Spin-controlled Mott-Hubbard bands in LaMnO_3 probed by optical ellipsometry

Spectral ellipsometry has been used to determine the dielectric function of an untwinned crystal of LaMnO_3 in the spectral range 0.5-5.6 eV at temperatures 50 K < T < 300 K. A pronounced redistribution of spectral weight is found at the Neel temperature T_N = 140 K. The anisotropy of the spectral weight transfer matches the magnetic ordering pattern. A superexchange model quantitatively describes spectral weight transfer induced by spin correlations. This analysis implies that the lowest-energy transitions around 2 eV are intersite d-d transitions, and that LaMnO_3 is a Mott-Hubbard insulator.Comment: 4 pages, 4 figure

lmmuno Histochemical Profile of Endometrium in Patients With Genital Endometriosis

The aim of present study was to investigate the occurence of different lymphocyte subsets in the endometrium of endometriosis patients and in healthy women on every day of the menstrual cycle with special emphasis to the proliferative activity of endometrial cells with Ki-S3 antibody. We also conducted immunohistochemical studies of T-lymphocytes, B-lympho-cytes, macrophages, natural-killer-cells and also of antigens class II of the histocompatibility complex (HLA-DR) during the different phases of the menstrual cycle in endometriosis and non-endometriosis patients

Development of the fuzzy sets theory: weak operations and extension principles

The paper considers the problems that arise when using the theory of fuzzy sets to solve applied problems. Unlike stochastic methods, which are based on statistical data, fuzzy set theory methods make sense to apply when statistical data are not available. In these cases, algorithms should be based on membership functions formed by experts who are specialists in this field of knowledge. Ideally, complete information about membership functions is required, but this is an impractical procedure. More often than not, even the most experienced expert can determine only their carriers or separate sets of the α -cuts for unknown fuzzy parameters of the system. Building complete membership functions of unknown fuzzy parameters on this basis is risky and unreliable. Therefore, the paper proposes an extension of the fuzzy sets theory axiomatics in order to introduce non-traditional (less demanding on the completeness of data on membership functions) extension principles and operations on fuzzy sets. The so-called α -weak operations on fuzzy sets are proposed, which are based on the use of separate sets of the α -cuts. It is also shown that all classical theorems of Cantor sets theory apply in the extended axiomatic theory. New extension principles of generalization have been introduced, which allow solving problems in conditions of significant uncertainty of information

Development of the fuzzy sets theory: weak operations and extension principles

The paper considers the problems that arise when using the theory of fuzzy sets to solve applied problems. Unlike stochastic methods, which are based on statistical data, fuzzy set theory methods make sense to apply when statistical data are not available. In these cases, algorithms should be based on membership functions formed by experts who are specialists in this field of knowledge. Ideally, complete information about membership functions is required, but this is an impractical procedure. More often than not, even the most experienced expert can determine only their carriers or separate sets of the α-cuts for unknown fuzzy parameters of the system. Building complete membership functions of unknown fuzzy parameters on this basis is risky and unreliable. Therefore, the paper proposes an extension of the fuzzy sets theory axiomatics in order to introduce non-traditional (less demanding on the completeness of data on membership functions) extension principles and operations on fuzzy sets. The so-called α-weak operations on fuzzy sets are proposed, which are based on the use of separate sets of the α-cuts. It is also shown that all classical theorems of Cantor sets theory apply in the extended axiomatic theory. New extension principles of generalization have been introduced, which allow solving problems in conditions of significant uncertainty of information

Синтез инвариантных систем автоматического регулирования с внутренней моделью

The article is devoted to the modernization of typical cascade automatic control systems with stabilizing and corrective PI controllers. Such automatic control systems, in addition to the main signal (of adjustable value), use an additional leading signal that reacts to the disturbance faster than the main one. The leading signal effectively compensates for internal disturbances arising in the system by adjusting the stabilizing controller. The temperature control system of superheated steam boiler units of thermal power plants may be taken as an example. The task of determining the configuration parameters of such dual-circuit systems is quite difficult. With a relatively low inertia of the internal circuit, the speed of the stabilizing controller is quite high, and transients in it do not affect the quality of regulation in the external circuit with a corrective controller. This makes it possible to calculate the optimal settings of the latter only by the dynamic characteristics of the inertial section using conventional methods developed for single-circuit systems. The main disadvantage of such automatic control systems is that they do not allow, with close inertia of the contours, to significantly improve the quality of working out the main impacts during the jump of the task, internal and external disturbances. To eliminate this drawback, an invariant cascade automatic control system with an internal model is proposed that takes into account the dynamics of both the internal and external contours with an inertial section of the object when choosing the structure and setting up the corrective controller. In this case, the internal model is used to fully compensate for the main feedback of the system when working out the task signal, as well as to isolate an equivalent external disturbance, for which an invariance differentiator is used to compensate. The invariant cascade automatic control system makes it possible to significantly increase the speed and accuracy compared to the standard one. Статья посвящена модернизации типовых каскадных систем автоматического регулирования со стабилизирующим и корректирующим ПИ-регуляторами. Такие системы автоматического регулирования кроме основного сигнала (регулируемой величины) используют дополнительный опережающий сигнал, который реагирует на возмущение быстрее, чем основной. Опережающий сигнал достаточно эффективно компенсирует возникающие в системе внутренние возмущения за счет настройки стабилизирующего регулятора. Примером может служить система регулирования температуры перегретого пара котельных агрегатов тепловых электрических станций. Задача определения параметров настройки таких двухконтурных систем довольно сложна. При относительно малой инерционности внутреннего контура быстродействие стабилизирующего регулятора достаточно высоко, и переходные процессы в нем не оказывают влияния на качество регулирования во внешнем контуре с корректирующим регулятором. Это позволяет рассчитывать оптимальные параметры настройки последнего только по динамическим характеристикам инерционного участка обычными методами, разрабатываемыми для одноконтурных систем. Главный недостаток таких систем автоматического регулирования состоит в том, что они не позволяют при близких инерционностях контуров существенно улучшить качество отработки основных воздействий при скачке задания, внутреннего и внешнего возмущения. Для устранения этого недостатка предложена инвариантная каскадная система автоматического регулирования с внутренней моделью, учитывающей при выборе структуры и настройке корректирующего регулятора динамику как внутреннего, так и внешнего контура с инерционным участком объекта. При этом внутренняя модель используется для полной компенсации главной обратной связи системы при отработке сигнала задания, а также выделения эквивалентного внешнего возмущения, для компенсации которого применяется дифференциатор инвариантности. Инвариантная каскадная система автоматического регулирования позволяет существенно повысить быстродействие и точность по сравнению с типовой

Raman spectra of MgB2 at high pressure and topological electronic transition

Raman spectra of the MgB2 ceramic samples were measured as a function of pressure up to 32 GPa at room temperature. The spectrum at normal conditions contains a very broad peak at ~590 cm-1 related to the E2g phonon mode. The frequency of this mode exhibits a strong linear dependence in the pressure region from 5 to 18 GPa, whereas beyond this region the slope of the pressure-induced frequency shift is reduced by about a factor of two. The pressure dependence of the phonon mode up to ~ 5GPa exhibits a change in the slope as well as a "hysteresis" effect in the frequency vs. pressure behavior. These singularities in the E2g mode behavior under pressure support the suggestion that MgB2 may undergo a pressure-induced topological electronic transition.Comment: 2 figure

Electron transport, penetration depth and upper critical magnetic field of ZrB12 and MgB2

We report on the synthesis and measurements of the temperature dependence of resistivity, R(T), the penetration depth, l(T), and upper critical magnetic field, Hc2(T), for polycrystalline samples of dodecaboride ZrB12 and diboride MgB2. We conclude that ZrB12 as well as MgB2 behave like simple metals in the normal state with usual Bloch-Gruneisen temperature dependence of resistivity and with rather low resistive Debye temperature, TR=280 K, for ZrB12 (as compared to MgB2 with TR=900 K). The R(T) and l(T) dependencies of ZrB12 reveal a superconducting transition at Tc=6.0 K. Although a clear exponential l(T)dependence in MgB2 thin films and ceramic pellets was observed at low temperatures, this dependence was almost linear for ZrB12 below Tc/2. These features indicate s-wave pairing state in MgB2, whereas a d-wave pairing state is possible in ZrB12. A fit to the data gives a reduced energy gap 2D(0)/kTc=1.6 for MgB2 films and pellets, in good agreement with published data for 3D \pi - sheets of the Fermi surface. Contrary to conventional theories we found a linear temperature dependence of Hc2(T) for ZrB12 (Hc2(0)=0.15 T).Comment: 8 pages, 10 figures, submitted to JET