82 research outputs found
THE ASYMPTOTICS OF A SOLUTION OF THE MULTIDIMENSIONAL HEAT EQUATION WITH UNBOUNDED INITIAL DATA
For the multidimensional heat equation,Ā the long-time asymptotic approximation of the solutionĀ of the Cauchy problem is obtained in the case when the initial functionĀ grows at infinity and contains logarithmsĀ in its asymptotics.Ā In addition to natural applicationsĀ to processes of heat conduction and diffusion,Ā the investigation of the asymptotic behaviorĀ of the solution of the problem under considerationĀ is of interest for the asymptotic analysisof equations of parabolic type.Ā The auxiliary parameter methodĀ plays a decisive role in the investigation
EVOLUTION OF A MULTISCALE SINGULARITY OF THE SOLUTION OF THE BURGERS EQUATION IN THE 4-DIMENSIONAL SPACEāTIME
The solution of the Cauchy problemĀ for the vector Burgers equationĀ with a small parameter of dissipation in the -dimensional space-time is studied: With the help of the ColeāHopfĀ transform the exact solution and its leadingĀ asymptotic approximation, depending on six space-time scales,Ā near a singular point are found. A formula for the growth of partial derivativesĀ of the components of the vector field Ā on the time interval from the initial moment to the singular point,Ā called the formula of the gradient catastrophe, is established: The asymptotics of the solutionĀ far from the singular point,Ā involving a multistep reconstruction of the space-time scales,Ā is also obtained: u_{\nu} (\mathbf{x}, t, \varepsilon) \approx - 2 \left( \frac{t}{\nu + 1} \right)^{1/2\nu} \tanh \left[ \frac{x_{\nu}}{\varepsilon} \left( \frac{t}{\nu + 1} \right)^{1/2\nu} \right]\!, \quad \frac{t}{\varepsilon^{\nu /(\nu + 1)} } \to +\infty. $
Numerical simulation of the stress-strain state of the dental system
We present mathematical models, computational algorithms and software, which
can be used for prediction of results of prosthetic treatment. More interest
issue is biomechanics of the periodontal complex because any prosthesis is
accompanied by a risk of overloading the supporting elements. Such risk can be
avoided by the proper load distribution and prediction of stresses that occur
during the use of dentures. We developed the mathematical model of the
periodontal complex and its software implementation. This model is based on
linear elasticity theory and allows to calculate the stress and strain fields
in periodontal ligament and jawbone. The input parameters for the developed
model can be divided into two groups. The first group of parameters describes
the mechanical properties of periodontal ligament, teeth and jawbone (for
example, elasticity of periodontal ligament etc.). The second group
characterized the geometric properties of objects: the size of the teeth, their
spatial coordinates, the size of periodontal ligament etc. The mechanical
properties are the same for almost all, but the input of geometrical data is
complicated because of their individual characteristics. In this connection, we
develop algorithms and software for processing of images obtained by computed
tomography (CT) scanner and for constructing individual digital model of the
tooth-periodontal ligament-jawbone system of the patient. Integration of models
and algorithms described allows to carry out biomechanical analysis on
three-dimensional digital model and to select prosthesis design.Comment: 19 pages, 9 figure
Joint statistics of amplitudes and phases in Wave Turbulence
Random Phase Approximation (RPA) provides a very convenient tool to study the
ensembles of weakly interacting waves, commonly called Wave Turbulence. In its
traditional formulation, RPA assumes that phases of interacting waves are
random quantities but it usually ignores randomness of their amplitudes.
Recently, RPA was generalised in a way that takes into account the amplitude
randomness and it was applied to study of the higher momenta and probability
densities of wave amplitudes. However, to have a meaningful description of wave
turbulence the RPA properties assumed for the initial fields must be proven to
survive over the nonlinear evolution time, and such a proof is the main goal of
the present paper. We derive an evolution equation for the full probability
density function which contains the complete information about the joint
statistics of all wave amplitudes and phases. We show that, for any initial
statistics of the amplitudes, the phase factors remain statistically
independent uniformly distributed variables. If in addition the initial
amplitudes are also independent variables (but with arbitrary distributions)
they will remain independent when considered in small sets which are much less
than the total number of modes. However, if the size of a set is of order of
the total number of modes then the joint probability density for this set is
not factorisable into the product of one-mode probabilities. In the other
words, the modes in such a set are involved in a ``collective'' (correlated)
motion. We also study new type of correlators describing the phase statistics.Comment: 27 pages, uses feynmf packag
Influence of CO2-laser pulse parameters on 13.5 nm extreme ultraviolet emission features from irradiated liquid tin target
Laser-produced plasma (LPP) induced during irradiation of a liquid tin
droplet with diameter of 150 um and 180 um by CO2 laser pulse with various
pulse durations and energies is considered. The two-dimensional radiative
magnetohydrodynamic (RMHD) plasma code is used to simulate the emission and
plasma dynamics of multicharged ion tin LPP. Results of simulations for various
laser pulse durations and 75-600 mJ pulse energies with Gaussian and
experimentally taken temporal profiles are discussed. It is found that if the
mass of the target is big enough to provide the plasma flux required (the
considered case) a kind of dynamic quasi-stationary plasma flux is formed. In
this dynamic quasi-stationary plasma flux, an interlayer of relatively cold tin
vapor with mass density of 1-2 g/cm3 is formed between the liquid tin droplet
and low density plasma of the critical layer. Expanding of the tin vapor from
the droplet provides the plasma flux to the critical layer. In critical layer
the plasma is heated up and expands faster. In the simulation results with
spherical liquid tin target, the CE into 2 is of 4% for 30 ns FWHM and
just slightly lower - of 3.67% for 240 ns FWHM for equal laser intensities of
14 GW/cm2. This slight decay of the in-band EUV yield with laser pulse duration
is conditioned by an increasing of radiation re-absorption by expanding plasma
from the target, as more cold plasma is produced with longer pulse. The
calculated direction diagrams of in-band EUV emission permit to optimize a
collector configuration
Energy cascades and spectra in turbulent Bose-Einstein condensates
We present a numerical study of turbulence in Bose-Einstein condensates
within the 3D Gross-Pitaevskii equation. We concentrate on the direct energy
cascade in forced-dissipated systems. We show that behavior of the system is
very sensitive to the properties of the model at the scales greater than the
forcing scale, and we identify three different universal regimes: (1) a
non-stationary regime with condensation and transition from a four-wave to a
three-wave interaction process when the largest scales are not dissipated, (2)
a steady weak wave turbulence regime when largest scales are dissipated with a
friction-type dissipation, (3) a state with a scale-by-scale balance of the
linear and the nonlinear timescales when the large-scale dissipation is a
hypo-viscosity.Comment: 10 pages, 5 figure
Interaction of Kelvin waves and nonlocality of energy transfer in superfluids
We argue that the physics of interacting Kelvin Waves (KWs) is highly nontrivial and cannot be understood on the basis of pure dimensional reasoning. A consistent theory of KW turbulence in superfluids should be based upon explicit knowledge of their interactions. To achieve this, we present a detailed calculation and comprehensive analysis of the interaction coefficients for KW turbuelence, thereby, resolving previous mistakes stemming from unaccounted contributions. As a first application of this analysis, we derive a local nonlinear (partial differential) equation. This equation is much simpler for analysis and numerical simulations of KWs than the Biot-Savart equation, and in contrast to the completely integrable local induction approximation (in which the energy exchange between KWs is absent), describes the nonlinear dynamics of KWs. Second, we show that the previously suggested Kozik-Svistunov energy spectrum for KWs, which has often been used in the analysis of experimental and numerical data in superfluid turbulence, is irrelevant, because it is based upon an erroneous assumption of the locality of the energy transfer through scales. Moreover, we demonstrate the weak nonlocality of the inverse cascade spectrum with a constant particle-number flux and find resulting logarithmic corrections to this spectrum
Gravity wave turbulence in a laboratory flume
We present an experimental study of the statistics of surface gravity wave turbulence in a flume of a horizontal size 12Ć6āām. For a wide range of amplitudes the wave energy spectrum was found to scale as EĻā¼Ļ-Ī½ in a frequency range of up to one decade. However, Ī½ appears to be nonuniversal: it depends on the wave intensity and ranges from about 6 to 4. We discuss our results in the context of existing theories and argue that at low wave amplitudes the wave statistics is affected by the flume finite size, and at high amplitudes the wave breaking effect dominates
DISPERSIVE RAREFACTION WAVE WITH A LARGE INITIAL GRADIENT
Consider the Cauchy problem forĀ the Korteweg-de Vries equationĀ with a small parameter at the highest derivativeĀ and a large gradient of the initial function.Ā Numerical and analytical methods show that the obtained using renormalization formal asymptotics,Ā corresponding to rarefaction waves, is an asymptotic solution of the KdV equation. The graphs of the asymptotic solutionsĀ are represented, including the case of non-monotonic initial data
New possibilities and tools for corporate strategic management for supporting its high competitiveness and economic effectiveness
The purpose of the article is to determine new possibilities and tools for corporate strategic management and to substantiate the necessity for their usage for supporting a companyās competitiveness and economic effectiveness in modern Russia. The information and analytical basis of the research consists of the materials of the Report on global competitiveness for 2016-2017, prepared within the World economic forum. For verification of the offered hypothesis, the methods of deduction, induction, synthesis, systemic, problem, and structural & functional analysis, as well as analysis of causal connections, and the methods of modeling and formalization were used.
Because of the research, a conclusion is made that imperfection of the process of strategic management is a reason for low competitiveness and economic effectiveness of modern Russian companies. To solve this problem, the authors substantiate the necessity for applying the principle of interactivity, which supposes consideration of new possibilities and usage of leading tools in the process of corporate strategic management and develop the recommendations and offer an interactive model for strategic management of a modern company in modern Russia for the purpose of supporting high competitiveness and economic effectiveness of domestic entrepreneurship.peer-reviewe
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