The Experts below are selected from a list of 144072 Experts worldwide ranked by ideXlab platform
Yaping Shao - One of the best experts on this subject based on the ideXlab platform.
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a note on the stochastic nature of particle cohesive force and implications to threshold friction velocity for aerodynamic dust entrainment
2016Co-Authors: Yaping Shao, Martina KloseAbstract:Abstract There is considerable interest to determine the threshold for aeolian dust emission on Earth and Mars. Existing schemes for threshold friction velocity are all deterministic in nature, but observations show that in the dust particle size range the threshold friction velocity scatters strongly due to stochastic inter-particle cohesion. In the real world, there always exists a certain amount of free dust which can be easily lifted from the surface by weak winds or even turbulence, as exemplified by dust devils. It has been proposed in the dust-devil research community, that the pressure drop at dust-devil center may be a major mechanism for dust-devil dust emission, known as the Δp effect. It is questioned here whether the Δp effect is substantial or whether the elevated dust concentration in dust devils is due to free dust emission. A Simple analysis indicates that the Δp effect appears to be small and the dust in dust devils is probably due to free dust emission and dust convergence. To estimate free dust emission, it is useful to define a lower limit of dust-particle threshold friction velocity. A Simple Expression for this velocity is proposed by making assumptions to the median and variance of inter-particle cohesive force. The Simple Expression is fitted to the data of the Arizona State University Vortex Generator. While considerable uncertainty remains in the scheme, this note highlights the need for additional research on the stochastic nature of dust emission.
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a Simple Expression for wind erosion threshold friction velocity
2000Co-Authors: Yaping ShaoAbstract:Threshold friction velocity u*t is the friction velocity at which wind erosion is initiated. While u*t is affected by a range of surface and soil properties, it is a function of particle size only for idealized soils. In this paper we present a Simple Expression for u*t for spherical particles loosely spread over a dry and bare surface. In this Expression we consider the balance between the driving forces (aerodynamic drag and lift) and the retarding forces (cohesion and gravity) and assume that the cohesive force is proportional to particle size. It is found that u*t can be expressed as Y1d+Y21d, with Y1 and Y2 being empirical constants. The new Expression is both Simple and effective.
Andreas Aste - One of the best experts on this subject based on the ideXlab platform.
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bound free pair production cross section in heavy ion colliders from the equivalent photon approach
2008Co-Authors: Andreas AsteAbstract:Exact calculations of the electron-positron pair production by a single photon in the Coulomb field of a nucleus with simultaneous capture of the electron into the K-shell are discussed for different nuclear charges. Using the equivalent photon method of Weizsacker and Williams, a Simple Expression for the bound-free production of e+e− pairs by colliding very-high-energy fully stripped heavy ions is derived for nuclei of arbitrary charge.
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bound free pair production cross section in heavy ion colliders from the equivalent photon approach
2007Co-Authors: Andreas AsteAbstract:Exact calculations of the electron-positron pair production by a single photon in the Coulomb field of a nucleus with simultaneous capture of the electron into the K-shell are discussed for different nuclear charges. Using the equivalent photon method of Weizsaecker and Williams, a Simple Expression for the bound-free production of electron-positron pairs by colliding very-high-energy fully stripped heavy ions is derived for nuclei of arbitrary charge.
Martina Klose - One of the best experts on this subject based on the ideXlab platform.
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a note on the stochastic nature of particle cohesive force and implications to threshold friction velocity for aerodynamic dust entrainment
2016Co-Authors: Yaping Shao, Martina KloseAbstract:Abstract There is considerable interest to determine the threshold for aeolian dust emission on Earth and Mars. Existing schemes for threshold friction velocity are all deterministic in nature, but observations show that in the dust particle size range the threshold friction velocity scatters strongly due to stochastic inter-particle cohesion. In the real world, there always exists a certain amount of free dust which can be easily lifted from the surface by weak winds or even turbulence, as exemplified by dust devils. It has been proposed in the dust-devil research community, that the pressure drop at dust-devil center may be a major mechanism for dust-devil dust emission, known as the Δp effect. It is questioned here whether the Δp effect is substantial or whether the elevated dust concentration in dust devils is due to free dust emission. A Simple analysis indicates that the Δp effect appears to be small and the dust in dust devils is probably due to free dust emission and dust convergence. To estimate free dust emission, it is useful to define a lower limit of dust-particle threshold friction velocity. A Simple Expression for this velocity is proposed by making assumptions to the median and variance of inter-particle cohesive force. The Simple Expression is fitted to the data of the Arizona State University Vortex Generator. While considerable uncertainty remains in the scheme, this note highlights the need for additional research on the stochastic nature of dust emission.
Alexandre Pouget - One of the best experts on this subject based on the ideXlab platform.
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insights from a Simple Expression for linear fisher information in a recurrently connected population of spiking neurons
2011Co-Authors: Jeffrey M Beck, Vikranth R Bejjanki, Alexandre PougetAbstract:A Simple Expression for a lower bound of Fisher information is derived for a network of recurrently connected spiking neurons that have been driven to a noise-perturbed steady state. We call this lower bound linear Fisher information, as it corresponds to the Fisher information that can be recovered by a locally optimal linear estimator. Unlike recent similar calculations, the approach used here includes the effects of nonlinear gain functions and correlated input noise and yields a surprisingly Simple and intuitive Expression that offers substantial insight into the sources of information degradation across successive layers of a neural network. Here, this Expression is used to (1) compute the optimal (i.e., information-maximizing) firing rate of a neuron, (2) demonstrate why sharpening tuning curves by either thresholding or the action of recurrent connectivity is generally a bad idea, (3) show how a single cortical expansion is sufficient to instantiate a redundant population code that can propagate across multiple cortical layers with minimal information loss, and (4) show that optimal recurrent connectivity strongly depends on the covariance structure of the inputs to the network.
Takayuki Fujii - One of the best experts on this subject based on the ideXlab platform.
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a note on the asymptotic distribution of the maximum likelihood estimator in a non regular case
2007Co-Authors: Takayuki FujiiAbstract:We consider the asymptotic distribution of the maximum likelihood estimator (MLE), when the log-likelihood ratio statistic weakly converges to the non-degenerated Gaussian process. We provide a Simple Expression for the density function of the asymptotic distribution by fundamental stochastic results. This note is helpful to investigate asymptotic properties of the MLE in a certain non-regular case.
