Vircator radiation controlled by axial current-carrying filament

The operation of a vircator system with an axial current-carrying filament was studied by computer modeling. It is demonstrated that, by correctly selecting the value of current in the filament, the electron beam dynamics can be controlled so as to excite the output feeder in an optimum regime, which provides for a fourfold increase in the output power.     

The influence of vacuum conditions on the microwave generation in a vircator

The effect of residual gases on the lifetime of a virtual cathode (VC) was studied. Dependence of the output pulse energy of a high-power vircator on the vacuum conditions was studied. It is demonstrated that a rough vacuum of 5×10^?4 Torr achieved with a mechanical pump is sufficient for a vircator operation without significant loss of the output radiation energy. The experimental data agree with a model of the mechanism of VC degradation as a result of the gas ionization.     

Transmission Line for 258 GHz Gyrotron DNP Spectrometry

We describe the design and test results of the transmission line for liquid-state (LS) and solid-state (SS) DNP spectrometers with the second-harmonic 258.6 GHz gyrotron at the Institute of the Biophysical Chemistry Center of Goethe University (Frankfurt). The 13-meter line includes a mode converter, HE11 waveguides, 4 mitre bends, a variable polarizer-attenuator, directional couplers, a water-flow calorimeter and a mechanical switch. A microwave power of about 15 W was obtained in the pure HE11 mode at the spectrometer inputs.     

Specific features of accumulating electrons in high-current trap

A symmetric dynamics of the virtual cathode (VC) formation in an electron beam and a scenario for attaining a compressed electron beam state have been numerically simulated. The parameters of this process are determined, including the moment of VC appearance and the total amount of charge accumulated by this moment. The established symmetric scenario qualitatively differs from those previously described in the literature.     

Ponderomotive transport of charged grains in dusty plasma

The ponderomotive force with which a rapidly oscillating electric field of dusty plasma acts on a charged grain in this plasma is considered. Allowance for the field-induced charge oscillations in the grain reveals new components of the ponderomotive force, which have not been previously described in the literature. One of these components is nonvanishing even in the case of homogeneous plasma and field, which results in a directed transport of the charged fraction of dusty plasma.     

Rare and unique communities in the South of Western Siberia of the Bolshaya Sogra natural complex (Kislukhinsky state natural regional reserve,the Altaisky Krai,Russia)

The paper presents floristic and geo-botanical characteristics of rare forest ecosystems of the south of Western Siberia – spruce forests on the site of the Ob river ancient bed within the modern Bolshaya Sogra within the boundaries of the state natural reserve ‘Kislukhinsky’ (Altai region). Spruce forests here are at the edge of their spread in the West Siberian Plain conditions. There are over 300 species of vascular plants found in these spruce forests. Among them are plants that are typical of the mountain taiga associations of Russian Altai, as well as orchids, which have high species diversity. Spruce forest set of associations is also varied. The uniqueness of the described communities to the south of Western Siberia, the large number of rare and endangered plant species listed in the Red Books of different ranks, as well as the boreal forest species complex rare to the lowland wooded steppe, which has a relict character, all served as the basis for allocating a special protection area in the ‘Kislukhinsky’ reserve and attributing the studied spruce forests to the forests of high conservation value.     

Synthesis of graphene nanoribbons encapsulated in single-walled carbon nanotubes

A novel material, graphene nanoribbons encapsulated in single-walled carbon nanotubes (GNR@SWNT), was synthesized using confined polymerization and fusion of polycyclic aromatic hydrocarbon (PAH) molecules. Formation of the GNR is possible due to confinement effects provided by the one-dimensional space inside nanotubes, which helps to align coronene or perylene molecules edge to edge to achieve dimerization and oligomerization of the molecules into long nanoribbons. Almost 100% filling of SWNT with GNR is achieved while nanoribbon length is limited only by the length of the encapsulating nanotube. The PAH fusion reaction provides a very simple and easily scalable method to synthesize GNR@SWNT in macroscopic amounts. First-principle simulations indicate that encapsulation of the GNRs is energetically favorable and that the electronic structure of the encapsulated GNRs is the same as for the free-standing ones, pointing to possible applications of the GNR@SWNT structures in photonics and nanoelectronics.     

The New General Biological Property of Stem-like Tumor Cells (Part II: Surface Molecules,Which Belongs to Distinctive Groups with Particular Functions,Form a Unique Pattern Characteristic of a Certain Type of Tumor Stem-like Cells)

An ability of poorly differentiated cells of different genesis, including tumor stem-like cells (TSCs), to internalize extracellular double-stranded DNA (dsDNA) fragments was revealed in our studies. Using the models of Krebs-2 murine ascites carcinoma and EBV-induced human B-cell lymphoma culture, we demonstrated that dsDNA internalization into the cell consists of several mechanistically distinct phases. The primary contact with cell membrane factors is determined by electrostatic interactions. Firm contacts with cell envelope proteins are then formed, followed by internalization into the cell of the complex formed between the factor and the dsDNA probe bound to it. The key binding sites were found to be the heparin-binding domains, which are constituents of various cell surface proteins of TSCs—either the C1q domain, the collagen-binding domain, or domains of positively charged amino acids. These results imply that the interaction between extracellular dsDNA fragments and the cell, as well as their internalization, took place with the involvement of glycocalyx components (proteoglycans/glycoproteins (PGs/GPs) and glycosylphosphatidylinositol-anchored proteins (GPI-APs)) and the system of scavenger receptors (SRs), which are characteristic of TSCs and form functional clusters of cell surface proteins in TSCs. The key provisions of the concept characterizing the principle of organization of the “group-specific” cell surface factors of TSCs of various geneses were formulated. These factors belong to three protein clusters: GPs/PGs, GIP-APs, and SRs. For TSCs of different tumors, these clusters were found to be represented by different members with homotypic functions corresponding to the general function of the cluster to which they belong.     

Novel indium(III) complexes with sterically hindered o-iminobenzoquinone

The first examples of indium(III) derivatives based on sterically hindered 4,6-di-tert-butyl-N-(2,6-di-iso-propylphenyl)-o-iminobenzoquinone (imQ) were synthesized and characterized in details. The interaction of sodium o-iminobenzosemiquinolate with indium(III) iodide produces bis[4,6-di-tert-butyl-N-(2,6-di-iso-propylphenyl)-o-iminobenzosemiquinonato]-iodo-indium(III) (1). The same product 1 was obtained by the reactions of imQ with InI or imQ disodium derivative with indium(III) iodide. The interaction of imQ with InI₃ results in the formation of indium(III) compound (2) containing neutral form of o-iminobenzoquinone ligand. Structures of complexes 1 and 2 were determined by X-ray diffraction analysis.     

Creep of the eye sclera

 Irreversible stretching (creep) of the eye sclera, considered as a cause of the high myopia, has been studied experimentally. Both dramatic acceleration and significant deceleration of the sclera creep have been observed in the presence of some enzymes. Creep of various connective tissues caused by static and cyclic mechanical stresses (gravity, blood pressure, etc.) can manifest in many age and pathological changes in human body. Authors express the hope that investigations in this area and finding appropriate inhibitors may replace surgery (eye, cosmetic) by prophylactic therapy. Received: 21 July 1998 / Accepted: 28 August 1998