bluuebunny/crossref_metadata_2025 huggingface dataset:
High‐speed video observations of positive ground flashes produced by intracloud lightning
Authors: Saba Marcelo M. F. , Campos Leandro Z. S. , Krider E. Philip , Pinto Osmar
Published: June 2009

High‐speed video recordings of two lightning flashes confirm that positive cloud‐to‐ground (CG) strokes can be produced by extensive horizontal intracloud (IC) discharges within and near the cloud base. These recordings constitute the first observations of CG leaders emanating from IC discharges of either polarity. In one case, the discharge began with a negative leader that propagated horizontally, went upward and produced an IC discharge. After the beginning of the IC discharge, a positive leader emanated from the lowest portion of the IC discharge, and initiated a positive return stroke. In the other case, the IC discharge began with a positive leader and then initiated a downward‐propagating positive leader that contained recoil processes and produced a bright return stroke followed by a long continuing luminosity. These observations help to understand the complex genesis of positive CG flashes, why IC lightning commonly precedes them and why extensive horizontal channels are often involved.
Psychrophilic methanogenic community development during long-term cultivation of anaerobic granular biofilms
Authors: McKeown Rory M , Scully Colm , Enright Anne-Marie , Chinalia Fabio A , Lee Changsoo , Mahony Thérèse , Collins Gavin , O'Flaherty Vincent
Published: June 2009

Granular biomass was temporally sampled from a cold (4–15 °C) anaerobic bioreactor, which was inoculated with mesophilic biomass and used to treat industrial wastewater in a long-term (3.4 year) study. Data from 16S rRNA gene clone libraries, quantitative PCR and terminal restriction fragment length polymorphism analyses indicated that microbial community structure was dynamic, with shifts in the archaeal and bacterial communities' structures observed following start-up and during temperature decreases from 15 to 9.5 °C (phase 1). Specifically, the relative abundance of architecturally important Methanosaeta-like (acetoclastic) methanogens decreased, which was concomitant with granule disintegration and the development of a putatively psychrophilic hydrogenotrophic methanogenic community. Genetic fingerprinting suggested the development of a psychroactive methanogenic community between 4 and 10 °C (phase 2), which was dominated by acetogenic bacteria and Methanocorpusculum-like (hydrogenotrophic) methanogens. High levels of Methanosaeta-like acetoclastic methanogens and granular biofilm integrity were maintained during phase 2. Overall, decreasing temperature resulted in distinctly altered microbial community structure during phase 1, and the development of a less dynamic psychroactive methanogenic consortium during phase 2. Moreover, psychrophilic H2-oxidizing methanogens emerged as important members of the psychroactive consortia after >1200 days of low-temperature cultivation. The data suggest that prolonged psychrophilic cultivation of mesophilic biomass can establish a well-functioning psychroactive methanogenic consortium, thus highlighting the potential of low-temperature anaerobic digestion technology.
Affective Responses to Increasing Levels of Exercise Intensity in Normal‐weight, Overweight, and Obese Middle‐aged Women
Authors: Ekkekakis Panteleimon , Lind Erik , Vazou Spiridoula
Published: June 2009

At least 60 min of daily physical activity (PA) are recommended for weight control, a target achieved by only 3% of obese (OB) women. The purposes of this study were to examine (i) the affective responses of normal‐weight (NW), overweight (OW), and OB middle‐aged sedentary women to exercise of increasing intensity and (ii) the relationship of affective responses to self‐efficacy and social physique anxiety. The women participated in a graded treadmill protocol to volitional exhaustion while providing ratings of pleasure–displeasure and perceived activation each minute. The Activation Deactivation Adjective Check List (AD ACL) was also completed before and after exercise. The affective responses of NW and OW women did not differ. However OB women gave lower pleasure ratings during the incremental protocol and reported lower Energy scores immediately after the protocol. Social physique anxiety, but not self‐efficacy, was inversely related to pleasure and energy. The lower levels of pleasure and energy experienced by OB than nonobese women could account in part for their dramatically low levels of PA participation. Modifying the cognitive antecedents of social physique anxiety might be a useful intervention strategy.
The Bias in Self‐reported Obesity From 1976 to 2005: A Canada–US Comparison
Authors: Gorber Sarah Connor , Tremblay Mark S.
Published: June 2009

The objective of this study was to determine whether the bias in self‐reported estimates of obesity has changed over time and followed different patterns in Canada and the United States. Using age‐standardized data from three waves of the National Health and Nutrition Examination Survey (NHANES) in the United States and the Canadian Community Health Survey (CCHS) and the Canadian Heart Health Survey (CHHS) in Canada, discrepancies were compared between reported and measured estimates of height, weight, and obesity (based on the BMI) from 1976 to 2005. Results indicated that obesity increased in both countries, but rates were higher in the United States. The discrepancy between self‐reported and measured obesity was small in the United States with reported data underestimating measured prevalence by about 3%; this stayed relatively constant over time. In Canada, the discrepancy was large and doubled in the past decade (from 4 to 8%). In the United States, self‐reported data may be more accurate in monitoring changes in obesity over time, as the estimates have consistently remained about 3% below the measured estimates, whereas in Canada, monitoring obesity based solely on self‐reported height and weight may produce inaccurate estimates because of the increasing discrepancy between self‐reported and measured data.
Instruction in Cause and Effect Paraphrasing Using Social Studies Text With a Secondary Bilingual Student: A Case Study
Authors: Bejos Karla
Published: June 2009

Purpose: This case study describes the use of the paraphrasing strategy with cause-and-effect (C/E) relations as a technique to improve a 14-year-old high school student's reading comprehension of social studies text in both his native (Spanish) and second language (English).

Method: The student used expository texts from state textbook adoption materials. Instruction was based on scaffolded dialogue that cued the student to attend to and paraphrase various aspects of the C/E concept.

Results: Despite the fact that the student began with texts at reading levels 5 and 6 years below his actual grade level, the comprehension of C/E relations in history text was a challenge. Several factors contributed to the complexity of the task for the student. By the final phase of intervention, he was successfully paraphrasing with texts that were 3 and 4 years above the baseline reading grade levels.

Implications: The salient points from this study that may be useful for educators or speech language pathologists are: a description of the difficulties that interfered with the student's comprehension and the thought processes he used, types of cues used to teach C/E relations, and evidence of the student's development of paraphrases and comprehension.
Spheroid 3C inclusions in 8° off-axis 4H-SiC epilayers grown by chemical vapor deposition
Authors: Zhang X. , Li L. , Skowronski M. , Sumakeris J. J. , Paisley M. J. , O’Loughlin M. J.
Published: June 2009

Spheroidal inclusions in 4H-SiC homoepitaxial layers deposited by silane-based chemical vapor deposition (CVD) process have been investigated by KOH etching, optical microscopy, and transmission electron microscopy. The inclusions consist of polycrystalline 3C silicon carbide bearing no orientational relationship with the substrate and cause characteristic corrugation of epilayer surface referred to as “arrow” defect. Their origin is interpreted as due to SiC particles deposited on the wafer surface at the initial stages of the CVD process.
Real-time data processing and magnetic field pitch angle estimation of the JET motional Stark effect diagnostic based on Kalman filtering
Authors: Coelho R. , Alves D. , Hawkes N. , Brix M. ,   JET EFDA Contributors
Published: June 2009

A novel technique for the real-time measurement of the magnetic field pitch angle in JET discharges using the motional Stark effect diagnostic is presented. Kalman filtering techniques are adopted to estimate the amplitude of the avalanche photodiode signals’ harmonics that are relevant for the pitch angle calculation. The proposed technique {for extended technical details of the generic algorithm see [R. Coelho and D. Alves, IEEE Trans. Plasma Sci. 37, 164 (2009)]} is shown to be much more robust and provides less noisy estimates than an equivalent lock-in amplifier scheme, in particular when dealing with edge localized modes.
Nonequilibrium Green’s function study on the electronic structure and transportation behavior of the conjugated molecular junction: Terminal connections and intramolecular connections
Authors: Liu Hongmei , Ni Wenbin , Zhao Jianwei , Wang Nan , Guo Yan , Taketsugu Tetsuya , Kiguchi Manabu , Murakoshi Kei
Published: June 2009

In the recent density functional-based calculations, it was found that the conductivity of naphthalene molecular wires can be modulated by altering the linking position of the molecule to the electrode [D. Walter, D. Neuhauser, and R. Baer, Chem. Phys. 299, 139 (2004)]. A quantum interference model was proposed to interpret the observation. In this paper, we further studied the conductance of a series of conjugated molecules containing aromatic rings using density functional theory combined with nonequilibrium Green’s function method. For polyacene systems with different terminal connections, the conductivity is dependent on the substitution position of anchoring groups even with similar electron transport distance. The conductance of trans-substitution can be ten times or more as large as that of the cis-substitution. However, for the biphenyl system with different intramolecular connections, adding more connections between two benzene rings does not change the junction conductance. All these results indicate that the junction conductance is strongly dependent on the particular electron transport pathway. The alternating double-single linkage is the most probable one, since others are impeded by the single bonds.
Carrier transport by field enhanced thermal detrapping in Si nanocrystals thin films
Authors: Zhou Xin , Uchida Ken , Mizuta Hiroshi , Oda Shunri
Published: June 2009

The carrier transport at high voltage region in Si nanocrystal (SiNC) thin films has been investigated. The current-voltage measurements demonstrate that at high voltage region, conductance exponentially depends on V1/2. The activation energy, measured from the temperature dependence of the current-voltage (I-V) characteristics, decreases with an increase in the applied voltage. These results indicate that field enhanced detrapping dominates transport mechanism in the SiNC films at high voltage region. The possible influence of metal/semiconductor contacts on V1/2 dependence has been excluded through the activation energy measurement on different work-function metals as electrodes. The position of the traps contributing to the detrapping processes is concluded to be at interfaces of SiNC/SiO2 since H2 annealing drastically decreases the activation energy. The reasons why experimental results demonstrate no accordance with the material parameter V∗ of Poole–Frenkel expression have been discussed based on nanostructure characteristics of SiNC film.
Observation of electromigration in a Cu thin line by in situ coherent x-ray diffraction microscopy
Authors: Takahashi Yukio , Nishino Yoshinori , Furukawa Hayato , Kubo Hideto , Yamauchi Kazuto , Ishikawa Tetsuya , Matsubara Eiichiro
Published: June 2009

Electromigration (EM) in a 1-μm-thick Cu thin line was investigated by in situ coherent x-ray diffraction microscopy (CXDM). Characteristic x-ray speckle patterns due to both EM-induced voids and thermal deformation in the thin line were observed in the coherent x-ray diffraction patterns. Both parts of the voids and the deformation were successfully visualized in the images reconstructed from the diffraction patterns. This result not only represents the first demonstration of the visualization of structural changes in metallic materials by in situ CXDM but is also an important step toward studying the structural dynamics of nanomaterials using x-ray free-electron lasers in the near future.
Composition and strain in SiGe/Si(001) “nanorings” revealed by combined x-ray and selective wet chemical etching methods
Authors: Stoffel M. , Malachias A. , Rastelli A. , Metzger T. H. , Schmidt O. G.
Published: June 2009

The authors used x-ray diffraction to investigate strain and composition in SiGe nanorings formed during partial Si capping of self-assembled SiGe/Si(001) islands. The obtained results are corroborated with selective wet chemical etching experiments. Clear evidence is provided that rings are composed of a Ge rich core surrounded by Si richer ridges indicating that a substantial material redistribution occurs during the shape transformation from SiGe islands to rings. The results suggest that SiGe ring formation is driven by strain relief.
Synthesis of silver nanoclusters on zeolite substrates
Authors: Posada Y.
Published: June 2009

Silver nanoclusters were synthesized by reducing silver nitrate with ethylene glycol at 160 °C in the presence of zeolite. A one-pot procedure has rendered uniform size distributions of quasispherical silver clusters of average sizes of 100–200 nm synthesized on the surfaces of cubiclike zeolite substrates of ∼1 μm side. Bulk material microanalysis measurements showed samples with silver mass percentages of 20%–38%. Surface atomic composition analysis found silver concentrations of 3.1%–5.7%, zeolite compounds and nontraces of nitrogen were measured. The binding energy for the Ag 3d5/2 core electrons was shifted to higher energies at 368.6 eV compared to that of metallic silver. Herein, is presented a cost-effective technique for producing a narrow size distribution of silver nanocomposites with great potential for optoelectronics, catalysis, and nanobiotechnological applications.
Postdeposition annealing induced transition from hexagonal Pr2O3 to cubic PrO2 films on Si(111)
Authors: Weisemoeller T. , Bertram F. , Gevers S. , Greuling A. , Deiter C. , Tobergte H. , Neumann M. , Wollschläger J. , Giussani A. , Schroeder T.
Published: June 2009

Films of hexagonal praseodymium sesquioxide (h-Pr2O3) were deposited on Si(111) by molecular beam epitaxy and thereafter annealed in 1 atm oxygen at different temperatures, ranging from 100 to 700 °C. The films of the samples annealed at 300 °C or more were transformed to PrO2 with B-oriented Fm3¯m structure, while films annealed at lower temperatures kept the hexagonal structure. The films are composed of PrO2 and PrO2−δ species, which coexist laterally and are tetragonally distorted due to the interaction at the interface between oxide film and Si substrate. Compared to PrO2, PrO2−δ has the same cubic structure but with oxygen vacancies. The oxygen vacancies are partly ordered and increase the vertical lattice constant of the film, whereas the lateral lattice constant is almost identical for both species and on all samples. The latter lattice constant matches the lattice constant of the originally crystallized hexagonal praseodymium sesquioxide. That means that no long range reordering of the praseodymium atoms takes place during the phase transformation.
Threshold displacement energy in GaN: Ab initio molecular dynamics study
Authors: Xiao H. Y. , Gao Fei , Zu X. T. , Weber W. J.
Published: June 2009

Large-scale ab initio molecular dynamics method has been used to determine the threshold displacement energies Ed along five specific directions and to determine the defect configurations created during low energy events. The Ed shows a significant dependence on direction. The minimum Ed is determined to be 39 eV along the ⟨1¯010⟩ direction for a gallium atom and 17.0 eV along the ⟨1¯010⟩ direction for a nitrogen atom, which are in reasonable agreement with the experimental measurements. The average Ed values determined are 73.2 and 32.4 eV for gallium and nitrogen atoms, respectively. The N defects created at low energy events along different crystallographic directions have a similar configuration (a N–N dumbbell configuration), but various configurations for Ga defects are formed in GaN.
Search for free holes in InN:Mg-interplay between surface layer and Mg-acceptor doped interior
Authors: Dmowski L. H. , Baj M. , Suski T. , Przybytek J. , Czernecki R. , Wang X. , Yoshikawa A. , Lu H. , Schaff W. J. , Muto D. , Nanishi Y.
Published: June 2009

We measured lateral ac transport (up to 20 MHz), thermopower, as well as resistivity and Hall effect in InN:Mg samples with various Mg content. The sign of the Hall effect for all the samples was negative (electrons), however, the thermopower (α) measurements have shown the p-type sign of α for moderate Mg content—in the window centered around 1×1019 cm−3. Further overdoping with Mg yields donor type of defects and the change of thermoelectric power sign. The ac measurements performed as a function of frequency revealed that in both samples exhibiting and nonexhibiting p-type sign of thermopower, the n-type inversion layer at the surface does not prevent the electric contact to the bulk layer. Therefore we conclude that the n-type Hall effect invariably reported for all the Mg-doped samples originates from electron domination in mobility-weighted contributions of both types of carriers.
Spectroscopic properties of Ho3+ doped Sc2O3 transparent ceramic for laser materials
Authors: Gheorghe C. , Lupei A. , Lupei V. , Gheorghe L. , Ikesue A.
Published: June 2009

Systematic high resolution spectral investigations of trivalent holmium doped in Sc2O3 polycrystalline transparent ceramic were performed. The spectral characteristics (Stark energy levels, absorption, and emission cross sections) as well as the Judd–Ofelt (JO) intensity parameters Ωt(t=2,4,6) for the f-f transitions of the C2-symmetry center of Ho3+ in Sc2O3 transparent ceramics were determined. The JO intensity parameters are used to estimate the emission probabilities, radiative lifetimes, and branching ratios of the different Ho3+ transitions. The emission gain cross section for the I57→I58 and I56→I58 transitions of special interest for laser application were determined.
Optical generation of long-lived surface vibrations in a periodic microstructure
Authors: Maznev A. A. , Wright O. B.
Published: June 2009

We use the laser-induced transient grating technique for the excitation and detection of surface vibrational modes of a periodic microstructure on a silicon substrate forming a one-dimensional phononic crystal. Two standing wave eigenmodes with zero-group velocity corresponding to the top and bottom of the bandgap in the dispersion of the zone-folded Rayleigh waves are produced by setting the spatial period of the excitation pattern to twice the structure period. These modes do not radiate acoustic energy into the substrate, yielding an enhanced lifetime. We show that the relative amplitude of the two modes is controlled by the spatial phase of the excitation pattern, and discuss the dependence of the confinement time of the acoustic oscillations within the excitation area on the curvature of the dispersion surface.
Use of IR pyrometry to measure free-surface temperatures of partially melted tin as a function of shock pressure
Authors: Seifter A. , Furlanetto M. R. , Grover M. , Holtkamp D. B. , Macrum G. S. , Obst A. W. , Payton J. R. , Stone J. B. , Stevens G. D. , Swift D. C. , Tabaka L. J. , Turley W. D. , Veeser L. R.
Published: June 2009

Equilibrium equation of state theory predicts that the free-surface release temperature of shock-loaded tin will show a plateau at 505 K in the stress range from 19.5 to 33.0 GPa, corresponding to the solid-liquid, mixed-phase region of tin. In this paper we report free-surface temperature measurements on shock-loaded tin from 15 to 31 GPa using multiwavelength optical pyrometry. The shock waves were generated by direct contact of detonating high explosive with a tin sample, and the stress in the sample was determined by free-surface velocity measurements using photon Doppler velocimetry. We measured the emitted thermal radiance in the near IR region at four wavelengths from 1.5 to 5.0 μm. Above 25 GPa the measured free-surface temperatures were higher than the predicted 505 K, and they increased with increasing stress. This deviation may be explained by hot spots and/or variations in surface emissivity, and it may indicate a weakness in the use of a simple analysis of multiwavelength pyrometry data for conditions, such as above the melt threshold, where hot spots or emissivity variations may be significant. We are continuing to study the discrepancy to determine its cause.
Recombination at textured silicon surfaces passivated with silicon dioxide
Authors: McIntosh Keith R. , Johnson Luke P.
Published: June 2009

The surfaces of solar cells are often textured to increase their capacity to absorb light. This optical benefit is partially offset, however, by an increase in carrier recombination at or near the textured surface. A review of past work shows that the additional recombination invoked by a textured surface varies greatly from one experiment to another. For example, in the most commonly investigated structure—pyramidal textured silicon diffused with phosphorus and passivated with a hydrogenated oxide—recombination ranges from being 1–12 times more than in an equivalently prepared planar {100} surface. Examination of these experiments reveals consistent trends: small increases in recombination occur when the surface is very heavily diffused and dominated by Auger recombination, while larger increases in recombination occur when the surface is lightly diffused and dominated by Shockley–Read–Hall recombination at the surface, making the latter depend critically on surface area and the density of surface states. Comparisons of pyramidal and planar {100} surfaces indicate that when lightly diffused, the difference in recombination is substantially greater than the difference in surface area (1.73) and it is regularly attributed to the pyramid facets having {111} orientations—well known for their higher density of dangling bonds than {100} orientations. This high dangling-bond density makes recombination at pyramidal facets strongly dependent on the passivation scheme, and it is variations in these schemes that led to the wide range of results observed in experimental studies. In addition to surface area and crystal orientation, some experiments suggest a third mechanism that enhances recombination on oxide-passivated pyramids. With capacitance-voltage and photoconductance measurements, we confirm this speculation, showing that oxide-passivated pyramidal textured silicon has a higher density of interface states than can be accounted for by surface area and orientation, and that the additional defects are predominantly acceptorlike when above, or donorlike when below, an energy of 0.3 eV higher than the valence band.
Diverse facets of InGaN quantum well microrings grown by selective area epitaxy
Authors: Feng Wen , Kuryatkov Vladimir V. , Rosenbladt Dana M. , Stojanovic Nenad , Nikishin Sergey A. , Holtz Mark
Published: June 2009

InGaN quantum well (QW) microrings were grown using selective area epitaxy on patterned (0001) AlN/sapphire. The well defined shapes are comprised of {112¯2} and {213¯3} facets on inner sidewalls, and {11¯01} facets on outer sidewalls, as well as (0001) top surfaces. The sidewall facets exhibit distinct emission spectra when investigated using cathodoluminescence. Differences in emission spectra are attributed to variations in growth rate and indium incorporation on the facets, with peak emission wavelength as long as 500 nm. The observed weak blueshift with increasing cathodoluminescence excitation current verifies that the internal piezoelectric fields of the semipolar sidewall facets are lower than reference (0001) InGaN QWs.
End of range defects in Ge
Authors: Koffel S. , Cherkashin N. , Houdellier F. , Hytch M. J. , Benassayag G. , Scheiblin P. , Claverie A.
Published: June 2009

We show that the solid-phase epitaxial regrowth of amorphous layers created by ion implantation in Ge results in the formation of extended defects of interstitial-type. During annealing, these defects evolve in size and density following, as in Si, an Ostwald ripening mechanism. However, this process becomes nonconservative as the annealing temperature increases to 600 °C. This suggests that the recombination/annihilation of Ge interstitial atoms becomes important at these temperatures. These results have important implications for the modeling of diffusion of implanted dopants in Ge.
Ab initio study of methyl-bromide photodissociation in the Ã band
Authors: Escure Christelle , Leininger Thierry , Lepetit Bruno
Published: June 2009

We performed a theoretical study of the photodissociation dynamics of CH3Br in the Ã band using a wave packet propagation technique on coupled ab initio potential energy curves. The present model involves the Q31 and Q11 excited states which can be populated from the ground state by a perpendicular transition and which are correlated at large methyl-bromide distance to the ground bromide spin-orbit state, as well as the Q30 and 4E states which can be excited by a parallel and perpendicular transition (respectively) and both correlate to excited Br∗ spin-orbit state. The model provides absorption cross sections and branching ratios in excellent agreement with experimental results. Due to weak spin-orbit interaction, the Q11 state is the dominant contributor to the absorption cross section, except for the red wing of the band where Q30 and Q31 states have significant absorption. However, spin-orbit coupling is strong enough to induce nonadiabatic transitions between the Q31 and Q11 states during the dissociation process which should be experimentally detectable in the alignment properties of the fragments. Nonadiabatic transitions at the conical intersection between Q30 and Q11 are shown to play a minor role in this system.
Variational principle for the Wheeler–Feynman electrodynamics
Authors: De Luca Jayme
Published: June 2009

We adapt the formally defined Fokker action into a variational principle for the electromagnetic-two-body problem. We introduce properly defined boundary conditions to construct a functional of a finite orbital segment into the reals. The boundary conditions for the variational principle are an end point along each trajectory plus the respective segment of trajectory for the other particle inside the light cone of each end point. We show that the conditions for an extremum of our functional are the mixed-type neutral equations with implicit state-dependent delay of the electromagnetic-two-body problem. We put the functional on a natural Banach space and show that the functional is Frechét differentiable. We develop a method to calculate the second variation for C2 orbital perturbations, in general, and, in particular, about circular orbits of large enough radii. We prove that our functional has a local minimum at circular orbits of large enough radii, at variance with the limiting Kepler action that has a minimum at circular orbits of arbitrary radii. Our results suggest a bifurcation at some O(1) radius below which the circular orbits become saddle-point extrema. We give a precise definition for the distributional-like integrals of the Fokker action and discuss a generalization to a Sobolev space H02 of trajectories where the equations of motion are satisfied almost everywhere. Last, we discuss the existence of solutions for the state-dependent delay equations with slightly perturbated arcs of circle as the boundary conditions and the possibility of nontrivial solenoidal orbits.
Generation of Mie size microdroplet aerosols with applications in laser-driven fusion experiments
Authors: Higginbotham A. P. , Semonin O. , Bruce S. , Chan C. , Maindi M. , Donnelly T. D. , Maurer M. , Bang W. , Churina I. , Osterholz J. , Kim I. , Bernstein A. C. , Ditmire T.
Published: June 2009

We have developed a tunable source of Mie scale microdroplet aerosols that can be used for the generation of energetic ions. To demonstrate this potential, a terawatt Ti:Al2O3 laser focused to 2×1019 W/cm2 was used to irradiate heavy water (D2O) aerosols composed of micron-scale droplets. Energetic deuterium ions, which were generated in the laser-droplet interaction, produced deuterium-deuterium fusion with approximately 2×103 fusion neutrons measured per joule of incident laser energy.
Quantum cascade lasers with voltage defect of less than one longitudinal optical phonon energy
Authors: Escarra Matthew D. , Hoffman Anthony J. , Franz Kale J. , Howard Scott S. , Cendejas Richard , Wang Xiaojun , Fan Jen-Yu , Gmachl Claire
Published: June 2009

Efficient use of applied voltage in quantum cascade (QC) lasers is a critical factor in achieving high wall-plug efficiency and low compliance voltage. We demonstrate a QC laser emitting at 4.2 μm featuring a low voltage defect and short injector with only four quantum wells. Devices with a voltage defect of 20 meV, well below the energy of the longitudinal optical phonons, and a voltage efficiency of 91%, a record value for QC lasers, are reported for pulsed operation at 180 K. Voltage efficiencies of greater than 80% are exhibited at room temperature. Overall performance showed wall-plug efficiencies ranging from 21% at cryogenic temperatures to 5.3% at room temperature.
Unsteady transitional swirling flow in the presence of a moving free surface
Authors: Bouffanais Roland , Lo Jacono David
Published: June 2009

Unsteady incompressible viscous flows of a fluid partly enclosed in a cylindrical container with an open top surface are presented in this article. These moving free-surface flows are generated by the steady rotation of the solid bottom end wall. Such type of flows belongs to a group of recirculating lid-driven cavity flows with geometrical axisymmetry. The top surface of the cylindrical cavity is left open so that the free surface can freely deform. The Reynolds regime corresponds to unsteady transitional flows with some incursions in the fully laminar regime. The approach taken here revealed new nonaxisymmetric flow states that are investigated based on a fully three-dimensional solution of the Navier–Stokes equations for the free-surface cylindrical swirling flow without resorting to any symmetry property unlike all other results available in the literature. The results are compared with those of Bouffanais and Lo Jacono [“Transitional cylindrical swirling flow in presence of a flat free surface,” Comput. Fluids 38, 1651 (2009)] corresponding to the exact same parameters but with a flat-and-fixed top free surface. These solutions are obtained through direct numerical simulations based on a highly accurate Legendre spectral element method combined with a moving-grid technique.
Analytical solution of thickness variations in selective area growth by organometallic chemical vapor deposition
Authors: Liu X. , Aspnes D. E.
Published: June 2009

Using conformal mapping, we derive an analytic expression for the thickness d of a deposited film as a function of the distance r from a mask edge in selective area growth by organometallic chemical vapor deposition (OMCVD). Adjacent to the mask d∼r−1/2, which is clearly different from the exponential dependence observed for large planar surfaces. The result provides a means of distinguishing growth mechanisms in OMCVD.
Fast reconnection evolution in an arcadelike magnetic loop structure
Authors: Ugai M.
Published: June 2009

In the previous three-dimensional (3D) studies, the fast reconnection mechanism builds up in a narrow extent in the sheet current (z) direction, leading to a compact flare loop. In the present study, the 3D fast reconnection is allowed to evolve in a wide extent in the z direction and hence to proceed in a large arcadelike magnetic loop structure. Magnetic reconnection is initiated by a reconnection disturbance with a nonuniformity periodic in the z direction. According to different magnitudes of the initial disturbance in the z direction, magnetic reconnection is triggered in different manners and the resulting 3D fast reconnection evolution leads to the corresponding flare loop structures. When the z-directional nonuniformity is relatively small, the fast reconnection evolution extends with time in the z direction, leading to evolution of a large arcadelike flare loop, where the temperature is distinctly enhanced in the shape of two ribbons in the loop footpoint. On the other hand, when the disturbance nonuniformity is large, the fast reconnection evolution becomes less effective and compact flare loops tend to be formed isolated.
Auxetic materials with large negative Poisson’s ratios based on highly oriented carbon nanotube structures
Authors: Chen Luzhuo , Liu Changhong , Wang Jiaping , Zhang Wei , Hu Chunhua , Fan Shoushan
Published: June 2009

Auxetic materials with large negative Poisson’s ratios are fabricated by highly oriented carbon nanotube structures. The Poisson’s ratio can be obtained down to −0.50. Furthermore, negative Poisson’s ratios can be maintained in the carbon nanotube/polymer composites when the nanotubes are embedded, while the composites show much better mechanical properties including larger strain-to-failure (∼22%) compared to the pristine nanotube thin film (∼3%). A theoretical model is developed to predict the Poisson’s ratios. It indicates that the large negative Poisson’s ratios are caused by the realignment of curved nanotubes during stretching and the theoretical predictions agree well with the experimental results.
A piezomagnetoelastic structure for broadband vibration energy harvesting
Authors: Erturk A. , Hoffmann J. , Inman D. J.
Published: June 2009

This letter introduces a piezomagnetoelastic device for substantial enhancement of piezoelectric power generation in vibration energy harvesting. Electromechanical equations describing the nonlinear system are given along with theoretical simulations. Experimental performance of the piezomagnetoelastic generator exhibits qualitative agreement with the theory, yielding large-amplitude periodic oscillations for excitations over a frequency range. Comparisons are presented against the conventional case without magnetic buckling and superiority of the piezomagnetoelastic structure as a broadband electric generator is proven. The piezomagnetoelastic generator results in a 200% increase in the open-circuit voltage amplitude (hence promising an 800% increase in the power amplitude).
Very high magnetocurrent in tris-(8-hydroxyquinoline) aluminum-based bipolar charge injection devices
Authors: Yusoff Abd R. B. M. , da Silva Wilson J. , Serbena José P. M. , Meruvia Michelle S. , Hümmelgen Ivo A.
Published: June 2009

Bipolar devices constructed using 60nm thick tris-(8-hydroxyquinoline) aluminum (Alq3) thin films sandwiched between a 200nm thick sulfonated polyaniline hole-injection electrode and Al∕Ca electron-injection electrode show very high (up to 103%) magnetocurrent values. True-hole-only and true-electron-only Alq3-based devices that make use of Si as charge carrier collecting electrode, and Al∕Ca as electron injecting electrode or Au as hole injecting electrode, are also proposed, prepared, and characterized. In these true-single-carrier devices magnetocurrent is not observed. This result provides strong evidence that bipolar injection is a necessary condition for very high magnetocurrent observation in Alq3.
Local explicitly correlated coupled-cluster methods: Efficient removal of the basis set incompleteness and domain errors
Authors: Adler Thomas B. , Werner Hans-Joachim
Published: June 2009

We propose an explicitly correlated local LCCSD-F12 method in which the basis set incompleteness error as well as the error caused by truncating the virtual orbital space to pair-specific local domains are strongly reduced. This is made possible by including explicitly correlated terms that are orthogonalized only to the pair-specific configuration space. Thus, the contributions of excitations outside the domains are implicitly accounted for by the explicitly correlated terms. It is demonstrated for a set of 54 reactions that the reaction energies computed with the new LCCSD-F12 method and triple-zeta basis sets deviate by at most 2.5 kJ/mol from conventional CCSD complete basis set results (RMS: 0.6 kJ/mol). The local approximations should make it possible to achieve linear scaling of the computational cost with molecular size.
APC/C
CCS52A
complexes control meristem maintenance in the
Arabidopsis
root
Authors: Vanstraelen Marleen , Baloban Mikhail , Da Ines Olivier , Cultrone Antonietta , Lammens Tim , Boudolf Véronique , Brown Spencer C. , De Veylder Lieven , Mergaert Peter , Kondorosi Eva
Published: June 2009

Plant organs originate from meristems where stem cells are maintained to produce continuously daughter cells that are the source of different cell types. The cell cycle switch gene
CCS52A
, a substrate specific activator of the anaphase promoting complex/cyclosome (APC/C), controls the mitotic arrest and the transition of mitotic cycles to endoreduplication (ER) cycles as part of cell differentiation.
Arabidopsis
, unlike other organisms, contains 2
CCS52A
isoforms. Here, we show that both of them are active and regulate meristem maintenance in the root tip, although through different mechanisms. The
CCS52A1
activity in the elongation zone of the root stimulates ER and mitotic exit, and contributes to the border delineation between dividing and expanding cells. In contrast,
CCS52A2
acts directly in the distal region of the root meristem to control identity of the quiescent center (QC) cells and stem cell maintenance. Cell proliferation assays in roots suggest that this control involves
CCS52A2
mediated repression of mitotic activity in the QC cells. The data indicate that the
CCS52A
genes favor a low mitotic state in different cell types of the root tip that is required for meristem maintenance, and reveal a previously undescribed mechanism for APC/C mediated control in plant development.
Binding-site geometry and flexibility in DC-SIGN demonstrated with surface force measurements
Authors: Menon Sindhu , Rosenberg Kenneth , Graham Sarah A. , Ward Eliot M. , Taylor Maureen E. , Drickamer Kurt , Leckband Deborah E.
Published: June 2009

The dendritic cell receptor DC-SIGN mediates pathogen recognition by binding to glycans characteristic of pathogen surfaces, including those found on HIV. Clustering of carbohydrate-binding sites in the receptor tetramer is believed to be critical for targeting of pathogen glycans, but the arrangement of these sites remains poorly understood. Surface force measurements between apposed lipid bilayers displaying the extracellular domain of DC-SIGN and a neoglycolipid bearing an oligosaccharide ligand provide evidence that the receptor is in an extended conformation and that glycan docking is associated with a conformational change that repositions the carbohydrate-recognition domains during ligand binding. The results further show that the lateral mobility of membrane-bound ligands enhances the engagement of multiple carbohydrate-recognition domains in the receptor oligomer with appropriately spaced ligands. These studies highlight differences between pathogen targeting by DC-SIGN and receptors in which binding sites at fixed spacing bind to simple molecular patterns.
Re-evaluation of forest biomass carbon stocks and lessons from the world's most carbon-dense forests
Authors: Keith Heather , Mackey Brendan G. , Lindenmayer David B.
Published: June 2009

From analysis of published global site biomass data (
n
= 136) from primary forests, we discovered (
i
) the world's highest known total biomass carbon density (living plus dead) of 1,867 tonnes carbon per ha (average value from 13 sites) occurs in Australian temperate moist
Eucalyptus regnans
forests, and (
ii
) average values of the global site biomass data were higher for sampled temperate moist forests (
n
= 44) than for sampled tropical (
n
= 36) and boreal (
n
= 52) forests (
n
is number of sites per forest biome). Spatially averaged Intergovernmental Panel on Climate Change biome default values are lower than our average site values for temperate moist forests, because the temperate biome contains a diversity of forest ecosystem types that support a range of mature carbon stocks or have a long land-use history with reduced carbon stocks. We describe a framework for identifying forests important for carbon storage based on the factors that account for high biomass carbon densities, including (
i
) relatively cool temperatures and moderately high precipitation producing rates of fast growth but slow decomposition, and (
ii
) older forests that are often multiaged and multilayered and have experienced minimal human disturbance. Our results are relevant to negotiations under the United Nations Framework Convention on Climate Change regarding forest conservation, management, and restoration. Conserving forests with large stocks of biomass from deforestation and degradation avoids significant carbon emissions to the atmosphere, irrespective of the source country, and should be among allowable mitigation activities. Similarly, management that allows restoration of a forest's carbon sequestration potential also should be recognized.
Universals and cultural variation in turn-taking in conversation
Authors: Stivers Tanya , Enfield N. J. , Brown Penelope , Englert Christina , Hayashi Makoto , Heinemann Trine , Hoymann Gertie , Rossano Federico , de Ruiter Jan Peter , Yoon Kyung-Eun , Levinson Stephen C.
Published: June 2009

Informal verbal interaction is the core matrix for human social life. A mechanism for coordinating this basic mode of interaction is a system of turn-taking that regulates who is to speak and when. Yet relatively little is known about how this system varies across cultures. The anthropological literature reports significant cultural differences in the timing of turn-taking in ordinary conversation. We test these claims and show that in fact there are striking universals in the underlying pattern of response latency in conversation. Using a worldwide sample of 10 languages drawn from traditional indigenous communities to major world languages, we show that all of the languages tested provide clear evidence for a general avoidance of overlapping talk and a minimization of silence between conversational turns. In addition, all of the languages show the same factors explaining within-language variation in speed of response. We do, however, find differences across the languages in the average gap between turns, within a range of 250 ms from the cross-language mean. We believe that a natural sensitivity to these tempo differences leads to a subjective perception of dramatic or even fundamental differences as offered in ethnographic reports of conversational style. Our empirical evidence suggests robust human universals in this domain, where local variations are quantitative only, pointing to a single shared infrastructure for language use with likely ethological foundations.
Whole-proteome phylogeny of large dsDNA virus families by an alignment-free method
Authors: Wu Guohong Albert , Jun Se-Ran , Sims Gregory E. , Kim Sung-Hou
Published: June 2009

The vast sequence divergence among different virus groups has presented a great challenge to alignment-based sequence comparison among different virus families. Using an alignment-free comparison method, we construct the whole-proteome phylogeny for a population of viruses from 11 viral families comprising 142 large dsDNA eukaryote viruses. The method is based on the feature frequency profiles (FFP), where the length of the feature (
l
-mer) is selected to be optimal for phylogenomic inference. We observe that (
i
) the FFP phylogeny segregates the population into clades, the membership of each has remarkable agreement with current classification by the International Committee on the Taxonomy of Viruses, with one exception that the mimivirus joins the phycodnavirus family; (
ii
) the FFP tree detects potential evolutionary relationships among some viral families; (
iii
) the relative position of the 3 herpesvirus subfamilies in the FFP tree differs from gene alignment-based analysis; (
iv
) the FFP tree suggests the taxonomic positions of certain “unclassified” viruses; and (
v
) the FFP method identifies candidates for horizontal gene transfer between virus families.
Linking molecular affinity and cellular specificity in cadherin-mediated adhesion
Authors: Katsamba P. , Carroll K. , Ahlsen G. , Bahna F. , Vendome J. , Posy S. , Rajebhosale M. , Price S. , Jessell T. M. , Ben-Shaul A. , Shapiro L. , Honig Barry H.
Published: June 2009

Many cell–cell adhesive events are mediated by the dimerization of cadherin proteins presented on apposing cell surfaces. Cadherin-mediated processes play a central role in the sorting of cells into separate tissues in vivo, but in vitro assays aimed at mimicking this behavior have yielded inconclusive results. In some cases, cells that express different cadherins exhibit homotypic cell sorting, forming separate cell aggregates, whereas in other cases, intermixed aggregates are formed. A third pattern is observed for mixtures of cells expressing either N- or E-cadherin, which form distinct homotypic aggregates that adhere to one another through a heterotypic interface. The molecular basis of cadherin-mediated cell patterning phenomena is poorly understood, in part because the relationship between cellular adhesive specificity and intermolecular binding free energies has not been established. To clarify this issue, we have measured the dimerization affinities of N-cadherin and E-cadherin. These proteins are similar in sequence and structure, yet are able to mediate homotypic cell patterning behavior in a variety of tissues. N-cadherin is found to form homodimers with higher affinity than does E-cadherin and, unexpectedly, the N/E-cadherin heterophilic binding affinity is intermediate in strength between the 2 homophilic affinities. We can account for observed cell aggregation behaviors by using a theoretical framework that establishes a connection between molecular affinities and cell–cell adhesive specificity. Our results illustrate how graded differences between different homophilic and heterophilic cadherin dimerizaton affinities can result in homotypic cell patterning and, more generally, show how proteins that are closely related can, nevertheless, be responsible for highly specific cellular adhesive behavior.
The Low-Affinity Receptor for Neurotrophins p75NTR Plays a Key Role for Satellite Cell Function in Muscle Repair Acting via RhoA
Authors: Deponti Daniela , Buono Roberta , Catanzaro Giuseppina , De Palma Clara , Longhi Renato , Meneveri Raffaella , Bresolin Nereo , Bassi Maria Teresa , Cossu Giulio , Clementi Emilio , Brunelli Silvia
Published: June 2009

Regeneration of muscle fibers, lost during pathological muscle degeneration or after injuries, is mediated by the production of new myofibres. This process, sustained by the resident stem cells of the muscle, the satellite cells, is finely regulated by local cues, in particular by cytokines and growth factors. Evidence in the literature suggests that nerve growth factor (NGF) is involved in muscle fiber regeneration; however, its role and mechanism of action were unclear. We have investigated this issue in in vivo mouse models of muscle regeneration and in primary myogenic cells. Our results demonstrate that NGF acts through its low-affinity receptor p75NTR in a developmentally regulated signaling pathway necessary to myogenic differentiation and muscle repair in vivo. We also demonstrate that this action of NGF is mediated by the down-regulation of RhoA-GTP signaling in myogenic cells.