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.

November 17, 2000 -- Vol. 4 Number 46

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Research is the process of going up alleys to
see if they are blind.
-- Marston Bates

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Section 1
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Contents of this Issue (Full reports in Section 2):

1. NEUROBIOLOGY:
ON REGIONAL DIFFERENCES IN CORTICAL ORGANIZATION
New postmortem studies of human brain tissue indicate that the
functional lateralization in Brodmann area 22 (an area involved
in speech) is accompanied by interhemispheric differences in the
organization of the intrinsic microcircuitry. Neuronal tract
tracing revealed a modular network of long-range intrinsic
connections linking regularly spaced clusters of neurons.
Although the neuron cluster diameter was similar in both
hemispheres, the spacing of the clusters was approximately 20
percent larger in the left hemisphere. These results are the
first evidence, for a particular function, of cytoarchitectonic
differences between paired areas in the dominant hemisphere and
non-dominant hemisphere. The authors suggest that the observed
interhemispheric differences in the layout of intrinsic
connections may be at least in part due to use-dependent
modifications of circuitry during early development.
(Science 15 Sep 00 289:1946)

2. BIOLOGY OF AGING:
ON FOOD RESTRICTION AND AGING
Yeast undergo only a finite number of divisions, after which the
yeast cells die; thus, the life-span in yeast is defined by the
number of divisions each cell completes. Researchers have now
induced caloric restriction in yeast by limiting glucose
availability or by genetically crippling the ability of yeast to
sense and respond to glucose. Caloric restriction extended yeast
longevity by 20 to 40 percent, similar to the relative life-span
extension induced by caloric restriction in mammals. This
extension was not observed in yeast strains mutant for the gene
SIR2 (which encodes the silencing protein SIR2p) or the gene NPT1
(a gene in a pathway in the synthesis of the oxidized form of
nicotinamide-adenine dinucleotide (NAD). These results may link
caloric restriction to the control of gene expression and to the
suppression of DNA damage (loss or rearrangement of DNA) caused
by mitotic recombination. (Science 22 Sep 00 289:2126)

3. CELL BIOLOGY:
ON INTRACELLULAR-MEMBRANE TRANSPORT
The compartmentalization of functions into distinct membrane-
bound organelles is a central characteristic of eukaryotic
biological cells. The protein and lipid composition of these
organelles is unique, a factor vital for their proper function.
This necessitates tightly controlled transport of biomolecules
from their sites of synthesis or uptake to specific destinations,
and in addition requires mechanisms that prevent promiscuous
interactions between cellular membranes that would lead to
deleterious mixing of organelle constituents. During the 1990s,
the cellular machinery responsible for decoding protein targeting
information and mediating the transport processes became
apparent, and several genetic diseases that directly affect the
intracellular sorting and transport machinery were identified.
(New England J. Med. 12 Oct 00 343:1095)

4. MATERIALS SCIENCE:
A NEW TITANIUM PURIFICATION METHOD
Titanium is often called a "space-age" metal because of its high
strength-to-weight ratio and its inertness to many corrosive
environments. But despite the availability of various ores, the
use of titanium as a substitute for steel has been modest because
of the relatively high cost of purification. Researchers now
report an electrochemical method for the direct reduction of
solid titanium dioxide. The simplicity and rapidity of this
process compared to conventional routes suggests that it should
result in reduced production costs. Early results of industrial
production trials in the UK offer hope that the process can be
developed on a commercial scale and contribute to the cost
reduction required to allow titanium to become a mainstream
engineering material. (Nature 21 Sep 00 407:361)

5. HISTORY OF EARTH SCIENCE:
ON THE DISCOVERY OF THE STRATOSPHERE
The first hint that Earth's atmosphere is a series of concentric
shells was provided by the meteorologist Leon Teisserenc de Bort
(1855-1913). This discovery influenced the discovery of similar
layering of the ocean, and the discovery of a similar
discontinuity in the solid Earth, the discontinuity now known as
the "Moho". In addition, the discovery that the Earth-ocean-
atmosphere system is composed of concentric shells of different
density, from the core of the Earth to the top of the atmosphere,
is the founding insight of modern geophysics, and the discovery
also profoundly influenced the thinking of the young
meteorologist Alfred Wegener (1880-1930), leading Wegener in 1912
to propose the theory of continental drift, with the continents
representing the remains of a formerly continuous Earth shell
above the ocean floors. Thus, Teisserenc de Bort was not only the
discoverer of the stratosphere but also an honorary grandfather
of continental drift. (Nature 26 Oct 00 407:947)

6. MATERIALS SCIENCE:
DISCOVERY OF THE SMALLEST CARBON NANOTUBE
Last month, researchers in Germany and the US reported synthesis
of the smallest fullerene, and this month researchers in Japan
and China report synthesis of the smallest carbon nanotube using
two different methods. The carbon nanotubes discovered by the
researchers in Japan using an arc-discharge method have a
diameter of 4 angstroms, which according to theory is the
narrowest attainable that can still remain energetically stable.
These nanotubes are confined inside multiwalled carbon nanotubes,
and their diameter corresponds to that of a C(sub20) dodecahedron
with a single carbon atom at each of its 20 apices. Unlike larger
carbon nanotubes, which, depending on their diameter and
helicity, can be either metallic or semiconducting, these
smallest nanotubes are always metallic. In a simultaneous
publication, researchers in China report they have prepared the
smallest carbon nanotubes possible by the pyrolysis of
tripropylamine molecules in the channels of single crystals of a
porous zeolite, and that these uniformly sized carbon nanotubes
have a diameter of 0.4 nanometers and are the best example of
one-dimensional quantum wires. (Nature 2 Nov 00 408:50)

7. IN FOCUS: ON TIME AND EVOLUTION

8. FROM THE SCIENCEWEEK ARCHIVE:
ON PHYSICS, BIOLOGY, AND CARTOONS

=-=-=-=-=-=-=-=-=
Section 2
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1. NEUROBIOLOGY:
ON REGIONAL DIFFERENCES IN CORTICAL ORGANIZATION
     What is called the "cerebrum" is the bulk of brain as seen
by the naked eye, the "great ravelled knot" that sits on top of
the phylogenetically older parts of the whole brain, the
brainstem and midbrain. The surface of the cerebrum, an
enormously extended surface because of the many deep folds of the
cerebrum, is a thin sheet called the "cerebral cortex" (cortex =
rind or bark).  In all mammals, the cortex consists of a sheet of
cells approximately 1 to 4 millimeters thick, this sheet usually
divided into cellular layers varying from 1 to 6 in number that
can be histologically differentiated. Most of the cerebral cortex
has 6 layers, and this part of the cortex is called "neocortex"
(it is also phylogenetically more recent). In general, each cubic
millimeter of neocortex contains approximately 50,000 neurons.
     The study of the laminar organization of the neurons in the
cerebral cortex began in the early part of the 20th century and
became known as "cytoarchitectonics", and this was applied by the
neurologist Korbinian Brodmann (1858-1918) to divide the
neocortex into 47 different cytological regions.
     What we call "thinking" and "consciousness" appears to
depend on the 1 to 4 millimeter thick cerebral cortex that covers
the four lobes of the brain (occipital, parietal, temporal, and
frontal lobes). The intricate and highly ordered architecture of
the cerebral cortex contains approximately 75 percent of the
estimated 5 x 10^(9) neurons in the brain, and the major
challenge of human neurobiology is to relate this architecture to
function, i.e., relate the architecture of the cerebral cortex to
thinking and consciousness. In essence, this is a problem in
reverse engineering, perhaps the most complex such problem
currently known (or ever imagined), and we are still far from a
solution.
     In the human cerebral cortex, primary and sensory motor
functions are localized to some specific areas, whereas general
cognitive functions such as attention, identification, and
planning appear to involve several regions in a particular
cortical lobe. The language functions are primarily associated
with 3 of the cytoarchitectonic areas defined by Brodmann: 1)
Brodmann area 22, at the junction of the parietal and temporal
lobes (also known as Wernicke's area); 2) Brodmann areas 44 and
45, in the ventral and posterior region of the frontal lobe (also
known as Broca's area).
     Until the 1960s, there was much controversy concerning
lateralization of language function, i.e., controversy concerning
whether one hemisphere dominates language function. The
pioneering studies of Roger Sperry (1913-1994) on so-called
*"split-brain" patients settled the controversy, and the current
consensus is that in most individuals the left hemisphere is
unequivocally the seat of the major language functions. However,
the right hemisphere in left-hemisphere-dominant individuals does
have some language function: the right hemisphere can produce
rudimentary words and phrases, and evidently contributes
emotional context to language. Moreover, the right hemisphere
understands language, since it can respond to written or spoken
commands. In summary, the left hemisphere is usually dominant in
language, but the right hemisphere is also involved.
... ... R.A.W. Galuske et al (4 authors at 3 installations, DE)
now report the first cytoarchitectonic evidence of cytological
right-left asymmetry in Brodmann's area 22, the authors making
the following points:
     1) The authors point out that neuropsychological,
electrophysiological, and *noninvasive imaging studies indicate
that language comprehension and language production are
accompanied by activation of certain cortical areas. Several of
these areas are activated only unilaterally in the dominant
hemisphere, and one of the regions exhibiting robust unilateral
activation during processing of language-related signals is
located in the posterior part of the first temporal *gyrus and
the posterior temporal plane. This region corresponds to a
discrete cytoarchitectonic entity, the posterior part of Brodmann
area 22 (also known as area TA1, after von Economo and Koskinas),
a region that is distinguished in both hemispheres on the basis
of common cytoarchitectonic features.
     2) The authors report that using a carbocyanine dye in
postmortem human brain tissue (7 subjects free of known
neurological disorders; 6 subjects males ages 34, 41, 51, 52, 53,
and 73 years old; and one 82-year-old female), they have found
that the functional lateralization in Brodmann area 22 was
accompanied by interhemispheric differences in the organization
of the intrinsic microcircuitry. *Neuronal tract tracing revealed
a modular network of long-range intrinsic connections linking
regularly spaced clusters of neurons. Although the neuron cluster
diameter was similar in both hemispheres, the spacing of the
clusters was approximately 20 percent larger in the left
hemisphere. Assuming similar relations between functional and
anatomical architecture as in visual cortex, the authors suggest
the present data indicate that more functionally distinct
*columnar systems are included per surface unity in the left than
in the right area 22.
     3) The authors conclude: "Because early lesions in language
areas of the dominant hemisphere can be compensated by the non-
dominant hemisphere, it is conceivable that the observed
interhemispheric differences in the layout of intrinsic
connections are at least in part due to use-dependent
modifications of circuitry during early development. Future
studies will have to determine the exact time-course of postnatal
maturation of this connection system."
... ... In a commentary on this work, Michael S. Gazzaniga
(Dartmouth College, US) states: "The elegant work of Galuske et
al demonstrates that the melding of neuropsychology, brain
anatomy, and the cellular and molecular biology of neurons is
underway. It is no longer a dream -- the exciting reality is
here."
-----------
R.A.W. Galuske et al: Interhemispheric asymmetries of the modular
structure in human temporal cortex.
(Science 15 Sep 00 289:1946)
QY: Ralf A.W. Galuske: galuske@mpih-frankfurt.mpg.de
-----------
Michael S. Gazzaniga: Regional differences in cortical
organization.
(Science 15 Sep 00 289:1887)
-----------
Text Notes:
... ... *"split-brain" patients: The human nervous system (and
the nervous systems of many other vertebrate species) has a
bilateral symmetry most noticeable in the existence of the two
cerebral hemispheres. The two halves of the brain, although
exhibiting certain functional specializations, ordinarily work in
an integrated manner to produce the conscious output of the
nervous system, namely thought and action. Epilepsy is the
general name given to a class of nervous system disorders
involving convulsive activity of large numbers of nerve cells,
and a classical surgical procedure in cases of severe epilepsy is
section of the corpus callosum, the large band of nerve fibers
that serves as the primary connection between the two halves of
the brain. (Also, see related background material below.)
... ... *noninvasive imaging studies: The studies referred to
here are studies involving functional magnetic resonance imaging,
a technique based on the fact that oxyhemoglobin, the
oxygen-carrying form of hemoglobin, has a different magnetic
resonance signal than deoxyhemoglobin, the oxygen-depleted form
of hemoglobin. Activated brain areas utilize more oxygen, which
transiently decreases the levels of oxyhemoglobin and increases
the levels of deoxyhemoglobin, and within seconds the brain
microvasculature responds to the local change by increasing the
flow of oxygen-rich blood into the active area. This local
response thus leads to an increase in the oxyhemoglobin-
deoxyhemoglobin ratio, which forms the basis for the fMRI signal
in this technique. Because of its high spatial resolution
(millimeters) and high temporal resolution (seconds) compared to
other imaging techniques, fMRI is now the technology of choice
for studies of the functional architecture of the human brain.
... ... *gyrus: The term "gyrus" refers to any of the visible
convoluted ridges of the cerebral hemispheres.
... ... *Neuronal tract: In this context, a neuronal tract is a
band of nerve fibers connecting one region of the brain with
another region of the brain, or with sensory or muscle systems.
... ... *columnar systems: In many regions of the cerebral
cortex, the multi-layered sheet has an evident columnar
organization of cells, with cell bodies and nerve fibers arranged
in apparent columns perpendicular to the plane of the layers.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 17Nov00
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
HUMAN NEUROBIOLOGY: SPLIT-BRAIN RESEARCH
... Michael S. Gazzaniga (Dartmouth College, US), a member of
Sperry's original group, presents a review of the history and
current status of human split-brain research, and makes the
following points: 1) In the classical split-brain patient, visual
information no longer moves between the two sides of the brain.
If an image is projected to the right visual field (i.e., to the
left hemisphere, which is where information to the right field is
processed) patients can describe what they see. But when the same
image is displayed to the left visual field (i.e., to the right
hemisphere), the patient cannot describe what they see. But if
the patient is asked to point to an object similar to the object
being projected, they do so with ease. The right brain sees the
image and can mobilize a nonverbal response, but it cannot talk
about what it sees. 2) The same situation obtains for touch,
smell, and sound. 3) Additionally, each half of the brain can
control the upper muscles of both arms, but the muscles
manipulating hand and finger movements can be orchestrated only
by the contralateral hemisphere. In other words, the right
hemisphere can control only the left hand and the left hemisphere
only the right hand. 4) Ultimately, it was discovered that the
two hemispheres control vastly different aspects of thought and
action. Each half of the brain has its own specialization, and
thus its own limitations and advantages. The left brain is
dominant for language and speech, the right brain excels at
visual-motor tasks. 5) During the past decades, research in
cognitive science, artificial intelligence, evolutionary
psychology, and neuroscience has directed attention to the idea
that brain and mind are built from discrete units -- or modules
-- that carry out specific functions. According to this theory,
the brain is not a general problem-solving device whose every
part is capable of any function. Rather it is a collection of
devices that assists the mind's information processing demands.
Gazzaniga concludes: "After many years of fascinating research on
the split brain, it appears that the inventive and interpreting
left hemisphere has a conscious experience very different from
that of the truthful, literal right brain. Although both
hemispheres can be viewed as conscious, the left brain's
consciousness far surpasses that of the right. Which raises
another set of questions that should keep us busy for the next 30
years or so."
QY: Michael S. Gazzaniga, Dartmouth College 603-646-2875.
(Scientific American July 1998) (Science-Week 10 Jul 98)
-------------------
Related Background:
ON MODULAR COGNITIVE SYSTEMS IN THE HUMAN BRAIN
One of the central challenges of cognitive neuroscience is to
unmask the apparent unitary nature of perceptual, memorial, and
cognitive systems. Neuropsychological analyses, functional brain-
imaging methods, and analyses of normal reaction times have
revealed that apparently unitary processes consist of multiple
components. Frequently, these multiple components are distributed
across the cerebral hemispheres, but appear unified because of
the integration possible via the corpus callosum.
... ... Baynes et al (4 authors at 3 installations, US) report a
case of elective surgery for a severe epileptic disorder, the
surgery involving a resection of the corpus callosum in a left-
handed woman with left-hemisphere dominance for spoken language.
The patient demonstrated a dissociation between spoken and
written language. Words flashed to the dominant left hemisphere
were easily spoken out loud, but could not be written. When words
were flashed to the patient's right hemisphere, she could not
speak them out loud but she could write them with her left hand.
The authors suggest this marked dissociation supports the view
that spoken and written language output can be controlled by
independent hemispheres, even if before hemispheric disconnection
spoken and written language appear as inseparable cognitive
entities.
-----------
QY: Kathleen Baynes: kbaynes@ucdavis.edu
(Science 8 May 98 280:902) (ScienceWeek 29 May 98)
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
NEUROBIOLOGY: ON LOCALIZATION OF FUNCTION IN THE HUMAN BRAIN
     For more than 200 years, neurobiologists have been concerned
with the general problem of what is called "localization of
function" in the human brain. That there is considerable
localization of function is indisputable: there are brain regions
involved with specific primary inputs such as vision, audition,
taste, etc., brain regions for specific primary outputs to
various muscle systems, and brain regions for speech and the
understanding of language. The still unclear aspects concern
anatomical localization of other so-called "higher faculties",
e.g., learning, memory, perceptual analysis, motivations, various
other cognitive abilities, etc.
     Classical studies of localization of function in the human
brain essentially began with Franz Joseph Gall (1758-1828), who
postulated that the shape of the human brain, especially its
convolutions, was related to "mental capacity", and that
different parts of the brain were involved with different parts
of the human body. This latter proposal concerning the relation
between different parts of the brain and different parts of the
body was essentially a correct view. But Gall also believed he
could correlate the shape of the human brain with various
emotional and temperamental qualities, and that the shape of the
brain, particularly its convolutions, could be deduced from the
irregularities existing in the topology of the overlying skull.
Thus began the 19th century pseudoscience of "phrenology", a
quackery that postulated that various human character traits
could be identified by literally feeling bumps on the head. The
public adored the idea, and so-called "phrenologists" continued
to bamboozle the public long after Gall was dead. What started as
a useful view that correlated brain anatomy with function, ended
in a popular pseudoscience that still had the public confused and
misled 100 years later.
     The next most important figure in this field was Pierre Paul
Broca (1824-1880), a neurosurgeon who in 1861 discovered the
motor area of the brain responsible for speech, and who studied a
series of patients with traumatic injuries in this area. As a
result of Broca's work, the idea that at least certain brain
functions are localized was put on a firm scientific footing, and
a long history of research by clinical neurologists attempting to
correlate traumatic brain injury to loss of specific brain
function began. Beginning in the 1950s, evidence from localized
electrophysiological studies was added to the data resulting from
studies of traumatic brain injury, and in the 1990s an entirely
new set of data from *functional magnetic resonance imaging of
the human brain in action became available to researchers
studying localization of brain function. This field is now
intensely active and of signal importance in neurology and
cognitive science. But the human brain is profoundly complex, and
there are still more questions than answers about how things get
done in this 1400-gram mass of tissue that makes us what we are.
     The term "cortex" (cerebral cortex), in this context, refers
to the thin surface layering of nerve cells of the brain, the
region only several millimeters thick but covering all of the
brain surface. This is the part of the central nervous system
most intimately involved with the so-called "higher faculties",
although the cortex generally operates in concert with other
parts of the brain. The structure is primitive in lower mammals,
and is found progressively more pronounced and with greater
surface area in primates and man. Many contemporary
neurobiologists who study the brain emphasize precise "mapping"
of the cerebral cortex into "areas" associated with specific
functions.
... ... Jonathan C. Horton (University of California San
Francisco, US) presents an essay on localization of function in
the human brain, the author making the following points:
     1) Given the limitations of histology, researchers often
designate areas in brain cortex by topography. For example, any
region that contains its own representation of the visual world
qualifies for "area" status. Unfortunately, topographic order in
other than primary visual areas ("higher" visual areas) is often
too crude to provide a reliable definition of boundaries. Another
limitation is that topography may not be meaningful outside
sensory and motor cortices. The author asks: "What constitutes
topography in regions concerned with language, motivation, or
personality?"
     2) The author points out that relentless experimental
efforts and a battery of technical advances have provided us with
better maps of the brain. But much of the cortex stubbornly
refuses to be mapped, and the author suggests it is worth
questioning the assumption that the cerebral cortex consists of a
finite number of areas with sharp borders. An alternative is that
only certain regions -- mostly motor and sensory cortex -- are
organized in this way. Other regions might be diffuse fields
separated by gradual transitions in function, properties, and
connections. As Broca said in 1861: "Although I believe in the
principle of localization, I have asked and still ask myself
within what limits this principle can be applied." The author
(Horton) concludes: "For brain cartographers, the last frontier
is in their heads."
-----------
Jonathan C. Horton: Boundary disputes.
(Nature 10 Aug 00 406:565)
QY: Jonathan C. Horton, Univ. of Calif. San Francisco 415-476-
4044.
-----------
Text Notes:
... ... *functional magnetic resonance imaging: See main report.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 1Sep00
For more information: http://scienceweek.com/swfr.htm

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2. BIOLOGY OF AGING:
ON FOOD RESTRICTION AND AGING
During the past decade, an important change has occurred in the
thrust of aging research. For the first time, we have the results
of a wide variety of systematic experiments in molecular biology
and biochemical cell physiology related to questions concerning
senescence in various organisms ranging from the most primitive
to the most complex, and researchers who work in this field are
more hopeful than ever before that important breakthroughs will
occur in the near future.
... ... S-J. Lin et al (3 authors at Massachusetts Institute of
Technology, US) now report that in a study involving mimicking of
caloric restriction in yeast by physiological or genetic means,
they found a substantial extension in life span. This extension
was not observed in yeast strains mutant for the gene SIR2 (which
encodes the *silencing protein SIR2p) or the gene NPT1 (a gene in
a pathway in the synthesis of the oxidized form of *nicotinamide-
adenine dinucleotide (NAD). The authors suggest their findings
indicate that the increased longevity induced by caloric
restriction requires the activation of SIR2p by NAD.
... ... In a commentary on this work, Judith Campisi (Lawrence
Berkeley National Laboratory, US) makes the following points:
     1) Current hypotheses concerning the cause of aging
generally fall into one or two categories: a) the involvement of
extrinsic or intrinsic factors that damage intracellular or
extracellular molecules; b) changes in *gene expression that are
either programmed or that are brought about by nonmutational
changes in DNA structure. To what extent these hypotheses overlap
or intersect is not known.
     2) Regardless of the hypothesis, however, caloric
restriction has been an important tool for testing ideas about
causes of aging in animals. Caloric restriction -- reducing the
food intake of animals by 50 to 70 percent -- reliably extends
the mean and maximum life-spans of several species, including
mammals. Caloric restriction postpones most age-related pathology
and alters many, but not all, age-related processes. It is
thought to do this primarily by reducing oxidative stress and
damage caused by reactive oxygen species. Yet despite more than
half a decade of research, the major pathway through which
caloric restriction acts remains enigmatic. Now S-J. Lin et al
describe intriguing results that may link caloric restriction to
the control of gene expression and to the suppression of DNA
damage (loss or rearrangement of DNA) caused by *mitotic
recombination.
     3) Yeast undergo only a finite number of divisions, after
which the yeast cells die; thus, the life-span in yeast is
defined by the number of divisions each cell completes. Lin et al
induced caloric restriction in yeast by limiting glucose
availability or by genetically crippling the ability of yeast to
sense and respond to glucose. Caloric restriction extended yeast
longevity by 20 to 40 percent, similar to the relative life-span
extension induced by caloric restriction in mammals.
     4) The author (Campisi) points out that a fundamental
difference between adult mammals and model organisms such as the
yeast, the *nematode, and the fruit fly is the prevalence of
cancer in mammals, and essentially the lack of cancer in yeast,
worms, and flies. In mammals, mutations, probably coupled to the
changes in cellular function that accompany aging, give rise to
cancer, which poses an additional threat to longevity. In
addition, most human cells undergo *telomere attrition with
successive cell divisions and aging (i.e., the ends of
chromosomes become progressively shorter. The extent to which
telomere-induced cellular senescence contributes to human aging
is not yet clear.
-----------
S-J. Lin et al: Requirement of NAD and _SIR2_ for life-span
extension by caloric restriction in Saccharomyces cerevisiae.
(Science 22 Sep 00 289:2126)
QY: Leonard Guarente: leng@mit.edu
-----------
Judith Campisi: Aging, chromatin, and food restriction --
connecting the dots.
(Science 22 Sep 00 289:2062)
QY: Judith Campisi: jcampisi@lbl.gov
-----------
Text Notes:
... ... *silencing protein: In general, a protein factor that
negatively controls (i.e., inhibits) expression of a specific
gene or genes.
... ... *nicotinamide-adenine dinucleotide (NAD): An important
coenzyme in *electron transfer reactions in biological cells, in
particular in oxidative reactions in *aerobic respiration.
... ... *electron transfer: (electron transport) This refers to a
sequence of steps in the final stage of the aerobic respiration
biochemical pathway in which high energy electrons are
effectively passed through a series of membrane-bound carrier
molecules to support a proton gradient involved in energy
storage. The term "transport" here  refers essentially to a
chemical flow diagram and not necessarily to an actual spatial
translocation of electrons.
... ... *aerobic respiration: In general, the direct utilization
of oxygen by a biological system.
... ... *gene expression: In general, the term "gene expression"
includes any gene activity, but particularly an activity that
produces the synthesis or activation of a specific protein.
... ... *mitotic recombination: In general, the term 
"recombination" refers to the integration of DNA fragments
into a particular site in a genome, sometimes with the formation
of new advantageous or deleterious genes. "Mitotic recombination"
refers to recombination that occurs during cell division. 
... ... *nematode: An abundant and ubiquitous phylum of
unsegmented roundworms.
... ... *telomere: Telomeres are defined ends of chromosomes
that contain specific repeated DNA sequences. They are essential
for normal chromosome replication, and since their length
shortens a bit with each replication, they are believed to be
involved in the aging of the cell.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 17Nov00
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
BIOLOGY OF AGING: CALORIC RESTRICTION AND GENE EXPRESSION
Most multicellular organisms exhibit a progressive and
irreversible physiological decline that characterizes what is
called "senescence" -- the aging process. The molecular basis of
this process is unknown, but various mechanisms have been
postulated, including: a) cumulative damage to DNA leading to
genome instability; b) biochemical pathway alterations that lead
to changes in *gene expression patterns; c) *telomere shortening
in replicative cells; d) oxidative damage to critical
macromolecules by reactive oxygen species; and e) nonenzymatic
*glycation of proteins. Experimental genetic manipulation of the
aging process in multicellular organisms has been achieved in the
fruit fly Drosophila through the overexpression of certain
enzymes, and in the nematode worm C. elegans through alterations
in the *insulin receptor pathway, and in both organisms through
the experimental selection of stress-resistant mutants. In
mammals, however, the only intervention that appears to slow the
intrinsic rate of aging is caloric restriction. Most studies of
caloric restriction in mammals have involved laboratory rodents
subjected to a long-term 25 to 50 percent reduction in caloric
intake without essential nutrient deficiency, and the result in
these rodents is a delayed onset of age-associated pathological
and physiological changes and an extension of maximum lifespan.
Various mechanisms have been postulated to explain this result,
including increased DNA repair capacity, altered gene expression,
depressed metabolic rate, and reduced oxidative stress.
... ... C-K. Lee et al (4 authors at University of Wisconsin, US)
now present a study to examine the molecular events associated
with aging in mammals, with experiments involving analysis of the
aging process in *skeletal muscle of mice. The authors report
that the use of high-density *oligonucleotide arrays representing
6347 genes (5 to 10 percent of the mouse genome) revealed that
aging resulted in a differential gene expression pattern
indicative of a marked stress response and lower expression of
metabolic and biosynthetic genes. Most alterations were either
completely or partially prevented by caloric restriction.
*Transcriptional patterns of calorie-restricted animals suggest
that caloric restriction retards the aging process by causing a
metabolic shift toward increased protein turnover and decreased
macromolecular damage. The authors state: "The data presented
here provide the first global assessment of the aging process in
mammals at the molecular level and underscore the utility of
large-scale parallel gene expression analysis in the study of
complex biological phenomena."
-----------
C-K. Lee et al: Gene expression profile of aging and its
retardation by caloric restriction.
(Science 27 Aug 99 285:1390)
QY: Tomas A. Prolla [taprolla@facstaff.wisc.edu]
-----------
Text Notes:
... ... *gene expression patterns: This refers to the profile of
genes in a genome that are actually operating (i.e., undergoing
expression) at any point in time. In a mammal, for example, a
liver cell is a liver cell because of a particular profile of
expressed genes, and what that liver cell is doing at any point
in time is determined by variations of that profile. It is the
operating patterns (gene expression patterns) of the genome that
are the paramount determinants of the behavior of cells.
... ... *telomere: Telomeres are defined ends of chromosomes
that contain specific repeated DNA sequences. They are essential
for normal chromosome replication, and since their length
shortens a bit with each replication, they are believed to be
involved in the aging of the cell.
... ... *glycation of proteins: "Glycation" is the post-
translational (i.e., after protein synthesis) modification of a
protein by the covalent attachment of a sugar residue, the
modification resulting from a spontaneous amino-carbonyl reaction
("Maillard reaction"). Glycation of various proteins has recently
been implicated in the etiology of various diseases such as the
development of Alzheimer's-type pathologies (e.g., dementias).
... ... *insulin receptor pathway: Insulin is a polypeptide
chemical messenger (hormone) comprising 51 amino acids in two
chains linked by disulphide bridges. The insulin receptor is a
specific membrane protein derived from an intracellular precursor
and transported from specialized intracellular structures to the
cell surface.
... ... *skeletal muscle: In general, the term "skeletal muscle"
refers to striated muscle fibers (singly or in a collection)
attached at one or both ends of a part of the body skeleton.
"Striated muscle" is muscle usually associated with voluntary
motion, the adjective "striated" arising from the microscopically
visible cross striations which occur in the fibers as a result of
regular overlapping of thick and thin muscle fiber filaments
(myofilaments). In general, such fibers are specialized for rapid
contraction and relaxation.
... ... *oligonucleotide arrays: The essential idea concerning
the use of "arrays" in determining gene expression patterns
involves the fact that for every gene (DNA sequence) undergoing
expression there exists in the cytoplasm a specific RNA whose
nucleotide sequence is a result of transcription of that gene
(see next note on "transcriptional patterns"). There exists now a
technique for profiling the large variety of RNAs that can be
extracted from tissue, the technique depending on highly ordered
arrays of large numbers of oligonucleotide probes (essentially
pieces of DNA) in a parallel format, with specific DNA-RNA
interactions producing localized fluorescences, and the array of
fluorescences providing a profile of detectable RNAs. A
determination of the profile of existing RNA sequences implies
the profile of the DNA sequences (genes) that are being naturally
expressed in the genome, and if one knows which genes are
involved with which functions in that particular cell or
organism, one has obtained a profile of existing functions. The
use of such arrays of nucleotide probes (sometimes called micro-
arrays or "chips") is now highly automated ("robotic"), and the
technique can be used to determine the expression profile of
thousands of genes in an ensemble of cells.
... ... *Transcriptional patterns: "Transcription" is the process
by which genetic information in DNA is converted into RNA.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 24Sep99
For more information: http://scienceweek.com/swfr.htm

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3. CELL BIOLOGY:
ON INTRACELLULAR-MEMBRANE TRANSPORT
The term "eukaryotic cell" refers to a biological cell with
internal membrane-bound compartments such as a nucleus.
An essential feature of virtually every such cell and almost
every subcellular compartment inside such cells is the ability to
accumulate a variety of organic metabolites and inorganic ions at
concentrations that are often strikingly different from those in
the surrounding milieu. The term "intracellular transport" refers
to the movement of substances across membranes or organelles
inside the cell. Intracellular transport is a eukaryotic
phenomenon and includes the molecular and ionic traffic into and
out of such organelles as the cell nucleus, *mitochondrion,
*lysosome, *peroxisome, *Golgi body, and *endoplasmic reticulum.
... ... V.M Olkkonen and E. Ikonen (National Public Health
Institute Helsinki, FI) make the following points concerning
intracellular transport:
     1) The authors point out that the compartmentalization of
functions into distinct membrane-bound organelles is a central
characteristic of eukaryotic biological cells. The protein and
lipid composition of these organelles is unique, a factor vital
for their proper function. This necessitates tightly controlled
transport of biomolecules from their sites of synthesis or uptake
to specific destinations, and in addition requires mechanisms
that prevent promiscuous interactions between cellular membranes
that would lead to deleterious mixing of organelle constituents.
One of the major processes responsible for the correct
localization of molecules within the cell is called "membrane (or
vesicular) transport". In this process, membranous carrier
structures bud off a donor compartment and subsequently fuse with
a recipient compartment, thus delivering their membrane-
associated and soluble luminal constituents to the target
organelle.
     2) Proteins to be transported within cells evidently contain
structural information that guides them to their correct
destinations. Proteins with aberrant structures are misdirected
and eventually degraded, as manifested in several inherited
diseases in humans, e.g., *cystic fibrosis and *Marfan's
syndrome. During the 1990s, the cellular machinery responsible
for decoding protein targeting information and mediating the
transport processes became apparent, and several genetic diseases
that directly affect the intracellular sorting and transport
machinery were identified.
     3) The major cellular routes of membrane transport are a)
the biosynthetic pathway responsible for the transport of
proteins from the endoplasmic reticulum, where they are
synthesized, to the extracellular space (i.e., "secretion") or to
other cellular membrane compartments; and b) the *endocytic
pathway responsible for the uptake of molecules from the
extracellular milieu to be used in cellular metabolism. Most
membrane proteins and proteins involved in secretion (secretory
proteins), as well as many lipids, are synthesized in the
endoplasmic reticulum, whose luminal environment is especially
suited to facilitate the proper folding of the synthesized
proteins and the initial steps of the *glycosylation of proteins.
Proteins that are destined to be transported out of the
endoplasmic reticulum move on to the *Golgi apparatus where
further modifications of these proteins occur. Subsequently, the
proteins are sorted according to their various destinations: the
plasma membrane (e.g., ion channels, adhesion molecules, various
membrane receptors), regulated secretory granules or vesicles
(e.g., hormones, enzymes, neurotransmitters), or organelles of
the endocytic pathway (e.g., lysosomal *hydrolysates). In the
past few years, the use of novel techniques to follow transport
intermediates in living cells has revealed that in vivo the
carriers not only are spherical but also in many cases they form
long tubular projections across the interior of the cell.
-----------
V.M. Olkkonen and E. Ikonen: Genetic defects of intracellular
membrane transport.
(New England J. Med. 12 Oct 00 343:1095)
QY: Vesa M. Olkkonen, Dept. of Biochemistry, National Public
Health Institute, Helsinki, FI.
-----------
Text Notes:
... ... *mitochondrion: Mitochondria (s. mitochondrion) are
double-membrane enclosed organelles of eukaryotic cells. They are
involved in several important biochemical pathways, including
electron transport and oxidative metabolism. Various types of
eukaryotic cells may contain from a few to several thousand
mitochondria in each individual cell.
... ... *lysosome: A lysosome is a cytoplasmic membrane-bound
vesicle 5 to 8 nanometers in diameter and containing a variety of
glycoprotein hydrolytic enzymes used to digest foreign material
or defective organelles.
... ... *peroxisome: A peroxisome is an organelle rich in
enzymes that act on or generate hydrogen peroxide.
... ... *Golgi body: The Golgi apparatus (Golgi complex) is a
collection of organelles (Golgi bodies) in eukaryotic cells that
essentially function as a collecting and packaging center for
substances that the cell manufactures for export.
... ... *endoplasmic reticulum: The term "endoplasmic reticulum"
refers to a complex system of flattened sacs, and it is the site
of many important syntheses, including the production of new
surface membrane and the intracellular transport of various
biochemical entities.
... ... *cystic fibrosis: An inherited disease of the exocrine
glands, primarily affecting the gastrointestinal tract and
respiratory systems. The "exocrine" glands are glands that secret
material via excretory ducts (e.g., mucous secreting glands).
... ... *Marfan's syndrome: (Marfan disease) A connective tissue
disorder caused by a mutation in a specific gene on chromosome
15q.
... ... *endocytic: In general, the term "endocytosis" refers to
the uptake of external materials by cells by means of
phagocytosis (uptake of particulate material) or pinocytosis
(uptake of liquid material). In both cases, the cell surface
membrane literally folds completely around the entity to be taken
up, and the membrane-bound is in effect pulled into the cell.
... ... *glycosylation: In this context, the substitution of one
or more glycosyl groups into a protein. 
... ... *Golgi apparatus: See "Golgi body" above.
... ... *hydrolysates: In general, any product of hydrolysis.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 17Nov00
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
CELL BIOLOGY: PROTEIN SORTING AND GOLGI COMPARTMENTS
     The historical differences between physics and biology in
the first half of this century are instructive. In 1950,
physicists could not see the various constituents of matter, but
they had physical theories that produced very good predictions of
the behavior of these constituents. In contrast, in 1950,
biologists could see many constituents of the biological cell,
but the cell in its ensemble of parts appeared so complex that
how these constituents behaved was a mystery. At that time, one
controversial constituent of the biological cell was the so-
called "Golgi apparatus", first discovered in 1898 by Camillo
Golgi (1843-1926). Golgi was the first to introduce the use of
silver salts in staining cells (he received the Nobel Prize for
Physiology and Medicine in 1906), and with this silver stain
method cellular components were revealed that were previously
invisible when cells were treated with organic dyes (the standard
classical method of staining cells). For half a century, however,
many biologists considered the Golgi apparatus a staining
artifact, and it was not until the 1950s and the use of the
electron microscope in biology that the Golgi apparatus was
finally confirmed as a real structure in cells. Still, at that
time there was no clear detailed idea concerning how the Golgi
apparatus contributed to the functioning of the cell, although it
did seem to be involved in secretion, since it appeared more
pronounced in secreting cells than in other cells. It took the
remaining decades of this century for the story of the Golgi
apparatus to be unfolded.
     The Golgi apparatus (Golgi complex) is a collection of
organelles (Golgi bodies) in eukaryotic cells (i.e., cells with
internal membrane-bound organelles) that essentially function as
a collecting and packaging center for substances that the cell
manufactures for export. Golgi bodies are thus particularly
abundant in secretory cells. They consist of stacks of membranous
sacs that are pinched off as Golgi vesicles for delivery to the
exterior of the cell.
     In this context, a "vesicle" is a small intracellular
membrane-bound volume in which substances are stored or
transported. Another cellular structure of importance in
understanding the operation of the Golgi apparatus is the so-
called "endoplasmic reticulum" (ER), which was first identified
with the use of the electron microscope in the 1950s. In general,
the endoplasmic reticulum is an extensive system of flattened
membranous sacs traversing the cytoplasm of all eukaryotic cells
and continuous with the envelope that surrounds the nucleus.
"Rough" endoplasmic reticulum (called rough because of its
electron-microscopic appearance) is covered with ribosomes. A
ribosome is a small particle, a complex of various ribonucleic
acid component subunits and proteins that functions as the site
of protein synthesis in the cell. The rough endoplasmic reticulum
essentially provides a transportation system for the delivery of
newly synthesized proteins to other parts of the cell, or for
secretion to the exterior (exocytosis) via the Golgi apparatus.
The other type of endoplasmic reticulum is "smooth" endoplasmic
reticulum, which lacks ribosomes, and which is involved in lipid
synthesis.
     The essentials of the operation of the endoplasmic
reticulum-Golgi apparatus system are as follows:
     The endoplasmic reticulum in effect divides the cytoplasm
into two compartments: the cytosol (the non-membranous part of
the cytoplasm outside the ER) and the cisternal space (the
connected lumens of the ER sacs). The cytosol contains enzymes
involved in metabolic pathways, whereas the ER cisternal space
provides a route for the movement of materials through various
intracellular compartments and, in some cases, to the cell
exterior.
     The rough endoplasmic reticulum plays a central role in the
synthesis of secretory proteins, integral membrane proteins, and
proteins destined to reside in the lumen of the endoplasmic
reticulum. Proteins synthesized in the rough endoplasmic
reticulum are routed to the Golgi apparatus by membrane vesicles
that shuttle back and forth between the two structures. Proteins
passing through the Golgi complex contain specific chemical
markers that target them to various locations, including the
endoplasmic reticulum, the Golgi apparatus itself, and secretory
vesicles.
     Cells exhibit two types of secretory processes: a) in
"constitutive secretion", protein products are moved to the cell
surface in a continuous fashion by nonselective bulk flow; b) in
contrast, "regulated secretion" occurs only in response to
external stimuli. In both types of secretion, membrane vesicles
fuse with the plasma membrane, discharging their contents into
the extracellular space (exocytosis), and after this process has
occurred, the membrane components are recycled back to the Golgi
apparatus by vesicles that bud from the plasma membrane.
     Formulating the above account of the operations of the
endoplasmic reticulum and Golgi apparatus, broad and brief as it
is, has required 50 years and the labor of thousands of
biologists. The outlined dynamics are literally a major part of
the workings of the eukaryotic biological cell.
... ... B.B. Allen and W.E. Balch (Scripps Research Institute,
US) present a review of current research concerning the operation
of the Golgi apparatus, the authors making the following points:
     1) Movement of cargo between cell compartments requires
transiently *coated vesicle carriers. Biosynthetic cargo exiting
the endoplasmic reticulum includes the newly synthesized proteins
and lipids that are moved to distinct cellular and extracellular
destinations. Other cargo incorporated into vesicles includes
proteins that are continuously recycled between compartments.
These components encompass the transport machinery involved in
cargo selection, vesicle formation, and targeting and fusion of
vesicles.
     2) A fundamental principle of membrane traffic is that
vesicle formation is initiated by the selection and concentration
of cargo. This occurs through interactions between sorting
determinants (markers) on the cargo and cytosolic coat components
that direct cargo to the forming vesicle. Soluble cargo (cargo
found in the lumen of the ER compartment) will necessarily
require sorting receptors to couple the protein to the cytosolic
coat machinery. A variety of coat complexes participate in
vesicle formation.
     3) The authors pose the question: How does the Golgi stack
of cisternae mediate transport of cargo from the endoplasmic
reticulum to the cell surface? The authors suggest a possibility
is that cargo-containing vesicles derived from the endoplasmic
reticulum form early Golgi compartments that then mature by
retrieval of processing enzymes from later Golgi compartments.
Maturation continues at terminal Golgi compartments by retrieval
of transport components from the *endocytic pathway to promote
sorting of cargo to multiple destinations. Thus, the authors
suggest, retrograde movement may integrate exocytic (secretory)
and endocytic (material uptake) pathways in eukaryotic cells and
coordinate membrane flow and cargo transport through the Golgi
stack.
-----------
B.B. Allan and W.E. Balch: Protein sorting by directed maturation
of Golgi compartments.
(Science 2 Jul 99 285:63)
QY: William E. Balch: webalch@scripps.edu
-----------
Text Notes:
... ... *coated vesicle carriers: Coated vesicles are observed in
the cytoplasm of many eukaryotic cells. They measure 50 to 250
nanometers in diameter, and are characterized by a coat made up
of a polyhedral lattice of clathrin subunits together with
smaller amounts of other proteins. Coated vesicles are concerned
with the rapid and continuous transport of molecules between
specific membranous organelles of the cell and to and from the
cell membrane.
... ... *endocytic pathway: See main report notes.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 20Aug99
For more information: http://scienceweek.com/swfr.htm

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4. MATERIALS SCIENCE:
A NEW TITANIUM PURIFICATION METHOD
The history of chemistry is replete with instances when a new
result had an almost immediate impact on industry in particular
and on society in general. Titanium is a metal element of group
IV-B, has a melting point of 1675 degrees centigrade, and an
atomic weight of 47.90. It is often called a "space-age" metal
because of its high strength-to-weight ratio and its inertness to
many corrosive environments. In general, titanium alloys have a
higher yield strength-to=density rating than either aluminum
alloys or steel. Titanium mineral occurs in nature primarily as
ilmenite [FeTiO(sub3)] and rutile [tetragonal TiO(sub2)], with
ore bodies uniformly distributed throughout the continents. But
despite the availability of various ores, the use of titanium as
a substitute for steel has been modest because of the relatively
high cost of purification, which results in high product cost (as
much as $40,000 per ton for aerospace titanium alloy products).
The current annual use of titanium worldwide is measured in only
tens of thousands of tons, as opposed to many millions of tons of
steel.
... ... G.Z. Chen et al (3 authors at 2 installations, UK) now
report a direct electrochemical reduction method for producing
pure titanium, the authors making the following points:
     1) The authors point out that many reactive metals are
difficult to prepare in pure form without complicated and
expensive procedures. Although titanium has many desirable
properties (it is light, strong, and corrosion-resistant), its
use has been restricted because of its high processing cost. In
the currently used pyrometallurgical process (the Kroll process),
the titanium minerals rutile and ilmenite are carbo-chlorinated
to remove oxygen, iron, and other impurities, producing a
TiCl(sub4) vapor. This is then reduced to titanium metal by
magnesium metal, and the by-product MgCl(sub2) is removed by
vacuum distillation. The prediction made in the past that the
Kroll process would be replaced by an electrochemical route has
so far not been fulfilled: attempts involving the
electrodeposition of titanium from ionic solutions have been
hampered by difficulties in eliminating the redox cycling of
multivalent titanium ions and in handling very reactive
nonuniform (dendritic) products.
     2) The authors report an electrochemical method for the
direct reduction of solid TiO(sub2), in which the oxygen is
ionized, dissolved in a molten salt, and discharged at the anode,
leaving pure titanium at the cathode. The authors suggest the
simplicity and rapidity of this process compared to conventional
routes should result in reduced production costs and the approach
should be applicable to a wide range of metal oxides. (Individual
mixed oxide powders of Al, B, Cr, Fe, Nd, and V have already been
reduced by the authors by this method.)
... ... In a commentary on this work, Harvey M. Flower (Imperial
College London, UK) states: "Translating laboratory-scale
experiments into industrial production inevitably poses problems
of materials handling, and of designing and operating large
electrolysis cells. However, the early results of trials being
conducted [by a UK government research agency] offer hope that
the process can be developed on a commercial scale and contribute
to the cost reduction required to allow titanium to become a
mainstream engineering material."
-----------
G.Z. Chen et al: Direct electrochemical reduction of titanium
dioxide to titanium in molten calcium chloride.
(Nature 21 Sep 00 407:361)
QY: Derek J. Fray: djf25@hermes.cam.ac.uk
-----------
Harvey M. Flower: A moving oxygen story.
(Nature 21 Sep 00 407:305)
QY: Harvey M. Flower: h.flower@ic.ac.uk
-------------------
Summary by SCIENCE-WEEK http://scienceweek.com 17Nov00
For more information: http://scienceweek.com/swfr.htm

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5. HISTORY OF EARTH SCIENCE:
ON THE DISCOVERY OF THE STRATOSPHERE
     The atmosphere of Earth is divisible into several layers,
each layer having a characteristic temperature range, pressure
range, and composition. The layers, from the surface of Earth,
are (with thicknesses varying at different latitudes):
troposphere (0 to approximately 10 kilometers), stratosphere
(from approximately 10 to 50 kilometers), mesosphere
(approximately 50 to 80 kilometers), thermosphere (approximately
80 to 500 kilometers), and exosphere (above approximately 500
kilometers. Other layers, essentially meta-layers, are also
recognized: a) the "chemosphere" is the region between
approximately 32 and 92 kilometers where many important chemical
reactions occur; b) the "ionosphere", above approximately 80
kilometers, is a shell of high electron concentration resulting
from very short wavelength sunlight stripping electrons from
atoms and molecules (mainly oxygen and nitrogen) to create an
ionized layer; c) the magnetosphere is the constantly changing
magnetic field generated by the Earth's dynamo, this magnetic
field influencing the behavior of electrically charged particles,
and the field extending approximately 10 Earth radii (64,000)
kilometers into space on the sunward side.
     The boundary between troposphere and stratosphere is called
the "tropopause"; that between stratosphere and mesosphere is
called the "stratopause"; and that between mesosphere and
thermosphere is called the "mesopause", in each case the root
"pause" used because of an inflection in the temperature-altitude
curve.
     The temperature of the atmosphere undergoes marked but
systematic variation with altitude. In the troposphere, the layer
closest to the surface, the temperature decreases by
approximately 6.5 degrees centigrade per kilometer of altitude,
until at the tropopause (10 to 11 kilometers) the temperature
stabilizes at approximately -53 degrees centigrade. The
temperature remains stable in the stratosphere, and even
increases with altitude to approximately 0 degrees centigrade at
the stratopause. Then in the mesosphere there occurs again a
decline in temperature with altitude, now down to -100 degrees
centigrade, and then after the mesopause and into the upper
atmosphere (thermosphere and exosphere), the temperature rises
markedly in these regions of extremely low air density, so that
at 200 kilometers the temperature range is 300 to 900 degrees
centigrade, depending on solar radiance.
     The first hint that Earth's atmosphere is a series of
concentric shells was provided by the meteorologist Leon
Teisserenc de Bort (1855-1913) [the surname is Teisserenc de
Bort]. From 1892 to 1896, Teisserenc de Bort served as chief
meteorologist at the Central Meteorological Bureau in Paris, but
in 1896 he resigned and carried out his meteorological balloon
investigations himself at his estate near Versailles. He
conducted experiments with high-flying instrumented balloons, and
he was one of the pioneers in the use of such devices. He
discovered that above approximately 11 kilometers the
temperature, which drops steadily from sea-level to that
altitude, remained constant up to the highest points he could
reach. Surprised by this result, he accumulated data from 236
balloon ascents before he suggested, in 1902, that the atmosphere
was divided into 2 layers. During the next few years, he termed
the lower layer, the layer involving air movements, the
"troposphere" ("sphere of change"), and the layer above that, a
layer he mistakenly thought consisted of internal further layers,
the "stratosphere" ("sphere of layers"). Thus, to Teisserenc de
Bort we owe both the discovery and the name of the stratosphere.  
... ... Mott T. Greene (University of Puget Sound Tacoma, US)
presents an essay on Teisserenc de Bort, the author making the
following points:
     1) The author suggests that ripples from Teisserenc de
Bort's discovery of the stratosphere spread far beyond
meteorology. Between 1902 and 1904, the oceanographer Vagn Ekman
(1874-1954) discovered similar layering of the ocean, and in
1909, the meteorologist Andrija Mohorovicic (1857-1936) used
seismology to establish the existence of a similar discontinuity
in the solid Earth, the discontinuity now known as the "Moho".
     2) The author (Greene) also suggests that the discovery that
the Earth-ocean-atmosphere system is composed of concentric
shells of different density, from the core of the Earth to the
top of the atmosphere, is the founding insight of modern
geophysics, and that the discovery also profoundly influenced the
thinking of the young meteorologist Alfred Wegener (1880-1930),
leading Wegener in 1912 to propose the theory of continental
drift, with the continents representing the remains of a formerly
continuous Earth shell above the ocean floors. Greene concludes:
"Just as air masses and ocean water masses moved under the
influence of the Earth's rotation, sliding along surfaces of
discontinuity, so, he [Wegener] reasoned, did the continents on a
longer time-scale -- making Teisserenc de Bort not only the
discoverer of the stratosphere but an honorary grandfather of
continental drift."
-----------
Mott T. Greene: High achiever.
(Nature 26 Oct 00 407:947)
QY: Mott T. Greene, History Department, University of Puget
Sound, Tacoma WA 98416 US.                                        
-------------------
Summary by SCIENCE-WEEK http://scienceweek.com 17Nov00
For more information: http://scienceweek.com/swfr.htm

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6. MATERIALS SCIENCE:
DISCOVERY OF THE SMALLEST CARBON NANOTUBE
     If one compares the materials available to engineering and
technology in the 20th century to those available in the 19th
century, the differences are enormous and likewise the impacts of
new 20th century materials on the way people lived and worked.
Similarly, now that we are in the 21st century, we can expect the
materials of this century to differ greatly from the materials of
the last century -- with concomitant impacts on society.
Materials scientists are particularly intrigued by new possible
discoveries and applications of microscale structures that have
the potential to generate entirely new technologies.
     Fullerenes are large molecules composed entirely of carbon,
with the chemical formula C(n), where n is any even number 20 or
greater. They apparently have the structure of a hollow
spheroidal cage (and certain other forms) with a surface network
of carbon atoms connected in hexagonal and pentagonal rings. They
were discovered by Richard E. Smalley, who in 1996 received the
Nobel Prize in Chemistry for the discovery.
     In general, fullerene graphite cage structures incorporate
exactly 12 pentagons, and the smallest possible fullerene is thus
C(sub20), which consists solely of pentagons. But the extreme
curvature and reactivity of this structure have led to doubts
about its existence and stability. Although theoretical
calculations have identified, besides this cage, a bowl and a
monocyclic ring isomer as low-energy members of the C(sub20)
cluster family, only ring isomers of C(sub20) have been observed.
     Carbon nanotubes are similar to fullerenes, except their
shape is tubular. They were first discovered by Sumio Iijima (NEC
Laboratories, JP) in 1991, they come in both multi-wall and
single-wall versions, and the most common nanotubes have
diameters of the order of 10 to 30 nanometers.
     Last month, researchers in Germany and the US reported
synthesis of the smallest fullerene, and this month researchers
in Japan and China report synthesis of the smallest carbon
nanotube using two different methods.
... ... L-C. Qin et al (6 authors at 2 installations, JP) report
a discovery of the smallest possible carbon nanotube, the authors
making the following points:
     1) The carbon nanotubes discovered by the authors have a
diameter of 4 angstroms, which according to theory is the
narrowest attainable that can still remain energetically stable.
These nanotubes are confined inside multiwalled carbon nanotubes,
and their diameter corresponds to that of a C(sub20) dodecahedron
with a single carbon atom at each of its 20 apices. Unlike larger
carbon nanotubes, which, depending on their diameter and
helicity, can be either metallic or semiconducting, these
smallest nanotubes are always metallic.
     2) The carbon nanotubes reported by the authors were seen in
cathodic deposits produced by *arc-discharge of graphite rods in
a hydrogen atmosphere without a metallic catalyst. Under these
conditions, more carbon nanotubes (all multiwalled) are kept open
as hydrogen etches away the capping atoms, a unique feature that
helps maintain a favorable environment for smaller carbon
nanotubes to form inside already grown multiwalled carbon
nanotubes.
     3) Although these tiny 4 angstrom carbon nanotubes should be
energetically stable, the severe steric distortion resulting from
the planar graphene structure changes the electronic structure
significantly. Electronic *band structure calculations indicate
that all such tubules tend to be metallic, regardless of their
helicity.
... ... In a contiguous report, N. Wang et al (4 authors at Hong
Kong University of Science and Technology, CN) report the
discovery of single-walled 4 angstrom carbon nanotube arrays, the
authors making the following points:
     1) The authors report they prepared the smallest carbon
nanotubes possible by the *pyrolysis of tripropylamine molecules
in the channels of single crystals of a porous *zeolite
[AlPO(sub4)-5]. These uniformly sized carbon nanotubes have a
diameter of 0.4 nanometers and are "the best example of one-
dimensional quantum wires."
     2) The authors point out that the zeolite used is a type of
transparent microporous crystal containing one-dimensional
channels packed in hexagonal arrays, the channels with an inner
diameter of 0.73 (+- 0.01) nanometers. The starting material used
by the authors for synthesizing single-walled carbon nanotubes
was tripropylamine, introduced into the channels during growth of
the zeolite crystals. Single-walled nanotubes form inside the
zeolite channels when the pyrolyzed carbon is thermally treated.
-----------
L-C. Qin et al: The smallest carbon nanotube.
(Nature 2 Nov 00 408:50)
QY: Lu-Chang Qin: qin@frl.cl.nec.co.jp
-----------
N. Wang et al: Single-walled 4 angstrom carbon nanotube arrays.
(Nature 2 Nov 00 408:50)
QY: Z.K. Tang: phzktang@ust.hk
-----------
Text Notes:
... ... *arc-discharge: See notes to background material below.
... ... *band structure: In this context, a "band" is a closely
spaced group of energy levels in atoms, in particular a range of
energies that electrons can have in a solid. Each band represents
a large number of allowed quantum states.
... ... *pyrolysis: In general, the decomposition of a substance
by heat.
... ... *zeolite: Zeolites are members of a group of hydrated
aluminosilicate minerals occurring in the cavities of igneous
rocks (rocks produced by solidification from a molten state,
e.g., granite) and various volcanogenic sediments. They are also
manufactured for their ion exchange properties (the exchange of
zeolite ions with solute ions) and selective adsorption
properties (specific adsorption of solutes). They have an open
crystal structure and can also be used as molecular sieves for
partitioning and sequestration of solutes according to the
dimensions of the zeolite pores and the dimensions of the solute
molecules.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 17Nov00
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
... ... H. Prinzbach et al (9 authors at 2 installations, DE US)
now report the production of C(sub20) fullerene, the authors
making the following points:
     1) The authors report a demonstration that the cage-
structured fullerene C(sub20) can be produced from its
perhydrogenated form [dodecahedrane C(sub20)H(sub20)] by
replacing the hydrogen atoms with relatively weakly bound bromine
atoms, followed by gas-phase debromination. For comparison, the
authors have also produced the bowl isomer of C(sub20) using the
same procedure.
     2) The authors characterized the generated C(sub20) clusters
using *mass-selective anion photoelectron spectroscopy. The
observed electron affinities and vibrational structures of these
two C(sub20) isomers (sphere and bowl) differ significantly from
each other, as well as from those of the known monocyclic isomer.
     3) The authors conclude: "The photoelectron spectrum of the
unique C(sub20) species derived from dodecahedrane... stands as a
benchmark test for [analysis of vibrational energies of this
system by] quantum-mechanical methods. It is hoped that the
experimental results reported here will stimulate further
theoretical activities. Until now, fullerenes have been produced
primarily by carbon condensation processes. The route to cage 1
[the spherical isomer] that we report here is, to our knowledge,
the first which makes use of a precursor with a rationally
designed carbon core."
-----------
H. Prinzbach et al: Gas-phase production and photoelectron
spectroscopy of the smallest fullerene, C(sub20).
(Nature 7 Sep 00 407:60)
QY: Horst Prinzbach:
horst.prinzbach@orgmail.chemie.uni-freiburg.de
-----------
Text Notes:
... ... *mass-selective anion photoelectron spectroscopy: In the
technique used here, C(sub20)(-) anions are irradiated with a
pulsed laser that detaches some of the extra electrons. The
kinetic energy of the photo-detached electrons is then determined
by precisely clocking their travel time over a predetermined
distance. The difference between the photon energy and the energy
of the fastest-moving electrons provides a measure of how
strongly the extra electron is held by the anion. If the
geometries of the initial anion and the resulting neutral
C(sub20) are slightly different, removing the electron leaves the
neutral C(20) vibrationally excited. The vibrational frequencies
can then be deduced from oscillations in the photoelectron
signal. (cf. Martin F. Jerrold: Nature 407:26 2000).
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 13Oct00
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
FIRST SYNTHESIS OF A LOW-MASS FULLERENE
Under appropriate non-equilibrium growth conditions, carbon atoms
form relatively stable hollow clusters of well-defined mass
number, collectively known as "fullerenes". The mass production,
purification, and condensation of such clusters into a molecular
solid is generally essential to full experimental
characterization. The initial discovery of C(sub60) in 1985, for
example, had to await a bulk synthesis method 6 years later
before detailed characterization of the molecule was possible.
Gas-phase experiments have indicated the existence of a wide
range of possible fullerene clusters, but beyond C(sub60) only a
few pure fullerene solids have been obtained, most notably
C(sub70). Low-mass fullerenes are of particular interest because
their high curvature and increased strain energy owing to
adjacent pentagonal rings could lead to solids with unusual
intermolecular bonding and electronic properties.
... ... Piskoti et al (3 authors at 3 installations, US) now
report the synthesis of the solid form of C(sub36) by the
*arc-discharge method. They report the development of
purification methods that separate C(sub36) from amorphous carbon
and other fullerenes to yield saturated solutions, thin films,
and polycrystalline powders of the pure solid form. The authors
report observation of large increases in the electrical
conductivity of the solid on doping with alkali metals, and they
suggest that if C(sub36) could be made sufficiently conducting --
either by doping or by structural rearrangement (e.g., induced by
pressure) -- one might expect high-temperature superconductivity
to be manifested.
QY: A. Zettl: azettl@physics.berkeley.edu
(Nature 25 Jun 98 393:771) (Science-Week 24 Jul 98)
-------------------
Related Background:
... ... *arc-discharge method: In the present instance, the
method involves an originally designed helium-environment arc-
discharge chamber, with an arc between two 0.25 inch-diameter
graphite electrodes, using a DC current of 100 amperes while
maintaining a 1 millimeter gap between the electrodes. Arcing is
maintained for several minutes, until a uniform carbon film of
approximately 10 microns thickness coats a removable metal
substrate 10 centimeters from the discharge region.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 24Jul98
For more information: http://scienceweek.com/swfr.htm

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7. IN FOCUS: ON TIME AND EVOLUTION
"A good many of the properties of living organisms that appear
unaccountable in terms of the inorganic world may stem from
events which would be highly improbable within our modern frame
of reference, but which, when we take into account the lavish
amount of time for them to have occurred in, become much less
improbable. The same argument may be applied to many properties
of the non-living world as well. To appreciate the importance of
time in the evolutionary process, one needs to grasp as well as
one can the tremendous extent of it which stretches between us
and the origin of our planet, and to gain an idea of the relative
positions of evolutionary events therein... The dating of
evolutionary events is based on the reasonable postulate that the
existing sedimentary rocks of the Earth's surface were formed in
layers, one after the other. They were formed in different ways,
however, and their relationships have been disturbed by various
changes, some catastrophic, some graded. Hence, their relative
positions often fail directly to reveal their chronological
order. The arrangement of these layers according to a logical
time sequence has called for fine detective skill as well as
laborious investigation on the part of geologists and
paleontologists examining the composition, structure, and fossil
content of the rocks as well as their relative positions. This
arrangement of the rocks according to their order in time --
which provides an outline of evolutionary events -- was possible
without any definite measure of the lengths of time involved in
forming the various layers. Indeed, the basic features of this
outline were established long before an accurate method of timing
was available. Early estimates of the relative time elapsed in
the building of given formations, as compared to others, have
proven quite accurate in many cases; but early estimates of
absolute time were ridiculously short compared to the values that
are now accepted. Whereas early estimates placed the age of the
Earth at 50 to 100 million years or even less, the newer
chronology, based upon the radioactive method, shows some of the
rocks of the Earth's crust to be at least as old as 4 billion
years. The age of the Earth is now thought to be nearly 5 billion
years. The recognition of this vast stretch of time available for
evolution makes a great difference in the perspective with which
this process may be viewed. Much more ample time is allowed for
the achievement of given steps than could ever have been imagined
in Darwin's time, or even until very recently."
-----------
Harold Blum: _Time's Arrow and Evolution_ (2nd edition)
(Princeton Univ. Press, Princeton 1955, pp.4,8.)
-------------------
SCIENCE-WEEK http://scienceweek.com 17Nov00
-------------------
Related Background:
IN FOCUS: ON INVERTEBRATE PALEONTOLOGY
"Little work of importance was done in paleontology until the
1700's, at which time both vertebrate and invertebrate fields
began to assume importance. Intensive work in the invertebrate
area arose from recognition of the fact, first clearly seen by
William Smith, an English civil engineer and amateur geologist of
the period, that a given set of beds tended to contain the same
species of shells over vast and widely separated areas. Accurate
determination of fossils could thus be of great practical use to
the stratigrapher; as a result, invertebrate paleontology tended
to develop not as an independent science, but as a handmaiden to
the geologist -- a working tool for the stratigrapher looking for
oil or ores or coal. The fossil shells were rarely thought of as
the remains of once-living organisms, but merely as convenient
markers for the identification of successive formations, and
would have been as useful had they been identifiable mineral
inclusions or distinctive assortments of nuts and bolts... With
this background, the invertebrate workers of Darwin's day not
merely lacked interest in evolutionary ideas, but were inclined
to view them with suspicion as detrimental to their work. For
clear-cut stratigraphic work, the species in a given formation
should be stable entities, clearly distinguishable from those in
the strata above and below. The idea of gradual change and of
transitional forms was abhorrent... With this to contend with, it
is apparent why Darwin was thrown on the defensive in his
treatment of the fossil record. He could not call on the
paleontologists for support; the most he could do was to attempt
appeasement, to show that it was at least possible to interpret
the geological story in evolutionary terms, and that there was no
insuperable objection."
-----------
A.S. Romer: "Darwin and the Fossil Record"
(in S.A. Barnett [ed.]: _A Century of Darwin_, 1958, Chap. 6)
-------------------
SCIENCE-WEEK http://scienceweek.com 25Jun99

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8. FROM THE SCIENCEWEEK ARCHIVE:
ON PHYSICS, BIOLOGY, AND CARTOONS
Each generation of scientists, it seems, passes through a phase
of bemusement with the idea that the application of physics to
biology will yield sudden and enormous rewards. Such a phase
occurred at the turn of the century, then again in the 1930s, and
again in the 1950s, and apparently still again in our present
era. In a lead editorial, the journal _Nature_ presents the
following headline: Can Physics Deliver Another Biological
Revolution? In the unsigned editorial, the author makes the
following points: 1) The main method of analysis in molecular
biology has been the cartoon representation of networks,
pathways, and complexes. "Indeed, superb papers have been written
for the purpose of adding a single arrow to an existing cartoon.
But to really understand the biochemical network thus represented
one needs to have numbers attached to the arrows, and equations
relating the numbers." 2) The author suggests there is nothing
new in biologists opting tools from the physical sciences, or of
physicists "doing physics" in biological systems. What is
apparently new, the author suggests, is that many physicists are
currently excited by the challenge of tackling important
questions in biology, using both the physical and mental tools of
physics, and that US funding agencies are apparently eager to
support such endeavors. 3) But the author suggests one should not
underestimate the extent of this challenge: Physicists are
addicted to simplification -- a habit viewed with suspicion by
biologists. And the theoretical physicist will find that most
molecular biologists have little time for mathematical theory,
which has played no significant role in their field's great
advances. 4) Nevertheless, there is apparently a considerable
will to overcome existing conceptual and institutional
obstacles... "Today, with physicists who can manipulate single
molecules in the laboratory, and simulate and quantitatively
analyze complex systems, who can say what might not be possible?"
[*Note #1]
-----------
[unsigned]: Can physics deliver another biological revolution?
(Nature 14 Jan 99 397:89)
QY: Philip Campbell [nature@nature.com]
... ... *Note #1: Irrespective of any ephemeral bemusements (some
of which may derive from current funding allocations), the impact
of physics on biology is continuing and pervasive: Physics
provides the foundations of new technology, and new technology
provides for new experimental approaches in biology. A similar
paradigm exists for the impact of chemistry on biology. These
paradigms have existed for the past three centuries, and they are
apparently of the utmost significance for any "revolutions" in
biology. Indeed, the revolutions in biology, in this century at
least, have most often depended on new tools rather than on new
concepts borrowed from the physical sciences. In the 1930s, for
example, many biologists and some physicists were enamored of the
idea of applying the principles of thermodynamics to biological
systems. The results of such applications were far from seismic.
It was the soon to be introduced electron microscope that
essentially finished the transition from classical biology to
modern biology. Following that transition, the dramatic and rapid
flowering of molecular biology had more to do with new techniques
involving the ultracentrifuge and electrophoresis than with new
concepts derived from the physical sciences. Nevertheless, since
a so-called "living" system is indeed a complex physical system
existing under specific physical constraints, any direct
application of the concepts of physics to biology has potential
significance and should be encouraged.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 9Apr99


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