bluuebunny/crossref_metadata_2025 huggingface dataset:
Absolute and convective instabilities of parallel propagating circularly polarized Alfvén waves: Beat instability
Authors: Simpson D. , Ruderman M. S.
Published: May 2005

Ruderman and Simpson [Phys. Plasmas 11, 4178 (2004)] studied the absolute and convective decay instabilities of parallel propagating circularly polarized Alfvén waves in plasmas where the sound speed cS is smaller than the Alfvén speed υA. We extend their analysis for the beat instability which occurs in plasmas with cS>υA. We assume that the dimensionless amplitude of the circularly polarized Alfvén wave (pump wave), a, is small. Applying Briggs’ method we study the problem analytically using expansions in power series with respect to a. It is shown that the pump wave is absolutely unstable in a reference frame moving with the velocity U with respect to the rest plasma if Ul<U<Ur, where Ul=−υA+O(a) and Ur=υA+O(a). When UUr, the instability is convective. The signaling problem is studied in a reference frame where the pump wave is convectively unstable. It is shown that the spatially amplifying waves exist only when the signaling frequency is in two narrow symmetric frequency bands with the widths of the order of a3. These results enable us to extend for the case when cS>υA the conclusions, previously made for the case when cS<υA, that circularly polarized Alfvén waves propagating in the solar wind are convectively unstable in a reference frame of any spacecraft moving with the velocity not exceeding a few tens of km/s in the solar reference frame. The characteristic scale of spatial amplification for these waves exceeds 1a.u.
Nonlinear gyrokinetic turbulence simulations of E×B shear quenching of transport
Authors: Kinsey J. E. , Waltz R. E. , Candy J.
Published: May 2005

The effects of E×B velocity shear have been investigated in nonliner gyrokinetic turbulence simulations with and without kinetic electrons. The impact of E×B shear stabilization in electrostatic flux-tube simulations is well modeled by a simple quench rule with the turbulent diffusivity scaling like 1−αEγE∕γmax, where γE is the E×B shear rate, γmax is maximum linear growth rate without E×B shear, and αE is a multiplier. The quench rule was originally deduced from adiabatic electron ion temperature gradient (ITG) simulations where it was found that αE≈1. The results presented in this paper show that the quench rule also applies in the presence of kinetic electrons for long-wavelength transport down to the ion gyroradius scale. Without parallel velocity shear, the electron and ion transport is quenched near γE∕γmax≈2 (αE≈1∕2). When the destabilizing effect of parallel velocity shear is included in the simulations, consistent with purely toroidal rotation, the transport may not be completely quenched by any level of E×B shear because the Kelvin–Helmholtz drive increases γmax faster than γE increases. Both ITG turbulence with added trapped electron drive and electron-directed and curvature-driven trapped electron mode turbulence are considered.
Numerical simulation of shock-wave structure for argon and helium
Authors: Elizarova Tatiana G. , Shirokov Ivan A. , Montero Salvador
Published: May 2005

We compare the thickness of shock-wave fronts at different Mach numbers, modeled via Navier–Stokes (NS) equations, with experimental results from the literature. Monoatomic argon and helium are considered. In this modeling a finite-difference scheme with second-order spatial accuracy is employed. For argon the calculated density thickness is in good agreement with the experimental results. For helium the NS results agree well with those from the bimodal model and with the few available experimental data.
Magnetic field effect on the terahertz emission from nanometer InGaAs/AlInAs high electron mobility transistors
Authors: Dyakonova N. , Teppe F. , Łusakowski J. , Knap W. , Levinshtein M. , Dmitriev A. P. , Shur M. S. , Bollaert S. , Cappy A.
Published: May 2005

The influence of the magnetic field on the excitation of plasma waves in InGaAs/AlInAs lattice matched high electron mobility transistors is reported. The threshold source-drain voltage of the excitation of the terahertz emission shifts to higher values under a magnetic field increasing from 0 to 6 T. We show that the main change of the emission threshold in relatively low magnetic fields (smaller than approximately 4 T) is due to the magnetoresistance of the ungated parts of the channel. In higher magnetic fields, the effect of the magnetic field on the gated region of the device becomes important.
Theoretical and experimental investigation of flexural wave propagation in straight beams with periodic structures: Application to a vibration isolation structure
Authors: Wen Jihong , Wang Gang , Yu Dianlong , Zhao Honggang , Liu Yaozong
Published: May 2005

A periodic binary straight beam with different cross sections is constructed and studied. The band structures of flexural waves in the structure are calculated with the plane-wave expansion method and the vibration attenuation spectra of a finite sample of it are calculated with the finite element method. Vibration experiment is performed in order to validate all the theoretical results, and the results match mainly. Finally, a vibration isolation structure is designed by using the feature of the flexural wave band gaps of the beam with periodic structure, which provides an attenuation of about 30dB in the frequency range of the band gaps.
Modeling of breakdown behavior in radio-frequency argon discharges with improved secondary emission model
Authors: Radmilović-Radjenović M. , Lee J. K.
Published: May 2005

This work represents the investigation of the dependence of the breakdown voltage on the gas pressure and on the frequency in radio-frequency argon discharges. Calculations were performed by using a one-dimensional particle-in-cell/Monte Carlo code with three velocity components with a new secondary emission model. The obtained results show that the multivalued nature of the left-hand branch of the breakdown curve can be achieved only by taking into account energy dependence of the yield per ion. The multivalued nature of the left-hand branch of the breakdown curve is attributed to the influence of the secondary emission characteristics of the electrodes on the breakdown voltage. Simulation results show a good agreement with the available experimental data. Disagreements between simulation results and theoretical predictions based on the phenomenological method indicate that a more accurate determination of molecular constants is needed. As a result of the satisfactory agreement between simulation and experimental data for dependence of the breakdown voltage on the frequency, a frequency scaling law is proposed.
Bright white organic light-emitting diodes based on two blue emitters with similar molecular structures
Authors: Wang Liduo , Lei Gangtie , Qiu Yong
Published: May 2005

We show that highly efficient and chromatically stable white organic electroluminescent devices can be obtained, based on two blue emitters with similar structures: 9,10-di-(2-naphthyl)-anthracene (ADN) and 9,10-di-(2-naphthyl)-2-terbutyl-anthracene doped with yellow-orange emitting 5,6,11,12-tetraphenylnaphthacene (rubrene) at ultralow doping concentrations (0.01%–0.05%). The relative intensity of the blue and orange-yellow emissions could be fine-tuned by varying the doping concentrations of rubrene in the host to achieve pure white emission. The energy-transfer mechanism of ADN and rubrene with ultralow doping concentrations is discussed in terms of the long exciton diffusion distance of ADN.
Coherent structure of zonal flow and onset of turbulent transport
Authors: Itoh K. , Hallatschek K. , Itoh S.-I. , Diamond P. H. , Toda S.
Published: May 2005

Excitation of the turbulence in the range of drift wave frequency and zonal flow in magnetized plasmas is analyzed. Nonlinear stabilization effect on zonal flow drive is introduced, and the steady state solution is obtained. The condition for the onset of turbulent transport is obtained and partition ratio of fluctuation energy into turbulence and zonal flows is derived. The turbulent transport coefficient, which includes the effect of zonal flow, is also obtained. Analytic result and direct numerical simulation show a good agreement.
Experimental and theoretical investigation on the sloshing of a two-liquid system with free surface
Authors: La Rocca M. , Sciortino G. , Adduce C. , Boniforti M. A.
Published: May 2005

In this paper a theoretical and experimental investigation is performed on the sloshing of a two-liquid system with both separation and free surface. The experimental configuration consists of an oscillating tank filled with two layers of immiscible liquids. The mathematical model is obtained by applying the Lagrangian variational approach to the potential formulation of the fluid motion, and a dynamical system which describes the dynamics of motion is derived. In order to account for the damping of the motion, generalized dissipative forces are considered. For this purpose, the logarithmic decrement coefficients are estimated by means of a wavelet analysis performed on the experimental free oscillations of the fluid system. Numerical integration of the mathematical model gives results which are in a fair agreement with the experimental results.
Heteroepitaxial growth of In-face InN on GaN (0001) by plasma-assisted molecular-beam epitaxy
Authors: Dimakis E. , Iliopoulos E. , Tsagaraki K. , Kehagias Th. , Komninou Ph. , Georgakilas A.
Published: May 2005

The thermodynamic aspects of indium-face InN growth by radio frequency plasma-assisted molecular-beam epitaxy (rf-MBE) and the nucleation of InN on gallium-face GaN (0001) surface were investigated. The rates of InN decomposition and indium desorption from the surface were measured in situ using reflected high-energy electron diffraction and the rf-MBE “growth window” of In-face InN (0001) was identified. It is shown that sustainable growth can be achieved only when the arrival rate of active nitrogen species on the surface is higher than the arrival rate of indium atoms. The maximum substrate temperature permitting InN growth as a function of the active nitrogen flux was determined. The growth mode of InN on Ga-face GaN (0001) surface was investigated by reflected high-energy electron diffraction and atomic force microscopy. It was found to be of the Volmer–Weber-type for substrate temperatures less than 350°C and of the Stranski–Krastanov for substrate temperatures between 350 and 520°C. The number of monolayers of initial two-dimensional growth, in the case of Stranski–Krastanov mode, varies monotonically with substrate temperature, from 2 ML at 400°C to about 12 ML at 500°C. The evolution and coalescence of nucleated islands were also investigated as a function of substrate temperature. It was found that at higher temperature their coalescence is inhibited leading to porous-columnar InN thin films, which exhibit growth rates higher than the nominal value. Therefore, in order to achieve continuous InN layers on GaN (0001) a two-step growth approach is introduced. In that approach, InN is nucleated at low temperatures on GaN and the growth continues until full coalescence of the nucleated islands. Subsequently, this nucleation layer is overgrown at higher substrate temperature in order to achieve high-quality continuous films. The InN films grown by the two-step method were investigated by x-ray diffraction, Hall-effect measurements, and transmission electron microscopy. It was found that the lattice mismatch between InN and GaN is almost completely accommodated by the development of a misfit dislocation network at the interface. Optimum group-III to active nitrogen flux ratios and substrate temperature conditions were identified for the two-step growth process. Films, grown under those conditions, exhibited full width at half maximum of x-ray rocking curves at (0004) and (101¯5) diffractions equal to 360 and 435arcsec, respectively. Room-temperature Hall mobility was found to depend sensitively on the group-III to active nitrogen flux ratio during growth of the main step and to be independent of the structural properties of the films. Mobilities up to 860cm2∕Vs at carrier concentration of 1.6×1019cm−3 were measured.
Weak-inertial flow between two rough surfaces
Authors: Lo Jacono D. , Plouraboué F. , Bergeon A.
Published: May 2005

“Oseen–Poiseuille” equations are developed from an asymptotic formulation of the three-dimensional Navier–Stokes equations in order to study the influence of weak inertia on flows between rough surfaces. The impact of the first correction on macroscopic flow due to inertia has been determined by solving these equations numerically. From the numerical convergence of the asymptotic expansion to the three-dimensional Navier–Stokes flows, it is shown that, at the macroscopic scale, the quadratic correction to the Reynolds equation in the weak-inertial regime vanishes generalizing a similar result in porous media.
Exploring excited-state hydrogen atom transfer along an ammonia wire cluster: Competitive reaction paths and vibrational mode selectivity
Authors: Tanner Christian , Manca Carine , Leutwyler Samuel
Published: May 2005

The excited-state hydrogen-atom transfer (ESHAT) reaction of the 7-hydroxyquinoline∙(NH3)3 cluster involves a crossing from the initially excited π1π* to a π1σ* state. The nonadiabatic coupling between these states induces homolytic dissociation of the O–H bond and H-atom transfer to the closest NH3 molecule, forming a biradical structure denoted HT1, followed by two more Grotthus-type translocation steps along the ammonia wire. We investigate this reaction at the configuration interaction singles level, using a basis set with diffuse orbitals. Intrinsic reaction coordinate calculations of the enol→HT1 step predict that the H-atom transfer is preceded and followed by extensive twisting and bending of the ammonia wire, as well as large O–H⋯NH3 hydrogen bond contraction and expansion. The calculations also predict an excited-state proton transfer path involving synchronous proton motions; however, it lies 20–25kcal∕mol above the ESHAT path. Higher singlet and triplet potential curves are calculated along the ESHAT reaction coordinate: Two singlet-triplet curve crossings occur within the HT1 product well and intersystem crossing to these Tn states branches the reaction back to the enol reactant side, decreasing the ESHAT yield. In fact, a product yield of ≈40% 7-ketoquinoline∙(NH3)3 is experimentally observed. The vibrational mode selectivity of the enol→HT1 reaction step [C. Manca, C. Tanner, S. Coussan, A. Bach, and S. Leutwyler, J. Chem. Phys. 121, 2578 (2004)] is shown to be due to the large sensitivity of the diffuse πσ* state to vibrational displacements along the intermolecular coordinates.
Fast electrons from electron-ion collisions in strong laser fields
Authors: Kull H.-J. , Tikhonchuk V. T.
Published: May 2005

Electron-ion collisions in the presence of a strong laser field lead to a distribution of fast electrons with maximum energy Emax=(k0+2v0)2∕2(a.u.), where k0 is the impact and v0 the quiver velocity of the electron. The energy spectrum is calculated by two approaches: (1) The time-dependent Schrödinger equation is numerically solved for wave packet scattering from a one-dimensional softcore Coulomb potential. Multiphoton energy spectra are obtained demonstrating a separation of the energy spectrum into an exponential distribution for transmission and a plateau distribution for reflection. (2) The energy spectrum is analytically calculated in the framework of classical instantaneous Coulomb collisions with random impact parameters and random phases of the laser field. An exact solution for the energy spectrum is obtained from which the fraction of fast electrons in the plateau region can be estimated.
Atomistic molecular-dynamics simulations of the size and shape of polyethylene in hexane at infinite dilution
Authors: Zifferer Gerhard , Kornherr Andreas
Published: May 2005

Parameters characteristic of size and shape of single polyethylene chains consisting of 15–60 monomer units dissolved in hexane are calculated by use of molecular-dynamics simulations based on a fully atomistic representation of the system. Results are compared with corresponding calculations in vacuum as well as Monte Carlo simulations of coarse-grained chains. The major concern of the study is a careful check of actual limits and possibilities of atomistic simulations of global properties of polymers. As expected such simulations are still restricted to rather small chain lengths but are already large enough to obey the characteristics of polymer coils.
Vibronic coupling in the excited cationic states of ethylene: Simulation of the photoelectron spectrum between 12 and 18eV
Authors: Hazra Anirban , Nooijen Marcel
Published: May 2005

The effect of vibronic coupling on structure and spectroscopy is investigated in the excited cationic states of ethylene. It is found from equation of motion coupled cluster singles and doubles method for ionization potential electronic structure calculations in a triple-zeta plus double polarization basis set that ethylene in its third (BAg2) and fourth (CB2u2) ionized states does not have a stable minimum-energy geometry. The potential-energy surfaces of these states are energetically distinct and well separated at the ground-state geometry of ethylene, but in a geometry optimization as the structure of the ion relaxes, these surfaces end up in conical intersections and finally in the stable equilibrium geometry of the second ionized state (AB3g2). The topology of the potential-energy surfaces can be clearly understood using a vibronic model Hamiltonian. Furthermore, by diagonalizing this model Hamiltonian, the photoelectron spectrum of ethylene corresponding to the second, third, and fourth ionized states (12–18eV) is simulated. Spectra from vibronic simulations including up to quartic coupling constants and using various normal-mode basis sets are compared to those from vertical Franck–Condon simulations to understand the importance of vibronic coupling and nonadiabatic effects and to examine the influence of individual normal modes on the spectrum.
Fluid-Maxwell simulation of laser pulse dynamics in overdense plasma
Authors: Berezhiani V. I. , Garuchava D. P. , Mikeladze S. V. , Sigua K. I. , Tsintsadze N. L. , Mahajan S. M. , Kishimoto Y. , Nishikawa K.
Published: May 2005

A one-dimensional model of collisionless electron plasma, described by the full system of Maxwell and relativistic hydrodynamic equations, is exploited to study the interaction of relativistic, strong, circularly polarized laser pulses with an overdense plasma. Numerical simulations for the ultrarelativistic pulses demonstrates that for the low as well as for the high background density, the major part of the penetrated energy remains trapped for a long time in a nonstationary layer near the plasma front end; only a minor portion resides in solitons. Important details of the interaction for the moderately intense and strongly relativistic pulses for semi-infinite and thin plasma layers are revealed. An interesting additional consequence of the long-time confinement of relativistic strong radiation in an overdense plasma is analyzed. It is shown that intensive pair production by the driven motion of plasma electrons takes place due to the trident process.
Two mechanisms of crater formation in ultraviolet-pulsed-laser irradiated SiO2 thin films with artificial defects
Authors: Papernov S. , Schmid A. W.
Published: May 2005

Atomic force microscopy was employed to investigate the morphology of ultraviolet nanosecond-pulsed-laser damage in SiO2 thin films. Gold nanoparticles, 18.5-nm diameter, embedded in the film were used as calibrated absorbing defects. Damage-crater diameter, depth, and cross-sectional profiles were measured as a function of laser fluence and the lodging depth of gold nanoparticles. The results indicate that, at laser fluences close to the crater-formation threshold and for lodging depths of a few particle diameters, the dominating regime of the material removal is melting and evaporation. The morphology of craters initiated by deep absorbing defects, with a lodging depth larger than ∼10 particle diameters, clearly points to a two-stage material-removal mechanism. The process starts with the material melting within the narrow channel volume and, upon temperature and pressure buildup, film fracture takes place. Crater-diameter variation with lodging depth and laser fluence is compared with theoretical predictions.
Solvable PT-symmetric model with a tunable interspersion of nonmerging levels
Authors: Znojil Miloslav
Published: May 2005

We study the spectrum in such a PT-symmetric square well (of a diameter L⩽∞) where the “strength of the non-Hermiticity” is controlled by the two parameters, viz., by an imaginary coupling ig and by the distance ℓ<L of its onset from the origin. We solve this problem and confirm that the spectrum is discrete and real in a nonempty interval of g⩽g0(ℓ,L). Surprisingly, a specific distinction between the bound states is found in their asymptotic stability∕instability with respect to an unlimited growth of g beyond g0(ℓ,L). In our model, all of the low-lying levels remain asymptotically unstable at the small ℓ⪡L and finite L while only the stable levels survive near ℓ≈L<∞ or in the purely imaginary force limit with 0<ℓ<L=∞. In between these two extremes, an unusual and tunable, variable pattern of the interspersed “robust” and “fragile” subspectra of the real levels is obtained.
The quantum mobility of a two-dimensional electron gas in selectively doped GaAs∕InGaAs quantum wells with embedded quantum dots
Authors: Pagnossin I. R. , da Silva E. C. F. , Quivy A. A. , Martini S. , Sergio C. S.
Published: May 2005

In this work we studied the transport properties of a two-dimensional electron gas (2DEG) in a series of GaAs∕InGaAs delta-modulation-doped quantum wells, in which an InAs layer was located in the vicinity of the electron channel. We observed that, even after illumination, all samples exhibited a total free-electron concentration slightly lower than the one measured in a reference sample (without the InAs layer), an effect that was attributed to the transfer of carriers from the 2DEG to the surface states. Our data also provided evidence that strain fields in and around the quantum dots act as additional scattering sources for the 2DEG.
Thermal effects on film development during spin coating
Authors: Dandapat B. S. , Santra B. , Kitamura A.
Published: May 2005

This study is an extended version of a previous analysis of thermal effects on the free-surface liquid film flow on a flat, heated rotating disk [A. Kitamura, “Thermal effects of liquid film flow during spin coating,” Phys. Fluids 13, 2788 (2001)]. The assumption of a constant disk temperature is extended to a nonuniform disk temperature, and the restriction on small radial distance used in the previous analysis is removed. The evolution equation for the transient film thickness is obtained and solved by the method of characteristics [B. S. Dandapat, P. Daripa, and P. C. Ray, “Asymptotic study of film thinning process on a spinning annular disk,” J. Appl. Phys. 94, 4144 (2003)]. The effect of both thermocapillary forces and variable viscosity on the flow is revealed. A physical explanation is provided to justify the results.
Convective transport in the scrape-off layer of tokamaks
Authors: Aydemir A. Y.
Published: May 2005

A detailed study of blob formation, dynamics, and the associated convective transport in the scrape-off layer (SOL) of tokamak plasmas is presented. Dissipation level in the system, in addition to the blob size, is shown to play an important role in determining whether a blob propagates as a coherent object. Nonlinear SOL interchange/ballooning modes are shown to be capable of creating blobs near the separatrix without relying on the core or edge-plasma dynamics. Finally, the SOL density profiles under diffusive and convective transport assumptions are compared. In the convective regime, here assumed to be driven by the SOL interchange modes, two different scaling with the machine size R is found for the characteristic density “e-folding” length λn. When the dominant loss mechanism for the blobs is diffusive, the scale length becomes independent of machine size as the connection length increases. In the less typical case where the parallel losses along the open field lines dominate, λn∼R1∕2.
New p-Ge THz laser spectrometer for the study of solutions: THz absorption spectroscopy of water
Authors: Bergner Andreas , Heugen Udo , Bründermann Erik , Schwaab Gerhard , Havenith Martina , Chamberlin Danielle R. , Haller Eugene E.
Published: May 2005

We present the development of a high power, tunable far-infrared p-germanium laser spectrometer for the study of dissolved biomolecules in the THz range. As a first application we report on the measurement of the absorption coefficient α for liquid water in the frequency range from 81to96cm−1. Using the p-Ge laser spectrometer we were able to penetrate through layers of up to 100μm thickness. We discuss the advantages and the limitations of this THz spectrometer. We present an analysis of the experimental data based on a χ2 test to provide an objective procedure to minimize the influence of systematic effects, for example of interference due to multiple reflections within the sample chamber. The measured absorption coefficient α lies between (410±6) and (490±6)cm−1 at 81 and 96cm−1, respectively.
Reconciling the cylindrical formulation with the spherical formulation in the kinematic descriptions of collision kernel
Authors: Wang Lian-Ping , Ayala Orlando , Xue Yan
Published: May 2005

Kinematic descriptions of the rate of collision between two groups of particles are central to a variety of problems in cloud microphysics, engineering applications, and statistical mechanics. When particles are uniformly distributed, the collision kernel Γ depends on the statistics of relative velocities among colliding particles. In the pioneering work by Saffman and Turner [“On the collision of drops in turbulent clouds,” J. Fluid Mech. 1, 16 (1956)], two different formulations were used to calculate Γ between two arbitrary particle size groups in a turbulent flow. The first or spherical formulation is based on the radial or longitudinal component wr of the relative velocity w between two particles at contact: Γsph=2πR2⟨∣wr∣⟩, where R is the geometric collision radius. The second or cylindrical formulation is based on the vector velocity itself: Γcyl=πR2⟨∣w∣⟩. It was shown previously by Wang et al. [“Statical mechanical descriptions of turbulent coagulation,” Phys. Fluids 10, 2647 (1998)] that the spherical formulation is always correct when applied to different situations, and that the cylindrical formulation overpredicts the collision kernel by about 20%–25% for collisions due to a uniform shear or due to nonuniform shears in a turbulent flow. In this paper, it is shown that the overpredictions in the cylindrical formulation are originated from the dependence of the probability distribution of w on the orientation of R, and can be corrected for all situations if this orientation dependence is explicitly accounted for. A generalized cylindrical formulation is then proposed and is shown to be identical to the spherical formulation for all collision mechanisms considered in Wang et al. (1998). Finally, we illustrate the difference between kinematic statistics and statistics for colliding particle pairs. For example, the relative velocity for colliding particle pairs can be 30%–60% larger than the kinematic relative velocity.
Dynamics of coupled vortices in layered magnetic nanodots
Authors: Guslienko K. Yu. , Buchanan K. S. , Bader S. D. , Novosad V.
Published: May 2005

The spin dynamics are calculated for a model system consisting of two ferromagnetic (F) cylindrical dots, each with a magnetic vortex ground state, are separated by a nonmagnetic spacer (N). The effects of interlayer magnetostatic interactions on the vortex dynamics were explored by applying the equations of motion for the vortex core positions. For trilayer F∕N∕F dots with opposite chiralities and the same core polarizations two eigenmodes are predicted. One mode is in the sub-GHz range for submicron dot diameters and corresponds to quasicircular rotation of the cores about the dot center. A second mode in the MHz range corresponds to a small amplitude rotation of the mean core position.
Analytic solution of the Schrödinger equation for the Coulomb-plus-linear potential. I. The wave functions
Authors: Plante Guillaume , Antippa Adel F.
Published: May 2005

We solve the Schrödinger equation for a quark–antiquark system interacting via a Coulomb-plus-linear potential, and obtain the wave functions as power series, with their coefficients given in terms of the combinatorics functions.
Controllable p and n doping of single-walled carbon nanotubes by encapsulation of organic molecules and fullerene: A theoretical investigation
Authors: Liang WanZhen , Yang Jinlong , Sun Jin
Published: May 2005

We report theoretical investigations on the changes in optical and electronic properties of single-walled carbon nanotubes (SWNTs) induced by chemical doping with organic molecules or fullerene C60. It is found that doping alters the electronic and optical properties of parent SWNTs and both p- and n-type doping can be realized on SWNTs by encapsulating organic molecules which have large electron affinities or small ionization energies. The doping-induced optical features and additions of donor∕acceptor states to the density of states provide compelling evidence that the standard rigid-band model breaks down and the band-structure changes play an important role on the solid state properties of doped SWNTs.
Microfabricated SrTiO3 ridge waveguides
Authors: Gaidi M. , Stafford L. , Margot J. , Chaker M. , Morandotti R. , Kulishov M.
Published: May 2005

We report the microfabrication and characterization of SrTiO3∕SiO2∕Si ridge waveguides. SrTiO3 films are very attractive for optical integrated systems as they present a high transparency in the visible and infrared wavelength range as well as a relatively high refractive index. In this work, SrTiO3 films were grown by means of a reactive pulsed-laser-deposition technique and patterned using UV photolithography and high-density plasma etching. Propagation and loss characteristics at the telecommunication wavelength of 1.55μm were investigated using top-view scattering and Fabry-Perot resonance methods. For specific ridge widths, we obtained single-mode propagation with relatively low losses (∼1.5dB∕cm), thereby demonstrating the strong potential of SrTiO3 films for guided-wave components for advanced optical integrated systems.
An infrared probe of tunable dielectrics in metal-oxide-semiconductor structures
Authors: Li Z. Q. , Wang G. M. , Mikolaitis K. J. , Moses D. , Heeger A. J. , Basov D. N.
Published: May 2005

A composite metal-polymer electrode is designed to investigate electric-field-induced changes of the dielectric function of gate insulators in metal-oxide-semiconductor structures using infrared spectroscopy. We studied structures based on TiO2 dielectric insulator on doped silicon, a combination commonly used in field-effect transistors. It is shown that the voltage-induced changes of the dielectric constant in TiO2 originate from a modification of the lattice vibration modes of this compound.
Deep impurity transitions involving cation vacancies and complexes in AlGaN alloys
Authors: Nam K. B. , Nakarmi M. L. , Lin J. Y. , Jiang H. X.
Published: May 2005

Deep ultraviolet (UV) photoluminescence (PL) spectroscopy has been employed to study deep impurity transitions in AlxGa1−xN (0⩽x⩽1) epilayers. Two groups of deep impurity transitions were observed, which are assigned to the recombination between shallow donors and two different deep level acceptors involving cation vacancies (Vcation) and Vcation complexes in AlxGa1−xN alloys. These acceptor levels are pinned to two different energy levels common to AlxGa1−xN alloys (0⩽x⩽1). The deep impurity transitions related with Vcation complexes were observed in AlxGa1−xN alloys between x=0 and 1, while those related with Vcation were only observed in AlxGa1−xN alloys between x=0.58 and 1. This points out to the fact that the formation of Vcation is more favorable in Al-rich AlGaN alloys, while Vcation complexes can be formed in the whole range of x between 0 and 1. The implications of our findings to the UV optoelectronic devices using AlGaN alloys are also discussed.
Unidirectional self-assembling of SiGe Stranski-Krastanow islands on Si(113)
Authors: Hanke M. , Boeck T. , Gerlitzke A.-K. , Syrowatka F. , Heyroth F.
Published: May 2005

We report on a dedicated two-step liquid phase epitaxy (LPE) experiment yielding ensembles of SiGe∕Si(113) nanoscale islands with unidirectional ordering along the [1¯10] direction. Initial homoepitaxy of silicon on a polished Si(113) wafer from an indium solution at 930°C results in a highly regular pattern consisting of (111) and (116) facets. For the subsequent heteroepitaxy with SiGe the solvent has been exchanged for bismuth since it enables an LPE process at considerably lower temperatures around 590°C, and thus preserves the initial template which strictly enforces the linear self-assembling of SiGe islands. However, with respect to the initial grooves the established island–island correlation length perpendicular to them has been increased by a factor of about 1.6 indicating that not every groove acts as a nucleation place. This can be explained by finite element calculations on the three-dimensional deformation field which proves energetically favorable nucleation sites in the island vicinity within and infavorable places in adjacent rows.
Characterization of CF4-plasma fluorinated HfO2 gate dielectrics with TaN metal gate
Authors: Lai Chao Sung , Wu Woei Cherng , Wang Jer Chyi , Chao Tien sheng
Published: May 2005

In this paper, fluorine incorporation into the HfO2 gate dielectrics by post CF4 plasma treatment was proposed to improve the electrical characterization. TaN–HfO2–p-Si capacitors were demonstrated in this work. The characteristics of fluorinated HfO2 gate dielectrics were improved, including the capacitance-voltage hysteresis and current-voltage behaviors. This may be attributed to the fluorine incorporated into the HfO2 gate dielectrics as revealed by secondary ion mass spectroscopy. Moreover, the formation of Hf-F bonding was observed through electron spectroscopy for chemical analysis spectra.
Burrowing seabirds drive decreased diversity and structural complexity, and increased productivity in insular-vegetation communities
Authors: Bancroft Wesley J. , Roberts J. Dale , Garkaklis Mark J.
Published: May 2005

Burrow-nesting seabirds, such as the wedge-tailed shearwater (Puffinus pacificus (Gmelin)) physically and chemically engineer the soil of their colonies in a manner that is likely to affect plant growth and ecology. We examined this functional interaction by measuring the diversity, vertical structure and productivity of vegetation in shearwater colonies on Rottnest Island, Western Australia, and by comparing these with those in the adjacent, non-colonised heath. The colony supported a distinct, less diverse vegetation community and was dominated by short-lived, succulent exotics. An ecotone was present between the two communities. Across all species, vegetation was shorter and denser in the colony and individual species that co-occurred in both locations were stunted in the colony. The percentage of bare soil in the colony was double that of the heath. The productivity of a phytometer (Rhagodia baccata) was significantly higher in colony soil than in heath soil. In a glasshouse experiment, cuttings grown in colony soil had 337% of the root mass and 537% of the foliage mass of plants grown in heath soil. Field measurements demonstrated increased leaf set and foliage extension in colony plants. Seed germination from the colony soil (2674 seedlings m–2) greatly exceeded that of the heath (59 seedlings m–2). Dense, productive and species-poor colony vegetation supports the assemblage-level thinning hypothesis as the mechanism for vegetation change, but we argue that prominent colony species are simply better adapted to high nutrient loads and frequent disturbance. A model of vegetation succession is also proposed.
Dynamics of a savanna-forest mosaic in the Australian monsoon tropics inferred from stand structures and historical aerial photography
Authors: Banfai Daniel S. , Bowman David M. J. S.
Published: May 2005

Stratified ground-truthing was undertaken within an area of approximately 30 km2 of tropical savanna across an abrupt sandstone escarpment in the monsoon tropics of Australia. Comparison of aerial photographs from 1941 and 1994 had previously revealed a landscape-wide expansion of closed forest and contraction of grassland patches. Good congruence between field measurements and the vegetation classifications from the 1994 aerial photography supported the authenticity of the vegetation changes. The relative abundance of rainforest and non-rainforest tree species also concurred with mapped vegetation transitions. Changes in individual size classes of rainforest species, which are relatively fire sensitive, were consistent with the primacy of fire in controlling the distribution of the closed-forest formation. Fire scars previously mapped from satellite imagery were used to derive a fire activity index for contrasting vegetation transitions. Savannas that had converted to closed forest had lower fire activity than did stable savannas. Conversely, closed forests that converted to savanna had the highest fire activity index. The landscape-wide expansion of rainforest is associated with the cessation of Aboriginal fire management, possibly in conjunction with elevated CO2 and increasing annual rainfall.
Microtubule-associated protein tau: A marker of paclitaxel sensitivity in breast cancer
Authors: Rouzier Roman , Rajan Radhika , Wagner Peter , Hess Kenneth R. , Gold David L. , Stec James , Ayers Mark , Ross Jeffrey S. , Zhang Peter , Buchholz Thomas A. , Kuerer Henry , Green Marjorie , Arun Banu , Hortobagyi Gabriel N. , Symmans W. Fraser , Pusztai Lajos
Published: May 2005

Breast cancers show variable sensitivity to paclitaxel. There is no diagnostic test to identify tumors that are sensitive to this drug. We used U133A chips to identify genes that are associated with pathologic complete response (pCR) to preoperative paclitaxel-containing chemotherapy in stage I-III breast cancer (
n
= 82). Tau was the most differentially expressed gene. Tumors with pCR had significantly lower (
P
< 0.3 × 10
-5
) mRNA expression. Tissue arrays from 122 independent but similarly treated patients were used for validation by immunohistochemistry. Seventy-four percent of pCR cases were tau protein negative; the odds ratio for pCR was 3.7 (95% confidence interval, 1.6-8.6;
P
= 0.0013). In multivariate analysis, nuclear grade (
P
< 0.01), age <50 (
P
= 0.03), and tau-negative status (
P
= 0.04) were independent predictors of pCR. Small interfering RNA experiments were performed to examine whether down-regulation of tau increases sensitivity to chemotherapy
in vitro
. Down-regulation of tau increased sensitivity of breast cancer cells to paclitaxel but not to epirubicin. Tubulin polymerization assay was used to assess whether tau modulates binding of paclitaxel to tubulin. Preincubation of tubulin with tau resulted in decreased paclitaxel binding and reduced paclitaxel-induced microtubule polymerization. These data suggest that low tau expression renders microtubules more vulnerable to paclitaxel and makes breast cancer cells hypersensitive to this drug. Low tau expression may be used as a marker to select patients for paclitaxel therapy. Inhibition of tau function might be exploited as a therapeutic strategy to increase sensitivity to paclitaxel.
TrwB, the coupling protein involved in DNA transport during bacterial conjugation, is a DNA-dependent ATPase
Authors: Tato I. , Zunzunegui S. , de la Cruz F. , Cabezon E.
Published: May 2005

Bacterial conjugation is an example of macromolecular trafficking between cells, based on the translocation of single-stranded DNA across membranes through a type IV secretion system. TrwBΔN70 is the soluble domain of TrwB, an essential integral membrane protein that couples the relaxosome (a nucleoprotein complex) to the DNA transport apparatus in plasmid R388 conjugation. TrwBΔN70 crystallographic structure revealed a hexamer with six equivalent subunits and a central channel. In this work, we characterize a DNA-dependent ATPase activity for TrwBΔN70. The protein displays positive cooperativity for ATP hydrolysis, with at least three catalytic sites involved. The activity is sensitive to pH and salt concentration, being more active at low pH values. The effective oligonucleotide size required for activation of the ATPase function is between 40 and 45 nucleotides, and the same length is required for the formation of high-molecular-weight TrwBΔN70–DNA complexes, as observed by gel filtration chromatography. A mutation in a tryptophan residue (W216A), placed in the central pore formed by the hexameric structure, resulted in a protein that did not hydrolyze ATP. In addition, it exerted a dominant negative effect, both on R388 conjugation frequency and ATP hydrolysis, underscoring the multimeric state of the protein. ATP hydrolysis was not coupled to a DNA unwinding activity under the tested conditions, which included forked DNA substrates. These results, together with TrwB structural similarity to F
1
-ATPase, lead us to propose a mechanism for TrwB as a DNA-translocating motor.
The effect of lucerne-protein concentrate in the diet on growth, reproduction and body composition of Rats
Authors: Hove E. L. , Lohrey Evelyn , Urs M. K. , Allison R. M.
Published: May 2005

1. Protein concentrates were prepared from freshly cut lucerne by the Pirie process and freeze-dried. When supplemented with methionine or cystine and given to rats as the sole source of protein at 120 g protein/kg diet, the adjusted mean protein efficiency ratio was 2.89 (casein standard at 2.50). As a supplement to protein from barley meal the lucerne leaf-protein concentrate (LPC) was similar to casein.

2. To investigate nutritional safety, lucerne LPC supplemented with methionine was given to rats at high levels for 6 months; exposure of these rats to diffuse daylight was avoided to prevent a severe disfiguring photosensitivity reaction. At a dietary protein concentration of 100 g/kg, rats grew equally well with lucerne LPC or casein. When the supplement was given at protein concentrations of 200 or 300 g/kg the rates of body-weight gain of male and female rats were less than those of control rats given casein. However, after 5 months on the diets, body-weights of male rats had nearly reached those of the controls.

3. Apparent protein digestibility ratio was about 0.80 with all three levels of lucerne LPC.

4. Reproduction was normal in seventeen of the eighteen female rats given the lucerne LPC at the three levels; lactation was also normal and litters were successfully raised to weaning.

5. Organ weights, liver histology and blood haemoglobin were normal in male rats given the lucerne LPC for 6 months.

6. Total body lipid of male rats given lucerne LPC was about half that of the control rats given casein. Body protein was slightly increased, and moisture content was higher in rats given lucerne LPC.

7. The ‘whey’ remaining after precipitation of the protein from lucerne juice strongly inhibited the initial growth of mice given a complete control diet. The mice soon accommodated to the depressive effect of ‘whey’, and body-weight gains were normal during the 3rd week.
Studies on unidentified growth factors
Authors: Bunyan J. , Murrell Elspeth A. , Cawthorne M. A. , Redman B. T.
Published: May 2005

1. Chicks at 10 d of age were given diets containing all the nutrients known to be required, with L-amino acids in place of protein. Dietary supplements were added isonitrogenously.

2. Ox liver (100 g/kg) greatly improved the chicks' growth rate, whereas torula yeast (50 g/kg) was inactive. The activity of fresh moist liver was considered to be due largely to an organic factor, because of the inactivity of water and the low activity of liver ash.

3. The growth rates of chicks receiving diets based upon casein and isolated soya-bean protein were significantly improved by the inclusion of 100 g fresh ox liver/kg, but not of 50 g torula yeast/kg.

4. These results show that chicks receiving an amino acid diet require an organic growth factor (Progressin) that differs from the yeast factor required by rats receiving an amino acid diet.
A compact machine for feeding sheep up to twelve times daily
Authors: Clapperton J. L. , Thomas P. C. , Stokes M. R. , Henderson J. M.
Published: May 2005

1. A machine is described which is small enough to fit into a respiration calorimeter and which enables sheep to be fed automatically up to twelve times daily.
Alcohol intake in relation to body mass index and waist-to-hip ratio: the importance of type of alcoholic beverage
Authors: Lukasiewicz Esther , Mennen Louise I , Bertrais Sandrine , Arnault Nathalie , Preziosi Paul , Galan Pilar , Hercberg Serge
Published: May 2005

Objective

Alcohol consumption may play a role in the development of obesity but the relationship between alcohol and weight is still unclear. The aim of our study was to assess the cross-sectional association of intakes of total alcohol and of specific alcoholic beverages (wine, beer and spirits) with waist-to-hip ratio (WHR) and body mass index (BMI) in a large sample of adults from all over France.

Design

Cross-sectional.

Setting

Participants were free-living healthy volunteers of the SU.VI.MAX study (an intervention study on the effects of antioxidant supplementation on chronic diseases).

Subjects

For 1481 women aged 35–60 years and 1210 men aged 45–60 years, intakes of total alcohol and specific alcoholic beverages were assessed by six 24-hour dietary records. BMI and WHR were measured during a clinical examination the year after.

Results

A J-shaped relationship was found between total alcohol consumption and WHR in both sexes and between total alcohol consumption and BMI in men only (P< 0.05). The same relationships were observed with wine (P< 0.05); men and women consuming less than 100 g day−1had a lower BMI (men only) and WHR than non-drinkers or those consuming more. Spirits consumption was positively associated with BMI (linear regression coefficient β = 0.21, 95% confidence interval (CI): 0.09–0.34 and β = 0.22, 95% CI: 0.06–0.39 for men and women, respectively) and WHR (β = 0.003, 95% CI: 0.001–0.005 and β = 0.003, 95%CI: 0.0002–0.006) in both sexes in a linear fashion. No relationship between beer consumption and BMI or WHR was found.

Conclusion

If confirmed in longitudinal studies, our results indicate that consumption of alcoholic beverages may be a risk factor for obesity.