Kh. Lotfy^{1}

Abstract: In the present investigation, a novel model of a rotating elastic semiconductor medium in the context of photothermal excitation is presented. This phenomenon has been studied using a two-temperatu...

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Topics: Context (language use) (54%), Thermal conductivity (51%)

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10 results found

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Abstract: The thermal variable conductivity of a rotator semiconductor elastic medium is investigated. The medium is exposed to beams of light and an initial external magnetic field during a diffusion proces...

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Topics: Thermal conductivity (52%), Excitation (50%)

7 Citations

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Abstract: This study investigates a strong magnetic field acting over an elastic rotator semiconductor medium. The Thomson effect due to the magnetic field during the photothermal transport process is studied, and the thermoelectricity theory is used to explain the behavior of waves in the homogenous and isotropic medium under the effect of variable thermal conductivity. The variable thermal conductivity is considered as a linear function of the temperature. The two-dimensional deformation equations are used to describe the overlaps among plasma, electrical, thermal, and magneto-elastic waves. The charge density of inertia-particles is considered as a function of time for studying the induced electric current. The normal mode analysis is used to obtain the exact solutions of the physical field distributions as part of this phenomenon. To obtain the complete solutions of the physical field quantities, the certain mechanical loads, electromagnetic effects, thermal effects, and plasma recombination process are applied herein. The results of the physical distributions are graphically depicted and discussed in consideration of the internal heat source, rotation, and Peltier coefficient.

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Topics: Thermal conductivity (56%), Electric current (56%), Magnetic field (55%) ... read more

6 Citations

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Abstract: The semiconductor elastic medium in the context of the photothermal theory under the influence of rotation field is studied. A novel model of the governing equations is investigated due to the refined multi-phase-lags with the thermal relaxation times of the heat equation with the hydrostatic initial stress during transport process of the photothermal phenomenon. The interaction between the multi-waves of elastic-thermal-plasma is obtained. The normal mode method in the two dimensions is applied to obtain the exact solutions of the basic physical quantities under investigation. Plasma, thermal and mechanical loads have been applied on the free surface of the semi-infinite semiconductor elastic medium to get the complete solutions of the basic physical fields. Some comparisons are shown graphically and they are discussed as a function of thermal memories with the variation of some parameters. Silicon (Si) material is used to make the numerical simulation and to display the sensitivity to the variation of the rotation parameter.

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Topics: Heat equation (54%), Free surface (53%), Stress (mechanics) (52%) ... read more

2 Citations

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Abstract: In this work, a novel model of semiconducting elastic material is studied during a process of photothermal excitation. The dual phase lag (DPL) for the heat conduction equation is introduced in the context of the variable of the thermal conductivity. The thermal conductivity can be chosen as a linear function of temperature (depend on temperature). The generalized thermoelasticy theory is investigated when an internal heat source is steady with a constant speed in the context of the gravitational field. The harmonic wave technique is used in two-dimensional deformations to obtain the considered physical fields. Some thermal loading subjected to thermal shock and other mechanical forces at the outer free surface of a semi-infinite elastic medium (semiconductor as silicon) are applied. The considered physical fields were illustrated graphically. The influences of some several variables are obtained which based on the DPL (thermal memories) model and the variable thermal conductivity. The results obtained are investigated and are depicted graphically.

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Topics: Thermal conductivity (62%), Heat equation (54%), Thermal shock (54%) ... read more

1 Citations

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Magneto-Photo-Thermo-Microstretch Semiconductor Elastic Medium Due to Photothermal Transport Process

Abstract: Electro-magnetic-thermal-microstretch elastic mathematical-physical model of semiconductor medium is investigated. The governing equations are studied in the context of photo-thermoelasticity theory during photothermal transport process. The semiconductor medium is exposed to an external magnetic field and a beam of laser. The coupled between electromagnetic field, thermal, elastic and plasma waves when the inertia-microstretch properties of elastic semiconductor material is taken into account. The main physical quantities are taken during two dimensions (2D) electronic-elastic deformation. The microinertia of microelement under the impact of external magnetic field is taken into consideration. The harmonic wave solutions in 2D with time variation is used to obtain the main physical fields. To obtain the complete solutions of the physical fields, some mechanical-thermal-elastic and plasma conditions for the semiconductor medium are taken at the boundary. The physical constants of the silicon (Si) material are used to make the numerical simulations and obtained the physical variables with the horizontal distance graphically. Many comparisons are made according to the thermal memories and the magnetic field influence.

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Topics: Electromagnetic field (53%), Magnetic field (52%), Plasma (50%)

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36 results found

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Abstract: In this work a generalized dynamical theory of thermoelasticity is formulated using a form of the heat transport equation which includes the time needed for acceleration of the heat flow. The theory takes into account the coupling effect between temperature and strain rate, but the resulting coupled equations are both hyperbolic. Thus, the paradox of an infinite velocity of propagation, inherent in the existing coupled theory of thermoelasticity, is eliminated. A solution is obtained using the generalized theory which compares favourably with a known solution obtained using the conventional coupled theory.

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Topics: Convection–diffusion equation (51%), Thermoelastic damping (51%)

2,848 Citations

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Abstract: A unified treatment is presented of thermoelasticity by application and further developments of the methods of irreversible thermodynamics. The concept of generalized free energy introduced in a previous publication plays the role of a ``thermoelastic potential'' and is used along with a new definition of the dissipation function in terms of the time derivative of an entropy displacement. The general laws of thermoelasticity are formulated in a variational form along with a minimum entropy production principle. This leads to equations of the Lagrangian type, and the concept of thermal force is introduced by means of a virtual work definition. Heat conduction problems can then be formulated by the methods of matrix algebra and mechanics. This also leads to the very general property that the entropy density obeys a diffusion‐type law. General solutions of the equations of thermoelasticity are also given using the Papkovitch‐Boussinesq potentials. Examples are presented and it is shown how the generalized coordinate method may be used to calculate the thermoelastic internal damping of elastic bodies.

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Topics: Entropy (classical thermodynamics) (61%), Non-equilibrium thermodynamics (58%), Thermoelastic damping (57%) ... read more

1,929 Citations

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Abstract: This paper reviews the theory and applications of photoacoustic (also called optoacoustic) methods belonging to the more general area of photothermal measurement techniques. The theory covers excitation of gaseous or condensed samples with modulated continuous light beams or pulsed light beams. The applications of photoacoustic methods include spectroscopy, monitoring deexcitation processes, probing physical properties of materials, and generating mechanical motions. Several other related photothermal methods, as well as particle-acoustics and wave-acoustics methods are also described. This review complements an earlier and narrower review [Rev. Mod. Phys. 53, 517 (1981)] that is mainly concerned with sensitive detection by pulsed photoacoustic spectroscopy in condensed matter.

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Topics: Photoacoustic spectroscopy (66%)

1,097 Citations

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Abstract: Buildup and decay transients were observed when polar or nonpolar liquid cells were placed within the resonator of a helium—neon laser operating in the red at 6328 A. Similar but smaller effects were also observed with two solids. Time constants were the order of a few seconds for all materials, which suggests a thermal phenomenon, but general heating effects were ruled out by the strong localization of the phenomenon. Transverse motion of the cell by about one beam width caused new transients similar to the initial ones.It is believed that the effects are caused by absorption of the red light in the material, producing a local heating in the vicinity of the beam and a lens effect arising from the transverse gradient of refractive index. Absorptions of 10−3 to 10−4 parts per centimeter are sufficient to produce the effects, and are believed to be reasonable values for the materials studied. One of the most important applications may in fact be for the measurement of small absorbancies.The experiments are ...

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Topics: Beam diameter (51%)

909 Citations

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Abstract: This review article is a continuation of a previous article by the author, Thermoelasticity with second sound: A review, which appeared in this journal in March, 1986 (Appl Mech Rev 39(3) 355-376). Here, attention is focused on papers published during the past 10-12 years. Contributions to the theory of thermoelasticity with thermal relaxation and the temperature-rate dependent thermoelasticity theory are reviewed. The recently developed theory of thermoelasticity without energy dissipation is described, and its characteristic features highlighted. A glance is made at the new thermoelasticity theory which includes the so-called dual-phase-lag effects. There are 338 references.

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863 Citations