Integral Equation Analysis of Plane Wave Scattering by Coplanar Graphene-Strip Gratings in the THz Range

The plane wave scattering and absorption by finite and infinite gratings of free-space standing infinitely long graphene strips are studied in the THz range. A novel numerical approach, based on graphene surface impedance, hyper-singular integral equations, and the Nystrom method, is proposed. This technique guarantees fast convergence and controlled accuracy of computations. Reflectance, transmittance, and absorbance are carefully studied as a function of graphene and grating parameters, revealing the presence of surface plasmon resonances. Specifically, larger graphene relaxation times increases the number of resonances in the THz range, leading to higher wave transmittance due to the reduced losses; on the other hand an increase of graphene chemical potential up-shifts the frequency of plasmon resonances. It is also shown that a relatively low number of graphene strips (>10) are able to reproduce Rayleigh anomalies. These features make graphene strips good candidates for many applications, including tunable absorbers and frequency selective surfaces.Comment: 11 pages, 26 figure

Validity and limitations of the median-line integral equation technique in the scattering by material strips of sub-wavellength thickness

Cataloged from PDF version of article.Considered is the 2-D scattering of a plane wave by a thin flat material strip. The data obtained by using the empirical method of generalized boundary conditions and singular integral equations on the strip median line are compared with the results of solving the Muller boundary integral equation that takes full account of strip thickness. Discretization of integral equations in both cases is performed using the Nystrom methods that lead to convergent algorithms. Numerical results cover E and H polarizations and two types of thin strips: conventional dielectric and metal in the optical range. The validity and limitations of approximate model are established and discussed

Essence and Determinants of Personal Crisis: Theoretical Interdisciplinary Analysis Attempt (Social-Psychological View)

У статті розкрито міждисциплінарний (із позицій психології й соціології) підхід до розгляду сутності, детермінації перебігу та розв’язання феномену особистісної кризи. The article reveals the interdisciplinary approach, from the positions of psychology and sociology, as a crucial point to considering the essence, determination and solving the phenomenon of personality crisis

Методика оптимизации выбора параметров климатических камер для испытаний

Проведено дослідження швидкості нагріву та охолодження в кліматичних камерах та на їх основі розроблено методику, яка дозволяє оптимізувати вибір кліматичної камери за параметрами потрібного та достатнього корисного об’єму залежно від теплофізичних властивостей та габаритних розмірів досліджуваних об’єктів та технологічних можливостей камери.Research of speed of heating and cooling is conducted in climatic chambers and on their basis a method which allows to optimize the choice of climatic chamber after the parameters of necessary and sufficient useful volume depending on thermophysical properties and overall sizes of the probed objects and technological possibilities of chamber is developed.Проведено исследование скорости нагрева и охлаждения в климатических камерах и на их основе разработана методика, которая позволяет оптимизировать выбор климатической камеры за параметрами нужного и достаточного полезного объема в зависимости от теплофизических свойств и габаритных размеров исследуемых объектов и технологических возможностей камеры

Charge Modulation at the Surface of High-T_c Superconductors

It is shown here that surfaces of high-temperature superconductors are covered by dipole layers. The charge density modulation is induced by the local suppression of the gap function at the surface. This effect is studied in the framework of the Ginzburg-Landau theory and crucially depends on the appropriate boundary conditions. Those are derived from Gor'kov's equations for a d-wave pairing symmetry. Within this framework the structure of the surface dipole layer is determined. The contribution of this charging to a lens-effect of superconducting films with holes, which has been studied in recent experiments, is discussed.Comment: 10 pages, RevTeX, 5 postscript figure

Vortex phases in mesoscopic cylinders with suppressed surface superconductivity

Vortex structures in mesoscopic cylinder placed in external magnetic field are studied under the general de Gennes boundary condition for the order parameter corresponding to the suppression of surface superconductivity. The Ginzburg-Landau equations are solved based on trial functions for the order parameter for vortex-free, single-vortex, multivortex, and giant vortex phases. The equilibrium vortex diagrams in the plane of external field and cylinder radius and magnetization curves are calculated at different values of de Gennes "extrapolation length" characterizing the boundary condition for the order parameter. The comparison of the obtained variational results with some available exact solutions shows good accuracy of our approach.Comment: RevTex, 11 pages, 10 figure

DEVELOPMENT OF A SUBPROGRAM FOR ANALYZING PRODUCTION STRATEGY IN A COMPETITIVE ENVIRONMENT

In this article, we will explore market dynamics in competitive conditions, using examples of competitions involving three, eight, and fifteen manufacturers. We will compare their development strategies in terms of resource allocation between advertising and product quality. We will also discuss the benefits of market forecasting. Additionally, we will delve into the strategy of optimal resource allocation and provide examples of when it is advisable to adhere to it and when taking risks may lead to higher productivity and profit in a particular product line

Approximate Ginzburg-Landau solution for the regular flux-line lattice. Circular cell method

A variational model is proposed to describe the magnetic properties of type-II superconductors in the entire field range between $H_{c1}$ and $H_{c2}$ for any values of the Ginzburg-Landau parameter $\kappa>1/\sqrt{2}$. The hexagonal unit cell of the triangular flux-line lattice is replaced by a circle of the same area, and the periodic solutions to the Ginzburg-Landau equations within this cell are approximated by rotationally symmetric solutions. The Ginzburg-Landau equations are solved by a trial function for the order parameter. The calculated spatial distributions of the order parameter and the magnetic field are compared with the corresponding distributions obtained by numerical solution of the Ginzburg-Landau equations. The comparison reveals good agreement with an accuracy of a few percent for all $\kappa$ values exceeding $\kappa \approx 1$. The model can be extended to anisotropic superconductors when the vortices are directed along one of the principal axes. The reversible magnetization curve is calculated and an analytical formula for the magnetization is proposed. At low fields, the theory reduces to the London approach at $\kappa \gg 1$, provided that the exact value of $H_{c1}$ is used. At high fields, our model reproduces the main features of the well-known Abrikosov theory. The magnetic field dependences of the reversible magnetization found numerically and by our variational method practically coincide. The model also refines the limits of some approximations which have been widely used. The calculated magnetization curves are in a good agreement with experimental data on high-T$_c$ superconductors.Comment: 8 pages, RevTex, 6 figures, submitted to Phys. Rev.

The Ethnic 'Other' in Ukrainian History Textbooks: The Case of Russia and the Russians

This paper examines portrayals of Russia and the Russians in two generations of Ukrainian history textbooks. It observes that the textbooks are highly condemning of Ukraine's main ethnic other in the guise of foreign ruler: the tsarist authorities and the Soviet regime are always attributed dubious and malicious intentions even if there is appreciation for some of their policies. By contrast, the books, certainly those of the second generation, refrain from presenting highly biased accounts of the ethnic other as a national group (i.e. Russians). Instances where negative judgements do fall onto Russians are counterbalanced by excerpts criticizing ethnic Ukrainians or highlighting conflicting interests within the Ukrainian ethnic group. The negative appraisal of the ethnic other as foreign ruler is clearly instrumental for the nation-building project as it sustains a discourse legitimating the existence of Ukraine as independent state. However, recent trends in history education, the paper concludes, suggest that the importance of nurturing patriotism as a national policy objective is diminishing