Mathematical Modeling of Torsional Surface Wave Propagation in a Non-Homogeneous Transverse Isotropic Elastic Solid Semi-Infinite Medium Under a Layer

Science.gov (United States)

Sethi, M.; Sharma, A.; Vasishth, A.

2017-05-01

The present paper deals with the mathematical modeling of the propagation of torsional surface waves in a non-homogeneous transverse isotropic elastic half-space under a rigid layer. Both rigidities and density of the half-space are assumed to vary inversely linearly with depth. Separation of variable method has been used to get the analytical solutions for the dispersion equation of the torsional surface waves. Also, the effects of nonhomogeneities on the phase velocity of torsional surface waves have been shown graphically. Also, dispersion equations have been derived for some particular cases, which are in complete agreement with some classical results.

Qualitative analysis of homogeneous universes

International Nuclear Information System (INIS)

Novello, M.; Araujo, R.A.

1980-01-01

The qualitative behaviour of cosmological models is investigated in two cases: Homogeneous and isotropic Universes containing viscous fluids in a stokesian non-linear regime; Rotating expanding universes in a state which matter is off thermal equilibrium. (Author) [pt

Progress in the analysis of non-axisymmetric wave propagation in a homogeneous solid circular cylinder of a piezoelectric transversely isotropic material

CSIR Research Space (South Africa)

Every, AG

2010-01-01

Full Text Available Non-axisymmetric waves in a free homogeneous piezoelectric cylinder of transversely isotropic material with axial polarization are investigated on the basis of the linear theory of elasticity and linear electromechanical coupling. The solution...

Longitudinal and transverse structure functions in decaying nearly homogeneous and isotropic turbulence

International Nuclear Information System (INIS)

Ahmad Imtiaz; Lu Zhi-Ming; Liu Yu-Lu

2014-01-01

Streamwise evolution of longitudinal and transverse velocity structure functions in a decaying homogeneous and nearly isotropic turbulence is reported for Reynolds numbers Re λ up to 720. First, two theoretical relations between longitudinal and transverse structure functions are examined in the light of recently derived relations and the results show that the low-order transverse structure functions can be well approximated by longitudinal ones within the sub-inertial range. Reconstruction of fourth-order transverse structure functions with a recently proposed relation by Grauer et al. is comparatively less valid than the relation already proposed by Antonia et al. Secondly, extended self-similarity methods are used to measure the scaling exponents up to order eight and the streamwise evolution of scaling exponents is explored. The scaling exponents of longitudinal structure functions are, at first location, close to Zybin's model, and at the fourth location, close to She—Leveque model. No obvious trend is found for the streamwise evolution of longitudinal scaling exponents, whereas, on the contrary, transverse scaling exponents become slightly smaller with the development of a steamwise direction. Finally, the stremwise variation of the order-dependent isotropy ratio indicates the turbulence at the last location is closer to isotropic than the other three locations. (electromagnetism, optics, acoustics, heat transfer, classical mechanics, and fluid dynamics)

A forgotten argument by Gordon uniquely selects Abraham's tensor as the energy-momentum tensor for the electromagnetic field in homogeneous, isotropic matter

International Nuclear Information System (INIS)

Antoci, S.; Mihich, L.

1997-01-01

Given the present status of the problem of the electromagnetic energy tensor in matter, there is perhaps use in recalling a forgotten argument given in 1923 by W. Gordon. Let us consider a material medium which is homogeneous and isotropic when observed in its rest frame. For such a medium, Gordon's argument allows to reduce the above-mentioned problem to an analogous one, defined in a general relativistic vacuum. For the latter problem the form of the Lagrangian is known already, hence the determination of the energy tensor is a straightforward matter. One just performs the Hamiltonian derivative of the Lagrangian chosen in this way with respect to the true metric g ik . Abraham's tensor is thus selected as the electromagnetic energy tensor for a medium which is homogeneous and isotropic in its rest frame

A generalized self-similar spectrum for decaying homogeneous and isotropic turbulence

Science.gov (United States)

Yang, Pingfan; Pumir, Alain; Xu, Haitao

2017-11-01

The spectrum of turbulence in dissipative and inertial range can be described by the celebrated Kolmogorov theory. However, there is no general solution of the spectrum in the large scales, especially for statistically unsteady turbulent flows. Here we propose a generalized self-similar form that contains two length-scales, the integral scale and the Kolmogorov scale, for decaying homogeneous and isotropic turbulence. With the help of the local spectral energy transfer hypothesis by Pao (Phys. Fluids, 1965), we derive and solve for the explicit form of the energy spectrum and the energy transfer function, from which the second- and third-order velocity structure functions can also be obtained. We check and verify our assumptions by direct numerical simulations (DNS), and our solutions of the velocity structure functions compare well with hot-wire measurements of high-Reynolds number wind-tunnel turbulence. Financial supports from NSFC under Grant Number 11672157, from the Alexander von Humboldt Foundation, and from the MPG are gratefully acknowledged.

Spectral non-equilibrium property in homogeneous isotropic turbulence and its implication in subgrid-scale modeling

Energy Technology Data Exchange (ETDEWEB)

Fang, Le [Laboratory of Mathematics and Physics, Ecole Centrale de Pékin, Beihang University, Beijing 100191 (China); Zhu, Ying [Laboratory of Mathematics and Physics, Ecole Centrale de Pékin, Beihang University, Beijing 100191 (China); National Key Laboratory of Science and Technology on Aero-Engine Aero-Thermodynamics, School of Energy and Power Engineering, Beihang University, Beijing 100191 (China); Liu, Yangwei, E-mail: liuyangwei@126.com [National Key Laboratory of Science and Technology on Aero-Engine Aero-Thermodynamics, School of Energy and Power Engineering, Beihang University, Beijing 100191 (China); Lu, Lipeng [National Key Laboratory of Science and Technology on Aero-Engine Aero-Thermodynamics, School of Energy and Power Engineering, Beihang University, Beijing 100191 (China)

2015-10-09

The non-equilibrium property in turbulence is a non-negligible problem in large-eddy simulation but has not yet been systematically considered. The generalization from equilibrium turbulence to non-equilibrium turbulence requires a clear recognition of the non-equilibrium property. As a preliminary step of this recognition, the present letter defines a typical non-equilibrium process, that is, the spectral non-equilibrium process, in homogeneous isotropic turbulence. It is then theoretically investigated by employing the skewness of grid-scale velocity gradient, which permits the decomposition of resolved velocity field into an equilibrium one and a time-reversed one. Based on this decomposition, an improved Smagorinsky model is proposed to correct the non-equilibrium behavior of the traditional Smagorinsky model. The present study is expected to shed light on the future studies of more generalized non-equilibrium turbulent flows. - Highlights: • A spectral non-equilibrium process in isotropic turbulence is defined theoretically. • A decomposition method is proposed to divide a non-equilibrium turbulence field. • An improved Smagorinsky model is proposed to correct the non-equilibrium behavior.

The suite of analytical benchmarks for neutral particle transport in infinite isotropically scattering media

International Nuclear Information System (INIS)

Kornreich, D.E.; Ganapol, B.D.

1997-01-01

The linear Boltzmann equation for the transport of neutral particles is investigated with the objective of generating benchmark-quality evaluations of solutions for homogeneous infinite media. In all cases, the problems are stationary, of one energy group, and the scattering is isotropic. The solutions are generally obtained through the use of Fourier transform methods with the numerical inversions constructed from standard numerical techniques such as Gauss-Legendre quadrature, summation of infinite series, and convergence acceleration. Consideration of the suite of benchmarks in infinite homogeneous media begins with the standard one-dimensional problems: an isotropic point source, an isotropic planar source, and an isotropic infinite line source. The physical and mathematical relationships between these source configurations are investigated. The progression of complexity then leads to multidimensional problems with source configurations that also emit particles isotropically: the finite line source, the disk source, and the rectangular source. The scalar flux from the finite isotropic line and disk sources will have a two-dimensional spatial variation, whereas a finite rectangular source will have a three-dimensional variation in the scalar flux. Next, sources emitting particles anisotropically are considered. The most basic such source is the point beam giving rise to the Green's function, which is physically the most fundamental transport problem, yet may be constructed from the isotropic point source solution. Finally, the anisotropic plane and anisotropically emitting infinite line sources are considered. Thus, a firm theoretical and numerical base is established for the most fundamental neutral particle benchmarks in infinite homogeneous media

Non-Almost Periodicity of Parallel Transports for Homogeneous Connections

International Nuclear Information System (INIS)

Brunnemann, Johannes; Fleischhack, Christian

2012-01-01

Let A be the affine space of all connections in an SU(2) principal fibre bundle over ℝ 3 . The set of homogeneous isotropic connections forms a line l in A. We prove that the parallel transports for general, non-straight paths in the base manifold do not depend almost periodically on l. Consequently, the embedding l ↪ A does not continuously extend to an embedding l-bar ↪ A-bar of the respective compactifications. Here, the Bohr compactification l-bar corresponds to the configuration space of homogeneous isotropic loop quantum cosmology and A-bar to that of loop quantum gravity. Analogous results are given for the anisotropic case.

Investigation of anomalous very fast decay regimes in homogeneous isotropic turbulence

Science.gov (United States)

Meldi, Marcello; Sagaut, Pierre

2018-05-01

The emergence of anomalous fast decay regimes in homogeneous isotropic turbulence (HIT) decay is investigated via both theoretical analysis and eddy-damped quasi-normal Markovian simulations. The work provides new insight about a fundamental issue playing a role in HIT decay, namely the influence of non-standard shapes of the energy spectrum, in particular in the large energetic scale region. A detailed analysis of the kinetic energy spectrum E(k) and the non-linear energy transfer T(k) shows that anomalous decay regimes are associated with the relaxation of initial energy spectra which exhibit a bump at energetic scales. This feature induces an increase in the energy cascade rate, toward solutions with a smooth shape at the spectrum peak. Present results match observations reported in wind-tunnel experiments dealing with turbulence decay in the wake of grids and bluff bodies, including scaling laws for the dissipation parameter Cɛ. They also indicate that the ratio between the initial eddy turnover time and the advection time determines of how fast anomalous regimes relax toward classical turbulence free-decay. This parameter should be used for consistent data comparison and it opens perspectives for the control of multiscale effects in industrial applications.

Steady- and transient-state analysis of fully ceramic microencapsulated fuel with randomly dispersed tristructural isotropic particles via two-temperature homogenized model-I: Theory and method

International Nuclear Information System (INIS)

Lee, Yoon Hee; Cho, Bum Hee; Cho, Nam Zin

2016-01-01

As a type of accident-tolerant fuel, fully ceramic microencapsulated (FCM) fuel was proposed after the Fukushima accident in Japan. The FCM fuel consists of tristructural isotropic particles randomly dispersed in a silicon carbide (SiC) matrix. For a fuel element with such high heterogeneity, we have proposed a two-temperature homogenized model using the particle transport Monte Carlo method for the heat conduction problem. This model distinguishes between fuel-kernel and SiC matrix temperatures. Moreover, the obtained temperature profiles are more realistic than those of other models. In Part I of the paper, homogenized parameters for the FCM fuel in which tristructural isotropic particles are randomly dispersed in the fine lattice stochastic structure are obtained by (1) matching steady-state analytic solutions of the model with the results of particle transport Monte Carlo method for heat conduction problems, and (2) preserving total enthalpies in fuel kernels and SiC matrix. The homogenized parameters have two desirable properties: (1) they are insensitive to boundary conditions such as coolant bulk temperatures and thickness of cladding, and (2) they are independent of operating power density. By performing the Monte Carlo calculations with the temperature-dependent thermal properties of the constituent materials of the FCM fuel, temperature-dependent homogenized parameters are obtained

Steady- and Transient-State Analyses of Fully Ceramic Microencapsulated Fuel with Randomly Dispersed Tristructural Isotropic Particles via Two-Temperature Homogenized Model—I: Theory and Method

Directory of Open Access Journals (Sweden)

Yoonhee Lee

2016-06-01

Full Text Available As a type of accident-tolerant fuel, fully ceramic microencapsulated (FCM fuel was proposed after the Fukushima accident in Japan. The FCM fuel consists of tristructural isotropic particles randomly dispersed in a silicon carbide (SiC matrix. For a fuel element with such high heterogeneity, we have proposed a two-temperature homogenized model using the particle transport Monte Carlo method for the heat conduction problem. This model distinguishes between fuel-kernel and SiC matrix temperatures. Moreover, the obtained temperature profiles are more realistic than those of other models. In Part I of the paper, homogenized parameters for the FCM fuel in which tristructural isotropic particles are randomly dispersed in the fine lattice stochastic structure are obtained by (1 matching steady-state analytic solutions of the model with the results of particle transport Monte Carlo method for heat conduction problems, and (2 preserving total enthalpies in fuel kernels and SiC matrix. The homogenized parameters have two desirable properties: (1 they are insensitive to boundary conditions such as coolant bulk temperatures and thickness of cladding, and (2 they are independent of operating power density. By performing the Monte Carlo calculations with the temperature-dependent thermal properties of the constituent materials of the FCM fuel, temperature-dependent homogenized parameters are obtained.

Steady- and transient-state analysis of fully ceramic microencapsulated fuel with randomly dispersed tristructural isotropic particles via two-temperature homogenized model-II: Applications by coupling with COREDAX

International Nuclear Information System (INIS)

Lee, Yoon Hee; Cho, Bum Hee; Cho, Nam Zin

2016-01-01

In Part I of this paper, the two-temperature homogenized model for the fully ceramic microencapsulated fuel, in which tristructural isotropic particles are randomly dispersed in a fine lattice stochastic structure, was discussed. In this model, the fuel-kernel and silicon carbide matrix temperatures are distinguished. Moreover, the obtained temperature profiles are more realistic than those obtained using other models. Using the temperature-dependent thermal conductivities of uranium nitride and the silicon carbide matrix, temperature-dependent homogenized parameters were obtained. In Part II of the paper, coupled with the COREDAX code, a reactor core loaded by fully ceramic microencapsulated fuel in which tristructural isotropic particles are randomly dispersed in the fine lattice stochastic structure is analyzed via a two-temperature homogenized model at steady and transient states. The results are compared with those from harmonic- and volumetric-average thermal conductivity models; i.e., we compare keff eigenvalues, power distributions, and temperature profiles in the hottest single channel at a steady state. At transient states, we compare total power, average energy deposition, and maximum temperatures in the hottest single channel obtained by the different thermal analysis models. The different thermal analysis models and the availability of fuel-kernel temperatures in the two-temperature homogenized model for Doppler temperature feedback lead to significant differences

A priori study of subgrid-scale flux of a passive scalar in isotropic homogeneous turbulence

International Nuclear Information System (INIS)

Chumakov, Sergei

2008-01-01

We perform a direct numerical simulation (DNS) of forced homogeneous isotropic turbulence with a passive scalar that is forced by mean gradient. The DNS data are used to study the properties of subgrid-scale flux of a passive scalar in the framework of large eddy simulation (LES), such as alignment trends between the flux, resolved, and subgrid-scale flow structures. It is shown that the direction of the flux is strongly coupled with the subgrid-scale stress axes rather than the resolved flow quantities such as strain, vorticity, or scalar gradient. We derive an approximate transport equation for the subgrid-scale flux of a scalar and look at the relative importance of the terms in the transport equation. A particular form of LES tensor-viscosity model for the scalar flux is investigated, which includes the subgrid-scale stress. Effect of different models for the subgrid-scale stress on the model for the subgrid-scale flux is studied.

A priori study of subgrid-scale flux of a passive scalar in isotropic homogeneous turbulence.

Science.gov (United States)

Chumakov, Sergei G

2008-09-01

We perform a direct numerical simulation (DNS) of forced homogeneous isotropic turbulence with a passive scalar that is forced by mean gradient. The DNS data are used to study the properties of subgrid-scale flux of a passive scalar in the framework of large eddy simulation (LES), such as alignment trends between the flux, resolved, and subgrid-scale flow structures. It is shown that the direction of the flux is strongly coupled with the subgrid-scale stress axes rather than the resolved flow quantities such as strain, vorticity, or scalar gradient. We derive an approximate transport equation for the subgrid-scale flux of a scalar and look at the relative importance of the terms in the transport equation. A particular form of LES tensor-viscosity model for the scalar flux is investigated, which includes the subgrid-scale stress. Effect of different models for the subgrid-scale stress on the model for the subgrid-scale flux is studied.

Homogenous isotropic invisible cloak based on geometrical optics.

Science.gov (United States)

Sun, Jingbo; Zhou, Ji; Kang, Lei

2008-10-27

Invisible cloak derived from the coordinate transformation requires its constitutive material to be anisotropic. In this work, we present a cloak of graded-index isotropic material based on the geometrical optics theory. The cloak is realized by concentric multilayered structure with designed refractive index to achieve the low-scattering and smooth power-flow. Full-wave simulations on such a design of a cylindrical cloak are performed to demonstrate the cloaking ability to incident wave of any polarization. Using normal nature material with isotropy and low absorption, the cloak shows light on a practical path to stealth technology, especially that in the optical range.

Electro-magnetostatic homogenization of bianisotropic metamaterials

OpenAIRE

Fietz, Chris

2012-01-01

We apply the method of asymptotic homogenization to metamaterials with microscopically bianisotropic inclusions to calculate a full set of constitutive parameters in the long wavelength limit. Two different implementations of electromagnetic asymptotic homogenization are presented. We test the homogenization procedure on two different metamaterial examples. Finally, the analytical solution for long wavelength homogenization of a one dimensional metamaterial with microscopically bi-isotropic i...

The offset-midpoint traveltime pyramid in 3D transversely isotropic media with a horizontal symmetry axis

KAUST Repository

Hao, Qi

2014-12-30

Analytic representation of the offset-midpoint traveltime equation for anisotropy is very important for prestack Kirchhoff migration and velocity inversion in anisotropic media. For transversely isotropic media with a vertical symmetry axis, the offset-midpoint traveltime resembles the shape of a Cheops’ pyramid. This is also valid for homogeneous 3D transversely isotropic media with a horizontal symmetry axis (HTI). We extended the offset-midpoint traveltime pyramid to the case of homogeneous 3D HTI. Under the assumption of weak anellipticity of HTI media, we derived an analytic representation of the P-wave traveltime equation and used Shanks transformation to improve the accuracy of horizontal and vertical slownesses. The traveltime pyramid was derived in the depth and time domains. Numerical examples confirmed the accuracy of the proposed approximation for the traveltime function in 3D HTI media.

Homogenization of linearly anisotropic scattering cross sections in a consistent B1 heterogeneous leakage model

International Nuclear Information System (INIS)

Marleau, G.; Debos, E.

1998-01-01

One of the main problems encountered in cell calculations is that of spatial homogenization where one associates to an heterogeneous cell an homogeneous set of cross sections. The homogenization process is in fact trivial when a totally reflected cell without leakage is fully homogenized since it involved only a flux-volume weighting of the isotropic cross sections. When anisotropic leakages models are considered, in addition to homogenizing isotropic cross sections, the anisotropic scattering cross section must also be considered. The simple option, which consists of using the same homogenization procedure for both the isotropic and anisotropic components of the scattering cross section, leads to inconsistencies between the homogeneous and homogenized transport equation. Here we will present a method for homogenizing the anisotropic scattering cross sections that will resolve these inconsistencies. (author)

Influence of polymer additives on turbulent energy cascading in forced homogeneous isotropic turbulence studied by direct numerical simulations

International Nuclear Information System (INIS)

Li Feng-Chen; Cai Wei-Hua; Zhang Hong-Na; Wang Yue

2012-01-01

Direct numerical simulations (DNS) were performed for the forced homogeneous isotropic turbulence (FHIT) with/without polymer additives in order to elaborate the characteristics of the turbulent energy cascading influenced by drag-reducing effects. The finite elastic non-linear extensibility-Peterlin model (FENE-P) was used as the conformation tensor equation for the viscoelastic polymer solution. Detailed analyses of DNS data were carried out in this paper for the turbulence scaling law and the topological dynamics of FHIT as well as the important turbulent parameters, including turbulent kinetic energy spectra, enstrophy and strain, velocity structure function, small-scale intermittency, etc. A natural and straightforward definition for the drag reduction rate was also proposed for the drag-reducing FHIT based on the decrease degree of the turbulent kinetic energy. It was found that the turbulent energy cascading in the FHIT was greatly modified by the drag-reducing polymer additives. The enstrophy and the strain fields in the FHIT of the polymer solution were remarkably weakened as compared with their Newtonian counterparts. The small-scale vortices and the small-scale intermittency were all inhibited by the viscoelastic effects in the FHIT of the polymer solution. However, the scaling law in a fashion of extended self-similarity for the FHIT of the polymer solution, within the presently simulated range of Weissenberg numbers, had no distinct differences compared with that of the Newtonian fluid case

Measurements of Turbulence Attenuation by a Dilute Dispersion of Solid Particles in Homogeneous Isotropic Turbulence

Science.gov (United States)

Eaton, John; Hwang, Wontae; Cabral, Patrick

2002-11-01

This research addresses turbulent gas flows laden with fine solid particles at sufficiently large mass loading that strong two-way coupling occurs. By two-way coupling we mean that the particle motion is governed largely by the flow, while the particles affect the gas-phase mean flow and the turbulence properties. Our main interest is in understanding how the particles affect the turbulence. Computational techniques have been developed which can accurately predict flows carrying particles that are much smaller than the smallest scales of turbulence. Also, advanced computational techniques and burgeoning computer resources make it feasible to fully resolve very large particles moving through turbulent flows. However, flows with particle diameters of the same order as the Kolmogorov scale of the turbulence are notoriously difficult to predict. Some simple flows show strong turbulence attenuation with reductions in the turbulent kinetic energy by up to a factor of five. On the other hand, some seemingly similar flows show almost no modification. No model has been proposed that allows prediction of when the strong attenuation will occur. Unfortunately, many technological and natural two-phase flows fall into this regime, so there is a strong need for new physical understanding and modeling capability. Our objective is to study the simplest possible turbulent particle-laden flow, namely homogeneous, isotropic turbulence with a uniform dispersion of monodisperse particles. We chose such a simple flow for two reasons. First, the simplicity allows us to probe the interaction in more detail and offers analytical simplicity in interpreting the results. Secondly, this flow can be addressed by numerical simulation, and many research groups are already working on calculating the flow. Our detailed data can help guide some of these efforts. By using microgravity, we can further simplify the flow to the case of no mean velocity for either the turbulence or the particles. In fact

Arbitrary quadratures determination of the monoenergetic neutron density in an homogeneous finite sphere with isotropic scattering

International Nuclear Information System (INIS)

Sanchez G, J.

2015-09-01

The solution of the so-called Canonical problems of neutron transport theory has been given by Case, who developed a method akin to the classical eigenfunction expansion procedure, extended to admit singular eigenfunctions. The solution is given as a set consisting of a Fredholm integral equation coupled with a transcendental equation, which has to be solved for the expansion coefficients by iteration. CASE's method make extensive use of the results of the theory of functions of a complex variable and many successful approaches to solve in an approximate form the above mentioned set have been reported in the literature. We present here an entirely different approach which deals with the canonical problems in a more direct and elementary manner. As far as we know, the original idea for the latter method is due to Carlvik who devised the escape probability approximation to the solution of the neutron transport equation in its integral form. In essence, the procedure consists in assuming a sectionally constant form of the neutron density that in turn yields a set of linear algebraic equations obeyed by the assumed constant values of the density. Very well established techniques of numerical analysis for the solution of integral equations consist in independent approaches that generalize the sectionally constant approach by assuming a sectionally low degree polynomial for the unknown function. This procedure also known as the arbitrary quadratures method is especially suited to deal with cases where the kernel of the integral equation is singular. The author wishes to present the results obtained with the arbitrary quadratures method for the numerical calculation of the monoenergetic neutron density in a critical, homogeneous sphere of finite radius with isotropic scattering. The singular integral equation obeyed by the neutron density in the critical sphere is introduced, an outline of the method's main features is given, and tables and graphs of the density

Arbitrary quadratures determination of the monoenergetic neutron density in an homogeneous finite sphere with isotropic scattering

Energy Technology Data Exchange (ETDEWEB)

Sanchez G, J., E-mail: julian.sanchez@inin.gob.mx [ININ, Carretera Mexico-Toluca s/n, 52750 Ocoyoacac, Estado de Mexico (Mexico)

2015-09-15

The solution of the so-called Canonical problems of neutron transport theory has been given by Case, who developed a method akin to the classical eigenfunction expansion procedure, extended to admit singular eigenfunctions. The solution is given as a set consisting of a Fredholm integral equation coupled with a transcendental equation, which has to be solved for the expansion coefficients by iteration. CASE's method make extensive use of the results of the theory of functions of a complex variable and many successful approaches to solve in an approximate form the above mentioned set have been reported in the literature. We present here an entirely different approach which deals with the canonical problems in a more direct and elementary manner. As far as we know, the original idea for the latter method is due to Carlvik who devised the escape probability approximation to the solution of the neutron transport equation in its integral form. In essence, the procedure consists in assuming a sectionally constant form of the neutron density that in turn yields a set of linear algebraic equations obeyed by the assumed constant values of the density. Very well established techniques of numerical analysis for the solution of integral equations consist in independent approaches that generalize the sectionally constant approach by assuming a sectionally low degree polynomial for the unknown function. This procedure also known as the arbitrary quadratures method is especially suited to deal with cases where the kernel of the integral equation is singular. The author wishes to present the results obtained with the arbitrary quadratures method for the numerical calculation of the monoenergetic neutron density in a critical, homogeneous sphere of finite radius with isotropic scattering. The singular integral equation obeyed by the neutron density in the critical sphere is introduced, an outline of the method's main features is given, and tables and graphs of the density

Analysis of non-axisymmetric wave propagation in a homogeneous piezoelectric solid circular cylinder of transversely isotropic material

CSIR Research Space (South Africa)

Shatalov, MY

2009-01-01

Full Text Available ). The main disadvantage of this approach is that the roots of characteristic arguments ( ( )0, 1, , 4k kξ = = … ) are also displayed on the surface plots as obvious artefacts. An elaborate discussion of these artefacts is given in Yenwong-Fai (2008...-matrix interface by guided waves: Axisymmetric case. J. Acoust. Soc. Am 89 (6), 2573-2583. Yenwong-Fai, A., 2008. Wave propagation in a piezoelectric solid cylinder of transversely isotropic material. Master’s thesis, University of Witwatersrand, Johannesburg...

A transversely isotropic medium with a tilted symmetry axis normal to the reflector

KAUST Repository

Alkhalifah, Tariq Ali

2010-05-01

The computational tools for imaging in transversely isotropic media with tilted axes of symmetry (TTI) are complex and in most cases do not have an explicit closed-form representation. Developing such tools for a TTI medium with tilt constrained to be normal to the reflector dip (DTI) reduces their complexity and allows for closed-form representations. The homogeneous-case zero-offset migration in such a medium can be performed using an isotropic operator scaled by the velocity of the medium in the tilt direction. For the nonzero-offset case, the reflection angle is always equal to the incidence angle, and thus, the velocities for the source and receiver waves at the reflection point are equal and explicitly dependent on the reflection angle. This fact allows for the development of explicit representations for angle decomposition as well as moveout formulas for analysis of extended images obtained by wave-equation migration. Although setting the tilt normal to the reflector dip may not be valid everywhere (i.e., on salt flanks), it can be used in the process of velocity model building, in which such constrains are useful and typically are used. © 2010 Society of Exploration Geophysicists.

A transversely isotropic medium with a tilted symmetry axis normal to the reflector

KAUST Repository

Alkhalifah, Tariq Ali; Sava, Paul C.

2010-01-01

The computational tools for imaging in transversely isotropic media with tilted axes of symmetry (TTI) are complex and in most cases do not have an explicit closed-form representation. Developing such tools for a TTI medium with tilt constrained to be normal to the reflector dip (DTI) reduces their complexity and allows for closed-form representations. The homogeneous-case zero-offset migration in such a medium can be performed using an isotropic operator scaled by the velocity of the medium in the tilt direction. For the nonzero-offset case, the reflection angle is always equal to the incidence angle, and thus, the velocities for the source and receiver waves at the reflection point are equal and explicitly dependent on the reflection angle. This fact allows for the development of explicit representations for angle decomposition as well as moveout formulas for analysis of extended images obtained by wave-equation migration. Although setting the tilt normal to the reflector dip may not be valid everywhere (i.e., on salt flanks), it can be used in the process of velocity model building, in which such constrains are useful and typically are used. © 2010 Society of Exploration Geophysicists.

Static deformation due to a long buried dip-slip fault in an isotropic

Indian Academy of Sciences (India)

Closed-form analytical expressions for the displacements and the stresses at any point of a two-phase medium consisting of a homogeneous, isotropic, perfectly elastic half-space in welded contact with a homogeneous, orthotropic, perfectly elastic half-space due to a dip-slip fault of finite width located at an arbitrary ...

Gravitational instability in isotropic MHD plasma waves

Science.gov (United States)

Cherkos, Alemayehu Mengesha

2018-04-01

The effect of compressive viscosity, thermal conductivity and radiative heat-loss functions on the gravitational instability of infinitely extended homogeneous MHD plasma has been investigated. By taking in account these parameters we developed the six-order dispersion relation for magnetohydrodynamic (MHD) waves propagating in a homogeneous and isotropic plasma. The general dispersion relation has been developed from set of linearized basic equations and solved analytically to analyse the conditions of instability and instability of self-gravitating plasma embedded in a constant magnetic field. Our result shows that the presence of viscosity and thermal conductivity in a strong magnetic field substantially modifies the fundamental Jeans criterion of gravitational instability.

On a hierarchical construction of the anisotropic LTSN solution from the isotropic LTSN solution

International Nuclear Information System (INIS)

Foletto, Taline; Segatto, Cynthia F.; Bodmann, Bardo E.; Vilhena, Marco T.

2015-01-01

In this work, we present a recursive scheme targeting the hierarchical construction of anisotropic LTS N solution from the isotropic LTS N solution. The main idea relies in the decomposition of the associated LTS N anisotropic matrix as a sum of two matrices in which one matrix contains the isotropic and the other anisotropic part of the problem. The matrix containing the anisotropic part is considered as the source of the isotropic problem. The solution of this problem is made by the decomposition of the angular flux as a truncated series of intermediate functions and replace in the isotropic equation. After the replacement of these into the split isotropic equation, we construct a set of isotropic recursive problems, that are readily solved by the classic LTS N isotropic method. We apply this methodology to solve problems considering homogeneous and heterogeneous anisotropic regions. Numerical results are presented and compared with the classical LTS N anisotropic solution. (author)

A micromechanical approach for homogenization of elastic metamaterials with dynamic microstructure.

Science.gov (United States)

Muhlestein, Michael B; Haberman, Michael R

2016-08-01

An approximate homogenization technique is presented for generally anisotropic elastic metamaterials consisting of an elastic host material containing randomly distributed heterogeneities displaying frequency-dependent material properties. The dynamic response may arise from relaxation processes such as viscoelasticity or from dynamic microstructure. A Green's function approach is used to model elastic inhomogeneities embedded within a uniform elastic matrix as force sources that are excited by a time-varying, spatially uniform displacement field. Assuming dynamic subwavelength inhomogeneities only interact through their volume-averaged fields implies the macroscopic stress and momentum density fields are functions of both the microscopic strain and velocity fields, and may be related to the macroscopic strain and velocity fields through localization tensors. The macroscopic and microscopic fields are combined to yield a homogenization scheme that predicts the local effective stiffness, density and coupling tensors for an effective Willis-type constitutive equation. It is shown that when internal degrees of freedom of the inhomogeneities are present, Willis-type coupling becomes necessary on the macroscale. To demonstrate the utility of the homogenization technique, the effective properties of an isotropic elastic matrix material containing isotropic and anisotropic spherical inhomogeneities, isotropic spheroidal inhomogeneities and isotropic dynamic spherical inhomogeneities are presented and discussed.

Negative refraction of inhomogeneous waves in lossy isotropic media

International Nuclear Information System (INIS)

Fedorov, V Yu; Nakajima, T

2014-01-01

We theoretically study negative refraction of inhomogeneous waves at the interface of lossy isotropic media. We obtain explicit (up to the sign) expressions for the parameters of a wave transmitted through the interface between two lossy media characterized by complex permittivity and permeability. We show that the criterion of negative refraction that requires negative permittivity and permeability can be used only in the case of a homogeneous incident wave at the interface between a lossless and lossy media. In a more general situation, when the incident wave is inhomogeneous, or both media are lossy, the criterion of negative refraction becomes dependent on an incidence angle. Most interestingly, we show that negative refraction can be realized in conventional lossy materials (such as metals) if their interfaces are properly oriented. (paper)

Particle-pair relative velocity measurement in high-Reynolds-number homogeneous and isotropic turbulence using 4-frame particle tracking velocimetry

Science.gov (United States)

Dou, Zhongwang; Ireland, Peter J.; Bragg, Andrew D.; Liang, Zach; Collins, Lance R.; Meng, Hui

2018-02-01

The radial relative velocity (RV) between particles suspended in turbulent flow plays a critical role in droplet collision and growth. We present a simple and accurate approach to RV measurement in isotropic turbulence—planar 4-frame particle tracking velocimetry—using routine PIV hardware. It improves particle positioning and pairing accuracy over the 2-frame holographic approach by de Jong et al. (Int J Multiphas Flow 36:324-332; de Jong et al., Int J Multiphas Flow 36:324-332, 2010) without using high-speed cameras and lasers as in Saw et al. (Phys Fluids 26:111702, 2014). Homogeneous and isotropic turbulent flow ({R_λ }=357) in a new, fan-driven, truncated iscosahedron chamber was laden with either low-Stokes (mean St=0.09, standard deviation 0.05) or high-Stokes aerosols (mean St=3.46, standard deviation 0.57). For comparison, DNS was conducted under similar conditions ({R_λ }=398; St=0.10 and 3.00, respectively). Experimental RV probability density functions (PDF) and mean inward RV agree well with DNS. Mean inward RV increases with St at small particle separations, r, and decreases with St at large r, indicating the dominance of "path-history" and "inertial filtering" effects, respectively. However, at small r, the experimental mean inward RV trends higher than DNS, possibly due to the slight polydispersity of particles and finite light sheet thickness in experiments. To confirm this interpretation, we performed numerical experiments and found that particle polydispersity increases mean inward RV at small r, while finite laser thickness also overestimates mean inward RV at small r, This study demonstrates the feasibility of accurately measuring RV using routine hardware, and verifies, for the first time, the path-history and inertial filtering effects on particle-pair RV at large particle separations experimentally.

Steady bound electromagnetic eigenstate arises in a homogeneous isotropic linear metamaterial with zero-real-part-of-impedance and nonzero-imaginary-part-of-wave-vector

Science.gov (United States)

Chen, Jiangwei; Dai, Yuyao; Yan, Lin; Zhao, Huimin

2018-04-01

In this paper, we shall demonstrate theoretically that steady bound electromagnetic eigenstate can arise in an infinite homogeneous isotropic linear metamaterial with zero-real-part-of-impedance and nonzero-imaginary-part-of-wave-vector, which is partly attributed to that, here, nonzero-imaginary-part-of-wave-vector is not involved with energy losses or gain. Altering value of real-part-of-impedance of the metamaterial, the bound electromagnetic eigenstate may become to be a progressive wave. Our work may be useful to further understand energy conversion and conservation properties of electromagnetic wave in the dispersive and absorptive medium and provides a feasible route to stop, store and release electromagnetic wave (light) conveniently by using metamaterial with near-zero-real-part-of-impedance.

Scanning anisotropy parameters in horizontal transversely isotropic media

KAUST Repository

Masmoudi, Nabil

2016-10-12

The horizontal transversely isotropic model, with arbitrary symmetry axis orientation, is the simplest effective representative that explains the azimuthal behaviour of seismic data. Estimating the anisotropy parameters of this model is important in reservoir characterisation, specifically in terms of fracture delineation. We propose a travel-time-based approach to estimate the anellipticity parameter η and the symmetry axis azimuth ϕ of a horizontal transversely isotropic medium, given an inhomogeneous elliptic background model (which might be obtained from velocity analysis and well velocities). This is accomplished through a Taylor\\'s series expansion of the travel-time solution (of the eikonal equation) as a function of parameter η and azimuth angle ϕ. The accuracy of the travel time expansion is enhanced by the use of Shanks transform. This results in an accurate approximation of the solution of the non-linear eikonal equation and provides a mechanism to scan simultaneously for the best fitting effective parameters η and ϕ, without the need for repetitive modelling of travel times. The analysis of the travel time sensitivity to parameters η and ϕ reveals that travel times are more sensitive to η than to the symmetry axis azimuth ϕ. Thus, η is better constrained from travel times than the azimuth. Moreover, the two-parameter scan in the homogeneous case shows that errors in the background model affect the estimation of η and ϕ differently. While a gradual increase in errors in the background model leads to increasing errors in η, inaccuracies in ϕ, on the other hand, depend on the background model errors. We also propose a layer-stripping method valid for a stack of arbitrary oriented symmetry axis horizontal transversely isotropic layers to convert the effective parameters to the interval layer values.

Complete set of homogeneous isotropic analytic solutions in scalar-tensor cosmology with radiation and curvature

Science.gov (United States)

Bars, Itzhak; Chen, Shih-Hung; Steinhardt, Paul J.; Turok, Neil

2012-10-01

We study a model of a scalar field minimally coupled to gravity, with a specific potential energy for the scalar field, and include curvature and radiation as two additional parameters. Our goal is to obtain analytically the complete set of configurations of a homogeneous and isotropic universe as a function of time. This leads to a geodesically complete description of the Universe, including the passage through the cosmological singularities, at the classical level. We give all the solutions analytically without any restrictions on the parameter space of the model or initial values of the fields. We find that for generic solutions the Universe goes through a singular (zero-size) bounce by entering a period of antigravity at each big crunch and exiting from it at the following big bang. This happens cyclically again and again without violating the null-energy condition. There is a special subset of geodesically complete nongeneric solutions which perform zero-size bounces without ever entering the antigravity regime in all cycles. For these, initial values of the fields are synchronized and quantized but the parameters of the model are not restricted. There is also a subset of spatial curvature-induced solutions that have finite-size bounces in the gravity regime and never enter the antigravity phase. These exist only within a small continuous domain of parameter space without fine-tuning the initial conditions. To obtain these results, we identified 25 regions of a 6-parameter space in which the complete set of analytic solutions are explicitly obtained.

Homogeneous and isotropic big rips?

CERN Document Server

Giovannini, Massimo

2005-01-01

We investigate the way big rips are approached in a fully inhomogeneous description of the space-time geometry. If the pressure and energy densities are connected by a (supernegative) barotropic index, the spatial gradients and the anisotropic expansion decay as the big rip is approached. This behaviour is contrasted with the usual big-bang singularities. A similar analysis is performed in the case of sudden (quiescent) singularities and it is argued that the spatial gradients may well be non-negligible in the vicinity of pressure singularities.

Bounds for nonlinear composites via iterated homogenization

Science.gov (United States)

Ponte Castañeda, P.

2012-09-01

Improved estimates of the Hashin-Shtrikman-Willis type are generated for the class of nonlinear composites consisting of two well-ordered, isotropic phases distributed randomly with prescribed two-point correlations, as determined by the H-measure of the microstructure. For this purpose, a novel strategy for generating bounds has been developed utilizing iterated homogenization. The general idea is to make use of bounds that may be available for composite materials in the limit when the concentration of one of the phases (say phase 1) is small. It then follows from the theory of iterated homogenization that it is possible, under certain conditions, to obtain bounds for more general values of the concentration, by gradually adding small amounts of phase 1 in incremental fashion, and sequentially using the available dilute-concentration estimate, up to the final (finite) value of the concentration (of phase 1). Such an approach can also be useful when available bounds are expected to be tighter for certain ranges of the phase volume fractions. This is the case, for example, for the "linear comparison" bounds for porous viscoplastic materials, which are known to be comparatively tighter for large values of the porosity. In this case, the new bounds obtained by the above-mentioned "iterated" procedure can be shown to be much improved relative to the earlier "linear comparison" bounds, especially at low values of the porosity and high triaxialities. Consistent with the way in which they have been derived, the new estimates are, strictly, bounds only for the class of multi-scale, nonlinear composites consisting of two well-ordered, isotropic phases that are distributed with prescribed H-measure at each stage in the incremental process. However, given the facts that the H-measure of the sequential microstructures is conserved (so that the final microstructures can be shown to have the same H-measure), and that H-measures are insensitive to length scales, it is conjectured

Isotropic extensions of the vacuum solutions in general relativity

Energy Technology Data Exchange (ETDEWEB)

Molina, C. [Universidade de Sao Paulo (USP), SP (Brazil); Martin-Moruno, Prado [Victoria University of Wellington (New Zealand); Gonzalez-Diaz, Pedro F. [Consejo Superior de Investigaciones Cientificas, Madrid (Spain)

2012-07-01

Full text: Spacetimes described by spherically symmetric solutions of Einstein's equations are of paramount importance both in astrophysical applications and theoretical considerations. And among those, black holes are highlighted. In vacuum, Birkhoff's theorem and its generalizations to non-asymptotically flat cases uniquely fix the metric as the Schwarzschild, Schwarzschild-de Sitter or Schwarzschild-anti-de Sitter geometries, the vacuum solutions of the usual general relativity with zero, positive or negative values for the cosmological constant, respectively. In this work we are mainly interested in black holes in a cosmological environment. Of the two main assumptions of the cosmological principle, homogeneity is lost when compact objects are considered. Nevertheless isotropy is still possible, and we enforce this condition. Within this context, we investigate spatially isotropic solutions close - continuously deformable - to the usual vacuum solutions. We obtain isotropic extensions of the usual spherically symmetric vacuum geometries in general relativity. Exact and perturbative solutions are derived. Maximal extensions are constructed and their causal structures are discussed. The classes of geometries obtained include black holes in compact and non-compact universes, wormholes in the interior region of cosmological horizons, and anti-de Sitter geometries with excess/deficit solid angle. The tools developed here are applicable in more general contexts, with extensions subjected to other constraints. (author)

Two-dimensional Haar wavelet Collocation Method for the solution of Stationary Neutron Transport Equation in a homogeneous isotropic medium

International Nuclear Information System (INIS)

Patra, A.; Saha Ray, S.

2014-01-01

Highlights: • A stationary transport equation has been solved using the technique of Haar wavelet Collocation Method. • This paper intends to provide the great utility of Haar wavelets to nuclear science problem. • In the present paper, two-dimensional Haar wavelets are applied. • The proposed method is mathematically very simple, easy and fast. - Abstract: This paper emphasizes on finding the solution for a stationary transport equation using the technique of Haar wavelet Collocation Method (HWCM). Haar wavelet Collocation Method is efficient and powerful in solving wide class of linear and nonlinear differential equations. Recently Haar wavelet transform has gained the reputation of being a very effective tool for many practical applications. This paper intends to provide the great utility of Haar wavelets to nuclear science problem. In the present paper, two-dimensional Haar wavelets are applied for solution of the stationary Neutron Transport Equation in homogeneous isotropic medium. The proposed method is mathematically very simple, easy and fast. To demonstrate about the efficiency of the method, one test problem is discussed. It can be observed from the computational simulation that the numerical approximate solution is much closer to the exact solution

On the role of the transformation eigenstrain in the growth or shrinkage of spheroidal isotropic precipitations

International Nuclear Information System (INIS)

Fischer, F.D.; Boehm, H.J.

2005-01-01

The jumps of the strain and stress tensors on the surface of elastic homogeneous or inhomogeneous ellipsoidal inclusions embedded in an elastic matrix are obtained from results reported in the literature. They are used to derive closed-form expressions for the thermodynamic force in such matrix-inclusion systems that are subjected to a generally defined homogeneous transformation eigenstrain. A detailed study is presented for an isotropic spheroidal inclusion in an isotropic matrix in which the most important parameters are the inclusion's aspect ratio α and an eigenstrain triaxiality parameter d-bar. The fluctuations of the thermodynamic force are investigated for a set of specific transformation eigenstrain tensors and are presented for inclusion shapes ranging from disk-like to fiber-like spheroids

On metallic gratings coated conformally with isotropic negative-phase-velocity materials

International Nuclear Information System (INIS)

Inchaussandague, Marina E.; Lakhtakia, Akhlesh; Depine, Ricardo A.

2008-01-01

Application of the differential method (also called the C method) to plane-wave diffraction by a perfectly conducting, sinusoidally corrugated metallic grating coated with a linear, homogeneous, isotropic, lossless dielectric-magnetic material shows that coating materials with negative index of refraction may deliver enhanced maximum nonspecular reflection efficiencies in comparison to coating materials with positive index of refraction

On metallic gratings coated conformally with isotropic negative-phase-velocity materials

Energy Technology Data Exchange (ETDEWEB)

Inchaussandague, Marina E. [GEA-Grupo de Electromagnetismo Aplicado, Departamento de Fisica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Pabellon I, 1428 Buenos Aires (Argentina); CONICET-Consejo Nacional de Investigaciones Cientificas y Tecnicas, Rivadavia 1917, Buenos Aires (Argentina)], E-mail: mei@df.uba.ar; Lakhtakia, Akhlesh [CATMAS-Computational and Theoretical Materials Sciences Group, Department of Engineering Science and Mechanics, Pennsylvania State University, University Park, PA 16802-6812 (United States)], E-mail: akhlesh@psu.edu; Depine, Ricardo A. [GEA-Grupo de Electromagnetismo Aplicado, Departamento de Fisica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Pabellon I, 1428 Buenos Aires (Argentina); CONICET-Consejo Nacional de Investigaciones Cientificas y Tecnicas, Rivadavia 1917, Buenos Aires (Argentina)], E-mail: rdep@df.uba.ar

2008-03-31

Application of the differential method (also called the C method) to plane-wave diffraction by a perfectly conducting, sinusoidally corrugated metallic grating coated with a linear, homogeneous, isotropic, lossless dielectric-magnetic material shows that coating materials with negative index of refraction may deliver enhanced maximum nonspecular reflection efficiencies in comparison to coating materials with positive index of refraction.

Quasi-Rayleigh waves in transversely isotropic half-space with inclined axis of symmetry

International Nuclear Information System (INIS)

Yanovskaya, T.B.; Savina, L.S.

2003-09-01

A method for determination of characteristics of quasi-Rayleigh (qR) wave in a transversely isotropic homogeneous half-space with inclined axis of symmetry is outlined. The solution is obtained as a superposition of qP, qSV and qSH waves, and surface wave velocity is determined from the boundary conditions at the free surface and at infinity, as in the case of Rayleigh wave in isotropic half-space. Though the theory is simple enough, a numerical procedure for the calculation of surface wave velocity presents some difficulties. The difficulty is conditioned by necessity to calculate complex roots of a non-linear equation, which in turn contains functions determined as roots of nonlinear equations with complex coefficients. Numerical analysis shows that roots of the equation corresponding to the boundary conditions do not exist in the whole domain of azimuths and inclinations of the symmetry axis. The domain of existence of qR wave depends on the ratio of the elastic parameters: for some strongly anisotropic models the wave cannot exist at all. For some angles of inclination qR wave velocities deviate from those calculated on the basis of the perturbation method valid for weak anisotropy, though they have the same tendency of variation with azimuth. The phase of qR wave varies with depth unlike Rayleigh wave in isotropic half-space. Unlike Rayleigh wave in isotropic half-space, qR wave has three components - vertical, radial and transverse. Particle motion in horizontal plane is elliptic. Direction of the major axis of the ellipsis coincide with the direction of propagation only in azimuths 0 deg. (180 deg.) and 90 deg. (270 deg.). (author)

Linearized holographic isotropization at finite coupling

Energy Technology Data Exchange (ETDEWEB)

Atashi, Mahdi; Fadafan, Kazem Bitaghsir [Shahrood University of Technology, Physics Department (Iran, Islamic Republic of); Jafari, Ghadir [Institute for Research in Fundamental Sciences (IPM), School of Physics, Tehran (Iran, Islamic Republic of)

2017-06-15

We study holographic isotropization of an anisotropic homogeneous non-Abelian strongly coupled plasma in the presence of Gauss-Bonnet corrections. It was verified before that one can linearize Einstein's equations around the final black hole background and simplify the complicated setup. Using this approach, we study the expectation value of the boundary stress tensor. Although we consider small values of the Gauss-Bonnet coupling constant, it is found that finite coupling leads to significant increasing of the thermalization time. By including higher order corrections in linearization, we extend the results to study the effect of the Gauss-Bonnet coupling on the entropy production on the event horizon. (orig.)

Using Non-linear Homogenization to Improve the Performance of Macroscopic Damage Models of Trabecular Bone.

Science.gov (United States)

Levrero-Florencio, Francesc; Pankaj, Pankaj

2018-01-01

Realistic macro-level finite element simulations of the mechanical behavior of trabecular bone, a cellular anisotropic material, require a suitable constitutive model; a model that incorporates the mechanical response of bone for complex loading scenarios and includes post-elastic phenomena, such as plasticity (permanent deformations) and damage (permanent stiffness reduction), which bone is likely to experience. Some such models have been developed by conducting homogenization-based multiscale finite element simulations on bone micro-structure. While homogenization has been fairly successful in the elastic regime and, to some extent, in modeling the macroscopic plastic response, it has remained a challenge with respect to modeling damage. This study uses a homogenization scheme to upscale the damage behavior from the tissue level (microscale) to the organ level (macroscale) and assesses the suitability of different damage constitutive laws. Ten cubic specimens were each subjected to 21 strain-controlled load cases for a small range of macroscopic post-elastic strains. Isotropic and anisotropic criteria were considered, density and fabric relationships were used in the formulation of the damage law, and a combined isotropic/anisotropic law with tension/compression asymmetry was formulated, based on the homogenized results, as a possible alternative to the currently used single scalar damage criterion. This computational study enhances the current knowledge on the macroscopic damage behavior of trabecular bone. By developing relationships of damage progression with bone's micro-architectural indices (density and fabric) the study also provides an aid for the creation of more precise macroscale continuum models, which are likely to improve clinical predictions.

Cosmic homogeneity: a spectroscopic and model-independent measurement

Science.gov (United States)

Gonçalves, R. S.; Carvalho, G. C.; Bengaly, C. A. P., Jr.; Carvalho, J. C.; Bernui, A.; Alcaniz, J. S.; Maartens, R.

2018-03-01

Cosmology relies on the Cosmological Principle, i.e. the hypothesis that the Universe is homogeneous and isotropic on large scales. This implies in particular that the counts of galaxies should approach a homogeneous scaling with volume at sufficiently large scales. Testing homogeneity is crucial to obtain a correct interpretation of the physical assumptions underlying the current cosmic acceleration and structure formation of the Universe. In this letter, we use the Baryon Oscillation Spectroscopic Survey to make the first spectroscopic and model-independent measurements of the angular homogeneity scale θh. Applying four statistical estimators, we show that the angular distribution of galaxies in the range 0.46 < z < 0.62 is consistent with homogeneity at large scales, and that θh varies with redshift, indicating a smoother Universe in the past. These results are in agreement with the foundations of the standard cosmological paradigm.

The revised geometric measure of entanglement for isotropic state

International Nuclear Information System (INIS)

Cao Ya

2011-01-01

Based on the revised geometric measure of entanglement (RGME), we obtain the analytical expression of isotropic state and generalize to n-particle and d-dimension mixed state case. Meantime, we obtain the relation about isotropic state E-tilde sin 2 (ρ) ≤ E re (ρ). The results indicate RGME is an appropriate measure of entanglement. (authors)

Halo-independent determination of the unmodulated WIMP signal in DAMA: the isotropic case

Energy Technology Data Exchange (ETDEWEB)

Gondolo, Paolo [Department of Physics, University of Utah, 115 South 1400 East #201, Salt Lake City, Utah 84112-0830 (United States); Scopel, Stefano, E-mail: paolo.gondolo@utah.edu, E-mail: scopel@sogang.ac.kr [Department of Physics, Sogang University, Seoul 121-742 (Korea, Republic of)

2017-09-01

We present a halo-independent determination of the unmodulated signal corresponding to the DAMA modulation if interpreted as due to dark matter weakly interacting massive particles (WIMPs). First we show how a modulated signal gives information on the WIMP velocity distribution function in the Galactic rest frame from which the unmodulated signal descends. Then we describe a mathematically-sound profile likelihood analysis in which the likelihood is profiled over a continuum of nuisance parameters (namely, the WIMP velocity distribution). As a first application of the method, which is very general and valid for any class of velocity distributions, we restrict the analysis to velocity distributions that are isotropic in the Galactic frame. In this way we obtain halo-independent maximum-likelihood estimates and confidence intervals for the DAMA unmodulated signal. We find that the estimated unmodulated signal is in line with expectations for a WIMP-induced modulation and is compatible with the DAMA background+signal rate. Specifically, for the isotropic case we find that the modulated amplitude ranges between a few percent and about 25% of the unmodulated amplitude, depending on the WIMP mass.

Micromechanical modeling of short glass-fiber reinforced thermoplastics-Isotropic damage of pseudograins

International Nuclear Information System (INIS)

Kammoun, S.; Brassart, L.; Doghri, I.; Delannay, L.; Robert, G.

2011-01-01

A micromechanical damage modeling approach is presented to predict the overall elasto-plastic behavior and damage evolution in short fiber reinforced composite materials. The practical use of the approach is for injection molded thermoplastic parts reinforced with short glass fibers. The modeling is proceeded as follows. The representative volume element is decomposed into a set of pseudograins, the damage of which affects progressively the overall stiffness and strength up to total failure. Each pseudograin is a two-phase composite with aligned inclusions having same aspect ratio. A two-step mean-field homogenization procedure is adopted. In the first step, the pseudograins are homogenized individually according to the Mori-Tanaka scheme. The second step consists in a self-consistent homogenization of homogenized pseudograins. An isotropic damage model is applied at the pseudograin level. The model is implemented as a UMAT in the finite element code ABAQUS. Model is shown to reproduce the strength and the anisotropy (Lankford coefficient) during uniaxial tensile tests on samples cut under different directions relative to the injection flow direction.

Anomaly detection in random heterogeneous media Feynman-Kac formulae, stochastic homogenization and statistical inversion

CERN Document Server

Simon, Martin

2015-01-01

This monograph is concerned with the analysis and numerical solution of a stochastic inverse anomaly detection problem in electrical impedance tomography (EIT). Martin Simon studies the problem of detecting a parameterized anomaly in an isotropic, stationary and ergodic conductivity random field whose realizations are rapidly oscillating. For this purpose, he derives Feynman-Kac formulae to rigorously justify stochastic homogenization in the case of the underlying stochastic boundary value problem. The author combines techniques from the theory of partial differential equations and functional analysis with probabilistic ideas, paving the way to new mathematical theorems which may be fruitfully used in the treatment of the problem at hand. Moreover, the author proposes an efficient numerical method in the framework of Bayesian inversion for the practical solution of the stochastic inverse anomaly detection problem.   Contents Feynman-Kac formulae Stochastic homogenization Statistical inverse problems  Targe...

A structure-based model for the transport of passive scalars in homogeneous turbulent flows

International Nuclear Information System (INIS)

Panagiotou, C.F.; Kassinos, S.C.

2016-01-01

Highlights: • The Interacting Particle Representation Model (IPRM) is extended for passive scalar transport. • We develop a structure-based set of scale equations for the scalar field and couple them to the IPRM. • The complete model is evaluated for several cases of homogeneous deformation with good results. • We outline steps for coupling the new scalar scales to the Algebraic Structure-Based Model (ASBM). - Abstract: A structure-based model has been constructed, for the first time, for the study of passive scalar transport in turbulent flows. The scalar variance and the large-scale scalar gradient variance are proposed as the two turbulence scales needed for closure of the scalar equations in the framework of the Interacting Particle Representation Model (IPRM). The scalar dissipation rate is modeled in terms of the scalar variance and the large-scale enstrophy of the velocity field. Model parameters are defined by matching the decay rates in freely isotropic turbulence. The model is validated for a large number of cases of deformation in both fixed and rotating frames, showing encouraging results. The model shows good agreement with DNS results for the case of pure shear flow in the presence of either transverse or streamwise mean scalar gradient, while it correctly predicts the presence of direct cascade for the passive scalar variance in two dimensional isotropic turbulence.

Efficient anisotropic quasi-P wavefield extrapolation using an isotropic low-rank approximation

KAUST Repository

Zhang, Zhendong

2017-12-17

The computational cost of quasi-P wave extrapolation depends on the complexity of the medium, and specifically the anisotropy. Our effective-model method splits the anisotropic dispersion relation into an isotropic background and a correction factor to handle this dependency. The correction term depends on the slope (measured using the gradient) of current wavefields and the anisotropy. As a result, the computational cost is independent of the nature of anisotropy, which makes the extrapolation efficient. A dynamic implementation of this approach decomposes the original pseudo-differential operator into a Laplacian, handled using the low-rank approximation of the spectral operator, plus an angular dependent correction factor applied in the space domain to correct for anisotropy. We analyze the role played by the correction factor and propose a new spherical decomposition of the dispersion relation. The proposed method provides accurate wavefields in phase and more balanced amplitudes than a previous spherical decomposition. Also, it is free of SV-wave artifacts. Applications to a simple homogeneous transverse isotropic medium with a vertical symmetry axis (VTI) and a modified Hess VTI model demonstrate the effectiveness of the approach. The Reverse Time Migration (RTM) applied to a modified BP VTI model reveals that the anisotropic migration using the proposed modeling engine performs better than an isotropic migration.

An Improved Isotropic Periodic Sum Method That Uses Linear Combinations of Basis Potentials

KAUST Repository

Takahashi, Kazuaki Z.; Narumi, Tetsu; Suh, Donguk; Yasuoka, Kenji

2012-01-01

Isotropic periodic sum (IPS) is a technique that calculates long-range interactions differently than conventional lattice sum methods. The difference between IPS and lattice sum methods lies in the shape and distribution of remote images for long-range interaction calculations. The images used in lattice sum calculations are identical to those generated from periodic boundary conditions and are discretely positioned at lattice points in space. The images for IPS calculations are "imaginary", which means they do not explicitly exist in a simulation system and are distributed isotropically and periodically around each particle. Two different versions of the original IPS method exist. The IPSn method is applied to calculations for point charges, whereas the IPSp method calculates polar molecules. However, both IPSn and IPSp have their advantages and disadvantages in simulating bulk water or water-vapor interfacial systems. In bulk water systems, the cutoff radius effect of IPSn strongly affects the configuration, whereas IPSp does not provide adequate estimations of water-vapor interfacial systems unless very long cutoff radii are used. To extend the applicability of the IPS technique, an improved IPS method, which has better accuracy in both homogeneous and heterogeneous systems has been developed and named the linear-combination-based isotropic periodic sum (LIPS) method. This improved IPS method uses linear combinations of basis potentials. We performed molecular dynamics (MD) simulations of bulk water and water-vapor interfacial systems to evaluate the accuracy of the LIPS method. For bulk water systems, the LIPS method has better accuracy than IPSn in estimating thermodynamic and configurational properties without the countercharge assumption, which is used for IPSp. For water-vapor interfacial systems, LIPS has better accuracy than IPSp and properly estimates thermodynamic and configurational properties. In conclusion, the LIPS method can successfully estimate

An Improved Isotropic Periodic Sum Method That Uses Linear Combinations of Basis Potentials

KAUST Repository

Takahashi, Kazuaki Z.

2012-11-13

Isotropic periodic sum (IPS) is a technique that calculates long-range interactions differently than conventional lattice sum methods. The difference between IPS and lattice sum methods lies in the shape and distribution of remote images for long-range interaction calculations. The images used in lattice sum calculations are identical to those generated from periodic boundary conditions and are discretely positioned at lattice points in space. The images for IPS calculations are "imaginary", which means they do not explicitly exist in a simulation system and are distributed isotropically and periodically around each particle. Two different versions of the original IPS method exist. The IPSn method is applied to calculations for point charges, whereas the IPSp method calculates polar molecules. However, both IPSn and IPSp have their advantages and disadvantages in simulating bulk water or water-vapor interfacial systems. In bulk water systems, the cutoff radius effect of IPSn strongly affects the configuration, whereas IPSp does not provide adequate estimations of water-vapor interfacial systems unless very long cutoff radii are used. To extend the applicability of the IPS technique, an improved IPS method, which has better accuracy in both homogeneous and heterogeneous systems has been developed and named the linear-combination-based isotropic periodic sum (LIPS) method. This improved IPS method uses linear combinations of basis potentials. We performed molecular dynamics (MD) simulations of bulk water and water-vapor interfacial systems to evaluate the accuracy of the LIPS method. For bulk water systems, the LIPS method has better accuracy than IPSn in estimating thermodynamic and configurational properties without the countercharge assumption, which is used for IPSp. For water-vapor interfacial systems, LIPS has better accuracy than IPSp and properly estimates thermodynamic and configurational properties. In conclusion, the LIPS method can successfully estimate

Control of the Radiation Patterns Using Homogeneous and Isotropic Impedance Metasurface

Directory of Open Access Journals (Sweden)

Fan Yang

2015-01-01

Full Text Available We propose to control the radiation patterns of a two-dimensional (2D point source by using impedance metasurfaces. We show that the radiation patterns can be manipulated by altering the surface impedance of the metasurface. Full-wave simulation results are provided to validate the theoretical derivations. The proposed design enjoys novel properties of isotropy, homogeneity, low profile, and high selectivity of frequency, making it potentially applicable in many applications. We also point out that this design can be implemented with active metasurfaces and the surface impedance can be tuned by modulating the value of loaded elements, like resistors, inductors, and capacitors.

Classification of integrable Volterra-type lattices on the sphere: isotropic case

International Nuclear Information System (INIS)

Adler, V E

2008-01-01

The symmetry approach is used for classification of integrable isotropic vector Volterra lattices on the sphere. The list of integrable lattices consists mainly of new equations. Their symplectic structure and associated PDE of vector NLS type are discussed

Improvement of the efficiency of two-dimensional multigroup transport calculations assuming isotropic reflection with multilevel spatial discretisation

International Nuclear Information System (INIS)

Stankovski, Z.; Zmijarevic, I.

1987-06-01

This paper presents two approximations used in multigroup two-dimensional transport calculations in large, very homogeneous media: isotropic reflection together with recently proposed group-dependent spatial representations. These approximations are implemented as standard options in APOLLO 2 assembly transport code. Presented example calculations show that significant savings in computational costs are obtained while preserving the overall accuracy

The albedo problem in the case of multiple synthetic scattering taking place in a plane-symmetric slab

International Nuclear Information System (INIS)

Shafiq, A.; Meyer, H.E. de; Grosjean, C.C.

1985-01-01

An approximate model based on an improved diffusion-type theory is established for treating multiple synthetic scattering in a homogeneous slab of finite thickness. As in the case of the exact treatment given in the preceding paper (Part I), it appears possible to transform the considered transport problem into an equivalent fictitious one involving multiple isotropic scattering, therefore permitting the application of an established corrected diffusion theory for treating isotropic scattering taking place in a convex homogeneous medium bounded by a vacuum in the presence of various types of sources. The approximate values of the reflection and transmission coefficients are compared with the rigorous values listed in Part I. In this way, the high accuracy of the approximation is clearly demonstrated. (author)

Heat-Induced, Pressure-Induced and Centrifugal-Force-Induced Exact Axisymmetric Thermo-Mechanical Analyses in a Thick-Walled Spherical Vessel, an Infinite Cylindrical Vessel, and a Uniform Disk Made of an Isotropic and Homogeneous Material

Directory of Open Access Journals (Sweden)

Vebil Yıldırım

2017-07-01

Full Text Available Heat-induced, pressure-induced, and centrifugal force-induced axisymmetric exact deformation and stresses in a thick-walled spherical vessel, a cylindrical vessel, and a uniform disk are all determined analytically at a specified constant surface temperature and at a constant angular velocity. The inner and outer pressures are both included in the formulation of annular structures made of an isotropic and homogeneous linear elastic material. Governing equations in the form of Euler-Cauchy differential equation with constant coefficients are solved and results are presented in compact forms. For disks, three different boundary conditions are taken into account to consider mechanical engineering applications. The present study is also peppered with numerical results in graphical forms.

Geometrical considerations in analyzing isotropic or anisotropic surface reflections.

Science.gov (United States)

Simonot, Lionel; Obein, Gael

2007-05-10

The bidirectional reflectance distribution function (BRDF) represents the evolution of the reflectance with the directions of incidence and observation. Today BRDF measurements are increasingly applied and have become important to the study of the appearance of surfaces. The representation and the analysis of BRDF data are discussed, and the distortions caused by the traditional representation of the BRDF in a Fourier plane are pointed out and illustrated for two theoretical cases: an isotropic surface and a brushed surface. These considerations will help characterize either the specular peak width of an isotropic rough surface or the main directions of the light scattered by an anisotropic rough surface without misinterpretations. Finally, what is believed to be a new space is suggested for the representation of the BRDF, which avoids the geometrical deformations and in numerous cases is more convenient for BRDF analysis.

Isotropic oscillator: spheroidal wave functions

International Nuclear Information System (INIS)

Mardoyan, L.G.; Pogosyan, G.S.; Ter-Antonyan, V.M.; Sisakyan, A.N.

1985-01-01

Solutions of the Schroedinger equation are found for an isotropic oscillator (10) in prolate and oblate spheroidal coordinates. It is shown that the obtained solutions turn into spherical and cylindrical bases of the isotropic oscillator at R→0 and R→ infinity (R is the dimensional parameter entering into the definition of prolate and oblate spheroidal coordinates). The explicit form is given for both prolate and oblate basis of the isotropic oscillator for the lowest quantum states

The isotropic radio background revisited

Energy Technology Data Exchange (ETDEWEB)

Fornengo, Nicolao; Regis, Marco [Dipartimento di Fisica Teorica, Università di Torino, via P. Giuria 1, I–10125 Torino (Italy); Lineros, Roberto A. [Instituto de Física Corpuscular – CSIC/U. Valencia, Parc Científic, calle Catedrático José Beltrán, 2, E-46980 Paterna (Spain); Taoso, Marco, E-mail: fornengo@to.infn.it, E-mail: rlineros@ific.uv.es, E-mail: regis@to.infn.it, E-mail: taoso@cea.fr [Institut de Physique Théorique, CEA/Saclay, F-91191 Gif-sur-Yvette Cédex (France)

2014-04-01

We present an extensive analysis on the determination of the isotropic radio background. We consider six different radio maps, ranging from 22 MHz to 2.3 GHz and covering a large fraction of the sky. The large scale emission is modeled as a linear combination of an isotropic component plus the Galactic synchrotron radiation and thermal bremsstrahlung. Point-like and extended sources are either masked or accounted for by means of a template. We find a robust estimate of the isotropic radio background, with limited scatter among different Galactic models. The level of the isotropic background lies significantly above the contribution obtained by integrating the number counts of observed extragalactic sources. Since the isotropic component dominates at high latitudes, thus making the profile of the total emission flat, a Galactic origin for such excess appears unlikely. We conclude that, unless a systematic offset is present in the maps, and provided that our current understanding of the Galactic synchrotron emission is reasonable, extragalactic sources well below the current experimental threshold seem to account for the majority of the brightness of the extragalactic radio sky.

The isotropic radio background revisited

International Nuclear Information System (INIS)

Fornengo, Nicolao; Regis, Marco; Lineros, Roberto A.; Taoso, Marco

2014-01-01

We present an extensive analysis on the determination of the isotropic radio background. We consider six different radio maps, ranging from 22 MHz to 2.3 GHz and covering a large fraction of the sky. The large scale emission is modeled as a linear combination of an isotropic component plus the Galactic synchrotron radiation and thermal bremsstrahlung. Point-like and extended sources are either masked or accounted for by means of a template. We find a robust estimate of the isotropic radio background, with limited scatter among different Galactic models. The level of the isotropic background lies significantly above the contribution obtained by integrating the number counts of observed extragalactic sources. Since the isotropic component dominates at high latitudes, thus making the profile of the total emission flat, a Galactic origin for such excess appears unlikely. We conclude that, unless a systematic offset is present in the maps, and provided that our current understanding of the Galactic synchrotron emission is reasonable, extragalactic sources well below the current experimental threshold seem to account for the majority of the brightness of the extragalactic radio sky

In-Situ Characterization of Isotropic and Transversely Isotropic Elastic Properties Using Ultrasonic Wave Velocities

NARCIS (Netherlands)

Pant, S; Laliberte, J; Martinez, M.J.; Rocha, B.

2016-01-01

In this paper, a one-sided, in situ method based on the time of flight measurement of ultrasonic waves was described. The primary application of this technique was to non-destructively measure the stiffness properties of isotropic and transversely isotropic materials. The method consists of

Macroscopic simulation of isotropic permanent magnets

International Nuclear Information System (INIS)

Bruckner, Florian; Abert, Claas; Vogler, Christoph; Heinrichs, Frank; Satz, Armin; Ausserlechner, Udo; Binder, Gernot; Koeck, Helmut; Suess, Dieter

2016-01-01

Accurate simulations of isotropic permanent magnets require to take the magnetization process into account and consider the anisotropic, nonlinear, and hysteretic material behaviour near the saturation configuration. An efficient method for the solution of the magnetostatic Maxwell equations including the description of isotropic permanent magnets is presented. The algorithm can easily be implemented on top of existing finite element methods and does not require a full characterization of the hysteresis of the magnetic material. Strayfield measurements of an isotropic permanent magnet and simulation results are in good agreement and highlight the importance of a proper description of the isotropic material. - Highlights: • Simulations of isotropic permanent magnets. • Accurate calculation of remanence magnetization and strayfield. • Comparison with strayfield measurements and anisotropic magnet simulations. • Efficient 3D FEM–BEM coupling for solution of Maxwell equations.

How isotropic can the UHECR flux be?

Science.gov (United States)

di Matteo, Armando; Tinyakov, Peter

2018-05-01

Modern observatories of ultra-high energy cosmic rays (UHECR) have collected over 104 events with energies above 10 EeV, whose arrival directions appear to be nearly isotropically distributed. On the other hand, the distribution of matter in the nearby Universe - and therefore presumably also that of UHECR sources - is not homogeneous. This is expected to leave an imprint on the angular distribution of UHECR arrival directions, though deflections by cosmic magnetic fields can confound the picture. In this work, we investigate quantitatively this apparent inconsistency. To this end we study observables sensitive to UHECR source inhomogeneities but robust to uncertainties on magnetic fields and the UHECR mass composition. We show, in a rather model-independent way, that if the source distribution tracks the overall matter distribution, the arrival directions at energies above 30 EeV should exhibit a sizeable dipole and quadrupole anisotropy, detectable by UHECR observatories in the very near future. Were it not the case, one would have to seriously reconsider the present understanding of cosmic magnetic fields and/or the UHECR composition. Also, we show that the lack of a strong quadrupole moment above 10 EeV in the current data already disfavours a pure proton composition, and that in the very near future measurements of the dipole and quadrupole moment above 60 EeV will be able to provide evidence about the UHECR mass composition at those energies.

Mapping of moveout in tilted transversely isotropic media

KAUST Repository

Stovas, A.; Alkhalifah, Tariq Ali

2013-01-01

The computation of traveltimes in a transverse isotropic medium with a tilted symmetry axis tilted transversely isotropic is very important both for modelling and inversion. We develop a simple analytical procedure to map the traveltime function from a transverse isotropic medium with a vertical symmetry axis (vertical transversely isotropic) to a tilted transversely isotropic medium by applying point-by-point mapping of the traveltime function. This approach can be used for kinematic modelling and inversion in layered tilted transversely isotropic media. © 2013 European Association of Geoscientists & Engineers.

Mapping of moveout in tilted transversely isotropic media

KAUST Repository

Stovas, A.

2013-09-09

The computation of traveltimes in a transverse isotropic medium with a tilted symmetry axis tilted transversely isotropic is very important both for modelling and inversion. We develop a simple analytical procedure to map the traveltime function from a transverse isotropic medium with a vertical symmetry axis (vertical transversely isotropic) to a tilted transversely isotropic medium by applying point-by-point mapping of the traveltime function. This approach can be used for kinematic modelling and inversion in layered tilted transversely isotropic media. © 2013 European Association of Geoscientists & Engineers.

Comparison between isotropic linear-elastic law and isotropic hyperelastic law in the finite element modeling of the brachial plexus.

Science.gov (United States)

Perruisseau-Carrier, A; Bahlouli, N; Bierry, G; Vernet, P; Facca, S; Liverneaux, P

2017-12-01

Augmented reality could help the identification of nerve structures in brachial plexus surgery. The goal of this study was to determine which law of mechanical behavior was more adapted by comparing the results of Hooke's isotropic linear elastic law to those of Ogden's isotropic hyperelastic law, applied to a biomechanical model of the brachial plexus. A model of finite elements was created using the ABAQUS ® from a 3D model of the brachial plexus acquired by segmentation and meshing of MRI images at 0°, 45° and 135° of shoulder abduction of a healthy subject. The offset between the reconstructed model and the deformed model was evaluated quantitatively by the Hausdorff distance and qualitatively by the identification of 3 anatomical landmarks. In every case the Hausdorff distance was shorter with Ogden's law compared to Hooke's law. On a qualitative aspect, the model deformed by Ogden's law followed the concavity of the reconstructed model whereas the model deformed by Hooke's law remained convex. In conclusion, the results of this study demonstrate that the behavior of Ogden's isotropic hyperelastic mechanical model was more adapted to the modeling of the deformations of the brachial plexus. Copyright © 2017 Elsevier Masson SAS. All rights reserved.

Value distribution of meromorphic solutions of homogeneous and non-homogeneous complex linear differential-difference equations

Directory of Open Access Journals (Sweden)

Luo Li-Qin

2016-01-01

Full Text Available In this paper, we investigate the value distribution of meromorphic solutions of homogeneous and non-homogeneous complex linear differential-difference equations, and obtain the results on the relations between the order of the solutions and the convergence exponents of the zeros, poles, a-points and small function value points of the solutions, which show the relations in the case of non-homogeneous equations are sharper than the ones in the case of homogeneous equations.

Spherical cloaking using nonlinear transformations for improved segmentation into concentric isotropic coatings.

Science.gov (United States)

Qiu, Cheng-Wei; Hu, Li; Zhang, Baile; Wu, Bae-Ian; Johnson, Steven G; Joannopoulos, John D

2009-08-03

Two novel classes of spherical invisibility cloaks based on nonlinear transformation have been studied. The cloaking characteristics are presented by segmenting the nonlinear transformation based spherical cloak into concentric isotropic homogeneous coatings. Detailed investigations of the optimal discretization (e.g., thickness control of each layer, nonlinear factor, etc.) are presented for both linear and nonlinear spherical cloaks and their effects on invisibility performance are also discussed. The cloaking properties and our choice of optimal segmentation are verified by the numerical simulation of not only near-field electric-field distribution but also the far-field radar cross section (RCS).

Regional homogeneity of electoral space: comparative analysis (on the material of 100 national cases

Directory of Open Access Journals (Sweden)

A. O. Avksentiev

2015-12-01

Full Text Available In the article the author examines dependence on electoral behavior from territorial belonging. «Regional homogeneity» and «electoral space» categories are conceptualized. It is argued, that such regional homogeneity is a characteristic of electoral space and can be quantified. Quantitative measurement of government regional homogeneity has direct connection with risk of separatism, civil conflicts, or legitimacy crisis on deviant territories. It is proposed the formulae for evaluation of regional homogeneity quantitative method which has been based on statistics analysis instrument, especially, variation coefficient. Possible directions of study with the use of this index according to individual political subjects and the whole political space (state, region, electoral district are defined. Calculation of appropriate indexes for Ukrainian electoral space (return of 1991­2015 elections and 100 other national cases. The dynamics of Ukraine regional homogeneity on the material of 1991­2015 electoral statistics is analyzed.

Modeling the subfilter scalar variance for large eddy simulation in forced isotropic turbulence

Science.gov (United States)

Cheminet, Adam; Blanquart, Guillaume

2011-11-01

Static and dynamic model for the subfilter scalar variance in homogeneous isotropic turbulence are investigated using direct numerical simulations (DNS) of a lineary forced passive scalar field. First, we introduce a new scalar forcing technique conditioned only on the scalar field which allows the fluctuating scalar field to reach a statistically stationary state. Statistical properties, including 2nd and 3rd statistical moments, spectra, and probability density functions of the scalar field have been analyzed. Using this technique, we performed constant density and variable density DNS of scalar mixing in isotropic turbulence. The results are used in an a-priori study of scalar variance models. Emphasis is placed on further studying the dynamic model introduced by G. Balarac, H. Pitsch and V. Raman [Phys. Fluids 20, (2008)]. Scalar variance models based on Bedford and Yeo's expansion are accurate for small filter width but errors arise in the inertial subrange. Results suggest that a constant coefficient computed from an assumed Kolmogorov spectrum is often sufficient to predict the subfilter scalar variance.

Thermalization vs. isotropization and azimuthal fluctuations

International Nuclear Information System (INIS)

Mrowczynski, Stanislaw

2005-01-01

Hydrodynamic description requires a local thermodynamic equilibrium of the system under study but an approximate hydrodynamic behaviour is already manifested when a momentum distribution of liquid components is not of equilibrium form but merely isotropic. While the process of equilibration is relatively slow, the parton system becomes isotropic rather fast due to the plasma instabilities. Azimuthal fluctuations observed in relativistic heavy-ion collisions are argued to distinguish between a fully equilibrated and only isotropic parton system produced in the collision early stage

Superfluid H3e in globally isotropic random media

Science.gov (United States)

Ikeda, Ryusuke; Aoyama, Kazushi

2009-02-01

Recent theoretical and experimental studies of superfluid H3e in aerogels with a global anisotropy created, e.g., by an external stress have definitely shown that the A -like phase with an equal-spin pairing in such aerogel samples is in the Anderson-Brinkman-Morel (ABM) (or axial) pairing state. In this paper, the A -like phase of superfluid H3e in globally isotropic aerogel is studied in detail by assuming a weakly disordered system in which singular topological defects are absent. Through calculation of the free energy, a disordered ABM state is found to be the best candidate of the pairing state of the globally isotropic A -like phase. Further, it is found through a one-loop renormalization-group calculation that the coreless continuous vortices (or vortex-Skyrmions) are irrelevant to the long-distance behavior of disorder-induced textures, and that the superfluidity is maintained in spite of lack of the conventional superfluid long-range order. Therefore, the globally isotropic A -like phase at weak disorder is, like in the case with a globally stretched anisotropy, a glass phase with the ABM pairing and shows superfluidity.

Elastic field of approaching dislocation loop in isotropic bimaterial

International Nuclear Information System (INIS)

Wu, Wenwang; Xu, Shucai; Zhang, Jinhuan; Xia, Re; Qian, Guian

2015-01-01

A semi-analytical solution is developed for calculating interface traction stress (ITS) fields due to elastic modulus mismatch across the interface plane of isotropic perfectly bounded bimaterial system. Based on the semi-analytical approaches developed, ITS is used to correct the bulk elastic field of dislocation loop within infinite homogenous medium, and to produce continuous displacement and stress fields across the perfectly-bounded interface. Firstly, calculation examples of dislocation loops in Al–Cu bimaterial system are performed to demonstrate the efficiency of the developed semi-analytical approach; Then, the elastic fields of dislocation loops in twinning Cu and Cu–Nb bimaterial are analyzed; Finally, the effect of modulus mismatch across interface plane on the elastic field of bimaterial system is investigated, it is found that modulus mismatch has a drastic impact on the elastic fields of dislocation loops within bimaterial system. (paper)

Induced piezoelectricity in isotropic biomaterial.

Science.gov (United States)

Zimmerman, R L

1976-01-01

Isotropic material can be made to exhibit piezoelectric effects by the application of a constant electric field. For insulators, the piezoelectric strain constant is proportional to the applied electric field and for semiconductors, an additional out-of-phase component of piezoelectricity is proportional to the electric current density in the sample. The two induced coefficients are proportional to the strain-dependent dielectric constant (depsilon/dS + epsilon) and resistivity (drho/dS - rho), respectively. The latter is more important at frequencies such that rhoepsilonomega less than 1, often the case in biopolymers.Signals from induced piezoelectricity in nature may be larger than those from true piezoelectricity. PMID:990389

Two-dimensional arbitrarily shaped acoustic cloaks composed of homogeneous parts

Science.gov (United States)

Li, Qi; Vipperman, Jeffrey S.

2017-10-01

Acoustic cloaking is an important application of acoustic metamaterials. Although the topic has received much attention, there are a number of areas where contributions are needed. In this paper, a design method for producing acoustic cloaks with arbitrary shapes that are composed of homogeneous parts is presented. The cloak is divided into sections, each of which, in turn, is further divided into two parts, followed by the application of transformation acoustics to derive the required properties for cloaking. With the proposed mapping relations, the properties of each part of the cloak are anisotropic but homogeneous, which can be realized using two alternating layers of homogeneous and isotropic materials. A hexagonal and an irregular cloak are presented as design examples. The full wave simulations using COMSOL Multiphysics finite element software show that the cloaks function well at reducing reflections and shadows. The variation of the cloak properties is investigated as a function of three important geometric parameters used in the transformations. A balance can be found between cloaking performance and materials properties that are physically realizable.

Angle gathers in wave-equation imaging for transversely isotropic media

KAUST Repository

Alkhalifah, Tariq Ali; Fomel, Sergey B.

2010-01-01

In recent years, wave-equation imaged data are often presented in common-image angle-domain gathers as a decomposition in the scattering angle at the reflector, which provide a natural access to analysing migration velocities and amplitudes. In the case of anisotropic media, the importance of angle gathers is enhanced by the need to properly estimate multiple anisotropic parameters for a proper representation of the medium. We extract angle gathers for each downward-continuation step from converting offset-frequency planes into angle-frequency planes simultaneously with applying the imaging condition in a transversely isotropic with a vertical symmetry axis (VTI) medium. The analytic equations, though cumbersome, are exact within the framework of the acoustic approximation. They are also easily programmable and show that angle gather mapping in the case of anisotropic media differs from its isotropic counterpart, with the difference depending mainly on the strength of anisotropy. Synthetic examples demonstrate the importance of including anisotropy in the angle gather generation as mapping of the energy is negatively altered otherwise. In the case of a titled axis of symmetry (TTI), the same VTI formulation is applicable but requires a rotation of the wavenumbers. © 2010 European Association of Geoscientists & Engineers.

Angle gathers in wave-equation imaging for transversely isotropic media

KAUST Repository

Alkhalifah, Tariq Ali

2010-11-12

In recent years, wave-equation imaged data are often presented in common-image angle-domain gathers as a decomposition in the scattering angle at the reflector, which provide a natural access to analysing migration velocities and amplitudes. In the case of anisotropic media, the importance of angle gathers is enhanced by the need to properly estimate multiple anisotropic parameters for a proper representation of the medium. We extract angle gathers for each downward-continuation step from converting offset-frequency planes into angle-frequency planes simultaneously with applying the imaging condition in a transversely isotropic with a vertical symmetry axis (VTI) medium. The analytic equations, though cumbersome, are exact within the framework of the acoustic approximation. They are also easily programmable and show that angle gather mapping in the case of anisotropic media differs from its isotropic counterpart, with the difference depending mainly on the strength of anisotropy. Synthetic examples demonstrate the importance of including anisotropy in the angle gather generation as mapping of the energy is negatively altered otherwise. In the case of a titled axis of symmetry (TTI), the same VTI formulation is applicable but requires a rotation of the wavenumbers. © 2010 European Association of Geoscientists & Engineers.

Uhlmann's geometric phase in presence of isotropic decoherence

International Nuclear Information System (INIS)

Tidstroem, Jonas; Sjoeqvist, Erik

2003-01-01

Uhlmann's mixed state geometric phase [Rep. Math. Phys. 24, 229 (1986)] is analyzed in the case of a qubit affected by isotropic decoherence treated in the Markovian approximation. It is demonstrated that this phase decreases rapidly with increasing decoherence rate and that it is most fragile to weak decoherence for pure or nearly pure initial states. In the unitary case, we compare Uhlmann's geometric phase for mixed states with that occurring in standard Mach-Zehnder interferometry [Phys. Rev. Lett. 85, 2845 (2000)] and show that the latter is more robust to reduction in the length of the Bloch vector. We also describe how Uhlmann's geometric phase in the present case could in principle be realized experimentally

Classical radiation theory of charged particles moving in electromagnetic fields in nonabsorbable isotropic media

International Nuclear Information System (INIS)

Konstantinovich, A.V.; Melnychuk, S.V.; Konstantinovich, I.A.

2002-01-01

The integral expressions for spectral-angular and spectral distributions of the radiation power of heterogeneous charged particles system moving on arbitrary trajectory in nonabsorbable isotropic media media with ε≠1 , μ≠1 are obtained using the Lorentz's self-interaction method. In this method a proper electromagnetic field, acting on electron, is defined as a semi difference between retarded and advanced potentials (Dirac, 1938). The power spectrum of Cherenkov radiation for the linear uniformly moving heterogeneous system of charged particles are obtained. It is found that the expression for the radiation power of heterogeneous system of charged particles becomes simplified when a system of charged particles is homogeneous. In this case the radiation power includes the coherent factor. It is shown what the redistribution effects in energy of the radiation spectrum of the studied system are caused by the coherent factor. The radiation spectrum of the system of electrons moving in a circle in this medium is discrete. The Doppler effect causes the appearance of the new harmonics for the system of electrons moving in a spiral. These harmonics form the region of continuous radiation spectrum. (authors)

Isotropic LQC and LQC-inspired models with a massless scalar field as generalised Brans-Dicke theories

Science.gov (United States)

Rama, S. Kalyana

2018-06-01

We explore whether generalised Brans-Dicke theories, which have a scalar field Φ and a function ω (Φ ), can be the effective actions leading to the effective equations of motion of the LQC and the LQC-inspired models, which have a massless scalar field σ and a function f( m). We find that this is possible for isotropic cosmology. We relate the pairs (σ , f) and (Φ , ω ) and, using examples, illustrate these relations. We find that near the bounce of the LQC evolutions for which f(m) = sin m, the corresponding field Φ → 0 and the function ω (Φ ) ∝ Φ ^2. We also find that the class of generalised Brans-Dicke theories, which we had found earlier to lead to non singular isotropic evolutions, may be written as an LQC-inspired model. The relations found here in the isotropic cases do not apply to the anisotropic cases, which perhaps require more general effective actions.

Parametric decay instabilities in an infinite, homogeneous, weakly anisotropic plasma

International Nuclear Information System (INIS)

Grandal, B.

1976-01-01

The parametric decay of a transverse electromagnetic (em) wave with a frequency close to, but larger than, the electron plasma frequency is investigated for an infinite, homogeneous, weakly magnetoactive plasma. A two-component fluid description is employed, and the damping of the linear plasma waves is introduced phenomenologically to include both Landau and collisional damping. The transverse em wave will decay into a longitudinal electron plasma wave and an em ion-acoustic wave. Only the latter wave is assumed to be affected by the weak, constant magnetic field. The threshold expression for growth of electron plasma waves is equal to that of the isotropic plasma when the em ion-acoustic wave's direction of propagation lies inside a wide double cone, whose axis is along the constant magnetic field. When the em ion-acoustic wave propagates outside this double cone, an additional factor, which depends directly upon the magnetic field, appears in the threshold expression. This factor can, under certain conditions, reduce the threshold for growth of electron plasma waves below that of the isotropic plasma

String pair production in non homogeneous backgrounds

Energy Technology Data Exchange (ETDEWEB)

Bolognesi, S. [Department of Physics “E. Fermi” University of Pisa, and INFN - Sezione di Pisa,Largo Pontecorvo, 3, Ed. C, 56127 Pisa (Italy); Rabinovici, E. [Racah Institute of Physics, The Hebrew University of Jerusalem,91904 Jerusalem (Israel); Tallarita, G. [Departamento de Ciencias, Facultad de Artes Liberales,Universidad Adolfo Ibáñez, Santiago 7941169 (Chile)

2016-04-28

We consider string pair production in non homogeneous electric backgrounds. We study several particular configurations which can be addressed with the Euclidean world-sheet instanton technique, the analogue of the world-line instanton for particles. In the first case the string is suspended between two D-branes in flat space-time, in the second case the string lives in AdS and terminates on one D-brane (this realizes the holographic Schwinger effect). In some regions of parameter space the result is well approximated by the known analytical formulas, either the particle pair production in non-homogeneous background or the string pair production in homogeneous background. In other cases we see effects which are intrinsically stringy and related to the non-homogeneity of the background. The pair production is enhanced already for particles in time dependent electric field backgrounds. The string nature enhances this even further. For spacial varying electrical background fields the string pair production is less suppressed than the rate of particle pair production. We discuss in some detail how the critical field is affected by the non-homogeneity, for both time and space dependent electric field backgrouds. We also comment on what could be an interesting new prediction for the small field limit. The third case we consider is pair production in holographic confining backgrounds with homogeneous and non-homogeneous fields.

String pair production in non homogeneous backgrounds

International Nuclear Information System (INIS)

Bolognesi, S.; Rabinovici, E.; Tallarita, G.

2016-01-01

We consider string pair production in non homogeneous electric backgrounds. We study several particular configurations which can be addressed with the Euclidean world-sheet instanton technique, the analogue of the world-line instanton for particles. In the first case the string is suspended between two D-branes in flat space-time, in the second case the string lives in AdS and terminates on one D-brane (this realizes the holographic Schwinger effect). In some regions of parameter space the result is well approximated by the known analytical formulas, either the particle pair production in non-homogeneous background or the string pair production in homogeneous background. In other cases we see effects which are intrinsically stringy and related to the non-homogeneity of the background. The pair production is enhanced already for particles in time dependent electric field backgrounds. The string nature enhances this even further. For spacial varying electrical background fields the string pair production is less suppressed than the rate of particle pair production. We discuss in some detail how the critical field is affected by the non-homogeneity, for both time and space dependent electric field backgrouds. We also comment on what could be an interesting new prediction for the small field limit. The third case we consider is pair production in holographic confining backgrounds with homogeneous and non-homogeneous fields.

Homogenization approach in engineering

International Nuclear Information System (INIS)

Babuska, I.

1975-10-01

Homogenization is an approach which studies the macrobehavior of a medium by its microproperties. Problems with a microstructure play an essential role in such fields as mechanics, chemistry, physics, and reactor engineering. Attention is concentrated on a simple specific model problem to illustrate results and problems typical of the homogenization approach. Only the diffusion problem is treated here, but some statements are made about the elasticity of composite materials. The differential equation is solved for linear cases with and without boundaries and for the nonlinear case. 3 figures, 1 table

Cosmology the homogeneous universe and the evolution of structures

CERN Multimedia

CERN. Geneva. Audiovisual Unit

2003-01-01

In my course I will first give and introduction to standard cosmology. I discuss the equations of the homogeneous and isotropic universe and I'll briefly summarize its thermal history. After that I want to concentrate on the fluctuations in the universe. We will study anisotropies in the cosmic microwave background, fluctuations of the matter density and the velocity field and weak lensing. I want to explain especially new cosmological data which are coming up right now and their implication for the cosmological model. N.B. This lecture series will be held in the Auditorium, bldg. 500 on 27, 28, 30, 31 January and in the Council room on 29 January.

Intra-connected three-dimensionally isotropic bulk negative index photonic metamaterial

International Nuclear Information System (INIS)

Guney, Durdu; Koschny, Thomas; Soukoulis, Costas

2010-01-01

Isotropic negative index metamaterials (NIMs) are highly desired, particularly for the realization of ultra-high resolution lenses. However, existing isotropic NIMs function only two-dimensionally and cannot be miniaturized beyond microwaves. Direct laser writing processes can be a paradigm shift toward the fabrication of three-dimensionally (3D) isotropic bulk optical metamaterials, but only at the expense of an additional design constraint, namely connectivity. Here, we demonstrate with a proof-of-principle design that the requirement connectivity does not preclude fully isotropic left-handed behavior. This is an important step towards the realization of bulk 3D isotropic NIMs at optical wavelengths.

On a wave-particle in closed and open isotropic universes

International Nuclear Information System (INIS)

Campos, L. M. B. C.

2011-01-01

The Klein-Gordon equation satisfied by the wave function in general relativity is solved for the metric of the closed and open universe corresponding to Einstein-De Sitter-Friedmann isotropic cosmological model. The angular dependences are specified by spherical harmonics for the longitude and latitude, and for the hyperlatitude by modified spherical harmonics having as variable circular functions for the closed universe and hyperbolic functions for the open universes. The time dependence of the probabilistic wave function is similar for the closed and open universes and is obtained in the following three cases: (I) constant Hubble parameter, (II) constant decceleration parameter, and (III) uniform matter and energy distribution, which corresponds to the Hubble parameter a linear function of time. Thus six solutions are obtained, namely, the three cases I-III each for closed and open isotropic universes. For each of these six solutions is considered: (i) the existence of singularities in space-time including asymptotic time in the future or past, (ii) the square integrability of the wave function over the full extent of the four-dimensional space-time, and (iii) the existence or otherwise of a positive probability density associated with the wave function.

Dynamical Symmetries of Two-Dimensional Dirac Equation with Screened Coulomb and Isotropic Harmonic Oscillator Potentials

International Nuclear Information System (INIS)

Wang Qing; Hou Yu-Long; Jing Jian; Long Zheng-Wen

2014-01-01

In this paper, we study symmetrical properties of two-dimensional (2D) screened Dirac Hydrogen atom and isotropic harmonic oscillator with scalar and vector potentials of equal magnitude (SVPEM). We find that it is possible for both cases to preserve so(3) and su(2) dynamical symmetries provided certain conditions are satisfied. Interestingly, the conditions for preserving these dynamical symmetries are exactly the same as non-relativistic screened Hydrogen atom and screened isotropic oscillator preserving their dynamical symmetries. Some intuitive explanations are proposed. (general)

High-frequency homogenization of zero frequency stop band photonic and phononic crystals

CERN Document Server

Antonakakis, Tryfon; Guenneau, Sebastien

2013-01-01

We present an accurate methodology for representing the physics of waves, for periodic structures, through effective properties for a replacement bulk medium: This is valid even for media with zero frequency stop-bands and where high frequency phenomena dominate. Since the work of Lord Rayleigh in 1892, low frequency (or quasi-static) behaviour has been neatly encapsulated in effective anisotropic media. However such classical homogenization theories break down in the high-frequency or stop band regime. Higher frequency phenomena are of significant importance in photonics (transverse magnetic waves propagating in infinite conducting parallel fibers), phononics (anti-plane shear waves propagating in isotropic elastic materials with inclusions), and platonics (flexural waves propagating in thin-elastic plates with holes). Fortunately, the recently proposed high-frequency homogenization (HFH) theory is only constrained by the knowledge of standing waves in order to asymptotically reconstruct dispersion curves an...

Crack Tip Creep Deformation Behavior in Transversely Isotropic Materials

International Nuclear Information System (INIS)

Ma, Young Wha; Yoon, Kee Bong

2009-01-01

Theoretical mechanics analysis and finite element simulation were performed to investigate creep deformation behavior at the crack tip of transversely isotropic materials under small scale creep (SCC) conditions. Mechanical behavior of material was assumed as an elastic-2 nd creep, which elastic modulus ( E ), Poisson's ratio (v ) and creep stress exponent ( n ) were isotropic and creep coefficient was only transversely isotropic. Based on the mechanics analysis for material behavior, a constitutive equation for transversely isotropic creep behavior was formulated and an equivalent creep coefficient was proposed under plain strain conditions. Creep deformation behavior at the crack tip was investigated through the finite element analysis. The results of the finite element analysis showed that creep deformation in transversely isotropic materials is dominant at the rear of the crack-tip. This result was more obvious when a load was applied to principal axis of anisotropy. Based on the results of the mechanics analysis and the finite element simulation, a corrected estimation scheme of the creep zone size was proposed in order to evaluate the creep deformation behavior at the crack tip of transversely isotropic creeping materials

Calculation of point isotropic buildup factors of gamma rays for water and lead

Directory of Open Access Journals (Sweden)

A. S. H.

2001-12-01

Full Text Available   Exposure buildup factors for water and lead have been calculated by the Monte-Carlo method for an isotropic point source in an infinite homogeneous medium, using the latest cross secions available on the Internet. The types of interactions considered are ,photoelectric effect, incoherent (or bound-electron Compton. Scattering, coherent (or Rayleigh scattering and pair production. Fluorescence radiations have also been taken into acount for lead. For each material, calculations were made at 10 gamma ray energies in the 40 keV to 10 MeV range and up to penetration depths of 10 mean free paths at each energy point. The results presented in this paper can be considered as modified gamma ray exposure buildup factors and be used in radiation shielding designs.

Sudden Relaminarization and Lifetimes in Forced Isotropic Turbulence.

Science.gov (United States)

Linkmann, Moritz F; Morozov, Alexander

2015-09-25

We demonstrate an unexpected connection between isotropic turbulence and wall-bounded shear flows. We perform direct numerical simulations of isotropic turbulence forced at large scales at moderate Reynolds numbers and observe sudden transitions from a chaotic dynamics to a spatially simple flow, analogous to the laminar state in wall bounded shear flows. We find that the survival probabilities of turbulence are exponential and the typical lifetimes increase superexponentially with the Reynolds number. Our results suggest that both isotropic turbulence and wall-bounded shear flows qualitatively share the same phase-space dynamics.

Isotropic Growth of Graphene toward Smoothing Stitching.

Science.gov (United States)

Zeng, Mengqi; Tan, Lifang; Wang, Lingxiang; Mendes, Rafael G; Qin, Zhihui; Huang, Yaxin; Zhang, Tao; Fang, Liwen; Zhang, Yanfeng; Yue, Shuanglin; Rümmeli, Mark H; Peng, Lianmao; Liu, Zhongfan; Chen, Shengli; Fu, Lei

2016-07-26

The quality of graphene grown via chemical vapor deposition still has very great disparity with its theoretical property due to the inevitable formation of grain boundaries. The design of single-crystal substrate with an anisotropic twofold symmetry for the unidirectional alignment of graphene seeds would be a promising way for eliminating the grain boundaries at the wafer scale. However, such a delicate process will be easily terminated by the obstruction of defects or impurities. Here we investigated the isotropic growth behavior of graphene single crystals via melting the growth substrate to obtain an amorphous isotropic surface, which will not offer any specific grain orientation induction or preponderant growth rate toward a certain direction in the graphene growth process. The as-obtained graphene grains are isotropically round with mixed edges that exhibit high activity. The orientation of adjacent grains can be easily self-adjusted to smoothly match each other over a liquid catalyst with facile atom delocalization due to the low rotation steric hindrance of the isotropic grains, thus achieving the smoothing stitching of the adjacent graphene. Therefore, the adverse effects of grain boundaries will be eliminated and the excellent transport performance of graphene will be more guaranteed. What is more, such an isotropic growth mode can be extended to other types of layered nanomaterials such as hexagonal boron nitride and transition metal chalcogenides for obtaining large-size intrinsic film with low defect.

General thermo-elastic solution of radially heterogeneous, spherically isotropic rotating sphere

Energy Technology Data Exchange (ETDEWEB)

Bayat, Yahya; EkhteraeiToussi, THamid [Ferdowsi University of Mashhad, Mashhad (Iran, Islamic Republic of)

2015-06-15

A thick walled rotating spherical object made of transversely isotropic functionally graded materials (FGMs) with general types of thermo-mechanical boundary conditions is studied. The thermo-mechanical governing equations consisting of decoupled thermal and mechanical equations are represented. The centrifugal body forces of the rotation are considered in the modeling phase. The unsymmetrical thermo-mechanical boundary conditions and rotational body forces are expressed in terms of the Legendre series. The series method is also implemented in the solution of the resulting equations. The solutions are checked with the known literature and FEM based solutions of ABAQUS software. The effects of anisotropy and heterogeneity are studied through the case studies and the results are represented in different figures. The newly developed series form solution is applicable to the rotating FGM spherical transversely isotropic vessels having nonsymmetrical thermo-mechanical boundary condition.

Isotropic nuclear graphites; the effect of neutron irradiation

International Nuclear Information System (INIS)

Lore, J.; Buscaillon, A.; Mottet, P.; Micaud, G.

1977-01-01

Several isotropic graphites have been manufactured using different forming processes and fillers such as needle coke, regular coke, or pitch coke. Their properties are described in this paper. Specimens of these products have been irradiated in the fast reactor Rapsodie between 400 to 1400 0 C, at fluences up to 1,7.10 21 n.cm -2 PHI.FG. The results show an isotropic behavior under neutron irradiation, but the induced dimensional changes are higher than those of isotropic coke graphites although they are lower than those of conventional extruded graphites made with the same coke

Process for the preparation of isotropic petroleum coke

International Nuclear Information System (INIS)

Kegler, W.H.; Huyser, M.E.

1975-01-01

A description is given of a process for preparing isotropic coke from oil residue charge. It includes blowing air into the residue until it reaches a softening temperature of around 49 to 116 deg C, the deferred coking of the residue having undergone blowing at a temperature of around 247 to 640 deg C, at a pressure between around 1.38x10 5 and 1.72x10 6 Pa, and the recovery of isotropic coke with a thermal expansion coefficient ratio under 1.5 approximately. The isotropic coke is used for preparing hexagonal graphite bars for nuclear reactor moderators [fr

Stochastic isotropic hyperelastic materials: constitutive calibration and model selection

Science.gov (United States)

Mihai, L. Angela; Woolley, Thomas E.; Goriely, Alain

2018-03-01

Biological and synthetic materials often exhibit intrinsic variability in their elastic responses under large strains, owing to microstructural inhomogeneity or when elastic data are extracted from viscoelastic mechanical tests. For these materials, although hyperelastic models calibrated to mean data are useful, stochastic representations accounting also for data dispersion carry extra information about the variability of material properties found in practical applications. We combine finite elasticity and information theories to construct homogeneous isotropic hyperelastic models with random field parameters calibrated to discrete mean values and standard deviations of either the stress-strain function or the nonlinear shear modulus, which is a function of the deformation, estimated from experimental tests. These quantities can take on different values, corresponding to possible outcomes of the experiments. As multiple models can be derived that adequately represent the observed phenomena, we apply Occam's razor by providing an explicit criterion for model selection based on Bayesian statistics. We then employ this criterion to select a model among competing models calibrated to experimental data for rubber and brain tissue under single or multiaxial loads.

Texture of low temperature isotropic pyrocarbons

International Nuclear Information System (INIS)

Pelissier, Joseph; Lombard, Louis.

1976-01-01

Isotropic pyrocarbon deposited on fuel particles was studied by transmission electron microscopy in order to determine its texture. The material consists of an agglomerate of spherical growth features similar to those of carbon black. The spherical growth features are formed from the cristallites of turbostratic carbon and the distribution gives an isotropic structure. Neutron irradiation modifies the morphology of the pyrocarbon. The spherical growth features are deformed and the coating becomes strongly anisotropic. The transformation leads to the rupture of the coating caused by strong irradiation doses [fr

Homogenization of neutronic diffusion models

International Nuclear Information System (INIS)

Capdebosq, Y.

1999-09-01

In order to study and simulate nuclear reactor cores, one needs to access the neutron distribution in the core. In practice, the description of this density of neutrons is given by a system of diffusion equations, coupled by non differential exchange terms. The strong heterogeneity of the medium constitutes a major obstacle to the numerical computation of this models at reasonable cost. Homogenization appears as compulsory. Heuristic methods have been developed since the origin by nuclear physicists, under a periodicity assumption on the coefficients. They consist in doing a fine computation one a single periodicity cell, to solve the system on the whole domain with homogeneous coefficients, and to reconstruct the neutron density by multiplying the solutions of the two computations. The objectives of this work are to provide mathematically rigorous basis to this factorization method, to obtain the exact formulas of the homogenized coefficients, and to start on geometries where two periodical medium are placed side by side. The first result of this thesis concerns eigenvalue problem models which are used to characterize the state of criticality of the reactor, under a symmetry assumption on the coefficients. The convergence of the homogenization process is proved, and formulas of the homogenized coefficients are given. We then show that without symmetry assumptions, a drift phenomenon appears. It is characterized by the mean of a real Bloch wave method, which gives the homogenized limit in the general case. These results for the critical problem are then adapted to the evolution model. Finally, the homogenization of the critical problem in the case of two side by side periodic medium is studied on a one dimensional on equation model. (authors)

Isotropic compression of cohesive-frictional particles with rolling resistance

NARCIS (Netherlands)

Luding, Stefan; Benz, Thomas; Nordal, Steinar

2010-01-01

Cohesive-frictional and rough powders are the subject of this study. The behavior under isotropic compression is examined for different material properties involving Coulomb friction, rolling-resistance and contact-adhesion. Under isotropic compression, the density continuously increases according

Nature of complex time eigenvalues of the one speed transport equation in a homogeneous sphere

International Nuclear Information System (INIS)

Dahl, E.B.; Sahni, D.C.

1990-01-01

The complex time eigenvalues of the transport equation have been studied for one speed neutrons, scattered isotropically in a homogeneous sphere with vacuum boundary conditions. It is shown that the complex decay constants vary continuously with the radius of the sphere. Our earlier conjecture (Dahl and Sahni (1983-84)) regarding disjoint arcs is thus shown to be true. We also indicate that complex decay constants exist even for large assemblies, though with rapid oscillations in the corresponding eigenvectors. These modes cannot be predicted by the diffusion equation as this behaviour of the eigenvectors contradicts the assumption of 'slowly varying flux' needed to derive the diffusion approximation from the transport equation. For an infinite system, the existence of complex modes is related to the solution of a homogeneous equation. (author)

Interactively variable isotropic resolution in computed tomography

International Nuclear Information System (INIS)

Lapp, Robert M; Kyriakou, Yiannis; Kachelriess, Marc; Wilharm, Sylvia; Kalender, Willi A

2008-01-01

An individual balancing between spatial resolution and image noise is necessary to fulfil the diagnostic requirements in medical CT imaging. In order to change influencing parameters, such as reconstruction kernel or effective slice thickness, additional raw-data-dependent image reconstructions have to be performed. Therefore, the noise versus resolution trade-off is time consuming and not interactively applicable. Furthermore, isotropic resolution, expressed by an equivalent point spread function (PSF) in every spatial direction, is important for the undistorted visualization and quantitative evaluation of small structures independent of the viewing plane. Theoretically, isotropic resolution can be obtained by matching the in-plane and through-plane resolution with the aforementioned parameters. Practically, however, the user is not assisted in doing so by current reconstruction systems and therefore isotropic resolution is not commonly achieved, in particular not at the desired resolution level. In this paper, an integrated approach is presented for equalizing the in-plane and through-plane spatial resolution by image filtering. The required filter kernels are calculated from previously measured PSFs in x/y- and z-direction. The concepts derived are combined with a variable resolution filtering technique. Both approaches are independent of CT raw data and operate only on reconstructed images which allows for their application in real time. Thereby, the aim of interactively variable, isotropic resolution is achieved. Results were evaluated quantitatively by measuring PSFs and image noise, and qualitatively by comparing the images to direct reconstructions regarded as the gold standard. Filtered images matched direct reconstructions with arbitrary reconstruction kernels with standard deviations in difference images of typically between 1 and 17 HU. Isotropic resolution was achieved within 5% of the selected resolution level. Processing times of 20-100 ms per frame

Random isotropic one-dimensional XY-model

Science.gov (United States)

Gonçalves, L. L.; Vieira, A. P.

1998-01-01

The 1D isotropic s = ½XY-model ( N sites), with random exchange interaction in a transverse random field is considered. The random variables satisfy bimodal quenched distributions. The solution is obtained by using the Jordan-Wigner fermionization and a canonical transformation, reducing the problem to diagonalizing an N × N matrix, corresponding to a system of N noninteracting fermions. The calculations are performed numerically for N = 1000, and the field-induced magnetization at T = 0 is obtained by averaging the results for the different samples. For the dilute case, in the uniform field limit, the magnetization exhibits various discontinuities, which are the consequence of the existence of disconnected finite clusters distributed along the chain. Also in this limit, for finite exchange constants J A and J B, as the probability of J A varies from one to zero, the saturation field is seen to vary from Γ A to Γ B, where Γ A(Γ B) is the value of the saturation field for the pure case with exchange constant equal to J A(J B) .

Contact mechanics and friction for transversely isotropic viscoelastic materials

NARCIS (Netherlands)

Mokhtari, Milad; Schipper, Dirk J.; Vleugels, N.; Noordermeer, Jacobus W.M.; Yoshimoto, S.; Hashimoto, H.

2015-01-01

Transversely isotropic materials are an unique group of materials whose properties are the same along two of the principal axes of a Cartesian coordinate system. Various natural and artificial materials behave effectively as transversely isotropic elastic solids. Several materials can be classified

Diffusion piecewise homogenization via flux discontinuity ratios

International Nuclear Information System (INIS)

Sanchez, Richard; Dante, Giorgio; Zmijarevic, Igor

2013-01-01

We analyze piecewise homogenization with flux-weighted cross sections and preservation of averaged currents at the boundary of the homogenized domain. Introduction of a set of flux discontinuity ratios (FDR) that preserve reference interface currents leads to preservation of averaged region reaction rates and fluxes. We consider the class of numerical discretizations with one degree of freedom per volume and per surface and prove that when the homogenization and computing meshes are equal there is a unique solution for the FDRs which exactly preserve interface currents. For diffusion sub-meshing we introduce a Jacobian-Free Newton-Krylov method and for all cases considered obtain an 'exact' numerical solution (eight digits for the interface currents). The homogenization is completed by extending the familiar full assembly homogenization via flux discontinuity factors to the sides of regions laying on the boundary of the piecewise homogenized domain. Finally, for the familiar nodal discretization we numerically find that the FDRs obtained with no sub-mesh (nearly at no cost) can be effectively used for whole-core diffusion calculations with sub-mesh. This is not the case, however, for cell-centered finite differences. (authors)

The nonlinear Galerkin method: A multi-scale method applied to the simulation of homogeneous turbulent flows

Science.gov (United States)

Debussche, A.; Dubois, T.; Temam, R.

1993-01-01

Using results of Direct Numerical Simulation (DNS) in the case of two-dimensional homogeneous isotropic flows, the behavior of the small and large scales of Kolmogorov like flows at moderate Reynolds numbers are first analyzed in detail. Several estimates on the time variations of the small eddies and the nonlinear interaction terms were derived; those terms play the role of the Reynolds stress tensor in the case of LES. Since the time step of a numerical scheme is determined as a function of the energy-containing eddies of the flow, the variations of the small scales and of the nonlinear interaction terms over one iteration can become negligible by comparison with the accuracy of the computation. Based on this remark, a multilevel scheme which treats differently the small and the large eddies was proposed. Using mathematical developments, estimates of all the parameters involved in the algorithm, which then becomes a completely self-adaptive procedure were derived. Finally, realistic simulations of (Kolmorov like) flows over several eddy-turnover times were performed. The results are analyzed in detail and a parametric study of the nonlinear Galerkin method is performed.

On the dual variable of the Cauchy stress tensor in isotropic finite hyperelasticity

Science.gov (United States)

Vallée, Claude; Fortuné, Danielle; Lerintiu, Camelia

2008-11-01

Elastic materials are governed by a constitutive law relating the second Piola-Kirchhoff stress tensor Σ and the right Cauchy-Green strain tensor C=FF. Isotropic elastic materials are the special cases for which the Cauchy stress tensor σ depends solely on the left Cauchy-Green strain tensor B=FF. In this Note we revisit the following property of isotropic hyperelastic materials: if the constitutive law relating Σ and C is derivable from a potential ϕ, then σ and lnB are related by a constitutive law derived from the compound potential ϕ○exp. We give a new and concise proof which is based on an explicit integral formula expressing the derivative of the exponential of a tensor. To cite this article: C. Vallée et al., C. R. Mecanique 336 (2008).

Three-dimensional isotropic T2-weighted cervical MRI at 3 T: Comparison with two-dimensional T2-weighted sequences

International Nuclear Information System (INIS)

Kwon, J.W.; Yoon, Y.C.; Choi, S.-H.

2012-01-01

Aim: To compare three-dimensional (3D) isotropic T2-weighted magnetic resonance imaging (MRI) sequences and reformation with two-dimensional (2D) T2-weighted sequences regarding image quality of the cervical spine at 3 T. Materials and methods: A phantom study was performed using a water-filled cylinder. The signal-to-noise and image homogeneity were evaluated. Fourteen (n = 14) volunteers were examined at 3 T using 3D isotropic T2-weighted sagittal and conventional 2D T2-weighted sagittal, axial, and oblique sagittal MRI. Multiplanar reformation (MPR) of the 3D T2-weighted sagittal dataset was performed simultaneously with image evaluation. In addition to artefact assessment, the visibility of anatomical structures in the 3D and 2D sequences was qualitatively assessed by two radiologists independently. Cohen’s kappa and Wilcoxon signed rank test were used for the statistical analysis. Result: The 3D isotropic T2-weighted sequence resulted in the highest signal-to-noise ratio (SNR) and lowest non-uniformity (NU) among the sequences in the phantom study. Quantitative evaluation revealed lower NU values of the cerebrospinal fluid (CSF) and muscles in 2D T2-weighted sagittal sequences compared to the 3D volume isotropic turbo spin-echo acquisition (VISTA) sequence. The other NU values revealed no statistically significant difference between the 2D turbo spin-echo (TSE) and 3D VISTA sequences (0.059 < p < 0.959). 3D VISTA images showed significantly fewer CSF flow artefacts (p < 0.001) and better delineated intradural nerve rootlets (p = 0.001) and neural foramina (p = 0.016) compared to 2D sequences. Conclusion: A 3D T2 weighted sequence is superior to conventional 2D sequences for the delineation of intradural nerve rootlets and neural foramina and is less affected by CSF flow artefacts.

Asymmetric modes and complex time eigenvalues of the one-speed neutron transport equation in a homogeneous sphere

International Nuclear Information System (INIS)

Paranjape, S.D.; Kumar, V.; Sahni, D.C.

1993-01-01

The one-speed, time-dependent, isotropically scattering, integral transport equation in a homogeneous sphere has been converted into a criticality-like problem by considering exponential time behaviour of the scalar flux. This criticality problem has been converted into a matrix eigenvalue problem using the Fourier transform technique. The time eigenvalues λ, which are complex in general, have been determined for spherically symmetric as well as asymmetric modes. For the former case, the real decay constants and the real parts of complex decay constants decrease monotonically with increasing system size and form two distinct families of single-valued functions. For the spherically asymmetric modes, certain new features emerge. The real decay constants are found to be multi-valued functions of system size and they do not always decrease monotonically with increasing system size. As the system size increases from zero onwards, the decay constants alternate between complex and real values and the real and complex decay constant curves interlace. (Author)

Visualization and computer graphics on isotropically emissive volumetric displays.

Science.gov (United States)

Mora, Benjamin; Maciejewski, Ross; Chen, Min; Ebert, David S

2009-01-01

The availability of commodity volumetric displays provides ordinary users with a new means of visualizing 3D data. Many of these displays are in the class of isotropically emissive light devices, which are designed to directly illuminate voxels in a 3D frame buffer, producing X-ray-like visualizations. While this technology can offer intuitive insight into a 3D object, the visualizations are perceptually different from what a computer graphics or visualization system would render on a 2D screen. This paper formalizes rendering on isotropically emissive displays and introduces a novel technique that emulates traditional rendering effects on isotropically emissive volumetric displays, delivering results that are much closer to what is traditionally rendered on regular 2D screens. Such a technique can significantly broaden the capability and usage of isotropically emissive volumetric displays. Our method takes a 3D dataset or object as the input, creates an intermediate light field, and outputs a special 3D volume dataset called a lumi-volume. This lumi-volume encodes approximated rendering effects in a form suitable for display with accumulative integrals along unobtrusive rays. When a lumi-volume is fed directly into an isotropically emissive volumetric display, it creates a 3D visualization with surface shading effects that are familiar to the users. The key to this technique is an algorithm for creating a 3D lumi-volume from a 4D light field. In this paper, we discuss a number of technical issues, including transparency effects due to the dimension reduction and sampling rates for light fields and lumi-volumes. We show the effectiveness and usability of this technique with a selection of experimental results captured from an isotropically emissive volumetric display, and we demonstrate its potential capability and scalability with computer-simulated high-resolution results.

Diffraction of SH-waves by topographic features in a layered transversely isotropic half-space

Science.gov (United States)

Ba, Zhenning; Liang, Jianwen; Zhang, Yanju

2017-01-01

The scattering of plane SH-waves by topographic features in a layered transversely isotropic (TI) half-space is investigated by using an indirect boundary element method (IBEM). Firstly, the anti-plane dynamic stiffness matrix of the layered TI half-space is established and the free fields are solved by using the direct stiffness method. Then, Green's functions are derived for uniformly distributed loads acting on an inclined line in a layered TI half-space and the scattered fields are constructed with the deduced Green's functions. Finally, the free fields are added to the scattered ones to obtain the global dynamic responses. The method is verified by comparing results with the published isotropic ones. Both the steady-state and transient dynamic responses are evaluated and discussed. Numerical results in the frequency domain show that surface motions for the TI media can be significantly different from those for the isotropic case, which are strongly dependent on the anisotropy property, incident angle and incident frequency. Results in the time domain show that the material anisotropy has important effects on the maximum duration and maximum amplitudes of the time histories.

Isotropic-nematic transition in shear flow: State selection, coexistence, phase transitions, and critical behavior

Science.gov (United States)

Olmsted, Peter D.; Goldbart, Paul M.

1992-10-01

Macroscopic fluid motion can have dramatic consequences near the isotropic-nematic transition in fluids of nematogens. We explore some of these consequences using both deterministic and stochastic descriptions involving coupled hydrodynamic equations of motion for the nematic order parameter and fluid velocity fields. By analyzing the deterministic equations of motion we identify the locally stable states of homogeneous nematic order and strain rate, thus determining the homogeneous nonequilibrium steady states which the fluid may adopt. By examining inhomogeneous steady states we construct the analog of a first-order phase boundary, i.e., a line in the nonequilibrium phase diagram spanned by temperature and applied stress, at which nonequilibrium states may coexist, and which terminates in a nonequilibrium analog of a critical point. From an analysis of the nematic order-parameter discontinuity across the coexistence line, along with properties of the interface between homogeneous states, we extract the analog of classical equilibrium critical behavior near the nonequilibrium critical point. We develop a theory of fluctuations about biaxial nonequilibrium steady states by augmenting the deterministic description with noise terms, to simulate the effect of thermal fluctuations. We use this description to discuss the scattering of polarized light by order-parameter fluctuations near the nonequilibrium critical point and also in weak shear flow near the equilibrium phase transition. We find that fluids of nematogens near an appropriate temperature and strain rate exhibit the analog of critical opalescence, the intensity of which is sensitive to the polarizations of the incident and scattered light, and to the precise form of the critical mode.

Nested structures approach in designing an isotropic negative-index material for infrared

DEFF Research Database (Denmark)

Andryieuski, Andrei; Malureanu, Radu; Lavrinenko, Andrei

2009-01-01

We propose a new generic approach for designing isotropic metamaterial with nested cubic structures. As an example, a three-dimensional isotropic unit cell design "Split Cube in Cage" (SCiC) is shown to exhibit an effective negative refractive index on infrared wavelengths. We report on the refra......We propose a new generic approach for designing isotropic metamaterial with nested cubic structures. As an example, a three-dimensional isotropic unit cell design "Split Cube in Cage" (SCiC) is shown to exhibit an effective negative refractive index on infrared wavelengths. We report...

Homogenization methods for heterogeneous assemblies

International Nuclear Information System (INIS)

Wagner, M.R.

1980-01-01

The third session of the IAEA Technical Committee Meeting is concerned with the problem of homogenization of heterogeneous assemblies. Six papers will be presented on the theory of homogenization and on practical procedures for deriving homogenized group cross sections and diffusion coefficients. That the problem of finding so-called ''equivalent'' diffusion theory parameters for the use in global reactor calculations is of great practical importance. In spite of this, it is fair to say that the present state of the theory of second homogenization is far from being satisfactory. In fact, there is not even a uniquely accepted approach to the problem of deriving equivalent group diffusion parameters. Common agreement exists only about the fact that the conventional flux-weighting technique provides only a first approximation, which might lead to acceptable results in certain cases, but certainly does not guarantee the basic requirement of conservation of reaction rates

Vibrational Averaging of the Isotropic Hyperfine Coupling Constants for the Methyl Radical

Science.gov (United States)

Adam, Ahmad; Jensen, Per; Yachmenev, Andrey; Yurchenko, Sergei N.

2014-06-01

Electronic contributions to molecular properties are often considered as the major factor and usually reported in the literature without ro-vibrational corrections. However, there are many cases where the nuclear motion contributions are significant and even larger than the electronic contribution. In order to obtain accurate theoretical predictions, nuclear motion effects on molecular properties need to be taken into account. The computed isotropic hyperfine coupling constants for the nonvibrating methyl radical CH_3 are far from the experimental values. For CH_3, we have calculated the vibrational-state-dependence of the isotropic hyperfine coupling constant in the electronic ground state. The vibrational wavefunctions used in the averaging procedure were obtained variationally with the TROVE program. Analytical representations for the potential energy surfaces and the hyperfine coupling constant surfaces are obtained in least-squares fitting procedures. Thermal averaging has been carried out for molecules in thermal equilibrium, i.e., with Boltzmann-distributed populations. The calculation methods and the results will be discussed in detail.

Asymmetric transmission in prisms using structures and materials with isotropic-type dispersion.

Science.gov (United States)

Gundogdu, Funda Tamara; Serebryannikov, Andriy E; Cakmak, A Ozgur; Ozbay, Ekmel

2015-09-21

It is demonstrated that strong asymmetry in transmission can be obtained at the Gaussian beam illumination for a single prism based on a photonic crystal (PhC) with isotropic-type dispersion, as well as for its analog made of a homogeneous material. Asymmetric transmission can be realized with the aid of refraction at a proper orientation of the interfaces and wedges of the prism, whereas neither contribution of higher diffraction orders nor anisotropic-type dispersion is required. Furthermore, incidence toward a prism wedge can be used for one of two opposite directions in order to obtain asymmetry. Thus, asymmetric transmission is a general property of the prism configurations, which can be obtained by using simple geometries and quite conventional materials. The obtained results show that strong asymmetry can be achieved in PhC prisms with (nearly) circular shape of equifrequency dispersion contours, in both cases associated with the index of refraction 01. For the comparison purposes, results are also presented for solid uniform non-magnetic prisms made of a material with the same value of n. It is shown in zero-loss approximation that the PhC prism and the ultralow-index material prism (01. Possible contributions of scattering on the individual rods and diffraction on the wedge to the resulting mechanism are discussed. Analogs of unidirectional splitting and unidirectional deflection regimes, which are known from the studies of PhC gratings, are obtained in PhC prisms and solid uniform prisms, i.e. without higher diffraction orders.

Three-dimensional magnetospheric equilibrium with isotropic pressure

International Nuclear Information System (INIS)

Cheng, C.Z.

1995-05-01

In the absence of the toroidal flux, two coupled quasi two-dimensional elliptic equilibrium equations have been derived to describe self-consistent three-dimensional static magnetospheric equilibria with isotropic pressure in an optimal (Ψ,α,χ) flux coordinate system, where Ψ is the magnetic flux function, χ is a generalized poloidal angle, α is the toroidal angle, α = φ - δ(Ψ,φ,χ) is the toroidal angle, δ(Ψ,φ,χ) is periodic in φ, and the magnetic field is represented as rvec B = ∇Ψ x ∇α. A three-dimensional magnetospheric equilibrium code, the MAG-3D code, has been developed by employing an iterative metric method. The main difference between the three-dimensional and the two-dimensional axisymmetric solutions is that the field-aligned current and the toroidal magnetic field are finite for the three-dimensional case, but vanish for the two-dimensional axisymmetric case. With the same boundary flux surface shape, the two-dimensional axisymmetric results are similar to the three-dimensional magnetosphere at each local time cross section

Pretransitional behaviour in the vicinity of the isotropic-nematic transition of strongly polar compounds

International Nuclear Information System (INIS)

Sridevi, S; Krishna Prasad, S; Shankar Rao, D S; Yelamaggad, C V

2008-01-01

The isotropic-nematic transition, being weakly first order, exhibits pretransitional effects signifying the appearance of the nematic-like regions in the isotropic phase. In the isotropic phase, strongly polar liquid crystals, such as the popular alkyl and alkoxy cyano biphenyl behave in a non-standard fashion: whereas far away from the transition the dielectric constant ε iso has a 1/T dependence (a feature also commonly seen in polar liquids), on approaching the nematic phase the trend reverses resulting in a maximum in ε iso , at a temperature slightly above the transition, an effect explained on the basis of short-range correlations with an antiparallel association of the neighbouring molecules. Recently, there has been a revival in studies on this behaviour to possibly associate it with the order of transition. Here we report dielectric measurements carried in the vicinity of this transition for a number of compounds having different molecular structures including a bent core system, but with a common feature that the molecules possess a strong terminal polar group, nitro in one case and cyano in the rest. Surprisingly, the convex shape of the thermal variation of ε iso was more an exception than the rule. In materials that exhibit such an anomaly we find a linear correlation between δε = (ε peak -ε IN )/ε IN and δT = T peak -T IN , where ε peak is the maximum value of the dielectric constant in the isotropic phase, ε IN the value at the transition, and T peak and T IN the corresponding temperatures.

Homogeneous deuterium exchange using rhenium and platinum chloride catalysts

International Nuclear Information System (INIS)

Fawdry, R.M.

1979-01-01

Previous studies of homogeneous hydrogen isotope exchange are mostly confined to one catalyst, the tetrachloroplatinite salt. Recent reports have indicated that chloride salts of iridium and rhodium may also be homogeneous exchange catalysts similar to the tetrachloroplatinite, but with much lower activities. Exchange by these homogeneous catalysts is frequently accompanied by metal precipitation with the termination of homogeneous exchange, particularly in the case of alkane exchange. The studies presented in this thesis describe two different approaches to overcome this limitation of homogeneous hydrogen isotope exchange catalysts. The first approach was to improve the stability of an existing homogeneous catalyst and the second was to develop a new homogeneous exchange catalyst which is free of the instability limitation

An asymptotic homogenization model for smart 3D grid-reinforced composite structures with generally orthotropic constituents

International Nuclear Information System (INIS)

Hassan, E M; Kalamkarov, A L; Georgiades, A V; Challagulla, K S

2009-01-01

A comprehensive micromechanical model for smart 3D composite structures reinforced with a periodic grid of generally orthotropic cylindrical reinforcements that also exhibit piezoelectric behavior is developed. The original boundary value problem characterizing the piezothermoelastic behavior of these structures is decoupled into a set of three simpler unit cell problems dealing, separately, with the elastic, piezoelectric and thermal expansion characteristics of the smart composite. The technique used is that of asymptotic homogenization and the solution of the unit cell problems permits determination of the effective elastic, piezoelectric and thermal expansion coefficients. The general orthotropy of the constituent materials is very important from the practical viewpoint and makes the analysis much more complicated. Several examples of practical interest are used to illustrate the work including smart 3D composites with cubic and conical embedded grids as well as diagonally reinforced smart structures. It is also shown in this work that in the limiting particular case of 2D grid-reinforced structures with isotropic reinforcements our results converge to earlier published results

Software development for specific geometry and safe design of isotropic material multicell beams

International Nuclear Information System (INIS)

Tariq, M.M.; Ahmed, M.A.

2011-01-01

Comparison of analytical results with finite element results for analysis of isotropic material multicell beams subjected to free torsion case is the main idea of this paper. Progress in the fundamentals and applications of advanced materials and their processing technologies involves costly experiments and prototype testing for reliability. The software development for design analysis of structures with advanced materials is a low cost but challenging research. Multicell beams have important industrial applications in the aerospace and automotive sectors. This paper explains software development to test different materials in design of a multicell beam. Objective of this paper is to compute the torsional loading of multicell beams of isotropic materials for safe design in both symmetrical and asymmetrical geometries. Software has been developed in Microsoft Visual Basic. Distribution of Saint Venant shear flows, shear stresses, factors of safety, volume, mass, weight, twist, polar moment of inertia and aspect ratio for free torsion in multicell beam have been calculated using this software. The software works on four algorithms, these are, Specific geometry algorithm, material selection algorithm, factor of safety algorithm and global algorithm. User can specify new materials analytically, or choose a pre-defined material from the list, which includes, plain carbon steels, low alloy steels, stainless steels, cast irons, aluminum alloys, copper alloys, magnesium alloys, titanium alloys, precious metals and refractory metals. Although this software is restricted to multicell beam comprising of three cells, however future versions can have ability to address more complicated shapes and cases of multicell beams. Software also describes nomenclature and mathematical formulas applied to help user understand the theoretical background. User can specify geometry of multicell beam for three rectangular cells. Software computes shear flows, shear stresses, safety factors

Collapse and dispersal of a homogeneous spin fluid in Einstein-Cartan theory

Science.gov (United States)

Hashemi, M.; Jalalzadeh, S.; Ziaie, A. H.

2015-02-01

In the present work, we revisit the process of gravitational collapse of a spherically symmetric homogeneous dust fluid which is described by the Oppenheimer-Snyder (OS) model (Oppenheimer and Snyder in Phys Rev D 56:455, 1939). We show that such a scenario would not end in a spacetime singularity when the spin degrees of freedom of fermionic particles within the collapsing cloud are taken into account. To this purpose, we take the matter content of the stellar object as a homogeneous Weyssenhoff fluid. Employing the homogeneous and isotropic FLRW metric for the interior spacetime setup, it is shown that the spin of matter, in the context of a negative pressure, acts against the pull of gravity and decelerates the dynamical evolution of the collapse in its later stages. Our results show a picture of gravitational collapse in which the collapse process halts at a finite radius, whose value depends on the initial configuration. We thus show that the spacetime singularity that occurs in the OS model is replaced by a non-singular bounce beyond which the collapsing cloud re-expands to infinity. Depending on the model parameters, one can find a minimum value for the boundary of the collapsing cloud or correspondingly a threshold value for the mass content below which the horizon formation can be avoided. Our results are supported by a thorough numerical analysis.

Collapse and dispersal of a homogeneous spin fluid in Einstein-Cartan theory

International Nuclear Information System (INIS)

Hashemi, M.; Jalalzadeh, S.; Ziaie, A.H.

2015-01-01

In the present work, we revisit the process of gravitational collapse of a spherically symmetric homogeneous dust fluid which is described by the Oppenheimer-Snyder (OS) model (Oppenheimer and Snyder in Phys Rev D 56:455, 1939). We show that such a scenario would not end in a spacetime singularity when the spin degrees of freedom of fermionic particles within the collapsing cloud are taken into account. To this purpose, we take the matter content of the stellar object as a homogeneous Weyssenhoff fluid. Employing the homogeneous and isotropic FLRW metric for the interior spacetime setup, it is shown that the spin of matter, in the context of a negative pressure, acts against the pull of gravity and decelerates the dynamical evolution of the collapse in its later stages. Our results show a picture of gravitational collapse in which the collapse process halts at a finite radius, whose value depends on the initial configuration. We thus show that the spacetime singularity that occurs in the OS model is replaced by a non-singular bounce beyond which the collapsing cloud re-expands to infinity. Depending on the model parameters, one can find a minimum value for the boundary of the collapsing cloud or correspondingly a threshold value for the mass content below which the horizon formation can be avoided. Our results are supported by a thorough numerical analysis. (orig.)

REDUCED ISOTROPIC CRYSTAL MODEL WITH RESPECT TO THE FOURTH-ORDER ELASTIC MODULI

Directory of Open Access Journals (Sweden)

O. Burlayenko

2018-04-01

Full Text Available Using a reduced isotropic crystal model the relationship between the fourth-order elastic moduli of an isotropic medium and the independent components of the fourth-order elastic moduli tensor of real crystals of various crystal systems is found. To calculate the coefficients of these relations, computer algebra systems Redberry and Mathematica for working with high order tensors in the symbolic and explicit form were used, in light of the overly complex computation. In an isotropic medium, there are four independent fourth order elastic moduli. This is due to the presence of four invariants for an eighth-rank tensor in the three-dimensional space, that has symmetries over the pairs of indices. As an example, the moduli of elasticity of an isotropic medium corresponding to certain crystals of cubic system are given (LiF, NaCl, MgO, CaF2. From the obtained results it can be seen that the reduced isotropic crystal model can be most effectively applied to high-symmetry crystal systems.

Scalar Statistics along Inertial Particle Trajectory in Isotropic Turbulence

International Nuclear Information System (INIS)

Ya-Ming, Liu; Zhao-Hui, Liu; Hai-Feng, Han; Jing, Li; Han-Feng, Wang; Chu-Guang, Zheng

2009-01-01

The statistics of a passive scalar along inertial particle trajectory in homogeneous isotropic turbulence with a mean scalar gradient is investigated by using direct numerical simulation. We are interested in the influence of particle inertia on such statistics, which is crucial for further understanding and development of models in non-isothermal gas-particle flows. The results show that the scalar variance along particle trajectory decreases with the increasing particle inertia firstly; when the particle's Stokes number S t is less than 1.0, it reaches the minimal value when S t is around 1.0, then it increases if S t increases further. However, the scalar dissipation rate along the particle trajectory shows completely contrasting behavior in comparison with the scalar variance. The mechanical-to-thermal time scale ratios averaged along particle, p , are approximately two times smaller than that computed in the Eulerian frame r, and stay at nearly 1.77 with a weak dependence on particle inertia. In addition, the correlations between scalar dissipation and now structure characteristics along particle trajectories, such as strain and vorticity, are also computed, and they reach their maximum and minimum, 0.31 and 0.25, respectively, when S t is around 1.0. (fundamental areas of phenomenology (including applications))

A finite-density calculation of the surface tension of isotropic-nematic interfaces

International Nuclear Information System (INIS)

Moore, B.G.; McMullen, W.E.

1992-01-01

The surface tension of the isotropic-nematic interface in a fluid of intermediate-sized hard particles is studied and calculated. The transition from isotropic to nematic is fixed to occur in a continuous fashion by varying the biaxiality of the model particles. A reversal in the preferred orientation of the bulk nematic relative to the isotropic-nematic interface suggests an oblique orientation of the bulk nematic. 32 refs., 8 figs

Multilevel Monte Carlo Approaches for Numerical Homogenization

KAUST Repository

Efendiev, Yalchin R.

2015-10-01

In this article, we study the application of multilevel Monte Carlo (MLMC) approaches to numerical random homogenization. Our objective is to compute the expectation of some functionals of the homogenized coefficients, or of the homogenized solutions. This is accomplished within MLMC by considering different sizes of representative volumes (RVEs). Many inexpensive computations with the smallest RVE size are combined with fewer expensive computations performed on larger RVEs. Likewise, when it comes to homogenized solutions, different levels of coarse-grid meshes are used to solve the homogenized equation. We show that, by carefully selecting the number of realizations at each level, we can achieve a speed-up in the computations in comparison to a standard Monte Carlo method. Numerical results are presented for both one-dimensional and two-dimensional test-cases that illustrate the efficiency of the approach.

Introduction of an electromagnetic field and an isotropic radiation in the Szekeres cosmological models

International Nuclear Information System (INIS)

Waga, I.

1983-01-01

A new class of inhogeneous cosmological models, whose curvature source is a mixture of dust fluid with a isotropic radiation not interacting among themselves and an electromagnetic field that also not interacting with the fluids, is presented. It is shown that this class evolue for homogeneity and isotropy, in the limit of big values of the time coordinate. The asymptotic behaviours, near to the singularity, of two models of the class is studied and it is exhibited that the magnetic field modifies the type of singularity, being able to reduce the anisotropy in the initial phase. Killing's equations are integrated and it is demonstrated that the space-time shows an isometry group of three parameters whose orbits are space-like two-dimensional surfaces. It is shown that the models are expansionists, geodeticals, irrotationals and of D-like Petrov's classification with conformally plane three-dimensional spatial sections. (L.C.) [pt

Comparison of three-dimensional isotropic and conventional MR arthrography with respect to the diagnosis of rotator cuff and labral lesions: Focus on isotropic fat-suppressed proton density and VIBE sequences

International Nuclear Information System (INIS)

Park, S.Y.; Lee, I.S.; Park, S.K.; Cheon, S.J.; Ahn, J.M.; Song, J.W.

2014-01-01

Aim: To compare the diagnostic accuracies of three-dimensional (3D) isotropic magnetic resonance arthrography (MRA) using fat-suppressed proton density (PD) or volume interpolated breath-hold examination (VIBE) sequences with that of conventional MRA for the diagnosis of rotator cuff and labral lesions. Materials and methods: Eighty-six patients who underwent arthroscopic surgery were included. 3D isotropic sequences were performed in the axial plane using fat-suppressed PD (group A) in 53 patients and using VIBE (group B) in 33 patients. Reformatted images were obtained corresponding to conventional images, and evaluated for the presence of labral and rotator cuff lesions using conventional and 3D isotropic sequences. The diagnostic performances of each sequence were determined using arthroscopic findings as the standard. Results: Good to excellent interobserver agreements were obtained for both 3D isotropic sequences for the evaluation of rotator cuff and labral lesions. Excellent agreement was found between two-dimensional (2D) and 3D isotropic MRA, except for supraspinatus tendon (SST) tears by both readers and for subscapularis tendon (SCT) tears by reader 2 in group B. 2D MRA and 3D isotropic sequences had high diagnostic performances for rotator and labral tears, and the difference between the two imaging methods was insignificant. Conclusions: The diagnostic performances of 3D isotropic VIBE and PD sequences were similar to those of 2D MRA

Isotropic Negative Thermal Expansion Metamaterials.

Science.gov (United States)

Wu, Lingling; Li, Bo; Zhou, Ji

2016-07-13

Negative thermal expansion materials are important and desirable in science and engineering applications. However, natural materials with isotropic negative thermal expansion are rare and usually unsatisfied in performance. Here, we propose a novel method to achieve two- and three-dimensional negative thermal expansion metamaterials via antichiral structures. The two-dimensional metamaterial is constructed with unit cells that combine bimaterial strips and antichiral structures, while the three-dimensional metamaterial is fabricated by a multimaterial 3D printing process. Both experimental and simulation results display isotropic negative thermal expansion property of the samples. The effective coefficient of negative thermal expansion of the proposed models is demonstrated to be dependent on the difference between the thermal expansion coefficient of the component materials, as well as on the circular node radius and the ligament length in the antichiral structures. The measured value of the linear negative thermal expansion coefficient of the three-dimensional sample is among the largest achieved in experiments to date. Our findings provide an easy and practical approach to obtaining materials with tunable negative thermal expansion on any scale.

New criteria for isotropic and textured metals

Science.gov (United States)

Cazacu, Oana

2018-05-01

In this paper a isotropic criterion expressed in terms of both invariants of the stress deviator, J2 and J3 is proposed. This criterion involves a unique parameter, α, which depends only on the ratio between the yield stresses in uniaxial tension and pure shear. If this parameter is zero, the von Mises yield criterion is recovered; if a is positive the yield surface is interior to the von Mises yield surface whereas when a is negative, the new yield surface is exterior to it. Comparison with polycrystalline calculations using Taylor-Bishop-Hill model [1] for randomly oriented face-centered (FCC) polycrystalline metallic materials show that this new criterion captures well the numerical yield points. Furthermore, the criterion reproduces well yielding under combined tension-shear loadings for a variety of isotropic materials. An extension of this isotropic yield criterion such as to account for orthotropy in yielding is developed using the generalized invariants approach of Cazacu and Barlat [2]. This new orthotropic criterion is general and applicable to three-dimensional stress states. The procedure for the identification of the material parameters is outlined. Illustration of the predictive capabilities of the new orthotropic is demonstrated through comparison between the model predictions and data on aluminum sheet samples.

Catsius Clay Project. Calculation and Testing of Behaviour of Unsaturated Clay as Barrier in Radioactive Waste Repositories. Stage 1: Verification Exercises

International Nuclear Information System (INIS)

Alonso, E. E.; Alcoverro, J.

1999-01-01

The prescribed flow in a rigid homogeneous isotropic unsaturated medium was considered, and two cases envisaged: i) vertical flow and ii) horizontal flow. In both cases, predictions were satisfactory for all partners. The flow in a rigid homogeneous isotropic and saturated porous medium due to a spherical source of heat was considered, and two cases envisaged: a) low porosity (analytical solution available) and b) high porosity (analytical solution not available). Temperature distributions for both case A and case B depend mainly on heat conduction. Correct predictions were found by AND, CLA, ISM, UPC, UOL and UWC. Pressure distribution for case A depends mainly on buoyancy effects. In this case correct predictions were found by AND, CLA, UPC, UOL and UWC. Pressure distribution for case B depends mainly on thermal expansion of the fluid. It has been found that only CLA, ISM, UPC and UOL found a satisfactory prediction in this case. (Author)

Catsius Clay Project. Calculation and Testing of Behaviour of Unsaturated Clay as Barrier in Radioactive Waste Repositories. Stage 1: Verification Exercises

Energy Technology Data Exchange (ETDEWEB)

Alonso, E E; Alcoverro, J

1999-07-01

The prescribed flow in a rigid homogeneous isotropic unsaturated medium was considered, and two cases envisaged: i) vertical flow and ii) horizontal flow. In both cases, predictions were satisfactory for all partners. The flow in a rigid homogeneous isotropic and saturated porous medium due to a spherical source of heat was considered, and two cases envisaged: a) low porosity (analytical solution available) and b) high porosity (analytical solution not available). Temperature distributions for both case A and case B depend mainly on heat conduction. Correct predictions were found by AND, CLA, ISM, UPC, UOL and UWC. Pressure distribution for case A depends mainly on buoyancy effects. In this case correct predictions were found by AND, CLA, UPC, UOL and UWC. Pressure distribution for case B depends mainly on thermal expansion of the fluid. It has been found that only CLA, ISM, UPC and UOL found a satisfactory prediction in this case. (Author)

Directional statistics-based reflectance model for isotropic bidirectional reflectance distribution functions.

Science.gov (United States)

Nishino, Ko; Lombardi, Stephen

2011-01-01

We introduce a novel parametric bidirectional reflectance distribution function (BRDF) model that can accurately encode a wide variety of real-world isotropic BRDFs with a small number of parameters. The key observation we make is that a BRDF may be viewed as a statistical distribution on a unit hemisphere. We derive a novel directional statistics distribution, which we refer to as the hemispherical exponential power distribution, and model real-world isotropic BRDFs as mixtures of it. We derive a canonical probabilistic method for estimating the parameters, including the number of components, of this novel directional statistics BRDF model. We show that the model captures the full spectrum of real-world isotropic BRDFs with high accuracy, but a small footprint. We also demonstrate the advantages of the novel BRDF model by showing its use for reflection component separation and for exploring the space of isotropic BRDFs.

Ellipsoidal basis for isotropic oscillator

International Nuclear Information System (INIS)

Kallies, W.; Lukac, I.; Pogosyan, G.S.; Sisakyan, A.N.

1994-01-01

The solutions of the Schroedinger equation are derived for the isotropic oscillator potential in the ellipsoidal coordinate system. The explicit expression is obtained for the ellipsoidal integrals of motion through the components of the orbital moment and Demkov's tensor. The explicit form of the ellipsoidal basis is given for the lowest quantum numbers. 10 refs.; 1 tab. (author)

MRI of the popliteofibular ligament: isotropic 3D WE-DESS versus coronal oblique fat-suppressed T2W MRI

International Nuclear Information System (INIS)

Rajeswaran, G.; Lee, J.C.; Healy, J.C.

2007-01-01

The objective was to compare isotropic 3D water excitation double-echo steady state (WE-DESS) MRI with coronal oblique fat-suppressed T2-weighted (FS T2W) images in the identification of the popliteofibular ligament (PFL). A prospective analysis of 122 consecutive knee MRIs was performed in patients referred for knee pain from the orthopaedic clinic. In addition to the standard knee sequences, isotropic WE-DESS volume acquisition through the whole knee and coronal oblique FS T2W fast spin echo sequences through the posterolateral corner were obtained. The presence of the popliteus and biceps femoris tendons, lateral collateral and PFL was documented. Anterior cruciate ligament injury was present in 33 cases and these were excluded from the study because of the risk of associated PFL injury, leaving a total of 89 cases. Of the 42 patients in whom arthroscopic evaluation was subsequently obtained, none were found to have an injury to the PFL. The lateral collateral ligament, biceps femoris and popliteus tendon were identified in all cases on all sequences. The PFL was seen in 81 (91.0%; 95% CI 85.1-97.0%) patients using the WE-DESS sequence and 63 (70.8%; 95% CI 61.3-80.2%) patients using the coronal oblique FS T2W sequence, a statistically significant difference (p < 0.00005). Isotropic 3D WE-DESS MRI significantly enhances our ability to identify the popliteofibular ligament compared with coronal oblique fat-suppressed T2-weighted images. (orig.)

Isotropic harmonic oscillator plus inverse quadratic potential in N-dimensional spaces

International Nuclear Information System (INIS)

Oyewumi, K.A.; Bangudu, E.A.

2003-01-01

Some aspects of the N-dimensional isotropic harmonic plus inverse quadratic potential were discussed. The hyperradial equation for isotropic harmonic oscillator plus inverse quadratic potential is solved by transformation into the confluent hypergeometric equation to obtain the normalized hyperradial solution. Together with the hyperangular solutions (hyperspherical harmonics), these form the complete energy eigenfunctions of the N-dimensional isotropic harmonic oscillator plus inverse quadratic potential and the energy eigenvalues are also obtained. These are dimensionally dependent. The dependence of radial solution on the dimensions or potential strength and the degeneracy of the energy levels are discussed. (author)

Validity of the isotropic thermal conductivity assumption in supercell lattice dynamics

Science.gov (United States)

Ma, Ruiyuan; Lukes, Jennifer R.

2018-02-01

Superlattices and nano phononic crystals have attracted significant attention due to their low thermal conductivities and their potential application as thermoelectric materials. A widely used expression to calculate thermal conductivity, presented by Klemens and expressed in terms of the relaxation time by Callaway and Holland, originates from the Boltzmann transport equation. In its most general form, this expression involves a direct summation of the heat current contributions from individual phonons of all wavevectors and polarizations in the first Brillouin zone. In common practice, the expression is simplified by making an isotropic assumption that converts the summation over wavevector to an integral over wavevector magnitude. The isotropic expression has been applied to superlattices and phononic crystals, but its validity for different supercell sizes has not been studied. In this work, the isotropic and direct summation methods are used to calculate the thermal conductivities of bulk Si, and Si/Ge quantum dot superlattices. The results show that the differences between the two methods increase substantially with the supercell size. These differences arise because the vibrational modes neglected in the isotropic assumption provide an increasingly important contribution to the thermal conductivity for larger supercells. To avoid the significant errors that can result from the isotropic assumption, direct summation is recommended for thermal conductivity calculations in superstructures.

Third-harmonic generation in isotropic media by focused pulses

International Nuclear Information System (INIS)

Tasgal, Richard S.; Band, Y.B.

2004-01-01

For focused pulses of light in isotropic nonlinear media, third-harmonic generation can be strongly affected by group-velocity mismatch between the fundamental and third-harmonic. There is a characteristic time determined by the group-velocity mismatch and the Rayleigh range of the focused pulse. The dynamics depend on two dimensionless quantities, namely the ratio of the characteristic time to the pulse duration and the phase-velocity mismatch times the Rayleigh range. Pulses shorter than the characteristic time have physics described by simple analytic formulas. Pulses near the characteristic time have an intermediate behavior given by an explicit but more complicated formula. Pulses longer than the characteristic time tend to the continuous-wave case

3D geometrically isotropic metamaterial for telecom wavelengths

DEFF Research Database (Denmark)

Malureanu, Radu; Andryieuski, Andrei; Lavrinenko, Andrei

2009-01-01

of the unit cell is not infinitely small, certain geometrical constraints have to be fulfilled to obtain an isotropic response of the material [3]. These conditions and the metal behaviour close to the plasma frequency increase the design complexity. Our unit cell is composed of two main parts. The first part...... is obtained in a certain bandwidth. The proposed unit cell has the cubic point group of symmetry and being repeatedly placed in space can effectively reveal isotropic optical properties. We use the CST commercial software to characterise the “cube-in-cage” structure. Reflection and transmission spectra...

Mechanized syringe homogenization of human and animal tissues.

Science.gov (United States)

Kurien, Biji T; Porter, Andrew C; Patel, Nisha C; Kurono, Sadamu; Matsumoto, Hiroyuki; Scofield, R Hal

2004-06-01

Tissue homogenization is a prerequisite to any fractionation schedule. A plethora of hands-on methods are available to homogenize tissues. Here we report a mechanized method for homogenizing animal and human tissues rapidly and easily. The Bio-Mixer 1200 (manufactured by Innovative Products, Inc., Oklahoma City, OK) utilizes the back-and-forth movement of two motor-driven disposable syringes, connected to each other through a three-way stopcock, to homogenize animal or human tissue. Using this method, we were able to homogenize human or mouse tissues (brain, liver, heart, and salivary glands) in 5 min. From sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis and a matrix-assisted laser desorption/ionization time-of-flight mass spectrometric enzyme assay for prolidase, we have found that the homogenates obtained were as good or even better than that obtained used a manual glass-on-Teflon (DuPont, Wilmington, DE) homogenization protocol (all-glass tube and Teflon pestle). Use of the Bio-Mixer 1200 to homogenize animal or human tissue precludes the need to stay in the cold room as is the case with the other hands-on homogenization methods available, in addition to freeing up time for other experiments.

On physical complementarity of Galileo and Lorentz groups in the electrodynamics of isotropic inertial moving media

International Nuclear Information System (INIS)

Barykin, V.N.

1989-01-01

A physical interpretation of the early detected ambiguity of the electrodynamic material equations of isotropic, inertially moving media which mathematically manifests itself through complementarity of the equations invariant under the Galileo group in some cases and in other ones - under the Lorentz group that can be experimentally discovered in the aberration phenomenon and Doppler effect

SuPer-Homogenization (SPH) Corrected Cross Section Generation for High Temperature Reactor

Energy Technology Data Exchange (ETDEWEB)

Sen, Ramazan Sonat [Idaho National Lab. (INL), Idaho Falls, ID (United States); Hummel, Andrew John [Idaho National Lab. (INL), Idaho Falls, ID (United States); Hiruta, Hikaru [Idaho National Lab. (INL), Idaho Falls, ID (United States)

2017-03-01

The deterministic full core simulators require homogenized group constants covering the operating and transient conditions over the entire lifetime. Traditionally, the homogenized group constants are generated using lattice physics code over an assembly or block in the case of prismatic high temperature reactors (HTR). For the case of strong absorbers that causes strong local depressions on the flux profile require special techniques during homogenization over a large volume. Fuel blocks with burnable poisons or control rod blocks are example of such cases. Over past several decades, there have been a tremendous number of studies performed for improving the accuracy of full-core calculations through the homogenization procedure. However, those studies were mostly performed for light water reactor (LWR) analyses, thus, may not be directly applicable to advanced thermal reactors such as HTRs. This report presents the application of SuPer-Homogenization correction method to a hypothetical HTR core.

On the spatial distribution of small heavy particles in homogeneous shear turbulence

Science.gov (United States)

Nicolai, C.; Jacob, B.; Piva, R.

2013-08-01

We report on a novel experiment aimed at investigating the effects induced by a large-scale velocity gradient on the turbulent transport of small heavy particles. To this purpose, a homogeneous shear flow at Reλ = 540 and shear parameter S* = 4.5 is set-up and laden with glass spheres whose size d is comparable with the Kolmogorov lengthscale η of the flow (d/η ≈ 1). The particle Stokes number is approximately 0.3. The analysis of the instantaneous particle fields by means of Voronoï diagrams confirms the occurrence of intense turbulent clustering at small scales, as observed in homogeneous isotropic flows. It also indicates that the anisotropy of the velocity fluctuations induces a preferential orientation of the particle clusters. In order to characterize the fine-scale features of the dispersed phase, spatial correlations of the particle field are employed in conjunction with statistical tools recently developed for anisotropic turbulence. The scale-by-scale analysis of the particle field clarifies that isotropy of the particle distribution is tendentially recovered at small separations, even though the signatures of the mean shear persist down to smaller scales as compared to the fluid velocity field.

Poisson-Jacobi reduction of homogeneous tensors

International Nuclear Information System (INIS)

Grabowski, J; Iglesias, D; Marrero, J C; Padron, E; Urbanski, P

2004-01-01

The notion of homogeneous tensors is discussed. We show that there is a one-to-one correspondence between multivector fields on a manifold M, homogeneous with respect to a vector field Δ on M, and first-order polydifferential operators on a closed submanifold N of codimension 1 such that Δ is transversal to N. This correspondence relates the Schouten-Nijenhuis bracket of multivector fields on M to the Schouten-Jacobi bracket of first-order polydifferential operators on N and generalizes the Poissonization of Jacobi manifolds. Actually, it can be viewed as a super-Poissonization. This procedure of passing from a homogeneous multivector field to a first-order polydifferential operator can also be understood as a sort of reduction; in the standard case-a half of a Poisson reduction. A dual version of the above correspondence yields in particular the correspondence between Δ-homogeneous symplectic structures on M and contact structures on N

Rocking Rotation of a Rigid Disk Embedded in a Transversely Isotropic Half-Space

Directory of Open Access Journals (Sweden)

Seyed Ahmadi

2014-06-01

Full Text Available The asymmetric problem of rocking rotation of a circular rigid disk embedded in a finite depth of a transversely isotropic half-space is analytically addressed. The rigid disk is assumed to be in frictionless contact with the elastic half-space. By virtue of appropriate Green's functions, the mixed boundary value problem is written as a dual integral equation. Employing further mathematical techniques, the integral equation is reduced to a well-known Fredholm integral equation of the second kind. The results related to the contact stress distribution across the disk region and the equivalent rocking stiffness of the system are expressed in terms of the solution of the obtained Fredholm  integral  equation. When the rigid disk is located on the surface or at the remote boundary, the exact closed-form solutions are presented. For verification purposes, the limiting case of an isotropic half-space is considered and the results are verified with those available in the literature. The jump behavior in the results at the edge of the rigid disk for the case of an infinitesimal embedment is highlighted analytically for the first time. Selected numerical results are depicted for the contact stress distribution across the disk region, rocking stiffness of the system, normal stress, and displacement components along the radial axis. Moreover, effects of anisotropy on the rocking stiffness factor are discussed in detail.

Alternate model of Chladni figures for the circular homogenous thin plate case with open boundaries

International Nuclear Information System (INIS)

Trejo-Mandujano, H A; Mijares-Bernal, G; Ordoñez-Casanova, E G

2015-01-01

The wave equation is a direct but a complex approach to solve analytically for the Chladni figures, mainly because of the complications that non-smooth and open boundary conditions impose. In this paper, we present an alternate solution model based on the principle of Huygens-Fresnel and on the ideas of Bohr for the hydrogen atom. The proposed model has been implemented numerically and compared, with good agreement, to our own experimental results for the case of a thin homogenous circular plate with open boundaries

On isotropic cylindrically symmetric stellar models

International Nuclear Information System (INIS)

Nolan, Brien C; Nolan, Louise V

2004-01-01

We attempt to match the most general cylindrically symmetric vacuum spacetime with a Robertson-Walker interior. The matching conditions show that the interior must be dust filled and that the boundary must be comoving. Further, we show that the vacuum region must be polarized. Imposing the condition that there are no trapped cylinders on an initial time slice, we can apply a result of Thorne's and show that trapped cylinders never evolve. This results in a simplified line element which we prove to be incompatible with the dust interior. This result demonstrates the impossibility of the existence of an isotropic cylindrically symmetric star (or even a star which has a cylindrically symmetric portion). We investigate the problem from a different perspective by looking at the expansion scalars of invariant null geodesic congruences and, applying to the cylindrical case, the result that the product of the signs of the expansion scalars must be continuous across the boundary. The result may also be understood in relation to recent results about the impossibility of the static axially symmetric analogue of the Einstein-Straus model

Precession of elastic waves in vibrating isotropic spheres and transversely isotropic cylinders subjected to inertial rotation

CSIR Research Space (South Africa)

Joubert, S

2006-05-01

Full Text Available and Manufacturing TRANSVERSELY ISOTROPIC CYLINDER - 1 φ φ r z a x y Ω P P O u v w z ( )1 1 1 2 1 1 rrr rz rr zr r zrz zz rz u r r z r v r r z r w r r z r ϕ ϕϕ ϕϕ ϕϕ ϕ ϕ σσ σ σ σ ρ ϕ σσ σ σ ρ ϕ σσ σ σ ρ ϕ... ∂ ∂ ∂ + + + − = ∂ ∂ ∂ ∂∂ ∂ + + + = ∂ ∂ ∂ ∂∂ ∂ + + + = ∂ ∂ ∂ && && && 6 CSIR Material Science and Manufacturing TRANSVERSELY ISOTROPIC CYLINDER - 2 ( )1 1 1 2 1 1 rrr rz rr zr r zrz zz rz u r r z r v r r z r w r r z r ϕ ϕϕ ϕϕ ϕϕ ϕ ϕ σσ σ σ σ ρ ϕ σσ σ σ ρ ϕ σσ σ σ ρ ϕ...

Application of group analysis to the spatially homogeneous and isotropic Boltzmann equation with source using its Fourier image

International Nuclear Information System (INIS)

Grigoriev, Yurii N; Meleshko, Sergey V; Suriyawichitseranee, Amornrat

2015-01-01

Group analysis of the spatially homogeneous and molecular energy dependent Boltzmann equations with source term is carried out. The Fourier transform of the Boltzmann equation with respect to the molecular velocity variable is considered. The correspondent determining equation of the admitted Lie group is reduced to a partial differential equation for the admitted source. The latter equation is analyzed by an algebraic method. A complete group classification of the Fourier transform of the Boltzmann equation with respect to a source function is given. The representation of invariant solutions and corresponding reduced equations for all obtained source functions are also presented. (paper)

Lagrangian velocity correlations in homogeneous isotropic turbulence

International Nuclear Information System (INIS)

Gotoh, T.; Rogallo, R.S.; Herring, J.R.; Kraichnan, R.H.

1993-01-01

The Lagrangian velocity autocorrelation and the time correlations for individual wave-number bands are computed by direct numerical simulation (DNS) using the passive vector method (PVM), and the accuracy of the method is studied. It is found that the PVM is accurate when K max /k d ≥2 where K max is the maximum wave number carried in the simulation and k d is the Kolmogorov wave number. The Eulerian and Lagrangian time correlations for various wave-number bands are compared. At moderate to high wave number the Eulerian time correlation decays faster than the Lagrangian, and the effect of sweep on the former is observed. The time scale of the Eulerian correlation is found to be (kU 0 ) -1 while that of the Lagrangian is [∫ 0 k p 2 E(p)dp] -1/2 . The Lagrangian velocity autocorrelation in a frozen turbulent field is computed using the DIA, ALHDIA, and LRA theories and is compared with DNS measurements. The Markovianized Lagrangian renormalized approximation (MLRA) is compared with the DNS, and good agreement is found for one-time quantities in decaying turbulence at low Reynolds numbers and for the Lagrangian velocity autocorrelation in stationary turbulence at moderate Reynolds number. The effect of non-Gaussianity on the Lagrangian correlation predicted by the theories is also discussed

Reconstruction of constitutive parameters in isotropic linear elasticity from noisy full-field measurements

International Nuclear Information System (INIS)

Bal, Guillaume; Bellis, Cédric; Imperiale, Sébastien; Monard, François

2014-01-01

Within the framework of linear elasticity we assume the availability of internal full-field measurements of the continuum deformations of a non-homogeneous isotropic solid. The aim is the quantitative reconstruction of the associated moduli. A simple gradient system for the sought constitutive parameters is derived algebraically from the momentum equation, whose coefficients are expressed in terms of the measured displacement fields and their spatial derivatives. Direct integration of this system is discussed to finally demonstrate the inexpediency of such an approach when dealing with noisy data. Upon using polluted measurements, an alternative variational formulation is deployed to invert for the physical parameters. Analysis of this latter inversion procedure provides existence and uniqueness results while the reconstruction stability with respect to the measurements is investigated. As the inversion procedure requires differentiating the measurements twice, a numerical differentiation scheme based on an ad hoc regularization then allows an optimally stable reconstruction of the sought moduli. Numerical results are included to illustrate and assess the performance of the overall approach. (paper)

The isotropic Universe

International Nuclear Information System (INIS)

Raine, D.J.

1981-01-01

This introduction to contemporary ideas in cosmology differs from other books on the 'expanding Universe' in its emphasis on physical cosmology and on the physical basis of the general theory of relativity. It is considered that the remarkable degree of isotropy, rather than the expansion, can be regarded as the central observational feature of the Universe. The various theories and ideas in 'big-bang' cosmology are discussed, providing an insight into current problems. Chapter headings are: quality of matter; expanding Universe; quality of radiation; quantity of matter; general theory of relativity; cosmological models; cosmological tests; matter and radiation; limits of isotropy; why is the Universe isotropic; singularities; evolution of structure. (U.K.)

Waterlike glass polyamorphism in a monoatomic isotropic Jagla model.

Science.gov (United States)

Xu, Limei; Giovambattista, Nicolas; Buldyrev, Sergey V; Debenedetti, Pablo G; Stanley, H Eugene

2011-02-14

We perform discrete-event molecular dynamics simulations of a system of particles interacting with a spherically-symmetric (isotropic) two-scale Jagla pair potential characterized by a hard inner core, a linear repulsion at intermediate separations, and a weak attractive interaction at larger separations. This model system has been extensively studied due to its ability to reproduce many thermodynamic, dynamic, and structural anomalies of liquid water. The model is also interesting because: (i) it is very simple, being composed of isotropically interacting particles, (ii) it exhibits polyamorphism in the liquid phase, and (iii) its slow crystallization kinetics facilitate the study of glassy states. There is interest in the degree to which the known polyamorphism in glassy water may have parallels in liquid water. Motivated by parallels between the properties of the Jagla potential and those of water in the liquid state, we study the metastable phase diagram in the glass state. Specifically, we perform the computational analog of the protocols followed in the experimental studies of glassy water. We find that the Jagla potential calculations reproduce three key experimental features of glassy water: (i) the crystal-to-high-density amorphous solid (HDA) transformation upon isothermal compression, (ii) the low-density amorphous solid (LDA)-to-HDA transformation upon isothermal compression, and (iii) the HDA-to-very-high-density amorphous solid (VHDA) transformation upon isobaric annealing at high pressure. In addition, the HDA-to-LDA transformation upon isobaric heating, observed in water experiments, can only be reproduced in the Jagla model if a free surface is introduced in the simulation box. The HDA configurations obtained in cases (i) and (ii) are structurally indistinguishable, suggesting that both processes result in the same glass. With the present parametrization, the evolution of density with pressure or temperature is remarkably similar to the

An Isotropic Light Sensor for Measurements of Visible Actinic Flux in Clouds

NARCIS (Netherlands)

Hage, J.C.H. van der; Roode, S.R. de

1999-01-01

A low-cost isotropic light sensor is described consisting of a spherical diffuser connected to a single photodiode by a light conductor. The directional response to light is isotropic to a high degree. The small, lightweight, and rugged construction makes this instrument suitable not only for

The combinational structure of non-homogeneous Markov chains with countable states

Directory of Open Access Journals (Sweden)

A. Mukherjea

1983-01-01

Full Text Available Let P(s,t denote a non-homogeneous continuous parameter Markov chain with countable state space E and parameter space [a,b], −∞0}. It is shown in this paper that R(s,t is reflexive, transitive, and independent of (s,t, shomogeneity condition holds. It is also shown that the relation R(s,t, unlike in the finite state space case, cannot be expressed even as an infinite (countable product of reflexive transitive relations for certain non-homogeneous chains in the case when E is infinite.

A generalized model for homogenized reflectors

International Nuclear Information System (INIS)

Pogosbekyan, Leonid; Kim, Yeong Il; Kim, Young Jin; Joo, Hyung Kook

1996-01-01

A new concept of equivalent homogenization is proposed. The concept employs new set of homogenized parameters: homogenized cross sections (XS) and interface matrix (IM), which relates partial currents at the cell interfaces. The idea of interface matrix generalizes the idea of discontinuity factors (DFs), proposed and developed by K. Koebke and K. Smith. The method of K. Smith can be simulated within framework of new method, while the new method approximates hetero-geneous cell better in case of the steep flux gradients at the cell interfaces. The attractive shapes of new concept are:improved accuracy, simplicity of incorporation in the existing codes, equal numerical expenses in comparison to the K. Smith's approach. The new concept is useful for: (a) explicit reflector/baffle simulation; (b)control blades simulation; (c) mixed UO 2 /MOX core simulation. The offered model has been incorporated in the finite difference code and in the nodal code PANBOX. The numerical results show good accuracy of core calculations and insensitivity of homogenized parameters with respect to in-core conditions

Calculated isotropic Raman spectra from interacting H2-rare-gas pairs

International Nuclear Information System (INIS)

Gustafsson, M; Głaz, W; Bancewicz, T; Godet, J-L; Maroulis, G; Haskapoulos, A

2014-01-01

We report on a theoretical study of the H 2 -He and H 2 -Ar pair trace-polarizability and the corresponding isotropic Raman spectra. The conventional quantum mechanical approach for calculations of interaction-induced spectra, which is based on an isotropic interaction potential, is employed. This is compared with a close-coupling approach, which allows for inclusion of the full, anisotropic potential. It is established that the anisotropy of the potential plays a minor role for these spectra. The computed isotropic collision-induced Raman intensity, which is due to dissimilar pairs in H 2 -He and H 2 -Ar gas mixtures, is comparable to the intensities due to similar pairs (H 2 -H 2 , He-He, and Ar-Ar), which have been studied previously

Mechanical and electronic properties of monolayer and bilayer phosphorene under uniaxial and isotropic strains.

Science.gov (United States)

Hu, Ting; Han, Yang; Dong, Jinming

2014-11-14

The mechanical and electronic properties of both the monolayer and bilayer phosphorenes under either isotropic or uniaxial strain have been systematically investigated using first-principles calculations. It is interesting to find that: 1) Under a large enough isotropic tensile strain, the monolayer phosphorene would lose its pucker structure and transform into a flat hexagonal plane, while two inner sublayers of the bilayer phosphorene could be bonded due to its interlayer distance contraction. 2) Under the uniaxial tensile strain along a zigzag direction, the pucker distance of each layer in the bilayer phosphorene can exhibit a specific negative Poisson's ratio. 3) The electronic properties of both the monolayer and bilayer phosphorenes are sensitive to the magnitude and direction of the applied strains. Their band gaps decrease more rapidly under isotropic compressive strain than under uniaxial strain. Also, their direct-indirect band gap transitions happen at the larger isotropic tensile strains compared with that under uniaxial strain. 4) Under the isotropic compressive strain, the bilayer phosphorene exhibits a transition from a direct-gap semiconductor to a metal. In contrast, the monolayer phosphorene initially has the direct-indirect transition and then transitions to a metal. However, under isotropic tensile strain, both the bilayer and monolayer phosphorene show the direct-indirect transition and, finally, the transition to a metal. Our numerical results may open new potential applications of phosphorene in nanoelectronics and nanomechanical devices by external isotropic strain or uniaxial strain along different directions.

Homogenization patterns of the world's freshwater fish faunas.

Science.gov (United States)

Villéger, Sébastien; Blanchet, Simon; Beauchard, Olivier; Oberdorff, Thierry; Brosse, Sébastien

2011-11-01

The world is currently undergoing an unprecedented decline in biodiversity, which is mainly attributable to human activities. For instance, nonnative species introduction, combined with the extirpation of native species, affects biodiversity patterns, notably by increasing the similarity among species assemblages. This biodiversity change, called taxonomic homogenization, has rarely been assessed at the world scale. Here, we fill this gap by assessing the current homogenization status of one of the most diverse vertebrate groups (i.e., freshwater fishes) at global and regional scales. We demonstrate that current homogenization of the freshwater fish faunas is still low at the world scale (0.5%) but reaches substantial levels (up to 10%) in some highly invaded river basins from the Nearctic and Palearctic realms. In these realms experiencing high changes, nonnative species introductions rather than native species extirpations drive taxonomic homogenization. Our results suggest that the "Homogocene era" is not yet the case for freshwater fish fauna at the worldwide scale. However, the distressingly high level of homogenization noted for some biogeographical realms stresses the need for further understanding of the ecological consequences of homogenization processes.

Protogalaxy formation from inhomogeneities in cosmological models

International Nuclear Information System (INIS)

Rankin, J.R.

1977-01-01

Equations governing the growth of protogalaxies in general homogeneous cosmological models were derived. Both non-relativistic Newtonian theory and general relativistic theory were covered. For the Newtonian case, by means of the concept of comoving Fourier analysis, the perturbation equations became coupled first order ordinary differential equations and were then further simplified. Bonnor's equation of galaxy formation in isotropic Newtonian cosmologies was generalized to anisotropic cases. The growth equations were solved for various background Newtonian models and gravitationally unstable solutions were found. By an approach analogous to Bonnor's non-relativistic approach, a relativistic version of the galaxy growth equation for the homogeneous isotropic cosmologies was derived. Galaxy growth in the anisotropic homogeneous Bianchi type I cosmologies was also considered. The full set of Einstein equations in synchronous coordinates was perturbed then simplified. The resulting equation was discussed in special cases of dust, axial symmetry and Kasner backgrounds. Finally the tetrad equations for perturbations in steady state cosmologies was set up with a view to considering the effect of rotation

Anomalies, effective action and Hawking temperatures of a Schwarzschild black hole in the isotropic coordinates

International Nuclear Information System (INIS)

Wu Shuangqing; Peng Junjin; Zhao Zhanyue

2008-01-01

Motivated by the universality of Hawking radiation and that of the anomaly cancellation technique as well as the effective action method, we investigate the Hawking radiation of a Schwarzschild black hole in the isotropic coordinates via the cancellation of gravitational anomaly. After performing a dimensional reduction from the four-dimensional isotropic Schwarzschild metric, we show that this reduction procedure will, in general, result in two classes of two-dimensional effective metrics: the conformal equivalent and the inequivalent ones. For the physically equivalent class, the two-dimensional effective metric displays such a distinct feature that the determinant is not equal to the unity √(-g)≠1, but also vanishes at the horizon, the latter of which possibly invalidates the anomaly analysis there. Nevertheless, in this paper we adopt the effective action method to prove that the consistent energy-momentum tensor T r t is divergent on the horizon but √(-g)T t r remains finite there. Meanwhile, through an explicit calculation we show that the covariant energy-momentum tensor T-tilde t r equals zero at the horizon. Therefore the validity of the covariant regularity condition that demands that T-tilde t r = 0 at the horizon has been justified, indicating that the gravitational anomaly analysis can be safely extrapolated to the case where the metric determinant vanishes at the horizon. It is then demonstrated that for the physically equivalent reduced metric, both methods can give the correct Hawking temperature of the isotropic Schwarzschild black hole, while for the inequivalent one with the determinant √(-g) = 1 it can only give half of the correct temperature. We further exclude the latter undesired result by taking into account the general covariance of the energy-momentum tensor under the isotropic coordinate transformation

Isotropic quantum walks on lattices and the Weyl equation

Science.gov (United States)

D'Ariano, Giacomo Mauro; Erba, Marco; Perinotti, Paolo

2017-12-01

We present a thorough classification of the isotropic quantum walks on lattices of dimension d =1 ,2 ,3 with a coin system of dimension s =2 . For d =3 there exist two isotropic walks, namely, the Weyl quantum walks presented in the work of D'Ariano and Perinotti [G. M. D'Ariano and P. Perinotti, Phys. Rev. A 90, 062106 (2014), 10.1103/PhysRevA.90.062106], resulting in the derivation of the Weyl equation from informational principles. The present analysis, via a crucial use of isotropy, is significantly shorter and avoids a superfluous technical assumption, making the result completely general.

Efficient positive, conservative, Maxwellian preserving and implicit difference schemes for the 1-D isotropic Fokker-Planck-Landau equation; Schemas positifs, implicites, conservant l'energie et les etats d'equilibre pour l'equation de Fokker-Planck-Landau isotrope

Energy Technology Data Exchange (ETDEWEB)

Buet, Ch. [CEA Bruyeres-le-Chatel, Dept. Sciences de la Simulation et de l' Information, Service Numerique Environnement et Constantes, 91 (France); Le Thanh, K.C. [CEA Bruyeres-le-Chatel, Service Physique des Plasmas et Electromagnetisme, 91 (France). Dept. de Physique Theorique et Appliquee

2008-07-01

The aim of this paper is to describe the discretization of the Fokker-Planck-Landau (FPL) collision term in the isotropic case, which models the self-collision for the electrons when they are totally isotropized by heavy particles background such as ions. The discussion focuses on schemes, which could preserve positivity, mass, energy and Maxwellian equilibrium. The Chang and Cooper method is widely used by plasma's physicists for the FPL equation (and for Fokker-Planck type equations). We present a new variant that is both positive and conservative contrary to the existing one's. We propose also a non Chang and Cooper 'type scheme on non-uniform grid, which is also both positive, conservative and equilibrium state preserving contrary to existing one's. The case of Coulombian potential is emphasized. We address also the problem of the time discretization. In particular we show how to recast some implicit methods to get band diagonal system and to solve it by direct method with a linear cost. (authors)

On the propagation of linear transverse acoustic waves in isotropic media with mechanical relaxation phenomena due to viscosity and a tensorial internal variable. II. Some cases of special interest (Poynting-Thomson, Jeffreys, Maxwell, Kelvin-Voigt, Hooke and Newton media)

NARCIS (Netherlands)

Turrisi, E.; Ciancio, V.; Kluitenberg, G.A.

1982-01-01

The propagation of linear transverse acoustic waves in isotropic media in which mechanical relaxation phenomena occur was considered in a previous paper. In particular expressions for the velocity and attenuation of the waves were obtained and the limiting cases of waves with high and low

Torsional vibration of a pipe pile in transversely isotropic saturated soil

Science.gov (United States)

Zheng, Changjie; Hua, Jianmin; Ding, Xuanming

2016-09-01

This study considers the torsional vibration of a pipe pile in a transversely isotropic saturated soil layer. Based on Biot's poroelastic theory and the constitutive relations of the transversely isotropic medium, the dynamic governing equations of the outer and inner transversely isotropic saturated soil layers are derived. The Laplace transform is used to solve the governing equations of the outer and inner soil layers. The dynamic torsional response of the pipe pile in the frequency domain is derived utilizing 1D elastic theory and the continuous conditions at the interfaces between the pipe pile and the soils. The time domain solution is obtained by Fourier inverse transform. A parametric study is conducted to demonstrate the influence of the anisotropies of the outer and inner soil on the torsional dynamic response of the pipe pile.

Design methodology of single-feed compact near-isotropic antenna design

KAUST Repository

Su, Zhen

2017-06-07

The abundance of mobile wireless devices is giving rise to a new paradigm known as Internet of Things. In this paradigm, wireless devices will be everywhere and communicating with each other. Since they will be oriented randomly in the environment, they should be able to communicate equally in all directions in order to have stable communication link. Hence, compact near isotropic antennas are required, which can enable orientation insensitive communication. In this paper, we propose a simple design methodology to design a compact near-isotropic wire antenna based on equal vector potentials. As a proof of concept, a quarter wavelength monopole antennas has been designed that is wrapped on a 3D-printed box keeping the vector potentials in three orthogonal different directions equal. By optimizing the dimension of the antenna arms, a nearly isotropic radiation pattern is thus achieved. The results show that the antenna has a maximum gain of 2.2dBi at 900 MHz with gain derivation of 9.4dB.

Isotropic covariance functions on graphs and their edges

DEFF Research Database (Denmark)

Anderes, E.; Møller, Jesper; Rasmussen, Jakob Gulddahl

We develop parametric classes of covariance functions on linear networks and their extension to graphs with Euclidean edges, i.e., graphs with edges viewed as line segments or more general sets with a coordinate system allowing us to consider points on the graph which are vertices or points...... on an edge. Our covariance functions are defined on the vertices and edge points of these graphs and are isotropic in the sense that they depend only on the geodesic distance or on a new metric called the resistance metric (which extends the classical resistance metric developed in electrical network theory...... functions in the spatial statistics literature (the power exponential, Matérn, generalized Cauchy, and Dagum classes) are shown to be valid with respect to the resistance metric for any graph with Euclidean edges, whilst they are only valid with respect to the geodesic metric in more special cases....

Homogenization models for thin rigid structured surfaces and films.

Science.gov (United States)

Marigo, Jean-Jacques; Maurel, Agnès

2016-07-01

A homogenization method for thin microstructured surfaces and films is presented. In both cases, sound hard materials are considered, associated with Neumann boundary conditions and the wave equation in the time domain is examined. For a structured surface, a boundary condition is obtained on an equivalent flat wall, which links the acoustic velocity to its normal and tangential derivatives (of the Myers type). For a structured film, jump conditions are obtained for the acoustic pressure and the normal velocity across an equivalent interface (of the Ventcels type). This interface homogenization is based on a matched asymptotic expansion technique, and differs slightly from the classical homogenization, which is known to fail for small structuration thicknesses. In order to get insight into what causes this failure, a two-step homogenization is proposed, mixing classical homogenization and matched asymptotic expansion. Results of the two homogenizations are analyzed in light of the associated elementary problems, which correspond to problems of fluid mechanics, namely, potential flows around rigid obstacles.

Cosmological simulations of isotropic conduction in galaxy clusters

International Nuclear Information System (INIS)

Smith, Britton; O'Shea, Brian W.; Voit, G. Mark; Ventimiglia, David; Skillman, Samuel W.

2013-01-01

Simulations of galaxy clusters have a difficult time reproducing the radial gas-property gradients and red central galaxies observed to exist in the cores of galaxy clusters. Thermal conduction has been suggested as a mechanism that can help bring simulations of cluster cores into better alignment with observations by stabilizing the feedback processes that regulate gas cooling, but this idea has not yet been well tested with cosmological numerical simulations. Here we present cosmological simulations of 10 galaxy clusters performed with five different levels of isotropic Spitzer conduction, which alters both the cores and outskirts of clusters, though not dramatically. In the cores, conduction flattens central temperature gradients, making them nearly isothermal and slightly lowering the central density, but failing to prevent a cooling catastrophe there. Conduction has little effect on temperature gradients outside of cluster cores because outward conductive heat flow tends to inflate the outer parts of the intracluster medium (ICM), instead of raising its temperature. In general, conduction tends reduce temperature inhomogeneity in the ICM, but our simulations indicate that those homogenizing effects would be extremely difficult to observe in ∼5 keV clusters. Outside the virial radius, our conduction implementation lowers the gas densities and temperatures because it reduces the Mach numbers of accretion shocks. We conclude that, despite the numerous small ways in which conduction alters the structure of galaxy clusters, none of these effects are significant enough to make the efficiency of conduction easily measurable, unless its effects are more pronounced in clusters hotter than those we have simulated.

The relationship between continuum homogeneity and statistical homogeneity in cosmology

International Nuclear Information System (INIS)

Stoeger, W.R.; Ellis, G.F.R.; Hellaby, C.

1987-01-01

Although the standard Friedmann-Lemaitre-Robertson-Walker (FLRW) Universe models are based on the concept that the Universe is spatially homogeneous, up to the present time no definition of this concept has been proposed that could in principle be tested by observation. Such a definition is here proposed, based on a simple spatial averaging procedure, which relates observable properties of the Universe to the continuum homogeneity idea that underlies the FLRW models. It turns out that the statistical homogeneity often used to describe the distribution of matter on a large scale does not imply spatial homogeneity according to this definition, and so cannot be simply related to a FLRW Universe model. Values are proposed for the homogeneity parameter and length scale of homogeneity of the Universe. (author)

Spontaneously broken symmetry of vacuum in external gravitational fields of isotropic cosmological models

International Nuclear Information System (INIS)

Veryaskin, A.V.; Lapchinskij, V.G.; Nekrasov, V.I.; Rubakov, V.A.

1981-01-01

Behaviour of vacuum symmetry in the model of self-acting scalar field in the open and closed isotropic cosmological spaces is investigated. Considered are the cases with the mass squared of the scalar field m 2 >0, m 2 =0 and m 2 2 2 =0 at exponentially large scale factors the study of the problem on the behaviour of the symmetry requires exceeding the limits of the perturbation theory. The final behaviour of the vacuum symmetry in the open model at small radii depends on combined effect of all the external factors [ru

Flows and chemical reactions in homogeneous mixtures

CERN Document Server

Prud'homme, Roger

2013-01-01

Flows with chemical reactions can occur in various fields such as combustion, process engineering, aeronautics, the atmospheric environment and aquatics. The examples of application chosen in this book mainly concern homogeneous reactive mixtures that can occur in propellers within the fields of process engineering and combustion: - propagation of sound and monodimensional flows in nozzles, which may include disequilibria of the internal modes of the energy of molecules; - ideal chemical reactors, stabilization of their steady operation points in the homogeneous case of a perfect mixture and c

The Isotropic Radio Background and Annihilating Dark Matter

Energy Technology Data Exchange (ETDEWEB)

Hooper, Dan [Fermi National Accelerator Laboratory (FNAL), Batavia, IL (United States); Belikov, Alexander V. [Institut d' Astrophysique (France); Jeltema, Tesla E. [Univ. of California, Santa Cruz, CA (United States); Linden, Tim [Univ. of California, Santa Cruz, CA (United States); Profumo, Stefano [Univ. of California, Santa Cruz, CA (United States); Slatyer, Tracy R. [Princeton Univ., Princeton, NJ (United States)

2012-11-01

Observations by ARCADE-2 and other telescopes sensitive to low frequency radiation have revealed the presence of an isotropic radio background with a hard spectral index. The intensity of this observed background is found to exceed the flux predicted from astrophysical sources by a factor of approximately 5-6. In this article, we consider the possibility that annihilating dark matter particles provide the primary contribution to the observed isotropic radio background through the emission of synchrotron radiation from electron and positron annihilation products. For reasonable estimates of the magnetic fields present in clusters and galaxies, we find that dark matter could potentially account for the observed radio excess, but only if it annihilates mostly to electrons and/or muons, and only if it possesses a mass in the range of approximately 5-50 GeV. For such models, the annihilation cross section required to normalize the synchrotron signal to the observed excess is sigma v ~ (0.4-30) x 10^-26 cm^3/s, similar to the value predicted for a simple thermal relic (sigma v ~ 3 x 10^-26 cm^3/s). We find that in any scenario in which dark matter annihilations are responsible for the observed excess radio emission, a significant fraction of the isotropic gamma ray background observed by Fermi must result from dark matter as well.

The Finite Deformation Dynamic Sphere Test Problem

Energy Technology Data Exchange (ETDEWEB)

Versino, Daniele [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Brock, Jerry Steven [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

2016-09-02

In this manuscript we describe test cases for the dynamic sphere problem in presence of finite deformations. The spherical shell in exam is made of a homogeneous, isotropic or transverse isotropic material and elastic and elastic-plastic material behaviors are considered. Twenty cases, (a) to (t), are thus defined combining material types and boundary conditions. The inner surface radius, the outer surface radius and the material's density are kept constant for all the considered test cases and their values are r_i = 10mm, r_o = 20mm and p = 1000Kg/m³ respectively.

Fuel micro-mechanics: homogenization, cracking, granular media

International Nuclear Information System (INIS)

Monerie, Yann

2010-01-01

This work summarizes about fifteen years of research in the field of micro-mechanics of materials. Emphasis is placed on the most recent work carried out in the context of nuclear safety. Micro-mechanics finds a natural place there, aiming to predict the behavior of heterogeneous materials with an evolving microstructure. The applications concerned mainly involve the nuclear fuel and its tubular cladding. The uranium dioxide fuel is modeled, according to the scales under consideration, as a porous ceramic or a granular medium. The strongly irradiated Zircaloy claddings are identified with a composite medium with a metal matrix and a gradient of properties. The analysis of these classes of material is rich in problems of a more fundamental nature. Three main themes are discussed: 1/ Homogenization, 2/ cracking, rupture and fragmentation, 3/ discrete media and fluid-grain couplings. Homogenization: The analytical scale change methods proposed aim to estimate or limit the linear and equivalent nonlinear behaviors of isotropic porous media and anisotropic composites with a metal matrix. The porous media under consideration are saturated or drained, with a compressible or incompressible matrix, and have one or two scales of spherical or ellipsoid pores, or cracks. The composites studied have a macroscopic anisotropy related to that of the matrix, and to the shape and spatial distribution of the inclusions. Thermoelastic, elastoplastic, and viscoplastic behaviors and ductile damage of these media are examined using different techniques: extensions of classic approaches, linear in particular, variational approaches and approaches using elliptical potentials with thermally activated elementary mechanisms. The models developed are validated on numerical finite element simulations, and their functional relevance is illustrated in comparison to experimental data obtained from the literature. The significant results obtained include a plasticity criterion for Gurson matrix

Mechanical Homogenization Increases Bacterial Homogeneity in Sputum

Science.gov (United States)

Stokell, Joshua R.; Khan, Ammad

2014-01-01

Sputum obtained from patients with cystic fibrosis (CF) is highly viscous and often heterogeneous in bacterial distribution. Adding dithiothreitol (DTT) is the standard method for liquefaction prior to processing sputum for molecular detection assays. To determine if DTT treatment homogenizes the bacterial distribution within sputum, we measured the difference in mean total bacterial abundance and abundance of Burkholderia multivorans between aliquots of DTT-treated sputum samples with and without a mechanical homogenization (MH) step using a high-speed dispersing element. Additionally, we measured the effect of MH on bacterial abundance. We found a significant difference between the mean bacterial abundances in aliquots that were subjected to only DTT treatment and those of the aliquots which included an MH step (all bacteria, P = 0.04; B. multivorans, P = 0.05). There was no significant effect of MH on bacterial abundance in sputum. Although our results are from a single CF patient, they indicate that mechanical homogenization increases the homogeneity of bacteria in sputum. PMID:24759710

Efficient anisotropic wavefield extrapolation using effective isotropic models

KAUST Repository

Alkhalifah, Tariq Ali; Ma, X.; Waheed, Umair bin; Zuberi, Mohammad

2013-01-01

Isotropic wavefield extrapolation is more efficient than anisotropic extrapolation, and this is especially true when the anisotropy of the medium is tilted (from the vertical). We use the kinematics of the wavefield, appropriately represented

Acoustic reflection log in transversely isotropic formations

Science.gov (United States)

Ronquillo Jarillo, G.; Markova, I.; Markov, M.

2018-01-01

We have calculated the waveforms of sonic reflection logging for a fluid-filled borehole located in a transversely isotropic rock. Calculations have been performed for an acoustic impulse source with the characteristic frequency of tens of kilohertz that is considerably less than the frequencies of acoustic borehole imaging tools. It is assumed that the borehole axis coincides with the axis of symmetry of the transversely isotropic rock. It was shown that the reflected wave was excited most efficiently at resonant frequencies. These frequencies are close to the frequencies of oscillations of a fluid column located in an absolutely rigid hollow cylinder. We have shown that the acoustic reverberation is controlled by the acoustic impedance of the rock Z = Vphρs for fixed parameters of the borehole fluid, where Vph is the velocity of horizontally propagating P-wave; ρs is the rock density. The methods of waveform processing to determine the parameters characterizing the reflected wave have been discussed.

Persymmetric Adaptive Detectors of Subspace Signals in Homogeneous and Partially Homogeneous Clutter

Directory of Open Access Journals (Sweden)

Ding Hao

2015-08-01

Full Text Available In the field of adaptive radar detection, an effective strategy to improve the detection performance is to exploit the structural information of the covariance matrix, especially in the case of insufficient reference cells. Thus, in this study, the problem of detecting multidimensional subspace signals is discussed by considering the persymmetric structure of the clutter covariance matrix, which implies that the covariance matrix is persymmetric about its cross diagonal. Persymmetric adaptive detectors are derived on the basis of the one-step principle as well as the two-step Generalized Likelihood Ratio Test (GLRT in homogeneous and partially homogeneous clutter. The proposed detectors consider the structural information of the covariance matrix at the design stage. Simulation results suggest performance improvement compared with existing detectors when reference cells are insufficient. Moreover, the detection performance is assessed with respect to the effects of the covariance matrix, signal subspace dimension, and mismatched performance of signal subspace as well as signal fluctuations.

Isotropic background for interacting two fluid scenario coupled with zero mass scalar field in modified gravity

International Nuclear Information System (INIS)

Chirde, V.R.; Shekh, S.H.

2016-01-01

The modified theories of gravity have engrossed much attention in the last decade, especially f(R) gravity. In this contextual exploration, we investigate interaction between barotropic fluid and dark energy with zero-mass scalar field for the spatially homogeneous and isotropic flat FRW universe. In this universe, the field equations correspond to the particular choice of f(R) = R+bR m . The exact solutions of the field equations are obtained by applying volumetric power law and exponential law of expansion. In power and exponential law of expansion, the universe shows both matter dominated and DE era for b ≤ 0 and b ≥ 0 and remain present in dark era respectively, but power law model is fully occupying with real matter for b > 0 and for b < 0 exponential model expands with negative pressure and remain present in matter dominated phase respectively. The physical behavior of the universe has been discussed by using some physical quantities

Classical and quantum treatments of the diffraction problem in the case of non-homogeneous media

International Nuclear Information System (INIS)

Datzeff, A.B.

1978-02-01

The diffraction of waves by an aperture is usually studied in the case of a homogeneous medium. In this paper, a method is proposed for the solution of the same problem in a medium of variable parameters (refractive index, external fields). It is successfully applied to diffraction of a classical scalar wave as well as of an electromagnetic vector wave and a Schroedinger wave, within the framework of this method, the scattering of particles may be considered as a particular case of the diffraction problem. Furthermore, the method is extended to cover the case of diffraction of dense electron beams. This has been achieved by means of a non-linear integro-differential equation, proposed by the author as a generalization of the well-known linear Schroedinger equation. A decisive experiment could be made which, besides showing whether the solution thus obtained is true, would also speak in favour of one of the two equations mentioned above. The latter is pertinent to the discussion of the physical essence of Quantum Mechanics

Some properties of spatially homogeneous spacetimes

International Nuclear Information System (INIS)

Coomer, G.C.

1979-01-01

This paper discusses two features of the universe which are influenced in a fundamental way by the spacetime geometry of the universe. The first is the growth of density fluctuations in the early stages of the evolution of the universe. The second is the propagation of electromagnetic radiation in the universe. A spatially homogeneous universe is assumed in both discussions. The gravitational instability theory of galaxy formation is investigated for a viscous fluid and for a charged, conducting fluid with a magnetic field added as a perturbation. It is found that the growth rate of density perturbations in both cases is lower than in the perfect fluid case. Spatially homogeneous but nonisotropic spacetimes are investigated next. Two perfect fluid solutions of Einstein's field equations are found which have spacelike hypersurfaces with Bianchi type II geometry. An expression for the spectrum of the cosmic microwave background radiation in a spatially homogeneous but nonisotropic universe is found. The expression is then used to determine the angular distribution of the intensity of the radiation in the simpler of the two solutions. When accepted values of the matter density and decoupling temperature are inserted into this solution, values for the age of the universe and the time of decoupling are obtained which agree reasonably well with the values of the standard model of the universe

Isotropic transmission of magnon spin information without a magnetic field.

Science.gov (United States)

Haldar, Arabinda; Tian, Chang; Adeyeye, Adekunle Olusola

2017-07-01

Spin-wave devices (SWD), which use collective excitations of electronic spins as a carrier of information, are rapidly emerging as potential candidates for post-semiconductor non-charge-based technology. Isotropic in-plane propagating coherent spin waves (magnons), which require magnetization to be out of plane, is desirable in an SWD. However, because of lack of availability of low-damping perpendicular magnetic material, a usually well-known in-plane ferrimagnet yttrium iron garnet (YIG) is used with a large out-of-plane bias magnetic field, which tends to hinder the benefits of isotropic spin waves. We experimentally demonstrate an SWD that eliminates the requirement of external magnetic field to obtain perpendicular magnetization in an otherwise in-plane ferromagnet, Ni 80 Fe 20 or permalloy (Py), a typical choice for spin-wave microconduits. Perpendicular anisotropy in Py, as established by magnetic hysteresis measurements, was induced by the exchange-coupled Co/Pd multilayer. Isotropic propagation of magnon spin information has been experimentally shown in microconduits with three channels patterned at arbitrary angles.

Central Andean temperature and precipitation measurements and its homogenization

Science.gov (United States)

Hunziker, Stefan; Gubler, Stefanie

2015-04-01

Observation of climatological parameters and the homogenization of these time series have a well-established history in western countries. This is not the case for many other countries, such as Bolivia and Peru. In Bolivia and Peru, the organization of measurements, quality of measurement equipment, equipment maintenance, training of staff and data management are fundamentally different compared to the western standard. The data needs special attention, because many problems are not detected by standard quality control procedures. Information about the weather stations, best achieved by station visits, is very beneficial. If the cause of the problem is known, some of the data may be corrected. In this study, cases of typical problems and measurement errors will be demonstrated. Much of research on homogenization techniques (up to subdaily scale) has been completed in recent years. However, data sets of the quality of western station networks have been used, and little is known about the performance of homogenization methods on data sets from countries such as Bolivia and Peru. HOMER (HOMogenizaton softwarE in R) is one of the most recent and widely used homogenization softwares. Its performance is tested on Peruvian-like data that has been sourced from Swiss stations (similar station density and metadata availability). The Swiss station network is a suitable test bed, because climate gradients are strong and the terrain is complex, as is also found in the Central Andes. On the other hand, the Swiss station network is dense, and long time series and extensive metadata are available. By subsampling the station network and omitting the metadata, the conditions of a Peruvian test region are mimicked. Results are compared to a dataset homogenized by THOMAS (Tool for Homogenization of Monthly Data Series), the homogenization tool used by MeteoSwiss.

Scanning anisotropy parameters in horizontal transversely isotropic media

KAUST Repository

Masmoudi, Nabil; Stovas, Alexey; Alkhalifah, Tariq Ali

2016-01-01

in reservoir characterisation, specifically in terms of fracture delineation. We propose a travel-time-based approach to estimate the anellipticity parameter η and the symmetry axis azimuth ϕ of a horizontal transversely isotropic medium, given an inhomogeneous

Wave propagation in isotropic- or composite-material piping conveying swirling liquid

International Nuclear Information System (INIS)

Chen, T.L.C.; Bert, C.W.

1977-01-01

An analysis is presented for the propagation of free harmonic waves in a thin-walled, circular cylindrical shell of orthotropic or isotropic material conveying a swirling flow. The shell motion is modeled by using the dynamic orthotropic version of the Sanders improved first-approximation linear shell theory and the fluid forces are described by using inviscid incompressible flow theory. Frequency spectra are presented for pipes made of isotropic material and composite materials of current engineering interest. (Auth.)

Effect of Boundary Conditions on the Axial Compression Buckling of Homogeneous Orthotropic Composite Cylinders in the Long Column Range

Science.gov (United States)

Mikulas, Martin M., Jr.; Nemeth, Michael P.; Oremont, Leonard; Jegley, Dawn C.

2011-01-01

Buckling loads for long isotropic and laminated cylinders are calculated based on Euler, Fluegge and Donnell's equations. Results from these methods are presented using simple parameters useful for fundamental design work. Buckling loads for two types of simply supported boundary conditions are calculated using finite element methods for comparison to select cases of the closed form solution. Results indicate that relying on Donnell theory can result in an over-prediction of buckling loads by as much as 40% in isotropic materials.

Isotrope und homogene Materie - Kosmen; On Dynamics and Thermodynamics of Isotropic Matter-Universes

Science.gov (United States)

Treder, H.-J.

Die Dynamik und Thermodynamik großer kosmischer Systeme ist fast unabhängig von den besonderen Theorien über die Gravitation. Nur die Feinstruktur der Kosmologie und Kosmonogie reflektiert die speziellen Hypothesen. Diese Neutralität gegenüber den konkreten Gravodynamiken ist die Konsequenz der fundamentalen Eigenschaften der Gravitation: Der Prinzipien der Äquivalenz von Trägheit und Schwere. The dynamics and thermodynamics of great cosmical systems are nearly independent of the theory of gravitation and only the fine-structure of cosmogony and cosmology reflects the special hypotheses.The neutrality against the concret gravodynamics is a consequence of the fundamental properties of gravitation: the principlies of equivalence of gravity and inertia.

Isotropic Optical Mouse Placement for Mobile Robot Velocity Estimation

Directory of Open Access Journals (Sweden)

Sungbok Kim

2014-06-01

Full Text Available This paper presents the isotropic placement of multiple optical mice for the velocity estimation of a mobile robot. It is assumed that there can be positional restriction on the installation of optical mice at the bottom of a mobile robot. First, the velocity kinematics of a mobile robot with an array of optical mice is obtained and the resulting Jacobian matrix is analysed symbolically. Second, the isotropic, anisotropic and singular optical mouse placements are identified, along with the corresponding characteristic lengths. Third, the least squares mobile robot velocity estimation from the noisy optical mouse velocity measurements is discussed. Finally, simulation results for several different placements of three optical mice are given.

Investigation into the temperature dependence of isotropic- nematic phase transition of Gay- Berne liquid crystals

Directory of Open Access Journals (Sweden)

A Avazpour

2014-12-01

Full Text Available Density functional approach was used to study the isotropic- nematic (I-N transition and calculate the values of freezing parameters of the Gay- Berne liquid crystal model. New direct and pair correlation functions of a molecular fluid with Gay- Berne pair potential were used. These new functions were used in density functional theory as input to calculate the isotropic- nematic transition densities for elongation at various reduced temperatures. It was observed that the isotropic- nematic transition densities increase as the temperature increases. It was found that the new direct correlation function is suitable to study the isotropic- nematic transition of Gay- Berne liquids. Comparison to other works showed qualitative agreement

On the second-order homogenization of wave motion in periodic media and the sound of a chessboard

Science.gov (United States)

Wautier, Antoine; Guzina, Bojan B.

2015-05-01

The goal of this study is to better understand the mathematical structure and ramifications of the second-order homogenization of low-frequency wave motion in periodic solids. To this end, multiple-scales asymptotic approach is applied to the scalar wave equation (describing anti-plane shear motion) in one and two spatial dimensions. In contrast to previous studies where the second-order homogenization has lead to the introduction of a single fourth-order derivative in the governing equation, present investigation demonstrates that such (asymptotic) approach results in a family of field equations uniting spatial, temporal, and mixed fourth-order derivatives - that jointly control incipient wave dispersion. Given the consequent freedom in selecting the affiliated lengthscale parameters, the notion of an optimal asymptotic model is next considered in a one-dimensional setting via its ability to capture the salient features of wave propagation within the first Brillouin zone, including the onset and magnitude of the phononic band gap. In the context of two-dimensional wave propagation, on the other hand, the asymptotic analysis is first established in a general setting, exposing the constant shear modulus as sufficient condition under which the second-order approximation of a bi-periodic elastic solid is both isotropic and limited to even-order derivatives. On adopting a chessboard-like periodic structure (with contrasts in both modulus and mass density) as a testbed for in-depth analytical treatment, it is next shown that the second-order approximation of germane wave motion is governed by a family fourth-order differential equations that: (i) entail exclusively even-order derivatives and homogenization coefficients that depend explicitly on the contrast in mass density; (ii) describe anisotropic wave dispersion characterized by the "sin4 θ +cos4 θ" term, and (iii) include the asymptotic model for a square lattice of circular inclusions as degenerate case. For

Dosimetric calculations by Monte Carlo for treatments of radiosurgery with the Leksell Gamma Knife, homogeneous and non homogeneous cases

International Nuclear Information System (INIS)

Rojas C, E.L.; Lallena R, A.M.

2004-01-01

In this work dose profiles are calculated that are obtained modeling treatments of radiosurgery with the Leksell Gamma Knife. This was made with the simulation code Monte Carlo Penelope for an homogeneous mannequin and one not homogeneous. Its were carried out calculations with the irradiation focus coinciding with the center of the mannequin as in near areas to the bone interface. Each one of the calculations one carries out for the 4 skull treatment that it includes the Gamma Knife and using a model simplified of their 201 sources of 60 Co. It was found that the dose profiles differ of the order of 2% when the isocenter coincides with the center of the mannequin and they ascend to near 5% when the isocenter moves toward the skull. (Author)

Scalar properties of transversely isotropic tuff from images of orthogonal cross sections

International Nuclear Information System (INIS)

Berge, P.A.; Berryman, J.G.; Blair, S.C.; Pena, C.

1997-01-01

Image processing methods have been used very effectively to estimate physical properties of isotropic porous earth materials such as sandstones. Anisotropic materials can also be analyzed in order to estimate their physical properties, but additional care and a larger number of well-chosen images of cross sections are required to obtain correct results. Although low-symmetry anisotropic media present difficulties for two-dimensional image processing methods, geologic materials are often transversely isotropic. Scalar properties of porous materials such as porosity and specific surface area can be determined with only minor changes in the analysis when the medium is transversely isotropic rather than isotropic. For example, in a rock that is transitively isotropic due to thin layers or beds, the overall porosity may be obtained by analyzing images of cross sections taken orthogonal to the bedding planes, whereas cross sections lying within the bedding planes will determine only the local porosity of the bed itself. It is known for translationally invariant anisotropic media that the overall specific surface area can be obtained from radial averages of the two-point correlation function in the full three-dimensional volume. Layered materials are not translationally invariant in the direction of the layering, but we show nevertheless how averages of cross sections may be used to obtain the specific surface area for a transversely isotropic rock. We report values of specific surface area obtained for thin sections of Topopah Spring Tuff from Yucca Mountain, Nevada. This formation is being evaluated as a potential host rock for geologic disposal of nuclear waste. Although the present work has made use of thin sections of tuff for the images, the same methods of analysis could also be used to simplify quantitative analysis of three-dimensional volumes of pore structure data obtained by means of x-ray microtomography or other methods, using only a few representative cross

Generalized Fractional Derivative Anisotropic Viscoelastic Characterization

Directory of Open Access Journals (Sweden)

Harry H. Hilton

2012-01-01

Full Text Available Isotropic linear and nonlinear fractional derivative constitutive relations are formulated and examined in terms of many parameter generalized Kelvin models and are analytically extended to cover general anisotropic homogeneous or non-homogeneous as well as functionally graded viscoelastic material behavior. Equivalent integral constitutive relations, which are computationally more powerful, are derived from fractional differential ones and the associated anisotropic temperature-moisture-degree-of-cure shift functions and reduced times are established. Approximate Fourier transform inversions for fractional derivative relations are formulated and their accuracy is evaluated. The efficacy of integer and fractional derivative constitutive relations is compared and the preferential use of either characterization in analyzing isotropic and anisotropic real materials must be examined on a case-by-case basis. Approximate protocols for curve fitting analytical fractional derivative results to experimental data are formulated and evaluated.

From Intensity Profile to Surface Normal: Photometric Stereo for Unknown Light Sources and Isotropic Reflectances.

Science.gov (United States)

Lu, Feng; Matsushita, Yasuyuki; Sato, Imari; Okabe, Takahiro; Sato, Yoichi

2015-10-01

We propose an uncalibrated photometric stereo method that works with general and unknown isotropic reflectances. Our method uses a pixel intensity profile, which is a sequence of radiance intensities recorded at a pixel under unknown varying directional illumination. We show that for general isotropic materials and uniformly distributed light directions, the geodesic distance between intensity profiles is linearly related to the angular difference of their corresponding surface normals, and that the intensity distribution of the intensity profile reveals reflectance properties. Based on these observations, we develop two methods for surface normal estimation; one for a general setting that uses only the recorded intensity profiles, the other for the case where a BRDF database is available while the exact BRDF of the target scene is still unknown. Quantitative and qualitative evaluations are conducted using both synthetic and real-world scenes, which show the state-of-the-art accuracy of smaller than 10 degree without using reference data and 5 degree with reference data for all 100 materials in MERL database.

Topography-specific isotropic tunneling in nanoparticle monolayer with sub-nm scale crevices.

Science.gov (United States)

Wang, Guisheng; Jiao, Weihong; Yi, Lizhi; Zhang, Yuejiao; Wu, Ke; Zhang, Chao; Lv, Xianglong; Qian, Lihua; Li, Jianfeng; Yuan, Songliu; Chen, Liang

2016-10-07

Material used in flexible devices may experience anisotropic strain with identical magnitude, outputting coherent signals that tend to have a serious impact on device reliability. In this work, the surface topography of the nanoparticles (NPs) is proposed to be a parameter to control the performance of strain gauge based on tunneling behavior. In contrast to anisotropic tunneling in a monolayer of spherical NPs, electron tunneling in a monolayer of urchin-like NPs actually exhibits a nearly isotropic response to strain with different loading orientations. Isotropic tunneling of the urchin-like NPs is caused by the interlocked pikes of these urchin-like NPs in a random manner during external mechanical stimulus. Topography-dependent isotropic tunneling in two dimensions reported here opens a new opportunity to create highly reliable electronics with superior performance.

Representations for implicit constitutive relations describing non-dissipative response of isotropic materials

Science.gov (United States)

Gokulnath, C.; Saravanan, U.; Rajagopal, K. R.

2017-12-01

A methodology for obtaining implicit constitutive representations involving the Cauchy stress and the Hencky strain for isotropic materials undergoing a non-dissipative process is developed. Using this methodology, a general constitutive representation for a subclass of implicit models relating the Cauchy stress and the Hencky strain is obtained for an isotropic material with no internal constraints. It is shown that even for this subclass, unlike classical Green elasticity, one has to specify three potentials to relate the Cauchy stress and the Hencky strain. Then, a procedure to obtain implicit constitutive representations for isotropic materials with internal constraints is presented. As an illustration, it is shown that for incompressible materials the Cauchy stress and the Hencky strain could be related through a single potential. Finally, constitutive approximations are obtained when the displacement gradient is small.

Isotropic Broadband E-Field Probe

Directory of Open Access Journals (Sweden)

Béla Szentpáli

2008-01-01

Full Text Available An E-field probe has been developed for EMC immunity tests performed in closed space. The leads are flexible resistive transmission lines. Their influence on the field distribution is negligible. The probe has an isotropic reception from 100 MHz to 18 GHz; the sensitivity is in the 3 V/m–10 V/m range. The device is an accessory of the EMC test chamber. The readout of the field magnitude is carried out by personal computer, which fulfils also the required corrections of the raw data.

Probing cosmology with the homogeneity scale of the Universe through large scale structure surveys

International Nuclear Information System (INIS)

Ntelis, Pierros

2017-01-01

This thesis exposes my contribution to the measurement of homogeneity scale using galaxies, with the cosmological interpretation of results. In physics, any model is characterized by a set of principles. Most models in cosmology are based on the Cosmological Principle, which states that the universe is statistically homogeneous and isotropic on a large scales. Today, this principle is considered to be true since it is respected by those cosmological models that accurately describe the observations. However, while the isotropy of the universe is now confirmed by many experiments, it is not the case for the homogeneity. To study cosmic homogeneity, we propose to not only test a model but to test directly one of the postulates of modern cosmology. Since 1998 the measurements of cosmic distances using type Ia supernovae, we know that the universe is now in a phase of accelerated expansion. This phenomenon can be explained by the addition of an unknown energy component, which is called dark energy. Since dark energy is responsible for the expansion of the universe, we can study this mysterious fluid by measuring the rate of expansion of the universe. The universe has imprinted in its matter distribution a standard ruler, the Baryon Acoustic Oscillation (BAO) scale. By measuring this scale at different times during the evolution of our universe, it is then possible to measure the rate of expansion of the universe and thus characterize this dark energy. Alternatively, we can use the homogeneity scale to study this dark energy. Studying the homogeneity and the BAO scale requires the statistical study of the matter distribution of the universe at large scales, superior to tens of Mega-parsecs. Galaxies and quasars are formed in the vast over densities of matter and they are very luminous: these sources trace the distribution of matter. By measuring the emission spectra of these sources using large spectroscopic surveys, such as BOSS and eBOSS, we can measure their positions

An isotropic suspension system for a biaxial accelerometer using electroplated thick metal with a HAR SU-8 mold

International Nuclear Information System (INIS)

Lee, Jin Seung; Lee, Seung S

2008-01-01

In this paper, a novel approach is developed to design an isotropic suspension system using thick metal freestanding micro-structures combining bulk micro-machining with electroplating based on a HAR SU-8 mold. An omega-shape isotropic suspension system composed of circular curved beams that have free switching of imaginary boundary conditions is proposed. This novel isotropic suspension design is not affected by geometric dimensional parameters and always achieves matching stiffness along the principle axes of elasticity. Using the finite element method, the isotropic suspension system was compared with an S-shaped meandering suspension system. In order to realize the suggested isotropic suspension system, a cost-effective fabrication process using electroplating with the SU-8 mold was developed to avoid expensive equipment and materials such as deep reactive-ion etching (DRIE) or a silicon-on-insulator (SOI) wafer. The fabricated isotropic suspension system was verified by electromagnetic actuation experiments. Finally, a biaxial accelerometer with isotropic suspension system was realized and tested using a vibration generator system. The proposed isotropic suspension system and the modified surface micro-machining technique based on electroplating with an SU-8 mold can contribute towards minimizing the system size, simplifying the system configuration, reducing the system price of and facilitating mass production of various types of low-cost sensors and actuators

Circular random motion in diatom gliding under isotropic conditions

International Nuclear Information System (INIS)

Gutiérrez-Medina, Braulio; Maldonado, Ana Iris Peña; Guerra, Andrés Jiménez; Rubio, Yadiralia Covarrubias; Meza, Jessica Viridiana García

2014-01-01

How cells migrate has been investigated primarily for the case of trajectories composed by joined straight segments. In contrast, little is known when cellular motion follows intrinsically curved paths. Here, we use time-lapse optical microscopy and automated trajectory tracking to investigate how individual cells of the diatom Nitzschia communis glide across surfaces under isotropic environmental conditions. We find a distinct kind of random motion, where trajectories are formed by circular arcs traveled at constant speed, alternated with random stoppages, direction reversals and changes in the orientation of the arcs. Analysis of experimental and computer-simulated trajectories show that the circular random motion of diatom gliding is not optimized for long-distance travel but rather for recurrent coverage of limited surface area. These results suggest that one main biological role for this type of diatom motility is to efficiently build the foundation of algal biofilms. (paper)

Isotropic gates and large gamma detector arrays versus angular distributions

International Nuclear Information System (INIS)

Iacob, V.E.; Duchene, G.

1997-01-01

Angular information extracted from in-beam γ ray measurements are of great importance for γ ray multipolarity and nuclear spin assignments. In our days large Ge detector arrays became available allowing the measurements of extremely weak γ rays in almost 4π sr solid angle (e.g., EUROGAM detector array). Given the high detector efficiency it is common for the mean suppressed coincidence multiplicity to reach values as high as 4 to 6. Thus, it is possible to gate on particular γ rays in order to enhance the relative statistics of a definite reaction channel and/or a definite decaying path in the level scheme of the selected residual nucleus. As compared to angular correlations, the conditioned angular distribution spectra exhibit larger statistics because in the latter the gate-setting γ ray may be observed by all the detectors in the array, relaxing somehow the geometrical restrictions of the angular correlations. Since the in-beam γ ray emission is anisotropic one could inquire that gate setting as mentioned above, based on anisotropic γ ray which would perturb the angular distributions in the unfolded events. As our work proved, there is no reason to worry about this if the energy gate runs over the whole solid angle in an ideal 4π sr detector, i.e., if the gate is isotropic. In real quasi 4π sr detector arrays the corresponding quasi isotropic gate preserves the angular properties of the unfolded data, too. However extraction of precise angular distribution coefficient especially a 4 , requires the consideration of the deviation of the quasi isotropic gate relative to the (ideal) isotropic gate

Efficiency measures for a non-homogeneous group of family farmers

Directory of Open Access Journals (Sweden)

Eliane Gonçalves Gomes

2012-12-01

Full Text Available DEA models assume the homogeneity of the units under evaluation (DMUs. However,in some cases, the DMUs use different production technologies. In such cases, they should be evaluated separately. In this paper we evaluate the efficiency of family farmers from the Brazilian Eastern Amazon, who use different agricultural production systems. We propose an alternative algorithm to assess the global efficiency, taking into account the non-homogeneity. The results show that the farmers that use the classical technology are more efficient than those considered "environmental friendly", as we took into account only the economic point of view.

Constraints on light WIMP candidates from the isotropic diffuse gamma-ray emission

International Nuclear Information System (INIS)

Arina, Chiara; Tytgat, Michel H.G.

2011-01-01

Motivated by the measurements reported by direct detection experiments, most notably DAMA, CDMS-II, CoGeNT and Xenon10/100, we study further the constraints that might be set on some light dark matter candidates, M DM ∼ few GeV, using the Fermi-LAT data on the isotropic gamma-ray diffuse emission. In particular, we consider a Dirac fermion singlet interacting through a new Z' gauge boson, and a scalar singlet S interacting through the Higgs portal. Both candidates are WIMP (Weakly Interacting Massive Particles), i.e. they have an annihilation cross-section in the pbarn range. Also they may both have a spin-independent elastic cross section on nucleons in the range required by direct detection experiments. Although being generic WIMP candidates, because they have different interactions with Standard Model particles, their phenomenology regarding the isotropic diffuse gamma-ray emission is quite distinct. In the case of the scalar singlet, the one-to-one correspondence between its annihilation cross-section and its spin-independent elastic scattering cross-section permits to express the constraints from the Fermi-LAT data in the direct detection exclusion plot, σ n 0 −M DM . Depending on the astrophysics, we argue that it is possible to exclude the singlet scalar dark matter candidate at 95% confidence level. The constraints on the Dirac singlet interacting through a Z' are comparatively weaker

Jordan's algebra of a facially homogeneous autopolar cone

International Nuclear Information System (INIS)

Bellissard, Jean; Iochum, Bruno

1979-01-01

It is shown that a Jordan-Banach algebra with predual may be canonically associated with a facially homogeneous autopolar cone. This construction generalizes the case where a trace vector exists in the cone [fr

Homogenization patterns of the world’s freshwater fish faunas

Science.gov (United States)

Villéger, Sébastien; Blanchet, Simon; Beauchard, Olivier; Oberdorff, Thierry; Brosse, Sébastien

2011-01-01

The world is currently undergoing an unprecedented decline in biodiversity, which is mainly attributable to human activities. For instance, nonnative species introduction, combined with the extirpation of native species, affects biodiversity patterns, notably by increasing the similarity among species assemblages. This biodiversity change, called taxonomic homogenization, has rarely been assessed at the world scale. Here, we fill this gap by assessing the current homogenization status of one of the most diverse vertebrate groups (i.e., freshwater fishes) at global and regional scales. We demonstrate that current homogenization of the freshwater fish faunas is still low at the world scale (0.5%) but reaches substantial levels (up to 10%) in some highly invaded river basins from the Nearctic and Palearctic realms. In these realms experiencing high changes, nonnative species introductions rather than native species extirpations drive taxonomic homogenization. Our results suggest that the “Homogocene era” is not yet the case for freshwater fish fauna at the worldwide scale. However, the distressingly high level of homogenization noted for some biogeographical realms stresses the need for further understanding of the ecological consequences of homogenization processes. PMID:22025692

Depth migration in transversely isotropic media with explicit operators

Energy Technology Data Exchange (ETDEWEB)

Uzcategui, Omar [Colorado School of Mines, Golden, CO (United States)

1994-12-01

The author presents and analyzes three approaches to calculating explicit two-dimensional (2D) depth-extrapolation filters for all propagation modes (P, SV, and SH) in transversely isotropic media with vertical and tilted axis of symmetry. These extrapolation filters are used to do 2D poststack depth migration, and also, just as for isotropic media, these 2D filters are used in the McClellan transformation to do poststack 3D depth migration. Furthermore, the same explicit filters can also be used to do depth-extrapolation of prestack data. The explicit filters are derived by generalizations of three different approaches: the modified Taylor series, least-squares, and minimax methods initially developed for isotropic media. The examples here show that the least-squares and minimax methods produce filters with accurate extrapolation (measured in the ability to position steep reflectors) for a wider range of propagation angles than that obtained using the modified Taylor series method. However, for low propagation angles, the modified Taylor series method has smaller amplitude and phase errors than those produced by the least-squares and minimax methods. These results suggest that to get accurate amplitude estimation, modified Taylor series filters would be somewhat preferred in areas with low dips. In areas with larger dips, the least-squares and minimax methods would give a distinctly better delineation of the subsurface structures.

A new class of Preisach-type isotropic vector model of hysteresis

Energy Technology Data Exchange (ETDEWEB)

Serpico, C.; D' Aquino, M.; Visone, C.; Davino, D

2004-01-01

A new class of scalar hysteresis operators is obtained from the classical Preisach scalar model of hysteresis by introducing a transformation of variables dependent on a suitable function g. The operators of this class are defined by means of a new type of Play operator and are characterized by the property of having the same scalar input-output relationship. These operators are then extended to the isotropic vector case by using the appropriate vector extension of the scalar Play operators. It is shown that the function g, which does not affect the scalar input-output relationship, does affect the vector hysteresis curves. The influence of the function g on vector hysteresis is illustrated by reporting numerically computed rotational hysteresis losses curves.

State operator, constants of the motion, and Wigner functions: The two-dimensional isotropic harmonic oscillator

DEFF Research Database (Denmark)

Dahl, Jens Peder; Schleich, W. P.

2009-01-01

For a closed quantum system the state operator must be a function of the Hamiltonian. When the state is degenerate, additional constants of the motion enter the play. But although it is the Weyl transform of the state operator, the Wigner function is not necessarily a function of the Weyl...... transforms of the constants of the motion. We derive conditions for which this is actually the case. The Wigner functions of the energy eigenstates of a two-dimensional isotropic harmonic oscillator serve as an important illustration....

About positive, energy conservative and equilibrium state preserving schemes for the isotropic Fokker-Planck-Landau equation; Sur les schemas positifs, conservant l'energie et les etats d'equilibre pour l'equation de Fokker-Planck-Landau isotrope

Energy Technology Data Exchange (ETDEWEB)

Buet, Ch. [CEA Bruyeres-le-Chatel, Dept. des Sciences de la Simulation et de l' Information, 91 (France); Le Thanh, K.C. [CEA Bruyeres-le-Chatel, Dept. de Physique Theorique et Appliquee, 91 (France)

2006-07-01

The aim of this paper is to describe the discretization of the Fokker-Planck-Landau (FPL) collision term in the isotropic case which models the self collision for the electrons when they are totally isotropized by heavy particles background such as ions. The discussion focus on schemes which could preserve positivity, mass, energy and Maxwellian equilibrium. First, we analyze in detail the popular Chang and Cooper method for this non-linear collision term: derivation, conservation and positivity properties. We show that some variants of this method, based on the drift-diffusion form of the FPL operator, could not be positive or could not conserve the energy. We present a new variant of the Chang and Cooper method derived from the Landau form that is both positive and conservative. We also propose two new alternatives and simpler schemes for the FPL operator which show that the Chang and Cooper method is not the only way to construct positive, energy conservative and equilibrium state preserving schemes for this operator. For all these schemes, we explain clearly the properties of conservation of the density and the energy, the positivity of the solution and the conservation of the equilibrium states, or their lack. The case of Maxwellian and Coulombian potentials are emphasized. (authors)

Estimation of transversely isotropic material properties from magnetic resonance elastography using the optimised virtual fields method.

Science.gov (United States)

Miller, Renee; Kolipaka, Arunark; Nash, Martyn P; Young, Alistair A

2018-03-12

Magnetic resonance elastography (MRE) has been used to estimate isotropic myocardial stiffness. However, anisotropic stiffness estimates may give insight into structural changes that occur in the myocardium as a result of pathologies such as diastolic heart failure. The virtual fields method (VFM) has been proposed for estimating material stiffness from image data. This study applied the optimised VFM to identify transversely isotropic material properties from both simulated harmonic displacements in a left ventricular (LV) model with a fibre field measured from histology as well as isotropic phantom MRE data. Two material model formulations were implemented, estimating either 3 or 5 material properties. The 3-parameter formulation writes the transversely isotropic constitutive relation in a way that dissociates the bulk modulus from other parameters. Accurate identification of transversely isotropic material properties in the LV model was shown to be dependent on the loading condition applied, amount of Gaussian noise in the signal, and frequency of excitation. Parameter sensitivity values showed that shear moduli are less sensitive to noise than the other parameters. This preliminary investigation showed the feasibility and limitations of using the VFM to identify transversely isotropic material properties from MRE images of a phantom as well as simulated harmonic displacements in an LV geometry. Copyright © 2018 John Wiley & Sons, Ltd.

Note on integrability of certain homogeneous Hamiltonian systems

Energy Technology Data Exchange (ETDEWEB)

Szumiński, Wojciech [Institute of Physics, University of Zielona Góra, Licealna 9, PL-65-407, Zielona Góra (Poland); Maciejewski, Andrzej J. [Institute of Astronomy, University of Zielona Góra, Licealna 9, PL-65-407, Zielona Góra (Poland); Przybylska, Maria, E-mail: M.Przybylska@if.uz.zgora.pl [Institute of Physics, University of Zielona Góra, Licealna 9, PL-65-407, Zielona Góra (Poland)

2015-12-04

In this paper we investigate a class of natural Hamiltonian systems with two degrees of freedom. The kinetic energy depends on coordinates but the system is homogeneous. Thanks to this property it admits, in a general case, a particular solution. Using this solution we derive necessary conditions for the integrability of such systems investigating differential Galois group of variational equations. - Highlights: • Necessary integrability conditions for some 2D homogeneous Hamilton systems are given. • Conditions are obtained analysing differential Galois group of variational equations. • New integrable and superintegrable systems are identified.

Permanent magnets prepared from Sm10.5Fe88.5Zr1.0Ny without homogenization

International Nuclear Information System (INIS)

Gebel, B.; Kubis, M.; Mueller, K.-H.

1997-01-01

In as-cast Sm 2 Fe 17 the high amount of α-Fe caused by a peritectic reaction can be considerably reduced by a small addition of about 1 at% Zr. X-ray diffraction showed that as-cast Sm 10.5 Fe 88.5 Zr 1.0 mainly consists of a phase with the Th 2 Zn 17 -type structure and SmFe 3 . Non-homogenized Sm 10.5 Fe 88.5 Zr 1.0 was milled and (i) annealed in vacuum or (ii) treated with a hydrogenation-disproportionation-desorp tion-recombination (HDDR) process. The annealed and subsequently nitrogenated powder is magnetically anisotropic and has a coercivity μ 0J H C up to 2.0 T and an energy product (BH) max up to 136 kJ/m 3 . HDDR-treated and nitrogenated powder is isotropic and exhibits values of μ 0J H C = 3.1 T and (BH) max 103 kJ/m 3 . Consequently, Sm 10.5 Fe 88.5 Zr 1.0 N y (y ∼ 16) permanent magnets with very good properties can be prepared without the time-consuming homogenization procedure. (orig.)

A New Theory of Non-Linear Thermo-Elastic Constitutive Equation of Isotropic Hyperelastic Materials

Science.gov (United States)

Li, Chen; Liao, Yufei

2018-03-01

Considering the influence of temperature and strain variables on materials. According to the relationship of conjugate stress-strain, a complete and irreducible non-linear constitutive equation of isotropic hyperelastic materials is derived and the constitutive equations of 16 types of isotropic hyperelastic materials are given we study the transformation methods and routes of 16 kinds of constitutive equations and the study proves that transformation of two forms of constitutive equation. As an example of application, the non-linear thermo-elastic constitutive equation of isotropic hyperelastic materials is combined with the natural vulcanized rubber experimental data in the existing literature base on MATLAB, The results show that the fitting accuracy is satisfactory.

A 3D printed dual GSM band near isotropic on-package antenna

KAUST Repository

Zhen, Su

2017-10-25

In this paper, we propose an on-package dual band monopole antenna with near-isotropic radiation pattern for GSM mobile applications. The proposed antenna is well matched for both GSM 900 and 1800 bands and provides decent gain for both the bands (1.67 and 3.27 dBi at 900 MHz and 1800 MHz respectively). The antenna is printed with silver ink on a 3D printed polymer based package. The package houses the GSM electronics and the battery. By optimizing the antenna arms width and length, a near-isotropic radiation pattern is achieved. Unlike the published isotropic antennas which are either single band or large in size, the proposed antenna covers both GSM bands with required bandwidth and is only half wavelength long. The design is low cost and highly suitable for various GSM applications such as localization, in additional to conventional communication applications.

Homogenization versus homogenization-free method to measure muscle glycogen fractions.

Science.gov (United States)

Mojibi, N; Rasouli, M

2016-12-01

The glycogen is extracted from animal tissues with or without homogenization using cold perchloric acid. Three methods were compared for determination of glycogen in rat muscle at different physiological states. Two groups of five rats were kept at rest or 45 minutes muscular activity. The glycogen fractions were extracted and measured by using three methods. The data of homogenization method shows that total glycogen decreased following 45 min physical activity and the change occurred entirely in acid soluble glycogen (ASG), while AIG did not change significantly. Similar results were obtained by using "total-glycogen-fractionation methods". The findings of "homogenization-free method" indicate that the acid insoluble fraction (AIG) was the main portion of muscle glycogen and the majority of changes occurred in AIG fraction. The results of "homogenization method" are identical with "total glycogen fractionation", but differ with "homogenization-free" protocol. The ASG fraction is the major portion of muscle glycogen and is more metabolically active form.

A program to calculate pulse transmission responses through transversely isotropic media

Science.gov (United States)

Li, Wei; Schmitt, Douglas R.; Zou, Changchun; Chen, Xiwei

2018-05-01

We provide a program (AOTI2D) to model responses of ultrasonic pulse transmission measurements through arbitrarily oriented transversely isotropic rocks. The program is built with the distributed point source method that treats the transducers as a series of point sources. The response of each point source is calculated according to the ray-tracing theory of elastic plane waves. The program could offer basic wave parameters including phase and group velocities, polarization, anisotropic reflection coefficients and directivity patterns, and model the wave fields, static wave beam, and the observed signals for pulse transmission measurements considering the material's elastic stiffnesses and orientations, sample dimensions, and the size and positions of the transmitters and the receivers. The program could be applied to exhibit the ultrasonic beam behaviors in anisotropic media, such as the skew and diffraction of ultrasonic beams, and analyze its effect on pulse transmission measurements. The program would be a useful tool to help design the experimental configuration and interpret the results of ultrasonic pulse transmission measurements through either isotropic or transversely isotropic rock samples.

Refined Weyl Law for Homogeneous Perturbations of the Harmonic Oscillator

Science.gov (United States)

Doll, Moritz; Gannot, Oran; Wunsch, Jared

2018-02-01

Let H denote the harmonic oscillator Hamiltonian on R}^d,} perturbed by an isotropic pseudodifferential operator of order 1. We consider the Schrödinger propagator {U(t)=e^{-itH},} and find that while sing-supp Tr U(t) \\subset 2 π Z as in the unperturbed case, there exists a large class of perturbations in dimensions {d ≥ 2 for which the singularities of {Tr U(t)} at nonzero multiples of {2 π} are weaker than the singularity at t = 0. The remainder term in the Weyl law is of order {o(λ^{d-1})} , improving in these cases the {o(λ^{d-1})} remainder previously established by Helffer-Robert.

Homogeneous and isotropic cosmologies with nonlinear electromagnetic radiation

International Nuclear Information System (INIS)

Vollick, Dan N.

2008-01-01

In this paper I examine cosmological models that contain a stochastic background of nonlinear electromagnetic radiation. I show that for Born-Infeld electrodynamics the equation of state parameter, w=P/ρ, remains close to 1/3 throughout the evolution of the universe if E 2 =B 2 in the late universe to a high degree of accuracy. Theories with electromagnetic Lagrangians of the form L=-(1/4)F 2 +αF 4 have recently been studied in magnetic universes, where the electric field vanishes. It was shown that the F 4 term can produce a bounce in the early universe, avoiding an initial singularity. Here I show that the inclusion of an electric field, with E 2 ≅B 2 in the late universe, eliminates the bounce and the universe begins with an initial singularity. I also examine theories with Lagrangians of the form L=-(1/4)F 2 -μ 8 /F 2 , which have been shown to produce a period of late time accelerated expansion in magnetic universes. I show that, if an electric field is introduced, the accelerated phase will only occur if E 2 2 .

Spectral calculations for pressure-velocity and pressure-strain correlations in homogeneous shear turbulence

Science.gov (United States)

Dutta, Kishore

2018-02-01

Theoretical analyses of pressure related turbulent statistics are vital for a reliable and accurate modeling of turbulence. In the inertial subrange of turbulent shear flow, pressure-velocity and pressure-strain correlations are affected by anisotropy imposed at large scales. Recently, Tsuji and Kaneda (2012 J. Fluid Mech. 694 50) performed a set of experiments on homogeneous shear flow, and estimated various one-dimensional pressure related spectra and the associated non-dimensional universal numbers. Here, starting from the governing Navier-Stokes dynamics for the fluctuating velocity field and assuming the anisotropy at inertial scales as a weak perturbation of an otherwise isotropic dynamics, we analytically derive the form of the pressure-velocity and pressure-strain correlations. The associated universal numbers are calculated using the well-known renormalization-group results, and are compared with the experimental estimates of Tsuji and Kaneda. Approximations involved in the perturbative calculations are discussed.

Temperature-dependent study of isotropic-nematic transition for a Gay-Berne fluid using density-functional theory

International Nuclear Information System (INIS)

Singh, Ram Chandra

2007-01-01

We have used the density-functional theory to study the effect of varying temperature on the isotropic-nematic transition of a fluid of molecules interacting via the Gay-Berne intermolecular potential. The nematic phase is found to be stable with respect to isotropic phase in the temperature range 0.80≤T*≤1.25. Pair correlation functions needed as input information in density-functional theory is calculated using the Percus-Yevick integral equation theory. We find that the density-functional theory is good for studying the isotropic-nematic transition in molecular fluids if the values of the pair-correlation functions in the isotropic phase are known accurately. We have also compared our results with computer simulation results wherever they are available

Extension theorems for homogenization on lattice structures

Science.gov (United States)

Miller, Robert E.

1992-01-01

When applying homogenization techniques to problems involving lattice structures, it is necessary to extend certain functions defined on a perforated domain to a simply connected domain. This paper provides general extension operators which preserve bounds on derivatives of order l. Only the special case of honeycomb structures is considered.

Phase-field-crystal model for magnetocrystalline interactions in isotropic ferromagnetic solids

Science.gov (United States)

Faghihi, Niloufar; Provatas, Nikolas; Elder, K. R.; Grant, Martin; Karttunen, Mikko

2013-09-01

An isotropic magnetoelastic phase-field-crystal model to study the relation between morphological structure and magnetic properties of pure ferromagnetic solids is introduced. Analytic calculations in two dimensions were used to determine the phase diagram and obtain the relationship between elastic strains and magnetization. Time-dependent numerical simulations in two dimensions were used to demonstrate the effect of grain boundaries on the formation of magnetic domains. It was shown that the grain boundaries act as nucleating sites for domains of reverse magnetization. Finally, we derive a relation for coercivity versus grain misorientation in the isotropic limit.

Bell inequalities stronger than the Clauser-Horne-Shimony-Holt inequality for three-level isotropic states

International Nuclear Information System (INIS)

Ito, Tsuyoshi; Imai, Hiroshi; Avis, David

2006-01-01

We show that some two-party Bell inequalities with two-valued observables are stronger than the CHSH inequality for 3x3 isotropic states in the sense that they are violated by some isotropic states in the 3x3 system that do not violate the CHSH inequality. These Bell inequalities are obtained by applying triangular elimination to the list of known facet inequalities of the cut polytope on nine points. This gives a partial solution to an open problem posed by Collins and Gisin. The results of numerical optimization suggest that they are candidates for being stronger than the I 3322 Bell inequality for 3x3 isotropic states. On the other hand, we found no Bell inequalities stronger than the CHSH inequality for 2x2 isotropic states. In addition, we illustrate an inclusion relation among some Bell inequalities derived by triangular elimination

Depression of nonlinearity in decaying isotropic turbulence

International Nuclear Information System (INIS)

Kraichnan, R.H.; Panda, R.

1988-01-01

Simulations of decaying isotropic Navier--Stokes turbulence exhibit depression of the normalized mean-square nonlinear term to 57% of the value for a Gaussianly distributed velocity field with the same instantaneous velocity spectrum. Similar depression is found for dynamical models with random coupling coefficients (modified Betchov models). This suggests that the depression is dynamically generic rather than specifically driven by alignment of velocity and vorticity

Computations of Quasiconvex Hulls of Isotropic Sets

Czech Academy of Sciences Publication Activity Database

Heinz, S.; Kružík, Martin

2017-01-01

Roč. 24, č. 2 (2017), s. 477-492 ISSN 0944-6532 R&D Projects: GA ČR GA14-15264S; GA ČR(CZ) GAP201/12/0671 Institutional support: RVO:67985556 Keywords : quasiconvexity * isotropic compact sets * matrices Subject RIV: BA - General Mathematics OBOR OECD: Pure mathematics Impact factor: 0.496, year: 2016 http://library.utia.cas.cz/separaty/2017/MTR/kruzik-0474874.pdf

The mechanical properties of human dentin for 3-D finite element modeling: Numerical and analytical evaluation.

Science.gov (United States)

Grzebieluch, Wojciech; Będziński, Romuald; Czapliński, Tomasz; Kaczmarek, Urszula

2017-07-01

The FEM is often used in investigations of dentin loading conditions; however, its anisotropy is mostly neglected. The purpose of the study was to evaluate the anisotropy and the elastic properties of an equivalent homogenous material model of human dentin as well as to compare isotropic and anisotropic dentin FE-models. Analytical and numerical dentin homogenization according to Luciano and Barbero was performed and E-modulus (E), Poisson's ratios (v) G-modulus (G) were calculated. The E-modulus of the dentin matrix was 28.0 GPa, Poisson's ratio (v) was 0.3; finite element models of orthotropic and isotropic dentin were created, loaded and compared using Ansys® 14.5 and CodeAster® 11.2 software. Anisotropy of the dentin ranged from 6.9 to 35.2%. E-modulus and G-modulus were as follows: E1 = 22.0-26.0 GPa, E2/E3 = 15.7-23.0 GPa; G12/G13 = 6.96-9.35 GPa and G23 = 6.08-8.09 GPa (highest values in the superficial layer). In FEM analysis of the displacement values were higher in the isotropic than in the orthotropic model, reaching up to 16% by shear load, 37% by compression and 23% in the case of shear with bending. Strain values were higher in the isotropic model, up to 35% for the shear load, 31% for compression and 35% in the case of shear with bending. The decrease in the volumetric fraction and diameter of tubules increased the G and E values. Anisotropy of the dentin applied during FEM analysis decreased the displacements and strain values. The numerical and analytical homogenization of dentin showed similar results.

Generalized squeezing rotating-wave approximation to the isotropic and anisotropic Rabi model in the ultrastrong-coupling regime

OpenAIRE

Zhang, Yu-Yu

2016-01-01

Generalized squeezing rotating-wave approximation (GSRWA) is proposed by employing both the displacement and the squeezing transformations. A solvable Hamiltonian is reformulated in the same form as the ordinary RWA ones. For a qubit coupled to oscillators experiment, a well-defined Schr\\"{o}dinger-cat-like entangled state is given by the displaced-squeezed oscillator state instead of the original displaced state. For the isotropic Rabi case, the mean photon number and the ground-state energy...

Correlations in plasma in thermodynamic equilibrium; Les correlations dans un plasma en equilibre

Energy Technology Data Exchange (ETDEWEB)

Yvon, J [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires

1958-07-01

This paper treats of a fully, ionized plasma in thermodynamic equilibrium. An attempt is made at reviewing the calculation of spatial correlations in such a plasma. The equation of recurrence and the principle of superposition are used. The linear approximation is first treated. The next higher approximation is studied in the case of a neutral homogeneous and isotropic plasma. (author) [French] Un plasma completement ionise est en equilibre thermodynamique. On tente une mise au point du calcul des correlations de position dans ce plasma. On utilise les equations de recurrence et le principe de superposition. On expose d'abord l'approximation lineaire. Dans le cas d'un plasma neutre homogene et isotrope l'etude est poursuivie a l'approximation suivante. (auteur)

Homogenization of High-Contrast Brinkman Flows

KAUST Repository

Brown, Donald L.

2015-04-16

Modeling porous flow in complex media is a challenging problem. Not only is the problem inherently multiscale but, due to high contrast in permeability values, flow velocities may differ greatly throughout the medium. To avoid complicated interface conditions, the Brinkman model is often used for such flows [O. Iliev, R. Lazarov, and J. Willems, Multiscale Model. Simul., 9 (2011), pp. 1350--1372]. Instead of permeability variations and contrast being contained in the geometric media structure, this information is contained in a highly varying and high-contrast coefficient. In this work, we present two main contributions. First, we develop a novel homogenization procedure for the high-contrast Brinkman equations by constructing correctors and carefully estimating the residuals. Understanding the relationship between scales and contrast values is critical to obtaining useful estimates. Therefore, standard convergence-based homogenization techniques [G. A. Chechkin, A. L. Piatniski, and A. S. Shamev, Homogenization: Methods and Applications, Transl. Math. Monogr. 234, American Mathematical Society, Providence, RI, 2007, G. Allaire, SIAM J. Math. Anal., 23 (1992), pp. 1482--1518], although a powerful tool, are not applicable here. Our second point is that the Brinkman equations, in certain scaling regimes, are invariant under homogenization. Unlike in the case of Stokes-to-Darcy homogenization [D. Brown, P. Popov, and Y. Efendiev, GEM Int. J. Geomath., 2 (2011), pp. 281--305, E. Marusic-Paloka and A. Mikelic, Boll. Un. Mat. Ital. A (7), 10 (1996), pp. 661--671], the results presented here under certain velocity regimes yield a Brinkman-to-Brinkman upscaling that allows using a single software platform to compute on both microscales and macroscales. In this paper, we discuss the homogenized Brinkman equations. We derive auxiliary cell problems to build correctors and calculate effective coefficients for certain velocity regimes. Due to the boundary effects, we construct

[Computer modeling the hydrostatic pressure characteristics of the membrane potential for polymeric membrane, separated non-homogeneous electrolyte solutions].

Science.gov (United States)

Slezak, Izabella H; Jasik-Slezak, Jolanta; Rogal, Mirosława; Slezak, Andrzej

2006-01-01

On the basis of model equation depending the membrane potential deltapsis, on mechanical pressure difference (deltaP), concentration polarization coefficient (zetas), concentration Rayleigh number (RC) and ratio concentration of solutions separated by membrane (Ch/Cl), the characteristics deltapsis = f(deltaP)zetas,RC,Ch/Cl for steady values of zetas, RC and Ch/Cl in single-membrane system were calculated. In this system neutral and isotropic polymeric membrane oriented in horizontal plane, the non-homogeneous binary electrolytic solutions of various concentrations were separated. Nonhomogeneity of solutions is results from creations of the concentration boundary layers on both sides of the membrane. Calculations were made for the case where on a one side of the membrane aqueous solution of NaCl at steady concentration 10(-3) mol x l(-1) (Cl) was placed and on the other aqueous solutions of NaCl at concentrations from 10(-3) mol x l(-1) to 2 x 10(-2) mol x l(-1) (Ch). Their densities were greater than NaCl solution's at 10(-3) mol x l(-1). It was shown that membrane potential depends on hydrodynamic state of a complex concentration boundary layer-membrane-concentration boundary layer, what is controlled by deltaP, Ch/Cl, RC and zetas.

Signature of non-isotropic distribution of stellar rotation inclination angles in the Praesepe cluster

Science.gov (United States)

Kovacs, Geza

2018-04-01

The distribution of the stellar rotation axes of 113 main sequence stars in the open cluster Praesepe are examined by using current photometric rotation periods, spectroscopic rotation velocities, and estimated stellar radii. Three different samples of stellar rotation data on spotted stars from the Galactic field and two independent samples of planetary hosts are used as control samples to support the consistency of the analysis. Considering the high completeness of the Praesepe sample and the behavior of the control samples, we find that the main sequence F - K stars in this cluster are susceptible to rotational axis alignment. Using a cone model, the most likely inclination angle is 76° ± 14° with a half opening angle of 47° ± 24°. Non-isotropic distribution of the inclination angles is preferred over the isotropic distribution, except if the rotation velocities used in this work are systematically overestimated. We found no indication of this being the case on the basis of the currently available data. Data are only available at the CDS, together with the other two compiled datasets used in this paper, via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/612/L2

Seeing is believing : communication performance under isotropic teleconferencing conditions

NARCIS (Netherlands)

Werkhoven, P.J.; Schraagen, J.M.C.; Punte, P.A.J.

2001-01-01

The visual component of conversational media such as videoconferencing systems communicates important non-verbal information such as facial expressions, gestures, posture and gaze. Unlike the other cues, selective gaze depends critically on the configuration of cameras and monitors. Under isotropic

Homogenization of Stokes and Navier-Stokes equations

International Nuclear Information System (INIS)

Allaire, G.

1990-04-01

This thesis is devoted to homogenization of Stokes and Navier-Stokes equations with a Dirichlet boundary condition in a domain containing many tiny obstacles. Tipycally those obstacles are distributed at the modes of a periodic lattice with same small period in each axe's direction, and their size is always asymptotically smaller than the lattice's step. With the help of the energy method, and thanks to a suitable pressure's extension, we prove the convergence of the homogenization process when the lattice's step tends to zero (and thus the number of obstacles tends to infinity). For a so-called critical size of the obstacles, the homogenized problem turns out to be a Brinkman's law (i.e. Stokes or Navier-Stokes equation plus a linear zero-order term for the velocity in the momentum equation). For obstacles which have a size smaller than the critical one, the limit problem reduces to the initial Stokes or Navier-Stokes equations, while for larger sizes the homogenized problem a Darcy's law. Furthermore, those results have been extended to the case of obstacles included in a hyperplane, and we establish a simple model of fluid flows through grids, which is based on a special form of Brinkman's law [fr

Development of a 10 m quasi-isotropic strand assembled from 2G wires

Science.gov (United States)

Kan, Changtao; Wang, Yinshun; Hou, Yanbing; Li, Yan; Zhang, Han; Fu, Yu; Jiang, Zhe

2018-03-01

Quasi-isotropic strands made of second generation (2G) high temperature superconducting (HTS) wires are attractive to applications of high-field magnets at low temperatures and power transmission cables at liquid nitrogen temperature in virtue of their high current carrying capability and well mechanical property. In this contribution, a 10 m length quasi-isotropic strand is manufactured and successfully tested in liquid nitrogen to verify the feasibility of an industrial scale production of the strand by the existing cabling technologies. The strand with copper sheath consists of 72 symmetrically assembled 2G wires. The uniformity of critical properties of long quasi-isotropic strands, including critical current and n-value, is very important for their using. Critical currents as well as n-values of the strand are measured every 1 m respectively and compared with the simulation results. Critical current and n-value of the strand are calculated basing on the self-consistent model solved by the finite element method (FEM). Effects of self-field on the critical current and n-value distributions in wires of the strand are analyzed in detail. The simulation results show good agreement with the experimental data and the 10 m quasi-isotropic strand has good critical properties uniformity.

How Isotropic is the Universe?

Science.gov (United States)

Saadeh, Daniela; Feeney, Stephen M; Pontzen, Andrew; Peiris, Hiranya V; McEwen, Jason D

2016-09-23

A fundamental assumption in the standard model of cosmology is that the Universe is isotropic on large scales. Breaking this assumption leads to a set of solutions to Einstein's field equations, known as Bianchi cosmologies, only a subset of which have ever been tested against data. For the first time, we consider all degrees of freedom in these solutions to conduct a general test of isotropy using cosmic microwave background temperature and polarization data from Planck. For the vector mode (associated with vorticity), we obtain a limit on the anisotropic expansion of (σ_{V}/H)_{0}Universe is strongly disfavored, with odds of 121 000:1 against.

7 CFR 58.920 - Homogenization.

Science.gov (United States)

2010-01-01

... 7 Agriculture 3 2010-01-01 2010-01-01 false Homogenization. 58.920 Section 58.920 Agriculture... Procedures § 58.920 Homogenization. Where applicable concentrated products shall be homogenized for the... homogenization and the pressure at which homogenization is accomplished will be that which accomplishes the most...

Higher gradient expansion for linear isotropic peridynamic materials

Czech Academy of Sciences Publication Activity Database

Šilhavý, Miroslav

2017-01-01

Roč. 22, č. 6 (2017), s. 1483-1493 ISSN 1081-2865 Institutional support: RVO:67985840 Keywords : peridynamics * higher-grade theories * non-local elastic-material model * representation theorems for isotropic functions Subject RIV: BA - General Mathematics OBOR OECD: Applied mathematics Impact factor: 2.953, year: 2016 http:// journals .sagepub.com/doi/10.1177/1081286516637235

Higher gradient expansion for linear isotropic peridynamic materials

Czech Academy of Sciences Publication Activity Database

Šilhavý, Miroslav

2017-01-01

Roč. 22, č. 6 (2017), s. 1483-1493 ISSN 1081-2865 Institutional support: RVO:67985840 Keywords : peridynamics * higher-grade theories * non-local elastic-material model * representation theorems for isotropic functions Subject RIV: BA - General Mathematics OBOR OECD: Applied mathematics Impact factor: 2.953, year: 2016 http://journals.sagepub.com/doi/10.1177/1081286516637235

Gamma rays from relativistic electrons undergoing Compton losses in isotropic photon fields

International Nuclear Information System (INIS)

Zdziarski, A.A.

1989-01-01

The kinetic equation describing Compton losses of relativistic electrons in an isotropic field of soft background photons is solved exactly including both continuous energy losses in the classical Thomson regime and catastrophic losses in the quantum Klein-Nishina regime. This extends the previous treatments of this problem, which assumed the validity of either one of these regimes alone. The problem is relevant to astrophysical sources containing relativistic electrons. Analytical solutions for the steady state electron and gamma-ray spectra in the case of power-law soft photons and monoenergetic and power-law electron injections are obtained. Numerical solutions are presented for monoenergetic, blackbody, and power-law soft photons. A comparison between the numerical and the available analytic solutions is made. 15 refs

Numerical implementation of a transverse-isotropic inelastic, work-hardening constitutive model

International Nuclear Information System (INIS)

Baladi, G.Y.

1978-01-01

The numerical implementation of a transverse-isotropic inelastic, work-hardening plastic constitutive model is documented. A brief review of the model is presented first to facilitate the understanding of its numerical implementation. This model is formulated in terms of 'pseudo' stress invariants, so that the incremental stress-strain relationship can be readily incorporated into existing finite-difference or infinite-element computer codes. The anisotropic model reduces to its isotropic counterpart without any changes in the mathematical formulation or in the numerical implementation (algorithm) of the model. A typical example of the model and its behavior in uniaxial strain and triaxial compression is presented. (Auth.)

ISOTROPIC LUMINOSITY INDICATORS IN A COMPLETE AGN SAMPLE

International Nuclear Information System (INIS)

Diamond-Stanic, Aleksandar M.; Rieke, George H.; Rigby, Jane R.

2009-01-01

The [O IV] λ25.89 μm line has been shown to be an accurate indicator of active galactic nucleus (AGN) intrinsic luminosity in that it correlates well with hard (10-200 keV) X-ray emission. We present measurements of [O IV] for 89 Seyfert galaxies from the unbiased revised Shapley-Ames (RSA) sample. The [O IV] luminosity distributions of obscured and unobscured Seyferts are indistinguishable, indicating that their intrinsic AGN luminosities are quite similar and that the RSA sample is well suited for tests of the unified model. In addition, we analyze several commonly used proxies for AGN luminosity, including [O III] λ5007 A, 6 cm radio, and 2-10 keV X-ray emission. We find that the radio luminosity distributions of obscured and unobscured AGNs show no significant difference, indicating that radio luminosity is a useful isotropic luminosity indicator. However, the observed [O III] and 2-10 keV luminosities are systematically smaller for obscured Seyferts, indicating that they are not emitted isotropically.

Large Deformation Constitutive Laws for Isotropic Thermoelastic Materials

Energy Technology Data Exchange (ETDEWEB)

Plohr, Bradley J. [Los Alamos National Laboratory; Plohr, Jeeyeon N. [Los Alamos National Laboratory

2012-07-25

We examine the approximations made in using Hooke's law as a constitutive relation for an isotropic thermoelastic material subjected to large deformation by calculating the stress evolution equation from the free energy. For a general thermoelastic material, we employ the volume-preserving part of the deformation gradient to facilitate volumetric/shear strain decompositions of the free energy, its first derivatives (the Cauchy stress and entropy), and its second derivatives (the specific heat, Grueneisen tensor, and elasticity tensor). Specializing to isotropic materials, we calculate these constitutive quantities more explicitly. For deformations with limited shear strain, but possibly large changes in volume, we show that the differential equations for the stress components involve new terms in addition to the traditional Hooke's law terms. These new terms are of the same order in the shear strain as the objective derivative terms needed for frame indifference; unless the latter terms are negligible, the former cannot be neglected. We also demonstrate that accounting for the new terms requires that the deformation gradient be included as a field variable

The Space-Time Continuum as a Transversely Isotropic Material and the Meaning of the Temporal Coordinate

International Nuclear Information System (INIS)

Christov, C. I.

2010-01-01

A transversely isotropic elastic continuum is considered in four dimensions, three of which are isotropic, and the properties of the material change only related to the fourth dimension. The model employs two dilational and three shear Lame coefficients. The isotropic dilational coefficient is assumed to be much larger than the second dilational coefficient, and the three shear coefficients. This amounts to a material that is virtually incompressible in the three isotropic dimensions. The first and third shear coefficients are positive, while the second shear coefficient is assumed to be negative. As a result, in the equations of elastic equilibrium, the second derivatives of the displacement with respect to the fourth coordinate enter with negative sign. This makes the equations hyperbolic, with a fourth dimension opposing to the other three. The hyperbolic nature of the fourth dimension allows to be interpreted as time.

Self-confinement of finite dust clusters in isotropic plasmas.

Science.gov (United States)

Miloshevsky, G V; Hassanein, A

2012-05-01

Finite two-dimensional dust clusters are systems of a small number of charged grains. The self-confinement of dust clusters in isotropic plasmas is studied using the particle-in-cell method. The energetically favorable configurations of grains in plasma are found that are due to the kinetic effects of plasma ions and electrons. The self-confinement phenomenon is attributed to the change in the plasma composition within a dust cluster resulting in grain attraction mediated by plasma ions. This is a self-consistent state of a dust cluster in which grain's repulsion is compensated by the reduced charge and floating potential on grains, overlapped ion clouds, and depleted electrons within a cluster. The common potential well is formed trapping dust clusters in the confined state. These results provide both valuable insights and a different perspective to the classical view on the formation of boundary-free dust clusters in isotropic plasmas.

Quantum groups and quantum homogeneous spaces

International Nuclear Information System (INIS)

Kulish, P.P.

1994-01-01

The usefulness of the R-matrix formalism and the reflection equations is demonstrated on examples of the quantum group covariant algebras (quantum homogeneous spaces): quantum Minkowski space-time, quantum sphere and super-sphere. The irreducible representations of some covariant algebras are constructed. The generalization of the reflection equation to super case is given and the existence of the quasiclassical limits is pointed out. (orig.)

Stress-induced birefringence in the isotropic phases of lyotropic mixtures

Science.gov (United States)

Fernandes, P. R. G.; Maki, J. N.; Gonçalves, L. B.; de Oliveira, B. F.; Mukai, H.

2018-02-01

In this work, the frequency dependence of the known mechano-optical effect which occurs in the micellar isotropic phases (I ) of mixtures of potassium laurate (KL), decanol (DeOH), and water is investigated in the range from 200 mHz to 200 Hz . In order to fit the experimental data, a model of superimposed damped harmonic oscillators is proposed. In this phenomenological approach, the micelles (microscopic oscillators) interact very weakly with their neighbors. Due to shape anisotropy of the basic structures, each oscillator i (i =1 ,2 ,3 ,...,N ) remains in its natural oscillatory rotational movement around its axes of symmetry with a frequency ω0 i. The system will be in the resonance state when the frequency of the driving force ω reaches a value near ω0 i. This phenomenological approach shows excellent agreement with the experimental data. One can find f ˜2.5 , 9.0, and 4.0 Hz as fundamental frequencies of the micellar isotropic phases I , I1, and I2, respectively. The different micellar isotropic phases I , I1, and I2 that we find in the phase diagram of the KL-DeOH-water mixture are a consequence of possible differences in the intermicellar correlation lengths. This work reinforces the possibilities of technological applications of these phases in devices such as mechanical vibration sensors.

Isotropic cosmic expansion and the Rubin-Ford effect

International Nuclear Information System (INIS)

Fall, S.M.; Jones, B.J.T.

1976-01-01

It is shown that the Rubin-Ford data (Astrophys. J. Lett. 183:L111 (1973)), often taken as evidence for large scale anisotropic cosmic expansion, probably only reflect the inhomogeneous distribution of galaxies in the region of the sample. The data presented are consistent with isotropic expansion, an unperturbed galaxy velocity field, and hence a low density Universe. (author)

Assessing the homogenization of urban land management with an application to US residential lawn care

Science.gov (United States)

Polsky, Colin; Grove, J. Morgan; Knudson, Chris; Groffman, Peter M.; Bettez, Neil; Cavender-Bares, Jeannine; Hall, Sharon J.; Heffernan, James B.; Hobbie, Sarah E.; Larson, Kelli L.; Morse, Jennifer L.; Neill, Christopher; Nelson, Kristen C.; Ogden, Laura A.; O’Neil-Dunne, Jarlath; Pataki, Diane E.; Roy Chowdhury, Rinku; Steele, Meredith K.

2014-01-01

Changes in land use, land cover, and land management present some of the greatest potential global environmental challenges of the 21st century. Urbanization, one of the principal drivers of these transformations, is commonly thought to be generating land changes that are increasingly similar. An implication of this multiscale homogenization hypothesis is that the ecosystem structure and function and human behaviors associated with urbanization should be more similar in certain kinds of urbanized locations across biogeophysical gradients than across urbanization gradients in places with similar biogeophysical characteristics. This paper introduces an analytical framework for testing this hypothesis, and applies the framework to the case of residential lawn care. This set of land management behaviors are often assumed—not demonstrated—to exhibit homogeneity. Multivariate analyses are conducted on telephone survey responses from a geographically stratified random sample of homeowners (n = 9,480), equally distributed across six US metropolitan areas. Two behaviors are examined: lawn fertilizing and irrigating. Limited support for strong homogenization is found at two scales (i.e., multi- and single-city; 2 of 36 cases), but significant support is found for homogenization at only one scale (22 cases) or at neither scale (12 cases). These results suggest that US lawn care behaviors are more differentiated in practice than in theory. Thus, even if the biophysical outcomes of urbanization are homogenizing, managing the associated sustainability implications may require a multiscale, differentiated approach because the underlying social practices appear relatively varied. The analytical approach introduced here should also be productive for other facets of urban-ecological homogenization. PMID:24616515

A simple mechanical model for the isotropic harmonic oscillator

International Nuclear Information System (INIS)

Nita, Gelu M

2010-01-01

A constrained elastic pendulum is proposed as a simple mechanical model for the isotropic harmonic oscillator. The conceptual and mathematical simplicity of this model recommends it as an effective pedagogical tool in teaching basic physics concepts at advanced high school and introductory undergraduate course levels.

A new concept of equivalent homogenization method

Energy Technology Data Exchange (ETDEWEB)

Kim, Young Jin; Pogoskekyan, Leonid; Kim, Young Il; Ju, Hyung Kook; Chang, Moon Hee [Korea Atomic Energy Research Institute, Taejon (Korea, Republic of)

1996-07-01

A new concept of equivalent homogenization is proposed. The concept employs new set of homogenized parameters: homogenized cross sections (XS) and interface matrix (IM), which relates partial currents at the cell interfaces. The idea of interface matrix generalizes the idea of discontinuity factors (DFs), proposed and developed by K. Koebke and K. Smith. The offered concept covers both those of K. Koebke and K. Smith; both of them can be simulated within framework of new concept. Also, the offered concept covers Siemens KWU approach for baffle/reflector simulation, where the equivalent homogenized reflector XS are derived from the conservation of response matrix at the interface in 1D simi-infinite slab geometry. The IM and XS of new concept satisfy the same assumption about response matrix conservation in 1D semi-infinite slab geometry. It is expected that the new concept provides more accurate approximation of heterogeneous cell, especially in case of the steep flux gradients at the cell interfaces. The attractive shapes of new concept are: improved accuracy, simplicity of incorporation in the existing codes, equal numerical expenses in comparison to the K. Smith`s approach. The new concept is useful for: (a) explicit reflector/baffle simulation; (b) control blades simulation; (c) mixed UO{sub 2}/MOX core simulation. The offered model has been incorporated in the finite difference code and in the nodal code PANDOX. The numerical results show good accuracy of core calculations and insensitivity of homogenized parameters with respect to in-core conditions. 9 figs., 7 refs. (Author).

Magnetization reversal processes of isotropic permanent magnets with various inter-grain exchange interactions

Directory of Open Access Journals (Sweden)

Hiroshi Tsukahara

2017-05-01

Full Text Available We performed a large-scale micromagnetics simulation on a supercomputing system to investigate the properties of isotropic nanocrystalline permanent magnets consisting of cubic grains. In the simulation, we solved the Landau–Lifshitz–Gilbert equation under a periodic boundary condition for accurate calculation of the magnetization dynamics inside the nanocrystalline isotropic magnet. We reduced the inter-grain exchange interaction perpendicular and parallel to the external field independently. Propagation of the magnetization reversal process is inhibited by reducing the inter-grain exchange interaction perpendicular to the external field, and the coercivity is enhanced by this restraint. In contrast, when we reduce the inter-grain exchange interaction parallel to the external field, the coercivity decreases because the magnetization reversal process propagates owing to dipole interaction. These behaviors show that the coercivity of an isotropic permanent magnet depends on the direction of the inter-grain exchange interaction.

Electron Cooling and Isotropization during Magnetotail Current Sheet Thinning: Implications for Parallel Electric Fields

Science.gov (United States)

Lu, San; Artemyev, A. V.; Angelopoulos, V.

2017-11-01

Magnetotail current sheet thinning is a distinctive feature of substorm growth phase, during which magnetic energy is stored in the magnetospheric lobes. Investigation of charged particle dynamics in such thinning current sheets is believed to be important for understanding the substorm energy storage and the current sheet destabilization responsible for substorm expansion phase onset. We use Time History of Events and Macroscale Interactions during Substorms (THEMIS) B and C observations in 2008 and 2009 at 18 - 25 RE to show that during magnetotail current sheet thinning, the electron temperature decreases (cooling), and the parallel temperature decreases faster than the perpendicular temperature, leading to a decrease of the initially strong electron temperature anisotropy (isotropization). This isotropization cannot be explained by pure adiabatic cooling or by pitch angle scattering. We use test particle simulations to explore the mechanism responsible for the cooling and isotropization. We find that during the thinning, a fast decrease of a parallel electric field (directed toward the Earth) can speed up the electron parallel cooling, causing it to exceed the rate of perpendicular cooling, and thus lead to isotropization, consistent with observation. If the parallel electric field is too small or does not change fast enough, the electron parallel cooling is slower than the perpendicular cooling, so the parallel electron anisotropy grows, contrary to observation. The same isotropization can also be accomplished by an increasing parallel electric field directed toward the equatorial plane. Our study reveals the existence of a large-scale parallel electric field, which plays an important role in magnetotail particle dynamics during the current sheet thinning process.

Hydraulic homogenization of a clayey porous rock with 3D statistical and deterministic discontinuities: application to THE 'EDZ' at the Bure Callovo-Oxfordian URL

International Nuclear Information System (INIS)

Ababou, R.; Canamon, I.; Poutrel, A.

2010-01-01

Document available in extended abstract form only. The present work, carried out in the Underground Research Laboratory at Bure operated by Andra, focuses on the hydraulic homogenization (up-scaling) of the Excavated Damaged Zone (EDZ) around a cylindrical excavation, taking into account the specific structure of the micro-fissures and of the larger fractures induced by the excavation, as well as the permeability of the intact rock (the Callovo-Oxfordian clay-stone, 130 m thick, and located between 400 m and 600 m depth at this site). Two types of discontinuities are distinguished: (1) a statistically isotropic network of micro-fissures, and (2) a quasi-periodic set of complex shaped, curved fractures (chevron pattern). Hydraulic up-scaling are expressed in terms of effective macro-permeability tensors, and they are compared, in the final stage of this work, against in situ data, including permeability profiles along boreholes. We firstly consider a 3D stretch of a cylindrical gallery with: (i) section length L = 20 m; (ii) drift diameter = 4 m; (iii) thickness of the annular EDZ around the drift = 4 m. The domain of investigation is a 3D rectangular box of size 20 x 13 x 13 m, which encloses the drift and its EDZ. The transverse scales correspond to those of the experimental drifts and EDZ observed at the URL site. - Statistical network of micro-fissures (randomly oriented plane discs). The micro-fissures and small fractures are modeled as statistical plane discs, with randomly isotropic orientations, and radially decreasing density and diameters away from the drift wall. - Deterministic set of curved fractures ('herringbone' or 'chevron' pattern).The extensive shear fractures ('chevrons') are modeled as a periodic set of mathematical surfaces (generalized elliptical conoids) analogous to those observed in the Bure drifts The method adopted here for hydraulic homogenization of a 3D porous fractured rock is based on a &apos

Effects of molecular elongation on liquid crystalline phase behaviour: isotropic-nematic transition

Science.gov (United States)

Singh, Ram Chandra; Ram, Jokhan

2003-08-01

We present the density-functional approach to study the isotropic-nematic transitions and calculate the values of freezing parameters of the Gay-Berne liquid crystal model, concentrating on the effects of varying the molecular elongation, x0. For this, we have solved the Percus-Yevick integral equation theory to calculate the pair-correlation functions of a fluid the molecules of which interact via a Gay-Berne pair potential. These results have been used in the density-functional theory as an input to locate the isotropic-nematic transition and calculate freezing parameters for a range of length-to-width parameters 3.0⩽ x0⩽4.0 at reduced temperatures 0.95 and 1.25. We observed that as x0 is increased, the isotropic-nematic transition is seen to move to lower density at a given temperature. We find that the density-functional theory is good to study the freezing transitions in such fluids. We have also compared our results with computer simulation results wherever they are available.

The generalized Cauchy relation: a probe for local structure in materials with isotropic symmetry

Energy Technology Data Exchange (ETDEWEB)

Bactavatchalou, R [Laboratoire Europeen de Recherche Universitaire Saarland- Lorraine- Luxembourg at Universitaet des Saarlandes (Luxembourg); Alnot, P [Universite Henri Poincare, Nancy I (France); Bailer, J [Universite du Luxembourg (Luxembourg); Kolle, M [Laboratoire Europeen de Recherche Universitaire Saarland- Lorraine- Luxembourg at Universitaet des Saarlandes (Luxembourg); Mueller, U [Laboratoire Europeen de Recherche Universitaire Saarland- Lorraine- Luxembourg at Universitaet des Saarlandes (Luxembourg); Philipp, M [Laboratoire Europeen de Recherche Universitaire Saarland- Lorraine- Luxembourg at Universitaet des Saarlandes (Luxembourg); Possart, W [Laboratoire Europeen de Recherche Universitaire Saarland- Lorraine- Luxembourg at Universitaet des Saarlandes (Luxembourg); Rouxel, D [Universite Henri Poincare, Nancy I (France); Sanctuary, R [Universite du Luxembourg (Luxembourg); Tschoepe, A [Laboratoire Europeen de Recherche Universitaire Saarland- Lorraine- Luxembourg at Universitaet des Saarlandes (Luxembourg); Vergnat, Ch [Laboratoire Europeen de Recherche Universitaire Saarland- Lorraine- Luxembourg at Universitaet des Saarlandes (Luxembourg); Wetzel, B [Institut fuer Verbundwerkstoffe TU Kaiserslautern 67663 Kaiserslautern (Germany); Krueger, J K [Laboratoire Europeen de Recherche Universitaire Saarland- Lorraine- Luxembourg at Universitaet des Saarlandes (Luxembourg)

2006-05-15

The elastic properties of the isotropic state of condensed matter are given by the elastic constants ell and c44. In the liquid state the static shear stiffness c44 vanishes whereas at sufficient high probe frequencies a dynamic shear stiffness may appear. In that latter case the question about the existence of a Cauchy relation appears. It will be shown that a pure Cauchy relation can appear only under special conditions which are rarely fulfilled. For all investigated materials, including ceramics, liquids and glasses, a linear relation between ell and c44 called generalized Cauchy relation is observed, which, surprisingly, follows a linear transformation.

Spatial homogenization method based on the inverse problem

International Nuclear Information System (INIS)

Tóta, Ádám; Makai, Mihály

2015-01-01

Highlights: • We derive a spatial homogenization method in slab and cylindrical geometries. • The fluxes and the currents on the boundary are preserved. • The reaction rates and the integral of the fluxes are preserved. • We present verification computations utilizing two- and four-energy groups. - Abstract: We present a method for deriving homogeneous multi-group cross sections to replace a heterogeneous region’s multi-group cross sections; providing that the fluxes, the currents on the external boundary, the reaction rates and the integral of the fluxes are preserved. We consider one-dimensional geometries: a symmetric slab and a homogeneous cylinder. Assuming that the boundary fluxes are given, two response matrices (RMs) can be defined concerning the current and the flux integral. The first one derives the boundary currents from the boundary fluxes, while the second one derives the flux integrals from the boundary fluxes. Further RMs can be defined that connects reaction rates to the boundary fluxes. Assuming that these matrices are known, we present formulae that reconstruct the multi-group diffusion cross-section matrix, the diffusion coefficients and the reaction cross sections in case of one-dimensional (1D) homogeneous regions. We apply these formulae to 1D heterogeneous regions and thus obtain a homogenization method. This method produces such an equivalent homogeneous material, that the fluxes and the currents on the external boundary, the reaction rates and the integral of the fluxes are preserved for any boundary fluxes. We carry out the exact derivations in 1D slab and cylindrical geometries. Verification computations for the presented homogenization method were performed using two- and four-group material cross sections, both in a slab and in a cylindrical geometry

Weak convergence to isotropic complex [Formula: see text] random measure.

Science.gov (United States)

Wang, Jun; Li, Yunmeng; Sang, Liheng

2017-01-01

In this paper, we prove that an isotropic complex symmetric α -stable random measure ([Formula: see text]) can be approximated by a complex process constructed by integrals based on the Poisson process with random intensity.

The Effect of Shear Flow on the Isotropic-Nematic Transition in Liquid Crystals.

Science.gov (United States)

Olmsted, Peter David

1991-08-01

In this thesis I will discuss the effects of shear flow on the Isotropic-Nematic phase transition in liquid crystals. Shear flow has dramatic orienting effects on the rod-like constituents of nematic liquid crystals, with the general effects of (1) inducing order in the high-temperature isotropic phase, and (2) dictating a direction of alignment for the low-temperature nematic phase. Shear flow also imposes a biaxial symmetry on both the high and low temperature phases, thereby changing the nature of the symmetry-breaking at the transition. We develop coupled deterministic dynamical equations for the 5-component nematic order parameter and the fluid velocity, which may be considered generalizations of the Leslie-Ericksen and Navier-Stokes equations, respectively. We examine the stable stationary solutions to these equations to determine the nature of the non-equilibrium phases, and discuss the analogies and differences between this system and equilibrium systems. From homogeneous solutions we obtain a state diagram analogous to that of a Van der Waals fluid, including a two-state region and a discontinuous transition which terminates at a critical point. To resolve the question of the analog of the Maxwell construction to distinguish locally stable states, we construct stable inhomogeneous interfacial states. From an analysis of these states we determine a coexistence line and find exponents characterizing the shape of the coexistence curve and the interface thickness as the critical point is approached. We find mean-field critical behavior, and comment on the possibility of the analogs of spinodal decomposition and nucleation. Finally, we develop a formalism for describing light scattering from biaxial steady state, and investigate the Gaussian level fluctuations about these states. In the vicinity of the critical point we find singular behavior analogous to critical opalescence of a simple fluid at its critical point. We also find anisotropic correlations at the

Hydrophobic matrix-free graphene-oxide composites with isotropic and nematic states

Science.gov (United States)

Wåhlander, Martin; Nilsson, Fritjof; Carlmark, Anna; Gedde, Ulf W.; Edmondson, Steve; Malmström, Eva

2016-08-01

We demonstrate a novel route to synthesise hydrophobic matrix-free composites of polymer-grafted graphene oxide (GO) showing isotropic or nematic alignment and shape-memory effects. For the first time, a cationic macroinitiator (MI) has been immobilised on anionic GO and subsequently grafted with hydrophobic polymer grafts. Dense grafts of PBA, PBMA and PMMA with a wide range of average graft lengths (MW: 1-440 kDa) were polymerised by surface-initiated controlled radical precipitation polymerisation from the statistical MI. The surface modification is designed similarly to bimodal graft systems, where the cationic MI generates nanoparticle repulsion, similar to dense short grafts, while the long grafts offer miscibility in non-polar environments and cohesion. The state-of-the-art dispersions of grafted GO were in the isotropic state. Transparent and translucent matrix-free GO-composites could be melt-processed directly using only grafted GO. After processing, birefringence due to nematic alignment of grafted GO was observed as a single giant Maltese cross, 3.4 cm across. Permeability models for composites containing aligned 2D-fillers were developed, which were compared with the experimental oxygen permeability data and found to be consistent with isotropic or nematic states. The storage modulus of the matrix-free GO-composites increased with GO content (50% increase at 0.67 wt%), while the significant increases in the thermal stability (up to 130 °C) and the glass transition temperature (up to 17 °C) were dependent on graft length. The tuneable matrix-free GO-composites with rapid thermo-responsive shape-memory effects are promising candidates for a vast range of applications, especially selective membranes and sensors.We demonstrate a novel route to synthesise hydrophobic matrix-free composites of polymer-grafted graphene oxide (GO) showing isotropic or nematic alignment and shape-memory effects. For the first time, a cationic macroinitiator (MI) has been

Study of open systems with molecules in isotropic liquids

Science.gov (United States)

Kondo, Yasushi; Matsuzaki, Masayuki

2018-05-01

We are interested in dynamics of a system in an environment, or an open system. Such phenomena as crossover from Markovian to non-Markovian relaxation and thermal equilibration are of our interest. Open systems have experimentally been studied with ultra cold atoms, ions in traps, optics, and cold electric circuits because well-isolated systems can be prepared here and thus the effects of environments can be controlled. We point out that some molecules solved in isotropic liquid are well isolated and thus they can also be employed for studying open systems in Nuclear Magnetic Resonance (NMR) experiments. First, we provide a short review on related phenomena of open systems that helps readers to understand our motivation. We, then, present two experiments as examples of our approach with molecules in isotropic liquids. Crossover from Markovian to non-Markovian relaxation was realized in one NMR experiment, while relaxation-like phenomena were observed in approximately isolated systems in the other.

Homogenization of neutronic diffusion models; Homogeneisation des modeles de diffusion en neutronique

Energy Technology Data Exchange (ETDEWEB)

Capdebosq, Y

1999-09-01

In order to study and simulate nuclear reactor cores, one needs to access the neutron distribution in the core. In practice, the description of this density of neutrons is given by a system of diffusion equations, coupled by non differential exchange terms. The strong heterogeneity of the medium constitutes a major obstacle to the numerical computation of this models at reasonable cost. Homogenization appears as compulsory. Heuristic methods have been developed since the origin by nuclear physicists, under a periodicity assumption on the coefficients. They consist in doing a fine computation one a single periodicity cell, to solve the system on the whole domain with homogeneous coefficients, and to reconstruct the neutron density by multiplying the solutions of the two computations. The objectives of this work are to provide mathematically rigorous basis to this factorization method, to obtain the exact formulas of the homogenized coefficients, and to start on geometries where two periodical medium are placed side by side. The first result of this thesis concerns eigenvalue problem models which are used to characterize the state of criticality of the reactor, under a symmetry assumption on the coefficients. The convergence of the homogenization process is proved, and formulas of the homogenized coefficients are given. We then show that without symmetry assumptions, a drift phenomenon appears. It is characterized by the mean of a real Bloch wave method, which gives the homogenized limit in the general case. These results for the critical problem are then adapted to the evolution model. Finally, the homogenization of the critical problem in the case of two side by side periodic medium is studied on a one dimensional on equation model. (authors)

A new traveltime approximation for TI media

KAUST Repository

Stovas, Alexey; Alkhalifah, Tariq Ali

2012-01-01

In a transversely isotropic (TI) medium, the trade-off between inhomogeneity and anisotropy can dramatically reduce our capability to estimate anisotropy parameters. By expanding the TI eikonal equation in power series in terms of the aneliptic parameter η, we derive an efficient tool to estimate (scan) for η in a generally inhomogeneous, elliptically anisotropic background medium. For a homogeneous-tilted transversely isotropic medium, we obtain an analytic nonhyperbolic moveout equation that is accurate for large offsets. In the common case where we do not have well information and it is necessary to resolve the vertical velocity, the background medium can be assumed isotropic, and the traveltime equations becomes simpler. In all cases, the accuracy of this new TI traveltime equation exceeds previously published formulations and demonstrates how η is better resolved at small offsets when the tilt is large.

A new traveltime approximation for TI media

KAUST Repository

Stovas, Alexey

2012-07-01

In a transversely isotropic (TI) medium, the trade-off between inhomogeneity and anisotropy can dramatically reduce our capability to estimate anisotropy parameters. By expanding the TI eikonal equation in power series in terms of the aneliptic parameter η, we derive an efficient tool to estimate (scan) for η in a generally inhomogeneous, elliptically anisotropic background medium. For a homogeneous-tilted transversely isotropic medium, we obtain an analytic nonhyperbolic moveout equation that is accurate for large offsets. In the common case where we do not have well information and it is necessary to resolve the vertical velocity, the background medium can be assumed isotropic, and the traveltime equations becomes simpler. In all cases, the accuracy of this new TI traveltime equation exceeds previously published formulations and demonstrates how η is better resolved at small offsets when the tilt is large.

Pyroxene Homogenization and the Isotopic Systematics of Eucrites

Science.gov (United States)

Nyquist, L. E.; Bogard, D. D.

1996-01-01

The original Mg-Fe zoning of eucritic pyroxenes has in nearly all cases been partly homogenized, an observation that has been combined with other petrographic and compositional criteria to establish a scale of thermal "metamorphism" for eucrites. To evaluate hypotheses explaining development of conditions on the HED parent body (Vesta?) leading to pyroxene homogenization against their chronological implications, it is necessary to know whether pyroxene metamorphism was recorded in the isotopic systems. However, identifying the effects of the thermal metamorphism with specific effects in the isotopic systems has been difficult, due in part to a lack of correlated isotopic and mineralogical studies of the same eucrites. Furthermore, isotopic studies often place high demands on analytical capabilities, resulting in slow growth of the isotopic database. Additionally, some isotopic systems would not respond in a direct and sensitive way to pyroxene homogenization. Nevertheless, sufficient data exist to generalize some observations, and to identify directions of potentially fruitful investigations.

Full three-dimensional isotropic carpet cloak designed by quasi-conformal transformation optics.

Science.gov (United States)

Silva, Daniely G; Teixeira, Poliane A; Gabrielli, Lucas H; Junqueira, Mateus A F C; Spadoti, Danilo H

2017-09-18

A fully three-dimensional carpet cloak presenting invisibility in all viewing angles is theoretically demonstrated. The design is developed using transformation optics and three-dimensional quasi-conformal mapping. Parametrization strategy and numerical optimization of the coordinate transformation deploying a quasi-Newton method is applied. A discussion about the minimum achievable anisotropy in the 3D transformation optics is presented. The method allows to reduce the anisotropy in the cloak and an isotropic medium could be considered. Numerical simulations confirm the strategy employed enabling the design of an isotropic reflectionless broadband carpet cloak independently of the incident light direction and polarization.

Homogenization of Mammalian Cells.

Science.gov (United States)

de Araújo, Mariana E G; Lamberti, Giorgia; Huber, Lukas A

2015-11-02

Homogenization is the name given to the methodological steps necessary for releasing organelles and other cellular constituents as a free suspension of intact individual components. Most homogenization procedures used for mammalian cells (e.g., cavitation pump and Dounce homogenizer) rely on mechanical force to break the plasma membrane and may be supplemented with osmotic or temperature alterations to facilitate membrane disruption. In this protocol, we describe a syringe-based homogenization method that does not require specialized equipment, is easy to handle, and gives reproducible results. The method may be adapted for cells that require hypotonic shock before homogenization. We routinely use it as part of our workflow to isolate endocytic organelles from mammalian cells. © 2015 Cold Spring Harbor Laboratory Press.

A Potential Method for Body and Surface Wave Propagation in Transversely Isotropic Half- and Full-Spaces

Directory of Open Access Journals (Sweden)

Mehdi Raoofian Naeeni

2016-12-01

Full Text Available The problem of propagation of plane wave including body and surface waves propagating in a transversely isotropic half-space with a depth-wise axis of material symmetry is investigated in details. Using the advantage of representation of displacement fields in terms of two complete scalar potential functions, the coupled equations of motion are uncoupled and reduced to two independent equations for potential functions. In this paper, the secular equations for determination of body and surface wave velocities are derived in terms of both elasticity coefficients and the direction of propagation. In particular, the longitudinal, transverse and Rayleigh wave velocities are determined in explicit forms. It is also shown that in transversely isotropic materials, a Rayleigh wave may propagate in different manner from that of isotropic materials. Some numerical results for synthetic transversely isotropic materials are also illustrated to show the behavior of wave motion due to anisotropic nature of the problem.

Overview of homogeneous versus heterogeneous core configuration trade-off studies

International Nuclear Information System (INIS)

Chang, Y.I.

1982-01-01

The most significant development in core design trend in the U.S. LMFBR program has been the increased attention given to the heterogeneous core design concept. In recent years, numerous core configuration trade-off studies have been carried out to quantify advantages and disadvantages of the heterogeneous concept relative to the homogeneous concept, and a consensus is emerging among the U.S. core designers. It appears that the technical and economic performance differences between homogeneous and heterogeneous core designs are very small; however, the heterogeneous concept provides a definite safety/licensing advantage. he technical and economic performance comparison between homogeneous and heterogeneous core configurations is difficult to quantify. In fact, in most cases, the perceived advantages and/or disadvantages are dictated by the consistency in the comparison (optimized for one concept versus non-optimized for the other, etc.) rather than by any inherent differences. Some of the technical and economic issues relevant to the homogeneous versus heterogeneous comparison are summarized

Overview of homogeneous versus heterogeneous core configuration trade-off studies

Energy Technology Data Exchange (ETDEWEB)

Chang, Y I [Applied Physics Division, Argonne National Laboratory, Argonne, IL (United States)

1982-01-01

The most significant development in core design trend in the U.S. LMFBR program has been the increased attention given to the heterogeneous core design concept. In recent years, numerous core configuration trade-off studies have been carried out to quantify advantages and disadvantages of the heterogeneous concept relative to the homogeneous concept, and a consensus is emerging among the U.S. core designers. It appears that the technical and economic performance differences between homogeneous and heterogeneous core designs are very small; however, the heterogeneous concept provides a definite safety/licensing advantage. he technical and economic performance comparison between homogeneous and heterogeneous core configurations is difficult to quantify. In fact, in most cases, the perceived advantages and/or disadvantages are dictated by the consistency in the comparison (optimized for one concept versus non-optimized for the other, etc.) rather than by any inherent differences. Some of the technical and economic issues relevant to the homogeneous versus heterogeneous comparison are summarized.

Functionality and homogeneity.

NARCIS (Netherlands)

2011-01-01

Functionality and homogeneity are two of the five Sustainable Safety principles. The functionality principle aims for roads to have but one exclusive function and distinguishes between traffic function (flow) and access function (residence). The homogeneity principle aims at differences in mass,

Experimental Verification of Isotropic Radiation from a Coherent Dipole Source via Electric-Field-Driven LC Resonator Metamaterials

Science.gov (United States)

Tichit, Paul-Henri; Burokur, Shah Nawaz; Qiu, Cheng-Wei; de Lustrac, André

2013-09-01

It has long been conjectured that isotropic radiation by a simple coherent source is impossible due to changes in polarization. Though hypothetical, the isotropic source is usually taken as the reference for determining a radiator’s gain and directivity. Here, we demonstrate both theoretically and experimentally that an isotropic radiator can be made of a simple and finite source surrounded by electric-field-driven LC resonator metamaterials designed by space manipulation. As a proof-of-concept demonstration, we show the first isotropic source with omnidirectional radiation from a dipole source (applicable to all distributed sources), which can open up several possibilities in axion electrodynamics, optical illusion, novel transformation-optic devices, wireless communication, and antenna engineering. Owing to the electric- field-driven LC resonator realization scheme, this principle can be readily applied to higher frequency regimes where magnetism is usually not present.

Distributions asymptotically homogeneous along the trajectories determined by one-parameter groups

International Nuclear Information System (INIS)

Drozhzhinov, Yurii N; Zav'yalov, Boris I

2012-01-01

We give a complete description of distributions that are asymptotically homogeneous (including the case of critical index of the asymptotic scale) along the trajectories determined by continuous multiplicative one-parameter transformation groups such that the real parts of all eigenvalues of the infinitesimal matrix are positive. To do this, we introduce and study special spaces of distributions. As an application of our results, we describe distributions that are homogeneous along such groups.

Manipulation of surface plasmon polariton propagation on isotropic and anisotropic two-dimensional materials coupled to boron nitride heterostructures

Energy Technology Data Exchange (ETDEWEB)

Inampudi, Sandeep; Nazari, Mina; Forouzmand, Ali; Mosallaei, Hossein, E-mail: hosseinm@coe.neu.edu [Department of Electrical and Computer Engineering, Northeastern University, 360 Huntington Ave., Boston, Massachusetts 02115 (United States)

2016-01-14

We present a comprehensive analysis of surface plasmon polariton dispersion characteristics associated with isotropic and anisotropic two-dimensional atomically thin layered materials (2D sheets) coupled to h-BN heterostructures. A scattering matrix based approach is presented to compute the electromagnetic fields and related dispersion characteristics of stacked layered systems composed of anisotropic 2D sheets and uniaxial bulk materials. We analyze specifically the surface plasmon polariton (SPP) dispersion characteristics in case of isolated and coupled two-dimensional layers with isotropic and anisotropic conductivities. An analysis based on residue theorem is utilized to identify optimum optical parameters (surface conductivity) and geometrical parameters (separation between layers) to maximize the SPP field at a given position. The effect of type and degree of anisotropy on the shapes of iso-frequency curves and propagation characteristics is discussed in detail. The analysis presented in this paper gives an insight to identify optimum setup to enhance the SPP field at a given position and in a given direction on the surface of two-dimensional materials.

Optical illusions induced by rotating medium

Science.gov (United States)

Zang, XiaoFei; Huang, PengCheng; Zhu, YiMing

2018-03-01

Different from the traditional single-function electromagnetic wave rotators (rotate the electromagnetic wavefronts), we propose that rotating medium can be extended to optical illusions such as breaking the diffraction limit and overlapping illusion. Furthermore, the homogeneous but anisotropic rotating medium is simplified by homogeneous and isotropic positive-index materials according to the effective medium theory, which is helpful for future device fabrication. Finite element simulations for the two-dimensional case are performed to demonstrate these properties.

Homogenization of resonant chiral metamaterials

DEFF Research Database (Denmark)

Andryieuski, Andrei; Menzel, C.; Rockstuhl, Carsten

2010-01-01

Homogenization of metamaterials is a crucial issue as it allows to describe their optical response in terms of effective wave parameters as, e.g., propagation constants. In this paper we consider the possible homogenization of chiral metamaterials. We show that for meta-atoms of a certain size...... an analytical criterion for performing the homogenization and a tool to predict the homogenization limit. We show that strong coupling between meta-atoms of chiral metamaterials may prevent their homogenization at all....

Metrical relationships in a standard triangle in an isotropic plane

OpenAIRE

Kolar-Šuper, R.; Kolar-Begović, Z.; Volenec, V.; Beban-Brkić, J.

2005-01-01

Each allowable triangle of an isotropic plane can be set in a standard position, in which it is possible to prove geometric properties analytically in a simplified and easier way by means of the algebraic theory developed in this paper.

Isotropic 2D quadrangle meshing with size and orientation control

KAUST Repository

Pellenard, Bertrand; Alliez, Pierre; Morvan, Jean-Marie

2011-01-01

We propose an approach for automatically generating isotropic 2D quadrangle meshes from arbitrary domains with a fine control over sizing and orientation of the elements. At the heart of our algorithm is an optimization procedure that, from a coarse

Testing the isotropic boundary algorithms method to evaluate the magnetic field configuration in the tail

International Nuclear Information System (INIS)

Sergeev, V.A.; Malkov, M.; Mursula, K.

1993-01-01

This paper describes tests done on one model system for studying the magnetic field in the magneotail, called the isotropic boundary algorithm method. The tail field lines map into the ionosphere, and there have been two direct methods applied to study tail fields, one a global model, and the other a local model. The global models are so broad in scope that they have a hard time dealing with specific field configurations at some time and some location. Local models rely upon field measurements being simultaneously available over a large region of space to study simultaneously the field configurations. In general this is either very fortuitous or very expensive. The isotropic boundary algorithm method relys upon measuring energetic particles, here protons with energies greater than 30 keV, in the isotropic boundary at low altitudes and interpreting them as representing the boundary between stochastic and adiabatic particle motion regions in the equatorial tail current sheet. The authors have correlated particle measurements by NOAA spacecraft to study the isotropic boundary, with magnetic measurements of tail magnetic fields by the geostationary GOES 2 spacecraft. Positive correlations are observed

Traveltime approximations for transversely isotropic media with an inhomogeneous background

KAUST Repository

Alkhalifah, Tariq

2011-05-01

A transversely isotropic (TI) model with a tilted symmetry axis is regarded as one of the most effective approximations to the Earth subsurface, especially for imaging purposes. However, we commonly utilize this model by setting the axis of symmetry normal to the reflector. This assumption may be accurate in many places, but deviations from this assumption will cause errors in the wavefield description. Using perturbation theory and Taylor\\'s series, I expand the solutions of the eikonal equation for 2D TI media with respect to the independent parameter θ, the angle the tilt of the axis of symmetry makes with the vertical, in a generally inhomogeneous TI background with a vertical axis of symmetry. I do an additional expansion in terms of the independent (anellipticity) parameter in a generally inhomogeneous elliptically anisotropic background medium. These new TI traveltime solutions are given by expansions in and θ with coefficients extracted from solving linear first-order partial differential equations. Pade approximations are used to enhance the accuracy of the representation by predicting the behavior of the higher-order terms of the expansion. A simplification of the expansion for homogenous media provides nonhyperbolic moveout descriptions of the traveltime for TI models that are more accurate than other recently derived approximations. In addition, for 3D media, I develop traveltime approximations using Taylor\\'s series type of expansions in the azimuth of the axis of symmetry. The coefficients of all these expansions can also provide us with the medium sensitivity gradients (Jacobian) for nonlinear tomographic-based inversion for the tilt in the symmetry axis. © 2011 Society of Exploration Geophysicists.

Traveltime approximations for transversely isotropic media with an inhomogeneous background

KAUST Repository

Alkhalifah, Tariq

2011-01-01

A transversely isotropic (TI) model with a tilted symmetry axis is regarded as one of the most effective approximations to the Earth subsurface, especially for imaging purposes. However, we commonly utilize this model by setting the axis of symmetry normal to the reflector. This assumption may be accurate in many places, but deviations from this assumption will cause errors in the wavefield description. Using perturbation theory and Taylor's series, I expand the solutions of the eikonal equation for 2D TI media with respect to the independent parameter θ, the angle the tilt of the axis of symmetry makes with the vertical, in a generally inhomogeneous TI background with a vertical axis of symmetry. I do an additional expansion in terms of the independent (anellipticity) parameter in a generally inhomogeneous elliptically anisotropic background medium. These new TI traveltime solutions are given by expansions in and θ with coefficients extracted from solving linear first-order partial differential equations. Pade approximations are used to enhance the accuracy of the representation by predicting the behavior of the higher-order terms of the expansion. A simplification of the expansion for homogenous media provides nonhyperbolic moveout descriptions of the traveltime for TI models that are more accurate than other recently derived approximations. In addition, for 3D media, I develop traveltime approximations using Taylor's series type of expansions in the azimuth of the axis of symmetry. The coefficients of all these expansions can also provide us with the medium sensitivity gradients (Jacobian) for nonlinear tomographic-based inversion for the tilt in the symmetry axis. © 2011 Society of Exploration Geophysicists.

High-Resolution Isotropic Three-Dimensional MR Imaging of the Extraforaminal Segments of the Cranial Nerves.

Science.gov (United States)

Wen, Jessica; Desai, Naman S; Jeffery, Dean; Aygun, Nafi; Blitz, Ari

2018-02-01

High-resolution isotropic 3-dimensional (D) MR imaging with and without contrast is now routinely used for imaging evaluation of cranial nerve anatomy and pathologic conditions. The anatomic details of the extraforaminal segments are well-visualized on these techniques. A wide range of pathologic entities may cause enhancement or displacement of the nerve, which is now visible to an extent not available on standard 2D imaging. This article highlights the anatomy of extraforaminal segments of the cranial nerves and uses select cases to illustrate the utility and power of these sequences, with a focus on constructive interference in steady-state. Copyright © 2017 Elsevier Inc. All rights reserved.

Distinguishing spin-aligned and isotropic black hole populations with gravitational waves.

Science.gov (United States)

Farr, Will M; Stevenson, Simon; Miller, M Coleman; Mandel, Ilya; Farr, Ben; Vecchio, Alberto

2017-08-23

The direct detection of gravitational waves from merging binary black holes opens up a window into the environments in which binary black holes form. One signature of such environments is the angular distribution of the black hole spins. Binary systems that formed through dynamical interactions between already-compact objects are expected to have isotropic spin orientations (that is, the spins of the black holes are randomly oriented with respect to the orbit of the binary system), whereas those that formed from pairs of stars born together are more likely to have spins that are preferentially aligned with the orbit. The best-measured combination of spin parameters for each of the four likely binary black hole detections GW150914, LVT151012, GW151226 and GW170104 is the 'effective' spin. Here we report that, if the magnitudes of the black hole spins are allowed to extend to high values, the effective spins for these systems indicate a 0.015 odds ratio against an aligned angular distribution compared to an isotropic one. When considering the effect of ten additional detections, this odds ratio decreases to 2.9 × 10 -7 against alignment. The existing preference for either an isotropic spin distribution or low spin magnitudes for the observed systems will be confirmed (or overturned) confidently in the near future.

Reconstruction of atomic effective potentials from isotropic scattering factors

International Nuclear Information System (INIS)

Romera, E.; Angulo, J.C.; Torres, J.J.

2002-01-01

We present a method for the approximate determination of one-electron effective potentials of many-electron systems from a finite number of values of the isotropic scattering factor. The method is based on the minimum cross-entropy technique. An application to some neutral ground-state atomic systems has been done within a Hartree-Fock framework

Magnetoelastic shear wave propagation in pre-stressed anisotropic media under gravity

Science.gov (United States)

Kumari, Nirmala; Chattopadhyay, Amares; Singh, Abhishek K.; Sahu, Sanjeev A.

2017-03-01

The present study investigates the propagation of shear wave (horizontally polarized) in two initially stressed heterogeneous anisotropic (magnetoelastic transversely isotropic) layers in the crust overlying a transversely isotropic gravitating semi-infinite medium. Heterogeneities in both the anisotropic layers are caused due to exponential variation (case-I) and linear variation (case-II) in the elastic constants with respect to the space variable pointing positively downwards. The dispersion relations have been established in closed form using Whittaker's asymptotic expansion and were found to be in the well-agreement to the classical Love wave equations. The substantial effects of magnetoelastic coupling parameters, heterogeneity parameters, horizontal compressive initial stresses, Biot's gravity parameter, and wave number on the phase velocity of shear waves have been computed and depicted by means of a graph. As a special case, dispersion equations have been deduced when the two layers and half-space are isotropic and homogeneous. The comparative study for both cases of heterogeneity of the layers has been performed and also depicted by means of graphical illustrations.

On the time-homogeneous Ornstein–Uhlenbeck process in the foreign exchange rates

Energy Technology Data Exchange (ETDEWEB)

Fonseca, Regina C.B. da, E-mail: regina@quimica-industrial.com [Department of Mathematics, Instituto Federal de Goiás, Goiânia, Goiás 74055-110 (Brazil); International Center for Condensed Matter Physics, Instituto de Física, Universidade de Brasília, Caixa Postal 04455, 70919-970, Brasília, Distrito Federal (Brazil); Matsushita, Raul Y. [Department of Statistics, Universidade de Brasília, 70919-970, Brasília, Distrito Federal (Brazil); Castro, Márcio T. de; Figueiredo, Annibal [International Center for Condensed Matter Physics, Instituto de Física, Universidade de Brasília, Caixa Postal 04455, 70919-970, Brasília, Distrito Federal (Brazil)

2015-10-02

Since Gaussianity and stationarity assumptions cannot be fulfilled by financial data, the time-homogeneous Ornstein–Uhlenbeck (THOU) process was introduced as a candidate model to describe time series of financial returns [1]. It is an Ornstein–Uhlenbeck (OU) process in which these assumptions are replaced by linearity and time-homogeneity. We employ the OU and THOU processes to analyze daily foreign exchange rates against the US dollar. We confirm that the OU process does not fit the data, while in most cases the first four cumulants patterns from data can be described by the THOU process. However, there are some exceptions in which the data do not follow linearity or time-homogeneity assumptions. - Highlights: • Gaussianity and stationarity assumptions replaced by linearity and time-homogeneity. • We revisit the time-homogeneous Ornstein–Uhlenbeck (THOU) process. • We employ the THOU process to analyze foreign exchange rates against the US dollar. • The first four cumulants patterns from data can be described by the THOU process.

On the time-homogeneous Ornstein–Uhlenbeck process in the foreign exchange rates

International Nuclear Information System (INIS)

Fonseca, Regina C.B. da; Matsushita, Raul Y.; Castro, Márcio T. de; Figueiredo, Annibal

2015-01-01

Since Gaussianity and stationarity assumptions cannot be fulfilled by financial data, the time-homogeneous Ornstein–Uhlenbeck (THOU) process was introduced as a candidate model to describe time series of financial returns [1]. It is an Ornstein–Uhlenbeck (OU) process in which these assumptions are replaced by linearity and time-homogeneity. We employ the OU and THOU processes to analyze daily foreign exchange rates against the US dollar. We confirm that the OU process does not fit the data, while in most cases the first four cumulants patterns from data can be described by the THOU process. However, there are some exceptions in which the data do not follow linearity or time-homogeneity assumptions. - Highlights: • Gaussianity and stationarity assumptions replaced by linearity and time-homogeneity. • We revisit the time-homogeneous Ornstein–Uhlenbeck (THOU) process. • We employ the THOU process to analyze foreign exchange rates against the US dollar. • The first four cumulants patterns from data can be described by the THOU process

MHODE: a local-homogeneity theory for improved source-parameter estimation of potential fields

Science.gov (United States)

Fedi, Maurizio; Florio, Giovanni; Paoletti, Valeria

2015-08-01

We describe a multihomogeneity theory for source-parameter estimation of potential fields. Similar to what happens for random source models, where the monofractal scaling-law has been generalized into a multifractal law, we propose to generalize the homogeneity law into a multihomogeneity law. This allows a theoretically correct approach to study real-world potential fields, which are inhomogeneous and so do not show scale invariance, except in the asymptotic regions (very near to or very far from their sources). Since the scaling properties of inhomogeneous fields change with the scale of observation, we show that they may be better studied at a set of scales than at a single scale and that a multihomogeneous model is needed to explain its complex scaling behaviour. In order to perform this task, we first introduce fractional-degree homogeneous fields, to show that: (i) homogeneous potential fields may have fractional or integer degree; (ii) the source-distributions for a fractional-degree are not confined in a bounded region, similarly to some integer-degree models, such as the infinite line mass and (iii) differently from the integer-degree case, the fractional-degree source distributions are no longer uniform density functions. Using this enlarged set of homogeneous fields, real-world anomaly fields are studied at different scales, by a simple search, at any local window W, for the best homogeneous field of either integer or fractional-degree, this yielding a multiscale set of local homogeneity-degrees and depth estimations which we call multihomogeneous model. It is so defined a new technique of source parameter estimation (Multi-HOmogeneity Depth Estimation, MHODE), permitting retrieval of the source parameters of complex sources. We test the method with inhomogeneous fields of finite sources, such as faults or cylinders, and show its effectiveness also in a real-case example. These applications show the usefulness of the new concepts, multihomogeneity and

Isotropic gates in large gamma detector arrays versus angular distributions

International Nuclear Information System (INIS)

Iacob, V.E.; Duchene, G.

1997-01-01

The quality of the angular distribution information extracted from high-fold gamma-gamma coincidence events is analyzed. It is shown that a correct quasi-isotropic gate setting, available at the modern large gamma-ray detector arrays, essentially preserves the quality of the angular information. (orig.)

Investigation of methods for hydroclimatic data homogenization

Science.gov (United States)

Steirou, E.; Koutsoyiannis, D.

2012-04-01

We investigate the methods used for the adjustment of inhomogeneities of temperature time series covering the last 100 years. Based on a systematic study of scientific literature, we classify and evaluate the observed inhomogeneities in historical and modern time series, as well as their adjustment methods. It turns out that these methods are mainly statistical, not well justified by experiments and are rarely supported by metadata. In many of the cases studied the proposed corrections are not even statistically significant. From the global database GHCN-Monthly Version 2, we examine all stations containing both raw and adjusted data that satisfy certain criteria of continuity and distribution over the globe. In the United States of America, because of the large number of available stations, stations were chosen after a suitable sampling. In total we analyzed 181 stations globally. For these stations we calculated the differences between the adjusted and non-adjusted linear 100-year trends. It was found that in the two thirds of the cases, the homogenization procedure increased the positive or decreased the negative temperature trends. One of the most common homogenization methods, 'SNHT for single shifts', was applied to synthetic time series with selected statistical characteristics, occasionally with offsets. The method was satisfactory when applied to independent data normally distributed, but not in data with long-term persistence. The above results cast some doubts in the use of homogenization procedures and tend to indicate that the global temperature increase during the last century is between 0.4°C and 0.7°C, where these two values are the estimates derived from raw and adjusted data, respectively.

Interbasis expansions for isotropic harmonic oscillator

Energy Technology Data Exchange (ETDEWEB)

Dong, Shi-Hai, E-mail: dongsh2@yahoo.com [Departamento de Física, Escuela Superior de Física y Matemáticas, Instituto Politécnico Nacional, Edificio 9, Unidad Profesional Adolfo López Mateos, Mexico D.F. 07738 (Mexico)

2012-03-12

The exact solutions of the isotropic harmonic oscillator are reviewed in Cartesian, cylindrical polar and spherical coordinates. The problem of interbasis expansions of the eigenfunctions is solved completely. The explicit expansion coefficients of the basis for given coordinates in terms of other two coordinates are presented for lower excited states. Such a property is occurred only for those degenerated states for given principal quantum number n. -- Highlights: ► Exact solutions of harmonic oscillator are reviewed in three coordinates. ► Interbasis expansions of the eigenfunctions is solved completely. ► This is occurred only for those degenerated states for given quantum number n.

Homogeneous crystal nucleation in polymers.

Science.gov (United States)

Schick, C; Androsch, R; Schmelzer, J W P

2017-11-15

The pathway of crystal nucleation significantly influences the structure and properties of semi-crystalline polymers. Crystal nucleation is normally heterogeneous at low supercooling, and homogeneous at high supercooling, of the polymer melt. Homogeneous nucleation in bulk polymers has been, so far, hardly accessible experimentally, and was even doubted to occur at all. This topical review summarizes experimental findings on homogeneous crystal nucleation in polymers. Recently developed fast scanning calorimetry, with cooling and heating rates up to 10 6 K s -1 , allows for detailed investigations of nucleation near and even below the glass transition temperature, including analysis of nuclei stability. As for other materials, the maximum homogeneous nucleation rate for polymers is located close to the glass transition temperature. In the experiments discussed here, it is shown that polymer nucleation is homogeneous at such temperatures. Homogeneous nucleation in polymers is discussed in the framework of the classical nucleation theory. The majority of our observations are consistent with the theory. The discrepancies may guide further research, particularly experiments to progress theoretical development. Progress in the understanding of homogeneous nucleation is much needed, since most of the modelling approaches dealing with polymer crystallization exclusively consider homogeneous nucleation. This is also the basis for advancing theoretical approaches to the much more complex phenomena governing heterogeneous nucleation.

A Dual Band Additively Manufactured 3D Antenna on Package with Near-Isotropic Radiation Pattern

KAUST Repository

Su, Zhen

2018-04-06

Internet of things (IoT) applications need wireless connectivity on devices with very small footprints, and in RF obscure environments. The antenna for such applications must work on multiple GSM bands (preferred choice for network connectivity), provide near isotropic radiation pattern to maintain orientation insensitive communication, be small in size so that it can be integrated with futuristic miniaturized IoT devices, and be low in cost to be implemented on billions of devices. This paper presents a novel 3D dual band near-isotropic wideband GSM antenna to fulfill these requirements. The antenna has been realized on the package of electronics through additive manufacturing to ensure efficient utilization of available space and lower cost. The proposed antenna consists of a meander line antenna that is folded on the faces of a 3D package with two variations, 0.375λ length for narrowband version and 0.67λ length for the wideband version. Theoretical conditions to achieve near isotropic radiation pattern with bent wire antennas on a 3D surface have been derived. The antenna has been optimized to operate with embedded electronics and a large metallic battery. The antenna provides 8.9% and 34.4% bandwidths, at 900 and 1800 MHz respectively with decent near isotropic radiation behavior.

Reflection and refraction of elastic waves at a corrugated interface in a bi-material transversely isotropic full-space

International Nuclear Information System (INIS)

Shad-Manamen, N.; Eskandari-Ghadi, M.

2008-01-01

The existing theory for wave propagation through a soil layer are not compatible with the real soil layers because in the theory the layers are flat and the sub-layers are parallel, while in real the soil layers are not flat and they may not be parallel. Thus, wave propagations through a corrugated interface are so important. In this paper, a two dimensional SH-wave propagation through a corrugated interface between two linear transversely isotropic half-spaces is assessed. In order to do this, Lord Rayleigh's method is accepted to express the non-flat surface by a Fourier series. In this way, the amplitude of the reflected and transmitted waves is analytically determined in terms of the incident SH-wave amplitude. It is shown that except for the regular reflected and refracted waves, some irregular reflected and refracted waves are exist, and the amplitudes of these waves vary in terms of the angle and frequency of incident wave, equation of surface, and the material properties of the domains. The numerical computations for some cases of different amplitude/wave-length ratio of the interface are done. This work is an extension of Asano's paper (1960) for a more complicated interface, where more non-zero coefficients are considered in expressing the equation of surface in the form of Fourier series. The analytical results for some simpler case of isotropic domain are collapsed on Asano's results (1960). In addition, the numerical evaluation is in good agreement with Asano's.

Evolution of the bonding mechanism of ZnO under isotropic compression: A first-principles study

International Nuclear Information System (INIS)

Zhou, G.C.; Sun, L.Z.; Wang, J.B.; Zhong, X.L.; Zhou, Y.C.

2008-01-01

The electronic structure and the bonding mechanism of ZnO under isotropic pressure have been studied by using the full-potential linear augmented plane wave (FP-LAPW) method within the density-functional theory (DFT) based on LDA+U exchange correlation (EXC) potential. We used the theory of Atoms in Molecules (AIM) method to analyze the change of the charge transfer and the bonding strength under isotropic pressure. The results of the theoretical analysis show that charge transfer between Zn and O atomic basins nearly linearly increases with the increasing pressure. Charge density along the Zn-O bond increases under the high pressure. The bonding strength and the ionicity of Zn-O bond also increase with the increasing pressure. The linear evolution process of the bonding mechanism under isotropic pressure was shown clearly in the present paper

A scheme to calculate higher-order homogenization as applied to micro-acoustic boundary value problems

Science.gov (United States)

Vagh, Hardik A.; Baghai-Wadji, Alireza

2008-12-01

Current technological challenges in materials science and high-tech device industry require the solution of boundary value problems (BVPs) involving regions of various scales, e.g. multiple thin layers, fibre-reinforced composites, and nano/micro pores. In most cases straightforward application of standard variational techniques to BVPs of practical relevance necessarily leads to unsatisfactorily ill-conditioned analytical and/or numerical results. To remedy the computational challenges associated with sub-sectional heterogeneities various sophisticated homogenization techniques need to be employed. Homogenization refers to the systematic process of smoothing out the sub-structural heterogeneities, leading to the determination of effective constitutive coefficients. Ordinarily, homogenization involves a sophisticated averaging and asymptotic order analysis to obtain solutions. In the majority of the cases only zero-order terms are constructed due to the complexity of the processes involved. In this paper we propose a constructive scheme for obtaining homogenized solutions involving higher order terms, and thus, guaranteeing higher accuracy and greater robustness of the numerical results. We present

Feasibility Study of Aseptic Homogenization: Affecting Homogenization Steps on Quality of Sterilized Coconut Milk

Directory of Open Access Journals (Sweden)

Phungamngoen Chanthima

2016-01-01

Full Text Available Coconut milk is one of the most important protein-rich food sources available today. Separation of an emulsion into an aqueous phase and cream phase is commonly occurred and this leads an unacceptably physical defect of either fresh or processed coconut milk. Since homogenization steps are known to affect the stability of coconut milk. This work was aimed to study the effect of homogenization steps on quality of coconut milk. The samples were subject to high speed homogenization in the range of 5000-15000 rpm under sterilize temperatures at 120-140 °C for 15 min. The result showed that emulsion stability increase with increasing speed of homogenization. The lower fat particles were generated and easy to disperse in continuous phase lead to high stability. On the other hand, the stability of coconut milk decreased, fat globule increased, L value decreased and b value increased when the high sterilization temperature was applied. Homogenization after heating led to higher stability than homogenization before heating due to the reduced particle size of coconut milk after aggregation during sterilization process. The results implied that homogenization after sterilization process might play an important role on the quality of the sterilized coconut milk.

Nonconformal scalar field in uniform isotropic space and the method of Hamiltonian diagonalization

International Nuclear Information System (INIS)

Pavlov, Yu.V.

2001-01-01

One diagonalized metric Hamiltonian of scalar field with arbitrary relation with curvature in N-dimensional uniform isotropic space. One derived spectrum of energies of the appropriate quasi-particles. One calculated energy of quasi-particle appropriate to the canonical Hamiltonian diagonal shape. One structured a modified tensor of energy-pulse with the following features. In case of conformal scalar field it coincides with the metric tensor of energy-pulse. When it is diagonalized the energies of the appropriate particles of nonconformal field are equal to oscillation frequency and the number of such particles produced in non-stationary metric is the finite one. It is shown that Hamiltonian calculated on the basis of the modified tensor of energy-pulse may be derived as a canonical one at certain selection of variables [ru

Migration using a transversely isotropic medium with symmetry normal to the reflector dip

KAUST Repository

Alkhalifah, Tariq Ali; Sava, P.

2011-01-01

A transversely isotropic (TI) model in which the tilt is constrained to be normal to the dip (DTI model) allows for simplifications in the imaging and velocity model building efforts as compared to a general TI (TTI) model. Although this model cannot be represented physically in all situations, for example, in the case of conflicting dips, it handles arbitrary reflector orientations under the assumption of symmetry axis normal to the dip. Using this assumption, we obtain efficient downward continuation algorithms compared to the general TTI ones, by utilizing the reflection features of such a model. Phase-shift migration can be easily extended to approximately handle lateral inhomogeneity using, for example, the split-step approach. This is possible because, unlike the general TTI case, the DTI model reduces to VTI for zero dip. These features enable a process in which we can extract velocity information by including tools that expose inaccuracies in the velocity model in the downward continuation process. We test this model on synthetic data corresponding to a general TTI medium and show its resilience. 2011 Tariq Alkhalifah and Paul Sava.

7 CFR 58.636 - Homogenization.

Science.gov (United States)

2010-01-01

... 7 Agriculture 3 2010-01-01 2010-01-01 false Homogenization. 58.636 Section 58.636 Agriculture Regulations of the Department of Agriculture (Continued) AGRICULTURAL MARKETING SERVICE (Standards... Procedures § 58.636 Homogenization. Homogenization of the pasteurized mix shall be accomplished to...

Transformation optics, isotropic chiral media and non-Riemannian geometry

International Nuclear Information System (INIS)

Horsley, S A R

2011-01-01

The geometrical interpretation of electromagnetism in transparent media (transformation optics) is extended to include chiral media that are isotropic but inhomogeneous. It was found that such media may be described through introducing the non-Riemannian geometrical property of torsion into the Maxwell equations, and it is shown how such an interpretation may be applied to the design of optical devices.

Migration velocity analysis using a transversely isotropic medium with tilt normal to the reflector dip

KAUST Repository

Alkhalifah, T.

2010-06-13

A transversely isotropic model in which the tilt is constrained to be normal to the dip (DTI model) allows for simplifications in the imaging and velocity model building efforts as compared to a general TTI model. Though this model, in some cases, can not be represented physically like in the case of conflicting dips, it handles all dips with the assumption of symmetry axis normal to the dip. It provides a process in which areas that meet this feature is handled properly. We use efficient downward continuation algorithms that utilizes the reflection features of such a model. For lateral inhomogeneity, phase shift migration can be easily extended to approximately handle lateral inhomogeneity, because unlike the general TTI case the DTI model reduces to VTI for zero dip. We also equip these continuation algorithms with tools that expose inaccuracies in the velocity. We test this model on synthetic data of general TTI nature and show its resilience even couping with complex models like the recently released anisotropic BP model.

Benchmarking monthly homogenization algorithms

Science.gov (United States)

Venema, V. K. C.; Mestre, O.; Aguilar, E.; Auer, I.; Guijarro, J. A.; Domonkos, P.; Vertacnik, G.; Szentimrey, T.; Stepanek, P.; Zahradnicek, P.; Viarre, J.; Müller-Westermeier, G.; Lakatos, M.; Williams, C. N.; Menne, M.; Lindau, R.; Rasol, D.; Rustemeier, E.; Kolokythas, K.; Marinova, T.; Andresen, L.; Acquaotta, F.; Fratianni, S.; Cheval, S.; Klancar, M.; Brunetti, M.; Gruber, C.; Prohom Duran, M.; Likso, T.; Esteban, P.; Brandsma, T.

2011-08-01

The COST (European Cooperation in Science and Technology) Action ES0601: Advances in homogenization methods of climate series: an integrated approach (HOME) has executed a blind intercomparison and validation study for monthly homogenization algorithms. Time series of monthly temperature and precipitation were evaluated because of their importance for climate studies and because they represent two important types of statistics (additive and multiplicative). The algorithms were validated against a realistic benchmark dataset. The benchmark contains real inhomogeneous data as well as simulated data with inserted inhomogeneities. Random break-type inhomogeneities were added to the simulated datasets modeled as a Poisson process with normally distributed breakpoint sizes. To approximate real world conditions, breaks were introduced that occur simultaneously in multiple station series within a simulated network of station data. The simulated time series also contained outliers, missing data periods and local station trends. Further, a stochastic nonlinear global (network-wide) trend was added. Participants provided 25 separate homogenized contributions as part of the blind study as well as 22 additional solutions submitted after the details of the imposed inhomogeneities were revealed. These homogenized datasets were assessed by a number of performance metrics including (i) the centered root mean square error relative to the true homogeneous value at various averaging scales, (ii) the error in linear trend estimates and (iii) traditional contingency skill scores. The metrics were computed both using the individual station series as well as the network average regional series. The performance of the contributions depends significantly on the error metric considered. Contingency scores by themselves are not very informative. Although relative homogenization algorithms typically improve the homogeneity of temperature data, only the best ones improve precipitation data

The determination of a neutron source position in an unknown homogeneous medium: The planar case

International Nuclear Information System (INIS)

Dubinski, S.; Talmor, A.; Presler, O.; Tshuva, A.; Yaar, I.; Orion, I.; Alfassi, Z.B.

2005-01-01

The possibility of localization of an unknown neutron source in various bulky homogeneous media (box) was studied. For the planar case, two 3 He detectors on the opposite faces of the box were used. A constant polypropylene shield around the box and detectors was used to eliminate the varying contribution from the environment to increase count rates of the detectors and to protect the experimentalist. It is shown that the location of a single small neutron emitting source in a large box can be found to a better than 7% by using two neutron detectors positioned on parallel faces of the box, coplanar with the source. The localization requires measurement of the count rate of both the unknown source and an extra source positioned on one of the faces of the box. The localization is based on the finding that the ratio of the count rates of the two detectors is an exponential function of the distance of the source from one of the detectors

On ternary species mixing and combustion in isotropic turbulence at high pressure

Science.gov (United States)

Lou, Hong; Miller, Richard S.

2004-05-01

Effects of Soret and Dufour cross-diffusion, whereby both concentration and thermal diffusion occur in the presence of mass fraction, temperature, and pressure gradients, are investigated in the context of both binary and ternary species mixing and combustion in isotropic turbulence at large pressure. The compressible flow formulation is based on a cubic real-gas state equation, and includes generalized forms for heat and mass diffusion derived from nonequilibrium thermodynamics and fluctuation theory. A previously derived formulation of the generalized binary species heat and mass fluxes is first extended to the case of ternary species, and appropriate treatment of the thermal and mass diffusion factors is described. Direct numerical simulations (DNS) are then conducted for both binary and ternary species mixing and combustion in stationary isotropic turbulence. Mean flow temperatures and pressures of =700 K and =45 atm are considered to ensure that all species mixtures remain in the supercritical state such that phase changes do not occur. DNS of ternary species systems undergoing both pure mixing and a simple chemical reaction of the form O2+N2→2NO are then conducted. It is shown that stationary scalar states previously observed for binary mixing persist for the ternary species problem as well; however, the production and magnitude of the scalar variance is found to be altered for the intermediate molecular weight species as compared to the binary species case. The intermediate molecular weight species produces a substantially smaller scalar variance than the remaining species for all flows considered. For combustion of nonstoichiometric mixtures, a binary species mixture, characterized by stationary scalar states, results at long times after the lean reactant is depleted. The form of this final scalar distribution is observed to be similar to that found in the binary flow situation. A series of lower resolution simulations for a variety of species is then

Spontaneous radiation of a chiral molecule located near a half-space of a bi-isotropic material

Science.gov (United States)

Guzatov, D. V.; Klimov, V. V.; Poprukailo, N. S.

2013-04-01

Analytical expressions for the rate of spontaneous emission from a chiral (optically active) molecule located near a half-space occupied by a chiral (bi-isotropic) material have been obtained and analyzed in detail. It is established that the rates of spontaneous emission from the "right" and "left" enantiomers of molecules occurring near the chiral medium may significantly differ in cases of chiral materials with (i) both negative dielectric permittivity and magnetic permeability (DNG metamaterial) and (ii) negative permeability and positive permittivity (MNG metamaterial). Based on this phenomenon, DMG and MNG metamaterials can be used to create devices capable of separating right and left enantiomers in racemic mixtures.

Spontaneous radiation of a chiral molecule located near a half-space of a bi-isotropic material

Energy Technology Data Exchange (ETDEWEB)

Guzatov, D. V., E-mail: vklimov@sci.lebedev.ru [Yanka Kupala Grodno State University (Belarus); Klimov, V. V., E-mail: klimov256@gmail.com [Russian Academy of Sciences, Lebedev Physical Institute (Russian Federation); Poprukailo, N. S. [Yanka Kupala Grodno State University (Belarus)

2013-04-15

Analytical expressions for the rate of spontaneous emission from a chiral (optically active) molecule located near a half-space occupied by a chiral (bi-isotropic) material have been obtained and analyzed in detail. It is established that the rates of spontaneous emission from the 'right' and 'left' enantiomers of molecules occurring near the chiral medium may significantly differ in cases of chiral materials with (i) both negative dielectric permittivity and magnetic permeability (DNG metamaterial) and (ii) negative permeability and positive permittivity (MNG metamaterial). Based on this phenomenon, DMG and MNG metamaterials can be used to create devices capable of separating right and left enantiomers in racemic mixtures.

Spontaneous radiation of a chiral molecule located near a half-space of a bi-isotropic material

International Nuclear Information System (INIS)

Guzatov, D. V.; Klimov, V. V.; Poprukailo, N. S.

2013-01-01

Analytical expressions for the rate of spontaneous emission from a chiral (optically active) molecule located near a half-space occupied by a chiral (bi-isotropic) material have been obtained and analyzed in detail. It is established that the rates of spontaneous emission from the “right” and “left” enantiomers of molecules occurring near the chiral medium may significantly differ in cases of chiral materials with (i) both negative dielectric permittivity and magnetic permeability (DNG metamaterial) and (ii) negative permeability and positive permittivity (MNG metamaterial). Based on this phenomenon, DMG and MNG metamaterials can be used to create devices capable of separating right and left enantiomers in racemic mixtures.

Isotopic homogeneity of iron in the early solar nebula.

Science.gov (United States)

Zhu, X K; Guo, Y; O'Nions, R K; Young, E D; Ash, R D

2001-07-19

The chemical and isotopic homogeneity of the early solar nebula, and the processes producing fractionation during its evolution, are central issues of cosmochemistry. Studies of the relative abundance variations of three or more isotopes of an element can in principle determine if the initial reservoir of material was a homogeneous mixture or if it contained several distinct sources of precursor material. For example, widespread anomalies observed in the oxygen isotopes of meteorites have been interpreted as resulting from the mixing of a solid phase that was enriched in 16O with a gas phase in which 16O was depleted, or as an isotopic 'memory' of Galactic evolution. In either case, these anomalies are regarded as strong evidence that the early solar nebula was not initially homogeneous. Here we present measurements of the relative abundances of three iron isotopes in meteoritic and terrestrial samples. We show that significant variations of iron isotopes exist in both terrestrial and extraterrestrial materials. But when plotted in a three-isotope diagram, all of the data for these Solar System materials fall on a single mass-fractionation line, showing that homogenization of iron isotopes occurred in the solar nebula before both planetesimal accretion and chondrule formation.

Accounting for Fiber Bending Effects in Homogenization of Long Fiber Reinforced Composites

DEFF Research Database (Denmark)

Poulios, Konstantinos; Niordson, Christian Frithiof

2015-01-01

The present work deals with homogenized finite-element models of long fiber reinforced composite materials in the context of studying compressive failure modes such as the formation of kink bands and fiber micro-buckling. Compared to finite-element models with an explicit discretization of the ma......The present work deals with homogenized finite-element models of long fiber reinforced composite materials in the context of studying compressive failure modes such as the formation of kink bands and fiber micro-buckling. Compared to finite-element models with an explicit discretization...... of the material micro-structure including individual fibers, homogenized models are computationally more efficient and hence more suitable for modeling of larger and complex structure. Nevertheless, the formulation of homogenized models is more complicated, especially if the bending stiffness of the reinforcing...... fibers is to be taken into account. In that case, so-called higher order strain terms need to be considered. In this paper, important relevant works from the literature are discussed and numerical results from a new homogenization model are presented. The new model accounts for two independent...

On the time-homogeneous Ornstein-Uhlenbeck process in the foreign exchange rates

Science.gov (United States)

da Fonseca, Regina C. B.; Matsushita, Raul Y.; de Castro, Márcio T.; Figueiredo, Annibal

2015-10-01

Since Gaussianity and stationarity assumptions cannot be fulfilled by financial data, the time-homogeneous Ornstein-Uhlenbeck (THOU) process was introduced as a candidate model to describe time series of financial returns [1]. It is an Ornstein-Uhlenbeck (OU) process in which these assumptions are replaced by linearity and time-homogeneity. We employ the OU and THOU processes to analyze daily foreign exchange rates against the US dollar. We confirm that the OU process does not fit the data, while in most cases the first four cumulants patterns from data can be described by the THOU process. However, there are some exceptions in which the data do not follow linearity or time-homogeneity assumptions.

Comment to “qS-waves in a vicinity of the axis of symmetry of homogeneous transversely isotropic media”, by M. Popov, G.F. Passos, and M.A. Botelho [Wave Motion 42 (2005) 191–201

Czech Academy of Sciences Publication Activity Database

Vavryčuk, Václav

2006-01-01

Roč. 44, č. 2 (2006), s. 128-136 ISSN 0165-2125 R&D Projects: GA AV ČR IAA3012309 Institutional research plan: CEZ:AV0Z30120515 Keywords : seismic waves * transversely isotropic media * ray theory Subject RIV: DC - Siesmology, Volcanology, Earth Structure Impact factor: 1.178, year: 2006

Enhancement of the nonlinear optical absorption of the E7 liquid crystal at the nematic-isotropic transition

International Nuclear Information System (INIS)

Gomez, S.L.; Lenart, V.M.; Bechtold, I.H.; Figueiredo Neto, A.M.

2012-01-01

We present an experimental study of the nonlinear optical absorption of the eutectic mixture E7 at the nematic-isotropic phase transition by the Z-scan technique, under continuous-wave excitation at 532 nm. In the nematic region, the effective nonlinear optical coefficient P, which vanishes in the isotropic phase, is negative for the extraordinary beam and positive for an ordinary beam. The parameter SNL, whose definition in terms of the nonlinear absorption coefficient follows the definition of the optical-order parameter in terms of the linear dichroic ratio, behaves like an order parameter with critical exponent 0.22 ± 0.05, in good agreement with the tricritical hypothesis for the nematic isotropic transition. (author)

A computational analysis on homogeneous-heterogeneous mechanism in Carreau fluid flow

Science.gov (United States)

Khan, Imad; Rehman, Khalil Ur; Malik, M. Y.; Shafquatullah

2018-03-01

In this article magnetohydrodynamic Carreau fluid flow towards stretching cylinder is considered in the presence of homogeneous-heterogeneous reactions effect. The flow model is structured by utilizing theoretical grounds. For the numerical solution a shooting method along with Runge-Kutta algorithm is executed. The outcomes are provided through graphs. It is observed that the Carreau fluid concentration shows decline values via positive iterations of homogeneous-heterogeneous reaction parameters towards both shear thinning and thickening case. The present work is certified through comparison with already existing literature in a limiting sense.

Revisiting polarimetry near the isotropic point of an optically active, non-enantiomorphous, molecular crystal.

Science.gov (United States)

Martin, Alexander T; Tan, Melissa; Nichols, Shane M; Timothy, Emily; Kahr, Bart

2018-07-01

Accurate polarimetric measurements of the optical activity of crystals along low symmetry directions are facilitated by isotropic points, frequencies where dispersion curves of eigenrays cross and the linear birefringence disappears. We report here the optical properties and structure of achiral, uniaxial (point group D 2d ) potassium trihydrogen di-(cis-4-cyclohexene-1,2-dicarboxylate) dihydrate, whose isotropic point was previously detected (S. A. Kim, C. Grieswatch, H. Küppers, Zeit. Krist. 1993; 208:219-222) and exploited for a singular measurement of optical activity normal to the optic axis. The crystal structure associated with the aforementioned study was never published. We report it here, confirming the space group assignment I 4¯c2, along with the frequency dependence of the fundamental optical properties and the constitutive tensors by fitting optical dispersion relations to measured Mueller matrix spectra. k-Space maps of circular birefringence and of the Mueller matrix near the isotropic wavelength are measured and simulated. The signs of optical rotation are correlated with the absolute crystallographic directions. © 2018 Wiley Periodicals, Inc.

Liquid crystalline states of surfactant solutions of isotropic micelles

International Nuclear Information System (INIS)

Bagdassarian, C.; Gelbart, W.M.; Ben-Shaul, A.

1988-01-01

We consider micellar solutions whose surfactant molecules prefer strongly to form small, globular aggregates in the absence of intermicellar interactions. At sufficiently high volume fraction of surfactant, the isotropic phase of essentially spherical micelles is shown to be unstable with respect to an orientationally ordered (nematic) state of rodlike aggregates. This behavior is relevant to the phase diagrams reported for important classes of aqueous amphiphilic solutions

A numerical homogenization method for heterogeneous, anisotropic elastic media based on multiscale theory

KAUST Repository

Gao, Kai

2015-06-05

The development of reliable methods for upscaling fine-scale models of elastic media has long been an important topic for rock physics and applied seismology. Several effective medium theories have been developed to provide elastic parameters for materials such as finely layered media or randomly oriented or aligned fractures. In such cases, the analytic solutions for upscaled properties can be used for accurate prediction of wave propagation. However, such theories cannot be applied directly to homogenize elastic media with more complex, arbitrary spatial heterogeneity. Therefore, we have proposed a numerical homogenization algorithm based on multiscale finite-element methods for simulating elastic wave propagation in heterogeneous, anisotropic elastic media. Specifically, our method used multiscale basis functions obtained from a local linear elasticity problem with appropriately defined boundary conditions. Homogenized, effective medium parameters were then computed using these basis functions, and the approach applied a numerical discretization that was similar to the rotated staggered-grid finite-difference scheme. Comparisons of the results from our method and from conventional, analytical approaches for finely layered media showed that the homogenization reliably estimated elastic parameters for this simple geometry. Additional tests examined anisotropic models with arbitrary spatial heterogeneity in which the average size of the heterogeneities ranged from several centimeters to several meters, and the ratio between the dominant wavelength and the average size of the arbitrary heterogeneities ranged from 10 to 100. Comparisons to finite-difference simulations proved that the numerical homogenization was equally accurate for these complex cases.

direct method of analysis of an isotropic rectangular plate direct

African Journals Online (AJOL)

eobe

This work evaluates the static analysis of an isotropic rectangular plate with various the static analysis ... method according to Ritz is used to obtain the total potential energy of the plate by employing the used to ..... for rectangular plates analysis, as the behavior of the ... results obtained by previous research work that used.

The sup-norm vs. the norm of the coefficients: equivalence constants for homogeneous polynomials

OpenAIRE

Galicer, Daniel; Mansilla, Martín; Muro, Santiago

2016-01-01

Let $A_{p,r}^m(n)$ be the best constant that fulfills the following inequality: for every $m$-homogeneous polynomial $P(z) = \\sum_{|\\alpha|=m} a_{\\alpha} z^{\\alpha}$ in $n$ complex variables, $$\\big( \\sum_{|\\alpha|=m} |a_{\\alpha}|^{r} \\big)^{1/r} \\leq A_{p,r}^m(n) \\sup_{z \\in B_{\\ell_p^n}} \\big|P(z) \\big| .$$ For every degree $m$, and a wide range of values of $ p,r \\in [1,\\infty]$ (including any $r$ in the case $p \\in [1,2]$, and any $r$ and $p$ for the 2-homogeneous case), we give the corre...

The SPH homogeneization method

International Nuclear Information System (INIS)

Kavenoky, Alain

1978-01-01

The homogeneization of a uniform lattice is a rather well understood topic while difficult problems arise if the lattice becomes irregular. The SPH homogeneization method is an attempt to generate homogeneized cross sections for an irregular lattice. Section 1 summarizes the treatment of an isolated cylindrical cell with an entering surface current (in one velocity theory); Section 2 is devoted to the extension of the SPH method to assembly problems. Finally Section 3 presents the generalisation to general multigroup problems. Numerical results are obtained for a PXR rod bundle assembly in Section 4

Homogeneity of Inorganic Glasses

DEFF Research Database (Denmark)

Jensen, Martin; Zhang, L.; Keding, Ralf

2011-01-01

Homogeneity of glasses is a key factor determining their physical and chemical properties and overall quality. However, quantification of the homogeneity of a variety of glasses is still a challenge for glass scientists and technologists. Here, we show a simple approach by which the homogeneity...... of different glass products can be quantified and ranked. This approach is based on determination of both the optical intensity and dimension of the striations in glasses. These two characteristic values areobtained using the image processing method established recently. The logarithmic ratio between...

Photo-electret effects in homogenous semiconductors

International Nuclear Information System (INIS)

Nabiev, G.A.

2004-01-01

In the given work is shown the opportunity and created the theory of photo-electret condition in semiconductors with Dember mechanism of photo-voltage generation. Photo-electret of such type can be created, instead of traditional and without an external field as a result of only one illumination. Polar factor, in this case, is the distinction of electrons and holes mobility. Considered the multilayered structure with homogeneous photoactive micro areas shared by the layers, which are interfering to alignment of carriers concentration. We consider, that the homogeneous photoactive areas contain deep levels of stick. Because of addition of elementary photo voltage in separate micro photo cells it is formed the abnormal-large photo voltage (APV-effect). Let's notice, that Dember photo-voltage in a separate micro photo-cell ≤kT/q. From the received expressions, in practically important, special case, when quasi- balance between valent zone and stick levels established in much more smaller time, than free hole lifetime, and we received, that photo-voltage is relaxing. Comparing of the received expressions with the laws of photo voltage attenuation in p-n- junction structures shows their identity; the difference is only in absolute meanings of photo voltage. During the illumination in the semiconductor are created the superfluous concentration of charge carriers and part from them stays at deep levels. At de-energizing light there is a gradual generation of carriers located at these levels

Active isotropic slabs: conditions for amplified reflection

Science.gov (United States)

Perez, Liliana I.; Matteo, Claudia L.; Etcheverry, Javier; Duplaá, María Celeste

2012-12-01

We analyse in detail the necessary conditions to obtain amplified reflection (AR) in isotropic interfaces when a plane wave propagates from a transparent medium towards an active one. First, we demonstrate analytically that AR is not possible if a single interface is involved. Then, we study the conditions for AR in a very simple configuration: normal incidence on an active slab immersed in transparent media. Finally, we develop an analysis in the complex plane in order to establish a geometrical method that not only describes the behaviour of active slabs but also helps to simplify the calculus.

Active isotropic slabs: conditions for amplified reflection

International Nuclear Information System (INIS)

Perez, Liliana I; Duplaá, María Celeste; Matteo, Claudia L; Etcheverry, Javier

2012-01-01

We analyse in detail the necessary conditions to obtain amplified reflection (AR) in isotropic interfaces when a plane wave propagates from a transparent medium towards an active one. First, we demonstrate analytically that AR is not possible if a single interface is involved. Then, we study the conditions for AR in a very simple configuration: normal incidence on an active slab immersed in transparent media. Finally, we develop an analysis in the complex plane in order to establish a geometrical method that not only describes the behaviour of active slabs but also helps to simplify the calculus. (paper)

Numerical simulation of homogenization time measurement by probes with different volume size

International Nuclear Information System (INIS)

Thyn, J.; Novy, M.; Zitny, R.; Mostek, M.; Jahoda, M.

2004-01-01

Results of continuous homogenization time measurement of liquid in a stirred tank depend on the scale of scrutiny. Experimental techniques use a probe, which is situated inside as a conductivity method, or outside of the tank as in the case of gamma-radiotracer methods. Expected value of homogenization time evaluated for a given degree of homogenization is higher when using the conductivity method because the conductivity probe measures relatively small volume in contrast to application of radiotracer, when the volume is much greater. Measurement through the wall of tank is a great advantage of radiotracer application but a comparison of the results with another method supposes a determination of measured volume, which is not easy. Simulation of measurement by CFD code can help to solve the problem. Methodology for CFD simulation of radiotracer experiments was suggested. Commercial software was used for simulation of liquid homogenization in mixed vessel with Rushton turbine. Numerical simulation of liquid homogenization time by CFD for different values of detected volume was confronted with measurement of homogenization time with conductivity probe and with different radioisotopes 198 Au, 82 Br and 24 Na. Detected size of the tank volume was affected by different energy of radioisotope used. (author)

Effect of homogenization on the properties and microstructure of Mozzarella cheese from buffalo milk.

Science.gov (United States)

Abd El-Gawad, Mona A M; Ahmed, Nawal S; El-Abd, M M; Abd El-Rafee, S

2012-04-02

The name pasta filata refers to a unique plasticizing and texturing treatments of the fresh curd in hot water that imparts to the finished cheese its characteristic fibrous structure and melting properties. Mozzarella cheese made from standardized homogenized and non-homogenized buffalo milk with 3 and 1.5%fat. The effect of homogenization on rheological, microstructure and sensory evaluation was carried out. Fresh raw buffalo milk and starter cultures of Streptococcus thermophilus and Lactobacillus delbrueckii ssp. bulgaricus were used. The coagulants were calf rennet powder (HA-LA). Standardized buffalo milk was homogenized at 25 kg/cm2 pressure after heating to 60°C using homogenizer. Milk and cheese were analysed. Microstructure of the cheese samples was investigated either with an application of transmission or scanning electron microscope. Statistical analyses were applied on the obtained data. Soluble nitrogen total volatile free fatty acids, soluble tyrosine and tryptophan increased with using homogenized milk and also, increased with relatively decrease in case of homogenized Mozzarella cheese. Meltability of Mozzarella cheese increased with increasing the fat content and storage period and decrease with homogenization. Mozzarella cheese firmness increased with homogenization and also, increased with progressing of storage period. Flavour score, appearance and total score of Mozzarella cheese increased with homogenization and storage period progress, while body and texture score decreased with homogenization and increased with storage period progress. Microstructure of Mozzarella cheese showed the low fat cheese tends to be harder, more crumbly and less smooth than normal. Curd granule junctions were prominent in non-homogenized milk cheese. Homogenization of milk cheese caused changes in the microstructure of the Mozzarella cheese. Microstructure studies of cheese revealed that cheese made from homogenized milk is smoother and has a finer texture than

Electrochemical isotropic texturing of mc-Si wafers in KOH solution

International Nuclear Information System (INIS)

Abburi, M.; Boström, T.; Olefjord, I.

2013-01-01

Boron doped multicrystalline Si-wafers were anodically polarized in 2 M KOH and 4 M KOH at 40 °C and 50 °C. The applied potentials were 25 V, 30 V, 40 V and 50 V. The morphology of the textured surfaces, the surface products and the light reflectivity were analyzed by utilizing SEM, XPS and Lambda UV/Vis/NIR spectrophotometer, respectively. Isotropic texturing was obtained. The lowest average reflectivity, 17%, was achieved after pre-etching for 10 min and polarization at 40 V for 10 min in 4 M KOH at 50 °C. That reflection value is half of that measured on a chemical pre-etched surface, 34%. By increasing the voltage to 50 V the reflectivity rises to 28%. Polarizations to 25 V and 30 V at 50 °C in both solutions give local pores in the μm-range. The etch attack initiation is located at protrusions on the surface. At 40 V and 50 V in both solutions the pores are extended onto the entire surface. The width of the pores is about 10 μm. Inside the micro-pores, nm-pores are formed; their lateral size is in the range 100 nm–200 nm. A mechanism for the anodic dissolution reactions is discussed. - Highlights: ► A method to form isotropic textures on mc-Si wafers in KOH solution is presented. ► The method is based on anodic polarization of silicon in KOH at high potentials. ► Evolution of surface morphology is studied by varying the etch parameters. ► Isotropic textures with lowest average reflectivity are obtained at 40 V. ► A reaction model for texturing mechanism is discussed in the light of XPS data

On two-dimensionalization of three-dimensional turbulence in shell models

DEFF Research Database (Denmark)

Chakraborty, Sagar; Jensen, Mogens Høgh; Sarkar, A.

2010-01-01

Applying a modified version of the Gledzer-Ohkitani-Yamada (GOY) shell model, the signatures of so-called two-dimensionalization effect of three-dimensional incompressible, homogeneous, isotropic fully developed unforced turbulence have been studied and reproduced. Within the framework of shell m......-similar PDFs for longitudinal velocity differences are also presented for the rotating 3D turbulence case....

Reflector homogenization

Energy Technology Data Exchange (ETDEWEB)

Sanchez, R.; Ragusa, J.; Santandrea, S. [Commissariat a l' Energie Atomique, Direction de l' Energie Nucleaire, Service d' Etudes de Reacteurs et de Modelisation Avancee, CEA de Saclay, DM2S/SERMA 91 191 Gif-sur-Yvette cedex (France)]. e-mail: richard.sanchez@cea.fr

2004-07-01

The problem of the determination of a homogeneous reflector that preserves a set of prescribed albedo is considered. Duality is used for a direct estimation of the derivatives needed in the iterative calculation of the optimal homogeneous cross sections. The calculation is based on the preservation of collapsed multigroup albedo obtained from detailed reference calculations and depends on the low-order operator used for core calculations. In this work we analyze diffusion and transport as low-order operators and argue that the P{sub 0} transfers are the best choice for the unknown cross sections to be adjusted. Numerical results illustrate the new approach for SP{sub N} core calculations. (Author)

Reflector homogenization

International Nuclear Information System (INIS)

Sanchez, R.; Ragusa, J.; Santandrea, S.

2004-01-01

The problem of the determination of a homogeneous reflector that preserves a set of prescribed albedo is considered. Duality is used for a direct estimation of the derivatives needed in the iterative calculation of the optimal homogeneous cross sections. The calculation is based on the preservation of collapsed multigroup albedo obtained from detailed reference calculations and depends on the low-order operator used for core calculations. In this work we analyze diffusion and transport as low-order operators and argue that the P 0 transfers are the best choice for the unknown cross sections to be adjusted. Numerical results illustrate the new approach for SP N core calculations. (Author)

Hybrid diffusion–transport spatial homogenization method

International Nuclear Information System (INIS)

Kooreman, Gabriel; Rahnema, Farzad

2014-01-01

Highlights: • A new hybrid diffusion–transport homogenization method. • An extension of the consistent spatial homogenization (CSH) transport method. • Auxiliary cross section makes homogenized diffusion consistent with heterogeneous diffusion. • An on-the-fly re-homogenization in transport. • The method is faster than fine-mesh transport by 6–8 times. - Abstract: A new hybrid diffusion–transport homogenization method has been developed by extending the consistent spatial homogenization (CSH) transport method to include diffusion theory. As in the CSH method, an “auxiliary cross section” term is introduced into the source term, making the resulting homogenized diffusion equation consistent with its heterogeneous counterpart. The method then utilizes an on-the-fly re-homogenization in transport theory at the assembly level in order to correct for core environment effects on the homogenized cross sections and the auxiliary cross section. The method has been derived in general geometry and tested in a 1-D boiling water reactor (BWR) core benchmark problem for both controlled and uncontrolled configurations. The method has been shown to converge to the reference solution with less than 1.7% average flux error in less than one third the computational time as the CSH method – 6 to 8 times faster than fine-mesh transport

[Computer modeling the dependences of the membrane potential for polymeric membrane separated non-homogeneous electrolyte solutions on concentration Rayleigh number].

Science.gov (United States)

Slezak, Izabella H; Jasik-Slezak, Jolanta; Bilewicz-Wyrozumska, Teresa; Slezak, Andrzej

2006-01-01

On the basis of model equation describing the membrane potential delta psi(s) on concentration Rayleigh number (R(C)), mechanical pressure difference (deltaP), concentration polarization coefficient (zeta s) and ratio concentration of solutions separated by membrane (Ch/Cl), the characteristics delta psi(s) = f(Rc)(delta P, zeta s, Ch/Cl) for steady values of zeta s, R(C) and Ch/Cl in single-membrane system were calculated. In this system neutral and isotropic polymeric membrane oriented in horizontal plane, the non-homogeneous binary electrolytic solutions of various concentrations were separated. Nonhomogeneity of solutions is results from creations of the concentration boundary layers on both sides of the membrane. Calculations were made for the case where on a one side of the membrane aqueous solution of NaCl at steady concentration 10(-3) mol x l(-1) (Cl) was placed and on the other aqueous solutions of NaCl at concentrations from 10(-3) mol x l(-1) to 2 x 10(-2) mol x l(-1) (Ch). Their densities were greater than NaCl solution's at 10(-3) mol x l(-1). It was shown that membrane potential depends on hydrodynamic state of a complex concentration boundary layer-membrane-concentration boundary layer, what is controlled by deltaP, Ch/Cl, Rc and Zeta(s).

Homogeneity and scale testing of generalized gamma distribution

International Nuclear Information System (INIS)

Stehlik, Milan

2008-01-01

The aim of this paper is to derive the exact distributions of the likelihood ratio tests of homogeneity and scale hypothesis when the observations are generalized gamma distributed. The special cases of exponential, Rayleigh, Weibull or gamma distributed observations are discussed exclusively. The photoemulsion experiment analysis and scale test with missing time-to-failure observations are present to illustrate the applications of methods discussed

Magnetic field sensor for isotropically sensing an incident magnetic field in a sensor plane

Science.gov (United States)

Pant, Bharat B. (Inventor); Wan, Hong (Inventor)

2001-01-01

A magnetic field sensor that isotropically senses an incident magnetic field. This is preferably accomplished by providing a magnetic field sensor device that has one or more circular shaped magnetoresistive sensor elements for sensing the incident magnetic field. The magnetoresistive material used is preferably isotropic, and may be a CMR material or some form of a GMR material. Because the sensor elements are circular in shape, shape anisotropy is eliminated. Thus, the resulting magnetic field sensor device provides an output that is relatively independent of the direction of the incident magnetic field in the sensor plane.

Nonlinear ionic transport through microstructured solid electrolytes: homogenization estimates

Science.gov (United States)

Curto Sillamoni, Ignacio J.; Idiart, Martín I.

2016-10-01

We consider the transport of multiple ionic species by diffusion and migration through microstructured solid electrolytes in the presence of strong electric fields. The assumed constitutive relations for the constituent phases follow from convex energy and dissipation potentials which guarantee thermodynamic consistency. The effective response is heuristically deduced from a multi-scale convergence analysis of the relevant field equations. The resulting homogenized response involves an effective dissipation potential per species. Each potential is mathematically akin to that of a standard nonlinear heterogeneous conductor. A ‘linear-comparison’ homogenization technique is then used to generate estimates for these nonlinear potentials in terms of available estimates for corresponding linear conductors. By way of example, use is made of the Maxwell-Garnett and effective-medium linear approximations to generate estimates for two-phase systems with power-law dissipation. Explicit formulas are given for some limiting cases. In the case of threshold-type behavior, the estimates exhibit non-analytical dilute limits and seem to be consistent with fields localized in low energy paths.

How the Spectre of Societal Homogeneity Undermines Equitable Healthcare for Refugees

Science.gov (United States)

Razum, Oliver; Wenner, Judith; Bozorgmehr, Kayvan

2017-01-01

Recourse to a purported ideal of societal homogeneity has become common in the context of the refugee reception crisis – not only in Japan, as Leppold et al report, but also throughout Europe. Calls for societal homogeneity in Europe originate from populist movements as well as from some governments. Often, they go along with reduced social support for refugees and asylum seekers, for example in healthcare provision. The fundamental right to health is then reduced to a citizens’ right, granted fully only to nationals. Germany, in spite of welcoming many refugees in 2015, is a case in point: entitlement and access to healthcare for asylum seekers are restricted during the first 15 months of their stay. We show that arguments brought forward to defend such restrictions do not hold, particularly not those which relate to maintaining societal homogeneity. European societies are not homogeneous, irrespective of migration. But as migration will continue, societies need to invest in what we call "globalization within." Removing entitlement restrictions and access barriers to healthcare for refugees and asylum seekers is one important element thereof. PMID:28812828

Feasibility of self-gated isotropic radial late-phase MR imaging of the liver

Energy Technology Data Exchange (ETDEWEB)

Weiss, Jakob; Taron, Jana; Othman, Ahmed E.; Kuendel, Matthias; Martirosian, Petros; Ruff, Christer; Schraml, Christina; Nikolaou, Konstantin; Notohamiprodjo, Mike [Eberhard Karls University Tuebingen, Department of Diagnostic and Interventional Radiology, Tuebingen (Germany); Grimm, Robert [Siemens Healthcare MR, Erlangen (Germany)

2017-03-15

To evaluate feasibility of a 3D-isotropic self-gated radial volumetric interpolated breath-hold examination (VIBE) for late-phase MRI of the liver. 70 patients were included and underwent liver MRI at 1.5 T. Depending on the diagnosis, either Gd-EOB-DTPA (35 patients) or gadobutrol (35 patients) were administered. During late (gadobutrol) or hepatocyte-specific phase (Gd-EOB-DTPA), a radial prototype sequence was acquired and reconstructed using (1) self-gating with 40 % acceptance (rVIBE{sub 40}); (2) with 100 % acceptance of the data (rVIBE{sub 100}) and compared to Cartesian VIBE (cVIBE). Images were assessed qualitatively (image quality, lesion conspicuity, artefacts; 5-point Likert-scale: 5 = excellent; two independent readers) and quantitatively (coefficient-of-variation (CV); contrast-ratio) in axial and coronal reformations. In eight cases only rVIBE provided diagnostic image quality. Image quality of rVIBE{sub 40} was rated significantly superior (p < 0.05) in Gd-EOB-DTPA-enhanced and coronal reformatted examinations as compared to cVIBE. Lesion conspicuity was significantly improved (p < 0.05) in coronal reformatted Gd-EOB-DTPA-enhanced rVIBE{sub 40} in comparison to cVIBE. CV was higher in rVIBE{sub 40} as compared to rVIBE{sub 100}/cVIBE (p < 0.01). Gadobutrol-enhanced rVIBE{sub 40} and cVIBE showed higher contrast-ratios than rVIBE{sub 100} (p < 0.001), whereas no differences were found in Gd-EOB-DTPA-enhanced examinations. Self-gated 3D-isotropic rVIBE provides significantly superior image quality compared to cVIBE, especially in multiplanar reformatted and Gd-EOB-DTPA-enhanced examinations. (orig.)

Feasibility of self-gated isotropic radial late-phase MR imaging of the liver

International Nuclear Information System (INIS)

Weiss, Jakob; Taron, Jana; Othman, Ahmed E.; Kuendel, Matthias; Martirosian, Petros; Ruff, Christer; Schraml, Christina; Nikolaou, Konstantin; Notohamiprodjo, Mike; Grimm, Robert

2017-01-01

To evaluate feasibility of a 3D-isotropic self-gated radial volumetric interpolated breath-hold examination (VIBE) for late-phase MRI of the liver. 70 patients were included and underwent liver MRI at 1.5 T. Depending on the diagnosis, either Gd-EOB-DTPA (35 patients) or gadobutrol (35 patients) were administered. During late (gadobutrol) or hepatocyte-specific phase (Gd-EOB-DTPA), a radial prototype sequence was acquired and reconstructed using (1) self-gating with 40 % acceptance (rVIBE_4_0); (2) with 100 % acceptance of the data (rVIBE_1_0_0) and compared to Cartesian VIBE (cVIBE). Images were assessed qualitatively (image quality, lesion conspicuity, artefacts; 5-point Likert-scale: 5 = excellent; two independent readers) and quantitatively (coefficient-of-variation (CV); contrast-ratio) in axial and coronal reformations. In eight cases only rVIBE provided diagnostic image quality. Image quality of rVIBE_4_0 was rated significantly superior (p < 0.05) in Gd-EOB-DTPA-enhanced and coronal reformatted examinations as compared to cVIBE. Lesion conspicuity was significantly improved (p < 0.05) in coronal reformatted Gd-EOB-DTPA-enhanced rVIBE_4_0 in comparison to cVIBE. CV was higher in rVIBE_4_0 as compared to rVIBE_1_0_0/cVIBE (p < 0.01). Gadobutrol-enhanced rVIBE_4_0 and cVIBE showed higher contrast-ratios than rVIBE_1_0_0 (p < 0.001), whereas no differences were found in Gd-EOB-DTPA-enhanced examinations. Self-gated 3D-isotropic rVIBE provides significantly superior image quality compared to cVIBE, especially in multiplanar reformatted and Gd-EOB-DTPA-enhanced examinations. (orig.)

Qualitative and quantitative assessment of wrist MRI at 3.0T - Comparison between isotropic 3D turbo spin echo and isotropic 3D fast field echo and 2D turbo spin echo

International Nuclear Information System (INIS)

Jung, Jee Young; Yoon, Young Cheol; Jung, Jin Young; Choe, Bong-Keun

2013-01-01

Background: Isotropic three-dimensional (3D) magnetic resonance imaging (MRI) has been applied to various joints. However, comparison for image quality between isotropic 3D MRI and two-dimensional (2D) turbo spin echo (TSE) sequence of the wrist at a 3T MR system has not been investigated. Purpose: To compare the image quality of isotropic 3D MRI including TSE intermediate-weighted (VISTA) sequence and fast field echo (FFE) sequence with 2D TSE intermediate-weighted sequence of the wrist joint at 3.0 T. Material and Methods: MRI was performed in 10 wrists of 10 healthy volunteers with isotropic 3D sequences (VISTA and FFE) and 2D TSE intermediate-weighted sequences at 3.0 T. The signal-to-noise ratio (SNR) was obtained by imaging phantom and noise-only image. Contrast ratios (CRs) were calculated between fluid and cartilage, triangular fibrocartilage complex (TFCC), and the scapholunate ligament. Two radiologists independently assessed the visibility of TFCC, carpal ligaments, cartilage, tendons and nerves with a four-point grading scale. Statistical analysis to compare CRs (one way ANOVA with a Tukey test) and grades of visibility (Kruskal-Wallis test) between three sequences and those for inter-observer agreement (kappa analysis) were performed. Results: The SNR of 2D TSE (46.26) was higher than those of VISTA (23.34) and 3D FFE (19.41). CRs were superior in 2D TSE than VISTA (P = 0.02) for fluid-cartilage and in 2D TSE than 3D FFE (P < 0.01) for fluid-TFCC. The visibility was best in 2D TSE (P < 0.01) for TFCC and in VISTA (P = 0.01) for scapholunate ligament. The visibility was better in 2D TSE and 3D FFE (P 0.04) for cartilage and in VISTA than 3D FFE (P < 0.01) for TFCC. The inter-observer agreement for the visibility of anatomic structures was moderate or substantial. Conclusion: Image quality of 2D TSE was superior to isotropic 3D MR imaging for cartilage, and TFCC. 3D FFE has better visibility for cartilage than VISTA and VISTA has superior visibility for

Qualitative and quantitative assessment of wrist MRI at 3.0T - Comparison between isotropic 3D turbo spin echo and isotropic 3D fast field echo and 2D turbo spin echo

Energy Technology Data Exchange (ETDEWEB)

Jung, Jee Young [Dept. of Radiology, Chungang Univ. Hospital, School of Medicine, Chungang Univ. (Korea, Republic of); Yoon, Young Cheol [Dept. of Radiology, Samsung Medical Center, School of Medicine, Sungkyunkwan Univ. (Korea, Republic of)], e-mail: ycyoon@skku.edu; Jung, Jin Young [Dept. of Radiology, Saint Paul' s Hospital, The Catholic Univ. (Korea, Republic of); Choe, Bong-Keun [Dept. of Preventive Medicine, School of Medicine, Kyung Hee Univ., Seoul (Korea, Republic of)

2013-04-15

Background: Isotropic three-dimensional (3D) magnetic resonance imaging (MRI) has been applied to various joints. However, comparison for image quality between isotropic 3D MRI and two-dimensional (2D) turbo spin echo (TSE) sequence of the wrist at a 3T MR system has not been investigated. Purpose: To compare the image quality of isotropic 3D MRI including TSE intermediate-weighted (VISTA) sequence and fast field echo (FFE) sequence with 2D TSE intermediate-weighted sequence of the wrist joint at 3.0 T. Material and Methods: MRI was performed in 10 wrists of 10 healthy volunteers with isotropic 3D sequences (VISTA and FFE) and 2D TSE intermediate-weighted sequences at 3.0 T. The signal-to-noise ratio (SNR) was obtained by imaging phantom and noise-only image. Contrast ratios (CRs) were calculated between fluid and cartilage, triangular fibrocartilage complex (TFCC), and the scapholunate ligament. Two radiologists independently assessed the visibility of TFCC, carpal ligaments, cartilage, tendons and nerves with a four-point grading scale. Statistical analysis to compare CRs (one way ANOVA with a Tukey test) and grades of visibility (Kruskal-Wallis test) between three sequences and those for inter-observer agreement (kappa analysis) were performed. Results: The SNR of 2D TSE (46.26) was higher than those of VISTA (23.34) and 3D FFE (19.41). CRs were superior in 2D TSE than VISTA (P = 0.02) for fluid-cartilage and in 2D TSE than 3D FFE (P < 0.01) for fluid-TFCC. The visibility was best in 2D TSE (P < 0.01) for TFCC and in VISTA (P = 0.01) for scapholunate ligament. The visibility was better in 2D TSE and 3D FFE (P 0.04) for cartilage and in VISTA than 3D FFE (P < 0.01) for TFCC. The inter-observer agreement for the visibility of anatomic structures was moderate or substantial. Conclusion: Image quality of 2D TSE was superior to isotropic 3D MR imaging for cartilage, and TFCC. 3D FFE has better visibility for cartilage than VISTA and VISTA has superior visibility for

Homogeneous wave turbulence driven by tidal flows

Science.gov (United States)

Favier, B.; Le Reun, T.; Barker, A.; Le Bars, M.

2017-12-01

When a moon orbits around a planet, the rotation of the induced tidal bulge drives a homogeneous, periodic, large-scale flow. The combination of such an excitation with the rotating motion of the planet has been shown to drive parametric resonance of a pair of inertial waves in a mechanism called the elliptical instability. Geophysical fluid layers can also be stratified: this is the case for instance of the Earth's oceans and, as suggested by several studies, of the upper part of the Earth's liquid Outer Core. We thus investigate the stability of a rotating and stratified layer undergoing tidal distortion in the limit where either rotation or stratification is dominant. We show that the periodic tidal flow drives a parametric subharmonic resonance of inertial (resp. internal) waves in the rotating (resp. stratified) case. The instability saturates into a wave turbulence pervading the whole fluid layer. In such a state, the instability mechanism conveys the tidal energy from the large scale tidal flow to the resonant modes, which then feed a succession of triadic resonances also generating small spatial scales. In the rotating case, we observe a kinetic energy spectrum with a k-2 slope for which the Coriolis force is dominant at all spatial scales. In the stratified case, where the timescale separation is increased between the tidal excitation and the Brunt-Väisälä frequencies, the temporal spectrum decays with a ω-2 power law up to the cut-off frequency beyond which waves do not exist. This result is reminiscent of the Garrett and Munk spectrum measured in the oceans and theoretically described as a manifestation of internal wave turbulence. In addition to revealing an instability driving homogeneous turbulence in geophysical fluid layers, our approach is also an efficient numerical tool to investigate the possibly universal properties of wave turbulence in a geophysical context.

Magnetic fields produced by rotating symmetrical bodies with homogeneous surface charge density

International Nuclear Information System (INIS)

Espejel-Morales, R; Murguía-Romero, G; Calles, A; Cabrera-Bravo, E; Morán-López, J L

2016-01-01

We present a numerical calculation for the stationary magnetic field produced by different rotating bodies with homogeneous and constant surface charge density. The calculation is done by superposing the magnetic field produced by a set of loops of current which mimic the magnetic field produced by belts of current defined by slices of fixed width. We consider the cases of a sphere, ellipsoids, open and closed cylinders and a combination of these in a dumbbell -like shell. We also plot their magnetic field lines using a technique that make use of the Runge–Kutta fourth-order method. Up to our knowledge, the case of closed cylinders was not calculated before. In contrast to previous results, we find that the magnetic field inside finite hollow bodies is homogeneous only in the case of a sphere. This is consequence of the fact that, for the sphere, the surface of any slice taken perpendicularly to the rotation axis, depends only on its thickness, like in the case of an infinite cylinder. (paper)

Functional homogeneous zones (fHZs) in viticultural zoning procedure: an Italian case study on Aglianico vine

Science.gov (United States)

Bonfante, A.; Agrillo, A.; Albrizio, R.; Basile, A.; Buonomo, R.; De Mascellis, R.; Gambuti, A.; Giorio, P.; Guida, G.; Langella, G.; Manna, P.; Minieri, L.; Moio, L.; Siani, T.; Terribile, F.

2015-06-01

This paper aims to test a new physically oriented approach to viticulture zoning at farm scale that is strongly rooted in hydropedology and aims to achieve a better use of environmental features with respect to plant requirements and wine production. The physics of our approach are defined by the use of soil-plant-atmosphere simulation models, applying physically based equations to describe the soil hydrological processes and solve soil-plant water status. This study (part of the ZOVISA project) was conducted on a farm devoted to production of high-quality wines (Aglianico DOC), located in southern Italy (Campania region, Mirabella Eclano, AV). The soil spatial distribution was obtained after standard soil survey informed by geophysical survey. Two homogeneous zones (HZs) were identified; in each one a physically based model was applied to solve the soil water balance and estimate the soil functional behaviour (crop water stress index, CWSI) defining the functional homogeneous zones (fHZs). For the second process, experimental plots were established and monitored for investigating soil-plant water status, crop development (biometric and physiological parameters) and daily climate variables (temperature, solar radiation, rainfall, wind). The effects of crop water status on crop response over must and wine quality were then evaluated in the fHZs. This was performed by comparing crop water stress with (i) crop physiological measurement (leaf gas exchange, chlorophyll a fluorescence, leaf water potential, chlorophyll content, leaf area index (LAI) measurement), (ii) grape bunches measurements (berry weight, sugar content, titratable acidity, etc.) and (iii) wine quality (aromatic response). This experiment proved the usefulness of the physically based approach, also in the case of mapping viticulture microzoning.

Solar fuels generation and molecular systems: is it homogeneous or heterogeneous catalysis?

Science.gov (United States)

Artero, Vincent; Fontecave, Marc

2013-03-21

Catalysis is a key enabling technology for solar fuel generation. A number of catalytic systems, either molecular/homogeneous or solid/heterogeneous, have been developed during the last few decades for both the reductive and oxidative multi-electron reactions required for fuel production from water or CO(2) as renewable raw materials. While allowing for a fine tuning of the catalytic properties through ligand design, molecular approaches are frequently criticized because of the inherent fragility of the resulting catalysts, when exposed to extreme redox potentials. In a number of cases, it has been clearly established that the true catalytic species is heterogeneous in nature, arising from the transformation of the initial molecular species, which should rather be considered as a pre-catalyst. Whether such a situation is general or not is a matter of debate in the community. In this review, covering water oxidation and reduction catalysts, involving noble and non-noble metal ions, we limit our discussion to the cases in which this issue has been directly and properly addressed as well as those requiring more confirmation. The methodologies proposed for discriminating homogeneous and heterogeneous catalysis are inspired in part by those previously discussed by Finke in the case of homogeneous hydrogenation reaction in organometallic chemistry [J. A. Widegren and R. G. Finke, J. Mol. Catal. A, 2003, 198, 317-341].

A new consistent definition of the homogenized diffusion coefficient of a lattice, limitations of the homogenization concept, and discussion of previously defined coefficients

International Nuclear Information System (INIS)

Deniz, V.C.

1978-01-01

The problem concerned with the correct definition of the homogenized diffusion coefficient of a lattice, and the concurrent problem of whether or not a homogenized diffusion equation can be formally set up, is studied by a space-energy angle dependent treatment for a general lattice cell; using an operator notation which applies to any eigen-problem. It is shown that the diffusion coefficient should represent only leakage effects. A new definition of the diffusion coefficient is given, which combines within itself the individual merits of each of the two definitions of Benoist, and reduces to the 'uncorrected' Benoist coefficient in certain cases. The conditions under which a homogenized diffusion equation can be obtained are discussed. A compatison is made between the approach via a diffusion equation and the approach via the eigen-coefficients of Deniz. Previously defined diffusion coefficients are discussed, and it is shown that the transformed eigen-coefficients proposed by Gelbard and by Larsen are unsuitable as diffusion coefficients, and that the cell-edge normalization of the Bonalumi coefficient is not physically justifiable. (author)

Inverse design of an isotropic suspended Kirchhoff rod: theoretical and numerical results on the uniqueness of the natural shape

Science.gov (United States)

Bertails-Descoubes, Florence; Derouet-Jourdan, Alexandre; Romero, Victor; Lazarus, Arnaud

2018-04-01

Solving the equations for Kirchhoff elastic rods has been widely explored for decades in mathematics, physics and computer science, with significant applications in the modelling of thin flexible structures such as DNA, hair or climbing plants. As demonstrated in previous experimental and theoretical studies, the natural curvature plays an important role in the equilibrium shape of a Kirchhoff rod, even in the simple case where the rod is isotropic and suspended under gravity. In this paper, we investigate the reverse problem: can we characterize the natural curvature of a suspended isotropic rod, given an equilibrium curve? We prove that although there exists an infinite number of natural curvatures that are compatible with the prescribed equilibrium, they are all equivalent in the sense that they correspond to a unique natural shape for the rod. This natural shape can be computed efficiently by solving in sequence three linear initial value problems, starting from any framing of the input curve. We provide several numerical experiments to illustrate this uniqueness result, and finally discuss its potential impact on non-invasive parameter estimation and inverse design of thin elastic rods.

Intracranial arterial wall imaging using three-dimensional high isotropic resolution black blood MRI at 3.0 Tesla.

Science.gov (United States)

Qiao, Ye; Steinman, David A; Qin, Qin; Etesami, Maryam; Schär, Michael; Astor, Brad C; Wasserman, Bruce A

2011-07-01

To develop a high isotropic-resolution sequence to evaluate intracranial vessels at 3.0 Tesla (T). Thirteen healthy volunteers and 4 patients with intracranial stenosis were imaged at 3.0T using 0.5-mm isotropic-resolution three-dimensional (3D) Volumetric ISotropic TSE Acquisition (VISTA; TSE, turbo spin echo), with conventional 2D-TSE for comparison. VISTA was repeated for 6 volunteers and 4 patients at 0.4-mm isotropic-resolution to explore the trade-off between SNR and voxel volume. Wall signal-to-noise-ratio (SNR(wall) ), wall-lumen contrast-to-noise-ratio (CNR(wall-lumen) ), lumen area (LA), wall area (WA), mean wall thickness (MWT), and maximum wall thickness (maxWT) were compared between 3D-VISTA and 2D-TSE sequences, as well as 3D images acquired at both resolutions. Reliability was assessed by intraclass correlations (ICC). Compared with 2D-TSE measurements, 3D-VISTA provided 58% and 74% improvement in SNR(wall) and CNR(wall-lumen) , respectively. LA, WA, MWT and maxWT from 3D and 2D techniques highly correlated (ICCs of 0.96, 0.95, 0.96, and 0.91, respectively). CNR(wall-lumen) using 0.4-mm resolution VISTA decreased by 27%, compared with 0.5-mm VISTA but with reduced partial-volume-based overestimation of wall thickness. Reliability for 3D measurements was good to excellent. The 3D-VISTA provides SNR-efficient, highly reliable measurements of intracranial vessels at high isotropic-resolution, enabling broad coverage in a clinically acceptable time. Copyright © 2011 Wiley-Liss, Inc.

Applications of elliptic operator theory to the isotropic interior transmission eigenvalue problem

Science.gov (United States)

Lakshtanov, E.; Vainberg, B.

2013-10-01

The paper concerns the isotropic interior transmission eigenvalue (ITE) problem. This problem is not elliptic, but we show that, using the Dirichlet-to-Neumann map, it can be reduced to an elliptic one. This leads to the discreteness of the spectrum as well as to certain results on a possible location of the transmission eigenvalues. If the index of refraction \\sqrt{n(x)} is real, then we obtain a result on the existence of infinitely many positive ITEs and the Weyl-type lower bound on its counting function. All the results are obtained under the assumption that n(x) - 1 does not vanish at the boundary of the obstacle or it vanishes identically, but its normal derivative does not vanish at the boundary. We consider the classical transmission problem as well as the case when the inhomogeneous medium contains an obstacle. Some results on the discreteness and localization of the spectrum are obtained for complex valued n(x).

Effective thermoelastic properties of discrete-fiber reinforced materials with transversally-isotropic components

Science.gov (United States)

Nazarenko, Lidiya; Khoroshun, Leonid; Müller, Wolfgang H.; Wille, Ralf

2009-02-01

In the present paper, we will illustrate the application of the method of conditional moments by constructing the algorithm for determination of the effective elastic properties of composites from the given elastic constants of the components and geometrical parameters of inclusions. A special case of two-component matrix composite with randomly distributed unidirectional spheroidal inclusions is considered. To this end it is assumed that the components of the composite show transversally isotropic symmetry of thermoelastic properties and that the axes of symmetry of the thermoelastic properties of the matrix and inclusions coincide with the coordinate axis x 3. As a numerical example a composite based on carbon inclusions and epoxide matrix is investigated. The dependencies of Young’s moduli, Poisson’s ratios and shear modulus from the concentration of inclusions and for certain values which characterize the shape of inclusions are analyzed. The results are compared and discussed in context with other theoretical predictions and experimental data.

Geometric Models for Isotropic Random Porous Media: A Review

Directory of Open Access Journals (Sweden)

Helmut Hermann

2014-01-01

Full Text Available Models for random porous media are considered. The models are isotropic both from the local and the macroscopic point of view; that is, the pores have spherical shape or their surface shows piecewise spherical curvature, and there is no macroscopic gradient of any geometrical feature. Both closed-pore and open-pore systems are discussed. The Poisson grain model, the model of hard spheres packing, and the penetrable sphere model are used; variable size distribution of the pores is included. A parameter is introduced which controls the degree of open-porosity. Besides systems built up by a single solid phase, models for porous media with the internal surface coated by a second phase are treated. Volume fraction, surface area, and correlation functions are given explicitly where applicable; otherwise numerical methods for determination are described. Effective medium theory is applied to calculate physical properties for the models such as isotropic elastic moduli, thermal and electrical conductivity, and static dielectric constant. The methods presented are exemplified by applications: small-angle scattering of systems showing fractal-like behavior in limited ranges of linear dimension, optimization of nanoporous insulating materials, and improvement of properties of open-pore systems by atomic layer deposition of a second phase on the internal surface.

Implementation of Canny and Isotropic Operator with Power Law Transformation to Identify Cervical Cancer

Science.gov (United States)

Amalia, A.; Rachmawati, D.; Lestari, I. A.; Mourisa, C.

2018-03-01

Colposcopy has been used primarily to diagnose pre-cancer and cancerous lesions because this procedure gives an exaggerated view of the tissues of the vagina and the cervix. But, the poor quality of colposcopy image sometimes makes physician challenging to recognize and analyze it. Generally, Implementation of image processing to identify cervical cancer have to implement a complex classification or clustering method. In this study, we wanted to prove that by only applying the identification of edge detection in the colposcopy image, identification of cervical cancer can be determined. In this study, we implement and comparing two edge detection operator which are isotropic and canny operator. Research methodology in this paper composed by image processing, training, and testing stages. In the image processing step, colposcopy image transformed by nth root power transformation to get better detection result and continued with edge detection process. Training is a process of labelling all dataset image with cervical cancer stage. This process involved pathology doctor as an expert in diagnosing the colposcopy image as a reference. Testing is a process of deciding cancer stage classification by comparing the similarity image of colposcopy results in the testing stage with the image of the results of the training process. We used 30 images as a dataset. The result gets same accuracy which is 80% for both Canny or Isotropic operator. Average running time for Canny operator implementation is 0.3619206 ms while Isotropic get 1.49136262 ms. The result showed that Canny operator is better than isotropic operator because Canny operator generates a more precise edge with a fast time instead.

Generalization of Asaoka method to linearly anisotropic scattering: benchmark data in cylindrical geometry

International Nuclear Information System (INIS)

Sanchez, Richard.

1975-11-01

The Integral Transform Method for the neutron transport equation has been developed in last years by Asaoka and others. The method uses Fourier transform techniques in solving isotropic one-dimensional transport problems in homogeneous media. The method has been extended to linearly anisotropic transport in one-dimensional homogeneous media. Series expansions were also obtained using Hembd techniques for the new anisotropic matrix elements in cylindrical geometry. Carlvik spatial-spherical harmonics method was generalized to solve the same problem. By applying a relation between the isotropic and anisotropic one-dimensional kernels, it was demonstrated that anisotropic matrix elements can be calculated by a linear combination of a few isotropic matrix elements. This means in practice that the anisotropic problem of order N with the N+2 isotropic matrix for the plane and spherical geometries, and N+1 isotropic matrix for cylindrical geometries can be solved. A method of solving linearly anisotropic one-dimensional transport problems in homogeneous media was defined by applying Mika and Stankiewicz observations: isotropic matrix elements were computed by Hembd series and anisotropic matrix elements then calculated from recursive relations. The method has been applied to albedo and critical problems in cylindrical geometries. Finally, a number of results were computed with 12-digit accuracy for use as benchmarks [fr

Bilipschitz embedding of homogeneous fractals

OpenAIRE

Lü, Fan; Lou, Man-Li; Wen, Zhi-Ying; Xi, Li-Feng

2014-01-01

In this paper, we introduce a class of fractals named homogeneous sets based on some measure versions of homogeneity, uniform perfectness and doubling. This fractal class includes all Ahlfors-David regular sets, but most of them are irregular in the sense that they may have different Hausdorff dimensions and packing dimensions. Using Moran sets as main tool, we study the dimensions, bilipschitz embedding and quasi-Lipschitz equivalence of homogeneous fractals.

Homogeneous anisotropic solutions of topologically massive gravity with a cosmological constant and their homogeneous deformations

International Nuclear Information System (INIS)

Moutsopoulos, George

2013-01-01

We solve the equations of topologically massive gravity (TMG) with a potentially non-vanishing cosmological constant for homogeneous metrics without isotropy. We only reproduce known solutions. We also discuss their homogeneous deformations, possibly with isotropy. We show that de Sitter space and hyperbolic space cannot be infinitesimally homogeneously deformed in TMG. We clarify some of their Segre–Petrov types and discuss the warped de Sitter spacetime. (paper)

Homogeneous anisotropic solutions of topologically massive gravity with a cosmological constant and their homogeneous deformations

Science.gov (United States)

Moutsopoulos, George

2013-06-01

We solve the equations of topologically massive gravity (TMG) with a potentially non-vanishing cosmological constant for homogeneous metrics without isotropy. We only reproduce known solutions. We also discuss their homogeneous deformations, possibly with isotropy. We show that de Sitter space and hyperbolic space cannot be infinitesimally homogeneously deformed in TMG. We clarify some of their Segre-Petrov types and discuss the warped de Sitter spacetime.

Homogenization of variational inequalities for obstacle problems

International Nuclear Information System (INIS)

Sandrakov, G V

2005-01-01

Results on the convergence of solutions of variational inequalities for obstacle problems are proved. The variational inequalities are defined by a non-linear monotone operator of the second order with periodic rapidly oscillating coefficients and a sequence of functions characterizing the obstacles. Two-scale and macroscale (homogenized) limiting variational inequalities are obtained. Derivation methods for such inequalities are presented. Connections between the limiting variational inequalities and two-scale and macroscale minimization problems are established in the case of potential operators.

GOLIA-RK, Structure Stress for Isotropic Materials with Creep and Temperature Fields

International Nuclear Information System (INIS)

Donea, J.; Giuliani, S.

1976-01-01

1 - Nature of the physical problem solved: Stress analysis of complex structures in presence of creep, dimensional changes and thermal field. Plane stress, plane strain, generalized plane strain and axisymmetric problems can be solved. The material is assumed to be either isotropic or transversely isotropic. Any laws of material behaviour can easily be incorporated by the user (see subroutines WIGNER and CLAW). 2 - Method of solution: Finite element method using triangular elements with linear local fields. The equations for the displacements are solved by Choleski's method. An algorithm is incorporated to calculate automatically the successive time steps in a creep problem. 3 - Restrictions on the complexity of the problem: Maximum number of elements is 700. Maximum number of nodal points is 400. The indexes of two adjacent nodes are not permitted to differ by more than 19

Benchmarking homogenization algorithms for monthly data

Science.gov (United States)

Venema, V. K. C.; Mestre, O.; Aguilar, E.; Auer, I.; Guijarro, J. A.; Domonkos, P.; Vertacnik, G.; Szentimrey, T.; Stepanek, P.; Zahradnicek, P.; Viarre, J.; Müller-Westermeier, G.; Lakatos, M.; Williams, C. N.; Menne, M. J.; Lindau, R.; Rasol, D.; Rustemeier, E.; Kolokythas, K.; Marinova, T.; Andresen, L.; Acquaotta, F.; Fratiannil, S.; Cheval, S.; Klancar, M.; Brunetti, M.; Gruber, C.; Prohom Duran, M.; Likso, T.; Esteban, P.; Brandsma, T.; Willett, K.

2013-09-01

The COST (European Cooperation in Science and Technology) Action ES0601: Advances in homogenization methods of climate series: an integrated approach (HOME) has executed a blind intercomparison and validation study for monthly homogenization algorithms. Time series of monthly temperature and precipitation were evaluated because of their importance for climate studies. The algorithms were validated against a realistic benchmark dataset. Participants provided 25 separate homogenized contributions as part of the blind study as well as 22 additional solutions submitted after the details of the imposed inhomogeneities were revealed. These homogenized datasets were assessed by a number of performance metrics including i) the centered root mean square error relative to the true homogeneous values at various averaging scales, ii) the error in linear trend estimates and iii) traditional contingency skill scores. The metrics were computed both using the individual station series as well as the network average regional series. The performance of the contributions depends significantly on the error metric considered. Although relative homogenization algorithms typically improve the homogeneity of temperature data, only the best ones improve precipitation data. Moreover, state-of-the-art relative homogenization algorithms developed to work with an inhomogeneous reference are shown to perform best. The study showed that currently automatic algorithms can perform as well as manual ones.

Monopole-fermion systems in the complex isotropic tetrad formalism

International Nuclear Information System (INIS)

Gal'tsov, D.V.; Ershov, A.A.

1988-01-01

The interaction of fermions of arbitrary isospin with regular magnetic monopoles and dyons of the group SU(2) and also with point gravitating monopoles and dyons of the Wu-Yang type described by the Reissner-Nordstrom metric are studied using the Newman-Penrose complex isotropic tetrad formalism. Formulas for the bound-state spectrum and explicit expressions for the zero modes are obtained and the Rubakov-Callan effect for black holes is discussed

How the Spectre of Societal Homogeneity Undermines Equitable Healthcare for Refugees; Comment on “Defining and Acting on Global Health: The Case of Japan and the Refugee Crisis”

Directory of Open Access Journals (Sweden)

Oliver Razum

2017-06-01

Full Text Available Recourse to a purported ideal of societal homogeneity has become common in the context of the refugee reception crisis – not only in Japan, as Leppold et al report, but also throughout Europe. Calls for societal homogeneity in Europe originate from populist movements as well as from some governments. Often, they go along with reduced social support for refugees and asylum seekers, for example in healthcare provision. The fundamental right to health is then reduced to a citizens’ right, granted fully only to nationals. Germany, in spite of welcoming many refugees in 2015, is a case in point: entitlement and access to healthcare for asylum seekers are restricted during the first 15 months of their stay. We show that arguments brought forward to defend such restrictions do not hold, particularly not those which relate to maintaining societal homogeneity. European societies are not homogeneous, irrespective of migration. But as migration will continue, societies need to invest in what we call “globalization within.” Removing entitlement restrictions and access barriers to healthcare for refugees and asylum seekers is one important element thereof.

Fermat's principle of least time in the presence of uniformly moving boundaries and media

International Nuclear Information System (INIS)

Gjurchinovski, Aleksandar; Skeparovski, Aleksandar

2007-01-01

The refraction of a light ray by a homogeneous, isotropic and non-dispersive transparent material half-space in uniform rectilinear motion is investigated theoretically. The approach is an amalgamation of the original Fermat's principle and the fact that an isotropic optical medium at rest becomes optically anisotropic in a frame where the medium is moving at a constant velocity. Two cases of motion are considered: (a) the material half-space is moving parallel to the interface; (b) the material half-space is moving perpendicular to the interface. In each case, a detailed analysis of the obtained refraction formula is provided, and in the latter case, an intriguing backward refraction of light is noticed and thoroughly discussed. The results confirm the validity of Fermat's principle when the optical media and the boundaries between them are moving at relativistic speeds

Fermat's principle of least time in the presence of uniformly moving boundaries and media

Energy Technology Data Exchange (ETDEWEB)

Gjurchinovski, Aleksandar; Skeparovski, Aleksandar [Department of Physics, Faculty of Natural Sciences and Mathematics, Sts. Cyril and Methodius University, PO Box 162, 1000 Skopje (Macedonia, The Former Yugoslav Republic of)

2007-09-15

The refraction of a light ray by a homogeneous, isotropic and non-dispersive transparent material half-space in uniform rectilinear motion is investigated theoretically. The approach is an amalgamation of the original Fermat's principle and the fact that an isotropic optical medium at rest becomes optically anisotropic in a frame where the medium is moving at a constant velocity. Two cases of motion are considered: (a) the material half-space is moving parallel to the interface; (b) the material half-space is moving perpendicular to the interface. In each case, a detailed analysis of the obtained refraction formula is provided, and in the latter case, an intriguing backward refraction of light is noticed and thoroughly discussed. The results confirm the validity of Fermat's principle when the optical media and the boundaries between them are moving at relativistic speeds.

Geometry of the isotropic oscillator driven by the conformal mode

Energy Technology Data Exchange (ETDEWEB)

Galajinsky, Anton [Tomsk Polytechnic University, School of Physics, Tomsk (Russian Federation)

2018-01-15

Geometrization of a Lagrangian conservative system typically amounts to reformulating its equations of motion as the geodesic equations in a properly chosen curved spacetime. The conventional methods include the Jacobi metric and the Eisenhart lift. In this work, a modification of the Eisenhart lift is proposed which describes the isotropic oscillator in arbitrary dimension driven by the one-dimensional conformal mode. (orig.)

Collision-free gases in spatially homogeneous space-times

International Nuclear Information System (INIS)

Maartens, R.; Maharaj, S.D.

1985-01-01

The kinematical and dynamical properties of one-component collision-free gases in spatially homogeneous, locally rotationally symmetric (LRS) space-times are analyzed. Following Ray and Zimmerman [Nuovo Cimento B 42, 183 (1977)], it is assumed that the distribution function f of the gas inherits the symmetry of space-time, in order to construct solutions of Liouville's equation. The redundancy of their further assumption that f be based on Killing vector constants of the motion is shown. The Ray and Zimmerman results for Kantowski--Sachs space-time are extended to all spatially homogeneous LRS space-times. It is shown that in all these space-times the kinematic average four-velocity u/sup i/ can be tilted relative to the homogeneous hypersurfaces. This differs from the perfect fluid case, in which only one space-time admits tilted u/sup i/, as shown by King and Ellis [Commun. Math. Phys. 31, 209 (1973)]. As a consequence, it is shown that all space-times admit nonzero acceleration and heat flow, while a subclass admits nonzero vorticity. The stress π/sub i/j is proportional to the shear sigma/sub i/j by virtue of the invariance of the distribution function. The evolution of tilt and the existence of perfect fluid solutions is also discussed

Theory of a spherical emissive probe in a low-density isotropic plasma

International Nuclear Information System (INIS)

Din, A.

2010-01-01

Emissive probes are widely being used by plasma experimentalists to determine plasma parameters. Here, a fairly general spherical-emissive-probe scenario based on trajectory integration of the Vlasov equation is formulated and specialized to the particular non-emissive situation considered by Bernstein and Rabinowitz (1959), which is monoenergetic isotropic ions and Boltzmann-distributed electrons originating from the plasma. Then, this formalism together with our newly developed analytic-numerical matching procedure is used for finding the potential profile in the entire plasma-probe transition (PPT) region, consisting of the 'inward' and 'outward' sheath solutions, and the quasineutral (plasma) solution. The analytically expanded outward sheath and plasma solutions, the quasineutral solution and the related matching procedure represent genuinely new results in the context of this particular non-emissive probe scenario, however with the underlying methodology also applicable to other probe scenarios in the future. For the emissive case we consider, in addition to the plasma ions and electrons of the Bernstein and Rabinowitz scenario, electrons emitted from the probe surface with zero tangential velocity and a 'waterbag' distribution with respect to the radial velocity. Using our newly developed numerical matching procedure, we calculate the entire potential profile also for this emissive case. Comparison of the potential profiles for the emissive and non-emissive cases shows visible differences, thus demonstrating the effect of electron emission from the probe. To our knowledge, the present work represents the first attempt at systematically developing a kinetic approach for spherical emissive probes. (author)

The opposing effects of isotropic and anisotropic attraction on association kinetics of proteins and colloids

Science.gov (United States)

Newton, Arthur C.; Kools, Ramses; Swenson, David W. H.; Bolhuis, Peter G.

2017-10-01

The association and dissociation of particles via specific anisotropic interactions is a fundamental process, both in biology (proteins) and in soft matter (colloidal patchy particles). The presence of alternative binding sites can lead to multiple productive states and also to non-productive "decoy" or intermediate states. Besides anisotropic interactions, particles can experience non-specific isotropic interactions. We employ single replica transition interface sampling to investigate how adding a non-productive binding site or a nonspecific isotropic interaction alters the dimerization kinetics of a generic patchy particle model. The addition of a decoy binding site reduces the association rate constant, independent of the site's position, while adding an isotropic interaction increases it due to an increased rebinding probability. Surprisingly, the association kinetics becomes non-monotonic for a tetramer complex formed by multivalent patchy particles. While seemingly identical to two-particle binding with a decoy state, the cooperativity of binding multiple particles leads to a kinetic optimum. Our results are relevant for the understanding and modeling of biochemical networks and self-assembly processes.

Non-homogeneous polymer model for wave propagation and its ...

African Journals Online (AJOL)

user

density are functions of space i.e. non-homogeneous engineering material. .... The Solution of equation Eq. (9) in the form of Eq. (10) can be obtained by taking a phase ..... Viscoelastic Model Applied to a Particular Case .... p m i exp m α α σ σ σ. = −. +. −. (35). The progressive harmonic wave which starts from the end. 0 x =.

Control rod homogenization in heterogeneous sodium-cooled fast reactors

International Nuclear Information System (INIS)

Andersson, Mikael

2016-01-01

The sodium-cooled fast reactor is one of the candidates for a sustainable nuclear reactor system. In particular, the French ASTRID project employs an axially heterogeneous design, proposed in the so-called CFV (low sodium effect) core, to enhance the inherent safety features of the reactor. This thesis focuses on the accurate modeling of the control rods, through the homogenization method. The control rods in a sodium-cooled fast reactor are used for reactivity compensation during the cycle, power shaping, and to shutdown the reactor. In previous control rod homogenization procedures, only a radial description of the geometry was implemented, hence the axially heterogeneous features of the CFV core could not be taken into account. This thesis investigates the different axial variations the control rod experiences in a CFV core, to determine the impact that these axial environments have on the control rod modeling. The methodology used in this work is based on previous homogenization procedures, the so-called equivalence procedure. The procedure was newly implemented in the PARIS code system in order to be able to use 3D geometries, and thereby be take axial effects into account. The thesis is divided into three parts. The first part investigates the impact of different neutron spectra on the homogeneous control-rod cross sections. The second part investigates the cases where the traditional radial control-rod homogenization procedure is no longer applicable in the CFV core, which was found to be 5-10 cm away from any material interface. In the third part, based on the results from the second part, a 3D model of the control rod is used to calculate homogenized control-rod cross sections. In a full core model, a study is made to investigate the impact these axial effects have on control rod-related core parameters, such as the control rod worth, the capture rates in the control rod, and the power in the adjacent fuel assemblies. All results were compared to a Monte

Study of the characteristics of forced homogeneous turbulence using band-pass Fourier filtering

Energy Technology Data Exchange (ETDEWEB)

Kareem, Waleed Abdel [Suez Canal University, Suez (Egypt)

2012-03-15

Simulations of forced homogeneous isotropic turbulence with resolutions of 128{sup 3} and 256{sup 3} using the Lattice Boltzmann method are carried out. The multi-scale vortical structures are identified using the band-pass Fourier cutoff filtering. Three fields at each simulation are extracted and their characteristics are studied. The vortical structures are visualized using the Q-identification method. A new lattice segmentation scheme to identify the central axes of the vortical structures is introduced. The central points of each vortex are identified and they are connected using the direction cosines technique. Results show that the Q-spectrum of the fine scale field survives at low and high wave-numbers. However, the large and intermediate Q-spectra survives till wave-numbers less than or equal to twice the used velocity cutoff wave-numbers. It is found that the extracted central axes clearly resemble the corresponding vortical structures at each scale. Using the central axes scheme, the radii and lengths of the vortical structures at each scale are determined and compared. It is also found that the radii of the identified vortical structures at each scale in both simulations are of the order of several times the Kolmogorov microscales.

Passage through X-ray protection having the structure of homogeneous fractals

OpenAIRE

Churikov Viktor Anatolyevich

2014-01-01

In this paper we generalize the law of Bouguer-Lambert in the case of a homogeneous fractal. With detailed analysis in terms of d-output operator generalized law of BouguerLambert-Beer law, which in particular includes the classical law of optics Bouguer-LambertBeer.

The zeroth law in quasi-homogeneous thermodynamics and black holes

Directory of Open Access Journals (Sweden)

Alessandro Bravetti

2017-11-01

Full Text Available Motivated by black holes thermodynamics, we consider the zeroth law of thermodynamics for systems whose entropy is a quasi-homogeneous function of the extensive variables. We show that the generalized Gibbs–Duhem identity and the Maxwell construction for phase coexistence based on the standard zeroth law are incompatible in this case. We argue that the generalized Gibbs–Duhem identity suggests a revision of the zeroth law which in turns permits to reconsider Maxwell's construction in analogy with the standard case. The physical feasibility of our proposal is considered in the particular case of black holes.

A local isotropic/global orthotropic finite element technique for modeling the crush of wood in impact limiters

International Nuclear Information System (INIS)

Attaway, S.W.; Yoshimura, H.R.

1989-01-01

Wood is often used as the energy absorbing material in impact limiters, because it begins to crush at low strains, then maintains a near constant crush stress up to nearly 60% volume reduction, and then locks up. Hill (Hill and Joseph, 1974) has performed tests that show that wood is an excellent absorber. However, wood's orthotropic behavior for large crush is difficult to model. In the past, analysts have used isotropic foam-like material models for modeling wood. A new finite element technique is presented in this paper that gives a better model of wood crush than the model currently in use. The orthotropic technique is based on locally isotropic, but globally orthotropic (LIGO) (Attaway, 1988) assumptions in which alternating layers of hard and soft crushable material are used. Each layer is isotropic; however, by alternating hard and soft thin layers, the resulting global behavior is orthotropic. In the remainder of this paper, the new technique for modeling orthotropic wood crush will be presented. The model is used to predict the crush behavior for different grain orientations of balsa wood. As an example problem, an impact limiter containing balsa wood as the crushable material is analyzed using both an isotropic model and the LIGO model

Homogenization of resonant chiral metamaterials

OpenAIRE

Andryieuski, Andrei; Menzel, Christoph; Rockstuhl, Carsten; Malureanu, Radu; Lederer, Falk; Lavrinenko, Andrei

2010-01-01

Homogenization of metamaterials is a crucial issue as it allows to describe their optical response in terms of effective wave parameters as e.g. propagation constants. In this paper we consider the possible homogenization of chiral metamaterials. We show that for meta-atoms of a certain size a critical density exists above which increasing coupling between neighboring meta-atoms prevails a reasonable homogenization. On the contrary, a dilution in excess will induce features reminiscent to pho...

About zone structure of a stack of a cholesteric liquid crystal and isotropic medium layers

International Nuclear Information System (INIS)

Gevorgyan, A H; Harutyunyan, E M; Matinyan, G K; Harutyunyan, M Z

2014-01-01

The optical properties of a stack of metamaterial-based cholesteric liquid crystal (CLC) layers and isotropic medium layers are investigated. CLCs with two types of chiral nihility are defined. The peculiarities of the reflection spectra of this system are investigated and it is shown that the reflection spectra of the stacks of CLC layers of these two types differ from each other. The influence of: the CLC sublayer thicknesses; incidence angle; local dielectric (magnetic) anisotropy of the CLC layers; refraction indices and thicknesses of the isotropic media layers on the reflection spectra and other optical characteristics of the system is investigated.

Multi-contrast, isotropic, single-slab 3D MR imaging in multiple sclerosis

NARCIS (Netherlands)

Moraal, Bastiaan; Roosendaal, Stefan; Pouwels, Petra; Vrenken, Hugo; Schijndel, van Ronald; Meier, Dominik; Guttmann, Charles; Geurts, Jeroen; Barkhof, Frederik

2008-01-01

To describe signal and contrast properties of an isotropic, single-slab 3D dataset [double inversion- recovery (DIR), fluid-attenuated inversion recovery (FLAIR), T2, and T1-weighted magnetization prepared rapid acquisition gradient-echo (MPRAGE)] and to evaluate its performance in detecting

Numerical implementation of a transverse-isotropic inelastic, work-hardening constitutive model

International Nuclear Information System (INIS)

Baladi, G.Y.

1977-01-01

During the past few decades the dramatic growth of computer technology has been paralleled by an increasing degree of complexity in material constitutive modeling. This paper documents the numerical implementation of one of these models, specifically a transverse-isotropic, inelastic, work-hardening constitutive model which is developed elsewhere by the author. (Auth.)

Homogeneous magnetic relaxation in iron-yttrium garnets in the vicinity of a phase transition

International Nuclear Information System (INIS)

Luzyanin, I.D.; Khavronin, V.P.

1977-01-01

Results are presented of an experimental investigation of the dynamics of homogeneous magnetization during a phase transition of the second kind in iron-yttrium garnet (IYG) single crystals of various shapes. It is shown that homogeneous relaxation significantly depends on both the magnitude of 4πchisub(st) (chisub(st) is static magnetic susceptibility) as well as on the relation between the variable field frequency (at which the investigation is carried out) and the characteristic energies. It is shown that beginning from temperatures such as 4πchisub(st) approximately 1, the characteristic dipole interaction energy becomes frequency dependent; this indicates that in this case Lorentz coupling between the dynamic susceptibility and homogeneous relaxation time is invalid. This is a principle point in investigations of homogeneous relaxation by radio-frequency techniques. The temperature dependence of the homogeneous relaxation time and static susceptibility is determined in the exchange region. It is found that the phase transition in IYG involves anomalous phenomena which manifest in release and absorption of heat by a sample and in the appearance of additional singularities in the temperature dependence of the homogeneous relaxation time

Study of an ultrasound-based process analytical tool for homogenization of nanoparticulate pharmaceutical vehicles.

Science.gov (United States)

Cavegn, Martin; Douglas, Ryan; Akkermans, Guy; Kuentz, Martin

2011-08-01

There are currently no adequate process analyzers for nanoparticulate viscosity enhancers. This article aims to evaluate ultrasonic resonator technology as a monitoring tool for homogenization of nanoparticulate gels. Aqueous dispersions of colloidal microcrystalline cellulose (MCC) and a mixture of clay particles with xanthan gum were compared with colloidal silicon dioxide in oil. The processing was conducted using a laboratory-scale homogenizing vessel. The study investigated first the homogenization kinetics of the different systems to focus then on process factors in the case of colloidal MCC. Moreover, rheological properties were analyzed offline to assess the structure of the resulting gels. Results showed the suitability of ultrasound velocimetry to monitor the homogenization process. The obtained data were fitted using a novel heuristic model. It was possible to identify characteristic homogenization times for each formulation. The subsequent study of the process factors demonstrated that ultrasonic process analysis was equally sensitive as offline rheological measurements in detecting subtle manufacturing changes. It can be concluded that the ultrasonic method was able to successfully assess homogenization of nanoparticulate viscosity enhancers. This novel technique can become a vital tool for development and production of pharmaceutical suspensions in the future. Copyright © 2011 Wiley-Liss, Inc.

An acoustic eikonal equation for attenuating transversely isotropic media with a vertical symmetry axis

KAUST Repository

Hao, Qi

2016-11-21

Seismic-wave attenuation is an important component of describing wave propagation. Certain regions, such as gas clouds inside the earth, exert highly localized attenuation. In fact, the anisotropic nature of the earth induces anisotropic attenuation because the quasi P-wave dispersion effect should be profound along the symmetry direction. We have developed a 2D acoustic eikonal equation governing the complex-valued traveltime of quasi P-waves in attenuating, transversely isotropic media with a vertical-symmetry axis (VTI). This equation is derived under the assumption that the complex-valued traveltime of quasi P-waves in attenuating VTI media are independent of the S-wave velocity parameter υS0 in Thomsen\\'s notation and the S-wave attenuation coefficient AS0 in Zhu and Tsvankin\\'s notation. We combine perturbation theory and Shanks transform to develop practical approximations to the acoustic attenuating eikonal equation, capable of admitting an analytical description of the attenuation in homogeneous media. For a horizontal-attenuating VTI layer, we also derive the nonhyperbolic approximations for the real and imaginary parts of the complex-valued reflection traveltime. These equations reveal that (1) the quasi SV-wave velocity and the corresponding quasi SV-wave attenuation coefficient given as part of Thomsen-type notation barely affect the ray velocity and ray attenuation of quasi P-waves in attenuating VTI media; (2) combining the perturbation method and Shanks transform provides an accurate analytic eikonal solution for homogeneous attenuating VTI media; (3) for a horizontal attenuating VTI layer with weak attenuation, the real part of the complex-valued reflection traveltime may still be described by the existing nonhyperbolic approximations developed for nonattenuating VTI media, and the imaginary part of the complex-valued reflection traveltime still has the shape of nonhyperbolic curves. In addition, we have evaluated the possible extension of the

Experimental study on the thermo-mechanical behaviour of stiff clay under non-isotropic stress state

International Nuclear Information System (INIS)

Tang, Anh Minh; Cui, Yu-Jun; Li, Xiang-Ling

2012-01-01

Document available in extended abstract form only. Stiff clay is usually considered as possible host-rock for geological radioactive waste disposal due to its low permeability and its self-sealing capacity. Boom Clay, for instance, is one of the clays currently considered by the Belgian radioactive waste management agency Ondraf/Niras as a potential host for a geological repository. In order to analyse the performance of this material, it is important to understand its behaviour under the coupled thermo-hydro-mechanical solicitations. In laboratory, several studies have been performed to study the volume change of clay under coupled thermomechanical loading. The results show that heating under drained conditions can induce thermal dilation at low confining stress and thermal contraction at high confining stress. On the other hand, compression tests performed at constant temperature show that the compressibility parameters of soil can be modified by temperature change. These features are now well considered in constitutive laws based on the framework of elasto-plasticity. Under undrained conditions, heating can increase pore-water pressure and this behaviour can be simulated using the theoretical thermo-poro-elastic framework. The temperature effect on the soil behaviour under triaxial compression is also often considered. It is commonly accepted that heating decreases the shear strength of clay but this softening can be hidden by the thermal contraction that occurs during heating which can induce at the same time soil hardening. In spite of these existing works, laboratory tests considering the thermo-mechanical loading path that the soil can be subjected to are still rare. Actually, in the case of geological radioactive waste disposal, after the installation of waste canisters, the soil is expected to be heated under non-isotropic stress state. Most of the existing laboratory works show heating tests in odometer cell or triaxial cell under isotropic stress

Permanent magnets prepared from Sm{sub 10.5}Fe{sub 88.5}Zr{sub 1.0}N{sub y} without homogenization

Energy Technology Data Exchange (ETDEWEB)

Gebel, B.; Kubis, M.; Mueller, K.-H. [Institut fuer Festkoerper- und Werkstofforschung Dresden e.V. (Germany). Inst. fuer Metallische Werkstoffe

1997-10-01

In as-cast Sm{sub 2}Fe{sub 17} the high amount of {alpha}-Fe caused by a peritectic reaction can be considerably reduced by a small addition of about 1 at% Zr. X-ray diffraction showed that as-cast Sm{sub 10.5}Fe{sub 88.5}Zr{sub 1.0} mainly consists of a phase with the Th{sub 2}Zn{sub 17}-type structure and SmFe{sub 3}. Non-homogenized Sm{sub 10.5}Fe{sub 88.5}Zr{sub 1.0} was milled and (i) annealed in vacuum or (ii) treated with a hydrogenation-disproportionation-desorp tion-recombination (HDDR) process. The annealed and subsequently nitrogenated powder is magnetically anisotropic and has a coercivity {mu}{sub 0J}H{sub C} up to 2.0 T and an energy product (BH){sub max} up to 136 kJ/m{sup 3}. HDDR-treated and nitrogenated powder is isotropic and exhibits values of {mu}{sub 0J}H{sub C} = 3.1 T and (BH){sub max} 103 kJ/m{sup 3}. Consequently, Sm{sub 10.5}Fe{sub 88.5}Zr{sub 1.0}N{sub y} (y {approx} 16) permanent magnets with very good properties can be prepared without the time-consuming homogenization procedure. (orig.). 11 refs.

Coupled thermal stress analysis of a hollow circular cylinder with transversely isotropic properties

International Nuclear Information System (INIS)

Tanigawa, Y.; Ootao, Y.

1987-01-01

If we shall analyze the thermal stress problems exactly in a transient state in continuum media, discussed with both the coupling and inertia effect, it has be shown that the thermomechanical coupling term shows a significant role than the inertia term for the common commercial alloys. In the present paper, we have considered the continuum medium with transversely isotropic material property, which has an isotropic property in r-θ plane, and analyzed the transient thermal stress problem of an infinitely long hollow circular cylinder due to an axisymmetrical partial heating. In order to get the thermal and thermoelastic fundamental differential equations separated in each field, we have introduced a perturbation technique. And then, we have carried out numerical calculations for several values of thermal and thermoelastic orthotropical parameters. (orig./GL)

Changes of the Temperature and Precipitation Extremes on Homogenized Data

Directory of Open Access Journals (Sweden)

LAKATOS, Mónika

2007-01-01

Full Text Available Climate indices to detect changes have been defined in several international projects onclimate change. Climate index calculations require at least daily resolution of time series withoutinhomogeneities, such as transfer of stations, changes in observation practice. In many cases thecharacteristics of the estimated linear trends, calculated from the original and from the homogenizedtime series are significantly different. The ECA&D (European Climate Assessment & Dataset indicesand some other special temperature and precipitation indices of own development were applied to theClimate Database of the Hungarian Meteorological Service. Long term daily maximum, minimum anddaily mean temperature data series and daily precipitation sums were examined. The climate indexcalculation processes were tested on original observations and on homogenized daily data fortemperature; in the case of precipitation a complementation process was performed to fill in the gapsof missing data. Experiences of comparing the climate index calculation results, based on original andcomplemented-homogenized data, are reported in this paper. We present the preliminary result ofclimate index calculations also on gridded (interpolated daily data.

Love waves in a structure with an inhomogeneous layer

International Nuclear Information System (INIS)

Ghazaryan, K.B.; Piliposyan, D.G.

2011-01-01

The problem of the propagation of Love type waves in a structure consisting of a finite inhomogeneous layer sandwiched between two isotropic homogeneous half spaces is investigated. Two types of inhomogeneity are considered. It is shown that in one case the amplitude of vibrations in the middle layer is a sinusoidal function of distance from the plane of symmetry, but that in the other case it may be non-sinusoidal for certain values of the parameters of the problem

Supersymmetry and the constants of motion of the two-dimensional isotropic harmonic oscillator

International Nuclear Information System (INIS)

Torres del Castillo, G.F.; Tepper G, T.

2002-01-01

It is shown that the constants of motion of the two-dimensional isotropic harmonic oscillator not related to the rotational invariance of the Hamiltonian can be derived using the ideas of supersymmetric quantum mechanics. (Author)

Multi-contrast, isotropic, single-slab 3D MR imaging in multiple sclerosis

NARCIS (Netherlands)

Moraal, B.; Roosendaal, S.D.; Pouwels, P.J.W.; Vrenken, H.; van Schijndel, R.A.; Meier, D.S.; Guttmann, C.R.G.; Geurts, J.J.G.; Barkhof, F.

2008-01-01

To describe signal and contrast properties of an isotropic, single-slab 3D dataset [double inversion-recovery (DIR), fluid-attenuated inversion recovery (FLAIR), T2, and T1-weighted magnetization prepared rapid acquisition gradient-echo (MPRAGE)] and to evaluate its performance in detecting multiple

A simple free energy for the isotropic-nematic phase transition of rods

NARCIS (Netherlands)

Tuinier, R.

2016-01-01

A free energy expression is proposed that describes the isotropic-nematic binodal concentrations of hard rods. A simple analytical form for this free energy was yet only available using a Gaussian trial function for the orientation distribution function (ODF), leading, however, to a significant

Orthogonality Measurement for Homogenous Projects-Bases

Science.gov (United States)

Ivan, Ion; Sandu, Andrei; Popa, Marius

2009-01-01

The homogenous projects-base concept is defined. Next, the necessary steps to create a homogenous projects-base are presented. A metric system is built, which then will be used for analyzing projects. The indicators which are meaningful for analyzing a homogenous projects-base are selected. The given hypothesis is experimentally verified. The…

A controllable viewing angle LCD with an optically isotropic liquid crystal

International Nuclear Information System (INIS)

Kim, Min Su; Lim, Young Jin; Yoon, Sukin; Kang, Shin-Woong; Lee, Seung Hee; Kim, Miyoung; Wu, Shin-Tson

2010-01-01

An optically isotropic liquid crystal (LC) such as a blue phase LC or an optically isotropic nano-structured LC exhibits a very wide viewing angle because the induced birefringence is along the in-plane electric field. Utilizing such a material, we propose a liquid crystal display (LCD) whose viewing angle can be switched from wide view to narrow view using only one panel. In the device, each pixel is divided into two parts: a major pixel and a sub-pixel. The main pixels display the images while the sub-pixels control the viewing angle. In the main pixels, birefringence is induced by horizontal electric fields through inter-digital electrodes leading to a wide viewing angle, while in the sub-pixels, birefringence is induced by the vertical electric field so that phase retardation occurs only at oblique angles. As a result, the dark state (or contrast ratio) of the entire pixel can be controlled by the voltage of the sub-pixels. Such a switchable viewing angle LCD is attractive for protecting personal privacy.

The Galactic Isotropic γ-ray Background and Implications for Dark Matter

Science.gov (United States)

Campbell, Sheldon S.; Kwa, Anna; Kaplinghat, Manoj

2018-06-01

We present an analysis of the radial angular profile of the galacto-isotropic (GI) γ-ray flux-the statistically uniform flux in angular annuli centred on the Galactic centre. Two different approaches are used to measure the GI flux profile in 85 months of Fermi-LAT data: the BDS statistical method which identifies spatial correlations, and a new Poisson ordered-pixel method which identifies non-Poisson contributions. Both methods produce similar GI flux profiles. The GI flux profile is well-described by an existing model of bremsstrahlung, π0 production, inverse Compton scattering, and the isotropic background. Discrepancies with data in our full-sky model are not present in the GI component, and are therefore due to mis-modelling of the non-GI emission. Dark matter annihilation constraints based solely on the observed GI profile are close to the thermal WIMP cross section below 100 GeV, for fixed models of the dark matter density profile and astrophysical γ-ray foregrounds. Refined measurements of the GI profile are expected to improve these constraints by a factor of a few.

Apparent splitting of S waves propagating through an isotropic lowermost mantle

KAUST Repository

Parisi, Laura

2018-03-24

Observations of shear‐wave anisotropy are key for understanding the mineralogical structure and flow in the mantle. Several researchers have reported the presence of seismic anisotropy in the lowermost 150–250 km of the mantle (i.e., D” layer), based on differences in the arrival times of vertically (SV) and horizontally (SH) polarized shear waves. By computing waveforms at period > 6 s for a wide range of 1‐D and 3‐D Earth structures we illustrate that a time shift (i.e., apparent splitting) between SV and SH may appear in purely isotropic simulations. This may be misinterpreted as shear wave anisotropy. For near‐surface earthquakes, apparent shear wave splitting can result from the interference of S with the surface reflection sS. For deep earthquakes, apparent splitting can be due to the S‐wave triplication in D”, reflections off discontinuities in the upper mantle and 3‐D heterogeneity. The wave effects due to anomalous isotropic structure may not be easily distinguished from purely anisotropic effects if the analysis does not involve full waveform simulations.

Apparent splitting of S waves propagating through an isotropic lowermost mantle

KAUST Repository

Parisi, Laura; Ferreira, Ana M. G.; Ritsema, Jeroen

2018-01-01

Observations of shear‐wave anisotropy are key for understanding the mineralogical structure and flow in the mantle. Several researchers have reported the presence of seismic anisotropy in the lowermost 150–250 km of the mantle (i.e., D” layer), based on differences in the arrival times of vertically (SV) and horizontally (SH) polarized shear waves. By computing waveforms at period > 6 s for a wide range of 1‐D and 3‐D Earth structures we illustrate that a time shift (i.e., apparent splitting) between SV and SH may appear in purely isotropic simulations. This may be misinterpreted as shear wave anisotropy. For near‐surface earthquakes, apparent shear wave splitting can result from the interference of S with the surface reflection sS. For deep earthquakes, apparent splitting can be due to the S‐wave triplication in D”, reflections off discontinuities in the upper mantle and 3‐D heterogeneity. The wave effects due to anomalous isotropic structure may not be easily distinguished from purely anisotropic effects if the analysis does not involve full waveform simulations.

Isotropic and anisotropic pinning in TFA-grown YBa2Cu3O7−x films with BaZrO3 nanoparticles

International Nuclear Information System (INIS)

Palau, A; Llordés, A; Puig, T; Obradors, X; Bartolomé, E

2011-01-01

YBCO films grown by the trifluoroacetate (TFA) method with increasing number of BaZrO 3 (BZO) nanoparticles have been measured by in-field angular transport measurements to investigate changes in the pinning landscape. The isotropic and anisotropic contributions to the critical current density, J c (H), with the magnetic field applied in H||c and H||ab orientation have been determined, allowing us to characterize the population of isotropic and correlated defects along the c axis and ab planes. First, the influence of the YBCO oxygenation process on the formation of different sorts of anisotropic defects in standard films is demonstrated. Next, we show that the addition of non-coherent BZO nanoparticles to the YBCO matrix produces an expansion of the single-vortex pinning regime toward higher fields, due to the presence of isotropic pinning centers. Moreover, by increasing the amount of isotropic defects in the BZO nanocomposites it is possible to extend the region dominated by strong isotropic pinning centers to large magnetic fields and thus enhance the irreversibility line.

Analytical solutions of time-fractional models for homogeneous Gardner equation and non-homogeneous differential equations

Directory of Open Access Journals (Sweden)

Olaniyi Samuel Iyiola

2014-09-01

Full Text Available In this paper, we obtain analytical solutions of homogeneous time-fractional Gardner equation and non-homogeneous time-fractional models (including Buck-master equation using q-Homotopy Analysis Method (q-HAM. Our work displays the elegant nature of the application of q-HAM not only to solve homogeneous non-linear fractional differential equations but also to solve the non-homogeneous fractional differential equations. The presence of the auxiliary parameter h helps in an effective way to obtain better approximation comparable to exact solutions. The fraction-factor in this method gives it an edge over other existing analytical methods for non-linear differential equations. Comparisons are made upon the existence of exact solutions to these models. The analysis shows that our analytical solutions converge very rapidly to the exact solutions.

Anisotropy in "isotropic diffusion" measurements due to nongaussian diffusion

DEFF Research Database (Denmark)

Jespersen, Sune Nørhøj; Olesen, Jonas Lynge; Ianuş, Andrada

2017-01-01

Designing novel diffusion-weighted NMR and MRI pulse sequences aiming to probe tissue microstructure with techniques extending beyond the conventional Stejskal-Tanner family is currently of broad interest. One such technique, multidimensional diffusion MRI, has been recently proposed to afford...... model-free decomposition of diffusion signal kurtosis into terms originating from either ensemble variance of isotropic diffusivity or microscopic diffusion anisotropy. This ability rests on the assumption that diffusion can be described as a sum of multiple Gaussian compartments, but this is often...

Oscillatory Dynamics of One-Dimensional Homogeneous Granular Chains

Science.gov (United States)

Starosvetsky, Yuli; Jayaprakash, K. R.; Hasan, Md. Arif; Vakakis, Alexander F.

The acoustics of the homogeneous granular chains has been studied extensively both numerically and experimentally in the references cited in the previous chapters. This chapter focuses on the oscillatory behavior of finite dimensional homogeneous granular chains. It is well known that normal vibration modes are the building blocks of the vibrations of linear systems due to the applicability of the principle of superposition. One the other hand, nonlinear theory is deprived of such a general superposition principle (although special cases of nonlinear superpositions do exist), but nonlinear normal modes ‒ NNMs still play an important role in the forced and resonance dynamics of these systems. In their basic definition [1], NNMs were defined as time-periodic nonlinear oscillations of discrete or continuous dynamical systems where all coordinates (degrees-of-freedom) oscillate in-unison with the same frequency; further extensions of this definition have been considered to account for NNMs of systems with internal resonances [2]...

Homogeneous Spaces and Equivariant Embeddings

CERN Document Server

Timashev, DA

2011-01-01

Homogeneous spaces of linear algebraic groups lie at the crossroads of algebraic geometry, theory of algebraic groups, classical projective and enumerative geometry, harmonic analysis, and representation theory. By standard reasons of algebraic geometry, in order to solve various problems on a homogeneous space it is natural and helpful to compactify it keeping track of the group action, i.e. to consider equivariant completions or, more generally, open embeddings of a given homogeneous space. Such equivariant embeddings are the subject of this book. We focus on classification of equivariant em

Reflectivity of stimulated back scattering in a homogeneous-slab medium in the case of negligible pump-wave damping

International Nuclear Information System (INIS)

Cho, G.S.; Cho, B.H.

1981-01-01

As to the backscatter instability which is one of nonlinear three-wave resonant interactions, the reflectivity(r) in the case of homogeneous-slab medium is calculated, assuming all the three wavepackets negligible damping caused by medium. The expression has turned out such that r = tanh 2 KAsub(p)L, where K, Asub(p), and L are the constant coupling coefficient, the constant pump-wave amplitude, and the thickness of the medium engaged in the interaction each. When this result is interpreted in terms of the stimulated Brillouin back-scattering in a so-called underdense plasma in controlled fusion, we find the reflectivity twice as large as that by others in the limit of large pump-wave damping, and unfitting to former experiments in the independence on the incident laser-light intensity. We see the incompatibility rise chiefly from neglecting the damping of pump-wave in the plasma. In contrast to the former results by others in the limit of large pump-wave damping, our result might be regarded as that for cases of negligible pump-wave damping, in general stimulated back-scattering phenomena. (author)

Critical test of isotropic periodic sum techniques with group-based cut-off schemes.

Science.gov (United States)

Nozawa, Takuma; Yasuoka, Kenji; Takahashi, Kazuaki Z

2018-03-08

Truncation is still chosen for many long-range intermolecular interaction calculations to efficiently compute free-boundary systems, macromolecular systems and net-charge molecular systems, for example. Advanced truncation methods have been developed for long-range intermolecular interactions. Every truncation method can be implemented as one of two basic cut-off schemes, namely either an atom-based or a group-based cut-off scheme. The former computes interactions of "atoms" inside the cut-off radius, whereas the latter computes interactions of "molecules" inside the cut-off radius. In this work, the effect of group-based cut-off is investigated for isotropic periodic sum (IPS) techniques, which are promising cut-off treatments to attain advanced accuracy for many types of molecular system. The effect of group-based cut-off is clearly different from that of atom-based cut-off, and severe artefacts are observed in some cases. However, no severe discrepancy from the Ewald sum is observed with the extended IPS techniques.

How the Spectre of Societal Homogeneity Undermines Equitable Healthcare for Refugees Comment on "Defining and Acting on Global Health: The Case of Japan and the Refugee Crisis".

Science.gov (United States)

Razum, Oliver; Wenner, Judith; Bozorgmehr, Kayvan

2016-10-17

Recourse to a purported ideal of societal homogeneity has become common in the context of the refugee reception crisis - not only in Japan, as Leppold et al report, but also throughout Europe. Calls for societal homogeneity in Europe originate from populist movements as well as from some governments. Often, they go along with reduced social support for refugees and asylum seekers, for example in healthcare provision. The fundamental right to health is then reduced to a citizens' right, granted fully only to nationals. Germany, in spite of welcoming many refugees in 2015, is a case in point: entitlement and access to healthcare for asylum seekers are restricted during the first 15 months of their stay. We show that arguments brought forward to defend such restrictions do not hold, particularly not those which relate to maintaining societal homogeneity. European societies are not homogeneous, irrespective of migration. But as migration will continue, societies need to invest in what we call "globalization within." Removing entitlement restrictions and access barriers to healthcare for refugees and asylum seekers is one important element thereof. © 2017 The Author(s); Published by Kerman University of Medical Sciences. This is an open-access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Stress state of transversally isotropic body with elliptical crack in the presence of a uniform heat flux at its surface

International Nuclear Information System (INIS)

Podil'chuk, Yu.N.

1995-01-01

An explicit solution of the state thermoelasticity problem is constructed for an infinite transversally isotropic body containing an internal elliptical crack in the isotropy plane. It is assumed that a uniform heat flux is specified at the crack surface and the body is free of external loads. Values of the stress-intensity coefficients depending on the heat flux, the crack dimensions, and the thermoelastic properties of the material are obtained. Note that the analogous problem was considered for an isotropic body. The static thermoelasticity problem for a transversally isotropic body with an internal elliptical crack at whose surface linear temperature variation is specified was solved

Vacuum solutions of Bianchi cosmologies in quadratic gravity

International Nuclear Information System (INIS)

Deus, Juliano Alves de; Muller, Daniel

2011-01-01

Full text: In this work we solve numerically the vacuum solutions of field equations of Bianchi homogeneous universes in the context of Semiclassical theory. Our interest is to study the quadratic theory of gravity with regard in the cosmological description of our universe in periods of intense fields. Bianchi cosmologies are anisotropic homogeneous cosmological models, but can include the isotropic models as particular cases (Bianchi I, VII and IX include homogeneous and isotropic Friedmann models plane, hyperbolic and spherical, respectively). Homogeneous models are good cosmological representations of our universe. With focus in solutions for intense fields, like the early universe, where isotropy is not necessarily required, the adopted scenario is the vacuum solutions, where the geometry is dominant in determining the gravitation. Still following in this way, the Semiclassical theory, which considers quantum matter fields propagating in classical geometrical background, is addressed to give the field equations. This formalism leads to fourth-order ordinary differential equations, in contrast to second-order equations from General Relativity. The Lagrangian of the theory is quadratic in the Ricci scalar and in the Ricci tensor. The equations system is highly non-linear and can be only numerically solved, except perhaps for few particular cases. We obtained numerical solutions for Bianchi V II A evolving to Minkowski and to de Sitter solutions, and also to singularities. The both first and second solutions were obtained choosing initial conditions near from respective exact vacuum solutions from Einstein theory, which are also exact solutions of the quadratic theory. Other Bianchi types are still under study. (author)

Integrated dual-tomography for refractive index analysis of free-floating single living cell with isotropic superresolution.

Science.gov (United States)

B, Vinoth; Lai, Xin-Ji; Lin, Yu-Chih; Tu, Han-Yen; Cheng, Chau-Jern

2018-04-13

Digital holographic microtomography is a promising technique for three-dimensional (3D) measurement of the refractive index (RI) profiles of biological specimens. Measurement of the RI distribution of a free-floating single living cell with an isotropic superresolution had not previously been accomplished. To the best of our knowledge, this is the first study focusing on the development of an integrated dual-tomographic (IDT) imaging system for RI measurement of an unlabelled free-floating single living cell with an isotropic superresolution by combining the spatial frequencies of full-angle specimen rotation with those of beam rotation. A novel 'UFO' (unidentified flying object) like shaped coherent transfer function is obtained. The IDT imaging system does not require any complex image-processing algorithm for 3D reconstruction. The working principle was successfully demonstrated and a 3D RI profile of a single living cell, Candida rugosa, was obtained with an isotropic superresolution. This technology is expected to set a benchmark for free-floating single live sample measurements without labeling or any special sample preparations for the experiments.

Internal homogenization: effective permittivity of a coated sphere.

Science.gov (United States)

Chettiar, Uday K; Engheta, Nader

2012-10-08

The concept of internal homogenization is introduced as a complementary approach to the conventional homogenization schemes, which could be termed as external homogenization. The theory for the internal homogenization of the permittivity of subwavelength coated spheres is presented. The effective permittivity derived from the internal homogenization of coreshells is discussed for plasmonic and dielectric constituent materials. The effective model provided by the homogenization is a useful design tool in constructing coated particles with desired resonant properties.

Renormalization of a tensorial field theory on the homogeneous space SU(2)/U(1)

Science.gov (United States)

Lahoche, Vincent; Oriti, Daniele

2017-01-01

We study the renormalization of a general field theory on the homogeneous space (SU(2)/ ≤ft. U(1)\\right){{}× d} with tensorial interaction and gauge invariance under the diagonal action of SU(2). We derive the power counting for arbitrary d. For the case d  =  4, we prove perturbative renormalizability to all orders via multi-scale analysis, study both the renormalized and effective perturbation series, and establish the asymptotic freedom of the model. We also outline a general power counting for the homogeneous space {{≤ft(SO(D)/SO(D-1)\\right)}× d} , of direct interest for quantum gravity models in arbitrary dimension, and point out the obstructions to the direct generalization of our results to these cases.

Observation of transverse patterns in an isotropic microchip laser

International Nuclear Information System (INIS)

Chen, Y.F.; Lan, Y.P.

2003-01-01

An isotropic microchip laser is used to study the characteristics of high-order wave functions in a two-dimensional (2D) quantum harmonic oscillator based on the identical functional forms. With a doughnut pump profile, the spontaneous transverse modes are found to, generally, be elliptic and hyperbolic transverse modes. Theoretical analyses reveal that the elliptic transverse modes are analogous to the coherent states of a 2D harmonic oscillator; the formation of hyperbolic transverse modes is a spontaneous mode locking between two identical Hermite-Gaussian modes

Analysis of dryout behaviour in laterally non-homogeneous debris beds using the MEWA-2D code

International Nuclear Information System (INIS)

Rahman, Saidur; Buerger, Manfred; Buck, Michael; Pohlner, Georg; Kulenovic, Rudi; Nayak, Arun Kumar; Sehgal, Bal Raj

2009-01-01

The present study analyses the impact of lateral non-homogeneities on the coolability of heated, initially water filled debris beds. Debris beds which may be formed in a postulated severe accident in light water reactors can not be expected to have a homogeneous structure. Lateral non-homogeneities are given e.g. already by a variation in height as in a heap of debris. Internally, less porous or more porous region may occur, the latter even as downcomer-like structures are considered to favour supply of water to the bed and thus coolability. In previous work it has been shown that such non-homogeneities are often strongly enhancing coolability, as compared to earlier investigations on laterally homogeneous beds. The present contribution aims at extending the view by analysing further cases of non-homogeneities with the MEWA-2D code. Especially, effects of capillary forces are considered in contrast to earlier analysis. Part of the paper deals with specific experiments performed in the POMECO facility at KTH in which a laterally stratified debris bed has been considered, whereby especially a strong jump of porosity, from 0.26 to 0.38, has been established. Astonishingly, under top as well as bottom flooding, dryout in these experiments occurred first in the lateral layer with higher porosity. Understanding is now provided by the effect of capillary forces: water is drawn from this layer to the less porous one. This effect improves the cooling in the less porous layer while it reduces coolability of the more porous layer. No real loop behaviour of inflow via the higher porosities with subsequent upflow in the less porous layer establishes here, in contrast to expectations. Other cases (different lateral heating in an otherwise homogeneous bed, closed downcomer in a homogeneous bed and heap-like debris) show, on the other hand, strongly improved coolability by such loops establishing due to the lateral differences in void and the corresponding pressure differences

The design of coils for the production of high homogeneous fields

International Nuclear Information System (INIS)

Desportes, H.

1964-01-01

The discovery of type II superconductors has considerably increased the possibilities of air-core coils, in particular with regard to the production of high homogeneous fields. The design of such magnets,calls for elaborate calculations which, in practise, can only be carried out on computers. The present report describes a complete set of programs for the calculation, in the case of cylindrical systems, of the magnetic field components at any point, the lines of flux, the forces, the self and mutual inductances, as well as the design of compensated coils for the production of high homogeneous fields. These programs have been employed for the calculation of two magnets which are described in detail. (author) [fr

An efficient eikonal solver for tilted transversely isotropic and tilted orthorhombic media

KAUST Repository

Waheed, Umair bin

2014-01-01

Computing first-arrival traveltimes in the presence of anisotropy is important for high-end near surface modeling, microseismic source localization, and fractured reservoir characterization. Anisotropy deviating from elliptical anisotropy introduces higher-order nonlinearity into the eikonal equation, which makes solving the equation a challenging task. We address this challenge by iteratively solving a sequence of simpler tilted elliptically anisotropic eikonal equations. At each iteration, the source function is updated to capture the effects due to the higher order nonlinear terms in the anisotropy. We use Aitken extrapolation to speed up the convergence rate of the iterative algorithm. The result is an efficient algorithm for firstarrival traveltime computations in tilted anisotropic media. We demonstrate the proposed method for the tilted transversely isotropic media and the tilted orthorhombic media. Numerical tests show that the proposed method is feasible and produces results that are comparable to wavefield extrapolation, even for strongly anisotropic and complex structures. Therefore, for the cases where one or two-point ray tracing fails, our method may be a potential substitute for computing traveltimes.

Homogeneous versus heterogeneous zeolite nucleation

NARCIS (Netherlands)

Dokter, W.H.; Garderen, van H.F.; Beelen, T.P.M.; Santen, van R.A.; Bras, W.

1995-01-01

Aggregates of fractal dimension were found in the intermediate gel phases that organize prior to nucleation and crystallization (shown right) of silicalite from a homogeneous reaction mixture. Small- and wide-angle X-ray scattering studies prove that for zeolites nucleation may be homogeneous or

Effective elastic properties of damaged isotropic solids

International Nuclear Information System (INIS)

Lee, U Sik

1998-01-01

In continuum damage mechanics, damaged solids have been represented by the effective elastic stiffness into which local damage is smoothly smeared. Similarly, damaged solids may be represented in terms of effective elastic compliances. By virtue of the effective elastic compliance representation, it may become easier to derive the effective engineering constants of damaged solids from the effective elastic compliances, all in closed form. Thus, in this paper, by using a continuum modeling approach based on both the principle of strain energy equivalence and the equivalent elliptical micro-crack representation of local damage, the effective elastic compliance and effective engineering constants are derived in terms of the undamaged (virgin) elastic properties and a scalar damage variable for both damaged two-and three-dimensional isotropic solids

Comparison between 3D isotropic and 2D conventional MR arthrography for diagnosing rotator cuff tear and labral lesions: A meta-analysis.

Science.gov (United States)

Lee, Sun Hwa; Yun, Seong Jong; Jin, Wook; Park, So Young; Park, Ji Seon; Ryu, Kyung Nam

2018-03-30

Although 3D-isotropic MR arthrography has been characterized as a substitute imaging tool for rotator cuff tear (RCT) and labral lesions, it has not been commonly used in clinical practice because of controversy related to image blurring and indistinctness of structural edges. To perform a comparison of the diagnostic performance of 3D-isotropic MR arthrography and 2D-conventional MR arthrography for diagnosis of RCT (solely RCT, full/partial-thickness supraspinatus [SST]-infraspinatus [IST] tear, or subscapularis [SSc] tear) and labral lesions. Meta-analysis. Patients with shoulder pain. 3D-isotropic and 2D-conventional MR arthrography at 3.0T or 1.5T. PubMed and EMBASE were searched following the PRISMA guidelines. Bivariate modeling and hierarchical summary receiver operating characteristic modeling were performed to compare the overall diagnostic performance of 3D-isotropic and 2D-conventional MR arthrography. Multiple-subgroup analyses were performed for diagnosing RCT, full/partial-thickness SST-IST tear, SSc tear, and labral lesions. Meta-regression analyses were performed according to subject, study, and MR arthrography characteristics including 3D-isotropic sequences (turbo spine echo [TSE] vs. gradient echo [GRE]). Eleven studies (825 patients) were included. Overall, 3D-isotropic MR arthrography had similar pooled sensitivity (0.90 [95% CI, 0.87-0.93]) (P = 0.95) and specificity (0.92 [95% CI, 0.87-0.95]) (P = 0.99), relative to 2D-conventional MR arthrography (sensitivity, 0.91 [95% CI, 0.86-0.94]); specificity, 0.92 [95% CI, 0.87-0.95]). Multiple-subgroup analyses showed that sensitivities (P = 0.13-0.91) and specificities (P = 0.26-0.99) on 3D-isotropic MR arthrography for diagnosing RCT, full/partial-thickness SST-IST tear, SSC tear, and labral lesions were not significantly different from 2D-conventional MR arthrography. On meta-regression analysis, 3D-TSE sequence demonstrated higher sensitivity (P 3D-GRE for RCT and labral

Hierarchy compensation of non-homogeneous intermittent atmospheric turbulence

Science.gov (United States)

Redondo, Jose M.; Mahjoub, Otman B.; Cantalapiedra, Inma R.

2010-05-01

In this work a study both the internal turbulence energy cascade intermittency evaluated from wind speed series in the atmospheric boundary layer, as well as the role of external or forcing intermittency based on the flatness (Vindel et al 2008)is carried out. The degree of intermittency in the stratified ABL flow (Cuxart et al. 2000) can be studied as the deviation, from the linear form, of the absolute scaling exponents of the structure functions as well as generalizing for non-isotropic and non-homogeneous turbulence, even in non-inertial ranges (in the Kolmogorov-Kraichnan sense) where the scaling exponents are not constant. The degree of intermittency, evaluated in the non-local quasi-inertial range, is explained from the variation with scale of the energy transfer as well as the dissipation. The scale to scale transfer and the structure function scaling exponents are calculated and from these the intermittency parametres. The turbulent diffusivity could also be estimated and compared with Richardson's law. Some two point correlations and time lag calculations are used to investigate the time and spatial integral length scales obtained from both Lagrangian and Eulerian correlations and functions, and we compare these results with both theoretical and laboratory data. We develop a theoretical description of how to measure the different levels of intermittency following (Mahjoub et al. 1998, 2000) and the role of locality in higher order exponents of structure function analysis. Vindel J.M., Yague C. and Redondo J.M. (2008) Structure function analysis and intermittency in the ABL. Nonlin. Processes Geophys., 15, 915-929. Cuxart J, Yague C, Morales G, Terradellas E, Orbe J, Calvo J, Fernández A, Soler M R, Infante C, Buenestado P, Espinalt A, Joergensen H E, Rees J M, Vilá J, Redondo J M, Cantalapiedra R and Conangla L (2000): Stable atmospheric boundary-layer experiment in Spain (Sables 98): a report, Boundary-Layer Meteorology 96, 337-370 Mahjoub O

Rapid-onset obesity, hypoventilation, hypothalamic dysfunction, autonomic dysregulation and neuroendocrine tumor syndrome with a homogenous enlargement of the pituitary gland: a case report.

Science.gov (United States)

Aljabban, Lama; Kassab, Lina; Bakoura, Nour Alhuda; Alsalka, Mohammad Fayez; Maksoud, Ismaeil

2016-11-22

Rapid-onset obesity with hypoventilation, hypothalamic dysfunction, and autonomic dysregulation syndrome is a rare pediatric disorder with a variable sequence of clinical presentations, undefined etiology, and high risk of mortality. Our patient presented an unusual course of the disease accompanied by a homogenous mild enlargement of her pituitary gland with an intact pituitary-endocrine axis which, to the best of our knowledge, represents a new finding in rapid-onset obesity with hypoventilation, hypothalamic dysfunction, and autonomic dysregulation syndrome. We present a documented case of a 4 years and 8-month-old Syrian Arabic girl with a distinctive course of signs and symptoms of rapid-onset obesity with hypoventilation, hypothalamic dysfunction, and autonomic dysregulation syndrome accompanied by mature ganglioneuroma in her chest, a homogenous mild enlargement of her pituitary gland, generalized cortical brain atrophy, and seizures. Three months after her first marked symptoms were noted she had a sudden progression of severe respiratory distress that ended with her death. The findings of this case could increase our understanding of the pathogenetic mechanisms of rapid-onset obesity with hypoventilation, hypothalamic dysfunction, and autonomic dysregulation, and place more emphases on pediatricians to consider rapid-onset obesity with hypoventilation, hypothalamic dysfunction, and autonomic dysregulation syndrome whenever early rapid onset of obesity, associated with any malfunction, is observed in children. This knowledge could be lifesaving for children with rapid-onset obesity with hypoventilation, hypothalamic dysfunction, and autonomic dysregulation syndrome.

Benchmarking homogenization algorithms for monthly data

Directory of Open Access Journals (Sweden)

V. K. C. Venema

2012-01-01

Full Text Available The COST (European Cooperation in Science and Technology Action ES0601: advances in homogenization methods of climate series: an integrated approach (HOME has executed a blind intercomparison and validation study for monthly homogenization algorithms. Time series of monthly temperature and precipitation were evaluated because of their importance for climate studies and because they represent two important types of statistics (additive and multiplicative. The algorithms were validated against a realistic benchmark dataset. The benchmark contains real inhomogeneous data as well as simulated data with inserted inhomogeneities. Random independent break-type inhomogeneities with normally distributed breakpoint sizes were added to the simulated datasets. To approximate real world conditions, breaks were introduced that occur simultaneously in multiple station series within a simulated network of station data. The simulated time series also contained outliers, missing data periods and local station trends. Further, a stochastic nonlinear global (network-wide trend was added.

Participants provided 25 separate homogenized contributions as part of the blind study. After the deadline at which details of the imposed inhomogeneities were revealed, 22 additional solutions were submitted. These homogenized datasets were assessed by a number of performance metrics including (i the centered root mean square error relative to the true homogeneous value at various averaging scales, (ii the error in linear trend estimates and (iii traditional contingency skill scores. The metrics were computed both using the individual station series as well as the network average regional series. The performance of the contributions depends significantly on the error metric considered. Contingency scores by themselves are not very informative. Although relative homogenization algorithms typically improve the homogeneity of temperature data, only the best ones improve

Unified double- and single-sided homogeneous Green's function representations

Science.gov (United States)

Wapenaar, Kees; van der Neut, Joost; Slob, Evert

2016-06-01

In wave theory, the homogeneous Green's function consists of the impulse response to a point source, minus its time-reversal. It can be represented by a closed boundary integral. In many practical situations, the closed boundary integral needs to be approximated by an open boundary integral because the medium of interest is often accessible from one side only. The inherent approximations are acceptable as long as the effects of multiple scattering are negligible. However, in case of strongly inhomogeneous media, the effects of multiple scattering can be severe. We derive double- and single-sided homogeneous Green's function representations. The single-sided representation applies to situations where the medium can be accessed from one side only. It correctly handles multiple scattering. It employs a focusing function instead of the backward propagating Green's function in the classical (double-sided) representation. When reflection measurements are available at the accessible boundary of the medium, the focusing function can be retrieved from these measurements. Throughout the paper, we use a unified notation which applies to acoustic, quantum-mechanical, electromagnetic and elastodynamic waves. We foresee many interesting applications of the unified single-sided homogeneous Green's function representation in holographic imaging and inverse scattering, time-reversed wave field propagation and interferometric Green's function retrieval.

Bel-Robinson energy and the nature of singularities in isotropic cosmologies

International Nuclear Information System (INIS)

Klaoudatou, Ifigeneia; Cotsakis, Spiros

2007-01-01

We review our recent work on the classification of finite time singularities that arise in isotropic universes. This scheme is based on the exploitation of the Bel Robinson energy in a cosmological setting. We comment on the relation between geodesic completeness and the Bel Robinson energy and present evidence that relates the divergence of the latter to the existence of closed trapped surfaces

New bounds on isotropic Lorentz violation

International Nuclear Information System (INIS)

Carone, Christopher D.; Sher, Marc; Vanderhaeghen, Marc

2006-01-01

Violations of Lorentz invariance that appear via operators of dimension four or less are completely parametrized in the Standard Model Extension (SME). In the pure photonic sector of the SME, there are 19 dimensionless, Lorentz-violating parameters. Eighteen of these have experimental upper bounds ranging between 10 -11 and 10 -32 ; the remaining parameter, k-tilde tr , is isotropic and has a much weaker bound of order 10 -4 . In this Brief Report, we point out that k-tilde tr gives a significant contribution to the anomalous magnetic moment of the electron and find a new upper bound of order 10 -8 . With reasonable assumptions, we further show that this bound may be improved to 10 -14 by considering the renormalization of other Lorentz-violating parameters that are more tightly constrained. Using similar renormalization arguments, we also estimate bounds on Lorentz-violating parameters in the pure gluonic sector of QCD

Effect of dynamic strain aging on isotropic hardening in low cycle fatigue for carbon manganese steel

International Nuclear Information System (INIS)

Huang, Zhi Yong; Chaboche, Jean-Louis; Wang, Qing Yuan; Wagner, Danièle; Bathias, Claude

2014-01-01

Carbon–manganese steel A48 (French standard) is used in steam generator pipes of nuclear reactor pressure vessels at high temperatures (about 200 °C). The steel is sensitive to dynamic strain aging in monotonic tensile test and low cycle fatigue test at certain temperature range and strain rate. Its isotropic hardening behavior observed from experiments has a hardening, softening and hardening evolution with the effect of dynamic strain aging. The isotropic hardening model is improved by coupling the dislocation and dynamic strain aging theory to describe the behavior of A48 at 200 °C

Effect of dynamic strain aging on isotropic hardening in low cycle fatigue for carbon manganese steel

Energy Technology Data Exchange (ETDEWEB)

Huang, Zhi Yong, E-mail: huangzy@scu.edu.cn [Sichuan University, School of Aeronautics and Astronautics, No. 29 Jiuyanqiao Wangjiang Road, Chengdu 610064 (China); Chaboche, Jean-Louis [ONERA, DMSM, 29 avenue de la Division Lecerc, F-92320 Chatillon (France); Wang, Qing Yuan [Sichuan University, School of Aeronautics and Astronautics, No. 29 Jiuyanqiao Wangjiang Road, Chengdu 610064 (China); Wagner, Danièle; Bathias, Claude [Université ParisOuest Nanterre La Défense (France)

2014-01-01

Carbon–manganese steel A48 (French standard) is used in steam generator pipes of nuclear reactor pressure vessels at high temperatures (about 200 °C). The steel is sensitive to dynamic strain aging in monotonic tensile test and low cycle fatigue test at certain temperature range and strain rate. Its isotropic hardening behavior observed from experiments has a hardening, softening and hardening evolution with the effect of dynamic strain aging. The isotropic hardening model is improved by coupling the dislocation and dynamic strain aging theory to describe the behavior of A48 at 200 °C.

A second stage homogenization method

International Nuclear Information System (INIS)

Makai, M.

1981-01-01

A second homogenization is needed before the diffusion calculation of the core of large reactors. Such a second stage homogenization is outlined here. Our starting point is the Floquet theorem for it states that the diffusion equation for a periodic core always has a particular solution of the form esup(j)sup(B)sup(x) u (x). It is pointed out that the perturbation series expansion of function u can be derived by solving eigenvalue problems and the eigenvalues serve to define homogenized cross sections. With the help of these eigenvalues a homogenized diffusion equation can be derived the solution of which is cos Bx, the macroflux. It is shown that the flux can be expressed as a series of buckling. The leading term in this series is the well known Wigner-Seitz formula. Finally three examples are given: periodic absorption, a cell with an absorber pin in the cell centre, and a cell of three regions. (orig.)

Sewage sludge solubilization by high-pressure homogenization.

Science.gov (United States)

Zhang, Yuxuan; Zhang, Panyue; Guo, Jianbin; Ma, Weifang; Fang, Wei; Ma, Boqiang; Xu, Xiangzhe

2013-01-01

The behavior of sludge solubilization using high-pressure homogenization (HPH) treatment was examined by investigating the sludge solid reduction and organics solubilization. The sludge volatile suspended solids (VSS) decreased from 10.58 to 6.67 g/L for the sludge sample with a total solids content (TS) of 1.49% after HPH treatment at a homogenization pressure of 80 MPa with four homogenization cycles; total suspended solids (TSS) correspondingly decreased from 14.26 to 9.91 g/L. About 86.15% of the TSS reduction was attributed to the VSS reduction. The increase of homogenization pressure from 20 to 80 MPa or homogenization cycle number from 1 to 4 was favorable to the sludge organics solubilization, and the protein and polysaccharide solubilization linearly increased with the soluble chemical oxygen demand (SCOD) solubilization. More proteins were solubilized than polysaccharides. The linear relationship between SCOD solubilization and VSS reduction had no significant change under different homogenization pressures, homogenization cycles and sludge solid contents. The SCOD of 1.65 g/L was solubilized for the VSS reduction of 1.00 g/L for the three experimental sludge samples with a TS of 1.00, 1.49 and 2.48% under all HPH operating conditions. The energy efficiency results showed that the HPH treatment at a homogenization pressure of 30 MPa with a single homogenization cycle for the sludge sample with a TS of 2.48% was the most energy efficient.

Simulation of ferric ions transfer in dosemeter Fricke-Xylenol-Gel in means no homogeneous

International Nuclear Information System (INIS)

Milani, Caio J.; Bevilacqua, Joyce da Silva; Cavinato, Christianne C.; Rodrigues Junior, Orlando; Campos, Leticia L.

2013-01-01

Dosimetry in three dimensions using Fricke-Xilenol-Gel dosimeters (FXG) allows the confirmation and a better understanding of a treatment by Radiotherapy. The technique involves the assessment of the irradiated volumes by magnetic resonance imaging (MRI) or optical-CT. On both cases, the time elapsed between the irradiation and the measurement is an important factor in the quality of results. The quality of the images can be compromised by the mobility of the ferric ions (Fe 3+ ), formed during the the interaction of the radiation with the matter, increasing the uncertainty in the determination of the isodoses in the volume. In this work, the phenomenon of the diffusion of the ferric ions formed by an irradiated region is simulated in a bidimensional domain. The dynamic of the Fe 3+ in Fricke-Gel is modeled by a parabolic partial differential equation and solved by the ADI-Peaceman-Rachford algorithm. Stability and consistency of the method guarantee the convergence of the numerical solution for a pre-defined error magnitude, based on choices for the discretization values of time and space. Homogeneous and non-homogeneous cases are presented considering an irradiated region and a physical barrier that prevents the movement of the ions, on the non-homogeneous case. Graphical visualizations of the phenomenon are presented for better understanding of the process. (author)

Coding of time-dependent stimuli in homogeneous and heterogeneous neural populations.

Science.gov (United States)

Beiran, Manuel; Kruscha, Alexandra; Benda, Jan; Lindner, Benjamin

2018-04-01

We compare the information transmission of a time-dependent signal by two types of uncoupled neuron populations that differ in their sources of variability: i) a homogeneous population whose units receive independent noise and ii) a deterministic heterogeneous population, where each unit exhibits a different baseline firing rate ('disorder'). Our criterion for making both sources of variability quantitatively comparable is that the interspike-interval distributions are identical for both systems. Numerical simulations using leaky integrate-and-fire neurons unveil that a non-zero amount of both noise or disorder maximizes the encoding efficiency of the homogeneous and heterogeneous system, respectively, as a particular case of suprathreshold stochastic resonance. Our findings thus illustrate that heterogeneity can render similarly profitable effects for neuronal populations as dynamic noise. The optimal noise/disorder depends on the system size and the properties of the stimulus such as its intensity or cutoff frequency. We find that weak stimuli are better encoded by a noiseless heterogeneous population, whereas for strong stimuli a homogeneous population outperforms an equivalent heterogeneous system up to a moderate noise level. Furthermore, we derive analytical expressions of the coherence function for the cases of very strong noise and of vanishing intrinsic noise or heterogeneity, which predict the existence of an optimal noise intensity. Our results show that, depending on the type of signal, noise as well as heterogeneity can enhance the encoding performance of neuronal populations.

The Effect of pH and High-Pressure Homogenization on Droplet Size

Directory of Open Access Journals (Sweden)

Ah Pis Yong

2017-12-01

Full Text Available The aims of this study are to revisit the effect of high pressure on homogenization and the influence of pH on the emulsion droplet sizes. The high-pressure homogenization (HPH involves two stages of processing, where the first stage involves in blending the coarse emulsion by a blender, and the second stage requires disruption of the coarse emulsion into smaller droplets by a high-pressure homogenizer. The pressure range in this review is in between 10-500 MPa. The homogenised droplet sizes can be reduced by increasing the homogenization recirculation, and there is a threshold point beyond that by applying pressure only, the size cannot be further reduced. Normally, homogenised emulsions are classified by their degree of kinetic stability. Dispersed phase present in the form of droplets while continuous phase also known as suspended droplets. With a proper homogenization recirculation and pressure, a more kinetically stable emulsion can be produced. The side effects of increasing homogenization pressure are that it can cause overprocessing of the emulsion droplets where the droplet sizes become larger rather than the expected smaller size. This can cause kinetic instability in the emulsion. The droplet size is usually measured by dynamic light scattering or by laser light scattering technique. The type of samples used in this reviews are such as chocolate and vanilla based powders; mean droplet sizes samples; basil oil; tomato; lupin protein; oil; skim milk, soymilk; coconut milk; tomato homogenate; corn; egg-yolk, rapeseed and sunflower; Poly(4-vinylpyridine/silica; and Complex 1 until complex 4 approaches from author case study. A relationship is developed between emulsion size and pH. Results clearly show that lower pH offers smaller droplet of emulsion and the opposite occurs when the pH is increased.

Weak convergence to isotropic complex S α S $S\\alpha S$ random measure

Directory of Open Access Journals (Sweden)

Jun Wang

2017-09-01

Full Text Available Abstract In this paper, we prove that an isotropic complex symmetric α-stable random measure ( 0 < α < 2 $0<\\alpha<2$ can be approximated by a complex process constructed by integrals based on the Poisson process with random intensity.

Singular characteristic tracking algorithm for improved solution accuracy of the discrete ordinates method with isotropic scattering

International Nuclear Information System (INIS)

Duo, J. I.; Azmy, Y. Y.

2007-01-01

A new method, the Singular Characteristics Tracking algorithm, is developed to account for potential non-smoothness across the singular characteristics in the exact solution of the discrete ordinates approximation of the transport equation. Numerical results show improved rate of convergence of the solution to the discrete ordinates equations in two spatial dimensions with isotropic scattering using the proposed methodology. Unlike the standard Weighted Diamond Difference methods, the new algorithm achieves local convergence in the case of discontinuous angular flux along the singular characteristics. The method also significantly reduces the error for problems where the angular flux presents discontinuous spatial derivatives across these lines. For purposes of verifying the results, the Method of Manufactured Solutions is used to generate analytical reference solutions that permit estimating the local error in the numerical solution. (authors)

Unbiased stereological estimation of d-dimensional volume in Rn from an isotropic random slice through a fixed point

DEFF Research Database (Denmark)

Jensen, Eva B. Vedel; Kiêu, K

1994-01-01

Unbiased stereological estimators of d-dimensional volume in R(n) are derived, based on information from an isotropic random r-slice through a specified point. The content of the slice can be subsampled by means of a spatial grid. The estimators depend only on spatial distances. As a fundamental ...... lemma, an explicit formula for the probability that an isotropic random r-slice in R(n) through 0 hits a fixed point in R(n) is given....

Decoupled equations for reverse time migration in tilted transversely isotropic media

KAUST Repository

Zhan, Ge; Pestana, Reynam C.; Stoffa, Paul L.

2012-01-01

Conventional modeling and migration for tilted transversely isotropic (TTI) media may suffer from numerical instabilities and shear wave artifacts due to the coupling of the P-wave and SV-wave modes in the TTI coupled equations. Starting with the separated P- and SV-phase velocity expressions for vertical transversely isotropic (VTI) media, we extend these decoupled equations for modeling and reverse time migration (RTM) in acoustic TTI media. Compared with the TTI coupled equations published in the geophysical literature, the new TTI decoupled equations provide a more stable solution due to the complete separation of the P-wave and SV-wave modes. The pseudospectral method is the most convenient method to implement these equations due to the form of wavenumber expressions and has the added benefit of being highly accurate and thus avoiding numerical dispersion. The rapid expansion method (REM) in time is employed to produce a broad band numerically stable time evolution of the wavefields. Synthetic results validate the proposed TTI decoupled equations and show that modeling and RTM in TTI media with the decoupled equations remain numerically stable even for models with strong anisotropy and sharp contrasts. © 2012 Society of Exploration Geophysicists.

Simulating faults and plate boundaries with a transversely isotropic plasticity model

Science.gov (United States)

Sharples, W.; Moresi, L. N.; Velic, M.; Jadamec, M. A.; May, D. A.

2016-03-01

In mantle convection simulations, dynamically evolving plate boundaries have, for the most part, been represented using an visco-plastic flow law. These systems develop fine-scale, localized, weak shear band structures which are reminiscent of faults but it is a significant challenge to resolve the large- and the emergent, small-scale-behavior. We address this issue of resolution by taking into account the observation that a rock element with embedded, planar, failure surfaces responds as a non-linear, transversely isotropic material with a weak orientation defined by the plane of the failure surface. This approach partly accounts for the large-scale behavior of fine-scale systems of shear bands which we are not in a position to resolve explicitly. We evaluate the capacity of this continuum approach to model plate boundaries, specifically in the context of subduction models where the plate boundary interface has often been represented as a planar discontinuity. We show that the inclusion of the transversely isotropic plasticity model for the plate boundary promotes asymmetric subduction from initiation. A realistic evolution of the plate boundary interface and associated stresses is crucial to understanding inter-plate coupling, convergent margin driven topography, and earthquakes.

Decoupled equations for reverse time migration in tilted transversely isotropic media

KAUST Repository

Zhan, Ge

2012-03-01

Conventional modeling and migration for tilted transversely isotropic (TTI) media may suffer from numerical instabilities and shear wave artifacts due to the coupling of the P-wave and SV-wave modes in the TTI coupled equations. Starting with the separated P- and SV-phase velocity expressions for vertical transversely isotropic (VTI) media, we extend these decoupled equations for modeling and reverse time migration (RTM) in acoustic TTI media. Compared with the TTI coupled equations published in the geophysical literature, the new TTI decoupled equations provide a more stable solution due to the complete separation of the P-wave and SV-wave modes. The pseudospectral method is the most convenient method to implement these equations due to the form of wavenumber expressions and has the added benefit of being highly accurate and thus avoiding numerical dispersion. The rapid expansion method (REM) in time is employed to produce a broad band numerically stable time evolution of the wavefields. Synthetic results validate the proposed TTI decoupled equations and show that modeling and RTM in TTI media with the decoupled equations remain numerically stable even for models with strong anisotropy and sharp contrasts. © 2012 Society of Exploration Geophysicists.

A literature review on biotic homogenization

OpenAIRE

Guangmei Wang; Jingcheng Yang; Chuangdao Jiang; Hongtao Zhao; Zhidong Zhang

2009-01-01

Biotic homogenization is the process whereby the genetic, taxonomic and functional similarity of two or more biotas increases over time. As a new research agenda for conservation biogeography, biotic homogenization has become a rapidly emerging topic of interest in ecology and evolution over the past decade. However, research on this topic is rare in China. Herein, we introduce the development of the concept of biotic homogenization, and then discuss methods to quantify its three components (...

A new approach to design of quasi-isotropic antenna systems for satellite applications

DEFF Research Database (Denmark)

Schjær-Jacobsen, Hans; Hansen, J.E.

1976-01-01

The new approach considered takes into account the maximum error of the quasi-isotropic radiation pattern relative to the ideal pattern. A design example involving a spherical satellite with quarter wave monopoles is used to demonstrate the effectiveness of the new approach. An investigation...

Assembly homogenization techniques for light water reactor analysis

International Nuclear Information System (INIS)

Smith, K.S.

1986-01-01

Recent progress in development and application of advanced assembly homogenization methods for light water reactor analysis is reviewed. Practical difficulties arising from conventional flux-weighting approximations are discussed and numerical examples given. The mathematical foundations for homogenization methods are outlined. Two methods, Equivalence Theory and Generalized Equivalence Theory which are theoretically capable of eliminating homogenization error are reviewed. Practical means of obtaining approximate homogenized parameters are presented and numerical examples are used to contrast the two methods. Applications of these techniques to PWR baffle/reflector homogenization and BWR bundle homogenization are discussed. Nodal solutions to realistic reactor problems are compared to fine-mesh PDQ calculations, and the accuracy of the advanced homogenization methods is established. Remaining problem areas are investigated, and directions for future research are suggested. (author)

Improving homogeneity by dynamic speed limit systems.

NARCIS (Netherlands)

Nes, N. van Brandenberg, S. & Twisk, D.A.M.

2010-01-01

Homogeneity of driving speeds is an important variable in determining road safety; more homogeneous driving speeds increase road safety. This study investigates the effect of introducing dynamic speed limit systems on homogeneity of driving speeds. A total of 46 subjects twice drove a route along 12

Coupling of discrete ordinates methods by transmission of boundary conditions in solving the neutron transport equation in slab geometry; Couplage de discretisations aux ordonnees discretes d`equations de transport 1D par passage de conditions frontieres

Energy Technology Data Exchange (ETDEWEB)

Bal, G. [Departement MMN, Service IMA, Direction des Etudes et Recherches, Electricite de France (EDF), 92 - Clamart (France)

1995-10-01

Neutron transport in nuclear reactors is quite well modelled by the linear Boltzmann transport equation. Its solution is relatively easy, but unfortunately too expensive to achieve whole core computations. Thus, we have to simplify it, for example by homogenizing some physical characteristics. However, the solution may then be inaccurate. Moreover, in strongly homogeneous areas, the error may be too big. Then we would like to deal with such an inconvenient by solving the equation accurately on this area, but more coarsely away from it, so that the computation is not too expensive. This problem is the subject of a thesis. We present here some results obtained for slab geometry. The couplings between the fine and coarse discretization regions could be conceived in a number of approaches. Here, we only deal with the coupling at crossing the interface between two sub-domains. In the first section, we present the coupling of discrete ordinate methods for solving the homogeneous, isotropic and mono-kinetic equation. Coupling operators are defined and shown to be optimal. The second and the third sections are devoted to an extension of the previous results when the equation is non-homogeneous, anisotropic and multigroup (under some restrictive assumptions). Some numerical results are given in the case of isotropic and mono-kinetic equations. (author) 15 refs.

Evaluation of effective material properties of spiral wound gasket through homogenization

International Nuclear Information System (INIS)

Mathan, G.; Siva Prasad, N.

2010-01-01

In this paper, a homogenization methodology is proposed to determine the material properties of spiral wound gaskets (SWGs) using finite element analysis through representative volume elements (RVE) of the gaskets. The constituents of this RVE are described by elasto-plastic material properties. The RVE are subjected to six load cases and the volume averaged responses are analyzed simultaneously to predict the anisotropic properties. The mechanical behaviour is simplified to an orthotropic material model with Hill's plasticity model and the properties are verified with micro-mechanical simulation and experimental results available in the literature. Reasonable agreement is obtained between the results. Formulae for elastic properties are also derived by a simplified analytical method based on lamination theory and compared with those obtained from homogenization.

Evaluation of effective material properties of spiral wound gasket through homogenization

Energy Technology Data Exchange (ETDEWEB)

Mathan, G. [Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai 600036 (India); Siva Prasad, N., E-mail: siva@iitm.ac.i [Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai 600036 (India)

2010-12-15

In this paper, a homogenization methodology is proposed to determine the material properties of spiral wound gaskets (SWGs) using finite element analysis through representative volume elements (RVE) of the gaskets. The constituents of this RVE are described by elasto-plastic material properties. The RVE are subjected to six load cases and the volume averaged responses are analyzed simultaneously to predict the anisotropic properties. The mechanical behaviour is simplified to an orthotropic material model with Hill's plasticity model and the properties are verified with micro-mechanical simulation and experimental results available in the literature. Reasonable agreement is obtained between the results. Formulae for elastic properties are also derived by a simplified analytical method based on lamination theory and compared with those obtained from homogenization.

Homogenization of non-uniformly bounded periodic diffusion energies in dimension two

International Nuclear Information System (INIS)

Braides, Andrea; Briane, Marc; Casado-Díaz, Juan

2009-01-01

This paper deals with the homogenization of two-dimensional oscillating convex functionals, the densities of which are equicoercive but not uniformly bounded from above. Using a uniform-convergence result for the minimizers, which holds for this type of scalar problems in dimension two, we prove in particular that the limit energy is local and recover the validity of the analogue of the well-known periodic homogenization formula in this degenerate case. However, in the present context the classical argument leading to integral representation based on the use of cut-off functions is useless due to the unboundedness of the densities. In its place we build sequences with bounded energy, which converge uniformly to piecewise-affine functions, taking point-wise extrema of recovery sequences for affine functions

Homogeneity and thermodynamic identities in geometrothermodynamics

Energy Technology Data Exchange (ETDEWEB)

Quevedo, Hernando [Universidad Nacional Autonoma de Mexico, Instituto de Ciencias Nucleares (Mexico); Universita di Roma ' ' La Sapienza' ' , Dipartimento di Fisica, Rome (Italy); ICRANet, Rome (Italy); Quevedo, Maria N. [Universidad Militar Nueva Granada, Departamento de Matematicas, Facultad de Ciencias Basicas, Bogota (Colombia); Sanchez, Alberto [CIIDET, Departamento de Posgrado, Queretaro (Mexico)

2017-03-15

We propose a classification of thermodynamic systems in terms of the homogeneity properties of their fundamental equations. Ordinary systems correspond to homogeneous functions and non-ordinary systems are given by generalized homogeneous functions. This affects the explicit form of the Gibbs-Duhem relation and Euler's identity. We show that these generalized relations can be implemented in the formalism of black hole geometrothermodynamics in order to completely fix the arbitrariness present in Legendre invariant metrics. (orig.)

A tilted transversely isotropic slowness surface approximation

KAUST Repository

Stovas, A.

2012-05-09

The relation between vertical and horizontal slownesses, better known as the dispersion relation, for transversely isotropic media with a tilted symmetry axis (TTI) requires solving a quartic polynomial equation, which does not admit a practical explicit solution to be used, for example, in downward continuation. Using a combination of the perturbation theory with respect to the anelliptic parameter and Shanks transform to improve the accuracy of the expansion, we develop an explicit formula for the vertical slowness that is highly accurate for all practical purposes. It also reveals some insights into the anisotropy parameter dependency of the dispersion relation including the low impact that the anelliptic parameter has on the vertical placement of reflectors for a small tilt in the symmetry angle. © 2012 European Association of Geoscientists & Engineers.

Isotropic and anisotropic surface wave cloaking techniques

International Nuclear Information System (INIS)

McManus, T M; Spada, L La; Hao, Y

2016-01-01

In this paper we compare two different approaches for surface waves cloaking. The first technique is a unique application of Fermat’s principle and requires isotropic material properties, but owing to its derivation is limited in its applicability. The second technique utilises a geometrical optics approximation for dealing with rays bound to a two dimensional surface and requires anisotropic material properties, though it can be used to cloak any smooth surface. We analytically derive the surface wave scattering behaviour for both cloak techniques when applied to a rotationally symmetric surface deformation. Furthermore, we simulate both using a commercially available full-wave electromagnetic solver and demonstrate a good level of agreement with their analytically derived solutions. Our analytical solutions and simulations provide a complete and concise overview of two different surface wave cloaking techniques. (paper)

Isotropic and anisotropic surface wave cloaking techniques

Science.gov (United States)

McManus, T. M.; La Spada, L.; Hao, Y.

2016-04-01

In this paper we compare two different approaches for surface waves cloaking. The first technique is a unique application of Fermat’s principle and requires isotropic material properties, but owing to its derivation is limited in its applicability. The second technique utilises a geometrical optics approximation for dealing with rays bound to a two dimensional surface and requires anisotropic material properties, though it can be used to cloak any smooth surface. We analytically derive the surface wave scattering behaviour for both cloak techniques when applied to a rotationally symmetric surface deformation. Furthermore, we simulate both using a commercially available full-wave electromagnetic solver and demonstrate a good level of agreement with their analytically derived solutions. Our analytical solutions and simulations provide a complete and concise overview of two different surface wave cloaking techniques.

Angular dependence of coercivity in isotropically aligned Nd-Fe-B sintered magnets

Science.gov (United States)

Matsuura, Yutaka; Nakamura, Tetsuya; Sumitani, Kazushi; Kajiwara, Kentaro; Tamura, Ryuji; Osamura, Kozo

2018-05-01

In order to understand the coercivity mechanism in Nd-Fe-B sintered magnets, the angular dependence of the coercivity of an isotropically aligned Nd15Co1.0B6Febal. sintered magnet was investigated through magnetization measurements using a vibrating sample magnetometer. These results are compared with the angular dependence calculated under the assumption that the magnetization reversal of each grain follows the Kondorskii law or, in other words, the 1/cos θ law for isotropic alignment distributions. The calculated angular dependence of the coercivity agrees very well with the experiment for magnetic fields applied between angles of 0 and 60°, and it is expected that the magnetization reversal occurs in each grain individually followed the 1/cos θ law. In contrast, this agreement between calculation and experiment is not found for anisotropic Nd-Fe-B samples. This implies that the coercivity of the aligned magnets depends upon the de-pinning of the domain walls from pinning sites. When the de-pinning occurs, it is expected that the domain walls are displaced through several grains at once.

Numerical study of the thermal degradation of isotropic and anisotropic polymeric materials

Energy Technology Data Exchange (ETDEWEB)

Soler, E. [Departamento de Lenguajes y Ciencias de la Computacion, ETSI Informatica, Universidad de Malaga, 29071 Malaga (Spain); Ramos, J.I. [Room I-320-D, ETS Ingenieros Industriales, Universidad de Malaga, Plaza El Ejido, s/n, 29013 Malaga (Spain)

2005-08-01

The thermal degradation of two-dimensional isotropic, orthotropic and anisotropic polymeric materials is studied numerically by means of a second-order accurate (in both space and time) linearly implicit finite difference formulation which results in linear algebraic equations at each time step. It is shown that, for both isotropic and orthotropic composites, the monomer mass diffusion tensor plays a role in initiating the polymerization kinetics, the formation of a polymerization kernel and the initial front propagation, whereas the later stages of the polymerization are nearly independent of the monomer mass diffusion tensor. In anisotropic polymeric composites, it has been found that the monomer mass diffusion tensor plays a paramount role in determining the initial stages of the polymerization and the subsequent propagation of the polymerization front, the direction and speed of propagation of which are found to be related to the principal directions of both the monomer mass and the heat diffusion tensors. It is also shown that the polymerization time and temperatures depend strongly on the anisotropy of the mass and heat diffusion tensors. (authors)

Homogeneity of Prototypical Attributes in Soccer Teams

Directory of Open Access Journals (Sweden)

Christian Zepp

2015-09-01

Full Text Available Research indicates that the homogeneous perception of prototypical attributes influences several intragroup processes. The aim of the present study was to describe the homogeneous perception of the prototype and to identify specific prototypical subcategories, which are perceived as homogeneous within sport teams. The sample consists of N = 20 soccer teams with a total of N = 278 athletes (age M = 23.5 years, SD = 5.0 years. The results reveal that subcategories describing the cohesiveness of the team and motivational attributes are mentioned homogeneously within sport teams. In addition, gender, identification, team size, and the championship ranking significantly correlate with the homogeneous perception of prototypical attributes. The results are discussed on the basis of theoretical and practical implications.

A Method of Function Space for Vertical Impedance Function of a Circular Rigid Foundation on a Transversely Isotropic Ground

Directory of Open Access Journals (Sweden)

Morteza Eskandari-Ghadi

2014-06-01

Full Text Available This paper is concerned with investigation of vertical impedance function of a surface rigid circular foundation resting on a semi-infinite transversely isotropic alluvium. To this end, the equations of motion in cylindrical coordinate system, which because of axissymmetry are two coupled equations, are converted into one partial differential equation using a method of potential function. The governing partial differential equation for the potential function is solved via implementing Hankel integral transforms in radial direction. The vertical and radial components of displacement vector are determined with the use of transformed displacement-potential function relationships. The mixed boundary conditions at the surface are satisfied by specifying the traction between the rigid foundation and the underneath alluvium in a special function space introduced in this paper, where the vertical displacements are forced to satisfy the rigid boundary condition. Through exercising these restraints, the normal traction and then the vertical impedance function are obtained. The results are then compared with the existing results in the literature for the simpler case of isotropic half-space, which shows an excellent agreement. Eventually, the impedance functions are presented in terms of dimensionless frequency for different materials. The method presented here may be used to obtain the impedance function in any other direction as well as in buried footing in layered media.

Constitutive relations in multidimensional isotropic elasticity and their restrictions to subspaces of lower dimensions

Science.gov (United States)

Georgievskii, D. V.

2017-07-01

The mechanical meaning and the relationships among material constants in an n-dimensional isotropic elastic medium are discussed. The restrictions of the constitutive relations (Hooke's law) to subspaces of lower dimension caused by the conditions that an m-dimensional strain state or an m-dimensional stress state (1 ≤ m < n) is realized in the medium. Both the terminology and the general idea of the mathematical construction are chosen by analogy with the case n = 3 and m = 2, which is well known in the classical plane problem of elasticity theory. The quintuples of elastic constants of the same medium that enter both the n-dimensional relations and the relations written out for any m-dimensional restriction are expressed in terms of one another. These expressions in terms of the known constants, for example, of a three-dimensional medium, i.e., the classical elastic constants, enable us to judge the material properties of this medium immersed in a space of larger dimension.

Homogenization theory in reactor lattices

International Nuclear Information System (INIS)

Benoist, P.

1986-02-01

The purpose of the theory of homogenization of reactor lattices is to determine, by the mean of transport theory, the constants of a homogeneous medium equivalent to a given lattice, which allows to treat the reactor as a whole by diffusion theory. In this note, the problem is presented by laying emphasis on simplicity, as far as possible [fr

Field-induced optically isotropic state in bent core nematic liquid crystals: unambiguous proof of field-induced optical biaxiality

International Nuclear Information System (INIS)

Elamain, Omaima; Komitov, Lachezar; Hegde, Gurumurthy; Fodor-Csorba, Katalin

2013-01-01

The behaviour of bent core (BC) nematic liquid crystals was investigated under dc applied electric field. The optically isotropic state of a sample containing BC nematic was observed under application of low dc electric fields. The quality of the dark state when the sample was inserted between two crossed polarizers was found to be superb and it did not change when rotating the sample between the polarizers. The coupling between the net molecular dipole moment and the applied dc electric field was considered as the origin of the out-of-plane switching of the BC molecules resulting in switching from the field-off bright state to the field-on dark state. The field-induced optically isotropic state is an unambiguous proof of the field-induced biaxiality in the BC nematic liquid crystal. A simple model explaining the appearance of the isotropic optical state in BC nematics and the switching of the sample slow axis between three mutually orthogonal directions under dc applied electric field is proposed. (paper)

Equilibrium sampling of environmental pollutants in fish: Comparison with lipid- normalized concentrations and homogenization effects on chemical activity

DEFF Research Database (Denmark)

Jahnke, Annika; Mayer, Philipp; Adolfsson-Erici, Margaretha

2011-01-01

of the equilibrium sampling technique, while at the same time confirming that the fugacity capacity of these lipid-rich tissues for PCBs was dominated by the lipid fraction. Equilibrium sampling was also applied to homogenates of the same fish tissues. The PCB concentrations in the PDMS were 1.2 to 2.0 times higher...... in the homogenates (statistically significant in 18 of 21 cases, phomogenization increased the chemical activity of the PCBs and decreased the fugacity capacity of the tissue. This observation has implications for equilibrium sampling and partition coefficients determined using tissue...... homogenates....

Efficient testing of the homogeneity, scale parameters and number of components in the Rayleigh mixture

International Nuclear Information System (INIS)

Stehlik, M.; Ososkov, G.A.

2003-01-01

The statistical problem to expand the experimental distribution of transverse momenta into Rayleigh distribution is considered. A high-efficient testing procedure for testing the hypothesis of the homogeneity of the observed measurements which is optimal in the sense of Bahadur is constructed. The exact likelihood ratio (LR) test of the scale parameter of the Rayleigh distribution is proposed for cases when the hypothesis of homogeneity holds. Otherwise the efficient procedure for testing the number of components in the mixture is also proposed

Nonlinear electroelastic deformations of dielectric elastomer composites: II - Non-Gaussian elastic dielectrics

Science.gov (United States)

Lefèvre, Victor; Lopez-Pamies, Oscar

2017-02-01

This paper presents an analytical framework to construct approximate homogenization solutions for the macroscopic elastic dielectric response - under finite deformations and finite electric fields - of dielectric elastomer composites with two-phase isotropic particulate microstructures. The central idea consists in employing the homogenization solution derived in Part I of this work for ideal elastic dielectric composites within the context of a nonlinear comparison medium method - this is derived as an extension of the comparison medium method of Lopez-Pamies et al. (2013) in nonlinear elastostatics to the coupled realm of nonlinear electroelastostatics - to generate in turn a corresponding solution for composite materials with non-ideal elastic dielectric constituents. Complementary to this analytical framework, a hybrid finite-element formulation to construct homogenization solutions numerically (in three dimensions) is also presented. The proposed analytical framework is utilized to work out a general approximate homogenization solution for non-Gaussian dielectric elastomers filled with nonlinear elastic dielectric particles that may exhibit polarization saturation. The solution applies to arbitrary (non-percolative) isotropic distributions of filler particles. By construction, it is exact in the limit of small deformations and moderate electric fields. For finite deformations and finite electric fields, its accuracy is demonstrated by means of direct comparisons with finite-element solutions. Aimed at gaining physical insight into the extreme enhancement in electrostriction properties displayed by emerging dielectric elastomer composites, various cases wherein the filler particles are of poly- and mono-disperse sizes and exhibit different types of elastic dielectric behavior are discussed in detail. Contrary to an initial conjecture in the literature, it is found (inter alia) that the isotropic addition of a small volume fraction of stiff (semi

Determination of point isotropic buildup factors of gamma rays including incoherent and coherent scattering for aluminum, iron, lead, and water by discrete ordinates method

International Nuclear Information System (INIS)

Kitsos, S.; Assad, A.; Diop, C.M.; Nimal, J.C.

1994-01-01

Exposure and energy absorption buildup factors for aluminum, iron, lead, and water are calculated by the SNID discrete ordinates code for an isotropic point source in a homogeneous medium. The calculation of the buildup factors takes into account the effects of both bound-electron Compton (incoherent) and coherent (Rayleigh) scattering. A comparison with buildup factors from the literature shows that these two effects greatly increase the buildup factors for energies below a few hundred kilo-electron-volts, and thus the new results are improved relative to the experiment. This greater accuracy is due to the increase in the linear attenuation coefficient, which leads to the calculation of the buildup factors for a mean free path with a smaller shield thickness. On the other hand, for the same shield thickness, exposure increases when only incoherent scattering is included and decreases when only coherent scattering is included, so that the exposure finally decreases when both effects are included. Great care must also be taken when checking the approximations for gamma-ray deep-penetration transport calculations, as well as for the cross-section treatment and origin

Reconstruction from one boundary measurement of a potential homogeneous of degree zero

DEFF Research Database (Denmark)

Cornean, Horia Decebal; Knudsen, Kim

We consider the inverse boundary value problem concerning the determination and reconstruction of an unknown potential in a Schrödinger equation in a bounded domain from measurements on the boundary of the domain. For the special case of a small potential homogeneous of degree zero we show that one...

Reconstruction from one boundary measurement of a potential homogeneous of degree zero

DEFF Research Database (Denmark)

Cornean, Horia; Knudsen, Kim

2006-01-01

We consider the inverse boundary value problem concerning the determination and reconstruction of an unknown potential in a Schrödinger equation in a bounded domain from measurements on the boundary of the domain. For the special case of a small potential homogeneous of degree zero we show that one...

Enhancement of anaerobic sludge digestion by high-pressure homogenization.

Science.gov (United States)

Zhang, Sheng; Zhang, Panyue; Zhang, Guangming; Fan, Jie; Zhang, Yuxuan

2012-08-01

To improve anaerobic sludge digestion efficiency, the effects of high-pressure homogenization (HPH) conditions on the anaerobic sludge digestion were investigated. The VS and TCOD were significantly removed with the anaerobic digestion, and the VS removal and TCOD removal increased with increasing the homogenization pressure and homogenization cycle number; correspondingly, the accumulative biogas production also increased with increasing the homogenization pressure and homogenization cycle number. The optimal homogenization pressure was 50 MPa for one homogenization cycle and 40 MPa for two homogenization cycles. The SCOD of the sludge supernatant significantly increased with increasing the homogenization pressure and homogenization cycle number due to the sludge disintegration. The relationship between the biogas production and the sludge disintegration showed that the accumulative biogas and methane production were mainly enhanced by the sludge disintegration, which accelerated the anaerobic digestion process and improved the methane content in the biogas. Copyright © 2012 Elsevier Ltd. All rights reserved.

Layered Fiberconcrete with Non-Homogeneous Fibers Distribution

OpenAIRE

Lūsis, V; Krasņikovs, A

2013-01-01

The aim of present research is to create fiberconcrete construction with non-homogeneous fibers distribution in it. Traditionally fibers are homogeneously dispersed in a concrete. At the same time in many situations fiberconcretes with homogeneously dispersed fibers are not optimal (majority of added fibers are not participating in a loads bearing process).

Radiotracer investigation of cement raw meal homogenizers. Pt. 2

International Nuclear Information System (INIS)

Baranyai, L.

1983-01-01

Based on radioisotopic tracer technique a method has been worked out to study the homogenization and segregation processes of cement-industrial raw meal homogenizers. On-site measurements were carried out by this method in some Hungarian cement works to determine the optimal homogenization parameters of operating homogenizers. The motion and distribution of different raw meal fractions traced with 198 Au radioisotope was studied in homogenization processes proceeding with different parameters. In the first part of the publication the change of charge homogenity in time was discussed which had been measured as the resultant of mixing and separating processes. In the second part the parameters and types of homogenizers influencing the efficiency of homogenization have been detailed. (orig.) [de

Radiotracer investigation of cement raw meal homogenizers. Pt. 2

Energy Technology Data Exchange (ETDEWEB)

Baranyai, L

1983-12-01

Based on radioisotopic tracer technique a method has been worked out to study the homogenization and segregation processes of cement-industrial raw meal homogenizers. On-site measurements were carried out by this method in some Hungarian cement works to determine the optimal homogenization parameters of operating homogenizers. The motion and distribution of different raw meal fractions traced with /sup 198/Au radioisotope was studied in homogenization processes proceeding with different parameters. In the first part of the publication the change of charge homogenity in time was discussed which had been measured as the resultant of mixing and separating processes. In the second part the parameters and types of homogenizers influencing the efficiency of homogenization have been detailed.

Raman study of pressure effects on frequencies and isotropic line shapes in liquid acetone

International Nuclear Information System (INIS)

Schindler, W.; Sharko, P.T.; Jonas, J.

1982-01-01

The Raman line shape of the symmetric C = O stretching band at 1710 cm -1 has been measured in liquid acetone as a function of pressure from 1 bar to 4 kbar over the temperature range from -25 to 50 0 C. The experimental data obtained show several unusual features. First, there is a frequency difference of about 7 cm -1 between the polarized and depolarized components. Sceond, the isotropic linewidth GAMMA/sub iso/ decreases with increasing density, in contrast to the opposite trend usually found in other liquids. Third, the second moment M 2 (V) of the isotropic band appears to decrease with increasing density. The consideration of the experimental linewidth and frequency data leads to a conclusion that intermolecular dipole--dipole coupling between polar acetone molecules are responsible for the observed unusual behavior of , GAMMA/sub iso/, and M 2

Water infiltration into homogeneous soils: a new concept

International Nuclear Information System (INIS)

Manfredni, S.

1977-10-01

A new concept for the analytical description of the process of water infiltration into homogeneous soils is presented. The concept uses a new definition of a 'gravitational diffusivity' which permits the generalization of both cases, horizontal and vertical infiltration. The efficiency of the new concept in describing the infiltration process, for short and intermediate times, is proved through experimental data obtained during water infiltration into air-dry soil columns. Its advantages are discussed comparing soil water contents predicted by the numerical solution proposed by PHILLIP (1955, 1957) [pt

Evaluation of homogeneity and dose conformity in IMRT planning in prostate radiotherapy

International Nuclear Information System (INIS)

Lopes, Juliane S.; Leidens, Matheus; Estacio, Daniela R.; Razera, Ricardo A.Z.; Streck, Elaine E.; Silva, Ana M.M. da

2015-01-01

The goal of this study was to evaluate the dose distribution homogeneity and conformity of radiation therapy plans of prostate cancer using IMRT. Data from 34 treatment plans of Hospital Sao Lucas of PUCRS, where those plans were executed, were retrospectively analyzed. All of them were done with 6MV X-rays from a linear accelerator CLINAC IX, and the prescription doses varied between 60 and 74 Gy. Analyses showing the homogeneity and conformity indices for the dose distribution of those plans were made. During these analyses, some comparisons with the traditional radiation therapy planning technic, the 3D-CRT, were discussed. The results showed that there is no correlation between the prescribed dose and the homogeneity and conformity indices, indicating that IMRT works very well even for higher doses. Furthermore, a comparison between the results obtained and the recommendations of ICRU 83 was carried out. It has also been observed that the indices were really close to the ideal values. 82.4% of the cases showed a difference below 5% of the ideal value for the index of conformity, and 88.2% showed a difference below 10% for the homogeneity index. Concluding, it is possible to confirm the quality of the analyzed radiation therapy plans of prostate cancer using IMRT. (author)

Disformal invariance of continuous media with linear equation of state

Energy Technology Data Exchange (ETDEWEB)

Celoria, Marco [Gran Sasso Science Institute (INFN), Viale Francesco Crispi 7, L' Aquila, I-67100 Italy (Italy); Matarrese, Sabino [Dipartimento di Fisica e Astronomia ' G. Galilei' , Università degli Studi di Padova, via Marzolo 8, Padova, I-35131 Italy (Italy); Pilo, Luigi, E-mail: marco.celoria@gssi.infn.it, E-mail: sabino.matarrese@pd.infn.it, E-mail: luigi.pilo@aquila.infn.it [Dipartimento di Fisica, Università di L' Aquila, L' Aquila, I-67010 Italy (Italy)

2017-02-01

We show that the effective theory describing single component continuous media with a linear and constant equation of state of the form p = w ρ is invariant under a 1-parameter family of continuous disformal transformations. In the special case of w =1/3 (ultrarelativistic gas), such a family reduces to conformal transformations. As examples, perfect fluids, irrotational dust (mimetic matter) and homogeneous and isotropic solids are discussed.

Turbulence modulation induced by interaction between a bubble swarm and decaying turbulence in oscillating-grid turbulence

International Nuclear Information System (INIS)

Imaizumi, Ryota; Morikawa, Koichi; Higuchi, Masamori; Saito, Takayuki

2009-01-01

In this study, the interaction between a bubble swarm and homogeneous isotropic turbulence was experimentally investigated. The objective is to clarify the turbulence modulation induced by interaction between the bubble swarm and the homogeneous isotropic turbulence without mean flow. In order to generate simultaneously ideally homogeneous isotropic turbulence and a sufficiently controlled bubble swarm, we employed both oscillating grid and bubble generators equipped with audio speakers. First, the homogeneous isotropic turbulence was formed by operating the oscillating grid cylindrical acrylic pipe (height: 600 mm, inner diameter: 149 mm) filled with ion-exchanged and degassed water. Second, we stopped the oscillating-grid in arbitrary time after the homogeneous isotropic turbulence was achieved. A few moments later, the controlled bubble swarm (number of bubbles: 3, average equivalent diameter of bubble: 3 mm, bubble Reynolds number: 859, Weber number: 3.48) was launched into the decaying turbulence described above, using the bubble generators. The bubble formation, bubble size and bubble-launch timing are controlled arbitrarily and precisely by this device. In this study, we conducted the following experiments: 1) measurement of the motion of bubbles in rest water and oscillating grid turbulence via high-speed visualization, 2) measurement of the liquid phase motion around the bubbles in rest water via PIV system with LIF method, 3) measurement of the liquid phase motion around the bubbles in oscillating-grid turbulence via PIV system with LIF method. In the vitalization of the liquid-phase motion of both experiments, two high speed video cameras were employed in order to simultaneously film large- and small-scale interrogation areas. The liquid-phase ambient turbulence hastened the change of the bubble motion from zigzag mode to spiral mode. The interaction between the bubble swarm and liquid-phase turbulence increased decay-rate of the turbulence. (author)

Cosmic no-hair theorem with a varying cosmological constant on brane scenario

CERN Document Server

Chakraborty, S

2002-01-01

In this work, we have studied cosmic no-hair theorem for homogeneous anisotropic Bianchi models with a varying cosmological constant (LAMBDA) in Randall-Sundrum braneworld-type scenarios. The matter fields are confined over the 3-brane onto which the five-dimensional Weyl tensor has a non-vanishing projection. The variation of LAMBDA is taken to be the recently proposed form of Vishwakarma and its generalization. In the first case, the universe will isotropize after power-law inflation while there is exponential expansion in the second case.

Genetic Homogenization of Composite Materials

Directory of Open Access Journals (Sweden)

P. Tobola

2009-04-01

Full Text Available The paper is focused on numerical studies of electromagnetic properties of composite materials used for the construction of small airplanes. Discussions concentrate on the genetic homogenization of composite layers and composite layers with a slot. The homogenization is aimed to reduce CPU-time demands of EMC computational models of electrically large airplanes. First, a methodology of creating a 3-dimensional numerical model of a composite material in CST Microwave Studio is proposed focusing on a sufficient accuracy of the model. Second, a proper implementation of a genetic optimization in Matlab is discussed. Third, an association of the optimization script and a simplified 2-dimensional model of the homogeneous equivalent model in Comsol Multiphysics is proposed considering EMC issues. Results of computations are experimentally verified.

Stimulus homogeneity enhances implicit learning: evidence from contextual cueing.

Science.gov (United States)

Feldmann-Wüstefeld, Tobias; Schubö, Anna

2014-04-01

Visual search for a target object is faster if the target is embedded in a repeatedly presented invariant configuration of distractors ('contextual cueing'). It has also been shown that the homogeneity of a context affects the efficiency of visual search: targets receive prioritized processing when presented in a homogeneous context compared to a heterogeneous context, presumably due to grouping processes at early stages of visual processing. The present study investigated in three Experiments whether context homogeneity also affects contextual cueing. In Experiment 1, context homogeneity varied on three levels of the task-relevant dimension (orientation) and contextual cueing was most pronounced for context configurations with high orientation homogeneity. When context homogeneity varied on three levels of the task-irrelevant dimension (color) and orientation homogeneity was fixed, no modulation of contextual cueing was observed: high orientation homogeneity led to large contextual cueing effects (Experiment 2) and low orientation homogeneity led to low contextual cueing effects (Experiment 3), irrespective of color homogeneity. Enhanced contextual cueing for homogeneous context configurations suggest that grouping processes do not only affect visual search but also implicit learning. We conclude that memory representation of context configurations are more easily acquired when context configurations can be processed as larger, grouped perceptual units. However, this form of implicit perceptual learning is only improved by stimulus homogeneity when stimulus homogeneity facilitates grouping processes on a dimension that is currently relevant in the task. Copyright © 2014 Elsevier B.V. All rights reserved.

Elastic Characterization of Transversely Isotropic Soft Materials by Dynamic Shear and Asymmetric Indentation

Science.gov (United States)

Namani, R.; Feng, Y.; Okamoto, R. J.; Jesuraj, N.; Sakiyama-Elbert, S. E.; Genin, G. M.; Bayly, P. V.

2012-01-01

The mechanical characterization of soft anisotropic materials is a fundamental challenge because of difficulties in applying mechanical loads to soft matter and the need to combine information from multiple tests. A method to characterize the linear elastic properties of transversely isotropic soft materials is proposed, based on the combination of dynamic shear testing (DST) and asymmetric indentation. The procedure was demonstrated by characterizing a nearly incompressible transversely isotropic soft material. A soft gel with controlled anisotropy was obtained by polymerizing a mixture of fibrinogen and thrombin solutions in a high field magnet (B = 11.7 T); fibrils in the resulting gel were predominantly aligned parallel to the magnetic field. Aligned fibrin gels were subject to dynamic (20–40 Hz) shear deformation in two orthogonal directions. The shear storage modulus was 1.08 ± 0. 42 kPa (mean ± std. dev.) for shear in a plane parallel to the dominant fiber direction, and 0.58 ± 0.21 kPa for shear in the plane of isotropy. Gels were indented by a rectangular tip of a large aspect ratio, aligned either parallel or perpendicular to the normal to the plane of transverse isotropy. Aligned fibrin gels appeared stiffer when indented with the long axis of a rectangular tip perpendicular to the dominant fiber direction. Three-dimensional numerical simulations of asymmetric indentation were used to determine the relationship between direction-dependent differences in indentation stiffness and material parameters. This approach enables the estimation of a complete set of parameters for an incompressible, transversely isotropic, linear elastic material. PMID:22757501

Isotropic extragalactic flux from dark matter annihilations: lessons from interacting dark matter scenarios

Energy Technology Data Exchange (ETDEWEB)

Moliné, Ángeles [CFTP, Instituto Superior Tecnico, Universidade Tecnica de Lisboa, Av. Rovisco Pais 1, 1049-001 Lisboa (Portugal); Schewtschenko, Jascha A.; Boehm, Céline [Institute for Particle Physics Phenomenology (IPPP), Durham University, Durham DH1 3LE (United Kingdom); Palomares-Ruiz, Sergio [Instituto de Física Corpuscular (IFIC), CSIC-Universitat de València, Apartado de Correos 22085, E-46071 Valencia (Spain); Baugh, Carlton M., E-mail: maria.moline@ist.utl.pt, E-mail: jascha@schewtschenko.net, E-mail: Sergio.Palomares.Ruiz@ific.uv.es, E-mail: c.m.boehm@durham.ac.uk, E-mail: c.m.baugh@durham.ac.uk [Institute for Computational Cosmology (ICC), Durham University, Durham DH1 3LE (United Kingdom)

2016-08-01

The extragalactic γ-ray and neutrino emission may have a contribution from dark matter (DM) annihilations. In the case of discrepancies between observations and standard predictions, one could infer the DM pair annihilation cross section into cosmic rays by studying the shape of the energy spectrum. So far all analyses of the extragalactic DM signal have assumed the standard cosmological model (ΛCDM) as the underlying theory. However, there are alternative DM scenarios where the number of low-mass objects is significantly suppressed. Therefore the characteristics of the γ-ray and neutrino emission in these models may differ from ΛCDM as a result. Here we show that the extragalactic isotropic signal in these alternative models has a similar energy dependence to that in ΛCDM, but the overall normalisation is reduced. The similarities between the energy spectra combined with the flux suppression could lead one to misinterpret possible evidence for models beyond ΛCDM as being due to CDM particles annihilating with a much weaker cross section than expected.

Isotropic extragalactic flux from dark matter annihilations: lessons from interacting dark matter scenarios

International Nuclear Information System (INIS)

Moliné, Ángeles; Schewtschenko, Jascha A.; Boehm, Céline; Palomares-Ruiz, Sergio; Baugh, Carlton M.

2016-01-01

The extragalactic γ-ray and neutrino emission may have a contribution from dark matter (DM) annihilations. In the case of discrepancies between observations and standard predictions, one could infer the DM pair annihilation cross section into cosmic rays by studying the shape of the energy spectrum. So far all analyses of the extragalactic DM signal have assumed the standard cosmological model (ΛCDM) as the underlying theory. However, there are alternative DM scenarios where the number of low-mass objects is significantly suppressed. Therefore the characteristics of the γ-ray and neutrino emission in these models may differ from ΛCDM as a result. Here we show that the extragalactic isotropic signal in these alternative models has a similar energy dependence to that in ΛCDM, but the overall normalisation is reduced. The similarities between the energy spectra combined with the flux suppression could lead one to misinterpret possible evidence for models beyond ΛCDM as being due to CDM particles annihilating with a much weaker cross section than expected.

Conservative constraints on dark matter from the Fermi-LAT isotropic diffuse gamma-ray background spectrum

Energy Technology Data Exchange (ETDEWEB)

Abazajian, Kevork N.; Agrawal, Prateek; Chacko, Zackaria [Maryland Center for Fundamental Physics, Department of Physics, University of Maryland, College Park, Maryland 20742 (United States); Kilic, Can, E-mail: kev@umd.edu, E-mail: apr@umd.edu, E-mail: zchacko@umd.edu, E-mail: kilic@physics.rutgers.edu [Department of Physics and Astronomy, Rutgers University, Piscataway, NJ 08854 (United States)

2010-11-01

We examine the constraints on final state radiation from Weakly Interacting Massive Particle (WIMP) dark matter candidates annihilating into various standard model final states, as imposed by the measurement of the isotropic diffuse gamma-ray background by the Large Area Telescope aboard the Fermi Gamma-Ray Space Telescope. The expected isotropic diffuse signal from dark matter annihilation has contributions from the local Milky Way (MW) as well as from extragalactic dark matter. The signal from the MW is very insensitive to the adopted dark matter profile of the halos, and dominates the signal from extragalactic halos, which is sensitive to the low mass cut-off of the halo mass function. We adopt a conservative model for both the low halo mass survival cut-off and the substructure boost factor of the Galactic and extragalactic components, and only consider the primary final state radiation. This provides robust constraints which reach the thermal production cross-section for low mass WIMPs annihilating into hadronic modes. We also reanalyze limits from HESS observations of the Galactic Ridge region using a conservative model for the dark matter halo profile. When combined with the HESS constraint, the isotropic diffuse spectrum rules out all interpretations of the PAMELA positron excess based on dark matter annihilation into two lepton final states. Annihilation into four leptons through new intermediate states, although constrained by the data, is not excluded.

Conservative constraints on dark matter from the Fermi-LAT isotropic diffuse gamma-ray background spectrum

International Nuclear Information System (INIS)

Abazajian, Kevork N.; Agrawal, Prateek; Chacko, Zackaria; Kilic, Can

2010-01-01

We examine the constraints on final state radiation from Weakly Interacting Massive Particle (WIMP) dark matter candidates annihilating into various standard model final states, as imposed by the measurement of the isotropic diffuse gamma-ray background by the Large Area Telescope aboard the Fermi Gamma-Ray Space Telescope. The expected isotropic diffuse signal from dark matter annihilation has contributions from the local Milky Way (MW) as well as from extragalactic dark matter. The signal from the MW is very insensitive to the adopted dark matter profile of the halos, and dominates the signal from extragalactic halos, which is sensitive to the low mass cut-off of the halo mass function. We adopt a conservative model for both the low halo mass survival cut-off and the substructure boost factor of the Galactic and extragalactic components, and only consider the primary final state radiation. This provides robust constraints which reach the thermal production cross-section for low mass WIMPs annihilating into hadronic modes. We also reanalyze limits from HESS observations of the Galactic Ridge region using a conservative model for the dark matter halo profile. When combined with the HESS constraint, the isotropic diffuse spectrum rules out all interpretations of the PAMELA positron excess based on dark matter annihilation into two lepton final states. Annihilation into four leptons through new intermediate states, although constrained by the data, is not excluded

Interaction between a punch and an arbitrary crack or inclusion in a transversely isotropic half-space

Science.gov (United States)

Fabrikant, I.; Karapetian, E.; Kalinin, S. V.

2018-02-01

We consider the problem of an arbitrary shaped rigid punch pressed against the boundary of a transversely isotropic half-space and interacting with an arbitrary flat crack or inclusion, located in the plane parallel to the boundary. The set of governing integral equations is derived for the most general conditions, namely the presence of both normal and tangential stresses under the punch, as well as general loading of the crack faces. In order to verify correctness of the derivations, two different methods were used to obtain governing integral equations: generalized method of images and utilization of the reciprocal theorem. Both methods gave the same results. Axisymmetric coaxial case of interaction between a rigid inclusion and a flat circular punch both centered along the z-axis is considered as an illustrative example. Most of the final results are presented in terms of elementary functions.

High heat flux experiment on isotropic graphite using pulsed laser beam

International Nuclear Information System (INIS)

Kizaki, Hiroshi; Tokunaga, Kazutoshi; Fukuda, Shigehisa; Yoshida, Naoaki; Muroga, Takeo.

1989-01-01

In order to examine the plasma-withstanding behavior of isotropic graphite which is the leading favorite material for the first wall of nuclear fusion reactors, the pulsed thermal loading experiment was carried out by using a laser. As the result of analyzing the gas which was emitted during the pulsed thermal loading, together with the formation and release of various hydrocarbon gases, also the formation of carbon clusters due to the sublimation of carbon was observed. The vacuum characteristics and the dependence on thermal loading condition and surface treatment condition of these released gases were determined, and the problems and the way of improvement in its application to nuclear fusion reactors were elucidated. Since the isotropic graphite is of low atomic number, the radiation loss in plasma is small, and the improvement of the plasma parameters can be expected. Besides, the heat resistance and high temperature stability in vacuum are good, and the induced radioactivity is low. On the other hand, the quantity of gas occlusion is much, various hydrocarbon gases are formed at high temperature, and the wear due to sublimation arises by very high thermal loading. The experimental method, the observation of graphite surface by SEM, and the effect of carbon coating due to thermal decomposition are reported. (K.I.)

Investigating source processes of isotropic events

Science.gov (United States)

Chiang, Andrea

explosion. In contrast, recovering the announced explosive yield using seismic moment estimates from moment tensor inversion remains challenging but we can begin to put error bounds on our moment estimates using the NSS technique. The estimation of seismic source parameters is dependent upon having a well-calibrated velocity model to compute the Green's functions for the inverse problem. Ideally, seismic velocity models are calibrated through broadband waveform modeling, however in regions of low seismicity velocity models derived from body or surface wave tomography may be employed. Whether a velocity model is 1D or 3D, or based on broadband seismic waveform modeling or the various tomographic techniques, the uncertainty in the velocity model can be the greatest source of error in moment tensor inversion. These errors have not been fully investigated for the nuclear discrimination problem. To study the effects of unmodeled structures on the moment tensor inversion, we set up a synthetic experiment where we produce synthetic seismograms for a 3D model (Moschetti et al., 2010) and invert these data using Green's functions computed with a 1D velocity mode (Song et al., 1996) to evaluate the recoverability of input solutions, paying particular attention to biases in the isotropic component. The synthetic experiment results indicate that the 1D model assumption is valid for moment tensor inversions at periods as short as 10 seconds for the 1D western U.S. model (Song et al., 1996). The correct earthquake mechanisms and source depth are recovered with statistically insignificant isotropic components as determined by the F-test. Shallow explosions are biased by the theoretical ISO-CLVD tradeoff but the tectonic release component remains low, and the tradeoff can be eliminated with constraints from P wave first motion. Path-calibration to the 1D model can reduce non-double-couple components in earthquakes, non-isotropic components in explosions and composite sources and improve