Non-homogeneous Configurations Research Articles

Chord length sampling with memory effects for spatially heterogeneous Markov media: Application to the rod model.

In this work we propose a modified Chord Length Sampling (CLS) algorithm, endowed with two layers of "memory effects," aimed at solving particle transport problems in one-dimensional spatially nonhomogeneous Markov media. CLS algorithms are a family of Monte Carlo methods which account for the stochastic nature of the media by sampling on-the-fly the random interfaces between material phases during the particle propagation. The possibility for the particles to remember the last crossed interfaces increases the accuracy of these models with respect to reference solutions obtained by solving the Boltzmann equationon a large number of realizations of the Markov media. In previous investigations, CLS models with memory have been tested exclusively for spatially uniform stochastic media: in this paper we extend this class of Monte Carlo methods to the case of spatially nonhomogeneous configurations. The effectiveness and the robustness of the modified CLS are probed considering several benchmark problems with varying material cross sectionsand Markov media densities. The obtained results are a stepping stone towards a generalization to three-dimensional models.

Entropy as a Geometrical Source of Information in Biological Organizations

Considering both biological and non-biological polygonal shape organizations, in this paper we introduce a quantitative method which is able to determine informational entropy as spatial differences between heterogeneity of internal areas from simulation and experimental samples. According to these data (i.e., heterogeneity), we are able to establish levels of informational entropy using statistical insights of spatial orders using discrete and continuous values. Given a particular state of entropy, we establish levels of information as a novel approach which can unveil general principles of biological organization. Thirty-five geometric aggregates are tested (biological, non-biological, and polygonal simulations) in order to obtain the theoretical and experimental results of their spatial heterogeneity. Geometrical aggregates (meshes) include a spectrum of organizations ranging from cell meshes to ecological patterns. Experimental results for discrete entropy using a bin width of 0.5 show that a particular range of informational entropy (0.08 to 0.27 bits) is intrinsically associated with low rates of heterogeneity, which indicates a high degree of uncertainty in finding non-homogeneous configurations. In contrast, differential entropy (continuous) results reflect negative entropy within a particular range (−0.4 to −0.9) for all bin widths. We conclude that the differential entropy of geometrical organizations is an important source of neglected information in biological systems.

Using site occupation disorder to build bulk structures of Ni1-xAlx

Raney nickel shows potential as an electrocatalyst for the oxygen evolution reaction (OER). However, the catalytic activity of Raney nickel varies with its properties. These properties are related to the composition of the bimetallic precursor used to synthesise Raney nickel. The bimetallic precursor consists of a combination of bimetallic phases. Various studies have been done on the well-known bimetallic phases, namely, Ni2Al3, NiAl and NiAl3. However, to get a more comprehensive understanding of the influence of the bimetallic precursor on the properties of Raney nickel, a larger spectrum of bimetallic phases needs to be evaluated. In this study, the Site Occupation Disorder (SOD) program was used to build solid-state structures (bimetallic phases) with various Ni1-xAlx bimetallic ratios. These Ni1-xAlx bimetallic phases were evaluated, and unique configurations for each Ni1-xAlx bimetallic ratio were obtained. The unique configurations were geometrically optimised using the General Utility Lattice Program (GULP) at 0K. These optimised unique configurations were thermodynamically evaluated over a range of 0.1K – 1200K, and the most stable configurations with a probability higher than 10% were identified. This study found that the stable non-homogeneous configurations fall within a range of 20% - 80% Ni content. A weight average combination of these configurations of the bimetallic phases will produce a non-homogeneous precursor with an average Ni content of 20% - 80%, which is in close agreement with experimental results. The approach in this study enables researchers to obtain a larger, repeatable spectrum of bimetallic phases for the investigation of Raney nickel precursors.

Inherent Effects of Homogenization in Non-Homogeneous Vehicle Platoons

In the light of increased interest in platooning and its application in non-homogeneous configurations, some fundamental observations on the inherent effects of grouping vehicles into a string are pointed out and investigated. The engine dynamics, which are the core of the actuation when one vehicle follows another, are examined. Their characteristics already shape the overall performance, which the methods of control engineering ultimately seek to improve. Nonetheless, this paper exposes some fundamental bounds for potential improvements. In particular, the effects of saturation within the engine model are considered and a proposition is derived to embrace them. Finally, the effects are considered in synopsis. For this purpose, the findings are applied to a current state-of-the-art controller and discussed.

Efficiency of high accuracy DRP schemes in direct numerical simulations of incompressible turbulent flows

We investigate the ability of Dispersion Relation Preserving (DRP) schemes to provide accurate numerical solutions in incompressible turbulent flows. DRP and compact schemes have been implemented in a finite differences Direct Numerical Simulation (DNS) of a fully developed turbulent channel flow. The results are compared with standard second order difference schemes and pseudo-spectral strategies. Compact and DRP schemes both lead to satisfactory results even when the wall normal grid spacing exceeds the Kolmogorov scale in high buffer and logarithmic layers. This is explained by the appropriate spectral characteristics of these schemes that can subsequently be efficiently used in other non-homogeneous configurations.

비 균일적 마이크로 원기둥 배열을 이용한 고성능 냉각 표면

본 논문은 비 균일적 마이크로 원기둥 배열을 이용한 고성능 냉각 표면에 대해 다루고 있다. 비균일적 원기둥 배열은 원기둥간의 거리 및 배열 규칙이 균일한 종전의 균일 배열과 달리, 두 개의 특성 공극 길이를 갖기 때문에 구조물의 모세관 능력을 획기적으로 향상시킬 수 있다. 본 연구에서는 비 균일적 마이크로 원기둥 배열을 제작하고, 모세관 상승률 실험을 통하여 모세관 능력을 측정하였다. 그리고 수치해석을 통하여 실험 결과를 검증하였고, 비 균일적 원기둥 배열의 모세관 능력 향상 원인에 대해 검토하였다. 실험 및 수치해석 결과, 마이크로 원기둥 배열의 모세관 능력은 배열의 고체 분율에 대한 일의적 함수로 주어지며, 고체 분율이 감소할수록 증가하는 것으로 나타났다. 하지만 고체 분율이 약 0.25 이하로 줄어들면 모세관 능력은 급격히 감소한다.

Study on the capillary performance of micro-post wicks with non-homogeneous configurations

In this study, the capillary performance of the micro-post wicks with non-homogeneous configurations is investigated and compared with a conventional micro-post wick with homogeneous configuration. The experimental and numerical studies show that the capillary performance of the micro-post wick can be significantly enhanced, compared with the homogeneous type wick, by employing non-homogeneous configurations: a groove type wick and a square array type wick have 35% and 31% higher capillary performances, respectively, compared with the homogeneous type wick having equal post size. The capillary performance is shown to be primarily a function of the solid fraction and increases linearly with decreasing solid fraction, regardless of the wick configuration. However, the capillary performance is found to be significantly reduced when the solid fraction falls below a threshold value.

Solitary waves in graphene-membrane

A two-dimensional crystalline membrane model usually adopted for free-standing monolayer graphene is considered for the search of solitary waves. An extended mean field analysis is performed and small deviations around this mean field exhibit a sinusoidal profile for the membrane. Non-homogeneous configurations are found to have stable localized energy that propagate along a transverse direction, being that their height and width are related to the elastic constants. Upper limits for the velocity of propagation of two different solitary wave solutions are found to be, respectively, of the order of 40 km/s and 100 km/s.

Simulation Study of Tissue-Specific Positron Range Correction for the New Biograph mMR Whole-Body PET/MR System

Positron range is a limiting factor in spatial resolution of positron emission tomography (PET) imaging. In this work we investigated the tissue-dependent nature of positron range and its effect on imaging with the new Biograph mMR 3 T whole-body PET/MR system. Positron range simulations were performed for Rb-82 and Ga-68 in homogeneous and non-homogeneous configurations of soft and lung tissue using Geant4. In addition, a 3D MLEM reconstruction framework was extended to incorporate correction kernels that compensate for the effect of positron range. We developed methods for selecting and adapting such correction kernels based on the MR-derived attenuation map and pre-simulated positron range data. The methods were evaluated using Monte Carlo (MC) simulation data on a model of the mMR system including the 3 T magnetic field (MF) and the MR body coil. The results prove that the use of tissue-specific positron range kernels results in better spatial resolution. Especially, the application of generalized kernels at the borders of different tissue types has the potential to provide better contrast and lesion localization.

Magneto-Electro-Elastic Bimorph Analysis by the Boundary Element Method

The influence of the magnetic configuration on the behavior of magneto-electro-elastic bimorph beams is analyzed by using a boundary element approach. The problem is formulated by using the generalized displacements and generalized tractions. The boundary integral equation formulation is obtained by extending the reciprocity theorem to magneto-electro-elastic problems; it is numerically implemented by using the boundary element method multidomain technique to address problems involving nonhomogeneous configurations. Results under different magnetic configurations are compared highlighting the characteristic features of magnetopiezoelectric behavior particularly focusing on the link between interlaminar stress and magnetic induction.

Expanding nonhomogeneous configurations of theλφ4model

A time dependent variational approach is considered to derive the equations of movement for the $\ensuremath{\lambda}{\ensuremath{\varphi}}^{4}$ model. The temporal evolution of the model is performed numerically in the frame of the Gaussian approximation in a lattice of $1+1$ dimensions given nonhomogeneous initial conditions (such as bubbles) for the classical and quantum parts of the field which expands. A schematic model for the initial conditions is presented considering the model at finite fermionic density. The nonzero fermionic density may lead either to the restoration of the symmetry or to an even more asymmetric phase. Both kinds of situations are considered as initial conditions and the eventual differences in early time dynamics are discussed. In the early time evolution there is strong energy exchange between the classical and quantum parts of the field as the initial configuration expands. The contribution of the quantum fluctuations is discussed especially in the strong coupling constant limit. The continuum limit is analyzed.

Application of wide band radiation models to non-homogeneous combustion systems

A spectral version of the exponential wide band model has been adapted for implementation within a computational fluid dynamic framework. The model has been assessed by comparing predicted spectral and integrated quantities with experimental data and statistical narrow band model results for a number of idealised homogeneous and non-homogeneous configurations, and for a jet flame. Overall, the spectral wide band approach has been shown to be in reasonable agreement with experimental data, and to have an accuracy, for total quantities, comparable to that of the narrow band model whilst requiring almost an order of magnitude less computer processor time.

Application of finite elements to the solution of Helmholtz's equation

A novel method, that of finite elements, for the solution of Helmholtz's equation is suggested. Various 2- and 3-dimensional problems are solved using this method, and the results are compared with more conventional techniques, particularly the finite-difference method, which it may be regarded to supersede. The ease with which various boundary conditions may be handled is discussed and illustrated. Nonhomogeneous configurations present no difficulty, nor do they require any special formulation.There is considerable scope for the further development of the technique, which has, until now, been applied mainly to the solution of Laplace or Poisson equations.