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Wyszukujesz frazę "62.65.+k" wg kryterium: Temat


Tytuł:
Sound Attenuation at High Temperatures in Pt
Autorzy:
Singh, R. K.
Pandey, K. K.
Tematy:
62.20.Dc
62.65.+k
Pokaż więcej
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Powiązania:
https://bibliotekanauki.pl/articles/2044642.pdf  Link otwiera się w nowym oknie
Opis:
Ultrasonic attenuation due to phonon-phonon interaction and thermoelastic loss was evaluated in VIII group transition metal Pt in a wide temperature range (100 K to 1500 K) for longitudinal and shear waves along〈100〉, 〈110〉 and〈111〉 directions and for shear waves polarised along different directions. Electrostatic and Born-Mayer potentials were used to obtain second and third order elastic constants, taking nearest-neighbour distance and hardness parameter as input data. Second and third order elastic constants data obtained at different temperatures were used to obtain Gruneisen parameters and non-linearity or anisotropy parameters which in turn were used to evaluate (α/f$\text{}^{2}$)$\text{}_{l}$ and (α/f$\text{}^{2}$)$\text{}_{s}$ in Akhiezer regime. The results were discussed and it was found that at lower temperatures (α/f$\text{}^{2}$) increases rapidly with temperature and then rate of increase becomes very small. Contribution to the total attenuation due to thermoelastic loss is negligible so that due to phonon-phonon interaction establishing that major part of energy from sound wave is removed due to interaction with thermal phonons (lattice vibrations).
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Ultrasonic Attenuation in Dielectric Crystals
Autorzy:
Kor, S. K.
Singh, R. K.
Tematy:
62.20.Dc
62.65.+K
Pokaż więcej
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Powiązania:
https://bibliotekanauki.pl/articles/1891964.pdf  Link otwiera się w nowym oknie
Opis:
Ultrasonic attenuation and non-linearity parameters have been evaluated for dielectric crystals RbCl, RbBr and RbI in a wide temperature range. Basic physical parameters, nearest neighbour distance and hardness parameters of the substance and Coulomb and Born-Mayer potentials have been used to obtain ultrasonic attenuation due to phonon-viscosity mechanism along (100) direction of propagation for longitudinal and shear waves. Results are as expected and it has been concluded that ultrasonic attenuation is a fundamental property of the substance.
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Critical Sound Attenuation and Spin-Lattice Relaxation
Autorzy:
Pawlak, A.
Tematy:
05.70.Jk
62.65.+k
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Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Powiązania:
https://bibliotekanauki.pl/articles/1930585.pdf  Link otwiera się w nowym oknie
Opis:
The nonasymptotic critical properties of sound propagation are studied in compressible magnetic system. The role of coupling of order parameter and acoustic phonons to spin-energy density is investigated and the ultrasonic attenuation scaling function is found.
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Diffusive Regime for Critical Sound Attenuation and Dispersion in Magnets
Autorzy:
Pawlak, A.
Błaszak, M.
Tematy:
05.70.Jk
62.65.+k
Pokaż więcej
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Powiązania:
https://bibliotekanauki.pl/articles/2013731.pdf  Link otwiera się w nowym oknie
Opis:
We consider a new regime of sound propagation in magnetic systems above the critical point. On the basis of a general statistical model including a flow of energy between spin and lattice subsystems we found that there is a region of parameters where the sound attenuation and dispersion can be expressed in a similar way as for noncritical systems for which only the heat conduction matters. Contrary to the case of the classical heat diffusion in the critical magnetic system both the specific heat, entering the reduced frequency, as well as the effective amplitude are frequency and temperature dependent reflecting the critical singularities present in the system near its critical point.
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Theory of Critical Sound Attenuation in Ising-Type Magnets
Autorzy:
Pawlak, A.
Tematy:
62.65.+k
05.70.Jk
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Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Powiązania:
https://bibliotekanauki.pl/articles/2014046.pdf  Link otwiera się w nowym oknie
Opis:
The critical behaviour of sound attenuation has been studied in an elastically isotropic Ising system above the critical point on the basis of a complete stochastic model including both spin-energy and lattice-energy modes linearly coupled to the longitudinal sound mode. The effect of spin-lattice relaxation on the ultrasonic attenuation is investigated. The crossover between Kawasaki behaviour and Murata-Iro-Schwabl behaviour is studied as dependent on the values of ultrasonic frequency, reduced temperature, relaxation times, etc. A new high-frequency regime is discussed in the magnetic systems. This new regime corresponds to an adiabatic sound propagation and is very similar to the ones in binary mixture and liquid helium. A new frequency-dependent specific heat being the harmonic average of the bare lattice and critical spin specific heats is introduced. It was shown that such specific heat describes the process of equilibration between spin and lattice subsystems and includes the most important features of critical sound attenuation.
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Magnetic Field Dependence of Critical Attenuation in Ferromagnet
Autorzy:
Pawlak, A.
Tematy:
05.70.Jk
62.65.+k
Pokaż więcej
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Powiązania:
https://bibliotekanauki.pl/articles/1427558.pdf  Link otwiera się w nowym oknie
Opis:
The influence of magnetic field on the sound attenuation is investigated in ferromagnets. With the aid of the Nelson method we derive frequency-, magnetic field- and temperature-dependent expression for the sound attenuation coefficient near a critical point in the Ising-type system. The shift of the ultrasonic attenuation peak under the influence of magnetic field towards higher temperatures is discussed.
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Spin-Lattice Relaxation Effects in Critical Sound Propagation
Autorzy:
Pawlak, A.
Tematy:
62.65.+k
05.70.Jk
Pokaż więcej
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Powiązania:
https://bibliotekanauki.pl/articles/1964802.pdf  Link otwiera się w nowym oknie
Opis:
The nonasymptotic critical properties of sound propagation are studied in compressible Ising system above T$\text{}_{C}$. In the present paper we analyse a model where in addition to the coupling to two order-parameter fluctuations the sound mode couples linearly to the fluctuations of spin-energy and lattice-energy densities. Both subsystems exchange energy with the rate determined by the bare spin-lattice relaxation time. The total energy may be conserved or not. The crossover between insulator-like behaviour ~t$\text{}^{-2α}$ and metal-like behaviour ~t$\text{}^{-(zν+α)}$ in ultrasonic attenuation is investigated according to the value of ultrasonic frequency, the reduced temperature t, bare relaxation times and various coupling constants.
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Magnetic Field Influence on Critical Sound Attenuation and Velocity Variation in Ferromagnets
Autorzy:
Pawlak, A.
Tematy:
05.70.Jk
62.65.+k
Pokaż więcej
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Powiązania:
https://bibliotekanauki.pl/articles/1810482.pdf  Link otwiera się w nowym oknie
Opis:
The ultrasound velocity and attenuation are investigated in ferromagnets under an application of magnetic field. In the magnetic field six different characteristic regimes are distinguished instead of traditional two (hydrodynamic and critical) found for the case of zero magnetic field. The mean-field Landau-Khalatnikov theory as well as the scaling predictions are given for each regime. Various critical exponents are identified for these regions and compared with the ultrasonic data for MnP. The shift of the ultrasonic attenuation peak under the influence of magnetic field towards higher temperatures is discussed.
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Ultrasonic Attenuation in Alloys
Autorzy:
Kor, S. K.
Singh, R. K.
Tematy:
62.20.Dc
62.65.+k
Pokaż więcej
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Powiązania:
https://bibliotekanauki.pl/articles/1929339.pdf  Link otwiera się w nowym oknie
Opis:
Ultrasonic attenuation was evaluated in metallic alloys, Ni$\text{}_{x}$Cu$\text{}_{1-x}$ (x = 1.00, 0.70, 0.60, 0.45 and 0) due to phonon-phonon (p-p) interaction and thermoelastic loss in a wide temperature region along ⟨110⟩ crystallographic direction for longitudinal and shear waves. Ultrasonic Grüneisen parameters, nonlinearity constants and ultrasonic attenuation due to p-p interaction and thermoelastic loss were determined from 50 K to 500 K using the Born-Mayer and electrostatic potentials. The results were compared with available experimental results.
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Acoustic-Emission Study of Intermittency of Plastic Flow during Twinning and Dislocation Glide
Autorzy:
Shashkov, I.
Lebedkina, T.
Lebyodkin, M.
Dobron, P.
Chmelik, F.
Kral, R.
Parfenenko, K.
Mathis, K.
Tematy:
62.20.F-
62.65.+k
05.65.+b
64.60.av
Pokaż więcej
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Powiązania:
https://bibliotekanauki.pl/articles/1418404.pdf  Link otwiera się w nowym oknie
Opis:
Recent studies of plastic deformation with the aid of acoustic emission techniques proved an intermittent, scale-invariant character of plastic processes, as reflected in power-law statistical distributions. In some cases, the power-law exponents display close values leading to hypothesis of universality of scaling laws for various mechanisms of plasticity. Nevertheless, the accurate determination of the power law may be impeded by some sources of errors inevitable in real conditions, in particular, by superposition of individual acoustic emission events. In the present work, the sensitivity of the apparent statistics to the variation of the parameters of individualization of acoustic emission events is examined using Mg and Al based alloys. Both these alloys exhibit a highly cooperative character of plastic deformation, leading to strong acoustic activity which is governed by distinct microscopic mechanisms - mechanical twinning and the Portevin-Le Chatelier effect, respectively.
Dostawca treści:
Biblioteka Nauki
Artykuł

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