Magnetic properties of the Ce2Fe17−xMnx helical magnets up to high magnetic fields

Magnetic properties of the Ce₂Fe_17−xMn_x, x=0–2, alloys in magnetic fields up to 40 T are reported. The compounds with x=0.5–1 are helical antiferromagnets and those with 1<x?2 are helical ferromagnets or helical antiferromagnets at low and high T, respectively. Mn ions in the system carry average magnetic moment of 3.0±0.2 μ_B that couple antiparallelly to the Fe moments. Easy-plane magnetic anisotropy in the Ce₂Fe_17−xMn_x compounds weakens upon substitution of Mn for Fe. The absolute value of the first anisotropy constant in the Ce₂Fe_17−xMn_x helical ferromagnets decreases slower with increasing temperature than that calculated from the third power of the spontaneous magnetization. Noticeable magnetic hysteresis in the Ce₂Fe_17−xMn_x, x=0.5–2, helical magnets over the whole range of magnetic fields reflects mainly irreversible deformation of the helical magnetic structure during the magnetization of the compounds. A contribution from short-range order (SRO) magnetic clusters to the magnetic hysteresis of the helical magnets has been also estimated.     

Thermal decomposition of tetraalkylammonium iodides

A number of tetramethylammonium (TMA) iodides, including mono-, tri-, and pentaiodide, were synthesized. Thermal decomposition of samples was investigated by simultaneous TG–DSC analysis accompanied by gaseous IR- and mass-spectrometry analyses. Two different reaction pathways have been observed for TMA pentaiodide at different heating rates. At low heating rates (1–5 K min^?1), a gradual mass loss takes place and a stability plateau due to monoiodide formation exists on TG curve. At high heating rates (10, 15 and 7 K min^?1 as the in-between stage), there are only two peaks on DTG curve (instead of three for lower heating rates) and no monoiodide formation is observed as the sample decomposes completely before 350 °C.     

Investigation into roll waves on the surface of a condensate falling film

A mathematical model that describes flowing of a thin liquid film along a vertical wall allowing for condensation on the interphase surface in the roll wave mode is considered. Families of exact and numerical generalized solutions are constructed in which roll waves are conjugated through a strong and weak discontinuities with each other or with a “residual” thickness. These solutions simulate flowing of the film condensate over the vertical heat exchange surface.     

Multiconformational Method for Analyzing the Biological Activity of Molecular Structures

A multiconformational method for analyzing the biological activity of compounds is proposed that combines conformer search algorithms and a 3DQSAR receptor modeling procedure. The method allows one to find highactivity and lowactivity conformers and determine the receptor shape. The biological activity of a substance is determined as a superposition of the activities of its conformers with allowance for their proportions in the substance. Agreement between calculated and experimental conformations and between calculated and experimental biological activities pIC _50%) is demonstrated by the example of agonists of the 5HT_1A receptor.     

Calculating heat transfer in liquid films based on the method of weighted residuals

The application of the weighted residuals method is considered for the calculation of heat transfer in flowing thin liquid films. As an example, the problem of the film moving under the action of the gas flow on the heated horizontal wall is solved. The solution demonstrates good agreement with the numerical one obtained by the finite-difference method.     

Genetic Algorithm for Predicting Structures and Properties of Molecular Aggregates in Organic Substances

A genetic algorithm for predicting the structures and properties of molecular aggregates in organic substances is proposed. It has been used for modeling the most probable dimers and trimers existing in 137 organic liquids. It has been shown that the geometric and energetic features of modeled aggregates agree with known data. The energy of aggregation correlates with the enthalpy of evaporation of substances. The dependence of the energetic and geometric features of aggregates on the chemical nature of their constituent molecules is discussed.     

Quantum-topological analysis of electron density in azachalcogenene crystals with aromatic substituents

A theoretical study was carried out to investigate the topological characteristics of electron density (DFT B3LYP/6-311G(d,p) ab initio basis set) for molecules and crystal structures of azachalcogenenes with Ar-S-N=S=N-S-Ar and Ar-S-N=S=N-S-Ar aryl substituents. The characteristics of electron density were determined at the critical points (3, ?1) corresponding to the S...S and Se...Se intramolecular contacts, which serve to close the S-N=S=N-S and S-N=S=N-S five-membered rings. The intermolecular interactions in crystals are described from the viewpoint of electron density analysis in the region of S…S, S…N, Se…N, and S…Hal intermolecular short contacts between the atomic pairs of interactant molecules.     

Exploring heterocyclic cations ability to form the iodide–iodine halogen bond: case study of chalcogenazolo(ino)quinolinium crystals

Structural Chemistry - Analysis of iodine-derived chalcogenazolo(ino)quinolinium mono- and triiodides shows that the covalently bonded iodine atoms in the fragments C(sp2)–I and...     

A quantum topological study of the electron density in monomers and dimers of acyclic azathiens with aromatic substituents

A theoretical study of electron density, ρ(r), and the Laplacian (ab initio, DFT B3LYP/6-31G(d, p) basis set) has been carried out for nine molecules of azathiens with aryl substituents (Ar-N=S=N-Ar₁) and for sixteen dimers corresponding to typical arrangements of neighboring molecules in the crystal structures of Ar-N=S=N-Ar₁. A dependence was established of the values of the electron density at (3, ?1) critical points in the area of inter-stack and intra-stack atom-atom contacts on the internuclear distance.