Wyniki wyszukiwania - Biblioteka Nauki

1

Dynamical properties of an asymmetric bistable system with quantum fluctuations in the strong-friction limit

100%

Zeng C. , Gong A. , Xie C.

Open Physics

|

2011

|

tom 9

|

nr 1

198-204

EN

The dynamical properties of an overdamped Brownian particle moving in an asymmetric bistable system with quantum fluctuations are investigated. Within the strong-friction limit (the quantum Smoluchowski regime), the analytic expression for the relaxation time of the system is derived by means of the projection-operator method, in which the effects of the memory kernels are taken into account. Based on the relaxation time, we consider both the overdamped quantum case and its classical counterpart.In these contexts, the effects of the quantum fluctuations and the asymmetry of the potential are discussed. It is found that: (i) The quantum effects in an asymmetric bistable system on time scales of the relaxation process are more prominent for lower temperatures and smaller asymmetries of the potential. (ii) The quantum effects speed up the rate of fluctuation decay of the state-space variable for lower temperatures. (iii) The asymmetry of the potential first slows down the rate of fluctuation decay of the state-space variable and then increases it.

2

Effects of time delay on the statistical fluctuations for a bistable system driven by cross-correlated noises

100%

Zeng C.-h. , Zhou X.-f. , Tao S.-f.

Open Physics

|

2009

|

tom 7

|

nr 3

534-540

EN

We study the effects of time delay on the normalized correlation function C(s) and the associated relaxation time T c for a bistable system with correlations between multiplicative and additive white noises under the condition of small time delay. Using the projection operator method, the expressions of T c and C(s) are obtained. Based on numerical computations, it is found that the delay time τ slows down the rate of fluctuation decay of dynamical variable for the presence of positive feedback intensity (∈ > 0), while speeds up the rate of fluctuation decay of dynamical variable for the presence of negative feedback intensity (∈ < 0). The effects of the delay time τ on the T c and C(s) are entirely opposite for ∈ 〉 0 and ∈ < 0.

3

Charge relaxation on surfaces of polymeric insulating materials for outdoor applications.

100%

Sjostedt H. , Montano R. , Serdyuk Y. , Gubański M.

|

tom Vol. 46, nr 19

17-20

EN

This paper presents studies on spatial and temporal distributions of surface charge on samples of Ethylene Propylene Diene Monomer (EPDM) and Silicon Rubber (SIR). The charge was deposited from a positive impulse corona source at 1 mm above the polymeric surfaces. During the experiments, the number of pulses and their voltage level were varied. It was observed that the spread of the charge over the surface of the samples as well as its magnitude were both increasing with increasing number of impulses applied. EPDM accumulated charge easier and had a longer relaxation time than SIR. A common feature frequently observed in both cases was that the resulting charge distributions had a saddle-like pattern. Performed computer simulations showed that this feature can be attributed to peculiarities of the corona charging proc the considered system, which took place in form of a burst corona, and the dynamics of the deposited charges could be related to burst corona pulses.

4

Interaction due to thermodiffusive and mechanical sources in micropolar elastic medium

88%

Kumar R. , Kaushal S. , Miglani A.

|

2009

|

tom Vol. 50, no 4

317-342

EN

In this present paper, first the equations of generalized micropolar thermodiffusive medium, based on the theory of Lord and Shulman with one relaxation time are derived and then, deformation in a micropolar thermoelastic diffusive medium has been studied due to various sources. Laplace and Fourier transforms are used to solve the problem. The application of concentrated normal force, thermal point source and chemical potential point source has been considered to show the utility of the solution obtained. The transformed components of stress, temperature distribution and chemical potential are inverted numerically using a numerical inversion technique. The effect of micropolarity and diffusion on these quantities are presented graphically in order to illustrate and compare the analytical results. Some special cases of micropolarity and diffusion are also deduced.

5

Time and temperature dependent Young's modulus for isotropic and highly oriented polymers

88%

Bronnikov S. V.

|

1999

|

tom Vol. 4, no spec.

69-74

EN

Experimental time and temperature dependencies of the complex Young's modulus components have been analyzed for isotropic and uniaxially oriented polymers of different chemical structures. In the regions of relaxation transitions, these dependencies have been described by the equations of viscoelasticity. For highly oriented polymers, the relaxation time distribution has been approximated by a rectangular ('box') function. Such an approximation results specific formulae for time and temperature relaxation of the Young's modulus components.

6

Thermoelastic waves at an interface between two solid half-spaces under hydrostatic initial stress

88%

Singh B. , Singh J. , Ailawalia P.

|

2010

|

tom Vol. 62, nr 3

177-193

EN

A model of two semi-infinite half-spaces of different thermoelastic solids is considered in welded contact under hydrostatic initial stress. The appropriate boundary conditions are satisfied at the interface to obtain the reflection and refraction coefficients of various reflected and refracted waves during incidence of the quasi-thermal wave. A particular numerical example is considered to show the effect of hydrostatic initial stress on these coefficients for a certain range of the angle of incidence.

7

Forced vibrations due to mechanical loads in piezothermoelastic half-space

75%

Sharma J. N. , Thakur A. D. , Sharma Y. D.

|

tom Vol. 17, no. 2

535-557

EN

The article studies disturbances in a homogeneous, transversely isotropic, generalized piezothermoelastic half-space due to impact/continuous strip mechanical loads acting on a thermally insulated/isothermal and electrically shorted (closed circuit) surface. Combinations of the Laplace transform with respect to time and Fourier transform with respect to a space variable are employed to solve the boundary value problem in the transformed domain, in the context of classical and non-classical theories of thermoelasticity. The systems of equations are solved by using the Gauss elimination process for the unknowns. The values of these unknowns are used in the formal solution which leads to the expressions of displacements, temperature change, electric potential, electric displacement and stresses in the transformed domain. In order to obtain solution in the physical domain the inverse transform integrals are evaluated by using the Romberg integration and Fourier series approximations numerically. Temperature change, stresses and electric displacement so obtained in the physical domain, are computed numerically from the relevant expressions and relations for PZT-5A material. The illustrations and comparisons of the results for classical and non-classical theories of thermoelasticity are presented graphically. This may find applications in buzzers inside pagers and cell phones, shakers inside ultrasonic cleaners and strain sensors inside pressure gages.

8

On the transient waves in a thermoelastic half space

75%

Sharma J. N. , Sharma P. K.

|

2001

|

tom Vol. 6, no 4

923-946

EN

The distribution due to line source in a homogeneous isotropic thermoelastic half space has been investigated by applying a combination of the Laplace and Fourier transform technique in the context of generalised theories of thermoelasticity. The inverse transform integrals have been evaluated by using the Cagniard method to obtain the exact closed algebraic expressions for the displacement and temperature as a function of time and horizontal distances, which are valid for all epicentral distances. The displacement and temperature so obtained in the physical domain have been computed numerically and are presented graphically for an aluminum epoxy composite material. A comparison of results valid in different theories of thermoelasticity has also been made.

9

Theory of space-time dissipative elasticity and scale effects

75%

Lurie S. A. , Belov P. A.

Nanoscale Systems: Mathematical Modeling, Theory and Applications

|

2013

|

tom 2

166-178

EN

In this article a model of irreversible dynamic thermoelasticity of an ideal continuua is constructed from an elasticity theory of asymmetrical, transversely isotropic in time direction, dissipative defectless 4D-continuum. In the model the fourth component of the 4D-displacement vector is locally irregular time R. The kinematic model comprises 3D-tensor of distortion, 3Dvector of velocity, 3D-gradient vector of local irregular time and entropy in unified tensor object which is an asymmetrical 4D-tensor of distortion of second rank. Consequently, the force model comprises 3D-tensor of stress, 3D-vector of impulses, 3D-vector of heat flow and temperature in unified tensor object which is an asymmetrical 4D-stress tensor of second rank. Hooke’s law equations have been formulated which connect components of asymmetrical 4D-tensors of stress and distortion. Physical interpretations have been given to the tensors’ components of thermomechanical properties of formulated continuum. Therefore, the article formulate an irreversible dynamic thermoelasticity covariant model of ideal (defectless) continua in which basic kinematic and force variables are components of unified tensor objects and theory is represented by 4D-vector equation. Sedov’s equation has been derived and resulted into Euler’s equations, space projections of which determine motion equations, and time projection determines heat conductivity equation as well as the whole spectrum of the space-time boundary value problems. The proposed theory allows one to describe the scale effects in the thermal processes and opens prospects for studying the scale effects of the coupled dynamic thermoelasticity and its nanoscience applications. A temperature-scale refinement can also broaden the range of applicability of the law of heat conduction in solids to allow for design of small-sized components, devices and nano-systems.

10

Transient thermo-elastic disturbances in a visco-elastic semi-space due to a moving internal heat source

63%

Lotfy K. H. , Fathy R. A.

|

2010

|

tom Vol. 15, no 4

1169-1184

EN

This paper investigates the transient disturbances created by an internal line heat source that suddenly starts moving uniformly inside a visco-elastic half-space. The generalised theory of thermo-elasticity with relaxation time proposed by Lord and Shulman (1967) is applied. The material of the semi-infinite medium is an isotropic visco-elastic solid of Kelvin-Voight type. Applying the Fourier and Laplace transform technique, expressions for displacement components in the transformed domain are found. These expressions prove the existence of three waves - a modified thermal wave, a visco-elastic wave of defused nature and a transverse visco-elastic wave. Surface displacement components are evaluated on the boundary for small time only. Numerical results are given and illustrated graphically to highlight the variations of surface displacement components with distance for different values of time, source depth and velocity of the source.

11

Transient thermo-elastic disturbances in a visco-elastic semi-space due to a moving internal heat source

63%

Lotfy K.

|

2011

|

tom Vol. 16, no 3

747-762

EN

This paper investigates the transient disturbances created by an internal line heat source that suddenly starts moving uniformly inside a visco-elastic half-space. The generalised theory of thermo-elasticity with relaxation time proposed by Lord-Shulman (1967) is applied. The material of the semi-infinite medium is isotropic visco-elastic solid of Kelvin-Voight type. Applying the Fourier and Laplace transform technique, expressions for displacement components in the transformed domain are found out. These expressions prove the existence of three waves - a modified thermal wave, a visco-elastic wave of defused nature and a transverse visco-elastic wave. Surface displacement components are evaluated on the boundary for small time only. Numerical results are given and illustrated graphically to highlight the variations of surface displacement components with distance for different values of time, source depth and velocity of the source.