727 research outputs found
On the first Townsend coefficient at high electric field
Based on the simplified approach it is shown and experimentally confirmed
that gas gain in wire chambers at very low pressure becomes higher on thicker
wires at the same applied high voltage. This is a consequence of the fact that
the first Townsend coefficient at high reduced electric field depends almost
entirely on the mean free path of electrons.Comment: 10 pages, 3 figures; version 2: revised, a few references adde
Influence of overload on low-frequency instability of working process in the combustion chamber of the solid propellant rocket engine
In the paper the real oscillatory process is reproduced by statement of direct numerical experiment and the mechanism of occurrence and refill of low-frequency acoustic instability in the combustion chamber of the solid propellant rocket engine with the account of flight overload is investigated for the first time. The direct numerical modeling of low-frequency acoustic instability is carried out by means of Davydov’s method (method of large particles), which is well-suited for the solutions of many problems of mechanics of the continuous media. The results of numerical modeling are presented here. The hydrodynamic highly nonlinear nature of low-frequency fluctuations connected to structure and character of current in the combustion chamber of the rocket engine on firm fuel are proved to be tru
A Variational Approach to Nonlocal Exciton-Phonon Coupling
In this paper we apply variational energy band theory to a form of the
Holstein Hamiltonian in which the influence of lattice vibrations (optical
phonons) on both local site energies (local coupling) and transfers of
electronic excitations between neighboring sites (nonlocal coupling) is taken
into account. A flexible spanning set of orthonormal eigenfunctions of the
joint exciton-phonon crystal momentum is used to arrive at a variational
estimate (bound) of the ground state energy for every value of the joint
crystal momentum, yielding a variational estimate of the lowest polaron energy
band across the entire Brillouin zone, as well as the complete set of polaron
Bloch functions associated with this band. The variation is implemented
numerically, avoiding restrictive assumptions that have limited the scope of
previous assaults on the same and similar problems. Polaron energy bands and
the structure of the associated Bloch states are studied at general points in
the three-dimensional parameter space of the model Hamiltonian (electronic
tunneling, local coupling, nonlocal coupling), though our principal emphasis
lay in under-studied area of nonlocal coupling and its interplay with
electronic tunneling; a phase diagram summarizing the latter is presented. The
common notion of a "self-trapping transition" is addressed and generalized.Comment: 33 pages, 11 figure
Influence of overload on low-frequency instability of working process in the combustion chamber of the solid propellant rocket engine
In the paper the real oscillatory process is reproduced by statement of direct numerical experiment and the mechanism of occurrence and refill of low-frequency acoustic instability in the combustion chamber of the solid propellant rocket engine with the account of flight overload is investigated for the first time. The direct numerical modeling of low-frequency acoustic instability is carried out by means of Davydov’s method (method of large particles), which is well-suited for the solutions of many problems of mechanics of the continuous media. The results of numerical modeling are presented here. The hydrodynamic highly nonlinear nature of low-frequency fluctuations connected to structure and character of current in the combustion chamber of the rocket engine on firm fuel are proved to be tru
Influence of overload on low-frequency instability of working process in the combustion chamber of the solid propellant rocket engine
In the paper the real oscillatory process is reproduced by statement of direct numerical experiment and the mechanism of occurrence and refill of low-frequency acoustic instability in the combustion chamber of the solid propellant rocket engine with the account of flight overload is investigated for the first time. The direct numerical modeling of low-frequency acoustic instability is carried out by means of Davydov’s method (method of large particles), which is well-suited for the solutions of many problems of mechanics of the continuous media. The results of numerical modeling are presented here. The hydrodynamic highly nonlinear nature of low-frequency fluctuations connected to structure and character of current in the combustion chamber of the rocket engine on firm fuel are proved to be tru
Experimental Modeling of Cosmological Inflation with Metamaterials
Recently we demonstrated that mapping of monochromatic extraordinary light
distribution in a hyperbolic metamaterial along some spatial direction may
model the flow of time and create an experimental toy model of the big bang.
Here we extend this model to emulate cosmological inflation. This idea is
illustrated in experiments performed with two-dimensional plasmonic hyperbolic
metamaterials. Spatial dispersion which is always present in hyperbolic
metamaterials results in scale-dependent (fractal) structure of the
inflationary "metamaterial spacetime". This feature of our model replicates
hypothesized fractal structure of the real observable universe.Comment: 17 pages, 3 figures. This version is accepted for publication in
Physics Letters
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A Method for Regeneration of Spent Electrochemical Decontamination Solution and Its Treatment for Final Disposal
This paper describes the method of regeneration of spent electrochemical decontamination solution. The proposed method allows separation of radionuclides and stable metals from spent decontamination solution in a form suitable for final disposal and repeated use of the remaining solution for electrochemical decontamination. Development of this method was based on the results of the speciation studies which showed that Fe(III) can be precipitated in the presence of organic complexing agents, in a form of iron hydroxide, and Ag-110m, Co-60, Mn-54 radionuclides can be coprecipitated on it. In order to verify the conclusions made as a result of the speciation studies, the experiments with electrochemically prepared simulant solution and real solution were carried out. The test results proved that the proposed method can be applied in practice. Treatment of the ultimately spent decontamination solutions can be also made applying iron precipitation, which allows for removal of the bulk amount of contaminants, as the first step. Then, if necessary the remaining radionuclides can be removed by sorption. A series of novel absorbers has been tested for their potential for the sorption removal of the remaining radionuclides from the supernate. The test results showed that most of them were more effective in neutral or alkaline range of pH, however, the high efficiency of the sorption removal can be achieved only after the removal of the oxalic and citric acids from solution
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