Electric and magnetic properties of the Kondo-lattice compound CeCu2Si2

Electric, magnetic, and thermoelectric properties of Ce _x La_1–x Cu₂Si₂ (0x1) compounds have been studied over a wide temperature interval 0.04 T300 K in magnetic fieldsH40 kOe. The paramagnetic-magnetic ordering transition temperatureT _M is found to rise from 0.32 K for cerium concentrationx=0.2 to 1.6 K forx=0.6. A further increase inx from 0.8 to 1.0 leads to a decrease inT _M . Simultaneously, the susceptibility kink is smeared out and atx1.0 it is transformed into temperature-independent enhanced Pauli paramagnetism. The magnetic phase diagram has been found to be similar to that proposed by Doniach for the one-dimensional Kondo-necklace model. The Kondo-lattice compound CeCu₂Si₂ exhibits a superconducting transition atT _c 0.5 K. The variation of the magnetic properties of Ce _x La_1–x Cu₂Si₂ from magnetic ordering at 0.2x0.8 to the nonmagnetic superconducting state atx 1.0 is caused by the crossover from the magnetic regimeT _RKKYT _K (in which the RKKY temperatureT _RKKY exceeds the Kondo temperatureT _K) to the nonmagnetic singlet ground state corresponding to the situation whenT _KT _RKKY. This crossover is accompanied by a sharp increase in the low-temperature Hall coefficientR _H(T) in Ce _x La_1–x Cu₂Si₂ compounds atx 1. At the same time, a minimum of the negative Seebeck coefficient with a high amplitude appears at 10<T<100 K. The anomalous low-temperature properties of Kondo lattices have been shown to be due to the rise of the narrow Abrikosov-Suhl resonance in the vicinity of the Fermi level _F as the temperature is lowered fromTT _K toTT _K. This resonance has a giant amplitude in concentrated Kondo systems and is responsible for the existence in CeCu₂Si₂ of heavy fermions with extremely low degeneracy temperatureT*_F estimated to be 10 K from theR _H versusT curve. Further increase of the Kondo coupling constantJ in CeCu₂Si₂ under pressure induces an increase in (1) the Hall coefficientR _H(T=4.2 K), (2) the superconducting transition temperatureT _c , (3) the derivative of the upper critical fielddH _c2/dT _c , and (4) the low-temperature Seebeck coefficientS(T), which have maximum values at the same pressurep _K13 kbar, corresponding to the Kondo-lattice state with the maximum amplitude of the Abrikosov-Suhl resonance in CeCu₂Si₂ atp=p _KL. At higher pressuresp>p _KL, a continuous transition from the Kondo lattice to the intermediate valence state is observed, which is accompanied by a complete smearing out of the resonance near the Fermi level. Therefore the Kondo lattices represent a new class of solids, which can be characterized as the link between stable magnetism of metals with a deep 4f level and unstable magnetism associated with fluctuating valence. This novel state can be described by a set of anomalous low-temperature properties related to the giant Abrikosov-Suhl resonance near the Fermi level.     

Systemic approach to fuzzy logic formalization for approximate reasoning

L.A. Zadeh, E.H. Mamdani, M. Mizumoto, et al., R.A. Aliev and A. Tserkovny have proposed methods for fuzzy reasoning in which antecedents and consequents involve fuzzy conditional propositions of the form “If x is A then y is B”, with A and B being fuzzy concepts (fuzzy sets). A formulation of fuzzy antecedent/consequent chains is one of the most important topics within a wide spectrum of problems in fuzzy sets in general and approximate reasoning, in particular. From the analysis of relevant research it becomes clear that for this purpose, a so-called fuzzy conditional inference rules comes as a viable alternative. In this study, we present a systemic approach toward fuzzy logic formalization for approximate reasoning. For this reason, we put together some comparative analysis of fuzzy reasoning methods in which antecedents contain a conditional proposition with fuzzy concepts and which are based on implication operators present in various types of fuzzy logic. We also show a process of a formation of the fuzzy logic regarded as an algebraic system closed under all its operations. We examine statistical characteristics of the proposed fuzzy logic. As the matter of practical interest, we construct a set of fuzzy conditional inference rules on the basis of the proposed fuzzy logic. Continuity and stability features of the formalized rules are investigated.     

Type-2 fuzzy neural networks with fuzzy clustering and differential evolution optimization

In many real-world problems involving pattern recognition, system identification and modeling, control, decision making, and forecasting of time-series, available data are quite often of uncertain nature. An interesting alternative is to employ type-2 fuzzy sets, which augment fuzzy models with expressive power to develop models, which efficiently capture the factor of uncertainty. The three-dimensional membership functions of type-2 fuzzy sets offer additional degrees of freedom that make it possible to directly and more effectively account for model’s uncertainties. Type-2 fuzzy logic systems developed with the aid of evolutionary optimization forms a useful modeling tool subsequently resulting in a collection of efficient “If-Then” rules.The type-2 fuzzy neural networks take advantage of capabilities of fuzzy clustering by generating type-2 fuzzy rule base, resulting in a small number of rules and then optimizing membership functions of type-2 fuzzy sets present in the antecedent and consequent parts of the rules. The clustering itself is realized with the aid of differential evolution.Several examples, including a benchmark problem of identification of nonlinear system, are considered. The reported comparative analysis of experimental results is used to quantify the performance of the developed networks.     

Electrical and Thermal Properties of the GaSb–FeGa1.3 Eutectic

The electrical conductivity, thermoelectric power, Hall coefficient, and thermal conductivity of the GaSb–FeGa_1.3 eutectic were measured in a wide temperature range at different relationships between the directions of the electric current, heat flux, magnetic field, and needlelike metallic inclusions. The results are interpreted in terms of electronic and phonon processes. The metallic inclusions are shown to have a significant effect on the transport properties of the eutectic.     

Peculiarities of the Interaction of Calcium Hydroxyapatite and Carbon Nanotubes Deposited from Aqueous Solutions

Technical Physics Letters - The codeposition of calcium salts, phosphorus, and multiwall carbon nanotubes (CNTs) from aqueous solutions in the Ca(OH)2–H3PO4–H2O–CNT system was...     

Structure and properties of composite sintered material of the type iron-cast iron

New antifriction alloys, synthesized from mixtures of iron and cast iron powders, have been developed. A special cast iron, with interdendritic point graphite inclusions, whose initial forms and sizes remain the same after sintering while being distributed among the grains, is used to create the composite materials. Starting at sintering temperatures of 800°C a pearlitic ferrite or pearlite structure forms with initial graphite inclusions that prevent formation of structure-free cementite. A composite antifriction material with a low friction coefficient can be obtained by optimizing the process parameters and charge composition as well as the microstructure of the alloys.Scientific and Industrial Association Bakkonditsioner. Translated from Poroshkovaya Metallurgiya, No. 1 (361), pp. 60–63, January, 1993.     

Improving the Quality of Dies from Steel Kh12M

The effect of heat treatment modes and cold treatment on the quality of dies from steel Kh12M is studied. A new mode of heat treatment involving cold treatment at – 100°C is suggested. Comparative tests of dies produced by standard and suggested methods are described for the case of embossing of a copper collector for starters. It is shown that the quality of dies treated by the new method is higher and their life increases by a factor of 2 – 2.5.