669 research outputs found
An observation of spin-valve effects in a semiconductor field effect transistor: a novel spintronic device
We present the first spintronic semiconductor field effect transistor.
The injector and collector contacts of this device were made from magnetic
permalloy thin films with different coercive fields so that they could be
magnetized either parallel or antiparallel to each other in different applied
magnetic fields. The conducting medium was a two dimensional electron gas
(2DEG) formed in an AlSb/InAs quantum well.
Data from this device suggest that its resistance is controlled by two
different types of spin-valve effect: the first occurring at the
ferromagnet-2DEG interfaces; and the second occuring in direct propagation
between contacts.Comment: 4 pages, 2 figure
Quantized charge transport through a static quantum dot using a surface acoustic wave
We present a detailed study of the surface acoustic wave mediated quantized
transport of electrons through a split gate device containing an impurity
potential defined quantum dot within the split gate channel. A new regime of
quantized transport is observed at low RF powers where the surface acoustic
wave amplitude is comparable to the quantum dot charging energy. In this regime
resonant transport through the single-electron dot state occurs which we
interpret as turnstile-like operation in which the traveling wave amplitude
modulates the entrance and exit barriers of the quantum dot in a cyclic fashion
at GHz frequencies. For high RF powers, where the amplitude of the surface
acoustic wave is much larger than the quantum dot energies, the quantized
acoustoelectric current transport shows behavior consistent with previously
reported results. However, in this regime, the number of quantized current
plateaus observed and the plateau widths are determined by the properties of
the quantum dot, demonstrating that the microscopic detail of the potential
landscape in the split gate channel has a profound influence on the quantized
acoustoelectric current transport.Comment: 9 page
Entanglement in SU(2)-invariant quantum spin systems
We analyze the entanglement of SU(2)-invariant density matrices of two spins
, using the Peres-Horodecki criterion. Such density
matrices arise from thermal equilibrium states of isotropic spin systems. The
partial transpose of such a state has the same multiplet structure and
degeneracies as the original matrix with eigenvalue of largest multiplicity
being non-negative. The case , can be solved completely
and is discussed in detail with respect to isotropic Heisenberg spin models.
Moreover, in this case the Peres-Horodecki ciriterion turns out to be a
sufficient condition for non-separability. We also characterize SU(2)-invariant
states of two spins of length 1.Comment: 5 page
Coset Space Dimensional Reduction and Wilson Flux Breaking of Ten-Dimensional N=1, E(8) Gauge Theory
We consider a N=1 supersymmetric E(8) gauge theory, defined in ten dimensions
and we determine all four-dimensional gauge theories resulting from the
generalized dimensional reduction a la Forgacs-Manton over coset spaces,
followed by a subsequent application of the Wilson flux spontaneous symmetry
breaking mechanism. Our investigation is constrained only by the requirements
that (i) the dimensional reduction leads to the potentially phenomenologically
interesting, anomaly free, four-dimensional E(6), SO(10) and SU(5) GUTs and
(ii) the Wilson flux mechanism makes use only of the freely acting discrete
symmetries of all possible six-dimensional coset spaces.Comment: 45 pages, 2 figures, 10 tables, uses xy.sty, longtable.sty,
ltxtable.sty, (a shorter version will be published in Eur. Phys. J. C
Simulation techniques for cosmological simulations
Modern cosmological observations allow us to study in great detail the
evolution and history of the large scale structure hierarchy. The fundamental
problem of accurate constraints on the cosmological parameters, within a given
cosmological model, requires precise modelling of the observed structure. In
this paper we briefly review the current most effective techniques of large
scale structure simulations, emphasising both their advantages and
shortcomings. Starting with basics of the direct N-body simulations appropriate
to modelling cold dark matter evolution, we then discuss the direct-sum
technique GRAPE, particle-mesh (PM) and hybrid methods, combining the PM and
the tree algorithms. Simulations of baryonic matter in the Universe often use
hydrodynamic codes based on both particle methods that discretise mass, and
grid-based methods. We briefly describe Eulerian grid methods, and also some
variants of Lagrangian smoothed particle hydrodynamics (SPH) methods.Comment: 42 pages, 16 figures, accepted for publication in Space Science
Reviews, special issue "Clusters of galaxies: beyond the thermal view",
Editor J.S. Kaastra, Chapter 12; work done by an international team at the
International Space Science Institute (ISSI), Bern, organised by J.S.
Kaastra, A.M. Bykov, S. Schindler & J.A.M. Bleeke
Ordovician (Floian-lower Darriwilian) conodont biofacies of the San Juan Formation in the Cerro Viejo of Huaco, Argentine Precordillera
The conodont biofacies from the San Juan Formation at the Cerro Viejo of Huaco, Central Precordillera of Argentina, are analyzed for the identification of faunal dynamics and sea-level changes. The Prioniodus elegans and Oepikodus evae zones, Floian in age (Lower Ordovician), are identified in the lower San Juan Formation at the inner part of the Huaco anticline. In the western flank of the anticline the succession of the carbonate stratigraphic unit extends from the Floian/Dapingian boundary (Lower-Middle Ordovician) up to the lower Darriwilian (Middle Ordovician) Lenodus variabilis Zone. For the interpretation of conodont biofacies through the Los Gatos creek section, 5044 conodonts from rock samples of the Floian to the lower Darriwilian are studied. Conodont abundance and generic diversity graphs, and cluster analysis, reveal the following biofacies. The Juanognathus-Bergstroemognathus, Protopanderodus-Reutterodus-Drepanodus, Protopanderodus-Oepikodus, Juanognathus-Semiacontiodus and Rossodus-Periodon-Protopanderodus biofacies are determined, which indicate various deposits stacking from inner to middle and outer carbonate ramp environments of the San Juan Formation. The associated analysis of biofacies and lithology allow for the recognition of two transgressive events in the San Juan Formation at the Los Gatos creek section, which could be related to transgressive systems tracts (TST) that occurred during the Lower and Middle Ordovician. The recovered conodonts have a CAI that varies from 2 to 2.5, indicating a burial paleotemperature between 60 and 155 °C. Furthermore, the variation of CAI in conodonts of the same sample, the presence of conodonts with corroded surface lamella, recrystallization and crystal overgrowths, and the presence of stylolites in limestone beds of the San Juan Formation indicate the circulation of hydrothermal fluids.Fil: Mango, Matías Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; ArgentinaFil: Albanesi, Guillermo Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentin
Shrinking a large dataset to identify variables associated with increased risk of Plasmodium falciparum infection in Western Kenya
Large datasets are often not amenable to analysis using traditional single-step approaches. Here, our general objective was to apply imputation techniques, principal component analysis (PCA), elastic net and generalized linear models to a large dataset in a systematic approach to extract the most meaningful predictors for a health outcome. We extracted predictors for Plasmodium falciparum infection, from a large covariate dataset while facing limited numbers of observations, using data from the People, Animals, and their Zoonoses (PAZ) project to demonstrate these techniques: data collected from 415 homesteads in western Kenya, contained over 1500 variables that describe the health, environment, and social factors of the humans, livestock, and the homesteads in which they reside. The wide, sparse dataset was simplified to 42 predictors of P. falciparum malaria infection and wealth rankings were produced for all homesteads. The 42 predictors make biological sense and are supported by previous studies. This systematic data-mining approach we used would make many large datasets more manageable and informative for decision-making processes and health policy prioritization
Global Search for New Physics with 2.0/fb at CDF
Data collected in Run II of the Fermilab Tevatron are searched for
indications of new electroweak-scale physics. Rather than focusing on
particular new physics scenarios, CDF data are analyzed for discrepancies with
the standard model prediction. A model-independent approach (Vista) considers
gross features of the data, and is sensitive to new large cross-section
physics. Further sensitivity to new physics is provided by two additional
algorithms: a Bump Hunter searches invariant mass distributions for "bumps"
that could indicate resonant production of new particles; and the Sleuth
procedure scans for data excesses at large summed transverse momentum. This
combined global search for new physics in 2.0/fb of ppbar collisions at
sqrt(s)=1.96 TeV reveals no indication of physics beyond the standard model.Comment: 8 pages, 7 figures. Final version which appeared in Physical Review D
Rapid Communication
Measurement of the Bottom-Strange Meson Mixing Phase in the Full CDF Data Set
We report a measurement of the bottom-strange meson mixing phase \beta_s
using the time evolution of B0_s -> J/\psi (->\mu+\mu-) \phi (-> K+ K-) decays
in which the quark-flavor content of the bottom-strange meson is identified at
production. This measurement uses the full data set of proton-antiproton
collisions at sqrt(s)= 1.96 TeV collected by the Collider Detector experiment
at the Fermilab Tevatron, corresponding to 9.6 fb-1 of integrated luminosity.
We report confidence regions in the two-dimensional space of \beta_s and the
B0_s decay-width difference \Delta\Gamma_s, and measure \beta_s in [-\pi/2,
-1.51] U [-0.06, 0.30] U [1.26, \pi/2] at the 68% confidence level, in
agreement with the standard model expectation. Assuming the standard model
value of \beta_s, we also determine \Delta\Gamma_s = 0.068 +- 0.026 (stat) +-
0.009 (syst) ps-1 and the mean B0_s lifetime, \tau_s = 1.528 +- 0.019 (stat) +-
0.009 (syst) ps, which are consistent and competitive with determinations by
other experiments.Comment: 8 pages, 2 figures, Phys. Rev. Lett 109, 171802 (2012
Towards a greater dialogue on disability between Muslims and Christians
Attitudes to disability and disabled people by Muslims – focusing on attitudes in the Middle East and North Africa - and Christians – focusing on the West (here taken to mean Europe, North America and Australasia) - were examined through a grounded theory literature search, with the study being divided into three phases of reading and analysis. The aims of study were to develop a dialogue on disability between the two cultures, to inform an understanding of the attitudes to disability in the two cultures, and to inform cultural practice in promoting support and equality in both cultures. The study finds that Islam and Christianity have much in common and are a force for good in promoting and developing disability equality in both Muslim and Christian cultures
- …