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ScienceWeek
SCIENCE-WEEK - Part 1
A Free Weekly Digest of the News of Science
January 16, 1997
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"We are the strangest species. We question everything,
measure the stars, sift the sand through our fingers,
gauge the bowels of the Earth. It is our destiny and
it will not stop."
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Contents of This Issue:
Part 1:
1. An Assessment of the Human Genome Project
2. On Analogies Between Condensed Matter and Particle Theories
3. Fractals and the Geometry of Nature
4. On Highest Energy Cosmic Rays
5. Galactic Black Holes: Radiation and Plasma Consumption
6. Analysis of a Supermassive Black Hole Accretion Disk
7. A Supernova Explosion at Half the Age of the Universe
8. A Model for the Migration of Massive Planets
9. Earthquakes and Friction Laws
Part 2:
10. Plate Tectonics: Coupling of Motion and Deformation
11. On Ultrahigh-Intensity Lasers
12. On the Physics of Noncoalescing Liquids
13. A Discovery of a Tooth Implant in An Ancient Roman Skull
14. More Evidence for DNA Damage via Long-Range Charge Transfer
15. Questions Concerning the Pathogen in Prion Diseases
16. Ultraviolet Cell Death Blocked by a Skin Virus
17. Chemotaxis of Neurons: Variable Response May Assist Targeting
18. Herpesvirus as a Viral Oncogene and Angiogenesis Activator
19. On the Clinical Aspects of Genetic Polymorphisms
20. Genomic Information and Drug Discovery
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1. AN ASSESSMENT OF THE HUMAN GENOME PROJECT
The Human Genome Project, sponsored by the US National Institutes
of Health and the US Department of Energy, was formally created
in 1990 to determine the complete nucleotide sequence of the
entire human genome. The sequence involves approximately 3 x
10^(9) base pairs of DNA, and the massive project, which is now
about 3% complete, has involved many installations and has an
overall target date of 2005. The apparent consensus is that
progress has been unsatisfactory. The current international
large-scale genome sequencing capacity is estimated at 100
megabases per year, but a rate of 400 megabases per year will be
required to achieve completion of the project by the target date.
S.E. Koonin (Californian Inst. Technol., US), a physicist and
head of a study chartered by the US Department of Energy (DOE) to
review the DOE component of the Human Genome Project, points out
that so-called "big science", an operation mode characteristic of
nuclear and particle physics, space and planetary science,
astronomy, and oceanography, requires coordinated efforts and
centralized management for the construction and allocation of
resources, but such centralized management is not yet apparent in
the genomics community and "the Human Genome Project is very much
in need of the coordination it would produce."
QY: Steven E. Koonin (Science 2 Jan 98)
2. ON ANALOGIES BETWEEN CONDENSED MATTER AND PARTICLE THEORIES
The relations between the microcosm and the macrocosm, between
microscopic domains and macroscopic domains, have always been of
fundamental importance in philosophy, and in the past 100 years,
of similar importance in theoretical physics. In physics, the
symmetry principle holds that physical laws remain invariant
under certain transformations, and the locality principle holds
that two events at spatially separated locations are entirely
independent of each other if the time interval between the events
is less than that required for a light signal to travel from one
location to the other. The term "upward heritability" refers to
microscopic laws that retain their character when consistently
applied to macroscopic domains. In the modern theory of element-
ary particles, empty space (the vacuum) is formulated as a richly
structured highly symmetrical medium. F. Wilczek (Inst. for
Advanced Study, Princeton US), in a review of the analogies
between condensed matter (solid-state) physics and the physics of
fundamental particles, suggests that the upwardly heritable
principles of locality and symmetry, together with the quasi-
material nature of apparently empty space, underlie most and
possibly all the modern analogies between the microscopic and
macroscopic domains. QY: Frank Wilczek, Inst. for Advanced Study,
Princeton, NJ US (Physics Today January 1998)
3. FRACTALS AND THE GEOMETRY OF NATURE
A fractal is a geometrical shape whose structure is such that
magnification by a given factor reproduces the original object.
During the past several decades, the idea that fractal geometry
is an appropriate geometry to describe nature has been proposed
by many researchers. The mathematical constructs involved are
appealing because of their symmetries, and as in the development
of many appealing ideas, the use of the term "fractal" has
increased to the point where experimental observations in all the
sciences are being analyzed and interpreted as examples of
systems with apparently fractal properties. To the mathematician,
however, the definition of the property of "fractality" involves
a quantitative requirement of infinitely many orders of magnitude
of power-law scaling of the parameters of the system -- certainly
at least a spanning of many orders of magnitude. Avnir et al (3
authors at 2 installations, IL), in a review of the application
of the mathematics of fractals to the geometry of natural
systems, point out that the application of the term "fractal" by
scientists to such systems is often unjustified. The authors
surveyed all experimental papers reporting fractal analysis of
data that appeared during a 7 year period in Physical Review
journals (Phys. Rev. A to E, and Phys. Rev. Lett., 1990-1996),
and found that in most cases the order of magnitude spanning
required for mathematical fractality was not achieved, and that
the use of the term "fractal" in these contexts has at most a
heuristic value. The authors suggest there is at present no
experimental evidence that the geometry of nature is fractal.
QY: David Avnir (Science 2 Jan 98)
4. ON HIGHEST ENERGY COSMIC RAYS
Cosmic rays are highly energetic particles moving at close to the
speed of light and continuously bombarding the Earth's atmosphere
from all directions. The energies of the particles are enormous
and range from 10^(8) to over 10^(19) electronvolts. The term
"highest energy cosmic rays" refers to cosmic rays with energies
of the order of 10^(20) electronvolts or greater, apparently from
extra-galactic sources, but the origins are not clear. Pions (or
pi-mesons) are subatomic particles with masses approximately 270
times the mass of the electron. The term "pion production losses"
refers to the losses of energy of cosmic rays particles as they
interact with the Earth's atmosphere at about 20 kilometers to
produce pions and the subsequent pion decay products of electrons
and photons. The term "grand unification energy" refers to the
energy above which (according to the grand unification theories)
the fundamental forces are related through symmetry, with the
fundamental forces comprising the gravitational force, the
electromagnetic force, the nuclear strong force, and the nuclear
weak force. O'Halloran et al (3 authors at 3 installations, US
JP), in a review of current work in highest energy cosmic ray
physics, outline the various projects planned for the near future
at various installations, and predict the next decade will
provide important data in this field. The authors suggest that if
the observed cosmic energy spectrum is not cut off by pion-
production losses, but instead the spectrum continues on to
energies approaching the grand unification energy of the order of
10^(23) eV, "twists and turns in astrophysical theory" will be
required to explain the results. QY: Thomas O'Halloran, Univ.
Illinois Urbana-Champaign 217-333-3090.
(Physics Today January 1998)
5. GALACTIC BLACK HOLES: RADIATION AND PLASMA CONSUMPTION
If the terminal stages of star death leave a remnant star mass
greater than 3 solar masses, the ultimate gravitational collapse
will produce a black hole, a relativistic singularity, a mass
that has collapsed to such a small volume that its gravity
prevents the escape of all radiation. The boundary of the black
hole is called the "event horizon", because any event within the
boundary is invisible outside, the invisibility resulting from
the fact that no radiation can escape to be detected. The radius
of the black hole depends upon how much matter has fallen into
the region; it is called the "Schwarzchild radius", and it is
usually a few kilometers. In physics, a plasma is a fully ionized
gas consisting of free electrons and positive ions, the plasma
formed at high temperatures such as the temperatures in stars or
by photoionization (e.g., in interstellar gas). R. Genzel (Max
Planck Inst. for Extraterrestrial Physics, DE), in a short review
of galactic center black holes, suggests there is probably a
massive black hole at the center of our own galaxy, and that the
apparently low radiation of such galactic center black holes may
be due to plasma effects involving the conversion of gravitat-
ional energy into thermal energy of ions rather than into
radiation produced by electrons.
QY: Reinhard Genzel
(Nature 1 Jan 98) (cf. Narayan et al, Astrophys. J. 10 Jan 98)
6. ANALYSIS OF A SUPERMASSIVE BLACK HOLE ACCRETION DISK
Matter with high angular momentum attracted to a black hole does
not fall directly into the black hole but forms a rapidly
spinning "accretion disk" around the black hole, and this can
produce considerable energy, particularly at x-ray wavelengths,
as the accretion disk loses angular momentum and spirals inward.
The dynamical evolution and fate of such accretion disks has been
the subject of much theoretical analysis and model simulations.
Supermassive black holes are black holes with masses of the order
of 10^(6) to 10^(9) solar masses and are believed to occupy the
centers of some galaxies. The term "iron-line emission" refers to
emission at the frequency characteristic (the "line") of iron
atoms in transit from excited states to lower energy states.
Because of the nature of nucleosynthesis -- the fusion reactions
in stars -- the cores of many stars consist of iron. Bromley et
al (3 authors at 3 installations, US RU) present an analysis of
the iron-line emission of galaxy MCG-6-30-15 that is independent
of parametric details of the disk model used, and they deduce
that from this galaxy there are being observed emissions from
gravitationally bound material in the strong-field region of a
supermassive black hole.
QY: B.C. Bromley (Nature 1 Jan 98)
7. A SUPERNOVA EXPLOSION AT HALF THE AGE OF THE UNIVERSE
Redshift (symbol: z) is a lengthening of the wavelengths of
electromagnetic radiation from a source caused either by the
movement of the source (Doppler effect) or by the expansion of
the universe (cosmological redshift). According to current ideas,
the expansion of the universe should be counteracted by gravit-
ational forces, and if the mass of the universe is sufficient,
this gravitational attraction will ultimately cause a cessation
of expansion and the beginning of a sustained gravitational
contraction. If expansion is indeed slowing, the cosmological
redshift should be time-dependent, and an analysis of the
redshift of objects in the ancient universe (by observations of
extremely distant objects) should reveal this slowing of
expansion due to gravitational forces produced by cosmic mass.
Supernovas are stellar explosions of stars with original masses
greater than about 3 solar masses, and type 1a supernovas are
believed to be white dwarf stars that have accreted enough matter
from another star to be pushed over a mass threshold and into a
thermonuclear explosion. S. Perlmutter et al (22 authors at 16
installations, US IT UK FR SE DE CL ES) report the most distant
spectroscopically confirmed supernova, SN1997ap, at an apparent
redshift z = 0.83. Spectra and photometry from the largest
telescopes on the ground and in space indicate this ancient
supernova is similar to nearby recent type Ia supernovas. The
authors suggest that these measurements, when combined with
recent measurements of nearer supernovas, indicate we may live in
a low-mass-density universe. QY: S. Perlmutter
(Nature 1 Jan 98)
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Related Background:
EVIDENCE FOR AN INTERMINABLE EXPANSION OF THE UNIVERSE
The Hubble Space Telescope, named after the astronomer Edwin
Hubble (1889-1953), was launched from a space shuttle in 1990
into a 600-kilometer low-Earth orbit and has been providing
extensive imaging and spectroscopic observations critical for the
development of astronomy and astrophysics. The new information
has concerned hot stars, stellar chromospheres and coronas, the
interstellar medium, galaxies and galactic clusters, quasars,
etc. -- all of it information uncorrupted by the Earth's
atmosphere, which is the problem for ground based telescopes.
White dwarf stars are extremely dense and compact stars that have
undergone gravitational collapse ... White dwarfs are of great
interest to cosmologists, because it is believed their masses
and luminosities have little variance and they can thus be used
as "standard candles" to estimate distances. With dependable
distance measurements, it is possible to refine various
cosmological theories, in particular the models of the expanding
universe. One major question is whether the expansion of the
universe will ever be halted and reversed by gravitational
forces. Another major question concerns the inflationary model of
the early universe. The inflationary model, first proposed by
Alan Guth in 1980, proposes that quantum fluctuations in the time
period 10^(-35) to 10^(-32) seconds were quickly amplified into
large density variations during the "inflationary" 10^(50)
expansion of the universe in that time frame. Now recent
observations using the Hubble Space Telescope of Type 1a
supernovae are evidently being interpreted as evidence that the
universe does not contain enough mass to terminate or reverse its
expansion through gravity forces, and that the simple form of the
inflationary model of the early universe may need serious
revision. Astrophysicists are calling the results exciting and
the method promising. (Science 31 Oct 97)
8. A MODEL FOR THE MIGRATION OF MASSIVE PLANETS
Planetesimals are bodies with dimensions of 10^(-3) to 10^(3)
meters that are believed to form planets by a process of
accretion. The term "accretion" refers to an aggregation, an
increase in the mass of a body by the addition of smaller bodies
that collide and adhere to it, provided the relative velocities
are low enough for coalescence. As the mass of the agglomerate
increases, so does the rate of accretion, and this accretion
process is believed to generally occur in the form of a disk. A
stellar accretion disk is a swarm of dust grains that evolve into
planetesimals and then planets. There is now evidence of apparent
massive planets in close orbits around stars, but the formation
of such massive planets in close orbits is unexplained. One
possibility is that these massive planets were formed in a more
distant orbit and then migrated inward. Murray et al (4 authors
at 2 installations, CA) now report a theoretical analysis of the
behavior of planets and planetesimals in a stellar disk. The
calculations predict that gravitational interactions and collis-
ions between planet and planetesimals, if total planetesimal
surface density exceeds a certain value, may drive the planet
inward a great distance. The authors suggest this mechanism may
explain the presence of Jupiter-mass objects in small orbits
around nearby stars. QY: N. Murray, Univ. of Toronto, Dept. of
Theoretical Astrophysics, Toronto, ON M5S 3H8 CA
(Science 2 Jan 98)
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Related Background:
GIANT PLANET EVIDENCE CONFOUNDS SOLAR SYSTEM THEORISTS
Until recently, speculations and theories about planets orbiting
other stars than our sun have depended on our own solar system as
the guiding model. But during the past two years, astronomers
have been able to gather information about nine such planets, and
the evidence is apparently not in harmony with expectations. The
three variables that are evidently making trouble for theorists
are planet size, proximity to the parent star, and orbital
eccentricity. For example, the planet orbiting the star 51 Pegasi
is large enough to have about half the mass of Jupiter, but seems
to be orbiting the star at a radius of one-sixth the radius of
Mercury's to our sun. This is a puzzle, although there appears to
be still controversy about whether this planet is actually a
planet. Others of the discovered planets are apparently in highly
eccentric and unexplained orbits. So the theorists are busy
revising models for planet formation, establishment of orbits,
planetary orbital drift, and so on. The major difficulty is that
there are no direct observations of these discovered planets --
their existence is proposed to explain perturbations in the
behavior of their parent stars. Stephen Lubow of the Space
Telescope Science Institute (Baltimore MD US) says of the recent
observations: "It's been a revolution." (Science 30 May 97)
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A GRAVITATIONAL INSTABILITY MODEL FOR GIANT PLANET FORMATION
Until recently, the consensus theory for the formation of large
planets such as Jupiter was the core accretion model involving
the formation of cores of approximately 10 times Earth mass,
followed by rapid accretion of gas from the primitive solar
nebula. The problem with this model is that the time needed for
accretion (about 1 million years) is of the order of magnitude of
the time during which a young solar-type star's gas dissipates.
The other possible model is one involving a gravitational
instability mechanism in which the solar nebula breaks up into
giant gaseous protoplanets which then contract and collapse to
form giant planets. This model was in the past abandoned because
the extant data concerning the masses of Jupiter and the outer
planets seemed incompatible with the model. But there is now new
data concerning the masses of Jupiter and the outer planets, and
this week Alan P. Boss (Carnegie Institution of Washington, DC
US) reported a revisit to the gravitational instability model,
with computer solutions of the relevant equations of
hydrodynamics coupled with the Poisson equation in a spherical
coordinate system, such solutions providing evidence that the
formation of giant protoplanets in a gaseous nebula disk can
indeed occur. The old gravitational instability model has
therefore apparently been revived. (Science 20 Jun 97)
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EVIDENCE OF A PROTOPLANETARY DISK AROUND A YOUNG STAR
The current nebula theory of planet formation proposes that star-
planet systems begin as a contracting cloud of gas and dust that
flattens into a rotating disk. The center of this cloud becomes
the star, and the planets eventually form in the disk of the
nebula. In the inner part of the nebula, the hottest part, only
high density minerals can form solid grains. The outer regions
are cooler, and in those regions icy materials of lower density
are formed. Planets grow from these solid materials, beginning as
dust grains, which grow by condensation and accretion into
planetesimals that range from a few centimeters to a few
kilometers in diameter. These planetesimals settle into a thin
plane around the star and accumulate into larger bodies, the
largest of which grow the fastest and eventually become
protoplanets. Once the star becomes a luminous object, the
remaining nebula is cleared as the star's radiation and the
stellar-wind (powerful streams of charged particles from the
star's surface) push the remnants out of the system. Thus ends
the phase of planet-building. As might be expected, the above
theory is also the current view of the history of our own solar
system. Since the details of disk formation, and the physical
properties of protoplanetary disks, can be modelled by
quantitative theory, the general idea is to investigate such
disks that are apparent around stars to test the theoretical
models. There is no way to do that with our own solar system,
because the protoplanetary disk is long gone. One needs young
stars. This week Vincent Mannings et al (California Institute of
Technology, CA US) report observations and analysis of the
apparent protoplanetary disk of a star only 6 million years old,
with a mass of 2.3 solar masses. The mass of the disk is
evidently greater than the minimum required to form a planetary
system like our own. QY: V. Mannings
(Nature 7 Aug 97)
9. EARTHQUAKES AND FRICTION LAWS
The term "lithosphere" refers to the outer layer of the Earth,
comprising the crust and upper mantle, and extending to a depth
of 50 to 70 kilometers. The traditional view of tectonics
(changes in the structure of the Earth's crust) is that the
lithosphere consists of a strong brittle layer overlying a weak
ductile layer, the system producing two forms of deformation,
namely, brittle fracture in the upper layer (accompanied by
earthquakes), and aseismic (without earthquakes) ductile flow in
the lower layer. The current consensus is that this view is
generally correct but imprecise, since the accumulated evidence
is now interpreted to indicate that frictional events along fault
lines, rather than new fractures, are the causes of earthquakes.
The essential idea is that fault lines, which are the interfaces
between the crustal plates, build up stresses resulting from the
movements of the plates, and at intervals these stresses are
suddenly relieved by interface slippages the surface manifest-
ations of which are earthquakes. In mechanics, "stick-slip"
friction is friction between two surfaces that are alternately at
rest and in motion with respect to each other, and in recent
years a number of laboratories have conducted model experiments
with stick-slip rock systems with the idea of obtaining a fuller
understanding of the physics of frictional phenomena occurring at
fault lines. C.H. Scholz (Columbia Univ., US), in a review of
current ideas concerning earthquake mechanics, points out that at
present the most precise and predictive model for earthquake
mechanisms is that an earthquake is a frictional rather than a
fractional phenomenon, with brittle fracture of the upper litho-
sphere layer playing a secondary role in the lengthening of
faults and frictional wear. The origin of earthquakes is evid-
ently a stick-slip frictional instability, and many of the
aspects of earthquake phenomena can apparently be explained by
the general laws applying to frictional stability regimes.
QY: Christopher H. Scholz, Columbia Univ., Dept. Earth and
Environmental Sciences, 212-854-1754 (Nature 1 Jan 98)
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Related Background:
THE PREDICTION OF EARTHQUAKES
Earthquake prediction, an aspect of geophysics of obvious
tremendous social and economic importance, demands from
geophysicists more than they are presently able to give.
Seismicity patterns, in conjunction with knowledge of where
historic earthquakes have occurred, permit reasonable judgments
of where future earthquakes are most likely to occur, but at
present it is not possible to predict when an earthquake is
likely to happen in an endangered area. And of course it is the
when that is of great social and economic and even political
importance. A recent published exchange of letters among
seismologists focuses on the problems of earthquake prediction,
the exchange provoked by a previous article which emphasized that
such predictions are not possible (R. J. Geller et al, Science
275:1616 1997). Max Wyss (University of Alaska, US) suggests that
research in the physics of preparation for catastrophic rupture
should not be halted, and that if the lack of funding for
earthquake prediction research continues in the US, the important
discoveries will be made in Japan, Europe, or China. Richard A.
Aceves and Stephen K. Park (University of California Riverside,
US) suggest that the review by Geller et al is "an unduly
negative view of research in a difficult field." But these
authors admit it is time for present earthquake prediction
research to be more honestly identified as earthquake monitoring.
They suggest, however, that considering the large benefit if and
when such research will bear fruit, earthquake prediction
research should definitely continue. Robert J. Geller et al (4
authors at 3 installations in JP, US, IT), the authors of the
review that provoked the letters, respond that they believe
emphasis should be placed on basic research in earthquake
science, real-time seismic warning systems, and long-term
probabilistic earthquake hazard studies. QY: R. Aceves
; R. Geller
(Science 17 Oct 97)
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DEFORMATIONS IN THE SAN ANDREAS FAULT LOWER CRUST
A geophysical fault is a break in rock structure that occurs when
pressures in the Earth's crust are strong enough to cause
fracture and displacement, and earthquakes are common at such
break points. Seismic velocity refers to the propagation velocity
of a seismic disturbance (e.g., an earthquake), and reflectivity
cross-section is a parameter associated with the reflective
properties of a propagated seismic wave. The Mohorovicic
Discontinuity (called "Moho" and named after Andrija Mohorovicic,
who first identified it in 1909) represents the boundary between
the crust and mantle, its depth varying from about 5 kilometers
to as much as 60 to 80 kilometers. A strike-slip fault is a
movement parallel to the fault plane, and the San Andreas fault
of California is of this type. Continental drift is the slow
movement of the Earth's land masses, a shifting across the
underlying molten material, and sea-floor spreading is the
process whereby sea floor is continuously created as the crustal
plates move apart and continuously destroyed where the plates
push against each other. And finally, plate tectonics is the
modern theory that unifies many of the features and character-
istics of continental drift and sea-floor spreading into a
coherent model. Timothy J. Henstock et al (3 authors at 2
installations, US) now report that analysis of a continuous
seismic velocity and reflectivity cross-section of the San
Andreas fault system in northern California reveals offsets in
the lower crust and the Mohorovicic Discontinuity near the San
Andreas and Maacama strike-slip faults, and that the northern
California continental margin to the eastern edge of the Coastal
Ranges is underlain by a high-velocity lowermost crustal layer
that may have been emplaced within 2 million years following the
removal of the plate slab known as the Gorda plate. The authors
suggest that the rapid emplacement and structure within this
layer are difficult to reconcile with existing tectonic models.
QY: T. Henstock, Rice Univ., Geol. and Geophys. (713) 527-4880)
(Science 24 Oct 97)
(continued in Part 2)
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
SCIENCE-WEEK - Part 2
A Free Weekly Digest of the News of Science
January 16, 1998
----------------------------------------------------------------
Contents of Part 2:
10. Plate Tectonics: Coupling of Motion and Deformation
11. On Ultrahigh-Intensity Lasers
12. On the Physics of Noncoalescing Liquids
13. A Discovery of a Tooth Implant in An Ancient Roman Skull
14. More Evidence for DNA Damage via Long-Range Charge Transfer
15. Questions Concerning the Pathogen in Prion Diseases
16. Ultraviolet Cell Death Blocked by a Skin Virus
17. Chemotaxis of Neurons: Variable Response May Assist Targeting
18. Herpesvirus as a Viral Oncogene and Angiogenesis Activator
19. On the Clinical Aspects of Genetic Polymorphisms
20. Genomic Information and Drug Discovery
----------------------------------------------------------------
10. PLATE TECTONICS: COUPLING OF MOTION AND DEFORMATION
Plate tectonics is the current consensus theory that the Earth's
lithosphere is broken into fairly rigid plates, seven major
plates and many smaller plates, and that convection within the
underlying less rigid "asthenosphere" causes the plates (and the
associated continents and crust) to move relative to each other,
the movement manifested in continental drift and sea-floor
spreading. The term "hot spot" (also, hotspot) refers to a long-
lasting center of surface volcanism and locally high heat flow,
and about 40 locations are now so labelled. Most hot spots are in
ocean basins, and at points where the lithosphere has apparently
upswelled, elevating the denser mantle material and creating mass
anomalies. Silver et al (3 authors at 2 installations, US) report
an analysis of the relative and absolute motion histories of the
African Plate and South American Plate over the last 80 million
years, using fracture-zone orientations, sea-floor magnetic
anomalies, and the apparent motion of the African Plate with
respect to the Atlantic basin hot spots Tristan da Cunha and St.
Helena. The movements of the two plates are evidently correlated
with an anomalous mantle upwelling. The authors suggest this
flow-coupled plate interaction causally links the Andean and
Alpine-Himalayan deformations that occurred about 30 million
years ago. QY: Paul G. Silver, Carnegie Inst. of Washington,
Dept. Terrestrial Magnetism, 5241 Broad Branch Rd. NW,
Washington, DC 20015 US (Science 2 Jan 98)
11. ON ULTRAHIGH-INTENSITY LASERS
In general, resonance is a marked increase in the oscillation
amplitude of a system when the system is subjected to an
oscillating force whose frequency is the same or close to the
natural frequency of the system as determined by the system
parameters. The phenomenon occurs in all systems, including
optical systems. Coherent light waves are light waves of similar
phase, direction, and amplitude, and a laser (light amplification
by stimulated emission of radiation) is a device that converts
input power into a very narrow intense beam of coherent visible
or infrared light, the conversion mechanism essentially involving
excitation of atoms to a higher energy state producing resonator-
forced in-phase radiation. During the past decade, achieved laser
intensities have increased by more than four orders of magnitude
to the order of 10^(20) watts/centimeter^(2). Such intense
energies can be used to produce extreme fields: electric,
magnetic, pressure, temperature, and acceleration -- field
intensities found only in stellar interiors or close to the
horizon of a black hole. The technological advances that have
made such laser intensities possible began in 1987 with the
development of the "chirped-pulse" laser, a device whose essent-
ial basis is the use of ultra-short pulses [10^(-15) seconds]
whose parameters are manipulated before amplification. Mourou et
al (3 authors at 3 installations, US), in a review of chirped
pulse amplification in laser physics, suggest this new technology
has opened a path to research in areas of physical extremes
previously inaccessible in university laboratories, and that
phenomena that could previously only be studied at large install-
ations or not at all will soon be accessible on student labor-
atory desktops. QY: Gerard A. Mourou, Univ. of Michigan 313-764-
7433 (Physics Today January 1998)
12. ON THE PHYSICS OF NONCOALESCING LIQUIDS
The coalescence or noncoalescence of two drops of the same liquid
provides a striking illustration of how particular thermodynamic
variables determine the behavior of matter. A system can be
arranged, for example, in which two drops of the same liquid will
permanently not coalesce if the drops are at different tempera-
tures. What is happening in the microscopic gap between the two
drops is that the temperature difference is forcing convection in
the drops and of the gas between the drops with the result that
the gas maintains just enough pressure to prevent coalescence.
Suppression of the wetting of solids by liquids that normally wet
those solids can thus be demonstrated: a drop of hot silicone oil
can be mechanically pressed against a cooler glass surface
(normally wetted by the oil) without the bulk drop making actual
contact with the glass. An emulsion is a system of two or more
liquids that do not dissolve in each other, usually with one or
more liquids forming microphases in a host liquid. Aversana and
Neitzel (2 installations, IT US), in a review of the physics of
liquid drops, suggest that the study of liquid drop coalescence
and noncoalescence is only in its beginning stages, but already
important applications involving enhancement of separation
processes, fuel droplet combustion, and emulsion stability are
becoming apparent. QY: Pasquale Dell'Aversana, Microgravity
Advanced Research and Support Center, Naples IT. (Physics Today
January 1998)
13. A DISCOVERY OF A TOOTH IMPLANT IN AN ANCIENT ROMAN SKULL
Osseointegration is a bonding between bone and a foreign
material, the bonding at the microscopic level involving a growth
of bone cells into microscopic cavitations in the foreign
material surface. In order for osseointegration to occur, the
foreign surface must have certain physical and chemical
properties, and much research effort has been expended on
perfecting materials and surfaces for dental implants. Until now,
there have been no documented cases of a functional implant
dating from ancient times. Crubezy et al (3 installations, FR)
now report a wrought iron dental implant of a right second upper
premolar from a Gallo-Roman necropolis (a large elaborate
cemetery) at Chantambre (Essonne, FR) from the 1st or 2nd century
AD (established by pottery and radiocarbon dating). The implant
and the socket fit together perfectly with an apparently viable
osseointegration. Examination of the surrounding bone suggests
the implant was fixed in place approximately one year before the
death of the individual. The authors suggest this discovery
reflects the technical potential of early medicine and the
validity of the osseointegration principle. QY: Eric Crubezy,
Univ. Toulouse III, 31000 Toulouse FR. (Nature 1 Jan 98)
14. MORE EVIDENCE FOR DNA DAMAGE VIA LONG-RANGE CHARGE TRANSFER
Charge transfer is classically a weak bond involving a coupling
between delocalized pi-electrons and a cation species, and in the
general sense, particularly in suitably composed polymers, the
term is used to describe an actual translocation of charge (an
electron transfer or an effective "hole" transfer) resulting from
classical charge-transfer coupling. Guanine (6-hydroxy-2-
aminopurine) is present in all living cells as a constituent (one
of the bases) of the nucleic acids DNA and RNA. Mutagenesis
refers to any change in DNA, and carcinogenesis refers to any
mutagenic change that produces cancer cells. Schuster and Gasper
(Georgia Inst. of Technol., US) report that injection of an
electron hole (radical cation) into a DNA strand can induce
damage at a guanine doublet site (GG-site) as much as 40
angstroms distant. These results are consistent with evidence
from other laboratories of apparent long-distance DNA damage. The
authors suggest that the guanine-doublet site, an easily damaged
site that has been implicated as a factor in mutagenesis and
carcinogenesis, can be oxidized via long range charge transfer
down the DNA double helix. QY: Gary B. Schuster, Georgia Inst. of
Technol. 404-894-2000 (J. Amer. Chem. Soc. 119:12762 1997)
(Chem. & Eng. News 5 Jan 98)
15. QUESTIONS CONCERNING THE PATHOGEN IN PRION DISEASES
Prions are a class of poorly understood proteins implicated in a
number of exotic human neurological diseases and in some common
animal diseases such as sheep scrapie and bovine spongiform
encephalopathy in cattle ("mad cow disease"). One human disease
in which prions have been strongly implicated is Creutzfeldt-
Jakob disease, which appears to have a genetic basis in about 15%
of the cases. What is remarkable about prions is that they
behave as infectious agents, but they are 100 times smaller than
viruses and their mechanism of replication is unclear. All the
prion diseases are apparently associated with the accumulation in
the brain of an abnormal protease-resistant isoform of the prion
protein PrP. In other words, an abnormal variant of the normal
PrP is somehow copied or produced by the disease process, which
can be initiated by introducing infectious prion into the system.
B. Chesebro (Rocky Mountain Labs., US), in a review of current
research in prion diseases, points out that although the idea of
prions as self-sufficient infectious proteins has received a
great deal of publicity because of the recent award of the Nobel
Prize in Medicine and Physiology to S. Prusiner for the discovery
of prions, "at the present time the fact remains that there are
no definitive data on the nature of prions." The author suggests
it would be tragic if the recent Nobel Prize award were to lead
to complacency regarding the obstacles still remaining in prion
research, and that "it is not mere detail, but rather the central
core of the problem, that remains to be solved."
QY: Bruce Chesebro (Science 2 Jan 98)
16. ULTRAVIOLET CELL DEATH BLOCKED BY A SKIN VIRUS
The largest and most complex animal viruses are the poxviruses,
among them smallpox and a related virus called monkeypox.
Selenium is a nonmetallic element (atomic number 34) found with
sulfur in various ores, and in soils and living systems. The
conductivity of selenium changes in response to light, and
because of this it has found application in photoelectric cells.
In animals, epithelial cells compose the cell layers that form
the interface between a tissue and the external environment, for
example, the cells of the skin, the lining of the intestinal
tract, and the lung airway passages, and "keratinocyte" is a
generic term for any mammalian epithelial cell. In most
biological systems, ultraviolet radiation is readily absorbed by
various molecular components, and often the result is cell death
(i.e., the radiation is "cytotoxic".) Shisler et al (4 authors at
2 installations, US) have now identified, in a skin poxvirus
(molluscum contagiosum) that infects humans, a gene expressing a
selenium-binding protein that protects human keratinocytes
against the cytotoxic effects of ultraviolet radiation and
hydrogen peroxide. This particular virus replicates only in skin
cells, and the authors suggest this is a viral mechanism to
maintain the viability of cell hosts necessary for viral
replication. QY: Bernard Moss, NIAID, US Nat. Inst. of Health,
Bethesda, MD 20892-0148 (Science 2 Jan 98)
17. CHEMOTAXIS OF NEURONS: VARIABLE RESPONSE MAY ASSIST TARGETING
In those animals that have nervous systems, one task of embryo-
logical development is to ensure the proper functional connect-
ions between nerve cells and other nerve cells, and between nerve
cells and muscle cells. The innervation must be exact, in the
sense that the growing nerve cell extension (the axon), which
will ultimately serve to propagate information, must reach a
specific and often distant target. In humans, for example, there
are nerve cells whose growing axons reach specific targets as
much as a meter distant from the cell body. The term chemotaxis
refers to movement of an organism in response to chemical
concentration gradients, and it is such gradients that in one way
or another apparently guide nerve cells during their growth
phase. The mesencephalon (midbrain) is located in the brainstem,
the region between the brain itself and the spinal cord, and a
commissure, of which there are many, is a band of nerve fibers
that cross from one side of the body to the other. Shirasaki et
al (3 authors at Osaka Univ., JP), in a study of growing cultured
rat embryo mesencephalon commissural axons, report evidence of a
change in the chemoattractant responsiveness of growing axons
during growth across an intermediate target. The authors suggest
such changes in responsiveness to chemoattractants may enable
developing axons to continue to navigate toward their final
destinations, and that encounters with the intermediate targets
might cause sensitization of growing axons to the next set of
cues necessary for guidance to the final target. QY: Ryuichi
Shirasaki (Science 2 Jan 98)
18. HERPESVIRUS AS A VIRAL ONCOGENE AND ANGIOGENESIS ACTIVATOR
Kaposi's sarcoma is an ordinarily rare cancer that can be common
in humans with compromised immune systems (for example, in AIDS),
and the herpesviruses are a class of viruses producing the
complex of herpes diseases, some of which are sexually transmit-
ted diseases clinically associated with AIDS. In cell biology,
the term "receptor" denotes a cell surface chemical entity,
usually a protein, that interacts with messenger molecules (e.g.,
hormones) in the extracellular solution. G-proteins are a family
of signal-coupling proteins that act as intermediaries between
activated cell receptors and effectors, for example, the trans-
duction of hormonal signals from the cell surface to the cell
interior. The G-protein is apparently embedded in the cell
membrane with parts exposed on the outside surface and inside
surface. The outside moiety is activated by the first messenger,
and the inside moiety activates the second messenger (which
begins a cascade of signals in the interior of the cell), the G-
protein thus acting as a trans-membrane signal transducer. In the
context of this report, the term "transformation" refers to the
conversion of normal cells into malignant cells exhibiting
uncontrolled growth and loss of functional specialization
(dedifferentiation). Angiogenesis, the origin and development of
blood vessels, is an important consideration in the growth of
cancerous tumors, since the tumor provokes directed angiogenesis
into itself with the end result that the tumor is supplied with
oxygen and nutrients. Without angiogenesis, tumors can attain
only a small size before becoming self-inhibiting. A cytokine is
any substance that promotes cell growth and cell division, and an
inflammatory cytokine is a cytokine involved in the inflammatory
response to tissue injury and infection. As a promoter of cell
growth and division, a cytokine acts as a messenger to cells, and
the transmission of the message requires a binding of the
cytokine molecule to a cytokine-specific receptor on the cell
surface. This receptor is either a protein or a protein complex
or a part of a protein. The lymphatic system is a complex network
for the distribution of lymph fluid (which is similar to blood
plasma -- blood without red cells), and lymphoma is a general
term for a tumor (benign or malignant) of tissue of the lymphatic
system. Bais et al (10 authors at 2 installations, US) report
that signaling by the Kaposi's sarcoma-associated herpesvirus G-
protein-coupled receptor leads to cell transformation and tumor
growth, and activates angiogenesis by mechanisms similar to those
produced by inflammatory cytokines. The authors suggest this is
the first demonstration that a Kaposi's sarcoma-associated
herpesvirus gene is capable of inducing both transformation and
angiogenesis, and that this evidence strongly supports the idea
that Kaposi's sarcoma-associated herpesvirus infection plays a
direct role in Kaposi's sarcoma pathogenesis and lymphoma-
genesis. QY: Enrique A. Mesri
(Nature 1 Jan 98)
19. ON THE CLINICAL ASPECTS OF GENETIC POLYMORPHISMS
A genetic polymorphism is a naturally occurring variation in the
normal nucleotide sequence of the genome within individuals in a
population, and an allele is one of two or more forms of a given
gene that control a particular characteristic, with the altern-
ative forms occupying corresponding loci on homologous chromo-
somes. Variations are denoted as polymorphisms only if they
cannot be accounted for by recurrent mutation and occur with a
frequency of at least about 1%. In general, perverse polymorph-
isms (as opposed to benign polymorphisms) are genetic variations
that are linked to pathological processes. Rosenthal and Schwartz
(Massachusetts Medical Society, US), in a short review of genetic
polymorphisms, suggest that in the future, with the entire human
genome represented on microchips, collections of allelic variants
will be screened in search of associations between specific
allelic combinations and susceptibility to a particular diseases,
and that human geneticists may soon have molecular tools powerful
enough to distinguish between benign and perverse polymorphic
combinations that contribute to a disease in a single patient.
QY: Nadia Rosenthal, New England J. of Med. 617-734-9800 (New
England J. Med. 8 Jan 98)
20. GENOMIC INFORMATION AND DRUG DISCOVERY
In its narrow sense, the term "drug discovery" refers to a
systematic search for pharmacological agents with specific inter-
actions of clinical utility. The usual primary targets for such
agents are enzymes and receptor-ligand pairs, and there are now
standard methods for proposing and screening selective inhibitors
of these molecules. Diseases with genetic etiology, however, may
involve molecular level loss-of-function mutations, in which case
targeting particular biochemical entities with drugs has little
use if the pathways of the entities have been switched off by the
genome. In such cases, there is now developing an alternative
method of drug discovery, termed "synthetic lethal screening",
which relies not on information concerning enzymes and receptors,
but on the genome itself. The essential idea of synthetic lethal
screening is as follows: If we call the mutation responsible for
a pathological process the "primary" mutation, there is evidence
that in many cases it is possible to produce a secondary mutation
such that the simultaneous existence of both mutations will be
lethal for cells carrying the two mutations. The idea is to
produce, with drugs, a numerically large array of secondary
mutations in apparently homologous systems in lower animal forms,
mutations that by themselves may not be lethal, and screen these
mutations to find those that are lethal when coupled with the
relevant primary mutations in these animal forms. New drugs are
thereby discovered, namely the drugs that produce secondary
mutations that are lethal for cells when combined in the same
cells with specific primary mutations, and apparently there is
already some evidence that the technique may be potentially
useful in the treatment of breast cancer and colon cancer: in
other words, malignant cells with an added (secondary) mutation
are selectively destroyed. Friend and Oliff (2 installations,
US), in a short review of the uses of genomic information in drug
discovery and the technique of synthetic lethal screening,
suggest that genetic screening in yeast, worms, and fruit flies,
and whole genome analyses, are quickly emerging as powerful tools
to accelerate the pace at which anti-cancer drugs are developed.
QY: Stephen H. Friend, Fred Hutchinson Cancer Res. Ctr., Seattle,
WA 98104 US (New England J. Med. 8 Jan 98)
---------------------------------------------
BOOK NOTES
R. Burlage, R. Atlas, D. Stahl, G. Geesey, G. Sayler:
TECHNIQUES IN MICROBIAL ECOLOGY
Oxford Univ., 1997, 480p, US65
A reference compendium of selected techniques. Microrganisms
associated with nutrient cycles, sampling techniques, nucleic
acid isolation and analysis techniques. The editors are
environmental scientists in biology and engineering.
W. Coleman and G. Tsongalis (eds.): MOLECULAR DIAGNOSTICS
For the Clinical Laboratorian
Humana Press, 1997, 400p, US79.50
A review of the current state and future prospects of diagnostic
medicine. Basic molecular biology, molecular technologies,
applications to molecular pathology, issues for the clinical
molecular pathology laboratory. Intended for medical
technologists, residents, and clinicians. The editors are
practicing pathologists.
J. Gribbin and S. Goodwin: ORIGINS
Our Place in Hubble's Universe
Overlook Press, 1998, 160p, US29.95
An illustrated non-technical review of contemporary astronomy and
cosmology with emphasis on images from various instruments:
Hubble Space Telescope, COBE Satellite, Galileo Spacecraft, ROSAT
X-Ray Satellite, etc. Simon Goodwin is an astronomer at the
University of Sussex, and John Gribbin is a science journalist
who has written several books explicating quantum physics and
astrophysics.
K. Riley, M. Hobson, S. Bence:
MATHEMATICAL METHODS FOR PHYSICS AND ENGINEERING
A Comprehensive Guide
Cambridge Univ., 1997, 975p, US44.95
An undergraduate text. Designed to be a complete review of
mathematics used in physics and engineering: from calculus and
matrices to Fourier series and group theory. 600 exercises. The
authors are at the University of Cambridge.
Brian Silver: THE ASCENT OF SCIENCE
Oxford Univ., 1998, 416p, US35
A non-technical history of Western science from the Renaissance
to the present. Galileo, Newton, Einstein, Heisenberg, plate
tectonics, particle physics, origin of life, universal entropy,
molecular biology, cosmology. The author is Professor of Physical
Chemistry at the Israel Institute of Technology.
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