bluuebunny/crossref_metadata_2025 huggingface dataset:
Electron Distribution Function in a Slightly Ionized Moving Gas
Authors: Mintzer David
Published: January 2006

The Lorentz gas approximation to the Boltzmann collision operator is generalized to the case of the heavy-molecule gas distribution function being non-Maxwellian; results are obtained to first order in the mass ratio, but can easily be generalized to higher orders. The equilibrium distribution for the light-molecule gas is then found. The results are applicable to any light-molecule trace gas in a heavy-molecule non-Maxwellian bath gas, and, in particular, to a slightly ionized gas.
Formulation of a Statistical Theory of Strong Plasma Turbulence
Authors: Weinstock Jerome
Published: January 2006

A new formulation of methods introduced by Dupree, and Orszag and Kraichnan, for solving the Vlasov equation for turbulent plasmas based on. algebraic use of an averaging operator is described. Formally exact sets of integrodifferential equations are thereby derived for determining the ensemble average of the one-particle distribution function, and the electric field spectrum of turbulent plasmas. The formal difference between these equations and the approximate equations of Dupree, and Orszag and Kraichnan, is that the average “Vlasov” propagator U(t,t0) of the latter is replaced by a new propagator UA(t,t0) which involves the averaging operator. The potential usefulness of the present equations can be judged by the fact that, in a simple lowest-order limit, they immediately reduce to the turbulence equation of Dupree. These equations are used to develop a modified perturbation theory which avoids certain time secularities. Cumulant expansions are introduced to evaluate average “Vlasov” propagators, and to rigorously treat the variation of the diffusion coefficient with velocity. It is explicitly shown that (diffusive) perturbed trajector corrections are equal to mean square deviations from the mean of “Vlasov” trajectories.
Relativistic Sheet Pinches with Current Shear
Authors: Holdren John P.
Published: January 2006

A new class of self-consistent, one-dimensionally confined, neutral solutions to the stationary Vlasov and Maxwell equations is presented. Apart from the special cases of conventional sheet pinches, these equilibria all display current shear (which, in analogy with magnetic shear, is defined as rotation of the current vector as the plasma is traversed in the confined direction). The new solutions are obtained numerically, after the relativistic Vlasov-Maxwell problem has been reduced to a single second-order nonlinear ordinary differential equation for the critical component of the self-consistent vector potential. The physical properties of representative equilibria are given in graphical form. Included in addition to thin sheet pinches are broader configurations with a region of nearly uniform plasma number density, bounded by rather sharp plasma/magnetic-field interfaces.
Waves in Collisionless Plasmas. III. Transverse Waves in a Hot, Magnetized Plasma
Authors: Levin Joel M.
Published: January 2006

The problem of the propagation of transverse waves parallel to a fixed magnetic field in an infinite, hot, collisionless plasma is treated by using the exact solution of the Vlasov equation to express the electron currents in terms of the fields. Maxwell's inhomogeneous equations are then expressed as an integrodifferential equation purely in terms of the electric field E (z, t). This equation is solved in terms of Green's functions which map the initial fields into the electric field E (z, t) for all 0 < t < ∞. The effects of the induced magnetic fields on the particle trajectories are ignored, but no other approximations are made.
Observation of Ion Cyclotron Waves in a Hot Plasma
Authors: Uman Myron F. , Hooke William M.
Published: January 2006

According to the theory of the propagation and absorption of ion cyclotron waves in a hot magnetized plasma, the wavelength approaches a minimum, nonzero value as the wave propagates into a magnetic beach where the wave frequency approaches the local ion cyclotron frequency. Furthermore, the damping of the waves is a sharply resonant function of the magnetic field strength, the width of the resonance being proportional to the square root of the ion temperature for motion parallel to the static magnetic field. These effects are observed in a plasma confined in a linear magnetic mirror geometry for perpendicular ion temperatures in the range 10–110 eV. The wave fields are measured with two magnetic probes, the plasma density is measured with two microwave interferometers, and the perpendicular ion temperature is measured with a diamagnetic probe. The theory is developed for the transport of spatially damped waves in a hot, finite plasma immersed in a slightly inhomogeneous magnetic field. Quantitative agreement between theory and experiment is obtained. These measurements represent the first experimental observations of thermally broadened collisionless cyclotron absorption in a laboratory plasma. Observations of collisional damping of ion cyclotron waves are also presented.
Collision Damping of Longitudinal Plasma Waves
Authors: Matsuda Kyoko
Published: January 2006

The dispersion relation including collision effects has been obtained by Rostoker's test particle method. The damping factor is calculated for the case of large wavelength. The result presents a correction to the previous calculations by other authors.
Collisional Damping of Waves in a Slightly Relativistic Plasma
Authors: McBride John B.
Published: January 2006

The dispersion and collisional damping of small amplitude, electron waves in a plasma are calculated to first order in the collisions treating the electrons relativistically. The treatment is to lowest order in the relativistic corrections. The Beliaev-Budker equation to order (p/mc)2 is used, and the dispersion calculated using an approximate solution to evaluate the electron current density. For no external fields, the longitudinal plasma oscillation, and transverse electromagnetic mode are treated. For a uniform magnetic field, the longitudinal plasma oscillation, the linearly polarized, and circularly polarized modes are treated. At higher temperatures the over-all damping decreases. In the longitudinal mode, the relativistic correction term increases the damping. In the linearly polarized transverse modes, the relativistic correction increases (decreases) the damping for ωp2 > 3c2k2(ωp2 < 3c2k2). The relativistic correction to the collisional part of the current in all the modes is due to electron-ion collisions, and in all but the circularly polarized modes results from the relativistic normalization constant of the equilibrium electron distribution function.
Experimental Verification of Electron Cyclotron Damping in a Plasma with Collisional Losses
Authors: Minami Kazuo , Takeda Susumu
Published: January 2006

The right-hand circularly polarized microwave (R wave) propagating along a magnetic field in a plasma is described by the hot-plasma theory near the electron cyclotron resonance where the thermal effect of the electron should be taken into account. The left-hand circularly polarized wave (L wave), which has no resonance, is described by the cold-plasma theory. In this paper, the plasma parameters such as the electron densities and the collision frequencies are measured by the reflection coefficient of the L wave at the plasma boundary. The attenuation constant αc of the R wave is then calculated by the cold-plasma theory from the plasma parameters thus obtained; αc is compared with the attenuation constant αh, measured directly by the R wave. The measurements are performed during the decaying period of the plasma produced in a circular waveguide filled with argon at a pressure of 0.1 Torr. The electron temperature Te deduced from αh/αc is compared with Te independently measured by a double probe. The experimental results of αh/αc indicate a reasonable enhancement of the attenuation of the R wave near the electron cyclotron resonance.
Parametric Excitation of Drift Waves in a Resistive Plasma
Authors: Weyl Guy , Goldman Martin
Published: January 2006

The parametric excitation of drift waves in an inhomogeneous resistive plasma is derived from the fluid equations. In the particular case studied, the plasma is pumped by a drift wave at ω0 and responds at a frequency ω1 = 12ω0. Plane geometry is assumed throughout this paper but periodic boundary conditions in z (direction of the uniform magnetic field) and in y (azimuthal direction) are assumed, to simulate experimental conditions with cylindrical or toroidal geometry. The resulting discrete spectrum of drift waves is assumed stabilized by end plate effects (for lower-frequency modes) or by ion-ion collisions (at higher frequencies). The threshold amplitude for parametric excitation is calculated and the enhancement of fluctuations below threshold leading to enhanced particle diffusion toward regions of decreasing density is calculated. The possibility of measuring the enhanced fluctuation spectrum by microwave scattering experiments is also studied.
Negative V″ System with Deep Magnetic Well
Authors: Ikuta Kazunari
Published: January 2006

Closed nested toroidal magnetic surfaces with very strong negative V″ property are obtained for the combinations of simple toroidal field, bumpy poloidal field, and conventional l = 1 helicalone. Well depth is estimated to be more than 80%.
High-β Mirror Instabilities
Authors: Freidberg J. P.
Published: January 2006

A stability criteria for mirror instabilities in a high-β theta pinch is derived by solving the Vlasov equations self-consistently for the equilibrium and perturbation.
Plasma Containment in a Quadrupole Configuration
Authors: Harries W. L. , Yoshikawa S. , Palladino R. W.
Published: January 2006

The containment times of afterglow plasmas in hydrogen, helium, and neon were measured in a linear quadrupole machine (LM-1), where ne ≲ 2 × 1012, Te ≲ 10 eV, Ti < 1 eV, mean free path λ ≲  100 cm, connection length ≈ 20 cm, and electron-ion collision time ≈ 10−7 sec. Particle collectors showed the losses to be mainly radial. The plasmas in the ∮ dl/B stable region decayed in times of order a millisecond (about 10 times the Bohm value) which increased with IQ) the conductor current, to a roughly constant value, and decreased as Te increased. An axial magnetic field which introduced shear (θ ≥ 1/30 rad/cm for the main plasma) caused negligible change to the containment time in helium, with a slight improvement in neon. Various instabilities were observed. Pronounced variations in probe signals and plasma loss rates at different axial positions suggested a convective structure which persisted in the afterglow for some milliseconds. The origin of the radial loss inside the stable region may be due to a low-frequency flutelike mode or possibly to the convective structure in the plasma.
Evolution of Nonlinear Waves in Rotating Fluids
Authors: Leibovich S.
Published: January 2006

The Korteweg-de Vries equation is shown to govern long nonlinear waves which propagate along the rotation axis in inviscid incompressible fluids. The main stream may have an arbitrary swirl profile. Both axisymmetric and spiralling waveforms are possible.
Equations for Errors in Turbulence Measurements with Inclined Hot Wires
Authors: Hill James C. , Sleicher Charles A.
Published: January 2006

Results of Champagne and Sleicher on the errors incurred in turbulence measurements by assuming normal-component cooling of hot wires are extended to include greater tangential cooling. Results are also presented for errors in turbulence heat-flux measurements.
Apparent Activation Energy of Chemical Reactions at High Temperature
Authors: Hansen C. Frederick
Published: January 2006

According to the usual form of measured cross sections, the slope of an Arrhenius plot differs from the activation energy by an electron volt or so at high T. Thus, cross-section shape is needed before activation energy can properly be deduced from rate data.
Nonlinear Effects in the Positive Column of a Modulated Gas Discharge
Authors: Polman J.
Published: January 2006

The dc properties of the positive column of a modulated gas discharge are strongly influenced by the modulation, even at small modulation depths. Calculations without linearization of the equations are in reasonable agreement with experiments.
Relativistic Correction to Bremsstrahlung from a Plasma
Authors: McBride John B. , Pytte Agnar
Published: January 2006

An electron-ion dipole correction of − 15VT2/8c2 to the transverse bremsstrahlung spectrum is found by including relativistic corrections to the electron kinetics. This correction is of the same order as the electron-ion and electron-electron k2λD2 corrections.
Numerical Solution of a Uniform Flow over a Sphere at Intermediate Reynolds Numbers
Authors: Rimon Y. , Cheng S. I.
Published: January 2006

Numerical solutions of the transient uniform flow around a sphere are obtained. The transition takes place between an initial potential flow and a fully developed viscous field. The fluid is incompressible, homogeneous, and its flow is governed by the complete Navier-Stokes equations. The range of Reynolds number studied is Re = 1–1000 where a recirculatory wake appears and the nonlinear terms are essential, that is, they cannot be neglected or approximated. The flow is assumed to be axisymmetric throughout this range. A time-dependent stream function-vorticity formulation is adopted. The solution is obtained by constructing a finite difference approximation to the vorticity transport equation on an expanding spherical polar grid system. Central differencing of second-order accuracy both in time (Dufort-Frankel) and space is utilized. Experiments with numerical stability show an appreciable deviation from linearized stability analysis due to the large gradients of vorticity in the field. Quantitative physical results are obtained. The geometrical parameters characterizing the recirculatory wake compare favorably with those recorded in physical experiments. The detailed distribution of the vorticity on the sphere agrees with results obtained via the steady-state approach at Re = 10, 40, and 100. The computed drag coefficient CD agrees well with the standard drag curve over the range of Reynolds numbers investigated.
Circumferential Nonuniform Heating during Transition on a Slender Cone at Hypersonic Mach Numbers
Authors: Nagamatsu H. T. , Wisler D. C. , Sheer R. E.
Published: January 2006

An experimental investigation was conducted to study nonuniform heating rates during laminar boundary-layer transition on a 4-ft 10° cone. The Mach number outside the boundary layer was 9.6 and the wall to stagnation temperature ratio was 0.214. Four sputtered platinum wedge heat-transfer probes were used to survey through the boundary layers at 0°, 90°, 180°, and 270° at 34.5 in. from the cone tip. In the laminar region there was no evidence of nonuniform heating rates. However, a small oscillation at all circumferential positions was observed near the outer edge of the boundary layer indicative of the location of the critical layer. For the transition and turbulent boundary layer there were indications of large nonuniform heating rates as much as 100% near the wall. In addition, the heating rates in the circumferential direction varied with time.
Steady Quasi-One-Dimensional Detonations in Idealized Systems
Authors: Erpenbeck Jerome J.
Published: January 2006

Steady, quasi-one-dimensional, shock-initiated reactive flow is investigated for an ideal-gas medium undergoing the reversible reaction A ⇄ B, having an Arrhenius rate constant. The lateral expansion is supposed to be given by A(x)/A(0) = [1 + βμx2/(β − 1)] [1 + μx2/(β − 1)]−1, where A denotes the cross-sectional area and x is the distance from the shock. Long-time solutions to the piston problem are constructed, where possible, from steady solutions having final mass velocity equal to the piston velocity. Solutions which can be plausibly amended by rarefaction waves so as to satisfy arbitrarily small piston velocities are regarded as quasi-one-dimensional Chapman-Jouguet detonations. Explicit numerical solutions are found for systems having fixed values of the heat of reaction, heat capacity ratio and activation energy for a wide range of values of the reaction rate k, relative to the expansion rate μ. Chapman-Jouguet waves are found to include equilibrium Chapman-Jouguet solutions, transonic solutions, and double-wave solutions involving an additional shock in the reaction zone.
Dispersion Relations of a Dissociated, Radiating Gas
Authors: Lea G. K. , Chang T. S.
Published: January 2006

The combined effects of molecular dissociation and radiative heat transfer on acoustic waves is examined. The Lighthill gas is used to describe the dissociation process and the moment approximation is used to treat the radiative heat transfer. Exact results, parametric expansions, and other approximations of the dispersion relations are presented.
Scattering of Monoenergetic Argon Beams from Heated Platinum: Planar Time-of-Flight Measurements
Authors: Moran James P. , Wachman Harold Y. , Trilling Leon
Published: January 2006

Time-of-flight measurements were made in the plane of incidence with initially monoenergetic argon beams (speeds 5.4 × 104 and 9.55 × 104 cm/sec) before and after reflection from heated platinum. The time-of-flight data were used to compute low-order moments of velocity distribution: relative number flux, momentum, and energy flux. Flux ratios yield mean speed, mean energy, and speed distribution as functions of angle of reflection. In all cases the mean speed and mean energy of the reflected stream show marked angular dependence, decreasing at a given incidence angle with increasing angle of reflection from the target normal. The mean tangential velocity of the reflected stream is close to that of the incident beam. Calculated incident beam speed distributions are near 0.1 whereas in the reflected streams values are closer to the Maxwellian limit 0.363.
Oriented Fluids and the Rheology of Suspensions
Authors: Kaloni P. N. , DeSilva C. N.
Published: January 2006

The application of the theory of oriented fluids to the behavior of dilute suspensions is considered. Constitutive equations for an oriented fluid with deformable but noninteracting substructure are given. The problem of a dilute suspension of viscoelastic spheres in steady laminar flow is solved within the framework of the theory.
Simulations of dusty plasmas using a special-purpose computer system designed for gravitational N-body problems
Authors: Yamamoto K. , Mizuno Y. , Hibino S. , Inuzuka H. , Cao Y. , Liu Y. , Yazawa K.
Published: January 2006

Simulations of dusty plasmas were performed using GRAPE-6, a special-purpose computer designed for gravitational N-body problems. The collective behavior of dust particles, which are injected into the plasma, was studied by means of three-dimensional computer simulations. As an example of a dusty plasma simulation, experiments on Coulomb crystals in plasmas are simulated. Formation of a quasi-two-dimensional Coulomb crystal has been observed under typical laboratory conditions. Another example was to simulate movement of dust particles in plasmas under microgravity conditions. Fully three-dimensional spherical structures of dust clouds have been observed. For the simulation of a dusty plasma in microgravity with 3×104 particles, GRAPE-6 can perform the whole operation 1000 times faster than by using a Pentium 4 1.6 GHz processor.
Variation of absorption coefficient and determination of critical dose of SU-8 at 365 nm
Authors: Gaudet Matthieu , Camart Jean-Christophe , Buchaillot Lionel , Arscott Steve
Published: January 2006

The absorption coefficient of thick-films of the negative photoresist SU-8 is observed to be time dependent during photolithographic exposure by I-line ultraviolet light (λ=365nm); varying linearly from 38±1cm−1 to 49±1cm−1 for a surface exposure dose of 415mJ∕cm2. We develop a general model which enables the exposure dose to be calculated at a given photoresist depth for a given exposure time. We determine the critical exposure dose for the subsequent polymerization of SU-8 having an arbitrary thickness to be 49.4±3.9mJcm−2.
Guided modes supported by plasmonic films with a periodic arrangement of subwavelength slits
Authors: Catrysse Peter B. , Veronis Georgios , Shin Hocheol , Shen Jung-Tsung , Fan Shanhui
Published: January 2006

We calculate the guided band diagram of a metallic film with a one-dimensional periodic arrangement of cut-through subwavelength slits. We find that this system supports two distinct types of guided modes propagating in a direction perpendicular to the slits when the metal obeys a plasmonic dispersion model. The first type is a well-known surface mode. The second type results from the presence of a subwavelength electromagnetic resonance inside the slits and closely resembles waveguide modes in a dielectric slab. We refer to them as effective dielectric slab modes. We show how the behavior of both modes is affected by film thickness and surface properties.
T-junction ion trap array for two-dimensional ion shuttling, storage, and manipulation
Authors: Hensinger W. K. , Olmschenk S. , Stick D. , Hucul D. , Yeo M. , Acton M. , Deslauriers L. , Monroe C. , Rabchuk J.
Published: January 2006

We demonstrate a two-dimensional 11-zone ion trap array, where individual laser-cooled atomic ions are stored, separated, shuttled, and swapped. The trap geometry consists of two linear rf-ion trap sections that are joined at a 90° angle to form a T-shaped structure. We shuttle a single ion around the corners of the T-junction and swap the positions of two crystallized ions using voltage sequences designed to accommodate the nontrivial electrical potential near the junction. Full two-dimensional control of multiple ions demonstrated in this system may be crucial for the realization of scalable ion trap quantum computation and the implementation of quantum networks.
Fabrication and design of an integrable subwavelength ultrabroadband dielectric mirror
Authors: Chen Lu , Huang Michael C. Y. , Mateus Carlos F. R. , Chang-Hasnain Connie J. , Suzuki Y.
Published: January 2006

We have designed and fabricated a subwavelength grating (SWG) broadband mirror whose performance depends on key factors, including SWG period, duty cycle, and angle of incident light. The fabricated SWGs exhibit high reflectivity (⩾96%), when the grating periods are varied from 650to750nm and duty cycles are varied from 55% to 65%. The bandwidth and reflectivity of these mirrors are remarkably robust to variations in design and fabrication. The SWGs can be designed as broadband mirrors from microwave to visible wavelengths.
Effect of thickness on the crystallization of ultrathin HfSiON gate dielectrics
Authors: Pant G. , Gnade A. , Kim M. J. , Wallace R. M. , Gnade B. E. , Quevedo-Lopez M. A. , Kirsch P. D.
Published: January 2006

The crystallization of ultrathin hafnium silicon oxynitride (HfSiON) gate dielectric is studied as a function of physical thickness. Grazing incidence x-ray diffraction (GI-XRD) was used to detect phase separation and crystallization of 1.5, 2.0, 2.5, and 4.0 nm HfSiON films after 1000°C10s dopant activation anneal. Crystallization peaks corresponding to monoclinic and tetragonal HfO2 were detected in 2.5 and 4.0 nm HfSiON films. These GI-XRD results were supported by plan-view transmission electron microscopy images of the HfSiON films. Film crystallinity seems to impact voltage instability in thicker HfSiON films.
Pressure-induced structural transitions in Tb-pyrochlore oxides
Authors: Kumar Ravhi S. , Cornelius Andrew L. , Nicol Malcolm F. , Kam Kinson C. , Cheetham Anthony K. , Gardner Jason S.
Published: January 2006

The structure of Tb2Ti2O7, Tb2Sn2O7, and Tb2TiSnO7 were studied at high pressures (P<1Mbar) using synchrotron radiation and angular dispersive x-ray diffraction. The cubic lattice was shown to distort into a monoclinic phase before exhibiting total structural disorder (amorphization) in all three samples. Our experiments demonstrate that partial replacement of Sn with Ti significantly enhances the bulk modulus and increases the structural stability (crystalline state) to much higher pressures. Furthermore, pressure induces anion before cation disorder during the order-disorder transition. These results are compared to radiation damage studies that show order-disorder transitions.
Photonic-crystal silicon-nanocluster light-emitting device
Authors: Presti Calogero D. , Irrera Alessia , Franzò Giorgia , Crupi Isodiana , Priolo Francesco , Iacona Fabio , Di Stefano Gianfranco , Piana Angelo , Sanfilippo Delfo , Fallica Pier Giorgio
Published: January 2006

We report on enhanced light extraction from a light-emitting device based on amorphous silicon nanoclusters, suitable for very-large-scale integration, and operating at room temperature. Standard low-cost optical lithography is employed to fabricate a two-dimensional photonic crystal onto the device. We measured a vertical emission with the extracted radiation enhanced by over a factor of 4, without the aid of any buried reflector. These achievements demonstrate that a cost-effective exploitation of photonic crystals is indeed within the reach of semiconductor industry and open the way to a new generation of nanostructured silicon devices in which photonic and electronic functions are integrated together.
Dielectric and photovoltaic phenomena in tungsten-doped Pb(Mg1∕3Nb2∕3)1−xTixO3 crystal
Authors: Tu Chi-Shun , Wang F.-T. , Chien R. R. , Schmidt V. Hugo , Hung C.-M. , Tseng C.-T.
Published: January 2006

This work investigates dielectric and photovoltaic behaviors in Pb(Mg1∕3Nb2∕3)0.64Ti0.36O3 single crystal doped with 0.5mol% WO3. Dielectric permittivities measured as functions of temperature and frequency reveal two first-order-type phase transitions upon heating and cooling. The photovoltaic response strongly depends on illumination wavelength, sample thickness, and prior electric-field poling. The relation of photovoltage and light intensity under near-ultraviolet (λ=406nm) illumination for the poled samples can be expressed by an exponential equation. Optical transmission reveals that the cutoff wavelength is near 400nm and indicates a minimum electronic energy gap of ∼3.0eV.
Widely tunable type-II interband cascade laser
Authors: Suchalkin Sergey , Kisin Mikhail V. , Luryi Serge , Belenky Gregory , Towner Fred J. , Bruno John D. , Monroy Carlos , Tober Richard L.
Published: January 2006

We discuss an ultrawide, voltage-tunable type-II mid-IR interband cascade laser. Its design has a charge accumulation layers outside of the optically active quantum wells that unclamps the electron-hole concentrations and facilitates above-threshold Stark shifts. Our results demonstrate laser tuning of 120nm (120cm−1).
Ultrasound-modulated optical parallel speckle measurement with stroboscopic illumination in a coaxial reflection system
Authors: Hisaka Masaki
Published: January 2006

Ultrasound-modulated optical parallel speckle measurement with stroboscopic illumination in a coaxial reflection system has been developed in order to investigate the biological speckle pattern behavior modulated by a pulsed-ultrasound wave propagating through strong scattering media. An optically absorptive object located at a distance of 5.0millimeters from the surface of a 10.0millimeter thick acoustically impedance-matched scattering media has been measured with submillimeter spatial resolution by detecting backscattered light with a charge-coupled device camera. In addition, a series of absorptive dependence measurements were also acquired.
Nickel-induced enhancement of photoluminescence from Si-rich silica films
Authors: He Y. , Ma K. , Bi L. , Feng J. Y. , Zhang Z. J.
Published: January 2006

The effect of Ni on the near-infrared luminescence emitting from silicon nanocrystals embedded in SiO2 matrix has been investigated. According to the thermodynamics calculation, nickel can give additional driving force to the phase separation process. The photoluminescence intensity increases with the increasing annealing temperature because of the crystallization of amorphous silicon in SiOx films. The intensity of near-infrared emission of SiO1.56∕Ni∕Si is stronger by a factor of 5 than that of regular specimen after annealing at 1000 or 1100°C due to the increase of the density of Si nanocrystals.
Low-field electron mobility in wurtzite InN
Authors: Polyakov V. M. , Schwierz F.
Published: January 2006

We report on the low-field electron mobility in bulk wurtzite InN at room temperature and over a wide range of carrier concentration calculated by the ensemble Monte Carlo (MC) method. All relevant phonon scatterings are included in the MC simulation. The scattering with ionized impurities is considered in the basic Brooks-Herring and Conwell-Weisskopf formulations. For the steady-state transport, the drift velocity attains a peak value of ∼5×107cm∕s at an electric field strength of 32kV∕cm. The highest calculated low-field mobility for undoped InN amounts to ∼14000cm2∕Vs at room temperature. We compare our theoretically calculated low-field mobilities with experimental data available in the literature and obtain a quite satisfactory agreement. Finally, an empirical low-field mobility model based on the MC simulation results and experimental mobility data is presented.
Slow relaxation of magnetization in MnAs nanomagnets on GaAs(001)
Authors: Takagaki Y. , Herrmann C. , Wiebicke E. , Herfort J. , Däweritz L. , Ploog K. H.
Published: January 2006

We demonstrate slow relaxation of the magnetization in MnAs nanoparticles fabricated from epitaxially grown films on GaAs(001). In disks having a diameter as small as 100nm and a thickness of 50nm, the decay of the magnetization at 27°C, which is merely ∼10°C below the Curie temperature TC, is less than 1% over a period of one day. The large uniaxial magnetocrystalline anisotropy and the abrupt loss of the ferromagnetism at TC of MnAs are responsible for the slow relaxation.
Thermal conductivity of Fe nanofluids depending on the cluster size of nanoparticles
Authors: Hong K. S. , Hong Tae-Keun , Yang Ho-Soon
Published: January 2006

Nanofluids have been attractive for the last few years with the enormous potential to improve the efficiency of heat transfer fluids. This work focuses on the effect of the clustering of nanoparticles on the thermal conductivity of nanofluids. Large enhancement of the thermal conductivity is observed in Fe nanofluids sonicated with high powered pulses. The average size of the nanoclusters and thermal conductivity of sonicated nanofluids are measured as time passes after the sonication stopped. It is found from the variations of the nanocluster size and thermal conductivity that the reduction of the thermal conductivity of nanofluids is directly related to the agglomeration of nanoparticles. The thermal conductivity of Fe nanofluids increases nonlinearly as the volume fraction of nanoparticles increases. The nonlinearity is attributed to the rapid clustering of nanoparticles in condensed nanofluids. The thermal conductivities of Fe nanofluids with the three lowest concentrations are fitted to a linear function. The Fe nanofluids show a more rapid increase of the thermal conductivity than Cu nanofluids as the volume fraction of the nanoparticles increases.
Spin filtering in single magnetic barrier structures revisited
Authors: Zhai Feng , Xu H. Q.
Published: January 2006

We reexamine spin-dependent transport properties of two-dimensional electrons modulated by the stray field of a ferromagnetic metal (FM) stripe on top. When the magnetization is along the transport direction of the electrons, the FM stripe generates not only a magnetic barrier but also an in-plane magnetic field component. Previous studies have omitted the in-plane magnetic field component and shown that such a device does not possess any spin-filtering effect. We show that with inclusion of this in-plane magnetic field component, a spin polarization of nearly 100% can be achieved in such a single FM-stripe modulated two-dimensional electron gas device.
Investigation of Co2FeSi: The Heusler compound with highest Curie temperature and magnetic moment
Authors: Wurmehl Sabine , Fecher Gerhard H. , Kandpal Hem Chandra , Ksenofontov Vadim , Felser Claudia , Lin Hong-Ji
Published: January 2006

This work reports on structural and magnetic investigations of the Heusler compound Co2FeSi. X-ray diffraction and Mößbauer spectrometry indicate an ordered L21 structure. Magnetic measurements by means of x-ray magnetic circular dichroism and magnetometry revealed that this compound is, currently, the material with the highest magnetic moment (6μB) and Curie temperature (1100K) in the classes of Heusler compounds as well as half-metallic ferromagnets.
Unexpected NO-dependent DNA binding by the CooA homolog from
Carboxydothermus hydrogenoformans
Authors: Clark Robert W. , Lanz Nicholas D. , Lee Andrea J. , Kerby Robert L. , Roberts Gary P. , Burstyn Judith N.
Published: January 2006

CooA, the CO-sensing heme protein from
Rhodospirillum rubrum
, regulates the expression of genes that encode a CO-oxidation system, allowing
R. rubrum
to use CO as a sole energy source. To better understand the gas-sensing regulation mechanism used by
R. rubrum
CooA and its homologs in other organisms, we characterized spectroscopically and functionally the Fe(II), Fe(II)-NO, and Fe(II)-CO forms of CooA from
Carboxydothermus hydrogenoformans
. Surprisingly, and unlike
R. rubrum
CooA,
C. hydrogenoformans
CooA binds NO to form a six-coordinate Fe(II)-NO heme that is active for DNA binding
in vitro
and
in vivo
. In contrast,
R. rubrum
CooA, which is exquisitely specific for CO, forms a five-coordinate Fe(II)-NO adduct that is inactive for DNA binding. Based on analyses of protein variants and temperature studies, NO-dependent DNA binding by
C. hydrogenoformans
CooA is proposed to result from a greater apparent stability of the six-coordinate Fe(II)-NO adduct at room temperature. Results from the present study strengthen the proposal that CO specificity in the CooA activation mechanism is based on the requirement for a small, neutral distal ligand, which in turn affects the relative positioning of the ligand-bound heme.
Dual signaling is differentially activated by different active states of the metabotropic glutamate receptor 1α
Authors: Tateyama Michihiro , Kubo Yoshihiro
Published: January 2006

The metabotropic glutamate receptor 1α (mGluR1α) is crucial for some forms of synaptic plasticity, by inducing various cell responses via coupling to various types of G proteins. Upon glutamate binding, an active conformation, closed–open/active, of the extracellular domain is stabilized, which induces dimeric rearrangement in the intracellular domains, resulting in the initiation of downstream signals. We have confirmed that mGluR1α functionally interacts with both Gq and Gs pathways; a combination of fluorescent indicators showed that glutamate increased intracellular Ca2+and cAMP concentration ([Ca2+]iand [cAMP]i). By contrast, Gd3+, a different type of ligand whose recognition site on mGluR1α is distinct from the glutamate site, increased only [Ca2+]iand the concentration-activation curve was bell-shaped. FRET analysis revealed that a low concentration of Gd3+induced dimeric rearrangement of the intracellular domains of mGluR1α as does glutamate, whereas a high concentration of Gd3+reversed the FRET efficiency, which was consistent with a bell-shaped relationship between concentration and Gq activation. These results suggest that Gd3+induces an active and a sort of “inactivated” conformation in mGluR1α. The Gd3+-induced active state is considered to correspond to the closed-closed/active conformation, revealed by previous x-ray crystallographic studies. In conclusion, the glutamate-induced closed–open/active state coupled both to Gs and Gq proteins whereas the Gd3+-induced closed-closed/active conformation state preferred Gq to Gs, suggesting that mGluR1α serves not only as a simple on/off switch but also as a multiple signaling path regulator.
Activation of the nuclear receptor FXR improves hyperglycemia and hyperlipidemia in diabetic mice
Authors: Zhang Yanqiao , Lee Florence Ying , Barrera Gabriel , Lee Hans , Vales Charisse , Gonzalez Frank J. , Willson Timothy M. , Edwards Peter A.
Published: January 2006

Farnesoid X receptor (FXR) plays an important role in maintaining bile acid and cholesterol homeostasis. Here we demonstrate that FXR also regulates glucose metabolism. Activation of FXR by the synthetic agonist GW4064 or hepatic overexpression of constitutively active FXR by adenovirus-mediated gene transfer significantly lowered blood glucose levels in both diabetic db/db and wild-type mice. Consistent with these data, FXR null mice exhibited glucose intolerance and insulin insensitivity. We further demonstrate that activation of FXR in db/db mice repressed hepatic gluconeogenic genes and increased hepatic glycogen synthesis and glycogen content by a mechanism that involves enhanced insulin sensitivity. In view of its central roles in coordinating regulation of both glucose and lipid metabolism, we propose that FXR agonists are promising therapeutic agents for treatment of diabetes mellitus.
Polyphosphate modulates blood coagulation and fibrinolysis
Authors: Smith Stephanie A. , Mutch Nicola J. , Baskar Deepak , Rohloff Peter , Docampo Roberto , Morrissey James H.
Published: January 2006

Inorganic polyphosphate is an abundant component of acidocalcisomes of bacteria and unicellular eukaryotes. Human platelet dense granules strongly resemble acidocalcisomes, and we recently showed that they contain substantial amounts of polyphosphate, which is secreted upon platelet activation. We now report that polyphosphate is a potent hemostatic regulator, accelerating blood clotting by activating the contact pathway and promoting the activation of factor V, which in turn results in abrogation of the function of the natural anticoagulant protein, tissue factor pathway inhibitor. Polyphosphate was also found to delay clot lysis by enhancing a natural antifibrinolytic agent, thrombin-activatable fibrinolysis inhibitor. Polyphosphate is unstable in blood or plasma, owing to the presence of phosphatases. We propose that polyphosphate released from platelets or microorganisms initially promotes clot formation and stability; subsequent degradation of polyphosphate by blood phosphatases fosters inhibition of clotting and activation of fibrinolysis during wound healing.
Direct neurophysiological evidence for spatial suppression surrounding the focus of attention in vision
Authors: Hopf J.-M. , Boehler C. N. , Luck S. J. , Tsotsos J. K. , Heinze H.-J. , Schoenfeld M. A.
Published: January 2006

The spatial focus of attention has traditionally been envisioned as a simple spatial gradient of enhanced activity that falls off monotonically with increasing distance. Here, we show with high-density magnetoencephalographic recordings in human observers that the focus of attention is not a simple monotonic gradient but instead contains an excitatory peak surrounded by a narrow inhibitory region. To demonstrate this center-surround profile, we asked subjects to focus attention onto a color pop-out target and then presented probe stimuli at various distances from the target. We observed that the electromagnetic response to the probe was enhanced when the probe was presented at the location of the target, but the probe response was suppressed in a narrow zone surrounding the target and then recovered at more distant locations. Withdrawing attention from the pop-out target by engaging observers in a demanding foveal task eliminated this pattern, confirming a truly attention-driven effect. These results indicate that neural enhancement and suppression coexist in a spatially structured manner that is optimal to attenuate the most deleterious noise during visual object identification.
Two peptide sequences can function cooperatively to facilitate binding and unfolding by ClpA and degradation by ClpAP
Authors: Hoskins Joel R. , Wickner Sue
Published: January 2006

Clp/Hsp100 proteins comprise a large family of AAA
+
ATPases. Some Clp proteins function alone as molecular chaperones, whereas others act in conjunction with peptidases, forming ATP-dependent proteasome-like compartmentalized proteases. Protein degradation by Clp proteases is regulated primarily by substrate recognition by the Clp ATPase component. The ClpA and ClpX ATPases of
Escherichia coli
generally recognize short amino acid sequences that are located near the N or C terminus of a substrate. However, both ClpAP and ClpXP are able to degrade proteins in which the end containing the recognition signal is fused to GFP such that the signal is in the interior of the primary sequence of the substrate. Here, we tested whether the internal ClpA recognition signal was the sole element required for targeting the substrate to ClpA. The results show that, in the absence of a high-affinity peptide recognition signal at the terminus, two elements are important for recognition of GFP-RepA fusion proteins by ClpA. One element is the natural ClpA recognition signal located at the junction of GFP and RepA in the fusion protein. The second element is the C-terminal peptide of the fusion protein. Together, these two elements facilitate binding and unfolding by ClpA and degradation by ClpAP. The internal site appears to function similarly to Clp adaptor proteins but, in this case, is covalently attached to the polypeptide containing the terminal tag and both the “adaptor” and “substrate” modules are degraded.
A gain-control theory of binocular combination
Authors: Ding Jian , Sperling George
Published: January 2006

In binocular combination, light images on the two retinas are combined to form a single “cyclopean” perceptual image, in contrast to binocular rivalry which occurs when the two eyes have incompatible (“rivalrous”) inputs and only one eye`s stimulus is perceived. We propose a computational theory for binocular combination with two basic principles of interaction: in every spatial neighborhood, each eye (
i
) exerts gain control on the other eye's signal in proportion to the contrast energy of its own input and (
ii
) additionally exerts gain control on the other eye's gain control. For stimuli of ordinary contrast, when either eye is stimulated alone, the predicted cyclopean image is the same as when both eyes are stimulated equally, coinciding with an easily observed property of natural vision. The gain-control theory is contrast dependent: Very low-contrast stimuli to the left- and right-eye add linearly to form the predicted cyclopean image. The intrinsic nonlinearity manifests itself only as contrast increases. To test the theory more precisely, a horizontal sine wave grating of 0.68 cycles per degree is presented to each eye. The gratings differ in contrast and phase. The predicted (and perceived) cyclopean grating also is a sine wave; its apparent phase indicates the relative contribution of the two eyes to the cyclopean image. For 48 measured combinations of phase and contrast, the theory with only one estimated parameter accounts for 95% of the variance of the data. Therefore, a simple, robust, physiologically plausible gain-control theory accurately describes an early stage of binocular combination.
Molecular basis for substrate recognition by MTMR2, a myotubularin family phosphoinositide phosphatase
Authors: Begley Michael J. , Taylor Gregory S. , Brock Melissa A. , Ghosh Partho , Woods Virgil L. , Dixon Jack E.
Published: January 2006

Myotubularins, a large family of catalytically active and inactive proteins, belong to a unique subgroup of protein tyrosine phosphatases that use inositol phospholipids, rather than phosphoproteins, as physiological substrates. Here, by integrating crystallographic and deuterium-exchange mass spectrometry studies of human myotubularin-related protein-2 (MTMR2) in complex with phosphoinositides, we define the molecular basis for this unique substrate specificity. Phosphoinositide substrates bind in a pocket located on a positively charged face of the protein, suggesting an electrostatic mechanism for membrane targeting. A flexible, hydrophobic helix makes extensive interactions with the diacylglycerol moieties of substrates, explaining the specificity for membrane-bound phosphoinositides. An extensive H-bonding network and charge–charge interactions within the active site pocket determine phosphoinositide headgroup specificity. The conservation of these specificity determinants within the active, but not the inactive, myotubularins provides insight into the functional differences between the active and inactive members.
Protection conferred by recombinantYersinia pestisantigens produced by a rapid and highly scalable plant expression system
Authors: Santi Luca , Giritch Anatoli , Roy Chad J. , Marillonnet Sylvestre , Klimyuk Victor , Gleba Yuri , Webb Robert , Arntzen Charles J. , Mason Hugh S.
Published: January 2006

Plague is still an endemic disease in different regions of the world. Increasing reports of incidence, the discovery of antibiotic resistance strains, and concern about a potential use of the causative bacteriaYersinia pestisas an agent of biological warfare have highlighted the need for a safe, efficacious, and rapidly producible vaccine. The use of F1 and V antigens and the derived protein fusion F1-V has shown great potential as a protective vaccine in animal studies. Plants have been extensively studied for the production of pharmaceutical proteins as an inexpensive and scalable alternative to common expression systems. In the current study the recombinant plague antigens F1, V, and fusion protein F1-V were produced by transient expression inNicotiana benthamianaby using a deconstructed tobacco mosaic virus-based system that allowed very rapid and extremely high levels of expression. All of the plant-derived purified antigens, administered s.c. to guinea pigs, generated systemic immune responses and provided protection against an aerosol challenge of virulentY. pestis.
Phase II Clinical Trial With Pegylated Liposomal Doxorubicin (CAELYX®/Doxil®) and Quality of Life Evaluation (EORTC QLQ‐C30) in Adult Patients With Advanced Soft Tissue Sarcomas: A study of the Spanish Group for Research in Sarcomas (GEIS)
Authors: Poveda A. , López-Pousa A. , Martín J. , Del Muro J. García , Bernabé R. , Casado A. , Balañá C. , Sanmartín O. , Menéndez M. D. , Escudero P. , Cruz J. , Belyakova Elena , Menéndez D. , Buesa J. M.
Published: January 2006

Background: Pegylated liposomal doxorubicin (PLD), a formulation with pharmacokinetic differences with respect
to doxorubicin (DXR), might benefit patients with advanced soft tissue sarcoma (STS) pretreated with DXR.

Patients and methods: Patients with measurable and progressive STS received PLD at 35 mg/m2 every 3 weeks. Quality of life before and during treatment was assessed with EORTC QLQ‐C30.

Results: Twenty‐eight patients, 22 DXR‐pretreated, were given 140 cycles (median 3, range 1–18). Activity in 27 patients
(5 GIST): one complete and one partial remission (both non‐GIST and without prior DXR), 12 stabilizations and
13 progressions (response rate 7.4%, 95% CI: 0–17%). Grade 3 toxicity: palmar‐plantar erythrodysesthesia (19% of
patients), stomatitis (4%) or cutaneous (4%). Neutropenia grade≥3 was detected in 16% of patients. Median relative
dose intensity was 95%. Progression‐free rate at 3 and 6 months was, respectively, 48 and 22%, median progression‐free
survival 5.8 months and median overall survival 8.7 months. QLQ‐C30 at baseline and at weeks 6–11 in 23 and 13 patients,
respectively, showed good reliability and validity. Quality of life did not seem to worsen during therapy.

Conclusions: PLD did not induce objective remissions in 22 STS patients pretreated with DXR, but progression‐free
rate figures support the use of this agent in patients who have not progressed under a DXR‐containing regimen.
The toxicity observed was comparable to that of other PLD schedules.