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Wyświetlanie 1-15 z 91
Tytuł:
Performance Prediction and Irreversibility Analysis of a Thermoelectric Refrigerator with Finned Heat Exchanger
Autorzy:
Meng, F.
Chen, L.
Sun, F.
Powiązania:
https://bibliotekanauki.pl/articles/1493399.pdf
Data publikacji:
2011-09
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
05.70.-a
05.60.Cd
05.70.Ln
Opis:
A developed model of commercial thermoelectric refrigerators with finned heat exchanger is established by introducing finite time thermodynamics. A significant novelty is that physical properties, dimension parameters, temperature parameters and flow parameters are all taken into account in the model. Numerical studies and comparative investigation on the performance of a typical commercial water-cooling thermoelectric refrigerator which consists of 127 thermoelectric elements, are performed for cooling load and coefficient of performance. The results show that the maximum cooling load is 2.33 W and the maximum coefficient of performance is 0.54 when the cooling temperature difference is 10 K. Comparing the simulation results of several models, it is found that the heat convection of the heat exchanger and the heat leakage through the air gap are the main factors, which cause irreversibility and decrease the performance. Moreover, the performance can be improved by optimizing the length and cross-section area of thermoelectric elements. The model and calculation method may be applied to not only the analysis and performance prediction of practical thermoelectric refrigerators, but also the design and optimization of heat exchangers.
Źródło:
Acta Physica Polonica A; 2011, 120, 3; 397-406
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Finite Element Method for Static Problems of Cubic Quasicrystals
Autorzy:
Yang, L.
He, F.
Gao, Y.
Powiązania:
https://bibliotekanauki.pl/articles/1202985.pdf
Data publikacji:
2014-08
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
61.44.Br
Opis:
We put forward a finite element method for static problems of cubic quasicrystals by variation of a suitable general potential functional. As an example we study a quasicrystal column containing a penny-shaped crack. The comparison with analytical results shows that the precision and efficiency of the numerical solution are satisfactory. The procedure can be used to solve more complicated boundary value problems and can be extended towards more sophisticated methods of crack tip loading analysis.
Źródło:
Acta Physica Polonica A; 2014, 126, 2; 471-473
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Influence of Atomic and Electronic Structure of a Tip on Stm Images
Autorzy:
Jurczyszyn, L.
Mingo, N.
Flores, F.
Powiązania:
https://bibliotekanauki.pl/articles/1968715.pdf
Data publikacji:
1998-02
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
07.79.Cz
61.16.Ch
Opis:
Theoretical studies of the influence of electronic and atomic structure of a tip on scanning tunneling microscopy images are presented. Results are discussed for the scanning of Al(001) and Al(001)+Xe surfaces performed within aluminum and nickel tips of a different geometry.
Źródło:
Acta Physica Polonica A; 1998, 93, 2; 307-315
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Edge Pinning Effects and Giant Thermal Instability of Magnetization Hysteresis Loops in Thin Nano-Scale Magnets
Autorzy:
Popkov, A. F.
Savchenko, L. L.
Vorotnikova, N. V.
Powiązania:
https://bibliotekanauki.pl/articles/2013138.pdf
Data publikacji:
2000-03
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.60.Ej
67.80.Jd
Opis:
Magnetization reversal modes of super-thin nano-scale particles with a high magnetization and low anisotropy are analyzed by solving magnetic moment motion equations. A new kind of thermal hysteresis instability connected with the random mutual transformation of the main magnetization modes is predicted by simulations.
Źródło:
Acta Physica Polonica A; 2000, 97, 3; 499-502
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Non-Perturbative Dynamics of Atoms in Strong Lrser Fields: Adiabatic Stability of Hydrogen Atom
Autorzy:
Faisal, F. H. M
Dimou, L.
Powiązania:
https://bibliotekanauki.pl/articles/1931518.pdf
Data publikacji:
1994-07
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
32.80.Fb
32.80.Wr
Opis:
Recent investigations of laser-atom interaction at high intensities have led to the discovery of several unexpected phenomena, and their studies have deepened our understanding of non-perturbative dynamics of quantum systems subjected to unusually strong radiation fields. For the analysis and interpretation of these phenomena. We have developed an ab initio non-perturbative method, the Floquet close-coupling method, and applied it to analyse the highly non-perturbative problem of adiabatic stability of hydrogen atom. Ab initio rates of ionization as a function of the laser intensity for the excited circular states as well as related non-circular states are obtained. Our quantitatively accurate results clearly show that the predictions of the previous approximate theories such as the well-known "high-frequency" theory are qualitatively similar but differ quantitatively. The analysis of the dependence of adiabatic stability on the principal quantum number, the angular momentum, as well as on the magnetic quantum number for the Rydberg states are complemented by investigations of the behavior of the ground state for frequencies below the ionization threshold. In the latter situation we found the existence of stability windows within which the ionization probability decreases with increasing intensity but outside of which the atom becomes more unstable. It is shown here that the mechanism for the occurrence of stability windows is the self-tuned anti-resonance at specific intensities.
Źródło:
Acta Physica Polonica A; 1994, 86, 1; 201-211
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Spatially Modulated Bragg Gratings
Autorzy:
Procházka, I.
Kotac̆ka, L.
Petrás̆, F.
Powiązania:
https://bibliotekanauki.pl/articles/2008273.pdf
Data publikacji:
1999-05
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
42.70.Dj
Opis:
A set of coupled mode differential equations which describe the light propagation in an optical fiber containing a photoinduced Bragg grating is derived. Reflection spectra based on numerical solution to these equations are presented when basic grating parameters are varied. In addition, the influence of these parameters on the maximum reflectivity and 3 dB bandwidth is examined. Finally, reflection spectra of the chirped grating and the grating with spatially modulated refractive index changes are discussed.
Źródło:
Acta Physica Polonica A; 1999, 95, 5; 821-835
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Spin Excitations in Doped Manganites
Autorzy:
Oleś, A. M.
Feiner, L. F.
Powiązania:
https://bibliotekanauki.pl/articles/2012881.pdf
Data publikacji:
2000-01
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.30.Ds
75.30.Et
71.27.+a
Opis:
We generalize the double exchange to describe holes doped in degenerate e$\text{}_{g}$ orbitals in La$\text{}_{1-x}$A$\text{}_{x}$MnO$\text{}_{3}$ manganites, where A are divalent alkaline earth ions. Assuming an orbital liquid of disordered e$\text{}_{g}$ orbitals we find isotropic ferromagnetic exchange interactions which increase with hole doping. The magnon dispersion agrees very well with the experimental data in ferromagnetic metallic manganites.
Źródło:
Acta Physica Polonica A; 2000, 97, 1; 193-196
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Characterization of Nitride Thin Films Using SEM and EDX
Autorzy:
Mammeri, F.
Chekour, L.
Rouag, N.
Powiązania:
https://bibliotekanauki.pl/articles/1399799.pdf
Data publikacji:
2013-02
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
67.25.dp
68.55.J-
81.15.-z
68.37.Hk
68.90.+g
Opis:
The chromium nitride thin films have became more and more popular in the last years because of their very good physical, chemical and mechanical properties. The present study relates to thermal stability of hard thin films of chromium nitride CrN, carried out physical vapour deposition. We studied the influence of the annealing temperature on the morphology of CrN films, deposited on silicon substrate using magnetron sputtering. The characterizations are examined using scanning electron microscope equipped with energy dispersive X-ray spectroscopy. Annealing treatments in $N_2$ at 600-1000C for 1 h are performed on CrN coating samples for 530 nm thickness. At low temperature, the results show a thermal stability of these coatings. The $Cr_2O_3$ phase is completely replaced by the CrN phase at temperature above 1000°C. The results given by scanning electron microscopy-energy dispersive X-ray spectroscopy and X-ray diffraction are compared.
Źródło:
Acta Physica Polonica A; 2013, 123, 2; 294-295
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Endoreversible Four-Reservoir Chemical Potential Transformer with Diffusive Mass Transfer Law
Autorzy:
Xia, D.
Chen, L.
Sun, F.
Powiązania:
https://bibliotekanauki.pl/articles/1493376.pdf
Data publikacji:
2011-09
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
05.70.Ln
82.60.Lf
Opis:
The performance of an isothermal endoreversible four-reservoir chemical potential transformer, in which the mass transfer between the mass reservoir and the working medium obeys diffusive law, is analyzed and optimized in this paper. The relation between the rate of energy pumping and the coefficient of performance of the isothermal chemical potential transformer is derived by using finite-time thermodynamics. Moreover, the optimal operating regions and the influences of some parameters on the performance of the cycle are studied. The results obtained herein can provide some new theoretical guidelines for the optimal design of a class of apparatus such as mass exchangers, as well as electrochemical, photochemical, and solid-state devices, and the fuel pumps for solar-energy conversion systems.
Źródło:
Acta Physica Polonica A; 2011, 120, 3; 378-383
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Endoreversible Modeling and Optimization of a Multistage Heat Engine System with a Generalized Heat Transfer Law via Hamilton-Jacobi-Bellman Equations and Dynamic Programming
Autorzy:
Xia, S.
Chen, L.
Sun, F.
Powiązania:
https://bibliotekanauki.pl/articles/1504513.pdf
Data publikacji:
2011-06
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
05.70.-a
05.60.Cd
05.70.Ln
Opis:
A multistage endoreversible Carnot heat engine system operating between a finite thermal capacity high-temperature fluid reservoir and an infinite thermal capacity low-temperature environment with a generalized heat transfer law [q ∝ ( Δ $(T^{n}))^{m}$] is investigated in this paper. Optimal control theory is applied to derive the continuous Hamilton-Jacobi-Bellman equations, which determine the optimal fluid temperature configurations for maximum power output under the conditions of fixed initial time and fixed initial temperature of the driving fluid. Based on the general optimization results, the analytical solution for the case with Newtonian heat transfer law [q ∝ Δ(T)] is further obtained. Since there are no analytical solutions for the other heat transfer laws, the continuous Hamilton-Jacobi-Bellman equations are discretized and the dynamic programming algorithm is adopted to obtain the complete numerical solutions of the optimization problem, and the relationships among the maximum power output of the system, the process period and the fluid temperature are discussed in detail. The results show that the optimal high-temperature fluid reservoir temperature for the maximum power output of the multistage heat engine system with Newtonian and linear phenomenological [q ∝ Δ $(T^{-1})$] heat transfer laws decrease exponentially and linearly with time, respectively, while those with the Dulong-Petit [q∝$(Δ T)^{1.25}$], radiative [q∝ Δ $(T^4)$] and [q∝$(Δ(T^4))^{1.25}$] heat transfer laws are different from the former two cases significantly.
Źródło:
Acta Physica Polonica A; 2011, 119, 6; 747-760
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Tunneling Magnetoresistance in Ferromagnetic Junctions: Bias Dependence
Autorzy:
Barnaś, J.
Lee, S. F.
Holody, P.
Schelp, L. F.
Petroff, F.
Fert, A.
Powiązania:
https://bibliotekanauki.pl/articles/1968769.pdf
Data publikacji:
1998-02
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
73.40.Gk
73.40.Rw
75.70.-i
Opis:
Electron tunneling between two ferromagnetic electrodes across an insulating barrier is analysed theoretically and experimentally. The barrier is either uniform or it includes a layer of small magnetic metallic particles. Particular attention is paid to the origin of the tunneling magnetoresistance and its bias dependence, as well as to the effects due to Coulomb blockade.
Źródło:
Acta Physica Polonica A; 1998, 93, 2; 387-391
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Comparison of Second Order Algorithms for Function Approximation with Neural Networks
Autorzy:
Boutalbi, E.
Ait Gougam, L.
Mekideche-Chafa, F.
Powiązania:
https://bibliotekanauki.pl/articles/1402013.pdf
Data publikacji:
2015-08
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
02.30.Mv
07.05.Mh
Opis:
The Neural networks are massively parallel, distributed processing systems representing a new computational technology built on the analogy to the human information processing system. They are usually considered as naturally parallel computing models. The combination of wavelets with neural networks can hopefully remedy each other's weaknesses, resulting in wavelet based neural network capable of approximating any function with arbitrary precision. A wavelet based neural network is a nonlinear regression structure that represents nonlinear mappings as the superposition of dilated and translated versions of a function, which is found both in the space and frequency domains. The desired task is usually obtained by a learning procedure which consists in adjusting the "synaptic weights". For this purpose, many learning algorithms have been proposed to update these weights. The convergence for these learning algorithms is a crucial criterion for neural networks to be useful in different applications. In this paper, we use different training algorithms for feed forward wavelet networks used for function approximation. The training is based on the minimization of the least-square cost function. The minimization is performed by iterative first and second order gradient-based methods. We make use of the Levenberg-Marquardt algorithm to train the architecture of the chosen network and, then, the training procedure starts with a simple gradient method which is followed by a BFGS (Broyden, Fletcher, Glodfarb et Shanno) algorithm. The conjugate gradient method is then used. The performances of the different algorithms are then compared. It is found that the advantage of the last training algorithm, namely, conjugate gradient method, over many of the other optimization algorithms is its relative simplicity, efficiency and quick convergence.
Źródło:
Acta Physica Polonica A; 2015, 128, 2B; B-271-B-272
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Theory of Magnetotunnelling through Donors in the Quantum Well of Double-Barrier Resonant-Tunnelling Structures
Autorzy:
Fromhold, T. M.
Sheard, F. W.
Eaves, L.
Powiązania:
https://bibliotekanauki.pl/articles/1921661.pdf
Data publikacji:
1992-11
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
73.40.Gk
71.55.Eq
85.30.Tv
Opis:
The tunnel current from a two-dimensional electron gas (2DEG) into donor impurities in the quantum well of a double-barrier heterostructure is studied using the Bardeen Transfer-Hamiltonian formalism. Resonant tunnelling occurs when the donor level lies within the energy range of occupied 2DEG states. It is shown that in the presence of a magnetic field B normal to the current flow, the magnetocurrent J(B) is determined by the Fourier probability density of the donor wave function corresponding to the momentum p0 transferred to the tunnelling electrons by the Lorentz force. Then experimental J(B) curves, in principle, directly measure the donor wave function. The magnetocurrent is quenched when p0 greatly exceeds the width of the distribution of momentum Fourier components of the donor wave function.
Źródło:
Acta Physica Polonica A; 1992, 82, 5; 737-740
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Phase Diagram of Spin-Orbital Model
Autorzy:
Oleś, A. M.
Feiner, L. F.
Zaanen, J.
Powiązania:
https://bibliotekanauki.pl/articles/1964677.pdf
Data publikacji:
1997-08
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.27.+a
75.30.Et
75.40.-s
75.10.Jm
Opis:
We show that the mean-field phase diagram of the realistic spin-orbital model derived for a perovskite lattice in three dimensions consists of four different classical magnetic phases which become degenerate at orbital degeneracy. The quantum fluctuations are drastically enhanced and suppress the classical long-range order, providing a new mechanism to stabilize a quantum spin liquid near the multicritical point.
Źródło:
Acta Physica Polonica A; 1997, 92, 2; 367-370
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Spontaneous Currents in a Ferromagnet-Normal Metal-Superconductor Trilayer
Autorzy:
Krawiec, M.
Annett, J. F.
Györffy, B. L.
Powiązania:
https://bibliotekanauki.pl/articles/2046734.pdf
Data publikacji:
2006-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
72.25.-b
74.50.+r
75.75.+a
Opis:
We discuss the ground state properties of the system composed of a normal metal sandwiched between ferromagnet and superconductor within a tight binding Hubbard model. We solved the spin-polarized Hartree-Fock-Gorkov equations together with the Maxwell equation (Ampere's law) and found a proximity induced Fulde-Ferrell-Larkin-Ovchinnikov state in this system. Here we show that the inclusion of the normal metal layer in between those subsystems does not necessarily lead to the suppression of the Fulde-Ferrell-Larkin-Ovchinnikov phase. Moreover, we found that depending on the thickness of the normal metal slab the system can be switched periodically between the state with the spontaneous current flowing to that one with no current. All these effects can be explained in terms of the Andreev bound states formed in such structures.
Źródło:
Acta Physica Polonica A; 2006, 109, 4-5; 507-512
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Wyświetlanie 1-15 z 91

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