171 research outputs found
Interference of outgoing electromagnetic waves generated by two point-like sources
An energy-momentum carried by electromagnetic field produced by two
point-like charged particles is calculated. Integration region considered in
the evaluation of the bound and emitted quantities produced by all points of
world lines up to the end points at which particles' trajectories puncture an
observation hyperplane . Radiative part of the energy-momentum contains,
apart from usual integrals of Larmor terms, also the sum of work done by
Lorentz forces of point-like charges acting on one another. Therefore, the
combination of wave motions (retarded Li\'enard-Wiechert solutions) leads to
the interaction between the sources.Comment: 38 pages, 13 figures, LaTeX2
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
Regional geographic information systems of health and environmental monitoring
The article describes a new scientific and methodological approach to designing geographic information systems of health and environmental monitoring for urban areas. Geographic information systems (GIS) are analytical tools of the regional health and environmental monitoring; they are used for an integrated assessment of the environmental status of a large industrial centre or a part of it. The authors analyse the environmental situation in Voronezh, a major industrial city, located in the Central Black Earth Region with a population of more than 1 million people. The proposed research methodology is based on modern approaches to the assessment of health risks caused by adverse environmental conditions. The research work was implemented using a GIS and multicriteria probabilistic and statistical evaluation to identify cause-and-effect links, a combination of action and reaction, in the dichotomy "environmental factors - public health". The analysis of the obtained statistical data confirmed an increase in childhood diseases in some areas of the city. Environmentally induced diseases include congenital malformations, tumors, endocrine and urogenital pathologies. The main factors having an adverse impact on health are emissions of carcinogens into the atmosphere and the negative impact of transport on the environment. The authors identify and characterize environmentally vulnerable parts of the city and developed principles of creating an automated system of health monitoring and control of environmental risks. The article offers a number of measures aimed at the reduction of environmental risks, better protection of public health and a more efficient environmental monitoring
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.
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
Pair creation by a photon in a strong magnetic field
The process of pair creation by a photon in a strong magnetic field is
investigated basing on the polarization operator in the field. The total
probability of the process is found in a relatively simple form. The
probability exhibits a "saw-tooth" pattern because of divergences arising when
the electron and positron are created at threshold of the Landau energy levels.
The pattern will be washed out at averaging over any smooth photon energy
distribution. The new results are obtained in the scope of the quasiclassical
approach: 1) in the case when the magnetic field is the
critical field) the new formulation extends the photon energy interval to the
case when the created particles are not ultrarelativistic; 2) the correction to
the standard quasiclassical approximation is found showing the range of
applicability of the approach at high photon energy as well. The very important
conclusion is that for both cases and the results of
the quasiclassical calculation are very close to averaged probabilities of
exact theory in a very wide range of photon energies. The quasiclassical
approximation is valid also for the energy distribution if the electron and
positron are created on enough high levels.Comment: 21 pages, 6 figure
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
The Nature of the Elongated Form of Diamond Crystals From Urals Placers
The article presents the results of a study of the internal structure of highly elongated diamond crystals from placers in the Krasnovishersky district of the Urals. Very elongated crystals are found within diamond-bearing placer with unrevealed primary sources. Determining the conditions of such crystals formation can help one to determine the primary deposits type. There are three hypotheses for the formation of the elongated shape of such crystals: 1) crys- tals initially elongated along the (strongly distorted octahedra); 2) individual crystals of columnar aggregates;
3) elongated crystals fragments. To study the internal structure, we selected three most elongated individuals of the 155 crystals samples. The study of the internal structure of selected crystals with the usage of photoluminescent (PL) tomography, cathodoluminescence (CL), and optical microscopy has shown that these samples are fragments of lar- ger single crystals. CL imaging allowed to determine slip lines within the crystal's volume. The recorded PL spectra show the 912, 946, and 986 nm peaks, which are characteristic of crystals with plastic deformation. The revealed fea- tures are indicators of plastic deformation accompanying the destruction of the crystals. The significant dissolution following the destruction of the crystals led to the rounding of the vertices and edges of their fragments. Apparently, most of the very elongated crystals from placers with unknown sources are also highly dissolved isometric crystal fragments. The obtained results have shown that the deformation and dissolution of diamond crystals are related events characteristic of diamonds from hitherto undetected, but highly productive primary deposits
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