8,421 research outputs found
Numerical computation of real or complex elliptic integrals
Algorithms for numerical computation of symmetric elliptic integrals of all
three kinds are improved in several ways and extended to complex values of the
variables (with some restrictions in the case of the integral of the third
kind). Numerical check values, consistency checks, and relations to Legendre's
integrals and Bulirsch's integrals are included
Detection of a Spin Accumulation in Nondegenerate Semiconductors
Electrical detection of a spin accumulation in a nondegenerate semiconductor using a tunnel barrier and ferromagnetic contact is shown to be fundamentally affected by the energy barrier associated with the depletion region. This prevents the ferromagnet from probing the spin accumulation directly, strongly suppresses the magnetoresistance in current or potentiometric detection, and introduces nonmonotonic variation of spin signals with voltage and temperature. Having no analogue in metallic systems, we identify energy mismatch as an obstacle for spin detection, necessitating control of the energy landscape of spin-tunnel contacts to semiconductors
Sign of tunnel spin polarization of low-work-function Gd/Co nanolayers in a magnetic tunnel junction
Magnetic tunnel junctions having a low-work-function Gd/Co nanolayer at the interface with an Al2O3 tunnel barrier are shown to exhibit both positive and negative values of the tunnel magnetoresistance. The sign of the tunnel spin polarization of the Gd/Co nanolayer electrode depends on the thickness of the Gd and Co layers, temperature, and applied voltage. This reflects the nature of the interaction between the conduction electrons of the rare-earth and transition metals. \u
Improved Approximation Algorithms for Stochastic Matching
In this paper we consider the Stochastic Matching problem, which is motivated
by applications in kidney exchange and online dating. We are given an
undirected graph in which every edge is assigned a probability of existence and
a positive profit, and each node is assigned a positive integer called timeout.
We know whether an edge exists or not only after probing it. On this random
graph we are executing a process, which one-by-one probes the edges and
gradually constructs a matching. The process is constrained in two ways: once
an edge is taken it cannot be removed from the matching, and the timeout of
node upper-bounds the number of edges incident to that can be probed.
The goal is to maximize the expected profit of the constructed matching.
For this problem Bansal et al. (Algorithmica 2012) provided a
-approximation algorithm for bipartite graphs, and a -approximation for
general graphs. In this work we improve the approximation factors to
and , respectively.
We also consider an online version of the bipartite case, where one side of
the partition arrives node by node, and each time a node arrives we have to
decide which edges incident to we want to probe, and in which order. Here
we present a -approximation, improving on the -approximation of
Bansal et al.
The main technical ingredient in our result is a novel way of probing edges
according to a random but non-uniform permutation. Patching this method with an
algorithm that works best for large probability edges (plus some additional
ideas) leads to our improved approximation factors
Tunnel spin polarization of Ni80Fe20/SiO2 probed with a magnetic tunnel transistor
The tunnel spin polarization of Ni80Fe20/SiO2 interfaces has been investigated using a magnetic tunnel transistor (MTT). The MTT with a Ni80Fe20/SiO2 emitter shows a magnetocurrent of 74% at 100 K, corresponding to a tunnel spin polarization of the Ni80Fe20/SiO2 interface of 27%. This is only slightly lower than the value of 34% for Ni80Fe20/Al2O3 interfaces determined in similar MTT structures. This suggests that SiO2 can be applied in semiconductor spintronic devices, for example in ferromagnet/SiO2/Si tunnel contacts for spin injection.\ud
\u
Opposite Spin Asymmetry of Elastic and Inelastic Scattering of Nonequilibrium Holes Injected into a Ferromagnet
The spin asymmetry of elastic and inelastic scattering of nonequilibrium holes injected into Co thin films is examined using a p-type magnetic tunnel transistor. Spin-dependent transmission yields a positive or negative magnetocurrent depending on Co thickness and hole energy. Up to a critical thickness of about 3 nm, (quasi)elastic scattering dominates with a short attenuation length (<1 nm) and preferential attenuation of holes in the majority spin bands, consistent with spin-wave emission. At a larger Co thickness, inelastic scattering dominates with a larger attenuation length (~4 nm) and opposite spin asymmetry
Preventive youth health care in 11 European countries: an exploratory analysis
Objective: To systematically identify similarities and differences in the way preventive youth health care (YHC) is organized in 11 European countries. - \ud
Method: Questionnaire survey to EUSUHM (European Union for School and University Health and Medicine) representatives. - \ud
Results: The greatest similarities were found in the age range of the YHC target group and the separation of curative and preventive services. Croatia, Germany and Switzerland show the greatest differences when compared to other European countries, for example, in the access to medical records, YHC professional input and the number of examinations, immunizations and screenings. In eight countries YHC is financed by national insurances or taxation. In Germany, FYR Macedonia, the Netherlands, Russia and Switzerland, different forms of financing exist in parallel. - Conclusion The results should be interpreted as a preliminary step in mapping organizational features of YHC in Europe
Socio-Economic Status of Rural Scheduled Caste Female Students in Higher Education
The present study is concerned with Scheduled Caste (SC) female students in higher education and its major focus is on socioeconomic background. It is indeed difficult to point the social and educational status of women including untouchability throughout Indian history till the down of the independence on the canvas of a limited space. To analyze the Socio-economic background of the SC female students in higher education,the area of the study has been confined to Tumkur town. The sample size of 250 students was drawn on the basis of simple random technique. The sample size was fixed in view of time and the availability of other resources. The major tool of collection of primary data has been the interview scheduled. The primary data collected from the students have been supplemented by relevant secondary data. Majority (98.80) of students are distributed in the younger or middle age group only a small 1.20 percent is in the older age group. Out of 250 respondents, the overwhelming majority (97.20) is unmarried and only a negligible 2.80 percent are a married. 234 (93.60%) respondents out of 250 belong to nuclear type families and a small 6.40 percent to extended families. Majority (60.40%) preferred Kannada as the medium of instructions for the present course while more than one third (39.60%) preferred English. This study is basically exploratory in nature. As such it cannot make tall climes about the relevance it its findings. But the prime motive of the study is SC women are institutional problems of the SCs including hour is to remodel or redesign our institutional arrangements
Landauer Theory, Inelastic Scattering and Electron Transport in Molecular Wires
In this paper we address the topic of inelastic electron scattering in
mesoscopic quantum transport. For systems where only elastic scattering is
present, Landauer theory provides an adequate description of transport that
relates the electronic current to single-particle transmission and reflection
probabilities. A formalism proposed recently by Bonca and Trugman facilitates
the calculation of the one-electron transmission and reflection probabilities
for inelastic processes in mesoscopic conductors connected to one-dimensional
ideal leads. Building on their work, we have developed a self-consistent
procedure for the evaluation of the non-equilibrium electron distributions in
ideal leads connecting such mesoscopic conductors to electron reservoirs at
finite temperatures and voltages. We evaluate the net electronic current
flowing through the mesoscopic device by utilizing these non-equilibrium
distributions. Our approach is a generalization of Landauer theory that takes
account of the Pauli exclusion principle for the various competing elastic and
inelastic processes while satisfying the requirement of particle conservation.
As an application we examine the influence of elastic and inelastic scattering
on conduction through a two site molecular wire with longitudinal phonons using
the Su-Schrieffer-Heeger model of electron-phonon coupling.Comment: 25 pages, 8 figure
Hamiltonian Analysis of Non-Linear Sigma Model on Supercoset Target
This paper is devoted to the study of the Hamiltonian formulation of
non-linear sigma models on supercoset targets. We calculate the Poisson
brackets of left-invariant currents. Then we introduce the Hamiltonian of the
system and determine the equations of motion for left-invariant currents. We
also determine the charge corresponding to the invariance of the action under
global left multiplication.Comment: 17. pages,v2: references added, v3: references added, minor
correction
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