Search

The charging of dust grains in a plasma with regularized kappa distributed electrons and ions has been investigated. The effects of the electrons’ and ions’ cutoff parameters and spectral indices on the dust grain surface potential are numerically analyzed. It is shown that the enhancement of energetic electrons increases with the decrease of the electron spectral index and cutoff parameter, leading to an increase in the magnitude of dust grain charge. Conversely, the magnitude of dust grain charge varies inversely with the decrease of ion spectral index and cutoff parameter. In addition, the critical ion spectral index for the charge of dust grain changing from negative to positive increases with the increase of the electron spectral index and cutoff parameter, and the decrease of the ion cutoff parameter. The results obtained can be helpful in understanding the dust charge state in laboratory and space dusty plasmas where the plasma particles deviate from the Maxwellian distribution. [ABSTRACT FROM AUTHOR]

Based on a combination of quantum chemical simulation and experimental studies, the formation of vanadium oxide structures on the silica surface when sequentially treated with VOCl3 and H2O vapors was analyzed. The synthesis products were identified by IR spectroscopy. Changes in the composition and structure of the resultant surface species according to the process temperature and VOCl3 vapor pressure in the reactor were predicted by quantum chemical methods. By the example of the synthesis at 473 K in a flow-through system and study of the chemical composition and structure of the new functional groups formed on the surface, a good agreement between the experimental and calculated data was demonstrated. The results of IR spectroscopic studies of the samples synthesized were processed using quantum chemical approaches. The characteristic IR absorption band due to vibrations of the bridging bonds of vanadium atoms with the Si–O–V matrix, localized at 920–945 or 960 cm–1 depending on the structure of the surface sites, was used as the basis for identification of the surface vanadium oxide groups. [ABSTRACT FROM AUTHOR]

Time dependence of edge plasma turbulence was investigated in the IR-T1 tokamak. Time dependence of fluctuation level and spectra were measured using Langmuir probe in the region r/a = 0.8-1. In all times of typical shot, the edge plasma was turbulently unstable, with a broad band fluctuation spectrum in the range of frequencies f = 10-1000 kHz. The relative fluctuation level as monitored by the ion saturation current J was very high, in the range ≅0.1-0.6 all over the time, while the fluctuation power spectra were roughly invariant in shape. [ABSTRACT FROM AUTHOR]

Charge transfer, or charge exchange, describes a process in which an ion takes one or more electrons from another atom. Investigations of this fundamental process have accompanied atomic physics from its very beginning, and have been extended to astrophysical scenarios already many decades ago. Yet one important aspect of this process, i.e. its high efficiency in generating X-rays, was only revealed in 1996, when comets were discovered as a new class of X-ray sources. This finding has opened up an entirely new field of X-ray studies, with great impact due to the richness of the underlying atomic physics, as the X-rays are not generated by hot electrons, but by ions picking up electrons from cold gas. While comets still represent the best astrophysical laboratory for investigating the physics of charge transfer, various studies have already spotted a variety of other astrophysical locations, within and beyond our solar system, where X-rays may be generated by this process. They range from planetary atmospheres, the heliosphere, the interstellar medium and stars to galaxies and clusters of galaxies, where charge transfer may even be observationally linked to dark matter. This review attempts to put the various aspects of the study of charge transfer reactions into a broader historical context, with special emphasis on X-ray astrophysics, where the discovery of cometary X-ray emission may have stimulated a novel look at our universe. [ABSTRACT FROM AUTHOR]

An argon magnetized plasma column is created with primary energetic electrons in the Mistral device. Low frequency instabilities regularly rotating around this column are observed with an ultra-fast camera and a spectroscopic device. Experimental results coupled to a coronal code show the presence of a few percents of fast (hot) electrons inside the ejected plasma. It also shows that ultra-fast camera analysis of the ejected plasma can only give information on the primary electron population. Finally, these results suggest that the radial decrease of the light emitted by the ejected plasma is essentially due to the radial decrease of the mean energy of the hot electrons. [ABSTRACT FROM AUTHOR]

The diffusion of plasma impurities in tokamak-edge-plasma turbulence is investigated numerically. The time-dependent potential governing particle motion was measured by 2D array of 8×8 Langmuir probes in edge region of CASTOR tokamak. The diffusion of particles is found to be classical in the radial direction, but it can be of an anomalous Lévy-walk type in the poloidal direction. The diffusion is found to be dependent on the ratio of particles’ mass and charge. When this ratio grows, the diffusion coefficient in radial direction grows as well, whereas poloidal diffusion coefficient drops down. Moreover, movement of particles in the time-frozen snapshot of this potential is investigated showing that also the time-independent potential is much more favorable for the particle diffusion in poloidal direction than in radial one. In the case of single ionized carbon ions the poloidal diffusion in time-independent potential transits to the Lévy-walk type for temperatures greater than 25 eV, for radial diffusion Lévy-walk was not observed even for 500 eV. [ABSTRACT FROM AUTHOR]

This essay surveys research about the value of individual members of boards of directors. When directors join or exit corporate boards, company stock prices respond, often in magnitudes of 1% of firm value or more. Related research shows that when a significant event impacts the stock price of one company, the effects are transmitted to other companies that share board members in common with the primary company. Share price reactions are sensitive to variables such as a director’s occupation, independence, and professional qualifications. Together, this evidence suggests that a well-functioning market for directors might already exist, making direct regulation unnecessary and possibly counter-productive. [ABSTRACT FROM AUTHOR]

Abstract We review possible mechanisms of blobby transport in fusion-related plasmas. The models dealing with the effective plasma gravity and caused by both ??Te and parallel shear of E × B drift instabilities are considered. [ABSTRACT FROM AUTHOR]

The spatial and temporal characteristics of the turbulence in the inboard and outboard scrape-off layer (SOL) of tokamak HYBTOK-II have been studied using poloidal probe array. Bursty behaviour with intermittent bursts was observed for both outboard and inboard SOL. In the inboard (high field side), high level of density fluctuations has been observed. The fluctuations in the high field side and low field side are identical in statistics that is non-Gaussian one. [ABSTRACT FROM AUTHOR]

It has been suggested that by electrically biasing the divertor tiles in a tokamak, one could create a toroidally-asymmetric potential structure in the scrape-off layer (SOL) plasma. The resulting E× B convective motion should increase the plasma transport in the SOL and thereby reduce the heat load on the divertor plates. This paper describes plans for such experiments on COMPASS-D and preliminary theoretical modelling. The COMPASS-D divertor target consists of 24 graphite tiled toroidal segments. The inner and outer strike point tiles on all these segments will be insulated from each other, and cabling will be installed to allow for biasing of individual tiles in any combination. Theoretical analysis suggests that the electrostatic potential perturbations caused by the biasing will be confined to the divertor region below the X-point, and that substantial SOL broadening can be achieved by applying modest voltages. Aside from active control of SOL transport, it is hoped that the biasing will be useful to probe other divertor and SOL physics issues. [ABSTRACT FROM AUTHOR]

The phytobilin chromophores of phycobiliproteins and phytochromes are biosynthesized from heme in a pathway that begins with the opening of the tetrapyrrole macrocycle of protoheme to form biliverdin IXα, in a reaction catalyzed by heme oxygenase. An Arabidopsis thaliana hy1 mutant was previously shown to be deficient in phytochrome responses, and these responses were regained when the plants were administered biliverdin IXα. A heme oxygenase-encoding gene, ho1, was recently cloned from the cyanobacterium Synechocystis sp. PCC 6803. When ho1 was expressed in Escherichia coli, the cells produced active ferredoxin-dependent soluble heme oxygenase. The open reading frame of ho1 was fused in frame with a chloroplast transit peptide-encoding sequence from the oli gene of Antirrhinum majus. This construct was placed in a binary plasmid vector containing a kanamycin resistance marker and a cauliflower mosaic virus 35S promoter to control expression of the chimeric oli-ho1 gene and used to transform A. thaliana hy1 plants. Two independent transformed lines were obtained that had the phenotype of the parental Landsberg erecta line and expressed the chimeric gene, as indicated by detection of its mRNA by reverse transcriptase-polymerase chain reaction. The results indicate that Synechocystis sp. PCC 6803 heme oxygenase encoded by ho1 can substitute for the defective HY1 gene product and that the only required enzyme activity of the HY1 gene product is heme oxygenase. [ABSTRACT FROM AUTHOR]

The magnetic separatrix in a diverted tokamak determines the boundary between closed and open magnetic field lines. Even though the main influences on the physics of SOL and core regions may be different and shift from the plasma-neutral coupling and impurity radiation in the scrape-off layer (SOL) to anomalous plasma transport in the core, the influence of this boundary persists over some width, both into the core region and into the SOL. We give a short review of the progress in the divertor-SOL physics and discuss the links between edge core and SOL plasmas which are likely to have an important role in different edge-plasma phenomena. [ABSTRACT FROM AUTHOR]

We have performed two dimensional fluid B2 simulations on detached recombining plasmas to compare with experimental observations in a linear divertor plasma simulator. In detached helium plasmas associated with volumetric electron-ion recombination (collisional radiative recombination), an electron-ion energy exchange process followed by ion-neutral charge exchange is found to be a key to reduce the electron temperature along the magnetic field to be less than leV. The structural change of detached plasmas associated with molecular activated recombination has been also discussed in detail. [ABSTRACT FROM AUTHOR]

We have applied the representational difference analysis (RDA) to isolate genetic markers for a deletion on the rat chromosome RNO5q22–33. This deletion occured in anchorage independent sublines of a normal rat fibroblast × mouse hepatoma cell hybrid (BS181), (Islam 1989). Normal rat tissue DNA provided the “tester” and the BS181 hybrid DNA the “driver” in the RDA hybridization/selection reactions. Out of twelve RDA derived DNA sequences that were analyzed in detail using a rat × mouse cell hybrid panel for chromosome mapping, nine (75%) were found to represent RRO5 deletions, whereas the other three were new RFLPs mapping to other chromosomes. In two cases, the RDA sequences were also analyzed by fluorescence in situ hybridization (FISH) and found to give distinct signals in the RNOq22–33 region. This result emphasizes the significance of the previous cytogenetic analysis of this hybrid, which indicated the presence of a gene for the suppression of anchorage independence, Sai 1, in this deletion region. The RDA derived sequences isolated by this, work will provide a valuable source of new genetic markers for the further detailed analysis of the Sai 1 deletion region. [ABSTRACT FROM AUTHOR]

Following a short introduction of heavy ion collision physics relevant to fusion plasma researches and related to fusion technology, some exotic features of plasmas as a target for heavy ion collisions and spectroscopy have been discussed. [ABSTRACT FROM AUTHOR]

The effect of lysozyme from three different sources- Staphylococcus aureus, hen egg white, and human urine-on adhesion to substrate and spreading of trypsinized human fibroblasts was studied. Several fibroblast strains were tested under various conditions. It was found that the different cell strains did not show the same capability of spreading and stably attaching to substrates when resuspended in media not containing serum. Some strains did not spread, whereas others spread even in the absence of serum. Cell spreading in these strains did not occur when the cells were pregrown for 5 weeks in media supplemented with 1% fetal bovine serum. Lysozyme from S. aureus allowed stable adhesion to substrate and spreading of all the fibroblast strains unable to elongate in nonsupplemented minimal essential medium. This enzyme accelerated and augmented spreading of the strains capable of elongating in the absence of serum. S. aureus lysozyme also allowed spreading and stable adhesion to substrates of all these strains when they were pregrown for 5 weeks in the presence of 1% fetal bovine serum. Furthermore, hen egg white lysozyme and the lysozyme purified from human urine were both capable of stimulating anchorage to substrate and spreading of trypsinized fibroblasts although their effect was less pronounced than that of the S. aureus lysozyme. Some tentative hypotheses for the mechanism of cell spreading in the presence of lysozyme are made. The possibility that lysozymes, virtually ubiquitous enzymes, may play a specific role in nature in the regulation of cell differentiation and tissue development is finally raised and discussed in light of several previous observations and findings. [ABSTRACT FROM AUTHOR]