961 research outputs found
Nonmonotonic inelastic tunneling spectra due to surface spin excitations in ferromagnetic junctions
The paper addresses inelastic spin-flip tunneling accompanied by surface spin
excitations (magnons) in ferromagnetic junctions. The inelastic tunneling
current is proportional to the magnon density of states which is
energy-independent for the surface waves and, for this reason, cannot account
for the bias-voltage dependence of the observed inelastic tunneling spectra.
This paper shows that the bias-voltage dependence of the tunneling spectra can
arise from the tunneling matrix elements of the electron-magnon interaction.
These matrix elements are derived from the Coulomb exchange interaction using
the itinerant-electron model of magnon-assisted tunneling. The results for the
inelastic tunneling spectra, based on the nonequilibrium Green's function
calculations, are presented for both parallel and antiparallel magnetizations
in the ferromagnetic leads.Comment: 9 pages, 4 figures, version as publishe
The Korringa-Kohn-Rostoker Non-Local Coherent Potential Approximation (KKR-NLCPA)
We introduce the Korringa-Kohn-Rostocker non-local coherent potential
approximation (KKR-NLCPA) for describing the electronic structure of disordered
systems. The KKR-NLCPA systematically provides a hierarchy of improvements upon
the widely used KKR-CPA approach and includes non-local correlations in the
disorder configurations by means of a self-consistently embedded cluster. The
KKR-NLCPA method satisfies all of the requirements for a successful cluster
generalization of the KKR-CPA; it remains fully causal, becomes exact in the
limit of large cluster sizes, reduces to the KKR-CPA for a single-site cluster,
is straightforward to implement numerically, and enables the effects of
short-range order upon the electronic structure to be investigated. In
particular, it is suitable for combination with electronic density functional
theory to give an ab-initio description of disordered systems. Future
applications to charge correlation and lattice displacement effects in alloys
and spin fluctuations in magnets amongst others are very promising. We
illustrate the method by application to a simple one-dimensional model.Comment: Revised versio
MMN and Differential Waveform
A mismatch negativity response (MMN) and a new differential waveform were derived in an effort to evaluate a neural refractory or recovery effect in adult listeners. The MMN was elicited using oddball test runs in which the standard and deviant stimuli differed in frequency. To derive the differential waveform, the same standard and deviant stimuli were presented alone. MMN responses were obtained by subtracting the averaged responses to standards from the deviants. The differential waveforms were obtained by subtracting the averaged responses to standards presented alone from deviants presented alone. Scalp topography for the MMN and differential waveforms were similar. A significant (p < .05) positive and negative correlation was found between the earlier and later components of the bimodal MMN and the N1 and P2 component of the differential waveform, respectively. Further, N1 and P2 of the differential waveform were significant (p < .05) predictor variables of early and late peak amplitudes of the MMN. These results suggest that refractory effects may overlay/modify the morphology of the MMN waveform
Towards optical polarization control of laser-driven proton acceleration in foils undergoing relativistic transparency
Control of the collective response of plasma particles to intense laser light is intrinsic to relativistic optics, the development of compact laser-driven particle and radiation sources, as well as investigations of some laboratory astrophysics phenomena. We recently demonstrated that a relativistic plasma aperture produced in an ultra-thin foil at the focus of intense laser radiation can induce diffraction, enabling polarization-based control of the collective motion of plasma electrons. Here we show that under these conditions the electron dynamics are mapped into the beam of protons accelerated via strong charge-separation-induced electrostatic fields. It is demonstrated experimentally and numerically via 3D particle-in-cell simulations that the degree of ellipticity of the laser polarization strongly influences the spatial-intensity distribution of the beam of multi-MeV protons. The influence on both sheath accelerated and radiation pressure accelerated protons is investigated. This approach opens up new routes to control laser-driven ion sources
Atmospheric Neutrino Oscillations and New Physics
We study the robustness of the determination of the neutrino masses and
mixing from the analysis of atmospheric and K2K data under the presence of
different forms of phenomenologically allowed new physics in the nu_mu--nu_tau
sector. We focus on vector and tensor-like new physics interactions which allow
us to treat, in a model independent way, effects due to the violation of the
equivalence principle, violations of the Lorentz invariance both CPT conserving
and CPT violating, non-universal couplings to a torsion field and non-standard
neutrino interactions with matter. We perform a global analysis of the full
atmospheric data from SKI together with long baseline K2K data in the presence
of nu_mu -> nu_tau transitions driven by neutrino masses and mixing together
with sub-dominant effects due to these forms of new physics. We show that
within the present degree of experimental precision, the extracted values of
masses and mixing are robust under those effects and we derive the upper bounds
on the possible strength of these new interactions in the nu_mu--nu_tau sector.Comment: 22 pages, LaTeX file using RevTEX4, 5 figures and 4 tables include
Random Series and Discrete Path Integral methods: The Levy-Ciesielski implementation
We perform a thorough analysis of the relationship between discrete and
series representation path integral methods, which are the main numerical
techniques used in connection with the Feynman-Kac formula. First, a new
interpretation of the so-called standard discrete path integral methods is
derived by direct discretization of the Feynman-Kac formula. Second, we
consider a particular random series technique based upon the Levy-Ciesielski
representation of the Brownian bridge and analyze its main implementations,
namely the primitive, the partial averaging, and the reweighted versions. It is
shown that the n=2^k-1 subsequence of each of these methods can also be
interpreted as a discrete path integral method with appropriate short-time
approximations. We therefore establish a direct connection between the discrete
and the random series approaches. In the end, we give sharp estimates on the
rates of convergence of the partial averaging and the reweighted
Levy-Ciesielski random series approach for sufficiently smooth potentials. The
asymptotic rates of convergence are found to be O(1/n^2), in agreement with the
rates of convergence of the best standard discrete path integral techniques.Comment: 20 pages, 4 figures; the two equations before Eq. 14 are corrected;
other typos are remove
Colloquium: Mechanical formalisms for tissue dynamics
The understanding of morphogenesis in living organisms has been renewed by
tremendous progressin experimental techniques that provide access to
cell-scale, quantitative information both on theshapes of cells within tissues
and on the genes being expressed. This information suggests that
ourunderstanding of the respective contributions of gene expression and
mechanics, and of their crucialentanglement, will soon leap forward.
Biomechanics increasingly benefits from models, which assistthe design and
interpretation of experiments, point out the main ingredients and assumptions,
andultimately lead to predictions. The newly accessible local information thus
calls for a reflectionon how to select suitable classes of mechanical models.
We review both mechanical ingredientssuggested by the current knowledge of
tissue behaviour, and modelling methods that can helpgenerate a rheological
diagram or a constitutive equation. We distinguish cell scale ("intra-cell")and
tissue scale ("inter-cell") contributions. We recall the mathematical framework
developpedfor continuum materials and explain how to transform a constitutive
equation into a set of partialdifferential equations amenable to numerical
resolution. We show that when plastic behaviour isrelevant, the dissipation
function formalism appears appropriate to generate constitutive equations;its
variational nature facilitates numerical implementation, and we discuss
adaptations needed in thecase of large deformations. The present article
gathers theoretical methods that can readily enhancethe significance of the
data to be extracted from recent or future high throughput
biomechanicalexperiments.Comment: 33 pages, 20 figures. This version (26 Sept. 2015) contains a few
corrections to the published version, all in Appendix D.2 devoted to large
deformation
Resonances of low orders in the planetary system of HD37124
The full set of published radial velocity data (52 measurements from Keck +
58 ones from ELODIE + 17 ones from CORALIE) for the star HD37124 is analysed.
Two families of dynamically stable high-eccentricity orbital solutions for the
planetary system are found. In the first one, the outer planets c and d are
trapped in the 2/1 mean-motion resonance. The second family of solutions
corresponds to the 5/2 mean-motion resonance between these planets. In both
families, the planets are locked in (or close to) an apsidal corotation
resonance. In the case of the 2/1 MMR, it is an asymmetric apsidal corotation
(with the difference between the longitudes of periastra ), whereas in the case of the 5/2 MMR it is a symmetric antialigned
one ().
It remains also possible that the two outer planets are not trapped in an
orbital resonance. Then their orbital eccentricities should be relatively small
(less than, say, 0.15) and the ratio of their orbital periods is unlikely to
exceed .Comment: 28 pages, 10 figures, 3 tables; Accepted to Celestial Mechanics and
Dynamical Astronom
Predictors of cardiac troponin release after a marathon
Objectives: Exercise leads to an increase in cardiac troponin I in healthy, asymptomatic athletes after a marathon. Previous studies revealed single factors to relate to post-race cardiac troponin I levels. Integrating these factors into our study, we aimed to identify independent predictors for the exercise-induced cardiac troponin I release. Design: Observational study. Methods: Ninety-two participants participated in a marathon at a self-selected speed. Demographic data, health status, physical activity levels and marathon experience were obtained. Before and immediately after the marathon fluid intake was recorded, body mass changes were measured to determine fluid balance and venous blood was drawn for analysis of high-sensitive cardiac troponin I. Exercise intensity was examined by recording heart rate. We included age, participation in previous marathons, exercise duration, exercise intensity and hydration status (relative weight change) in our model as potential determinants to predict post-exercise cardiac troponin I level. Results: Cardiac troponin I increased significantly from 14. ±. 12. ng/L at baseline to 94. ±. 102. ng/L post-race, with 69% of the participants demonstrating cardiac troponin I levels above the clinical cut-off value (40. ng/L) for an acute myocardial infarction. Linear backward regression analysis identified younger age (β=. -0.27) and longer exercise duration (β=. 0.23) as significant predictors of higher post-race cardiac troponin I levels (total r=. 0.31, p<. 0.05), but not participation in previous marathons, relative weight change and exercise intensity. Conclusions: We found that cardiac troponin I levels significantly increased in a large heterogeneous group of athletes after completing a marathon. The magnitude of this response could only be partially explained, with a lower age and longer exercise duration being related to higher post-race cardiac troponin I levels
Search for W' bosons decaying to an electron and a neutrino with the D0 detector
This Letter describes the search for a new heavy charged gauge boson W'
decaying into an electron and a neutrino. The data were collected with the D0
detector at the Fermilab Tevatron proton-antiproton Collider at a
center-of-mass energy of 1.96 TeV, and correspond to an integrated luminosity
of about 1 inverse femtobarn. Lacking any significant excess in the data in
comparison with known processes, an upper limit is set on the production cross
section times branching fraction, and a W' boson with mass below 1.00 TeV can
be excluded at the 95% C.L., assuming standard-model-like couplings to
fermions. This result significantly improves upon previous limits, and is the
most stringent to date.Comment: submitted to Phys. Rev. Let
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