bluuebunny/crossref_metadata_2025 huggingface dataset:
Principal processes occurring at simultaneous bombardment of tungsten by carbon and deuterium ions
Authors: Bizyukov Ivan , Krieger Karl
Published: October 2007

Simultaneous bombardment of tungsten with deuterium and carbon leads to both tungsten erosion and implantation of carbon and deuterium in the W surface. These processes have been studied experimentally by simultaneous bombardment of magnetron deposited W layers with D and C ions at energies in the keV range. The experimental results were compared to numerical simulations using the TRIDYN code. The key parameter separating steady-state W erosion from continuous growth of a C layer on the surface is the C fraction in the incident flux. The dynamical change of the surface composition with increasing fluence was monitored in situ by ion beam analysis. The experimental results are well reproduced by the TRIDYN simulations, which are based on a kinematic model of ion scattering in the target. Significant contributions by chemical effects outside the scope of the TRIDYN model can therefore be excluded. A negligible contribution of chemical effects is also supported by the measured concentrations of retained D, which are not sufficient to create a significant contribution of chemical reactions with carbon to implantation and sputtering. Surface roughness of the specimens was found to be the key parameter for the observed shift of the transition point from continuous C layer growth to steady-state tungsten erosion with increasing D fraction in the incident ions.
Low temperature deposition and effect of plasma power on tin oxide thin films prepared by modified plasma enhanced chemical vapor deposition
Authors: Ansari S. G. , Dar M. A. , Dhage M. S. , Kim Young Soon , Shin Hyung-Shik , Ansari Z. A.
Published: October 2007

This work presents low temperature (200 and 300°C) thin film deposition of tin oxide (SnO2) using modified plasma enhanced chemical vapor deposition as a function of radio frequency power (100–500W). Stannic chloride (SnCl4) was used as precursor and oxygen (O2, 300SCCM) as reactant gas. Fine granular morphology was observed with tetragonal rutile structure grown along the [110] direction, at all the deposition conditions. Higher plasma power resulted in smoother morphology, improved crystallinity, and enhanced conductivity. Electrical resistivity value of as low as ∼0.01Ωcm was obtained at the deposition temperature of 300°C and 250W of plasma power.
Photoluminescence degradation in GaN induced by light enhanced surface oxidation
Authors: Liu Wenbao , Sun Xian , Zhang Shuang , Chen Jun , Wang Hui , Wang Xiaolan , Zhao Degang , Yang Hui
Published: October 2007

The exponential degradation of the photoluminescence (PL) intensity at the near-band-gap was observed in heavily doped or low-quality GaN with pristine surface under continuous helium-cadmium laser excitation. In doped GaN samples, the degradation speed increased with doping concentration. The oxidation of the surface with laser irradiation was confirmed by x-ray photoemission spectroscopy measurements. The oxidation process introduced many oxygen impurities and made an increase of the surface energy band bending implied by the shift of Ga 3d binding energy. The reason for PL degradation may lie in that these defect states act as nonradiative centers and/or the increase of the surface barrier height reduces the probability of radiative recombination.
The effect of plasma shaping on turbulent transport and E×B shear quenching in nonlinear gyrokinetic simulations
Authors: Kinsey J. E. , Waltz R. E. , Candy J.
Published: October 2007

Nonlinear gyrokinetic simulations with kinetic electron dynamics are used to study the effects of plasma shaping on turbulent transport and E×B shear in toroidal geometry including the presence of kinetic electrons using the GYRO code. Over 120 simulations comprised of systematic scans were performed around several reference cases in the local, electrostatic, collisionless limit. Using a parameterized local equilibrium model for shaped geometry, the GYRO simulations show that elongation κ (and its gradient) stabilizes the energy transport from ion temperature gradient (ITG) and trapped electron mode (TEM) instabilities at fixed midplane minor radius. For scans around a reference set of parameters, the GYRO ion energy diffusivity, in gyro-Bohm units, approximately follows a κ−1 scaling which is qualitatively similar to recent experimental energy confinement scalings. Most of the κ scaling is due to the shear in the elongation rather than the local κ itself. The κ scaling for the electrons is found to vary and can be stronger or weaker than κ−1 depending on the wavenumber where the transport peaks. The κ scaling is weaker when the energy diffusivity peaks at low wavenumbers and is stronger when the peak occurs at high wavenumbers. The simulations also demonstrate a nonlinear upshift in the critical temperature gradient as the elongation increases due to an increase in the residual zonal flow amplitude. Triangularity is found to be slightly destabilizing and its effect is strongest for highly elongated plasmas. Finally, we find less E×B shear is needed to quench the transport at high elongation and low aspect ratio. A new linear E×B shear quench rule, valid for shaped tokamak geometry, is presented.
Heterodyne speckle velocimetry of Poiseuille flow
Authors: Alaimo M. D. , Potenza M. A. C. , Magatti D. , Ferri F.
Published: October 2007

We review the technique named heterodyne speckle velocimetry and present two applications for testing the method with a fluid moving under the conditions of Poiseuille flow. The fluid was seeded with small tracking particles (diameter 300 nm) and fluxed between the two parallel planes of a cell with constant or variable cross section. In the first case the velocity distribution was constant along the direction parallel to the planes and was in excellent agreement with the expected Poiseuille profile along the orthogonal direction. In the second case, where velocity gradients were present also along the planes, the technique was able to reconstruct both the orthogonal Poiseuille profile and the in-plane two dimensional mapping of the velocity vectors, with the possibility of measuring the fluid flux within an accuracy of 1%.
Dielectric diffuseness and conductivity study of CuNb2O6 incorporated BaTiO3 synthesized by chemical route
Authors: Dhak Debasis , Dhak Prasanta , Ghorai Tanmay , Pramanik Panchanan
Published: October 2007

The dielectric ceramics of BaTi1−3xCuxNb2xO3 (BTCN) with x=0.0, 0.1, 0.2, and 0.3 were prepared by chemical route with the help of soluble tartarate complexes of Ti4+ and Nb5+ ions. It was found that the substitution of Cu2+ and Nb5+ at the Ti site of BTCN ceramics caused a diffused phase transition. Discontinuous grain growth accompanied with excellent dielectric diffuseness was found with increasing concentration of substitution. The dielectric diffuseness (γ) was found to be maximum to 1.92 at the substitution of BTCN, x=0.1. The maximum solubility limit was found up to the entire composition range studied. A dielectric study of these compounds as a function of temperature suggested that with increasing substitution concentration the dielectric constant increased to maximum at x=0.3 with minimum tangent loss and the Curie temperature shifted onwards to the higher temperature side. The bulk conductivity indicated an Arrhenius-type thermally activated process. The variation of ac conductivity as a function of frequency obeyed the Jonscher power law.
Incongruent reaction of Cu–(InGa) intermetallic precursors in H2Se and H2S
Authors: Hanket G. M. , Shafarman W. N. , McCandless B. E. , Birkmire R. W.
Published: October 2007

The reaction pathways to form Cu(InGa)Se2 or Cu(InGa)S2 films at 450°C from metallic precursors were evaluated by reacting Cu–In–Ga films in H2Se or H2S for 10, 30, or 90min and characterizing the phase composition of the resulting films. A starting composition comprising Cu9(In0.64Ga0.36)4 and In phases was detected by x-ray diffraction in Cu–Ga–In precursors annealed at 450°C in an Ar atmosphere. When the precursors were reacted in H2Se, a graded Cu(InGa)Se2 film was formed with a Ga-rich composition and residual Cu–Ga intermetallics at the interface with the Mo back contact. The intermetallic compounds were observed to evolve from Cu9(In0.64Ga0.36)4 to Cu9Ga4 with increasing selenization time. Reaction in H2S formed inhomogeneous Cu(InGa)S2 with Cu–In intermetallics. The results are consistent with thermochemical predictions of the preferential reaction of In with Se, and Ga with S. These reaction preferences can explain the formation of a graded Cu(InGa)Se2 film during reaction in H2Se and provide a refined understanding of the reaction sequence in two-step H2Se∕H2S processes.
Allan variance of frequency fluctuations due to momentum exchange and thermomechanical noises
Authors: Palasantzas George A.
Published: October 2007

We investigate the Allan variance of nanoresonators with random rough surfaces under the simultaneous influence of thermomechanical and momentum exchange noises. Random roughness is observed in various surface engineering processes, and it is characterized by the roughness amplitude w, the lateral correlation length ξ, and the roughness exponent 0<H<1. The roughness influence becomes significant for measurement time τA so that ωoτA∼1, with ωo the fundamental resonance frequency. The Allan variance increases significantly with increasing roughness (decreasing H and/or increasing ratio w∕ξ) if the quality factor due to gas collisions is smaller than the intrinsic quality factor associated with thermomechanical noise.
Molecular discrimination of a mixture with single-beam Raman control
Authors: von Vacano Bernhard , Motzkus Marcus
Published: October 2007

A single beam of shaped femtosecond pulses is used to coherently control the Raman excitation and to simultaneously observe the resulting vibrations of molecules in a mixture resolved in time. This experimentally simple scheme opens up exciting new possibilities for the selective detection of dangerous chemical or bacterial species, such as spores, and will serve to enhance contrast in nonlinear Raman chemical imaging.
Semiclassical coherent-state propagator for many spins
Authors: Braun Carol , Garg Anupam
Published: October 2007

We obtain the semiclassical coherent-state propagator for a many-spin system with an arbitrary Hamiltonian.
Efficient evaluation of analytic vibrational frequencies in Hartree-Fock and density functional theory for periodic nonconducting systems
Authors: Izmaylov Artur F. , Scuseria Gustavo E.
Published: October 2007

We report a method for the efficient evaluation of analytic energy second derivatives with respect to in-phase nuclear coordinate displacements within Hartree-Fock and Kohn-Sham density functional theories using Gaussian orbitals and periodic boundary conditions. The use of an atomic orbital formulation for all computationally challenging steps allows us to adapt the direct space fast multipole method for the Coulomb-type infinite summations. Our implementation also exploits the local character of the exact Hartree-Fock exchange in nonconducting systems. Exchange-correlation contributions are computed using extensive screening and fast numerical quadratures. We benchmark our scheme for in-phase vibrational frequencies of a trans-polyacetylene chain, a two-dimensional boron nitride sheet, and bulk diamond with the 6-31G** basis set and various density functionals. A study of computational scaling with the size of the unit cell for trans-polyacetylene reveals subquadratic scaling for our scheme.
A statistical simulation approach for early stage thin-film growth from vapor-deposited atoms
Authors: Chen Peilong , Wang T. Y. , Luo M. F.
Published: October 2007

We present a statistical simulation method for the early stage of thin-film growth from vapor-deposited atoms, which simulate evolution of density, size, and spatial distribution of the growing islands on a supported substrate. The method describes surface processes of the deposited atoms by random walks and the Arrhenius form. However, we utilize the statistical behavior of the atomic surface processes over a time scale significantly larger than the typical attempt time (10−13s). This novel method saves enormous simulation time and thus overcomes the difficulty resulting from the remarkable gap between the typical experimental deposition rates and the attempt frequency. The statistical approach is verified by comparisons with direct step-by-step (kinetic Monte Carlo) simulations at large deposition rates. Results obtained for low deposition rates matching experimental conditions are also presented.
The influence of sample conductivity on local anodic oxidation by the tip of atomic force microscope
Authors: Cambel Vladimír , Šoltýs Ján
Published: October 2007

We analyze the role of the electric field distribution in the nano-oxidation process realized by the tip of atomic force microscope (AFM) experimentally and theoretically as well. We show the importance of the sample conductivity and the water bridge in the process applied to bulk GaAs and Ga[Al]As heterostructures in both contact and noncontact AFM modes. The experimental results show that the lines written in contact mode are much wider then those written in noncontact mode. Moreover, saddlelike profile lines can appear for high-resistive samples. These effects are explained by the numerical simulations using finite-element method. We show that the electric field distribution in the system tip-sample is controlled by the sample conductivity. In the case of low-conductive samples, maximum field is located apart from the tip apex for both contact and noncontact AFM modes.
Deterministic processing of alumina with ultrashort laser pulses
Authors: Furmanski J. , Rubenchik A. M. , Shirk M. D. , Stuart B. C.
Published: October 2007

Ultrashort pulsed lasers can accurately ablate materials which are refractory, transparent, or are otherwise difficult to machine by other methods. The typical method of machining surfaces with ultrashort laser pulses is by raster scanning, or the machining of sequentially overlapping linear trenches. Experiments in which linear trenches were machined in alumina at various pulse overlaps and incident fluences are presented, and the dependence of groove depth on these parameters established. A model for the machining of trenches based on experimental data in alumina is presented, which predicts and matches observed trench geometry. This model is then used to predict optimal process parameters for the machining of trenches for maximal material removal rate for a given laser.
Effect of bifurcation angle in tree-shaped microchannel networks
Authors: Wang Xiang-Qi , Mujumdar Arun S. , Yap Christopher
Published: October 2007

Tree-shaped microchannel networks are being considered for thermal designs that require high heat transfer densities for the cooling of modern electronics. Here we investigate the effect of the bifurcation angles in the constructal nets on the fluid flow and heat transfer characteristics of such networks using a three-dimensional computational fluid dynamics approach. Results show that the bifurcation angle is an important factor which determines the performance of such cooling nets. Surface temperature distributions and pressure drop along the flow paths are analyzed and compared. For the same boundary conditions, a lower temperature and pressure variation is observed at lower bifurcation angles.
Geometrical modeling of fibrous materials under compression
Authors: Maze Benoit , Vahedi Tafreshi Hooman , Pourdeyhimi Behnam
Published: October 2007

Many fibrous materials such as nonwovens are consolidated via compaction rolls in a so-called calendering process. Hot rolls compress the fiber assembly and cause fiber-to-fiber bonding resulting in a strong yet porous structure. In this paper, we describe an algorithm for generating three dimensional virtual fiberwebs and simulating the geometrical changes that happen to the structure during the calendering process. Fibers are assumed to be continuous filaments with square cross sections lying randomly in the x or y direction. The fibers are assumed to be flexible to allow bending over one another during the compression process. Lateral displacement is not allowed during the compaction process. The algorithm also does not allow the fibers to interpenetrate or elongate and so the mass of the fibers is conserved. Bending of the fibers is modeled either by considering a constant “slope of bending” or constant “span of bending.” The influence of the bending parameters on the propagation of compression through the material’s thickness is discussed. In agreement with our experimental observations, it was found that the average solid volume fraction profile across the thickness becomes U shaped after the calendering. The application of these virtual structures in studying transport phenomena in fibrous materials is also demonstrated.
Low-voltage organic thin-film transistors with large transconductance
Authors: Klauk Hagen , Zschieschang Ute , Halik Marcus
Published: October 2007

We have developed an organic thin-film transistor (TFT) technology that aims at providing a good balance of static and dynamic performance parameters. An inverted staggered (bottom-gate, top-contact) device structure with patterned metal gates, a room-temperature-deposited gate dielectric providing a capacitance of 0.7μF∕cm2, and vacuum-deposited pentacene as the semiconductor were employed. The TFTs have a channel length of 10μm, a carrier mobility of 0.4cm2∕Vs, an on/off current ratio of 107, a subthreshold swing of 100mV/decade, and a transconductance per channel width of 40μS∕mm. Ring oscillators operate with supply voltages as low as 2V and with signal propagation delays as low as 200μs per stage.
Mechanism of enhancement/deterioration of boiling heat transfer using stable nanoparticle suspensions over vertical tubes
Authors: Narayan G. Prakash , Anoop K. B. , Das Sarit K.
Published: October 2007

Boiling heat transfer using nanofluids has been a subject of a few investigations in the past few years and incongruous results have been reported in literature regarding the same. Conflicting explanations for deterioration of pool boiling heat transfer coefficient at higher concentrations (4–16wt%) have been presented by various researchers. Recently, a few works have reported a significant enhancement in pool boiling heat transfer coefficient at lower concentrations (0.32–1.25wt%) and the physical reasons for this have not been explained. The present work is aimed at removing these ambiguities. Experiments have been carried out by using stable water based nanofluids containing alumina nanoparticles (average sizes of 47 and 150nm) with vertical tubular heaters of various surface roughnesses (48, 98, and 524nm). It has been observed that with the rough heater (Ra=524nm), heat transfer is significantly enhanced and the enhancement reaches ∼70% at a particle loading of 0.5wt%. With the smooth heater (Ra=48nm), heat transfer is significantly deteriorated and the heat flux reduction reaches ∼45% at a particle loading of 2wt%. Further, it has been observed that a parameter which is the ratio of average size of the particle to the average roughness value of the heater can explain the reported controversy in the pool boiling behavior of these suspensions.
Spallation in laser shock-loaded tin below and just above melting on release
Authors: de Rességuier T. , Signor L. , Dragon A. , Severin P. , Boustie M.
Published: October 2007

Spall damage in solid materials has been one of the most widely studied shock-induced phenomena for several decades, for both applied and basic scientific motivations. Comparatively, very little data can be found yet about spallation in liquid metals. In a recent paper, we have reported an exploratory investigation of liquid spall in tin samples melted upon laser shocks of very high intensities. Here, we present further experimental results obtained over a lower pressure range, where we focus on the transition from the ductile fracture behavior of solid tin to the cavitating spall expected above melting. This transition is clearly evidenced from both time-resolved free surface velocity measurements and post-test examination of the recovered targets. The drop in tensile strength associated with melting is evaluated from the velocity profiles. Detailed views of the fracture surfaces in the spall craters provide an insight into the cavitation process. Experimental data are compared to preliminary computations to determine the loading pressures and to assess the overall consistency of our interpretation of the results.
The growth of interfacial passive layers under thermal passivation of integrated Pb(Zr,Ti)O3 thin films
Authors: Jiang A. Q. , Lin Y. Y. , Tang T. A.
Published: October 2007

Pb ( Zr , Ti ) O 3 thin films suffer from progressive degradation of remanent polarization after thermal shocks of step-by-step integration of ferroelectric random access memories. The polarization degradation accelerates with the enhancement of the shocked number per time interval as well as thermal duration at 350°C in the flowing air. However, the degradation progresses in a slow rate for the sample heated in a sealed furnace with a homogeneous distribution of a thermal field. The previous steplike current transient of domain switching with time in the film becomes tilted in conjunction with polarization degradation, which is recognized as the growth of interfacial passive layers during thermal treatment. The interfacial passive layers can grow throughout the film thickness under the thermal stressing for 279h with a dielectric constant of εi=48, as estimated from capacitance-voltage (C-V) measurements, and time evolution of interfacial-layer thickness at 350°C is thus derived from domain switching performance. The thickened interfacial passive layers essential for polarization degradation can build in an enhanced internal field in backswitching of partial domains to block the total polarization reversal.
High resolution gamma ray tomography scanner for flow measurement and non-destructive testing applications
Authors: Hampel U. , Bieberle A. , Hoppe D. , Kronenberg J. , Schleicher E. , Sühnel T. , Zimmermann F. , Zippe C.
Published: October 2007

We report on the development of a high resolution gamma ray tomography scanner that is operated with a Cs-137 isotopic source at 662keV gamma photon energy and achieves a spatial image resolution of 0.2linepairs∕mm at 10% modulation transfer function for noncollimated detectors. It is primarily intended for the scientific study of flow regimes and phase fraction distributions in fuel element assemblies, chemical reactors, pipelines, and hydrodynamic machines. Furthermore, it is applicable to nondestructive testing of larger radiologically dense objects. The radiation detector is based on advanced avalanche photodiode technology in conjunction with lutetium yttrium orthosilicate scintillation crystals. The detector arc comprises 320 single detector elements which are operated in pulse counting mode. For measurements at fixed vessels or plant components, we built a computed tomography scanner gantry that comprises rotational and translational stages, power supply via slip rings, and data communication to the measurement personal computer via wireless local area network.
Density measurements of noncrystalline materials at high pressure with diamond anvil cell
Authors: Hong Xinguo , Shen Guoyin , Prakapenka Vitali B. , Rivers Mark L. , Sutton Stephen R.
Published: October 2007

We describe an x-ray absorption method for in situ density measurement of non-crystalline materials in the diamond anvil cell using a monochromatic synchrotron x-ray microbeam. Sample thickness, which is indispensable in the absorption method, can be determined precisely by extrapolating the thickness profile of the gasket obtained by x-ray absorption and diffraction measurements. Diamond deformation across the sample chamber becomes noticeable at high pressures above 10GPa, which can be monitored with a precision better than 1%, as demonstrated by measurements on crystalline Ag. We have applied the developed method to measure densities of the classic network-forming GeO2 glass in octahedral form at pressures up to 56GPa. The fit to the pressure-volume data with the Birch-Murnaghan equation from 13to56GPa gives parameters of V0=23.2±0.4cm3∕mol and K=35.8±3.0GPa, assuming that K′=4. This method could be applicable for in situ determination of the density of liquids and other noncrystalline materials using a diamond anvil cell up to ultrahigh pressures.
Performance trade-offs in single-photon avalanche diode miniaturization
Authors: Finkelstein Hod , Hsu Mark J. , Zlatanovic Sanja , Esener Sadik
Published: October 2007

Single-photon avalanche diodes (SPADs) provide photons’ time of arrival for various applications. In recent years, attempts have been made to miniaturize SPADs in order to facilitate large-array integration and in order to reduce the dead time of the device. We investigate the benefits and drawbacks of device miniaturization by characterizing a new fast SPAD in a commercial 0.18μm complementary metal oxide semiconductor technology. The device employs a novel and efficient guard ring, resulting in a high fill factor. Thanks to its small size, the dead time is only 5ns, resulting in the fastest reported SPAD to date. However, the short dead time is accompanied by a high after-pulsing rate, which we show to be a limiting parameter for SPAD miniaturization. We describe a new and compact active-recharge scheme which improves signal-to-noise tenfold compared with the passive configuration, using a fraction of the area of state-of-the-art active-recharge circuits, and without increasing the dead time. The performance of compact SPADs stands to benefit such applications as high-resolution fluorescence-lifetime imaging, active-illumination three-dimensional imagers, and quantum key distribution systems.
Monitoring x-ray beam damage on lipid films by an integrated Brewster angle microscope/x-ray diffractometer
Authors: Danauskas Stephen M. , Ratajczak Maria K. , Ishitsuka Yuji , Gebhardt Jeffrey , Schultz David , Meron Mati , Lin Binhua , Lee Ka Yee C.
Published: October 2007

We describe an integrated Brewster angle microscope (BAM), Langmuir trough, and grazing incidence x-ray diffraction assembly. The integration of these three techniques allows for the direct observation of radiative beam damage to a lipid monolayer at the air-water interface. Although beam damage has been seen in x-ray measurements, it has not been directly observed in situ at the micron scale. Using this integrated assembly, we examined the effects of radiative beam damage on Langmuir monolayers of 1,2-dimyristoyl-sn-glycero-3-[phospho-L-serine] (DMPS), 1:1 DMPS:1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine, and 1:1 DMPS:1,2-dioleoyl-sn-glycero-3-phosphocholine held at a constant surface pressure. For constant surface pressure experiments, we observed a marked decrease in the surface area of the film upon exposure to the beam due to photodissociation. For a condensed lipid film, a change in refractive index of the film was observed post-beam-exposure, indicating areas of damage. For DMPS in an oxygenated environment, the Bragg peak intensity decreased with beam exposure. In mixed monolayer systems, with saturated and unsaturated lipids, an increase in the number of small saturated lipid domains was seen as the unsaturated lipid was preferentially damaged and lost from the monolayer. We show that BAM is a highly effective technique for in situ observation of the effects of radiative damage at the air/water interface during a synchrotron experiment.
2-amino-1-propanol versus 1-amino-2-propanol: Valence band and C 1s core-level photoelectron spectra
Authors: Catone D. , Turchini S. , Contini G. , Zema N. , Irrera S. , Prosperi T. , Stener M. , Di Tommaso D. , Decleva P.
Published: October 2007

Valence band and C 1s core-level photoelectron spectra of S-(+)-2-amino-1-propanol (alaninol) and S-(+)-1-amino-2-propanol (isopropanolamine) have been studied by means of synchrotron radiation photoelectron spectroscopy in gas phase. The alaninol, the reduced derivative of the alanine, is a good test system of amino acid-like structures. The isopropanolamine, presenting the inversion of the two functional groups of the alaninol at the chiral carbon, offers the opportunity to study the effect of –OH and –NH2 structural position on the photoelectron spectra. The influence of the conformational contribution on the electronic structure and the photoelectron spectra has been interpreted using density functional and ab initio theoretical calculations. Agreement has been achieved by taking into account the presence, in gas phase, of two conformers with different population ratios in both chiral systems. The C 1s core-level spectra of alaninol and isopropanolamine are reported and the peak positions of the three carbon atoms of the molecules are assigned.
Current-in-plane magnetoresistance of spin valve elliptical rings
Authors: Jung W. , Castaño F. J. , Ross C. A.
Published: October 2007

The giant magnetoresistance of NiFe∕Cu∕Co∕IrMn spin valve elliptical rings with 3.2∕1.9μm major/minor diameter and widths of 340–370nm has been characterized in a current-in-plane geometry. Spin valve rings show asymmetric magnetoresistance curves with three different resistance levels. Minor loop magnetoresistance measurements, which correspond to the switching of only the NiFe free layer, demonstrate that individual control of the chirality of the magnetization vortex in each ferromagnetic layer is possible, enabling at least 16 distinct magnetic configurations to be formed in a spin valve ring.
Suppression of suprathermal ions from a colloidal microjet target containing SnO2 nanoparticles by using double laser pulses
Authors: Higashiguchi Takeshi , Kaku Masanori , Katto Masahito , Kubodera Shoichi
Published: October 2007

We have demonstrated suppression of suprathermal ions from a colloidal microjet target plasma containing tin-dioxide (SnO2) nanoparticles irradiated by double laser pulses. We observed a significant decrease of the tin and oxygen ion signals in the charged-state-separated energy spectra when double laser pulses were irradiated. The peak energy of the singly ionized tin ions decreased from 9to3keV when a preplasma was produced. The decrease in the ion energy, considered as debris suppression, is attributed to the interaction between an expanding low-density preplasma and a main laser pulse.
Investigation of magnetic and electronic coupling between two (Ga,Mn)As layers in (Ga,Mn)As∕GaAs∕(Ga,Mn)As magnetic tunnel junctions
Authors: Ge Z. , Zhou Y. Y. , Cho Y.-J. , Liu X. , Furdyna J. K. , Dobrowolska M.
Published: October 2007

The coupling between the two magnetic layers in a series of (Ga,Mn)As∕GaAs∕(Ga,Mn)As magnetic tunnel junctions with different nonmagnetic spacer thicknesses tNM were studied by magnetization and planar Hall effect (PHE) measurements. The PHE data indicate that the magnetization reversals of the two layers are strongly correlated when the tNM is less than 3nm and are independent when tNM is larger than 15nm. From the results, it is concluded that considerable redistribution of hole wave functions plays a major role for small tNM. The PHE results for the sample with 6nm spacer also suggest an antiferromagnetic interlayer exchange coupling.
Enhanced transmission of periodic, quasiperiodic, and random nanoaperture arrays
Authors: Rockstuhl Carsten , Lederer Falk , Zentgraf Thomas , Giessen Harald
Published: October 2007

We numerically and experimentally show that the enhanced transmission of an array of annular nanoapertures is independent of the nanoaperture’s arrangement. This holds if this enhancement primarily relies on Fabry-Pérot resonances of guided modes in the nanoapertures. We observe a comparable transmission spectrum for a periodic, a quasiperiodic, and even a random nanoaperture arrangement. This complements previous findings where the enhanced transmission of a circular nanoaperture array was shown to rely on the excitation of surface-plasmon polaritons at the metal surface and thus strongly depended on the nanoaperture’s arrangement.
Thickness dependency of 180° stripe domains in ferroelectric ultrathin films: A first-principles-based study
Authors: Lai Bo-Kuai , Ponomareva Inna , Kornev Igor , Bellaiche L. , Salamo Greg
Published: October 2007

A first-principles-based scheme is used to investigate the thickness dependency of domain width of 180° stripe domains in Pb(Zr,Ti)O3 ultrathin films. Our study shows that (1) more metastable states with energy closer to the 180° stripe domain ground state occur in thicker films, (2) the Kittel law is valid for 180° stripe domains when the film thickness is above 1.6nm, and (3) below 1.2nm, the Kittel law cannot be applied anymore due to the disappearance of domains. The thickness dependency of the domain morphology is also discussed.
Coherent anti-Stokes Raman scattering polarized microscopy of three-dimensional director structures in liquid crystals
Authors: Kachynski A. V. , Kuzmin A. N. , Prasad P. N. , Smalyukh I. I.
Published: October 2007

We demonstrate three-dimensional vibrational imaging of director structures in liquid crystals using coherent anti-Stokes Raman scattering (CARS) polarized microscopy. Spatial mapping of the structures is based on sensitivity of a polarized CARS signal to the orientation of anisotropic molecules in liquid crystals. As an example, we study structures in a smectic material and demonstrate that single-scan CARS and two-photon fluorescence images of molecular orientation patterns are consistent with each other and with the structure model.
Control of corolla monosymmetry in the Brassicaceae
Iberis amara
Authors: Busch Andrea , Zachgo Sabine
Published: October 2007

Establishment of morphological novelties has contributed to the enormous diversification of floral architecture. One such novelty, flower monosymmetry, is assumed to have evolved several times independently during angiosperm evolution. To date, analysis of monosymmetry regulation has focused on species from taxa where monosymmetry prevails, such as the Lamiales and Fabaceae. In
Antirrhinum majus
, formation of a monosymmetric corolla is specified by the activity of the
TCP
transcription factors
CYCLOIDEA
(
CYC
) and
DICHOTOMA
(
DICH
). It was shown that establishment of monosymmetry likely requires an early asymmetric floral expression of
CYC
homologs that needs to be maintained until late floral stages. To understand how
CYC
homologs might have been recruited during evolution to establish monosymmetry, we characterized the likely
CYC
ortholog
IaTCP1
from
Iberis amara
(Brassicaceae). Species of the genus
Iberis
form a monosymmetric corolla, whereas the Brassicaceae are otherwise dominated by genera developing a polysymmetric corolla. Instead of four equally sized petals,
I. amara
produces two small adaxial and two large abaxial petals. The timing of
IaTCP1
expression differs from that of its
Arabidopsis
homolog
TCP1
and other
CYC
homologs.
IaTCP1
lacks an asymmetric early expression but displays a very strong differential expression in the corolla at later floral stages, when the strongest unequal petal growth occurs. Analysis of occasionally occurring
peloric Iberis
flower variants and comparative functional studies of
TCP
homologs in
Arabidopsis
demonstrate the importance of an altered temporal
IaTCP1
expression within the Brassicaceae to govern the formation of a monosymmetric corolla.
Grass roots chemistry:
meta
-Tyrosine, an herbicidal nonprotein amino acid
Authors: Bertin Cécile , Weston Leslie A. , Huang Tengfang , Jander Georg , Owens Thomas , Meinwald Jerrold , Schroeder Frank C.
Published: October 2007

Fine fescue grasses displace neighboring plants by depositing large quantities of an aqueous phytotoxic root exudate in the soil rhizosphere. Via activity-guided fractionation, we have isolated and identified the nonprotein amino acid
m
-tyrosine as the major active component.
m
-Tyrosine is significantly more phytotoxic than its structural isomers
o
- and
p
-tyrosine. We show that
m
-tyrosine exposure results in growth inhibition for a wide range of plant species and propose that the release of this nonprotein amino acid interferes with root development of competing plants. Acid hydrolysis of total root protein from
Arabidopsis thaliana
showed incorporation of
m
-tyrosine, suggesting this as a possible mechanism of phytotoxicity.
m
-Tyrosine inhibition of
A. thaliana
root growth is counteracted by exogenous addition of protein amino acids, with phenylalanine having the most significant effect. The discovery of
m
-tyrosine, as well as a further understanding of its mode(s) of action, could lead to the development of biorational approaches to weed control.
Short-term meditation training improves attention and self-regulation
Authors: Tang Yi-Yuan , Ma Yinghua , Wang Junhong , Fan Yaxin , Feng Shigang , Lu Qilin , Yu Qingbao , Sui Danni , Rothbart Mary K. , Fan Ming , Posner Michael I.
Published: October 2007

Recent studies suggest that months to years of intensive and systematic meditation training can improve attention. However, the lengthy training required has made it difficult to use random assignment of participants to conditions to confirm these findings. This article shows that a group randomly assigned to 5 days of meditation practice with the integrative body–mind training method shows significantly better attention and control of stress than a similarly chosen control group given relaxation training. The training method comes from traditional Chinese medicine and incorporates aspects of other meditation and mindfulness training. Compared with the control group, the experimental group of 40 undergraduate Chinese students given 5 days of 20-min integrative training showed greater improvement in conflict scores on the Attention Network Test, lower anxiety, depression, anger, and fatigue, and higher vigor on the Profile of Mood States scale, a significant decrease in stress-related cortisol, and an increase in immunoreactivity. These results provide a convenient method for studying the influence of meditation training by using experimental and control methods similar to those used to test drugs or other interventions.
Hydrogen bond dynamics in aqueous NaBr solutions
Authors: Park Sungnam , Fayer M. D.
Published: October 2007

Hydrogen bond dynamics of water in NaBr solutions are studied by using ultrafast 2D IR vibrational echo spectroscopy and polarization-selective IR pump–probe experiments. The hydrogen bond structural dynamics are observed by measuring spectral diffusion of the OD stretching mode of dilute HOD in H
2
O in a series of high concentration aqueous NaBr solutions with 2D IR vibrational echo spectroscopy. The time evolution of the 2D IR spectra yields frequency–frequency correlation functions, which permit quantitative comparisons of the influence of NaBr concentration on the hydrogen bond dynamics. The results show that the global rearrangement of the hydrogen bond structure, which is represented by the slowest component of the spectral diffusion, slows, and its time constant increases from 1.7 to 4.8 ps as the NaBr concentration increases from pure water to ≈6 M NaBr. Orientational relaxation is analyzed with a wobbling-in-a-cone model describing restricted orientational diffusion that is followed by complete orientational randomization described as jump reorientation. The slowest component of the orientational relaxation increases from 2.6 ps (pure water) to 6.7 ps (≈6 M NaBr). Vibrational population relaxation of the OD stretch also slows significantly as the NaBr concentration increases.
S
-nitrosohemoglobin deficiency: A mechanism for loss of physiological activity in banked blood
Authors: Reynolds James D. , Ahearn Gregory S. , Angelo Michael , Zhang Jian , Cobb Fred , Stamler Jonathan S.
Published: October 2007

RBCs distribute oxygen to tissues, but, paradoxically, blood transfusion does not always improve oxygen delivery and is associated with ischemic events. We hypothesized that storage of blood would result in loss of NO bioactivity, impairing RBC vasodilation and thus compromising blood flow, and that repleting NO bioactivity would restore RBC function. We report that
S
-nitrosohemoglobin (SNO-Hb) concentrations declined rapidly after storage of fresh venous blood and that hypoxic vasodilation by banked RBCs correlated strongly with the amounts of SNO-Hb (
r
2
= 0.90;
P
< 0.0005). Renitrosylation of banked blood during storage increased the SNO-Hb content and restored its vasodilatory activity. In addition, canine coronary blood flow was greater during infusion of renitrosylated RBCs than during infusion of
S
-nitrosothiol-depleted RBCs, and this difference in coronary flow was accentuated by hypoxemia (
P
< 0.001). Our findings indicate that NO bioactivity is depleted in banked blood, impairing the vasodilatory response to hypoxia, and they suggest that SNO-Hb repletion may improve transfusion efficacy.
Evolution of adverse changes in stored RBCs
Authors: Bennett-Guerrero Elliott , Veldman Tim H. , Doctor Allan , Telen Marilyn J. , Ortel Thomas L. , Reid T. Scott , Mulherin Melissa A. , Zhu Hongmei , Buck Raymond D. , Califf Robert M. , McMahon Timothy J.
Published: October 2007

Recent studies have underscored questions about the balance of risk and benefit of RBC transfusion. A better understanding of the nature and timing of molecular and functional changes in stored RBCs may provide strategies to improve the balance of benefit and risk of RBC transfusion. We analyzed changes occurring during RBC storage focusing on RBC deformability, RBC-dependent vasoregulatory function, and
S
-nitrosohemoglobin (SNO-Hb), through which hemoglobin (Hb) O
2
desaturation is coupled to regional increases in blood flow
in vivo
(hypoxic vasodilation). Five hundred ml of blood from each of 15 healthy volunteers was processed into leukofiltered, additive solution 3-exposed RBCs and stored at 1–6°C according to AABB standards. Blood was subjected to 26 assays at 0, 3, 8, 24 and 96 h, and at 1, 2, 3, 4, and 6 weeks. RBC SNO-Hb decreased rapidly (1.2 × 10
−4
at 3 h vs. 6.5 × 10
−4
(fresh) mol
S
-nitrosothiol (SNO)/mol Hb tetramer (
P
= 0.032, mercuric-displaced photolysis-chemiluminescence assay), and remained low over the 42-day period. The decline was corroborated by using the carbon monoxide-saturated copper-cysteine assay [3.0 × 10
−5
at 3 h vs. 9.0 × 10
−5
(fresh) mol SNO/mol Hb]. In parallel, vasodilation by stored RBCs was significantly depressed. RBC deformability assayed at a physiological shear stress decreased gradually over the 42-day period (
P
< 0.001). Time courses vary for several storage-induced defects that might account for recent observations linking blood transfusion with adverse outcomes. Of clinical concern is that SNO levels, and their physiological correlate, RBC-dependent vasodilation, become depressed soon after collection, suggesting that even “fresh” blood may have developed adverse biological characteristics.
Determination of the density of air: a comparison of the CIPM thermodynamic formula and the gravimetric method
Authors: Madec Tanguy , Meury Paul-André , Sutour Christophe , Rabault Thierry , Zerbib Serge , Gosset André
Published: October 2007

Today, the determination of the density of air is the main source of uncertainty (10 µg) in a comparison of a platinum–iridium alloy national prototype with a stainless steel reference standard. The method currently recommended by the BIPM is to calculate this density, using a formula developed in 1981 and revised in 1991 by the CIPM, from the measured values of the pressure, temperature, hygrometry and molar fraction of CO2in air. Recent work has found significant differences between the values given by this formula and those given by a method using artefacts having identical masses and very different volumes (6.4 × 10−5with a relative uncertainty of 1.2 × 10−5). To investigate this difference, the BIPM asked the member laboratories of the Consultatitve Committee for Mass (CCM) to investigate two lines of approach:

- check the composition of the air, in particular the argon content, which may explain the discrepancies found; this is the object of a study by the chemical metrology unit of LNE (see the article by Sutouret alin this issue),

- study the behavior of artefacts during the air–vacuum transfer in a comparator that can work both in a controlled atmosphere and in a vacuum, to confirm or not confirm the discrepancies; this latter study is the object of this paper.
A Ligation-Independent Cloning Tobacco Rattle Virus Vector for High-Throughput Virus-Induced Gene Silencing Identifies Roles forNbMADS4-1and -2in Floral Development
Authors: Dong Yiyu , Burch-Smith Tessa M. , Liu Yule , Mamillapalli Padmavathi , Dinesh-Kumar Savithramma P.
Published: October 2007

Virus-induced gene silencing (VIGS) is a widely used, powerful technique for reverse genetics. VIGS vectors derived from the Tobacco rattle virus (TRV) are among the most popular for VIGS. We have developed a TRV RNA2 vector that allows the insertion of gene silencing fragments by ligation-independent cloning (LIC). This new vector has several advantages over previous vectors, particularly for applications involving the analysis of large numbers of sequences, since TRV-LIC vectors containing the desired insert are obtained with 100% efficiency. Importantly, this vector allows the high-throughput cloning of silencing fragments without the use of costly enzymes required for recombination, as is the case with GATEWAY-based vectors. We generated a collection of silencing vectors based on 400 tomato (Solanum lycopersicum) expressed sequence tags in this TRV-LIC background. We have used this vector to identify roles for SlMADS1 and its Nicotiana benthamiana homologs, NbMADS4-1 and -2 in flowering. We find that NbMADS4-1 and -2 act nonredundantly in floral development and silencing of either gene results in loss of organ identity. This TRV-LIC vector should be a valuable resource to the plant community.
Zeaxanthin Has Enhanced Antioxidant Capacity with Respect to All Other Xanthophylls in Arabidopsis Leaves and Functions Independent of Binding to PSII Antennae
Authors: Havaux Michel , Dall'Osto Luca , Bassi Roberto
Published: October 2007

The ch1 mutant of Arabidopsis (Arabidopsis thaliana) lacks chlorophyll (Chl) b. Leaves of this mutant are devoid of photosystem II (PSII) Chl-protein antenna complexes and have a very low capacity of nonphotochemical quenching (NPQ) of Chl fluorescence. Lhcb5 was the only PSII antenna protein that accumulated to a significant level in ch1 mutant leaves, but the apoprotein did not assemble in vivo with Chls to form a functional antenna. The abundance of Lhca proteins was also reduced to approximately 20% of the wild-type level. ch1 was crossed with various xanthophyll mutants to analyze the antioxidant activity of carotenoids unbound to PSII antenna. Suppression of zeaxanthin by crossing ch1 with npq1 resulted in oxidative stress in high light, while removing other xanthophylls or the PSII protein PsbS had no such effect. The tocopherol-deficient ch1 vte1 double mutant was as sensitive to high light as ch1 npq1, and the triple mutant ch1 npq1 vte1 exhibited an extreme sensitivity to photooxidative stress, indicating that zeaxanthin and tocopherols have cumulative effects. Conversely, constitutive accumulation of zeaxanthin in the ch1 npq2 double mutant led to an increased phototolerance relative to ch1. Comparison of ch1 npq2 with another zeaxanthin-accumulating mutant (ch1 lut2) that lacks lutein suggests that protection of polyunsaturated lipids by zeaxanthin is enhanced when lutein is also present. During photooxidative stress, α-tocopherol noticeably decreased in ch1 npq1 and increased in ch1 npq2 relative to ch1, suggesting protection of vitamin E by high zeaxanthin levels. Our results indicate that the antioxidant activity of zeaxanthin, distinct from NPQ, can occur in the absence of PSII light-harvesting complexes. The capacity of zeaxanthin to protect thylakoid membrane lipids is comparable to that of vitamin E but noticeably higher than that of all other xanthophylls of Arabidopsis leaves.