees, Cambridge University, UK.
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Text Notes:
... ... *quasars: (quasi-stellar objects). 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.
... ... *Big Bang: The Big Bang theory is the general
cosmological model that proposes that all matter and radiation in
the universe originated in an explosion at a finite time in the
past.
... ... *Quantum Gravity Era: Quantum field theory is the
mathematical fusion of quantum mechanics with special relativity
theory, and the term "quantum gravity" refers to the fusion of
quantum mechanics with general relativity theory. The essential
basis for these fusions is the so-called "equivalence principle",
which identifies the mass involved in the gravitational force
equation with the inertial mass in the equation that relates any
force to the product of inertial mass and acceleration. The
"quantum gravity era" is the time-frame during which both quantum
effects and gravity determined the behavior of particles.
... ... *Era of 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.
... ... *quarks: A quark is a hypothetical fundamental particle,
having charges whose magnitudes are one-third or two-thirds of
the electron charge, and from which the elementary particles may
in theory be constructed.
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Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 28Jan00
[For more information: http://scienceweek.com/search/search.htm]
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Related Background:
COSMOLOGY: OPEN, CLOSED, OR FLAT UNIVERSE?
Marc Kamionkowski (Columbia University, US) reviews current
research in cosmology, making the following points: 1)
Determination of the geometry of the universe has been a central
goal of cosmology ever since Hubble discovered its expansion 75
years ago. 2) The central question is whether the universe is a
multi- dimensional equivalent of a 2-dimensional surface
("flat"), a sphere ("closed"), or a saddle ("open"). The
geometry, in the context of current theory and observations,
determines whether the universe will expand forever or eventually
collapse. 3) Until now, most astronomers have pursued the
geometry by attempting to measure the mass density of the
universe. According to general relativity, if the density is
equal to, larger than, or smaller than a critical density fixed
by the expansion rate, then the universe is flat, open, or
closed, respectively. 4) Another possibility is to look directly
at the predicted observational effects of a curved (open or
closed) universe versus a flat universe, and in particular at the
angular power spectrum of the cosmic microwave background. The
authors suggest that in the near future a new generation of
experiments will provide substantial advances in these
observations, enabling more definitive statements about the
geometry of the universe, and that these results will in turn
provide clues to the new particle physics required to understand
the inflation phase following the Big Bang origin of the
universe.
QY: Marc Kamionkowski (kamion@phys.columbia.edu)
(Science 29 May 98 280:1397) (ScienceWeek 19 Jun 98)
For more information: http://scienceweek.com/swfr.htm
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2. GEOPHYSICS:
ON SEISMIC TOMOGRAPHY AND MANTLE DYNAMICS
Seismic studies indicate the interior of the Earth consists
of three parts: a metallic core, a dense rocky mantle, and a thin
low-density crust. The central part of the core is solid, but the
outer part of the core is evidently liquid. The mantle, the layer
of dense rock and metal oxides between the molten part of the
core and the surface, has plastic properties (i.e., it is a solid
capable of flow under pressure).
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.
The term "subduction" refers to the process of
underthrusting of the edge of an oceanic plate into the mantle
underlying an adjacent plate. In this context, the term "plate"
derives from "plate tectonics", the current consensus theory that
the Earth's lithosphere is broken into fairly rigid plates, seven
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.
In general, the term "tomography" refers to a representation
in cross-section in which neighboring 2-dimensional cross-
sections are combined to provide a 3-dimensional model. The use
of computer-aided tomography (CAT) in medical diagnosis is well-
known as a non-invasive method of examining internal organs for
abnormal regions. X-rays or ultrasonic waves are absorbed
unequally be different materials, and computer-aided tomography
consists of studying the attenuation of x-rays or ultrasonic
waves that pass through the body in distinctly controlled planar
sections. The technique of "seismic tomography" uses the same
principles, with the difference that the travel-times of the
signals, rather than their attenuation, are observed. Thus, the
technique of seismic tomography may be described as the 3-
dimensional modeling of the velocity distribution of seismic
waves in the Earth. In general, the technique requires powerful
computational facilities and sophisticated programming.
... ... T. Tanimoto and T. Ley (2 installations, US) present a
review of current research on mantle dynamics and seismic
tomography, the authors making the following points:
1) The authors point out that the advent of the theory of
plate tectonics approximately 30 years ago established that most
near-surface geological phenomena such as earthquakes, volcanoes,
and mountain belts can be understood in the context of a unifying
model of interacting surface plates. However, our understanding
of this system has largely been limited to detailed kinematics of
plate motions, leaving the nature of the driving motions in the
interior as a puzzle. Questions such as what is the configuration
of convection, and how are surface tectonics controlled by
internal processes, have long been raised, but a lack of tools
and a lack of evidence prevented evaluation of various
hypotheses. Thus, most views regarding mantle dynamics remained
highly speculative until recently. Seismic tomography, which
emerged in the early 1980s, has provided a major probe of the
dynamical system of which plates are just the surface veneer.
2) The primary question concerning mantle dynamics is
whether mantle convection occurs in mantle-wide convective cells
or whether it involves a layered system, with separate flow
regimes in the upper mantle (i.e., above 650 kilometers) and
lower mantle. One of the most exciting results from work during
the last 5 years is the verification of deep penetration of
former oceanic lithosphere into the lower mantle. Tomography
shows thickened tabular extensions of subducted material to
depths as great as 2000 kilometers directly below deep subduction
zones where earthquakes occur in oceanic slabs down to
approximately 650-kilometer depth. Thus, strictly layered mantle
convection can now be ruled out with good confidence.
3) In summary, seismic tomography has resulted in
breakthrough advances in the last two decades, revealing
fundamental geodynamical processes throughout the Earth's mantle
and core. Convective circulation of the entire mantle is taking
place, with subducted oceanic lithosphere sinking into the lower
mantle, overcoming the resistance to penetration provided by the
phase boundary near 650-kilometer depth that separates the upper
and lower mantle. The boundary layer at the base of the mantle
has been revealed to have complex structure, involving local
stratification, extensive structural anisotropy, and massive
regions of partial melt. The Earth's high *Rayleigh number
convective regime is now recognized to be much more interesting
and complex than suggested by textbook cartoons, and continued
advances in seismic tomography, geodynamic modeling, and high-
pressure-high-temperature mineral physics will be needed to fully
quantify the complex dynamics of our planet's interior.
-----------
T. Tanimoto and T. Ley: Mantle dynamics and seismic tomography.
(Proc. Natl. Acad. Sci. US 7 Nov 00 97:12409)
QY: Toshiro Tanimoto, Univ. of Calif. Santa Barbara 805-893-8000.
-----------
Text Notes:
... ... *Rayleigh number: The Rayleigh number is a dimensionless
parameter used in the theory of fluid dynamics. In general, the
Rayleigh number provides a determination of when convection is
initiated in a fluid.
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Summary & Notes by SCIENCE-WEEK http://scienceweek.com 24Nov00
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
IN FOCUS: THE LAYERED EARTH
"During the nineteenth century, the nature of the Earth's
interior was a matter of fierce and fascinating debate. All
theories were hampered by a lack of evidence -- the nature of
rocks deep below the surface was unknown. In 1906, Richard D.
Oldham observed that compressional seismic waves (P waves) slow
abruptly deep within the Earth and can penetrate no further. This
was strong evidence in favor of a liquid core. Three years later,
Andrija Mohorovicic noticed that the velocity of seismic waves
leaps from 7.2 to 8.0 km/s at around 60 km deep. He had
discovered the 'Moho' seismic discontinuity that marks the crust-
mantle boundary. In 1926, Beno Gutenberg obtained evidence for a
seismic discontinuity at the core-mantle boundary. This, the
Gutenberg discontinuity, was confirmed during the 1950s when
world-wide records of blasts from underground nuclear detonations
were scrutinized. Subsequent studies of the Earth's seismic
properties, using seismic waves propagated by earthquakes and by
controlled explosions to 'x-ray' the planet (a technique called
seismic tomography), have revealed a series of somewhat distinct
layers or concentric shells in the solid Earth. Each shell has
different chemical and physical properties..."
-----------
Richard John Huggett: _Environmental Change_
(Routledge, London 1997, p.56)
[The author is Senior Lecturer in Geography at the University of
Manchester, UK]
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3. PHYSICAL CHEMISTRY:
VIBRATIONAL MOTIONS AND REACTIVITY
Since a chemical reaction involves the breaking and making
of bonds between atoms, the course and kinetics of a reaction
should be partly dependent on the motions of the reactants. If
the reactants are two molecular species, the motions of concern
are translational, rotational, and vibrational motions, each type
of motion affecting the breaking and making of bonds in a
specific manner.
In general, the term "transition state" (activated state)
refers to the relatively high energy configuration through which,
in many reactions, reactants must pass before becoming products.
One long-standing problem in physical chemistry is to understand
how reactant vibrational motions influence the dynamics of
chemical reactions, and in particular how such motions influence
"activated" reactions, i.e., reactions in which a potential
energy barrier must be overcome for the reaction to occur.
... ... George C. Schatz (Northwestern University, US) presents a
commentary on some recent work investigating the influence of
molecular vibrational modes on reactivity, the author making the
following points:
1) The author points out that the potential barrier in
activated reactions can sometimes be overcome more efficiently by
exciting vibrational modes of the reactants (reagents) than by
supplying the same amount of energy in the form of heat.
Branching into different reaction pathways (with different
resultant products) can also be controlled by vibrational
excitation. Thus, the control of chemical reaction rates by
vibrational excitation has been a long-sought goal in chemistry.
There has also been much interest in determining the amount of
excitation in the vibrational modes of the products, which
provides a signature of the path by which the reaction occurs.
2) In general, a reaction is considered "vibration mode-
specific" if it is preferentially accelerated by exciting some
vibrational modes but not others. For nearly 20 years, the H +
H(sub2)O reaction has served as a prototype for mode-specific
bimolecular reactions, and two recent reports (B.R. Strazisar et
al: Science 290:958 2000)(D.H. Zhang et al: Science 290:961 2000)
present important new results on this topic. Strazisar et al used
crossed *molecular beam experiments to determine the distribution
of vibrational states of the HOD product in the reaction OH +
D(sub2). The results indicate that the energy is preferentially
released into the O-D stretch mode, with much less excitation of
the HOD bend. The results are in excellent agreement with recent
theoretical predictions, but are substantially different from
earlier theory, suggesting the energy surfaces used in the
earlier studies were inaccurate. Zhang et al present quantum
dynamics simulations of the H + H(sub2)O reaction using *ab
initio potential energy surfaces that are much more accurate than
in earlier studies, and they again demonstrate that O-H stretch
excitation efficiently pushes the system over the barrier to
reaction, whereas bend excitation is much less efficient. Shatz
states: "The two studies provide a consistent picture of the role
of vibrations in the H + H(sub2)O reaction."
3) In summarizing the results of their experiments,
Strazisar et al state: "This [work] demonstrates that quantum
theoretical calculations, which in the past decade have achieved
remarkable accuracy for 3-atom reactions involving 3-dimensions,
have progressed to the point where it is now possible to
accurately predict energy disposal in 4-atom reactions involving
six dimensions."
-----------
George C. Schatz: Stretched water is more reactive.
(Science 3 Nov 00 290:950)
QY: George C. Schatz: Northwestern University 847-491-3741.
-----------
Text Notes:
... ... *molecular beam: The essential idea in molecular beam
research in this context is to allow a gas to escape from a very
small hole into a high vacuum. Since the escaping molecules
experience virtually no scattering in the vacuum, they form a
straight "beam" of moving particles. The present experiment
consisted of two fixed pulsed molecular beams and a rotatable
detector assembly housed within a large vacuum chamber. The beam
of OH radicals was produced by photodissociation, and the D(sub2)
beam was produced by pulsed supersonic expansion of 20 percent
D(sub2) seeded in H(sub2). The beams were collimated and crossed
at 90 degrees in a separately pumped scattering chamber.
... ... *ab initio potential energy surfaces: In this context, a
"potential energy surface" is a mathematical surface that
describes how the potential energy of the system depends on the
relative position of the atoms, and such a surface may be derived
using *density functional theory or *ab initio theory.
... ... *density functional theory: The name of the theory
derives from its predicted connection between the total ground
state electronic energy of a system and the electronic charge
density. The theory was first proposed in 1964 and has since been
useful as a simplifying alternative to more rigorous but
intractable many-electron wavefunction calculations. In general,
in density functional theory, it is the electron density which is
the fundamental variable: the ground state of a system is defined
by that electron density distribution which minimizes the total
energy. In this approach, once the ground state electron density
is known, all other ground state properties (lattice constants,
cohesive energies, etc.) follow, at least in principle. In
mathematics, a "functional" is a function whose value depends on
the set of all values of another function. In density functional
theory, the ground state properties of a system are functionals
of the ground state electron density function.
... ... *ab initio theory: (ab initio quantum chemical theory)
The ultimate goal of quantum mechanical calculations as applied
to molecular modeling (i.e., as applied to any study of molecules
utilizing physical or theoretical models to explain observed or
predicted molecular behavior) is the a priori computation of
properties of molecules with the highest possible accuracy (i.e.,
rivaling experiment), but utilizing the fewest approximations in
the description of the wavefunction. "Ab initio" (from first
principles) calculations utilize experimental data on atomic
systems to facilitate the adjustment of parameters such as the
exponents of the Gaussian functions used to describe the orbitals
within the quantum mechanical formalism. The excellent
performance of ab initio techniques distinguishes them from their
predecessors, the "semiempirical" methods, with the quantitative
predictions of ab initio techniques usually falling within
experimental error when comparisons are made to experimental
measurements.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 24Nov00
For more information: http://scienceweek.com/swfr.htm
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
4. CELL BIOLOGY:
PLANT CELL WALLS AND EXPANSINS
Plant and bacterial cells are almost always surrounded by a
rigid non-living "cell wall" that both protects and contains the
cell. The presence of a cell wall allows the cell to withstand
osmotic and mechanical stresses that would almost certainly
rupture cells without such a wall (e.g., animal cells, which do
not have cell walls).
The walls that surround plant cells resemble bacterial cell
walls only in that they define shape and confer rigidity.
Chemically, there is little similarity between plant cell walls
and bacterial cell walls. Plant cell walls consist of rigid
microfibrils of cellulose molecules embedded in a non-cellulose
gel-like matrix in a manner that has been likened to the
embedding of metal rods in concrete to reinforce the concrete and
give it added strength.
Cellulose is an unbranched polymer of glucose, with beta-1,4
glycosidic bonds, and as the principal structural material of
plants, cellulose is the most abundant organic compound on Earth.
The fibrous matrix in which the cellulose microfibrils are
embedded contains hemicellulose, pectin, lignin, and protein.
Despite the name, hemicellulose bears no chemical resemblance to
cellulose at all, but is in fact a pentose polymer. Pectin is a
polymer of hexuronic acid, and lignin is a complex organic
polymer and major component of wood.
The walls that surround growing plant cells are called
"primary cell walls", and they are characterized by an
extensibility that allows them to expand in response to cell
growth under the influence of the plant hormone auxin. Once a
plant cell has achieved its final size and shape, it may deposit
a "secondary cell wall" on the inner surface of the primary wall.
The secondary wall usually contains more cellulose than the
primary wall and often has a high lignin content as well,
rendering the wall inextensible and thus definitively specifying
the ultimate size and shape of the cell.
... ... Daniel J. Cosgrove (Pennsylvania State University, US)
presents a review of current research on plant cell walls, the
author making the following points:
1) The author points out that for plants, the cell wall is
an important structure that determines cell shape, glues cells
together, provides essential mechanical strength and rigidity,
and acts as a critical barrier against pathogens. Secreted by
growing cells, the primary wall is a polymeric network of
crystalline cellulose microfibrils embedded in a hydrophilic
matrix of hemicellulose and pectins. Unlike the bacterial cell
wall, which may form one giant covalently linked macromolecule,
the polysaccharides of the growing plant cell wall are mostly
separate long-chained polymers that form a cohesive network
through non-covalent lateral associations and physical
entanglements.
2) In plant cells, cellulose microfibrils are synthesized by
large complexes in the plasma membrane. Newly secreted cellulose
then associates with matrix glycans (hemicelluloses and pectins),
which are synthesized in the *Golgi apparatus of the cell and
delivered to the cell wall by *secretory vesicles. The cellulose
microfibril is a thin ribbon, approximately 5 nanometers in
diameter and many microns in length. It consists of an ordered
array of many parallel chains of an unbranched glucose polymer
(1,4-beta-glucan). Hemicelluloses are generally branched
polysaccharides characterized by a strong tendency to bind to
cellulose, whereas pectins are generally acidic polysaccharides
with a strong tendency to form ionic gels. A small amount of
structural protein is also found on the plant cell wall, but its
function is unclear.
3) The growing plant cell wall possesses a remarkable
combination of strength and pliancy, enabling it to withstand the
large mechanical forces that arise from cell *turgor pressure,
while at the same time permitting a controlled polymer "creep"
that distends the wall and creates space for the enlarging
protoplast. Cellulose microfibrils themselves are effectively
inextensible, and wall expansion occurs by slippage or
rearrangement of the matrix polymers that coat the microfibrils
and hold them in place. Until recently, this was thought to occur
primarily by hydrolysis of matrix polysaccharides.
4) It has recently become apparent that during growth, plant
cells secrete a protein called "expansin", a protein that unlocks
the network of cell wall polysaccharides, permitting turgor-
driven cell enlargement. The action of expansin has puzzling
implications for plant cell-wall structure; in addition, the
recent explosion of gene sequences and expression data has
provided new hints of further biological functions for expansins.
This class of proteins appears to have evolved specifically in
the land plant lineage, with biological functions in cell growth
and in other situations where the movement, adhesion, and
enzymatic accessibility of cell wall polysaccharides are
important. Expansins offer potential applications for
bioengineering of cell walls, either to manipulate the growth and
texture of plants or to modify the structure and physical
properties of cell walls used in commercial products such as
wood, textiles, and polymers.
-----------
Daniel J. Cosgrove: Loosening of plant cell walls by expansins.
(Nature 21 Sep 00 407:321)
QY: Daniel J. Cosgrove: dcosgrove@psu.edu
-----------
Text Notes:
... ... *Golgi apparatus: The Golgi apparatus (Golgi complex) is
a collection of organelles (Golgi bodies) in eukaryotic cells
that essentially function as a collecting and packaging center
for substances that the cell manufactures for export.
... ... *secretory vesicles: The term "secretory vesicles" refers
to intracellular spheroids with sizes ranging from 30 nanometers
to 2 microns in diameter and bounded by a bimolecular layer
membrane, various vesicles containing various chemical messenger
substances.
... ... *turgor pressure: (wall pressure) In this context, the
term "turgor" refers to the rigidity of a plant and its cells and
organs resulting from hydrostatic pressure exerted on the cell
walls. The term "turgor pressure" is sometimes replaced by
"pressure potential".
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 24Nov00
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
CONSTRUCTION OF PLANT CELL WALLS: A GEOMETRICAL MODEL
Cell wall deposition is a key process in the formation, growth,
and differentiation of plant cells. The most important structural
components of the wall are long cellulose "microfibrils" that are
synthesized by special enzymes (synthases) embedded in the plasma
membrane of the plant cell. The microfibrils in higher plants are
made of cellulose, the most abundant macromolecule on Earth. They
are long (>> 1 micron) and thin (3-4 nanometers), and in the cell
wall, they are linked to wall matrix molecules excreted into the
wall by *exocytosis. A fundamental question is how the
microfibrils become oriented during deposition at the plasma
membrane. The current textbook explanation for the orientation
mechanism is a guidance system mediated by so-called cortical
*microtubules, but there too many apparent exceptions,
particularly in the case of the helicoidal arrangements that
occur in many systems. An additional construction mechanism that
has been proposed involves liquid crystalline self-assembly, but
the required amount of bulk material able to equilibrate
thermally is not normally present at any stage of the wall
deposition process. ... ... Emons and Mulder (2 installations,
NL) present a report in which they pose the question of whether
the complex ordered structure of helicoidal cell walls can be
formed in the absence of direct cellular guidance mechanisms.
They propose that such walls can indeed be formed by a mechanism
based on geometrical considerations. The most important
geometrical constraint in this model is stated by the authors as
follows: "Given the space-limiting conditions and the absence of
gaps in the microfibril pattern, the deposition process can be
viewed as analogous to winding strings around a cylinder in such
a way that its surface is fully covered. Therefore, a simple
geometrical rule must link the number of strings being wound
simultaneously per cell circumference to the angle they make with
a plane perpendicular to the cell axis." The authors suggest
their model explains the genesis of the complicated helicoidal
texture, and that the model indicates the cell has intrinsic,
versatile tools for creating a variety of textures. The authors
further suggest that a compelling feature of their model is that
"local rules generate global order, a typical phenomenon of
life."
QY: Anne Mie C. Emons: annemie.emons@algem.pcm.wau.nl
(Proc. Natl. Acad. Sci. US 9 Jun 98 95:7215)
-----------
Text Notes:
... ... *exocytosis: This refers to the bulk transport of
materials out of the cell across the cell membrane (plasma
membrane). The process generally involves the encasing of the
material within intracellular membranes, forming a "vacuole", and
the subsequent transport of the vacuole to the cell surface. At
the cell surface, the vacuole fuses with the plasma membrane, and
the contents of the vacuole are deposited outside the cell.
Various aspects of the process are visible with both light and
electron microscopy in a variety of cell systems, and this is the
process primarily responsible for excretion and secretion by
individual cells.
... ... *microtubules: Composed of the protein tubulin,
microtubules are part of the cytoskeleton of biological cells,
the quasi-rigid matrix that among other things determines cell
shape. The microtubules are 25 nanometers in diameter and occur
in regular arrays. Cortical microtubules are microtubules
structuring the surfaces of cells.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 10Jul98
For more information: http://scienceweek.com/swfr.htm
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
5. PALEOBIOLOGY:
CULTIVATION OF A 250-MILLION YEAR OLD BACTERIUM
The term "bacillus" (plural: bacilli) is derived from the
Latin word _bacillus_, literally meaning "a stick". Bacilli are
rod-shaped bacteria that come in a variety of forms, some
relatively short and fat, others long and slender. Often the end
of the cell is swollen to accommodate its spore (endospore). Only
certain bacterial species (including bacilli) form spores, which
are specialized cell structures that may allow survival in
extreme environments. In general, under conditions of nutritional
depletion, each bacterium forms a single internal spore that is
liberated when the mother cell undergoes destruction (autolysis).
The spore is a resting system, highly resistant to desiccation,
heat, and chemical agents. In general, bacterial spores have a
thick protective protein coat, and the cytoplasm is partially
dehydrated and mineralized, causing enzymes to become inactive,
and the DNA in the spore is stabilized. When returned to
favorable nutritional conditions and activated, the spore
germinates to produce a single bacterium.
There have been claims of cultivatable spores found in
various ancient materials, including rocks millions of years old,
but for most of these claims there has been considerable doubt
about the origin of the cultivated bacteria. In 1995, however,
R.J. Cano and M. Barucki reported the revival and identification
of bacterial spores (bacillus species) in 25 to 40 million year
old amber, the spores obtained from a bee preserved in the amber.
Because of the care taken to avoid contamination of the sample,
this finding is currently accepted as valid.
The term "halophilic bacteria" (halobacteria) refers to
bacteria that thrive in environments of high salt concentration.
Despite its name, the Dead Sea, which has a salt content of 28
percent, is very much alive, with various species of algae and
bacteria tolerating the extreme salinity, a salinity that would
be lethal for most other kinds of cells. The main inhabitants of
the salty brine of the Dead Sea are a special group of
halobacteria (halophilic *archaea) which have adapted to the Dead
Sea environment so thoroughly that they cannot live at salt
concentrations below 15 percent.
Some researchers reserve the term "halophilic" for the
Archaea, and use the term "halotolerant" for all other bacteria
that can thrive in high salt concentrations. Non-archaean
bacteria (i.e., most bacteria on Earth) are often called
"eubacteria". Together, the archaea and eubacteria make up the
prokaryotes -- single-celled organisms without intracellular
membrane-bound organelles such as a nucleus.
... ... R.H. Vreeland et al (West Chester University, US) report
the isolation and growth of a previously unrecognized spore-
forming bacterium (Bacillus species, designated 2-9-3) from a
brine inclusion within a 250-million-year-old salt crystal from
the *Permian Salado Formation. Delicate crystal structures and
sedimentary features indicate the salt has not recrystallized
since formation. The authors state samples were rejected if brine
inclusions showed physical signs of possible contamination, and
surfaces of salt crystal samples were sterilized with strong
alkali and acid before extracting brines from inclusions. The
authors suggest their sterilization procedures reduce the
probability of contamination to less than 1 in 10^(9). The
authors call their discovered spore-forming Bacillus species
"halotolerant"; halophilic archaea are not known to form spores.
... ... In a commentary on this work, R. John Parkes (University
of Bristol, UK) states: "Given the care that Vreeland et al took
to avoid contamination, their results are the best evidence yet
for the extremely long-term survival of microorganisms. The
potential implications are profound. For instance, can spores
effectively be immortal? What is the biochemistry that allows
them to survive for so long? Where else on Earth, and to what
depths, might ancient bacterial life be lurking? And given this
startling example of apparent bacterial durability, do spores in
rocks even provide a mechanism for life to be transported between
planets by "*panspermia", as has been proposed?"
-----------
R.H. Vreeland et al: Isolation of a 250 million-year-old
halotolerant bacterium from a primary salt crystal.
(Nature 19 Oct 00 407:897)
QY: Russell H. Vreeland: rvreeland@wcupa.edu
-----------
R. John Parkes: A case of bacterial immortality?
(Nature 19 Oct 00 407:844)
QY: R. John Parkes: j.parkes@bristol.ac.uk
-----------
Text Notes:
... ... *archaea: The archaebacteria (also called the Archaea)
are considered to be ancient compared to other kingdoms, and
possibly the most ancient life forms and the ancestors of all
eukaryotes (see Eukarya note above). They typically exist in
extreme environments, and include the methane-producing bacteria
(methanogens), the "salt-loving" bacteria (halophilic bacteria),
and the sulfur-acid tolerant thermoacidophilic bacteria. There is
presently a controversy concerning whether the Archaea should be
classified as a kingdom separate from the Bacteria.
... ... *Permian Salado Formation: The Salado Formation is
located in southeast New Mexico (US), and it contains rock salt
and potash salts. The formation has been dated as Permian, i.e.,
in the time-frame 290 to 245 million years ago.
... ... *panspermia: In general, the term "panspermia" is the
name given to the idea that life was introduced on Earth from
elsewhere in the Universe. This is a classical notion, fostered
by the chemist Svante A. Arrhenius (1859-1927) in the early part
of the 20th century.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 24Nov00
For more information: http://scienceweek.com/swfr.htm
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
6. MEDICAL BIOLOGY:
SMOKING PREVALENCE AMONG ADULTS IN THE US 1998
One of the ironies of contemporary society is that toxic
chemicals that enter the body through the digestive tract are
more tightly regulated by governments than toxic chemicals that
enter the body through the lungs. If the plant called "lettuce"
were found to cause millions of cases of cancer, stroke, heart
disease, and lung disease, lettuce would quickly vanish as a
marketable commodity, no matter how many lettuce growers squealed
in protest. But the plant tobacco, which does cause millions of
cases of cancer, stroke, heart disease, and lung disease, is not
only still a marketable commodity in the US, but more young
people than ever in the US, and more people worldwide, are
smoking cigarettes. In the US, a contagious disease that caused
as many deaths as cigarette-selling would be called a plague;
instead, in the US, cigarette-selling is called an "industry".
Well, if it is an industry, it's an industry devoted to the sale
of an addictive lethal drug, a drug no less lethal because it
kills people in 20 or more years rather than killing people
immediately.
... ... The US Centers for Disease Control and Prevention (CDC)
presents the results of a 1998 survey administered to a
nationally representative sample (n = 32,440) of the US non-
institutionalized civilian population aged >= 18 years. The
report makes the following points:
1) Participants were asked, "Have you smoked at least 100
cigarettes in your entire life? and "Do you now smoke cigarettes
every day, some days, or not at al?" "Current smokers" were
defined as persons who reported both having smoked greater than
or equal to 100 cigarettes during their lifetime and having
smoked every day or some days at the time of the interview.
"Former smokers" were defined as those who had smoked >= 100
cigarettes during their lifetime but did not currently smoke.
2) In 1998 in the US, an estimated 47.2 million adults (24.1
percent of the adult population), comprising 24.8 million men
(26.4 percent) and 22.4 million women (22.0 percent) were current
smokers. Overall, 19.7 percent of adults were every day smokers,
and 4.2 percent were some day smokers. Every day smokers
constituted 82.4 percent of all smokers.
3) Prevalence of smoking was highest among persons aged 18
to 24 years (27.9 percent) and aged 25 to 44 years (27.5
percent), and lowest among persons aged >= 65 years (10.9
percent).
4) Among specific groups, prevalence of current smoking was
as follows:
... ... American Indians/Alaska Natives: 40 percent
... ... Non-Hispanic whites: 25 percent
... ... Non-Hispanic blacks: 24.7 percent
... ... Hispanics: 19.1 percent
... ... Asian/Pacific Islanders: 13.7 percent
5) Current smoking prevalence was lowest among persons with
at least 16 years of education (11.3 percent) and highest among
persons with 9 to 11 years of education (36.8 percent). Smoking
prevalence was higher among persons living below the poverty
level (32.3 percent) than among those living at or above the
poverty level (23.5 percent).
6) In 1998, an estimated 44.8 million adults (22.9 percent
of the adult population) were former smokers (25.7 million men
and 19.1 million women). Former smokers constituted 48.7 percent
of persons who had ever smoked >= 100 cigarettes. Among current
daily smokers in 1998, an estimated 15.2 million (39.2 percent)
had stopped smoking for at least 1 day during the preceding 12
months because they were trying to stop smoking.
7) The report concludes: "A comprehensive approach to
tobacco control will require treatment for nicotine dependence
and efforts at national, state, and local levels to reduce youth
smoking, promote smoke-free environments, support
countermarketing efforts, and eliminate disparities in tobacco
use among population subgroups. Increased attention must be
focused on groups that show no decline in smoking prevalence,
including persons aged 18 to 24 years, adults with low education
levels, and American Indians/Alaska Natives. Approaches with the
widest scope (i.e., economic, regulatory, and comprehensive) are
likely to have the greatest long-term population impact."
-----------
CDC: Cigarette smoking among adults -- United States, 1998
(Morbidity and Mortality Weekly Report 2000 49:881)
(J. Amer. Med. Assoc. 1 Nov 00 284:2180)
QY: Centers for Disease Control and Prevention, Atlanta, GA 30333
-------------------
Summary by SCIENCE-WEEK http://scienceweek.com 24Nov00
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
ON EDUCATING PHYSICIANS CONCERNING TOBACCO DEPENDENCE
Tobacco use is the leading cause of preventable death and
disability in the US, accounting for nearly 500,000 premature
deaths per year. Although 70 percent of smokers visit a physician
each year, most patients are not advised or assisted in an
attempt to quit smoking. A 1991 survey indicated that only 21
percent of practicing physicians felt their formal medical
training prepared them to help patients stop smoking.
... ... L.H. Ferry et al (3 authors at Loma Linda University, US)
now present the results of a survey designed to assess the
content and extent of tobacco curricula in US undergraduate
medical education. In this context, the phrase "tobacco
curricula" includes epidemiology of tobacco use, prevention, risk
of tobacco-related diseases, and tobacco dependence treatment.
The phrase "smoking cessation" includes behavior modification
techniques, pharmacotherapy, and counseling skills. The authors
received data from 122 US medical schools (98.6 percent of the
total medical schools in the US). The authors report that a
majority of US medical school graduates are not adequately
trained to treat nicotine dependence. The authors suggest that
the major deficit is the lack of smoking cessation instruction
and evaluation in the clinical years of medical training, and
that a model core tobacco curricula that meets national
recommendations should be developed and implemented in all US
medical schools. The authors conclude: "Until all medical schools
place sufficient emphasis on the knowledge base and intervention
skills needed to prevent and treat chronic tobacco-related
diseases, it is unlikely we will see a decline in tobacco-related
morbidity and mortality. However, if medical schools provide
universal training of medical students in nicotine dependence
intervention, tobacco users will have access to the professional
expertise they need to end the deadly cycle of nicotine
addiction."
-----------
L.H. Ferry et al: Tobacco dependence curricula in US
undergraduate medical education.
(J. Amer. Med. Assoc. 1 Sep 99 282:825)
QY: Linda Hyder Ferry: lferry@sph.llu.edu
-------------------
Summary by SCIENCE-WEEK http://scienceweek.com 1Oct99
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
ON THE TOBACCO INDUSTRY AND NICOTINE AS AN ADDICTIVE DRUG
In 1994 the state of Minnesota filed suit against the tobacco
industry, and although this trial is now history, there are many
people who feel the legacy of the trial will carry on into the
21st century because of the revelations contained in the millions
of pages of previously secret internal tobacco industry documents
made public in the trial. ... ... R.D. Hurt and C.R. Robertson
now present an extensive review of the material in a medical
journal from the perspective of medical science, and the authors
make the following points: 1) The litigation tobacco industry
documents reveal that for decades the tobacco industry knew and
internally acknowledged that *nicotine is an addictive drug and
that cigarettes are the ultimate nicotine delivery device. The
following statements by executives, for example, are found in
tobacco industry documents: "Very few consumers are aware of the
effects of nicotine, i.e., its addictive nature and that nicotine
is a poison." (H.D. Steele, Brown and Williamson Tobacco Company,
1978). And in another Brown and Williamson memo: "Nicotine is the
addicting agent in cigarettes." (A.J. Mellman, Brown and
Williamson Tobacco Company, 1983). Concerning cigarettes as a
drug delivery device, the litigation documents reveal that C.E.
Teague Jr., assistant director of research at R.J. Reynolds
Tobacco Company, wrote in 1972 in an internal memorandum: "In a
sense, the tobacco industry may be thought of as being a
specialized, highly ritualized and stylized segment of the
pharmaceutical industry. Tobacco products, uniquely, contain and
deliver nicotine, a potent drug with a variety of physiological
effects... Thus a tobacco product is, in essence, a vehicle for
delivery of nicotine." 2) The authors report that perhaps their
most surprising finding in the document review was the evidence
of tobacco industry efforts spanning 3 decades to alter the
chemical form of nicotine to increase the percentage of freebase
nicotine delivered to smokers. Depending on pH, nicotine exists
as a diprotonated salt, a monoprotonated salt, or an uncharged
neutral species. The salt forms are called the "bound" forms, and
the neutral species is called the "freebase" form. Nicotine
favors the salt form at low values of pH (e.g., pH = 3) and the
freebase form at high values of pH (e.g., pH = 8). Freebase
nicotine apparently crosses biological membranes more easily than
the charged counterparts, and this affects the physiological
response to the drug. The tobacco industry was apparently well
aware of these properties of nicotine as far back as 1966, and
for 3 decades the tobacco industry had a focus on developing high
pH delivery of nicotine to increase its physiological effects.
The authors conclude: "When the breadth and depth of tobacco
industry actions are understood, it becomes evident that allowing
a tobacco settlement that honors the industry demands for legal
and financial immunity would be a public health disaster of epic
proportions and would allow the industry to continue to promote
its deadly product throughout the 21st century. Congress must use
its power to stop the carnage of more than 400,000 Americans
dying each year of cigarette-related diseases."
-----------
R.D. Hurt and C.R. Robertson (2 installations, US)
Prying open the door to the tobacco industry's secrets about
nicotine.
(J. Amer. Med. Assoc. 7 Oct 1998 280:1173)
QY: Richard D. Hurt, Mayo Clinic, 200 First St. SW, Rochester, MN
55905 US.
-----------
Text Notes:
... ... *nicotine: The alkaloid nicotine
[3-(1-methyl-pyrrolidyl)pyridine] is a tertiary amine composed of
pyridine and pyrrolidine rings. The current consensus among
neuropharmacologists is that nicotine is the psychoactive drug
primarily responsible for the addictive nature of tobacco use.
Nicotine is highly selective for so-called "nicotinic receptors"
for *acetylcholine in the peripheral and central nervous systems,
and activation of these receptors is the likely source of the
psychoactive effects of the drug. The nicotinic-acetylcholine
receptor is a molecularly well-characterized receptor, and its
activation evidently leads to conformation changes in its 5
subunits that result in a transient increase of permeability of
the neuron membrane to the sodium ion. The nicotinic-
acetylcholine receptor is therefore characterized as a
neurotransmitter-gated ion channel. Concentrations of nicotine in
blood rise quickly during cigarette smoking and peak at its
completion. Nicotine is also deposited in the lungs, spleen,
liver, and brain, where concentrations are typically twice those
of measurable blood concentrations. Nicotine readily crosses the
*blood-brain barrier, leading to the release of acetylcholine,
*norepinephrine, *dopamine, *serotonin, *vasopressin, *growth
hormone, *cortisol, *prolactin, *neurophysin 1, and
*adrenocorticotropic hormone, and release of these substances
causes various neuropharmacological effects. Apart from the
neuropharmacological effects of nicotine, nicotine and other
constituents in cigarette smoke elevate blood pressure, cause
*tachycardia, *arrhythmia, and *vasoconstriction in *cutaneous
tissue and skin; lower body temperature; inhibit *diuresis;
increase *gastrointestinal tonus; antagonize ulcer healing; and
decrease pain threshold.
... ... *acetylcholine: A prevalent *neurotransmitter substance,
both in the brain and in the peripheral nervous system, where it
controls the actions of skeletal and smooth muscle.
... ... *neurotransmitter substance: Neurotransmitters are
chemical substances released at the terminals of nerve axons in
response to the propagation of an impulse to the end of that
axon. The neurotransmitter substance diffuses into the synapse,
the junction between the presynaptic nerve ending and the
postsynaptic neuron, and at the membrane of the postsynaptic
neuron the transmitter substance interacts with a receptor.
Depending on the type of receptor, the result may be an
excitatory or an inhibitory effect on the postsynaptic nerve
cell.
... ... *blood-brain barrier: A selective mechanism opposing the
passage of most ions and large molecular-weight compounds from
the blood to brain tissue, the mechanism operating in a
continuous layer of endothelial cells connected by tight
junctions between cells. (Endothelial cells are flat cells
forming a layer lining blood vessels, lymphatic vessels, the
heart, etc.)
... ... *norepinephrine: The principal neurotransmitter substance
released from nerve endings of the sympathetic nervous system.
(The sympathetic nervous system is a part of the autonomic
nervous system involved in the mobilization of energy resources
during stress and arousal.
... ... *dopamine: A neurotransmitter substance.
... ... *serotonin: A neurotransmitter substance involved in
nearly everything occurring in the brain, including psychological
states such as anxiety and depression, and dysfunctions producing
migraine and epilepsy.
... ... *vasopressin: A peptide hormone important in the
regulation of *diuresis.
... ... *growth hormone: A vertebrate polypeptide hormone that
regulates growth. In general, hormones are signaling molecules
secreted into the blood stream by endocrine cells and acting on
target cells that possess receptors for the hormone.
... ... *cortisol: A corticosteroid hormone secreted by the
adrenal gland.
... ... *prolactin: A polypeptide hormone synthesized and
released by the pituitary gland.
... ... *neurophysin 1: Neurophysins are a family of proteins
synthesized in the hypothalamus, and function as carriers in the
transport and storage of a number of hypothalamic-pituitary
hormones.
... ... *adrenocorticotropic hormone: (ACTH) A pituitary hormone.
... ... *tachycardia: Rapid beating of the heart, conventionally
applied to rates over 100 per minute.
... ... *arrhythmia: Irregularity of the heartbeat.
... ... *vasoconstriction: Narrowing of the blood vessels.
... ... *cutaneous tissue: In general, tissue associated with
skin.
... ... *diuresis: Excretion of large volumes of urine.
... ... *gastrointestinal tonus: In general, contraction of
gastrointestinal muscle.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 13Nov98
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
EFFECTS OF NICOTINE ON BRAIN NERVE CELLS
... Dopamine is a neurotransmitter found in several major areas
of the brain, and the degeneration of so-called dopamine neurons
is apparently involved in Parkinson's disease. Dopamine has also
been implicated in the intricate effects of the psychostimulating
drugs associated with drug abuse. The dietary precursors of
dopamine are phenylalanine and l-tyrosine. The mesolimbic
dopamine system is a dopamine-involved system of nerve cells and
nerve fibers connecting the mesencephalon (the midbrain) to the
limbic system and cerebral cortex.
... ... Pidoplichko et al (4 authors at 2 installations, US)
report that the same concentration of nicotine achieved by
smokers activates and desensitizes multiple nicotinic receptors
with a resultant regulation of the activity of dopamine neurons.
The authors suggest these results further support the hypothesis
that the mesolimbic dopamine system is involved in the cellular
and behavioral effects of many addictive drugs.
-----------
QY: John A. Dani: jdani@bcm.tmc.edu
(Nature 27 Nov 97) (Science-Week 19 Dec 97)
-------------------
Related Background:
SECOND-HAND TOBACCO SMOKE DOUBLES RISK OF CORONARY PATHOLOGY
The most significant public health news of the week was probably
the report of a 10 year study by Ichiro Kawachi and colleagues
(Harvard School of Public Health, Cambridge MA US), which
tracked more than 32,000 healthy women who never smoked and
found that regular exposure to the smoke of other people at home
or work almost doubled the risk of heart disease. These new
findings are the largest increase in risk ever reported for
second-hand smoke, and the researchers state the findings apply
equally to men and women.
(Circulation 20 May 97) (Science-Week 22 May 97)
-------------------
Related Background:
IN BRIEF: BIDI USE AMONG US URBAN YOUTH 1999
"Bidis" are small brown hand-rolled cigarettes primarily made in
India and southeast Asian countries, and consisting of tobacco
wrapped in a tendu or temburni leaf (Diospyros melanoxylon). In
the US, bidis are purchased for $1.50 to $4.00 for one package of
20 and are available in different flavors (e.g., cherry,
chocolate, and mango). Bidi use was first observed in the US
during the mid-1990s and is apparently now widespread among
various minority youth groups. Adolescents report a preference
for the taste of bidis over cigarettes and a belief that bidis
are less expensive, easier to buy, and safer than cigarettes. The
US Centers for Disease Control and Prevention (CDC) recently
presented a report on bidi use, the report making the following
points:
1) Preliminary data collected from a sample of adolescents
surveyed during March and early April 1999 in Massachusetts (US)
on the prevalence of bidi use among urban youth indicate that of
642 youth surveyed, 40 percent had smoked bidis at least once
during their lifetimes and 16 percent were current bidi smokers.
2) When tested on a standard smoking machine, bidis produced
higher levels of carbon monoxide, nicotine, and tar than
cigarettes, with one study reporting that bidis produced
approximately 3 times the amount of carbon monoxide and nicotine
and approximately five times the amount of tar as cigarettes.
Because of low combustibility of the tendu leaf wrapper, bidi
smokers inhale more often and more deeply, breathing in greater
quantities of tar and other toxins than cigarette smokers. Like
all tobacco products, bidis are mutagenic and carcinogenic. Bidi
smokers risk coronary heart disease, cancers of the oral cavity,
pharynx, larynx, lung, esophagus, stomach, and liver. Mortality
of both the fetus and newborn infant is also associated with bidi
use during pregnancy.
3) The report states that this investigation is the first in
the US to estimate the prevalence of bidi smoking among students
in grades 7 through 12, and that preliminary findings from this
study support the need for additional research on bidis,
particularly on smoking prevalence among youth from differing
geographic, educational, and socioeconomic backgrounds.
-----------
US Centers for Disease Control and Prevention: Bidi use among
urban youth -- Massachusetts, March-April 1999.
(Morbidity and Mortality Weekly Report 1999 48:796)
(J. Amer. Med. Assoc. 20 Oct 99 282:1416)
-------------------
Summary by SCIENCE-WEEK [http://scienceweek.com] 10Dec99
For more information: http://scienceweek.com/swfr.htm
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7. IN FOCUS: SCIENCE VERSUS DOGMA
"For someone playing the game of science, the method by which he
ascertains what he believes is crucial. He has to evaluate data
and arguments and decide for himself on their validity. A
scientist communicating to others has the task of convincing the
hearer of the validity of his statements in terms of the data and
their explanations. He is not playing the game correctly if he
wins support by the strength of his personality or prestige... It
is the system of data-based explanation that distinguishes
science from dogma. The scientist has both the right and the
responsibility to decide for himself, on the basis of the
evidence at hand, the best explanation of a set of phenomena. He
also has the right and the responsibility as a scientist to
investigate thoroughly the bases of his beliefs. He cannot accept
statements unsupported by data. On the other hand, dogma
(religious, economic, political, social, or any other kind)
depends on pronouncements by established authorities (for
example, the dogma that the Earth was created in 4004 B.C.). The
goal of the student learning a dogma is to accept the
pronouncements as they are given to him. If he disagrees with the
dogma, he is not playing the game of dogmatism correctly. It is
his right and responsibility to believe the dogma. He has to
search his soul until he accepts it or be considered an outcast
and suffer the consequences. It would not matter if he could
present strong arguments in support of his personal beliefs. In
dogma, arguments and facts are forced to coincide with the dogma.
The student cannot accept statements that do not agree with the
dogma. (Continuing the previous example, he must reject the
existence of prehistoric man around 10,000 B.C.). One way of
contrasting science and dogma is to say that a scientist accepts
facts as given and belief systems as tentative, whereas a
dogmatist accepts the beliefs systems as given -- facts are
irrelevant."
-----------
G. McCain and E.M. Segal: _The Game of Science_
(Wadsworth Publishing, Belmont CA (US), p.38)
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8. FROM THE SCIENCEWEEK ARCHIVE:
GRADUATE STUDENT STRESS: A PROPOSAL IN THE WAKE OF A TRAGEDY
In August of 1998, a 5th year graduate student in the Department
of Chemistry at Harvard University (US) wrote a note castigating
the department for the power professors have over the lives of
graduate students and then committed suicide by ingesting
cyanide. The student, Jason Altom, was the 3rd Harvard graduate
student to commit suicide since 1997, and the event prompted much
discussion, many recriminations, and the formation of committees
at Harvard and at other universities, in both chemistry
departments and other departments. Altom was working on the
synthesis of a complex molecule under the supervision of organic
chemist Elias J. Corey, winner of the 1990 Nobel Prize in
Chemistry. In his suicide note, Altom elaborated on the pressures
affecting graduate students: the pressure to succeed and the
pressure of an intense relationship with a single supervisor. In
an editorial in October 1998, the journal _Nature_ wrote of this
case: "Such situations raise a key issue that lies behind a broad
swathe of current concerns, from scientific misconduct to the
plight of contract research staff: is a culture of achievement,
fanned by an increasingly competitive job market and tight
competition for research grants, now in danger of driving out the
culture of mutual support from which both science and its
protagonists have gained so much in the past?"
... ... Now Carl Djerassi (Stanford University, US), an eminent
chemist, considers the Altom suicide case and proposes a solution
to the problems that apparently played a role in the tragedy.
Djerassi makes the following points: 1) Although in his suicide
note Altom suggested a 3-member faculty oversight committee would
"provide protection for graduate students from abusive research
advisors", Djerassi questions the efficacy of such a committee by
pointing out that the faculty members of such a committee would
generally be unwilling to confront a colleague with a complaint,
and any junior faculty member on such a committee might seriously
damage his or her career by confronting a senior renowned
colleague with a complaint. 2) Djerassi suggests that an
alternative solution concerning complaints about "abusive
research advisors" (Altom's terms) and other ill-defined
behaviors is to have the complaints handled anonymously outside
the "intensely collegial and competitive department setting." The
procedure would be similar to that now in place in many US
universities for evaluation of faculty by undergraduates, often
with written assessment and numerical ratings of various
qualities, the data gathered by a central university office.
Djerassi suggests annual evaluations by graduate students and
postdoctoral fellows "of the many components of an appropriate
mentor-disciple relationship". 3) Djerassi concludes: "The social
structure of the professor-graduate student relationship in the
sciences is distinct. Although an undergraduate mentoring fiasco
rarely causes permanent damage -- mainly because other mentors
are readily available -- the same can hardly be said of graduate
school, where the effects of this one-on-one mentor-disciple
relationship may last a lifetime. Must people die before research
universities will place serious emphasis on monitoring,
evaluating and, crucially, on mentoring the mentors in their
graduate school science faculties?"
-----------
Carl Djerassi: Who will mentor the mentors?
(Nature 28 Jan 99 397:291)
QY: Carl Djerassi [djerassi@stanford.edu]
-------------------
Summary by SCIENCE-WEEK http://scienceweek.com 23Apr99
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