Electron Diffraction Study of Epitaxial Graphene Structure Grown upon SiC (0001) Thermal Destruction in Ar Atmosphere and in High Vacuum

Physics of the Solid State - We have studied the structure of epitaxial graphene obtained as a result of thermal desorption of the silicon carbide surface under conditions of vacuum synthesis and...     

Selective Activation of Fluoroalkenes with N‐Heterocyclic Carbenes: Synthesis of N‐Heterocyclic Fluoroalkenes and Polyfluoroalkenyl Imidazolium Salts

Selective reactions between nucleophilic N,N′‐diaryl‐heterocyclic carbenes (NHCs) and electrophilic fluorinated alkenes afford NHC fluoroalkenes in high yields. These stable compounds undergo efficient and selective fluoride abstraction with Lewis acids to give polyfluoroalkenyl imidazolium salts. These salts react at Cβ with pyrrolidine to give ammonium fluoride‐substituted salts, which give rise to conjugated imidazolium‐enamine salts through loss of HF. Alternatively, reaction with 4‐(dimethylamino)‐pyridine provides a Cα‐pyridinium‐substituted NHC fluoroalkene. These compounds were studied using multinuclear NMR spectroscopy, mass spectrometry, and X‐ray crystallography. Insight into their electronic structure and reactivity was gained through the use of DFT calculations.     

Advances in the Study of Gas Hydrates by Dielectric Spectroscopy

The influence of kinetic hydrate inhibitors on the process of natural gas hydrate nucleation was studied using the method of dielectric spectroscopy. The processes of gas hydrate formation and decomposition were monitored using the temperature dependence of the real component of the dielectric constant ε′(T). Analysis of the relaxation times τ and activation energy ΔE of the dielectric relaxation process revealed the inhibitor was involved in hydrogen bonding and the disruption of the local structures of water molecules.     

Non-Exponential 1H and 2H NMR Relaxation and Self-Diffusion in Asphaltene-Maltene Solutions

The distribution of NMR relaxation times and diffusion coefficients in crude oils results from the vast number of different chemical species. In addition, the presence of asphaltenes provides different relaxation environments for the maltenes, generated by steric hindrance in the asphaltene aggregates and possibly by the spatial distribution of radicals. Since the dynamics of the maltenes is further modified by the interactions between maltenes and asphaltenes, these interactions—either through steric hindrances or promoted by aromatic-aromatic interactions—are of particular interest. Here, we aim at investigating the interaction between individual protonic and deuterated maltene species of different molecular size and aromaticity and the asphaltene macroaggregates by comparing the maltenes’ NMR relaxation (T1 and T2) and translational diffusion (D) properties in the absence and presence of the asphaltene in model solutions. The ratio of the average transverse and longitudinal relaxation rates, describing the non-exponential relaxation of the maltenes in the presence of the asphaltene, and its variation with respect to the asphaltene-free solutions are discussed. The relaxation experiments reveal an apparent slowing down of the maltenes’ dynamics in the presence of asphaltenes, which differs between the individual maltenes. While for single-chained alkylbenzenes, a plateau of the relaxation rate ratio was found for long aliphatic chains, no impact of the maltenes’ aromaticity on the maltene–asphaltene interaction was unambiguously found. In contrast, the reduced diffusion coefficients of the maltenes in presence of the asphaltenes differ little and are attributed to the overall increased viscosity.     

Electron-Diffraction Study of the Structure of Epitaxial Graphene Grown by the Method of Thermal Destruction of 6H- and 4H-SiC (0001) in Vacuum

Physics of the Solid State - The method of reflection high-energy electron diffraction (RHEED) is used for studying the structure of graphene layers formed on the surface of the Si-face of...     

Metal-semiconductor interface in extreme temperature conditions

We present an investigation of electrons’ and phonons’ temperatures in the volume of a semiconductor (or metal) sample and at the interface between metal and semiconductor. Two types of mismatch between electrons’ and phonons’ temperatures take place: at metal-semiconductor interfaces and in the volume of the sample. The temperature mismatch leads to nonlinear terms in expressions for heat and electricity transport. The nonlinear effects should be taken into consideration in the study of electrical and heat transport in composites and in electronic chips.     

Aggregation of sodium dodecyl sulfate in micellar solution of β-casein analyzed by 1H NMR self-diffusion, relaxation and Fourier transform IR spectroscopy

Micellization of anionic sodium dodecyl sulfate (SDS) in the presence of -casein (-CN) micelles in aqueous media was studied by ¹H NMR and Fourier transform IR spectroscopy. At low concentrations SDS molecules incorporate into -CN micelles and modify the protein secondary structure, increasing the portion of helical domains. It was shown that SDS micelles do not appear until binding sites located in the hydrophobic core of -CN micelles are saturated.     

Rock deformation problems

Studies into the stress-strain state of rock mass are reviewed. The solutions of a wide range of applied problems are analyzed and methods used to solve them are generalized. Important areas of further research in rock mechanics are pointed out.__________Translated from Prikladnaya Mekhanika, Vol. 40, No. 12, pp. 3–17, December 2004.     

Optimized effective potentials in finite basis sets

The finite basis optimized effective potential (OEP) method within density functional theory is examined as an ill-posed problem. It is shown that the generation of nonphysical potentials is a controllable manifestation of the use of unbalanced, and thus unsuitable, basis sets. A modified functional incorporating a regularizing smoothness measure of the OEP is introduced. This provides a condition on balanced basis sets for the potential, as well as a method to determine the most appropriate OEP and energy from calculations performed with any finite basis set.     

Synthesis of 1,2,3-triazolyl nucleoside analogues and their antiviral activity

Molecular Diversity - Based on the fact that a search for influenza antivirals among nucleoside analogues has drawn very little attention of chemists, the present study reports the synthesis of a...