bluuebunny/crossref_metadata_2025 huggingface dataset:
Torsional oscillation of vortex tangles. Possible applications to oscillations of solid 4He
Authors: Nemirovskii Sergey K.
Published: July 2011

Torsional oscillation of vessels containing quantum fluids are one of oldest and most popular methods for the study of quantized vortices. One recent and very brilliant example is the discovery of the supersolidity of solid helium. In torsional oscillation experiments, a drop in the period of the oscillations is observed when some low temperature is reached. This effect has been attributed to the appearance of the superfluid component. It depends on many factors and has various explanations. But, assuming (at least hypothetically, at this stage) that the phenomenon of “supersolidity” (dissipationless flow) does occur, we must consider the relaxation of a vortex system (we can call it a vortex tangle, vortex fluid, chaotic set of vortices, etc.). This is necessary because the only way to involve the superfluid component in rotation is through polarized vortices (with nonzero mean polarization along their axis of rotation). Here we consider a vortex tangle relaxation model for the torsional oscillation response of quantum systems, with the aim of using it to study solid 4He. It is shown that the rotation of the superfluid component occurs as a relaxation effect with a relaxation time that depends on the amplitude of the oscillations (as well as on temperature and pressure). This problem has a quasi-linear solution which explains the (amplitude dependent) shift in the period. There is also an imaginary shift of the frequency (also amplitude dependent), which represents an additional dissipation. The theoretical results are compared with recent measurements.
Thermal conductivity of molecular crystals of monatomic alcohols: From methanol to butanol
Authors: Korolyuk O. A.
Published: July 2011

Experimental data on the thermal conductivity κ(T) of some simple alcohols have been compared, analyzed, and generalized. The objects of study were methyl, protonated and deuterated ethyl, 1-propyl and 1-butyl alcohols in the thermodynamically equilibrium phase with complete orientational order. The temperature ranged from 2 K to the melting point at the equilibrium vapor pressure. In the region above the temperature of the maximum thermal conductivity, κ(T) deviates from a 1/T dependence. This is because the total thermal conductivity has an extra contribution κII(T) from short-lived phonons in addition to kI(T) owing to propagating phonons; i.e., κ(T) = kI(T) + κII(T). kI(T) is well described by the Debye-Peierls model for phonon-phonon processes and scattering of phonons by dislocations. For T > 40 K, kI(T) varies as A/T and κII(T) is essentially temperature-independent. The Debye temperature ΘD of the alcohols depends on the molecular mass as ΘD = 678М−0.42 K and the coefficient А characterizing the rate of phonon-phonon scattering increases with the molecular mass of the simple monatomic alcohols as А = 0.85М0.8 W/m, which suggests a decreasing intensity of the phonon-phonon process.
Numerical study of the diffusion-like decay of vortex tangles without mutual friction
Authors: Kondaurova Luiza P. , Nemirovskii Sergey K.
Published: July 2011

The diffusion-like decay of vortex tangles without mutual friction is simulated numerically using the localized induction approximation. This algorithm, previously developed by the authors, is based on an examination of crossing lines, and has been used to study vortex reconnection processes. We have examined the effect of various factors on the decay of inhomogeneous vortex tangles: diffusion (large vortex loops break up into smaller ones which move away from an initial volume), changes in length owing to reconnection processes, the elimination of small vortices below the spatial resolution, and the insertion and removal of points to ensure stability of the numerical algorithm. The simulations show that a vortex tangle initially localized in a small region will spread into the surrounding space. The time evolution of the vortex line density inside the initial region agrees satisfactorily with that obtained by solving a diffusion equation.
Seeking for parameter-free double-hybrid functionals: The PBE0-DH model
Authors: Brémond Eric , Adamo Carlo
Published: July 2011

A new double hybrid functional is herein presented, in which the ratio of the Hartree-Fock, Kohn-Sham, and perturbation terms (MP2) is determined on the basis of physical considerations. This functional, denominated PBE0 Double Hybrid (PBE0-DH), contains a small MP2 contribution (12.5%) and it has been tested on a number of different molecular properties, including atomization energies, weak interactions, and reaction energies. From the obtained results, PBE0-DH seems to represent a significant improvement with respect to the parent PBE0 functional, a parameter-free hybrid. Overall its performances are comparable to the ones found using other parameterized double hybrids. From a more general point of view, our work points out that, already showed for classes of other functionals, reliable and general-purpose double hybrids can be obtained on purely theoretical bases, without the use of any empirical fitting.
Transparent conductive oxides: Plasmonic materials for telecom wavelengths
Authors: Noginov M. A. , Gu Lei , Livenere J. , Zhu G. , Pradhan A. K. , Mundle R. , Bahoura M. , Barnakov Yu. A. , Podolskiy V. A.
Published: July 2011

We show that despite of low loss, silver and gold are not suitable for a variety of nanoplasmonic applications in the infrared range, which require compact modes in single-interface plasmonic waveguides. At the same time, degenerate wide-band-gap semiconductors can serve as high-quality plasmonic materials at telecom wavelengths, combining fairly high compactness and relatively low loss. Their plasmonic properties in the near-infrared can be compared to those of gold in the visible range. The same materials can be used in a variety of non-plasmonic metamaterials applications, including transformation optics and invisibility cloaking.
The coincidence counting technique for orders of magnitude background reduction in data obtained with the magnetic recoil spectrometer at OMEGA and the NIF
Authors: Casey D. T. , Frenje J. A. , Séguin F. H. , Li C. K. , Rosenberg M. J. , Rinderknecht H. , Manuel M. J.-E. , Gatu Johnson M. , Schaeffer J. C. , Frankel R. , Sinenian N. , Childs R. A. , Petrasso R. D. , Glebov V. Yu. , Sangster T. C. , Burke M. , Roberts S.
Published: July 2011

A magnetic recoil spectrometer (MRS) has been built and successfully used at OMEGA for measurements of down-scattered neutrons (DS-n), from which an areal density in both warm-capsule and cryogenic-DT implosions have been inferred. Another MRS is currently being commissioned on the National Ignition Facility (NIF) for diagnosing low-yield tritium-hydrogen-deuterium implosions and high-yield DT implosions. As CR-39 detectors are used in the MRS, the principal sources of background are neutron-induced tracks and intrinsic tracks (defects in the CR-39). The coincidence counting technique was developed to reduce these types of background tracks to the required level for the DS-n measurements at OMEGA and the NIF. Using this technique, it has been demonstrated that the number of background tracks is reduced by a couple of orders of magnitude, which exceeds the requirement for the DS-n measurements at both facilities.
A new x-ray interface and surface scattering environmental cell design for in situ studies of radioactive and atmosphere-sensitive samples
Authors: Schmidt M. , Eng P. J. , Stubbs J. E. , Fenter P. , Soderholm L.
Published: July 2011

We present a novel design of a purpose-built, portable sample cell for in situ x-ray scattering experiments of radioactive or atmosphere sensitive samples. The cell has a modular design that includes two independent layers of containment that are used simultaneously to isolate the sensitive samples. Both layers of containment can be flushed with an inert gas, thus serving a double purpose as containment of radiological material (either as a solid sample or as a liquid phase) and in separating reactive samples from the ambient atmosphere. A remote controlled solution flow system is integrated into the containment system that allows sorption experiments to be performed on the diffractometer. The cell's design is discussed in detail and we demonstrate the cell's performance by presenting first results of crystal truncation rod measurements. The results were obtained from muscovite mica single crystals reacted with 1 mM solutions of ThIV with 0.1 M NaCl background electrolyte. Data were obtained in specular as well as off-specular geometry.
Soluble fullerene derivatives: The effect of electronic structure on transistor performance and air stability
Authors: Ball James M. , Bouwer Ricardo K. M. , Kooistra Floris B. , Frost Jarvist M. , Qi Yabing , Domingo Ester Buchaca , Smith Jeremy , de Leeuw Dago M. , Hummelen Jan C. , Nelson Jenny , Kahn Antoine , Stingelin Natalie , Bradley Donal D. C. , Anthopoulos Thomas D.
Published: July 2011

The family of soluble fullerene derivatives comprises a widely studied group of electron transporting molecules for use in organic electronic and optoelectronic devices. For electronic applications, electron transporting (n-channel) materials are required for implementation into organic complementary logic circuit architectures. To date, few soluble candidate materials have been studied that fulfill the stringent requirements of high carrier mobility and air stability. Here we present a study of three soluble fullerenes with varying electron affinity to assess the impact of electronic structure on device performance and air stability. Through theoretical and experimental analysis of the electronic structure, characterization of thin-film structure, and characterization of transistor device properties we find that the air stability of the present series of fullerenes not only depends on the absolute electron affinity of the semiconductor but also on the disorder within the thin-film.
The kinetics of homogeneous melting beyond the limit of superheating
Authors: Alfè D. , Cazorla C. , Gillan M. J.
Published: July 2011

Molecular dynamics simulation is used to study the time-scales involved in the homogeneous melting of a superheated crystal. The interaction model used is an embedded-atom model for Fe developed in previous work, and the melting process is simulated in the microcanonical (N, V, E) ensemble. We study periodically repeated systems containing from 96 to 7776 atoms, and the initial system is always the perfect crystal without free surfaces or other defects. For each chosen total energy E and number of atoms N, we perform several hundred statistically independent simulations, with each simulation lasting for between 500 ps and 10 ns, in order to gather statistics for the waiting time τw before melting occurs. We find that the probability distribution of τw is roughly exponential, and that the mean value 〈τw〉 depends strongly on the excess of the initial steady temperature of the crystal above the superheating limit identified by other researchers. The mean 〈τw〉 also depends strongly on system size in a way that we have quantified. For very small systems of ∼100 atoms, we observe a persistent alternation between the solid and liquid states, and we explain why this happens. Our results allow us to draw conclusions about the reliability of the recently proposed Z method for determining the melting properties of simulated materials and to suggest ways of correcting for the errors of the method.
Internal friction and phase transitions of solid oxygen
Authors: Erenburg A. I. , Leont’eva A. V. , Varyukhin V. N. , Marinin G. A. , Prokhorov A. Yu.
Published: July 2011

We report an experimental study of low-frequency internal friction (LTIF) in solid oxygen at temperatures of 7–52 K. Comparison of the temperature dependence of the IF with data on x-ray diffraction and other thermodynamic and elastic properties shows that the anomalies in the temperature dependence of the internal friction arise from phase transitions in solid oxygen.
A simple low-temperature adiabatic calorimeter for small samples
Authors: Bagatskii M. I. , Sumarokov V. V. , Dolbin A. V.
Published: July 2011

A simple adiabatic calorimeter has been built to investigate the heat capacity of small (≤1 cm3) samples of carbon nanomaterials at temperatures ranging from 1 to 300 K. It enables (i) rapid mounting of samples (ii) doping of samples with gases directly in the calorimeter, and (iii) rapid cooling of samples to liquid helium temperatures. It can be placed in the helium vessel of a portable Dewar or in a helium cryostat. The heat capacity of a fullerite sample is measured in the temperature range 1–30 K.
Joint analysis of the Cs2 $a^3\Sigma _u^+$a3Σu+ and 1g (33Π1g) states
Authors: Xie F. , Li Li , Li D. , Sovkov V. B. , Minaev K. V. , Ivanov V. S. , Lyyra A. M. , Magnier S.
Published: July 2011

Sets of experimental data on the Cs2 \documentclass[12pt]{minimal}\begin{document}$a^3\Sigma _u^+$\end{document}a3Σu+ and 1g (33Π1g) states, including the bound-bound and bound-free fluorescence spectra, are analyzed simultaneously to produce the potential energy curves of both states in the form of the Morse long range multiparameter function. The attractive branch of the \documentclass[12pt]{minimal}\begin{document}$a^3\Sigma _u^+$\end{document}a3Σu+ state potential is improved relative to the one reported in our earlier work [F. Xie, V. B. Sovkov, A. M. Lyyra, D. Li, S. Ingram, J. Bai, V. S. Ivanov, S. Magnier, and L. Li, J. Chem. Phys. 130, 051102 (2009)]10.1063/1.3075580, in which the data on this state alone were analyzed. Besides, the new potential of this state also includes the repulsive branch in the range spanned by the bound-free fluorescence spectra. We have not found experimental evidence of the double minimum character of the 33Π1g state potential, predicted by ab initio calculations, at least up to v = 8. This fact testifies that the upper state observed is better described by the Hund coupling case (c), in which the case (a) electronic basis states are intermixed by the strong spin-orbit interaction.
The origin of p-type conduction in Li-N codoped ZnO: An ab initio calculation study
Authors: Tang Xin , Cheng Xiangfeng , Wagner Dustin , Lü Haifeng , Zhang Qingyu
Published: July 2011

An ab initio calculation based on density functional theory is applied to study the new source of p-type conductivity in Li-N codoped ZnO. The calculated results show that the interstitial Li (Lii) easily binds with the substitutional Li defect at the Zn site (LiZn) and the substitutional N defect at the O site (NO). This induces the formation of Lii-LiZn and Lii-NO passive complex. However, only Lii-NO can introduce an impurity band above the valence band maximum of the pure ZnO and decrease the ionization energies of the relative complexes. The possible configurations of Lii-NO combining with other additional acceptors LiZn and NO are discussed. It is found that NO-Lii-NO may be a possible source of p-type conductivity under Zn-rich conditions.
Thermoelectric properties of Ga-added CoSb3 based skutterudites
Authors: Harnwunggmoung Adul , Kurosaki Ken , Plirdpring Theerayuth , Sugahara Tohru , Ohishi Yuji , Muta Hiroaki , Yamanaka Shinsuke
Published: July 2011

Filled skutterudite compounds are known as excellent thermoelectric (TE) materials. It is known that the voids in the structure of the skutterudite compounds, such as CoSb3, can be filled or partially filled with a variety of different atoms, and, thus, obtained filled skutterudite compounds exhibit quite low thermal conductivity (κ). In the present study, we tried to fill Ga into the voids of CoSb3. The polycrystalline samples of GaxCo4Sb12 (x = 0.05, 0.10, 0.15, 0.20, 0.25, and 0.30) were prepared, and the TE properties were examined from room temperature to 750 K. All the samples were composed of two phases: GaxCo4Sb12 (x = ∼0.02) as the matrix phase and Ga metal as the second phase. All the samples exhibited negative values of the Seebeck coefficient (S). The Hall carrier concentration slightly increased with increasing x, while the carrier mobility decreased. Although the maximum Ga filling ratio was really low, the κ was reduced effectively by Ga adding. The maximum value of the dimensionless figure of merit ZT ( = S2T/ρ/κ, where T is the absolute temperature and ρ is the electrical resistivity) was 0.18 at 500 K obtained for Ga0.25Co4Sb12.
Short-range order in amorphous SiOx by x ray photoelectron spectroscopy
Authors: Novikov Yu. N. , Gritsenko V. A.
Published: July 2011

The Si 2p x ray photoelectron spectra of SiOx with a different composition of 0 ≤ x ≤ 2 have been studied experimentally and theoretically. The SiOx films were prepared by low-pressure chemical vapor deposition from SiH4 and N2O source at 750 °C. Neither random bonding nor random mixture models can adequately describe the structure of these compounds. The interpretation of the experimental results is discussed according to a large scale potential fluctuation due to the spatial variation of chemical composition in SiOx.
Effects of signal diffusion on x-ray phase contrast images
Authors: Ignatyev K. , Munro P. R. T. , Speller R. D. , Olivo A.
Published: July 2011

We discuss the problem of signal diffusion among neighbouring pixels in x-ray phase contrast imaging (XPCi) specifically for coded-aperture (CA) XPCi, but many of the discussed observations are directly transferable to other XPCi modalities. CA XPCi exploits the principle of pixel edge illumination by means of two CA masks. The first mask, placed in contact with the detector, creates insensitive regions between adjacent pixels; the second one, placed immediately before the sample, creates individual beams impinging on the boundaries between sensitive and insensitive regions on the detector, as created by the detector mask. In this way, edge illumination is achieved for all pixels of an area detector illuminated by a divergent and polychromatic beam generated by a conventional source. As the detector mask redefines the resolution properties of the detector, sample dithering can be used to effectively increase the system spatial resolution, without having to apply any post-processing procedure (e.g., deconvolution). This however creates artifacts in the form of secondary fringes (which have nothing to do with phase-related secondary fringes) if there is signal diffusion between adjacent pixels. In non-dithered images, signal diffusion between adjacent pixels causes a reduction in image contrast. This effect is investigated both theoretically and experimentally, and its direct implications on image quality are discussed. The interplay with the sample positioning with respect to the detector pixel matrix, which also has an effect on the obtained image contrast, is also discussed.
A combined arc-melting and tilt-casting furnace for the manufacture of high-purity bulk metallic glass materials
Authors: Soinila E. , Pihlajamäki T. , Bossuyt S. , Hänninen H.
Published: July 2011

An arc-melting furnace which includes a tilt-casting facility was designed and built, for the purpose of producing bulk metallic glass specimens. Tilt-casting was chosen because reportedly, in combination with high-purity processing, it produces the best fatigue endurance in Zr-based bulk metallic glasses. Incorporating the alloying and casting facilities in a single piece of equipment reduces the amount of laboratory space and capital investment needed. Eliminating the sample transfer step from the production process also saves time and reduces sample contamination. This is important because the glass forming ability in many alloy systems, such as Zr-based glass-forming alloys, deteriorates rapidly with increasing oxygen content of the specimen. The challenge was to create a versatile instrument, in which high purity conditions can be maintained throughout the process, even when melting alloys with high affinity for oxygen. Therefore, the design provides a high-vacuum chamber to be filled with a low-oxygen inert atmosphere, and takes special care to keep the system hermetically sealed throughout the process. In particular, movements of the arc-melting electrode and sample manipulator arm are accommodated by deformable metal bellows, rather than sliding O-ring seals, and the whole furnace is tilted for tilt-casting. This performance of the furnace is demonstrated by alloying and casting Zr55Cu30Al10Ni5 directly into rods up to ø 10 mm which are verified to be amorphous by x-ray diffraction and differential scanning calorimetry, and to exhibit locally ductile fracture at liquid nitrogen temperature.
Image sensor as a three-channel spectrometer with application to in situ monitoring of wet etching
Authors: Gerling John , Cheung Nathan W.
Published: July 2011

A three-channel spectrometer is constructed with a 460 nm high brightness light-emitting diode (LED) source (250 mW peak optical power output, 1 mm sq, 150 μm thick) and a red-green-blue (RGB) image sensor (3 × 4 mm, 1 mm thick) for purposes of a small form factor spectrometer to monitor reflectance/emission spectra from chemical wet etching experiments. The linearity and spectral response of the RGB image sensor is characterized and a three-channel spectral model is fitted to the extracted spectral response. We use this information to quantify time developments of the RGB image sensor outputs for in situ copper and aluminum etching experiments in terms of three defined spectral bands.
High-voltage isolation transformer for sub-nanosecond rise time pulses constructed with annular parallel-strip transmission lines
Authors: Homma Akira
Published: July 2011

A novel annular parallel-strip transmission line was devised to construct high-voltage high-speed pulse isolation transformers. The transmission lines can easily realize stable high-voltage operation and good impedance matching between primary and secondary circuits. The time constant for the step response of the transformer was calculated by introducing a simple low-frequency equivalent circuit model. Results show that the relation between the time constant and low-cut-off frequency of the transformer conforms to the theory of the general first-order linear time-invariant system. Results also show that the test transformer composed of the new transmission lines can transmit about 600 ps rise time pulses across the dc potential difference of more than 150 kV with insertion loss of −2.5 dB. The measured effective time constant of 12 ns agreed exactly with the theoretically predicted value. For practical applications involving the delivery of synchronized trigger signals to a dc high-voltage electron gun station, the transformer described in this paper exhibited advantages over methods using fiber optic cables for the signal transfer system. This transformer has no jitter or breakdown problems that invariably occur in active circuit components.
A synchrotron beamline for extreme-ultraviolet photoresist testing
Authors: Tarrio C. , Grantham S. , Hill S. B. , Faradzhev N. S. , Richter L. J. , Knurek C. S. , Lucatorto T. B.
Published: July 2011

Before being used in an extreme-ultraviolet (EUV) scanner, photoresists must first be evaluated for sensitivity and tested to ensure that they will not contaminate the scanner optics. The new NIST facility described here provides data on the contamination potential of the outgas products of a candidate resist by simultaneously irradiating a multilayer optic and a nearby resist-coated wafer with EUV radiation. The facility can also be used without changing its configuration to provide accurate resist dose-to-clear measurements. Detailed, real-time information on the rate of contamination growth is given by a unique, in situ imaging ellipsometer. We will describe the optical layout, mechanical design, and capabilities of the beamline, finally presenting experimental examples of its capabilities.
Ultrafast vibrational relaxation dynamics of carbonyl stretching modes in Os3(CO)12
Authors: Yan Suxia , Seidel Marco Thomas , Zhang Zhengyang , Leong Weng Kee , Tan Howe-Siang
Published: July 2011

The vibrational relaxation dynamics of the four infrared active carbonyl (CO) stretching normal modes of Os3(CO)12 at 2068 cm−1, 2034 cm−1, 2014 cm−1, and 2002 cm−1 were measured using broad-band frequency resolved pump-probe spectroscopy. Transient absorption spectra of these modes were collected, and the fundamental, overtone, and combination bands were assigned. The frequency resolved pump-probe traces measured at the fundamental frequencies for the four stretching normal modes exhibited marked differences: the two axial modes at frequencies of 2068 cm−1 and 2034 cm−1 yielded similar bi-exponential decay traces, while the two equatorial modes at 2014 cm−1 and 2002 cm−1 showed a rising component, in addition to a bi-exponential decay. Due to the independence of the axial and equatorial stretching modes, it is shown that the axial-equatorial combination anharmonicity constants are near zero. This results in the appearance of the pump-probe signals of these combination bands at the same frequencies as the fundamental transitions, thus leading to interference and the resultant anomalous rising features. If unaccounted for, these interferences may lead to erroneous conclusions about the dynamics of these vibrational stretches. To avoid such pitfalls, it is therefore imperative to resolve such ambiguities. A corrected dynamical picture of the equatorial modes can be obtained by varying the center frequency of the pump pulse. The four modes have a slow vibrational excited population decay time of between 400 to 600 ps. We observe no obvious direct vibrational energy transfer between the axial and equatorial CO stretching modes.
Realization of a nonlinear interferometer with parametric amplifiers
Authors: Jing Jietai , Liu Cunjin , Zhou Zhifan , Ou Z. Y. , Zhang Weiping
Published: July 2011

We construct an interferometer with parametric amplifiers as beam splitters. Because of the gain in the parametric amplifiers, the maximum output intensity of the interferometer can be much bigger than the input intensity as well as the intensity inside the interferometer (the phase sensing intensity). We find that the fringe intensity depends quadratically on the intensity of the phase sensing field at high gain. This type of nonlinear interferometer has better sensitivity than the traditional linear interferometer made of beam splitters with the same phase sensing intensity.
4-dimensional spin-foam model with quantum Lorentz group
Authors: Han Muxin
Published: July 2011

We study the quantum group deformation of the Lorentzian EPRL spin-foam model. The construction uses the harmonic analysis on the quantum Lorentz group. We show that the quantum group spin-foam model so defined is free of the infra-red divergence, thus gives a finite partition function on a fixed triangulation. We expect this quantum group spin-foam model is a spin-foam quantization of discrete gravity with a cosmological constant.
Mineral concentration dependent modulation of mechanical properties of bone-inspired bionanocomposite scaffold
Authors: Biswas Abhijit , Ovaert Timothy C. , Slaboch Constance , Zhao He , Bayer Ilker S. , Biris Alexandru S. , Wang Tao
Published: July 2011

We demonstrate tunable mechanical properties of bone-inspired bionanocomposite scaffolds while maintaining the required viscoelasticity. Mechanical properties such as hardness and elastic modulus of the bionanocomposite scaffolds were controlled by varying mineral concentrations of the bioscaffold. In particular, higher calcium and oxygen contents in the bioscaffold resulted in a significant enhancement in hardness and modulus of the bionanocomposite. Moreover, the phosphorous content appeared to be a determining factor in the hardness and mechanical properties of the bionanocomposites. These results open up the possibility of designing new engineered biocompatible nanoscaffolds with desired and tunable biomimetic functions and biomechanical properties with significant potential for advanced bone tissue engineering platforms and bone substitutes.
Bolometric THz-to-IR converter for terahertz imaging
Authors: Kuznetsov Sergey A. , Paulish Andrey G. , Gelfand Alexander V. , Lazorskiy Pavel A. , Fedorinin Victor N.
Published: July 2011

The quasi-optical bolometric converter of terahertz (THz) waves into infrared (IR) radiation is proposed and experimentally investigated. The converter includes an ultra-thin THz absorber (with a thickness 1/50 of the operating free-space wavelength) based on an artificial impedance surface with close to perfect resonant absorptivity at 0.3 THz and a high-performance IR emissive layer. Absorption of THz waves induces converter heating that yields enhancement of IR emission from the emissive layer. The experimental testing of the THz-to-IR converter demonstrates the applicability of a converter to THz imaging with spectral and polarization discrimination in real-time operation.
Bias current dependence of spin accumulation signals in a silicon channel detected by a Schottky tunnel contact
Authors: Ando Y. , Kasahara K. , Yamane K. , Baba Y. , Maeda Y. , Hoshi Y. , Sawano K. , Miyao M. , Hamaya K.
Published: July 2011

We study the electrical detection of spin accumulation at a ferromagnet-silicon interface, which can be verified by measuring a Hanle effect in three-terminal lateral devices. The device structures used consist of a semiconducting Si channel and a Schottky tunnel contact. In a low current-bias region, the Hanle-effect curves are observed only under forward bias conditions. This can be considered that the electrical detectability at the forward-biased contact is higher than that at the reverse-biased contact. This is possible evidence for the detection of spin-polarized electrons created in a Si channel.
Microwave frequency-comb generation in a tunneling junction by intermode mixing of ultrafast laser pulses
Authors: Hagmann Mark J. , Efimov Anatoly , Taylor Antoinette J. , Yarotski Dzmitry A.
Published: July 2011

We present a method for hyper-spectral characterization of the nonlinear effects in a tunneling junction. Harmonics up to 1 GHz were measured in a frequency comb in the tunneling current when 15-fs laser pulses at a repetition rate of 74.25 MHz were focused on the tunneling junction of a scanning tunneling microscope. The typical output power is −120 dBm at the fundamental frequency, which is the pulse repetition rate and decreases by several dB for the higher harmonics. The observed square-law dependence of the signal power on the tunneling current and incident laser power is in good agreement with theoretical predictions.
Edge dislocation induced self-assembly of InGaN nano-flower on GaN by metal organic vapor phase epitaxy
Authors: Zhao Wei , Wang Lai , Wang Jiaxing , Hao Zhibiao , Luo Yi
Published: July 2011

InGaN nano-flowers are self-assembled on GaN by metal organic vapor phase epitaxy. Scanning electron microscopy and transmission electron microscopy photos show the nano-flower structure is formed through InGaN quantum dots aggregating around the exposure site of the edge dislocation extending to the surface. Calculation on the strain states indicates that the edge dislocation can generate lateral tensile and compressive strain regions on the surface, but the screw dislocation cannot. And the tensile strain regions are corresponding to the shape of the nano-flower. This is attributed to that the tensile GaN lattices on surface are easy to attract adatoms to form InGaN quantum dots.
Potential energy surface and rotational cross sections for methyl formate colliding with helium
Authors: Faure Alexandre , Szalewicz Krzysztof , Wiesenfeld Laurent
Published: July 2011

A potential energy surface for helium interacting with methyl formate has been computed using high-level electronic structure methods. The interaction energies obtained on a three-dimensional grid have been fitted by an analytic function of interatomic distances with correct asymptotic behavior for large intermonomer separations. This potential has then been refitted using partial wave expansion in terms of the distance between centers of mass and spherical angles. The latter potential has been used to compute cross sections for the rotational excitations of methyl formate at the full quantum close-coupling level. Collisional propensity rules and astrophysical implications are discussed.
Anomalous optical magnetic shift of self-assembled GaSb/GaAs quantum dots
Authors: Lin Ta-Chun , Li Liang-Chen , Lin Sheng-Di , Suen Yuen-Wuu , Lee Chien-Ping
Published: July 2011

We report the magneto-photoluminescence (PL) measurement results on type-II self-assembled GaSb/GaAs quantum dots with the magnetic field applied in Faraday and Voigt configurations. The emission of the quantum dots exhibited a typical diamagnetic blueshift when the magnetic field was applied in a Faraday configuration. However, when the magnetic field was in the Voigt configuration, an unusual redshift in the emission peak accompanied with a rapid increase of the PL intensity was observed. Guided by numerical calculations, the magnetic field applied in the Voigt configuration is found to provide an additional vertical confinement to electrons, and therefore, substantially enhance the radiative electron-hole recombination. The resulting decrease of the steady-state hole concentration gives rise to the observed anomalous magnetic redshift.
Erratum: “Analysis of a DNA simulation model through hairpin melting experiments” [J. Chem. Phys. 133, 125101 (2010)]
Authors: Linak Margaret C. , Dorfman Kevin D.
Published: July 2011

Changes have been made to this article. See the full text for a description of the changes.
Strain-balanced InAs/GaSb type-II superlattice structures and photodiodes grown on InAs substrates by metalorganic chemical vapor deposition
Authors: Huang Yong , Ryou Jae-Hyun , Dupuis Russell D. , Zuo Daniel , Kesler Benjamin , Chuang Shun-Lien , Hu Hefei , Kim Kyou-Hyun , Ting Lu Yen , Hsieh K. C. , Zuo Jian-Min
Published: July 2011

We propose and demonstrate strain-balanced InAs/GaSb type-II superlattices (T2SLs) grown on InAs substrates employing GaAs-like interfacial (IF) layers by metalorganic chemical vapor deposition (MOCVD) for effective strain management, simplified growth scheme, improved materials crystalline quality, and reduced substrate absorption. The in-plane compressive strain from the GaSb layers in the T2SLs on the InAs was completely balanced by the GaAs-like IF layers formed by controlled precursor carry-over and anion exchange effects, avoiding the use of complicated IF layers and precursor switching schemes that were used for the MOCVD growth of T2SLs on GaSb. An infrared (IR) p-i-n photodiode structure with 320-period InAs/GaSb T2SLs on InAs was grown and the fabricated devices show improved performance characteristics with a peak responsivity of ∼1.9 A/W and a detectivity of ∼6.78 × 109 Jones at 8 μm at 78 K. In addition, the InAs buffer layer and substrate show a lower IR absorption coefficient than GaSb substrates in most of the mid- and long-IR spectral range.
Graphene-based quantum Hall effect infrared photodetector operating at liquid Nitrogen temperatures
Authors: Kalugin Nikolai G. , Jing Lei , Bao Wenzhong , Wickey Lee , Del Barga Christopher , Ovezmyradov Mekan , Shaner Eric A. , Lau Chun Ning
Published: July 2011

We demonstrate a quantum Hall effect (QHE) graphene-based infrared photodetector that functions at 70K—a temperature achievable using liquid Nitrogen in vapor evacuation regime. This result opens up the possibility of wider use of QHE photodetectors if graphene is utilized instead of “classical” materials with two-dimensional electron gas. The potential advantages to this approach are increased operating temperature, reduced magnetic field, and wider range of operating frequency compared to previous implementations of QHE detectors.
Retention mechanism study of the ferroelectric field effect transistor
Authors: Pan Xiao , Ma T. P
Published: July 2011

Single-transistor ferroelectric field effect transistor offers attractive features for future memory applications, such as scalable cell structure, high speed, and low power consumption. However, its relatively short retention time has prevented its application as a non-volatile memory. In order to investigate its retention mechanism, we have developed an automatic retention measurement technique, which enables direct flatband voltage tracking shortly after programming. Two mechanisms, based on the effects of the depolarization field and the gate leakage followed by trapping, respectively, have been identified responsible for the memory window loss in different time regimes, according to the data obtained from this technique.
Ab initio calculation of effective work functions for a TiN/HfO2/SiO2/Si transistor stack
Authors: Prodhomme Pierre-Yves , Fontaine-Vive Fabien , Geest Abram Van Der , Blaise Philippe , Even Jacky
Published: July 2011

Ab initio techniques are used to calculate the effective work function (Weff) of a TiN/HfO2/SiO2/Si stack representing a metal-oxide-semiconductor (MOS) transistor gate taking into account first order many body effects. The required band offsets were calculated at each interface varying its composition. Finally, the transitivity of local density approximation (LDA) calculated bulk band lineups were used and completed by many body perturbation theory (MBPT) bulk corrections for the terminating materials (Si and TiN) of the MOS stack. With these corrections the ab initio calculations predict a Weff of a TiN metal gate on HfO2 to be close to 5.0 eV.
Laser-induced radial birefringence and spin-to-orbital optical angular momentum conversion in silver-doped glasses
Authors: Amjad Jafar Mostafavi , Khalesifard Hamid Reza , Slussarenko Sergei , Karimi Ebrahim , Marrucci Lorenzo , Santamato Enrico
Published: July 2011

Samples of Ag+/Na+ ion-exchanged glass that have been subject to intense laser irradiation may develop novel optical properties, as a consequence of the formation of patterns of silver nanoparticles and other structures. Here, we report the observation of a laser-induced permanent transverse birefringence, with the optical axis forming a radial pattern, as revealed by the spin-to-orbital angular momentum conversion occurring in a probe light beam. The birefringence pattern can be modeled well as resulting from thermally-induced stresses arising in the silver-doped glass during laser exposure, although the actual mechanism leading to the permanent anisotropy is probably more complex.
Ageing in embryos from wheat grains stored at different temperatures: oxidative stress and antioxidant response
Authors: Spanò Carmelina , Bottega Stefania , Lorenzi Roberto , Grilli Isa
Published: July 2011

In the present work we studied oxidative stress as an important cause of seed deterioration during ageing in embryos from durum wheat grains stored at room temperature and at low temperature (10°C). The protective role of low temperature on seed viability was confirmed. The increase of hydrogen peroxide content during dry storage was strongly correlated with the decrease of germinability. Ascorbate and glutathione showed a good correlation with grain germinability and significantly increased upon imbibition, in particular in embryos from viable grains. Ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR), glutathione reductase (GR), glutathione peroxidase (GPX) and catalase (CAT) were studied quantitatively (enzymatic assays). APX, GR, and GPX were also studied qualitatively by native PAGE. The enzymes were active in dry, still viable, embryos whereas no activity was detected in non-viable embryos. With the exception of APX, all enzymatic activities decreased upon imbibition. The study of grains stored in different conditions indicated a negative correlation between the efficiency of the antioxidant enzymatic machinery and the age of the grain. The differences detected in differently stored materials confirmed that both germination parameters and the length of storage period are important in determining grain condition.
A phylogenetic networks approach to the classification of English-based Atlantic creoles
Authors: Daval-Markussen Aymeric , Bakker Peter
Published: July 2011

This paper deals with the issue of genetic relationships between English-based Atlantic creoles. A method borrowed from biology will be applied to a set of lexical and structural features found in the sample presented in Hancock (1987) in order to assess the degrees of affinity between these languages and their evolutionary histories. We will argue that the phylogenetic networks approach proposed here is the most suitable for the classification of creole languages. At the same time, we will show that this tool can also be used to assess the degree of radicalness of a creole, another issue which has been at the heart of creole studies.
The Black Kenyan English vowel system
Authors: Hoffmann Thomas
Published: July 2011

While acoustic phonetic studies have been carried out on all types of Englishes around the world, the second language variety spoken in Kenya has so far not been investigated acoustically. The present paper closes this gap by presenting an acoustic phonetic analysis of acrolectal Kenyan English. The data presented here consist of nine male speakers of acrolectal Kenyan English reading the “The North Wind and the Sun”-passage and were analysed using PRAAT (Boersma 2001; Boersma and Weenink 2008). As I will show, a careful visual and statistical analysis of the data unearthes several features of the Kenyan English vowel system that so far have gone unnoticed (e.g. a trend towards a seven vowel system with two front and two back mid vowels). Furthermore I will argue that some of these features can be traced back to the local L1 feature pool.
Bahamian Standard English
Authors: Bruckmaier Elisabeth , Hackert Stephanie
Published: July 2011

This article presents both quantitative and qualitative information on the orthography, lexis, and morphosyntax of Bahamian Standard English. Employing a press corpus of over 100 000 words, it aims not only at a descriptive account but also at initial answers to two research questions. First, is Standard English as spoken in the Bahamas still following the traditional British norm or has it shifted toward an American orientation; and second, what role does the local creole play in shaping the variety? An overview of the current sociolinguistic situation obtaining in the Bahamas complements the analysis.
Uh and Um as sociolinguistic markers in British English
Authors: Tottie Gunnel
Published: July 2011

This study is based on the British National Corpus (BNC) and also takes data from the London-Lund Corpus (LLC) into account. It shows that the so-called filled pauses er/uh and erm/um are sociolinguistic markers that differentiate between registers of English and along gender, age and socio-economic class. Men, older people and educated speakers use more fillers than women, younger speakers and less educated speakers. Nasalization is used more often by women, younger speakers and more educated speakers. These sociolinguistic factors can probably partly explain the fact that the use of fillers is higher in the LLC and the context-governed sample of the BNC than in the demographic sample of the BNC. It is argued that a more positive view should be taken of fillers as planning signals, or planners, and that their functions should be submitted to careful discourse analytic study. Their recognition as words will facilitate such an undertaking.
Windows on the mind
Authors: Rühlemann Christoph , Bagoutdinov Andrej , O'Donnell Matthew Brook
Published: July 2011

This paper investigates four different types of pauses in conversational narrative: the filled pauses er and erm, and short and long silent pauses. The study is based on the Narrative Corpus (NC), a recently created corpus of everyday narratives. The texts, which include both the narrative and some context, have been annotated for important textual components. The current analysis reveals that pauses are more frequent in conversational narrative than in general conversation. We suggest three factors that account for this high frequency: (i) the need for narrators, in the opening utterance of the story, to provide specific information to orient listeners to the situation in which the events unfolded, (ii) the need to coordinate narrative clauses to match the story events, and (iii) the preference of narrators to present speech, thought, emotion and gesture using direct-mode discourse presentation, which is more “dramatic” but also more costly in terms of reference resolution.
Well I’m not sure I think… The use of well by non-native speakers
Authors: Aijmer Karin
Published: July 2011

Pragmatic markers are an important part of the grammar of conversation and not simply markers of disfluency. They have a number of functions that help the speaker to organise the conversation and to express feelings and attitudes. Advanced EFL learners use frequent pragmatic markers such as well. However their use of well diverges from the native speaker norm. The present study uses data from the Swedish component of the LINDSEI corpus and its native speaker counterpart (LOCNEC) to examine similarities and differences between native and non-native speakers. The overall picture is that Swedish learners overuse well, although there are considerable individual differences. Thus learners use well above all as a fluency device to cope with speech management problems but underuse it for attitudinal purposes. Pragmatic markers cannot be taught in the same way as other lexical items but it is important to discuss how and where they are used.
Cognitive load in simultaneous interpreting
Authors: Seeber Kilian G.
Published: July 2011

This paper sets out to describe and graphically illustrate the amount of cognitive load generated during the simultaneous interpretation of structurally different languages based on theories developed and evidence gathered in cognitive psychology and psycholinguistics. To that end, a German verb-final and verb-initial construction are analyzed and contrasted in terms of the load they cause to an inherently capacity-limited system when interpreted simultaneously into a verb-initial language like English. A series of analytical cognitive load models are introduced providing a detailed illustration of conjectured cognitive resource allocation during simultaneous interpreting of verb-final structures.
Hybridized images
Authors: Wu Doreen D. , Chung Agatha Man-kwan
Published: July 2011

As advertising can be a social factor and cultural artifact, this study analyzes the images of “modern Chinese woman” via an investigation of their role portrayals, appearance/projection, and verbal characteristics represented in a total of 164 award-winning Chinese TV commercials from 2007 to 2009. Results show that a much larger percentage of females in the Chinese TV commercials embody modern rather than traditional representations. The commercials from Mainland China have also manifested modern representations of the women in more dimensions than their counterparts in Hong Kong. Furthermore, hybridization of both the traditional and modern features are most frequently found in the Chinese TV commercials. It is concluded that the modern forms of Chinese femininity is generated from a synthesis of both the traditional and modern values and that the dichotomous approach of globalization vs localization debate in advertising practice has oversimplified the intricate process as well as the product of image representation and transformation of women in Cultural China.