Wyniki wyszukiwania - Biblioteka Nauki

1

Crystal order and magnetic properties of Fe2.4V0.6Al alloy studied by magnetostatic and Mössbauer methods

100%

Popiel E. , Zarek W. , Kapuśniak Z. , Tuszyński M.

Nukleonika

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2003

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tom Vol. 48,suppl.1

65-70

EN

Performed investigations showed that the magnetic properties of the Fe2.4V0.6Al alloy markedly depend on the degree of atomic order of its cubic structure. The atomically disordered alloy with A2 (bcc) type structure exhibits ferromagnetic properties. Its Mössbauer spectra can be described by the hyperfine field distribution connected with various local environments of Fe atoms. Alloys with B2 (sc) and DO3 (fcc) type structure do not exhibit magnetic transition above 4.2 K. High values of the magnetization and its strongly non-linear variation with magnetic field intensity in a wide temperature range suggest the presence of magnetic iron clusters in these alloys. Superparamagnetic relaxation times of the order of 10-9 s and 5 × 10-8 s correspond to the largest magnetic clusters with a magnetic moment of 4 × 103 žB in B2 and 104 žB in DO3-type structure, respectively. Mössbauer spectra of these alloys confirm lack of the magnetic order and also suggest the presence of the Fe magnetic clusters with those relaxation times. It was shown that the increase of atomic order of the crystal structure causes formation of the Fe magnetic clusters and disappearing of the magnetic order.

2

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

100%

Zeng C. , Gong A. , Xie C.

Open Physics

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2011

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tom 9

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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.

3

Standard deviation in the simulation of statistical measurements

100%

Przystupa K. , Kolodiy Z. , Yatsyshyn S. , Majewski J. , Khoma Y. , Petrovska I. , Lasarenko S. , Hut T.

Metrology and Measurement Systems

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2023

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tom Vol. 30, nr 1

17--30

EN

Is this article simulation of statistical measurements is performed on the basis of which the analysis of the standard deviation of the obtained results is carried out. It is shown that the standard deviation is minimum and independent from measurement duration while an object is in the state of equilibrium. For objects in a stationary non-equilibrium state the standard deviation depends on the duration measurements and the parameters of the state. The influence of these factors on the standard deviation is assessed with equation which includes the relaxation time. The value of the relaxation time is determined by approximating the energy spectrum of the studied signals. The analysis of energy spectra showed that the spectrum of white noise is inherent in objects in equilibrium; the flicker component of the spectrum occurs when the state of the object deviates from equilibrium.

4

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

100%

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

Prace Naukowe Instytutu Podstaw Elektrotechniki i Elektrotechnologii Politechniki Wrocławskiej. Konferencje

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2007

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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.

5

Charge relaxation on surfaces of polymeric insulating materials for outdoor applications

100%

Sjöstedt H. , Montano R. , Serdyuk Y. , Gubanski S. M.

Materials Science Poland

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2009

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tom Vol. 27, No. 4/2

1129--1137

EN

The studies have been presented 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 located 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 in the considered system, which took place in a form of a burst corona, and the dynamics of the deposited charges could be related to burst corona pulses.

6

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

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2009

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tom 7

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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.

7

Viscoelastic model of waterhammer in single pipeline - problems and questions

88%

Weinerowska-Bords K.

Archives of Hydro-Engineering and Environmental Mechanics

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2006

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tom Vol. 53, nr 4

331-351

EN

In the paper, viscoelastic model of waterhammer in a single polymer pipeline is analysed. The theoretical background of viscoelastic behaviour of the structure is shown and the mathematical model of waterhammer in a polymer pipeline is presented. The main problems connected with applying the model are discussed. The main emphasis is on the question of parameter estimation. Important aspects of wave speed calibration are presented. Estimation of a second group of parameters - retardation time and creep compliance values - was analysed. Problems and questions connected with the number of parameters, methods of estimation, potential non-uniqueness of the solution and accuracy of obtained calculations were discussed.

8

Interaction due to thermodiffusive and mechanical sources in micropolar elastic medium

88%

Kumar R. , Kaushal S. , Miglani A.

Journal of Technical Physics

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2009

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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.

9

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

88%

Bronnikov S. V.

Applied Mechanics and Engineering

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1999

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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.

10

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

88%

Singh B. , Singh J. , Ailawalia P.

Archives of Mechanics

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2010

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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.

11

Forced vibrations due to mechanical loads in piezothermoelastic half-space

75%

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

International Journal of Applied Mechanics and Engineering

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2012

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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.

12

Elastodynamics of time harmonic sources in a thermally conducing cubic crystal

75%

Kumar R. , Rani L.

International Journal of Applied Mechanics and Engineering

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2003

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tom Vol. 8, no 4

637-650

EN

The disturbance due to a time harmonic mechanical, horizontal or vertical and thermal source in a homogeneous, thermally conducting cubic crystal, elastic half-plane is investigated by applying the Fourier transform. The displacements, stresses and temperature distribution so obtained in the physical domain are computed numerically and illustrated graphically. The numerical results of these quantities for magnesium crystal-like material are illustrated to compare the results for different theories of generalized thermoelasticity for insulated boundary and temperature gradient boundary.

13

On the systemic approach to balance deficiency

75%

Kowalska-Napora E.

Zeszyty Naukowe Uniwersytetu Przyrodniczo-Humanistycznego w Siedlcach. Seria: Administracja i Zarządzanie

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2013

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nr 25[98]

14

Theory of space-time dissipative elasticity and scale effects

75%

Lurie S. A. , Belov P. A.

Nanoscale Systems: Mathematical Modeling, Theory and Applications

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2013

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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.

15

On the transient waves in a thermoelastic half space

75%

Sharma J. N. , Sharma P. K.

International Journal of Applied Mechanics and Engineering

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2001

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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.

16

On the dynamic responses with and without energy dissipation in the thermoelastic rotating media

63%

Verma K. L. , Hasebe N.

International Journal of Applied Mechanics and Engineering

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2002

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tom Vol. 7, no 4

1329-1348

EN

The generalized dynamical theories of thermoelasticity with and without energy dissipation are applied to study the propagation of thermoelastic waves in an infinite, homogenous, isotropic medium rotating uniformly with constant angular velocity. A generalized characteristic equation is derived to investigate the effects of rotation, the relaxation time constants and thermomechanical coupling on the dispersion behavior of thermoelastic waves. Results of earlier works are deduced as particular cases of the more general results obtained here.

17

Internal friction in the ferroelectric – ferromagnetic composites

63%

Zachariasz R. , Bartkowska J. A. , Bochenek D. , Niemiec P.

Archives of Metallurgy and Materials

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2013

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tom Vol. 58, iss. 4

1327--1330

EN

In the work, temperature Q-1(T) and amplitude Q-1 (ε) dependences of internal friction for ferroelectric - ferromagnetic composites on the base of the PZT and ferrite were determined. The temperature dependences of internal friction Q-1 reveal the peak in the range of high temperatures. We have investigated the peak associated with the viscous-elastic mobility of ferroelectric domain walls. The internal friction due to the viscous-elastic mobility of ferroelectric domain walls was calculated and compared with the experimental data in the reference to the Wang’s theory. Based on internal friction measurements and theoretical considerations, the peak was described. Additionally the amplitude (isothermal) Q-1 (ε) dependences for the composites were made. This allowed for the interpretation of the maximum observed on the temperature dependences of the internal friction Q-1(T).

PL

W pracy wyznaczano temperaturowe Q-1(T) i amplitudowe Q-1 (ε) zależności tarcia wewnętrznego dla ferroelektryczno - ferromagnetycznych kompozytów powstałych na bazie PZT i ferrytu. Na wykresach temperaturowych zależności tarcia wewnętrznego, uzyskanych dla badanych materiałów, obserwowano występowanie maksimum w zakresie wysokich temperatur. Do opisu maksimum zastosowany został model Wanga, który uwzględnia oddziaływania związane z lepko-sprężystym ruchem ferroelektrycznych ścian domenowych. Model ten bardzo dobrze opisał wyniki doświadczalne zależności tarcia wewnętrznego Q-1 od temperatury. Dobra zgodność pomiędzy modelem, a danymi pomiarowymi sugeruje, że za powstanie maksimum odpowiedzialne są lepko-sprężyste ruchy ścian domenowych. Ponadto przeprowadzono pomiary amplitudowych (izotermicznych) zależności tarcia wewnętrznego Q-1 (ε) dla badanych kompozytów. Pozwoliło to na interpretację maksimum obserwowanego wcześniej na temperaturowych zależnościach tarcia wewnętrznego.

18

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

63%

Lotfy K.

International Journal of Applied Mechanics and Engineering

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2011

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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.

19

Investigation of Dimensional Changes During Garment Production and Suggestions for Solutions

63%

Kalkanci M. , Kurumer G.

Fibres & Textiles in Eastern Europe

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2015

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tom Vol. 23, no. 3 (111)

8--13

EN

Dimensional change problems experienced in textile products have always been an important subject and in the focus of attention. Today it is expected that dimensional changes in fabrics, the basic material of textile products, must range within certain limitations. Fabrics processed in the finishing divisions are wound or decatized in various forms according to the fabric structure and the demands of garment manufacturers. However, fabrics may be distorted in these storing processes, which results in undesired dimensional changes under the stress incurred. Nevertheless fabrics are required to be delivered to garment manufacturers at specific tension values. Indeed these values are not acquired as expected; consequently, it is known that they represent a core conflict subject between finishing plants and garment manufacturers. The present study investigated the structures of garment manufacturers and dimensional change problems they experience during fabric layout. The aim was to determine the severity of the problem in terms of the garment manufacturer and fabric types, which cause problems frequently, and to search for solutions to overcome this issue by means of a survey study. Solutions which would increase production efficiency and reduce processing time have been emphasized.

PL

Problem zmiany wymiarów tekstyliów w czasie produkcji odzieży jest bardzo ważnym problemem, a zakres zmian musi być poddany określonym ograniczeniom. Tekstylia obrabiane w procesach wykończalniczych są następnie nawijane i dekatyzowane w określonych warunkach i powinny być dostarczane do wytwórcy pod określonym naprężeniem. Celem artykułu jest zwrócenie uwagi na ważność problemu z punktu widzenia wytwórcy odzieży oraz określenie rozwiązań, które prowadziłyby do zwiększenia wydajności i skrócenia czasu produkcji.

20

Prędkość opadania ciężkiej cząstki w polu burzliwym

63%

Nowosielski J.

Inżynieria Chemiczna i Procesowa

|

2001

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tom T. 22, z. 3D

1025--1030

PL

Rozważono opadanie ciężkiej cząstki w płynie burzliwym. Stwierdzono, że stosowane powszechnie wzory do obliczeń czasu relaksacji cząstki nie są właściwe. Gdy opadanie odbywa się poza zakresem Stokesa, wartość czasu relaksacji dla przemieszczania się cząstki w kierunku zgodnym z działaniem siły zewnętrznej jest inna niż w kierunku prostopadłym, zaś rozkład składowej prędkości cząstki jest niesymetryczny, co wynika z nieliniowej zależności siły oporu od prędkości względem płynu.

EN

Falling of a heavy particle in turbulent fluid apart from Stokes law was considered. It was shown the relaxation time for the longitudinal dispersion differs from the value of the parameter for the transverse displacement of the particle. The distribution of the particle fluctuating velocity in the direction parallel to the external force is asymmetric because of the non-linear dependence of the drag force on the slip velocity.