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ScienceWeek
SCIENCE-WEEK
A Weekly Email Digest of the News of Science
A journal devoted to the improvement of communication
between the scientific disciplines, and between scientists,
science educators, and science policy makers.
July 16, 1999 -- Vol. 3 Number 29
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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.
-- Anonymous
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Contents of This Issue:
1. On the Inventor of Modern Science
2. Gamma Ray Bursts: The Largest Explosions in the Universe
3. On Active Galactic Nuclei
4. Mechanisms of Chemotaxis in Biological Cells
5. A Nerve Cell Type Unique to Humans and Great Apes
6. An Ethics Debate Concerning Research on Mental Illness
In Focus: On Cosmic History
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1. ON THE INVENTOR OF MODERN SCIENCE
There are two broad approaches to the writing of intellectual
history. One can focus on movements, on changing and evolving
concepts and attitudes; or one can focus on individuals, on a
series of key players whose personal discoveries and influences
on each other form a chain that connects the past to the present.
The second method, which considers the histories and
contributions of real people, their fortunes and misfortunes, is
usually more amenable to dramatic presentation and concrete
images. The first method, which primarily considers the complex
flow of ideas in time, is more abstract, of more interest to
scholars, and more frightening to the editors of weeklies who
fear losing their readers. But, in truth, no one is holding a gun
to our heads and telling us we must use one approach or the other
exclusively; each approach has its merits, and each approach can
be instructive and interesting in its own way. ... ... In a short
essay entitled, "The Inventor of Modern Science", physicist
Freeman J. Dyson (Institute for Advanced Study Princeton, US)
considers the life and contributions of the 18th century
astronomer James Bradley (1693-1762), with Dyson making the
following points:
1) Modern science began in 1729, when it became based on
measurements of high precision, and since James Bradley was the
first to make high-precision measurements, James Bradley can be
called the inventor of modern science. Bradley was the first to
understand that accurate measurement requires meticulous
monitoring and control of possible sources of error. In addition
to a number of important discoveries, Bradley was the first to
record temperature and barometric pressure whenever he made an
observation.
2) Using a plumb-line and micrometer screw, Bradley measured
the angle between a star and the local vertical with 6-figure
accuracy. He was the first person to measure anything with 6-
figure accuracy. He measured angles a hundred times more
accurately than the astronomers of Newton's time, and this
accuracy was responsible for his discovery of "aberration", the
displacement of the image of a star in the sky due to the speed
of the Earth in its orbit and the finite velocity of light. Over
the course of a year, Bradley found the displacements of each
star to form a closed ellipse. At that time, both astronomers and
the educated public in Europe considered these elliptical
displacements the first direct demonstration that the Copernican
view of the Universe was correct, the elliptical motions visual
proof that the Earth is moving around the Sun [*Note #1].
3) By considering the aberration displacements
quantitatively, Bradley was able to provide the first accurate
determination of the velocity of light, calculating a value
within 1 percent of the modern value [*Note #2].
4) The influence of Bradley extended far beyond astronomy,
his insistence on 6-figure accuracy spreading to other countries
and to other sciences. One hundred and fifty years after Bradley,
Michelson and Morley attempted to measure the 2nd-order
aberration of light caused by the Earth's motion through the
ether, and by their negative result led the way to the theory of
relativity.
-----------
Freeman J. Dyson: The inventor of modern science.
(Nature 1 Jul 99 400:27)
QY: Freeman J. Dyson, Institute for Advanced Study, Princeton NJ
08540 US.
... ... *Note #1: In his essay, the author states: "Bradley found
that all stars moved in elliptical paths in the sky, coming back
to their original positions after a year." This should perhaps be
qualified, since the ellipse becomes a circle for a star at the
pole of the ecliptic (the mean plane of the Earth's orbit around
the Sun), and the ellipse becomes a straight line for a star on
the ecliptic.
... ... *Note #2: The angular displacement (a) of an observed
star is given by the relation tan(a) = v/c, where v is the
Earth's orbital velocity and c is the speed of light.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 16Jul99
2. GAMMA RAY BURSTS: THE LARGEST EXPLOSIONS IN THE UNIVERSE
Gamma rays are extremely high energy electromagnetic radiation
with wavelengths of less than approximately 0.01 nanometers.
X-rays are radiation of wavelengths approximately 0.01 to 10
nanometers, shorter than ultraviolet radiation but longer than
gamma rays. Gamma ray bursts are intense flashes of gamma rays
and x-rays detected at energies up to 10^(6) *electron volts.
They were discovered by US Air Force satellites in 1967 but not
declassified until 1973. The detection of these bursts averages
approximately 1 per day, and measurements indicate the
distribution of bursts is isotropic, i.e., they are uniformly
distributed across the sky. The nature of gamma ray bursts
remains mysterious. Astronomers have obtained rigorous distance
estimates only recently, placing gamma ray bursts definitely in
the realm of cosmology. *Redshift measurements suggest extremely
large distances, making gamma ray bursts the most powerful
catastrophic energy releases known to mankind. ... ... Dieter H.
Hartmann (Clemson University, US) presents a review of current
research concerning gamma ray bursts, the author making the
following points:
1) Gamma ray bursts are short flashes of almost pure high-
energy emission (x-rays and gamma rays) that occur randomly on
the sky, and from loci which apparently do not emit more than
once. Typical durations are of the order of seconds, but can
range from a few milliseconds to over 1000 seconds. The bursts
are extremely bright, outshining all other objects on the gamma
ray sky, but their spectra are featureless and reveal little
about the underlying physical processes. Integrating burst
spectra over energy and time yields large fluences (received
energy per unit area), but does not determine the total burst
energy until the distance is known.
2) Although the statistical properties of gamma ray bursts
long supported the idea that bursts occur at cosmological
distances, this distance scale was finally established by a burst
on 8 May 1997, for which a faint extended object was optically
identified as the host, the object showing clear evidence of
absorption lines that indicated a lower redshift limit of z =
0.835. On 14 December 1997, another burst showed absorption lines
at z = 3.42, and then a third burst on 3 July 1998 had associated
absorption lines at z = 0.966 -- all of this indicating that
gamma ray bursts, along with *quasars, are the most distant
objects in the Universe. Such large distances imply large
energies, and in fact the assumption of isotropic emission
implies burst energies in excess of 10^(53) ergs, comparable to
*supernova energies but released predominantly in the gamma ray
band. The optical afterglows of gamma ray bursts are much
brighter than supernova, hence the name "hypernova" has been
proposed.
3) Studies of gamma ray burst host galaxies suggest they are
normal star-forming galaxies, and not galaxies with *active
nuclei. The estimated star formation rates in these hosts,
together with other evidence from x-ray spectra and photometry of
the gamma ray burst afterglows suggests that gamma ray bursts may
be directly associated with star-forming regions. If that turns
out to be correct, astronomers would have a powerful new tool for
the study of structure formation in the Universe, a tool that
could reach further back in time than quasars.
4) Despite recent breakthroughs in gamma ray burst
observations, many questions remain about the nature of the
underlying processes and the evolutionary sequences leading up to
the creation of the central engine driving these outbursts. The
ultimate goal of understanding this engine may be accomplished
through simultaneous optical observations, and such is the
objective of dedicated experiments under development throughout
the world.
-----------
Dieter H. Hartmann: Afterglows from the largest explosions in the
Universe.
(Proc. Natl. Acad. Sci. US 27 Apr 99 96:4752)
QY: Dieter H. Hartmann, Clemson University, Clemson SC 29634 US.
-----------
Text Notes:
... ... *electron volts: 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.
... ... *Redshift: 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). Redshift is
defined as the change in wavelength of a particular spectral line
divided by the unshifted wavelength of that line. Large redshifts
imply large radial velocities (which imply large distances,
according to current cosmological theory), but at redshifts
greater than about 0.2 there is a relativistic divergence from a
linear relation. A redshift of 4.0 corresponds to an object
receding with a radial velocity 92% that of the velocity of
light. The largest astrophysical redshifts so far observed are of
the order of z = 5.
... ... *quasars: (quasi-stellar objects) Extremely luminous
sources radiating energy over the entire spectrum from x-rays to
radio waves, and which are apparently among oldest and most
distant objects in the universe.
... ... *supernova: A violent explosion in which certain stars
end their lives. The star may become more than 10^(9) times as
bright as the Sun and may outshine its host galaxy for weeks.
... ... *active nuclei: (active galactic nuclei) Central regions
of galaxies in which considerable energy is generated by
processes other than those operating in ordinary stars. The
energy may result from the accretion of material into a massive
black hole situated at the core of the galaxy. (See Report #3
this issue.)
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Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 16Jul99
-------------------
Related Background:
ASTROPHYSICS: SUPERNOVAE AND GAMMA RAY BURSTS
Supernovae are violent explosions marking the terminal stage of
certain stars. They are classified into two broad types, Type I
and Type II. A Type II supernova shows hydrogen in its spectrum,
while a Type I supernova shows no hydrogen in its spectrum. Type
I supernovae are further classified as Type 1a, Type 1b, and Type
Ic. A Type 1a supernova is believed to be due to the explosion of
a *white dwarf star in a binary star system, the result of matter
falling onto it from the companion star. When the mass of the
white dwarf exceeds the *Chandrasekhar limit, the white dwarf
undergoes runaway carbon burning and explodes. Type Ib and Ic
supernovae are thought to result from the collapse of the cores
of massive stars which have lost their hydrogen envelopes. Type
II supernovae arise from the explosion of stars of more than 8
solar masses. In this case, the explosion involves a violent
blow-off of outer-layer material after the massive star has
collapsed into a *neutron star or a black hole. Despite the
existing classification scheme, Type Ib and Type Ic supernovae
are more closely related to Type II supernovae than to Type Ia
supernovae. Gamma ray bursts are intense flashes of *gamma rays
detected at energies up to 10^(6) *electronvolts. They were
discovered by US Air Force satellites in 1967 but not
declassified until 1973. The detection of these bursts averages
about 1 per day, and measurements indicate the distribution of
bursts is isotropic, i.e., they are uniformly distributed across
the sky. The current consensus is that gamma ray bursts are
produced by the merger of two neutron stars, and up to this
point, the bursts that have been noted apparently originate
outside our own galaxy. ... ... In 3 contiguous reports in the
same journal, 3 research teams now report an association of the
gamma ray burst of 25 April 1998 (GRB980425) with the supernova
SN1998bw, which exploded at approximately the same time as the
gamma ray burst. Although in general the properties of supernovae
are very different from those of gamma ray bursts, the apparent
new consensus is that supernova SN1998bw establishes a second
class of gamma ray burst which is distinctly different from the
cosmological kind. It is suggested that in some supernovae the
outer layer of the exploding star is given sufficient energy to
cause it to expand at speeds approaching the speed of light, and
that this initially produces a burst of gamma rays and a
subsequent radio emission. If this suggestion is correct, gamma
ray bursts may be produced by two substantially different
mechanisms. [Editor's note: A collection of previous SW reports
on gamma ray bursts can be found in the SW Focus Report
"Astrophysics: Gamma Ray Bursts" which is available at URL
]
-----------
S.R. Kulkarni et al (9 authors at 5 installations, US AU)
Radio emission from the unusual supernova 1998bw and its
association with the gamma-ray burst of 25 April 1998.
(Nature 15 Oct 98 395:663)
QY: S.R. Kulkarni
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T.J. Galama et al (50 authors at 21 installations, NL US CL IT JP
UK DE AU)
An unusual supernova in the error box of the gamma-ray burst of
25 April 1998.
(Nature 15 Oct 98 395:670)
QY: T.J. Galama
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K. Iwamoto et al (27 authors at 9 installations, JP IT CL DE NL
US)
A hypernova model for the supernova associated with the gamma-ray
burst of 25 April 1998.
(Nature 15 Oct 98 395:672)
QY: K. Nomoto
-----------
Text Notes:
... ... *white dwarf star: White dwarf stars are extremely dense
and compact stars that have undergone gravitational collapse.
They are the final stage in the evolution of low-mass stars after
they have lost their outer layers. White dwarf stars are about
the size of Earth, but with a mass about that of the Sun.
... ... *Chandrasekhar limit: The remnant mass after the blow-off
during the terminal stage of the life of a star determines the
ultimate fate of the star. If the remnant mass is less than 1.44
solar masses (the Chandrasekhar limit for a star with no hydrogen
content), the star collapses into a white dwarf. If the remnant
mass is greater than 1.44 solar masses, depending on the remnant
mass, the star collapses into either a neutron star or a black
hole. Named after Subrahmanyan Chandrasekhar (1910-1995), who
first proposed the modern theory of stellar gravitational
collapse, and who received the Nobel Prize in Physics 1983.
... ... *neutron star: If, following its terminal stages, the
remnant mass of a star is between 1.4 and 2 to 3 solar masses,
the star will collapse into a neutron star, a body with a radius
of 10 to 15 kilometers, with a core so dense that its component
protons and electrons have merged into neutrons. The average
density of a neutron star is 10^(15) grams per cubic centimeter,
and the weight of an object on the surface of a neutron star
would be 10^(11) its weight on the surface of the Earth. Neutron
stars apparently have an outer shell of iron, but it is iron like
no Earth iron, an iron of 4 orders of magnitude greater density.
... ... *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: (eV) A unit of energy defined as the
energy acquired by an electron in falling through a potential
difference of 1 volt. 1 electronvolt = 1.602 x 10^(-19) joule.
-------------------
Summary & Notes by SCIENCE-WEEK 30Oct98
-------------------
Related Background:
ANALYSIS OF A GAMMA RAY BURST FROM A HIGH REDSHIFT GALAXY
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. Gamma ray bursts are intense
flashes of gamma rays detected at energies up to 10^(6) electron
volts. Knowledge of the properties of gamma-ray bursts has
increased substantially following recent detections of
counterparts at x-ray, optical, and radio wavelengths. But the
nature of the underlying physical mechanism that powers these
sources remains unclear. An important question is the total
energy in the burst, for which an satisfactory estimate of the
distance is required, and until now the best estimate is that the
bursts lie at cosmological distances. ... ... Kulkarni et al (16
authors at 9 installations, US IN IT) now report identification
of the host galaxy of a previously optically detected burst
(GRB971214), with a determination of the galaxy redshift at z =
3.42. When combined with the measured flux of gamma-rays from the
burst, this large redshift implies an energy of 3 x 10^(53) ergs
in the gamma-rays alone, assuming the emission is isotropic. This
is much larger than the energies previously considered, and the
authors suggest it poses a challenge for theoretical models of
the bursts.
QY: S.R. Kulkarni (srk@surya.caltech.edu)
(Nature 7 May 98 393:35) (Science-Week 29 May 98)
-------------------
Related Background:
GAMMA RAY BURST FIREBALL MODEL MAY NEED REVISION
... The current consensus is that gamma ray bursts are produced
by the merger of two neutron stars, and up to this point, the
bursts that have been noted apparently originate outside our own
galaxy. ... ... Castro- Tirado et al (27 authors at 15
installations, ES DE SE DK IT UK US) report an optical transient
from a gamma ray burst (GRB 970508) imaged 4 hours after the
event, displaying a strong ultraviolet excess and reaching
maximum brightness 2 days later. The optical spectra did not show
any emission lines, and no variations on time scales of minutes
were observed for 1 hour during the decline phase. The authors
suggest the observations are incompatible with the fireball and
afterglow models of gamma ray bursts, and that another physical
mechanism may be responsible for the constant phase seen the
first few hours after the burst occurs. QY: T. Broadhurst, Univ.
of Calif. Berkeley, Dept. Astronomy 510-643-8520
(Science 13 Feb 98)
-------------------
Related Background:
OPTICAL STUDIES OF A GAMMA-RAY BURST SUGGEST FIREBALL MODEL
Studies of the mysterious gamma-ray bursts seen in every part of
the sky daily continue to be reported. This week we have the
results of observations of gamma ray burst (GRB) GRB970508, which
occurred on May 8, 1997 (hence the name). Optical studies of the
source of the burst by M. R. Metzger et al (California Institute
of Technology, US; National Radio Astronomy Observatory, US;
Institute of Space Astrophysics, Frascati IT; University of
Ferrara, IT) using data from the recently orbited Italian-Dutch
satellite BeppoSAX indicate the source of the GRB is extra-
galactic at a distance of 5 billion parsecs (1 parsec = about 20
trillion miles). Taking into account the recorded energy and its
loss by intervening absorption across that distance, we are
considering an initial energy burst with a magnitude equal to
the total radiation from our Sun during the entire age of the
universe. The computed energy figure is 10^(51) ergs of
gamma-rays. A consensus among astrophysicists is forming that
these GRBs involve "relativistic fireballs" produced by
colliding neutron stars, either two neutron stars colliding with
each other, or single neutron stars colliding with black holes.
The various radiant energy data are coming in so rapidly now,
there is a feeling the physical nature of GRBs will soon be
completely understood.
(Nature 26 Jun 97)
-------------------
Related Background:
GAMMA RAY BURSTS AND POSSIBLE TERRESTRIAL DISASTER
... Neutron stars are one of the possible end-products of
stellar evolution. If, following its terminal stages, the remnant
mass of a star is between 1.4 and 2 to 3 solar masses, the star
will collapse into a neutron star, a body with a radius of 10 to
15 kilometers, with a core so dense that its component protons
and electrons have merged into neutrons. The average density of a
neutron star is 10^(15) grams per cubic centimeter, and the
weight of an object on the surface of a neutron star would be
10^(11) its weight on the surface of the Earth. Neutron stars
apparently have an outer shell of iron, but it is iron like no
Earth iron, an iron of 4 orders of magnitude greater density.
Theory predicts that a neutron star should rotate very rapidly,
be extremely hot, and have an intense magnetic field.
... ... Leonard and Bonnell (US National Aeronautics and Space
Administration, US), in a review of gamma ray bursts and the
important data on these phenomena collected during 1997, point
out the following: 1) The current consensus is that gamma ray
bursts are produced by the merger of two neutron stars; 2) up to
this point, the bursts that have been noted apparently originate
outside our own galaxy; 3) considering the known neutron stars
inside our own galaxy, a case can be made that evolutionary
disjunctions in Earth's past may have been caused not only by
asteroid impacts, but also by gamma- ray bursts from merging
neutron stars a few thousand light years distant in our galaxy.
QY: Peter J.T. Leonard, NASA Goddard Space Flight Center,
Greenbelt, MD US (Sky & Telescope February 1998)
-------------------
Related Background:
EVIDENCE FOR DISTANT SOURCE OF GAMMA RAY BURSTS
Gamma Ray Bursts have been much in the news recently. They were
first accidentally discovered some 30 years ago by military
satellites, and then interest was rekindled when the Compton
Gamma Ray Observatory was launched by NASA in 1991. The Compton
orbiting device has been detecting Gamma Ray Bursts in all parts
of the sky on a daily basis. One controversy among astronomers
is whether the source is within our galaxy or extra-galactic.
Now Mark R. Metzger, leader of a team at the California
Institute of Technology (Pasadena CA US), reports that the
bursts detected here are coming to us through a stellar gas
cloud about 7 billion light-years away, which means the source
of the bursts must be at least that far, certainly
extra-galactic, and travelling to us for about half the age of
the universe. At least one part of a 30 year old puzzle has
apparently been solved -- the source of the bursts.
(UPI 15 May 97)
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DETECTION OF X-RAY AFTERGLOW ASSOCIATED WITH GAMMA-RAY SOURCE
Gamma ray bursts (GRBs) continue to tantalize astrophysicists.
The distribution of these bursts is isotropic across the sky, but
inhomogeneous in space, and with a deficit of faint bursts. The
problem is that present gamma ray telescopes have poor imaging
capabilities, and the phenomenology is unusual in that the bursts
last only from a fraction of a second to hundreds of seconds. At
present, it is not clear whether the bursts are produced in our
own galaxy or at cosmological distances. This week Costa et al (a
team of 26 researchers in IT and NL) report an analysis of a GRB
of 28 February 1997 (GRB970228). The major discovery is that of
an associated x-ray afterglow which fades within a few days
according to a power-law decay function (empirical). The authors
suggest that for the first time since the discovery of GRBs, it
will now be possible to correlate gamma-ray, x-ray, optical, and
radioastronomy observations. (Nature 19 Jun 97)
---------------------
AN HISTORIC MEETING DEVOTED TO GAMMA RAY BURSTS
Gamma ray bursts (GRBs) have been much in the news the past 10
months, principally because of correlative data from x-ray,
optical, and radio instruments. Last month saw the Fourth
Huntsville Symposium on Gamma Ray Bursts (15-20 Sep 1997,
Huntsville AL US), and the meeting is being called "historic".
There is apparently now a consensus that GRBs are cosmological
rather than galactic in origin, in other words from outside our
Milky Way galaxy. So that part of the 30-year puzzle concerning
GRBs is evidently solved. The other part of the puzzle concerns
the physical events producing the bursts, and for that part of
the puzzle there is apparently no consensus yet. It has recently
been proposed that GRBs are associated with the cataclysmic end
of massive stars, and if this is true, it is believed the
appearance of GRBs should provide data concerning the rate of
formation of such stars, a critical parameter that has evidently
been established by observation. In any case, the gamma ray burst
field has apparently now shifted to data analysis at new
wavelengths of the electromagnetic spectrum, with the emphasis
now on x-ray, optical, and radio observations from several
instrument sources, including the valuable BeppoSAX satellite,
the Hubble Space Telescope, and the Burst and Transient Source
Experiment (BATSE) aboard the Compton Gamma Ray Observatory.
QY: Bohdan Paczynski
(Nature 9 Oct 97)
3. ON ACTIVE GALACTIC NUCLEI
The term "active galactic nucleus" refers to the central regions
of certain galaxies, regions in which considerable energy is
generated by processes apparently other than those operating in
ordinary stars. It is currently believed the energy may result
from the accretion of material onto a massive *black hole
situated at the core of the galaxy. ... ... Andrew C. Fabian
(Cambridge University, UK) presents a short account of current
views in this field, the author making the following points:
1) Active galactic nuclei involve the most powerful steady
sources of luminosity in the Universe. They range from the nuclei
of some nearby galaxies emitting approximately 10^(40) *erg/sec
to distant *quasars emitting more than 10^(47) erg/sec. The
emission is spread widely across the electromagnetic spectrum,
often peaking in the ultraviolet, but with significant luminosity
in the x-ray and infrared bands. The emission is spatially
unresolved except in the radio band, where there is sometimes
evidence for collimated outflows at *relativistic speeds. The
power output of active galactic nuclei are often variable on time
scales of years and sometimes on time scales of days, hours, or
even minutes.
2) An upper limit to the dimensions of active galactic
nuclei can be estimated from theoretical considerations. The
principle of causality (in general, in this context, that an
effect cannot precede its cause) implies that the variation
period of an object whose radiation emission varies in time must
be greater than the time for light to cross that object. Observed
emission variability, therefore, provides an upper bound to the
diameter of an active galactic nucleus.
3) High luminosities imply high masses whose gravity can
combat the radiation pressure that would otherwise blow the
object apart (in other words, the luminosity must be less than
the *Eddington limit). Active galactic nuclei therefore are of
very high mass density, and considering their apparent relatively
small dimensions and high mass density, it has long been assumed
that each active galactic nucleus consists of a massive black
hole, of approximately 10^(8) solar-mass or more, the black-hole
mass accreting gas and dust at the center of the galaxy. The
gravitational energy liberated during accretion onto a black hole
is estimated to be approximately 10 percent of the rest mass
energy of that accreting matter, and is the most efficient mass-
energy conversion process known involving normal matter. The
efficiency is at least an order of magnitude greater than that of
stellar nuclear burning, which releases at most 0.7 percent of
mass-energy.
3) The current view is that the accreting matter of the
black hole of an active galactic nucleus probably has some
angular momentum, which causes the accreting matter to orbit the
black hole and, through dissipation of energy, flatten to form a
disk within which *magnetic viscosity transfers the angular
momentum outward and the mass inward. Unless the accretion rate
is either high or very low, it is likely that the gravitational
energy liberated is radiated locally, much of it as thermal
radiation from the surface of the disk, peaking in the UV as
expected. Some energy, however, is probably stored temporarily in
magnetic fields before being released in flares, which make the
x-ray emission particularly variable.
-----------
Andrew C. Fabian: Active galactic nuclei.
(Proc. Natl. Acad. Sci. US 27 Apr 99 96:4749)
QY: Andrew C. Fabian, Institute of Astronomy, Madingley Road,
Cambridge CB3 0HA UK.
-----------
Text Notes:
... ... *black hole: 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 black hole is a localized region of space from
which neither matter nor radiation can escape. The "trapping"
occurs because the requisite escape velocity, which can be
calculated from the relevant equations, exceeds the velocity of
light and is therefore unattainable. Another view of a black hole
is that it is a mass that has collapsed to such a small volume
that its gravity prevents the escape of all radiation. Space and
time essentially have no meaning in a black hole. The boundary of
the black hole is called the "event horizon", because any event
within the boundary is invisible outside, the invisibility
resulting from the fact that no radiation can escape to be
detected. The radius of the black hole depends upon how much
matter has fallen into the region; it is called the "Schwarzchild
radius", and it is usually a few kilometers. However, massive
black holes are possible and, in addition to providing the
engines for active galactic nuclei, as described above, are also
thought to be the source of quasars (quasi-stellar objects),
which are extremely luminous sources radiating energy over the
entire spectrum from x-rays to radio waves, and which are
apparently the oldest and most distant objects in the universe.
If quasars indeed involve black holes, the radiation is from
material just outside the black hole, and not from anything
within it. Nothing inside a black hole can get out of it.
... ... *erg: The work done by a force of 1 dyne acting through a
distance of 1 centimeter. 1 joule = 10^(7) erg. 1 kilocal = 4.2 x
10^(10) erg.
... ... *quasars: (quasi-stellar objects) Extremely luminous
sources radiating energy over the entire spectrum from x-rays to
radio waves, and which are apparently among oldest and most
distant objects in the universe.
... ... *relativistic speeds: In general, speeds approaching the
speed of light. At such velocities, the mass of an object becomes
significantly greater than its rest mass.
... ... *Eddington limit: The theoretical upper limit to the
luminosity of a star of given mass, at which limit the outward
force of radiation just balances the inward force of gravity.
Stars with a greater luminosity would be blown apart by their own
radiation. Named after A.S. Eddington (1882-1944).
... ... *magnetic viscosity: In this context (plasma physics),
the term "magnetic viscosity" refers to an effect, possessed by a
magnetic field in the absence of sizable mechanical forces or
electric fields, of damping motions of a conducting fluid
perpendicular to the field, the effect similar to the effect of
ordinary viscosity. (The "conducting fluid" in this context is
the "plasma" of ionized gases.)
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 16Jul99
4. MECHANISMS OF CHEMOTAXIS IN BIOLOGICAL CELLS
All biological cells possess mechanisms that effectively enable
them to sense their environment. The term "directional sensing"
refers to the ability of a cell to determine the direction and
proximity of an extracellular stimulus. Direction sensing is
needed to detect *morphogens that control *differentiation, and
to detect attractants that direct cell migration (chemotaxis).
The chemotaxis phenomenon is critical in immunity, *angiogenesis,
wound healing, *embryogenesis, and *neuronal patterning. A
striking example of chemotaxis is exhibited during the life cycle
of the "social" amoeba *Dictyostelium discoideum. During growth,
these cells behave as essentially individual entities, tracking
down and eating bacteria (*phagocytosis). When the individual
entities of D. discoideum are starved, they move toward secreted
*adenosine 3',5'-monophosphate (cAMP) signals, form an aggregate,
and differentiate into spore and stalk cells, with a ball of
spore cells perched above the substrate on the stalk. The
fundamental role of chemotaxis in this simple and well-
characterized *eukaryote has provided a powerful system for
genetic analysis of chemotaxis, and recent observations in D.
discoideum, as well as in yeast and mammalian *leukocytes, have
clarified views of directional sensing. ... ... C.A. Parent and
P.N. Devreotes (Johns Hopkins University, US) present an
extensive review of recent research on cellular directional
sensing, with a focus on the signal transduction events involved
in gradient detection. The authors make the following points:
1) In eukaryotic cells, directional sensing is mediated by
signal pathways involving heterodimeric guanine nucleotide-
binding protein (*G protein).
2) In D. discoideum amoebae and mammalian leukocytes, the
receptors and G protein subunits are uniformly distributed around
the cell perimeter. Chemoattractants induce the transient
appearance of binding sites for several *pleckstrin homology
domain-containing proteins on the inner surface of the cell
membrane. In gradients of attractant, these sites are
persistently present on the side of the cell facing the higher
concentration of attractant, even in the absence of a functional
*actin cytoskeleton or cell movement.
3) Thus, the biological cell senses direction by spatially
regulating the activity of a signal transduction pathway.
-----------
[Editor's note: Although the terminology in this report is indeed
characteristic of current biology, to say that a cell "senses"
direction perhaps invites an awkward anthropomorphic connotation.
The "sensing" by biological cells in this context is no different
in character from the "sensing" by chemical reactant molecules of
each other in a non-biological solution. Certainly, the responses
of cells to chemical attractants are complicated, involving a
sequence of chemical reactions, but they are indeed chemical
reactions, and biologists consider them exactly that. In a
broader intellectual context, since all human "sensations" can
also be reduced to specific chemical reactions (or specific
chemical reactions following specific physical events), the
chemotaxis events considered here at the level of a single cell
are ultimately joined to the classical "mind vs. body"
philosophical problem.]
-----------
C.A. Parent and P.N. Devreotes: A cell's sense of direction.
(Science 30 Apr 99 284:765)
QY: Peter N. Devreotes [pnd@welchlink.welch.jhu.edu]
-----------
Text Notes:
... ... *morphogens: In general, a "morphogen" is any substance
responsible for some aspect of morphogenesis (the generation of
form and structure during development of an individual organism).
... ... *differentiation: In general, in this context, the term
"differentiation" refers to the structural and functional
specialization of cells, developmental cell specialization
(morphology and biochemistry) resulting from activation of
specific parts of the cell genome.
... ... *angiogenesis: The origin and development of blood
vessels. Angiogenesis 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.
... ... *embryogenesis: In general, the formation and development
of an embryo.
... ... *neuronal patterning: The "patterning" here refers to the
patterns of connections between nerve cells, i.e., the
"circuitry".
... ... *Dictyostelium discoideum: Although often called a
"cellular slime mold", D. discoideum is not a mold, nor is it
consistently slimy. The term "social amoeba" is more accurate.
When the organism is individualized, the entities are called
"myxamoebae". When they aggregate into a slug, the organism is
called a "pseudoplasmodium" or termed the "grex". The aggregation
into a unitary grex may involve tens of thousands of individual
amoebae. (Cf. the background report that follows.)
... ... *phagocytosis: Literally, "cell eating". A cell capable
of phagocytosis (e.g., an amoeba) has a mobile boundary which can
engulf particles or smaller cells, followed by incorporation of
the particles or smaller cells into the engulfing cell interior.
... ... *adenosine 3',5'-monophosphate (cAMP; cyclic AMP): ATP
(adenosine triphosphate) is the most important chemical energy
source in all living cells, intimately involved in various cell
functions and cell metabolism, and an entity in numerous cyclic
chemical pathways involved in the synthesis of components. One of
the reaction products of ATP is cyclic AMP, which acts as an
intracellular hormone (i.e., a chemical messenger). Cyclic AMP is
derived from ATP in a reaction catalyzed by the enzyme adenylyl
cyclase (also called adenyl cyclase and adenylate cyclase).
Cyclic AMP is called the second messenger; the first messenger is
the hormone that interacts with the receptor for that hormone on
the cell surface.
... ... *eukaryote: In general, any biological cell containing
internal membrane-bound organelles such as a nucleus.
... ... *leukocytes: "White" blood cells, some types of which are
amoeba-like, exhibiting phagocytosis and pronounced chemotaxis.
... ... *G protein: G-proteins are a family of signal-coupling
proteins that act as intermediaries between activated cell
receptors and effectors, for example, the transduction 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, the G-protein thus acting as a
trans-membrane signal transducer.
... ... *pleckstrin homology domain-containing proteins:
Pleckstrin is a protein found in certain blood components, and a
"pleckstrin homology domain-containing protein" is a protein
containing a domain consisting of approximately 100 amino acid
residues found in pleckstrin and that has also been found in more
than 60 different proteins, particularly in those proteins
associated with intracellular signal transduction.
... ... *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] 16Jul99
-------------------
Related Background:
A NEW METHOD FOR FOLLOWING INDIVIDUAL CELLS IN SLIME MOLD
Dictyostelium discoideum is an organism that has been intriguing
biologists for most of this century. Although this organism is
often called a "cellular slime mold", it is not a mold and it is
not consistently slimy. A better common name for it is a "social
amoeba". What is most remarkable about the organism is its life
cycle. In one part of it life cycle, the "organism" consists of
individual dispersed amoebas living on decaying logs, eating
bacteria and reproducing by binary fission like most other
protozoans. Then, when the local food supply becomes exhausted,
a rather astounding event occurs: tens of thousands of these
amoeba join together to form moving streams of cells that
converge at a central point, and there they aggregate to produce
a slug (grex) 2 to 4 millimeters long. The slug migrates as a
single body towards light, and when it reaches an illuminated
area, migration ceases, and the slug differentiates into a
fruiting body composed of spore cells and a stalk, the stalk
rising approximately 1 centimeter high above the plane of the
surface on which the slug has migrated. Inside the globular end
of the fruiting body, each spore cell is cellulose encapsulated.
In the denouement, the stalk cells die and the spore cells are
widely dispersed to become new amoeba, each of which will begin a
separate new population of cells both individual and social.
Thus, in this organism, initially identical cells are
differentiated into one of two alternative cell types, spore
cells and stalk cells. It is an organism where individual cells
come together to form a cohesive structure, aggregating into a
single organism, a quite remarkable feat of organization that
challenges biologists, chemists, and physicists. Much has been
learned about this organism in the past few decades, in
particular the apparent important role of release of cyclic
adenosine monophosphate (cAMP) in the initial aggregation that
produces the slug. ... ... J.T. Bonner (who has spent more than
50 years studying the social amoeba) points out that one of the
obstacles in studying D. discoideum is that it has been difficult
to follow the movements of individual cells within the slug. The
author now describes a new method for studying D. discoideum, the
method producing flat slugs one cell thick at a mineral oil-water
interface where one can follow the movement of all the cells. The
author reports that observations of time-lapse videos reveal the
following about slug migration: 1) While the posterior cells move
straight forward, the anterior cells swirl about rapidly in a
chaotic fashion. 2) Turning of the slug involves shifting the
high point of these hyperactive cells. 3) Both the anterior and
posterior cells move forward on their own power as the slug moves
forward. 4) There are no visible regular oscillations within the
slug. 5) The number of prestalk and prespore cells is
proportionate for a range of sizes of the mini-slugs involved in
these experiments (approximately 300 to 400 cells in each of
these mini-slugs). The author suggests that all of the
observations on thin slugs are consistent with observations of
normal 3-dimensional slugs, and that experiments with 2-
dimensional slugs may provide new insights into differentiation
and movements in this organism.
-----------
J.T. Bonner (Princeton University, US): A way of following
individual cells in the migrating slugs of Dictyostelium
discoideum. (Proc. Natl. Acad. Sci. US 4 Aug 98)
QY: J.T. Bonner, Princeton University 609-258-3000
-------------------
Summary by SCIENCE-WEEK 18Sep98
ON THE MOLECULAR MECHANISMS OF SWARMING IN BACTERIA
Flagella are whiplike extensions from certain types of cells, and
in bacteria that have them, they are responsible for locomotion
of the organism. The term "chemotaxis" refers to the movement of
cells in response to chemical stimuli, and in the context of this
report, "chemoreceptors" are the receptors on the surfaces of
mobile cells that initiate the chemotactic response. Substances
that produce chemotaxis are called "chemoeffectors". In bacteria,
"swarming" is an organized surface translocation on solid media
that depends on extensive flagellar activity and cell-cell
contact. Previous studies of bacteria that swarm have indicated
the chemotaxis system is involved, but the mechanism is not
known. ... ... Now Burkhart et al (University of Texas Austin,
US) report that two of the four chemoreceptors in E. coli can
support swarming individually, but sensing their most powerful
chemoattractants (serine, or aspartate, or maltose) is not
necessary for swarming. The authors suggest that during swarming,
the chemoreceptors signal through the chemotaxis pathways and
induce swarmer cell differentiation (e.g., increased number of
flagella) in response to still unknown signals other than their
known chemoeffectors.
QY: Rasika M. Harshey (rasika@uts.cc.utexas.edu)
(Proc. Natl. Acad. Sci. US 3 Mar 98) (Science-Week 10 Apr 98)
-------------------
Related Background:
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) (Science-Week 16 Jan 98)
5. A NERVE CELL TYPE UNIQUE TO HUMANS AND GREAT APES
The human brain consists of 3 main parts: the brainstem, the
cerebellum, and the cerebral hemispheres. The cerebral
hemispheres are best envisioned as comprising 8 discrete lobes (4
in each hemisphere), these lobes infolded, corrugated, and
essentially "crunched up" to pack tightly into the confining
brain case (the cranium). The entire convoluted surface of the
cerebral hemispheres of the brain consists of a laminated rind of
neurons and supporting cells approximately 2 millimeters thick,
the rind called the "cerebral cortex". The infoldings of the
brain permit a great deal more cortical surface area to exist
with the confines of the cranium, the total surface area of the
cerebral cortex on average equal to 1.6 square meters. This 2-
millimeter thick rind contains approximately 10^(10) nerve cells
in more or less discrete layers, usually 6 layers in most regions
of the cortex. Since the cerebral cortex is the region of the
nervous system involved in all the so-called "higher mental
faculties", as might be imagined it has been the focus of
considerable comparative anatomical research, particularly
research comparing the human cerebral cortex with the cerebral
cortices of our closest evolutionary relatives. The term
"neocortex" refers to the most recently evolved part of the
cerebral cortex. The term "cingulate cortex", of relevance in
this report, refers to a specific region of the cerebral cortex,
a region located deep within the central divide between the two
hemispheres. Concerning neurons in the layers of the cerebral
cortex, various cell types can be recognized, the types
essentially distinguished by morphology -- the various shapes of
the cells. Concerning the evolving cerebral cortex, the evolution
of the neocortex in primates has consisted of a great expansion
of cortical areas, with a several-hundredfold increase in
cortical volume between prosimians (lower primates: lemurs,
lorises, tarsiers) and humans. However, the neuronal types that
populate the neocortex have apparently remained remarkably
constant, and are morphologically recognizable across primate
species. An exception is the so-called "spindle neuron", found in
the anterior cingulate cortex. These neurons are characterized by
an elongate, gradually tapering, large-sized cell body that is
virtually symmetrical about its vertical and horizontal axes.
This neuron type has been described in the human cortex and in
the cortex of the common chimpanzee, and recent studies in humans
apparently indicate that spindle cells are especially vulnerable
to degeneration in *Alzheimer's disease, with a loss of
approximately 60 percent of these particular nerve cells.
... ... E.A. Nimchinsky et al (6 authors at 3 installations, US)
now report a study of 28 primate species representing all
superfamilies of prosimian and anthropoid primates, the results
indicating that spindle neurons are a feature of the anterior
cingulate cortex of all humans and great apes (Pongidae: orang-
utan, gorilla, chimpanzee), but not of any other primate species.
The authors suggest these observations are of particular interest
when considering primate neocortical evolution, revealing
possible adaptive changes and functional modifications over the
last 15 to 20 million years in the anterior cingulate cortex, a
region that plays a major role in the regulation of many aspects
of *autonomic function and of certain cognitive processes. The
authors suggest that the fact that these unique neurons are
apparently severely affected in the degenerative process of
Alzheimer's disease indicates that some of the differential
neuronal susceptibility that occurs in the human brain in the
course of age-related dementing illnesses may have appeared only
recently during primate evolution. Finally, the authors suggest
the present study indicates some of the possible limitations of
making comparisons between humans and more distantly related
nonhuman primates, while emphasizing the importance of studies of
great apes in the context of aging and of age-related diseases
affecting the cerebral cortex.
-----------
E.A. Nimchinsky et al: A neuronal morphologic type unique to
humans and great apes.
(Proc. Natl. Acad. Sci. US 27 Apr 99 96:5268)
QY: Patrick R. Hof [hof@neuro.mssm.edu]
-----------
Text Notes:
... ... *Alzheimer's disease: The term "dementia" refers to a
pathological failure of memory and other cognitive functions.
Alzheimer's disease, first characterized by Alois Alzheimer
(1864-1915) is the most common dementia, afflicting 5 to 10
percent of the population over the age of 65 and an even higher
percentage of the population over 85. The earliest manifestation
of Alzheimer's disease is typically an impairment of recent
memory function and attention; this deficit is followed by a
deterioration of language skills, visuospatial orientation,
abstract thinking, and judgment. There is no effective therapy.
The diagnosis of Alzheimer's disease can only be established by
the above characteristic clinical features in association with a
distinctive postmortem histopathology, since the same clinical
symptoms can be produced by various pathologies distinct from
Alzheimer's disease. Histopathologically, Alzheimer's disease is
characterized by specific intracellular changes in neurons, the
deposition of abnormal extracellular material called amyloid
(senile) plaques, and an accompanying loss of neurons in many
important areas of the brain.
... ... *autonomic: In this context, the term "autonomic" refers
to the autonomic nervous system, which is an anatomically
distinct ensemble of nervous system structures and pathways
involved in the regulation of a number of important "automatic"
physiological functions (e.g., beating of the heart, secretions
of the glands, breathing rate, temperature regulation, and all
physiological activities related to strong emotions.)
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 16Jul99
6. AN ETHICS DEBATE CONCERNING RESEARCH ON MENTAL ILLNESS
The problem is both easily stated and profound: Given as a
premise that no medical research on human disease should involve
human subjects unless these subjects have provided their informed
consent to participate in the research, how does one conduct
medical research in the area of mental illness when in many cases
"informed consent" of the subjects may be compromised by their
mental incapacities? Five of the world's 10 leading causes of
disability are psychiatric: depression, alcohol abuse, bipolar
mood disorder, schizophrenia, and obsessive-compulsive disorder.
There is evidence that each of these disorders has important
genetic determinants and biologic correlates, and in the past 40
years, specific effective pharmacological treatments for each
have replaced previous nonspecific concern and mere caretaker
support. Thus, although we know that biologically based medical
research in the area of mental illness can produce important
therapeutic results (and we expect even more important results to
be produced in the future), we still do not have the answer to
the problem posed by the need for "informed consent" of the
patient-subject of research. There are essentially two current
approaches to this difficult problem, one approach relying on the
judgment of the health-care professionals closest to the patient,
and the other approach relying on the judgment of independent
reviewers coupled with more stringent guidelines than those
previously in use. The two views have been recently expounded in
two contiguous papers in a major medical journal. It is not
possible to give full deserved measure to either argument in this
brief report, but we can at least confront the outlines of the
problem.
... ... Robert Michels (Cornell University, US), a physician,
makes the following points:
1) There has been much concern about the ethical aspects of
psychiatric research. Are mentally ill subjects especially
vulnerable to exploitation? Are they competent to give informed
consent? Are psychiatric research methods particularly dangerous?
Are special procedures or regulations needed for such research?
There have been attacks and defenses of psychiatric research in
the courts, in the media, and in statements made by groups that
advocate for the rights of the mentally ill.
2) The National Bioethics Advisory Commission (NBAC) is the
latest federal panel to address the issue. Its 17 members were
appointed by President Clinton in 1995 to advise the government
on bioethical issues, and especially to "consider the problem of
the rights and welfare of human research subjects." Its report
was released in 1998.
3) Currently, the capacity to consent to research is
assessed in much the same way as the more familiar capacity to
consent to treatment -- i.e., by the health care professionals
and care givers who are closest to the patient. The NBAC would
change this approach for all research involving more than minimal
risk. The category of "more than minimal risk", as defined by the
NBAC, is quite broad. It includes, for example, non-invasive
*magnetic resonance imaging (MRI) of the brain (because the
noise, confinement, and apparatus could be distressing to a
subject), or explicit questions about sexual preferences (which
might upset a subject). According to the NBAC, such research
requires an assessment by an "independent qualified
professional"; even the treating clinician would be disqualified
from judging the capacity to consent to research if he or she
were either participating in the research or employed by the
institution conducting it. Many psychiatric researchers consider
the NBAC recommended procedures expensive, cumbersome, and
clinically insensitive to the experience of impaired subjects,
and some patient advocates fear that the implied mistrust of care
givers may have a negative effect on the doctor-patient
relationship.
4) If the mentally ill are different in a way that raises
questions about their civil liberties and prevents them from
participating in research, and if psychiatric research is
dangerous and researchers are not to be trusted, the strategy
recommended by the NBAC has merit. On the other hand, if persons
with psychiatric disorders are as able and entitled as those
without such disorders to take part in and benefit from research,
if creative researchers can design valuable yet safe studies, if
clinicians and researchers regularly place their research
subjects' interest first, and if the public, patients, ethicists,
researchers, and clinicians all share a common goal, then it is
time to expand the dialogue and collect data about the strengths
and weaknesses of the current system. We should search for
solutions that will protect all persons who have impaired
decision-making capacity without further stigmatizing the
mentally ill, undermining the research agenda for mental illness,
or diluting the moral responsibility of researchers.
... ... In the contiguous commentary, Alexander M. Capron
(University of Southern California, US), an attorney and a member
of the NBAC, makes the following points:
1) In the 50-odd years since the 10 principles of the
Nuremberg Code were set forth by the US judges who convicted the
Nazi concentration-camp physicians of crimes against humanity,
the tensions inherent in using human beings as a means to advance
biomedical knowledge have surfaced repeatedly. Indeed, the lesson
of the past half-century is that suffering, death, and violation
of human rights can arise not only when dictators give inhumane
scientists free rein to treat human beings as guinea pigs, but
also when well-meaning physicians conduct research in a free and
enlightened society. The most recent evidence of this phenomenon
can be seen in two sets of problems: those associated with local
supervision of research with human subjects in general, and those
that arise in psychiatric research, particularly research
involving children and patients who are unable to make informed,
voluntary decisions about their participation in such research.
2) As a general rule, with regard to children and mentally
infirm patients, we should set higher requirements for consent,
and impose additional safeguards on therapy combined with
experimentation, than on research with normal adult volunteers,
lest investigators even unwittingly expose "consenting" patient-
subjects to unreasonable risks.
3) Experience over the past two decades has made clear the
need for special protection for patients with mental disorders.
The regulations and official actions -- as well as the
recommendations for institutional review boards -- of the
National Bioethics Advisory Commission are the minimum needed.
-----------
Robert Michels: Are research ethics bad for our mental health?
(New England J. Med. 6 May 99 340:1427)
QY: Robert Michels, Cornell Univ. Medical College 212-746-1067
-----------
Alexander M. Capron: Ethical and human-rights issues in research
on mental disorders that may affect decision-making capacity.
(New England J. Med. 6 May 99 340:1430)
QY: Alexander M. Capron [mmiller@law.usc.edu]
-----------
Text Notes:
... ... *magnetic resonance imaging: Magnetic resonance imaging
(MRI) is essentially a technique for examining morphology (as
opposed to _functional_ magnetic resonance imaging, which is a
technique for examining anatomical correlates of function). In
general, MRI involves magnetic coils producing a static magnetic
field parallel to the long axis of the patient or subject,
combined with inner concentric magnetic coils producing a static
magnetic field perpendicular to the long axis. A radio-frequency
coil specifically designed for the head perturbs the static
fields to generate a magnetic resonance image. The interaction
physics in this technique is that between the magnetic fields and
atomic nuclei in brain tissue. "Sliced" views can be obtained
from any angle, and the resolution is quite high and on the order
of millimeters for magnetic field strengths of 1.5 tesla. MRI
produces better resolution than computer assisted tomography
(CAT). The consensus medical view is that MRI involves no known
risk to the patient. A wide spectrum of neuropathologies can be
detected more easily by MRI than by any other technique.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 16Jul99
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
IN FOCUS: ON COSMIC HISTORY
"The history of our Universe divides into three parts. 1) The
first millisecond, a brief but eventful era spanning 40 powers of
10 in time, starting at the Planck era [10^(-43) seconds]. This
is the intellectual habitat of mathematical physicists and
quantum cosmologists. The relevant physics is still speculative
-- indeed, one motive for studying cosmology is that the early
Universe may offer the only real clues to the laws of nature at
extreme energies. 2) The second stage runs from a millisecond to
about 1 million years. It's an era where cautious empiricists
feel more at home. The densities are far below nuclear density,
but everything is still expanding quite smoothly. There is good
quantitative evidence -- the cosmic helium and deuterium
abundances, the background radiation, and so on -- and the
relevant physics is well tested in the lab. Part two of cosmic
history, though it lies in the remote past, is the easiest to
understand. 3) But the tractability lasts only so long as the
Universe remains amorphous and structureless. When the first
gravitationally bound structures condense out -- when the first
stars, galaxies, and quasars have formed and lit up -- the era
studied by traditional astronomers begins. We then witness
complex manifestations of well-known basic laws. Part three of
cosmic history is difficult for the same reason as all
environmental sciences -- from meteorology to ecology -- are
difficult: they involve ultracomplex manifestations of simple
laws."
-- Martin Rees: _Before the Beginning_
(Helix Books, Reading 1997, p.160)
[Sir Martin Rees is Astronomer Royal of the UK and former
Director of the Cambridge University Institute of Astronomy.]
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been published regularly each week since that date. We welcome
comments, suggestions, and criticisms from our subscribers.
Public letters relevant to any report are also welcome. Editorial
contact: [editors@scienceweek.com].
Editor/Publisher: Dan Agin
Managing Editor: Claire Haller
Associate Editor: Joan Oliner
Copyright (c) 1997-1999 SCIENCE-WEEK/Spectrum Press Inc.
All Rights Reserved
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