An improved adsorption method for the characterization of water-based supercapacitor electrodes

The specific surface area is a key characteristic of carbon materials used in supercapacitor electrodes. In this paper, the use of a methylene blue technique for specific surface area determination is presented. Values for the specific surface area, determined by a new method, provide better correlation with theoretical values for the specific electrical capacity of highly-porous carbon electrodes than the values measured by the common BET method. Additionally, the methylene blue adsorption method is thought to characterize carbon adsorption activity in relation to a supercapacitor electrolyte

The Zakharov-Shabat spectral problem on the semi-line: Hilbert formulation and applications

The inverse spectral transform for the Zakharov-Shabat equation on the semi-line is reconsidered as a Hilbert problem. The boundary data induce an essential singularity at large k to one of the basic solutions. Then solving the inverse problem means solving a Hilbert problem with particular prescribed behavior. It is demonstrated that the direct and inverse problems are solved in a consistent way as soon as the spectral transform vanishes with 1/k at infinity in the whole upper half plane (where it may possess single poles) and is continuous and bounded on the real k-axis. The method is applied to stimulated Raman scattering and sine-Gordon (light cone) for which it is demonstrated that time evolution conserves the properties of the spectral transform.Comment: LaTex file, 1 figure, submitted to J. Phys.

Root polytopes and abelian ideals

We study the root polytope $\mathcal P_\Phi$ of a finite irreducible crystallographic root system $\Phi$ using its relation with the abelian ideals of a Borel subalgebra of a simple Lie algebra with root system $\Phi$. We determine the hyperplane arrangement corresponding to the faces of codimension 2 of $\mathcal P_\Phi$ and analyze its relation with the facets of $\mathcal P_\Phi$. For $\Phi$ of type $A_n$ or $C_n$, we show that the orbits of some special subsets of abelian ideals under the action of the Weyl group parametrize a triangulation of $\mathcal P_\Phi$. We show that this triangulation restricts to a triangulation of the positive root polytope $\mathcal P_\Phi^+$.Comment: 41 pages, revised version, accepted for publication in Journal of Algebraic Combinatoric

О РОЛИ ВЛИЯНИЯ ЛЕГИРУЮЩИХ ДОБАВОК НА СТРУКТУРУ И СВОЙСТВА МАГНИЙ–ЦИНКОВЫХ ФЕРРИТОВ

Promising absorbing materials along with Ni−Zn−ferrites are Mg—Zn−ferrites, as they are also intensively absorb electromagnetic waves in the frequency range from 50 MHz to 1000 MHz. The main advantage of the Mg−Zn−ferrite is that it is an inexpensive raw material magnesium oxide. The aim of this work was to study the effect of alloying elements — TiO2 and Bi2O3, — as well as impurities on the microstructure and properties of radar Mg—Zn−ferrite. The influence of alloying elements and impurities on the magnetic and dielectric constant of Mg—Zn−ferrite absorbing materials has been revealed. The addition of bismuth oxide causes a reduction of the permittivity and permeability Mg—Zn−ferrite in the range of up to 1000 MHz. Addition of titanium oxide increases the dielectric constant in the range of up to 1000 MHz, which is important to reduce the wavelength of radar ferrite materials. Addition of titanium oxide leads to a frequency shift of the absorption Mg—Zn−polycrystalline ferrite material towards lower frequencies, and bismuth — towards high frequencies.Thus, the dopant can be regarded as a tool to regulate the wavelength range of the absorption of radar and ferrite materials.К перспективным радиопоглощающим материалам, наряду с Ni—Zn−ферритами, относятся Mg—Zn− ферриты. Эти материалы интенсивно поглощают электромагнитные волны в интервале частот от 50 до 1000 МГц. Основным преимуществом Mg—Zn− ферритов является использование в качестве сырья недорогого оксида магния. Изучено влияние легирующих добавок ТiO2 и Bi2O3, а также примесей на микроструктуру и свойства радиопоглощающих Mg—Zn−ферритов.Установлено влияние легирующих добавок и примесей на магнитную и диэлектрическую проницаемость Mg— Zn−ферритовых радиопоглощающих материалов. Добавка оксидов висмута приводит к некоторому снижению диэлектрической и магнитной проницаемостей Mg—Zn−феррита в диапазоне до 1000 МГц. Добавка оксида титана увеличивает диэлектрическую проницаемость в диапазоне до 1000 МГц, что важно для уменьшения длины электромагнитной волны радиопоглощающих ферритовых материалов. Добавка оксида титана приводит к сдвигу частоты поглощения поликристалличе- ского Mg—Zn−ферритового материала в сторону нижних частот, а висмута — в сторону верхних частот.Показано, что легирующие добавки можно рассматривать как инструмент, регулирующий длину волны и диапазон поглощения радиопоглощающих ферритовых материалов

ВЛИЯНИЕ БАЗОВОГО СОСТАВА И МИКРОСТРУКТУРЫ НИКЕЛЬ–ЦИНКОВЫХ ФЕРРИТОВ НА УРОВЕНЬ ПОГЛОЩЕНИЯ ЭЛЕКТРОМАГНИТНОГО ИЗЛУЧЕНИЯ

Promising absorbing materials include Ni—Zn−ferrites, as they quite intensively absorb electromagnetic waves in the 50 MHz to 1000 MHz frequency range. In this paper we have studied the electromagnetic properties of Ni—Zn ferrite absorbing materials obtained in different technological modes. We propose a model that allows one to evaluate the dielectric constant of the ferrite material depending on the parameters of the microstructure and electrical properties of grain boundaries. Influence of base composition and microstructure on the level of absorption of electromagnetic radiation by Ni—Zn ferrite absorbing materials has been found. An increase in Fe₂O₃ excess to 51 % has been found to shift the frequency interval of electromagnetic radiation absorption towards lower frequencies, and this effect can be explained by an increase in the dielectric and magnetic constants of ferrite. Introduction of excess Fe₂O₃ in step 2 of grinding proved to be more efficient. An increase in the sintering temperature to 1350 °C also provides for a shift of electromagnetic radiation absorption frequency interval towards lower frequencies, which can be explained by an increase of the dielectric and magnetic constants of ferrite and resonance frequency shift of domain walls due to the formation of a coarse−grained structure.Никель−цинковые ферриты относятся к перспективным радиопоглощающим материалам, так как они интенсивно поглощают электромагнитные волны в интервале частот от 50 до 1000 МГц. Проведены исследования электромагнитных свойств Ni—Zn−ферритовых радиопоглощающих материалов, полученных по различным технологическим режимам. Предложена модель, позволяющая оценить диэлектрическую проницаемость ферритового материала в зависимости от параметров микроструктуры и электрофизических свойств границ зерен. Установлено влияние базового состава и микроструктуры на уровень поглощения электромагнитного излучения Ni—Zn− ферритовыми радиопоглощающими материалами. Установлено, что увеличение содержания избытка Fe2O3 до 51 % (мол.) приводит к смещению частотного интервала поглощения электромагнитного излучения в сторону низких частот. Это можно объяснить увеличением магнитной и диэлектрической проницаемостей феррита. Показано, что более эффективно введение избытка Fe2O3 на стадии измельчения синтезированной шихты. Обнаружено, что увеличение температуры спекания до 1350 °С  также обеспечивает смещение частотного интервала поглощения электромагнитного излучения в сторону низких частот. Вероятно, это обусловлено увеличением магнитной и диэлектрической проницаемостей феррита и смещением частоты резонанса доменных стенок в результате формирования крупнозернистой структуры

Radiotechnical properties of metallized fabrics

A number of electromagnetic field shielding materials based on metallized fabric have been produced and investigated. High screening coefficient of the fabrics samples under testing in the frequency range 1×1–2…1×104MHz shown that these materials can be used in applications where fabric-based high conductivity materials are necessary – design of radioelectronic equipment, radio shielded rooms and anechoic chambers, information safeguard problems, ecology tasks, protection of the personnel against high frequency radiations, etc. Ni-metallized fabrics of different type (polyamide, polyester, silica, glass, cotton and mixed) have been investigated in a frequency range 1 MHz … 1.25 GHz. A protective radio shielding individual set has been designed using some of these metallized materials

Shielding and absorbing materials for the equipment of the measuring radioengineering complexes

The research-and-production enterprise "Radiosrtim Ltd" develops and masters in manufacturing a vast nomenclature of materials and designs able to interact actively with electromagnetic radiation (EMR) in wide bandwidths between the 3 mm and 3 m bands. Among these products there are EMR-shielding classes of materials and fabrics as well as EMR-absorbing materials and absorbers. Wherein there is a valid mixture regarding the experience in traditional approaches to creating materials and designs interacting with EMR and in principally new ones based on the latest achievements in materials science and materials processing technology. Most of the materials have certifications and are in serial production. A number of such-like new materials of world-level are being worked at now