25,109 research outputs found
Electronic Effects in Expansive Flow Under Hypersonic Conditions
Plasma effects in hypersonic shock tunnel nozzle using ai
A New Low-Mass Eclipsing Binary from SDSS-II
We present observations of a new low-mass double-lined eclipsing binary
system discovered using repeat observations of the celestial equator from the
Sloan Digital Sky Survey II. Using near-infrared photometry and optical
spectroscopy we have measured the properties of this short-period
[P=0.407037(14) d] system and its two components. We find the following
parameters for the two components: M_1=0.272+/-0.020 M_sun, R_1=0.268+/-0.010
R_sun, M_2=0.240+/-0.022 M_sun, R_2=0.248+/-0.0090 R_sun, T_1=3320+/-130 K,
T_2=3300+/-130 K. The masses and radii of the two components of this system
agree well with theoretical expectations based on models of low-mass stars,
within the admittedly large errors. Future synoptic surveys like Pan-STARRS and
LSST will produce a wealth of information about low-mass eclipsing systems and
should make it possible, with an increased reliance on follow-up observations,
to detect many systems with low-mass and sub-stellar companions. With the large
numbers of objects for which these surveys will produce high-quality
photometry, we suggest that it becomes possible to identify such systems even
with sparse time sampling and a relatively small number of individual
observations.Comment: 15 Pages, 9 Figures, 6 Tables. Replaced with version accepted to Ap
Neutral genetic drift can aid functional protein evolution
BACKGROUND: Many of the mutations accumulated by naturally evolving proteins
are neutral in the sense that they do not significantly alter a protein's
ability to perform its primary biological function. However, new protein
functions evolve when selection begins to favor other, "promiscuous" functions
that are incidental to a protein's biological role. If mutations that are
neutral with respect to a protein's primary biological function cause
substantial changes in promiscuous functions, these mutations could enable
future functional evolution.
RESULTS: Here we investigate this possibility experimentally by examining how
cytochrome P450 enzymes that have evolved neutrally with respect to activity on
a single substrate have changed in their abilities to catalyze reactions on
five other substrates. We find that the enzymes have sometimes changed as much
as four-fold in the promiscuous activities. The changes in promiscuous
activities tend to increase with the number of mutations, and can be largely
rationalized in terms of the chemical structures of the substrates. The
activities on chemically similar substrates tend to change in a coordinated
fashion, potentially providing a route for systematically predicting the change
in one function based on the measurement of several others.
CONCLUSIONS: Our work suggests that initially neutral genetic drift can lead
to substantial changes in protein functions that are not currently under
selection, in effect poising the proteins to more readily undergo functional
evolution should selection "ask new questions" in the future
A Patchwork of Progress
Outlines changes in childhood obesity and overweight rates in California between 2005 and 2010 by county. Considers implications of regional variations, including public policy options for promoting healthy diets and physical activity
Bloom-Gilman duality of the nucleon structure function and the elastic peak contribution
The occurrence of the Bloom-Gilman duality in the nucleon structure function
is investigated by analyzing the Q**2-behavior of low-order moments, both
including and excluding the contribution arising from the nucleon elastic peak.
The Natchmann definition of the moments has been adopted in order to cancel out
target-mass effects. It is shown that the onset of the Bloom-Gilman duality
occurs around Q**2 ~ 2 (GeV/c)**2 if only the inelastic part of the nucleon
structure function is considered, whereas the inclusion of the nucleon elastic
peak contribution leads to remarkable violations of the Bloom-Gilman duality.Comment: in Proc. of the XVI European Conference on Few-body Problems in
Physics, Autrans (France), July 199
Electromagnetic containerless processing requirements and recommended facility concept and capabilities for space lab
Containerless melting, reaction, and solidification experiments and processes which potentially can lead to new understanding of material science and production of new or improved materials in the weightless space environment are reviewed in terms of planning for spacelab. Most of the experiments and processes discussed are amenable to the employment of electromagnetic position control and electromagnetic induction or electron beam heating and melting. The spectrum of relevant properties of materials, which determine requirements for a space laboratory electromagnetic containerless processing facility are reviewed. Appropriate distributions and associated coil structures are analyzed and compared on the basis of efficiency, for providing the functions of position sensing, control, and induction heating. Several coil systems are found capable of providing these functions. Exchangeable modular coils in appropriate sizes are recommended to achieve the maximum power efficiencies, for a wide range of specimen sizes and resistivities, in order to conserve total facility power
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