7,547 research outputs found

    Traces, high powers and one level density for families of curves over finite fields

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    Anisotropic Electron Spin Lifetime in (In,Ga)As/GaAs (110) Quantum Wells

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    Anisotropic electron spin lifetimes in strained undoped (In,Ga)As/GaAs (110) quantum wells of different width and height are investigated by time-resolved Faraday rotation and time-resolved transmission and are compared to the (001)-orientation. From the suppression of spin precession, the ratio of in-plane to out-of-plane spin lifetimes is calculated. Whereas the ratio increases with In concentration in agreement with theory, a surprisingly high anisotropy of 480 is observed for the broadest quantum well, when expressed in terms of spin relaxation times.Comment: 4 pages, 4 figures, revise

    Large magnetic circular dichroism in resonant inelastic x-ray scattering at the Mn L-edge of Mn-Zn ferrite

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    We report resonant inelastic x-ray scattering (RIXS) excited by circularly polarized x-rays on Mn-Zn ferrite at the Mn L2,3-resonances. We demonstrate that crystal field excitations, as expected for localized systems, dominate the RIXS spectra and thus their dichroic asymmetry cannot be interpreted in terms of spin-resolved partial density of states, which has been the standard approach for RIXS dichroism. We observe large dichroic RIXS at the L2-resonance which we attribute to the absence of metallic core hole screening in the insulating Mn-ferrite. On the other hand, reduced L3-RIXS dichroism is interpreted as an effect of longer scattering time that enables spin-lattice core hole relaxation via magnons and phonons occurring on a femtosecond time scale.Comment: 7 pages, 2 figures, http://link.aps.org/doi/10.1103/PhysRevB.74.17240

    Goals and their associations with beliefs about success in and perceptions of the purpose of physical education

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    This is the publisher's version, also found at http://ehis.ebscohost.com/ehost/detail?vid=3&sid=f2fadc72-30ec-4818-a6be-17c24af97fd1%40sessionmgr13&hid=2&bdata=JnNpdGU9ZWhvc3QtbGl2ZQ%3d%3d#db=s3h&AN=SPH367545This study examined the relationship of students' goal orientation to their beliefs about what leads to success in physical education and perceptions of the purposes of physical education. High school students {N = 144,78 females and 66 males) completed a modified version of the Task and Ego Orientation in Sport Questionnaire and measures of beliefs and perceived purposes specific to physical education class. Results indicated that students high in task orientation were significantly more likely to believe that success is achieved through intrinsic interest/effort/cooperation than were those low in task orientation. High ego-oriented students believed that success is achieved when students possess high ability more so than low ego-oriented students. The high task/low ego students were most likely to reject the notion that success in physical education occurs when students know how to use deceptive tactics and were less likely to perceive that an important function of physical education is to provide an easy class

    Dynamic quantum clustering: a method for visual exploration of structures in data

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    A given set of data-points in some feature space may be associated with a Schrodinger equation whose potential is determined by the data. This is known to lead to good clustering solutions. Here we extend this approach into a full-fledged dynamical scheme using a time-dependent Schrodinger equation. Moreover, we approximate this Hamiltonian formalism by a truncated calculation within a set of Gaussian wave functions (coherent states) centered around the original points. This allows for analytic evaluation of the time evolution of all such states, opening up the possibility of exploration of relationships among data-points through observation of varying dynamical-distances among points and convergence of points into clusters. This formalism may be further supplemented by preprocessing, such as dimensional reduction through singular value decomposition or feature filtering.Comment: 15 pages, 9 figure

    Identification of network modules by optimization of ratio association

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    We introduce a novel method for identifying the modular structures of a network based on the maximization of an objective function: the ratio association. This cost function arises when the communities detection problem is described in the probabilistic autoencoder frame. An analogy with kernel k-means methods allows to develop an efficient optimization algorithm, based on the deterministic annealing scheme. The performance of the proposed method is shown on a real data set and on simulated networks

    A semi-implicit version of the MPAS-atmosphere dynamical core

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    An important question for atmospheric modeling is the viability of semi-implicit time integration schemes on massively parallel computing architectures. Semi-implicit schemes can provide increased stability and accuracy. However, they require the solution of an elliptic problem at each time step, creating concerns about their parallel efficiency and scalability. Here, a semi-implicit (SI) version of the Model for Prediction Across Scales (MPAS) is developed and compared with the original model version, which uses a split Runge-Kutta (SRK3) time integration scheme. The SI scheme is based on a quasi-Newton iteration toward a Crank-Nicolson scheme. Each Newton iteration requires the solution of a Helmholtz problem; here, the Helmholtz problem is derived, and its solution using a geometric multigrid method is described. On two standard test cases, a midlatitude baroclinic wave and a small-planet nonhydrostatic gravity wave, the SI and SRK3 versions produce almost identical results. On the baroclinic wave test, the SI version can use somewhat larger time steps (about 60%) than the SRK3 version before losing stability. The SI version costs 10%-20% more per step than the SRK3 version, and the weak and strong scalability characteristics of the two versions are very similar for the processor configurations the authors have been able to test (up to 1920 processors). Because of the spatial discretization of the pressure gradient in the lowest model layer, the SI version becomes unstable in the presence of realistic orography. Some further work will be needed to demonstrate the viability of the SI scheme in this case.UK Natural Environment Research Council as part of the G8 ICOMEX projec
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