628 research outputs found
SuperConga: an open-source framework for mesoscopic superconductivity
We present SuperConga, an open-source framework for simulating equilibrium
properties of unconventional and ballistic singlet superconductors, confined to
two-dimensional (2D) mesoscopic grains in a perpendicular external magnetic
field, at arbitrary low temperature. It aims at being both fast and easy to
use, enabling research without access to a computer cluster, and visualization
in real-time with OpenGL. The core is written in C++ and CUDA, exploiting the
embarrassingly parallel nature of the quasiclassical theory of
superconductivity by utilizing the parallel computational power of modern GPUs.
The framework self-consistently computes both the superconducting
order-parameter and the induced vector potential, and finds the current
density, free energy, induced flux density, local density of states, as well as
the magnetic moment. A user-friendly Python frontend is provided, enabling
simulation parameters to be defined via intuitive configuration files, or via
the command-line interface, without requiring a deep understanding of
implementation details. For example, complicated geometries can be created with
relative ease. The framework ships with simple tools for analyzing and
visualizing the results, including an interactive plotter for spectroscopy. An
overview of the theory is presented, as well as examples showcasing the
framework's capabilities and ease of use. The framework is free to download
from https://gitlab.com/superconga/superconga, which also links to the
extensive user manual, containing even more examples, tutorials and guides.Comment: Accepted version. Review-style article, 31 pages and link to software
at https://gitlab.com/superconga/supercong
Dark Matter Constraints from a Joint Analysis of Dwarf Spheroidal Galaxy Observations with VERITAS
We present constraints on the annihilation cross section of WIMP dark matter
based on the joint statistical analysis of four dwarf galaxies with VERITAS.
These results are derived from an optimized photon weighting statistical
technique that improves on standard imaging atmospheric Cherenkov telescope
(IACT) analyses by utilizing the spectral and spatial properties of individual
photon events. We report on the results of 230 hours of observations of
five dwarf galaxies and the joint statistical analysis of four of the dwarf
galaxies. We find no evidence of gamma-ray emission from any individual dwarf
nor in the joint analysis. The derived upper limit on the dark matter
annihilation cross section from the joint analysis is at 1 TeV for the bottom quark () final state,
at 1 TeV for the tau lepton
() final state and at 1 TeV for the gauge boson () final state.Comment: 14 pages, 9 figures, published in PRD, Ascii tables containing
annihilation cross sections limits are available for download as ancillary
files with readme.txt file description of limit
A Search for Very High-Energy Gamma Rays from the Missing Link Binary Pulsar J1023+0038 with VERITAS
The binary millisecond radio pulsar PSR J1023+0038 exhibits many
characteristics similar to the gamma-ray binary system PSR B1259--63/LS 2883,
making it an ideal candidate for the study of high-energy non-thermal emission.
It has been the subject of multi-wavelength campaigns following the
disappearance of the pulsed radio emission in 2013 June, which revealed the
appearance of an accretion disk around the neutron star. We present the results
of very high-energy gamma-ray observations carried out by VERITAS before and
after this change of state. Searches for steady and pulsed emission of both
data sets yield no significant gamma-ray signal above 100 GeV, and upper limits
are given for both a steady and pulsed gamma-ray flux. These upper limits are
used to constrain the magnetic field strength in the shock region of the PSR
J1023+0038 system. Assuming that very high-energy gamma rays are produced via
an inverse-Compton mechanism in the shock region, we constrain the shock
magnetic field to be greater than 2 G before the disappearance of the
radio pulsar and greater than 10 G afterwards.Comment: 7 pages, 3 figures, accepted for publication in Ap
Very-High-Energy -Ray Observations of the Blazar 1ES 2344+514 with VERITAS
We present very-high-energy -ray observations of the BL Lac object
1ES 2344+514 taken by the Very Energetic Radiation Imaging Telescope Array
System (VERITAS) between 2007 and 2015. 1ES 2344+514 is detected with a
statistical significance above background of in hours
(livetime) of observations, making this the most comprehensive very-high-energy
study of 1ES 2344+514 to date. Using these observations the temporal properties
of 1ES 2344+514 are studied on short and long times scales. We fit a constant
flux model to nightly- and seasonally-binned light curves and apply a
fractional variability test, to determine the stability of the source on
different timescales. We reject the constant-flux model for the 2007-2008 and
2014-2015 nightly-binned light curves and for the long-term seasonally-binned
light curve at the level. The spectra of the time-averaged emission
before and after correction for attenuation by the extragalactic background
light are obtained. The observed time-averaged spectrum above 200 GeV is
satisfactorily fitted () by a power-law function with
index and extends to at least 8
TeV. The extragalactic-background-light-deabsorbed spectrum is adequately fit
() by a power-law function with index while an F-test indicates that the power-law with
exponential cutoff function provides a marginally-better fit ( =
) at the 2.1 level. The source location is found to be
consistent with the published radio location and its spatial extent is
consistent with a point source.Comment: 7 pages, 2 figures. Published in Monthly Notices of the Royal
Astronomical Societ
A search for spectral hysteresis and energy-dependent time lags from X-ray and TeV gamma-ray observations of Mrk 421
Blazars are variable emitters across all wavelengths over a wide range of
timescales, from months down to minutes. It is therefore essential to observe
blazars simultaneously at different wavelengths, especially in the X-ray and
gamma-ray bands, where the broadband spectral energy distributions usually
peak.
In this work, we report on three "target-of-opportunity" (ToO) observations
of Mrk 421, one of the brightest TeV blazars, triggered by a strong flaring
event at TeV energies in 2014. These observations feature long, continuous, and
simultaneous exposures with XMM-Newton (covering X-ray and optical/ultraviolet
bands) and VERITAS (covering TeV gamma-ray band), along with contemporaneous
observations from other gamma-ray facilities (MAGIC and Fermi-LAT) and a number
of radio and optical facilities. Although neither rapid flares nor significant
X-ray/TeV correlation are detected, these observations reveal subtle changes in
the X-ray spectrum of the source over the course of a few days. We search the
simultaneous X-ray and TeV data for spectral hysteresis patterns and time
delays, which could provide insight into the emission mechanisms and the source
properties (e.g. the radius of the emitting region, the strength of the
magnetic field, and related timescales). The observed broadband spectra are
consistent with a one-zone synchrotron self-Compton model. We find that the
power spectral density distribution at Hz from the
X-ray data can be described by a power-law model with an index value between
1.2 and 1.8, and do not find evidence for a steepening of the power spectral
index (often associated with a characteristic length scale) compared to the
previously reported values at lower frequencies.Comment: 45 pages, 15 figure
Landesque capital as an alternative to food storage in Melanesia: Irrigated taro terraces in New Georgia, Solomon Islands
In the Pacific islands, subsistence diversity made possible continuous production of food while welldeveloped exchange networks redistributed these foodstuffs as well as items within the prestige economy. All these were aspects of the âstorage structuresâ that enabled social and nutritional value to be saved, accumulated and later mobilised. In addition, there were investments in the land, landesque capital, which secured future food surpluses and so provided an alternative to food storage, in a region where the staple foods were mostly perishable, yams excepted, and food preservation was difficult. Landesque capital included such long-term improvements to productivity as terraces, mounds, irrigation channels, drainage ditches, soil structural changes and tree planting. These investments provided an effective alternative to food storage and made possible surplus production for exchange purposes. As an example, in the New Georgia group of the western Solomon Islands irrigated terraces, termed ruta, were constructed for growing the root crop taro (Colocasia esculenta). Surplus taro from ruta enabled inland groups to participate in regional exchange networks and so obtain the shell valuables that were produced by coastal groups. In this paper, we reconstruct how this exchange system worked in New Georgia using ethno-archaeological evidence, we chart its prehistoric rise and post-colonial fall, and we outline the factors that constrained its long-term expansion.Our gratitude for support during earlier fieldwork in the New Georgia group has already been expressed in previous publications. The 2014 project was supported by the Smuts Fund and Foreign Travel Fund, University of Cambridge, and by St Johnâs College, Cambridge.This is the accepted manuscript. The final version is available from Maney at http://dx.doi.org/10.1179/1749631414Y.000000004
The combination of electron capture dissociation and fixed charge derivatization increases sequence coverage for O-glycosylated and O-phosphorylated peptides
Low level of physical activity in women with rheumatoid arthritis is associated with cardiovascular risk factors but not with body fat mass - a cross sectional study
<p>Abstract</p> <p>Background</p> <p>As many patients with rheumatoid arthritis (RA) have increased fat mass (FM) and increased frequency of cardiovascular diseases we evaluated if total physical activity (MET-hours) had impact on body composition and cardiovascular risk factors in women with RA.</p> <p>Methods</p> <p>Sixty-one out-ward RA women, 60.8 (57.3-64.4) years, answered a self-administered questionnaire, to estimate total daily physical activity during the previous year. Physical activity level was given as metabolic equivalents (MET) Ă h/day. Diet content was assessed by a food frequency questionnaire and body composition by whole-body dual-energy X-ray absorptiometry. Blood lipids and antibodies against phosphorylcholine (anti-PC) were determined.</p> <p>Results</p> <p>Forty-one percent of the women had BMI > 25, 6% were centrally obese and 80% had FM% > 30%. The median (IQR) total physical activity was 40.0 (37.4-47.7), i.e. the same activity level as healthy Swedish women in the same age. Total physical activity did not significantly correlate with disease activity, BMI or FM%. Disease activity, BMI and FM% did not differ between those in the lowest quartile of total physical activity and those in the highest quartile. However, the women in the lowest quartile of physical activity had lower HDL (p = 0.05), Apo A1 (p = 0.005) and atheroprotective natural anti-PC (p = 0.016) and higher levels of insulin (p = 0.05) and higher frequency of insulin resistance than those in the highest quartile. Women in the lowest quartile consumed larger quantities of saturated fatty acids than those in the highest quartile (p = 0.042), which was associated with high oxidized low-density lipoprotein (oxLDL).</p> <p>Conclusion</p> <p>This cross sectional study demonstrated that RA women with fairly low disease activity, good functional capacity, high FM and high frequency of central obesity had the same total physical activity level as healthy Swedish women in the same age. The amount of total physical activity was not associated with functional capacity or body composition. However, low total physical activity was associated with dyslipidemia, insulin resistance, low levels of atheroprotective anti-PC and consumption of saturated fatty acids, which is of interest in the context of increased frequency of cardiovascular disease in RA.</p
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