Condensation of all-cis-tetraphenylcyclotetrasiloxanetetraol in ammonia: new method for preparation of ladder-like polyphenylsilsesquioxanes

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Synthesis and antimycobacterial activity of purine conjugates with (S)-lysine and (S)-ornithine

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Synthetic analogs of natural flavolignans. V. A new synthesis of 6-halogeno-1,3-benzodioxane analogs of silandrin and hydnocarpin

6-Halogeno-1,3-benzodioxane analogs of chalcones have been synthesized by various methods. Flavanone and flavone analogs of silandrin and hydnocarpin have been obtained from them. The structures of the new flavonoids have been shown by their PMR spectra.     

Construction of the fundamental solution of disturbed parabolic equation

In present paper the parabolic equation solution is built. The construction is reduced to iterative procedure. And convergence of the latter is proven.     

Trends in sorption preconcentration combined with noble metal determination.

Nowadays much attention is being paid to the determination of trace amounts of noble metals in geological, industrial, biological and environmental samples. The most promising techniques, such as inductively coupled plasma atomic emission spectrometry (ICP-AES), inductively coupled plasma mass spectrometry (ICP-MS) and electrothermal atomic absorption spectrometry (ETAAS) are characterized by high sensitivity. However, the accurate determination of trace noble metals has been limited by numerous interferences generated from the presence of matrix elements. To decrease, or eliminate, these interferences, the sorption preconcentration of noble metals is often used prior to their instrumental detection. A great number of hyphenated methods of noble metal determination using sorption preconcentration have been developed. This review describes the basic types of available sorbents, preconcentration procedures and preparations of the sorbent to the subsequent determination of noble metals. The specific features of instrumental techniques and examples of ETAAS, FAAS, ICP-AES, ICP-MS determinations after the sorption preconcentration of noble metals are considered. The references cited here were selected mostly from the period 1996 - 2006.     

Influence of the prehistory of NaNbO3-Gd1/3NbO3 ceramics and single crystals on their dielectric properties

The dielectric properties of a ceramic and a single crystal of the same composition 0.9NaNbO₃-0.1Gd_1/3NbO₃ (NNG10) with different prehistories of the material are investigated in the low-and infralow-frequency ranges. It is revealed that the dielectric aging of the material based on the NaNbO₃ antiferroelectric with a smeared phase transition differs in character from similar phenomena observed in relaxor ferroelectrics.     

Determination of the surface potential of a dielectric layer on a target bombarded by an ion beam

The electric field at the surface of a charge spot created by an ion beam on a dielectric coating of a target is calculated. An expression is obtained which relates the surface potential of the insulator to the potential of the collector corresponding to saturation of the collector secondary-electron current. It permits determination of the potential drop across the oxide layer of a cold cathode without introducing complications in the construction of the experimental apparatus. Zh. Tekh. Fiz. 68, 126–128 (September 1998)     

Highly efficient lens couplers for laser-diodes based on long period grating in special graded-index fiber

A theoretical scheme of a new device consisting of a lensed fiber and a long period grating (LPG) imprinted in a special single mode gradient-index fiber (SSMGIF) is presented. The SSMGIF consists of the single mode uniform core and the graded-index cladding. The performance of the proposed device is based on specific properties of SSMGIF. For high efficiency coupling between number of cladding modes and co-propagating core mode in this special type of the fiber we can use a number of weak LPGs with the same amplitudes of the refractive index modulation and with almost the same lengths. This scheme provides higher coupling efficiency, relaxed longitudinal alignment tolerance, and smaller device size, than an identical scheme with the LPG imprinted in a step-index (SI) fiber. Two different types of fiber lenses (hemispherical and hyperbolic) are presented for comparison.