1,387 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
Low – frequency acoustic instability of the working process in the combustion chamber of the solid propellant rocket engine
The following problems is investigated by statement of direct numerical experiment in offered paper. 1) The real oscillatory process is reproduced. 2) The mechanism of occurrence and refill of low-frequency acoustic instability in the combustion chamber of the solid propellant rocket.. The direct numerical modeling of low-frequency acoustic instability will be carried out by a Davydov’s method. This powerful numerical method was discovered by Yuri M. Davydov 40 years ago as the method of large particles The further modern complex improvement of this numerical technique was titled Davydov’s method. It is good itself recommending at the decision of many tasks of the mechanics of continuous media. The description of physical and mathematical model of flow in the rocket engine combustion chamber is given. The results of numerical modeling are resulted. The hydrodynamical deeply nonlinear nature of low-frequency fluctuations connected to structure and character of current in the combustion chamber of the solid propellant rocket engine proves to be tru
Order statistics and heavy-tail distributions for planetary perturbations on Oort cloud comets
This paper tackles important aspects of comets dynamics from a statistical
point of view. Existing methodology uses numerical integration for computing
planetary perturbations for simulating such dynamics. This operation is highly
computational. It is reasonable to wonder whenever statistical simulation of
the perturbations can be much more easy to handle. The first step for answering
such a question is to provide a statistical study of these perturbations in
order to catch their main features. The statistical tools used are order
statistics and heavy tail distributions. The study carried out indicated a
general pattern exhibited by the perturbations around the orbits of the
important planet. These characteristics were validated through statistical
testing and a theoretical study based on Opik theory.Comment: 9 pages, 12 figures, submitted for publication in Astronomy and
Astrophysic
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
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