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ScienceWeek
SCIENCE-WEEK
A Weekly Email Digest of the News of Science
A journal devoted to the improvement of communication
between the scientific disciplines, and between scientists,
science educators, and science policy-makers.
August 11, 2000 -- Vol. 4 Number 32
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All these fifty years of conscious brooding have
brought me no nearer to the answer to the question,
"what are light quanta?" Nowadays every Tom, Dick,
and Harry thinks he knows it, but he is mistaken."
-- Albert Einstein (1879-1955)
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PLEASE NOTE: The ScienceWeek front website page now
contains a list of more than 30 web-links to sources
of recent and breaking news in science, medicine, and
technology. The links are located in the middle section
left panel. We will continue adding to the list.
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Contents of this Issue:
1. Earth Sciences:
Causes of Climate Change Over the Past 1000 Years
-------------------------------------------------
The agreement between model results and observations for the past
1000 years suggests that natural variability plays only a
subsidiary role in the 20th century warming, and that the most
parsimonious explanation for most of the warming is that it is
due to the anthropogenic increase in greenhouse gases.
(Includes related background material.)
2. Astrophysics:
On the Ages of Pulsars
----------------------
New evidence indicates certain pulsars may be much older than
previously believed, which is a challenge to current models of
supernova explosions and neutron-star structure.
(Includes related background material.)
3. Particle Physics:
On Quantum Chromodynamics
-------------------------
A review of current concepts in quantum chromodynamics, the prime
working theory in particle physics.
(Includes related background material.)
4. Biophysics:
Magnetite in a Vertebrate Magnetoreceptor
-----------------------------------------
Evidence is presented that 1-micron chains of magnetite crystals
are involved in magnetic field detection in a species of fish.
(Includes related background material.)
5. Medical Biology:
Experimental Evidence Supporting the Prion Hypothesis
-----------------------------------------------------
New experimental evidence supports the prion hypothesis that a
protein (prion), by virtue of its ability to propagate in an
altered conformation, can act as an infectious agent.
(Includes related background material.)
6. Medical Biology:
Use of Poliovirus to Treat a Cancer
-----------------------------------
A genetically engineered poliovirus can specifically infect and
propagate in cell lines derived from malignant gliomas, and the
virus may be suitable for the treatment of malignant disease of
the central nervous system.
(Includes related background material.)
7. In Brief:
AIDS and Negative Population Growth in Africa
8. Focus Report: On Hadrons, Leptons, and Quarks
9. From the SW Archive:
Science and Society: On the Great Asymmetry
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
1. EARTH SCIENCES:
CAUSES OF CLIMATE CHANGE OVER THE PAST 1000 YEARS
The physical basis of the so-called "greenhouse effect" is
essentially as follows: Carbon dioxide gas is transparent to
visible light but relatively opaque to infrared radiation. The
same is true of glass. Relatively high-energy visible light
radiation from the sun passes inward through the atmosphere,
warms the surface of the Earth, which then radiates lower energy
in the form of infrared radiation (heat) back to the atmosphere.
But if the atmosphere has a concentration of infrared
impenetrable gases such as carbon dioxide, the infrared radiation
cannot pass out, and the surface of the Earth underlying the
atmosphere cannot cool, and the surface of the Earth thus will
continue to grow hotter.
There is no significant disagreement concerning the
mechanism of the greenhouse effect, but the consequences of the
effect, particularly for future global climate, are unclear.
... ... Thomas J. Crowley (Texas A & M University, US) presents a
detailed study of the causes of climate change over the past 1000
years, the author making the following points:
1) The author points out that the origin of the late-20th
century increase in global temperatures has prompted considerable
discussion. Detailed comparisons of climate-model results with
observations suggest that anthropogenic changes, particularly
greenhouse gas increases, are probably responsible for this
climate change. There are, however, a number of persistent
questions concerning these conclusions that involve uncertainties
in the level of low-frequency unforced variability in the climate
system, and whether factors such as an increase in *solar
irradiance or a reduction in *volcanism might account for a
substantial amount of the observed 20th century warming. Although
many studies have addressed these issues from the paleoclimate
perspective of the past few centuries, robust conclusions have
been hampered by inadequate lengths of the time series evaluated.
2) The author reports that the agreement between model
results and observations for the past 1000 years is sufficiently
compelling to allow one to conclude that natural variability
plays only a subsidiary role in the 20th century warming, and
that the most parsimonious explanation for most of the warming is
that it is due to the anthropogenic increase in greenhouse gases.
3) The data used in this study included physically based
reconstruction of Northern Hemisphere temperatures and indices of
volcanism, solar variability, and changes in greenhouse gases and
*tropospheric aerosols.
4) The author concludes: "There are... two independent lines
of evidence pointing to the unusual nature of late-20th century
temperatures. First, the warming over the past century is
unprecedented in the past 1000 years. Second, the same climate
model that can successfully explain much of the variability in
Northern Hemisphere temperature over the interval 1000-1850
indicates that only about 25% of the 20th-century temperature
increase can be attributed to natural variability. The bulk of
the 20th-century warming is consistent with that predicted from
greenhouse gas increases. These two lines of evidence provide
further support for the idea that the greenhouse effect is
already here."
-----------
Thomas J. Crowley: Causes of climate change over the past 1000
years.
(Science 14 Jul 00 289:270)
QY: Thomas J. Crowley [tcrowley@ocean.tamu.edu]
-----------
Text Notes:
... ... *solar irradiance: In general, the amount of solar
irradiation received from the Sun.
... ... *volcanism: In general, the eruption of lava.
... ... *tropospheric aerosols: The term "troposphere" refers to
the lowest 10 to 20 kilometers of the atmosphere (with the lower
boundary the surface of the Earth). The term "aerosol" refers to
a dispersion in which a finely divided solid is suspended in air
and the particles are of colloidal dimensions. The term
"colloidal dimensions" refers to the range approximately 1
nanometer to 100 nanometers in diameter.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 11Aug00
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
CLIMATOLOGY:
ANTHROPOGENIC ATMOSPHERIC AEROSOLS AND GLOBAL CLIMATE CHANGE
As was pointed out in the previous report in this issue (SW 23
Jun 00 report #5), aerosols are an important component of
atmospheric chemical dynamics, with the contributions of aerosols
to global and regional climate far from simple.
... ... S.E. Schwartz and P.R. Buseck (2 installations, US)
present a commentary on recent research on anthropogenic
atmospheric aerosols, the authors making the following points:
1) Most considerations of global climate change caused by
human activities have focused on the warming influence of
greenhouse gases. However, aerosols are another important
atmospheric constituent that influences climate and that has been
affected by human activities. In general, aerosol particles
increase scattering and absorption of shortwave (solar)
radiation, increase cloud reflectance, enhance cloud lifetimes,
and suppress precipitation. These phenomena are all thought to
exert a cooling influence on climate. Recent data indicate that
anthropogenic aerosols reduce cloud droplet size and suppress
precipitation downward of major urban areas and industrial
facilities, which is consistent with earlier hypotheses.
2) The influences of aerosols on climate are more complex
than those of greenhouse gases. Bulk aerosol composition is
highly variable spatially and temporally because of different
sources and production mechanisms and short atmospheric residence
times (from less than a day to more than a month). Particles
sizes range from nanometers to microns, and within the same size
class, particles can exhibit widely different compositions and
morphologies, with different constituents present within the same
particle (e.g., 10 nanometer carbon spherules can be found
embedded within much larger sulfate particles). The
inhomogeneities in properties and geographical distribution of
aerosols make it difficult to characterize their influences on
climate and to represent these influences in models.
3) Recent analysis of the consequence of absorption of
shortwave radiation by aerosols indicates that the heating of the
atmosphere can evaporate clouds. Clouds exert both cooling and
warming influences on climate: cooling in the shortwave (because
of their reflectance), and warming in the longwave (because of
absorption and re-emission of thermal infrared radiation). The
shortwave component dominates, so a reduction in cloud coverage
would result in a net warming influence.
5) The authors conclude: "Recent studies demonstrate both
the importance of aerosol effects on climate and the complexity
of aerosol-cloud interactions. Unfortunately for those would like
a quick and accurate assessment of anthropogenic climate forcing
over the industrial period, the studies also demonstrate that
there is much to be learned before such an assessment can
confidently be given."
-----------
S.E. Schwartz and P.R. Buseck: Absorbing phenomena
(Science 12 May 00 288:989)
QY: S.E. Schwartz [ses@bnl.gov]
-------------------
Summary by SCIENCE-WEEK http://scienceweek.com 23Jun00
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
ON CLIMATE FORCINGS IN THE INDUSTRIAL ERA
A "climate forcing" is an imposed perturbation of the Earth's
energy balance with space, for example, a change of the solar
radiation incident on the planet, or a change of carbon dioxide
in the Earth's atmosphere. The unit of measure of climate forcing
is Watts per square meter. Thus, the forcing due to the increase
of atmospheric carbon dioxide since pre-Industrial times is
approximately 1.5 Watts per square meter. Climate change is
combination of deterministic response to forcings and *chaotic
fluctuations -- the chaos a consequence of the nonlinear
equations governing the dynamics of the system. Quantitative
knowledge of all significant climate forcings is needed to
establish the contribution of deterministic factors in observed
climate change and to predict future climate. J.E. Hansen et al,
in a review of current considerations concerning climate forcings
in the Industrial era, make the following points: 1) The forcings
that drive long-term climate change are not known with an
accuracy sufficient to define future climate change. 2)
Anthropogenic greenhouse gases, which are well-measured, cause a
strong positive (warming) force. But other, poorly measured,
anthropogenic forcings, especially changes of atmospheric
aerosols, clouds, and land-use patterns, cause a negative forcing
that tends to offset greenhouse warming. 3) One consequence of
this partial balance is that the natural forcing due to solar
irradiance changes may play a larger role in long-term climate
change than inferred from comparison with greenhouse gases alone.
Current trends in greenhouse gas climate forcings are smaller
than in popular "business as usual" or 1 percent per year carbon
dioxide growth scenarios. The authors suggest that a summary
implication of their considerations is a paradigm change for
long-term climate projections: uncertainties in climate forcings
have supplanted global climate sensitivity as the predominant
issue. The authors further suggest that climate forcing scenarios
are essential for climate predictions, but if only one forcing
scenario is used in climate simulations, as has been a recent
tendency, the scenario itself is likely to be taken as a
prediction, as well as the calculated climate change. The authors
recommend that the use of multiple scenarios will aid objective
analysis of climate change as it unfolds in coming years.
-----------
J.E. Hansen et al (6 authors at National Aeronautics and Space
Administration, US)
Climate forcings in the Industrial era.
(Proc. Natl. Acad. Sci. US 27 Oct 98 95:12753)
QY: James E. Hansen [jhansen@giss.nasa.gov]
-----------
Text Notes:
... ... *chaotic fluctuations: The term "chaotic", in this
context, is specific. In the study of physical systems, the
term "chaotic behavior" has a specific meaning: the behavior of a
system is said to be "chaotic" if its final state is so sensitive
to the system's precise initial conditions that the behavior of
the system is in effect unpredictable and cannot be distinguished
from a random process, even though the behavior of the system is
strictly determinate in a mathematical sense. In other words, a
deterministic system characterized by extremely sensitive
instabilities, despite the system being determinate, can exhibit
behavior that is unpredictable, and the system is then called
"chaotic". During the past several decades, the analysis of such
chaotic systems has intrigued both physicists and mathematicians.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 4Dec98
For more information: http://scienceweek.com/swfr.htm
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
2. ASTROPHYSICS:
ON THE AGES OF PULSARS
Neutron stars are believed to form when a massive star
exhausts its fuel and the mass of the stellar core remaining
after a consequent supernova explosion is between 1.4 solar-
masses (the Chandrasekhar limit) and 2 to 3 solar-masses. With
diameters of only 10 to 15 kilometers, intense magnetic fields
[e.g., 10^(8) tesla], and extremely rapid spin (e.g., as much as
500-700 rotations per second), young neutron stars are evidently
responsible for various intrinsic pulsation phenomena, and thus
are called "pulsars".
Current views concerning the life and death of a star are
based primarily on quantitative models which are designed to
predict astrophysical observations, and each new set of
observations becomes a test of any extant related model. In
theory, the total energy emitted by a pulsar is a combination of
emitted radiation and outflow of particles. These particles
transfer part of their energy to the cloud of atoms surrounding
the pulsar, which forces the cloud to glow as a bright region of
ionized gas. As pulsars lose energy through emitted radiation,
their period of rotation becomes longer, so that the present
observed period of rotation depends on both the initial period
and the rate of its increase. Theoretically, if one assumes a
very fast initial period and energy loss from pure radiation
(i.e., without consideration of emitted particles), a
"characteristic age" can be calculated for a pulsar based on its
present period of pulsation. In general, it is believed the
characteristic age should be close to the true age of the pulsar,
and any set of observations which would contradict this would
have important theoretical ramifications.
... ... B.M. Gaensler and D.A. Frail (2 installations, US)
present data concerning the age of a particular pulsar (B1757-24)
determined by analysis of its motions. The authors make the
following points:
1) The assumption that the characteristic age of a pulsar is
approximately its true age has led to some puzzling results,
including many pulsars with small characteristic ages having no
associated supernova remnants. The properties of the pulsar
B1757-24, which is located just outside the edge of a supernova
remnant, indicate that the pulsar was born at the center of the
remnant with a substantial velocity, and that it has subsequently
overtaken the expanding blast wave. With a characteristic age of
16,000 years, this pulsar is expected to have a proper motion of
63 to 80 milliarcseconds (mas) per year.
2) The authors report observations of the nebula surrounding
pulsar B1757-24, and the observations limit the proper motion of
this pulsar to 25 milliarcseconds per year. This implies a
minimum age of 39,000 years. A more detailed analysis suggests
the true age of this pulsar may be 170,000 years, which is
significantly larger than the characteristic age. The authors
suggest from this result and from other discrepancies associated
with pulsars, that characteristic ages greatly underestimate the
true ages of pulsars.
3) The authors conclude: "If other pulsars are indeed older
than they seem, our understanding of pulsar velocities,
asymmetries in supernova explosions, the fraction of supernovae
that produce pulsars, and the physics of neutron star structure
and cooling must be reconsidered."
4) In a commentary on the above work, John H. Seiradakis
(University of Thessaloniki, GR) states: "This discrepancy
between the characteristic age of the pulsar [B-1757-24] and the
age of the supernova remnant poses a serious problem to either
the association between the pulsar and the supernova remnant or
[to] the common belief that the characteristic age of pulsars
represents their true age."
-----------
B.M. Gaensler and D.A. Frail: A large age for the pulsar B1757-24
from an upper limit on its proper motion.
(Nature 13 Jul 00 406:158)
QY: B.M. Gaensler [bmg@space.mit.edu]
-----------
John H. Seiradakis: Older than they look.
(Nature 13 Jul 00 406:139)
QY: John H. Seiradakis [jhs@astro.auth.gr]
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 11Aug00
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
ON THE BIRTH AND LIFE OF NEUTRON STARS
In this century, astronomy and astrophysics have contributed
greatly to what might be called the "Hall of Wonders", the
gallery of real-world spellbinding objects. Perhaps the two most
outstanding contributions to this gallery are black holes and
neutron stars. Black holes, born of the death of super-massive
stars, are in this century the most spectacular astronomical
objects known; neutron stars, born of the death of merely massive
stars, are not far behind on any gauge of the extraordinary. A
neutron star is an extremely dense and compact star that has
undergone gravitational collapse to such an extent that much of
the material has been compressed into neutrons. Such stars were
theoretically postulated in the 1930s, but it was not until 1967
that their existence was actually confirmed by observations...
It is also thought that gamma-ray bursts may have neutron star
origins. Models of the structure of neutron stars have been
derived from study of the sudden changes in pulsar spin rates
("glitches").
... ... Joshua N. Winn (Massachusetts Institute of Technology,
US) presents a review of current research on neutron stars, the
author making the following points:
1) Perhaps one problem with the "jaw-dropping" statistics
concerning pulsars is that the statistics are too extreme. Using
Earthly analogies, it is difficult to comprehend an entity with a
density of 10^(14) grams per cubic centimeter [*Note #1] in a
gravitational field that produces an acceleration of free fall
(g) 600 billion times that produced at the surface of Earth. It
is even more difficult to visualize such a dense city-size object
"as it spins furiously, squirting plasma (ionized gases) from
electric arcs near the poles of its inconceivable magnetic field
and swirling up a superfluid of neutrons in its interior." But
after 30 years of research, enough is known about pulsars to
reconstruct the outlines of their existences.
2) The newborn neutron star, produced by a dead massive
star, possesses four salient characteristics: a) a fast rotation
rate, typically 50 times per second; b) a directed velocity in
excess of 1000 kilometers per second that may be caused by
violent asymmetry in the supernova explosion of the parent star;
c) extreme temperature due to the small radiative surface area
(e.g., temperatures of 100,000 to 1 million degrees kelvin; d) an
immense magnetic field, typically a million times stronger than
that of the Earth. (The author notes: "It is easier to write the
figure 10^(12) gauss than to ponder its zeros.")
3) A spinning magnet generates voltages, as was demonstrated
by Michael Faraday in 1831, and a neutron star is a gargantuan
spinning magnet, the resultant voltage tearing electrons,
positrons, and ions from its surface and flinging them outward
into space along the magnetic field lines. This is the so-called
"pulsar wind", whose effects can observed in the turbulence of
gas clouds associated with supernova, the so-called "pulsar-wind
nebula."
4) A second consequence of the intense magnetic field of the
spinning neutron star is the pulsation of the pulsar. The
magnetic poles of neutron stars emit narrow beams of radiation in
addition to the pulsar-wind, and since the magnetic axis is
offset from the spin axis, the beams execute an oscillation in
space observed from Earth as a pulsing of radiation. The
pulsation rate of neutron stars declines with their age, and the
pulse period (P) and the "spin-down rate" ("P-dot"; the time-
derivative of P) are at present the two most important
observables concerning pulsars. A plot or P-dot versus P of the
approximately 700 pulsars that have been identified has been
useful in research on these objects in the same way that the
*Hertzsprung-Russell diagram, plotting luminosity versus
temperature, has been useful in understanding the general
evolution of ordinary stars.
5) Most pulsars slow down at a steady rate, but a few
pulsars exhibit slight and sudden "glitches" in their periods,
and these glitches have been used as the basis for studying the
structure of pulsars. It is presently believed that glitches
probably originate beneath the thin crust of a pulsar, in a dense
mantle of heavy nuclei permeated by a *superfluid of neutrons,
and that the *angular momentum of the superfluid is broken up
into discrete quantized vortices which migrate outward to the
crust as the neutron spin-rate decreases. It is believed the
migrations and surface eruptions of superfluid quantum vortices
(which transfer angular momentum to the crust) cause the sudden
changes in spin-rate which are observed as "glitches" in pulsar
behavior [*Note #2].
-----------
Editor's note: In addition to the background material below, see
the SW Focus Report "The Death of Stars" available at URL
http://scienceweek.com/swfr002.htm
-----------
Joshua N. Winn: The life of a neutron star.
(Sky & Telescope July 1999)
QY: Joshua N. Winn, Mass. Inst. of Technology 617-253-1000.
-----------
Text Notes:
... ... *Note #1: At such a density, the entire human species
could exist as an object the size of small marble -- with the
total mass of the entire human species retained: i.e., the marble
would weigh approximately 10^(14) grams.
... ... *Hertzsprung-Russell diagram: The Hertzsprung-Russell
diagram is a plot of stellar absolute magnitude against spectral
type (luminosity vs. temperature), and is one of the most useful
diagrammatic aids in astrophysics. 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.
... ... *superfluid: In general, a "superfluid" is a fluid that
flows without any resistance (i.e., zero viscosity).
... ... *angular momentum: The momentum of a body by virtue of
its rotation and/or orbital revolution. It is a conserved
quantity, and as a consequence a body spins faster as it becomes
smaller.
... ... *Note #2: Quantum vortices were discussed in the last
issue of SW (20 Aug 99 #34) in connection with the superfluid
behavior of liquid helium-3. Here is the material from that issue
on quantum vortices: A quantum vortex is a type of flow pattern
exhibited by superfluids under certain experimental conditions,
e.g., liquid helium in a rotating container. The term "vortex"
designates the familiar whirlpool pattern where the fluid moves
circularly around a central line and the velocity decreases in
inverse proportion to the distance from the center. A superfluid
is considered to be characterized by a macroscopic
quantum-mechanical wave function that locks the superfluid into a
*coherent state. This forces certain mathematical constraints on
the wave function, so that for a superfluid in a rotating
container, the system (the wave equation for the system) produces
a lattice of quantized vortex lines, each line the axis of a
microscopic vortex, with the entire array of vortex lines
rotating rigidly with the container. The essential idea is that
when superfluid helium is in a rotating container, the
mathematics of the system wave function are such that a set of
discrete microscopic vortex states are produced by each
particular set of boundary conditions, and these microscopic
vortex states are experimentally observable [*Note #3]. In short,
the result is a system where the "quantum world" becomes visible
on a macroscopic scale.
... ... *coherent state: In quantum physics, coherence is matter
of locking of phase differences between wave functions. The wave
functions of two or more particles are said to be coherent if the
phase difference between their wave functions remains constant.
In general, a perfectly coherent system of particles can be
described by a single macroscopic wave function.
... ... *Note #3: Below a certain rotation speed threshold, no
vortices exist, and the superfluid remains at rest while the
container rotates (the Landau state). At the threshold speed, the
first vortex appears and corresponds to the first excited
rotational state of the system. If the container continues to
accelerate, additional quantized vortices appear, and at any
given speed the vortices form a regular array that rotates with
the vessel.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 27Aug99
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
ON NEUTRON STARS
During the terminal stages of the evolution of a star, part of
the mass of the star is blown off and lost. If the remnant mass
is between 1.4 and 2 to 3 solar-masses, the star will collapse
into a neutron star, a body with a radius of only 10 to 15
kilometers, but 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)
times 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. A
few pulsars have been found in *binary systems, and the empirical
estimated masses of the pulsars are consistent with the masses
predicted by neutron star models. ... ... L. Bildsten and T.
Strohmayer (2 installations, US) present a review of current
research concerning neutron stars, the authors making the
following points: 1) With a density comparable to that of an
atomic nucleus, a neutron star provides an extreme environment
for fast and violent phenomena. Matter orbiting a neutron star
can have a period as short as a millisecond. When such matter
crashes into the star (i.e., is "accreted" by the star), such
matter can be moving at one-third the speed of light. In general,
because their behavior can vary over readily observable
timescales, neutron stars can be rich sources of information
about nuclear physics, general relativity, and astrophysics. 2)
Though relatively elusive, neutron stars have been detected and
studied over a broad range of electromagnetic frequencies, from
radio frequencies to *gamma rays. To date, astronomers have
identified more than 1000 of the estimated 10^(8) neutron stars
in our galaxy. New orbiting astronomical satellites have produced
recent rapid growth in our knowledge of these objects, with much
of the progress occurring in our understanding of neutron stars
that undergo sudden large energy releases. 3) Although most
neutron stars have been discovered as radio pulsars, only a small
fraction of the radiated energy of a neutron star (typically
approximately 10^(-5)) is expected to be radio emission energy.
Most of the energy instead departs as photons with energies above
10^(8) *electronvolts. 4) The precise timing of radio pulsars has
yielded astonishing astronomical discoveries, such as multiple
Earth-mass planets orbiting a neutron star, and the direct
confirmation of the loss of orbital angular momentum due to
gravitational radiation in a double neutron star binary system
(for which Russell Hulse and Joseph Taylor received the 1993
Nobel Prize in Physics). 4) The brightest accreting neutron stars
reside in binary systems and accrete matter from their
companions. These accreting neutron stars typically have
luminosities more than a thousand times that of the Sun. 5) There
is every reason to believe that new classes of neutron stars will
be discovered by continued observations from the currently
orbiting satellites combined with the international fleet of new
x-ray and gamma-ray satellites planned for launch during the next
two years.
-----------
Editor's note: In addition to the background material below, see
the SW Focus Report "The Death of Stars" available at URL
[http://scienceweek.com/swfr002.htm]
-----------
L. Bildsten and T. Strohmayer: New views of neutron stars.
(Physics Today February 1999)
QY: Lars Bildsten, Univ. of Calif. Berkeley, 510-643-8520.
-----------
Text Notes:
... ... *Pulsars: Pulsars 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.
... ... *binary systems: Binary stars are a pair of stars
revolving around a common center of mass under the influence of
their mutual gravitational attraction, and apparently the
majority of stars in the Universe are binaries and not singlets.
In some cases the binary system is resolvable into two
components, and in other cases the presence of a second star is
inferred by perturbations in the motion or emitted radiation of
the first star. If the binaries are close enough, they may share
stellar material, and this results in a particular kind of
stellar evolution.
... ... *gamma rays: Gamma rays are radiation of high energy,
from about 10^(5) *electronvolts to more than 10^(14)
electronvolts -- radiation with the shortest wavelengths and
highest frequencies, the gamma ray region of the electromagnetic
spectrum merging into the adjacent lower energy x-ray region.
... ... *electronvolts: An electronvolt is defined as the energy
acquired by an electron falling freely through a potential
difference of one volt, and is equal to 1.6022 x 10^(-19) joule.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 16Apr99
For more information: http://scienceweek.com/swfr.htm
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
3. PARTICLE PHYSICS:
ON QUANTUM CHROMODYNAMICS
According to the Standard Model of physics, the fundamental
forces comprise the gravitational force, the electromagnetic
force, the nuclear strong force, and the nuclear weak force. The
strong force is approximately 100 times stronger than the
electromagnetic interaction and in general is the force
responsible for the stability of the atomic nucleus.
Quantum field theory is the mathematical fusion of quantum
mechanics with special relativity theory, and there are
essentially 2 branches: quantum electrodynamics (applicable to
charged particles involved in electromagnetic interactions) and
quantum chromodynamics (applicable to nuclear particles involved
in strong force interactions).
A quark is a hypothetical fundamental particle, having
charges whose magnitudes are one-third or two-thirds of the
electron charge, and from which the elementary particles may in
theory be constructed. Quantum chromodynamics (QCD) is a theory
that describes the strong interaction in terms of quarks and
antiquarks and the exchange of massless "gluons" between them.
The "chromo-" in chromodynamics derives from the use of
designated "color" attributes of quarks, the various "colors"
labels for various quark properties.
The equations of quantum chromodynamics are difficult to
solve, but improvements in computing power and computing
techniques have made it possible to demonstrate that the theory
has considerable success in predicting the outcome of experiments
at high energy particle accelerators.
... ... Frank Wilczek (Institute of Advanced Study Princeton, US)
presents a review of current concepts in quantum chromodynamics,
the author making the following points:
1) Whereas in quantum electrodynamics (QED) there is just
one kind of charge (electric charge), quantum chromodynamics
(QCD) has 3 different kinds of charge labeled by "color". The QCD
color names are arbitrary: the color charges of QCD have nothing
to do with physical colors. Rather, the color charges have
properties analogous to electric charge. In particular, the color
charges are conserved in all physical processes, and there are
photon-like massless particles, called "color gluons", that
respond in appropriate ways to the presence or motion of color
charge, very similar to the way photons respond to electric
charge.
2) The quarks are a class of particles that carry color
charge, and there are 6 different kinds ("flavors") of quarks:
up, down, strange, charmed, bottom, top. Of these, only up and
down quarks play a significant role in the structure of ordinary
matter. The other, much heavier quarks, are all unstable. A quark
of any one of the 6 flavors can also carry a unit of any of the 3
color charges. Although the different quark flavors all have
different masses, the theory is perfectly symmetrical with
respect to the three colors.
3) Despite their similarities, there are crucial differences
between quantum chromodynamics and quantum electrodynamics:
... ... a) The response of gluons to color charge is much more
vigorous than the response of photons to electric charge.
... ... b) In addition to just responding to color charge, gluons
can also change one color charge into another. All possible
changes of this kind are allowed, and yet color charge is
conserved. So the gluons themselves can carry unbalanced color
charges. For example, if absorption of a gluon changes a blue
quark into a red quark, then the gluon itself must have carried
one unit of red charge and minus one unit of blue charge.
... ... c) The 3rd difference between QCD and QED is the most
profound and follows from the 2nd: Because gluons respond to the
presence and motion of color charge, and also carry unbalanced
color charge, it follows that gluons, quite unlike photons,
respond directly to one another. Photons, in contrast, are
electrically neutral.
4) At first sight, it is difficult to accept that the
equations of quantum chromodynamics can describe the real world
of the strongly interacting particles. None of the particles that
have actually been seen appear in QCD, and none of the particles
that appear in QCD have every been observed. In particular, we
have never seen particles that carry fractional electric charge,
which we nonetheless ascribe to the quarks. And certainly we have
not seen anything like gluons -- massless particles mediating
long-range strong forces. So if quantum chromodynamics is to
describe the world, it must explain why quarks and gluons cannot
exist as isolated particles. That is the so-called "confinement
problem".
-----------
Frank Wilczek: QCD made simple.
(Physics Today August 2000)
QY: Frank Wilczek [wilczek@ias.edu]
-------------------
Summary by SCIENCE-WEEK http://scienceweek.com 11Aug00
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
PARTICLE PHYSICS: ON GLUONS AND GLUEBALLS
The physics of elementary particles is in the midst of an era of
conceptual complexity that some people find unsettling and other
people find invigorating. A quark is a hypothetical fundamental
particle, having charges whose magnitudes are one-third or
two-thirds of the electron charge, and from which the elementary
particles that have an apparent internal structure may in theory
be constructed. Quarks are believed to be held together through
the exchange of gluons, massless particles that carry the *strong
force. At the present time, 18 different quarks with various
properties are thought to exist, with a corresponding number of
*antiquarks. Gluons have a "sticking" property -- they can
agglomerate -- and agglomerations of gluons alone are called
"glueballs". ... ... F.E. Close and P.R. Page review current
ideas concerning gluons and glueballs, and the authors make the
following points: 1) Along with fractional electric charge,
quarks also have "flavor" in 6 varieties (up, down, charm,
strange, top, and bottom), and "color" (red, yellow, or blue).
[*Note #1] 2) Quarks may also attach to antiquarks, particles
that have opposite charge, and an antiquark comes in anticolors
(antired, antiyellow, antiblue). An anticolor is mathematically
denoted by negative color, and a color and its anticolor attract.
3) The theory of electromagnetism describes the attraction
between opposite electric charges. In the 1940s, physicists
merged electromagnetism with relativity and quantum theory,
creating quantum electrodynamics (QED). This theory -- the most
successful theory known to physics -- holds that the
electromagnetic force is transmitted by massless objects called
photons. These quanta of light banish the classical idea of
action at a distance. It can be said that photons bounce between
an electron and an antiparticle (the positron) in such a manner
as to draw the two together. 4) The equivalent theory of color
charges, which communicate via the *strong force, is called
quantum chromodynamics (QCD). Gluons, the massless quanta of the
strong force, transmit the color interactions. 5) Gluons are
fundamentally different from photons. Photons do not have charge,
so one photon cannot push or pull on another photon. Gluons,
however, are themselves colored. A red quark, for example, can
turn into a blue quark by radiating a red/antiblue gluon.
Basically, a gluon can attract another gluon. Another difference
between photons and gluons is that while photons uniformly
surround electrons, forming a shell with spherical symmetry whose
density falls off with distance, gluons are not uniformly
distributed and instead clump together into a tube linking a
quark and an antiquark. The color originating in the quark can be
thought to "flow" through the tube to the antiquark, where it
becomes absorbed. 6) In 1972 H. Fritzch and M. Gell-Mann
predicted that two or more gluons can combine into a strongly
bound, neutral-colored particle of pure "glue". This hypothetical
object is called a "glueball". A glueball is thought to have a
radius of 0.5 x 10^(-15) meters (less than that of a proton), and
exist for less time than light takes to cross a hydrogen atom. 7)
The authors state that although the idea of glueballs was
elegant, quantum chromodynamics is a "rather messy theory", since
the peculiar "sticky" character of the strong force makes it
impossible to perform exact calculations. Almost everything known
about color and glue comes not from direct calculation but from
massive computer simulations known as "lattice QCD". 8) Finally,
the authors discuss various current and planned future attempts
to detect the existence of glueballs, and they conclude: "One of
these experiments will, we fondly hope, upturn unambiguous
evidence of unadulterated glue."
----------
F.E. Close and P.R. Gage (2 installations, UK US)
Glueballs.
(Scientific American November 1998)
QY: Frank E. Close, University of Oxford, UK.
-----------
Text Notes:
... ... *strong force: The fundamental forces comprise the
gravitational force, the electromagnetic force, the nuclear
strong force, and the nuclear weak force.
... ... *antiquarks: The antimatter quark entity. In general,
antiparticles are homologs of elementary particles but with
opposite charge. The positron, for example, is the antimatter
particle homologous to the electron. Matter composed entirely of
antiparticles is called antimatter.
... ... *Note #1: In this context, flavors and colors are labels
for specific sets of properties associated with specific types of
quarks. Some people call these labels "whimsical", but perhaps
there is some sense to the whimsy, since it emphasizes that at
the present time we are apparently unable to describe the
properties and behaviors of the fundamental particles with
classical language (i.e., with the language of old models).
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 6Nov98
-------------------
Related Background:
EVIDENCE FOR A QUARK-GLUON PLASMA
... According to current theory, quarks and gluons cannot exist
in isolation. But theory also predicts that at temperatures
10^(12) degrees Kelvin or greater (such as existed during the
first 0.01 second of the history of the universe) a drastic
change in the structure of nuclear matter occurs, and only
descriptions in terms of quarks and gluons apply. A plasma is a
gas consisting entirely of equal numbers of positive and negative
charges. ... ... F. Wilczek (Institute for Advanced Study
Princeton, US), in a short review of recent experiments that for
the first time apparently produced a quark-gluon plasma, "an
extraordinary new state of matter", suggests that an important
question is whether, as a function of temperature, the transition
from ordinary matter to a quark-gluon plasma is continuous or
discontinuous. A discontinuous transition could imply explosive
instabilities, which in turn may have been important in the
evolution of the early universe.
QY: Frank Wilczek [wilczek@ias.edu]
(Nature 22 Jan 98) (Science-Week 23 Jan 98)
-------------------
Related Background:
FIRST EVIDENCE OF AN EXOTIC MESON
In particle physics, the term "meson" has had an interesting
history. Between 1939 and 1947, it was used to refer to what are
now called "muons". In 1947, the definition changed, and meson
now refers to an unstable, strongly interacting sub-nuclear
particle that consists of a quark bound to an anti-quark. There
is more than one type of meson, but they all consist of quarks
and anti-quarks bound together by "gluons". In the 1970s,
theorists predicted the existence of "exotic" mesons whose gluon
linkages between quarks and anti-quarks had the mathematical
properties of vibrating strings. But no one had or has yet
provided evidence of exotic mesons. ... ... Now Suh-Urk Chung et
al (Brookhaven National Laboratory, Upton NY US) have apparently
finally identified such a particle in collisions of fast-moving
mesons called "pions" with protons in a liquid hydrogen target.
They have determined the exotic meson's mass to be approximately
1.4 Gev (billion-electron-volts), and another laboratory, using a
completely different experimental method, has evidently
independently confirmed an exotic meson with the same mass of 1.4
Gev. But whatever excitement there is about finally identifying
the exotic meson, it is apparently combined with puzzlement,
because the revealed mass is less than what had been predicted.
Revisions of theory may be in order, since in the arena of
particle physics, revisions are the usual consequence of
puzzlement.
QY: S-H. Chung, Brookhaven National Lab. (516) 344-8000.
(Phys. Rev. Lett. 1 September) (Science-Week 12 Sep 97)
For more information: http://scienceweek.com/swfr.htm
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
4. BIOPHYSICS:
MAGNETITE IN A VERTEBRATE MAGNETORECEPTOR
An enormous variety of what are essentially experiments in
viability has occurred during the more than 3.5 billion years of
biological evolution on Earth, and among these experiments is a
striking diversity of biological devices that function to sense
changes in the environment of the organism. Consider, for
example, magnetic field detection:
... ... C.E. Diebel et al (5 authors at 2 installations, NZ US)
report on a vertebrate magnetoreceptor, the authors making the
following points:
1) The key behavioral, physiological, and anatomical
components of a magnetite-based magnetic sense have been
previously demonstrated in rainbow trout (Oncorynchus mykiss),
with candidate receptor cells located within a discrete sub-layer
of the olfactory tissues (olfactory lamellae) in the nose of the
trout. These receptor cells were shown to contain iron-rich
crystals similar in size and shape to magnetite crystals
extracted from salmon.
2) The authors now demonstrate that these crystals, mapped
to individual receptors by *confocal and atomic force microscopy,
are magnetic: the crystals are uniquely associated with dipoles
detected by *magnetic force microscopy. Analysis of their
magnetic properties identifies the crystals as *single-domain
magnetite particles. In addition, 3-dimensional reconstruction of
the candidate receptors using confocal and atomic microscopy
imaging confirm that several magnetite crystals are arranged in a
chain of approximately 1 micron length within the receptor, and
that the receptor is a multi-lobed single cell.
3) The authors suggest these results are consistent with a
magnetite-based detection mechanism, since 1-micron chains of
single-domain magnetite crystals are highly suitable for the
behavioral and physiological responses to magnetic intensity
previously reported for the trout.
4) The authors conclude that "understanding should now be
sought of how the chains of crystals could transduce a magnetic
field into an electrical signal in the nervous system."
-----------
C.E. Diebel et al: Magnetite defines a vertebrate
magnetoreceptor.
(Nature 20 Jul 00 406:299)
QY: Carol E. Diebel [cdiebel@akmuseum.org.nz]
-----------
Text Notes:
... ... *confocal and atomic force microscopy: In general, a
"confocal microscope" is a microscope in which an aperture in the
illuminating system confines the illumination to a small spot on
the specimen, and a corresponding aperture in the imaging system
(which may be the same aperture in reflecting and fluorescence
devices) allows only light transmitted, reflected, or emitted by
the same spot to contribute to the image. By suitable mechanical
or optical means, the spots are made to scan the specimen as in a
television raster. Compared to conventional microscopy, confocal
techniques offer improved resolution and improved rejection of
out-of-focus noise. In atomic force microscopy, a tip is fixed to
a cantilever whose position is monitored while the tip scans the
surface. The force between the tip and the surface determines the
position of the cantilever. When recorded in atomic resolution,
the image represents a map of atomic forces at the surface. The
advantage of atomic force microscopy is that the probed surface
does not need to be electrically conducting.
... ... *magnetic force microscopy: This technique is capable of
determining magnetic domain structure in a variety of magnetic
materials, including small particles with a spatial resolution of
less than 100 nanometers. Because it is sensitive to magnetic
forces, the technique can also image magnetic structures that are
covered by a layer of non-magnetic material.
... ... *single-domain magnetite particles: An oxide of iron,
magnetite (magnetic iron ore) is attracted by a magnet but does
not attract particles of iron to itself. In this context, the
term "domain" refers to a region in which magnetic moments are
uniformly arrayed.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 11Aug00
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
STRUCTURE AND FUNCTION OF VERTEBRATE MAGNETIC SENSE ORGANS
One of the more exhilarating moments in science occurs when a
long-standing mystery is finally solved. It has been thought for
some time that many diverse animals are able to use the Earth's
magnetic field for navigation during migration and homing, but
both the detection mechanism and the neural pathways involved
have never been elucidated. There have been theories linking the
detection of magnetic fields to vision, electroreception, and
magnetite particles, but until now no evidence has been forth-
coming to support any theory, and there is contrary evidence for
the involvement of both vision and electroreception. Magnetite is
an iron ore strongly attracted by a magnet, and now it appears
that magnetite particles are indeed the essential components of
magnetic field detection, at least in one vertebrate. Walker et
al (6 authors at Univ. of Auckland, NZ) describe the key
components of the magnetic sense ability of the rainbow trout
(Oncorhynchus mykiss), identify an area in the nose of the trout
where candidate magnetoreceptor magnetite-containing cells are
located, and present results of behavioral and
electrophysiological studies of trout responses to magnetic
fields. The authors suggest their work provides experimental
support for the idea that animals use the magnetic sense for
navigation.
-----------
QY: Michael M. Walker [m.walker@auckland.ac.nz]
(Nature 27 Nov 97) (Science-Week 19 Dec 97)
For more information: http://scienceweek.com/swfr.htm
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
5. MEDICAL BIOLOGY:
EXPERIMENTAL EVIDENCE SUPPORTING THE PRION HYPOTHESIS
In general, the "prion hypothesis" postulates that a protein
(prion), by virtue of its ability to propagate in an altered
conformation, can act as an infectious agent.
Prions are apparently infectious agents that lack nucleic
acid and are composed of a *beta-sheet-rich altered conformation
of a normal cellular protein. Prion infectivity is believed to
result from the ability of the prion protein in its altered
conformation to bind to the normal form of the protein and
catalyze the conversion of the normal protein to the infectious
conformation.
While originally identified as the causative agent for a set
of related transmissible spongiform encephalopathies, including
Cruetzfeldt-Jacob disease in humans, scrapie in sheep, and "mad
cow disease" in cattle, self-propagating beta-sheet-rich protein
aggregates also underlie a variety of noninfectious
neurodegenerative diseases. These include the relatively common
disorders Alzheimer's disease and Parkinson's disease, as well as
inherited polyglutamine repeat disorders such as Huntington's
disease. [For more on the above pathologies, see related
background material below.]
... ... H.E. Sparrer et al (4 authors at University of California
San Francisco, US) report experimental evidence supporting the
prion hypothesis, the authors making the following points:
1) In addition to a role in human pathogenesis, beta-sheet-
rich aggregates of glutamine and asparagine-rich domains mediate
inheritance of certain prion-like traits ([PSI+] and [URE3]) in
the yeast Saccharomyces cerevisiae, and the easily manipulated
genetics of this organism has made yeast prions a rich source of
information concerning the mechanism of prion propagation in vivo
as well as the role of prion-based inheritance in the normal
physiology of a cell.
2) Starting with purified, bacterially produced protein, the
authors created a yeast prion-like trait- ([PSI+]) inducing
agent, the agent based on an altered (prion) conformation of a
yeast protein (Sup35p). After converting this protein to its
prion conformation in vitro, the authors introduced it into the
cytoplasm of living yeast, and this resulted in a greatly
increased rate of appearance of the well-characterized prion-like
trait, which is known to result from self-propagating aggregates
of the altered form of the cellular protein Sup35p [*Note #1].
The authors state: "Thus, as predicted by the prion hypothesis,
proteins can act as infectious agents by causing self-propagating
conformational changes."
3) In a commentary on the above work, Mick F. Tuite
(University of Kent Canterbury, UK) states: "[Sparrer et al] show
that the prion form of the normal yeast protein Sup35p
effectively seeds a self-propagating conformational change in
normal Sup35p of living yeast cells. Their demonstration provides
the finishing touches to an extensive body of data that supports
the protein-only hypothesis."
-----------
H.E. Sparrer et al: Evidence for the prion hypothesis: Induction
of the yeast [PSI+] factor by in vitro-converted Sup35 protein.
(Science 28 Jul 00 289:595)
QY: Jonathan S. Weissman [jsw1@itsa.ucsf.edu]
-----------
Mick F. Tuite: Sowing the protein seeds of prion propagation.
(Science 28 Jul 00 289:556)
QY: Mick F. Tuite [m.f.tuite@ukc.ac.uk]
-----------
Text Notes:
... ... *beta-sheet: In general, protein chains fold into
alpha-helices or beta-sheet structures. The beta-sheet is a
protein structure where the peptide is extended and stabilized by
hydrogen bonding between NH and CO groups of different
polypeptide chains or of separate regions of the same chain.
... ... *Note #1: The normal form of the protein Sup35p is
essential for decoding *messenger RNA (mRNA) in yeast. The normal
protein is hydrolyzed by *protease and does not aggregate. The
functionally inactive prion form of Sup35p confers the so-called
[PSI+] *phenotype on yeast cells. In such strains of yeast,
Sup35p is found almost exclusively as a protease-resistant, high
molecular weight-aggregate.
... ... *messenger RNA (mRNA): The ribonucleic acid molecule
transcribed from DNA that carries the coded information
specifying the sequence of amino acids in a protein.
... ... *protease: In general, any enzyme that cleaves proteins,
usually by hydrolysis.
... ... *phenotype: In general, term "phenotype" refers to the
organism as determined by the interaction between its genetic
constitution (genotype) and the environment.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 11Aug00
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
MEDICAL BIOLOGY: ELIMINATION OF PRIONS BY BRANCHED POLYAMINES
During the past several decades, a number of discoveries
have led to the molecular and genetic characterization of the
transmissible agent causing "*scrapie", a degenerative central
nervous system disease of sheep. Studies have identified a
scrapie-specific protein in preparations from scrapie-infected
brains of sheep, this protein capable of producing the symptoms
of scrapie in previously uninfected sheep. Attempts to identify
additional components of the infectious agent, such as nucleic
acid, have been unsuccessful. To distinguish this agent from
viruses and *viroids, the term "prion" was introduced to
emphasize its combined proteinaceous and infectious nature.
The prion protein (PrP) is encoded by the host's chromosomal
DNA, and an abnormal isoform of the protein is apparently
associated with disease transmissibility. The abnormal isoform
differs physically from the normal cellular isoform by its
configuration (high *beta-sheet content), its insolubility in
detergents, its propensity to aggregate, and its relative
resistance to breakdown by hydrolysis (proteolysis).
In addition to sheep scrapie, prions have been found to be
involved in a number of human diseases: *Kuru, *Creutzfeldt-Jakob
disease, *Gerstmann-Straussler-Sheinker disease, and *fatal
familial insomnia. *Bovine spongiform encephalopathy ("mad cow
disease"), which is thought to result from the ingestion of feeds
and bone meal prepared from rendered sheep offal, has been
responsible for deaths of more than 150,000 cattle in the UK
since 1986, and there is evidence that suggests the possibility
of transmission of prion disease from such animals to humans.
There are two forms of prion disease: a) infectious forms
result from *horizontal transmission of infectious prions, e.g.,
bovine spongiform encephalopathy, non-familial Creutzfeldt-Jakob
disease, and kuru; b) inherited forms of prion disease, e.g.,
Gerstmann-Straussler-Scheinker disease, fatal familial insomnia,
and familial Creutzfeldt-Jakob disease, comprise 10 to 15 percent
of all cases and are associated with mutations in the PrP gene.
... ... S. Supattapone et al (University of California San
Francisco, US) report a discovery of a possible chemotherapy for
prion diseases, the authors making the following points:
1) The normal cellular form of prion protein contains 3
*alpha-helices and little beta-sheet content. In contrast, the
scrapie prion form is rich in beta-sheet structure. The
accumulation of scrapie prion in the central nervous system
precedes neurologic dysfunction accompanied by neuronal
vacuolization and astrocyte gliosis.
2) The spectrum of prion diseases now includes a new form of
human prion disease, "new variant Creutzfeldt-Jakob disease"
(nvCJD), which has emerged in the UK and France. Several lines of
evidence have suggested a link between the new variant
Creutzfeldt-Jakob outbreak and a preceding epidemic in the UK of
bovine spongiform encephalopathy. Although it too early to
predict the number of nvCJD cases that might eventually arise in
the UK and elsewhere, it is clear that effective therapeutics for
prion diseases are urgently needed. Unfortunately, although a
number of compounds, including amphoteracins, sulfated
polyanions, Congo red dye, and anthracycline antibiotics, have
been reported as prospective therapeutic agents, all have
demonstrated only modest potential to impede prion propagation,
and none have been shown to effect the removal of preexisting
prions from an infected host.
3) The authors report that non-cytotoxic concentrations of
*branched polyamines can rapidly eliminate scrapie prions from
cultured chronically infected *neuroblastoma cells (culture type
ScN2a). These compounds appear to act by stimulating normal
cellular mechanisms to destroy scrapie prions. Once purged of
scrapie prions, the treated cells remain free from evidence of
scrapie infection during repeated serial passage in polyamine-
free media. The authors suggest that branched polyamines might be
useful therapeutic agents for treatment of prion diseases and
"other degenerative central nervous system disorders
characterized by deposits of abnormal proteins such as
Alzheimer's disease, Parkinson's disease, amyotrophic lateral
sclerosis, and fronto-temporal dementia."
-----------
S. Supattapone et al: Elimination of prions by branched
polyamines and implications for therapeutics.
(Proc. Natl. Acad. Sci. US 7 Dec 99 96:14529)
QY: Stanley B. Prusiner, University of California San Francisco
415-476-4044.
-----------
Text Notes:
... ... *scrapie: Susceptibility to scrapie varies among
different breeds of sheep, with goats 100 percent susceptible.
The disease is transmissible to laboratory monkeys, mice, and
hamsters.
... ... *viroids: The term "viroids" refers to the pathological
agents of a number of transmissible plant diseases. The pathogens
are small, single-stranded, covalently closed circular RNA
molecules existing as highly base-paired rod-like structures
without protein coats (i.e., without capsids).
... ... *beta-sheet: The "secondary structure" of a protein is
determined by interactions between the sequential units,
particularly hydrogen bonding between particular amino acids and
nonpolar interactions between hydrophobic regions, the
interactions producing, in general, three local or global
secondary structure variants: alpha helix, beta sheet, and tight
turn. An "alpha helix" is a spiral configuration of a polypeptide
chain in which successive turns of the helix are held together by
hydrogen bonds between the amide (peptide) links, the carbonyl
group of any given residue being hydrogen-bonded to the imino
group of the 3rd residue behind it in the chain. The term "beta
sheet" (beta-pleated sheet) refers to an array of two or more
"beta strands", with each beta strand consisting of two
polypeptide chains in a so-called "beta configuration", which in
turn is a stable configuration of a polypeptide chain in which
the chain is almost fully extended and hydrogen-bonded to an
adjacent polypeptide chain. The third secondary structure
variant, "tight turn" (beta bend; beta turn) refers to a bending
of a short stretch of polypeptide chain that allows the main
direction of the chain to change. The turn consists of 4 amino
acid residues in which the CO group of residue n is
hydrogen-bonded to the NH group of residue n + 3.
... ... *Kuru: This disease is similar to Creutzfeldt-Jakob
disease, and is a human spongiform encephalopathy. (The term
"spongiform" refers to the sponge-like appearance of the infected
brain.) Kuru occurs only in the easter highlands of New Guinea,
occurs more frequently in women than in men, which apparently
coincides with the customs surrounding cannibalism in a society
where the remains of dead relatives are handled and eaten
primarily by children and women. After cannibalism was outlawed,
the incidence of the disease decreased, and the current consensus
is that cannibalism was the primary mode of transmission of the
pathological agent.
... ... *Creutzfeldt-Jakob disease: Until 30 years ago,
Creutzfeldt-Jakob disease was an obscure form of dementia unknown
to most physicians. The name is now familiar to the medical
community as the major *transmissible spongiform encephalopathy
(or prion disease) in humans, and familiar to research scientists
because of its strange causative agent (prions) that exhibit
apparently novel modes of replication and transmission.
... ... *transmissible spongiform encephalopathy: In general, an
encephalopathy is any disorder of the brain. In this context, the
term "spongiform" refers to the sponge-like texture or appearance
of the brain upon autopsy. In this context, the term
"transmissible" means capable of being transmitted from one
individual to another.
... ... *Gerstmann-Straussler-Sheinker disease: A familial (i.e.,
inherited) form of Creutzfeldt-Jakob disease. The disease is
transmissible to animals, has an earlier onset than C-J disease
(40 vs. 60 years), and a longer average duration of disease (5
years vs. 9 months).
... ... *fatal familial insomnia: Another familial form of
Creutzfeldt-Jakob disease. This very rare disease is difficult to
transmit to experimental animals. The age of onset varies widely,
the course of the disease averaging 13 months. (Note: All the
human spongiform encephalopathies are invariably fatal.)
... ... *Bovine spongiform encephalopathy: "Mad cow disease" is
similar to scrapie. In 1996, the new variant of Creutzfeldt-Jakob
disease (new-variant CJD) was recognized in the UK population,
primarily in younger people, the new disease with distinctive
pathological characteristics similar to those seen in macaque
monkeys infected with the agent of bovine spongiform
encephalopathy. The major present concern is that the pathogen of
bovine spongiform encephalopathy may have spread to humans in the
UK and continental Europe through ingestion of infected cattle
meat.
... ... *horizontal transmission: In general, in this context,
transmission from one contemporaneous individual to another in a
population, as opposed to "vertical transmission", which is
transmission from parent to offspring.
... ... *alpha-helices: See note on "beta-sheet" above.
... ... *branched polyamines: The branched polyamines involved in
this study ranged in molecular weight from 517 to 800,000
daltons, with primary NH(sub2) groups ranging in number from 4 to
more than 500.
... ... *neuroblastoma cells: "Neuroblastomas" are malignant
neoplasms characterized by only slightly differentiated immature
nerve cells of embryonic type. Such cells are readily maintained
in laboratory culture dishes.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 11Feb00
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
EVIDENCE FOR TRANSMISSION OF ANIMAL PRION DISEASE TO HUMANS
... M.R. Scott et al (7 authors at 2 installations, US UK)
present transgenetic evidence for transmission of bovine
spongiform encephalopathy prions to humans, the authors making
the following points:
1) There is concern that bovine spongiform encephalopathy
may have been recently passed from cattle to humans, resulting in
approximately 50 cases of an atypical new variant of Creutzfeldt-
Jakob disease in teenagers and young adults. Epidemiological
findings, *gel electrophoresis of the prion protein, and
transmission to inbred mice and primates have each raised the
possibility of a link between bovine spongiform encephalopathy
and the new variant of Creutzfeldt-Jakob disease.
2) More than 175,000 cattle, primarily dairy cows, have died
of bovine spongiform encephalopathy over the past decade. How
many more cattle were exposed to BSE prions but slaughtered
before developing clinical signs is uncertain. Given the enormity
of the affected cattle population in the UK, a means of assessing
risks to the human population is paramount, and more sensitive
methods for the detection of prions are urgently needed. The
magnitude of the potential risk to the human population is still
speculative, but the death rates from new-variant-Creutzfeldt-
Jakob disease per year had remained approximately constant until
recently, when a disturbing high number of deaths from the
disease, a total of 9 new cases, was reported in the last quarter
of 1998. Although it is not yet known whether this trend will
continue, the possibility that a large section of the population
is at high risk must be seriously entertained.
3) The authors report their new studies indicate that
*transgenic mice expressing bovine prion protein *serially
propagate bovine spongiform encephalopathy prions, and that there
is no species barrier for transmission from cattle to mice. These
same mice were also highly susceptible to a new variant of
Creutzfeldt-Jakob disease and natural sheep scrapie. The
incubation times (approximately 250 days), neuropathology, and
disease-causing prion protein isoforms in the experimental mice
inoculated with human new-variant Creutzfeldt-Jakob disease and
bovine spongiform encephalopathy brain extracts were
indistinguishable and differed dramatically from those seen in
these mice with natural scrapie prions.
4) The authors suggest their findings provide the most
compelling evidence to date that prions from cattle with bovine
spongiform encephalopathy have infected humans and caused fatal
neurodegeneration.
-----------
[Editor's note: Although we do not disagree with the
interpretations and conclusions of the authors, it should be
pointed out that despite the title of their paper, the authors
provide direct evidence for transmission of new-variant
Creutzfeldt-Jakob disease from humans to mice, but evidence only
by implication for transmission from mice (or any other species)
to humans. The import of the work is the apparent experimental
absence of a significant species barrier to transmission of this
disease, at least in experiments involving human to animal
transmission in the reported population of transgenic mice.]
-----------
M.R. Scott et al: Compelling transgenetic evidence for
transmission of bovine spongiform encephalopathy prions to
humans.
(Proc. Natl. Acad. Sci. US 21 Dec 99 96:15137)
QY: Michael R. Scott [abbott@itsa.ucsf.edu]
-----------
Text Notes:
... ... *protease-resistant isoform: A "protease" is any enzyme
that breaks down proteins by hydrolysis. In this context, an
"isoform" is any one of multiple forms of a functional protein
that differ in amino acid sequence and *electrophoretic mobility.
... ... *electrophoretic mobility: In general, electrophoresis is
a laboratory technique used to separate macromolecules on the
basis of electric charge and size, the technique involving
application of an electric field to a population of
macromolecules dispersing according to their electric mobilities.
... ... *gel electrophoresis: Gel electrophoresis is a type of
"zone electrophoresis" in which the supporting medium is a gel of
uniform concentration. In zone electrophoresis, a solution of
protein (or other molecules) is placed at the starting position
as a thin band or spot in an inert supporting medium (paper,
starch gel, polyacrylamide gel, etc.) containing buffer solution.
An electric potential is then applied to the supporting medium,
causing the proteins (or other substances) to migrate to give
distinct bands or zones which can be located in situ by staining,
light absorption, etc., or by analysis after elution of discrete
pieces of the supporting medium.
... ... *transgenic mice: A "transgenic mouse" is a mouse into
which genetic material from another organism has been
transferred, the transferred and incorporated new genes then
being expressed with the resultant production of specific
proteins.
... ... *serially propagate: The general paradigm for "serial
propagation" of a disease is as follows: After infection of
individual (or group) A by the disease, following the incubation
period, infectious material is removed from A and used to infect
B; then, after the incubation period, infectious material is
removed from B and used to infect C; and so on.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 21Jan00
For more information: http://scienceweek.com/swfr.htm
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6. MEDICAL BIOLOGY:
USE OF POLIOVIRUS TO TREAT A CANCER
In general, "glial cells" are cells of the central and
peripheral nervous system that metabolically support neurons,
with certain of such cells also producing the multiple membrane
layers called myelin and enfolding nerve cell axons with it. The
glial cells are found everywhere in the brain and spinal cord,
and they are usually categorized according to morphology.
"Astrocytes" (astroglia) are the largest glial cells, with many
extensions radiating outward like a starburst, and at least one
of their functions is apparently to maintain the so-called
"blood-brain barrier" effectively separating neural tissue from
blood.
A malignant glioma, in general, is a cancer of any type of
glial cell, and in humans, malignant gliomas are the most common
primary tumors of the central nervous system. Such tumors are
usually diffuse and spread rapidly throughout the brain;
treatment is usually limited in effectiveness, and death usually
occurs within 1 or 2 years after first symptoms. The resistance
of malignant gliomas to conventional therapies has produced a
search for novel strategies, and recently these strategies have
involved animal viruses, either as delivery vehicles for foreign
genetic material intended to result in the self-destruction of
tumor cells, or as attenuated variants of pathogenic viral
species that can directly and specifically invade and destroy
tumor cells during the viral replication process.
Poliovirus is an RNA virus that is the causative agent of
the human disease paralytic poliomyelitis. The majority of
poliovirus infections remain asymptomatic, but 1 to 2 percent of
such infections result in neurological complications within the
spinal cord and brainstem, the complications producing a
characteristic clinical syndrome dominated by flaccid paralysis.
Selective targeting of neurons that innervate muscle
(motorneurons) in the spinal cord by poliovirus apparently
involves a specific motorneuron cell-surface receptor (CD155),
with a contribution of certain favorable intracellular
conditions.
... ... M. Gromeier et al (5 authors at 3 installations, US) now
report that genetically engineered poliovirus (PV1RIPO) can
specifically infect and propagate in cell lines derived from
malignant gliomas. The authors make the following points:
1) The study involved a genetically engineered (recombinant)
polio virus containing genome components of a human common cold
virus (rhinovirus type 2), the resultant genome hybrid (chimera)
characterized by exceedingly poor growth in normal neuron tissue
cultures, and the chimera virus nonpathogenic in both mice and
monkeys.
2) The authors report that treatment of mice bearing
subcutaneous or intracerebral human glioma *xenografts with the
indicated genetically engineered polio virus halted tumor
progression and resulted in tumor elimination.
3) The authors conclude: "This study provides evidence that
highly attenuated poliovirus/human rhinovirus type 2 chimeras
possess strong *oncolytic activity against malignant gliomas. The
neuropathogenic properties inherent to poliovirus are greatly
reduced in the recombinant poliovirus described. This *phenotype,
combined with a natural *tropism for malignant cells that express
CD155, suggests that polio/human rhinovirus type 2 chimeras may
be suitable for the treatment of malignant disease of the central
nervous system."
... ... In a commentary on the above work, Eric C. Holland (M.D.
Anderson Cancer Center Houston, US) states: "The paper by
Gromeier et al... [describes] a hybrid virus that infects and
kills clonal human glioma cell lines, in culture and *athymic
mice, without affecting nonneoplastic cells within the brain. For
those viewing this battle from a distance, the continued
unsuccessful attempts at novel therapies for this disease
[specifically, glioblastoma multiforme, the most aggressive of
the malignant gliomas] may be difficult to understand. However,
for those treating these patients, and certainly for the patients
themselves, the importance and urgency of each attempt is clear."
-----------
M. Gromeier et al: Intergeneric poliovirus recombinants for the
treatment of malignant glioma.
(Proc. Natl. Acad. Sci. US 6 Jun 00 97:6803)
QY: Eckard Wimmer [ewimmer@ms.cc.sunysb.edu]
-----------
Eric C. Holland: Glioblastoma multiforme: The terminator
(Proc. Natl. Acad. Sci. US 6 Jun 00 97:6242)
QY: Eric C. Holland [eholland@mdanderson.org]
-----------
Text Notes:
... ... *xenografts: In general, a graft of tissue from one
species into the body of another species.
... ... *oncolytic activity: In general, activity that destroys
tumor cells.
... ... *phenotype: In this context, the term "phenotype" refers
to the specific individuality of a cell line as determined by the
interaction between its genetic constitution (genotype) and the
environment.
... ... *tropism: In this context, an affinity for specific
locations in the body.
... ... *athymic mice: An "athymic mouse" is a mouse with an
absent thymus gland. This study involved so-called "nude mice", a
mutant strain of mice lacking the thymus gland. The reported
experiments involved xenografts, in this case the grafting of
human glioma cell lines into mice, and such grafts ordinarily do
not endure long enough for experimental study because of
rejection by the host immune system. Use of mice without a thymus
gland, the maturation site of a major component of immune system
cells (immune system T lymphocytes), is one way to achieve
relatively long-lasting xenografts.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 11Aug00
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
REOVIRUS DESTRUCTION OF TUMORS
An oncogene is the activated form of a proto-oncogene. A proto-
oncogene is a normal cellular gene that upon specific alteration
(activation), acts to induce a cancerous state. Transformation
from proto-oncogene to oncogene may involve a virus, a mutation,
chromosomal translocation, etc. Reoviruses are a genus within the
*Reoviridae family of medium-sized viruses (60 to 80 nanometers
in diameter), the viruses in this family having a double-stranded
RNA genome. The family includes human rotaviruses, the most
important cause of infant gastroenteritis around the world.
Reoviruses (again, a genus [subset] of the family Reoviridae)
are not known to be an important cause of any serious human
disease, although there is a human reovirus that infects the
upper respiratory and gastrointestinal tracts with mild or no
symptoms. Active mutations of a proto-oncogene called "Ras" have
been found in approximately 30 percent of all human tumors,
primarily in pancreatic tumors (90 percent), *sporadic colorectal
tumors (50 percent), lung *carcinomas (40 percent), and *myeloid
leukemia (30 percent). Human reovirus is known to require an
active *Ras signaling pathway for infection of cultured cells.
... ... M.C. Coffey et al now present the results of a study to
investigate whether the requirement of human reovirus for an
active Ras pathway can be exploited for cancer therapy. Immune-
deficient mice bearing tumors were treated with the virus. The
authors report that a single intratumoral injection of virus
resulted in regression of tumors in 65 to 80 percent of the mice.
Treatment of immune-competent mice bearing tumors also resulted
in tumor regression, although a series of injections were
required. The authors suggest that with further work reovirus may
have applicability in the treatment of cancer.
-----------
M.C. Coffey et al (University of Calgary, CA)
Reovirus therapy of tumors with activated Ras pathway.
(Science 13 Nov 98 282:1332)
QY: Patrick W.K. Lee [plee@acs.ucalgary.ca]
-----------
Text Notes:
... ... *Reoviridae: The nomenclature here is confusing. The
family Reoviridae contains 6 genera (subsets): reovirus,
orbivirus, rotavirus, cypovirus, phytoreovirus, fijivirus. The
last two are plant viruses. The prefix "reo-" derives from
(r)espiratory (e)nteric (o)rphan.
... ... *sporadic: In this context, the term "sporadic" means
non-familial.
... ... *carcinomas: In general, a carcinoma is any malignancy
derived from epithelial tissue. 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.
... ... *myeloid leukemia: (granulocytic leukemia) In general, a
form of leukemia characterized by proliferation of bone marrow
cells or cells derived from bone marrow cells.
... ... *Ras signaling pathway: _Ras_ is an oncogene of which
there are at least 3 varieties. The Ras proteins play a pivotal
role in regulating growth and differentiation in nearly every
eukaryotic cell studied. The 2 Ras subfamilies of proteins, Rho
and Rac, are involved in relaying signals from cell-surface
receptors to the *actin cytoskeleton.
... ... *actin cytoskeleton: Actin is a family of ubiquitous
structural proteins present in all eukaryote cells, and the term
"cytoskeleton" refers to the quasi-rigid matrix that among other
things determines cell shape.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 25Dec98
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
NEW TECHNIQUE USES COMMON COLD VIRUS TO KILL TUMOR CELLS
Human cells have a suicide program that is triggered by a protein
(p53) when the cell's genetic machinery is damaged. Some viruses
possess a gene that inactivates the protein p53, which enables
them to use the cell's genetic apparatus to reproduce, with the
eventual death of the host cell. Adenovirus, a common respiratory
virus, is one of these viruses. That is fact #1. Fact #2 is that
in many kinds of tumor cells, the protein p53 has become
intrinsically inactivated. Fact #3 is that a mutant strain of
adenovirus exists that has lost the p53 jamming gene. This mutant
adenovirus will therefore be lethal to tumor cells with already
inactivated p53, but not to ordinary cells. So Frank McCormack
and his colleagues (Onyx Pharmaceuticals, US) injected the mutant
strain of adenovirus into head and neck tumors in patients who
had failed to respond to surgery, radiation, or chemotherapy, and
they found significant destruction of tumors in 25% of the
patients. The mutant adenovirus killed the tumor cells in these
large, refractory cancers. These are preliminary trials, but the
beginning of what may be an extremely important approach to
cancer therapy -- the use of pathogens with a specificity for
tumor cells. The results were reported at the recent meeting of
the American Society of Clinical Oncology.
(New York Times 20 May) (Science-Week 22 May 97)
For more information: http://scienceweek.com/swfr.htm
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7. IN BRIEF:
AIDS AND NEGATIVE POPULATION GROWTH IN AFRICA
According to projections from a new study commissioned by the US
Agency for International Development, by 2003, Botswana, South
Africa, and Zimbabwe will be experiencing negative population
growth, and 5 other countries in Africa will be experiencing a
growth rate of nearly zero. Writing from a recent international
AIDS conference in Durban (ZA), Joan Stephenson states: "Not
since the Black Death devastated medieval Europe has humankind
observed infectious disease deaths on such a massive scale that a
country's population has shrunk rather than grown. But that
scenario is playing out again in the 21st century, with HIV/AIDS
replacing bubonic plague as the killer."
-----------
Joan Stephenson: Apocalypse Now: HIV/AIDS in Africa exceeds the
experts' worst predictions.
(J. Amer. Med. Assoc. 2 Aug 00 284:556)
QY: Joan Stephenson JAMA [http://www.jama.com]
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8. FOCUS REPORT: ON HADRONS, LEPTONS, AND QUARKS
"By the 1950s, scientists studying the collisions of protons with
nuclei began to realize that when a nucleus is torn apart, all
sorts of strange and wonderful things can be found in the debris.
There were, of course, the protons and neutrons you would expect
to find, but in addition there was a whole collection of new
particles. These particles seemed to live inside the nucleus, but
when freed from this environment they decayed -- came apart --
in very short times. The instability of these particles explains
why we were not previously aware of them -- they can be seen only
briefly and under very special conditions such as those that
exist in the laboratory. It quickly became evident, in fact, that
there were two classes of particles in nature. There were
particles like the proton, the neutron, and the stuff that was
seen in the debris of nuclear collisions. These particles seemed
to be at home in the nucleus and to contribute in some way to
holding it together. The other class of particles were those like
the electron -- particles that are normally found not inside the
nucleus but outside of it. The former class of particles was
christened "hadrons" (after the Greek for 'strongly interacting
ones'). The latter particles were called "leptons", or weakly
interacting ones. It turned out that going into the nucleus after
the hadrons had opened a real Pandora's box. Throughout the 1960s
and into the 1970s the number of hadrons being discovered
skyrocketed. The last time I looked there were over 200, but no
one is counting anymore. It's clear that a system of the world
with 200 kinds of 'elementary' particles just isn't going to
work. Some way of ordering the hadrons had to be found. In the
late 1960s such a scheme was proposed, and since then this scheme
has come to dominate the study of the basic structure of matter.
The scheme is actually very similar to the simple proton-neutron-
electron picture of the 1930s. The idea is that just as all
nuclei are merely different arrangements of the hadrons, all
hadrons are themselves simply different arrangements of things
more fundamental still, things for which the name 'quarks' was
invented. The name actually comes from a line in James Joyce's
_Finnegan's Wake_ that goes 'Three quarks for Muster Mark,' and
it reflects the fact that in its earliest incarnation the quark
model had three different kinds of quarks in it."
-----------
James Trefil: "The New Physics and the Universe"
in: Byron Preis (ed.): _The Universe_
(Bantam Books, New York 1987)
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9. FROM THE SW ARCHIVE:
SCIENCE AND SOCIETY: ON THE GREAT ASYMMETRY
The zoologist Stephan Jay Gould, in an essay concerning the uses
and misuses of science, and public attitudes toward science, and
in particular the perpetual quandary concerning the positive and
negative potentials of science, dismisses the myths that science
is either intrinsically good or intrinsically evil, and intro-
duces what he calls "the great asymmetry", an intrinsic aspect of
the applications of science that can be viewed as the origin of
public ambivalence toward scientific progress. The idea of the
great asymmetry is that the beneficial applications of science
are usually incremental and incrementally produce adaptive
systems in a complex structure over time (e.g., advanced
civilizations), while the destructive applications of science can
in a relatively short period of "building" time be truly
catastrophic (e.g., the murder of millions by a single dictator).
In essence, the idea is that it is usually easier to destroy a
house than to build a house, and it is this great asymmetry that
must be addressed and explained to the public. Gould concludes:
"In any case, we have no choice, for humans must wonder, ask, and
seek -- and science must therefore break through the strictures
of custom to become either our greatest glory, and our most
potent engine of benevolent change, or an accelerator of
destruction on the wrong side of the great asymmetry."
QY: Stephen Jay Gould, Harvard University 617-495-1000.
(Science 6 Feb 98) (Science-Week 20 Feb 98)
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