Plasma oscillations of an electron beam in an external electric field

Many papers have been devoted to the problem of the interaction of beams of charged particles with a plasma (a detailed bibliography is given, for example, in [1]). Analysis of the dispersion equation shows that in the case of a sufficiently slow monoenergetic electron beam of low density, growing longitudinal waves are not excited in a system consisting of such a beam and a plasma [2–4].The problem of the penetration of an external longitudinal electric field into a semiconfined plasma with an electron beam in the absence of instabilities in the system is studied (the boundary-value problem for growing waves was examined in [5]). This problem is, in a certain sense, an extension of the second part of L. D. Landau's well-known work [6] to include the case of a plasma with a beam. On the other hand, in the absence of an external electric field, this problem may be considered a boundary-value problem of the interaction of a weakly modulated electron beam with a plasma.The authors thank M. L. Levin for his useful comments.     

Octahedral rhodium cluster [Rh6Cp6(μ6-C)]2+(PF6 -)2

The 86-electron dicationic octahedral rhodium cluster [Rh₆Cp₆(_μ6-C)]²⁺(PF₆ ^-)₂ containing Cp ligands and the interstitial carbon atom was synthesized by the reaction of Rh₃Cp₃(μ-CO)₃ with RhCp(C₂H₄)₂ Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 395–396, February, 1999     

Hard-Sphere Fluid: Structure and Viscosities

JETP Letters - As demonstrated earlier, the mode-coupling approach taking into account the interaction between shear dynamic modes and soft density fluctuations gives the expression for shear...     

Solution of the Fracture Detection Problem by Machine Learning Methods

Doklady Mathematics - Inverse problems of fracture exploration seismology are solved using machine learning methods. A single fracture of fixed size and subvertical orientation is considered in the...     

Excursions in Sequences of Alpha-Particle Flux Counts

Physics of Atomic Nuclei - In this paper, it is shown using one-, two-, and three-dimensional spectrometry that the excursion distributions in random sequences of counts $$k(\Delta t)$$ of...     

Easy Access to Versatile Catalytic Systems for C−H Activation and Reductive Amination Based on Tetrahydrofluorenyl Rhodium(III) Complexes

On the basis of the 1,2,3,4-tetrahydrofluorenyl ligand, a simple approach was developed to new effective rhodium catalysts for the construction of C−C and C−N bonds. The halide compounds [(η⁵-tetrahydrofluorenyl)RhX₂]₂ ( 2 a : X=Br; 2 b : X=I) were synthesized by treatment of the bis(ethylene) derivative (η⁵-tetrahydrofluorenyl)Rh(C₂H₄)₂ ( 1 a ) with halogens. An analogous reaction of the cyclooctadiene complex (η⁵-tetrahydrofluorenyl)Rh(cod) ( 1 b ) with I₂ is complicated by the side formation of [(cod)RhI]₂. The reaction of 2 b with 2,2′-bipyridyl leads to cation [(η⁵-tetrahydrofluorenyl)Rh(2,2′-bipyridyl)I]⁺ ( 3 ). The halide abstraction from 2 a , b with thallium or silver salts allowed us to prepare sandwich compounds with incoming cyclopentadienyl, dicarbollide and mesityleneligands [(η⁵-tetrahydrofluorenyl)RhCp]⁺ ( 4 ), (η⁵-tetrahydrofluorenyl)Rh(η-7,8-C₂B₉H₁₁) ( 5 ), and [(η⁵-tetrahydrofluorenyl)Rh(η-mesitylene)]²⁺ ( 6 ). The structures of 1 b , 2 b ⋅ 2I₂, 3 PF₆, 4 TlI₄, 5 , and [(cod)RhI]₂ were determined by X-ray diffraction. Compounds 2 a , b efficiently catalyze the oxidative coupling of benzoic acids with alkynes to selectively give isocoumarins or naphthalenes, depending on the reaction temperature. Moreover, they showed moderate catalytic activity in other annulations of alkynes with aromatic compounds (such as benzamide, acetanilide, etc.) which proceed through CH activation. Compound 2 b also effectively catalyzes the reductive amination of aldehydes and ketones in the presence of carbon monoxide and water via water-gas shift reaction, giving amines in high yields (67–99 %).     

Computational assessment of environmental hazards of nitroaromatic compounds: influence of the type and position of aromatic ring substituents on toxicity

Structural Chemistry - This study summarizes the results of our recent QSAR and QSPR investigations on prediction of numerous aspects of environmental behavior of nitro compounds. In this study, we...     

Degradation versus self-assembly of block co-polymer micelles

The stability of micelles self-assembled from block co-polymers can be altered by the degradation of the blocks. Slow degradation shifts the equilibrium size distribution of block co-polymer micelles and changes their properties. The quasi-equilibrium scaling theory shows that the degradation of hydrophobic blocks in the core of micelles destabilizes the micelles, reducing their size, while the degradation of hydrophilic blocks forming coronas of micelles favors larger micelles and may, at certain conditions, induce the formation of micelles from individual chains.     

Applicability domains for classification problems: Benchmarking of distance to models for Ames mutagenicity set

The estimation of accuracy and applicability of QSAR and QSPR models for biological and physicochemical properties represents a critical problem. The developed parameter of "distance to model" (DM) is defined as a metric of similarity between the training and test set compounds that have been subjected to QSAR/QSPR modeling. In our previous work, we demonstrated the utility and optimal performance of DM metrics that have been based on the standard deviation within an ensemble of QSAR models. The current study applies such analysis to 30 QSAR models for the Ames mutagenicity data set that were previously reported within the 2009 QSAR challenge. We demonstrate that the DMs based on an ensemble (consensus) model provide systematically better performance than other DMs. The presented approach identifies 30-60% of compounds having an accuracy of prediction similar to the interlaboratory accuracy of the Ames test, which is estimated to be 90%. Thus, the in silico predictions can be used to halve the cost of experimental measurements by providing a similar prediction accuracy. The developed model has been made publicly available at http://ochem.eu/models/1 .     

Synthesis of 5-(hydroxy-, chloro-, bromomethyl)furan-2-enones Based on Fructose and their Antioxidant Activity

Chemistry of Natural Compounds - New enones were synthesized from 5-hydroxymethylfurfurol (5-HMF) and its derivatives using Wittig reactions of various phosphoranes. The synthesized enones were...