On the role of crystal water in the conduction of synthetic borates

The dispersion of permittivity and conductivity of crystals containing aqua complexes of different types (γ-HBO₂, Ca₂B₆O₁₁ · H₂O, La[B₅O₈]OH)₂ · 1.5H₂O, and TRB₆O₉(OH)₃(TR-Tb, Tu)) is studied for the first time. The compounds were synthesized under hydrothermal conditions at T = 270–280°C and P = 70–100 atm. Depending on the contained aqua complex, the compounds display different temperature and frequency behavior of the electric properties. The measurements are carried out in the frequency range from 10^?2 to 10⁶ Hz and in the temperature range from ?20 to 140°C.     

Dielectric loss as an indication of the kinetics of the ferroelectric phase transition

The dependences tanδ(f, T) for triglycine sulfate and diglycine nitrate single crystals are investigated in the frequency range f = 1?2 × 10⁷ Hz at temperatures from ?150 to 50°C for triglycine sulfate and from ?150 to ?60°C for diglycine nitrate. The results are discussed in the framework of the model according to which two or more types of media with different dielectric properties are formed in the ferroelectric phase. The polar volumes of domains themselves and the volumes of domain walls with different symmetries are treated as individual media. The dependences tanδ(f, T) make it possible to separate the contribution of a particular medium and to trace its evolution with temperature. The results of the analysis of the relaxation properties confirm that the phase transitions lead to the formation of two media (the polar medium and domain walls) in triglycine sulfate and three media (the polar medium and two types of domain walls) in diglycine nitrate. It is demonstrated that the relaxation properties are not steady-state characteristics of the samples but depend on their prehistory.     

Radio-wave tomography of inhomogeneous media

Results of experimental investigations on radar sensing of inhomogeneous media and objects with the use of both superbroadband (from 0.5 to 17 GHz) multifrequency scanning and supershort nanosecond and subnanosecond radar pulses are considered. It is demonstrated that addition of angular and spatial scanning and subsequent synthesis of a large aperture allow a three-dimensional tomography of low-contrast inhomogeneities to be realized with a spatial resolution of about 1 cm. Examples are presented that confirm a high efficiency of the method for contactless tomography of the forest structure and detection and visualization of infantry mines below a rough sand surface. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 20–25, September, 2006.     

How Neighborly Can a Centrally Symmetric Polytope Be?

We show that there exist k-neighborly centrally symmetric d-dimensional polytopes with 2(n + d) vertices, where

Effects of Salts of Varying Nature on the Energy Stability of the Structure of Aqueous Solutions

For cyclopentane used as a model hydrocarbon, solubility in water and aqueous solutions of various salts (chlorides, bromides, iodides, rhodanides, alkali metal acetates and sulfates, and calcium and zinc chlorides) at 20±1°C has been determined. Variations of the increment of the methylene group ( ) induced by salt additions to water, are calculated. When the salt is added to the solution, the increment increases drastically irrespective of the nature of the ions, thus stabilizing the structure of the solution. The increase, however, depends significantly on the nature of the salt, which is explained by different degrees of structuring of the aqueous solution caused by the ions of the salts.     

Diagnostics of density fluctuations by enhanced scattering with frequency-tunable microwave sources

The enhanced scattering diagnostics method based on the scattering of microwaves close to the upper hybrid resonance in the plasma has a high sensitivity and spatial resolution and makes it possible to observe the plasma density fluctuations with characteristic scale-lengths much smaller than the wavelength of the probing radiation in vacuum. Good spatial resolution for spatial positioning of the scattering volume by fast tuning of the source frequency ±5% around the reference frequency in the range 100–300 GHz at high power makes this diagnostic method particularly suitable for fluctuation and high energy particle measurements in tokamak plasmas with relatively flat density and temperature profiles.     

Aggregation and spectral properties of Mg(II) tetracarboxyphthalocyanine in aqueous solutions and solid xerogels

Based on spectroscopic studies of magnesium(II) tetracarboxyphthalocyanine molecules in liquid solutions, we have determined the role of the carboxyl groups and the aqueous medium during formation of associates. We have shown that the Q band of the associated form is split into two components of frequency separated by ∼250 cm⁻¹. The effect of the nature of the gel matrices on the spectral luminescence properties of magnesium(II) tetracarboxyphthalocyanine has been studied by incorporating the pigment into a series of xerogels differing in the chemical structure of the inorganic framework and the nanopore surface area. We discuss the reasons for the appearance of associated forms of the pigment in different xerogels. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 2, pp. 211–217, March–April, 2007.     

A Short Simplicial h -Vector and the Upper Bound Theorem

   Abstract. The Upper Bound Conjecture is verified for a class of odd-dimensional simplicial complexes that in particular includes all Eulerian simplicial complexes with isolated singularities. The proof relies on a new invariant of simplicial complexes—a short simplicial h -vector.