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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.
July 27, 2001 -- Vol. 5 Number 30
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I would rather do an experiment. That doesn't mean
I think theory is unimportant. It just means I would
rather do an experiment.
-- Costas Spyropoulos (1928-1984)
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Section 1
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Contents of this Issue (Full reports in Section 2):
1. IN BRIEF: Brain volume changes in schizophrenia...
Interspecies prion transmission... Future of plant biology...
Meningococcal disease... Probability of Earth-like planets...
Development of young stars... Magnetic vortices in
superconductors... Ancient cores of the continents.
2. SCIENCE POLICY: NEW LISTS OF NIH FUNDING STARS
Big science is a permanent fixture of our society, although which
particular science is "big" depends on fashion and societal needs
and sometimes political considerations. These days, certain areas
in biology are "big science" in a way never seen before in the
history of biology.
3. CELL BIOLOGY: ACTIN-BASED MOTILITY
The term "actin-based motility" describes a variety of cellular
processes through which living cells change shape in response to
environmental signals, or extend protrusions such as lamellipodia
and filopodia, or wrap around a particle in a phagocytic cup. All
of these phenomena are driven by the assembly of actin filaments.
4. ASTROPHYSICS: ON BLACK HOLES AND EVENT HORIZONS
Because any object with an event horizon must be a black hole,
detection of such a horizon proves the existence of a black hole.
Also, since some theories of gravity that are consistent with
general relativity do not predict the existence of black holes
and event horizons, detection of event horizons may be another
method of confirming the validity of general relativity.
5. CHEMISTRY: CHIRALITY AND CRYSTAL SYMMETRIES
Addition of chiral amino acid growth modifiers alters the energy
landscape seen by adsorbing and desorbing calcite species at the
surface of the mineral, thus changing the rates of attachment and
detachment and/or the surface configuration that is lowest in
energy.
6. EARTH SCIENCES:
THE ANCIENT CARBON CYCLE AND GLOBAL BIODIVERSITY
Under the explicit assumption that global biodiversity grows with
global biomass, an analysis demonstrates that the long-term
fluctuations of carbon dioxide levels were dominated by
complimentary changes in the biological and fluid reservoirs of
carbon, while the much larger geological reservoir remained
relatively constant in size.
7. IN FOCUS: ON ESTABLISHED AUTHORITY IN SCIENCE
The great classical physicist Lord Kelvin is almost as well known
for his errors as for his contributions to physics, and Kelvin
illustrates what can be considered one of the laws of the history
of science: The straightest road to ultimate derision is to
assume that all that can be known in the future is already known
in the present.
8. FROM THE SCIENCEWEEK ARCHIVE:
HISTORY OF SCIENCE:
THE 18TH CENTURY WOMEN SCIENTISTS OF BOLOGNA
Although the 18th century was an era that produced a great and
influential flowering of human thought, in all the countries in
Europe except one, women were forbidden to study and lecture in
universities, and women had hardly any participation in the
sciences. The one exception was Italy.
9. SOURCES
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Section 2
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1. IN BRIEF:
... ... BRAIN VOLUME CHANGES IN SCHIZOPHRENIA:
Researchers report the results of a study designed to determine
if brain morphological changes previously observed in patients
with schizophrenia progress over time and whether such
progression is related to the severity of the course of the
illness. In a controlled study of 24 schizophrenic patients and
25 controls, the study involving 2 brain magnetic resonance
imaging scans on average 4 years apart, it was found that
schizophrenic patients exhibited more rapid brain volume decline
than control subjects in various brain regions, as well as more
rapid cerebrospinal fluid expansion in various brain regions.
There were correlations with severity of illness and length of
time hospitalized. The researchers conclude their study reveals
that patients with chronic schizophrenia exhibit accelerated
frontotemporal cortical gray matter decline and cortical sulcal
and lateral ventricular expansion. In addition, greater clinical
severity of the disorder is associated with faster rates of
frontotemporal brain volume changes. The authors suggest these
observations are consistent with a progressive pathophysiological
process, but the observations need to be replicated on a larger
sample. (AGP 2001 58:148)
... ... INTERSPECIES PRION TRANSMISSION:
Prion diseases have two particularly intriguing features. First,
clinically different prion diseases (strains) can occur within
one animal species. It appears that although the prion gene does
not differ between individuals of any one species, the shape of
the protein it encodes can differ, and different conformations of
the protein are responsible for different disease strains. The
second intriguing feature is the "species barrier" that limits
the spread of infection between species. Factors influencing this
barrier are of particular interest because transmissible
spongiform encephalopathies are occasionally transmitted from
cattle to humans. A new study suggests the possibility that
conformational differences between prion proteins with the same
amino-acid sequence contribute to the barrier that limits prion
propagation between species, and the results are taken to
indicate that "it may be time to consider the disturbing
possibility that certain bovine prion forms have an enhanced
ability to cross the species barrier to humans." (NAT 2001
410:161,223)
... ... FUTURE OF PLANT BIOLOGY:
Historically, plant biologists had a simple model for the
science, with emphasis on plant identity (taxonomy), distribution
(plant geography), morphology, and physiology. The burgeoning
explosion of knowledge and great advances in molecular biology,
to the extent that genes for specific plant traits can be added
or deleted at will, have created a revolution in the study of
plants. Genomics in agriculture has made it possible to address
many important issues in crop production by the identification
and manipulation of genes in crop plants. The current model of
plant study differs from the old model in that it places greater
emphasis on developmental controls and on evolution by
differential fitness. In a rapidly changing environment, the
current model also explicitly considers the phenotypic variation
among individuals on which selection operates. In a recent
commentary, F.A. Bazzaz of Harvard University suggests that
genetic engineering technologies are and will continue to be an
important component of agriculture, but the evolutionary
implications of these new technologies must be considered.
"Meeting these demands requires drastic changes in the
undergraduate curriculum. Students of biology should be trained
in molecular, cellular, organismal, and ecosystem biology,
including all living organisms." (PNAS 2001 98:5441)
... ... MENINGOCOCCAL DISEASE:
Meningococcal disease was first identified in 1805, and the
causative pathogen, the bacterium Neisseria meningitides, was
first isolated in 1887. Since then, despite improved
understanding of the epidemiological aspects and pathogenesis of
this disease, the disease remains a leading cause of bacterial
meningitis and sepsis in the US and a major cause of epidemics in
sub-Saharan Africa. In the US, there occur approximately 2500 to
3000 cases per year, with the highest incidence in infants in
whom protective antibodies have not yet developed. In adults,
active or passive exposure to tobacco smoke, as well as
concurrent viral infection of the upper respiratory tract,
increases the risk of meningococcal disease by enhancing the
formation and spread of respiratory droplets or diminishing the
functional and mechanical integrity of the respiratory mucosa as
a barrier to invasion. Tobacco use is believed to be responsible
for approximately one-third of adult cases. Humans are the only
natural reservoir of N. meningitides, and the nasopharynx is the
site from which meningococci are transmitted by aerosol or
secretions from one individual to another. Routine vaccination of
high-risk populations is a reasonable public health strategy for
controlling meningococcal disease, but the shortcomings of the
currently available vaccine limit its usefulness. New vaccines
now being developed are unlikely to be available in the next 5
years, and their expected efficacy is not known.
(NEJM 2001 344:1378)
... ... PROBABILITY OF EARTH-LIKE PLANETS:
In 1995, astronomers reported the first tentative evidence of
planets orbiting stars outside our Solar System, and since then
astronomers have detected perturbations in the motions of dozens
of nearby stars, these perturbations presumably due to the
gravity of orbiting planets. Currently, the identification and
study of extrasolar planets depends for the most part on indirect
methods such as those involving the measurement of perturbations
of the observed brightness or motions of their parent stars. The
already discovered extrasolar planets demonstrate the large
diversity of planetary systems, and current research aims at
detecting an even greater variety of such systems, and also aims
at a systematic explanation of the origins of extrasolar planets
and the origin of our Solar System. Current models of planet
formation, and data from apparently giant Jupiter-like planets
orbiting stars, suggest that the metal content of parent stars
may be used as a basis for categorizing stellar planetary
systems. Using this idea, a new study estimates the distribution
of Earth-like planets in the Universe, and concludes that 74
percent of the possible Earth-like planets in the Universe are
older than Earth by approximately 2 billion years.
(ICAR 2001 151:307)
... ... DEVELOPMENT OF YOUNG STARS:
Although visible light is unable to penetrate the dust cloud
surrounding an embryonic star, infrared radiation does penetrate
the dust. Such radiation has been detected for decades, but until
recently infrared telescopes lacked the sensitivity and
resolution to provide detailed information about the youngest
prenatal stars, the "protostars". The life of a protostar is
approximately 100,000 years, and is defined by the rapid
accumulation of mass from a surrounding envelope of gas and dust.
The rate of such accumulation is the equivalent of approximately
one Earth-sized planet each year. Throughout this period, the
protostar progressively increases in density as it shrinks in
size. With the development of giant telescopes and extremely
sensitive infrared detectors in the past decade, astronomers are
now able to observe these secluded stellar embryos. Many of the
protostars that have now been observed in the infrared will not
be seen in visible light for another 100,000 years, although
their luminosities, sizes, ages, masses, rates of rotation, and
the presence of circumstellar matter are already known.
(AS 2001 89:316)
... ... MAGNETIC VORTICES IN SUPERCONDUCTORS:
The defining property of a superconductor is the ability to carry
an electric current without resistance when cooled below a
critical transition temperature, usually a few degrees above
absolute zero. Below the transition temperature, many of the
useful properties of a superconductor are governed by its
response to external magnetic fields. Under certain conditions,
magnetic field lines can permeate some superconductors and
produce magnetic vortices. Such vortices have non-superconducting
cores that carry magnetic field lines, the cores surrounded by
swirling "supercurrents". The behavior of these magnetic vortices
determines the physical properties of superconductors, including
the maximum electrical current the superconductor can support.
The movement of vortices is particularly damaging because it
creates electrical resistance, and thereby destroys the
superconducting state. In 1986, a new class of high temperature
(above 77 kelvins) superconductors was discovered, and in these
superconductors magnetic vortices are exotic and apparently less
stable than the vortices in low-temperature superconductors. A
new study of a copper-oxide high-temperature superconductor
examines the response of magnetic vortices to changing
temperatures and fields and provides a more comprehensive view of
the vortex phase diagram in this material. (NAT 2001 411:434,448)
... ... ANCIENT CORES OF THE CONTINENTS:
The existence of the small and ancient cores of continents,
called "cratons", has long been a puzzle. Cratons were apparently
created during the Archaean time-frame, 4 billion to 2.5 billion
years ago, and they form the oldest parts of Earth's tectonic
plates. Yet cratons have somehow remained unmodified by tectonic
forces, while younger parts of the continents exhibit the
geological scars of repeated tectonic buffeting and appear to be
weaker and less stable than cratons. Not much is known about the
process that formed cratons, but it is believed their tectonic
longevity derives from "keels" that extend deep into the Earth.
These keels are composed of lithospheric mantle more than 2.5
billion years old and more than 200 kilometers deep. The chemical
composition of craton keels is believed to derive from depletion
of basaltic constituents and volatile molecules. According to
theory, a combination of the loss of basalt and volatiles results
in the keels being strong enough to resist destruction by
tectonic forces. A new study confirms that depletion of basaltic
constituents does indeed influence the strength of lithospheric
mantle, mainly by controlling the thickness to which the keel can
grow. The study also suggests that more continental crust may
have formed 2.5 billion years ago than is indicated by the
present distribution of cratons. (NAT 2001 411:38,69)
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2. SCIENCE POLICY: NEW LISTS OF NIH FUNDING STARS
A generation ago, in 1963, Derek J. De Solla Price noted the
following concerning "big science":
"Without doubt, the most abnormal thing in this age of Big
Science is money... If the costliness of science were distributed
in the same way as its productivity or excellence, there would be
no problem. If the per capita cost of supporting scientists were
constant, we should only spend in proportion to their number, so
that the money they cost would double every 10 to 15 years. But
in fact our expenditure, measured in constant dollars, doubles
every 5.5 years, so that the cost per scientist seems to have
been doubling every 10 years. To put it another way, the cost of
science has been increasing as the square of the number of
scientists. Since we know that in general the number of average
scientists increases as the square of the number of eminent
highly productive ones, we derive the frightening costly
principle that research expenditure increases as the fourth power
of the number of good scientists... In fields of scientific study
where once there was a natural sorting of people into various
subjects according to their predilections and the caprice of
opportunity and inspiration, society now offers various
inducements and facilities designed to attract men to specific
areas. Thus, the law of supply and demand begins to obey these
different forces and the distribution changes just as effectively
as if there only a constant supply and a rapidly increasing
demand."
There are perhaps two truths here about the past: a) The old
days of science are gone. b) An argument can be made that the old
days of science were terrible. Certainly, doing science a
generation ago was more congenial, less competitive, based more
on intellectual interests, and generally a more stately activity.
But there was hardly any money, most laboratories were in
shambles, and in many places laboratory equipment was constructed
at the bench from components cannibalized from obsolete machines
and other devices. All that has changed. Big science is a
permanent fixture of our society, although which particular
science is "big" depends on fashion and societal needs and
sometimes political considerations. These days, certain areas in
biology are "big science" in a way never seen before in the
history of biology. A recent study of NIH grants in the year 2000
revealed the following:
1) The top-funded basic research principal investigator in
the US is Stanley Prusiner (University of California San
Francisco), who received $12.5 million in research grants last
year. Prusiner's area is prion diseases, and he already holds a
Nobel Prize in Physiology and Medicine for his work in that
field. After Prusiner are the following top-funded principal
investigators, their research grants, and their areas of basic
research:
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Alfred Gilman $9.8 million Cell signaling
Ronald Crystal 6.6 Gene therapy
George Stamatoyannopoulos 6.4 Blood diseases
Seigo Izumo 6.1 Cardiovascular genomics
Ian A. Wilson 5.6 Structural genomics
Rainer Storb 5.4 Bone marrow transplants
Richard Boucher 5.1 Cystic fibrosis
Paul Greengard 5.0 Signal transduction
Michael Gimbrone 4.9 Vascular endothelium
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2) NIH grants for genome sequencing laboratories were in
another class altogether, with the following top principal
investigators, their institutions, and their grants:
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Eric Lander Whitehead Institute $65.3 million
Robert Waterston Washington University 44.6
Richard Gibbs Baylor College of Medicine 23.8
Gerald Rubin Univ. California Berkeley 14.1
Ronald Davis Stanford University 9.4
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3) For sustained funding, the winner is apparently the noted
protein chemist Harold Scheraga (Cornell University), who has
been renewing the same research grant for 45 years, is now 79
years old, has published over 1000 papers, and who received an
NIH grant last year of $717,000.
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Derek J. De Solla Price: _Little Science, Big Science_
Columbia University Press, New York 1963, p.92
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Jocelyn Kaiser: Even in a time of plenty, some do better than
others.
(SCI 2001 292:1995)
QY: editors@aaas.org
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Summary by SCIENCE-WEEK http://scienceweek.com 27Jul01
For more information: http://scienceweek.com/swfr.htm
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Related Background:
A NOBEL LAUREATE COMES OUT AGAINST BLOCK RESEARCH GRANTS
In general, there are two methods for providing financial support
for scientific research. One method involves awarding funds to an
institution, or to departments within an institution, with the
idea that bureaucratic entities within the institution will then
disburse funds to individual investigators heading particular
research programs. Such awards are called "block grants", the
awarding of funds en bloc to an institution or institutional
department. The other method is to simply award research funds to
individual researchers, usually on the basis of competitive
individual applications. It is easy to provide arguments and
counter-arguments for either method, and as usual in areas of
public policy where no one has ever done a controlled public
policy experiment, the result is a vacillation of public policy
from one era to another depending on the public mood and public
priorities and the efficacy of public rhetoric. In fact, what
works in one place and time may not work in another place and
time, and even if everyone knows this, the debate continues and
has continued for the past 50 years. In the US, the tendency has
been to favor individual competitive research grants over block
grants, while in some other countries the opposite has been true.
Nobel Laureate Arthur Kornberg, in an editorial in the journal
Science, notes that recently the US National Institutes of Health
budget allocations have been shifting in favor of block grants,
"program projects in some of which a director can select the
investigators and choose projects that might not withstand peer
review." Kornberg says it is a common illusion that "strategic"
objectives are necessary to solve the problems of major diseases,
but the idea is misguided. "Basic research," Kornberg says, "has
been the province of the individual investigator and remains the
lifeline of medicine."
-----------
QY: Arthur Kornberg: Stanford U., Dept. of Biochem. 415-723-2300.
(SCI 1997 12 December) (SW 1998 2 January)
-------------------
Related Background:
BIOLOGY FUNDING VS. PHYSICS FUNDING: UNEASE EXPRESSED
The journal _Nature_, in a recent editorial, criticizes US
President Bill Clinton for asserting that the next 50 years will
be "very likely characterized predominantly as the age of
biology." The journal also criticizes the emphasis on the news of
biology, "trumpeted by the media worldwide". Politicians ought to
understand, Nature says, that the results of physics "have a way
of unobtrusively and unpredictably invigorating apparently
unrelated disciplines and technologies, even to a revolutionary
extent..." Ergo, support for the physical sciences continues to
be in the best interests of society.
(NAT 1998 8 January) (SW 1998 23 January)
-------------------
Related Background:
ON FASHIONS IN SCIENCE AND TECHNOLOGY
Rolf Landauer (IBM Corp., US), in a review of fashions in science
and technology, points out both the negative and positive aspects
of such fashions in general, and in particular in his own field,
condensed matter physics. Among other problems, Landauer notes:
1) Fashions in science and technology draw attention away from
other deserving areas. 2) Funding agencies make an apparently
sensible initial decision to support a particular exploratory
scientific path, but they too easily become emotionally tied to
their choice. 3) The competition for grants and employment causes
public relations activities to have an increasing greater role in
the practice of science. 4) Whereas in the past judgments in an
institution about the quality of a colleague's work were based on
an assumed understanding of that work, at present promotions
depend on the ability to get funding, citation index scores,
etc., and in-house evaluations often are less important than
external evaluations. 5) These days a single publication is lost
in the deluge of papers, and the only way to be heard in the
scientific community is to repeatedly publish essentially the
same information over and over again. This produces a large
publication volume per researcher, which in turn forces other
researchers to do the same if they want to advance in status in
their installations and in their field. As any working scientist
is aware, these are only some of the problems inherent in the
present structure of professional science. Landauer suggests that
fashions in science have a mostly negative impact, and that more
serious debate is needed about how fashions affect professional
science and the training of new scientists.
-----------
QY: Rolf Landauer,
Thomas J. Watson Research Center, IBM Corp., Yorktown Hts, NY US
(PT 1997 December) (SW 1997 12 December)
-------------------
Related Background:
AGAINST PROGRAMMING FUTURE FUNDAMENTAL RESEARCH
Given that science is an enterprise essential to the well-being
of society, the perennial questions are how to fund it, what to
fund, and with how much money? Often, the attitude is that there
is all this money to be used, and with clever policy decisions we
ought to be able to choose and spur the right horse to get us
where we want to go as fast as possible. The difficulty is that
choosing the "right" horse is never obvious, and there is often a
danger that a management process may retard rather than enhance
scientific progress. ... ... Paul Berg and Maxine Singer, in an
opinion piece, consider the dangers of managed science in the
context of modern biology. The authors make the following points:
1) Considering the past 150 years of biological research
(especially genetics), it is clear that success has frequently
been contingent on the choice of the experimental system, and
that often what turned out to be an important experimental system
was first developed on the fringes of science and not in the
mainstream. 2) Mendel's 19th century breeding experiments with
*pea plants defined the early science of genetics, and his work
was first rediscovered at the turn of the century by plant
breeders who contributed to the extension and generalization of
mendelian ideas and to the development of the American corn
industry. 3) By 1914, the fruit fly *Drosophila melanogaster had
displaced corn as the more advantageous organism for genetic
investigation, resulting in the work of T.H. Morgan, A.H.
Sturtevant, C.B. Bridges, H.J. Muller, and their students. 4) At
about 1935, Drosophila proved inadequate to pursue the extant
questions in genetics, and the new experimental system was the
common bread mold *Neurospora crassa, adopted as an experimental
tool by B.O. Dodge, C. Lindegren, G.W. Beadle, and E. Tatum. From
this work came the idea that each gene is responsible for one
enzyme required for the synthesis of a particular cellular
constituent. 5) By the late 1940s, Tatum had adopted a new
experimental system for examining the relation between genes and
cellular functions, the common intestinal bacterium *Escherichia
coli. 6) In the 1950s, attention shifted to still another
experimental system, the viruses (*bacteriophages) that attack
the E. coli bacterium, these viruses having a simpler structure
than bacteria but containing organized genomes. It was the study
of bacteriophages that stimulated Watson and Crick's efforts to
determine the structure of DNA. 7) In the 1960s and 1970s, *yeast
became an experimental system essential to biological research,
with certain yeast genes virtually identical to certain human
genes. 8) More recently, the *nematode worm *Caenorhabditis
elegans has revealed unexpected attributes of the developmental
process, especially the programmed cell death (*apoptosis) of
certain *differentiated cells. 9) Current genetic analysis takes
advantage of decades of work on mutant mice, and recently
genetically altered mice have provided special tools for the
study of gene replacement, very early development, and disease
pathology. 10) Plant genetics research has become a focus again
with attention on the plant *Arabidopsis thaliana, an easily
maintained laboratory plant with a small genome and a rapid life
cycle. The authors conclude: "Nothing in the human-made world
rivals the complexity and diversity of living things. There are,
in nature, concepts that no one has yet imagined. Looking back
over the past 150 years... it seems that the fringes, not the
mainstream, are the most promising places to discover
revolutionary advances. Attempts to program the direction and
tools of genetic research could not have foreseen the diverse
sources from which progress resulted. The lesson is that those
who attempt to program future fundamental research, however well
motivated by medical, agricultural, or social needs, are likely
to divert researchers from the fringes where the most promising
discoveries are often made."
-----------
P. Berg and M. Singer (2 installations, US)
Inspired choices.
(SCI 1998 282:873)
QY: Paul Berg, Stanford University 415-723-3058.
-----------
Text Notes:
... ... *pea plants: The advantage of Mendel's pea plants was the
possibility of controlled pollination and development of highly
inbred varieties with clearly defined traits. Although it is
often not mentioned, the monk and priest Gregor Mendel (1822-
1884) had training in mathematics and science at the University
of Vienna, and he was in fact a science teacher before his work
with peas began in 1857. When Mendel sent his unpublished paper
to Nageli, an eminent but classical biologist, Nageli was
apparently repelled by the mathematics. Mendel finally published
in 1865 in an obscure journal, the *Transactions of the Brno
Natural History Society*. The work remained ignored and unnoticed
until 1900, when the botanist Hugo De Vries came across the paper
and brought the Mendelian laws of inheritance to the attention of
the scientific world.
... ... *Drosophila melanogaster: A major advantage of this
experimental system is the presence of giant chromosomes in the
insect's salivary glands. (In cells with chromosomes, the
chromosomes are the physical structure into which DNA is
organized and on which genes are carried.) Drosophila also has a
short reproductive cycle (approximately 10 days), and it produces
100 to 400 progeny per mating.
... ... *Neurospora crassa: In the wild (i.e., natural) state
this mold will grow on a nutrient medium containing sugar as the
only organic compound except for a small required concentration
of biotin. Induced mutations (e.g., produced by x-rays) can
result in mutants that require other organic substances, and
systematic analysis of the genetics of these mutants and their
new requirements made possible an understanding of the genetics
of a number of biochemical pathways and of the enzymes that
control these pathways.
... ... *Escherichia coli: This is a rather ubiquitous bacterium
present in the intestinal tracts of animals, in soil, and in
water. Its advantage as an experimental system is its simple
genetic machinery and rapid growth characteristics. E. coli was
the first animal organism used for cloning and propagating the
genes of other species.
... ... *bacteriophages: Bacteriophage is a virus that
infects bacteria, the virus consisting essentially of a naked
strand of DNA surrounded by a complex polyhedral shell ("capsid")
composed mainly of glycoproteins.
... ... *yeast: Yeast are unicellular fungi that reproduce by
budding. The most important yeast species in research is the
common bread and beer yeast Saccharomyces cerevisiae.
... ... *nematode: An abundant and ubiquitous phylum of
unsegmented roundworms.
... ... *Caenorhabditis elegans: This is a small (1 mm) nematode
worm. It is transparent, hermaphroditic, free-living, and found
in soil. It has a relatively small genome (approximately 3000
genes), and only a few types of cells in its body. It has a 16-hr
embryogenesis that can be achieved in a petri dish, and is thus
highly suitable for the study of developmental and behavioral
genetics.
... ... *apoptosis: In general, the term "apoptosis" refers to
programmed cell death, whether as a part of normal tissue
differentiation and development, or as a program activated in a
defective cell. In the molecular biology of cancer, apoptosis is
the name given to the programmed cell death provoked by the
proteins expressed by tumor suppressor genes. Thus, malignant
cells are defective cells with a deactivated apoptosis program,
and this allows malignant cells to survive and replicate.
... ... *differentiated cells: Refers to developmental cell
specialization (morphology and biochemistry) resulting from
activation (and/or deactivation) of specific parts of the cell
genome.
... ... *Arabidopsis thaliana: (thale cress) A weed of the
mustard family with a small genome of 120 million base pairs.
Arabidopsis is now an important laboratory species, and it is
presently the model for physiological, biochemical, cell
biological, and developmental studies of over 250,000 plant
species.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 20Nov98
For more information: http://scienceweek.com/swfr.htm
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3. CELL BIOLOGY: ACTIN-BASED MOTILITY
During the first half of the 20th century, the biological
cell was considered explicitly or implicitly as a collection of
physically independent organelles suspended in an amorphous fluid
called "protoplasm". One could see a certain graininess with the
light microscope, and fixation and chemical staining with various
dyes usually revealed other structures invisible in living cells,
but for the most part there seemed to be nothing but various
organelles and fluid inside the cell, at least at the resolution
of the light microscope, which is approximately 0.5 microns.
The advent of electron microscopy in the 1950s, with
practical resolutions at that time of the order of 10 or 20
angstroms, completely changed our view of the interior of
biological cells, and for the first time networks of
interconnected filaments in protoplasm were recognized as a
cytoplasmic framework inside all cells. This framework, called
the "cytoskeleton" was demonstrated to be involved in at least
two basic functions: a) the provision of a scaffolding supporting
and organizing the cell interior, the scaffolding a structured
framework that permits cells to assume elaborate shapes, and
which organizes and guides interactions among intracellular
organelles; and b) The generation of movement, the cytoskeleton
containing elements that permit both movement of the cell as a
whole and movement of various intracellular components.
The intracellular cytoskeleton is apparently constructed
from 3 classes of protein filaments: actin filaments,
microtubules, and intermediate filaments. In some cases, a single
type of filament is responsible for a particular function; in
other cases, interactions between different filament types are
involved.
In general, the term "actin filaments" refers to specific
cytoskeletal filaments of eukaryotic cells (i.e., cells with
internal organelles), the filaments approximately 6 nanometers in
diameter and composed of actin, a globular 42 kilodalton protein.
The term "microtubules" refers to hollow cytoskeletal
tubules approximately 25 nanometers in diameter and composed of
tubulin, a globular 50 kilodalton protein. Microtubules are also
found only in eukaryotic cells.
The term "intermediate filaments" refers to eukaryotic
cytoskeletal filaments approximately 10 nanometers in diameter,
such filaments characterized by high strength and constructed
from a family of proteins exhibiting a "coiled-coil" (supercoil;
superhelix) configurational motif.
"Lamellipodia" are flattened protrusions that transiently
emerge from the surface of various eukaryotic cells during cell
crawling, the protrusions apparently supported by actin
filaments. "Filopodia" are long and thin protrusions that also
are apparently supported by actin filaments.
Two interesting bacterial pathogens are relevant in this
context, two types of bacteria that are able to invade mammalian
cells and move within the cells once they are inside:
a) The various species of Shigella are *gram-negative, rod-
shaped bacteria that cause a bloody diarrhea (dysentery) and
which are commonly found in mammalian gastrointestinal tracts.
The bacterium is taken up by an *epithelial host cell, the
bacterium internalized in a host cell vesicle, and once inside
the host cell, the bacterium breaks out of the vesicle,
multiplies, and host-cell actin filaments begin to condense
around one end of the bacterium. These actin filaments propel the
bacterium through the host cell to the host-cell membrane and
then into an adjacent host cell, where replication and movement
begins anew. The advantage to the bacterium is that by moving
within host-cells and directly from one host cell to another, the
bacterium is protected from the host immune system. Medical
textbooks usually classify Shigella as "nonmotile" because these
bacteria do not move when placed in a drop of liquid, but these
bacteria are certainly motile inside host cells, their motility
made possible by host-cell actin filaments.
b) The bacterium Listeria monocytogenes is a gram-positive
motile rod potentially more dangerous than the notorious
Salmonella group that often causes food poisoning. Listeria can
grow over a wide range of temperatures, including the
temperatures in household refrigerators. In fact, when
refrigerated, Listeria may increase in numbers more rapidly than
at higher temperatures. Listeria enters the body via engulfment
(phagocytosis) by mucosal cells (M cells). Listeria then breaks
out of the intracellular sequestering structure (the
"phagolysosome") by secreting a protein that digests the wall of
the structure, secretion of the protein apparently signaled by
the low pH inside the phagolysosome. The bacterium then
multiplies and moves from one mucosal cell to another by
polymerizing host-cell actin, with each bacterium acquiring a
microscopically visible actin "comet-tail" as it moves through
the cytoplasm to penetrate adjacent host cells.
... ... D. Pantaloni et al (3 authors at CNRS, FR) present a
review of current research on actin-based motility, the authors
making the following points:
1) The authors point out that eukaryotic cells have the
ability to organize directed movements in order to migrate, feed,
divide, or drive internal transport of materials. The direction
of movement is mediated in different ways in cells and is
associated with dissipation of energy. Molecular motors are the
archetype of protein machines that transport organelles along
microtubules and actin filaments in a unidirectional fashion,
converting the free energy derived from *ATP hydrolysis into
directed movement. Another type of directional and ATP-consuming
movement is amoeboid crawling motion mediated by the polarizing
assembly of a polymer. The most widespread example is actin-based
motility, which is driven by the assembly of actin filaments.
2) The authors point out that actin-based motility describes
a variety of cellular processes through which living cells change
shape in response to environmental signals, or extend protrusions
such as lamellipodia and filopodia, or wrap around a particle in
a phagocytic cup. Progress in understanding the mechanism by
which actin polymerization generates movement has resulted from
advances in different fields: a) genetic and *immunocytochemical
studies have identified several important actin-binding proteins
in motility; b) biochemical analysis has characterized the
function of these proteins; c) observations of actin dynamics in
motile regions of cells has provided hints about the reactions
involved; d) the bacterial pathogens Listeria monocytogenes and
Shigella flexneri, which exhibit actin-movement in the host
cytoplasm, have been instrumental in identifying essential
factors in motility and in developing biophysical assays for
movement analysis.
-----------
D. Pantaloni et al: Mechanism of actin-based motility.
(SCI 2001 292:1501)
QY: Marie-France Carlier: carlier@lebs.cnrs-gif.fr
-----------
Text Notes:
... ... *gram-negative: Most bacteria can be classified into two
types, depending on the chemistry of their outer coat, which
chemistry determines whether a bacterium will admit certain dyes
into the interior. The classification, according to the
differential staining technique, is "gram-negative" vs.
"gram-positive", named after the bacteriologist H.C. Gram
(1853-1938). Gram-positive bacteria take up a crystal violet
stain and turn purple, while gram- negative bacteria exclude the
crystal violet and counterstain instead with stains such as
safranin, eosin red, or brilliant green. As might be expected,
since the technique differentiates the outer coats of bacteria,
some antibiotics are effective against one type and not the other
type, and vice versa. In general, gram-positive bacteria have a
structure consisting of a cytoplasmic core, a plasma membrane,
and a rigid external capsule. Gram-negative bacteria, however,
have two plasma membranes between the inner cytoplasmic core and
the external capsule: the two plasma membranes are separated by a
"periplasmic space" packed with various enzymes.
... ... *epithelial: In animals, "epithelial cells" compose
the cell layers that form the interface between a tissue and the
external environment, for example, the cells of the skin, the
lining of the intestinal tract, and the lung airway passages.
... ... *ATP: (adenosine triphosphate) ATP is the most important
chemical energy source in all living cells, intimately involved
in various cell functions and cell metabolism, and an entity in
numerous cyclic chemical pathways involved in the synthesis of
components.
... ... *immunocytochemical: In general, cell chemistry
techniques (cytochemistry) using appropriately labelled antibody
preparations to detect specific cellular components. In general,
antibodies are glycoproteins capable of combining noncovalently,
reversibly, and in a specific manner with a corresponding
chemical moiety (antigen). They are produced naturally by
vertebrate immune systems to fight invasion by foreign antigens.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 27Jul01
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
BIOPHYSICS:
MEASUREMENT OF THE CRAWLING FORCE GENERATED BY AMOEBOID CELLS
The term "amoeba" (ameba) refers to a genus of single-celled
protozoa characterized by the ability to continuously change
shape by localized extension (pseudopod formation) and
retraction, with shape-change used for both locomotion and
engulfment of food. In contrast, the term "amoeboid movement"
("amoeboid cells"; "amoeba-like movement") refers to the
movements of any cell of any genus, where the movement is
effected by means of pseudopods and the shape of the cell is
subject to constant change.
The organism Dictyostelium discoideum is a special case of a
simple organism occurring in two basic forms: free individual
cells and the same cells in an organized colony. Although often
called a "cellular slime mold", D. discoideum is not a mold, nor
is it consistently slimy. The term "social amoeba" is more
accurate. When the organism is individualized, the entities are
called "myxamoebae". When they aggregate into a slug, the
organism is called a "pseudoplasmodium" or termed the "grex". The
aggregation into a unitary grex may involve tens of thousands of
individual amoebae. Experiments have demonstrated that the
directional locomotion of myxamoebae is dependent on ambient
gradients of cyclic adenosine-3',5'-monophosphate (cAMP).
"Motor proteins" are mechanico-chemical enzymes involved in
locomotion of cells or transport of materials in cells, and there
are three families of such proteins: kinesins, dyneins, and
myosins. Kinesins and dyneins are microtubule-based motor
proteins, while myosin is a microfilament-based motor protein.
The microtubules are hollow cylinders approximately 24 nanometers
in diameter, many microns in length, and consist of heterodimers
of alpha- and beta-tubulin proteins plus a variable set of other
proteins. Microfilaments are 4 to 6 nanometers in diameter,
highly variable in length, and are found in all cells with
internal membrane-bound organelles (eukaryotic cells). In
general, as mechanico-chemical enzymes, motor proteins convert
energy from hydrolysis of nucleotides to mechanical force, and
since they are involved in many important cellular events, the
molecular details are currently the focus of intensive research.
... ... Y. Fukui et al (4 authors at 3 installations, US JP)
present an analysis of the crawling force generated by cells
undergoing amoeboid locomotion, the authors making the following
points:
1) Generation of mechanical forces is essential for cell
locomotion, cell division, embryonic development, and
morphogenesis. Although the forces involved in some of these
biological activities have been measured as mechanical properties
in local regions of living cells, few measurements have been made
of the maximum ability of an entire cell to propel itself. An
example is the measurement of the maximum propulsive force of 7 x
10^(3) piconewtons generated by a swimming ciliated protozoan,
Paramecium caudatum, measured using a centrifuge microscope.
In contrast, little is known of the propulsive forces that can be
generated by any cell undergoing amoeboid movement.
2) The authors report measurement of the maximum "apparent
weight" centrifugal force against which ordinary (wild-type) and
myosin mutants of D. discoideum amoebae were able to crawl
"upward". The small mass of the amoebae required the use of a
recently developed centrifuge polarizing microscope capable of
generating fields of greater than 11,465 g (where g = Earth's
gravitational acceleration), with image resolution of better than
1 micron.
3) The authors report that D. discoideum mutant amoeba
lacking myosin ("myosin knockout mutants") stall or cease to be
able to crawl up against the imposed apparent weight at
characteristic centrifugal accelerations, so they are least able
to overcome that much external force. Those lacking the muscle
type myosin (myosin II) stall at very much lower centrifugal
acceleration.
4) The authors suggest that the mechanism of stalling, or
inability of the amoeba to maintain directional locomotion
against the centrifugal field, depends on the very high local
density of its leading pseudopod rather than on the apparent
weight felt by the whole amoeba. Even in media whose density is
greater than that of the whole amoeba, amoebae lacking myosin II
are unable to sustain the forward protrusion of the high-density
pseudopod that is apparently needed for directional amoeboid
locomotion against the external field.
5) The authors conclude: "We believe that the forward
protrusion of the leading pseudopod is not simply a phenomenon
observed in Dictyostelium and other amoebae, but that it is an
essential feature for the directional migration of cells
undergoing amoeboid locomotion in general. Once the direction of
propagation is defined by some cue (e.g., cyclic
adenosine-3',5'-monophosphate gradient for Dictyostelium amoebae)
and a pseudopod starts forming in that direction, we suggest that
the contractile force generated by the trailing cell cortex must
provide adequate support for the pseudopod to penetrate into that
direction without collapsing against the external force, whether
gravitational or a barrier presented (e.g., against leukocytes,
parasitic *protista, or migrating embryonic cells) by a tissue
layer... We postulate that the directional locomotion of an
amoeboid cell requires the contractile cortical framework to
provide the turgidity needed for the leading pseudopod to direct
the locomotion in that direction."
-----------
Y. Fukui et al: How well can an amoeba climb?
(PNAS 2000 97:10020)
QY: Yoshio Fukui: y-fukui@northwestern.edu
-----------
Text Notes:
... ... *protista: (Protoctista; protists) The term "protista"
refers to one of the phylogenetic kingdoms, this category defined
mostly by exclusion and containing all the eukaryotic nucleated
organisms that cannot be classified as animal, plant, or fungus.
Protists include protozoans, algae, kelps, slime molds, and many
obscure eukaryotes.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 13Oct00
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
CELL CYTOSKELETON: PLECTIN REGULATION OF ACTIN DYNAMICS
Plectin is a multidomain protein of large size and apparently
versatile binding properties. It has been shown to interact in
vitro with *intermediate filament proteins of various types and
to physically link intermediate filament proteins with
*microfilaments and *microtubules. In various cell types and
tissues, plectin has been localized at specific *cytoskeleton-
*plasma membrane junctional complexes (e.g., *epidermal
hemidesmosomes, *dense plaques of smooth muscle, and *focal
adhesions). Other prominent locations of plectin are *Z-lines,
intracellular junctional structures of *striated muscle, and
*intercalated disks of cardiac muscle. Consistent with its
versatile binding properties and strategic cellular localization,
various studies have shown that plectin is essential for the
mechanical integrity of skin and muscle cells.
... ... K. Andra et al now report a study of *fibroblast and
*astroglial cell cultures derived from genetically engineered
plectin-deficient mice, and the authors report the following
results: 1) Only minor changes in microtubule and intermediate
filament network organization were detectable in plectin-
deficient cells. 2) Plectin deficiency leads to an increased
number of *actin stress fibers and focal adhesion contacts. 3)
The capability of plectin-deficient cells to rearrange their
actin cytoskeleton upon short-term stimulation with soluble
ligands was compromised. 4) Plectin-deficient fibroblasts exhibit
reduced motility and increased adherence. The authors suggest
their results reveal a novel role of plectin as a regulator of
cellular processes involving actin filament dynamics that goes
beyond its proposed role in scaffolding and mechanical
stabilization of cells.
-----------
K. Andra et al (5 authors at 2 installations, AT DE)
Not just scaffolding: plectin regulates actin dynamics in
cultured cells.
(GD 1998 12:3442)
QY: Gerhard Wiche: wiche@abc.univie.ac.at
-----------
Text Notes:
... ... *intermediate filament proteins, *microfilaments,
*microtubules, *cytoskeleton: The structural framework of
eukaryotic cells (cells with nuclei and other membrane-bound
internal structures), called the "cytoskeleton", consists of an
arrangement of macromolecular structures: microtubules,
intermediate filaments, and microfilaments. The microtubules are
hollow cylinders about 24 nanometers in diameter, many microns in
length, and consist of heterodimers of alpha- and beta-tubulin
proteins plus a variable set of other proteins. They form the
scaffolding of the mitotic spindle (an important structure in
cell division), organize other cytoplasmic structures, and are
the structural core of various organelles involved in cell
movement (cilia and flagella). The intermediate filaments are
about 10 nanometers in diameter, many microns in length, are
specific for various cell types, and are not found in all cell
types. Microfilaments are 4 to 6 nanometers in diameter, highly
variable in length, and are found in all eukaryotic cells. They
are composed of a protein called "actin" and several other
accessory proteins, and they are important in cell locomotion and
in the molecular dynamics of muscle cells.
... ... *plasma membrane: In general, this refers to the surface
membrane of cells, 5 to 10 nanometers in thickness, comprising a
lipid bilayer and embedded or attached proteins.
... ... *epidermal hemidesmosomes: A desmosome is a site of
adhesion between 2 *epithelial cells, the site consisting of a
dense attachment plaque separated from a similar structure in the
other cell by a thin layer of extracellular material. A
hemidesmosome is a half desmosome occurring in certain types of
epithelial cells. The term "epidermal" refers to the superficial
epithelial portion of the skin.
... ... *epithelial cells: In animals, epithelial cells compose
the cell layers that form the interface between a tissue and the
external environment, for example, the cells of the skin, the
lining of the intestinal tract, and the lung airway passages.
... ... *dense plaques of smooth muscle: (dense bodies of smooth
muscle) Smooth muscle fibers are found in the viscera, blood
vessels, and the eye. The fibers are non-striated (smooth) and
contract more slowly than the striated fibers of the skeletal
muscle system. In general, smooth muscle is involved in
"involuntary" action, while striated muscle is involved in
"voluntary" action. The dense bodies of smooth muscle fibers are
anchoring structures to which intermediate filaments are
attached.
... ... *focal adhesions: (adhesion plaques) In general, a focal
adhesion is an intracellular attachment structure under the cell
surface where the cell attaches to the extracellular matrix in
vivo or to the substrate in cultured cells. Internal actin
filaments connect to the focal adhesion.
... ... *Z-lines: (Z-disks, intermediate disks) A cross-striation
bisecting the I band of striated muscle myofibrils (muscle
filaments) and serving as the anchoring point of actin filaments
at either end of the *sarcomere.
... ... *sarcomere: Region extending from one Z disk to the next
in skeletal (striated) muscle fibers.
... ... *striated muscle: skeletal or voluntary muscle in which
cross striations occur in the fibers as a result of regular
overlapping of thick and thin filaments. Although cardiac muscle
is not "voluntary" muscle, it is also striated in appearance.
... ... *intercalated disks: Specialized intercellular attachment
structures found in cardiac muscle.
... ... *fibroblast: A type of connective tissue cell, secreting
structural proteins (e.g., collagen) that form certain tissue
components, including the extracellular matrix.
... ... *astroglial cell: (astrocyte) Neuroglia are non-neuronal
cellular elements of the central and peripheral nervous systems,
and astroglia are a type of neuroglia. In general, neuroglia are
thought to have important metabolic functions.
... ... *actin stress fibers: In general, stress fibers are
bundles of contractile filaments resembling tiny myofibrils
(muscle fibrils). They occur in the cytoplasm of cultured
fibroblasts and are composed of actin, myosin, or other
cytoskeletal proteins.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 27Nov98
-------------------
Related Background:
RHO ENZYMES AND THE ACTIN CYTOSKELETON
... Guanosine triphosphate is a high-energy compound that
provides energy to drive other chemical reactions in biological
cells, and the G-proteins are a class of guanosine triphosphate
binding proteins that are membrane-bound and that serve as signal
transducers between the cell surface and the cell interior. The
ras-proteins are a group of G-protein enzymes that among other
things catalyze the hydrolysis of guanosine triphosphate (they
are thus guanosine triphosphatases), and the rho-proteins are a
subgroup of ras-proteins. All of these proteins have been
implicated in trans-membrane cell signaling and in the effects of
such signals on the intracellular cytoskeleton. ... ... A. Hall
(University College London, UK) reviews the mediation by the
actin cytoskeleton of a variety of essential biological functions
in eukaryotic cells: cell shape, cell polarity, cell movement,
and cell division. The author suggests that understanding the
biochemical mechanisms that control the organization of actin is
a major goal of contemporary cell biology with implications for
health and disease, and that members of the rho family of small
guanosine triphosphatases have emerged as key regulators of the
actin cytoskeleton. In addition, the interaction of these rho
enzymes with multiple target proteins apparently ensures
coordinated control of many other important cellular activities,
including gene transcription and chemotaxis.
QY: Alan Hall
(SCI 1998 23 Jan) (SW 1998 6 Feb)
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
4. ASTROPHYSICS: ON BLACK HOLES AND EVENT HORIZONS
At the end of the life of a star, when the nuclear fuel has
been exhausted and the outward pressure can no longer balance the
inward-pulling gravitational forces, a series of events occurs,
one event of which is a "blowing-off" of considerable stellar
material. If the terminal stages of star death leave a remnant
star mass greater than approximately 3 solar masses, the ultimate
gravitational collapse will produce a black hole, a relativistic
singularity. A black hole is a localized region of space from
which neither matter nor radiation can escape. The "trapping"
occurs because the requisite escape velocity, which can be
calculated from the relevant equations, exceeds the velocity of
light and is therefore unattainable. Another view of a black hole
is that it is a mass that has collapsed to such a small volume
that its gravity prevents the escape of all radiation. Since
black holes are centers of essentially infinite gravity, they
naturally accrete material from any surrounding astronomical
objects.
In this context, the term "singularity" refers to a
mathematical singularity, in general a point at which a function
takes on infinite values.
So-called "neutron stars" also derive from the terminal
stages of star death. If, following its terminal stages, the
remnant mass of a star is between 1.4 and approximately 3 solar
masses, the star will collapse into a neutron star, a body with a
radius of 10 to 15 kilometers, with a core so dense that its
component protons and electrons have merged into neutrons. The
average density of a neutron star is 10^(15) grams per cubic
centimeter, and the weight of an object on the surface of a
neutron star would be 10^(11) its weight on the surface of the
Earth. Neutron stars apparently have an outer shell of iron, but
it is iron like no Earth iron, an iron of 4 orders of magnitude
greater density.
Another possible consequence of the death of a star is the
formation of a "white dwarf star". If the remnant mass after
star-death blow-off is less than 1.44 solar masses (the
Chandrasekhar limit for a star with no hydrogen content), the
star collapses into a white dwarf. Such stars are approximately
the size of Earth, but with a mass approximately that of the Sun.
Space and time essentially have no meaning in a black hole.
The boundary of the black hole is called the "event horizon",
because any event within the boundary is invisible outside, the
invisibility resulting from the fact that no radiation can escape
to be detected. The radius of the black hole depends upon how
much matter has fallen into the region; it is called the
"Schwarzschild radius", and it is usually a few kilometers.
However, massive black holes are possible and are thought to be
the source of quasars and also the centers of certain galaxies.
Our own galaxy is believed to have a massive black hole at its
center.
Once matter has disappeared into a black hole, only three
original properties can be ascertained: the total mass, the net
electric charge, and the total angular momentum. (So-called
"black-hole emissions" are really emissions of matter immediately
outside the black hole.) Since all black holes must have mass,
there are 4 possible types of black hole, each type derived from
equations of the general theory of relativity:
a) A "Schwarzschild black hole" (first derived 1916) has no
charge and no angular momentum.
b) A "Reissner-Nordstrom" black hole (first derived 1918)
has charge but no angular momentum.
c) A "Kerr black hole" (first derived 1963) has angular
momentum but no charge.
d) A "Kerr-Newman black hole" (first derived 1965) has both
charge and angular momentum.
It is currently believed that real black holes are almost
certainly rotating and have very little electric charge, so that
the Kerr solution should be the most applicable.
The so-called "event horizon" constitutes the effective
surface of a black hole. For a non-rotating black hole it is a
spherical boundary at the Schwarzschild radius of the black hole.
For a rotating black hole, the event horizon is elliptical.
A central problem in the study of black holes has been to
discover how to distinguish them from neutron stars. In recent
years, a method has been developed, a method based on x-ray
emissions from the vicinity of each type of body. This method has
allowed the demonstration that black holes are indeed a reality.
The x-ray emissions of x-ray binary systems have been
particularly revealing. An "x-ray binary" is an x-ray emitting
binary system apparently consisting of a neutron star (or in some
cases a black hole or a white dwarf star) and a normal star. The
x-ray emission is an expected result of accretion of material by
gravity from the normal companion to the compact massive
gravitationally collapsed object.
The term "Doppler effect" is a lengthening (shift to red) of
the wavelengths of electromagnetic radiation from a source caused
by the movement of the source away from the observer, or a
shortening (shift to the blue) of wavelengths as the source moves
towards the observer.
The first indications for the actual existence of black
holes came from x-ray observations of the UHURU satellite
(launched in 1970), but black holes were predicted theoretically
60 years ago, and in fact Laplace in 1796 already noted that
light cannot leave a star when its free-fall velocity as
determined by the star's mass and radius is larger than the speed
of light as we have measured it. At the present time, if the
apparent mass of a discovered compact object exceeds the limiting
mass, and if we hold the general theory of relativity to be
valid, we say we have discovered a black hole. There are now
dozens of such objects that have been identified, many of them
super-massive objects each containing millions and billions of
solar masses and surrounded by dense stellar clusters in the
strong gravity of a black hole.
The "general theory of relativity" is the theory announced
by Albert Einstein (1879-1955) in 1915, the theory describing how
space and time are affected by the gravitational fields of
matter. General relativity was essentially developed from the
principal of equivalence between gravitational and inertial
forces, and testing the various predictions of the theory is a
central focus of much research in astrophysics.
... ... Joseph F. Dolan presents a commentary on current research
on black holes, the author making the following points:
1) The author points out that black holes are now widely
accepted as the cause of many phenomena in astrophysics, from
supermassive black holes at the center of galaxies to stellar-
mass black holes in x-ray binaries. In general, black holes are
the simplest objects that can be conceived to explain the
behavior of these systems. The author points out, however, that
there remains the theoretical possibility that these objects may
be more exotic than black holes.
2) The author points out that every black hole will have an
event horizon, so the naked point singularity determining the
existence of the black hole is forever shielded from our view.
But because any object with an event horizon must be a black
hole, detection of such a horizon would prove the existence of a
black hole.
3) One approach to detecting the event horizon of a black
hole was proposed by W.R. Stoeger in 1980, who suggested that
individual flare patches -- clumps of material whose radiative
characteristics stand out above the mean radiative flux of the
system -- would appear to emit pulsed radiation because of the
aberration of light away from the direction of Earth when the
clumps of material orbit on the far side of the black hole. The
separation between pulses should decrease as the material spirals
into the event horizon, and the peak intensity of the pulses
should also decrease as the material approaches the event horizon
because of the Doppler effect. The last visible pulse should thus
be the weakest. In contrast, if the accreting object was not a
black hole and had a solid surface, as in a neutron star, the
last pulse would be the largest pulse as the material impacted
the surface.
4) The author (Dolan) points out that some theories of
gravity that are consistent with general relativity do not
predict the existence of black holes and event horizons, and this
may provide a test of the general theory of relativity. In these
theories, collapsed objects that are not point singularities can
exist, but only radiation directed nearly radially outward can
escape from their surface. If the impact of accreting material
occurs on a part of their surface not visible from Earth, no
radiation would reach us. If the theoretical orbital topography
near compact objects in these competing theories does not predict
astronomical observations, then detection of event horizons may
be another method of confirming the validity of general
relativity.
-----------
Joseph F. Dolan: How to find a stellar black hole.
(SCI 2001 291:1079)
QY: Joseph F. Dolan: tejfd@stars.gsfc.nasa.gov
-------------------
Summary by SCIENCE-WEEK http://scienceweek.com 27Jul01
For more information: http://scienceweek.com/swfr.htm
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
5. CHEMISTRY: CHIRALITY AND CRYSTAL SYMMETRIES
In general, chirality is a property of certain asymmetric
objects such that the object and its mirror image cannot be
superimposed one on the other while both objects are restricted
to the same plane (e.g., a left- and right-handed glove). In
chemistry, chiral molecules are optically active, a phase of each
form rotating the plane of incident polarized light. The two
possible forms are called "optical isomers", and each form is
called an "enantiomer".
Suppose the surface of a growing crystal that binds a chiral
organic molecule is exposed to that chiral molecule, how does the
chirality of the organic molecule affect the growth of the
crystal? The answer to this question is of relevance not only to
the chemistry of crystals, but also to the biology of
mineralization in biological systems.
In an increasing number of laboratories, the technique of
atomic force microscopy is being used to examine interactions
on crystal surfaces at angstrom-scale distances. In general, in
atomic force microscopy, a tip is fixed to a cantilever whose
position is monitored while the tip scans a surface. The force
between the tip and the surface determines the position of the
cantilever, and when recorded in atomic resolution, one can
obtain an image that represents a map of atomic forces at the
surface. But the technique has also been used to investigate the
behavior of single atoms and molecules at surfaces, and it is
beginning to provide important insights into the physical
chemistry of adsorption phenomena.
The term "calcite" refers to the most common form of natural
calcium carbonate, CaCO(sub3), a widely distributed mineral known
for the great variety of its crystals and the aesthetic
properties of their development.
... ... C.A. Orme et al (8 authors at 4 installations, US) report
a study of calcite crystal growth in the presence of chiral amino
acids, the authors making the following points:
1) The authors point out that many living organisms contain
biominerals and composites with finely tuned properties that
reflect a remarkable level of control over the nucleation,
growth, and shape of the constituent crystals. Peptides and
proteins play an important role in achieving this control. But
the general view that organic molecules affect mineralization
through stereochemical recognition, where geometrical and
chemical constraints dictate their binding to a mineral, seems
difficult to reconcile with a mechanistic understanding, where
crystallization is controlled by thermodynamic and kinetic
factors. Indeed, traditional crystal growth models emphasize the
inhibiting effect of so-called "modifiers" on surface-step
growth, rather than stereochemical matching to newly expressed
crystal facets.
2) The authors report in situ atomic force microscope
observations and molecular modeling studies of calcite growth in
the presence of chiral amino acids, the studies reconciling the
two seemingly divergent views of such a system. The authors
report that enantiomer-specific binding of the amino acids to
those surface-step edges that offer the best geometric and
chemical fit changes the step-edge free-energies, which in turn
results in macroscopic crystal shape modifications.
3 In conclusion, the authors suggest their results indicate
that the addition of organic growth modifiers alters the energy
landscape seen by adsorbing and desorbing calcite species at the
surface of the mineral, thus changing the rates of attachment and
detachment and/or the surface configuration that is lowest in
energy. In particular, the site-specific binding of amino acid
residues to surface steps changes the step-edge free energies,
giving rise to direction-specific binding energies unique to
individual amino acid enantiomers and leading to chiral
modifications that propagate from atomic length scales to
macroscopic length scales. The authors conclude: "Although
stereochemical recognition describes the structural and chemical
relationships present during the mineralization process, our
findings indicate that the mechanism underlying crystal
modification is better understood by considering surfactant-
mediated changes to interfacial energies."
-----------
C.A. Orme et al: Formation of chiral morphologies through
selective binding of amino acids to calcite surface steps.
(NAT 2001 411:775)
QY: C.A. Orme: orme1@llnl.gov
-------------------
Summary by SCIENCE-WEEK http://scienceweek.com 27Jul01
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
MATERIALS SCIENCE:
AFFINITIES OF PEPTIDES FOR SEMICONDUCTOR SURFACES AND DIRECTED
NANOCRYSTAL ASSEMBLY
In biological systems, organic molecules exert control over
the nucleation and mineral phase of a number of inorganic
materials such as calcium carbonate and silica, and also exert
control over the assembly of crystallites and other nanoscale
building blocks into various complex structures required for
biological function. This ability to direct the assembly of
nanoscale components into controlled and sophisticated structures
has motivated intense efforts in materials science to develop
assembly methods that mimic or exploit the recognition
capabilities and interactions found in biological systems. Of
particular interest are methods that could be applied to
materials with interesting electronic or optical properties.
Biological assembly systems, however, have evolved by natural
evolution, and evolution has not selected for interactions
between biomolecules and materials of interest in electronic and
optical engineering. Nevertheless, peptides with limited
selectivity for binding to metal surfaces and metal oxide
surfaces have been successfully "selected" in the laboratory.
... ... S.R. Whaley (5 authors at 2 installations, US) now report
that *combinatorial phage-display libraries can be used to evolve
peptides that bind to a range of semiconductor surfaces with high
specificity, with binding depending on the crystallographic
orientation and composition of the surface. The phage-display
libraries used in this work were based on a combinatorial library
of random peptides containing 12 amino acids. Approximately
10^(9) different peptides were investigated. The experiments used
5 different single-crystal semiconductors. The authors suggest
that since various electronic devices contain structurally
related materials in close proximity, such peptides may find use
in the controlled placement and assembly of a variety of
practically important materials, and thus broaden the scope of
"bottom-up" fabrication approaches.
... ... In a commentary on this work, C.A. Mirkin and T.A. Taton
(Northwestern University, US) state as follows: "In principle,
[the approach of Whaley et al] applies to all materials, so they
may have discovered a way of directly interfacing biomolecules
with any inorganic structure. Moreover, different parts of the
same biomolecule could be designed to selectively recognize and
organize multiple inorganic building blocks, creating structures
with even greater spatial control. Although the work is at a
preliminary stage and practical applications are some way off,
this approach is likely to become a powerful technique for the
design of materials in years to come."
-----------
S.R. Whaley: Selection of peptides with semiconductor binding
specificity for directed nanocrystal assembly.
(NAT 2000 405:665)
QY: Angela M. Belcher: belcher@mail.utexas.edu
-----------
C.A. Mirkin and T.A. Taton: Semiconductors meet biology.
(NAT 2000 405:627)
QY: Chad A. Mirkin camirkin@chem.northwestern.edu
-----------
Text Notes:
... ... *combinatorial phage-display libraries: Bacteriophage
(phage; bacterial virus) is a virus that infects bacteria, the
virus consisting essentially of naked DNA or RNA surrounded by a
complex polyhedral shell ("capsid") composed mainly of
glycoproteins. The smallest phages are approximately 25
nanometers in diameter. In general, a chemical "combinatorial
library" is any system capable of producing a large number of
different substances from a small number of building blocks. In
this context, a "fusion protein" is essentially a protein
expression product resulting from the laboratory fusion of two
genes. In general, a "phage-display library" is a gene library
encoding fusion proteins consisting of a foreign polypeptide
sequence and a coat protein of a particular phage. When cloned,
the engineered phage displays on its surface the foreign
polypeptide sequence fused with the phage coat protein, with each
phage clone randomly expressing a single polypeptide sequence. In
the work discussed here, sequences are selected ("evolved") for a
particular binding characteristic by serially allowing the phages
expressing the various sequences to bind to substrate, separating
phages that bind, allowing selected phages to replicate in their
natural bacterial host, and at exposure to substrate invoking
increasingly stringent binding requirements for selection. After
a number of passes, phage with strong binding properties to the
substrate have been evolved. The genomes (in this case, DNA) of
these strong-binding phages are then sequenced, and the
corresponding fusion-protein foreign peptide sequences
identified.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 18Aug00
For more information: http://scienceweek.com/swfr.htm
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6. EARTH SCIENCES:
THE ANCIENT CARBON CYCLE AND GLOBAL BIODIVERSITY
In its most general outline, the term "carbon cycle" in
the Earth sciences refers to the movement of carbon from an
inorganic state to an organic state and then back to an inorganic
state. In contrast, some researchers define the term "carbon
cycle" more specifically as the movement of carbon from
atmosphere to biosphere to atmosphere. But this latter definition
essentially deemphasizes the contributions of the crust and upper
mantle (lithosphere) and aquatic domains (hydrosphere) to the
carbon cycle. An even more restricted definition of the term
considers only the biosphere itself, with "carbon cycle" defined
as the conversion of carbon dioxide by plants to organic
compounds, the consumption of these organic compounds by plants
and animals, and the return of carbon to the biosphere in the
form of inorganic compounds by the processes of metabolism and
decay.
In this report, we focus on the carbon cycle as the general
cycle of carbon movements from inorganic to organic to inorganic
forms, with contributions from atmosphere, biosphere,
hydrosphere, and lithosphere.
Both biotic factors and abiotic factors such as volcanic
activity and rock weathering are involved in the carbon cycle.
The major carbon-fixation process is photosynthesis by plants,
*phytoplankton, marine and fresh-water algae, and *cyanobacteria,
with the incorporation of carbon dioxide from the atmosphere and
oceans into organic carbon-containing compounds, coupled with the
release of oxygen. All organisms break down organic compounds in
metabolic processes and release carbon dioxide, thus resulting in
the cycling of carbon. Concerning carbon fixation, approximately
75 billion metric tons of carbon a year are bound into carbon
compounds by photosynthesis. Organisms that feed on plants, and
organisms that feed on these organisms, use the organic products
of photosynthesis for their own metabolism and release carbon
dioxide into the atmosphere and oceans. The oceans and the
atmosphere have carbon sinks of approximately 500 billion to 700
billion metric tons respectively. Other large carbon reservoirs
exist in the Earth's crust as coil and oil, and also in limestone
rocks and as peat in wetlands.
... ... Daniel H. Rothman (Massachusetts Institute of Technology,
US) presents an analysis of the correlation between global
biodiversity and the carbon cycle, the author making the
following points:
1) The author points out that partly as a result of the
episodic nature of sedimentary processes, studies of the Earth's
biologic, geologic, and climatic history have typically focused
on isolated extreme events such as mass extinctions or anomalous
excursions of stable chemical isotope records. Although the
importance of unusual events may be nearly self-evident, a
different and potentially powerful approach is to consider not
the uniqueness of events but that which is common to them all.
With this approach, one may learn how fundamental invariants --
e.g., the conserved mass of certain chemical species -- manifest
themselves over geologic time.
2) The author focuses on biologic aspects of the carbon
cycle during the past 570 million years (Phanerozoic time-frame),
with analysis of two types of records: a) paleontological data
for the diversity of marine animals and terrestrial plant life;
and b) the sedimentary record of carbon isotope fractionation
between carbon buried in organic form and carbon buried as
carbonates.
3) The author reports he finds an unexpected significant
correlation between the paleontological and geochemical records
for the last 400 million years, and he provides evidence that
this correlation reflects the fluctuation of carbon dioxide
levels in the atmosphere and oceans. The author suggests his
analysis demonstrates not only that the diversification of life
appears to have depressed carbon dioxide levels, but also how
deep this depression appears to have been.
4) The author points out that the revealed correlation can
be deduced from the assumption that increasing plant diversity
led to increasing chemical weathering of rocks and therefore to
an increasing flux of carbon from the atmosphere to rocks, and to
a flux of nutrients from the continents to the oceans. The carbon
dioxide concentration dependence of photosynthetic carbon isotope
fractionation then indicates that the diversification of land
plants led to decreasing carbon dioxide levels, while the
diversification of marine animals derived from increasing
nutrient availability. Under the explicit assumption that global
biodiversity grows with global biomass, the conservation of
carbon demonstrates that the long-term fluctuations of carbon
dioxide levels were dominated by complimentary changes in the
biological and fluid reservoirs of carbon, while the much larger
geological reservoir remained relatively constant in size. As a
consequence, the paleontological record of biodiversity provides
an indirect estimate of the fluctuations of ancient carbon
dioxide levels.
-----------
Daniel H. Rothman: Global biodiversity and the ancient carbon
cycle.
(PNAS 2001 98:4305)
QY: Daniel H. Rothman: dan@segovia.mit.edu
-----------
Text Notes:
... ... *phytoplankton: Small, usually microscopic, aquatic
plants capable of photosynthesis; e.g., unicellular algae.
Phytoplankton and plankton are not equivalent. The term
"plankton" is a general designation for various drifting
microscopic aquatic organisms in the upper regions of the oceans,
both photosynthetic and non-photosynthetic.
... ... *cyanobacteria: A phylum of bacteria characterized by
blue-green (cyan) photosynthetic pigments, abundant in a variety
of habitats, particularly in fresh water and soil. Cyanobacteria
are responsible for generating a large portion of the free oxygen
in the Earth's atmosphere. They apparently produced stromatolite
limestone deposits, as well as the bulk of modern petroleum
deposits. (Stromatolites are laminated calcareous microbial
fossil deposits formed principally by cyanobacteria and algae.)
-------------------
Summary by SCIENCE-WEEK http://scienceweek.com 27Jul01
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
GEOCHEMISTRY: ON RIVER CARBON AND THE CARBON CYCLE
... In detail, there are several pathways from biospheric organic
carbon to atmospheric inorganic carbon, one of which, of great
importance, is the movement of organic carbon into the
hydrosphere, principally via rivers that empty into oceans, with
oceanic dissolved organic carbon a reservoir for movement of
organic carbon to an atmospheric inorganic state. Concerning the
transfer of dissolved organic carbon from rivers to oceans, there
are puzzles that have not yet been solved.
... ... Wolfgang Ludwig (University of Perpignon, FR) presents a
commentary on new data concerning river carbon (P.A. Raymond and
J.E. Bauer: Nature 25 Jan 01 409:497), the author (Ludwig) making
the following points:
1) The author points out that dissolved organic carbon in
the oceans is one of the largest reservoirs in the global carbon
cycle, this reservoir comparable in size to all of the carbon in
terrestrial plants, or to all of the carbon in form of carbon
dioxide in the atmosphere. The input of terrestrial organic
carbon from rivers, the main source of most constituents of sea
water, could fill the oceanic reservoir in only a few thousand
years, which (according to radiocarbon dating) is apparently the
average age of oceanic organic carbon. But although there ought
to be a great amount of terrestrial-derived organic carbon in the
oceans, geochemical studies indicate there is apparently very
little, and the fate of river-transported carbon ("riverine
carbon") once it enters the oceans is unclear.
2) Almost all of the organic carbon on Earth is created via
photosynthesis, whether on land or in water, but on land the
process produces characteristic markers, so that terrestrial
carbon should be traceable after it has entered the oceans. For
example, many land plants synthesize certain compounds, such as
*lignin or *tannin, which are absent in marine *phytoplankton. In
principle, therefore, detecting these biomarkers in the oceans
can reveal if carbon had a terrestrial origin. The other widely
used method involves measuring the ratio between the two stable
carbon isotopes, C-13 and C-12, in the bulk organic matter. Most
land plants produce carbon that is more depleted in C-13 than
carbon produced by marine phytoplankton, which results in higher
isotopic ratios in marine than in terrestrial carbon.
3) Raymond and Bauer (2001) now present an analysis of
organic materials in four rivers (Amazon [BR], Hudson [New York,
US], (York [Virginia, US], Parker [Massachusetts, US] by
radiocarbon dating (carbon-14, carbon-13 measurements), and they
report the organic carbon in these rivers is up to several
thousand years old [*Note #1]. This is in sharp contrast with the
general belief that most of the organic carbon in rivers should
be relatively "fresh". The particulate organic carbon (i.e., the
fraction retained on a filter) was especially old (C-14-
depleted). From these results, and laboratory evidence that
suggests selective degradation of young (C-14-rich) dissolved
organic carbon over the residence times of river and coastal
waters, Raymond and Bauer conclude that pre-aging and degradation
may alter significantly the structure, distribution, and
quantities of terrestrial organic matter before its delivery to
the oceans. The implication is that the absence of riverine
carbon in the oceans is only apparent and due to the fact that we
have not been able to distinguish riverine carbon from marine-
generated carbon.
-----------
Wolfgang Ludwig: The age of river carbon.
(NAT 2001 409:466)
QY: Wolfgang Ludwig: ludwig@univ-perp.fr
-----------
Text Notes:
... ... *Note #1: Carbon-14 dating depends on the decay of
carbon-14 to nitrogen. Carbon-14 is continually formed in nature
by the interaction of neutrons with nitrogen-14 in the Earth's
atmosphere, the required neutrons produced by cosmic rays
interacting with the atmosphere. The carbon-14 from this reaction
is converted to carbon dioxide by reaction with atmospheric
oxygen and mixed and uniformly distributed with the atmospheric
carbon dioxide containing stable carbon-12. Since living
organisms use atmospheric carbon dioxide either directly or
indirectly, their systems contain the constant ratio of carbon-12
to carbon-14 that exists in the atmosphere. Death of an organism
terminates the equilibrium process: no fresh carbon dioxide is
added to the dead substance, and the carbon-14 present in the
dead substance decays with a half-life of 5730 years, while
carbon-12 in the dead substance remains what it was at death.
Measurement of the carbon-14 activity at a given time thus allows
calculation of the time elapsed after the death of the organism.
... ... *lignin: A complex organic polymer and major component of
wood.
... ... *tannin: A complex astringent substance occurring widely
in plants, particularly in leaves, unripe fruits, and tree bark.
... ... *phytoplankton: See main report.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 23Feb01
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
ON THE CHEMISTRY AND BIOLOGY OF THE OCEANS
The combination of vast areas of liquid water on its surface
together with a high concentration of free molecular oxygen in
its atmosphere is unique to Earth in this solar system.
Calculations based on *ultraviolet absorption cross sections
indicate that whereas direct photolysis of water could have
produced small amounts of O(sub2), almost all of the gas was
produced by biological systems through the photobiologically
catalyzed oxidation of the liquid.
... ... Falkowski et al (3 authors at 3 installations, US DE)
review the controls and feedbacks between oceanic *phytoplankton
and geochemical processes with an emphasis on factors that cause
a deviation from the steady state. The authors make the following
points:
1) Changes in oceanic primary production, linked to changes
in the network of global biogeochemical cycles, have profoundly
influenced the geochemistry of Earth for over 3 billion years.
2) In the contemporary ocean, photosynthetic *carbon
fixation by marine phytoplankton leads to the formation of
approximately 45 gigatons of organic carbon per year, of which 16
gigatons are exported to the ocean interior.
3) Changes in the magnitude of total and export production
can strongly influence atmospheric CO(sub2) levels (and hence
climate) on geological time scales, as well as set upper bounds
for sustainable fisheries harvest.
4) Because the average turnover time of phytoplankton carbon
in the ocean is on the order of a week or less, total and export
production are extremely sensitive to external forcing, and
consequently are seldom in steady state.
5) Elucidating the biogeochemical controls and feedbacks on
primary production is essential to understanding how oceanic
biota responded to and affected natural climate variability in
the geological past, and to understanding how oceanic biota will
respond in the coming decades to changes influenced by human
activities.
-----------
QY: Paul G. Falkowski: falko@IMCS.rutgers.edu
(SCI 1998 281:200) (SW 31 Jul 98)
-------------------
Related Background:
... ... *ultraviolet absorption cross sections: The ratios of the
amount of energy removed from incident UV by absorption to the
total energy of incident UV. In other words, in this context, a
measure of how much energy is (was) actually available for direct
photolysis of liquid water.
... ... *phytoplankton: See main report.
... ... *carbon fixation: Refers to the process of converting the
carbon in a substance into a form usable by an organism. For
example, the conversion of the carbon in CO(sub2) into organic
carbon (the carbon in organic compounds).
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 31Jul98
For more information: http://scienceweek.com/swfr.htm
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7. IN FOCUS: ON ESTABLISHED AUTHORITY IN SCIENCE
"Lord Kelvin [William Thomson (1824-1907)] was such a brilliant
scientist that he became perhaps the principal authority in
matters of the physical universe. He applied the known laws of
heat dissipation to the problem of the Earth's temperature. From
the known temperature increase with distance below the surface,
he deduced that the Earth was not nearly old enough for Darwin's
estimates of the duration of certain geological processes or for
his theory of the origin of the species to operate. He [Kelvin]
also estimated the possible active lifetime of the Sun from its
energy output, assuming that the energy source was gravitational
infall. The result was more or less consistent with his
conclusions about the age of the Earth. Late in Kelvin's life,
radiochemists confirmed the antiquity of the Earth proposed
previously by geologists. Kelvin remained adamant that while the
Earth might perhaps be 20 million years old, and just possibly an
order of magnitude older, it could not possibly be billions of
years old. What he had not reckoned with, of course, was the
steady evolution of heat from the radioactive elements deep
within the Earth or the nuclear reactions powering the Sun.
Kelvin also disputed Maxwell's theory of the electromagnetic
nature of light, and proclaimed that heavier-than-air aircraft
were impossible. This is not to disparage his genius and his
enormous accomplishments, or even his genuine modesty. Even such
giants can err, and that, itself, is a lesson worth learning."
-----------
Lawrence S. Bartell: JCE 2001 78:1059
-------------------
SCIENCE-WEEK http://scienceweek.com 27Jul01
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8. FROM THE SCIENCEWEEK ARCHIVE:
HISTORY OF SCIENCE:
THE 18TH CENTURY WOMEN SCIENTISTS OF BOLOGNA
In the history of Europe, the 18th century is known as the Age of
Reason (the Enlightenment), a period when the educated upper
classes doted on rational thought and the beginnings of modern
science. This was an era that produced a great and influential
flowering of human thought, but in all the countries in Europe
except one, women were forbidden to study and lecture in
universities, and women had hardly any participation in the
sciences. The one exception was Italy.
... ... M. Cieslak-Golonka and B. Morten (2 installations, PL IT)
present an account of the 18th century women scientists of the
University of Bologna, the authors making the following points:
1) The authors point out that in the 18th century, the
education of Italian women from the higher social classes was
exactly the same as that of men, the special attitude toward the
education of women apparently stemming from the influence of
ancient Rome. In the universities of Salerno, Bologna, Padua, and
elsewhere in Italy, women competed on an equal footing with men,
particularly in the fields of literature, natural sciences, and
medicine.
2) The University of Bologna, founded in 1088, was a place
where the students elected both the faculty and the rector, and a
university distinguished by the unusual number of women
scientists it graduated and hired during the 18th century. At the
University of Bologna, intellectually gifted women from the upper
classes, and occasionally from the lower classes, had access to a
level of education not seen in most Western nations until the
20th century. Some of these women flourished as scholars and
scientists:
... ... a) Laura Bassi (1711-1778): Bassi was the pioneer among
the women professors of the University of Bologna. She became the
first woman to earn a doctor of philosophy degree, the
university's first female professor, and the first woman to
occupy a chair in physics. She focused on mechanics, hydraulics,
and anatomy, and she was particularly intrigued with the works of
Newton (1642-1727). She conducted physics tutorials and
experiments for her students throughout her academic career, and
for over 30 years, she offered an annual public lecture on
experimental physics. Her academic duties were combined with an
active family life: in 1738 she married a physician, and together
they had 12 children.
... ... b) Anna Morandi Manzolini (1716-1774): Morandi was
considered to be the finest practitioner of artistic anatomy of
her time. She is frequently cited as the first to make models of
internal organs, and her work showing details of the abdominal
cavity and the uterus gained her special notice. She produced a
model of the ear that could be taken apart to be used in the
instruction of medical students. At the present time, in the
Anatomical Museum at the University of Bologna, one can still see
Morandi's wax models, including her self-portrait.
... ... c) Maria Gaetana Agnesi (1718-1799): Agnesi was a
brilliant linguist and a talented mathematician, the eldest of 21
children born to Pietro Agnesi, a professor of mathematics at the
University of Bologna. Her most famous work, in two volumes, was
_Analytical Institutions_, which for the first time provided a
synthesis of many different branches of mathematics. The first
volume focuses on algebra and its applications in geometry. One
chapter describes a curve that has become well-known as "Agnesi's
curl", or "versiera della Agnesi", which has become mistranslated
to "the witch of Agnesi". This curve, expressed by the equation
x^(2)y = a^(2)[a-y], was first described by Fermat (1601-1665).
The second volume of Agnesi's _Analytical Institutions_ contains
an analysis of differential and integral calculus. Agnesi was
admitted into the Academy of Sciences in Bologna, and in 1750 she
was offered an honorary chair at the University of Bologna in
Mathematics and Natural Philosophy.
... ... d) Maria Dalle Donne (1778-1842): Dalle Donne was born to
a peasant family in a small village on the outskirts of Bologna.
Her talents were recognized early, and she was encouraged to
study medicine. In 1799, she presented her dissertation and took
the examination that made her the first female doctorate in
medicine. She passed the examination with highest honors (maxima
cum laude). In 1800, Dalle Donne published three important
scientific papers. The first paper, on anatomy and physiology,
was a review and commentary on work previously done on female
reproduction and fertility, fetal malformations, and blood
circulation in the uterus. The second paper suggested for the
first time that diseases be classified on the basis of symptoms.
The third paper focused on midwifery and the care of newborns. In
1829, Dalle Donne became only the second woman, after Laura
Bassi, to become a member of the prestigious Ordine de
Benedettini Academici Pensionati, in which she was awarded the
title of "Academic". In 1832, Dalle Donne became Director of the
Department of Midwifery at the University of Bologna.
-----------
M. Cieslak-Golonka and B. Morten: The women scientists of
Bologna.
(AS 2000 88:68)
QY: Maria Cieslak-Golonka: golonka@ichn.ch.pwr.wroc.pl
-------------------
Summary by SCIENCE-WEEK http://scienceweek.com 31Mar00
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9. SOURCES:
AGP: Archives of General Psychiatry
APL: Applied Physics Letters
AS: American Scientist
CEN: Chemical & Engineering News
GD: Genes & Development
GR: Genome Research
ICAR: Icarus
JAMA: Journal of the American Medical Association
JCE: Journal of Chemical Education
NAT: Nature
NEJM: New England Journal of Medicine
NYT: New York Times
PNAS: Proceedings of the National Academy of Sciences
PRL: Physical Review Letters
PT: Physics Today
SA: Scientific American
SCI: Science
SW: ScienceWeek
TB: The Biochemist
TS: The Scientist
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