bluuebunny/crossref_metadata_2025_split huggingface dataset:
A computer simulation of the plasma resonance probe
Authors: Hellberg M. A. 
Published: March 2009

A numerical experiment is described in which a one-dimensional plasma model is used to simulate the resonance probe. The trajectories of a large number of plane electron sheets are followed in a self-consistent calculation which takes account of a spatially dependent but smeared-out ion background, and externally applied static and r.f. potentials. No differentiation between sheath and plasma regions is introduced, nor is there any linearization.The typical resonant rectification curves, with resonance below ωp, are obtained. A comparison is made between the plasma behaviour at resonance and in frequency ranges above and below the resonance. For example, the phase of current collection w.r.t. probe potential is studied. Fourier analysis of potential and density variations is used to obtain further information on phase relationships. Orbit diagrams of electrons forming the current under resonant conditions are presented, and a model for the mechanism of resonant rectification in terms of electrons at the sheath edge put forward.
Non-linear coupling of waves in a magnetized plasma with particle drift motions
Authors: wilhelmsson H. 
Published: March 2009

We study non-linear interaction between three monochromatic waves which propagate parallel to the direction of a magnetic field in a plasma. The approach to the problem is hydromagnetic, including temperature effects, and the method of solution is that of coupled mode theory. In particular drift motions of the particles along the magnetic field are considered taking into account relativistic effects. The interaction of two transverse waves and one longitudinal wave is treated as well as that of three longitudinal waves. Besides, the case of two longitudinal waves and one perpendicular wave has been studied in some detail assuming the latter to have a long wavelength.The present paper represents a generalization of the problem of three-wave interaction in a plasma to situations more complex than have been treated before. The most essential limitation consists in the assumptions made for the directions of propagation of the waves.
A temperature-anisotropy instability for electromagnetic waves propagating across a static magnetic field
Authors: Landau R. W. , Cuperman S. 
Published: March 2009

The instability of electromagnetic waves propagating across a static magnetic field in the presence of a thermal anisotropy (T∥ > T⊥) is investigated. The marginal stabifity criterion as well as the rate of growth of the instability are derived. When compared with the fire hose instability (of electromagnetic waves propagating along the static magnetic field) it is found that higher electron pressures are required for this new instability to be set up; however, the maximal rate of growth is much larger than in the fire hose case.The interplanetary plasma is stable to this thermal anisotropy instability; high β plasma devices may be unstable.The T⊥ = 0 case treated by Hamasaki is recovered.
Linear stability of exponential density profiles
Authors: Croci R. , Saison R. 
Published: March 2009

The problem of the linear stability of a plasma with density profilesin a homogeneous magnetic field B = îzB0 has been solved exactly. The dispersion relation leads to stability criteria less severe than those obtained in the local approximation. As examples, we consider Bernstein waves and the low-frequency drift instability. In the second example the marginal stability curveis given for different values of the parameters kx, Ri, Ri n′/n, with Ti = Te. Further, the same method is applied to a plasma with equilibrium distribution function in a linear electric potential φ = αx and a homogeneous magnetic field B = îxB0.
Quasi-wave trains in a cold collisionless plasma
Authors: Inoue Yoshinori 
Published: March 2009

Non-linear hydromagnetic waves in a cold collisionless plasma are investigated by numerical and analytic methods. For this problem, Saffman has already implied that there may exist a non-periodic wave different from the well-known solitary wave (or wave train). His analysis is based on the assumption that the quasi-ergodic theorem can be applied to the present problem. However, the propriety of the assumption has not been discussed.It is seen from the computer calculations that in general the waves do not have periodicity, as Saffman pointed out. Furthermore, some concrete examples show the behaviour of these ergodic waves more clearly. The width of the waves is of the order of ion Larmor radius. These waves are here called quasi-wave trains. In some special cases, the waves reduce to wave trains (with periodicity). Some of them have a length scale of the geometric mean between the Larmor radii of the electron and of the ion.
Non-turbulent electric fields in soliton and shock-like structures in magnetized plasmas
Authors: Mendel C. W. , Wright T. P. 
Published: March 2009

A new treatment of soliton and laminar shock-like structures in single ion species and counter-streaming plasmas in perpendicular magnetic fields is presented. Charge separation effects are treated exactly, and may become important for high Alfvén Mach number flows. The theory contains the familiar quasi-neutrality theory in the limitB20≪ Μ0nmec2and the Longmire theory in the limitB20≫ Μ0nmec2. The introduction of the potential ψ as the primary dependent variable, instead of the magnetic fieldB, clarifies the role of ion dynamics. New pseudo-potential functions are defined which generate classes of solutions for single ion species, rigid piston problems, and multispecies problems. They also provide information about the evolution of particle piston solutions. Results include the fact that a small amount of resistivity allows shock solutions for very large Mach numbers, and for zero dissipation the parameterdoes not affect the solutions except in the scale length.
A.C. conductivity in a homogeneous plasma from a convergent collision integral
Authors: Mondt J. P. , Guernsey R. L. 
Published: March 2009

Recently a spatially uniform expression for the time asymptotic binary correlation function of a Landau-stable plasma was derived from the BBGKY hierarchy equations. In this paper, the high-frequency (Vei ≪ ‖w‖ ≪ ωpe) electrical conductivity of a spatially homogeneous, unmagnetized Lorentz plasmais calculated from this expression; the result is compared with those obtained from other convergent collision integrals.
Analytical solutions for the current driven by a rotating magnetic field in a cylindrical plasma with azimuthal field
Authors: Watterson Peter A. 
Published: March 2009

The generation of steady currents by a rotating magnetic field (RMF) in a cylindrical plasma permeated by a steady azimuthal (or toroidal) magnetic field is studied analytically. Solutions are presented for the following limiting cases:(1) high resistivity, when the penetration of the RMF and current drive are confined to a skin depth layer;(2) low resistivity and weak toroidal field (small compared with the RMF), when the RMF fully penetrates the plasma and the toroidal current is that due to nearly synchronous rotation of the electron fluid with the RMF;(3) low resistivity and intermediate toroidal field (comparable to the axial field associated with synchronous current), when the toroidal current is a significant fraction of its synchronous value, but large oscillating fields are generated; and(4) strong toroidal field, when the RMF fully penetrates the plasma but current is only driven in a boundary layer at the plasma edge.The applicability of these solutions is governed by the relative sizes of three dimensionless parameters.
Resistive instability in a uniformly rotating magnetoplasma
Authors: Lunn A. D. 
Published: March 2009

A closed set of guiding centre equations, derived for a rotating plasma in a static magnetic field, is applied to the problem of the stability of a plasma in a sheared field. The rotation is found to have a stabilizing effect in the absence of resistivity.A pair of coupled, linear differential equations is derived for the rotating plasma in a weakly sheared field. Dispersion relations are obtained by phase integral methods and, in the absence of finite Larmor radius effects and rotation, instability growth rates proportional to η½13 are found which become proportional to when either is included. The inclusion of both finite Larmor radius and rotation gives growing instabilities proportional to η which are stabilized by the rotation when the finite Larmor radius terms predominate.
The multiple water-bag model for forced oscillations in a warm isotropic plasma
Authors: Noyer M. L. , Navet M. , Feix M. R. 
Published: March 2009

It is shown that the multiple water-bag model, with both analytic and numerical properties, is fairly well suited to the study of forced oscillations launched by grid systems, for different geometries with possible non-uniform charge distribution, and for any distance within the range 0–100 Debye lengths.Freeston (1968) and Freeston & Malik (1971) compared measurements precisely with theoretical values of the electric field near a system of grids and antennas immersed in a plasma. Results provided a valuable diagnostic tool in space research; and radio-frequency probing was used successfully (Beghin & Debrie 1972; Chasseriaux, Debrie & Renard 1972).
On the linear cross-field instability problem
Authors: Dysthe K. B. , Misra K. D. 
Published: March 2009

A re-examination of the linear E x B instability problem for infinite stratified media gives results differing from those published. The main point is to warn against the application to inhomogeneous media of the usual instability criterion, as developed for
homogeneous media. The fact that the dispersion relation gives complex values of ω for real k does not always indicate the existence of an instabifity. It could also describe propagation of a constant wave energy through an inhomogeneous medium. It is demonstrated that in certain situations it is possible to choose dependent variables in such a way that these two effects disentangle, allowing for a definite solution of the instability problem.In this paper the linear stability' problem for an infinite inhomogeneous, partially ionized gas penetrated by crossed electric and magnetic fields, is re-examined. Several authors (e.g. Reid 1968; Whitehead 1967, 1971; Cunnold 1969; Chimonas 1969; Linson & Workman 1970; looper & Walker 1971; Sato 1971; Sato & Tsuda 1972; Kato 1972) have considered the possibility that the so-called cross-field instability exists in the ionosphere. Our reason for treating the problem again is to point out a deficiency in the literature.
A proposed high-current nanosecond source of energetic ions
Authors: Nation John A. 
Published: March 2009

Experiments by Friedman (1972), and theoretical analysis by Sudan & Lovelace (1973), Rostoker (1972), Rostoker & Poukey (1971) and Wheeler (1974), considered ion emissionin a vacuum diode. The ions emitted (e.g. in the Friedman experiment) were generated by laser irradiation of the anode. Using this technique, multiply-ionized species
could be obtained. The ion currentwas limited non-relativistically to the square root of the mass ratio times the electron current, so that energy transfer to the ions was relatively inefficient. Some improvement was obtained at relativistic electron energies.Sloan & Drummond (1973) proposed a high-current ion accelerator, where the transfer of energy to the ions is achieved by a negative energy cyclotron wave on an intense E beam. Such an accelerator requires an ion source capable of providing several hundred Amperes of protons at energies in the range of a few hundred keV to several MeV. In this article, we propose a suitable ion source for an accelerator.
A focus for biophysical research in energy problems
Authors: Moss Thomas H. 
Published: March 2009

AbstractThere is widespread agreement that solar energy is the most promising long-range energy source. However, contemporary technology for bulk energy storage is so primitive that full use of the inevitably erratic solar energy flux is severely limited. Biological systems have perfected methods of storing solar energy for later use in periods of darkness, and it is argued in this symposium presentation that there are many frontiers in biophysics related to the solar energy storage problem. Moreover, the conceivable biological storage systems span a wide range of technology, with appropriate applications in societies of widely varying degrees of industrial development. Use of biological systems to produce hydrogen from solar energy may be among the most versatile of these applications. The entire problem of bioconversion of solar energy presents an excellent example of how the needs for basic scientific understanding and application engineering can be very tightly interwoven.
Forward scattering of light, X-rays and neutrons
Authors: Eisenberg Henryk 
Published: March 2009

The central points of this paper can now be summarized. We consider here, for simplicity only, vanishing particle concentration. In equilibrium sedimentation equation (6) applies. The density increment is a measurable quantity. It can either be introduced into equation (6) to calculateM2, or it can be analysed by equations (7) and (8) to provide additional information on specific volumes and solute interactions.Light scattering is determined by the analogous equation (20). The refractive index increment is also experimentally accessible and its structure (not considered here) is similar to that of the density increment. Small angle X-ray scattering is determined by equation (31) and the electron density increment which appears in this equation cannot be directly determined by experiment. Yet it can be obtained in straightforward fashion from the mass density increment, by equation (34). Similarly, in the case of neutron scattering (equation (38)), the scattering length density increment is obtained from the mass density increment by equation (40), or it may now be directly evaluated by neutron interferometry.
Molecular electrostatic potential of the nucleic acids
Authors: Pullman Alberte , Pullman Bernard 
Published: March 2009

It is generally acknowledged that geometrical and conformational properties of biopolymers have an important effect on their biochemical behaviour. It is less easily recognized that these properties depend also on their macromolecular electronic characteristics.The aim of this review is to demonstrate the significance of such macromolecular electronic effects. Particularly useful for this sake is the recently much developed concept of ‘molecular electrostatic potential’ (MEP) (Scrocco & Tomasi, 1973, 1978) by which is defined the electrostatic (Coulomb) potential created in the neighbouring space by the nuclear charges and the eletronic distribution of a molecule.
The potential and limitations of neutrons, electrons and X-rays for atomic resolution microscopy of unstained biological molecules
Authors: Henderson Richard 
Published: March 2009

SummaryRadiation damage is the main problem which prevents the determination of the structure of a single biological macromolecule at atomic resolution using any kind of microscopy. This is true whether neutrons, electrons or X-rays are used as the illumination. Forneutrons, the cross-section for nuclear capture and the associatedenergy deposition and radiation damage could be reduced by using samples that are fully deuterated and15N-labelled and by using fast neutrons, but single molecule biological microscopy is still not feasible. For naturally occurring biological material,electronsat present provide the most information for a given amount of radiation damage. Using phase contrast electron microscopy on biological molecules and macromolecular assemblies of ˜ 105molecular weight and above, there is in theory enough information present in the image to allow determination of the position and orientation of individual particles: the application of averaging methods can then be used to provide an atomic resolution structure. The images of approximately 10000 particles are required. Below 105molecular weight, some kind of crystal or other geometrically ordered aggregate is necessary to provide a sufficiently high combined molecular weight to allow for the alignment. In practice, the present quality of the best images still falls short of that attainable in theory and this means that a greater number of particles must be averaged and that the molecular weight limitation is somewhat larger than the predicted limit. ForX-rays, the amount of damage per useful elastic scattering event is several hundred times greater than for electrons at all wavelengths and energies and therefore the requirements on specimen size and number of particles are correspondingly larger. Because of the lack of sufficiently bright neutron sources in the foreseeable future, electron microscopy in practice provides the greatest potential for immediate progress.
Methodology of magnetic resonance imaging
Authors: Ernst R. R. 
Published: March 2009

AbstractA survey of magnetic resonance imaging techniques is presented. Emphasis is put on the basic types of measurement procedures rather than, discussing all variants proposed so far. The general experimental procedure consists of two phases, the preconditioning period and the image formation period. While the preconditioning period determines the image contrast, the image formation process is responsible for image resolution. Means to improve sensitivity and to minimize measurement time are discussed.
Constraints on the accuracy of messenger RNA movement
Authors: Kurland C. G. , Ehrenberg Måns 
Published: March 2009

SUMMARYTheoretical as well as experimental studies of translational accuracy have most often been concerned with the selection of aminoacyl-tRNA by codon-programmed ribosomes. The selection of the successive codons on the mRNA has received much less attention, probably because it represents both conceptually and experimentally, a much more demanding physical problem. Nevertheless, it would seem that errors in the selection of the codon are potentially much more destructive than errors in selection of aminoacyl-tRNA species. This can be appreciated from the following.
Role of uncoupled and non-coupled oxidations in maintenance of safely low levels of oxygen and its one-electron reductants
Authors: Skulachev Vladimir P. 
Published: March 2009

AbstractTo proceed at a high rate, phosphorylating respiration requires ADP to be available. In the resting state, when the energy consumption is low, the ADP concentration decreases so that phosphorylating respiration ceases. This may result in an increase in the intracellular concentrations of O2as well as of one-electron O2reductants such asThese two events should dramatically enhance non-enzymatic formation of reactive oxygen species, i.e. of, and OHׁ, and, hence, the probability of oxidative damage to cellular components. In this paper, a concept is put forward proposing that non-phosphorylating (uncoupled or non-coupled) respiration takes part in maintenance of low levels of both O2and the O2reductants when phosphorylating respiration fails to do this job due to lack of ADP.In particular, it is proposed that some increase in the H+leak of mitochondrial membrane in State 4 lowers, stimulates O2consumption and decreases the level ofwhich otherwise accumulates and serves as one-electron O2reductant. In this connection, the role of natural uncouplers (thyroid hormones), recouplers (male sex hormones and progesterone), non-specific pore in the inner mitochondrial membrane, and apoptosis, as well as of non-coupled electron transfer chains in plants and bacteria will be considered.
The continuous spread of West Nile virus (WNV): seroprevalence in asymptomatic horses
Authors: ALONSO-PADILLA J. , LOZA-RUBIO E. , ESCRIBANO-ROMERO E. , CÓRDOBA L. , CUEVAS S. , MEJÍA F. , CALDERÓN R. , MILIÁN F. , TRAVASSOS DA ROSA A. , WEAVER S. C. , ESTRADA-FRANCO J. G. , SAIZ J. C. 
Published: March 2009

SUMMARYWest Nile virus (WNV) was probably introduced in southern and northern Mexico from the USA in two independent events. Since then, WNV activity has been reported in several Mexican states bordering the USA and the Gulf of Mexico, but disease manifestations seen there in humans and equids are quite different to those observed in the USA. We have analysed WNV seroprevalence in asymptomatic, unvaccinated equids from two Mexican states where no data had been previously recorded. WNV IgG antibodies were detected in 31·6% (91/288) of equine sera from Chiapas and Puebla states (53·3% and 8·0%, respectively). Analysis by plaque reduction neutralization test (PRNT) showed good specificity (99·4%) and sensitivity (84·9%) with the ELISA results. Further analyses to detect antibodies against three different flaviviruses (WNV, St Louis encephalitis virus, Ilheus virus) by haemagglutination inhibition (HI) tests on a subset of 138 samples showed that 53% of the 83 HI-positive samples showed specific reaction to WNV. These data suggest continuous expansion of WNV through Mexico.
Biochemical characterization of GSK1070916, a potent and selective inhibitor of Aurora B and Aurora C kinases with an extremely long residence time1
Authors: Anderson Kelly , Lai Zhihong , Mcdonald Octerloney B. , Stuart J. Darren , Nartey Eldridge N. , Hardwicke Mary Ann , Newlander Ken , Dhanak Dashyant , Adams Jerry , Patrick Denis , Copeland Robert A. , Tummino Peter J. , Yang Jingsong 
Published: March 2009

The Aurora kinases AurA, B and C are serine/threonine protein kinases that play essential roles in mitosis and cytokinesis. Among them, AurB is required for maintaining proper chromosome alignment, separation and segregation during mitosis, and regulating a number of critical processes involved in cytokinesis. AurB overexpression has been observed in a variety of cancer cell lines, and inhibition of AurB has been shown to induce tumour regression in mouse xenograft models. In the present study we report the enzymatic characterization of a potent and selective AurB/AurC inhibitor. GSK1070916 is a reversible and ATP-competitive inhibitor of the AurB–INCENP (inner centromere protein) enzyme. It selectively inhibits AurB–INCENP (Ki*=0.38±0.29 nM) and AurC–INCENP (Ki*=1.5±0.4 nM) over AurA–TPX2 (target protein for Xenopus kinesin-like protein 2) (Ki=490±60 nM). Inhibition of AurB–INCENP and AurC–INCENP is time-dependent, with an enzyme-inhibitor dissociation half-life of &gt;480 min and 270±28 min respectively. The extremely slow rate of dissociation from the AurB and AurC enzymes distinguishes GSK1070916 from two other Aurora inhibitors in the clinic, AZD1152 and VX-680 (also known as MK-0457).