6,642 research outputs found
Oceanographic influences on the sea ice cover in the Sea of Okhotsk
Sea ice conditions in the Sea of Okhotsk, as determined by satellite images from the electrically scanning microwave radiometer on board Nimbus 5, were analyzed in conjunction with the known oceanography. In particular, the sea ice coverage was compared with the bottom bathymetry and the surface currents, water temperatures, and salinity. It is found that ice forms first in cold, shallow, low salinity waters. Once formed, the ice seems to drift in a direction approximating the Okhotsk-Kuril current system. Two basic patterns of ice edge positioning which persist for significant periods were identified as a rectangular structure and a wedge structure. Each of these is strongly correlated with the bathymetry of the region and with the known current system, suggesting that convective depth and ocean currents play an important role in determining ice patterns
An in-host model of HIV incorporating latent infection and viral mutation
We construct a seven-component model of the in-host dynamics of the Human
Immunodeficiency Virus Type-1 (i.e, HIV) that accounts for latent infection and
the propensity of viral mutation. A dynamical analysis is conducted and a
theorem is presented which characterizes the long time behavior of the model.
Finally, we study the effects of an antiretroviral drug and treatment
implications.Comment: 10 pages, 7 figures, Proceedings of AIMS Conference on Differential
Equations and Dynamical Systems (2015
Classification and Ranking of Fermi LAT Gamma-ray Sources from the 3FGL Catalog using Machine Learning Techniques
We apply a number of statistical and machine learning techniques to classify
and rank gamma-ray sources from the Third Fermi Large Area Telescope (LAT)
Source Catalog (3FGL), according to their likelihood of falling into the two
major classes of gamma-ray emitters: pulsars (PSR) or Active Galactic Nuclei
(AGN). Using 1904 3FGL sources that have been identified/associated with AGN
(1738) and PSR (166), we train (using 70% of our sample) and test (using 30%)
our algorithms and find that the best overall accuracy (>96%) is obtained with
the Random Forest (RF) technique, while using a logistic regression (LR)
algorithm results in only marginally lower accuracy. We apply the same
techniques on a sub-sample of 142 known gamma-ray pulsars to classify them into
two major subcategories: young (YNG) and millisecond pulsars (MSP). Once more,
the RF algorithm has the best overall accuracy (~90%), while a boosted LR
analysis comes a close second. We apply our two best models (RF and LR) to the
entire 3FGL catalog, providing predictions on the likely nature of {\it
unassociated} sources, including the likely type of pulsar (YNG or MSP). We
also use our predictions to shed light on the possible nature of some gamma-ray
sources with known associations (e.g. binaries, SNR/PWN). Finally, we provide a
list of plausible X-ray counterparts for some pulsar candidates, obtained using
Swift, Chandra, and XMM. The results of our study will be of interest for both
in-depth follow-up searches (e.g. pulsar) at various wavelengths, as well as
for broader population studies.Comment: Accepted by Ap
Spinful bosons in an optical lattice
We analyze the behavior of cold spin-1 particles with antiferromagnetic
interactions in a one-dimensional optical lattice using density matrix
renormalization group calculations. Correlation functions and the dimerization
are shown and we also present results for the energy gap between ground state
and the spin excited states. We confirm the anticipated phase diagram, with
Mott-insulating regions of alternating dimerized S=1 chains for odd particle
density versus on-site singlets for even density. We find no evidence for any
additional ordered phases in the physically accessible region, however for
sufficiently large spin interaction, on-site singlet pairs dominate leading,
for odd density, to a breakdown of the Mott insulator or, for even density, a
real-space singlet superfluid.Comment: Minor revisions and clarification
Magnetocaloric effect in integrable spin-s chains
We study the magnetocaloric effect for the integrable antiferromagnetic
high-spin chain. We present an exact computation of the Gr\"uneisen parameter,
which is closely related to the magnetocaloric effect, for the quantum spin-s
chain on the thermodynamical limit by means of Bethe ansatz techniques and the
quantum transfer matrix approach. We have also calculated the entropy S and the
isentropes in the (H,T) plane. We have been able to identify the quantum
critical points H_c^{(s)}=2/(s+1/2) looking at the isentropes and/or the
characteristic behaviour of the Gr\"uneisen parameter.Comment: 6 pages, 3 figure
Probable absence of a quadrupolar spin-nematic phase in the bilinear-biquadratic spin-1 chain
We study numerically the ground-state phase diagram of the
bilinear-biquadratic spin-1 chain near the ferromagnetic instability point,
where the existence of a gapped or gapless nondimerized quantum nematic phase
has been suggested. Our results, obtained by a highly accurate density-matrix
renormalization-group (DMRG) calculation are consistent with the view that the
order parameter characterizing the dimer phase vanishes only at the point where
the system becomes ferromagnetic, although the existence of a gapped or gapless
nondimerized phase in a very narrow parameter range between the ferromagnetic
and the dimerized regimes cannot be ruled out.Comment: 6 pages, 6 figure
The Bacterial Chemotactic Response Reflects a Compromise Between Transient and Steady State Behavior
Swimming bacteria detect chemical gradients by performing temporal
comparisons of recent measurements of chemical concentration. These comparisons
are described quantitatively by the chemotactic response function, which we
expect to optimize chemotactic behavioral performance. We identify two
independent chemotactic performance criteria: in the short run, a favorable
response function should move bacteria up chemoattractant gradients, while in
the long run, bacteria should aggregate at peaks of chemoattractant
concentration. Surprisingly, these two criteria conflict, so that when one
performance criterion is most favorable, the other is unfavorable. Since both
types of behavior are biologically relevant, we include both behaviors in a
composite optimization that yields a response function that closely resembles
experimental measurements. Our work suggests that the bacterial chemotactic
response function can be derived from simple behavioral considerations, and
sheds light on how the response function contributes to chemotactic
performance.Comment: 19 pages, 5 figure
Study on Doping Prevention: A map of Legal, Regulatory and Prevention Practice Provisions in EU 28
Historically, anti-doping efforts have focused on the detection and deterrence of doping in elite and competitive sport. There is, however, a growing concern that doping is occurring outside the organised sporting system; giving rise to the belief that the misuse of doping agents in recreational sport has become a societal problem and a public health issue that must be addressed. The EU Commission awarded a contract (EAC/2013/0617) to a Consortium to undertake this Study with the aim of developing the evidence-base for policies designed to combat doping in recreational sport. Fourteen internationally recognised experts shaped the Study which comprised (i) the collection of primary data through a structured survey, and (ii) secondary data through literature searches and website analysis. All 28 Member States participated in the information-gathering process. Specifically, this involved a systematic study of the ethical considerations, legal position, prevention research landscape, and current practise in relation to the prevention of doping in recreational sport. The Study provides a comprehensive overview of current practice and legislation as it applies to the prevention of doping and promotes and supports the sharing of best practices in the EU regarding the fight against doping in recreational sport. It concludes with seven recommendations for future action that focus on the need for a coordinated response in relation to the problems arising from doping in recreational sport
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