Assessment of a Heterogeneous Environment

An approach to the assessment of a heterogeneous environment in accordance with the proposed concept of a heterogeneous environment is described. The classification of industrial heterogeneous media by technological feature is proposed. The processes described by the proposed approach include the process of metal cutting, surface plastic deformation, chemical-thermal treatment, formation of coatings, welding, most of the processes that change the level and gradient of hardness and internal stresses in the surface layer of the material. Application of the proposed principles makes it possible to find new directions in the study of such processes.

The Influence of Thermal Dilution on the Microstructure Evolution of Some Combustion-Synthesized Refractory Ceramic Composites

Modeling the self-sustained high-temperature synthesis (SHS) reaction via thermal dilution and transformation of the reaction heterogeneous media into a moderate exothermic one has unlimited potential for designing inorganic powders of a certain morphology beneficial for advanced consolidation. Thermal/inert dilution of the high-exothermic mixtures leads to the fluent decrease of both the combustion temperature and velocity, thus allowing to tailor the thermal regime of the combustion process, therewith contributing to high yield of reaction and governing the microstructural features of the combustion products. In the current review, we shed on light on the possibilities of this effective strategy to control the thermal behavior of the SHS process for the preparation of applicable powder precursors for the subsequent successful sintering. Since the SHS process of some refractory ceramics (MoSi2, TiB2, TiC, etc.) involves a relatively violent reaction rate and high combustion temperature, achieving a high level of microstructure control in these systems is often challenging. The challenge was tackled with a thermal dilution approach, attaining considerable enhancement in the homogeneity among phases with an increase of diluent content along with microstructure refinement.

Numerical Solutions of Space-Fractional Advection–Diffusion–Reaction Equations

Background: solute transport in highly heterogeneous media and even neutron diffusion in nuclear environments are among the numerous applications of fractional differential equations (FDEs), being demonstrated by field experiments that solute concentration profiles exhibit anomalous non-Fickian growth rates and so-called “heavy tails”. Methods: a nonlinear-coupled 3D fractional hydro-mechanical model accounting for anomalous diffusion (FD) and advection–dispersion (FAD) for solute flux is described, accounting for a Riesz derivative treated through the Grünwald–Letnikow definition. Results: a long-tailed solute contaminant distribution is displayed due to the variation of flow velocity in both time and distance. Conclusions: a finite difference approximation is proposed to solve the problem in 1D domains, and subsequently, two scenarios are considered for numerical computations.

On modelling of thermodynamic interaction of particles suspended in two-dimensional medium

Analytical description of temperature distribution in a medium with foreign inclusions is difficult due to the complicated geometry of the problem, so asymptotic and numerical methods are usually used to model thermodynamic processes in heterogeneous media. To be convinced in convergence of these methods the authors consider model problem about two identical round particles in infinite planar medium with temperature gradient which is constant at infinity. Authors refine multipole expansion of the solution obtained earlier by continuing it up to higher powers of small parameter, that is nondimensional radius of thermodynamically interacting particles. Numerical approach to the problem using ANSYS software is described; in particular, appropriate choice of approximate boundary conditions is discussed. Authors ascertain that replacement of infinite medium by finite-sized domain is important source of error in FEM. To find domain boundaries in multiple inclusions’ problem the authors develop “fictituous particle” method; according to it the cloud of particles far from the center of the cloud acts approximately as a single equivalent particle of greater size and so may be replaced by it. Basing on particular quantitative data the dependence of domain size that provides acceptable accuracy on thermal conductivities of medium and of particles is explored. Authors establish series of numerical experiments confirming convergence of multipole expansions method and FEM as well; proximity of their results is illustrated, too.

Dosimetric Evaluation of a Treatment Planning System Using the Aapm Medical Physics Practice Guideline 5.a (MPPG 5.a) Validation Tests

In this work, the AAPM Medical Physics Practice Guideline 5.a (MPPG 5.a) validation tests package was used to evaluate the dosimetric performance of a new version of the Eclipse treatment planning system (TPS) algorithms. A series of tests were developed and comparisons between TPS calculated and corresponding beam data measurements have been performed for basic beam validation, heterogeneity correction and IMRT/VMAT dose validation tests. Measurements were performed using a Varian IX Linear Accelerator with the 6 MV, 6MV FFF and 18 MV photon beams, and 6, 9, 12, 16, 20 MeV electron beams. Results for basic dose validation tests yielded differences within 3% for all point doses and pass rate greater than 95% for all depth profiles using 3%/3mm criteria. For testing the ability of the TPS in accounting for tissue inhomogeneity, corresponding comparisons were performed with the presence of a heterogeneous media to simulate an air inhomogeneity. Results showed a mean deviation between the TPS calculated and measured of 1.9%, reaching a maximum of 2.8% for the AAA algorithm. For IMRT/VMAT validation tests, our local criteria passing rate of 95% was used, but no consensus of the tolerance exists. Our results agree well with the data reported accuracy in previous studies of Eclipse TPS. In summary, the AAPM MPPG 5.a validation tests are a valuable package for evaluating dose calculation accuracy and are very useful for TPS upgrade checks, commissioning tests and routine TPS QA.

SIMULATION STUDIES OF THE MOLIERE RADIUS FOR EM CALORIMETER MATERIALS

The Monte-Carlo calculations of the Moliere radius (RM) for some homogeneous and heterogeneous media used in electromagnetic calorimetry in the energy range from 50 MeV to 10 GeV are presented in detail. The obtained results, the uncertainties in determining RM, estimations of the absorbed energy, methods for approximating the absorbed energy, and the accuracy of the results are discussed as well. Some RM are shown for calorimeter proto-types of the Spin Physics Detector experiment (SPD). A one-parameter function of the Moliere radius dependence on the absorber-scintillator thickness ratio is obtained.