New functionalized dithia-12(13)-crown-4 ethers: Synthesis,complex formation,and extraction capacity

1,4-Dioxa-7,10-dithiacyclododecane-8-carbonitrile, 1,4-dioxa-7,11-dithiacyclotridecan-9-one, its 2,4-dinitrophenylhydrazone, and unsubstituted 7,10-dithia-12-crown-4 were synthesized. The complexing ability of the four synthesized dioxadithiacrown compounds toward Ag(I), Pb(II), Hg(II), and Cd(II) ions was assessed by ¹H NMR. The extracting ability of the three dioxadithiacrown compounds with respect to the Sn(II) ion from aqueous solutions was studied. The thermal stability of 1,4-dioxa-7,10-dithia-cyclododecane and the corresponding 8-carbonitrile was investigated. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 992–1000, July, 2007.     

Rational approximation with varying weights I

We investigate two problems concerning uniform approximation by weighted rationals {w ⁿr_n～ _∞ ⁿ⁼¹ }, wherer _n=p_n Namely, forw(x):=e ^x we prove that uniform convergence to 1 ofw ⁿr_n is not possible on any interval [0,a] witha>2π. Forw(x):=x ^?, ?>1, we show that uniform convergence to 1 ofw ⁿr_n is not possible on any interval [b, 1] withb<tan ⁴(π(??1)/4?). (The latter result can be interpreted as a rational analogue of results concerning “incomplete polynomials.”) More generally, for α≥0, β≥0, α+β>0, we investigate forw(x)=e ^x andw(x)=x ^?, the possibility of approximation byw ⁿ p_n/q_n～ _∞ ⁿ⁼¹ , where depp _n≤αn, degq _n≤βn. The analysis utilizes potential theoretic methods. These are essentially sharp results though this will not be established in this paper.     

Do Orthogonal Polynomials Dream of Symmetric Curves?

The complex or non-Hermitian orthogonal polynomials with analytic weights are ubiquitous in several areas such as approximation theory, random matrix models, theoretical physics and in numerical analysis, to mention a few. Due to the freedom in the choice of the integration contour for such polynomials, the location of their zeros is a priori not clear. Nevertheless, numerical experiments, such as those presented in this paper, show that the zeros not simply cluster somewhere on the plane, but persistently choose to align on certain curves, and in a very regular fashion. The problem of the limit zero distribution for the non-Hermitian orthogonal polynomials is one of the central aspects of their theory. Several important results in this direction have been obtained, especially in the last 30 years, and describing them is one of the goals of the first parts of this paper. However, the general theory is far from being complete, and many natural questions remain unanswered or have only a partial explanation. Thus, the second motivation of this paper is to discuss some “mysterious” configurations of zeros of polynomials, defined by an orthogonality condition with respect to a sum of exponential functions on the plane, that appeared as a results of our numerical experiments. In this apparently simple situation the zeros of these orthogonal polynomials may exhibit different behaviors: for some of them we state the rigorous results, while others are presented as conjectures (apparently, within a reach of modern techniques). Finally, there are cases for which it is not yet clear how to explain our numerical results, and where we cannot go beyond an empirical discussion.     

The stationary sine-Gordon equation on metric graphs: Exact analytical solutions for simple topologies

We consider the stationary sine-Gordon equation on metric graphs with simple topologies. Exact analytical solutions are obtained for different vertex boundary conditions. It is shown that the method can be extended for tree and other simple graph topologies. Applications of the obtained results to branched planar Josephson junctions and Josephson junctions with tricrystal boundaries are discussed.     

The stability of wide high-temperature superconducting films with varying transport current

The current-carrying capacity of a wide high-temperature superconducting film under conditions of rapid injection of current is investigated theoretically. An analytic expression is derived for the rate of current injection into the film at which a marked degradation of the current-carrying capacity of the film occurs. The obtained results may be important from the standpoint of analyzing the stability of superconducting ac devices.     

Facile Transformation of the Hydroxy‐Substituted Oxathiacrown Ethers

9(12)‐Hydroxy‐dithia‐13(16)‐crown‐4(6)‐ethers have been prepared by the condensing an oligoethylene glycol dithiol with 2,3‐dibromo‐1‐propanol. Methods of oxidation, halogenation, amination, and esterification of the 9‐hydroxythiacrown ether, producing corresponding oxathiacrown ether derivatives in good yields, have been developed. Cyclic destruction has not been found in the studied reactions. The change of the oxathiamacrocyclic ring size in the course of the halogenation and amination reactions was revealed.     

Effect of polyvinylpyrrolidone on the morphology and spectral luminescence of Y3Al5O12:Ce+3

Results from investigating the effect of different molecular masses and amounts of polyvinylpirrolidone (PVP) on the structural-phase, morphological, and spectral luminescence properties of YAG:Ce powders produced using a colloid chemical approach to synthesis (co-precipitation from solutions of the respective salts followed by thermal treatment of xerogels in air) are presented. The optimum thermal treatment regimes for precursors synthesized in the presence of PVP and its concentration in precipitation solutions that facilitate the formation of weakly aggregated nanosized powders of well-crystallized garnet characterized by enhanced (by a factor of 1.5–2) luminescence relative to a standard sample (without PVP) are determined.     

Tunneling magnetoresistance of phase-separated manganites

A simple model of phase separation is used to study the magnetoresistance of manganites in the nonmetallic state. It is assumed that the phase separation corresponds to the emergence of small ferromagnetic metallic droplets (ferrons) in a nonconducting antiferromagnetic or paramagnetic medium, with the metallic phase concentration being far from the percolation threshold. The charge transfer is accomplished by way of electron jumps between droplets. The magnetoresistance in such a system is defined both by the variation of the volume of the metal phase and by the dependence of the probabilities of electron transitions on the magnitude of the magnetic field. It is demonstrated that, in the region of low magnetic fields, the magnetoresistance is quadratic with respect to the field and decreases with temperature by the T ^?n law, where n takes values from 1 to 5 depending on the correlation between the parameters. In the high-field limit, the magnetoresistance increases abruptly with the volume of the metal phase. The crossover of the field dependence from quadratic to a stronger one may be accompanied by the emergence of a platean in the magnetoresistance. The correlation between the obtained results and the available experimental data is discussed.     

Conversion of C<Subscript>19</Subscript>–C<Subscript>38</Subscript> <Emphasis Type="Italic">n</Emphasis>-paraffins into components of kerosene and diesel fuels on Pt-containing amorphous aluminosilicate

The behavior of Pt-containing catalysts based on mesoporous amorphous aluminosilicate in the process of hydroconversion of C₁₉–C₃₈n-paraffins with the goal to produce diesel and kerosene fractions with improved cold flow properties was investigated. These systems were characterized by high efficiency and selectivity in the process of producing diesel and kerosene fractions. A 91% degree of conversion was achieved with a yield of liquid hydrocarbons of 76% (320°C, volume feed rate 0.5 h^–1, molar ratio hydrogen: feed = 600: 1, pressure 50 atm). The initial freezing point of the isolated kerosene fraction was below minus 50°C, and the cold filter plugging point of the diesel fraction was minus 34°C.