I receive e-mails from Science Magazine once a month out of Stanford University and they cover all disciplines of science and the two I received today are very interesting in many fields including geosciences. Though they are a little lengthy they are easily scrolled through and I'll post each one separately, but I would like to share them with you, just once. If you find the material interesting you can secure your own free subscription....Petra

This Week in SCIENCE, Volume 312, Issue 5776,
dated May 19 2006, is now available at:

http://www.sciencemag.org/content/vol312/issue5776/twis.dtl

A plain-text copy of the "This Week in SCIENCE" section has been
appended below.

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This Week in SCIENCE
May 19 2006, 312 (5776)

THIS WEEK IN SCIENCE
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Controlling the Coming of Catkins
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The regulation of flowering in annual plants is controlled by a pair of
genes, FT and CO. Are similar genes also involved in regulating flowering
time in trees? The juvenile phase in trees can last for decades before the
first flower is formed. During this time, the tree is nonresponsive to
environmental factors that potentially influence flowering time. Bohlenius
et al. (p. 1040, published online 4 May) show that the FT ortholog from
Populus trees (poplars, aspen, and cottonwoods) is a critical determinant
of flowering time in trees. The poplar FT is also responsible for a
completely different developmental process in trees, the timing of the
short-day induced growth cessation and bud set that occurs in the fall.

CREDIT: BOHLENIUS ET AL.

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Heavy Metal and Hard Rock
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Drilling through a complete sequence of layers of the Earth's crust into
the underlying pristine igneous rocks is a major goal of earth science. The
thinnest crust occurs near fast-spreading mid-ocean ridges, so bore holes
have targeted these regions. Wilson et al. (p. 1016, published online 20
April) drilled a 1.6-kilometer-deep bore hole through intact crust near the
East Pacific Rise to reach gabbro, a layer of dark crystalline igneous rock
formed from solidified magma that underlies much of the Earth's ocean
floor. Determining the depth to gabbro layers confirms that magma chambers
form at shallow levels in the crust at very high spreading rates; gabbros
are brought up into these chambers from depth. Also, seismic bands do not
correspond to compositional rock layers, implying that seismic velocities
are controlled more by porosity than rock type.

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Poised for Polymerization
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The networks of conjugated-orbitals in conducting polymers are stabilized
either by bulky polyatomic side groups or phenyl groups incorporated within
the backbone chains. Sun et al. (p. 1030; see the Perspective by Baughman)
have prepared a polymer composed of strictly alternating C=C double and CC
triple bonds, with only iodine atoms as side groups. The synthesis relied
on prior templating of the diiododiacetylene monomer in a cocrystal with a
dinitrile oxalamide host. Packing contacts between the nitriles and iodines
allow the host structure to align the monomers in a column with relative
spacings that changed little after polymerization. The product is a
potential precursor to carbyne, a hypothesized but elusive linear allotrope
of carbon.

CREDIT: SUN ET AL.

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Spin Sequences
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The control of coupling between spins in small structures could find use in
spintronics and quantum computing. Hirjibehedin et al. (p. 1021, published
online 30 March; see the Perspective by Brune) assembled chains of Mn atoms
with a scanning tunneling microscope on a thin insulating surface (a
monolayer of CuN grown on a Cu surface). They then used inelastic tunneling
spectroscopy to measure spin excitation spectra as a function of chain
length (up to 10 atoms) under cryogenic conditions. Comparison of the
spectra with a Heisenberg model of an open spin chain with
antiferromagnetic exchange coupling revealed the collective spin
configurations as well as the strength of the coupling.

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Selective Si-H Scission
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Breaking a chemical bond by exciting its stretching vibration is an
appealing idea that rarely works because the energy redistributes rapidly
into other vibrational or rotational motions. Liu et al. (p. 1024; see the
Perspective by Tully) found that H atoms adsorbed on a silicon (111)
surface can be expelled as H2 by irradiation with intense pulses of
infrared light tuned to the Si-H stretching frequency. Although local
heating of the surface could also cleave the Si-H bonds, the authors rule
out this thermal mechanism by irradiating a mixture of adsorbed H and D
atoms under the same conditions. Whereas simple heating of the surface
favors D2 over H2 production by ~17:1, resonant excitation of the Si-H
stretch reverses the selectivity to favor H2 by a factor of 200.

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Beating a Bottleneck
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Knudsen diffusion occurs when the mean free path of atoms or molecules is
relatively long compared to the pore or channel through which they move, so
that wall collisions become more frequent than those between particles.
This model holds for pores between 2 and 50 nanometers, but what happens
during flow in smaller channels? Holt et al. (p. 1034, see the cover and
the Perspective by Sholl and Johnson) fabricated membranes using double-
and multiwalled carbon nanotubes to form the pores. For gases, flow rates
were an order of magnitude greater than those predicted by Knudsen
diffusion, and water flow rates greatly exceeded values calculated from
hydrodynamics. The authors argue that the enhanced transport is caused by
the smoothness of the inner nanotube surfaces, in agreement with results
from computer simulations.

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Evolution by Reduction?
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The origins of eukaryotes remain controversial and somewhat enigmatic.
Kurland et al. (p. 1011) provide a counterpoint to current models in which
the eukaryotic cell is derived from structurally and genetically less
complex prokaryotic cells. On the basis of genomic and proteomic evidence,
they suggest that the essence of eukaryotic cellular complexity existed in
the common ancestor of eucarya, bacteria, and archaea, and that the
bacteria and archaea have evolved by genome reduction driven by
specialization for fast growth and cell division and/or adaptation to
extreme environments.

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Being Prepared
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Planning ahead requires a host of cognitive skills, not the least of which
is the capacity to foresee a future state of need, provocatively termed
mental time travel. There is persuasive evidence that scrub jays can
relocate their food caches to avoid losing them to their observant
neighbors, thus preserving them for future consumption (see Dally et al.,
published online May 18). Mulcahy and Call (p. 1038; see the Perspective by
Suddendorf) present a series of experiments that assess whether bonobos and
orangutans can be coaxed to display these skills. Both species of great
apes can select a suitably useful object, keep it with them overnight, and
bring it back for use the next day as a tool for retrieving a food reward.

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Special Speciation in Madagascar
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A high percentage of the fauna and flora of Madagascar is endemic to the
island, a consequence of its isolation from the African mainland since the
Jurassic. Madagascar is also noted for a high degree of local endemism
within the island, often to particular watersheds, a pattern that has long
puzzled biogeographers. On the basis of a database of species distributions
in relation to rivers and watersheds, Wilme et al. (p. 1063) show how
patterns of climate fluctuation have reinforced local isolation of
populations, particularly of forest-dwelling species, to give rise to
conditions suitable for speciation on a local scale.

CREDIT: WILME ET AL.

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Marshalling DNA Defenses
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Cells recognize damaged DNA and initiate a complex signaling mechanism that
help cells cope with the damage and initiate repair. But it is not just the
enzymes required for DNA repair that undergo increased expression in
response to DNA damage--other events such as progression through the cell
cycle, stress responses, and metabolic pathways are also regulated. Workman
et al. (p. 1054) used a systems-level approach to map such signaling
pathways that respond to DNA damage. The results revealed unanticipated
regulatory interactions and pave the way to when such maps may be used to
predict the patient-specific effects of particular drugs.

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Who Gets the Credit?
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In working backward from outcomes to behavior or in strategic planning for
future scenarios, one important issue is who gets the credit (and how much)
for the eventual result. In the trust game, the first player has to decide
how much money to invest, and the second player has to decide how much of
the multiplied investment to give back. Tomlin et al. (p. 1047) have
carried out a large-scale simultaneous brain imaging study and suggest that
different regions of the cingulate cortex become active when what the
"other" player has chosen to do is revealed, compared with situations when
"I" have done the choosing.

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Controlling the Synapse
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Synapses in the neuromuscular junction are key components involved in
control of muscle movement. Kittel et al. (p. 1051, published online 13
April; see the Perspective by Atwood) describe the role of Drosophila
Bruchpilot (BRP), a coiled-coil domain protein, in the establishment and
maintenance of synapses. BRP was localized to donut-shaped structures
centered at the transmitter release sites (active zones) of Drosophila
neuromuscular synapses. In mutants lacking BRP, presynaptic membranes were
defective. The authors suggest that BRP is needed to form a fully
functional synapse and might mediate presynaptic changes in vivo by
establishing a close proximity between Ca2 channels and vesicles at release
sites.

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