bluuebunny/crossref_metadata_2025 huggingface dataset:
Taylor’s regime of an autocatalytic reaction front in a pulsative periodic flow
Authors: Leconte M. , Jarrige N. , Martin J. , Rakotomalala N. , Salin D. , Talon L.
Published: May 2008

Autocatalytic reaction fronts between reacted and unreacted species may propagate as solitary waves, that is, at a constant front velocity and with a stationary concentration profile, which result from a balance between molecular diffusion and chemical reaction. A velocity field in the supporting medium may affect the propagation of such fronts through different phenomena: advection, diffusion enhancement, front shape changes, etc. Here, we report on an experimental study and lattice Bhatnagar–Gross–Krook numerical simulations of the effect of an oscillating flow on the autocatalytic reaction between iodate and arsenous acid in a Hele–Shaw cell. In the low frequency range covered by the experiments, the front behavior is controlled by the flow across the gap and is reproduced with two-dimensional numerical simulations. It is shown that the front velocity oscillates at the frequency of the flow, whereas the front width oscillates at twice that frequency. Moreover, the Taylor regime in the presence of a Poiseuille flow is fully investigated: The description obtained in the case of a stationary flow provides an analytical prediction for the sinusoidal flow. The range of parameters, for which the prediction applies, is delineated and discussed.
Laser induced fluorescence spectroscopy of NC3O
Authors: Yoshikawa Takashi , Sumiyoshi Yoshihiro , Takada Hideyuki , Hoshina Kennosuke , Endo Yasuki
Published: May 2008

Laser induced fluorescence spectra of the NC3O radical in a supersonic jet have been observed. The radical was produced in a pulsed electric discharge of HC3N and O2 diluted to 0.3% with Ar. A total of 17 vibronic bands with a radiative lifetime of ∼30ns have been observed in a region from 27000to27500cm−1. The observed vibronic bands are classified as Π1∕22–Π1∕22, Π3∕22–Π3∕22, and Σ2–Σ2 types. The upper states of the Σ2–Σ2 bands have large spin-rotation constants, which should be denoted as Σ(+) and Σ(−). From high-level ab initio calculations and rotational analyses, the observed transition was assigned to the B̃Π2–X̃A″2 transition. Dispersed fluorescence spectra from the upper Σ2 and Π2 vibronic levels have also been observed, yielding fundamental vibrational frequencies for the ν1, ν2, ν3, and ν7 modes of the ground state.
Flow mode transitions in turbulent thermal convection
Authors: Xi Heng-Dong , Xia Ke-Qing
Published: May 2008

We report an experimental study of structures and dynamics of the large-scale mean flow in Rayleigh–Bénard convection cells with aspect ratio (Γ)1, 1∕2, and 1∕3. It is found that both a single circulating roll flow structure and one with two vertically stacked counter-rotating rolls exist in the three aspect ratio cells. The average percentages of time that the large-scale mean flow spends in the single-roll mode (SRM) and the double-roll mode (DRM) are 87.1% and 0.8% for Γ=1, 69.5% and 7.9% for Γ=1∕2, and 26.7% and 34.1% for Γ=1∕3. Several routes of transitions among the different flow modes are identified. In addition, different structures for the DRM are found and their relative weights are determined. We also show direct evidence that the SRM is more efficient for heat transfer than the DRM. Although the difference is very small, it shows how changes in internal flow state can manifest in the global transport properties of the system. It is also found that the time interval between successive flow mode transitions has an exponential distribution, suggesting a Poisson process for the underlying dynamics. The duration of the flow mode transition is found to be log-normally distributed.
Determination of free energy profiles by repository based adaptive umbrella sampling: Bridging nonequilibrium and quasiequilibrium simulations
Authors: Zheng Han , Zhang Yingkai
Published: May 2008

We propose a new adaptive sampling approach to determine free energy profiles with molecular dynamics simulations, which is called as “repository based adaptive umbrella sampling” (RBAUS). Its main idea is that a sampling repository is continuously updated based on the latest simulation data, and the accumulated knowledge and sampling history are then employed to determine whether and how to update the biasing umbrella potential for subsequent simulations. In comparison with other adaptive methods, a unique and attractive feature of the RBAUS approach is that the frequency for updating the biasing potential depends on the sampling history and is adaptively determined on the fly, which makes it possible to smoothly bridge nonequilibrium and quasiequilibrium simulations. The RBAUS method is first tested by simulations on two simple systems: a double well model system with a variety of barriers and the dissociation of a NaCl molecule in water. Its efficiency and applicability are further illustrated in ab initio quantum mechanics/molecular mechanics molecular dynamics simulations of a methyl-transfer reaction in aqueous solution.
The effect of high-Z dopant on laser-driven acceleration of a thin plastic target
Authors: Badziak J. , Kasperczuk A. , Parys P. , Pisarczyk T. , Rosiński M. , Ryć L. , Wołowski J. , Suchańska R. , Krása J. , Krousky E. , Láska L. , Mašek K. , Pfeifer M. , Rohlena K. , Skala J. , Ullschmied J. , Dhareshwar L. J. , Földes I. B. , Suta T. , Borrielli A. , Mezzasalma A. , Torrisi L. , Pisarczyk P.
Published: May 2008

Acceleration of a thin (10 or 20μm) plastic foil by 120J, 0.438μm, 0.3ns laser pulse of intensity up to 1015W∕cm2 has been investigated. It is shown that the introducing a high-Z dopant to the foil causes an increase in the ablating plasma density, velocity, and collimation which, in turn, results in a remarkably higher kinetic energy and energy fluence of the flyer foil.
Evaluation of magnetoelectric coupling in a BaTiO3–Ni composite ferroic film by impedance spectroscopy
Authors: Qiao Liang , Bi Xiaofang
Published: May 2008

A ferroic film of BaTiO3 (BTO) containing 22.7at.% Ni was fabricated by the radio frequency cosputtering method. It reveals that the Ni spontaneously stays apart from the BTO phase and congregates around the BaTiO3 grains by using a high resolution transmission electron microscopy equipped with an electron dispersive spectroscopy. The impedance characterization for the BTO grains in the Ni-containing film is greatly varied with the application of different magnetic fields, while that of a BTO film remains unaffected. This indicates that a magnetoelectric coupling is induced in the ferroic film through an elastic interaction between the magnetostrictive Ni and the BTO.
On particle transport in Weibel generated magnetic fluctuations
Authors: Tautz R. C. , Shalchi A.
Published: May 2008

The problem of particle scattering in the turbulent magnetic fields generated by the Weibel instability is investigated on the basis of analytical calculations. From the dispersion relation, the growth and damping rate is calculated and inserted into a quasilinear Fokker–Planck coefficient for pitch-angle scattering, from which the scattering parallel mean free path is determined. A weak background magnetic field is included to ensure the validity of the assumption of uncorrelated wave modes, which is essential for quasilinear calculations. It is shown that, for higher values of the temperature and counterstreaming anisotropy, the parallel mean free path is reduced due to the stronger magnetic turbulence generated by the instability. Furthermore, it is shown that for relativistic particles, the parallel mean free path becomes energy independent.
On the correlation between the photoexcitation pathways and the critical energies required for ablation of poly(methyl methacrylate): A molecular dynamics study
Authors: Conforti Patrick F. , Prasad Manish , Garrison Barbara J.
Published: May 2008

The energetics initiating ablation in poly(methyl methacrylate) (PMMA) are studied using molecular dynamics (MD) simulation. The critical energy to initiate ablation in PMMA following the absorption of photons is investigated for two penetration depths along a range of fluences using a coarse-grained, hybrid Monte Carlo-MD scheme. Both heating and direct bond scission are simulated separately after photon absorption with additional transformation of material occurring via chemical reactions following the photochemical bond cleavage. For a given type of absorption and reaction channel, a critical energy can well describe the amount of energy required to initiate ablation. The simulations show a decrease in the critical energy when a greater amount of photochemistry is introduced in the system. The simulations complement experimental studies and elucidate how enhanced photochemistry lowers ablation thresholds in polymer substrates.
Shear stresses of colloidal dispersions at the glass transition in equilibrium and in flow
Authors: Crassous J. J. , Siebenbürger M. , Ballauff M. , Drechsler M. , Hajnal D. , Henrich O. , Fuchs M.
Published: May 2008

We consider a model dense colloidal dispersion at the glass transition, and investigate the connection between equilibrium stress fluctuations, seen in linear shear moduli, and the shear stresses under strong flow conditions far from equilibrium, viz., flow curves for finite shear rates. To this purpose, thermosensitive core-shell particles consisting of a polystyrene core and a cross-linked poly(N-isopropylacrylamide) shell were synthesized. Data over an extended range in shear rates and frequencies are compared to theoretical results from integrations through transients and mode coupling approaches. The connection between nonlinear rheology and glass transition is clarified. While the theoretical models semiquantitatively fit the data taken in fluid states and the predominant elastic response of glass, a yet unaccounted dissipative mechanism is identified in glassy states.
Collinear source of polarization-entangled photon pairs at nondegenerate wavelengths
Authors: Trojek P. , Weinfurter H.
Published: May 2008

We report on a simple but highly efficient source of polarization-entangled photon pairs at nondegenerate wavelengths. The fully collinear configuration of the source enables very high coupling efficiency into a single optical mode and allows the use of long nonlinear crystals. With optimized dispersion compensation, it is possible to use a free-running laser diode as pump source and to reach an entanglement fidelity of 99.4% at rates as high as 27000pairs∕s∕mW of pump power.
Enhancement of wall friction by fixed cap bubbles
Authors: Legendre Dominique , Colin Catherine
Published: May 2008

The three-dimensional flow around a hemispherical bubble fixed on a wall in a viscous linear shear flow is solved by using direct numerical simulation. The results are used to analyze the effect of the bubble presence on the wall friction. The wall drag is found to be increased by the presence of the bubble fixed on the wall whatever the value of the shear Reynolds number.
Surface kinetic roughening caused by dental erosion: An atomic force microscopy study
Authors: Quartarone Eliana , Mustarelli Piercarlo , Poggio Claudio , Lombardini Marco
Published: May 2008

Surface kinetic roughening takes place both in case of growth and erosion processes. Teeth surfaces are eroded by contact with acid drinks, such as those used to supplement mineral salts during sporting activities. Calcium-phosphate based (CPP-ACP) pastes are known to reduce the erosion process, and to favour the enamel remineralization. In this study we used atomic force microscopy (AFM) to investigate the surface roughening during dental erosion, and the mechanisms at the basis of the protection role exerted by a commercial CPP-ACP paste. We found a statistically significant difference (p<0.01) in the roughness of surfaces exposed and not exposed to the acid solutions. The treatment with the CPP-ACP paste determined a statistically significant reduction of the roughness values. By interpreting the AFM results in terms of fractal scaling concepts and continuum stochastic equations, we showed that the protection mechanism of the paste depends on the chemical properties of the acid solution.
Nuclear and excitonic spin polarization formed using cross-linearly polarized pulse pair via half-localized state in a single self-assembled quantum dot
Authors: Sasakura H. , Adachi S. , Muto S. , Hirose S. , Song H. Z. , Takatsu M.
Published: May 2008

The oscillations of excitonic and nuclear spin polarizations in an optically pumped single self-assembled In0.8Al0.2As/Al0.35Ga0.65As quantum dot (QD) were clearly observed under the excitation of a wetting layer edge at B=5 T. This indicates that an exciton pair with opposite spins is alternatively created via the half-localized state only by changing the delay time between cross-linearly polarized pulse pair. Furthermore, periodic modulation of Zeeman energy synchronizes the degree of circular polarization of photoluminescence from a single QD, indicating that the Overhauser field follows the optically created electron spin polarization in half-localized states of a QD, and the half-localized state in a QD consists of a confined electron in a discrete state and hole in the continuum state.
Size-dependent surface stress, surface stiffness, and Young’s modulus of hexagonal prism [111] β-SiC nanowires
Authors: Zhang Tong-Yi , Luo Miao , Chan Wing Kin
Published: May 2008

The present work studies the size-dependent surface stress, surface stiffness, and Young’s modulus of a prism crystalline nanowire, which is theoretically treated to be composed of a hypothetical nanowire phase, a true two-dimensional geometric surface phase, and a true one-dimensional geometric edge phase. The hypothetical nanowire phase could be elastically deformed due to relaxation of a free-standing nanowire, without any applied load, with respect to its bulk counterpart. The initially deformed nanowire phase is taken as reference in the present work in the determination of excess surface and edge energies. The theoretical results indicate that the edge phase causes the nominal specific surface energy, surface stress, and surface stiffness to be size dependent, and the surface phase and the edge phase make the nominal Young’s modulus size dependent. The edge and surface effects are more significant as the cross-sectional area of a nanowire becomes smaller. Molecular dynamics simulations on hexagonal prism [111] β-SiC nanowires were conducted and the results verified the theoretical approach and illustrated the intrinsic mechanism of the size-dependent surface properties and Young’s modulus of nanowires. The theoretical analysis and methodology are universal when the continuum concepts of surface energy, surface stress, and Young’s modulus are used to characterize mechanical properties of nanowires.
Monte Carlo simulation of carrier transport and output characteristics of terahertz quantum cascade lasers
Authors: Li H. , Cao J. C. , Lü J. T.
Published: May 2008

An ensemble Monte Carlo method, including electron-phonon, electron-electron, electron-impurity scatterings and the hot phonon effect, is used to simulate the carrier transport and output characteristics of a lasing terahertz quantum cascade laser. A simulated I-V curve fits well with the measurement at the lasing domain. Extracted output characteristics, e.g., the gain, threshold current density, and threshold bias, are in good agreement with the experimental results. All the above indicate that the proposed Monte Carlo model is a useful tool for investigating the physical characteristics of terahertz quantum cascade lasers, as well as for analyzing and optimizing device performances.
Enhanced efficiency in near-infrared inorganic/organic hybrid optical upconverter with an embedded mirror
Authors: Chen Jun , Ban Dayan , Feng Xiaodong , Lu Zhenghong , Fathololoumi Saeed , SpringThorpe Anthony J. , Liu H. C.
Published: May 2008

We report a hybrid organic-inorganic optical upconverter with an embedded mirror, which converts 1.5μm infrared light to visible light. The device was fabricated through direct tandem integration of an organic light-emitting diode with an inorganic InGaAs∕InP photodetector. It was found that the device with an embedded mirror exhibited a low turn-on voltage (∼3.2V) and an enhanced efficiency. The ratio of photocurrent-induced light with an input power density of 0.67mW∕mm2 versus dark-current-induced visible light was over 500 at a device bias of 6V at room temperature. The results show that the embedded mirror at the inorganic-organic interface plays a vital role in the performance enhancement of a hybrid upconverter.
Determination of effective shear modulus of shock-compressed LY12 Al from particle velocity profile measurements
Authors: Yu Yuying , Tan Hua , Hu Jianbo , Dai Chengda , Chen Danian , Wang Huanran
Published: May 2008

Unloading wave profile measurements using the velocity interference system for any reflector technique were performed on LY12 Al over shock stress ranging from ∼20to∼100GPa, from which longitudinal and bulk sound velocities along the quasielastic release path were evaluated. Based on the intrinsic relations under uniaxial strain conditions, the effective shear modulus defined by Cochran and Guinan (Lawrence Livermore National Laboratory Report No. UCID-17105, 1976) was correlated to the longitudinal and bulk sound velocities. Results show that the effective shear modulus calculated from the measured sound velocities decreases rapidly with the release stress and can be expressed approximately as a linear function of the release stress; the slope of the linear function depends the initial shock-loading stress. By using this linear function of the effective shear modulus, the performed numerical simulations well reproduce the release wave traces of the Al alloys observed in the present work and reported in literature.
Metamorphic approach to single quantum dot emission at 1.55μm on GaAs substrate
Authors: Semenova E. S. , Hostein R. , Patriarche G. , Mauguin O. , Largeau L. , Robert-Philip I. , Beveratos A. , Lemaître A.
Published: May 2008

We report on the fabrication and the characterization of InAs quantum dots (QDs) embedded in an indium rich In0.42Ga0.58As metamorphic matrix grown on a GaAs substrate. Growth conditions were chosen so as to minimize the number of threading dislocations and other defects produced during the plastic relaxation. Sharp and bright lines, originating from the emission of a few isolated single quantum dots, were observed in microphotoluminescence around 1.55 μm at 5 K. They exhibit, in particular, a characteristic exciton/biexciton behavior. These QDs could offer an interesting alternative to other approaches as InAs/InP QDs for the realization of single photon emitters at telecom wavelengths.
Cavity-enhanced thermal emission from semiconductor lasers
Authors: Ziegler Mathias , Tomm Jens W. , Elsaesser Thomas , Monte Christian , Hollandt Jörg , Kissel Heiko , Biesenbach Jens
Published: May 2008

The thermal emission properties of GaAs-based semiconductor diode lasers are studied with a calibrated setup for quantitative measurements of spectrally resolved emittances. Emission spectra are measured for a stack of high-power diode-laser bars and for n-doped bulk GaAs reference samples and are compared to a calibrated blackbody radiator. The thermal radiation measurements are analyzed with a formalism providing the directional spectral emittance, transmittance, and reflectance under normal incidence. The thermal emission properties are related to the underlying materials properties such as absorption coefficients and carrier concentrations. The thermal emission from the semiconductor lasers displays a pronounced enhancement compared to the bulk reference samples. The metallic contacts and the heavily p-doped layers of the diodes are identified as the origin of this cavity enhancement. The semitransparent nature of the semiconductor materials influences the results of thermal infrared imaging substantially. We derive guidelines for extracting reliable information on device temperatures and discuss limitations of the technique.
X-ray absorption spectra of hexagonal ice and liquid water by all-electron Gaussian and augmented plane wave calculations
Authors: Iannuzzi Marcella
Published: May 2008

Full potential x-ray spectroscopy simulations of hexagonal ice and liquid water are performed by means of the newly implemented methodology based on the Gaussian augmented plane waves formalism. The computed spectra obtained within the supercell approach are compared to experimental data. The variations of the spectral distribution determined by the quality of the basis set, the size of the sample, and the choice of the core-hole potential are extensively discussed. The second part of this work is focused on the understanding of the connections between specific configurations of the hydrogen bond network and the corresponding contributions to the x-ray absorption spectrum in liquid water. Our results confirm that asymmetrically coordinated molecules, in particular, those donating only one or no hydrogen bond, are associated with well identified spectral signatures that differ significantly from the ice spectral profile. However, transient local structures, with half formed hydrogen bonds, may still give rise to spectra with dominant postedge contributions and relatively weaker oscillator strengths at lower energy. This explains why by averaging the spectra over all the O atoms of liquid instantaneous configurations extracted from ab initio molecular dynamics trajectories, the spectral features indicating the presence of weak or broken hydrogen bonds turn out to be attenuated and sometimes not clearly distinguishable.
Interfacial contribution to the dielectric response in semiconducting LaBiMn4∕3Co2∕3O6
Authors: Filippi M. , Kundys B. , Ranjith R. , Kundu Asish K. , Prellier W.
Published: May 2008

Impedance measurements have been performed on a sintered polycrystalline sample of the perovskite LaBiMn4∕3Co2∕3O6. Colossal dielectric permittivity is often measured in this class of semiconducting materials as a result of extrinsic factors. Our results show that a large offset in the capacitance, measured on a series of samples with different thickness, is due to the interfacial polarization. This contribution can then be removed from the data, creating a general procedure for dielectric measurements in semiconducting samples.
A quantum mechanical study of the reactivity of (SiO)2-defective silica surfaces
Authors: Rimola Albert , Ugliengo Piero
Published: May 2008

The reactivity of the strained (SiO)2-four atom ring defect at the silica surfaces has been studied in a cluster approach adopting the ONIOM2[B3LYP∕6-31+G(d,p):MNDO] method to compute the ring opening reaction by interaction with H2O and NH3. The vibrational “fingerprints” of the isolated defect are computed at 921, 930, and 934cm−1 in reasonable agreement with experimental evidence on amorphous silica outgassed at T>900K. The opening of the (SiO)2-four-member ring by the considered molecules is exergonic and the actual value depends on the possible constraints enforced on the reaction products by the silica surrounding. The free kinetic energy barriers result from the interplay between the nucleophilic/electrophilic character of the adsorbed molecule and are 22 and 25kcalmol−1 for NH3 and H2O, respectively. All free energy profiles envisage an activated complex in which the nucleophilic part of the molecule interacts on the coordinatively strained silicon atom of the (SiO)2 defect followed by the proton transfer from the coordinated molecule towards the oxygen of the defective ring. Calculations show that this step can be speed up by the presence of more than one adsorbed molecule or even more (about seven orders of magnitude), by the copresence of water molecules acting as “proton transfer helpers.” In these cases, the free energy barriers decrease to ≈13 and 15kcalmol−1 for NH3 and H2O, respectively. For the case of H2O adsorption, benchmark test calculations reveal that MP2, BLYP, and B3LYP energy profiles are in very good agreement with each other, whereas for PBE, both the reaction energy and the activation barrier are underestimated. Present data also show that the molecular model mimicking the (SiO)2 defect is far less reactive than what appears to occur on the real defect at the surface of amorphous silica. So, only a combination of some further geometrical strains imparted by the solid on the (SiO)2 defect, not accounted for by the cluster models, and higher adsorbate loadings are needed to reharmonize experiment and simulation. Notwithstanding, the vibrational features of the reaction products have been characterized and support the available experimental measurements.
GaInSn usage in the research laboratory
Authors: Morley N. B. , Burris J. , Cadwallader L. C. , Nornberg M. D.
Published: May 2008

GaInSn, a eutectic alloy, has been successfully used in the Magneto-Thermofluid Research Laboratory at the University of California-Los Angeles and at the Princeton Plasma Physics Laboratory for the past six years. This paper describes the handling and safety of GaInSn based on the experience gained in these institutions, augmented by observations from other researchers in the liquid metal experimental community. GaInSn is an alloy with benign properties and shows considerable potential in liquid metal experimental research and cooling applications.
Spin transfer switching in the nanosecond regime for CoFeB/MgO/CoFeB ferromagnetic tunnel junctions
Authors: Aoki Tatsuya , Ando Yasuo , Watanabe Daisuke , Oogane Mikihiko , Miyazaki Terunobu
Published: May 2008

Detailed spin transfer switching properties in the nanosecond region for CoFeB/MgO(001)/CoFeB magnetic tunnel junctions are reported. The switching current (IC) was greatly increased in the <10 ns region. This characteristic resembles that of current-perpendicular-to-plane giant magnetoresistance (CPP-GMR), although both the junction geometry and resistance differ from those of a CPP-GMR device. We discussed the switching properties considering the contribution of high frequency loss and the theoretical limitation of the analytical model. Furthermore, we observed real-time switching in the nanosecond region. Using these results, we discuss the spin transfer switching mechanism in the nanosecond region with both adiabatic and thermally activated models.
Ultraviolet and blue photoluminescence from sputter deposited Ge nanocrystals embedded in SiO2 matrix
Authors: Giri P. K. , Bhattacharyya S. , Kumari Satchi , Das Kaustuv , Ray S. K. , Panigrahi B. K. , Nair K. G. M.
Published: May 2008

Ge nanocrystals (NCs) embedded in silicon dioxide (SiO2) matrix are grown by radio-frequency magnetron sputtering and studied in order to understand the origin of ultraviolet (UV) and blue photoluminescence (PL) from the NC-SiO2 system. Ge NCs of diameter 7–8 nm are formed after postdeposition annealing, as confirmed by transmission electron microscopy and Raman scattering studies. Optical Raman studies indicate the presence of strain in the embedded Ge NCs. Polarization dependent low frequency Raman studies reveal surface symmetrical and surface quadrupolar acoustic phonon modes of Ge NCs. PL studies with 488 nm excitation shows a broad emission band peaked at ∼545 nm, which is attributed to oxygen deficient defects in the SiO2 matrix. PL studies with 325 nm excitation show additional strong peaks in the 377–400 nm region. Time resolved PL studies in the UV-blue range show double exponential decay dynamics in the nanosecond time scale, irrespective of the NC size. Comparative studies of PL emission from SiO2 layers with no Ge content and with Ge content show that the ∼400 nm PL emission is originated from a defective NC/SiO2 interface and the band is not unique to the presence of Ge. PL excitation spectroscopy measurements show large Stokes shift for the UV emission bands. We propose that the intense UV peaks at ∼377 nm is originated from the twofold coordinated silicon defect at the interface between NC and SiO2 matrix and it is not necessarily specific to the presence of Ge in the oxide matrix. It is believed that due to the influence of strain on the NCs and interface states, PL from quantum confined carriers may be partially quenched for the embedded Ge NCs.
Microwave properties of DyBa2Cu3O7−x monodomains and related compounds in magnetic fields
Authors: Pompeo N. , Silva E. , Ausloos M. , Cloots R.
Published: May 2008

We present a microwave characterization of a DyBa2Cu3O7−x single domain, grown by the top-seeded melt-textured technique. We report the (a,b) plane field-induced surface resistance, ΔRs(H), at 48.3 GHz, measured by means of a cylindrical metal cavity in the end-wall-replacement configuration. Changes in the cavity quality factor Q against the applied magnetic field yield ΔRs(H) at fixed temperatures. The temperature range (70 K;Tc) was explored. The magnetic field μ0H<0.8 T was applied along the c axis. The field dependence of ΔRs(H) does not exhibit the steep, steplike increase at low fields typical of weak links. This result indicates the single-domain character of the sample under investigation. ΔRs(H) exhibits a nearly square-root dependence on H, as expected for fluxon motion. From the analysis of the data in terms of motion of Abrikosov vortices, we estimate the temperature dependences of the London penetration depth λ and the vortex viscosity η, and their zero-temperature values λ(0)=165 nm and η(0)=3×10−7 N s m−2, which are found in excellent agreement with reported data in YBa2Cu3O7−x single crystals. Comparison of microwave properties with those of related samples indicates the need for reporting data as a function of T/Tc in order to obtain universal laws.
Highly efficient electrochemiluminescence from Ru(II) complex with PEO-PHP-PEO as a buffer layer
Authors: Wang Fu Zhi , Fan Jiang Feng , Dang Xiang Nan , Fan Xing , Wang Ping , Wan Xin Hua , Zou De Chun , Kim Shin Han , Lee Do Nam , Kim Byeong Hyo
Published: May 2008

A blended layer composed of a coil-rod-coil triblock oligomer and LiCF3SO3 was introduced into light-emitting electrochemical cells. The response rate and efficiency of the device were greatly improved, and a low operating voltage was maintained. The device, with a structure of indium tin oxide/PEO-PHP-PEO(LiCF3SO3)/[Ru(bpy)3](PF6)2/Au, showed a turn-on voltage as low as 2.85 V, while its luminance and efficiency were approximately twice those of a single-layer device. The power, luminance, and external quantum efficiency at 1000 cd/m2 reach 2.1 cd/A, 1.5l m/W, and 2.6%, respectively. We attribute these improvements to the enhancement in the hole injection and electron blocking effect resulting from the blended layer.
Influence of the L21 ordering degree on the magnetic properties of Co2MnSi Heusler films
Authors: Gaier O. , Hamrle J. , Hermsdoerfer S. J. , Schultheiß H. , Hillebrands B. , Sakuraba Y. , Oogane M. , Ando Y.
Published: May 2008

We report on the influence of the improved L21 ordering degree on the magnetic properties of Co2MnSi Heusler films. Different fractions of the L21 phase are obtained by different postgrowth annealing temperatures ranging from 350 °C to 500 °C. Room temperature magneto-optical Kerr effect measurements reveal an increase of the coercivity at an intermediate annealing temperature of 425 °C. This is probably a result of an increasing number of pinning centers on the one hand and a drop of the cubic anisotropy constant K1 by a factor of 10 on the other for an increasing amount of the L21 phase. Furthermore, Brillouin light scattering studies show that the improvement of the L21 order in the Co2MnSi films is correlated with a decrease of the saturation magnetization by about 7%. The exchange stiffness constant of Co2MnSi, however, increases by about 8% when the L21 order is improved.
Comment on “Cleaning properties of atomic oxygen excited to metastable state 2s22p4(S1) [J. Appl. Phys. 102, 083304 (2007)]”
Authors: Sadeghi Nader
Published: May 2008

It is shown that the spectrum attributed in the work of Shun’ko and Belkin [J. Appl. Phys. 102, 083304 (2007)] to the 557 nm forbidden transition of oxygen, O(S10→D12), induced by collision with argon atoms is probably the chemiluminescence from the O+NO reaction. Also, given the less than 0.1 ms lifetime of O(S10) atoms in the gas flow, they cannot survive during the transport to the surface, and hence they cannot be responsible for the observed cleaning effect.
Possible application of carbon nanotube bundles for low temperature sensing
Authors: Mahanandia P. , Singh L. T. , Nanda K. K.
Published: May 2008

We report on the R-T measurement of carbon nanotube bundles from room temperature down to 1K. The resistance at a particular temperature depends on the diameter of the bundle. The larger the bundle diameter is, the lower the value of the resistance. The resistance increases with the decrease in temperature as in the case of carbon, carbon glass resistance thermometer, and carbon nanotubes reported in the literature. The rate of the variation of resistance depends on the resistance of the bundle at room temperature which can be explored for the low temperature thermometry. Overall, the resistance and the sensitivity of the bundle depend on the bundle diameter which can be monitored easily.
Optimization of magneto-optical Kerr setup: Analyzing experimental assemblies using Jones matrix formalism
Authors: Polisetty S. , Scheffler J. , Sahoo S. , Wang Yi , Mukherjee T. , He Xi , Binek Ch.
Published: May 2008

We present a comparative study on an experimental and theoretical optimization of magneto-optical Kerr setups based on photoelastic modulation and phase sensitive detector methodology. The first and second harmonics, Iω,2ω, of the reflected light intensity are measured for a CoO∕Co magnetic reference film. The magnetic field dependence of the optical off-diagonal Fresnel reflection coefficients rps and rsp follows the sample magnetization. Different Kerr setups provide various dependencies of Iω,2ω on the reflection coefficients and, hence, on the Kerr ellipticity εK and rotation θK. Jones matrix formalism has been used to analyze the impact of a systematic variation of relative analyzer and polarizer orientations with respect to each other and with respect to the retardation axis of the modulator involved in longitudinal Kerr setups for incoming s-polarized light. We find one particular setup which maximizes Iω as well as I2ω and maximizes the signal-to-noise ratio. Inefficient setups are characterized by Iω,2ω intensities involving large nonmagnetic contributions of rp and rs.
Current driven resonant plasma wave detection of terahertz radiation: Toward the Dyakonov–Shur instability
Authors: Boubanga-Tombet S. , Teppe F. , Coquillat D. , Nadar S. , Dyakonova N. , Videlier H. , Knap W. , Shchepetov A. , Gardès C. , Roelens Y. , Bollaert S. , Seliuta D. , Vadoklis R. , Valušis G.
Published: May 2008

The experiments on the dc current influence on resonant terahertz plasma wave detection in InGaAs∕InAlAs multichannel high electron mobility transistors are reported. We observed the line width shrinking when a dc current is applied. We show that this line width decrease is due to the current induced reduction of plasma wave damping and takes place because the current drives the system toward the Dyakonov-Shur plasma wave instability.
DNA-modified indium phosphide Schottky device
Authors: Güllü Ömer , Çankaya Murat , Barış Özlem , Türüt Abdulmecit
Published: May 2008

High quality Schottky sandwich devices were fabricated on an InP single crystal by solution processing a semiconducting polymer, DNA, as the metal electrodes. We observed that DNA-based on this structure showed an excellent rectifying behavior with a typical ideality factor of 1.26, and that DNA film increased the effective barrier height by influencing the space charge region of InP. Modeling, which includes a transport mechanism, reveals thermionic emission to be the dominant transport mechanisms for the diode (ideality factor n<1.3). We proposed that DNA could be a semiconductorlike material with a wide optical band energy gap of 3.95eV from its optical absorbance characteristics. We also evaluated photovoltaic characteristic of the device under an illumination condition.
High efficiency and stability in air of the encapsulation-free hybrid organic-inorganic light-emitting diode
Authors: Morii Katsuyuki , Kawase Takeo , Inoue Satoshi
Published: May 2008

High efficiency and stability in an encapsulation-free hybrid organic-inorganic light-emitting diode (HOILED) have been achieved by controlling the hole carrier concentration by the use of a cesium compound layer acting as a hole-blocking unit. The low efficiency and brightness of the conventional HOILED are caused by insufficient blocking on the titanium dioxide (TiO2) interface. Electroluminescence with high brightness (>10000Cd∕m2 at 4V) and efficiency (7.2Cd∕A at 3.6V) was observed. Higher than required emission reaching 600Cd∕m2 at 6V can be observed after keeping the TiO2-free improved HOILED in air for 172h.
Coherence properties of infrared thermal emission from heated metallic nanowires
Authors: Klein Levente J. , Hamann Hendrik F. , Au Yat-Yin , Ingvarsson Snorri
Published: May 2008

Coherence properties of the infrared thermal radiation from individual heated nanowires are investigated as a function of nanowire dimensions. Interfering the thermally induced radiation from a heated nanowire with its image in a nearby moveable mirror, well-defined fringes are observed. From the fringe visibility, the coherence length of the thermal emission radiation from the narrowest nanowires was estimated to be at least 20μm, which is much larger than expected from a classical blackbody radiator. Significant increases in coherence and emission efficiency are observed for smaller nanowires.
Electrical conduction control of carbon nanowalls
Authors: Takeuchi Wakana , Ura Masato , Hiramatsu Mineo , Tokuda Yutaka , Kano Hiroyuki , Hori Masaru
Published: May 2008

The electrical conduction behavior of carbon nanowalls (CNWs) has been evaluated by Hall measurement. CNWs, which comprise stacks of graphene sheets standing on the substrate, are fabricated by fluorocarbon/hydrogen plasma enhanced chemical vapor deposition. We have investigated the effect of N2 addition to C2F6∕H2 system on the electrical properties of CNWs. The CNWs grown with the C2F6∕H2 plasma exhibit p-type conduction. As a result of the nitrogen inclusion in the CNWs, the conduction type of the CNWs changes to n type. The carrier concentration is controllable by changing the flow rate of the additional N2 during the CNW growth process.
Rapid thermal annealing of ion beam synthesized β-FeSi2 nanoparticles in Si
Authors: Sun C. M. , Tsang H. K. , Wong S. P. , Cheung W. Y. , Ke N. , Hark S. K.
Published: May 2008

High crystal-quality β-FeSi2 nanoparticles in silicon, prepared by ion beam synthesis and subjected to rapid thermal annealing (RTA), are investigated. Completely amorphous Fe–Si layers are formed by Fe implantation at cryogenic temperature, with a dosage of 5×1015cm−2, into float-zone silicon. After RTA at 900°C for 60s, β-FeSi2 precipitates are aggregated in the Si matrix and give ∼1.5μm photoluminescence. High-resolution plan-view transmission electron microscopy revealed that some strain is present in the RTA treated FeSi2 particles. Silicon dislocations, coming from the strain relaxation during the additional long-term annealing, are observed around β-FeSi2 particles.
Robust detection of deeply subwavelength pits in simulated optical data-storage disks using photonic jets
Authors: Kong Soon-Cheol , Sahakian Alan V. , Heifetz Alexander , Taflove Allen , Backman Vadim
Published: May 2008

We report a means to detect deeply subwavelength pits in optical data-storage media by employing the recently observed giant backscattering perturbation phenomenon of the photonic jet. We conducted microwave experiments with dimensionally scaled-up pits and lands in a simulated optical data-storage device. These measurements were backed up by three-dimensional finite-difference time-domain computational solutions of Maxwell's equations. Results indicate that pits having a lateral area of 0.025 square wavelengths, i.e., much smaller than current BluRay™ device features, can be robustly detected with a contrast ratio approximately 28dB greater than that provided by a lens system.
1.59
μ
m
room temperature emission from metamorphic InAs∕InGaAs quantum dots grown on GaAs substrates
Authors: Seravalli L. , Frigeri P. , Trevisi G. , Franchi S.
Published: May 2008

We present design, preparation by molecular beam epitaxy, and characterization by photoluminescence of long-wavelength emitting, strain-engineered quantum dot nanostructures grown on GaAs, with InGaAs confining layers and additional InAlAs barriers embedding InAs dots. Quantum dot strain induced by metamorphic lower confining layers is instrumental to redshift the emission, while a-few-nanometer thick InAlAs barriers allow to significantly increase the activation energy of carriers’ thermal escape. This approach results in room temperature emission at 1.59μm and, therefore, is a viable method to achieve efficient emission in the 1.55μm window and beyond from quantum dots grown on GaAs substrates.
Multiferroicity in the square-lattice antiferromagnet of Ba2CoGe2O7
Authors: Yi H. T. , Choi Y. J. , Lee S. , Cheong S.-W.
Published: May 2008

We have discovered the appearance of ferroelectricity below the Neel temperature of 6.7K in the antiferromagnetic Ba2CoGe2O7 with square magnetic lattice. The ferroelectric polarization is rather small in magnitude and aligned along the c axis, but its magnitude increases remarkably and its direction rotates away smoothly from the c axis when magnetic fields are applied along the c axis. The electric polarization’s behavior of smooth rotation, rather than a sudden flip, is unique. It also accompanies a linear increase in magnetization and a smooth change of dielectric constant with little hysteresis, which may be important for certain technological applications.
Role of optical phonon in Ge thermal conductivity
Authors: Kazan M. , Pereira S. , Coutinho J. , Correia M. R. , Masri P.
Published: May 2008

We report on the contribution of optical phonon decay into acoustic phonon to the thermal conductivity [k(T)] of semiconductors. We have considered this mechanism as an acoustic phonon generation rate within the full modified Callaway theory to accurately describe experimental data of k(T) for Ge as a function of isotopic composition. The proposed model requires only one adjustable parameter for each mode. Our approach to describe k(T) in semiconductors is found to provide much better agreement with the experimental results than previously reported models, which did not account for the role of optical phonon.
Influence of charge ordering on magnetocaloric properties of nanocrystalline Pr0.65(Ca0.7Sr0.3)0.35MnO3
Authors: Biswas Anis , Samanta Tapas , Banerjee S. , Das I.
Published: May 2008

Nanocrystalline Pr0.65(Ca0.7Sr0.3)MnO3 show large magnetocaloric effect at their charge order transition temperature (TCO) as well as at the temperature at which the spontaneous destabilization of charge ordered state occurs (TM). In comparison to their polycrystalline bulk form, TM’s are substantially enhanced in the cases of nanocrystalline samples, whereas their TCO’s remain almost unchanged. Although there is no clear signature of charge order transition in the temperature dependence of magnetic susceptibility and resistivity for the sample with the lower particle size, a clear maxima due to charge order transition is visible in its temperature dependence of change in magnetic entropy.
Spatial characterization of the magnetic field profile of a probe tip used in magnetic resonance force microscopy
Authors: Nazaretski E. , Akhadov E. A. , Martin I. , Pelekhov D. V. , Hammel P. C. , Movshovich R.
Published: May 2008

We have developed the experimental approach to characterize spatial distribution of the magnetic field produced by cantilever tips used in magnetic resonance force microscopy (MRFM). We performed MRFM measurements on a well characterized diphenylpicrylhydrazyl film and mapped the three-dimensional field profile produced by a Nd2Fe14B probe tip. Using our technique, field profiles of arbitrarily shaped probe magnets can be imaged.
Absolute external luminescence quantum efficiency of zinc oxide
Authors: Hauser Mario , Hepting Alexander , Hauschild Robert , Zhou Huijuan , Fallert Johannes , Kalt Heinz , Klingshirn Claus
Published: May 2008

We report on the measurement of the absolute external luminescence quantum efficiency of various ZnO samples using a miniature integrating sphere fitted into a cryostat. Even the absolute luminescence quantum efficiencies per spectral interval are directly accessible. Measurements have been carried out on high quality bulk samples and different commercially available ZnO powders from 8K up to room temperature. Activated processes lead to an overall decrease in the efficiency with temperature. All efficiencies are considerably below unity, making the identification of the luminescence decay time with the radiative life time very questionable.
Ultrasonic particle trapping in microfluidic devices using soft lithography
Authors: Guo S. S. , Zhao L. B. , Zhang K. , Lam K. H. , Lau S. T. , Zhao X. Z. , Wang Y. , Chan H. L. W. , Chen Y. , Baigl D.
Published: May 2008

We report on the feasible fabrication of microfluidic devices for noncontact particle trapping. A half-wavelength resonator was constructed using standard soft lithography to generate ultrasonic standing waves through a miniature piezoelectric transducer. Microparticles (400nm to 10μm in diameter) flowing through polydimethylsiloxane microchannels were efficiently trapped to levitate in the middle depth of a resonance cavity. Such a device could potentially offer a flexible platform for particle-based assays for a large variety of applications.
p53 stabilization in response to DNA damage requires Akt/PKB and DNA-PK
Authors: Boehme Karen A. , Kulikov Roman , Blattner Christine
Published: May 2008

The p53 protein is one of the major tumor suppressor proteins. In response to DNA damage, p53 is prevented from degradation and accumulates to high levels. Ionizing radiation leads to hypophosphorylation of the p53 ubiquitin ligase Mdm2 at sites where phosphorylation is critical for p53 degradation and to the phosphorylation and activation of Akt/PKB, a kinase that phosphorylates and inhibits GSK-3. GSK-3, which normally phosphorylates Mdm2, is inactivated in response to ionizing radiation. We show that p53 accumulates in lymphoblasts from patients with the hereditary disorder ataxia telangiectasia in response to ionizing radiation despite the absence of a functional ATM kinase. Also, knockdown of ATR did not prevent p53 accumulation in response to ionizing radiation. Instead, p53 stabilization in response to ionizing radiation depended on the inactivation of GSK-3 and the presence of Akt/PKB. Akt/PKB is a target of DNA-PK, a kinase that is activated after ionizing radiation. Correspondingly, down-regulation of DNA-PK prevented phosphorylation of Akt/PKB and GSK-3 after ionizing radiation and strongly reduced the accumulation of p53. We therefore propose a signaling cascade for the regulation of p53 in response to ionizing radiation that involves activation of DNA-PK and Akt/PKB and inactivation of GSK-3 and Mdm2.