18,527 research outputs found
Calculation of minor hysteresis loops under metastable to stable transformations in vortex matter
We present a model in which metastable supercooled phase and stable
equilibrium phase of vortex matter coexist in different regions of a sample.
Minor hysteresis loops are calculated with the simple assumption of the two
phases of vortex matter having field-independent critical current densities. We
use our earlier published ideas that the free energy barrier separating the
metastable and stable phases reduces as the magnetic induction moves farther
from the first order phase transition line, and that metastable to stable
transformations occur in local regions of the sample when the local energy
dissipation exceeds a critical value. Previously reported anomalous features in
minor hysteresis loops are reproduced, and calculated field profiles are
presented.Comment: 9pages, 7 figure
Is early diagnose for Vitamin A deficiency better than the current supplementation programme of Nepal?
This editorial concludes that prevention is still better than cure, but instead of a mass Vitamin A supplementation in Nepal, we need a health promotion intervention aiming to increase the intake of relatively cheap vegetables and fruit (containing ÎČ carotene). In addition we need better surveillance and help to identify children with Vitamin A Deficiency and provide them with Vitamin A supplements. The primary focus should be on adopting sustainable food based approaches to combat vitamin A deficiency. In Public Health terms: rather than a blanket coverage of Vitamin A supplementation to whole population we should consider a targeted intervention aimed at those who need it most
Frequency shift keying in vortex-based spin torque oscillators
Vortex-based spin-torque oscillators can be made from extended spin valves
connected to an electrical nanocontact. We study the implementation of
frequency shift keying modulation in these oscillators. Upon a square
modulation of the current in the 10 MHz range, the vortex frequency follows the
current command, with easy identification of the two swapping frequencies in
the spectral measurements. The frequency distribution of the output power can
be accounted for by convolution transformations of the dc current vortex
waveform, and the current modulation. Modeling indicates that the frequency
transitions are phase coherent and last less than 25 ns. Complementing the
multi-octave tunability and first-class agility, the capability of frequency
shift keying modulation is an additional milestone for the implementation of
vortex-based oscillators in RF circuit.Comment: 6 pages, 5 figure
Quantitative Study of Magnetotransport through a (Ga,Mn)As Single Ferromagnetic Domain
We have performed a systematic investigation of the longitudinal and
transverse magnetoresistance of a single ferromagnetic domain in (Ga,Mn)As. We
find that, by taking into account the intrinsic dependence of the resistivity
on the magnetic induction, an excellent agreement between experimental results
and theoretical expectations is obtained. Our findings provide a detailed and
fully quantitative validation of the theoretical description of
magnetotransport through a single ferromagnetic domain. Our analysis
furthermore indicates the relevance of magneto-impurity scattering as a
mechanism for magnetoresistance in (Ga,Mn)As.Comment: 5 pages, 4 figures; v2: missing references included, figures
recompressed to improve readabilit
Social Entrepreneurship and Performance: The Role of Perceived Barriers and Risk
This study investigates if and in what way social entrepreneurs are hampered in turning their efforts into sustainable organizations. Using binary logit regressions and unique data containing approximately 26,000 individual-level data points for 36 countries, this
Concurrent constraint programming with process mobility
We propose an extension of concurrent constraint programming with primitives for process migration within a hierarchical network, and we study its semantics. To this purpose, we first investigate a "pure " paradigm for process migration, namely a paradigm where the only actions are those dealing with transmissions of processes. Our goal is to give a structural definition of the semantics of migration; namely, we want to describe the behaviour of the system, during the transmission of a process, in terms of the behaviour of the components. We achieve this goal by using a labeled transition system where the effects of sending a process, and requesting a process, are modeled by symmetric rules (similar to handshaking-rules for synchronous communication) between the two partner nodes in the network. Next, we extend our paradigm with the primitives of concurrent constraint programming, and we show how to enrich the semantics to cope with the notions of environment and constraint store. Finally, we show how the operational semantics can be used to define an interpreter for the basic calculus.
Distance Dependence in the Solar Neighborhood Age-Metallicity Relation
The age-metallicity relation for F and G dwarf stars in the solar
neighborhood, based on the stellar metallicity data of Edvardsson et al.
(1993), shows an apparent scatter that is larger than expected considering the
uncertainties in metallicities and ages. A number of theoretical models have
been put forward to explain the large scatter. However, we present evidence,
based on Edvardsson et al. (1993) data, along with Hipparcos parallaxes and new
age estimates, that the scatter in the age-metallicity relation depends on the
distance to the stars in the sample, such that stars within 30 pc of the Sun
show significantly less scatter in [Fe/H]. Stars of intermediate age from the
Edvardsson et al. sample at distances 30-80 pc from the Sun are systematically
more metal-poor than those more nearby. We also find that the slope of the
apparent age-metallicity relation is different for stars within 30 pc than for
those stars more distant. These results are most likely an artifact of
selection biases in the Edvardsson et al. star sample. We conclude that the
intrinsic dispersion in metallicity at fixed age is < 0.15 dex, consistent with
the < 0.1 dex scatter for Galactic open star clusters and the interstellar
medium.Comment: 15 pages, 5 figures, uses AASTex aaspp4 style; accepted for
publication in the Astrophysical Journa
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