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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.
March 3, 2000 -- Vol. 4 Number 9
-----------------------------------------------
Scientifically speaking, a butterfly is at least as
mysterious as a superstring. When something ceases
to be mysterious, it ceases to be of absorbing concern
to scientists. Almost all the things scientists think
and dream about are mysterious.
-- Freeman J. Dyson
-----------------------------------------------
Contents of This Issue:
1. Science Policy:
Gender Discrimination in European Science
A recent report suggests the existence of considerable bias
against women in European science, and provides evidence of a
scarcity of women in national science academies worldwide.
2. Medical Biology:
Isolation of West Nile Virus in US Mosquitoes and Birds
Two independent research groups provide evidence that the viral
pathogen in the 1999 New York City encephalitis outbreak was West
Nile virus probably transmitted from birds to humans via
mosquitoes.
3. Public Health Sciences:
Food Safety 1900-1999
During the 20th century, a series of government public health
measures and improved public education led to a marked reduction
in the incidence of certain serious diseases caused by foodborne
pathogens and nutritional deficiencies.
4. Molecular Biology:
Synexpression Gene Groups in Eukaryotes
Genes whose expression is associated in space or time reflect the
functional compartmentalization of the eukaryote genome and have
a striking parallel to the prokaryote operon.
5. Physics:
On Statistical Physics and Its Applications
Statistical physics remains the central scaffold of modern
physics and is currently the most useful approach to phenomena
based on the collective behavior of many-body systems,
particularly phenomena involving transitions between states of
matter in both physical and biological domains.
6. Physics:
First Molecules in a Bose-Einstein Condensate
Using a system of ultracold atoms essentially at rest, a new
experimental effort provides the first observation of molecule
formation in a Bose-Einstein condensate, and a method for the
ultraprecise measurement of molecular binding energies.
In Focus: On Radiocarbon Dating
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1. SCIENCE POLICY:
GENDER DISCRIMINATION IN EUROPEAN SCIENCE
The first systematic attempt to gather statistics on European
women in science has apparently revealed serious
underrepresentation of women and discriminatory employment
practices. The report, compiled by the European Technology
Assessment Network states that the number of women in senior
scientific positions remains low despite the different cultures
and research systems in the member states of the European Union.
In virtually all the European states, women constitute less than
15 percent of full university professors. The report states that
data on membership of the world's national scientific academies
reveal an extraordinary undemocratic picture of the institutions
that shape science policy. The following is a tabulation of the
percentage of women members of national scientific academies:
-------------------
Turkey 14.6
Iceland 12.3
Norway 11.1
Finland 8.0
New Zealand 7.3
Ireland 6.4
Croatia 6.3
US 6.2
Sweden 5.5
Canada 5.3
China 5.1
Scotland 4.5
Austria 4.2
Germany 4.0
France 3.6
UK 3.6
Denmark 3.5
Hungary 3.3
India 3.1
Spain 2.7
Italy 2.6
Ukraine 2.6
Poland 2.5
Russia 1.7
Japan 0.8
Netherlands 0.4
-------------------
Commenting on the report, Agnes Wold (Goteborg University, SE),
author of a report on gender bias in Swedish science, states:
"Scientists have a special talent -- like the military -- for
keeping out women."
-----------
Natasha Loder: Gender discrimination "undermines science".
(Nature 25 Nov 99 402:337)
QY: Natasha Loder [editors@nature.com]
-------------------
Related Background:
M.I.T ACKNOWLEDGES BIAS AGAINST FEMALE SCIENCE PROFESSORS
One would suppose that in science, an enterprise that emphasizes
rationality, the general attitude would be to maximize the
utilization of scientific talent irrespective of gender. But as
in other areas of human endeavor, suppositions are not realities.
In what has been called an extraordinary admission, top officials
at the Massachusetts Institute of Technology, the most
prestigious science and engineering university in the US, have
issued a report acknowledging that female professors at the
institution suffer from pervasive discrimination. The report
concerns discrimination against women in the M.I.T. School of
Science, and documents a pattern of discrimination in areas
including employment, awards, promotions, inclusion in important
committees, and allocation of resources such as laboratory space
and research funds. At the present time, the M.I.T. School of
Science faculty consists of 8 percent women, and this percentage
has remained virtually unchanged for approximately 20 years. In
February 1999, the American Association of University Professors
issued a report indicating that although the percentage of
faculty women in general in the US grew to 34 percent from 23
percent since 1975, the salary gap for male and female professors
actually widened during this period. In the US, women now
comprise a substantial portion of undergraduate science students,
but only a minor portion of science faculties. Concerning gender
discrimination, Charles M. Vest, the president of M.I.T., is
quoted as saying, "I have always believed that contemporary
gender discrimination within universities is part reality and
part perception. True, but I now understand that reality is by
far the greater part of the balance."
-----------
Carey Goldberg: M.I.T. acknowledges bias against female
professors.
(The New York Times 23 Mar 98)
-------------------
Summary by SCIENCE-WEEK [http://scienceweek.com] 2Apr99
-------------------
Related Background:
WOMEN ON CHEMISTRY FACULTIES: EVIDENCE OF SLOW PROGRESS
Data compiled by the American Chemical Society for 1996, the most
recent year for which data are available, indicate that in the US
30.7 percent of PhDs in chemistry were awarded to women, up from
12.5 percent in 1976. But on chemistry faculties at the major US
research universities, women are barely represented. Here are
figures for some of the major US academic research installations:
-----
(Total tenure or tenure-track chemistry faculty/Women on tenure
or tenure-track chemistry faculty 1996-1997)
University of California Berkeley 53/5
California Institute of Technology 25/3
Harvard University 20/1
Stanford University 21/1
Massachusetts Institute of Technology 31/2
Cornell University 30/2
Columbia University 19/1
University of Illinois Urbana-Champaign 47/2
University of Wisconsin Madison 39/2
University of Chicago 24/1
University of California Los Angeles 37/6
-----
QY: Mairin B. Brennan
(Chem. & Eng. News 20 Jul 98) (Science-Week 7 Aug 98)
-------------------
Related Background:
US WOMEN IN SCIENCE LESS ACCEPTED THAN WOMEN IN BUSINESS
A meeting last month at the New York Academy of Sciences (US)
focused on the past 25 years of progress for women scientists and
engineers in the US. The apparent consensus at the conference was
that the climate for women in both industry and government has
improved much faster than in academia, with the changes in
industry mostly due to a drive by industry for diversity. The
Motorola Corporation (US) now has 43 women vice-presidents. In
1996, women were 51% of the US population, 46% of the labor
force, but only 22% of scientists and engineers. Nobel Laureate
Gertrude Elion advised women in science to follow Farragut's
order: "Damn the torpedoes -- full speed ahead."
(Chem. & Eng. News 6 Apr 98) (Science-Week 17 Apr 98)
-------------------
Related Background:
WOMEN NOW SUBSTANTIAL PORTION OF ALL NEW US CHEMISTS
The latest survey of the American Chemical Society, covering
chemists and chemical engineers who graduated between July 1996
and June 1997, shows the following statistics for new women
graduates (percentage of total graduates who are women):
Chemistry Bachelor's Degree: 48.2%
Chemistry Master's Degree: 46.2%
Chemistry PhD Degree: 31.6
Chemical Engineering Bachelor's Degree: 35.4%
Chemical Engineering Master's Degree: 29.3%
Chemical Engineering PhD Degree: 22.9%
-----------
QY: Michael Heylin
(Chem. & Eng. News 9 Mar 98) (Science-Week 20 Mar 98)
-------------------
Related Background:
SWEDISH STUDY SHOWS SEX BIAS AFFECTS SCIENCE EMPLOYMENT
Two female Swedish scientists have published a study which
indicates that women must publish more often than men to compete
successfully for scientific jobs in Sweden. This is the first
scientific study of sex discrimination in the awarding of a
large number of research positions, and was financed by a
Swedish government grant. The researchers, Christine Wenneras
and Agnes Wold, are both from the University of Goteborg. The
journal Nature, which published the study, states that
the "results severely undermine the credibility of the
peer-review system, not just in Sweden but elsewhere in the
world.
(Nature 22 May 97) (Science-Week 22 May 97)
-------------------
Related Background:
IN FOCUS: ON WOMEN IN PHYSICS
"Forty-nine years old; strong-featured face, brooding eyes, a
mass of dark sexy hair she tosses about like a forties movie
vamp, the walk seductive and knowing, the mouth sullen and
grievance-collecting in repose, then surprisingly girlish in
laughter when the eyes fill with a sudden shimmering light. Alma
Norovsky is a theoretical physicist at a university renowned for
its devotion to the life of the mind. Of her colleagues, Alma
says drily: 'They're very theoretical. People are always asking
me how women are treated here. "Women?" I answer. "They're a
theoretical concept."'... Divorced four years from the physicist
husband she married in graduate school, on her own for the first
time in her life, in love with her new independence and happy to
be working here, Alma nevertheless sighs. 'How do you work in
physics, or live among academic liberal men, and not explode all
day long every day? Once in a while I'm able to control myself...
Last year at a conference I was standing with a group of
physicists, all men, and I was introduced to a new member of the
group. He said, "You're the first good-looking physicist I've
ever met." I casually indicated the man standing beside me and
said, "Oh, that's not true. You know Richard here. He's good-
looking, and he's a physicist." They all looked startled, and
then some of them nodded their heads appreciatively. I was proud
of myself then, but usually it's awful. Still. Always. At every
dinner table, in the office, the constant little indications that
you don't really exist. You've got to remind them that you're a
thinking, working being just like themselves all the time. It's
wearing.'"
-----------
Vivian Gornick: _Women in Science: Portraits from a World in
Transition_. (Simon & Schuster, New York 1983)
(Science-Week 15 Oct 99)
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2. MEDICAL BIOLOGY:
ISOLATION OF WEST NILE VIRUS IN US MOSQUITOES AND BIRDS
In a medical context, an "inflammation" is a complex
pathological process occurring in a tissue in response to injury
or invasion by various agents. In general, the term
"encephalitis" refers to any inflammatory disease of the brain,
and "viral encephalitis" is such a disease caused by direct viral
invasion.
The term "arbovirus" is a general designation for any
ARthropod-BOrne virus, with more than 250 genomically distinct
arbovirus entities ("species") currently recognized, of which at
least 80 distinct arboviruses cause diseases in humans.
Arboviruses are transmitted among vertebrates by biting
arthropods, primarily mosquitoes and ticks. Birds are often the
sources of infection for mosquitoes, which then transmit the
infection to domestic animals and humans. Flaviviruses are a
family of 70 genomically different arboviruses 45 to 60
nanometers in diameter, the viruses with a single-stranded RNA
genome and a viral envelope containing lipid and two
glycoproteins. Flaviviruses are usually transmitted between
vertebrates by mosquitoes and ticks, and many of these viruses
have worldwide distribution.
West Nile Fever is an acute febrile disease that occurs in
the Middle East, tropical and subtropical Africa, and southeast
Asia. The disease is usually mild, but sometimes it is fatal, and
it is caused by a flavivirus.
In late August and early September 1999, New York City and
surrounding areas experienced an outbreak of human encephalitis
consistent with an arboviral etiology. Two independent research
groups have now provided evidence that the viral pathogen in this
outbreak was West Nile virus probably transmitted from birds to
humans via mosquitoes.
... ... R.S. Lanciotti et al (24 authors at 8 installations, US
FR AU IL) point out that the New York encephalitis outbreak was
concurrent with extensive mortality in crows (species: Corvus) as
well as the deaths of several exotic birds at a zoological park
in the same area. Complete genome sequencing by the authors of a
flavivirus isolated from the brain of a dead Chilean flamingo
(Phoenicopterus chilensis), together with partial sequence
analysis of viral envelope glycoprotein genes amplified from
several other species (including mosquitoes and two fatal human
cases), revealed the West Nile virus was responsible for the 1999
human disease outbreak in New York City. The authors also make
the following points:
1) The northeastern US outbreak is the first documented
incidence of the West Nile virus in the Western Hemisphere. The
recent epidemic of West Nile virus in New York City is
unprecedented and underscores the ease with which pathogens can
move among the population centers of the world.
2) It is not yet known how the virus was introduced, nor how
long it has been in the US. The extent of its geographic
distribution remains a mystery, as does the long-term impact it
may have on human and animal health. The authors suggest the West
Nile virus could have entered the Western Hemisphere through a
number of mechanisms, including travel by infected humans,
importation of illegal birds or other domestic pets, or
unintentional introduction of virus-infected ticks or mosquitoes.
3) The authors conclude: "Because it cannot be predicted
whether the West Nile virus will reappear in the year 2000
transmission season, all components of the public health system
must be prepared with rapid surveillance and clinical detection
systems in place."
... ... In a contiguous report in the same journal, J.F. Anderson
et al (8 authors at 3 installations, US) report they isolated
West Nile virus from 2 species of mosquitoes (Culex pipiens and
Aedes vexans), and from brain tissues of 28 American crows
(Corvus brachyrhynchos), and one Cooper's hawk (Accipiter
cooperii) in Connecticut. The authors conclude: "Our isolation of
West Nile virus from mosquitoes and birds conclusively documented
the presence of this virus in Connecticut during September and
October 1999. If established in North America, West Nile virus
likely will continue to have severe effects on human health and
on avian populations, such as American crows and *raptors, which
heretofore have never been exposed to this virus."
-----------
R.S. Lanciotti et al: Origin of the West Nile virus responsible
for an outbreak of encephalitis in the northeastern United
States.
(Science 17 Dec 99 286:2333)
QY: R.S. Lanciotti [rsl2@cdc.gov]
-----------
J.F. Anderson et al: Isolation of West Nile virus from
mosquitoes, crows, and a Cooper's hawk in Connecticut.
(Science 17 Dec 99 286:2331)
QY: John F. Anderson [john.f.anderson@po.state.ct.us]
-----------
Text Notes:
... ... *raptors: In general, the term "raptor" refers to any
species adapted for seizing prey.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 3Mar00
[For more information: http://scienceweek.com/search/search.htm]
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3. PUBLIC HEALTH SCIENCES:
FOOD SAFETY 1900-1999
During the early 20th century, contaminated food, milk, and water
caused many foodborne infections, including typhoid fever,
tuberculosis, botulism, and scarlet fever. In the US in 1906, the
writer Upton Sinclair (1878-1968), in his novel _The Jungle_,
described the unwholesome working environment in the Chicago
meat-packing industry and the unsanitary conditions under which
food was produced. Public awareness dramatically increased and
led to the passage of the US Pure Food and Drug Act (1906). Long
before vaccines and antibiotics, identification of the sources
and characteristics of foodborne diseases resulted in the control
of these diseases by handwashing, sanitation, refrigeration,
pasteurization, and pesticide application.
... ... A recent US government report reviews the history of food
safety in the US during the 20th century, the report making the
following points:
1) In 1900, the US incidence of typhoid fever was
approximately 100 per 100,000 population; by 1920, it had
decreased to 33.8; and by 1950, it had decreased to 1.7.
2) During the 1940s, studies of autopsied muscle samples
demonstrated that 16 percent of persons in the US had
*trichinosis. 300-400 cases were diagnosed every year, and 10 to
20 deaths occurred. From 1991 to 1996, 3 deaths and an average of
38 cases per year were reported.
3) Nutritional sciences were in their infancy in 1900, and
the concept that minerals and vitamins were necessary to prevent
diseases caused by dietary deficiencies was unknown. Recurring
nutritional deficiency diseases, including *rickets, *scurvy,
*beri-beri, and *pellagra were thought to be infectious diseases.
By 1900, biochemists and physiologists had identified protein,
fat, and carbohydrates as the basic nutrients in food. By 1916,
new data had led to the discovery that food contained vitamins
("vital amines") and that the lack of vitamins could cause
disease [*Note #1]. These scientific discoveries and the
resultant public health policies, such as food fortification
programs, led to substantial reductions in nutritional deficiency
diseases during the first half of the 20th century. The focus in
the second half of the 20th century shifted from disease
prevention to control of chronic conditions such as
cardiovascular disease and obesity.
4) Perishable foods contain nutrients required for the
reproduction of pathogenic bacteria, and at room temperature
these organisms can multiply quickly in sufficient numbers to
cause illness. In 1900, consumers kept food fresh by placing food
on a block of ice or, in cold weather, burying food outdoors or
storing food on an outdoor windowsill. During the 1920s,
refrigerators with freezer compartments became available for
household use [*Note #2]. Pasteurization of milk also became
prevalent at this time.
5) Before 1910, no legislation existed in the US to ensure
the safety of food and feed crops that were sprayed and dusted
with pesticides. In 1910, the first pesticide legislation was
designed to protect consumers from impure or improperly labeled
products. During the 1950s and 1960s, pesticide regulation
evolved to require maximum allowable residue levels of pesticides
in foods and to deny registration for unsafe or ineffective
products. During the 1970s, the newly formed US Environmental
Protection Agency removed DDT and several other highly persistent
pesticides from the marketplace.
-----------
US Centers for Disease Control: Safer and Healthier Foods --
1900-1999.
(Morbidity and Mortality Weekly Report 1999 48:905)
(J. Amer. Med. Assoc. 24 Nov 99 282:1909)
-----------
Text Notes:
... ... *trichinosis: (trichinelliasis; trichinellosis;
trichiniasis) This disease is caused by the ingestion of raw or
inadequately cooked pork (also bear or walrus meat) that contains
encysted larvae of the nematode parasitic worm Trichinella
spiralis (trichina worm). Nematodes are a large class of
unsegmented roundworms.
... ... *rickets: A disease caused by vitamin D deficiency.
... ... *scurvy: A disease caused by vitamin C deficiency.
... ... *beri-beri: A disease caused by vitamin B(sub1) (thiamin;
thiamine) deficiency.
... ... *pellagra: A disease by niacin (nicotinic acid;
nicotinamide) deficiency.
... ... *Note #1: A number of people were involved in the
discovery of vitamins, but especially Casimir Funk (1884-1967).
In 1912, Funk advanced the concept (proposed earlier by others)
that diseases such as beri-beri, scurvy, pellagra, and rickets
were caused by a lack of substances needed in the diet in small
quantities. The first known anti-beri-beri factor was an amine,
and Funk erroneously supposed that all similar substances were
amines. He named the factors "vitamines". When it subsequently
became apparent that not all the factors were amines, the final
"e" was dropped to give the current spelling: vitamin.
... ... *Note #2: Although refrigerators were indeed available in
the US in the 1920s, most people could not afford them. It was
not until the mid-1930s that refrigerators were common in the
kitchens of most urban dwellings. As an invention, the first
practical refrigerator was developed by Karl Linde (1842-1934) in
1876, the device based on liquid ammonia.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 3Mar00
[For more information: http://scienceweek.com/search/search.htm]
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4. MOLECULAR BIOLOGY:
SYNEXPRESSION GENE GROUPS IN EUKARYOTES
Biologists categorize all living cells into two types,
eukaryotes and prokaryotes, the former containing internal
membrane-bound organelles such as a nucleus and mitochondria,
while cells of the latter type do not contain such structures.
But this is only one view of the distinction between eukaryotes
and prokaryotes, since there are other important differences,
including differences in gene expression and its regulation.
The regulation of gene expression is perhaps the most
important ongoing phenomenon in the life of any biological cell.
The DNA of a cell contains the genes coding for every protein the
cell is potentially capable of synthesizing, but the need for
these proteins varies considerably, depending upon the cell type,
its physiological state, the availability of external nutrients,
and changing environmental conditions. To respond to these
changing needs, biological cells have evolved a wide range of
precise mechanisms for turning on and off the expression of
individual genes.
Forty years ago, F. Jacob and J. Monod (1910-1976)
introduced the idea of the bacterial (prokaryote) "operon", a
cluster of functionally interacting genes whose expression is
tightly coordinated. This concept, although of fundamental
importance for understanding intracellular dynamics of bacteria,
was dismissed for eukaryotes because of the apparent different
mode of gene regulation and expression in eukaryotes. Recently,
however, it has become evident that the highly coordinated
expression of genes that function in common processes is also a
widespread phenomenon in eukaryotic cells.
... ... C. Niehrs and N. Pollet (Deutsches Krebs Forschungs-
zentrum Heidelberg, DE) present a review of recent work in the
field of coordinated eukaryote gene expression, the authors
making the following points:
1) The authors propose the term "synexpression groups" to
designate sets of genes that share a complex spatial expression
pattern (multiple tissues), and that function in the same
process. They also propose that the term could be extended to
groups of genes that share complex temporal (multiple time
points) or experimental (multiple experimental conditions)
expression profiles, since the currently used term "gene cluster"
is ill-defined.
2) The authors point out that traditionally, the term "gene
cluster" refers to physically linked genes, and it is therefore
misleading in the context of co-expression. Also, consideration
of synexpression groups allows the prediction of gene function
with high precision (unlike consideration of many "gene
clusters"), and synexpression groups probably result in emergent
properties during evolution.
3) In general, the authors use the term "synexpression" to
refer to groups of genes co-expressed under diverse conditions,
and hence the identification of such groups typically requires
expression profiling at high resolution (e.g., with *DNA micro-
array technology).
4) The authors suggest that synexpression groups reflect the
functional compartmentalization of the eukaryote genome and have
a striking parallel to the prokaryote operon.
5) DNA micro-array expression analysis is clearly the most
efficient way to identify synexpression groups, and a future
challenge will be to carry out profiling over hundreds or
thousands of conditions to map the genomic program at high
resolution. Synexpression groups that make no sense at first
glance will probably be encountered in the future, in other
words, groups in which the functions of the co-expressed genes
have no apparent common denominator, and these groups might be
particularly interesting because they may reveal an otherwise
hidden logic of cellular regulation. Where synexpression groups
couple seemingly unrelated tissues, one might search for adaptive
reasons for their integration.
6) The authors conclude: "The hard-wired correspondence
between gene function and regulation shown by synexpression
groups unveils a degree of order that was previously unsuspected
and provides us with new opportunities to study genetic
networks."
-----------
C. Niehrs and N. Pollet: Synexpression groups in eukaryotes.
(Nature 2 Dec 99 402:483)
QY: Christof Niehrs, Division of Molecular Embryology, Deutsches
Krebs Forschungszentrum, Im Neuenheimer Feld 280, D-69120
Heidelberg, DE.
-----------
Text Notes:
... ... *DNA micro-array technology: The essential idea
concerning the use of "arrays" in determining gene expression
patterns involves the fact that for every gene (DNA sequence)
undergoing expression there exists in the cytoplasm a specific
RNA whose nucleotide sequence is a result of transcription (DNA
to RNA coding) of that gene. There exists now a technique for
profiling the large variety of RNAs that can be extracted from
tissue, the technique depending on highly ordered arrays of large
numbers of oligonucleotide probes (essentially pieces of DNA) in
a parallel format, with specific DNA-RNA interactions producing
localized fluorescences, and the array of fluorescences providing
a profile of detectable RNAs. A determination of the profile of
existing RNA sequences implies the profile of the DNA sequences
(genes) that are being naturally expressed in the genome, and if
one knows which genes are involved with which functions in that
particular cell or organism, one has obtained a profile of
existing functions. The use of such arrays of nucleotide probes
(sometimes called micro- arrays or "chips") is now highly
automated ("robotic"), and the technique can be used to determine
the expression profile of thousands of genes in an ensemble of
cells.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 3Mar00
[For more information: http://scienceweek.com/search/search.htm]
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5. PHYSICS:
ON STATISTICAL PHYSICS AND ITS APPLICATIONS
Statistical physics (statistical mechanics) is the branch of
physics that attempts to explain the macroscopic properties of a
system on the basis of the properties of its microscopic
constituents. Usually the number of constituents is extremely
large, and all the characteristics of the constituents and their
interactions are presumed to be known. Although as a distinct
research area, statistical physics dates back to James Clerk
Maxwell (1831-1879) and Ludwig Boltzmann (1844-1906) and their
work on probability distributions in the kinetic theory of gases,
the field was substantially transformed in the 20th century, and
it has now been fruitfully applied to nearly all states of matter
including biological systems.
... ... Philip Ball (_Nature_, UK) presents a commentary on the
history and applications of statistical physics, the author
making the following points:
1) Statistical physics, and more specifically the theory of
transitions between states of matter, more or less defines what
we know about everyday matter and its transformations. In
addition, statistical physics provides a conceptual apparatus for
dealing with complex collective quantum phenomena of current
intense interest, particularly: a) Bose-Einstein condensation (in
which a collection of particles all occupy the same quantum
ground state); and b) high-temperature superconductivity (i.e.,
superconductivity above 35 degrees kelvin). Many of the states of
condensed matter that promise new technological applications,
ranging from *block copolymers to magnetic multilayers, can be
understood as the consequence of the kind of collective behavior
that statistical physics describes.
2) From the 1960s to the 1980s, statistical physicists were
primarily concerned with "critical points", the points in
thermodynamic phase diagrams at which two or more phases become
identical. The reasons for this interest are twofold: a) the
behavior of a system at its critical point also determines its
behavior in the broad vicinity of the critical point (within a
so-called "critical region"; b) the behavior of a system at a
critical point reveals kinships between different systems. For
example, liquid-gas criticality and the behavior of some magnets
at their Curie point (the temperature above which they lose their
*ferromagnetism) have numerically equal *critical exponents, and
both can be modeled by the so-called "*Ising model", a model
based on a lattice of two-state *spins. Commonality of critical
exponents gives rise to the idea of universality, the idea that
there are generic models in statistical physics that describe a
variety of apparently different many-body systems. This means
that solving one problem in statistical physics generally
delivers solutions for several other problems at the same time.
In addition, there is an implication that many-body behavior is
fundamentally determined only by global aspects such as the range
of interparticle forces, the dimensionality of the system, and
the nature of the "*order parameter" (whose abrupt change from a
zero to a non-zero value defines the transition from one state to
another).
3) A fruitful present area of research is the intersection
of statistical physics with quantum mechanics, in particular, the
many-body behavior of electrons in condensed matter. Correlated
behavior of electrons, in which electrons display a degree of
collective or coherent dynamics, produces superconductivity, the
*integer and fractional quantum Hall effect, so-called "*heavy-
fermion" behavior, *spin density waves, and *colossal
magnetoresistance. All of these collective phenomena have in
recent years been shown to underlie unexpected and potentially
useful properties of novel materials. Colossal magnetoresistance,
for example, may lead to the development of highly-sensitive
read-out heads for magnetic memories.
4) The author suggests that despite the proven value to cell
biology of some concepts from the study of phase transitions (for
example, the entropic effect of fluctuations on interactions of
lipid membranes), there remains much skepticism as to whether
biological phenomena can be approached as arising from collective
emergent behavior of statistical interacting ensembles rather
than from the closely controlled protein relays to which cell
biologists are accustomed. Yet statistical physics must
inevitably provide the baseline even in the cell: proteins may
phase-separate and membranes may adopt equilibrium conformations
unless actively opposed by cell processes.
-----------
Philip Ball: Transitions still to be made.
(Nature 2 Dec 99 402supp:C73)
QY: Philip Ball [p.ball@nature.com]
-----------
Text Notes:
... ... *block copolymers: A copolymer in which a number of units
of the same monomer are located adjacent to one another (in
"blocks" of monomers).
... ... *ferromagnetism: A "ferromagnet" is a material (such as
iron) in which there may be a permanent *magnetic moment, and in
which the *spins of the atoms are aligned parallel to each other.
... ... *magnetic moments: (magnetic dipole moment) The intrinsic
spins of the electrons in an atom, together with the motion of
the electrons around the nucleus, give rise to a magnetic field
around the atom, and the magnitude of this field is related to
the magnetic dipole moment of the atom or ion.
... ... *critical exponents: In this context, a "critical
exponent" is a parameter that characterizes the temperature
dependence of a thermodynamic property of a substance near its
critical point. The temperature dependence has the form
|T-T(subc)|^(n), where T is the temperature, T(subc) is the
critical temperature, and (n) is the critical exponent.
... ... *Ising model: In general, a simplified model in which the
atomic *spins are assumed to be aligned parallel or antiparallel
in a given direction.
... ... *spins: In quantum mechanics, electrons, protons, and
neutrons have an intrinsic angular momentum known as "spin", and
a magnetic moment parallel or antiparallel to that angular
momentum. When electrons are combined together to form an atom or
ion, there is a resultant angular momentum which is a combination
of the intrinsic spin of the electrons and the angular momentum
due to their motion about the nucleus, and this is the "spin" of
the atom or ion. Atoms or ions with non-zero spin are magnetic
atoms or ions. The idea of electron spin was first proposed by
Goudsmit and Uhlenbeck in 1925 to explain the splitting of atomic
spectroscopic emission lines in the presence of a magnetic field.
Elementary particle spin involves a virtual rotation about the
axis of the particle, which means only two spin states are
possible, one clockwise and one counterclockwise.
... ... *order parameter: In general, a quantity that
characterizes the phase of a system below its transition
temperature, the parameter having a nonzero value below the
transition temperature and a zero value above the transition
temperature. If the phase transition is continuous, the order
parameter falls to zero continuously as the transition
temperature is approached.
... ... *integer and fractional quantum Hall effect: In classical
physics, the Hall effect is the development of a transverse
voltage across a current-carrying conductor in a magnetic field,
the voltage being perpendicular to both the direction of the
current and the direction of the magnetic field. In quantum
physics, there are two other Hall effects, an integer charge
quantum Hall effect, and a fractional charge quantum Hall effect,
these quantum Hall effects being observed at extremely low
temperatures (a few degrees Kelvin) and extremely intense
magnetic fields (at least several tesla). Both quantum Hall
effects were first noted in the 1980s, and the fractional quantum
Hall effect, although experimentally observed, has not been
theoretically resolved.
... ... *heavy-fermion: "Heavy-fermion systems" are solids in
which electrons behave as if they have masses several hundred
times their normal masses. Substances containing such electrons
have unusual thermodynamic, magnetic, and superconducting
properties that are not completely understood.
... ... *spin density waves: In general, propagating collective
spin-variation excitations associated with certain magnetic
systems.
... ... *colossal magnetoresistance: (giant magnetoresistance)
The term "magnetoresistance" refers to a change in the electrical
resistance of a conductor or semiconductor upon the application
of a magnetic field, a property of certain systems. Giant
magnetoresistance is a quantum mechanical effect observed in
magnetic thin-film structures composed of alternating
ferromagnetic and nonmagnetic layers.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 3Mar00
[For more information: http://scienceweek.com/search/search.htm]
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6. PHYSICS:
FIRST MOLECULES IN A BOSE-EINSTEIN CONDENSATE
In 1997, Steven Chu, Claude Cohen-Tannoudji, and William D.
Philips shared the Nobel Prize in Physics for their work in the
1980s involving laser-cooled atoms, work that ultimately led to
the cooling of atoms to extremes close to absolute zero degrees
kelvin, and finally to the creation by Anderson et al (Science
269:198 1995) of a Bose-Einstein condensation in a dilute gas of
rubidium atoms. The essential idea behind these techniques
involves a reduction in the momentum of an atom when it absorbs a
photon. Bose-Einstein statistics is the statistical mechanics of
a system of indistinguishable particles for which there is no
restriction on the number of particles that may simultaneously
exist in the same quantum energy state. Bosons are particles that
obey Bose-Einstein statistics, and they include photons, pi
mesons, all nuclei having an even number of particles, and all
particles with integer spin. In low temperature physics, the
Bose-Einstein condensation is a phenomenon that occurs in the
study of systems of bosons: below a critical temperature, the
quantum ground state becomes highly populated, individual wave
equations merging into a single wave equation, the particles
indistinguishable, and the condensate of particles behaving as a
singe entity.
... ... R. Wynar et al (5 authors at University of Texas Austin,
US) now report the production of rubidium-87 dimers that are
essentially at rest by assembling them from ultracold rubidium
atoms in an atomic Bose-Einstein condensate. In a commentary in
the same journal, C.J. Williams and P.S. Julienne (National
Institute of Standards and Technology, US) point out that this
work is the first observation of molecule formation in a Bose-
Einstein condensate, that a method for the ultraprecise
measurement of molecular binding energies has now been
introduced, and that the work is the first measurement of the
interaction energy between a condensate and a molecule.
-----------
R. Wynar et al: Molecules in a Bose-Einstein Condensate.
(Science 11 Feb 00 287:1016)
QY: D.J. Heinzen [heinzen@physics.utexas.edu]
-----------
C.J. Williams and P.S. Julienne: Molecules at rest.
(Science 11 Feb 00 287:986)
QY: paul.julienne@nist.gov
-------------------
Summary by SCIENCE-WEEK [http://scienceweek.com] 3Mar00
[For more information: http://scienceweek.com/search/search.htm]
-------------------
Related Background:
FESHBACH RESONANCES IN A BOSE-EINSTEIN CONDENSATE
... The term "Feshbach resonance" refers to a transient
"sticking" of two colliding atoms, the sticking involving a
resonance coupling that occurs when the molecular state has
nearly zero energy. The term "optical trapping" refers to the
confinement of entities in a restricted geometry by the
controlled action of light. In this report, the term "inelastic"
refers to a collision process in which the total kinetic energy
of the colliding particles is not the same after the collision as
before it, and the term "coherent beams of atoms" refers to beams
composed of atoms moving in unison. ... ... Inouye et al (6
authors at Massachusetts Institute of Technology, US) report new
observations in a Bose-Einstein condensate. It has long been
predicted that the scattering of ultra-cold atoms can be altered
significantly through a so-called "Feshbach resonance". Two such
resonances have now been observed in optically trapped Bose-
Einstein condensates of sodium atoms by varying an external
magnetic field. The resonances gave rise to enhanced inelastic
processes and a dispersion variation of the scattering length by
a factor of over two. The authors suggest these results open new
possibilities for the study and manipulation of Bose-Einstein
condensates, may also be important in atom optics, for modifying
the atomic interactions in an atom laser, or more generally, for
controlling nonlinear coefficients in atom optics with coherent
beams of atoms.
QY: W. Ketterle, Mass. Inst. of Technology 617- 253-1000
(Nature 12 Mar 98) (Science-Week 27 Mar 98)
[For more information: http://scienceweek.com/search/search.htm]
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IN FOCUS: ON RADIOCARBON DATING
"Radiocarbon dating depends on a chain of natural events, some
having taken place in deep space long ago. The sequence begins in
various parts of the Galaxy, where charged particles are
accelerated to immense velocities, forming what are known as
cosmic rays. A fraction of these particles eventually rain down
on the Earth and strike molecules of atmospheric gas, producing
neutrons. Some of these neutrons in turn react with nitrogen,
(sup14)N, to form (sup14)C, which quickly combines with oxygen to
form molecules of radioactive carbon dioxide [(sup14)CO(sub2)].
By the time the radioactive carbon dioxide reaches the Earth's
surface, it has mixed fully with normal carbon dioxide and
accounts for about one molecule in 10^(12). The vast majority of
this (sup14)C eventually enters the oceans. But 1 or 2 percent
goes into the terrestrial biosphere, because plants absorb carbon
from carbon dioxide in the air during photosynthesis. Thus
vegetation, and the animals that feed on it, are tagged with
(sup14)C. Living things maintain a (sup14)C content that is about
equal to the atmospheric concentration because the carbon atoms
that undergo radioactive decay within their bodies are
continually replaced [*Note #1]. But once an organism dies and
its metabolic processes cease, the amount of (sup14)C begins to
diminish. The rate of decline is measured by the (sup14)C half-
life, about 5730 years." [*Note #2]
-----------
R.E. Taylor: Fifty years of radiocarbon dating.
(American Scientist Jan-Feb 2000 88:60)
-----------
Text Notes:
... ... *Note #1: Carbon-14 decays by beta emission back to
nitrogen-14. Beta emission (beta-decay) is a type of interaction
in which an unstable atomic nucleus changes into a nucleus of the
same mass number but different proton number. In general, the
change involves the conversion of a neutron into a proton with
the emission of an electron plus energy or a positron plus
energy. The electrons or positrons emitted are called "beta
particles". (Positrons are electron antiparticles; they have the
same mass as the electron, but are of opposite charge.) Carbon-14
to nitrogen-14 decay involves the emission of an electron plus
energy, another fundamental particle (electron antineutrino)
accounting for the energy released.
... ... *Note #2: The accelerator mass spectrometry dating method
makes use of smaller quantities of material than required for
conventional radiocarbon dating and extends the radiocarbon
dating range to beyond 50,000 years from the approximately 0 to
25,000 years for conventional radiocarbon dating. The technique
of accelerator mass spectroscopy involves the combination of a
mass spectrometer and an accelerator to measure the concentration
of rare isotopes such as carbon-14 at levels lower than parts per
trillion. An accelerator mass spectrometer can be used to count
the carbon-14 atoms from only a milligram sample of carbon,
whereas the conventional radiocarbon dating method would require
as much as a gram of the same material to achieve the same
resolution by counting current beta particle emission.
-------------------
Notes by SCIENCE-WEEK [http://scienceweek.com] 3Mar00
[For more information: http://scienceweek.com/search/search.htm]
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