A vector percolation modeling of oil–gas relative permeabilities

We presented exact analytical formulae and numerical calculation of diffusitivity curves with different law for a local pore behavior and have obtained critical exponent, different from conductivity. The connectivity percolation theory was built only on the conductivity, (the diffusion critical exponent was supposed to be equal to the conductivity exponent) and therefore sees only one side of problem-the scalar side. In many topological problems involving mechanical properties and fluid flow the connectivity scalar percolation geometry does not enough to apply.

One of the most useful aspects of percolation is that many very complicated systems have the same behavior with the same critical exponents. Universality of vector percolation is shown in the coincidence between the experimental measured relative hydraulic permeability of fluid and gas flow through unconsolidated sand and effective conductivity and diffusitivity curves of the bond–site percolation models. Comparisons of our calculation results to natural matches are quite good. We have argued that experimental data may be interpreted as a variant of pure vector percolation and to belong to the same universality class.     

Mechanism of phase transitions in the (NH4)2WO2F4 ferroelastic

Precision studies of the thermophysical properties and structure of an (NH₄)₂WO₂F₄ crystal have been performed. It was established reliably that there is a sequence of two phase transitions at T ₁ = 201 K and T ₂ = 160 K characterized by wedging out of an intermediate phase with an increase in pressure. The role of tetrahedral and octahedral ionic groups in the mechanism of the structural transitions was determined.     

Concurrent combined verification: reducing false positives in automated NMR structure verification through the evaluation of multiple challenge control structures

Automated structure verification using ¹H NMR data or a combination of ¹H and heteronuclear single‐quantum correlation (HSQC) data is gaining more interest as a routine application for qualitative evaluation of large compound libraries produced by synthetic chemistry. The goal of this automated software method is to identify a manageable subset of compounds and data that require human review. In practice, the automated method will flag structure and data combinations that exhibit some inconsistency (i.e. strange chemical shifts, conflicts in multiplicity, or overestimated and underestimated integration values) and validate those that appear consistent. One drawback of this approach is that no automated system can guarantee that all passing structures are indeed correct structures. The major reason for this is that approaches using only ¹H or even ¹H and HSQC spectra often do not provide sufficient information to properly distinguish between similar structures. Therefore, current implementations of automated structure verification systems allow, in principle, false positive results. Presented in this work is a method that greatly reduces the probability of an automated validation system passing incorrect structures (i.e. false positives). This novel method was applied to automatically validate 127 non‐proprietary compounds from several commercial sources. Presented also is the impact of this approach on false positive and false negative results. Copyright © 2012 John Wiley & Sons, Ltd.     

Characterization of a didehydrobenzoxazine intermediate in a novel carbene-to-carbene transformation

Irradiation of N(2) matrix-isolated 3-chloro-3-(2-benzoxazolyl)diazirine gives a mixture of syn- and anti-benzoxazolylchlorocarbenes which could be characterized by IR, UV/vis, and B3LYP modeling. Subsequent irradiation of the carbene caused ring opening to the corresponding quinoimine, which was similarly characterized. In turn, the quinoimine photochemically underwent ring-closure to a novel, highly strained cyclic ketenimine. Unrestricted singlet DFT calculations were required to fit the IR spectrum of the ketenimine, suggesting significant diradical character. Photolysis of the ketenimine led to ring cleavage in yet another fashion, to give an isonitrile-phenoxychlorocarbene, whose spectra were similar to those of the previously characterized phenoxychlorocarbene. Finally, at shorter wavelengths, the phenoxycarbene underwent the expected rearrangement to the corresponding benzoyl chloride.     

Electron transition in intercalated disulfide CuCrS<Subscript>2</Subscript>

Electrical, resonant, and magnetic properties of intercalated copper chromium disulfide CuCrS₂ are studied. It is established that CuCrS₂ is an antiferromagnetic semiconductor with Néel temperature T_N=40.7 K and an effective magnetic moment of 4.3µ_B. Anomalies in the electrical, magnetic, and resonant properties of CuCrS₂ are found at T_c=110 K, which suggest an electron transition accompanied by alteration of the valences of the 3d-metal ions.     

Polarization-optical and X-ray diffraction investigations on the symmetry of distorted phases of ammonium cryolite (NH4)3 ScF6

Single-crystal plates of different sections of the (NH₄)₃ScF₆ crystal have been investigated by polarization-optical microscopy and X-ray diffraction over a wide temperature range, including the temperatures of two known phase transitions and the third transition found recently. It is established that the symmetry of 5 phases changes in the following sequence: $\begin{gathered} O_h^5 - Fm3m(Z = 4) \leftrightarrow C_{2h}^5 - {{P12_1 } \mathord{\left/ {\vphantom {{P12_1 } {n1}}} \right. \kern-0em} {n1}}(Z = 2) \leftrightarrow C_{2h}^3 - {{I12} \mathord{\left/ {\vphantom {{I12} {m1}}} \right. \kern-0em} {m1}} \\ (Z = 16) \leftrightarrow C_i^1 - I\bar 1(Z = 16) \\ \end{gathered} $ .     

Magnetic properties of aerugite Co<Subscript>10</Subscript>Ge<Subscript>3</Subscript>O<Subscript>16</Subscript>

This paper reports on the first study of the temperature and field dependences of the magnetization, heat capacity, and electrical properties of synthesized polycrystalline samples of aerugite Co₁₀Ge₃O₁₆, as well as on x-ray diffraction analysis of this compound. It is shown that the cobalt ions in this compound occupy three nonequivalent positions. The results of the experimental and theoretical studies suggest that aerugite is a ferrimagnet with two uncompensated magnetic moments of the cobalt atom per formula unit.     

Low-temperature metal-insuslator transition and magnetic properties in the VxMn1−x S disordered system

A study of the structure and electrical and magnetic properties of the V_xMn_1−x S disordered system is reported. The existence of a low-temperature metal-insulator transition for Fermi-glass 0.4<x<0.5 compositions in paramagnetic phase, which is accompanied by a change in the structure and magnetic properties, has been established. An analysis of the magnetic properties permits a conjecture that current carriers become delocalized in these solid solutions at the metal-insulator transition temperature to form small ferromagnetically ordered regions (ferrons). Fiz. Tverd. Tela (St. Petersburg) 39, 1428–1431 (August 1997)     

Incommensurate phase in the layered hexagonal crystal Cs3Bi2I9

An incommensurate phase is observed in a Cs₃Bi₂I₉ crystal, which belongs to the family of layered A₃B₂X₉ structures. Data from ¹²⁷I NQR and x-ray powder diffraction patterns show that the second-order normal phase—incommensurate phase transition at T _i=220 K is accompanied by a P6₃/mmc↔P2₁/m symmetry change and takes place at the center of the Brillouin zone. The nature of the instability leading to the appearance of this little-studied form of incommensurability is discussed. Fiz. Tverd. Tela (St. Petersburg) 39, 1105–1108 (June 1997)