38,884 research outputs found
Cronin Effect in Hadron Production off Nuclei
Recent data from RHIC for high- hadrons in gold-gold collisions raised
again the long standing problem of quantitatively understanding the Cronin
effect, i.e. nuclear enhancement of high- hadrons due to multiple
interactions in nuclear matter. In nucleus-nucleus collisions this effect has
to be reliably calculated as baseline for a signal of new physics in high-
hadron production. The only possibility to test models is to compare with
available data for collisions, however, all existing models for the Cronin
effect rely on a fit to the data to be explained. We develop a phenomenological
description based on the light-cone QCD-dipole approach which allows to explain
available data without fitting to them and to provide predictions for
collisions at RHIC and LHC. We point out that the mechanism causing Cronin
effect drastically changes between the energies of fixed target experiments and
RHIC-LHC. High- hadrons are produced incoherently on different nucleons at
low energies, whereas the production amplitudes interfere if the energy is
sufficiently high.Comment: the final version to appear in Phys. Rev. Let
Vickrey Auctions for Irregular Distributions
The classic result of Bulow and Klemperer \cite{BK96} says that in a
single-item auction recruiting one more bidder and running the Vickrey auction
achieves a higher revenue than the optimal auction's revenue on the original
set of bidders, when values are drawn i.i.d. from a regular distribution. We
give a version of Bulow and Klemperer's result in settings where bidders'
values are drawn from non-i.i.d. irregular distributions. We do this by
modeling irregular distributions as some convex combination of regular
distributions. The regular distributions that constitute the irregular
distribution correspond to different population groups in the bidder
population. Drawing a bidder from this collection of population groups is
equivalent to drawing from some convex combination of these regular
distributions. We show that recruiting one extra bidder from each underlying
population group and running the Vickrey auction gives at least half of the
optimal auction's revenue on the original set of bidders
Breakdown of QCD factorization at large Feynman x
Recent measurements by the BRAHMS collaboration of high-pT hadron production
at forward rapidities at RHIC found the relative production rate(d-Au)/(p-p) to
be suppressed, rather than enhanced. Examining other known reactions (forward
production of light hadrons, the Drell-Yan process, heavy flavor production,
etc.), one notes that all of these display a similar property, namely, their
cross sections in nuclei are suppressed at large xF. Since this is the region
where x2 is minimal, it is tempting to interpret this as a manifestation of
coherence, or of a color glass condensate, whereas it is actually a simple
consequence of energy conservation and takes place even at low energies. We
demonstrate that in all these reactions there is a common suppression mechanism
that can be viewed, alternatively, as a consequence of a reduced survival
probability for large rapidity gap processes in nuclei, Sudakov suppression, an
enhanced resolution of higher Fock states by nuclei, or an effective energy
loss that rises linearly with energy. Our calculations agree with data.Comment: 12 pages Latex, 8 figures (only technical corrections in the
replacement
Communications of the Lunar and Planetary Laboratory, volume 4, part 3 - Ubvrijkl photometry of the bright stars
Multicolor photometric analysis of bright stars - table
Production Systems Involving Stocker Cattle and Soft Red Winter Wheat
A three year study at the Livestock and Forestry Research Station near Batesville, Arkansas evaluated production systems involving stocker cattle and soft red winter wheat. Grazing of soft red winter wheat forage from October through February followed by harvesting wheat grain or grazing through April with stocker cattle offers an alternative to conventional farming. Soft red winter wheat, when planted by September 15, produces an ample supply of high-quality forage that supports rapid growth of stocker cattle during October through April. Net income from stocker cattle averaged over 75,000,000 per year if 750,000 acres of wheat are grazed
Synthesis of single-component metallic glasses by thermal spray of nanodroplets on amorphous substrates
We show that single component metallic glasses can be synthesized by thermal spray coating of nanodroplets onto an amorphous substrate. We demonstrate this using molecular dynamics simulations of nanodroplets up to 30 nm that the spreading of the nanodroplets during impact on a substrate leads to sufficiently rapid cooling (10^(12)–10^(13) K/s) sustained by the large temperature gradients between the thinned nanodroplets and the bulk substrate. However, even under these conditions, in order to ensure that the glass transition outruns crystal nucleation, it is essential that the substrate be amorphous (eliminating sites for heterogeneous nucleation of crystallization)
Self-paced aerobic exercise performance is attenuated following four hours cold water immersion
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Charged two-dimensional magnetoexciton and two-mode squeezed vacuum states
A novel unitary transformation of the Hamiltonian that allows one to
partially separate the center-of-mass motion for charged electron-hole systems
in a magnetic field is presented. The two-mode squeezed oscillator states that
appear at the intermediate stage of the transformation are used for
constructing a trial wave function of a two-dimensional (2D) charged
magnetoexciton.Comment: 9 pages, 1 figur
3-D Models of Embedded High-Mass Stars: Effects of a Clumpy Circumstellar Medium
We use 3-D radiative transfer models to show the effects of clumpy
circumstellar material on the observed infrared colors of high mass stars
embedded in molecular clouds. We highlight differences between 3-D clumpy and
1-D smooth models which can affect the interpretation of data. We discuss
several important properties of the emergent spectral energy distribution
(SED): More near-infrared light (scattered and direct from the central source)
can escape than in smooth 1-D models. The near- and mid-infrared SED of the
same object can vary significantly with viewing angle, depending on the clump
geometry along the sightline. Even the wavelength-integrated flux can vary with
angle by more than a factor of two. Objects with the same average circumstellar
dust distribution can have very different near-and mid-IR SEDs depending on the
clump geometry and the proximity of the most massive clump to the central
source.
Although clumpiness can cause similar objects to have very different SEDs,
there are some observable trends. Near- and mid-infrared colors are sensitive
to the weighted average distance of clumps from the central source and to the
magnitude of clumpy density variations (smooth-to-clumpy ratio). Far-infrared
emission remains a robust measure of the total dust mass. We present simulated
SEDs, colors, and images for 2MASS and Spitzer filters. We compare to
observations of some UCHII regions and find that 3-D clumpy models fit better
than smooth models. In particular, clumpy models with fractal dimensions in the
range 2.3-2.8, smooth to clumpy ratios of <50%, and density distributions with
shallow average radial density profiles fit the SEDs best.Comment: accepted to ApJ; version with full-res figures:
http://www.astro.virginia.edu/~ri3e/clumpy3d.pd
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