Optical Properties of Single-Crystal Germanium in the THz Range

Optics and Spectroscopy - The transmission of intrinsic, antimony-doped, and gallium-doped Ge single crystals in the THz spectral range have been experimentally investigated. It is shown that the...     

Approximation of Potentiometric Titration Curves by Logarithmic Functions: Titration of a Mixture of Two Monobasic Acids

The approximation of titration curves by logarithmic functions was described for the titration of a mixture of two monobasic acids. It was demonstrated with the titration of a mixture of CHCl₂COOH, CH₂ClCOOH, C₆H₅COOH, and H₃BO₃ that this method can be used for the precise determination of equivalence points. The relative error in the determination of titration end-points depends on the values of the corresponding jumps and, to some extent, on the choice of a weight function and lies in the range from 0.1 to 1%.     

Utilization of α-olefins obtained by pyrolysis of waste high density polyethylene to synthesize α-olefin-succinic-anhydride based cold flow improvers

A new route of utilization of α-olefin rich hydrocarbon fractions obtained by waste polymer pyrolysis was investigated. α-olefin-succinic-anhydride intermediate-based pour point depressant additives for diesel fuel were synthesized, in which reactions needed α-olefins were obtained by pyrolysis of waste high-density polyethylene (HDPE). Fraction of α-olefins was produced by the de-polymerization of plastic waste in a tube reactor at 500℃ in the absence of catalysts and air. C_17~22 range of mixtures of olefins and paraffins were separated for synthesis and then, these hydrocarbons were reacted with maleic-anhydride (MA) for formation of α-olefin-succinic-anhydride intermediates. The olefin-rich hydrocarbon fraction contained approximately 60% of olefins, including 90%~95% α-olefins. Other intermediates were produced in the same way by using commercial C₂₀ α-olefin instead of C_17~22 olefin mixture. The two different experimental intermediates with number average molecular weights of 1850g/mol and 1760g/mol were reacted with different alcohols: 1-butanol, 1-hexanol, 1-octanol, i-butanol, and c-hexanol to produce their ester derivatives. The synthesized ten experimental pour point depressants were added in different concentrations to conventional diesel fuel, which had no other additive content before. The structure and efficiency of experimental additives were followed by different standardized and non-standardized methods. Results showed that the experimental additives on the basis of the product of waste pyrolysis were able to decrease not only the pour but also the cloud point and cold filter plugging point (CFPP) of diesel fuel, whose effects could be observed even if the concentration of additives was low. Furthermore, all additives had anti-wear and anti-friction effects in diesel fuel.     

An efficient method for feature selection in linear regression based on an extended Akaike’s information criterion

A method for feature selection in linear regression based on an extension of Akaike’s information criterion is proposed. The use of classical Akaike’s information criterion (AIC) for feature selection assumes the exhaustive search through all the subsets of features, which has unreasonably high computational and time cost. A new information criterion is proposed that is a continuous extension of AIC. As a result, the feature selection problem is reduced to a smooth optimization problem. An efficient procedure for solving this problem is derived. Experiments show that the proposed method enables one to efficiently select features in linear regression. In the experiments, the proposed procedure is compared with the relevance vector machine, which is a feature selection method based on Bayesian approach. It is shown that both procedures yield similar results. The main distinction of the proposed method is that certain regularization coefficients are identical zeros. This makes it possible to avoid the underfitting effect, which is a characteristic feature of the relevance vector machine. A special case (the so-called nondiagonal regularization) is considered in which both methods are identical.     

An alternating direction scheme on a nonuniform mesh for reaction-diffusion parabolic problems

In this paper we develop a numerical method for two-dimensionaltime-dependent reaction-diffusion problems. This method, whichcan immediately be generalized to higher dimensions, is shownto be uniformly convergent with respect to the diffusion problems.This method, which can immediately be generalized to higherdimensions, is shown to be uniformly convergent with respectto the diffusion parameter.     

Approximation of potentiometric titration curves by logarithmic functions: Prediction of random errors in titration parameters

Two possible types of the propagation of random errors in measurements of potential (pH) and the volume of the titrant to titration parameters determined using logarithmic functions are considered. It is demonstrated that errors in calculated values are variously related to the errors in initial data. Expressions that provide the estimation of errors in characteristics of the titration curve from known errors in measurement are obtained.     

On the Transparency of Alkali-Halide Crystal in the Terahertz Spectral Range

Optics and Spectroscopy - The transmission of THz (to 3000 μm) radiation by alkali halide single crystals of sodium chloride (NaCl), potassium chloride (KCl), potassium bromide (KBr), and...     

Knowledge representation and acquisition in expert systems for pattern recognition

A new approach to the design of fuzzy expert systems is proposed. The representation of knowledge and the formation of statements by fuzzy logic tools are discussed in detail. A model of fuzzy inference is described. Primary attention is given to automatic extraction of knowledge (fuzzy inference rules) from a set of precedents. Various performance criteria for rules are introduced, and an algorithm for their generation (the method of effective restrictions) is proposed. An extension of the type of admissible rules by introducing a fuzzy disjunction operation is described. The possibility of optimizing the rules found is explored. The benefits of the approaches proposed are illustrated by experiments.     

Diffractive lenses for high-power terahertz radiation beams

Techniques for manufacturing silicon binary (two-level) diffractive lenses and polypropylene kinoform diffractive lenses for the terahertz spectrum range are described. The elements are 1 and 0.8 mm thick, respectively. The silicon lens is manufactured in two versions: with no coating and with a parylene C (polyparaxylylene) antireflection coating. Characteristics of the diffractive optical elements are studied in the beam of a pulse-periodic free electron laser at a radiation wavelength of 141 μm and a repetition rate of 5.6MHz. The radiation resistance of the parylene coating, tested on the Novosibirsk free electron laser, was not impaired when the coating was exposed to an average power density of 4 kW cm^?2, the peak power in a 100-picosecond pulse being almost 8 MW cm^?2.