An expression for ponderomotive force caused by electromagnetic fields is derived from Valsov-Maxwell equations in a non-stationary, unmagnetized plasma. Comparison between our result and earlier ones is given.
An expression for ponderomotive force caused by electromagnetic fields is derived from Valsov-Maxwell equations in a non-stationary, unmagnetized plasma. Comparison between our result and earlier ones is given.
Previous results on nonlearnability of visual concepts relied on the assumption that such concepts are represented as sets of pixels [1]. This correspondence uses an approach developed by Haussler [2] to show that und...
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Previous results on nonlearnability of visual concepts relied on the assumption that such concepts are represented as sets of pixels [1]. This correspondence uses an approach developed by Haussler [2] to show that under an alternative, feature-based representation, recognition is PAC learnable from a feasible number of examples in a distribution-free manner.
Infinite, recursive versions of NP optimization problems are defined. For example, MAX CLIQUE becomes the question of whether a recursive graph contains an infinite clique. The work was motivated by trying to understa...
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Infinite, recursive versions of NP optimization problems are defined. For example, MAX CLIQUE becomes the question of whether a recursive graph contains an infinite clique. The work was motivated by trying to understand what makes some NP problems highly undecidable in the infinite case, while others remain on low levels of the arithmetical hierarchy. Two results are proved; one enables using knowledge about the infinite case to yield implications to the finite case, and the other enables implications in the other direction. Taken together, the two results provide a method for proving (finitary) problems to be outside the syntactic class MAX NP, hence outside MAX SNP too. The technique is illustrated with many examples.< >
Auger rates, average absorption oscillator strengths (corresponding average wavelengths) and level-to-level dielectronic recombination rate coefficients describing dielectronic recombination for F-like and Ne-like ger...
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Auger rates, average absorption oscillator strengths (corresponding average wavelengths) and level-to-level dielectronic recombination rate coefficients describing dielectronic recombination for F-like and Ne-like germanium ions are explicitly calculated. Our calculations are based on Cowan's non-relativistic multi-configuration Hartree-Fock (HFR) code which includes relativistic mass-velocity and Darwin corrections and successive subroutines for calculating average oscillator strengths and average wavelengths and dielectronic recombination rate coefficients are developed. The dielectronic recombination rate coefficients as the function of temperature of free electrons are given in an analytical form which is very convenient in practice.
For ill-posed initial value problems, step by step marching comput.tions are unconditionally unstable, and necessarily blow-up numerically as the mesh is refined. However, for the 1D nonlinear inverse heat conduction ...
For ill-posed initial value problems, step by step marching comput.tions are unconditionally unstable, and necessarily blow-up numerically as the mesh is refined. However, for the 1D nonlinear inverse heat conduction problem, we show how to construct consistent marching schemes that blow-up much more slowly than the counterpart analytical problem. Several new space marching finite difference schemes are formulated and compared with existing schemes relative to their error amplification properties. Using the Lax-Richtmyer theory, we evaluate the L2 norms of the linearized discrete solution operators mapping the sensor data into the desired temperature and gradient histories at the inaccessible active surface. Various combinations of space and time differencing are examined, leading to 18 different algorithms. A non-dimensional parameter-OMEGA, involving the time step DELTA-t, the effective thermal diffusivity-alpha, and the distance-iota from the sensor to the active surface, is shown to provide a measure of the numerical difficulty of the inverse calculation. All 18 schemes blow-up like 10-lambda-OMEGA, where the constant-lambda depends on the particular numerical method. There are substantial differences in the lambda's however, and some new algorithms, employing forward time differences at non-adjacent mesh points, are shown to produce relatively low values of lambda. Next, using synthetic noisy data, a nonlinear reconstruction problem is considered for which OMEGA = 25. This problem simulates heat transfer in gun barrels when a shell is fired. It is shown that while most of the 18 schemes cannot recover the thermal pulses at the gun tube wall, two of the new methods provide reasonably accurate results. A tendency to underestimate peak values in fast, narrow thermal pulses, is also noted.
The topics discussed here are network models of object recognition; a comput.tional theory of recognition; psychophysical support for a view-interpolation model: and an open issue, features of recognition. The authors...
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The topics discussed here are network models of object recognition; a comput.tional theory of recognition; psychophysical support for a view-interpolation model: and an open issue, features of recognition. The authors survey a successful replication of central characteristics of performance in 3-D object recognition by a comput.tional model based on interpolation among a number of stored views of each object. Network models of 3-D object recognition based on interpolation among specific stored views behave in several respects similarly to human observers in a number of recognition tasks. Even closer replication of human performance in recognition should be expected, once the issue of the features used to represent object views is resolved.< >
The energy spectrum and the eigenvectors of a charged particle in a uniform electric field with alternating site energies are studied for infinite systems. For the case of large energy mismatch, exact solutions are pr...
The energy spectrum and the eigenvectors of a charged particle in a uniform electric field with alternating site energies are studied for infinite systems. For the case of large energy mismatch, exact solutions are presented by using perturbation theory, from which it is found that the spectrum is that of two interspaced Stark ladders. The character of these Stark ladders is that the difference of the ratio of the energy and the field between two energies on a same rung is an even number.
Steady-state solutions of the 2D incompressible Euler equations (which we call V-states) are studied analytically. That is, a local expansion is done in the neighborhood of any point on the boundary of a V-state (whic...
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Steady-state solutions of the 2D incompressible Euler equations (which we call V-states) are studied analytically. That is, a local expansion is done in the neighborhood of any point on the boundary of a V-state (which consists of piecewise constant regions of vorticity). The analytical results contained in paper I by Wu, Overman, and Zabusky are proven. In particular, the limiting V-states for the numerically calculated translating and rotating V-states have $90^\circ$ corners and not cusps. It is also proven that at a point which lies on the boundary of only one region and at which the tangent angle has a jump discontinuity then the difference in tangent angles can only be $90^\circ$ (a corner) or $180^\circ$ (a cusp). The analytical behavior of doubly and triply connected rotating V-states is also investigated.
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