2,942 research outputs found
Wind Atlas for South Africa (WASA) Observational wind atlas for 10 met. stations in Northern, Western and Eastern Cape provinces
Wind Atlas for South Africa (WASA) Observational wind atlas for 10 met. stations in Northern, Western and Eastern Cape provinces
Velocity Distributions from Nonextensive Thermodynamics
There is no accepted mechanism that explains the equilibrium structures that
form in collisionless cosmological N-body simulations. Recent work has
identified nonextensive thermodynamics as an innovative approach to the
problem. The distribution function that results from adopting this framework
has the same form as for polytropes, but the polytropic index is now related to
the degree of nonextensiveness. In particular, the nonextensive approach can
mimic the equilibrium structure of dark matter density profiles found in
simulations. We extend the investigation of this approach to the velocity
structures expected from nonextensive thermodynamics. We find that the
nonextensive and simulated N-body rms-velocity distributions do not match one
another. The nonextensive rms-velocity profile is either monotonically
decreasing or displays little radial variation, each of which disagrees with
the rms-velocity distributions seen in simulations. We conclude that the
currently discussed nonextensive models require further modifications in order
to corroborate dark matter halo simulations. (adapted from TeX)Comment: 3 color figures, accepted for publication in Ap
Dynamics of monatomic liquids
We present a theory of the dynamics of monatomic liquids built on two basic
ideas: (1) The potential surface of the liquid contains three classes of
intersecting nearly-harmonic valleys, one of which (the ``random'' class)
vastly outnumbers the others and all whose members have the same depth and
normal mode spectrum; and (2) the motion of particles in the liquid can be
decomposed into oscillations in a single many-body valley, and nearly
instantaneous inter-valley transitions called transits. We review the
thermodynamic data which led to the theory, and we discuss the results of
molecular dynamics (MD) simulations of sodium and Lennard-Jones argon which
support the theory in more detail. Then we apply the theory to problems in
equilibrium and nonequilibrium statistical mechanics, and we compare the
results to experimental data and MD simulations. We also discuss our work in
comparison with the QNM and INM research programs and suggest directions for
future research.Comment: 53 pages, 16 figures. Differs from published version in using
American English spelling and grammar (published version uses British
English
Identification of a bacteriocin and its cognate immunity factor expressed by Moraxella catarrhalis
<p>Abstract</p> <p>Background</p> <p>Bacteriocins are antimicrobial proteins and peptides ribosomally synthesized by some bacteria which can effect both intraspecies and interspecies killing.</p> <p>Results</p> <p><it>Moraxella catarrhalis </it>strain E22 containing plasmid pLQ510 was shown to inhibit the growth of <it>M. catarrhalis </it>strain O35E. Two genes (<it>mcbA </it>and <it>mcbB</it>) in pLQ510 encoded proteins predicted to be involved in the secretion of a bacteriocin. Immediately downstream from these two genes, a very short ORF (<it>mcbC</it>) encoded a protein which had some homology to double-glycine bacteriocins produced by other bacteria. A second very short ORF (<it>mcbI</it>) immediately downstream from <it>mcbC </it>encoded a protein which had no significant similarity to other proteins in the databases. Cloning and expression of the <it>mcbI </it>gene in <it>M. catarrhalis </it>O35E indicated that this gene encoded the cognate immunity factor. Reverse transcriptase-PCR was used to show that the <it>mcbA</it>, <it>mcbB</it>, <it>mcbC</it>, and <it>mcbI </it>ORFs were transcriptionally linked. This four-gene cluster was subsequently shown to be present in the chromosome of several <it>M. catarrhalis </it>strains including O12E. Inactivation of the <it>mcbA</it>, <it>mcbB</it>, or <it>mcbC </it>ORFs in <it>M. catarrhalis </it>O12E eliminated the ability of this strain to inhibit the growth of <it>M. catarrhalis </it>O35E. In co-culture experiments involving a <it>M. catarrhalis </it>strain containing the <it>mcbABCI </it>locus and one which lacked this locus, the former strain became the predominant member of the culture after overnight growth in broth.</p> <p>Conclusion</p> <p>This is the first description of a bacteriocin and its cognate immunity factor produced by <it>M. catarrhalis</it>. The killing activity of the McbC protein raises the possibility that it might serve to lyse other <it>M. catarrhalis </it>strains that lack the <it>mcbABCI </it>locus, thereby making their DNA available for lateral gene transfer.</p
Formation of Super-Earths
Super-Earths are the most abundant planets known to date and are
characterized by having sizes between that of Earth and Neptune, typical
orbital periods of less than 100 days and gaseous envelopes that are often
massive enough to significantly contribute to the planet's overall radius.
Furthermore, super-Earths regularly appear in tightly-packed multiple-planet
systems, but resonant configurations in such systems are rare. This chapters
summarizes current super-Earth formation theories. It starts from the formation
of rocky cores and subsequent accretion of gaseous envelopes. We follow the
thermal evolution of newly formed super-Earths and discuss their atmospheric
mass loss due to disk dispersal, photoevaporation, core-cooling and collisions.
We conclude with a comparison of observations and theoretical predictions,
highlighting that even super-Earths that appear as barren rocky cores today
likely formed with primordial hydrogen and helium envelopes and discuss some
paths forward for the future.Comment: Invited review accepted for publication in the 'Handbook of
Exoplanets,' Planet Formation section, Springer Reference Works, Juan Antonio
Belmonte and Hans Deeg, Ed
Isotropic-nematic phase transition in suspensions of filamentous virus and the neutral polymer Dextran
We present an experimental study of the isotropic-nematic phase transition in
an aqueous mixture of charged semi-flexible rods (fd virus) and neutral polymer
(Dextran). A complete phase diagram is measured as a function of ionic strength
and polymer molecular weight. At high ionic strength we find that adding
polymer widens the isotropic-nematic coexistence region with polymers
preferentially partitioning into the isotropic phase, while at low ionic
strength the added polymer has no effect on the phase transition. The nematic
order parameter is determined from birefringence measurements and is found to
be independent of polymer concentration (or equivalently the strength of
attraction). The experimental results are compared with the existing
theoretical predictions for the isotropic-nematic transition in rods with
attractive interactions.Comment: 8 Figures. To be published in Phys. Rev. E. For more information see
http://www.elsie.brandeis.ed
Multifunctionality of Prostatic Acid Phosphatase in Prostate Cancer Pathogenesis
The role of human prostatic acid phosphatase (PAcP, P15309|PPAP_HUMAN) in prostate cancer was investigated using a new proteomics tool termed signal sequence swapping (replacement of domains from the native cleaved amino terminal signal sequence of secretory/membrane proteins with corresponding regions of functionally distinct signal sequence subtypes). This manipulation preferentially redirects proteins to different pathways of biogenesis at the endoplasmic reticulum (ER), magnifying normally difficult to detect subsets of the protein of interest. For PAcP, this technique reveals three forms identical in amino acid sequence but profoundly different in physiological functions, subcellular location, and biochemical properties. These three forms of PAcP can also occur with the wildtype PAcP signal sequence. Clinical specimens from patients with prostate cancer demonstrate that one form, termed PLPAcP, correlates with early prostate cancer. These findings confirm the analytical power of this method, implicate PLPAcP in prostate cancer pathogenesis, and suggest novel anticancer therapeutic strategies
- …