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1
Content available remote

Effect of Pressure on the Solitary Wave Propagation in One-Dimensional Lattice

100%
Sabirov R.
Acta Physica Polonica A
|
1992
|
vol. 81
|
issue 4-5
535-542
EN
The solitary wave propagation in an anharmonic monoatomic linear chain for the case of an external pressure is investigated. The potential energy of the crystal with anharmonicities of the third and fourth orders is considered. Two kinds of solitary waves are obtained. The first kind corresponds to the compressive soliton and the second one - to the rarefactive soliton. In the case of the lattice with the cubic anharmonicity the exact theoretical study was done. Numerical calculations were performed for the general case. It is found that when pressure rises, amplitudes of solitons also increase.
2
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Lattice Thermal Conductivity of GaAs

51%
Ataullah Ansari M., Ashokan V., Indu B., Kumar R.
Acta Physica Polonica A
|
2012
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vol. 121
|
issue 3
639-646
EN
A new approach to evaluate the relaxation times of various collision events responsible for thermal transport has been reported through which various deficiencies of earlier models of lattice thermal conductivity have been resolved. These investigations involve the evaluation of the phonon Green functions via a non-perturbative approach. The new expressions of relaxation times expressions for scattering of phonons by boundaries, atomic impurities, phonon-phonon scattering, electron-phonon scattering are the new features of the theory. The lattice thermal conductivity of three samples of GaAs has been analyzed on the basis of modified Callaway model and fairly good agreement between theory and experimental observations has been reported.
3
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Phonon Deformation Potentials from Raman Measurements on Semiconductor Membranes

51%
Trzeciakowski W., Martinez-Pastor J., Martinez-Criado G.
Acta Physica Polonica A
|
1997
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vol. 92
|
issue 5
1033-1037
EN
It is shown that the phonon deformation potentials in semiconductors can be determined by Raman scattering on hydrostatically and biaxially deformed samples. The complete data includes biaxial deformation in the (100), (111), and (110) planes. Biaxial strain is applied to the sample using the recently developed membrane method. The phonon displacement under biaxial strain can be directly obtained from Raman measurements on a single membrane provided we determine the strain from the splitting of the band gap using e.g. the photoreflectance technique. Alternatively, the ratios of different phonon shifts can supply the necessary information. The method is illustrated with experimental results for GaP.
4
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Thermodynamics of Pseudospin-Electron Model in the U=0 Limit

51%
Stasyuk I., Shvaika A., Tabunshchyk K.
Acta Physica Polonica A
|
2000
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vol. 97
|
issue 3
411-414
EN
Analytical consideration of a pseudospin-electron model in the absence of electron correlations is presented. Pseudospin and electron number mean values, thermodynamic potential, pair correlation functions are obtained in the same self-consistent approximation. The possibility of either first or second order phase transitions between different uniform phases (bistability) as well as between the uniform and the chessboard one is shown. In the regime n=const, an instability with respect to phase separation can take place.
5
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On Bright and Dark Breathers in Lattices with Saturable Nonlinearity

51%
Maluckov A., Stepić M., Hadžievski L.
Acta Physica Polonica A
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2007
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vol. 112
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issue 5
903-908
EN
The moving bright and dark localized modes in one-dimensional optical lattices with saturable nonlinearity are considered with respect to the grand canonical free energy concept and linear stability analysis of the eigenvalue spectra.
6
Content available remote

Low-Loss Microwave Dielectrics for Different Frequency Ranges

38%
Belous A., Ovchar O.
Acta Physica Polonica A
|
2010
|
vol. 117
|
issue 1
221-227
EN
Depending on the operating frequency range of modern communication systems various microwave elements are required for effective operation of radio equipment. In this work potential ways of developing the microwave dielectric materials for different frequency ranges are discussed. It has been shown that temperature stable dielectrics with the permittivity of about 100, which are intended for the utilization in the decimetre wavelength band, can be developed by means of alio- and isovalent substitution in the cation sublattices of barium lanthanide titanates (BLTss) Ba_{6-x}Ln_{8 + 2x/3}Ti_{18}O_{54} (Ln = La-Gd). The temperature behaviour of the permittivity and dielectric loss in the BLTss has been discussed in terms of both harmonic and anharmonic contributions to the phonons of the BLT crystal lattice. It has been shown that a slight deviation from the compositional stoichiometry in both A-site and B-site deficient perovskites Ba(M_{1/3}^{2+}Nb_{2/3})O_{3} (M = Co, Zn, Mg) allows a prominent enhancement of their microwave quality factor (Q). As a consequence, new dielectrics with the extremely high quality factor (Qxf = 90000-150000 GHz), which are intended for the utilization in the centimetre wavelength band, can be developed. Some examples of the possible implementation of the developed materials are also discussed.
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