Mathematical Modeling of Electrical Conductivity of Anisotropic Nanocomposite with Periodic Structure

Composite materials consisting of a dielectric matrix with conductive inclusions are promising in the field of micro- and optoelectronics. The properties of a nanocomposite material are strongly influenced by the characteristics of the substances included in its composition, as well as the shape and size of inclusions and the orientation of particles in the matrix. The use of nanocomposite material has significantly expanded and covers various systems. The anisotropic form of inclusions is the main reason for the appearance of optical anisotropy. In this article, models and methods describing the electrical conductivity of a layered nanocomposite of a self-similar structure are proposed. The method of modeling the electrical conductivity of individual blocks, layers, and composite as a whole is carried out similarly to the method of determining the dielectric constant. The advantage of the method proposed in this paper is the removal of restrictions imposed on the theory of generalized conductivity associated with the need to set the dielectric constant.

A cortical locus for anisotropic overlay suppression of stimuli presented at fixation

Human contrast sensitivity for narrowband Gabor targets is suppressed when superimposed on narrowband masks of the same spatial frequency and orientation (referred to as overlay suppression), with suppression being broadly tuned to orientation and spatial frequency. Numerous behavioral and neurophysiological experiments have suggested that overlay suppression originates from the initial lateral geniculate nucleus (LGN) inputs to V1, which is consistent with the broad tuning typically reported for overlay suppression. However, recent reports have shown narrowly tuned anisotropic overlay suppression when narrowband targets are masked by broadband noise. Consequently, researchers have argued for an additional form of overlay suppression that involves cortical contrast gain control processes. The current study sought to further explore this notion behaviorally using narrowband and broadband masks, along with a computational neural simulation of the hypothesized underlying gain control processes in cortex. Additionally, we employed transcranial direct current stimulation (tDCS) in order to test whether cortical processes are involved in driving narrowly tuned anisotropic suppression. The behavioral results yielded anisotropic overlay suppression for both broadband and narrowband masks and could be replicated with our computational neural simulation of anisotropic gain control. Further, the anisotropic form of overlay suppression could be directly modulated by tDCS, which would not be expected if the suppression was primarily subcortical in origin. Altogether, the results of the current study provide further evidence in support of an additional overlay suppression process that originates in cortex and show that this form of suppression is also observable with narrowband masks.

Microstructure analysis of carbon–carbon preform

The microstructure of three kinds of porous carbon–carbon preforms prepared for carbon–carbon/aluminum composites was identified by x-ray diffraction, Raman spectroscopy, and field emission scan electronic microscope. Although manufactured at same processing conditions, including the temperature, type of organic gas, and pressure of pyrolysis, the structure of the pyrolytic carbon (Cpy) in three kinds of preforms is different. The morphology of the Cpy is influence by the topology of the preforms greatly, and the crystal structure of the Cpy is influenced by the crystal structure of the carbon fiber greatly, on which surface the Cpy was deposited. The degree of graphitization of the Cpy had been enhanced and the structure of the Cpy changed to more anisotropic form when the preforms were annealed at 2773 K.

A comparison of several eddy viscosity turbulence models in two and three dimensional boundary layer flows

SummaryFour flow cases are calculated using a boundary layer method with five turbulence models. The Johnson-King model, in particular, is modified and two variant forms are used in the present work. The variant forms involve an anisotropic form of three-dimensional eddy viscosity formulations and a modification in the outer viscosity expression. It is found that the Johnson-King model generally performs very well as compared to the others, and the variant forms provide further improvement in most cases.

Representation of the Microstructural Dependence of the Anisotropic Elastic Constants of Textured Materials

This paper addresses the question of representing the dependence of the elastic coefficients in the anisotropic form of Hooke's law upon the microstructure of a material. The concern is with textured material symmetries, that is to say materials such as natural and man-made composites whose material symmetry is determined by microstructural organization. The approach is to relate the anisotropic elastic coefficients to local geometric or stereological measures of the microstructure. The predictions of micromechanical models and continuum mechanical models are compared and are found to be consistent with each other.