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Wyszukujesz frazę "phase problem" wg kryterium: Temat


Wyświetlanie 1-8 z 8
Tytuł:
The effect of noise, a constant background, and bit depth on the phase retrieval of pure phase objects
Autorzy:
Karitans, Varis
Tokmakovs, Andrejs
Antonuka, Adele
Powiązania:
https://bibliotekanauki.pl/articles/1835795.pdf
Data publikacji:
2021
Wydawca:
Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
Tematy:
phase retrieval
phase problem
diffraction
Opis:
In the current study, we investigate the effect of uniform white noise, Poisson noise and a constant background on the phase retrieval of pure phase objects. We also study the influence of the aforementioned factors on phase retrieval at different bit depths of intensity measurements. An algorithm called PhaseLift is used for phase retrieval as it requires a small number of modulating masks and can retrieve the phase of an object from sparse intensity measurements of low bit depth. A test object is modulated by eight random masks generated from a single mask and the phase of the object is retrieved from coded diffraction patterns. Different levels of uniform white noise, Poisson noise and constant background are superimposed on the diffraction patterns and the root-mean-square error (RMSE) of the retrieved object is calculated at each level. The results suggest that Poisson noise and a constant background at the same level cause similar RMSE compared to uniform white noise. Lowering the bit depth from 18-bits to 14-bits resulted in the decrease of the RMSE caused by Poisson noise and a constant background. We conclude that the effects of noise and constant background can be reduced by lowering the bit depth.
Źródło:
Optica Applicata; 2021, 51, 2; 257-269
0078-5466
1899-7015
Pojawia się w:
Optica Applicata
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Pseudo-phase mapping of speckle fields using 2D Hilbert transformation
Autorzy:
Zenkova, C. Y.
Gorsky, M. P.
Ryabiy, P. A.
Powiązania:
https://bibliotekanauki.pl/articles/174971.pdf
Data publikacji:
2016
Wydawca:
Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
Tematy:
speckle field
singular points
saddle points
phase problem
Opis:
The use of a "window" 2D Hilbert transform for the reconstruction of the phase distribution of the intensity of a speckle field is proposed. It is shown that the advantage of this approach consists in the invariance of a phase map to a change of the position of the kernel of transformation and in the possibility to reconstruct the structure-forming elements of the skeleton of an optical field, including singular points and saddle points. We demonstrate the possibility to reconstruct the equi-phase lines within a narrow confidence interval, and introduce an additional algorithm for solving the phase problem for random 2D intensity distributions.
Źródło:
Optica Applicata; 2016, 46, 1; 153-162
0078-5466
1899-7015
Pojawia się w:
Optica Applicata
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Group and Phase Velocity of Love Waves Propagating in Elastic Functionally Graded Materials
Autorzy:
Kiełczyński, P.
Szalewski, M.
Balcerzak, A.
Wieja, K.
Powiązania:
https://bibliotekanauki.pl/articles/177447.pdf
Data publikacji:
2015
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
surface Love waves
group velocity
phase velocity
functionally graded materials
profiles of elastic constants
direct Sturm-Liouville problem
Opis:
This paper presents a theoretical study of the propagation behaviour of surface Love waves in nonhomogeneous functionally graded elastic materials, which is a vital problem in acoustics. The elastic properties (shear modulus) of a semi-infinite elastic half-space vary monotonically with the depth (distance from the surface of the material). Two Love wave waveguide structures are analyzed: 1) a nonhomogeneous elastic surface layer deposited on a homogeneous elastic substrate, and 2) a semi-infinite nonhomogeneous elastic half-space. The Direct Sturm-Liouville Problem that describes the propagation of Love waves in nonhomogeneous elastic functionally graded materials is formulated and solved 1) analytically in the case of the step profile, exponential profile and 1cosh2 type profile, and 2) numerically in the case of the power type profiles (i.e. linear and quadratic), by using two numerical methods: i.e. a) Finite Difference Method, and b) Haskell-Thompson Transfer Matrix Method. The dispersion curves of phase and group velocity of surface Love waves in inhomogeneous elastic graded materials are evaluated. The integral formula for the group velocity of Love waves in nonhomogeneous elastic graded materials has been established. The results obtained in this paper can give a deeper insight into the nature of Love waves propagation in elastic nonhomogeneous functionally graded materials.
Źródło:
Archives of Acoustics; 2015, 40, 2; 273-281
0137-5075
Pojawia się w:
Archives of Acoustics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Estimation of relaxation and thermalization times in microscale heat transfer model
Autorzy:
Mochnacki, B.
Paruch, M.
Powiązania:
https://bibliotekanauki.pl/articles/279599.pdf
Data publikacji:
2013
Wydawca:
Polskie Towarzystwo Mechaniki Teoretycznej i Stosowanej
Tematy:
microscale heat transfer
laser heating
dual phase lag model
inverse problem
Opis:
The energy equation corresponding to the dual phase lag model (DPLM) results from the generalized form of the Fourier law, in which the two ‘delay times’ (relaxation and thermalization time) are introduced. The DPLM should be used in the case of microscale heat transfer analysis, in particular when thermal processes are characterized by extremely short duration (e.g. ultrafast laser pulse), considerable temperature gradients and very small dimensions (e.g. thin metal film). In this paper, the problem of relaxation and thermalization time identification is discussed, at the same time the heat transfer processes proceeding in the domain of a thin metal film subjected to a laser beam are analyzed. The solution presented bases on the application of evolutionary algorithms. The additional information concerning the transient temperature distribution on a metal film surface is assumed to be known. At the stage of numerical realization, the finite difference method (FDM) is used. In the final part of the paper, an example of computations is presented.
Źródło:
Journal of Theoretical and Applied Mechanics; 2013, 51, 4; 837-845
1429-2955
Pojawia się w:
Journal of Theoretical and Applied Mechanics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
An abstract Cauchy problem for higher order functional differential inclusions with infinite delay
Autorzy:
Ke, Tran
Obukhovskii, Valeri
Wong, Ngai-Ching
Yao, Jen-Chih
Powiązania:
https://bibliotekanauki.pl/articles/729357.pdf
Data publikacji:
2011
Wydawca:
Uniwersytet Zielonogórski. Wydział Matematyki, Informatyki i Ekonometrii
Tematy:
Cauchy problem
functional differential inclusion
infinite delay
higher order
existence family
phase space
fixed point
multivalued map
measure of noncompactness
condensing map
Opis:
The existence results for an abstract Cauchy problem involving a higher order differential inclusion with infinite delay in a Banach space are obtained. We use the concept of the existence family to express the mild solutions and impose the suitable conditions on the nonlinearity via the measure of noncompactness in order to apply the theory of condensing multimaps for the demonstration of our results. An application to some classes of partial differential equations is given.
Źródło:
Discussiones Mathematicae, Differential Inclusions, Control and Optimization; 2011, 31, 2; 199-229
1509-9407
Pojawia się w:
Discussiones Mathematicae, Differential Inclusions, Control and Optimization
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Analytic-numerical method of determining the freezing front location
Autorzy:
Grzymkowski, R.
Hetmaniok, E.
Pleszczyński, M.
Powiązania:
https://bibliotekanauki.pl/articles/381964.pdf
Data publikacji:
2011
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
solidification process
information technology
foundry industry
one-phase Stefan problem
moving boundary problem
proces krzepnięcia
technologia informacyjna
przemysł odlewniczy
jednofazowy problem Stefana
problem brzegowy
Opis:
Mathematical modeling of thermal processes combined with the reversible phase transitions of type: solid phase – liquid phase leads to formulation of the parabolic boundary problems with the moving boundary. Solution of such defined problem requires, most often, to use sophisticated numerical techniques and far advanced mathematical tools. Excellent illustration of the complexity of considered problems, as well as of the variety of approaches used for finding their solutions, gives the papers [1-4]. In the current paper, the authors present the, especially attractive from the engineer point of view, analytic-numerical method for finding the approximate solution of selected class of problems which can be reduced to the one-phase solidification problem of a plate with the unknown a priori, varying in time boundary of the region in which the solution is sought. Proposed method is based on the known formalism of initial expansion of the sought function describing the temperature field into the power series, some coefficients of which are determined with the aid of boundary conditions, and on the approximation of the function defining the location of freezing front with the broken line, parameters of which are numerically determined.
Źródło:
Archives of Foundry Engineering; 2011, 11, 3 spec.; 75-80
1897-3310
2299-2944
Pojawia się w:
Archives of Foundry Engineering
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Estimation of dual phase lag model parameters using the evolutionary algorithms
Autorzy:
Mochnacki, B.
Paruch, M.
Powiązania:
https://bibliotekanauki.pl/articles/380526.pdf
Data publikacji:
2011
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
microscale heat transfer
dual phase lag model
inverse problem
numerical modeling
przepływ mikroskalowy
model dwufazowy
zadanie odwrotne
model numeryczny
Opis:
Generalization of Fourier law, in particular the introduction of two ‘delay times’ (relaxation time τq and thermalization time τT) leads to the new form of energy equation called the dual-phase-lag model (DPLM). This equation should be applied in a case of microscale heat transfer modeling. In particular, DPLM constitutes a good approximation of thermal processes which are characterized by extremely short duration (e.g. ultrafast laser pulse), extreme temperature gradients and geometrical features of domain considered (e.g. thin metal film). The aim of considerations presented in this paper is the identification of two above mentioned positive constants τq, τT. They correspond to the relaxation time, which is the mean time for electrons to change their energy states and the thermalization time, which is the mean time required for electrons and lattice to reach equilibrium. In this paper the DPLM equation is applied for analysis of thermal processes proceeding in a thin metal film subjected to a laser beam. At the stage of computations connected with the identification problem solution the evolutionary algorithms are used. To solve the problem the additional information concerning the transient temperature distribution on a metal film surface is assumed to be known.
Źródło:
Archives of Foundry Engineering; 2011, 11, 3 spec.; 277-281
1897-3310
2299-2944
Pojawia się w:
Archives of Foundry Engineering
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Boundary optimal control problem for the phase-field transition system using fractional steps method
Zadanie sterowania optymalnego brzegiem dla układu pola ze zmianą fazy z wykorzystaniem metody kroków ułamkowych
Autorzy:
Moroşanu, C.
Powiązania:
https://bibliotekanauki.pl/articles/206721.pdf
Data publikacji:
2003
Wydawca:
Polska Akademia Nauk. Instytut Badań Systemowych PAN
Tematy:
zagadnienie ze swobodnym brzegiem
sterowanie optymalne
metoda kroków ułamkowych
warunki optymalności
metoda elementu skończonego
metoda gradientowa
układ ze zmianą fazy
phase-field transition system
free boundary problem
optimal control
fractional steps method
optimality conditions
finite element method
gradient method
Opis:
In this paper we prove the convergence of an iterative scheme of fractional steps type for boundary optimal control problem which is governed by the phase-field transition system. The existence of an optimal control and necessary optimality conditions are given for approximating problem. A gradient type algorithm and numerical implementation of this algorithm are discussed.
W artykule dowodzi się zbieżności procedury iteracyjnej typu kroków ułamkowych dla zagadnienia sterowania optymalnego brzegiem w układzie pola ze zmianą fazy. Wykazano istnienie sterowania optymalnego i podano warunki konieczne optymalności dla zagadnienia aproksymującego. Rozpatrzono odpowiedni algorytm gradientowy oraz realizację numeryczną tego algorytmu.
Źródło:
Control and Cybernetics; 2003, 32, 1; 5-32
0324-8569
Pojawia się w:
Control and Cybernetics
Dostawca treści:
Biblioteka Nauki
Artykuł
    Wyświetlanie 1-8 z 8

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