bluuebunny/crossref_metadata_2025 huggingface dataset:
Empirical solvent correction for multiple amide group vibrational modes
Authors: Bouř Petr , Michalík David , Kapitán Josef
Published: April 2005

Previously proposed solvent correction to the amide I peptide vibration was extended so that it can be applied to a general solvated chromophore. The combined molecular and quantum mechanics (MM∕QM) method is based on a linear dependence of harmonic force field and intensity tensor components of the solute on solvent electrostatic field. For N-methylacetamide, realistic solvent frequency and intensity changes as well as inhomogeneous band widths were obtained for amide A,I,II, and III modes. A rather anomalous basis set size dependence was observed for the amide A and I vibrations, when bigger basis lead to narrowing of spectral bands and lesser molecular sensibility to the environment. For a model α-helical peptide, a W-shape of the vibrational circular dichroism signal observed in deuterated solvent for the amide I band was reproduced correctly, unlike with previous vacuum models.
Explicit threshold of the toroidal ion temperature gradient mode instability
Authors: Sandberg I.
Published: April 2005

The explicit stability threshold of the toroidal ion temperature gradient mode instability is analytically derived using the standard reactive fluid model. It is shown that in the peak density region, the threshold gets significantly smaller due to finite ion Larmor radius effects, and the marginal unstable modes acquire finite wavelengths.
Phase space properties and the short distance structure in quantum field theory
Authors: Bostelmann Henning
Published: April 2005

The paper investigates relations between the phase space structure of a quantum field theory (“nuclearity”) and the concept of pointlike localized fields. Given a net of local observable algebras, a phase space condition is introduced that allows a very detailed description of the theory’s field content. An appendix discusses noninteracting models as examples.
ZnO nanowires with high aspect ratios grown by metalorganic chemical vapor deposition using gold nanoparticles
Authors: Kim Sang-Woo , Fujita Shizuo , Fujita Shigeo
Published: April 2005

ZnO nanowires with diameters ranging from 20 to 60 nm and lengths in the range 5–15 μm were synthesized by metalorganic chemical vapor deposition, assisted by colloidal gold nanoparticles with a diameter of 20 nm dispersed on SiO2∕Si substrates. The ZnO nanowires were found to have a high-internal quantum efficiency and negligibly weak deep-level emission, as evidenced by photoluminescence measurements. The clear observation of free-exciton and biexciton emission indicates that the ZnO nanowires prepared by this method are of high quality.
Spatial Landau damping in plasmas with three-dimensional κ distributions
Authors: Podesta J. J.
Published: April 2005

The increase in linear Landau damping in κ-distributed plasmas compared to thermal equilibrium plasmas is studied by solving a boundary value problem for the spatially damped plasma waves generated by a planar grid electrode with an applied time harmonic potential. Solutions are computed for the plasma potential versus the distance from the electrode for different values of the parameter κ (kappa). The velocity parameter v0 of the distribution function is chosen so that, as the parameter κ varies, the kinetic temperature of the plasma remains constant. The exact solutions of this problem are also compared to approximate solutions derived from the theory of normal modes, that is, from the roots of the dispersion relation. This model problem demonstrates the significant increase in Landau damping by electrons which occurs for small values of the parameter κ.
Sagdeev’s approach to study the effect of the kinematic viscosity on the dust ion-acoustic solitary waves in dusty plasma
Authors: Maitra Sarit , Roychoudhury Rajkumar
Published: April 2005

Sagdeev’s technique is used to study the dust ion-acoustic solitary waves (DIASWs) in a dusty plasma comprising ions, electrons, and charged dust grains taking into account the ion kinematic viscosity. Exact analytical results for the solitary wave solutions were obtained for small amplitude DIASW. The effects of the ion kinematic viscosity and the ion temperature on the feature of DIASW have been investigated.
Azimuthal clumping instabilities in a Z-pinch wire array
Authors: Strickler Trevor , Lau Y. Y. , Gilgenbach R. M. , Cuneo M. E. , Mehlhorn T. A.
Published: April 2005

A simple model is constructed to evaluate the temporal evolution of azimuthal clumping instabilities in a cylindrical array of current-carrying wires. An analytic scaling law is derived, which shows that randomly seeded perturbations evolve at the rate of the fastest unstable mode, almost from the start. This instability is entirely analogous to the Jeans instability in a self-gravitating disk, where the mutual attraction of gravity is replaced by the mutual attraction among the current-carrying wires.
Deep level defects in Si-doped AlxGa1−xN films grown by molecular-beam epitaxy
Authors: Park Y. S. , Park C. J. , Park C. M. , Na J. H. , Oh J. S. , Yoon I. T. , Cho H. Y. , Kang T. W. , Oh Jae-Eung
Published: April 2005

The deep trap levels of AlxGa1−xN films with x in the range from 0 to 0.15 grown on c-plane sapphire substrates using rf-plasma-assisted molecular-beam epitaxy have been investigated by deep level transient spectroscopy measurements. Two distinct defect levels (denoted as Ei and Di) were observed. The origins of the Ei and the Di are associated with point defects such as the N vacancies and extended defects, such as the threading dislocations, respectively. According to Al content (x), the activation energy and capture cross section for the Di defect ranged from 0.19to0.41eV and 1.1–6.6×10−15cm2, respectively. The trap energy levels of Di defects in AlxGa1−xN were calculated and the values were nonlinear with Al content. The bowing parameter of AlxGa1−xN films was determined to be b=1.22.
On reflection algebras and twisted Yangians
Authors: Doikou Anastasia
Published: April 2005

It is well known that integrable models associated to rational R matrices give rise to certain non-Abelian symmetries known as Yangians. Analogously boundary symmetries arise when general but still integrable boundary conditions are implemented, as originally argued by Delius, Mackay, and Short from the field theory point of view, in the context of the principal chiral model on the half-line. In the present study we deal with a discrete quantum mechanical system with boundaries, that is the N site gl(n) open quantum spin chain. In particular, the open spin chain with two distinct types of boundary condition known as soliton preserving and soliton nonpreserving is considered. For both types of boundaries we present a unified framework for deriving the corresponding boundary nonlocal charges directly at the quantum level. The nonlocal charges are simply coproduct realizations of particular boundary quantum algebras called boundary or twisted Yangians, depending on the choice of boundary conditions. Finally, with the help of linear intertwining relations between the solutions of the reflection equation and the generators of the boundary or twisted Yangians we are able to exhibit the exact symmetry of the open spin chain, namely we show that a number of the boundary nonlocal charges are in fact conserved quantities.
Impact of 7-TeV∕c large hadron collider proton beam on a copper target
Authors: Tahir N. A. , Goddard B. , Kain V. , Schmidt R. , Shutov A. , Lomonosov I. V. , Piriz A. R. , Temporal M. , Hoffmann D. H. H. , Fortov V. E.
Published: April 2005

The large hadron collider (LHC) will allow for collision between two 7TeV∕c proton beams, each comprising 2808 bunches with 1.1×1011 protons per bunch, traveling in opposite direction. The bunch length is 0.5ns and two neighboring bunches are separated by 25ns so that the duration of the entire beam is about 89μs. The beam power profile in the transverse direction is a Gaussian with a standard deviation of 0.2mm. The energy stored in each beam is about 350MJ that is sufficient to melt 500kg of copper. In case of a failure in the machine protection systems, the entire beam could impact directly onto an accelerator equipment. A first estimate of the scale of damage resulting from such a failure has been assessed for a solid copper target hit by the beam by carrying out three-dimensional energy deposition calculations and two-dimensional numerical simulations of the hydrodynamic and thermodynamic response of the target. This work has shown that the penetration depth of the LHC protons will be between 10 and 40m in solid copper. These calculations show that material conditions obtained in the target are similar to those planned for beam impact at dedicated accelerators designed to study the physics of high-energy-density states of matter, for example, the Facility for Antiprotons and Ion Research at the Gesellschaft für Schwerionenforschung, Darmstadt [W. F. Henning, Nucl. Instrum Methods Phys. Res. B 214, 211 (2004)].
Dual-frequency capacitive discharges: Effect of low-frequency current on electron distribution function
Authors: Kim H. C. , Lee J. K.
Published: April 2005

In low-pressure dual-frequency capacitive discharges, the effect of the low-frequency current on the electron distribution function (EDF) was investigated through the particle-in-cell simulation with Monte Carlo collision model. As the low-frequency (2MHz) current increases for the fixed high-frequency (27MHz) current, the EDF changes from Druyvesteyn to bi-Maxwellian (in the absence of secondary electron emission) or Maxwellian type (in case with secondary electron emission), along with the significant drop in the effective electron temperature. When the role of secondary electron emission is negligible, the EDF transition is attributed to the transition from collisional to collisionless property (but not stochastic heating) of the low-energy electrons. The Ramsauer minimum which makes low-energy electrons less collisional plays an important role in making this transition as well as in determining the spatial electric field structure. When the role of secondary electron emission is significant, the transition is attributed to the α-γ transition.
Stochastic heating of dust particles with fluctuating charges
Authors: de Angelis U. , Ivlev A. V. , Morfill G. E. , Tsytovich V. N.
Published: April 2005

The results from the kinetic theory of dusty plasmas, which consistently takes into account the charging and Coulomb collisions of plasma particles with dust, are used to show that, due to the dust charge fluctuations in dust-dust interactions, energy is not conserved in the subsystem of dust particles. The growth rate of the dust mean energy is found proportional to the mean square dust charge fluctuations, as physically expected.
Self-similarity of Rayleigh–Taylor mixing rates
Authors: George E. , Glimm J.
Published: April 2005

We establish a renormalized self-similar scaling law for fluid mixing in the deeply compressible regime. Compressibility introduces a new length scale into the mixing but our time dependent analysis of the density contrast largely removes the effects of this length scale, so that self-similarity is maintained. Dynamically induced density changes lead to a dynamic Atwood number to measure density contrasts. We improve previous density renormalizations to allow a unified treatment of mass diffusion and compressible density stratification in a range of weakly to strongly compressible three-dimensional multimode Rayleigh–Taylor simulations. Some of these simulations use front tracking to prevent numerical interfacial mass diffusion, while the others are untracked and diffusive. Using the dynamic Atwood number A(t) as opposed to the customary t=0 Atwood number A=A(t=0) to define growth rate constants, approximate universality of the mixing rate constant αb is obtained at low compressibility. Furthermore, earlier results giving consistent simulation, experiment and theory for nearly incompressible mixing, are now extended to show renormalized self-similar scaling with increases in the mixing rates for simulations of highly compressible mixing. The renormalized (i.e., dynamic Atwood number corrected) mixing rates of the diffusive and nondiffusive simulations agree, and show very similar compressibility dependence, with self-similar mixing rates tripling as compressibility becomes strong.
Quantitative measurement of sheet resistance by evanescent microwave probe
Authors: Wang Zhengyu , Kelly Michael A. , Shen Zhi-Xun , Shao Lin , Chu Wei-Kan , Edwards Hal
Published: April 2005

Quantitative measurement of microwave sheet resistance by a novel type of near-field microwave microscope—Evanescent Microwave Probe (EMP)—has been demonstrated. The data cover a wide range of sheet resistance from the metal limit to the insulator limit. Both finite element analysis (FEA) and a simple coaxial ring model have been shown to fit the data well. The demonstration of sheet resistance measurement with high spatial resolution in the GHz range shows the potential of EMP for semiconductor metrology applications. The data also reveal issues related to the large penetration depth, allowing substrate properties to affect the signal.
Stokes constants for a singular wave equation
Authors: Linnæus Staffan
Published: April 2005

The Stokes constants for arbitrary-order phase-integral approximations are calculated when the square of the wave number has either two simple zeros close to a second-order pole or one simple zero close to a first-order pole. The treatment is based on uniform approximations. All parameters may assume general complex values.
Liquefaction of catalyst during carbon single-walled nanotube growth
Authors: Harutyunyan A. R. , Tokune T. , Mora E.
Published: April 2005

Two groups of cobalt nanoparticles with spherical and disk shape were used to grow carbon single-walled nanotubes by chemical vapor deposition. To elucidate the synthesis conditions and for comparison purpose, a third group of cobalt catalyst prepared by common wet chemistry was used. After the synthesis, electron-microscopic studies revealed that the disk-shape particles with size less than 20nm were transformed into spheres. Meanwhile, calorimetric measurements showed that the given synthesis temperature was lower than the melting point of the catalyst nanoparticles. Our result supports a growth concept based on the formation of nanotubes on carbon-induced liquefied metal nanoparticles.
Negative refraction of a combined double S-shaped metamaterial
Authors: Chen Hongsheng , Ran Lixin , Huangfu Jiangtao , Zhang Xianmin , Chen Kangsheng , Grzegorczyk Tomasz M. , Kong Jin Au
Published: April 2005

We present a combined double S-shaped metamaterial structure that exhibits a left-handed property over a wide frequency band of 6GHz. The transmission experiment, phase measurement, and prism refraction experiment from the structure confirm the presence of the negative index of refraction.
Mechanical strength of nanocrystalline/amorphous Al90Fe5Gd5 composites produced by rolling
Authors: Jiang W. H. , Atzmon M.
Published: April 2005

Mechanical deformation is expected to be an alternative route for synthesizing nanocrystalline/amorphous matrix composites. However, it is found that nanocrystalline/amorphous Al90Fe5Gd5 composites produced by cold rolling have lower hardness than the as-spun, fully amorphous, alloy. Much smaller pileups are observed around indents in rolled samples than in the as-spun sample. Combining high-resolution transmission electron microscopy with Fourier transform and image filtering, many nanovoids are observed in the shear bands near the boundary with the undeformed matrix.
Laser stimulated radiative attachment
Authors: Zon B. A.
Published: April 2005

A mechanism for molecular negative ion (anion) formation under irradiation of neutral molecules by synchronized laser and electron pulses is considered. Numerical estimates are obtained for the efficiency of this process in cases of valence-bound and dipole-bound anions. The proposed mechanism allows, in principle, one to detect molecules with their absolute concentration at the level of ∼106cm−3 corresponding to a relative concentration of ∼10−13 under atmospheric pressure.
Nd-doped GdVO4 films prepared by pulsed-laser deposition on SiO2∕Si substrate
Authors: Dong Z. G. , Wang F. Y. , Fan Y. X. , Lu P. , Zhu S. N. , Lim P. K. , Tang T. B.
Published: April 2005

Nd-doped GdVO4(Nd:GdVO4) films with a-axis preferred orientation were fabricated on SiO2∕Si substrate by pulsed-laser deposition. Fluorescences at around 1065.0 and 1342.5 nm, corresponding to F3∕24→I11∕24 and F3∕24→I13∕24 transitions, respectively, were excited simultaneously with an 808 nm diode laser. Waveguide behaviors in the film were investigated by using the prism coupling technique at the wavelength of 632.8 nm. Both TE and TM mode spectra revealed that favorable light confinements were achieved within the Nd:GdVO4 waveguide layer. Additionally, the optically anisotropic properties of the film were studied in detail.
Realization of inverse saturable absorption by intracavity third-harmonic generation for efficient nonlinear mirror mode-locking
Authors: Datta P. K. , Mukhopadhyay S. , Samanta G. K. , Das S. K. , Agnesi A.
Published: April 2005

A technique of suppressing passive Q-switching by inverse saturable absorption in a cw nonlinear mirror mode-locked laser is presented. The nonlinear mirror saturable absorber consists of a second-harmonic generation crystal and a dichroic mirror while the inverse saturable loss is realized by intracavity third-harmonic generation. The inverse saturation reduces significantly the critical intracavity pulse energy for stable, self-starting, self-sustained, and power scalable cw mode-locking. Two LiB3O5 crystals are employed to realize the technique in a diode array pumped Nd:YVO4 oscillator providing a peak power of 918W, pulse width of 29ps, and repetition rate of 170MHz.
Electrical properties of plasma display panel with Mg1−xZnxO protecting thin films deposited by a radio frequency magnetron sputtering method
Authors: Jung E. Y. , Lee S. G. , Sohn S. H. , Lee D. K. , Kim H. K.
Published: April 2005

In order to improve the material properties of the protective layer for alternating current plasma display panels, a small amount of ZnO was added to the MgO protective layer. The electrical properties and the surface characteristics of the Mg1−xZnxO films, deposited by a radio frequency magnetron sputtering method, were investigated. As the concentration of ZnO increases, the crystallinity of Mg1−xZnxO thin films improves and the grain size becomes larger. The firing and the sustaining voltages of panels with the Mg1−xZnxO protective layers, when the concentration of ZnO was 0.5at.%, was reduced by 20V, compared with the conventional panels with the MgO protective layers. It was also found that the panels with Mg1−xZnxO protective layers show the higher discharge intensity as the ZnO content increases at the same applied voltages, compared with panels with the conventional MgO protective layers.
Collapse of stamps for soft lithography due to interfacial adhesion
Authors: Hsia K. J. , Huang Y. , Menard E. , Park J.-U. , Zhou W. , Rogers J. , Fulton J. M.
Published: April 2005

Collapse of elastomeric elements used for pattern transfer in soft lithography is studied through experimental measurements and theoretical modeling. The objective is to identify the driving force for such collapse. Two potential driving forces, the self-weight of the stamp and the interfacial adhesion, are investigated. An idealized configuration of periodic rectangular grooves and flat punches is considered. Experimental observations demonstrate that groove collapse occurs regardless of whether the gravitational force promotes or suppresses such collapse, indicating that self-weight is not the driving force. On the other hand, model predictions based on the postulation that interfacial adhesion is the driving force exhibit excellent agreement with the experimentally measured collapse behavior. The interfacial adhesion energy is also evaluated by matching an adhesion parameter in the model with the experimental data.
Plasma-photocatalyst interaction: Production of oxygen atoms in a low pressure discharge
Authors: Guaitella O. , Gatilova L. , Rousseau A.
Published: April 2005

A pulsed dc low pressure discharge in air (210 Pa) is used to study the mechanisms of activation of a photocatalytic material (TiO2) under plasma exposure. It is first shown that the presence of TiO2 inside the plasma region leads to a strong increase of the reduced electric field. Time resolved measurement of the atomic oxygen density is performed by actinometry during a 10 ms pulse at a low repetition rate (1 Hz) with and without TiO2 pellets inside the plasma region. The presence of TiO2 pellets strongly increases the O atom density during the first millisecond, but this effect saturates for longer exposure times.
Resolving hydrogen binding sites by pressure—A first-principles prediction for ZnO
Authors: Limpijumnong Sukit , Zhang S. B.
Published: April 2005

The binding sites and vibrational frequencies ω of H in ZnO are studied by first-principles total-energy calculations. In the past, different experiments have observed different primary H vibrational modes, making the comparison with theory, and hence the identification of the most favorable H site, difficult. Here, we show that by applying a hydrostatic pressure, one should be able to make an unambiguous distinction, in particular, between the bond center sites and antibonding sites. This is because ω should increase with pressure for the former but decrease for the latter with the magnitude of calculated slopes about 4cm−1∕GPa, which should be large enough to measure.
Site-controlled InAs quantum dots regrown on nonlithographically patterned GaAs
Authors: Meneou K. , Cheng K. Y. , Zhang Z. H. , Tsai C. L. , Xu C. F. , Hsieh K. C.
Published: April 2005

In this letter, a nonlithographic method for fabrication of high-quality site-controlled InAs quantum dots on GaAs is explored. The self-organized pores in nanochannel alumina (NCA) are used to define the nucleation sites of the site-controlled quantum dots. The pattern from the NCA is transferred to the GaAs substrate by electrochemical etching. The first layer of regrown InAs dots preferentially locate at the bottom of the etch pits on the GaAs substrate. Furthermore, cross-sectional transmission electron microscopy shows that when multiple layers of InAs dots are regrown, the dots will exhibit vertical alignment. To show the excellent optical quality of the regrown quantum dots, photoluminescence spectra are studied; room-temperature photo luminescence from the regrown dots is achieved.
Growth of InN quantum dots on N-polarity GaN by molecular-beam epitaxy
Authors: Yoshikawa A. , Hashimoto N. , Kikukawa N. , Che S. B. , Ishitani Y.
Published: April 2005

We investigated the growth behaviors of InN quantum dots (QDs) on N-polarity GaN by molecular-beam epitaxy. The N-polarity growth has been intentionally used to raise the temperature to facilitate formation of high-quality dots. It was found that the InN QDs could be grown up to 550°C the Stranski–Kastanov growth mode with the wetting layer thickness of about 1 monolayer, which was confirmed by the simultaneous in situ observations of reflection high-energy electron diffraction and spectroscopic ellipsometry. The density and the diameter of typical InN QDs grown at 450–550°C were the order of 1011cm−2 and 15–20nm, respectively.
Cooling to 208K by optical refrigeration
Authors: Thiede J. , Distel J. , Greenfield S. R. , Epstein R. I.
Published: April 2005

We report cooling to record low temperatures by optical refrigeration with ytterbium-doped zirconium–barium–lanthanum–aluminum–sodium-fluoride glass. The glass cooling element was mounted in vacuum in a low-thermal-emissivity chamber and pumped with the light from a diode-pumped solid state Yb:YAG (ytterbium-doped yttrium-aluminum-garnet) laser. Starting from room temperature, the glass cooling element reached a minimum temperature of ∼208K when pumped with ∼10W of 1026-nm light. The heat load at minimum temperature was ∼29mW.
Effects of light illumination on field emission from CuO nanobelt arrays
Authors: Chen Jun , Huang N. Y. , Deng S. Z. , She J. C. , Xu N. S. , Zhang Weixin , Wen Xiaogang , Yang Shihe
Published: April 2005

Effects of pulsed and continuous light illumination on field emission from CuO nanobelt arrays have been studied by using a transparent anode technique. It is found that, at low-field emission current level, the field emission current generally increases under a pulsed irradiation; at an emission current level of 1.1μA, a 19% increase in emission current was recorded. The photoinduced current increase is reduced with increasing emission current and is undetectable when the emission current is higher than 15μA. On the other hand, a long time illumination of the sample decreases the field emission current. Possible physical mechanisms behind the observed phenomena are discussed.
Thermoelectric properties of InSb and Ga0.03In0.97Sb thin films grown by metalorganic vapor-phase epitaxy
Authors: Yamaguchi Shigeo , Nagawa Yoshihito , Kaiwa Nakaba , Yamamoto Atsushi
Published: April 2005

We studied the thermoelectric properties of InSb and Ga0.03In0.97Sb thin films grown by metalorganic vapor-phase epitaxy targeting a thermoelectric device with a high electron mobility. For InSb on sapphire, the maximum power factor (Pf) was 3.5×10−3W∕mK at 723K, and for InSb on SiO2 glass, the maximum Pf was 2.4×10−3W∕mK at 723K. For Ga0.03In0.97Sb on sapphire, the maximum Pf was 2.5×10−3W∕mK at 723K, and for Ga0.03In0.97Sb on SiO2 glass, the maximum Pf was 3.4×10−3W∕mK at 723K.
Tb 3 + -doped KPb2Br5: Low-energy phonon mid-infrared laser crystal
Authors: Roy U. N. , Hawrami R. H. , Cui Y. , Morgan S. , Burger A. , Mandal Krishna C. , Noblitt Caleb C. , Speakman S. A. , Rademaker K. , Payne S. A.
Published: April 2005

Crystals of potassium lead bromide (KPB), a moisture-insensitive low-energy phonon laser host, were synthesized and purified. High-quality undoped and Tb3+-doped (nominal doping concentration was 5mol% TbBr3) KPb2Br5 were grown by the vertical Bridgman technique. X-ray diffraction measurements indicated that, at room temperature, the material was monoclinic with space group P21∕c, while at a high temperature the phase transformed to orthorhombic form. A reversible phase transition was observed around 256°C upon the heating and cooling cycle from differential scanning calorimetric measurements. The material was found to be transparent in the broad range from ∼0.4μmto25μm and above. The transmission spectrum of a Tb3+-doped crystal showed different absorption bands of Tb3+ at 4.5μm, 3μm, 2.3μm, and 2μm corresponding to F67–Fα7 transitions, for α=2–5. The maximum phonon energy of undoped KPb2Br5 at room temperature was determined to be 134cm−1 from Raman scattering spectrum.
Peculiarities of electron emission from the cathode in an abnormal glow discharge
Authors: Bokhan A. P. , Bokhan P. A. , Zakrevsky D. E.
Published: April 2005

Emissive properties of cold cathodes under the conditions of abnormal glow discharges are considered. Unlike the earlier made investigations, account is taken of alloying the surface layer by fast atoms generated in the cathode fall region. Atom implantation into the cathode to a depth of 10 nm changes the electron emission in a gas discharge radically as compared with vacuum conditions. Potential emission is reduced because of an increase in the surface work function. Kinetic emission is enhanced owing to an increase of the inelastic energy losses by fast atoms in the cathode material. Also greatly amplified is photoemission; moreover, its mechanism is changed.
Anomalous bias dependence of tunnel magnetoresistance in a magnetic tunnel junction
Authors: Mukhopadhyay Soumik , Das I. , Pai S. P. , Raychaudhuri P.
Published: April 2005

We have fabricated a spin-polarized tunneling device based on half-metallic manganites incorporating Ba2LaNbO6 as an insulating barrier. An anomalous bias dependence of tunnel magnetoresistance (TMR) has been observed, the first of its kind in a symmetric electrode tunnel junction with a single insulating barrier. The bias dependence of TMR shows an extremely sharp zero-bias anomaly, which can be considered as a demonstration of the drastic density of states variation around the Fermi level of the half-metal. This serves as strong evidence for the existence of minority-spin tunneling states at the half-metal–insulator interface.
Efficient organic light-emitting diodes with phosphorescent platinum complexes containing N∧C∧N-coordinating tridentate ligand
Authors: Sotoyama Wataru , Satoh Tasuku , Sawatari Norio , Inoue Hiroshi
Published: April 2005

We describe the phosphorescent characteristics of two platinum complexes containing an N∧C∧N-coordinating tridentate ligand: platinum(II) 3,5-di(2-pyridyl)toluene chloride [Pt(dpt)Cl] and a newly synthesized platinum(II) 3,5-di(2-pyridyl)toluene phenoxide [Pt(dpt)(oph)], together with the performance of organic light-emitting diodes (OLEDs) prepared with these complexes as phosphors. Films containing each one of the complexes in a 4,4’-N,N’-dicalbazolylbiphenyl (CBP) host showed highly efficient photoluminescence. The fabricated OLEDs exhibited high efficiencies; the maximum external quantum efficiency of the device with Pt(dpt)(oph) phosphor after correction of angular dependence of emission was found to be 16.5%. The luminance half decay time of the Pt(dpt)(oph) device under a constant-current operation was considerably longer than that of the Pt(dpt)Cl device.
Pressure-dependent photoluminescence study of ZnO nanowires
Authors: Shan W. , Walukiewicz W. , Ager J. W. , Yu K. M. , Zhang Y. , Mao S. S. , Kling R. , Kirchner C. , Waag A.
Published: April 2005

The pressure dependence of the photoluminescence (PL) transition associated with the fundamental bandgap of ZnO nanowires has been studied at pressures up to 15 GPa. The near-bandedge luminescence emission is found to shift toward higher energy with applied pressure at a rate of 29.2 meV/GPa with a small second-order term of −0.38meV∕GPa2. An effective hydrostatic deformation potential −3.92±0.15eV for the direct bandgap of the ZnO nanowires is derived from the results. The broad green emission band in ZnO depends on pressure with a linear slope of 15.9 meV/GPa and a quadratic coefficient of −0.71meV∕GPa2. The results indicate that the initial states involved in the emission process are deep localized states.
Distance control for a near-field scanning microwave microscope in liquid using a quartz tuning fork
Authors: Kim Songhui , Yoo Hyunjun , Lee Kiejin , Friedman Barry , Gaspar Mariafrancis A. , Levicky Rastislav
Published: April 2005

We demonstrate a scanning near-field microwave microscope (NSMM) in the liquid environment using a tuning fork shear-force feedback method to control the distance between tip and sample. Only the probe tip for the NSMM is immersed in water. The dry part of the probe is attached to one prong of a quartz tuning fork and directly coupled to a high-quality dielectric resonator at an operating frequency f=4.5–5.5GHz. This distance control method is independent of the local microwave characteristics. The amplitude of the tuning fork was used as a set point of the distance control parameter in the liquid. To demonstrate the distance regulation system, we present the NSMM images of a copper film in air and liquid without and with readjustment of the distance set point, as well as an image of a DNA film in buffer solution. Imaging under buffer environments is of particular interest for future studies of biomolecular association reactions on solid supports.
Measurement of the phase shift upon reflection from photonic crystals
Authors: Istrate Emanuel , Sargent Edward H.
Published: April 2005

The phase dependence of light reflected from colloidal photonic crystals is measured using a large resonant cavity and self-assembled colloidal photonic crystals. We measure the expected phase shift upon reflection from the photonic crystal, which varies from 0to180deg across the photonic crystal stop band. These measurements are then fed directly into the design of photonic crystal cavities. We obtain a measure for the precision needed in the fabrication of photonic crystal resonant cavities.
The Mediated Electrodeposition of Polypyrrole on Aluminium Alloy
Authors: Levine Kirill L. , Tallman Dennis E. , Bierwagen Gordon P.
Published: April 2005

The direct electrodeposition of conjugated polymers onto active metals such as aluminium and its alloys is complicated by the concomitant oxidation of the metal that occurs at the positive potential required for polymer formation/deposition. We have developed an approach that uses electron transfer mediation to reduce the deposition potential of polypyrrole on aluminium and aluminium alloy by nearly 500 mV, permitting film deposition from aqueous solution with nearly 100% current efficiency. The mediator used in this initial work was 4,5-dihydroxy-1,3-benzenedisulfonate (DHBDS, disodium salt), which also served as the dopant or counter ion in the polymer. To better understand the mediation process, a series of substituted benzene compounds have been explored for their mediating properties. From these studies, we conclude that both the hydroxyl and the sulfonate functionalities of DHBDS appear to play a role in the mediated electrodeposition at aluminium alloy. New mediators for the electrodeposition of polypyrrole on Al alloy are suggested.
The Rotating Cylinder Electrode (RCE) and its Application to the Electrodeposition of Metals
Authors: Low C. T. John , Ponce de Leon Carlos , Walsh Frank C.
Published: April 2005

The application of rotating cylinder electrodes (RCEs) to electrodeposition has progressed significantly over the last decade. New tools for theoretical and experimental investigations have been developed in academia and in industry, with some RCE devices being commercially developed. This paper reviews the continued application of RCEs to quantitative electrodeposition studies of single metals, alloys, and composite, multilayered, and nanostructured electrodeposits with a constant or controlled range of current densities along the RCE under turbulent flow conditions. Rotating cylinder electrode electrochemical reactors, enhanced mass transport, rotating cylinder Hull cell, and uniform and non-uniform current and potential distributions are considered. The applications of ultrasound, porous reticulated vitreous carbon cathodes, expanded metal/baffles, and jet flow around the RCE are also included. The effects of electrolyte flow and cathode current density on electrodeposition have been rationalized. Directions for future RCE studies are proposed.
The Thermodynamics of Solid - Solid Interfaces in Systems of Fixed Mass
Authors: Fletcher Stephen
Published: April 2005

The textbook approach to interfacial excess quantities, due to Gibbs, is valid only at fixed volume. In the present work we develop an alternative approach to interfacial excess quantities, valid at fixed mass. For solid–solid interfaces this has several advantages over the Gibbs treatment such as (a) non-zero interfacial excess volumes appear naturally in the treatment, (b) analogues of the bulk-phase Maxwell relations are readily obtained, and (c) formulae for the pressure and temperature dependence of the interfacial tension are derived in a transparent way.
The rate of water entry into dry sand and calculation of the advancing contact angle
Authors: Emerson WW , Bond RD
Published: April 2005

For water entry into a vertical column of dry sand, the height of capillary rise, h, is defined for the present purposes as the maximum height of capillary rise in the sand, below which the moisture content is uniform. Previous experimental results on water entry into dry sand have been reviewed to show the validity and usefulness of this definition. The rise of the wetting front into a vertical column of sand was measured, the rate of rise of the wetting front was plotted against the reciprocal of the height of rise, and 1/h was found by extrapolating the line to zero rate of rise. For water-repellent sand a positive hydrostatic head was applied to the base of the sand to obtain an adequate number of points for the extrapolation. This pressure was adjusted so that the initial rate of advance of water into the sand was about equal to that of water into the ignited sand with no positive applied pressure. The advancing contact angle averaged over the wetted surface area of the sand was then calculated from the ratio of the values of h obtained with sand before and after ignition. The contact angle of a water-repellent sand has been shown to be higher than 90�. This explains the difficulty experienced in the field of wetting these sands. Two remedial measures are suggested: one is to cultivate and mix the soil to give a uniform average contact angle, the other is to cut slots so that a positive hydrostatic pressure can be applied to the deeper patches of high contact angle sand.
Solubility of simple aluminium compounds expected in soils. I. Hydroxides and oxyhydroxides
Authors: Raupach MR
Published: April 2005

Results from dissolution equilibria with four aluminium hydroxide and oxyhydroxide compounds in M/100 K2SO4 over pH range 3.5-10, when examined by plotting the negative logarithm of the aluminium ion concentration against the pH, showed that AlOH2+, Al(OH)2+, and Al(OH)4-, hydrated and possibly polymeric, were formed. For pH>7, precipitated aluminium hydroxide (containing mostly boehmite) gave bayerite equilibria while gibbsite, diaspore, and bauxite gave gibbsite equilibria. For p H t 7 amorphous A1(OH)3 and corundum equilibria were observed. Using accepted free energy values, the following were estimated at 2.5�: KS1 = log [(AlOH2+)(OH-)2] = -23.31 and KS2 = log [(Al(OH)2+)(OH-)] = - 14.04 for amorphous Al(OH), and KS1 = -24.41 and KS2 = -15.14 for corundum and also �F� values of 164.9, -215.1, and -313.9 kcal for A10H2+, Al(OH)2+, and Al(0H)-4 respectively in aqueous solution.
Solubility of simple aluminium compounds expected in soils. II. Hydrolysis and conductance of Al3+
Authors: Raupach M
Published: April 2005

The results of conductimetric measurements on dilute aluminium chloride solutions at 25� were found to be best fitted by the limiting equivalent conductances A01/3Al3 + = A01/2AlOH2+ = 58.2 with the parameter for ionic diameter 6.0A and by *K1 = log [(AlOH2+)(H+)/(Al3+)] = - 5.05 when it was assumed that AlOH2+ and H+ concentrations produced by hydrolysis were equal in the measured solutions. Potentiometric measurements and calculations from solubility work gave *K1 = -5.00 and -4.97 respectively. After small changes, e.g. by aging, dilute aluminium salt solutions conform to the solubility expression for aluminium hydroxide, log [(AlOH2+) (OH-)2] = -23.31.
Solubility of simple aluminium compounds expected in soils. III. Aluminium ions in soil solutions and aluminium phosphates in soils
Authors: Raupach M
Published: April 2005

Many published values for the aluminium contents of displaced solutions and extracts from soils at varying pH values have been examined and found to be quite compatible with recent findings that A1OH2+, Al(OH)2+, or their polymers are dissolution products from aluminium hydroxide. Variation of phosphate content has also been considered and no case can be made for the presence of variscite in the systems examined. As far as aluminium compounds are concerned, the evidence is in favour of sorption of phosphate by the aluminium oxyhydroxide surfaces in the soil.
Solubility of simple aluminium compounds expected in soils. IV. Reactions of aluminium hydroxide under acid conditions
Authors: Raupach M
Published: April 2005

Solubility constants for aluminium hydroxides and oxyhydroxides previously obtained (Raupach 1963a) were supported by further studies at 20� and 50�. Polymeric aluminium ions were not present in systems obeying Ks1 = -log [ AlOH2+) (OH-) 2] = 23.31 at 25�C When 5 < -log [AlOH2+] < 3 no Al3+ ions are found in solution because the aluminium hydroxide surface readily binds Al3' ions, produced slowly in solution, and releases AlOH2+ ions. This also happens in soil solutions.
Activity of polyphenolic constituents of leaves of Eucalyptus and other species in complexing and dissolving iron oxide
Authors: Hingston FJ
Published: April 2005

The polyphenolic constituents of aqueous extracts from the leaves of 11 Eucalyptus species and 7 other Western Australian tree and shrub species are examined in relation to their capacity to complex iron and dissolve iron oxides. The leaves of the Eucalyptus species contain mainly gallic acid, ellagic acid, hydrolysable tannins, leucoanthocyanins, and flavonol glycosides. Gallic acid forms soluble complexes with ferrous and ferric iron which are relatively less stable than ferrous aa'-dipyridyl. Tannic acid forms a soluble ferrous complex which is more stable than ferrous aa'-dipyridyl. The complexes formed on addition of ferric iron to the hydrolysable tannins, leucoanthocyanins, and flavonol glycosides are apparently insoluble, but can be solubilized by reduction to ferrous iron in the presence of sufficiently strong reducing agents. Ferrous complexes with flavonol glycosides and leucoanthocyanins are less stable than ferrous aa'-dipyridyl. No simple correlation could be established between the total quantity of polyphenols and iron oxide solubilized under aerobic conditions. This may be due to the contrasting effects of solution and precipitation of iron-polyphenol complexes which are shown by different classes of polyphenols and to the appreciable capacity shown by substances other than polyphenols to dissolve iron oxides.
Soil studies at Swan Hill, Victoria, Australia. II. Dune moulding and parna formation
Authors: Churchward HM
Published: April 2005

The study involving a granulometric examination of the sedimentary nature of layers of aeolian material at Swan Hill, Vic., shows that the wind erosion of soils leading to the sorting of the components can result in the formation of a dust or suspended component and a saltation or dune-sand component. The former material, parna, contains most of the clay and lime of the original soil material. This is considered to be composed of fine aggregates associated with a companion sand which, in the neighbourhood of the dunes, has a diameter range of 70 to 90 �. This material is normally separated from the saltation sand by wind action. However, under conditions of accession of parna at a site where saltation sand is in motion the parna becomes mixed with the saltation sand in a graduated manner, least being deposited at the crest. The periodic moulding of the dunes by local erosion and deposition and accession of regional parna is discussed.
Soil studies at Swan Hill, Victoria, Australia. III. Some aspects of soil development on aeolian materials
Authors: Churchward HM
Published: April 2005

The progress of soil development at Swan Hill has been examined by the comparison of four successively older soil profiles which have all developed on aeolian materials at different times in history. The initial development is one of homogenization effected by biotic agencies that obliterates the depositional fabric and structure. There are found to be several other trends in profile differentiation which have advanced further in each older soil. These trends include the leaching of lime from the surface and its concentration into concretions, and the removal of clay from the surface and its deposition as coatings to grains, pores, and peds and as a dense matrix.
The measurement of chemical potential of phosphate in soil suspensions
Authors: Fordham AW
Published: April 2005

The dependence of Schofield's phosphate potential on the soil/solution ratio and the time of shaking of the suspensions was reaffirmed and studied in some detail. Some factors which could affect the measurement of potential were investigated, but the cause of the observed variations of potential was not resolved.
Studies on soluble silica in soils. I. The sorption of silicic acid by soils and minerals
Authors: Beckwith RS , Reeve R
Published: April 2005

Soils, representing a variety of great soil groups, were shaken with solutions containing monosilicic acid at concentrations not exceeding 135 p.p.m. The residual concentrations of monosilicic acid under near-equilibrium conditions depended on the nature of the soil, the level of added monosilicic acid, the solution : soil ratio and the pH of the soil suspension. The experimental results indicate that the residual concentration of monosilicic acid is controlled by an adsorption equilibrium which is dependent on pH; with acidification below pH 8-9 the residual concentration in soil suspensions steadily increases. Several samples of oxides and hydroxides of iron and aluminium were also shown to sorb monosilicic acid from solution. This sorption resembled that recorded for soils in its strong dependence on pH in the range 4-9. Sesquioxides appear to be responsible for much of the capacity of soils to sorb monosilicic acid. Wyoming bentonite and two kaolinite samples also sorbed monosilicic acid, at least from suspensions of pH above 7, and some natural and synthetic carbonates sorbed monosilicic acid at their natural pH values. Such minerals may contribute to the ability of some alkaline soils to sorb monosilicic acid. The avidity with which some soils sorb added monosilicic acid suggests that some native silica occurs in soils in the sorbed state. Some implications of this suggestion and of the other results are discussed in relation to some previous work on soils and natural waters, possible adsorption mechanisms, and some pedogenetic processes.
Isotopic studies on the uptake of nitrogen by pasture grasses. I. Recovery of fertilizer nitrogen from the soil : plant system using rhodes grass in pots
Authors: Martin AE , Henzell EF , Ross PS , Haydock KP
Published: April 2005

Results are reported of the first of a series of studies on the fate of nitrogen applied to soil under pasture. Two series of pretreatments (nil and 200 lb/ac N) were imposed on Rhodes grass, Chloris gayana Kunth, grown on a light-textured soil in pots in a glasshouse. Subsequently the grass was cut 3.3 cm above the soil surface and labelled ammonium nitrate (15NH4NO3) was added in amounts up to the equivalent of 800 lb/ac N. The fate of this added nitrogen was determined at the end of the experiment by analyzing the total contents of each pot for nitrogen and for 15N. The quantity of total nitrogen found in the pots (which included both labelled and unlabelled forms), and that of labelled nitrogen, were each linearly related to the amount of ammonium nitrate added. Regression analysis showed that 93.6% of added total nitrogen, and 94.0% of added labelled nitrogen, was recovered from the soil : plant system. These recoveries did not differ significantly from one another, indicating that the loss fell equally on labelled ammonium nitrogen and some unlabelled form of nitrogen; it is possible that this loss took place from the added ammonium nitrate fertilizer. There was no evidence to indicate the stage at which this loss occurred. Nitrogen pretreatment had a marked effect on the weight of stubble and roots in the pots when the ammonium nitrate was applied, but had no effect on nitrogen loss. Errors encountered during chemical and mass spectrometric analysis of the soil and plant material are discussed.
The chemical nature of soil organic phosphorus. I. Inositol phosphates
Authors: Cosgrove DJ
Published: April 2005

Gradient elution chromatography, using a column of anion exchange resin, Dowex AG I-X8, has been used to separate and isolate constituents of the 'phytin' fraction of soil organic matter. In addition to the commonly occurring myoinositol hexaphosphate the presence of the corresponding derivatives of DL-inositol and scylloinositol was demonstrated. Of the lower inositol phosphates present pentaphosphates appeared to be the major constituents. The occurrence in nature of inositols, other than the myoinositol, as phosphorylated derivatives, has not previously been recorded. Present knowledge is insufficient to decide whether soil inositol phosphates are of plant origin or accumulated through the activities of soil microorganisms.