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    Wyświetlanie 1-7 z 7
    Tytuł:
    The Nonlinear Diffusion Equation Describing Spread of Impurities of High Density
    Autorzy:
    Janavičius, A. J.
    Lūža, G.
    Jurgaitis, D.
    Powiązania:
    https://bibliotekanauki.pl/articles/2038073.pdf
    Data publikacji:
    2004-05
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    66.30.-h
    Opis:
    The nonlinear diffusion equation is derived by taking into account the local variations in the solvent density, within a mechanism of diffusion driven by random particle collisions. Analytical solutions for the case of spherical-symmetric nonlinear diffusion equation for spread of impurities in gas and solids are obtained and discussed. In this case, the solutions of the nonlinear diffusion equation are similar to solutions of Bernoulli equation. We note that the obtained solutions can be used to describe the shapes of impurity gas of high concentration or smoke clouds.
    Źródło:
    Acta Physica Polonica A; 2004, 105, 5; 475-483
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Analytical Solution of Nonlinear Diffusion Equation in Two-Dimensional Surface
    Autorzy:
    Janavičius, A. J.
    Turskienė, S.
    Powiązania:
    https://bibliotekanauki.pl/articles/2044566.pdf
    Data publikacji:
    2005-12
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    66.30.-h
    Opis:
    We considered practically important case of nonlinear diffusion in the anisotropic plane where diffusion coefficients for diffusion in x and y axis directions can be different. This equation was transformed using similarity variables. The approximate analytical solution of the transformed equation expressed by power-series expansion for two variables about the zero point including only the first terms. The graphic representations show sufficient accuracy of the obtained analytical solution.
    Źródło:
    Acta Physica Polonica A; 2005, 108, 6; 979-983
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    The Nonlinear Diffusion in the Nonisothermical Case
    Autorzy:
    Janavičius, A. J.
    Powiązania:
    https://bibliotekanauki.pl/articles/1968857.pdf
    Data publikacji:
    1998-02
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    66.30.-h
    Opis:
    We will discuss the properties of the nonlinear equation in the nonisothermical case. In our previous papers the diffusion coefficient directly proportional to the concentration of the impurities was proposed and it was exactly defined. Now the nonlinear diffusion equation is solved for the temperature and for the diffusion coefficient depending on time in a special way. The temperature function T(t) has the singularity at the free chosen time moment t$\text{}_{0}$. The obtained analytical solutions define the diffusion profiles for increasing temperatures and in the case of excited systems when the vacancies and the impurity's atoms are not in the thermal equilibrium with lattice. Considering the connection between temperature function and the population of excited states for atoms surrounding vacancies the possibility of the superdiffusion is shown.
    Źródło:
    Acta Physica Polonica A; 1998, 93, 3; 505-512
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Nonlinear Diffusion Equation with Diffusion Coefficient Directly Proportional to Concentration of Impurities
    Autorzy:
    Janavičius, A. J.
    Poškus, A.
    Powiązania:
    https://bibliotekanauki.pl/articles/2042120.pdf
    Data publikacji:
    2005-03
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    66.30.-h
    Opis:
    We analyzed a diffusion model based on the assumption that the sufficient condition for the mass flux at point x+L to be different from zero is a nonzero value of the impurity gradient and of impurity concentration at point x. In our model, the length of the jump of diffusing particles from one equilibrium position to another has a defined value L. By describing variation of impurity concentration with time when the frequency of the jumps depends on coordinates and L, the nonlinear diffusion equation was derived. We found that the diffusion coefficient in this nonlinear equation is directly proportional to the concentration of impurities, as it had been proposed in earliest papers. The derived nonlinear diffusion equation was solved numerically for the case of spherical symmetry.
    Źródło:
    Acta Physica Polonica A; 2005, 107, 3; 519-524
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Modeling of Thermodiffusion Inertia in Metal Films Heated with Ultrashort Laser Pulses
    Autorzy:
    Janavičius, A. J.
    Turskienė, S.
    Powiązania:
    https://bibliotekanauki.pl/articles/2047101.pdf
    Data publikacji:
    2006-10
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    66.30.-h
    79.20.Ds
    Opis:
    Previously, we considered the analytical solution of nonlinear diffusion equation in two-dimensional surface. This allows us to consider the same nonlinear heat conduction equation for metals heated by a picosecond laser. After fast thermalization (within a few femtoseconds) of the laser energy and electron excitation in the conductivity band, electrons ballistically diffuse and transfer their energies to the target atoms and equilibrium electrons from the conductivity band. In this case, we have thermal diffusion of nonequilibrium excited electrons and thermal inertia for thermodiffusion. The relaxation time of excited conductivity electrons is directly connected with thermal inertia and depends on electron-electron collision frequencies. The theoretical temperature surface plots for the thermodiffusion of excited electrons were obtained from analytical solutions of nonlinear thermodiffusion equations.
    Źródło:
    Acta Physica Polonica A; 2006, 110, 4; 511-521
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Nonlinear Diffusion in Excited HgCdTe and Si Crystals
    Autorzy:
    Janavičius, A. J.
    Norgėla, Ž.
    Purlys, R.
    Powiązania:
    https://bibliotekanauki.pl/articles/2036987.pdf
    Data publikacji:
    2003-11
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    66.30.-h
    66.30.Hs
    78.70.Ck
    Opis:
    We discuss the properties of the nonlinear diffusion equation for the case of diffusion in excited systems. The diffusion coefficient is directly proportional to the concentration of impurities and depends on time in a special way. For the description of the excited systems, we used a special temperature function, which defined the time dependent diffusion coefficient and the Boltzmann distribution of the excited vacancies or impurity atoms in solids. This model was used for the approximation of indium concentration profiles in HgCdTe of a rapid diffusion component and very fast diffusion of metastable vacancies irradiated by soft X-rays in an excited Si crystal.
    Źródło:
    Acta Physica Polonica A; 2003, 104, 5; 459-467
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Fast Diffusion of Metastable Vacancies in Surface of Excited Si Crystals
    Autorzy:
    Janavičius, A. J.
    Turskienė, S.
    Powiązania:
    https://bibliotekanauki.pl/articles/2047100.pdf
    Data publikacji:
    2006-10
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    66.30.-h
    66.30.Hs
    78.70.Ck
    Opis:
    We considered the practically interesting, very fast nonlinear diffusion of metastable vacancies in the surface of Si crystal, excited by soft X-rays. Here we used experimentally defined diffusion coefficients of singly and doubly negatively charged very fast vacancies generated by soft X-rays. These high concentration (about 10$\text{}^{13}$ cm$\text{}^{-3}$) metastable vacancies at room temperature can diffuse and exist in the crystal for a very long time (about 24 hours for not so fast neutral vacancies) changing electrical conductivity, the Hall mobility of carriers and generating some resonance phenomena in the lattice of Si crystal. We measured superdiffusivity of negatively charged vacancies, generated by the Auger effect in the regions of the sample, where X-rays did not acted. In the paper we modified the formerly obtained analytical solution of nonlinear diffusion equation for calculation of distribution of vacancies in two-dimensional surface.
    Źródło:
    Acta Physica Polonica A; 2006, 110, 4; 505-510
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-7 z 7

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