7,899 research outputs found
Transversity and Collins functions from SIDIS and e+e- data
A global analysis of the experimental data on azimuthal asymmetries in
semi-inclusive deep inelastic scattering (SIDIS), from the HERMES and COMPASS
Collaborations, and in e+e- --> h1 h2 X processes, from the BELLE
Collaboration, is performed. It results in the extraction of the Collins
fragmentation function and, for the first time, of the transversity
distribution function for u and d quarks. These turn out to have opposite signs
and to be sizably smaller than their positivity bounds. Predictions for the
azimuthal asymmetry A_{UT}^{sin(phi_h + phi_S)}, as will soon be measured at
JLab and COMPASS operating on a transversely polarized proton target, are then
presented.Comment: Revised version to appear in Phys. Rev. D. Few misprints corrected,
new figure
The Sivers Function from SIDIS Data
We study the Sivers effect in transverse single spin asymmetries (SSA) for
pion and kaon production in Semi-Inclusive Deep Inelastic Scattering (SIDIS)
processes. We perform a fit of A^{sin(phi_h-phi_S)}_UT taking into account the
recent data from HERMES and COMPASS Collaborations, which allow a new
determination of the Sivers distribution functions for quark and anti-quark
with u, d and also s flavours. Estimates for forthcoming SIDIS experiments at
COMPASS and JLab are given.Comment: 4 pages, 1 figure. To appear in the proceedings of the XVI
International Workshop on Deep-Inelastic Scattering and Related Subjects, DIS
2008, London, U.K., 7-11 April 200
Pomelo, a tool for computing Generic Set Voronoi Diagrams of Aspherical Particles of Arbitrary Shape
We describe the development of a new software tool, called "Pomelo", for the
calculation of Set Voronoi diagrams. Voronoi diagrams are a spatial partition
of the space around the particles into separate Voronoi cells, e.g. applicable
to granular materials. A generalization of the conventional Voronoi diagram for
points or monodisperse spheres is the Set Voronoi diagram, also known as
navigational map or tessellation by zone of influence. In this construction, a
Set Voronoi cell contains the volume that is closer to the surface of one
particle than to the surface of any other particle. This is required for
aspherical or polydisperse systems.
Pomelo is designed to be easy to use and as generic as possible. It directly
supports common particle shapes and offers a generic mode, which allows to deal
with any type of particles that can be described mathematically. Pomelo can
create output in different standard formats, which allows direct visualization
and further processing. Finally, we describe three applications of the Set
Voronoi code in granular and soft matter physics, namely the problem of
packings of ellipsoidal particles with varying degrees of particle-particle
friction, mechanical stable packings of tetrahedra and a model for liquid
crystal systems of particles with shapes reminiscent of pearsComment: 4 pages, 9 figures, Submitted to Powders and Grains 201
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Symbiotic unicellular cyanobacteria fix nitrogen in the Arctic Ocean.
Biological dinitrogen (N2) fixation is an important source of nitrogen (N) in low-latitude open oceans. The unusual N2-fixing unicellular cyanobacteria (UCYN-A)/haptophyte symbiosis has been found in an increasing number of unexpected environments, including northern waters of the Danish Straight and Bering and Chukchi Seas. We used nanoscale secondary ion mass spectrometry (nanoSIMS) to measure 15N2 uptake into UCYN-A/haptophyte symbiosis and found that UCYN-A strains identical to low-latitude strains are fixing N2 in the Bering and Chukchi Seas, at rates comparable to subtropical waters. These results show definitively that cyanobacterial N2 fixation is not constrained to subtropical waters, challenging paradigms and models of global N2 fixation. The Arctic is particularly sensitive to climate change, and N2 fixation may increase in Arctic waters under future climate scenarios
Contaminant removal from enclosed atmospheres by regenerable adsorbents
A system for removing contaminants from spacecraft atmospheres was studied, which utilizes catalyst-impregnated activated carbon followed by in-situ regeneration by low-temperature catalytic oxidation of the adsorbed contaminants. Platinum was deposited on activated carbon by liquid phase impregnation with chloroplatinic acid, followed by drying and high-temperature reduction. Results were obtained for the seven selected spacecraft contaminants by means of three experimental test systems. The results indicate that the contaminants could be removed by oxidation with very little loss in adsorptive capacity. The advantages of a catalyst-impregnated carbon for oxidative regeneration are found to be significant enough to warrent its use
Appearance of the Single Gyroid Network Phase in Nuclear Pasta Matter
Nuclear matter under the conditions of a supernova explosion unfolds into a
rich variety of spatially structured phases, called nuclear pasta. We
investigate the role of periodic network-like structures with negatively curved
interfaces in nuclear pasta structures, by static and dynamic Hartree-Fock
simulations in periodic lattices. As the most prominent result, we identify for
the first time the {\it single gyroid} network structure of cubic chiral
symmetry, a well known configuration in nanostructured soft-matter
systems, both as a dynamical state and as a cooled static solution. Single
gyroid structures form spontaneously in the course of the dynamical
simulations. Most of them are isomeric states. The very small energy
differences to the ground state indicate its relevance for structures in
nuclear pasta.Comment: 7 pages, 4 figure
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The self-relevance system?
We suggest that the Self Attention Network (SAN) maybe part of a larger self-regulatory system, which we term the Self-Relevance System (SRS) of which the “core” or default network is a major part. It is within the core network that memories are generated and the future imagined. Such memories and imaginings are the basis of preoccupations. Within the SRS then preoccupations drive the emergence of attentional biases (ABs). ABs in turn are modulated by the SAN activating and inhibiting circuits that shape behavior. We consider briefly how this might function in dysfunctional appetitive behaviors, e.g., substance abuse
In Situ Diazotroph Population Dynamics Under Different Resource Ratios in the North Pacific Subtropical Gyre.
Major advances in understanding the diversity, distribution, and activity of marine N2-fixing microorganisms (diazotrophs) have been made in the past decades, however, large gaps in knowledge remain about the environmental controls on growth and mortality rates. In order to measure diazotroph net growth rates and microzooplankton grazing rates on diazotrophs, nutrient perturbation experiments and dilution grazing experiments were conducted using free-floating in situ incubation arrays in the vicinity of Station ALOHA in March 2016. Net growth rates for targeted diazotroph taxa as well as Prochlorococcus, Synechococcus and photosynthetic picoeukaryotes were determined under high (H) and low (L) nitrate:phosphate (NP) ratio conditions at four depths in the photic zone (25, 45, 75, and 100 m) using quantitative PCR and flow cytometry. Changes in the prokaryote community composition in response to HNP and LNP treatments were characterized using 16S rRNA variable region tag sequencing. Microzooplankton grazing rates on diazotrophs were measured using a modified dilution technique at two depths in the photic zone (15 and 125 m). Net growth rates for most of the targeted diazotrophs after 48 h were not stimulated as expected by LNP conditions, rather enhanced growth rates were often measured in HNP treatments. Interestingly, net growth rates of the uncultivated prymnesiophyte symbiont UCYN-A1 were stimulated in HNP treatments at 75 and 100 m, suggesting that N used for growth was acquired through continuing to fix N2 in the presence of nitrate. Net growth rates for UCYN-A1, UCYN-C, Crocosphaera sp. (UCYN-B) and the diatom symbiont Richelia (associated with Rhizosolenia) were uniformly high at 45 m (up to 1.6 ± 0.5 d-1), implying that all were growing optimally at the onset of the experiment at that depth. Differences in microzooplankton grazing rates on UCYN-A1 and UCYN-C in 15 m waters indicate that the grazer assemblage preyed preferentially on UCYN-A1. Deeper in the water column (125 m), both diazotrophs were grazed at substantial rates, suggesting grazing pressure may increase with depth in the photic zone. Constraining in situ diazotroph growth and mortality rates are important steps for improving parameterization for diazotrophs in global ecosystem models
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