bluuebunny/crossref_metadata_2025 huggingface dataset:
Automatic Aspects in Face Perception
Authors: Anaki David , Nica Elena I. , Moscovitch Morris
Published: April 2010

We examined the perceptual dependency of local facial information on the whole facial context. In Experiment 1 participants matched a predetermined facial feature that appeared in two sequentially presented faces judging whether it is identical or not, while ignoring an irrelevant dimension in the faces. This irrelevant dimension was either (a) compatible or incompatible with the target’s response and (b) same or different in either featural characteristics or metric distance between facial features in the two faces. A compatibility effect was observed for upright but not inverted faces, regardless of the type of change that differentiated between the faces in the irrelevant dimension. Even when the target was presented upright in the inverted faces, to attenuate perceptual load, no compatibility effect was found (Experiment 2). Finally, no compatibility effects were found for either upright or inverted houses (Experiment 3). These findings suggest that holistic face perception is mandatory.
Tolerating Ambiguity
Authors: Hargreaves Ian S. , Pexman Penny M. , Pittman Daniel J. , Goodyear Bradley G.
Published: April 2010

Many models of word recognition predict a lexical ambiguity disadvantage in semantic categorization tasks (SCTs). However, recent evidence suggests that an ambiguity disadvantage in SCT results from a bias in the decision-making phase of the task and not in the meaning-activation phase: Behavioral effects of ambiguity disappear when these decision biases are controlled ( Pexman, Hino, & Lupker, 2004 ). The current study used event-related functional magnetic resonance imaging to examine the neural correlates of ambiguity in a task that produced no behavioral ambiguity effect (i.e., SCT with a well-defined decision category). Twenty healthy adults participated. Results showed that despite producing no behavioral effect of ambiguity, ambiguous words were associated with the recruitment of cortical structures implicated in top-down modulation of noisy activity (e.g., left inferior frontal gyrus) when compared to unambiguous words. These results are interpreted as evidence that multiple meanings are activated for ambiguous words in SCT.
Counterconditioning
Authors: Kerkhof Inneke , Vansteenwegen Debora , Baeyens Frank , Hermans Dirk
Published: April 2010

The evidence for the effectiveness of counterconditioning as a strategy for changing conditioned preferences is rather scarce and inconclusive. The present experiment reinvestigated this issue and compared the effect of further conditioning, extinction, and a counterconditioning procedure on recently acquired conditioned preferences in a picture-taste paradigm. Self-report and affective priming data indicated that whereas further conditioning and extinction trials were ineffective in fully eliminating the previously acquired evaluations, the counterconditioning treatment did succeed in doing this. A follow-up valence assessment revealed that all these effects persisted after a 7-day delay period.
Role of instantaneous force magnitude and duration on particle entrainment
Authors: Valyrakis Manousos , Diplas Panayiotis , Dancey Clint L. , Greer Krista , Celik Ahmet O.
Published: April 2010

A new criterion for the onset of entrainment of coarse sediment grains is presented here. It is hypothesized that not only the magnitude, but also the duration of energetic near bed turbulent events is relevant in predicting grain removal from the bed surface. It is therefore proposed that the product of force and its duration, or impulse, is a more appropriate and universal criterion for identifying conditions for particle dislodgement. This conjecture is investigated utilizing two theoretical models, representative of two modes of entrainment: saltation and rolling. In these models, instantaneous, highly fluctuating turbulent forces are simulated as short‐lived pulses of characteristic magnitude and duration, which transfer adequate fluid momentum to the particle, to trigger its entrainment. The analytical solution of the respective equations of motion is employed in deriving representations of threshold conditions in terms of the impulse characteristics. It is shown that hydrodynamic forces of sufficiently high magnitude are capable of entraining a particle only when they last long enough so that their impulse exceeds a critical value. To illustrate further the validity of the critical impulse concept, as well as extend and generalize its application to different entrainment levels of an individual grain, a novel experimental setup is utilized. This setup facilitates observations of angular displacement of a steel mobile particle in air due to electromagnetic pulses of different magnitude and duration. The experimentally obtained conditions for partial or complete entrainment support the concept of a critical impulse.
Thermospheric density enhancements in the dayside cusp region during strong BY conditions
Authors: Crowley G. , Knipp D. J. , Drake K. A. , Lei J. , Sutton E. , Lühr H.
Published: April 2010

Tri‐axial accelerometer data from the Challenging Minisatellite Payload (CHAMP) satellite have revealed the thermospheric density and its variability in unprecedented detail. The data often contain regions of high density located in the cusp sector at high latitudes. In this paper we provide the first detailed explanation of a high latitude density enhancement observed by CHAMP, focusing on the August 24, 2005 interval. The Thermosphere Ionosphere Mesosphere Electrodynamics General Circulation Model (TIMEGCM) was driven by high‐fidelity high‐latitude inputs specified by the Assimilative Mapping of Ionospheric Electrodynamics (AMIE) algorithm, and reproduced the main features of the density enhancements. The TIMEGCM and AMIE provide a global framework for interpretation of the CHAMP densities. Our simulations reveal that the observed density enhancement in the dayside cusp region resulted from unexpectedly large amounts of energy entering the Ionosphere‐Thermosphere system at cusp latitudes during an interval of strong (+20 nT) BY.
Assessment of the breakup of the Antarctic polar vortex in two new chemistry‐climate models
Authors: Hurwitz M. M. , Newman P. A. , Li F. , Oman L. D. , Morgenstern O. , Braesicke P. , Pyle J. A.
Published: April 2010

Successful simulation of the breakup of the Antarctic polar vortex depends on the representation of tropospheric stationary waves at Southern Hemisphere middle latitudes. This paper assesses the vortex breakup in two new chemistry‐climate models (CCMs). The stratospheric version of the UK Chemistry and Aerosols model is able to reproduce the observed timing of the vortex breakup. Version 2 of the Goddard Earth Observing System (GEOS V2) model is typical of CCMs in that the Antarctic polar vortex breaks up too late; at 10 hPa, the mean transition to easterlies at 60°S is delayed by 12–13 days as compared with the ERA‐40 and National Centers for Environmental Prediction reanalyses. The two models' skill in simulating planetary wave driving during the October–November period accounts for differences in their simulation of the vortex breakup, with GEOS V2 unable to simulate the magnitude and tilt of geopotential height anomalies in the troposphere and thus underestimating the wave driving. In the GEOS V2 CCM the delayed breakup of the Antarctic vortex biases polar temperatures and trace gas distributions in the upper stratosphere in November and December.
Identification of trends and interannual variability of sulfate and black carbon in the Canadian High Arctic: 1981–2007
Authors: Gong S. L. , Zhao T. L. , Sharma S. , Toom‐Sauntry D. , Lavoué D. , Zhang X. B. , Leaitch W. R. , Barrie L. A.
Published: April 2010

Trends and interannual variations of the Canadian High Arctic aerosol record at Alert, Canada (82.5°N), from 1981 to 2007 are investigated and attributed to the influences of anthropogenic emissions and long‐range transports. Sulfate and black carbon (BC) atmospheric mass concentrations declined from the mid 1980s to the late 1990s but have been relatively steady since. These tendencies are closely associated with those of the anthropogenic emissions of Eurasia (Europe and the Asian part of the former Soviet Union) and North America (United States and Canada). Interannual variations correlate with two indices derived from the 700 hPa geopotential heights. Variations in the emissions and the geopotential height indices can be used to reproduce up to 75% of the variations of the observed Arctic sulfate and BC mass concentrations. Over the 27 years of observational record, the relative contribution to sulfate and BC at Alert from Eurasia has decreased from more than 90% to about 75%. During the same time, the contributions from North American emissions has increased from less than 10% to about 25%. The increasing influence from North America was due to the faster reductions of sulfur and black carbon emissions in Eurasia during the period of these observations.
Spatiotemporal gradients in aerosol radiative forcing and heating rate over Bay of Bengal and Arabian Sea derived on the basis of optical, physical, and chemical properties
Authors: Kedia Sumita , Ramachandran S. , Kumar Ashwini , Sarin M. M.
Published: April 2010

Spatiotemporal heterogeneity in aerosol radiative forcing and heating rate have been studied over Bay of Bengal and Arabian Sea during premonsoon (March–May 2006) using aerosol optical depth (AOD), total mass, aerosol chemical composition, and radiative transfer model. Mean 0.5 μm AOD over Bay of Bengal and Arabian Sea is 0.36 and 0.25, respectively. Water‐soluble aerosols, sea salt, and mineral dust constitute ∼98% of total aerosol mass while black carbon aerosols contribute ≤2% over the two oceanic regions. Sensitivity tests reveal that (1) curvature effect in AOD spectra has insignificant impact in modifying the aerosol radiative forcing and heating rate and (2) the net Earth‐atmosphere energy content shows minor differences when aerosol vertical profiles are used. Over Bay of Bengal the average aerosol forcing is estimated to be −12.0, −22.4, and 10.4 W m−2 at the top of the atmosphere (TOA), at the surface (SFC), and in atmosphere (ATM), respectively. The average aerosol radiative forcing is less negative over Arabian Sea and is −10.5, −15.8, and 5.3 W m−2 at TOA, SFC, and ATM, respectively. Aerosol radiative forcing decreases in magnitude from north to south over Bay of Bengal whereas an opposite trend is noteworthy over Arabian Sea. The average atmospheric heating rate over Bay of Bengal is ∼0.3 K/d, a factor of 2 higher than that over Arabian Sea. Furthermore, ATM warming and associated heating rate are the lowest compared to earlier results as scattering aerosols are dominant during premonsoon (March–May). These results have implications to the assessment of regional and seasonal climate impacts.
The east‐west effect in solar proton flux measurements in geostationary orbit: A new GOES capability
Authors: Rodriguez J. V. , Onsager T. G. , Mazur J. E.
Published: April 2010

Since 1998, the GOES system has made eastward and westward observations of multi‐MeV solar proton fluxes. The gyrocenters of the fluxes observed looking westward (eastward) lie outside (inside) geostationary orbit. Due to this “east‐west effect,” eastward observations of 4.2–82 MeV protons vary with respect to their westward equivalents. At times of high solar wind dynamic pressure (Pdyn > 10 nPa), the “inside” and “outside” fluxes are approximately equal. As Pdyn decreases to ∼1 nPa and the ring current decreases, the “inside” fluxes decrease as much as an order of magnitude with respect to the “outside” fluxes. Under low Pdyn, the “inside” fluxes exhibit short‐lived (1–3 hr) increases, sometimes to the levels of the “outside” fluxes, during periods of enhanced AE index activity. This association suggests that magnetotail topologies associated with substorms enhance the access of solar protons to lower L shells under low Pdyn.
The hollow corporation revisited: Can governance mechanisms substitute for technical expertise in managing buyer‐supplier relationships?
Authors: Parmigiani Anne , Mitchell Will
Published: April 2010

AbstractThis article considers how a firm's system of exchange skills including internal technical expertise and supplier governance mechanisms influence supplier performance, both independently and jointly. The core question is whether inter‐firm governance mechanisms, including both relational and contractual mechanisms, can substitute for a firm's internal technical skills in maintaining supplier performance or, alternatively, whether a firm risks hollowing itself out by de‐emphasizing internal expertise when it outsources. The arguments build on the capabilities, inter‐organizational governance, and supply management literatures. We find that internal technical expertise influences multiple dimensions of supplier performance, including cooperation, price, quality, delivery, and communication, while relational governance also affects supplier performance though in a more focused way. In turn, combinations of technical expertise, relational governance, and contractual agreements jointly affect supplier performance. Thus, firms generate superior supplier performance if they retain internal technical skills as well as increase their use of external governance mechanisms to manage buyer‐supplier relationships.
Magnetic properties of Fe3O4 nanoparticles coated with oleic and dodecanoic acids
Authors: Barbeta V. B. , Jardim R. F. , Kiyohara P. K. , Effenberger F. B. , Rossi L. M.
Published: April 2010

Magnetic nanoparticles (NP) of magnetite (Fe3O4) coated with oleic acid (OA) and dodecanoic acid (DA) were synthesized and investigated through transmission electron microscopy (TEM), magnetization M, and ac magnetic susceptibility measurements. The OA coated samples were produced with different magnetic concentrations (78%, 76%, and 65%) and the DA sample with 63% of Fe3O4. Images from TEM indicate that the NP have a nearly spherical geometry and mean diameter ∼5.5 nm. Magnetization measurements, performed in zero-field cooled (ZFC) and field cooled processes under different external magnetic fields H, exhibited a maximum at a given temperature TB in the ZFC curves, which depends on the NP coating (OA or DA), magnetite concentration, and H. The temperature TB decreases monotonically with increasing H and, for a given H, the increase in the magnetite concentration results in an increase in TB. The observed behavior is related to the dipolar interaction between NP, which seems to be an important mechanism in all samples studied. This is supported by the results of the ac magnetic susceptibility χac measurements, where the temperature in which χ′ peaks for different frequencies follows the Vogel–Fulcher model, a feature commonly found in systems with dipolar interactions. Curves of H versus TB/TB(H=0) for samples with different coatings and magnetite concentrations collapse into a universal curve, indicating that the qualitative magnetic behavior of the samples may be described by the NP themselves, instead of the coating or the strength of the dipolar interaction. Below TB, M versus H curves show a coercive field (HC) that increases monotonically with decreasing temperature. The saturation magnetization (MS) follows the Bloch’s law and values of MS at room temperature as high as 78 emu/g were estimated, a result corresponding to ∼80% of the bulk value. The overlap of M/MS versus H/T curves for a given sample and the low HC at high temperatures suggest superparamagnetic behavior in all samples studied. The overlap of M/MS versus H curves at constant temperature for different samples indicates that the NP magnetization behavior is preserved, independently of the coating and magnetite concentration.
Studies of emittance growth and halo particle production in intense charged particle beams using the Paul Trap Simulator Experiment
Authors: Gilson Erik P. , Davidson Ronald C. , Dorf Mikhail , Efthimion Philip C. , Majeski Richard , Chung Moses , Gutierrez Michael S. , Kabcenell Aaron N.
Published: April 2010

The Paul Trap Simulator Experiment (PTSX) is a compact laboratory experiment that places the physicist in the frame-of-reference of a long, charged-particle bunch coasting through a kilometers-long magnetic alternating-gradient (AG) transport system. The transverse dynamics of particles in both systems are described by the same set of equations, including nonlinear space-charge effects. The time-dependent voltages applied to the PTSX quadrupole electrodes in the laboratory frame are equivalent to the spatially periodic magnetic fields applied in the AG system. The transverse emittance of the charge bunch, which is a measure of the area in the transverse phase space that the beam distribution occupies, is an important metric of beam quality. Maintaining low emittance is an important goal when defining AG system tolerances and when designing AG systems to perform beam manipulations such as transverse beam compression. Results are reviewed from experiments in which white noise and colored noise of various amplitudes and durations have been applied to the PTSX electrodes. This noise is observed to drive continuous emittance growth and increase in root-mean-square beam radius over hundreds of lattice periods. Additional results are reviewed from experiments that determine the conditions necessary to adiabatically reduce the charge bunch’s transverse size and simultaneously maintain high beam quality. During adiabatic transitions, there is no change in the transverse emittance. The transverse compression can be achieved either by a gradual change in the PTSX voltage waveform amplitude or frequency. Results are presented from experiments in which low emittance is achieved by using focusing-off-defocusing-off waveforms.
Large signal electromechanical properties of low loss (1−x)Pb(Mg1/3Nb2/3)O3−xPbTiO3 single crystals
Authors: Sherlock Nevin P. , Zhang Shujun , Luo Jun , Lee Ho-Yong , Shrout Thomas R. , Meyer Richard J.
Published: April 2010

The use of single crystals based on the solid solution (1−x)Pb(Mg1/3Nb2/3)O3−xPbTiO3 (PMNT) has been demonstrated in many piezoelectric devices, but the low mechanical quality factor has limited its use in high power projector applications. In this work, 33-mode properties of PMNT single crystals with various modifications were evaluated to see if self-heating may be reduced by decreasing the mechanical and electrical losses within the active material. Three modifications were evaluated: incorporating ternary components, adding acceptor dopants, or orienting the crystal along different crystallographic directions. The electromechanical properties of these modified crystals were evaluated under increasing levels of dynamic strain. The results suggest that modified single crystal PMNT may improve the source level from a projector while reducing thermal effects from self-heating, making them appropriate for high power applications.
Effect of a lattice-matched GaAsSb capping layer on the structural properties of InAs/InGaAs/InP quantum dots
Authors: Ulloa J. M. , Koenraad P. M. , Bonnet-Eymard M. , Létoublon A. , Bertru N.
Published: April 2010

The influence of a lattice-matched GaAsSb capping layer on the structural properties of self-assembled InAs quantum dots (QDs) grown on InP substrates is studied on the atomic scale by cross-sectional scanning tunneling microscopy. While lattice-matched In0.53Ga0.47As-capped QDs are clearly truncated pyramids, GaAs0.51Sb0.49-capped QDs grown under the same conditions look like full pyramids and exhibit a larger height, indicating that capping with GaAsSb reduces dot decomposition. Since there are no differences in strain between the two capping layers, this behavior is most likely related to the surfactant effect of Sb, which stabilizes the growth front and avoids adatom migration.
High-pressure in situ structure measurement of low-Z noncrystalline materials with a diamond-anvil cell by an x-ray diffraction method
Authors: Sato Tomoko , Funamori Nobumasa , Kikegawa Takumi
Published: April 2010

We have developed techniques for high-pressure in situ structure measurement of low-Z noncrystalline materials with a diamond-anvil cell (DAC) by an x-ray diffraction method. Since the interaction between low-Z materials and x rays is small and the sample thickness in a DAC is also small, the incoherent scattering from the anvils overwhelms the coherent scattering from the sample at a high-Q range. By using a cubic boron nitride gasket to increase the sample thickness and the energy-dispersive x-ray diffraction method with a slit system to narrow the region from which detected x rays are scattered, we can reduce unfavorable effects of the incoherent scattering from the anvils and correct them accurately. We have successfully measured the structure factor of SiO2 glass in a DAC over a relatively wide range of Q under high pressure.
A molecular picture of motion in polyolefins
Authors: Boland Erin K. , Liu Jiahong , Maranas Janna K.
Published: April 2010

We examined three united atom models in light of their description of polyolefin dynamics and investigated the relative influence of various potentials on the resulting dynamics. Results were compared with a collection of experimental data on polyethylene, poly(ethylene-alt-propylene), polypropylene, and head-to-head polypropylene, including quasielastic neutron scattering measurements that we report for two of these materials. For materials with branching, differences between force fields are apparent at low temperature, with the NERD force field most accurate. Differences between NERD and the others are the strength of nonbonded interactions and the height of torsional barriers. We artificially raised each, both of which leads to a slow down in dynamics similar to that observed when lowering temperature. Increasing nonbonded interaction strength slows dynamics with the Vogel dependence of the α-relaxation, while raising torsional barriers, slows dynamics with the Arrhenius dependence of the β-relaxation.
Efficient ab initio path integral hybrid Monte Carlo based on the fourth-order Trotter expansion: Application to fluoride ion-water cluster
Authors: Suzuki Kimichi , Tachikawa Masanori , Shiga Motoyuki
Published: April 2010

We propose an efficient path integral hybrid Monte Carlo (PIHMC) method based on fourth-order Trotter expansion. Here, the second-order effective force is employed to generate short trial trajectories to avoid computationally expensive Hessian matrix, while the final acceptance is judged based on fourth-order effective potential. The computational performance of our PIHMC scheme is compared with that of conventional PIHMC and PIMD methods based on second- and fourth-order Trotter expansions. Our method is applied to on-the-fly ab initio PIHMC calculation of fluoride ion-water complexes, F−(H2O) and F−(D2O), at ambient temperature, particularly focusing on the geometrical isotope effect.
Dual-band relativistic backward wave oscillators based on a single beam and dual beams
Authors: Ting Wang , Jian-de Zhang , Bao-liang Qian , Xiao-ping Zhang
Published: April 2010

Two types of relativistic backward wave oscillators (RBWOs) used to produce dual-band microwaves are proposed and investigated by use of the particle-in-cell (PIC) simulation code KARAT [V. P. Tarakanov, User’s Manual for Code Karat (Berkeley Research Associates, Springfield, VA, 1992)]. The first type of RBWO, for generation of C-band and X-band microwaves, is designed based on a single beam and a sectioned structure. With an electron beam of 650 keV and 5.0 kA guided by a magnetic field of 2.0 T, an average power of 380 MW with a total power conversion efficiency of 11.7% is obtained and the frequencies are 5.48 and 9.60 GHz, respectively. By changing the distance between the two sections, single-band oscillations are realized with higher power conversion efficiency than that of the dual-band oscillation. The second type, based on a coaxial structure and dual parallel annular beams, is a dual-band RBWO designed with separated beam-wave interaction regions for generation of C-band and X-band microwaves. With a dual beam of 650 keV and 11.8 kA (the outer beam current is 6.4 kA and inner beam current is 5.4 kA) guided by a magnetic field of 2.0 T, an output power of 1400 MW with a total power conversion efficiency of 18.3% is generated and the frequencies are 4.60 and 8.40 GHz, respectively. PIC simulations demonstrate that the two beam-wave interaction regions operate independently. The two types of dual-band RBWO are also compared and analyzed.
Effect of preionization on soft x-ray emission and plasma dynamics in a small plasma focus system
Authors: Khan H. U. , Shafiq M. , Hussain S. S. , Zakaullah M.
Published: April 2010

A conventional plasma focus device is operated in a volumetric mixture ratio of Ne+He (50:50) to produce a hot and dense plasma without and with preionization which emits radiation in the soft x-ray region. A ring of depleted uranium is employed as a preionization source. Quantrad silicon PIN diodes and a multipinhole camera with suitable filters are used for x-ray analysis. X-ray emission in 4π geometry is measured as a function of Ne+He mixture filling pressure. The experimental results show that preionization not only enhances the yield of the soft x-rays but also increases the focus duration and shot to shot reproducibility of plasma focus. The x-ray images reveal that preionization makes the focus filament symmetric and also enhances its volume.
Photoinduced broadening of cholesteric liquid crystal reflectors
Authors: White Timothy J. , Freer Alexander S. , Tabiryan Nelson V. , Bunning Timothy J.
Published: April 2010

The selective reflection of cholesteric liquid crystals (CLCs) is well-known and has been utilized in a number of dynamic optical applications. This work presents a novel approach to passively (e.g., all-optically) cue reflection notch broadening in photoresponsive CLC formulations based on high helical twisting power (HTP) bis(azo) chiral dopants. The original reflection bandwidth of approximately 100 nm is increased to as much as 1700 nm, by exposing 36 μm thick cells to UV light. The maximum attainable bandwidth is shown to be a function of cell thickness, light intensity, and strongly related to the HTP of the photoresponsive chiral dopants. An all-optical technique of simultaneous UV and green light exposure is demonstrated to trap the reflection notch at a predetermined position and bandwidth.
Room temperature ferromagnetic behavior in the hollandite-type titanium oxide
Authors: Noami K. , Muraoka Y. , Wakita T. , Hirai M. , Kato Y. , Muro T. , Tamenori Y. , Yokoya T.
Published: April 2010

A hollandite-type KxTi8O16 polycrystalline sample has been prepared and studied by magnetization, resistivity and x-ray photoelectron spectroscopy (XPS). Room temperature ferromagnetic behavior is observed in the magnetic hysteresis measurement. The sample shows a semiconductive temperature dependence in the resistivity measurement. Analysis of the Ti 2p3/2 core-level XPS spectrum indicates that the titanium ions have a mixed valence of Ti4+ and Ti3+. In addition, the valence band spectrum reveals that the 3d electrons tend to localize on Ti3+ ions in the hollandite-type TiO2 lattice. Also, analysis of the valence band spectrum shows that the prepared sample is a wide-gap oxide with a band gap of 3.6 eV. These results indicate that the present hollandite-type KxTi8O16 sample can be classified as a TiO2-based wide-gap semiconductor with Curie temperature above room temperature. Room temperature ferromagnetism (RTFM) decreases in the sample prepared under a strong reducing gas atmosphere, accompanied with the decrease in the resistivity. The results imply that the localized 3d electrons are responsible for the RTFM of the KxTi8O16 sample.
Experimental investigations on the propagation of the plasma jet in the open air
Authors: Xiong Q. , Lu X. , Xian Y. , Liu J. , Zou C. , Xiong Z. , Gong W. , Chen K. , Pei X. , Zou F. , Hu J. , Jiang Z. , Pan Y.
Published: April 2010

The fundamental of the generation and propagation of the atmospheric pressure nonequilibrium plasma jets has recently attracted significant interests. In this paper, investigations on the effects of the parameters of the pulsed dc voltages on the optical emission intensity of the plasma jet and the bullet propagation behavior are carried out based on the temporal-spatial resolved optical emission spectroscopy measurements and the high-speed photography. It is found that, with the increase in the applied voltage, the bullet propagates out from the nozzle earlier and accelerates to higher peak-velocities. The increase in the pulse frequency exerts no significant influences on the optical emission of the plasma jet and the bullet propagation velocity. But it can induce the bullet propagates out from the nozzle earlier. Besides, it is interesting to notice that, with the increase in the pulse width in the beginning, the bullet propagates out from the nozzle with longer delay time. However, when the pulse width is increased to be more than 100 μs, the delay time of the bullet propagating out from the nozzle becomes much shorter. On the other hand, with the increase in the pulse width, the optical emission intensity of the plasma jet drops and the maximum bullet velocity decreases too. Detailed analysis shows that it may be due to the accumulation of the charges and radicals, which can shorten the prebreakdown of the discharge inside the syringe and result in the bullet propagating out earlier from the nozzle.
Effect of carriers transfer behavior on the optical properties of InAs quantum dots embedded in AlGaAs/GaAs heterojunction
Authors: Khmissi H. , Sfaxi L. , Bouzaïene L. , Saidi F. , Maaref H. , Bru-Chevallier C.
Published: April 2010

In this paper, we have investigated the optical properties of InAs quantum dots (Qds) embedded near the channel of a delta-doped AlGaAs/GaAs high electron mobility transistor. In order to study the influence of the two-dimensional electron gas (2DEG) on the luminescence of QDs, we have prepared different structures in which we varied the thickness (d) separating the interface of AlGaAs/GaAs heterojunction from the InAs quantum dot layer. Various photoluminescence (PL) behaviors are observed when d decreases. PL spectra show the existence of two peaks which can be attributed to transition energies from the ground state (E1-HH1) and the first excited state (E2-HH2). A blueshift, a decrease in the PL intensity and an increase in the full width at half maximum of the PL peaks are observed, when the InAs QDs layer is closer to the 2DEG.
Spherical codes, maximal local packing density, and the golden ratio
Authors: Hopkins Adam B. , Stillinger Frank H. , Torquato Salvatore
Published: April 2010

The densest local packing (DLP) problem in d-dimensional Euclidean space Rd involves the placement of N nonoverlapping spheres of unit diameter near an additional fixed unit-diameter sphere such that the greatest distance from the center of the fixed sphere to the centers of any of the N surrounding spheres is minimized. Solutions to the DLP problem are relevant to the realizability of pair correlation functions for packings of nonoverlapping spheres and might prove useful in improving upon the best known upper bounds on the maximum packing fraction of sphere packings in dimensions greater than 3. The optimal spherical code problem in Rd involves the placement of the centers of N nonoverlapping spheres of unit diameter onto the surface of a sphere of radius R such that R is minimized. It is proved that in any dimension, all solutions between unity and the golden ratio τ to the optimal spherical code problem for N spheres are also solutions to the corresponding DLP problem. It follows that for any packing of nonoverlapping spheres of unit diameter, a spherical region of radius less than or equal to τ centered on an arbitrary sphere center cannot enclose a number of sphere centers greater than 1 more than the number that than can be placed on the region’s surface.
Giant magnetoelectric effect in magnet-cymbal-solenoid current-to-voltage conversion device
Authors: Zeng Min , Or Siu Wing , Chan Helen Lai Wa
Published: April 2010

A giant magnetoelectric (ME) effect is reported in a current-to-voltage (I-to-V) conversion device formed by sandwiching a PZT piezoelectric cymbal transducer between an NdFeB magnet and a Fe-core solenoid. The observed ME effect results from the direct coupling of the electromagnetically induced attractive-repellent force effect in the magnet-solenoid assembly with the amplified piezoelectric effect in the cymbal transducer. The device exhibits a colossal I-to-V conversion factor (S) of 27.1 V/A with a giant ME coefficient (αV) of 1.24 V/Oe at a low resonance frequency of 2.33 kHz, besides a large S of 0.74 V/A with a high αV of 34 mV/Oe in the nonresonance frequency range of 40 Hz–1 kHz. A physical model based on the combination of electromagnetomechanics in the magnet-solenoid assembly and amplified piezoelectricity in the cymbal transducer is present to explain the observed ME effect and the resulting I-to-V conversion in the device.
Development of absolute hot-wire anemometry by the 3ω method
Authors: Heyd Rodolphe , Hadaoui Abdallah , Fliyou Mohamed , Koumina Abdelaziz , Ameziane Lahcen El Hassani , Outzourhit Abdelkader , Saboungi Marie-Louise
Published: April 2010

We have developed hot-wire anemometry applying the 3ω method. The approach is based on the same heat transfer process as traditional anemometry, but substituting the constant current by a sinusoidal current and using synchronous detection to measure the conductive-convective exchange coefficient and the gas flow rate. Our theoretical model is tested with air flow at 300 K under atmospheric pressure: The experimental results are in agreement with the numerical simulation, justifying the technical choices in the 3ω method and the approximations made. The effectiveness of the 3ω method for measuring the flow rate and the conductive-convective exchange coefficient between the hot wire and flowing gas is discussed.
Fast integrator based data acquisition system for the SST-1 Thomson scattering system
Authors: Patel Kiran , Kumar Ajai
Published: April 2010

An operational transconductance amplifier based fast charge-integrating module (FCIM) is designed and developed for an easy acquisition of fast Thomson scattered and background signal. FCIM based data acquisition technique can be used for the measurement of charge pulses of <20 ns duration. The response of the module is tested using a standard pulsed charge-generating module. The measuring charge range of the module depends on the integrating capacitor. Comparison of the performance of FCIM to commercially available module shows that it has better dynamic range with higher sensitivity and less measurement error. The module is quite cost effective and has many new features.
Applying uniform reversible strain to epitaxial oxide films
Authors: Biegalski M. D. , Dörr K. , Kim D. H. , Christen H. M.
Published: April 2010

We demonstrate using four-circle x-ray diffraction that the piezoelectric substrate of Pb(Mg1/3Nb2/3)0.72Ti0.28O3(001) induces uniform reversible in-plane strain to epitaxially-grown oxide films and bilayers. The biaxial in-plane strain depends linearly on the applied electrical voltage. Utilizing the reversible strain, the strain-dependent lattice structure and the Poisson number characterizing the elastic response is determined for 200 nm thick SrTiO3, LaScO3, and BiFeO3 films. The uniformity and reversibility of the strain provides access to the direct quantitative measurement of strain-dependent properties of epitaxial oxide films.
Runaway electron dynamics during impurity gas puffing on HT-7 tokamak
Authors: Sajjad S. , Gao X. , Ling B. , Bhatti S. H. , Ang T.
Published: April 2010

Runaway electrons have been studied by injection/gas puffing of argon and neon gases during low-density, current ramp-down deuterium discharges in the HT-7 tokamak [X. Gao, Plasma Sci. Technol. 1, 25 (1999)]. The argon and neon gases have been injected/puffed separately during runaway Ohmic discharges, and the effects of these gases on runaway electron dynamics have been observed with different gas pulse widths and varied injection times. It has been found that the injection of a noble gas such as argon or neon can terminate the already generated runaway currents in the discharge before the runaway electrons hit the limiter or vessel structures. It has also been observed that runaway electrons cannot gain high energies in the presence of noble gas, and thereby are cooled down to their thermal velocities. During puffing of argon gas, a time delay has been observed before triggering the secondary emission of runaway electrons with a gas pulse width of 10–20 ms, whereas the same effect has also been observed with neon gas with a gas pulse width of 40–50 ms. For a 60–100 ms gas pulse width the runaway electrons have been partially suppressed, and earlier termination of the discharges was observed due to sawtooth collapse of heat energy in the center of the discharge, characterized by hard x-ray and γ ray emissions. The maximum energy of runaway electrons (12 MeV) inferred from gamma spectra is in agreement with the runaway limiting energy predicted by a test particle description of the runaway dynamics [J. R. Martín-Solís et al., Phys. Plasmas 5, 2370 (1998)].
Ion-beam driven dust ion-acoustic solitary waves in dusty plasmas
Authors: Adhikary N. C. , Misra A. P. , Bailung H. , Chutia J.
Published: April 2010

The nonlinear propagation of small but finite amplitude dust ion-acoustic waves (DIAWs) in an ion-beam driven plasma consisting of Boltzmannian electrons, positive ions, and stationary negatively charged dust grains is studied by using the standard reductive perturbation technique. It is shown that there exist two critical values (γc1 and γc2) of ion beam to ion phase velocity ratio (γ), above and below which the beam generated solitons are not possible. The effects of the parameters, namely, γ, the ratio of the ion beam to plasma ion density (μi), the dust to ion density ratio (μd), and the ion beam to plasma ion mass ratio (μ) on both the amplitude and width of the stationary DIAWs, are analyzed numerically, and applications of the results to laboratory ion beam as well as space plasmas (e.g., auroral plasmas) are explained.
Constraints on an empirical equation for asymmetry-induced transport
Authors: Eggleston D. L.
Published: April 2010

Previous work on asymmetry-induced transport in a modified Malmberg–Penning trap showed that the radial particle flux was empirically constrained to be of the form Γ(ϵ)=−(B0/B)1.33D(ϵ)[∇n0+f(ϵ)], where ϵ=ω−lωR, ωR(r)=vθ/r is the column rotation frequency, ω and l are the asymmetry frequency and azimuthal mode number, ∇n0 is the radial density gradient, B is the magnetic field, B0 is an empirical constant, and D(ϵ) and f(ϵ) are unknown functions. In this paper, it is shown that further constraints can be placed upon D(ϵ) and f(ϵ) by comparing data near the ϵ=0 points to a first order expansion of Γ(ϵ). It is shown that dD/dϵ(0)≠0, in contradiction to resonant particle theory, and that f(ϵ) can only be a fraction of the size predicted by that theory. Finally, it is shown that dD/dϵ(0) exhibits a power-law scaling with radius, magnetic field, and the bias of the center conductor of the trap.
Ion beam formation in a very low magnetic field expanding helicon discharge
Authors: Lafleur T. , Charles C. , Boswell R. W.
Published: April 2010

An ion beam has been measured emerging from a low pressure (0.04 Pa) helicon plasma reactor over a narrow range of magnetic field values (1 mT<B0<3 mT). The presence of the ion beam occurs simultaneously with a large increase in the plasma density for the same applied magnetic field, produced using a single solenoid half the length of the m=1 rf antenna. The peak central plasma density of 1.5×1017 m−3 is measured to be almost 15 times larger than that occurring before or after the increase, and is associated with a steep axial density gradient which follows the gradient of the magnetic field. During this low magnetic field transition the antenna power transfer efficiency is measured to increase from less than 10% to 50%, suggesting some form of localized bulk electron heating in the source region associated with the helicon wave.
Nonequilibrium adiabatic molecular dynamics simulations of methane clathrate hydrate decomposition
Authors: Alavi Saman , Ripmeester J. A.
Published: April 2010

Nonequilibrium, constant energy, constant volume (NVE) molecular dynamics simulations are used to study the decomposition of methane clathrate hydrate in contact with water. Under adiabatic conditions, the rate of methane clathrate decomposition is affected by heat and mass transfer arising from the breakup of the clathrate hydrate framework and release of the methane gas at the solid-liquid interface and diffusion of methane through water. We observe that temperature gradients are established between the clathrate and solution phases as a result of the endothermic clathrate decomposition process and this factor must be considered when modeling the decomposition process. Additionally we observe that clathrate decomposition does not occur gradually with breakup of individual cages, but rather in a concerted fashion with rows of structure I cages parallel to the interface decomposing simultaneously. Due to the concerted breakup of layers of the hydrate, large amounts of methane gas are released near the surface which can form bubbles that will greatly affect the rate of mass transfer near the surface of the clathrate phase. The effects of these phenomena on the rate of methane hydrate decomposition are determined and implications on hydrate dissociation in natural methane hydrate reservoirs are discussed.
Atomistic model of the spider silk nanostructure
Authors: Keten Sinan , Buehler Markus J.
Published: April 2010

Spider silk is an ultrastrong and extensible self-assembling biopolymer that outperforms the mechanical characteristics of many synthetic materials including steel. Here we report atomic-level structures that represent aggregates of MaSp1 proteins from the N. Clavipes silk sequence based on a bottom-up computational approach using replica exchange molecular dynamics. We discover that poly-alanine regions predominantly form distinct and orderly beta-sheet crystal domains while disorderly structures are formed by poly-glycine repeats, resembling 31-helices. These could be the molecular source of the large semicrystalline fraction observed in silks, and also form the basis of the so-called “prestretched” molecular configuration. Our structures are validated against experimental data based on dihedral angle pair calculations presented in Ramachandran plots, alpha-carbon atomic distances, as well as secondary structure content.
Single-crystal II-VI on Si single-junction and tandem solar cells
Authors: Carmody M. , Mallick S. , Margetis J. , Kodama R. , Biegala T. , Xu D. , Bechmann P. , Garland J. W. , Sivananthan S.
Published: April 2010

CdTe is one of the leading materials used in solar photovoltaics. However, the maximum reported CdTe cell efficiencies are considerably lower than the theoretically expected efficiencies for the ∼1.48 eV CdTe band gap. We report a class of single crystal CdTe-based solar cells grown epitaxially on crystalline Si that show promise for enhancing the efficiency and greatly lowering the cost per watt of single-junction and multijunction solar cells. The current-voltage results for our CdZnTe on Si solar cells show open-circuit voltages significantly higher than previously reported for any II-VI cells and as close to the thermodynamic limit as the best III-V-based cells.
Giant reversible magnetocaloric effect in metamagnetic HoCuSi compound
Authors: Chen J. , Shen B. G. , Dong Q. Y. , Hu F. X. , Sun J. R.
Published: April 2010

The magnetic properties and magnetocaloric effect (MCE) of antiferromagnetic HoCuSi compound have been studied. It is found that HoCuSi undergoes a field-induced first order metamagnetic transition from antiferromagnetic (AFM) to ferromagnetic (FM) states below the Néel temperature (TN). A giant MCE without hysteresis loss is observed in HoCuSi around TN. The maximal magnetic entropy change (−ΔSM) and refrigerant capacity are 33.1 J/kgK and 385 J/kg, respectively, for a field change of 0–5 T. The excellent magnetocaloric properties can result from the field-induced AFM-FM transition below TN and the increase in magnetization change caused by the change in lattice volume at TN.
Size dependence of transverse electric transport in single ZnO nanoneedles
Authors: Yang Ya , Qi Junjie , Guo Wen , Zhao Jing , Wang Xueqiang , Zhang Yue
Published: April 2010

We report a size dependence of transverse electric transport in single ZnO nanoneedles with diameters ranging from 5 to 50 nm. Under the same voltages, the measured transverse current through the single ZnO nanoneedle was found to decrease dramatically with the decreasing diameters from 50 to 20 nm, and no current were detected when the diameters are smaller than 20 nm. A spherical electric transport model is proposed to explore the origin of the size dependence.
Anharmonic effects in ZnO optical phonons probed by Raman spectroscopy
Authors: Millot Marius , Tena-Zaera Ramon , Munoz-Sanjose Vicente , Broto Jean-Marc , Gonzalez Jesus
Published: April 2010

We report Raman spectroscopy measurements on ZnO crystals grown by the vapor transport method and annealed. Vacuum annealing is found to yield single crystals with ultra low density of defects. We focus on the optical E2 phonon linewidth temperature dependence in the 10–500 K range. The linewidth decrease at low temperature is analyzed and discussed in the light of anharmonic up- and down-conversion processes, unveiling strongly different behaviors for the two E2 phonons.
Quantum capacitance and density of states of graphene
Authors: Dröscher S. , Roulleau P. , Molitor F. , Studerus P. , Stampfer C. , Ensslin K. , Ihn T.
Published: April 2010

We report on measurements of the quantum capacitance in graphene as a function of charge carrier density. A resonant LC-circuit giving high sensitivity to small capacitance changes is employed. The density of states, which is directly proportional to the quantum capacitance, is found to be significantly larger than zero at and around the charge neutrality point. This finding is interpreted to be a result of potential fluctuations with amplitudes of the order of 100 meV in good agreement with scanning single-electron transistor measurements on bulk graphene and transport studies on nanoribbons.
Properties of a nanodielectric cryogenic resin
Authors: Polizos Georgios , Tuncer Enis , Sauers Isidor , More Karren L.
Published: April 2010

Physical properties of a nanodielectric composed of in situ synthesized titanium dioxide (TiO2) nanoparticles (≤5 nm in diameter) and a cryogenic resin are reported. The dielectric losses were reduced by a factor of 2 in the nanocomposite, indicating that the presence of small TiO2 nanoparticles restricted the mobility of the polymer chains. Dielectric breakdown data of the nanodielectric was distributed over a narrower range than that of the unfilled resin. The nanodielectric had 1.56 times higher 1% breakdown probability than the resin, yielding 0.64 times thinner insulation thickness for the same voltage level, which is beneficial in high voltage engineering.