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Wyświetlanie 1-15 z 1295
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:
New High Performance Scintillators Based on Re-Activated Insulator Materials
Autorzy:
Wojtowicz, A. J.
Powiązania:
https://bibliotekanauki.pl/articles/1945553.pdf
Data publikacji:
1996-07
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.90.+t
78.55.-m
61.80.Ed
29.40.-n
Opis:
In this paper we address the problem of the host-to-ion energy transfer in some RE-activated wide band gap materials excited by ionizing radiation. We argue that, despite the expected self-localization of holes, the dominant mechanism in efficient materials involves sequential trapping of both charge carriers (holes and electrons) by an activating RE-ion followed by a radiative recombination via the ion producing scintillation light. Selected experimental results are presented to illustrate how various energy transfer processes manifest themselves in the spectroscopy of scintillator materials. Experimental results combined with simple considerations are used to identify these RE-ions which are likely to act as hole or electron traps in tri- and difluorides, thus initiating the recombination sequence leading to efficient scintillation.
Źródło:
Acta Physica Polonica A; 1996, 90, 1; 215-222
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Application of EXAFS to Catalysis and Surface Science
Autorzy:
Renouprez, A. J.
Powiązania:
https://bibliotekanauki.pl/articles/1931691.pdf
Data publikacji:
1994-11
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
61.10.Lx
78.70.Dm
Opis:
The paper gives recent applications of EXAFS to the structural study of microcrystalline bimetallic particles. Special attention has been paid to the case of systems composed of neighbouring elements. Also it is shown how the use of X-ray diffraction techniques and surface science methods like ion scattering can be indispensable to interpret the EXAFS data correctly. In catalysis and surface science, experiments performed in total reflection mode can provide a detailed description of the adsorption site of atoms on a flat surface.
Źródło:
Acta Physica Polonica A; 1994, 86, 5; 663-674
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Some Aspects of Solid State Radioluminescence
Autorzy:
Wojtowicz, A. J.
Powiązania:
https://bibliotekanauki.pl/articles/1994522.pdf
Data publikacji:
1999-01
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.60.Ya
78.30.Hv
78.60.Kn
29.40.Mc
Opis:
In this paper we review results of radioluminescence studies on two scintillator materials, LuAlO$\text{}_{3}$ and YAlO$\text{}_{3}$, activated with Ce. The experiments include measurements of ther moluminescence, isothermal phosphorescence decays, scintillation light yield as function of temperature, and scintillation time profiles under gamma excitation. Experimental results are interpreted in the frame of a simple kinetic model that includes a number of electron traps. We have identified and characterized a number of deep and shallow traps and demonstrated that traps in LuAlO$\text{}_{3}$:Ce are deeper than corresponding traps in YAlO$\text{}_{3}$:Ce. Unlike deep traps which are responsible for some scintillation light loss but otherwise do not have any impact on generation of scintillation light, shallow traps are shown to actively interfere with the process of radiative recombination via Ce ions. We demonstrate that shallow traps are responsible for some as yet unexplained observations including a higher room temperature light yield of YAlO$\text{}_{3}$:Ce and its longer scintillation decay time, as well as a longer scintillation rise time in LuAlO$\text{}_{3}$:Ce.
Źródło:
Acta Physica Polonica A; 1999, 95, 1; 165-178
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:
Vibrational Corrections to Transition Properties
Autorzy:
Pluta, T.
Sadlej, A. J.
Powiązania:
https://bibliotekanauki.pl/articles/2014250.pdf
Data publikacji:
2000-10
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
33.20.Fb
Opis:
The vibrational contributions to second-order transition properties are considered in the framework of the Born-Oppenheimer approximation. It is shown that the usual formula for vibrational second-order transition matrix elements is incomplete and needs to be supplemented by a term of purely vibrational origin. This pure vibrational contribution is calculated for vibrational transition polarizabilities in LiH and BeF and found to be quite significant. Its inclusion in theoretically calculated data for the Raman intensities appears to be necessary.
Źródło:
Acta Physica Polonica A; 2000, 98, 4; 363-371
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
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:
Adaptive Testing of Ferromagnetic Materials Utilizing Barkhausen Noise
Autorzy:
Pal'a, J.
Bydžovský, J.
Powiązania:
https://bibliotekanauki.pl/articles/1205257.pdf
Data publikacji:
2014-08
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
81.40.Rs
75.60.Ej
Opis:
A new method of the Barkhausen noise measurement and optimization of the measured data processing with respect to non-destructive evaluation of ferromagnetic materials is proposed. The measuring method is based on well-known method of magnetic adaptive testing where a complex set of minor hysteresis loops is measured. Collecting the sets of obtained Barkhausen noise envelopes into suitable designed matrices and optimizing the data processing with respect to the maximum sensitivity to the evaluated variable were developed. The method is illustrated on the evaluation of plastic deformation of a steel sample. It is shown that the proposed measuring method and measured data processing bring an improvement of the sensitivity to the evaluated variable when comparing with measuring the traditional Barkhausen noise parameter (root mean square).
Źródło:
Acta Physica Polonica A; 2014, 126, 3; 855-859
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
On the Accuracy of the Discretization Techniques in Approximate Relativistic Methods
Autorzy:
Woźniak, D.
Sadlej, A. J.
Powiązania:
https://bibliotekanauki.pl/articles/2014523.pdf
Data publikacji:
2000-12
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
31.30.Jv
31.15.-p
Opis:
Several non-singular 2-component methods for relativistic calculations of the electronic structure of atoms and molecules lead to cumbersome operators which are partly defined in the coordinate representation and partly in the momentum representation. The replacement of the Fourier transform technique by the approximate resolution of identity in the basis set of approximate eigenvectors of the p$\text{}^{2}$ operator is investigated in terms of the possible inaccuracies involved in this method. The dependence of the accuracy of the evaluated matrix elements on the composition of the subspace of these eigenvectors is studied. Although the method by itself appears to be quite demanding with respect to the faithfulness of the representation of the p$\text{}^{2}$ operator, its performance in the context of the standard Gaussian basis sets is found to be encouragingly accurate. This feature is interpreted in terms of approximately even-tempered structure of the majority of Gaussian basis sets used in atomic and molecular calculations.
Źródło:
Acta Physica Polonica A; 2000, 98, 6; 673-690
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Investigation of two-stage magnetic Barkhausen noise measurement method at power line frequency
Autorzy:
Pal'a, J.
Šoka, M.
Powiązania:
https://bibliotekanauki.pl/articles/1070541.pdf
Data publikacji:
2016-03
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
81.40.Rs
75.60.Ej
Opis:
The aim of the paper was to study the features of measurement of the magnetic Barkhausen noise by the new two-stage method in the high excitation frequency region (power line frequency). The magnetic Barkhausen noise was investigated on grain oriented Fe-3%Si steel subjected to different heat treatment. By application of an air coil on the output of the power amplifier we were able to linearize the excitation field. At the same time, the air coil suppressed the unwanted noise from the output of the power amplifier. We have found that the two-stage method is able to reveal a peak of the power spectrum even if it is located at low frequency, in contrast to the classical one-stage method. Further, we successfully applied a model of the power spectrum to the real magnetic Barkhausen noise obtained from the two-stage measurement.
Źródło:
Acta Physica Polonica A; 2016, 129, 3; 383-387
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:
Micro-optical and Optoelectronic Components for Optical Interconnection Applications
Autorzy:
Taghizadeh, M. R.
Waddie, A. J.
Powiązania:
https://bibliotekanauki.pl/articles/2030320.pdf
Data publikacji:
2002-01
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
42.79.Ta
Opis:
The advances in the design and fabrication of microlaser arrays, photodetectors, and free-space optical interconnection elements have driven the creation of ever more "real world" demonstrator systems. In this paper we review the progress made to date on two separate demonstrator projects which have been assembled at Heriot-Watt University. We shall describe some of the enabling technologies used in the creation of these systems and outline the potential for scaling the architectures described up to sizes where the computational advantages of the optics-in-computing paradigm become highly attractive.
Źródło:
Acta Physica Polonica A; 2002, 101, 1; 175-187
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Thermoluminescence and Scintillation Time Profiles of BaF$\text{}_{2}$:Ce
Autorzy:
Głodo, J.
Szupryczyński, P.
Wojtowicz, A. J.
Powiązania:
https://bibliotekanauki.pl/articles/1994962.pdf
Data publikacji:
1999-02
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.60.Kn
78.60.Ya
78.55.Hx
29.40.Mc
Opis:
In this communication we present results of measurements of low temperature thermoluminescence, isothermal decays, steady state radioluminescence yield, and scintillation time profiles at various temperatures on two scintillator materials, BaF$\text{}_{2}$:Ce and undoped BaF$\text{}_{2}$. We find that all these results can be consistently interpreted in the frame of a model that includes several relatively shallow charge traps. We have identified and characterized one particular shallow trap that causes the decay of the dominant scintillation component of BaF$\text{}_{2}$:Ce to be slower than radiative, as well as a set of others that are responsible for even slower components in the scintillation time profile of this material.
Źródło:
Acta Physica Polonica A; 1999, 95, 2; 259-268
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Spin-Orbit Coupling in Cr$\text{}^{3+}$ Ion in Solid State Materials
Autorzy:
Wojtowicz, A. J.
Grinberg, M.
Łempicki, A.
Powiązania:
https://bibliotekanauki.pl/articles/1879947.pdf
Data publikacji:
1991-02
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.55.Hx
Opis:
In this paper we introduce a new model describing the coupling of $\text{}^{2}$E and $\text{}^{4}$T$\text{}_{2}$ states of octahedrally coordinated Cr$\text{}^{3+}$ ion, which includes spin-orbit and electron-lattice interactions and takes into account the electronic structure of both states. The model is used to calculate doublet lifetime. We have applied this model to the series of Cr$\text{}^{3+}$ doped garnets characterized by the varying crystal field parameter 10 Dq and O$\text{}_{h}$ symmetry of the Cr site and to the kyanite (Al$\text{}_{2}$O$\text{}_{3}$:SiO$\text{}_{2}$), which is the case of different Cr$\text{}^{3+}$ sites in one material, characterized by the relatively large component of the low symmetry crystal field. The agreement with experiment is reasonable.Z
Źródło:
Acta Physica Polonica A; 1991, 79, 2-3; 235-238
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Wyświetlanie 1-15 z 1295

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