bluuebunny/crossref_metadata_2025 huggingface dataset:
III-nitride integration on ferroelectric materials of lithium niobate by molecular beam epitaxy
Authors: Namkoong Gon , Lee Kyoung-Keun , Madison Shannon M. , Henderson Walter , Ralph Stephen E. , Doolittle W. Alan
Published: October 2005

Integration of III-nitride electrical devices on the ferroelectric material lithium niobate (LiNbO3) has been demonstrated. As a ferroelectric material, lithium niobate has a polarization which may provide excellent control of the polarity of III-nitrides. However, while high temperature, 1000°C, thermal treatments produce atomically smooth surfaces, improving adhesion of GaN epitaxial layers on lithium niobate, repolarization of the substrate in local domains occurs. These effects result in multi domains of mixed polarization in LiNbO3, producing inversion domains in subsequent GaN epilayers. However, it is found that AlN buffer layers suppress inversion domains of III-nitrides. Therefore, two-dimensional electron gases in AlGaN∕GaN heterojunction structures are obtained. Herein, the demonstration of the monolithic integration of high power devices with ferroelectric materials presents possibilities to control LiNbO3 modulators on compact optoelectronic/electronic chips.
Molecular-dynamics simulations of dimethylsulfoxide-methanol mixtures
Authors: Vechi Sérgio M. , Skaf Munir S.
Published: October 2005

We present molecular-dynamics (MD) computer simulation results for the local structures, hydrogen (H)-bond distribution, and dynamical properties of methanol (MeOH) and dimethylsulfoxide (DMSO) binary mixtures at ambient conditions over the entire composition range. The simulated heat of mixing and site-site pair distribution functions suggest that the intermolecular structures of the pure liquids are not markedly altered upon mixing. Nevertheless, H-bonding statistics show that aggregates of the type 1DMSO:1MeOH are formed and represent the predominant form of molecular association in these mixtures. Only a small fraction (10%) of DMSO molecules in MeOH-rich mixtures (85% in mole) forms H-bonding trimers of type 1DMSO:2MeOH. No evidence of other types of interspecies association is found. The self-diffusion coefficient for DMSO (MeOH) increases (decreases) upon mixing. The characteristic reorientation time τ1 of both species increases in the mixture, but the composition dependence is weak. The frequency spectrum of MeOH reorientational time-correlation function shows significant redshifts of the principal librational band as DMSO is added to the system, whereas the librational band of DMSO shows small alterations upon mixing. Our results are discussed in the light of previous simulation analyses for a similar system, DMSO-water mixtures, and compared with available experimental results.
Application of polyamorphism in water to spontaneous crystallization of emulsified LiCl-H2O solution
Authors: Mishima Osamu
Published: October 2005

Aqueous solutions are widely explained by the hydration or the bound water∕free water notion. Amorphous polymorphism (polyamorphism) in pure water, which is presently under vigorous discussion, may provide a different view over the solutions. Here, I changed pressure, P, temperature, T, and concentration, C, of emulsified LiCl-H2O solutions and studied their freezing by detecting its heat evolution. It was experimentally indicated that the homogeneous nucleation of low-density crystalline ice I (phase Ih or Ic), in pure water and in solutions, connects to the polyamorphic transition of high-density amorphous ice (HDA) to low-density amorphous ice (LDA). Thus, the polyamorphism of water relates to the phase behavior of aqueous solution. In accordance with the recent simulation result, the nucleation was thought to occur in two stages: the appearance of the LDA-like state and the crystallization. Usefulness of the polyamorphic point of view about the solutions was seen.
Spin-polarized conduction in localized ferromagnetic materials: The case of Fe3O4 on MgO(100)
Authors: Vescovo E. , Kim H.-J. , Ablett J. M. , Chambers S. A.
Published: October 2005

The surface electronic structure of 1500-Å-thick Fe3O4(100) films has been investigated by spin-resolved photoemission spectroscopy with vacuum ultraviolet synchrotron radiation. The films, epitaxially grown on MgO(100) substrates using plasma-assisted molecular-beam deposition, are briefly exposed to air during transfer to the photoemission chamber. It is shown that clean surfaces of Fe3O4 films after exposure to air can be recovered through mild annealing in an oxygen atmosphere. The presence of the characteristic Verwey transition, as detected in the valence-band photoemission spectra, provides evidence for the excellent electronic quality at the surface of these films. The top of the valence band is found to be negatively spin polarized, with a value of ≈−50%; this result strongly points towards the localized nature of the 3d states in this system.
Laser-induced motion in nanoparticle suspension droplets on a surface
Authors: Dietzel Mathias , Poulikakos Dimos
Published: October 2005

The fluid and particle motion in a volatile colloidal nanoparticle suspension droplet (“nano-ink”) spreading on a flat surface upon local heating through a laser beam is investigated numerically. The laser diameter, laser intensity, and the absorption coefficient of the nano-ink as well as the substrate thermal diffusivity were varied. The simulations are conducted with a finite-element method discretization of the extended axisymmetric Navier-Stokes equations in Lagrangian coordinates, accounting for evaporation, thermocapillarity, and Young-force-driven wetting for the fluid phase as well as for inertia-controlled particle motion for the solid phase. An additional continuous particle coagulation model with a locally monodispersed particle distribution is solved on the locations of the discrete computational particles for example cases. The localized heating leads, through the action of thermocapillarity, to a displacement of the liquid in the radial (outward) direction. A dimple in the droplet center region is formed as a consequence, which becomes flattened for larger laser beam diameters due to a significant enlargement in spreading. Substrates with high thermal diffusivity or large thermal contact resistance to the liquid can inhibit the Marangoni-induced enlargement of the droplet footprint. The coagulation model predicts for large absorption coefficients particle clustering primarily at the free surface, which prevents the formation of structures (built by the coagulated nanoparticles) with a uniform thickness.
Electroluminescence of type II broken-gap p-Ga0.84In0.16As0.22Sb0.78∕p-InAs heterostructures with a high-mobility electron channel at the interface
Authors: Oswald J. , Pangrác J. , Hulicius E. , Šimeček T. , Moiseev K. D. , Mikhailova M. P. , Yakovlev Yu. P.
Published: October 2005

Ga 0.84 In 0.16 As 0.22 Sb 0.78 quaternary solid solutions, lattice matched to InAs, were grown by liquid phase epitaxy on (100)-oriented p-InAs substrates from In-rich melt. The p-type Ga0.84In0.16As0.22Sb0.78 layers were intentionally undoped or slightly doped with Sn to the hole concentration about p∼5×1016cm−3. This allowed us to obtain a high-mobility∼(3.5−5.0)×104cm2V−1s−1 electron channel at the type II broken-gap p-Ga0.84In0.16As0.22Sb0.78∕p-InAs heterointerface. Low-temperature (T=5K) electroluminescence spectra exhibited two pronounced emission bands hν1=0.372eV and hν2=0.400eV under forward bias. The emission band hν2 was split into two lines and was attributed to interband transitions through acceptor and valence-band states in the bulk InAs, whereas emission band hν1 was ascribed to interface-related radiative transitions of electrons from the two-dimensional electron channel to the interface states at the p-Ga0.84In0.16As0.22Sb0.78∕p-InAs heteroboundary.
Control of the plasmon absorption of gold nanoparticles with a two-color excitation
Authors: Kityk I. V. , Plucinski K. J. , Ebothé J. , Umar A. Ali , Oyama M.
Published: October 2005

Substantial photoinduced changes of ultraviolet (UV) -visible (UV-vis) optical spectra were observed for the Au nanoparticles prepared by a “touch” seed-mediated growth technique on the surface of indium-tin-oxide substrate. The phototreatment was performed by two-color coherent laser beams with a wavelength of 1060 nm (fundamental beam) and double frequency 530 nm (writing beam). The maximal photoinduced changes of the UV-vis spectra were observed for the surfaces possessing low resistivity (about 4Ω∕sq). Those of higher resistivity (about 50Ω∕sq) demonstrate only slight shifts of the main Au particle surface-plasmon resonance maxima at λ=570nm. The effect observed is a consequence of a superposition of optically induced surface plasmon resonance, scattering on optically induced grating and electron-phonon relaxation.
Simulation of an asymmetric single dielectric barrier plasma actuator
Authors: Singh K. P. , Roy Subrata
Published: October 2005

Continuity equations governing electron and ion density are solved with Poisson’s equation to obtain spatial and temporal profiles of electron density, ion density, and voltage. The motion of electrons and ions results in charge separation and generation of an electrostatic electric field. Electron deposition downstream of the overlap region of the electrode results in formation of a virtual negative electrode that always attracts the charge separation. The value of charge separation e(ni−ne) and the force per volume F=e(ni−ne)E have been obtained near the dielectric surface for the 50th cycle. Domain integration of the force F=e(ni−ne)E has been obtained for different plasma densities, frequencies, and rf voltage wave forms. The time average of the x force is positive and the y force is negative over the domain; therefore there is an average net force on the plasma in the positive x and negative y directions. This will result in a moving wave of plasma over the dielectric surface in the positive x direction, which can find application in flow control.
Strong enhancement of band-edge photoluminescence in CdS quantum dots prepared by a reverse-micelle method
Authors: Kim D. , Miyamoto M. , Mishima T. , Nakayama M.
Published: October 2005

We have investigated the effects of surface modification on photoluminescence (PL) properties of CdS quantum dots (QDs) prepared by a reverse-micelle method. It is demonstrated that the modification of QD surface with a Cd(OH)2 layer leads to a strong enhancement of the band-edge PL intensity of CdS QDs in reverse micelles. The PL-decay profile before the surface modification exhibits a fast decay component less than 50ps. After the modification, the fast-decay component disappears. The drastic change of the PL-decay profiles before and after the surface modification corresponds to the marked increase of the PL intensity. This suggests that the strong enhancement of the band-edge PL intensity originates from the remarkable reduction of nonradiative recombination processes, which usually result in a very short decay time, due to surface defects of QDs.
Electrically aligned binary system of nanoparticles
Authors: Pal B. N. , Basu S. , Chakravorty D.
Published: October 2005

Aligned arrays of binary nanoparticles of silver and silver oxide, respectively, with mean diameters of 8.5nm have been prepared within a polymethylmethacrylate film. The alignment along an electric-field direction has been achieved by applying an electric field of ∼10V∕mm at frequency ranging from 1kHzto1MHz. This behavior has been explained as arising due to a dipole-dipole interaction between the metal and oxide nanoparticles, respectively. The electrical resistivity is shown to arise due to variable range hopping mechanism. These nanocomposites exhibit three orders of magnitude resistivity changes as the relative humidity is varied from 35% to 95%.
Patterning lyotropic liquid crystals as precursors for carbon nanotube arrays
Authors: Sousa M. E. , Cloutier S. G. , Jian K. Q. , Weissman B. S. , Hurt R. H. , Crawford G. P.
Published: October 2005

We report on a simple patterning technique using lyotropic liquid-crystal solutions to fabricate organized arrays of high aspect ratio carbon nanostructures. An automated pen writing system is used in conjunction with nanochannel alumina templates to produce ordered arrays of nanotubes and nanofibers in a variety of shapes, widths, and carbon crystal structures set by surface anchoring phenomena. The nanostructure arrays are characterized with optical and electron microscopy and Raman spectroscopy to establish the morphology and crystal structures of the carbon nanoform arrays.
A theoretical and experimental study of atomic-layer-deposited films onto porous dielectric substrates
Authors: TravaIy Y. , Schuhmacher J. , Baklanov M. R. , Giangrandi S. , Richard O. , Brijs B. , Van Hove M. , Maex K. , Abell T. , Somers K. R. F. , Hendrickx M. F. A. , Vanquickenborne L. G. , Ceulemans A. , Jonas A. M.
Published: October 2005

Gaseous precursors for the atomic layer deposition (ALD) process can penetrate and deposit inside porous dielectrics. Understanding the relationship between the substrate porosity and the size and shape of precursor molecules used for the ALD of dielectric or metal films on these substrates is crucial for the formation and fabrication of reliable nanostructures. Sealing the surface pores is highly desirable to prevent the deposition of gaseous ALD precursors inside the porous network. In this study, in-diffusion of precursors is investigated using x-ray reflectivity, transmission electron microscopy, and Rutherford backscattering spectrometry for different porous substrates and binary (TaN) and ternary (WNC) ALD systems. Experimental observations are complemented with computational molecular modeling performed in the framework of the density-functional-theory formalism to determine the size and shape of ALD precursors. Pore sealing treatments are used to prevent a precursor penetration and to provide a suitable starting surface for the nucleation and growth of ALD films.
Optimization of two-layer electromagnetic wave absorbers composed of magnetic and dielectric materials in gigahertz frequency band
Authors: He Yanfei , Gong Rongzhou , Nie Yan , He Huahui , Zhao Zhensheng
Published: October 2005

Both experimentally and theoretically, a two-layer electromagnetic (EM) wave absorber exhibits the possibility of meeting the demand for effective EM wave absorbers. The first layer, made up of magnetic micpowder (MMP), has a large permeability and magnetic loss, while the second layer, comprised of MMP and nanotitanium powder, has a frequency dispersion with the parameters of permittivity and permeability to match the incidence free space over a wide frequency range. The predicted results are based on the modulus of permittivity (permeability) which obeys a logarithmic law of mixtures, and the loss tangent is related through a linear law of mixtures. A linear regression analysis performed on the data points provides constants that can be used to predict the effective parameters at different frequencies. Finally, a program is presented that computes the optimum amount of MMP in the second layer and the required thickness for each layer. The predicted results agree quite well with the measured data.
Comparison between Langmuir probe and microwave autointerferometry measurements at intermediate pressure in an argon surface wave discharge
Authors: Rousseau A. , Teboul E. , Béchu S.
Published: October 2005

This paper is devoted to the validation of Langmuir probe technique by microwave autointerferometry in a surface wave discharge at medium pressure (from 0.1 up to 10Torr). Temperatures of neutrals, obtained from Rayleigh scattering, and electrons, given by double probe measurements, have been used to estimate the mean free path and the sheath length. Hence, the number of collisions in the sheath has been obtained. We have verified that two different phenomena occur in the sheath, while the pressure increases. These phenomena are depicted, in literature, as two different coefficients used to modify the value of the noncollisional current of Laframboise. Coefficients given by various authors have been investigated with accuracy knowing the number of collisions in the sheath. Very good agreements are obtained between Zakrzewski and Kopiczynski theory and autointerferometry measurements which are unaffected by collisional phenomena.
Second-harmonic performance of a-axis-oriented ZnO nanolayers on sapphire substrates
Authors: Neumann Uwe , Grunwald Ruediger , Griebner Uwe , Steinmeyer Günter , Schmidbauer Martin , Seeber Wolfgang
Published: October 2005

We report on the nonlinear optical performance of sub-μm ZnO films grown by metal organic aerosol deposition on r-plane sapphire substrates. These films display scale-like nanocrystalline structures. Layers of different crystallite sizes and shapes are studied. Both, x-ray diffractometry and the characteristic angular and polarization dependence of the second harmonic generation, indicate a strongly uniform a-axis orientation of the crystallites. Using 35-fs Ti:sapphire laser pulses, we demonstrate much higher conversion efficiencies for ZnO layers than previously reported. The robust performance at normal incidence makes this device suitable for advanced pulse characterization techniques.
A numerical experiment to determine whether surface shear-stress fluctuations are a true sound source
Authors: Shariff Karim , Wang Meng
Published: October 2005

The sound generated due to a localized flow over a large (compared to the acoustic wavelength) plane no-slip wall is considered. It has been known since 1960 that for inviscid flow the pressure, while appearing to be a source of dipole sound in a formal solution to the Lighthill equation, is, in fact, not a true dipole source, but rather represents the surface reflection of volume quadrupoles. The subject of the present work—namely, whether a similar surface shear stress term constitutes a true source of dipole sound—has been controversial. Some have boldly assumed it to be a true source and have used it to calculate the noise in boundary-layer flows. Others have argued that, like the surface pressure, the surface shear stress is not a valid source of sound but rather represents a propagation effect. Here, a numerical experiment is undertaken to investigate the issue. A portion of an otherwise static wall is oscillated tangentially in an acoustically compact region to create shear stress fluctuations. The resulting sound field, computed directly from the compressible Navier-Stokes equations, is nearly dipolar and its amplitude agrees with an acoustic analogy prediction that regards the surface shear as acoustically compact and as a true source of sound. However, there is a correction that becomes noticeable for observers near wall-grazing angles as the computational domain size Ld along the wall is increased. An estimate, validated by the simulations, shows that as Ld→∞ the correction to the sound in the Fraunhofer zone is proportional to δbl∕λ (the ratio of oscillatory boundary-layer thickness to acoustic wavelength) times a directivity factor that becomes large at angles close to grazing. For observers at such angles, Lighthill’s acoustic analogy does not apply.
Growth and magnetism of Cr-doped InN
Authors: Rajaram R. , Ney A. , Solomon G. , Harris J. S. , Farrow R. F. C. , Parkin S. S. P.
Published: October 2005

We present structural and magnetic characterization of Cr-doped InN films grown by plasma-assisted molecular beam epitaxy on c-plane sapphire substrates. Low-temperature GaN buffer layers grown by metalorganic vapor-phase epitaxy were used to accommodate the large lattice mismatch between InN and sapphire. A high n-type carrier concentration of 1.5×1020cm−3 was measured in InN films with 3% Cr doping. Films of this type, with high structural perfection, as measured in situ, with reflection high-energy electron diffraction, exhibit a well-defined in-plane magnetic hysteresis loop for temperatures varying from 5to300K. Thus, we show evidence of magnetic order in Cr-doped InN.
Temperature-dependent carrier-transport and light-emission processes in a phosphorescent organic light-emitting device
Authors: Tanaka Isao , Tokito Shizuo
Published: October 2005

We report on carrier-transport, electroluminescence, and photoluminescence processes in a phosphorescent organic light-emitting device based on fac tris(2-phenylpyridine) iridium doped 4,4′-N,N′-dicarbazole-biphenyl over a wide temperature range from 5 to 295 K. The current flow could be described in terms of a space-charge-limited current with an exponential trap distribution at temperatures above 150 K. The electroluminescence intensity gradually decreased with decreasing temperature, whereas the photoluminescence intensity was almost independent of temperature. The difference between the temperature-dependent electroluminescence and photoluminescence intensities suggests that the carrier mobility depends on the electric field and the temperature.
Comparison of gate and drain current detection of hydrogen at room temperature with AlGaN∕GaN high electron mobility transistors
Authors: Wang Hung-Ta , Kang B. S. , Ren F. , Fitch R. C. , Gillespie J. K. , Moser N. , Jessen G. , Jenkins T. , Dettmer R. , Via D. , Crespo A. , Gila B. P. , Abernathy C. R. , Pearton S. J.
Published: October 2005

Pt-gated AlGaN∕GaN high electron mobility transistors can be used as room-temperature hydrogen gas sensors at hydrogen concentrations as low as 100ppm. A comparison of the changes in drain and gate current-voltage (I-V) characteristics with the introduction of 500ppm H2 into the measurement ambient shows that monitoring the change in drain-source current provides a wider gate voltage operation range for maximum detection sensitivity and higher total current change than measuring the change in gate current. However, over a narrow gate voltage range, the relative sensitivity of detection by monitoring the gate current changes is up to an order of magnitude larger than that of drain-source current changes. In both cases, the changes are fully reversible in <2–3min at 25°C upon removal of the hydrogen from the ambient.
Electrical and dielectric behaviors of Ti3SiC2∕Yttria-stabilized zirconia composites
Authors: Shi Sui-Lin , Pan Wei , Fang Ming-Hao , Fang Zhen-Yi
Published: October 2005

Ti 3 Si C 2 ∕ 3 Y - TZP (3mol% Yttria-stabilized zirconia) composites were prepared by spark plasma sintering. The effective dc conductivities of the composites have been measured and the percolation threshold was determined. The dielectric behavior of the composites was studied in the frequency range 102–4×107Hz. The results show that the dielectric constant increased remarkably with the Ti3SiC2 concentration, when the Ti3SiC2 concentration was close to percolation threshold. This may be attributed to the critical behavior of the dielectric constant near the percolation threshold as well as to the polarization effects between the clusters inside the composites.
Strong visible light emission from well-aligned multiwalled carbon nanotube films under infrared laser irradiation
Authors: Zhang Yong , Gong Tao , Liu Wenjin , Zhang Xianfeng , Chang Jianguo , Wang Kunlin , Wu Dehai
Published: October 2005

We report strong and brilliant visible light emission from well-aligned multiwalled carbon nanotube (AMWNT) films under infrared (IR) laser irradiation with wavelength at 1.06 and 10.6μm, respectively. The AMWNT film shows a high durability against laser irradiation and achieved a conversion from IR laser to visible light. It is a good candidate for optical converter. Light emission spectra versus different wavelengths and various powers were found to have similar line shapes. It could be explained as combination of laser-induced photoluminescence and resistive heating.
Production of native donors in ZnO by annealing at high temperature in Zn vapor
Authors: Halliburton L. E. , Giles N. C. , Garces N. Y. , Luo Ming , Xu Chunchuan , Bai Lihai , Boatner L. A.
Published: October 2005

Zinc oxide crystals grown by the seeded chemical vapor transport method have been annealed in zinc vapor at 1100 °C for 30 min. These thermochemical reduction treatments produce a deep red coloration in the crystals and increase their n-type electrical conductivity. Electron paramagnetic resonance (EPR), optical absorption, and Hall measurements were used to monitor changes in the crystals. After an anneal, an intense optical absorption band is present that extends from the band edge out to approximately 550 nm, and the EPR signal near g=1.96 (due to shallow donors and/or conduction-band electrons), the free-carrier absorption, and the Hall electron concentration are all larger. Hydrogen was not present during these anneals, thus leaving oxygen vacancies and zinc interstitials as candidates for the added donors. Neutral oxygen vacancies are produced at high temperature by the additive-coloration mechanism, and are responsible for the broad near-edge absorption band. The observed increase in the number of free carriers is a result of either (1) the formation of zinc interstitials or (2) having the ground state of the neutral oxygen vacancy near the conduction band.
High mobility ambipolar charge transport in a cross-linked reactive mesogen at room temperature
Authors: Kreouzis T. , Baldwin R. J. , Shkunov M. , McCulloch I. , Heeney M. , Zhang W.
Published: October 2005

By photochemically cross linking the molecules of a reactive end group functionalized calamitic liquid crystal (bis(heptylphenyl)-bithiophene-oxetane) in the smectic mesophase, an insoluble rigid molecular network is formed which remains structurally unchanged on cooling to room temperature. The charge transport is investigated by the time-of-flight method and the resulting material shows long-range (∼10μm) ambipolar transport with nondispersive field independent hole mobility, μhole=0.016cm2∕Vs and dispersive field dependent electron mobility, typically μelectron=0.028cm2∕Vs (both at 4×104Vcm−1 and at 15 °C). These desirable charge transport properties make this system a promising candidate for organic electronic applications, such as charge transport layers in organic light-emitting diodes and field effect transistors.
Effect of alloying and cladding on the failure of silver metallization under high temperature and current stressing
Authors: Misra E. , Alford T. L.
Published: October 2005

Pure Ag layers were cladded with thin alloy (Ag with 3 at. % aluminum) layers to form a [Ag(Al)∕Ag∕Ag(Al)] structure on SiO2. The effective resistivity of the cladded Ag metallization is slightly greater than pure silver and less than the Ag(Al) alloy metallization. The clad structures showed a nearly 38 times enhancement in electromigration resistance when compared to pure Ag and seven times greater than the Ag(Al) alloy. The enhancement in lifetime of the clad structure was attributed to enhanced thermal stability due to segregation of Al2O3 at the Ag grain boundaries leading to reduced grain size and changes in thermodynamic properties and also reduced atomic mobility because of the topmost layer acting as a passivation layer.
Electron-phonon scattering and ballistic behavior in semiconducting carbon nanotubes
Authors: d’Honincthun H. Cazin , Galdin-Retailleau S. , Sée J. , Dollfus P.
Published: October 2005

We study the steady-state and ballistic transport properties of semiconducting zig-zag carbon nanotubes (CNTs) using semiclassical Monte Carlo simulation. Electron-phonon scattering is the only type of interaction included in the model. The band structure and phonon dispersion are derived from that of graphene by the zone folding method. Steady-state drift velocity and low-field mobility are calculated for CNTs with wrapping index ranging from n=10 to n=59, i.e., for a diameter range of 0.78−4.62nm. Principally, a transient analysis of transport under uniform driving field is realized and gives the fraction of ballistic electrons as a function of CNT length and the mean free path (MFP) for acoustic and optical phonons scattering. The probability to have ballistic electrons on a given distance appears to be higher for nanotubes of large diameter and depends on the field applied.
Lateral electron transport in Cu(In,Ga)Se2 investigated by electro-assisted scanning tunneling microscopy
Authors: Romero Manuel J. , Jiang Chun-Sheng , Noufi Rommel , Al-Jassim Mowafak
Published: October 2005

We investigate the lateral electron transport across grain boundaries in Cu(In,Ga)Se2 (CIGS) by a combination of scanning tunneling microscopy (STM) with the excitation provided by the electron beam in electron microscopy—or electro-assisted STM. Using this method, we report evidence for a significant barrier for electron diffusion across grain boundaries in CuGaSe2 (CGS), which is not present in CuInSe2 (CIS). Finally, we discuss the effects of gallium addition.
Lasing action in colloidal CdS∕CdSe∕CdS quantum wells
Authors: Xu Jianfeng , Xiao Min
Published: October 2005

Lasing action is observed in random medium of colloidal CdS∕CdSe∕CdS quantum wells (QWs) at 77 K. Sharp lasing peaks appear over a broad spectral range as pumping power increases. The lasing threshold is around 3W∕cm2, which is much lower than that of other random or nanocrystal laser systems. Such improvement in lasing threshold opens the door to practical applications of QW random laser. The characteristic cavity length is determined by the Fourier transform of the lasing spectrum.
Water reaction with chlorine-terminated silicon (111) and (100) surfaces
Authors: Rivillon Sandrine , Brewer Rhett T. , Chabal Yves J.
Published: October 2005

Hydroxylation of chlorine-terminated silicon (111) and (100) by water vapor exposure has been studied as a function of substrate temperature using in situ infrared absorption spectroscopy. No hydroxyl is observed, as would have been expected from the surface reaction: Si–Cl(ads)+H2O(g)→Si–OH(ads)+HCl(g) (ads referring to adsorbed surface species). Instead, silicon oxide is formed upon removal of the Si–Cl bond at ∼325°C. This indicates that, while hydroxylation of the Cl-terminated silicon surface may occur, the hydroxylated surface formed by this reaction is not stable at the temperature necessary for the reaction.
Influence of surface/interface roughness and grain size on magnetic property of Fe∕Co bilayer
Authors: Aurongzeb Deeder , Ram K. Bhargava , Menon Latika
Published: October 2005

In this work, we report the influence of surface roughness and cluster size on coercivity of Fe∕Co bilayer. Coercivity was tuned by thermal annealing. No systematic trend was found for temperature dependent annealing. However, after annealing at 350 °C, we find systematic increase in coercivity with anneal time. For as-deposited film, we find unusually low coercivity (0.39 Oe). By increasing annealing time, coercivity was tuned to values as high as 600 Oe. Surface characterization using atomic force microscopy showed uniform clusters at this temperature after 2 h of annealing. The observed magnetic properties are discussed in terms of cluster size and surface/interface roughness.
Epitaxial growth of multiferroic YMnO3 on GaN
Authors: Posadas A. , Yau J.-B. , Ahn C. H. , Han J. , Gariglio S. , Johnston K. , Rabe K. M. , Neaton J. B.
Published: October 2005

In this work, we report on the epitaxial growth of multiferroic YMnO3 on GaN. Both materials are hexagonal with a nominal lattice mismatch of 4%, yet x-ray diffraction reveals an unexpected 30° rotation between the unit cells of YMnO3 and GaN that results in a much larger lattice mismatch (10%) compared to the unrotated case. Estimates based on first principles calculations show that the bonding energy gained from the rotated atomic arrangement compensates for the increase in strain energy due to the larger lattice mismatch. Understanding the energy competition between chemical bonding energy and strain energy provides insight into the heteroepitaxial growth mechanisms of complex oxide-semiconductor systems.
Evolutionary population genetics of promoters: Predicting binding sites and functional phylogenies
Authors: Mustonen Ville , Lässig Michael
Published: October 2005

We study the evolution of transcription factor-binding sites in prokaryotes, using an empirically grounded model with point mutations and genetic drift. Selection acts on the site sequence via its binding affinity to the corresponding transcription factor. Calibrating the model with populations of functional binding sites, we verify this form of selection and show that typical sites are under substantial selection pressure for functionality: for cAMP response protein sites in
Escherichia coli
, the product of fitness difference and effective population size takes values
2N
Δ
F
of order 10. We apply this model to cross-species comparisons of binding sites in bacteria and obtain a prediction method for binding sites that uses evolutionary information in a quantitative way. At the same time, this method predicts the functional histories of orthologous sites in a phylogeny, evaluating the likelihood for conservation or loss or gain of function during evolution. We have performed, as an example, a cross-species analysis of
E. coli
,
Salmonella typhimurium
, and
Yersinia pseudotuberculosis
. Detailed lists of predicted sites and their functional phylogenies are available.
Fine-scale processes regulate the response of extreme events to global climate change
Authors: Diffenbaugh Noah S. , Pal Jeremy S. , Trapp Robert J. , Giorgi Filippo
Published: October 2005

We find that extreme temperature and precipitation events are likely to respond substantially to anthropogenically enhanced greenhouse forcing and that fine-scale climate system modifiers are likely to play a critical role in the net response. At present, such events impact a wide variety of natural and human systems, and future changes in their frequency and/or magnitude could have dramatic ecological, economic, and sociological consequences. Our results indicate that fine-scale snow albedo effects influence the response of both hot and cold events and that peak increases in extreme hot events are amplified by surface moisture feedbacks. Likewise, we find that extreme precipitation is enhanced on the lee side of rain shadows and over coastal areas dominated by convective precipitation. We project substantial, spatially heterogeneous increases in both hot and wet events over the contiguous United States by the end of the next century, suggesting that consideration of fine-scale processes is critical for accurate assessment of local- and regional-scale vulnerability to climate change.
Genetically encoded short peptide tag for versatile protein labeling by Sfp phosphopantetheinyl transferase
Authors: Yin Jun , Straight Paul D. , McLoughlin Shaun M. , Zhou Zhe , Lin Alison J. , Golan David E. , Kelleher Neil L. , Kolter Roberto , Walsh Christopher T.
Published: October 2005

An 11-residue peptide with the sequence D
S
LEFIASKLA was identified from a genomic library of
Bacillus subtilis
by phage display as an efficient substrate for Sfp phosphopantetheinyl transferase-catalyzed protein labeling by small molecule-CoA conjugates. We name this peptide the “ybbR tag,” because part of its sequence is derived from the
ybbR
ORF in the
B. subtilis
genome. The site of Sfp-catalyzed ybbR tag labeling was mapped to the underlined Ser residue, and the ybbR tag was found to have a strong tendency for adopting an α-helical conformation in solution. Here we demonstrate that the ybbR tag can be fused to the N or C termini of target proteins or inserted in a flexible loop in the middle of a target protein for site-specific protein labeling by Sfp. The short size of the ybbR tag and its compatibility with various target proteins, the broad substrate specificity of Sfp for labeling the ybbR tag with small-molecule probes of diverse structures, and the high specificity and efficiency of the labeling reaction make Sfp-catalyzed ybbR tag labeling an attractive tool for expanding protein structural and functional diversities by posttranslational modification.
Low-frequency normal mode in DNA HhaI methyltransferase and motions of residues involved in the base flipping
Authors: Luo Jia , Bruice Thomas C.
Published: October 2005

The results of normal-mode analyses are in accord with the proposal that a low-frequency motion of the HhaI methyltransferase enzyme is responsible for base flipping in bound DNA. The vectors of the low-frequency normal mode of residues Ser-85 and Ile-86 point directly to the phosphate and ribose moieties of the DNA backbone near the target base in position to rotate the dihedral angles and flip the base out of the DNA duplex. The vector of residue Gln-237 on the major groove is in the proper orientation to assist base separation. Our results favor the major groove pathway and the protein active process in base flipping.
Negative regulation of Toll-like-receptor signaling by IRF-4
Authors: Negishi Hideo , Ohba Yusuke , Yanai Hideyuki , Takaoka Akinori , Honma Kiri , Yui Katsuyuki , Matsuyama Toshifumi , Taniguchi Tadatsugu , Honda Kenya
Published: October 2005

The recognition of microbial components by Toll-like receptors (TLRs) is an event central to the activation of innate and adaptive immune systems. TLR activation triggers the induction of downstream target genes, wherein the TLR-interacting adaptor molecule MyD88 recruits various signaling molecules and transcription factors. Two members of the IFN regulatory factor (IRF) family of transcription factors, IRF-5 and IRF-7, interact with MyD88 and induce proinflammatory cytokines and type I IFNs, respectively. Here, we show that IRF-4 also interacts with MyD88 and acts as a negative regulator of TLR signaling. IRF-4 mRNA is induced by TLR activation, and IRF-4 competes with IRF-5, but not with IRF-7, for MyD88 interaction. The TLR-dependent induction of proinflammatory cytokines is markedly enhanced in peritoneal macrophages from mice deficient in the
Irf4
gene, whereas the induction is inhibited by the ectopic expression of IRF-4 in a macrophage cell line. The critical function of IRF-4 in TLR signaling
in vivo
is underscored by the observation that
Irf4
-deficient mice show hypersensitivity to DNA-induced shock, with elevated serum proinflammatory cytokine levels. This study may provide an insight into the complex regulatory mechanisms of MyD88 signaling by IRFs.
Over-expression of GbRac1 gene in transgenic tobacco enhances disease resistance to Alternaria alternata in vitro
Authors: Wei-Min Li , Zhi-Xing Wang , Shi-Rong Jia
Published: October 2005

GbRac1 gene was cloned from Gossypium barbadense with degenerate primers and 3′-RACE. Northern blot analysis indicated that GbRac1 mRNA was expressed abundantly in G. barbadense seedlings inoculated with Verticillium dehliae compared with mock-inoculated plants. A plant constitutive expression vector pRac harbouring GbRac1 gene was constructed and leaf discs of tobacco (Nicotiana tabacum L. cv. NC89) were transformed with pRac by Agrobacterium-mediated transformation. Disease challenge test of detached leaves of the transgenic plants by inoculation with Alternaria alternata showed that resistance was enhanced dramatically compared with the non-transgenic plants. Results suggest that GbRac1 gene might have potential application in the genetic engineering of plants with enhanced disease resistance.
RAPD and large subunit nuclear rDNA sequence analyses of the entomogenous fungus Aschersonia
Authors: Jun-Zhi Qiu , Zhi-Peng Huang , Jie-Ru Pan , Xue-Qin Xie , Yan-Ping Zhu , Fang Fang , Shao-Sheng Zhang , Xiong Guan
Published: October 2005

Eleven isolates within four species of the entomogenous fungus Aschersonia from China, the USA, Japan, the Philippines, Malaysia and Columbia were characterized using 17 RAPD primers. Genetic diversity among these strains of Aschersonia was found. The clustering results showed that the genetic variability among interspecies was more than that among intraspecies of Aschersonia. In the constructed phylogenetic tree, these isolates were not clustered according to their geographic origins or hosts. Furthermore, sequences of the divergent domain at the 5′-end of the large subunit (LSU) in nuclear rRNA from the mitosporic entomogenous fungi were employed to analyse the phylogenetic relationships of 11 Aschersonia isolates. The relationships of interspecies or intraspecies shown in the phylogenetic tree were almost consistent with the results of the morphological study. Different species isolated from different geographic origins could be clearly distinguished in the tree. But there were no close relationships among species isolated from the same family or order of insect hosts. The tree indicated that isolate Aa, belonging to A. aleyrodis, was the same as Aa992 and Aa3.4485. Moreover, results of RAPD analyses were consistent with those of LSU nuclear rDNA analysis for the same isolates tested, which consequently indicates that both methods can be independently applied for classification and identification of Aschersonia.
Construction and characterization of a recombinantFowlpox virusexpressing chicken type II interferon
Authors: Yong-Ke Sun , Yun-Feng Wang , Hai-Dong Zhi , Sheng-Wang Liu , Mei Wang , Guang-Zhi Tong
Published: October 2005

Interferon, an important cytokine, is an immunomodulator and possesses antiviral and anti-tumour activity.In vitro, it can be administrated in the treatment of diseases alone or with genetically engineered vaccine to enhance the immune effect of the latter. The recombinant transferring vector pSY681–ChIFN-γ was obtained in this study by inserting the chicken type II interferon (ChIFN-γ) gene into theFowlpox virus(FPV) transferring vector pSY681. The resulting plasmid was then transfected into chicken embryo fibroblast (CEF) cell cultures pre-infected with the parental FPV S-FPV-017. Finally, the recombinantFowlpox virus(rFPV) expressingChIFN-γ (rFPV–ChIFN-γ) was produced by homologous recombination with the FPV gene in CEF. rFPV-positive plaques were verified by polymerase chain reaction (PCR), restriction analysis and indirect immunofluorescence assays. The rFPV–ChIFN-γ supernatants, cultured in CEF for 72 h and inoculated into rat fibroblasts (L929), had an inhibitory effect on the replication ofRous sarcoma virus(RSV) with an antiviral titre of 2048 U/ml.
cDNA cloning and prokaryotic expression of β-glucosidase in tea plant [Camellia sinensis (L.) O. Kutze]
Authors: Chang-Jun Jiang , Yuan-Hua Li , Wan-Ping Fang
Published: October 2005

The β-glucosidase gene has important effects on alcoholic aroma precursors and insect resistance of the tea plant [Camellia sinensis (L.) O. Kutze]. The complete cDNA sequence of β-glucosidase of the tea plant was cloned; its full length was 1475 bp, and shared 40–60% similarity with corresponding parts of the nucleotide sequence of β-glucosidase gene from other plants. Its secondary structure contains 14.33% α-helix, 25.43% β-pleated sheet and many functional amino acid domains. The β-glucosidase gene was cloned into the pET-32a expression system and expressed at high-efficiently in Escherichia coli BL21 (DE3); the molecular weight of expressed fusion protein was 63 kDa. The results of enzymic reaction showed that the fusion protein possessed normal bioactivity, and it could catalyse the dehydration of the glycosidic bond. The soluble fusion protein was expressed mainly in the cytoplasm.
Development and preliminary application of gE enzyme-linked immunosorbent assay for detection of the antibody to gE protein ofPseudorabies virusin pigs
Authors: Yong Tang , Huan-Chun Chen , Ya-Li Qin , Qi-Gai He , Mei-Lli Jin , Bin Wu , Zheng-Fei Liu
Published: October 2005

To differentiate pigs infected withPseudorabies virus(PrV) from pigs vaccinated with gE-PrV, a glycoprotein E enzyme-linked immunosorbent assay (gE-ELISA) based on recombinant glycoprotein E (gE) (which was expressed byEscherichia coli, purified, denatured and renatured) was developed. By testing 115 serum samples, the diagnostic specificity and sensitivity of the developed gE-ELISA were evaluated to be 94.5% and 96.7%, respectively. Five serum samples were tested with plates from five lots, and the results had a coefficient of variation of less than 10%, showing good reproducibility of gE-ELISA. This gE-ELISA was compared with a commercial blocking ELISA by testing 356 serum samples. The agreement rate of the two assays was 92.13% (328/356). These results suggested that the gE-ELISA developed in our laboratory could be used in differentiating PrV-infected and gE-PrV-vaccinated pigs.
Cloning and sequencing of DNA components of Banana bunchy top virus Hainan isolate
Authors: Zhuang Jun Tian E. , Zhi-Xin Liu
Published: October 2005

Six DNA components of Banana bunchy top virus (BBTV) were amplified by polymerase chain reaction (PCR) using total DNA from banana tissues having the typical BBTV symptoms as template. The sequence analysis indicated that the six fragments (1104 nt, 1067 nt, 1059 nt, 1045 nt, 1014 nt and 1081 nt) were all full-length components of BBTV. The viral sequences from different countries were compared. Results revealed that the sequence of component 1 was more conservative than other components, DNA1 of the Hainan isolate shared 95.4% homology with that of the Vietnam isolate, while sequences of both components 2 and 4 showed less homology. DNA2 of the Hainan isolate only shared 83% homology with that of the Guangzhou isolate. According to the results of the DNA1 sequence comparison, the BBTV Hainan isolate should belong to the Asian sub-group.
Sequencing of cDNA clones and analysis of the expressed sequence tags (ESTs) of tea plant [Camellia sinensis (L.) O. Kuntze] young shoots
Authors: Li-Ping Zhao , Qi-Kang Gao , Liang Chen
Published: October 2005

The construction of two cDNA libraries from young shoots of tea plant [Camellia sinensis cv. Longjing 43 and Anji Baicha], the sequencing of Longjing 43 cDNA clones and the analysis of expressed sequence tags (ESTs) are reported. Totally, 4320 clones from the cDNA library of Longjing 43 were sequenced, and 2963 useful sequences were obtained, corresponding to 68.6% of clones. A total of 416 clones shorter than 150 bp and 863 repeated clones were excluded, the first 1684 valid tea plant ESTs were generated. Most of the ESTs were between 300 and 700 bp, with an average of 478 bp. Six hundred and seven ESTs with known function or putative function were identified by BlastN searches against the National Center of Biotechnology Institute (NCBI) non-redundant nucleotide databases, corresponding to more than 130 functional genes in the tea plant. The rest, 1077 ESTs, were novel gene partial or full sequences. The results indicated that EST sequencing was a rapid and effective approach to identification of novel functional genes for tea plant.
Spectral radius inequalities for Hilbert space operators
Authors: Kittaneh Fuad
Published: October 2005

We prove several spectral radius inequalities for sums, products, and commutators of Hilbert space operators. Pinching inequalities for the spectral radius are also obtained.
A C-symplectic free 𝑆¹-manifold with contractible orbits and 𝐂𝐀𝐓=\frac12𝐃𝐈𝐌
Authors: Allday Christopher , Oprea John
Published: October 2005

An interesting question in symplectic geometry concerns whether or not a closed symplectic manifold can have a free symplectic circle action with orbits contractible in the manifold. Here we present a c-symplectic example, thus showing that the problem is truly geometric as opposed to topological. Furthermore, we see that our example is the only known example of a c-symplectic manifold having non-trivial fundamental group and Lusternik-Schnirelmann category precisely half its dimension.
A note on the special unitary group of a division algebra
Authors: Sethuraman B. , Sury B.
Published: October 2005

If

D
D

is a division algebra with its center a number field

K
K

and with an involution of the second kind, it is unknown if the group

S
U
(
1
,
D
)

/

[
U
(
1
,
d
)

SU(1,D)/[U(1,d)

,

U
(
1
,
D
)
]

U(1,D)]

is trivial. We show that, by contrast, if

K
K

is a function field in one variable over a number field, and if

D
D

is an algebra with center

K
K

and with an involution of the second kind, the group

S
U
(
1
,
D
)

/

[
U
(
1
,
d
)
,
U
(
1
,
D
)
]

SU(1,D)/[U(1,d),U(1,D)]

can be infinite in general. We give an infinite class of examples.