Steady-state axisymmetric configurations of a weakly ionized plasma in the field of a rotating magnetized spherical body

Self-consistent steady-state axisymmetric configurations of a plasma envelope with a uniform anisotropic conductivity around a rotating magnetized spherical body are considered. A set of electrodynamic and magnetohydrodynamic equations is analyzed under the assumption that the mass velocity of a moving weakly ionized plasma has only the azimuthal component. The equations describing the profile of the angular frequency of the rotating plasma envelope, the magnetic field, the conduction currents, and the plasma density distribution are solved in the limit of a strong anisotropy of the conductivity of a weakly ionized gas. The applicability of the results obtained to a qualitative interpretation of the phenomena occurring in the plasmaspheres of magnetized planets is discussed.     

Decay instability of a laser pulse propagating in a transverse direction in a magnetized plasma

The decay instability of a lser pulse propagating across an external magnetic field in a subscritical plasma is investigated analytically and numerically. It is shown that, when the relaxation of the pulse is taken into account, the hydrodynamic growth rate of the decay instability is slower than that obtained earlier in the constant-amplitude pump wave approximation. The results of numerical simulations by a particle-in-cell method demonstrate that an increase in the amplitude of the parametrically excited waves is accompanied by a decrease in their group velocity; in this case, up to 85% of the laser energy is converted into the energy of the plasma particles. It is found that, under resonance conditions, the magnetic field acts to increase the energy of the accelerated ions that escape from the plasma slab through its front boundary.     

On the theory of Cherenkov emission from a short laser pulse in a magnetized plasma

Cherenkov emission from a short laser pulse propagating in an underdense plasma along a constant magnetic field is considered. The spectral, angular, energy, and spatiotemporal parameters of the emitted radiation are investigated. It is shown that the spectral content of the radiation and its directionality depend sensitively on the plasma and laser-pulse parameters. For instance, the most intense backward radiation at the upper hybrid frequency is generated by a tightly focused laser pulse.     

Concept of the divertor of a fusion neutron source based on a spherical tokamak

A concept of the divertor and the technology for organizing the edge plasma in a fusion neutron source based on a spherical tokamak (FNS-ST) are described. The experimental data on the characteristics of the peripheral plasma in modern tokamaks are extrapolated to the FNS-ST conditions with the help of semi-analytical models. The effects depending on the magnetic configuration and on the geometry and materials of the divertor and the first-wall elements are considered. Possible designs of the FNS-ST divertor and the first wall are described. Using an original model, it is shown that the maximum density of the heat flux at the divertor plates in a double-null magnetic configuration does not exceed 5?C6 MW/m², which complies with modern engineering capabilities. Methods for further improvement of the FNS-ST divertor concept are analyzed.     

High-affinity target binding engineered via fusion of a single-domain antibody fragment with a ligand-tailored SH3 domain

Monoclonal and recombinant antibodies are ubiquitous tools in diagnostics, therapeutics, and biotechnology. However, their biochemical properties lack optimal robustness, their bacterial production is not easy, and possibilities to create multifunctional fusion proteins based on them are limited. Moreover, the binding affinities of antibodies towards their antigens are suboptimal for many applications where they are commonly used. To address these issues we have made use of the concept of creating high binding affinity based on multivalent target recognition via exploiting some of the best features of immunoglobulins (Ig) and non-Ig-derived ligand-binding domains. We have constructed a small protein, named Neffin, comprised of a 118 aa llama Ig heavy chain variable domain fragment (VHH) fused to a ligand-tailored 57 aa SH3 domain. Neffin could be readily produced in large amounts (>18 mg/L) in the cytoplasm of E. coli, and bound with a subpicomolar affinity (K(d) 0.54 pM) to its target, the HIV-1 Nef protein. When expressed in human cells Neffin could potently inhibit Nef function. Similar VHH-SH3 fusion proteins could be targeted against many other proteins of interest and could have widespread use in diverse medical and biotechnology applications where biochemical robustness and strong binding affinity are required.     

Fast ignition of an inertial fusion target with a solid noncryogenic fuel by an ion beam

The burning efficiency of a preliminarily compressed inertial confinement fusion (ICF) target with a solid noncryogenic fuel (deuterium-tritium beryllium hydride) upon fast central ignition by a fast ion beam is studied. The main aim of the study was to determine the extent to which the spatial temperature distribution formed under the heating of an ICF target by ion beams with different particle energy spectra affects the thermonuclear gain. The study is based on a complex numerical modeling including computer simulations of (i) the heating of a compressed target with a spatially nonuniform density and temperature distributions by a fast ion beam and (ii) the burning of the target with the initial spatial density distribution formed at the instant of maximum compression of the target and the initial spatial temperature distribution formed as a result of heating of the compressed target by the ion beam. The threshold energy of the igniting ion beam and the dependence of the thermonuclear gain on the energy deposited in the target are determined.     

Premature activation of the paramyxovirus fusion protein before target cell attachment with corruption of the viral fusion machinery

Paramyxoviruses, including the childhood pathogen human parainfluenza virus type 3, enter host cells by fusion of the viral and target cell membranes. This fusion results from the concerted action of its two envelope glycoproteins, the hemagglutinin-neuraminidase (HN) and the fusion protein (F). The receptor-bound HN triggers F to undergo conformational changes that render it competent to mediate fusion of the viral and cellular membranes. We proposed that, if the fusion process could be activated prematurely before the virion reaches the target host cell, infection could be prevented. We identified a small molecule that inhibits paramyxovirus entry into target cells and prevents infection. We show here that this compound works by an interaction with HN that results in F-activation prior to receptor binding. The fusion process is thereby prematurely activated, preventing fusion of the viral membrane with target cells and precluding viral entry. This first evidence that activation of a paramyxovirus F can be specifically induced before the virus contacts its target cell suggests a new strategy with broad implications for the design of antiviral agents.     

Laser induced cell fusion in combination with optical tweezers: the laser cell fusion trap.

A single-beam gradient force optical trap was combined with a pulsed UV laser microbeam in order to perform laser induced cell fusion. This combination offers the possibility to selectively fuse two single cells without critical chemical or electrical treatment. The optical trap was created by directing a Nd:YAG laser, at a wavelength of 1.06 microns, into a microscope and focusing the laser beam with a high numerical aperture objective. The UV laser microbeam, produced by a nitrogen-pumped dye laser (366 nm), was collinear with the trapping beam. Once inside the trap, two cells could be fused with several pulses of the UV laser microbeam, attenuated to an energy of approximately 1 microJ/pulse in the object plane. This method of laser induced cell fusion should provide increased selectivity and efficiency in generating viable hybrid cells.     

Crater formation in a target under the action of a high-power laser pulse

The formation of craters in targets of various materials under the action of a high-power neodymium-laser pulse at radiation intensities from 10¹⁰ to 10¹⁴ W/cm² was studied experimentally and theoretically. The interaction between the laser beam and solid targets is investigated to determine the efficiency of the ablation loading of various materials and the transformation of the laser energy into the energy of a shock wave.     

Spectra of langmuir waves in a magnetized plasma with low-frequency turbulence

A study is made of the formation of the spectra of Langmuir waves excited as a result of the development of beam-plasma instability in a collisionless magnetized plasma with low-frequency turbulence. Equations are derived that describe the dynamics of the formation of spectra in the quasilinear statistical approximation.The equations obtained account for small-and large-angle scattering of the electron-beam-excited waves by given background plasma density fluctuations. The scattering of Langmuir waves leads to the redistribution of their energy in phase space and, under appropriate conditions, to the appearance of a characteristic dent in the wave spectra in the frequency range where the spectral intensity is maximum. Numerical simulations carried out for plasma parameters typical of the polar cap of the Earth’s magnetosphere help to explain the shape of the spectra of Langmuir waves that were recorded by the Interball-2 satellite when it was flying through this magnetospheric region.     

Diagnostics of plasma produced by femtosecond laser pulse impact upon a target with an internal nanostructure

X-ray diagnostics of the interaction of femtosecond laser pulses with intensities of 10¹⁶–10¹⁸ W/cm² with CO₂ clusters and frozen nanosize water particles is carried out. The stage of cluster expansion and the formation of a plasma channel, which governs the parameters of the formed X-ray radiation source and accelerated ion flows, is studied. The measurements are based on recording spatially resolved X-ray spectra of H- and He-like oxygen ions. Utilization of Rydberg transitions for spectra diagnostics makes it possible to determine plasma parameters on a time scale of t ∼ 10 ps after the beginning of a femtosecond pulse. The role of the rear edge of the laser pulse in sustaining the plasma temperature at a level of ∼100 eV in the stage of a nonadiabatic cluster expansion is shown. The analysis of the profiles and relative intensities of spectral lines allows one to determine the temperature and density of plasma electrons and distinguish the populations of “thermal” ions and ions that are accelerated up to energies of a few tens of kiloelectronvolts. It is shown that the use of solid clusters made of frozen nanoscale water droplets as targets leads to a substantial increase in the number of fast He-like ions. In this case, however, the efficiency of acceleration of H-like ions does not increase, because the time of their ionization in plasma exceeds the time of cluster expansion.     

Technique of stereotactic biopsy of two cranial target employing spherical coordinates to define a single trajectory

A 'spherical coordinate system' has been developed to allow either stereotactic biopsy of two intracranial lesions using a single predetermined trajectory or biopsy of a single lesion through an existing burr hole. By means of the Gildenberg technique, the CT coordinates of the targets (or target and burr hole) are obtained. These are employed in three simple trigonometric equations to give three coordinates-two angles for the probe carrier (theta and alpha) and the radius (T) of a sphere, defined by one target as the center and the other target on the surface. These can be utilized in the Todd-Wells stereotactic frame. This system was evaluated using hollow skulls and crossed 30-gauge wire for phantom targets. The system was tried on ten different target combinations, and eight successful trajectories were obtained to within 3 mm. Two target combinations were inaccessible because of technical limitations of the Todd-Wells frame. This 'spherical coordinate system' can decrease the time to localize multiple targets as well as minimize the number of passes.     

On the dispersion properties of waveguides filled with a magnetized plasma

A study is made of the dispersion properties of waveguides filled with a magnetized plasma. It is shown that the eigenmodes of the waveguides filled with a low-density magnetized plasma fall into two families, which are weakly coupled to one another at all frequencies, in particular, in the cyclotron resonance frequency range. These families differ in transverse wavenumbers and the modes in them have hybrid polarization. Attention is focused on the study of the modes that have predominantly TE polarization at frequencies close to the cutoff frequency. The dependence of the critical frequencies of the TE modes on the plasma frequency, as well as the influence of the plasma on the energy flux and energy density of these modes, is investigated. The effect of mode crowding (the existence of an arbitrarily large number of dispersion curves in a finite frequency range between the cyclotron frequency and the upper hybrid frequency) is examined in detail. The results obtained are used to analyze how the plasma affects the electromagnetic properties of the cavity of the 1-MW 140-GHz continuous-wave gyrotron developed at the Institute of Pulsed and Microwave Technology of the Research Center in Karlsruhe, Germany (Institut für Hochleistungsimpuls-und Mikrowellentechnik Forschungszentrum Karlsruhe) for plasma heating in the W7-X stellarator, which is being constructed in Greifswald, Germany.     

Protein-induced fusion can be modulated by target membrane lipids through a structural switch at the level of the fusion peptide

Regulatory features of protein-induced membrane fusion are largely unclear, particularly at the level of the fusion peptide. Fusion peptides being part of larger protein complexes, such investigations are met with technical limitations. Here, we show that the fusion activity of influenza virus or Golgi membranes is strongly inhibited by minor amounts of (lyso)lipids when present in the target membrane but not when inserted into the viral or Golgi membrane itself. To investigate the underlying mechanism, we employ a membrane-anchored peptide system and show that fusion is similarly regulated by these lipids when inserted into the target but not when present in the peptide-containing membrane. Peptide-induced fusion is regulated by a reversible switch of secondary structure from a fusion-permissive alpha-helix to a nonfusogenic beta-sheet. The "on/off" activation of this switch is governed by minor amounts of (lyso)-phospholipids in targets, causing a drop in alpha-helix and a dramatic increase in beta-sheet contents. Concomitantly, fusion is inhibited, due to impaired peptide insertion into the target membrane. Our observations in biological fusion systems together with the model studies suggest that distinct lipids in target membranes provide a means for regulating membrane fusion by causing a reversible secondary structure switch of the fusion peptides.     

Collisionless expansion of a plasma with doubly charged ions in a rarefied magnetized plasma

The collisionless interaction between an expanding cylindrical plasma cloud containing singly and doubly charged ions and a magnetized background plasma is investigated numerically using a method combining the kinetic and hydrodynamic approaches. The results presented were obtained from simulations carried out under conditions corresponding to active space experiments on the expansion of plasma clouds in the Earth’s ionosphere.     

Electrostatic solitary structures in a magnetized nonextensive plasma with q-distributed electrons

A rigorous theoretical investigation has been made of obliquely propagating electrostatic solitary structures in a magnetized plasma, taking into account the effect of nonextensive electrons. By employing the reductive perturbation method, the basic characteristics of obliquely propagating ion-acoustic (IA) solitary waves (SWs) in a cold magnetized electron-ion plasma (consisting of inertial ions and noninertial q-distributed electrons) have been addressed. The Korteweg-de Vries equation is derived and its numerical solution is obtained. It has been shown that the effects of electron nonextensivity and external magnetic field significantly modify the natures of the small but finite-amplitude IA SWs. The present analysis may be useful to understand and demonstrate the dynamical properties of IA SWs in different astrophysical and cosmological scenarios (viz. stellar polytropes, hadronic matter, quark-gluon plasma, protoneutron stars, dark-matter halos, etc.).     

Direct observation of laser generated free radicals from a myocardium target site.

The first direct observation of unstable free radicals generated by laser irradiation of myocardium samples has been performed by EPR at 100 K. Characteristic iron signals are measured for pulsed laser ablation of the sample. The EPR results are discussed in relation to the relative efficiency of the various types of lasers to produce free radicals. A comparison is made of the types of free radicals produced by the action of pulsed vs continuous wave (cw) laser energy.     

Electromagnetic wave in a relativistic magnetized plasma

Results are presented from a theoretical investigation of the dispersion properties of a relativistic plasma in which an electromagnetic wave propagates along an external magnetic field. The dielectric tensor in integral form is simplified by separating its imaginary and real parts. A dispersion relation for an electromagnetic wave is obtained that makes it possible to analyze the dispersion and collisionless damping of electromagnetic perturbations over a broad parameter range for both nonrelativistic and ultrarelativistic plasmas.     

Nef does not affect the efficiency of human immunodeficiency virus type 1 fusion with target cells

The human immunodeficiency virus type 1 (HIV-1) accessory protein Nef stimulates viral infectivity by an unknown mechanism. Recent studies have suggested that Nef may act by regulating the efficiency of virus entry into cells. Here we provide evidence to the contrary. Using a quantitative assay of HIV-1 virus-cell fusion, we observed equivalent rates and extents of fusion of wild-type and Nef-defective HIV-1 particles with MT-4 cells and CD4-expressing HeLa cells. In studies using soluble CD4 (sCD4) to inhibit infection, wild-type and Nef-defective HIV-1 escaped the sCD4 block with similar kinetics. We conclude that Nef acts at a postentry step in infection, probably by facilitating intracellular transport of the HIV-1 ribonucleoprotein complex.