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 30, 1999 -- Vol. 3 Number 31

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The medical people are a special breed among us.
In the histories of towns and villages everywhere,
one can find quiet ironies: children laughed at
for their books and science, who grow up to save
the lives of those who laughed at them.
-- Anonymous

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Contents of This Issue:

1. On the Dual-Career-Couple Problem in Physics
2. On the Search for Planets and Life Around Other Stars
3. Helioseismology: Probing the Interior of the Sun
4. Neuroscience: On Alan Hodgkin
5. Effect of Estrogen on Human Brain Activation Patterns
6. Fetal Effects of Exposure to Organic Solvents During Pregnancy

In Focus: On Quantum Gravity

Corrections

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1. ON THE DUAL-CAREER-COUPLE PROBLEM IN PHYSICS
We are in an age of changing or vanishing gender-based divisions
of labor, with more and more women working side by side with men
as professionals in scientific research. One natural consequence
of this is a substantial increase in the number of dual-research
married couples. Since research productivity depends to a large
extent upon specialization, and since the more specialized one's
field of research the less likely a position in that
specialization will be available in any specific geographical
location, there is a chronic employment problem for many dual-
research couples. It is a considerable irony that society can
commit substantial resources to the training of young scientists,
and then have those same scientists unable to work in science
because the commitment of society ends abruptly with their
training. Such problems are not unique to the physics community,
but the problems in that community are currently highlighted and
a cause of particular concern.
... ... L. McNeil and M. Sher (2 installations, US) present a
review of the problem in the physics community, the authors
making the following points:
     1) The authors conducted a survey via several branches of
the American Physical Society, and received responses from 632
individuals who were members of dual-career couples. The purpose
of the survey was to gather data on the extent of the dual-career
problem in physics and consider possible solutions to the
problem. Of the respondent group, 89 percent were physicists
married to other scientists, and 45 percent were physicists
married to other physicists. The authors queried physicists whose
partners are scientists about their experiences in finding
employment and about the kinds of positions they had accepted,
and the published report consists primarily of anecdotal data.
The primary goal of the study was to obtain information about
possible approaches to the problem, and no attempt was made to
use rigorous statistical sampling techniques or sophisticated
quantitative analysis of the responses to the survey.
     2) The authors report that in the 3 decades since 1966, the
percentage of women earning PhDs in physics each year has grown
from approximately 2 percent to approximately 13 percent. At
present, women constitute only 6 percent of US physicists
overall, but they make up approximately 13 percent of all
physicists under the age of 31. Approximately half of all women
physicists are married, compared to 74 percent of all male
physicists.
     3) The authors report that female physicists are far more
likely to be married to physicists and other scientists than are
male physicists. Thus, the dual-career-couple problem has a
disproportionate effect on women. Although statistics are
difficult to obtain, anecdotal evidence suggests that dual-career
employment problems may cause some women to leave physics
altogether.
     4) As possible solutions to the problem, the authors suggest
and discuss split positions, spousal hiring programs, alternative
academic positions, and long-distance commuting.
     5) The authors conclude: "As women represent a growing
fraction of younger physicists, the number of new hires facing
the two-body problem can be expected to increase. It is in the
interests of institutions to take an active role in addressing
these dual-career situations."
-----------
L. McNeil and M. Sher: The dual-career-couple problem.
(Physics Today July 1999)
QY: Laurie McNeil, Dept. of Physics and Astronomy, University of
North Carolina Chapel Hill 919-966-3621
-------------------
Summary by SCIENCE-WEEK [http://scienceweek.com] 30Jul99


2. ON THE SEARCH FOR PLANETS AND LIFE AROUND OTHER STARS
Of all the questions that the human species can ask of nature,
there is one set of questions of enormous emotional and
intellectual significance: Are there other worlds like the Earth
orbiting around distant stars; and if there are such worlds, are
they inhabited by life; and if life does exist on other worlds,
is any of that life intelligent? These questions will no doubt be
asked as long as our species exists, or until answers of one kind
or another are obtained. That is the "long-haul" of a supreme
quest that is of itself a most significant aspect of the human
species and its destiny. But in the "short-haul", there have been
recent developments of great interest: in recent years, for the
first time, we have observations that can be interpreted as good
evidence for the existence of planets around distant stars, and
not only is this evidence a significant step forward in this
supreme quest of our species, but this new evidence, coupled with
new technology and new theory, is allowing us to refine our
observational and theoretical approaches so that the next step
forward in this quest becomes better defined.
... ... Jonathan I. Lunine (Institute of Space Astrophysics Rome,
IT) reviews current efforts in the search for planets and life
around other stars, the author making the following points:
     1) At the present time, 18 objects with masses in the
approximate range 0.08 to 0.4 times the mass of Jupiter have been
found orbiting *main-sequence stars. In addition, several
planetary-mass bodies have been detected orbiting *pulsars. But
although the bodies orbiting pulsars are interesting, the exotic
environments around the *neutron stars apparently constituting
pulsars make it unlikely that pulsar-associated planets are the
abode of life. It is the finding of planets around Sun-like stars
that has been the important step forward in the search for
planets and life around other stars.
     2) So far, the only technique to have succeeded in finding
Jupiter-mass companions to main-sequence stars involves
measurements of periodic variations in the apparent *radial
velocity of the target star as seen from Earth. These variations
are caused by gravitational tugging of the planetary companion as
it orbits around the star. Typical velocity perturbations are
tens of meters per second and can be detected only by measuring
the *Doppler shift of spectral lines in the *photosphere of the
star on the order of 1 part in 10 million wavelength shift.
Measurement of the transverse perturbed velocity, by astrometric
determination of the shift of the star against the stellar
background, has yet to produce a definitive detection of an
extrasolar planet.
     3) Concerning the formation of extrasolar planets, there is
more than one possible mechanism. There is no apparent physical
reason, for example, why the direct gravitational collapse of
*interstellar cloud material cannot produce a body with a mass
less that 0.07 to 0.08 times the mass of the Sun -- the threshold
below which self-sustained *hydrogen fusion is not possible.
Stars too small to undergo hydrogen fusion are called "brown
dwarfs", and like planets, they too have proved to be
observationally elusive. Unlike main-sequence stars, whose
brilliance is steady or slowly increasing with age, brown dwarf
stars dim dramatically over time. Thus, brown dwarf stars are
difficult to detect directly unless they are very young or close
to the Solar System, and only in the past 5 years has success
been achieved in their detection and study. One important
question is whether the Jupiter-size objects apparently orbiting
around distant stars are brown dwarfs or planets.
     4) No matter the distinction between brown dwarf stars and
planets, it is clear that the star-planet architectures now being
detected by radial velocity measurements do not resemble that of
our own Solar System. These extrasolar architectures involve
Jupiter-sized objects in apparent close orbits. But if a system
identical to ours were under surveillance by existing radial
velocity surveys, only Jupiter would be detected (and with
difficulty). In this respect, the search for extrasolar planets
is not yet a search for Solar System-like architectures of Earth-
mass planets.
     5) Concerning the question of extraterrestrial life, the
search for habitable planets within and beyond the Solar System
has focused on the search for environments in which liquid water
is stable for the billions of years required by advanced life for
development on Earth. To validate or contradict speculations
about the inhabitability of Earth-sized planets in other solar
systems is a daunting task. Earth-sized planets must be found
around stars in our solar neighborhood, and their habitability
determined. The detection of Earth-mass planets is extremely
difficult with existing indirect techniques, and radial-velocity
measurements are ultimately limited by photospheric noise to
detecting planets larger than Neptune.
     6) Concerning possible direct techniques, a complete survey
of the solar neighborhood with the sensitivity to detect Earth-
like planets, and to determine habitability, requires a
technological step beyond current direct techniques and
instruments planned for the near future. Direct detection of an
Earth-sized planet is exceedingly difficult: the Earth is 10^(7)
times less bright than the Sun at 10 microns wavelength (and
orders of magnitude dimmer still in the optical wavelength
region), and to directly see planets from many *parsecs distance
therefore requires novel developments in large-*aperture optical
and infrared *interferometry.
-----------
Jonathan I. Lunine: In search of planets and life around other
stars.
(Proc. Natl. Acad. Sci. US 11 May 99 96:5353)
QY: Jonathan I. Lunine [jlunine@lpl.arizona.edu]
-----------
Text Notes:
... ... *main-sequence stars: The Hertzsprung-Russell diagram is
a plot of stellar absolute magnitude against spectral type, and
is one of the most useful diagrammatic aids in astrophysics. The
Main Sequence is a region on the Hertzsprung-Russell diagram
where most stars, including our own Sun, are situated. The course
of a star's evolution can be traced as a particular path in the
H-R diagram, with the paths of various types of stars showing
significant differences.
... ... *pulsars: A pulsar is a pulsing source of stellar
radiation believed to originate with a *neutron star. They were
originally discovered at radio wavelengths, but there are
optical, gamma-ray, and x-ray pulsars, and some of the gamma-ray
pulsars are extremely powerful gamma-ray emitters.
... ... *neutron stars: If, following its terminal stages, the
remnant mass of a star is between 1.4 and 2 to 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.
Theory predicts that a neutron star should rotate very rapidly,
be extremely hot, and have an intense magnetic field. Pulsars,
sources of pulsed radio energy, are evidently spinning neutron
stars which emit beams of radiation from their magnetic poles.
... ... *radial velocity: In general, radial velocity is a
measure of the velocity of an astronomical object along its line
of sight to Earth. The radial velocity is obtained by comparing
the wavelengths of lines in the object's spectrum with laboratory
wavelength values, the difference being due to the *Doppler
shift.
... ... *Doppler shift: In general, the term "Doppler shift"
refers to the change in wavelength of electromagnetic radiation
as a result of relative movement between the source and the
observer.
... ... *photosphere: In general, the visible surface of a star,
from which most of its energy is emitted in the form of visible
and infrared radiation.
... ... *interstellar cloud material: (interstellar matter) In
general, gas and dust occurring between stars.
... ... *hydrogen fusion: In general, a series of nuclear
reactions in which hydrogen nuclei (protons) fuse to form a
helium nucleus, with associated release of nuclear energy.
... ... *parsecs: 1 parsec equals 3.262 light-years, or 30.86 x
10^(12) kilometers.
... ... *aperture: In general, in this context, the diameter of 
the main lens or mirror of a telescope, or in radio astronomy, of
the collecting dish. In radio astronomy, an array of telescopes
can be used to simulate a single telescope of large aperture.
... ... *interferometry: In general, an interferometer is any
instrument that detects the interference patterns of light
(radiation) split into two or more beams that are subsequently
combined again. In this context, high angular resolution can be
achieved by connecting two or more telescopes or radio antennas
to operate as a single interferometric instrument.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 30Jul99
-------------------
Related Background:
A SUGGESTION THAT LARGE INTERSTELLAR PLANETS MAY HARBOR LIFE
David J. Stevenson (California Institute of Technology, US), in a
brief report, argues that interstellar planets with an effective
temperature of 30 degrees kelvin may in fact have a surface
temperature exceeding the melting point of water, that such
bodies may therefore have water oceans whose surface pressure and
temperature are like those found at the base of Earth's oceans,
and that such potential homes for life would be difficult to
detect. The author's idea is that during planet formation, rock
and ice protoplanets of the order of Earth's mass may be ejected
from the Solar System while retaining atmospheres rich in
molecular hydrogen, and that when such hydrogen cools it can have
basal pressures of 10^(2) to 10^(4) bars, and the pressure-
induced far-infrared opacity of molecular hydrogen may prevent
these planetary bodies from eliminating internal radioactive heat
except by developing an extensive convective atmosphere which is
adiabatic, i.e., without loss or gain of heat. The author
suggests such planetary bodies may provide a stable long-lived
environment for life.
(Nature 1 Jul 99) (SW Bulletin 7 Jul 99)
-------------------
Related Background:
EXTRASOLAR PLANETS: IMAGING VIA A NULLING-INTERFEROMETER
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 ideal method
would be direct imaging of extrasolar planets, and this would
considerably enhance the possibilities for understanding their
nature. A major problem in direct imaging of extrasolar planets
is that the bright light from the parent star (more particularly,
its diffracted halo in the imaging apparatus) can easily
overwhelm nearby faint light sources such as orbiting planets.
Exactly 20 years ago, R.N. Bracewell proposed a method for direct
imaging of extrasolar planets that eliminates or at least reduces
the problem of overwhelmed faint light, the method based on the
selective removal of starlight before detection by the
superposition of light from 2 telescopes so that the stellar
wavefronts destructively interfere. In principle, such a "nulling
interferometer" could be used to search for extrasolar Earth-like
planets through their thermal emission, with spectroscopic
analysis used to identify planets that possess the atmospheric
signatures of life. ... ... P.M. Hinz et al now report mid-
infrared observations using 2 co-mounted telescopes of the
*Multiple Mirror Telescope that demonstrate the feasibility of
the Bracewell technique. The authors report that interfering
light of unresolved stars is seen to disappear almost completely,
while light from a nearby source as close as 0.2 *arc seconds
remains, as shown by images of *Betelgeuse. With this star
canceled, there remains the thermal image of its surrounding
small dust nebula. The authors suggest that in the future larger
ground-based interferometers that correct for atmospheric
distortions should achieve better cancellation, and thus allow
direct detection of warm Jupiter-size planets and detection of
the faint *zodiacal dust around other nearby stars.
-----------
P.M. Hinz et al (8 authors at 2 installations, US)
Imaging circumstellar environments with a nulling interferometer.
(Nature 17 Sep 98 395:251)
QY: Phillip M. Hinz [phinz@as.arizona.edu]
-----------
Text Notes: 
... ... *Multiple Mirror Telescope: Completed and operational in
1980, this telescope near Tucson, Arizona (US) originally
comprised 6 identical mirrors, each 1.8 meters in diameter,
arranged symmetrically about a central axis, with a complex
alignment and electronic guidance to bring all 6 images to a
common focus.
... ... *arc seconds: (arcsec) A unit of angular measure equal to
1/3600 of a degree. 60 arcsec = 1 arc minute. The full Moon is
approximately 30 arc minutes in diameter.
... ... *Betelgeuse: (Alpha orionis) 10th brightest star in the
sky. Distance estimated at 400 light years. This is an extremely
large semiregular variable star, hundreds of times the diameter
of the Sun, with variations in brightness as swells and contracts
in size.
... ... *zodiacal dust: This refers to particles of 1 to 300
microns in size and originating from decaying comets and
asteroids spiraling inward to a star. In our Solar System, this
is the dust cloud primarily responsible for the "zodiacal light",
a permanent faint sky glow visible from Earth. The glow is
apparently caused by dust particle-scattering of sunlight.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 16Oct98
-------------------
Related Background:
EXTRASOLAR PLANETS: ON YOUNG STARS AND PROTOPLANETARY DISKS
During the past decade, astronomers have been accumulating
evidence interpreted to display the history of the formation of
planets around stars other than our Sun. ... ... R. Jayawardhana
reviews this field and makes the following points: 1) In 1995,
astronomers reported the first tentative evidence of planets
orbiting another solar-type star, and since then astronomers have
detected perturbations in the motions of a dozen nearby stars,
these perturbations presumably due to the gravity of planets. 2)
An important focus of extrasolar planetary research is the dust
disks from which such planets form, and within the past year
astronomers have obtained detailed images of dust disks
surrounding a host of nearby young stars, the images showing dust
disks at different stages of evolution. 3) One-million-year-old
disks contain mostly gas and show no evidence for planet
formation. Disks can form around binary stars as well as single
stars, but the evolution of dust disks in binary star systems is
not clarified. Perhaps as much as 70 to 80 percent of the young
stars in the center of the *Orion Nebula show evidence of disks.
It is estimated that the mass of young circumstellar disks such
as those in Orion range from 1 to 10 percent of the mass of the
Sun, which is 10 times the mass needed to make a planetary system
like our own. Dust accounts for approximately 1 percent of the
mass of the disk, and the remaining 99 percent is mostly hydrogen
and helium gas. 4) The generally accepted theory is that dust
disks produce planetary systems at approximately the age of 10
million years. The evolutionary sequence is that dust grains
adhere to make entities as large as pebbles, the pebbles then
collide and adhere to make planetesimals, and the gravity of the
planetesimals begins to gather in more and more material, until a
planetesimal may grow as large as the Moon in about 100,000
years. Within several million years, rocky planets the size of
Mercury, Venus, and Earth would complete their agglomeration. In
summary, as the disk ages, planets begin forming in the central
regions, clearing gaps near the star; by 10 million years, most
of the gas is gone, and either planets or planetesimals have
already formed. In the outer regions analogous to the *Kuiper
belt in our Solar System, collisions between asteroids and comets
continue to generate small amounts of dust.
-----------
R. Jayawardhana (Harvard University, US)
Planetary nurseries.
(Astronomy November 1998)
QY: Ray Jayawardhana, Harvard University 617-495-1000.
-----------
Text Notes:
... ... *Orion Nebula: A gaseous nebula visible to the naked eye
as a diffuse glow marking Orion's sword in the Orion
constellation. The nebula is approximately 1500 light years from
Earth, and contains a group of newborn stars (the Trapezium)
probably less than 1 million years old, with star formation near
this group still occurring.
... ... *Kuiper belt: In 1951 the astronomer Gerard P. Kuiper
(1905-1973) postulated the existence of a belt of objects beyond
the orbit of Pluto. Both the existence and nature of the objects
were matters of speculation for decades, and finally in 1992
Jewitt and Luu identified the first Kuiper object. The current
estimate is that as many as 10^(8) objects larger than 10
kilometers in diameter may exist in what is called the "Kuiper
belt", a disc that hugs the plane of the planetary system and
lies between 35 and 1000 *AU from the Sun. Observations to date 
have yielded some 55 trans-Neptune bodies with radii on the order
of 100 km or larger, and Pluto is considered by some astronomers
to be a member of this population.
... ... *AU: Astronomical Unit. 1 AU = the mean distance from the
Sun to the Earth = approximately 93 million miles, and exactly
149,597,870 kilometers.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 16Oct98
-------------------
Related Background:
GIANT PLANETS VS. BROWN DWARFS
Filipe D. Santos (Centro de Fisica da Universidade de Lisboa, PT)
presents a short review of current ideas concerning giant
extrasolar planets and *brown dwarf stars. The author makes the
following points: 1) The recent discoveries of planets orbiting
nearby Sun-like stars have revealed that planetary systems can be
surprisingly diverse. The initial discovery in 1995 of the planet
around the star 51 Pegasi was a surprise because it is apparently
a planet with mass about that of Jupiter (at least 0.44 Jupiter-
mass) and an orbital period of only 4.2 days, which implies that
the planet is 20 times closer to its star than Earth is to the
sun. 2) Seven additional planets around solar-type stars have
since been discovered, with Jupiter-mass values ranging from 0.44
to 6.84. 3) Two critical questions are, a) Where should we set
the dividing line that distinguishes massive planets from brown
dwarfs? and, b) What are the mechanisms leading to the formation
of massive planets and brown dwarfs? 4) Brown dwarfs are expected
to have masses smaller than the hydrogen-burning limit of
approximately 0.075 solar-mass (approximately 75 Jupiter-mass),
but probably larger than the deuterium-burning limit of 0.013
solar-mass (approximately 13 Jupiter-mass). 5) Like the companion
massive planets mentioned, several companion brown dwarfs to
solar-type stars have also been identified. One method of
investigating brown dwarfs involves *astrometric measurements,
and in all cases of brown dwarfs investigated by the astrometric
method, the masses are above or very close to the hydrogen-
burning limit. The extant data thus suggest that the distribution
of mass of brown dwarfs does not extend to masses as small as
giant planets. Also, the new measurements indicate that brown
dwarfs orbiting solar-type stars are very rare. 6) The discovery
of Jupiter-mass planets with orbits very close to their stars
poses a considerable problem, because it is difficult to
understand how such planets could form in place. (Five known
Jupiter-mass planets have orbital radii smaller than the distance
from Mercury to the Sun.) The suggestion has been made that these
planets formed at larger distances and migrated inward, but the
proposed migration mechanisms are not yet empirically
distinguishable. The author concludes: "Clearly the discovery of
planetary systems outside our solar system has opened a Pandora's
box of startling phenomena and new questions."
QY: Filipe D. Santos [fdsantos@milkyway.cii.fc.ul.pt]
(Science 17 Jul 98 281:359) (Science-Week 31 Jul 98)
-------------------
Related Background:
... ... *brown dwarf stars: Brown dwarf stars are formed by the
contraction of a lump of gas with a mass too small for nuclear
reactions to begin in the core. Such a star has a relatively
short-lived luminosity (approximately 100 million years) as the
result of conversion of gravitational energy to radiation. The
surface temperature of a brown dwarf is below 2500 degrees
kelvin. As recently as 1994, brown dwarfs were "theoretical"
stars, with no brown dwarfs considered to be unambiguously
identified.
... ... *astrometric measurements: This method of detection
infers the presence of a companion to a star by measuring the
position of the star as it orbits the center of mass of the
entire system. From the orbital inclination, the real mass of the
companion can be derived.
-------------------
Related Background:
ASTROMETRIC SIGNATURES OF GIANT PLANET FORMATION
The discoveries during the past two years of giant planets
orbiting nearby solar-type stars has raised again the question of
how these planets are formed. Two different models have been
proposed. The gravitational instability model involves formation
of planets directly from the gas in the accretion disk around the
young star. The alternative model is the core-accretion model, in
which rocky cores of about 10 Earth masses form first, with that
followed by hydrodynamical accretion of gas to form the massive
envelopes of the giant planets. ... ... Alan P. Boss (Carnegie
Institution of Washington, US) now proposes, on the basis of
calculations, that these two processes have very different
astrometric signatures, and that it should be observationally
possible to distinguish between them. Planets that form through
gravitational instabilities do so rapidly, so that within just a
few hundred years of the onset of the instability the nascent
planet is making the young stellar object wobble in its orbit.
This can be seen in the youngest stellar objects, with ages as
little as 0.1 million years. If planets form by core accretion,
an observable wobble will not be visible for 10-20 million years.
The author suggests that observations of a suitable ensemble of
optically visible young stellar objects (such as those in the
Taurus molecular cloud) over a period of several decades should
be able to determine which of the two processes is responsible
for the formation of giant planets.
QY: Alan P. Boss [boss@dtm.ciw.edu]
(Nature 14 May 98 393:141) (Science-Week 5 Jun 98)
-------------------
Related Background:
ON STELLAR PLANETARY SYSTEMS
Extrasolar planetary systems are planetary systems involving one
or more planets in orbit around stars other than our own Sun, and
there is growing evidence that such systems do indeed exist.
The term "Doppler-shift" refers to an observed change in spectrum
frequencies when the source of the spectrum or the observer move
toward or away from each other, and certain perturbations in
Doppler-shifts can be interpreted as indicating the presence of
dark massive objects orbiting stars. The Keck telescopes are a
pair of twin telescopes at the W.M. Keck Observatory on Mauna
Kea, HI US, each with 10 meter mirrors, the pair constructed
1992-1996. The installation is managed by the University of
California (US) and the California Institute of Technology (US).
An optical interferometer is a system involving separate but
linked telescopes whose collection of optical waves is combined
to improve spatial resolution, the resolving power becoming
equivalent to that of a single instrument with an aperture equal
to the largest distance separating the component telescopes.
... ... Marcy and Butler (2 installations, US AU), in a review of
extrasolar planetary systems, note that within the next 5 years
Doppler surveys of nearly a thousand stars will be undertaken,
that the two Keck telescopes will be linked as an optical
interferometer with sufficient precision to detect extrasolar
planets by stellar positional perturbations, and that the US
National and Aeronautics Space Agency's space-borne interfero-
meter, if funded, should be able to obtain actual images of
extrasolar orbiting planets. The authors suggest that by the year
2010 we should have completed the first true census of planets of
nearby stars.
QY: Geoffrey Marcy, San Francisco State Univ. 415-338-2017
(Sky & Telescope March 1998) (Science-Week 30 Jan 98)
-------------------
Related Background:
FURTHER EVIDENCE FOR A PLANET ORBITING STAR 51 PEGASI
Doppler-shift is an observed change in spectrum frequencies when
the source of the spectrum or the observer move either toward or
away from each other. In astronomy, radial velocity is the
velocity of a star along the line of sight of an observer,
determined by measuring the Doppler-shift in the star's spectrum,
and periodic perturbations of an observed stellar Doppler-shift
have in some cases been interpreted as evidence for the existence
of a massive object orbiting the star. A massive planet around
the star 51 Pegasi was reported last year by Mayor and Queloz,
but a subsequent paper by D. Gray challenged their interpretation
of the data on the basis of spectral line-shape oscillations that
would indicate the Doppler-shift perturbations originated in the
stellar surface. ... ... D. Gray (Univ. of Western Ontario, CA)
now reports that recent new monitoring of 51 Pegasi showed an
absence of his previously published spectral line-shape
oscillations that previously called into question the
Doppler-shift data as indicating an orbiting planet. The author
suggests his previous results were noise, and that these new
results, together with other high-precision measurements by other
researchers, indicate the planet hypothesis as the best
explanation for the radial-velocity perturbations. (cf.
contiguous paper by Hatzes et al).
QY: David F. Gray [dfgray@uwo.ca]
(Nature 8 Jan 98) (Science-Week 23 Jan 98)


3. HELIOSEISMOLOGY: PROBING THE INTERIOR OF THE SUN
The Sun, a *main-sequence star 1.4 million kilometers in
diameter, is composed predominantly of hydrogen and helium
(approximately 70 percent hydrogen by mass, 28 percent helium by
mass, and 2 percent heavy elements by mass) and it generates its
energy via nuclear fusion processes, particularly via the
*proton-proton chain reaction. As a result, the Sun is losing
mass at a rate of approximately 4 million metric tons per second.
The generation of energy occurs in the "central core", which has
a temperature of approximately 15 million degrees kelvin, is
approximately 400,000 kilometers in diameter, and contains
approximately 60 percent of the mass of the Sun in 2 percent of
its volume. Outside the core is the "radiative zone", an envelope
of unevolved material through which energy from the core is
diffusively transported by successive absorption and emission of
radiation in collisions between atomic particles. It has been
estimated that it may take as long as 10 to 20 million years for
the energy generated in the core to reach the surface. The
radiative zone extends to within 200,000 kilometers of the
surface. In the surface layer (the "convective zone"), where the
temperature is only 1 million degrees kelvin, convection is the
most important mode of energy transport. The science of
helioseismology is the study of the solar interior using
observations of solar surface manifestations of resonant sound
waves (pressure modes; p-modes) traveling in the solar interior.
In other words, helioseismology is the study of the solar
interior structure by using the oscillations of its surface.
Since p-mode frequencies are *Doppler-shifted by motions in the
line of sight, they can also be used to study the internal
dynamics of the Sun, such as internal rotation and convection.
... ... P. Demarque and D.B. Guenther (2 installations, US CA)
present a review of current research in helioseismology, the
authors making the following points:
     1) In 1962, Leighton et al discovered patches of the surface
of the Sun moving up and down with a velocity of the order of 15
centimeters per second, with periods of approximately 5 minutes.
Called the "5-minute oscillation", the motions were originally
believed to be local in character and somehow related to
turbulent convection in the solar atmosphere. In 1970, Ulrich
suggested that the phenomenon is global and that the observed
oscillations are the manifestation at the solar surface of
resonant sound waves (pressure modes or "p-modes") traveling in
the solar interior.
     2) Stellar oscillation theory, the main theoretical
framework for helioseismology, also predicts the existence of
buoyancy driven modes (gravity modes, or "g-modes") that have
been observed in other astrophysical contexts, but it is not
clear at present whether g-modes are excited in the Sun. G-modes
are expected to be exponentially damped in convective regions, so
their amplitudes at the top of the solar convective envelope are
expected to be much smaller than in the radiative core. In
contrast to p-modes, which have maximum amplitudes in the outer
parts of the Sun, g-modes exhibit their largest amplitudes in the
solar core. If observable, g-modes would be sensitive probes of
the solar core, where p-modes are least sensitive.
     3) There are many facets of helioseismology, and the field
has contributed to the study of stellar evolution and to
astrophysics and physics in general. The interpretation of a
wealth of ground-based data, most recently provided by the Global
Oscillation Network Group (GONG) project, a network of observing
stations distributed around the globe to observe the Sun
continuously, and the Solar and Heliospheric Observatory (SOHO)
space mission, have led to many advances. The most important
accomplishments of helioseismology include the following:
... ... a) The testing of the physical assumptions of stellar
evolution theory.
... ... b) The determination of the depth of the solar convection
zone.
... ... c) The reconstruction of the internal rotation profile in
the outer half of the solar radius.
... ... d) The detailed probing of the *superadiabatic transition
layer near the solar surface.
... ... e) The realization of the important role played by the
diffusion of helium in the interior of the Sun and the seismic
determination of the helium abundance in the convection zone.
... ... f) The determination of the age of the Sun by seismic
means.
... ... g) The setting of a strong constraint on *varying-
gravitational-constant cosmologies.
... ... h) The demonstration that the *solar neutrino discrepancy
is likely to reveal fundamental new knowledge about neutrinos and
their interaction with matter.
-----------
P. Demarque and D.B. Guenther: Helioseismology: Probing the
interior of a star.
(Proc. Natl. Acad. Sci. US 11 May 99 96:5356)
QY: P. Demarque, Yale University, 203-432-4771.
-----------
Text Notes:
... ... *main-sequence star: The Hertzsprung-Russell diagram is
a plot of stellar absolute magnitude against spectral type, and
is one of the most useful diagrammatic aids in astrophysics. The
Main Sequence is a region on the Hertzsprung-Russell diagram
where most stars, including our own Sun, are situated. The course
of a star's evolution can be traced as a particular path in the
H-R diagram, with the paths of various types of stars showing
significant differences.
... ... *proton-proton chain reaction: A chain of nuclear
reactions inside a star that converts hydrogen to helium, with
the associated release of energy. In the reaction, 4 hydrogen
nuclei (protons) fuse to form one nucleus of helium, with the
production of a number of intermediate nuclei such as deuterium
and isotopes of lithium, beryllium, and boron. The proton-proton
reaction is the most important stellar reaction at temperatures
below 18 million degrees kelvin, and thus operates chiefly in
stars of less than 2 solar masses.
... ... *Doppler-shifted: In general, the term "Doppler shift"
refers to the change in wavelength of electromagnetic radiation
as a result of relative movement between the source and the
observer.
... ... *superadiabatic transition layer: An adiabatic process is
any thermodynamic process, reversible or irreversible, that takes
place in a system without exchange of heat with the surroundings
of the system. All real processes are nonadiabatic in the sense
that some heat exchange always occurs. But close approximation to
an adiabatic ideal can be realized in practice. In the context of
this report, the "superadiabatic transition layer" is the
transition between deep convection, where the temperature
gradient is nearly adiabatic, and the shallow outer layers of the
Sun, where radiative losses dominate.
... ... *varying-gravitational-constant cosmologies: In general,
this term refers to cosmological theories dependent on a time-
varying universal gravitational constant. Recent
helioseismological data have provided a strong limit on the
variation of the universal gravitational constant during the
lifetime of the Sun, and this limit is stronger by almost one
order of magnitude than previous constraints.
... ... *solar neutrino discrepancy: Neutrinos are fundamental
particles with zero charge, possibly zero mass, and an angular
momentum factor (spin) of 1/2. Various processes produce
neutrinos: stellar nuclear reactions, reactions occurring during
supernova explosions, cosmic ray collisions with matter, etc.
Measurements of solar neutrinos have produced a mystery: the
neutrino density measured by detectors is approximately one-third
that expected from theoretical calculations of solar neutrino
emission. Two kinds of solutions have been proposed to resolve
this mystery, one solution involving revisions to the theory of
stellar structure, and the other solution involving revisions to
nuclear particle theory.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 30Jul99
-------------------
Related Background:
ANALYSIS OF SUB-SURFACE MATERIAL FLOW IN THE SUN
... Helioseismology is the analysis of wave motions of the Sun's
surface to determine the structure of the Sun's interior, and
helioseismic tomography is simply such an analysis in terms of
sections of the Sun's sphere. In general, the idea is that
systematic and quantitative analysis of surface wave phenomena
can reveal the sub-surface conditions that produce these
phenomena. Giles et al (4 authors at 3 installations, US) report
the detection, using helioseismic tomography, of the
longitude-averaged sub-surface flow in the outer 4 percent of the
Sun. The sub-surface flow is apparently constant in this depth
range, and its speed is similar to that seen on the surface. (In
this context, "speed" is the scalar quantity -- distance per unit
time.) The authors suggest the observations demonstrate that
surface flow penetrates deeply and is likely to be an important
factor in solar dynamics.
QY: P. M. Giles [pgiles@solar.stanford.edu]
(Nature 6 Nov 97) (Science-Week 28 Nov 97)


4. NEUROSCIENCE: ON ALAN HODGKIN
The decade between 1950 and 1960 produced a renaissance in
structural and genetic biology, the former case involving the
introduction of the electron microscope as a biological research
tool, and the latter case involving the introduction of the
Watson-Crick molecular model of DNA. Some other fields in biology
had their own less public rebirths, particularly the field now
called "neuroscience". In the early 1950s, as the direct result
of a series of 5 papers which appeared in the _Journal of
Physiology (London)_, the field of neuroscience was effectively
turned on its head and irreversibly transformed. The senior
author of those 5 papers was Alan L. Hodgkin (1914-1998). Co-
authors of the first paper in the series were Bernard Katz and
Andrew F. Huxley, the latter remaining co-author of the last four
papers. In 1963, Hodgkin and Huxley shared the Nobel Prize for
Physiology or Medicine for this work; in 1970, Katz received the
Nobel Prize for Physiology or Medicine for related but different
work, and that same year Hodgkin became president of the UK Royal
Society. The subject of the 5 papers which appeared in 1952 was
the ionic basis of the neuron action potential (the "nerve
impulse"). Since Bernard Katz worked independently on other
problems after that first paper, the 1952 work is usually
referred to as the work of Hodgkin and Huxley. Like all
scientific efforts of great significance, there are many aspects
of the story of this research that are worth considering, but
there is one aspect that is particularly noteworthy. Examination
of the history of research on the electrical activity of nerve
cells before and after the work of Hodgkin et al reveals that
perhaps the essential contribution of the Hodgkin group was to
ask the right questions while everyone else was asking the wrong
questions. For nearly two decades prior to the 1950s, the favored
questions in research on nerve cells were questions concerning
the electrical behavior of nerve cells without serious
consideration of charge carriers. The favored questions often
involved sophisticated physical analysis, the application of
electric circuit theory and the Maxwell-Kelvin wave equation to
what was obviously a highly nonlinear system that behaved in some
ways very much like an electrical transmission line. But although
neurobiologists with training in physics were captivated by these
aspects of neuron behavior, it was not until Alan Hodgkin started
work on the *giant axon of the squid in the late 1930s (work
halted during World War II and then continued after it) that
anyone paid serious attention to the most fundamental and
important question that can be asked of any electrically
conducting system: What are the charge carriers? In short, what
Hodgkin et al accomplished in the series of 1952 papers was a
demonstration, with both experimental data and a quantitative
formulation, of the detailed dynamic contributions of the various
ionic charge carriers to the electric behavior of nerve cells.
The study of the behavior of nerve cells was suddenly and
profoundly reduced to the physical chemistry and biochemistry of
ion movements, and a new era in neuroscience quickly came into
being.
... ... Peter B. Detwiler (University of Washington Seattle, US)
presents a short biographical essay on Alan Hodgkin, Detwiler
noting the following: "Alan Hodgkin was a tall man, with a quiet
disposition, a good sense of humor, and lively eyes that could
express a full range of emotions. He was modest despite his
achievements. He did not put his name on any work that he did not
fully participate in. He had no interest in having a large
research group and felt that one collaborator at a time was best,
two were awkward, and more than that impossible. He was fun to
work with. Experiments were rarely planned ahead of time, as
there was the unexpressed sense that this would somehow ruin the
chase by quenching the feeling of exploration and discovery that
was, after all, the point of the process."
-----------
Peter B. Detwiler: Sir Alan Hodgkin (1914-1998)
(Science 30 Apr 99 284:753)
QY: Peter B. Detwiler [detwiler@u.washington.edu]
-----------
Text Notes:
... ... *giant axon of the squid: Certain species of molluscs,
crustaceans, and insects, have evolved relatively large-diameter
nerve axons which facilitate function by allowing rapid
propagation of the nerve action potential. The giant axon of the
squid, the largest-diameter of these invertebrate axons, was
reintroduced to neurobiologists by the neuroanatomist J.Z. Young
in 1936. This was a seminal event in the history of neurobiology,
since the giant axon of the squid made feasible experiments
previously out of the question. Only 22 years old at the time,
Hodgkin immediately began working on this axon, and the 1952
series of papers was essentially a detailed analysis of the ionic
basis of the electrical behavior of the squid giant axon. The
fundamentals of the analysis are in general universally
applicable to all nerve cells.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 30Jul99


5. EFFECT OF ESTROGEN ON HUMAN BRAIN ACTIVATION PATTERNS
Estrogen is a collective term for the female hormones, the most
powerful of which is estradiol. They control female secondary
sexual characteristics, and prepare and maintain the uterine
lining. Perhaps the single most important biological event for
most middle-aged women is menopause, which results in decreased
levels of circulating estrogen. The declining estrogen levels
characteristic of menopause affect a range of systems, including,
in addition to the reproductive system, the cardiovascular and
skeletal systems. There is also evidence that estrogen affects
basic neural processes in mature animals, and estrogen has been
shown to affect cognitive function in animals. There have been
studies of the effect of estrogen on cognitive function in
postmenopausal women, but the results have been inconsistent.
Recent advances in technology now permit the noninvasive
measurement of brain function as individuals perform memory and
other cognitive tasks. This technique, called "*functional
magnetic resonance imaging", exploits the differences in the
magnetic properties of oxygenated compared with deoxygenated
blood. In performing a cognitive task, such as *working memory,
blood flow and oxygen  concentration are altered in those brain
regions engaged in the task. ... ... S.E. Shaywitz et al (16
authors at 2 installations, US) report a study to investigate the
effects of estrogen on brain activation patterns in
postmenopausal women as they performed verbal and nonverbal
working memory tasks. The study involved 46 right-handed
postmenopausal women age 33 to 61 years in a randomized, *double-
blind, placebo-controlled, *crossover trial from 1996 through
1998. The intervention consisted of a 21 day treatment with
*conjugated equine estrogens (1.25 milligrams/day), randomly
crossed over with identical placebo, and a 14-day washout between
treatments. The authors measured brain activation patterns using
functional magnetic resonance imaging, and the authors report
that treatment with estrogen increased activation in the
*inferior parietal lobe during storage of verbal material, and
decreased activation in the inferior parietal lobe during storage
of nonverbal material. Estrogen also increased activation in the
*right superior frontal gyrus during retrieval tasks, accompanied
by greater left-hemisphere activation during *encoding. The
authors conclude that estrogen in a therapeutic dosage alters
brain activation patterns in postmenopausal women in specific
brain regions during the performance of the sorts of memory
function that are called upon frequently during any given day.
The authors suggest these results indicate that estrogen affects
brain organization for memory in postmenopausal women.
-----------
S.E. Shaywitz: Effect of estrogen on brain activation patterns in
postmenopausal women during working memory tasks.
(J. Amer. Med. Assoc. 7 Apr 99 281:1197)
QY: Sally E. Shaywitz [Sally.Shaywitz@yale.edu]
-----------
Text Notes:
... ... *functional magnetic resonance imaging: First, we
distinguish between magnetic resonance imaging (MRI) and
"functional" magnetic resonance imaging (fMRI) as applied to the
brain. The former is essentially a technique for examining
morphology, while the latter is a technique for examining
activity of brain tissue. Both techniques involve computerized
analysis of data. In general, MRI involves magnetic coils
producing a static magnetic field parallel to the long axis of
the patient or subject, combined with inner concentric magnetic
coils producing a static magnetic field perpendicular to the long
axis. A radio-frequency coil specifically designed for the head
perturbs the static fields to generate a magnetic resonance
image. The interaction physics in this technique is that between
the magnetic fields and atomic nuclei in brain tissue. "Sliced"
views can be obtained from any angle, and the resolution is quite
high and on the order of millimeters for current magnetic field
strengths of 1.5 tesla. Functional magnetic resonance imaging
(fMRI), the variant of MRI discussed here, is based on the fact
that oxyhemoglobin, the oxygen-carrying form of hemoglobin, has a
different magnetic resonance signal than deoxyhemoglobin, the
oxygen-depleted form of hemoglobin. Activated brain areas utilize
more oxygen, which transiently decreases the levels of
oxyhemoglobin and increases the levels of deoxyhemoglobin, and
within seconds the brain microvasculature responds to the local
change by increasing the flow of oxygen-rich blood into the
active area. This local response thus leads to an increase in the
oxyhemoglobin-deoxyhemoglobin ratio, which forms the basis for
the fMRI signal in this technique. Because of its high spatial
resolution (millimeters) and high temporal resolution (seconds)
compared to other imaging techniques, fMRI is now the technology
of choice for studies of the functional architecture of the human
brain.
... ... *working memory: In this context, the term "working
memory" refers to a particular type of short-term memory
involving the ability to hold things in mind long enough to carry
out sequential actions.
... ... *double-blind: In general, a "double-blind" experimental
procedure is one in which neither the subjects nor the
experimenters know the makeup of the test and control group
during the actual course of the experiments.
... ... *crossover trial: In general, a "crossover trial" is an
experimental or clinical procedure in which subjects are divided
randomly into at least as many groups as there are kinds of
treatment to be given, and then the groups are interchanged until
every subject has received each treatment.
... ... *conjugated equine estrogens: This is an amorphous
preparation of naturally occurring water-soluble conjugated forms
of mixed estrogens obtained from the urine of pregnant mares. The
principal estrogen present is sodium estrone sulfate.
... ... *inferior parietal lobe: the parietal lobe is
approximately the middle portion of each cerebral hemisphere seen
from the side. In this context, the term "inferior" refers to the
lower part.
... ... *right superior frontal gyrus: The term "gyrus" refers to
any of the visible convoluted ridges of the cerebral hemispheres.
Seen from the side, the superior frontal gyrus is the foremost
ridge of the frontal lobe.
... ... *encoding: In this context, the term "encoding" refers to
the first stage of the memory process, prior to storage and
retrieval, and associated with receiving stimuli through one or
more of the senses.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 30Jul99


6. FETAL EFFECTS OF EXPOSURE TO ORGANIC SOLVENTS DURING PREGNANCY
Biological membranes are essentially lipid barriers with a
secondary population of attached or embedded proteins. Organic
solvents are particularly potent in their chemical action on
biological systems because they readily and quickly pass through
lipid domains such as biological membranes, including membranes
of the skin, the digestive tract, and the respiratory system.
Many women of child-bearing age are occupationally exposed to
organic solvents, and since fetal tissue is even more vulnerable
to such solvents than adult tissue, the question of the effects
on the fetus of occupational exposure of the mother to organic
solvents is of some significance. The most important women-
dominated occupations with potential chemical exposures are
health care professions and work tasks in the clothing and
textile industries, all of which involve exposures to organic
solvents. Many industrial solvents are teratogenic (i.e., capable
of producing a malformed fetus) in laboratory animals, and there
are reports of limb and central nervous system defects in mice,
marked developmental toxic effects and retardation of skeletal
growth in rats, and congenital malformations in rabbits. However,
the animal studies typically use high doses of single solvents
and a variety of routes of administration. In the human
occupational setting, exposure usually occurs to a multitude of
solvents at much lower doses by inhalation, making extrapolations
from animals to humans problematic.
... ... S. Khattak et al (6 authors at University of Toronto, CA)
now report a study to evaluate pregnancy and fetal outcome
following maternal occupational exposure to organic solvents. The
study involved 125 pregnant women who were exposed occupationally
to organic solvents and seen during the first trimester between
1987 and 1996, and 125 matched controls. The organic solvents to
which the women were occupationally exposed included aliphatic
and aromatic hydrocarbons, phenols, trichloroethylene, xylene,
vinyl chloride, acetone, and related compounds. These women
worked in the following occupations (number of women): factory
worker (37), laboratory technician (21), artist (16), printing
industry (14), chemist (13), painter (8), office worker (4), car
cleaning service (3), veterinary technician (3), orthotist (2),
funeral home service (2), carpenter (1), social worker (1). Only
women known individually to be exposed to organic solvents were
in the above groupings. The authors tabulated the occurrence of
major congenital malformations in the infants delivered by these
women. The authors report that significantly more major
malformations occurred among fetuses of women exposed to organic
solvents than matched controls (13 vs. 1). In other words, 10.4
percent of the women in the organic-solvent-exposed group
produced a malformed fetus, as opposed to 0.8 percent of the
women in the control group. 12 of the 13 malformations occurred
among the 75 women who had symptoms of exposure during their
exposure, while no malformations occurred among the exposed women
who did not exhibit symptoms during their exposure. The authors
conclude that occupational exposure to organic solvents during
pregnancy is associated with an increased risk of major fetal
malformations, and that this risk appears to be increased among
women who report symptoms associated with organic solvent
exposure. The authors suggest that exposure of women to organic
solvents should be minimized during pregnancy, and that "health
care professionals who counsel families of reproductive age
should inform their patients that some types of employment may
influence reproductive outcomes."
-----------
S. Khattak et al: Pregnancy outcome following gestational
exposure to organic solvents.
(J. Amer. Med. Assoc. 24/31 Mar 99 281:1106)
QY: Gideon Koren, The Hospital for Sick Children, 555 University
Avenue, Toronto, Ontario CA M5G 1X8.
-------------------
Summary by SCIENCE-WEEK [http://scienceweek.com] 30Jul99


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

IN FOCUS: ON QUANTUM GRAVITY
"Gravity is by far the weakest force in the Universe: in the
hydrogen atom, the electromagnetic force between the proton and
electron is about 10^(40) times as great as the gravitational
force between them. This is fairly representative of the
difference in scales between the quantum and gravitational
realms, and accounts for our ability [in cosmology] to separate
the two theories without ambiguity. Yet they must inevitably
meet. Near a singularity, the curvature of space-time must be so
great that the scale of gravity becomes comparable to that of the
other fundamental forces. To describe such a state, we must find
a theory of quantum gravity. Moreover, quantum mechanics has
already been applied to the explanation of the other three
forces, the electromagnetic force and the strong and weak
interactions; should not gravity be similar? It might seem as
though the challenge of developing quantum gravity should not be
so great. After all, special relativity and quantum mechanics
were united in the 1920s by the British physicist Paul A.M.
Dirac. The most significant result of Dirac's theory was its
requirement that antiparticles exist, a prediction that was
confirmed in 1932 by the discovery of the positron (the anti-
electron). The Dirac theory is now well-established as the
special relativistic quantum mechanics. More than 70 years later,
however, general relativity has still not been successfully
incorporated into a consistent quantum formulation."

-- J.F. Hawley and K.A. Holcomb: Foundations of Modern Cosmology
   (Oxford University Press, New York 1998, p.441)


=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
CORRECTIONS:
In issue #30 (23 July 1999) report #3, Edouard A. Roche 1820-1823
should be Edouard A. Roche 1820-1883.

In issue #30 (23 July 1999) report #6, Kerry Mullis should be
Kary Mullis.
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