874 research outputs found
Neutrino Constraints on Inelastic Dark Matter after CDMS II
We discuss the neutrino constraints from solar and terrestrial dark matter
(DM) annihilations in the inelastic dark matter (iDM) scenario after the recent
CDMS II results. To reconcile the DAMA/LIBRA data with constraints from all
other direct experiments, the iDM needs to be light ( GeV) and
have a large DM-nucleon cross section ( 10 pb in the
spin-independent (SI) scattering and 10 pb in the
spin-dependent (SD) scattering). The dominant contribution to the iDM capture
in the Sun is from scattering off Fe/Al in the SI/SD case. Current bounds from
Super-Kamiokande exclude the hard DM annihilation channels, such as ,
, and . For soft channels such as and
, the limits are loose, but could be tested or further constrained
by future IceCube plus DeepCore. For neutrino constraints from the DM
annihilation in the Earth, due to the weaker gravitational effect of the Earth
and inelastic capture condition, the constraint exists only for small mass
splitting 40 keV and GeV even in the channel.Comment: 11 pages, 8 figure
Nucleon Mass Splitting at Finite Isospin Chemical Potential
We investigate nucleon mass splitting at finite isospin chemical potential in
the frame of two flavor Nambu--Jona-Lasinio model. It is analytically proved
that, in the phase with explicit isospin symmetry breaking the proton mass
decreases and the neutron mass increases linearly in the isospin chemical
potential.Comment: 3 pages and no figure
Non-Abelian Medium Effects in Quark-Gluon Plasma
Based on the kinetic theory, the non-Abelian medium property of hot
Quark-Gluon Plasma is investigated. The nonlinearity of the plasma comes from
two aspects: The nonlinear wave-wave interaction and self-interaction of color
field. The non-Abelian color permittivity is obtained by expanding the kinetic
equations to third order. As an application, the nonlinear Landau damping rate
and the nonlinear eigenfrequency shift are calculated in the longwave length
limit.Comment: 12 pages(Revtex), no figure
Influence of Equatorial Diatom Processes on Si Deposition and Atmospheric CO(2) Cycles at Glacial/Interglacial Timescales
The causes of the glacial cycle remain unknown, although the primary driver is changes in atmospheric CO(2), likely controlled by the biological pump and biogeochemical cycles. The two most important regions of the ocean for exchange of CO(2) with the atmosphere are the equatorial Pacific and the Southern Ocean ( SO), the former a net source and the latter a net sink under present conditions. The equatorial Pacific has been shown to be a Si(OH)(4)-limited ecosystem, a consequence of the low source Si(OH)(4) concentrations in upwelled water that has its origin in the SO. This teleconnection for nutrients between the two regions suggests an oscillatory relationship that may influence or control glacial cycles. Opal mass accumulation rate (MAR) data and delta(15)N measurements in equatorial cores are interpreted with predictions from a one- dimensional Si(OH)(4)-limited ecosystem model (CoSINE) for the equatorial Pacific. The results suggest that equatorial Pacific surface CO(2) processes are in opposite phase to that of the global atmosphere, providing a negative feedback to the glacial cycle. This negative feedback is implemented through the effect of the SO on the equatorial Si(OH)(4) supply. An alternative hypothesis, that the whole ocean becomes Si(OH)(4) poor during cooling periods, is suggested by low opal MAR in cores from both equatorial and Antarctic regions, perhaps as a result of low river input. terminations in this scenario would result from blooms of coccolithophorids triggered by low Si(OH)(4) concentrations
Energy hole mitigation through cooperative transmission in wireless sensor networks
The energy balancing capability of cooperative communication is utilized to solve the energy hole problem in wireless sensor networks. We first propose a cooperative transmission strategy, where intermediate nodes participate in two cooperative multi-input single-output (MISO) transmissions with the node at the previous hop and a selected node at the next hop, respectively. Then, we study the optimization problems for power allocation of the cooperative transmission strategy by examining two different approaches: network lifetime maximization (NLM) and energy consumption minimization (ECM). For NLM, the numerical optimal solution is derived and a searching algorithm for suboptimal solution is provided when the optimal solution does not exist. For ECM, a closed-form solution is obtained. Numerical and simulation results show that both the approaches have much longer network lifetime than SISO transmission strategies and other cooperative communication schemes. Moreover, NLM which features energy balancing outperforms ECM which focuses on energy efficiency, in the network lifetime sense
Connected-Sea Partons
According to the path-integral formalism of the hadronic tensor, the nucleon
sea contains two distinct components called connected sea (CS) and disconnected
sea (DS). We discuss how the CS and DS are accessed in the lattice QCD
calculation of the moments of the parton distributions. We show that the CS and
DS components for can be extracted by using recent data
on the strangeness parton distribution, the CT10 global fit, and the lattice
result of the ratio of the strange to moments in the disconnected
insertion. The extracted CS and DS for have distinct
Bjorken dependence in qualitative agreement with expectation. The analysis
also shows that the momentum fraction of the is about
equally divided between CS and DS at . Implications on
future global analysis for parton distributions are presented.Comment: Revised version to be published in Phys. Rev. Let
Superconductivity in Ti-doped Iron-Arsenide Compound Sr4Cr0.8Ti1.2O6Fe2As2
Superconductivity was achieved in Ti-doped iron-arsenide compound
Sr4Cr0.8Ti1.2O6Fe2As2 (abbreviated as Cr-FeAs-42622). The x-ray diffraction
measurement shows that this material has a layered structure with the space
group of \emph{P4/nmm}, and with the lattice constants a = b = 3.9003 A and c =
15.8376 A. Clear diamagnetic signals in ac susceptibility data and
zero-resistance in resistivity data were detected at about 6 K, confirming the
occurrence of bulk superconductivity. Meanwhile we observed a superconducting
transition in the resistive data with the onset transition temperature at 29.2
K, which may be induced by the nonuniform distribution of the Cr/Ti content in
the FeAs-42622 phase, or due to some other minority phase.Comment: 3 pages, 3 figure
What do we currently know from in vivo bone strain measurements in humans
Introduction It is well accepted that bones adapt to different types of loading, e.g. by various exercises or by disuse, the former being followed by anabolic responses and the latter by bone losses. Literature suggests that specific exercises or training can improve people's bone mass and strength 1 . On the other hand, disuse during space flight was shown to induce a loss of more than 2% in hip trabecular volumetric bone mineral density (vBMD) per month 2 . Inevitably, bone deformation will be induced by dynamic loading (because the static bone loading rarely happens in vivo, it is not included in this discussion). The effects of the various factors involved in bone loading, which include strain magnitude, strain rate, and the number of loading cycles are well documented Abstract Bone strains are the most important factors for osteogenic adaptive responses. During the past decades, scientists have been trying to describe the relationship between bone strain and bone osteogenic responses quantitatively. However, only a few studies have examined bone strains under physiological condition in humans, owing to technical difficulty and ethical restrictions. The present paper reviews previous work on in vivo bone strain measurements in humans, and the various methodologies adopted in these measurements are discussed. Several proposals are made for future work to improve our understanding of the human musculoskeletal system. Literature suggests that strains and strain patterns vary systematically in response to different locomotive activities, foot wear, and even different venues. The principal compressive, tension and engineering shear strain, compressive strain rate and shear strain rate in the tibia during running seem to be higher than those during walking. The high impact exercises, such as zig-zag hopping and basketball rebounding induced greater principal strains and strain rates in the tibia than normal activities. Also, evidence suggests an increase of tibia strain and strain rate after muscle fatigue, which strongly supports the opinion that muscle contractions play a role on the alteration of bone strain patterns
Pressure induced high-spin to low-spin transition in FeS evidenced by x-ray emission spectroscopy
We report the observation of the pressure-induced high-spin to low-spin
transition in FeS using new high-pressure synchrotron x-ray emission
spectroscopy techniques. The transition is evidenced by the disappearance of
the low-energy satellite in the Fe K emission spectrum of FeS. Moreover,
the phase transition is reversible and closely related to the structural phase
transition from a manganese phosphide-like phase to a monoclinic phase. The
study opens new opportunities for investigating the electronic properties of
materials under pressure.Comment: ReVTeX, 4 pages, 3 figures inserted with epsfig. minor modifications
before submission to PR
Open-source genomic analysis of Shiga-toxin–producing E. coli O104:H4
An outbreak caused by Shiga-toxin–producing Escherichia coli O104:H4 occurred in Germany in May and June of 2011, with more than 3000 persons infected. Here, we report a cluster of cases associated with a single family and describe an open-source genomic analysis of an isolate from one member of the family. This analysis involved the use of rapid, bench-top DNA sequencing technology, open-source data release, and prompt crowd-sourced analyses. In less than a week, these studies revealed that the outbreak strain belonged to an enteroaggregative E. coli lineage that had acquired genes for Shiga toxin 2 and for antibiotic resistance
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