yoric
09.12.05, 01:43
Wklejam spis abstraktów. Co prawda to tylko po kilkadziesiąt słów na artykuł,
ale często można podłapać coś ciekawego. Dodam, że wiele bibliotek
uniwersyteckich (np. UMK) prenumeruje Science, co pozwala na przeglądanie tego
pisma elektornicznie.
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DNA Twisted into Tetrahedra
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One strategy for building molecular nanostructures in three dimensions is
to exploit the connectivity afforded by nucleic acid structures. In many
cases, the steps needed to select particular base pairing to create
structures such as cubes lead to long, multistep syntheses. Goodman et al.
(p. 1661) have developed a rapid self-assembly process that creates DNA
tetrahedra that have 10 to 30 base pairs on each edge. Four single strands
that contain the complementary sequences for six edges anneal in seconds in
95% yield, and single diastereomeric products are formed. The authors also
present atomic force microscopy studies of the compression of a single DNA
tetrahedron.
CREDIT: GOODMAN ET AL.
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Restoring the Forests
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Deforestation in the tropics has had seriously adverse consequences for
biodiversity, ecosystem services, and the human inhabitants of the tropical
forest. In recent years, projects have been set in motion to restore
degraded forest lands in some countries. Lamb et al. (p. 1628) review the
range of approaches to restoration and assess the extent to which these
approaches might be successful in achieving their aims, particularly with
respect to human well-being.
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Superconducting Qubit Interferometry
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Mach-Zehnder interferometry is a powerful technique to probe quantum
optical effects. Such interferometers contain two beam splitters. The first
sends two beams of photons along separate paths. The acquired path or phase
difference the two beams may acquire creates interference fringes after the
second beam splitter recombines the two beams. Oliver et al. (p. 1653,
published online 10 November) show that a two-level superconducting qubit
can also be made to exhibit similar interference fringes. In this case, the
anti-crossing between the ground and excited states acts as the beam
splitter, and the energy level splitting between them corresponds to the
optical path difference. Multiple photon transitions (up to 20) can be
induced, thus illustrating a potentially useful route for the manipulation
of superconducting qubits in quantum computing schemes.
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Going Softer
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Whether added deliberately or by accident, impurities or solutes have long
been used to strengthen metals. A more recent discovery was that impurities
can soften some metals, but the underlying reasons have not been fully
understood. Using simulations, Trinkle and Woodward (p. 1665; see the
Perspective by Chrzan ) show that for molybdenum, certain transition metal
solutes can influence the energy barriers for dislocation motion, and in
some cases, these changes lead to a softening of the metal. By reducing the
strength, and thus the tendency to fracture abruptly, these modified metals
may find expanded use in structural components.
CREDIT: TRINKLE AND WOODWARD
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Rapid Glacial Erosion
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Determining the relative importance of incision by rivers and glaciers in
the creation of alpine valleys is often hampered by difficulties in
quantifying rates of glacial erosion. Shuster et al. (p. 1668; see the
cover) assessed the timing and rate of glacial erosion by 4He/3He
thermochronometry. Using an example from the Coast Mountains of British
Columbia, Canada, they determined erosion rates both before and during
alpine glaciation. The Klinaklini Valley deepened rapidly by 2 kilometers
or more around 1.8 million years ago when it became glaciated, at least six
times as fast as during its preglacial state.
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Moon Magma
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A giant impact into the early Earth is thought to have ejected a huge
amount of debris into orbit that coalesced to form the Moon. Heat from the
impact also apparently melted much of the Moon and created a huge ocean of
magma. One means of dating these processes is by detecting 182W, the
daughter product of a short-lived isotope, 182Hf. Differences in the
abundances of 182W are produced when magma, rocks, and crystals separate
while 182Hf is still present. Kliene et al. (p. 1671; published online 24
November) report accurate measurements of tungsten isotopes by analyzing
metals returned in Apollo samples (metals provide the most accurate
measure). The data imply that the giant impact occurred about 30 million
years after the formation of the solar system and that the magma ocean had
solidified by about 50 million years.
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Protein Interaction in the Gaseous Phase
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The identification of transient or readily reversible interactions between
proteins is a difficult problem that has been addressed with a variety of
methods. Ruotolo et al. (p. 1658; published online 17 November) have now
applied mass spectrometry to the problem in order to exploit its advantages
of sensitivity and speed. They show that the trp RNA-binding attenuator
protein (TRAP) maintains its 11-membered ringlike structure in the gas
phase and that binding of RNA and tryptophan influences the shape and
stability of the ring in a fashion consistent with its known behavior in
aqueous solution.
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The Liver and the Control of Glucose Metabolism
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The protein kinase and tumor suppressor LKB1 is a potential activator of
the adenosine monophosphate. activated protein kinase (AMPK), a kinase that
senses cellular energy levels by binding the metabolite AMP. Shaw et al.
(p. 1642; published online 24 November) engineered mice so that LKB1
expression could be acutely blocked only in the liver; they found that its
expression plays a critical role in the control of metabolism in the liver
and in glucose homeostasis. In the absence of LKB1, AMPK was almost
completely inactive. Animals lacking LKB1 in the liver showed hyperglycemia
and increased expression of genes encoding enzymes of gluconeogenesis and
lipogenesis.
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Predicting Responses on the Death Pathway
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Multiple signaling pathways can influence whether a cell commits to the
cell death program known as apoptosis. For many years, it has been possible
to categorize signals as contributing to the "gas" or to the "brakes."
However, predicting the biological outcome of multiple signals that apply
some gas here, and a stomp on the brakes there, has remained a challenge.
Janes et al. (p. 1646) applied a systems-level approach to this problem and
created a model to analyze coupling between almost 8000 measurements of
signaling parameters in cultu
