101 research outputs found
Amplitude-Frequency Characteristic of a Neural Control Based DC Drive
The paper interprets characteristics of a neural-control-based DC servodrive in terms of the classical theory of automatic control. It also touches on the problem of choosing training patterns to synthesize a nonlinear PID-controller with a desired amplitude-frequency characteristic and analyses the efficiency of using for this purpose input signals in form of a step function and a harmonic one. Synthesis of the neurocontroller has been performed within the framework of a three-layer perceptron. To train it, a genetic algorithm has been developed
Geoinformation modeling of socio-ecological safety of rural areas on the example of settlements of the Belgorod region
In the course of the study, geoinformation resources were created for the rural areas of the Belgorod region. The created GIS consists of a system of hierarchically subordinate sections of rural territories of the Belgorod region - agrolandscapes of Strigunovsky (Borisovsky district), as well as Obukhovsky (Starooskolsky urban district) and Dolgopolyansky (Starooskolsky district) rural settlement
Photon propagation in magnetic and electric fields with scalar/pseudoscalar couplings: a new look
We consider the minimal coupling of two photons to neutral scalar and
pseudoscalar fields, as for instance in the case of the Higgs boson and axion,
respectively. In this framework, we analyze the photon dispersion relations in
the presence of static and homogeneous external magnetic and electric fields,
by taking into account the contribution of the imaginary part of the
scalar/pseudoscalar self-energy. We show that this contribution cannot be
neglected when it is of the same order as the photon-scalar/pseudoscalar mixing
term. In addition to the usual light-like photon propagation mode, with a
refraction index n > 1, a massive mode with mass of the order of the coupled
boson mass can be induced, provided that the external field is above a
particular critical value. Depending on the values of the external field,
photon energy, and mass of the scalar/pseudoscalar particle, the
scalar/pseudoscalar width could induce a sizeable rate of photon splitting in
two photons due to a strong resonant phenomenon. This effect has no practical
laboratory applications for the Higgs physics due to the very large critical
external magnetic or electric fields involved, for a photon energy of the order
of a TeV. However, it can have relevant consequences in the axion physics or in
any other scenario where light neutral scalar/pseudoscalar fields have minimal
coupling with two photons.Comment: 40 pages, LaTeX, 5.eps Figures, new appendix and results included,
misprints corrected, conclusions unchanged. Version to appear on Phys. Rev.
Axions, their Relatives and Prospects for the Future
The observation of a non-vanishing rotation of linear polarized laser light
after passage through a strong magnetic field by the PVLAS collaboration has
renewed the interest in light particles coupled to photons. Axions are a
species of such particles that is theoretically well motivated. However, the
relation between coupling and mass predicted by standard axion models conflicts
with the PVLAS observation. Moreover, light particles with a coupling to
photons of the strength required to explain PVLAS face trouble from
astrophysical bounds. We discuss models that can avoid these bounds. Finally,
we present some ideas to test these possible explanations of PVLAS
experimentally.Comment: 11 pages, 4 figures. Contributed to the ``Third Symposium on Large
TPCs for Low Energy Rare Event Detection'' in Paris, December 200
Scattering of scalar and Dirac particles by a magnetic tube of finite radius
We consider the Dirac equation in cylindrically symmetric magnetic fields and
find its normal modes as eigenfunctions of a complete set of commuting
operators. This set consists of the Dirac operator itself, the -components
of the linear and the total angular momenta, and of one of the possible spin
polarization operators. The spin structure of the solution is completely fixed
independently of the radial distribution of the magnetic field which influences
only the radial modes. We solve explicitly the radial equations for the uniform
magnetic field inside a solenoid of a finite radius and consider in detail the
scattering of scalar and Dirac particles in this field. For particles with low
energy the scattering cross section coincides with the Aharonov-Bohm scattering
cross section. We work out the first order corrections to this result caused by
the fact that the solenoid radius is finite. At high energies we obtain the
classical result for the scattering cross section.Comment: LaTeX file, 17 page
Electron-positron pair production in the Aharonov-Bohm potential
In the framework of QED we evaluate the cross section for electron-positron
pair production by a single photon in the presence of the external
Aharonov-Bohm potential in first order of perturbation theory. We analyse
energy, angular and polarization distributions at different energy regimes:
near the threshold and at high photon energies.Comment: LaTeX file, 13 page
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