bluuebunny/crossref_metadata_2025 huggingface dataset:
Erosion and mobility in granular collapse over sloping beds
Authors: Mangeney A. , Roche O. , Hungr O. , Mangold N. , Faccanoni G. , Lucas A.
Published: September 2010

We describe laboratory experiments of granular material flowing over an inclined plane covered by an erodible bed, designed to mimic erosion processes of natural flows travelling over deposits built up by earlier events. Two controlling parameters are the inclination of the plane and the thickness of the erodible layer. We show that erosion processes can increase the flow mobility (i.e., runout) over slopes with inclination close to the repose angle of the grains θr by up to 40%, even for very thin erodible beds. Erosion efficiency is shown to strongly depend on the slope of the topography. Entrainment begins to affect the flow at inclination angles exceeding a critical angle θc ≃ θr/2. Runout distance increases almost linearly as a function of the thickness of the erodible bed, suggesting that erosion is mainly supply‐dependent. Two regimes are observed during granular collapse: a first spreading phase with high velocity followed by a slow thin flow, provided either the slope or the thickness of the erodible bed is high enough. Surprisingly, erosion affects the flow mostly during the deceleration phase and the slow regime. The avalanche excavates the erodible layer immediately at the flow front. Waves are observed behind the front that help to remove grains from the erodible bed. Steep frontal surges are seen at high inclination angles over both rigid or erodible bed. Finally, simple scaling laws are proposed making it possible to obtain a first estimate of the deposit and emplacement time of a granular collapse over a rigid or erodible inclined bed.
Report finds hypoxia increasing
Authors: Showstack Randy
Published: September 2010

The occurrence of hypoxia is increasing in coastal waters worldwide and represents a significant threat to the health and economy of U.S. coasts and the Great Lakes, according to a 3 September report issued by the U.S. Interagency Working Group on Harmful Algal Blooms, Hypoxia, and Human Health. The report found that the incidence of hypoxia—low dissolved oxygen that can negatively affect fish and other aquatic species—has increased tenfold globally in the past 50 years and almost thirtyfold in the United States since 1960.

Noting that federal research programs are addressing many aspects of eutrophication, enrichment, and hypoxia, the report indicates, “Despite decades of research, however, management efforts to reduce nutrients—particularly from nonpoint sources—and their adverse impacts on coastal ecosystems have not made significant headway, in part due to increased development and population in coastal watersheds.”
Geophysical Research Letters: New Policies Improve Top‐Cited Geosciences Journal
Authors: Calais Eric , Diffenbaugh Noah , D'Odorico Paolo , Harris Ruth , Knorr Wolfgang , Lavraud Benoit , Mueller Anne , Peterson William , Rignot Eric , Srokosz Meric , Strutton Peter , Tyndall Geoff , Wysession Michael , Williams Paul
Published: September 2010

Geophysical Research Letters (GRL) is the American Geophysical Union's premier journal of fast, groundbreaking communication. It rapidly publishes high‐ impact,letter‐length articles, and it is the top‐cited multidisciplinary geosciences journal over the past 10 years, with an impact factor that increased again in 2009, to 3.204. For manuscripts submitted to GRL, the median time to first and final decision is 23 and 27 days, respectively—a 35% improvement since 2007—and the median time from submission to publication is 13 weeks for90% of GRL papers—a 25% improvement since 2007. Among high‐impact publications in the geosciences, GRL has the fastest turnaround.
A global view of one‐dimensional solar radiative transfer through oceanic water clouds
Authors: Di Girolamo Larry , Liang Lusheng , Platnick Steven
Published: September 2010

Solar radiative transfer through a cloudy atmosphere is commonly computed assuming clouds to be one‐dimensional, i.e., plane‐parallel. Here we provide a global perspective on how often and with what degree oceanic water clouds may be considered plane‐parallel by fusing multi‐view‐angle and multi‐spectral satellite data. We show that the view‐angular distribution of the retrieved reflectance, spherical albedo and cloud optical thickness measured at 1 km resolution are indistinguishable from plane‐parallel clouds 24%, 25% and 79% of the time, respectively, at the 95% confidence level of our measurement method. These plane‐parallel clouds occur most frequently within regions dominated by stratiform clouds under solar zenith angles <60°. For all other regions or sun‐angles, the frequency in which clouds are indistinguishable from plane‐parallel drops sharply to as low as a few percent. Our results provide a basis for interpreting space‐time variability within many satellite‐retrieved variables and reveal a need for continued efforts to handle three‐dimensional radiative transfer in environmental modeling and monitoring systems.
Lidar measurements of clouds in the planetary boundary layer on Mars
Authors: Dickinson C. , Whiteway J. A. , Komguem L. , Moores J. E. , Lemmon M. T.
Published: September 2010

The LIDAR instrument on the Phoenix mission provided observations of clouds within the Planetary Boundary Layer (PBL) on Mars. In mid to late summer there was a regular Sol‐to‐Sol pattern with cloud formation at around midnight and dissipation before midday. The ice water content (IWC) of the clouds was estimated from the measurements with peak values at 6 am of 1 mg/m3, associated with total column IWC of up to 5 g/m2. The time of cloud formation did not change throughout the second half of the mission. This is consistent with the expected atmospheric cooling, if the observed decreasing trend in the column amount of water occurred mainly within the PBL.
Electron‐impact excitation heating rates in the atmosphere of Titan
Authors: Campbell L. , Kato H. , Brunger M. J. , Bradshaw M. D.
Published: September 2010

A previous study of various heating rates in the atmosphere of Titan included electron‐impact excitation of molecular nitrogen as one component. This work examines this component in more detail, using a statistical equilibrium calculation to avoid approximations made in the earlier work. The sensitivity of the results to different cross‐section sets is investigated. It is found that using recent and more physical cross sections for vibrational excitation produces a significant increase in the heating rate. On the other hand, using more accurate cross sections for the electronic states had little apparent effect on the heating rates when used within the approximations made in the previous model. However, the inclusion of more transitions in this study produces a significant increase in the electronic state heating rates, as states that were originally neglected are now accounted for here.
Turbulence generation by Kelvin‐Helmholtz instability in the tropical tropopause layer observed with a 47 MHz range imaging radar
Authors: Mega Tomoaki , Yamamoto Masayuki K. , Luce Hubert , Tabata Yoshikazu , Hashiguchi Hiroyuki , Yamamoto Mamoru , Yamanaka Manabu D. , Fukao Shoichiro
Published: September 2010

Detailed structure of Kelvin‐Helmholtz (KH) instability in the tropical tropopause layer is presented using a 47 MHz clear‐air Doppler radar, referred to as the Equatorial Atmosphere Radar (EAR), installed at West Sumatra, Indonesia (0.20°S, 100.32°E). During 12–20 December 2008, radiosondes revealed that the altitude of temperature minimum was 16.1–16.4 km from 12–14 December and then descended with time and reached 13.4 km on 20 December. The altitude of easterly wind maximum corresponded well with that of the temperature minimum, and enhanced eastward vertical wind shear was produced above it because of a sharp decrease of easterly wind with altitude. During this period, to attain high range resolution of a few tens of meters, the EAR was operated in range imaging mode using frequency diversity. EAR observations revealed that enhanced radar echo above the temperature minimum had a thin, layered structure less than or about 200 m in depth during 12–14 December and then frequently showed upward wisp‐like structures resulting from KH instability. In the intensive KH instability cases on 16 and 18 December, KH billows had a depth of up to ∼1 km, and upward and downward velocities reaching greater than 2 m s−1 were observed within the billows. Considerations using the linear wave theory suggest that a breaking of equatorial Kelvin wave might have been responsible for the onset of well‐developed KH instability.
Sensitivity of the NOy budget over the United States to anthropogenic and lightning NOx in summer
Authors: Fang Y. , Fiore A. M. , Horowitz L. W. , Levy H. , Hu Y. , Russell A. G.
Published: September 2010

We examine the implications of new estimates of the anthropogenic and lightning nitrogen oxide (NOx) source for the budget of oxidized nitrogen (NOy) over the United States in summer using a 3‐D global chemical transport model (Model of Ozone and Related Tracers‐4). As a result of the Environmental Protection Agency (EPA) State Implementation call, power plant NOx emissions over the eastern United States decreased significantly, as reflected by a 23% decrease in summer surface emissions from the 1999 U.S. EPA National Emissions Inventory to our 2004 inventory. We increase the model lightning NOx source over northern midlatitude continents (by a factor of 10) and the fraction emitted into the free troposphere (FT, from 80% to 98%) to better match the recent observation‐based estimates. While these NOx source updates improve the simulation of NOx and O3 compared to the Intercontinental Chemical Transport Experiment‐North America aircraft observations, a bias in the partitioning between nitric acid (HNO3) and peroxyacetylnitrate (PAN) remains especially above 8 km, suggesting gaps in the current understanding of upper tropospheric processes. We estimate a model NOy export efficiency of 4%−14% to the North Atlantic in the FT, within the range of previous plume‐based estimates (3%−20%) and lower than the 30% exported directly from the continental boundary layer. Lightning NOx contributes 24%−43% of the FT NOy export from the U.S. to the North Atlantic and 28%−34% to the NOy wet deposition over the United States, with the ranges reflecting different assumptions. Increasing lightning NOx decreases the fractional contribution of PAN to total NOy export, increases the O3 production in the northern extratropical FT by 33%, and decreases the regional mean ozone production efficiency per unit NOx (OPE) by 30%. If models underestimate the lightning NOx source, they would overestimate the background OPE in the FT and the fractional contribution of PAN to NOy export. Therefore, a model underestimate of lightning NOx would likely lead to an overestimate of the downwind O3 production due to anthropogenic NOx export. Better constraints on the lightning NOx source are required to more confidently assess the impacts of anthropogenic emissions and their changes on air quality over downwind regions.
Observed connection of the stratospheric quasi‐biennial oscillation with El Niño–Southern Oscillation in radiosonde data
Authors: Taguchi M.
Published: September 2010

Using a stratospheric zonal wind data archive of radiosonde observations at equatorial stations for 1953–2008, this study investigates whether or not signals of the quasi‐biennial oscillation (QBO) vary with the El Niño–Southern Oscillation (ENSO) cycle. The signals of the QBO are represented by trajectories in a phase space spanned by time series of two leading modes of wind variability. Two properties of the trajectories, distance from the origin and time rate of change in argument, which are proxies for amplitude and phase progression rate of the QBO, respectively, are first examined in relation to seasons and QBO phases. The examination confirms known features of the QBO including the so‐called seasonal locking and more regular phase propagation for the westerly phase. A further comparison of the properties between cold and warm ENSO conditions (La Niña and El Niño, respectively) reveals unprecedented evidence of clear variations of the QBO with ENSO: the QBO signals exhibit weaker amplitude and faster phase propagation for El Niño conditions. Such variations are also supported by a composite analysis of zonal wind anomalies. We also discuss a possible connection of the ENSO‐associated changes in the QBO with those in equatorial wave activity.
Long‐wavelength stagnant lid convection with hemispheric variation in lithospheric thickness: Link between Martian crustal dichotomy and Tharsis?
Authors: Šrámek Ondřej , Zhong Shijie
Published: September 2010

A dynamic link between the early evolution of Tharsis and the crustal dichotomy on Mars was recently proposed by Zhong (2009). We address in detail the fundamental aspects of the proposed model using 3‐D spherical shell modeling of convection. We investigate the conditions under which a spherical harmonic degree 1 flow is produced in the mantle of Mars in layered viscosity models with different depths of viscosity layering and different viscosity ratios between the bottom and top layers. We find that a thinner weak layer requires a larger viscosity decrease in order to produce degree‐1 planform, in qualitative accordance with existing analytical studies. A lithospheric keel of hemispheric extent, which may represent melt residue after dichotomy formation process, is then introduced in the models. As a consequence, thermal upwellings are first formed and oriented below the center of the melt residue cap. For keels of maximum thickness ≳100 km, a rotation of the entire single‐plate lithosphere relative to the underlying mantle follows until the plume is stabilized near the edge of the keel, which can be identified as the dichotomy boundary. This model may explain the early migration of the Tharsis volcanic center from southern latitudes to the vicinity of the dichotomy boundary. For keels ≳200 km thick, the modeled time scales agree with observationally inferred migration rate. If the Tharsis migration is caused by the rotation of the lithosphere, the requirement on the amount and location of upper mantle melting would argue for an endogenic origin of the dichotomy.
Identifying the genetic determinants of transcription factor activity
Authors: Lee Eunjee , Bussemaker Harmen J
Published: September 2010

Analysis of parallel genotyping and expression profiling data has shown that mRNA expression levels are highly heritable. Currently, only a tiny fraction of this genetic variance can be mechanistically accounted for. The influence of trans‐acting polymorphisms on gene expression traits is often mediated by transcription factors (TFs). We present a method that exploits prior knowledge about the in vitro DNA‐binding specificity of a TF in order to map the loci (‘aQTLs’) whose inheritance modulates its protein‐level regulatory activity. Genome‐wide regression of differential mRNA expression on predicted promoter affinity is used to estimate segregant‐specific TF activity, which is subsequently mapped as a quantitative phenotype. In budding yeast, our method identifies six times as many locus‐TF associations and more than twice as many trans‐acting loci as all existing methods combined. Application to mouse data from an F2 intercross identified an aQTL on chromosome VII modulating the activity of Zscan4 in liver cells. Our method has greatly improved statistical power over existing methods, is mechanism based, strictly causal, computationally efficient, and generally applicable.
Understanding the physiology of Lactobacillus plantarum at zero growth
Authors: Goffin Philippe , van de Bunt Bert , Giovane Marco , Leveau Johan H J , Höppener‐Ogawa Sachie , Teusink Bas , Hugenholtz Jeroen
Published: September 2010

Situations of extremely low substrate availability, resulting in slow growth, are common in natural environments. To mimic these conditions, Lactobacillus plantarum was grown in a carbon‐limited retentostat with complete biomass retention. The physiology of extremely slow‐growing L. plantarum—as studied by genome‐scale modeling and transcriptomics—was fundamentally different from that of stationary‐phase cells. Stress resistance mechanisms were not massively induced during transition to extremely slow growth. The energy‐generating metabolism was remarkably stable and remained largely based on the conversion of glucose to lactate. The combination of metabolic and transcriptomic analyses revealed behaviors involved in interactions with the environment, more particularly with plants: production of plant hormones or precursors thereof, and preparedness for the utilization of plant‐derived substrates. Accordingly, the production of compounds interfering with plant root development was demonstrated in slow‐growing L. plantarum. Thus, conditions of slow growth and limited substrate availability seem to trigger a plant environment‐like response, even in the absence of plant‐derived material, suggesting that this might constitute an intrinsic behavior in L. plantarum.
Higher 24‐h Respiratory Quotient and Higher Spontaneous Physical Activity in Nighttime Eaters
Authors: Gluck Marci E. , Venti Colleen A. , Salbe Arline D. , Votruba Susanne B. , Krakoff Jonathan
Published: September 2010

We have previously shown that a higher 24‐h respiratory quotient (24‐h RQ) predicts greaterad‐libitumfood intake and that nighttime eaters (NE) ingested more calories during an in‐patient food intake study and gained more weight over time. We investigated whether 24‐h RQ was higher in individuals who exhibited nighttime eating behavior. Healthy nondiabetic Pima Indians (PI;n= 97, 54 male/43 female) and whites (W;n= 32, 22 male/10 female) were admitted to our Clinical Research Unit. After 3 days of a weight maintaining diet, 24‐h energy expenditure (24‐h EE), 24‐h RQ, rates of carbohydrate (CHOX) and lipid oxidation (LIPOX), and spontaneous physical activity (SPA) were measured in a metabolic chamber whereas volunteers were in energy balance and unable to consume excess calories. Individuals subsequently atead libitumfrom a computerized vending machine for 3 days with amount and timing of food intake recorded. Fifty‐five individuals (36%; 39 PI, 16 W) were NE, who ate between 11pmand 5amon at least one of the 3 days on the vending machines. There were no differences in BMI or percentage body fat between NE and non‐NE. After adjusting for age, sex, race, fat‐free mass, fat mass, and energy balance, NE had a higher 24‐h RQ (P= 0.01), higher CHOX (P= 0.009), and lower LIPOX (P= 0.03) and higher 24‐h SPA (P= 0.04) compared to non‐NE. There were no differences in adjusted 24‐h EE or sleep RQ between the groups. Individuals with nighttime eating behavior have higher 24‐h RQ, higher CHOX and lower LIPOX, a phenotype associated with increased food intake and weight gain.
Folic Acid Treatment Normalizes NOS‐Dependence of Vascular Tone in the Metabolic Syndrome
Authors: Schneider Markus P. , Schlaich Markus P. , Harazny Joanna M. , Raff Ulrike , Ritt Martin , Ott Christian , Schmieder Roland E.
Published: September 2010

Obese subjects with the metabolic syndrome (MS+) are more prone to microvascular complications than obese subjects without the metabolic syndrome (MS−). Excessive vascular nitric oxide (NO) production has been demonstrated in MS+ compared to MS−, perhaps driven by increased inflammation or oxidative stress. We tested whether in MS+, folic acid (FA) treatment could normalize NO synthase (NOS)‐dependence of vascular tone in the retina and kidney. MS+ (n = 49) and MS− (n = 26) subjects were included in a randomized, double‐blind, crossover trial. After 4‐weeks' treatment with placebo or FA (5 mg/day), several cytokines (C‐reactive protein (CRP), interleukin‐1β, adiponectin), and markers of oxidative stress (glutathione/oxidized glutathione (GSH/GSSG) ratio, total antioxidant capacity (TAC)) were determined. NOS‐dependence of retinal and renal vascular tone was assessed by retinal scanning laser Doppler flowmetry and renal clearance technique, respectively. FA had no effect on cytokine levels, but increased GSH/GSSG ratio overall (36 ± 76 vs. 102 ± 200, P = 0.04), indicative of a reduction in oxidative stress. In MS+, treatment with FA reduced NOS‐dependence of retinal and renal vascular tone compared to placebo (P = 0.03 and P = 0.04, respectively). FA had no effect in MS−. After treatment with FA, NOS‐dependence of retinal and renal vascular tone was similar between MS+ and MS−. Retinal and renal vascular tone in MS+ subjects is characterized by increased dependence on NOS. NOS‐dependence in MS+ could be corrected by FA treatment to levels not dissimilar in MS−, and this was associated with a reduction in oxidative stress. Future trials should test whether these effects translate into a reduction of microvascular complications.
Systems analysis of bacterial glycomes
Authors: Kay Emily , Lesk Victor I. , Tamaddoni-Nezhad Alireza , Hitchen Paul G. , Dell Anne , Sternberg Michael J. , Muggleton Stephen , Wren Brendan W.
Published: September 2010

Bacteria produce an array of glycan-based structures including capsules, lipo-oligosaccharide and glycosylated proteins, which are invariably cell-surface-located. For pathogenic bacteria, such structures are involved in diverse roles in the life cycle of the bacterium, including adhesion, colonization, avoidance of predation and interactions with the immune system. Compared with eukaryotes, bacteria produce huge combinatorial variations of glycan structures, which, coupled to the lack of genetic data, has previously hampered studies on bacterial glycans and their role in survival and pathogenesis. The advent of genomics in tandem with rapid technological improvements in MS analysis has opened a new era in bacterial glycomics. This has resulted in a rich source of novel glycan structures and new possibilities for glycoprospecting and glycoengineering. However, assigning genetic information in predicted glycan biosynthetic pathways to the overall structural information is complex. Bioinformatic analysis is required, linked to systematic mutagenesis and functional analysis of individual genes, often from diverse biosynthetic pathways. This must then be related back to structural analysis from MS or NMR spectroscopy. To aid in this process, systems level analysis of the multiple datasets can be used to make predictions of gene function that can then be confirmed experimentally. The present paper exemplifies these advances with reference to the major gastrointestinal pathogen Campylobacter jejuni.
Loop vertex expansion for Φ2k theory in zero dimension
Authors: Rivasseau Vincent , Wang Zhituo
Published: September 2010

In this paper we extend the method of loop vertex expansion to interactions with degree higher than 4. As an example we provide through this expansion an explicit proof that the free energy of ϕ2k scalar theory in zero dimension is Borel–Le Roy summable of order k−1. We detail the computations in the case of a ϕ6 interaction.
Reducing carrier escape in the InAs/GaAs quantum dot intermediate band solar cell
Authors: Antolín E. , Martí A. , Farmer C. D. , Linares P. G. , Hernández E. , Sánchez A. M. , Ben T. , Molina S. I. , Stanley C. R. , Luque A.
Published: September 2010

Intermediate band solar cells (IBSCs) fabricated to date from In(Ga)As/GaAs quantum dot arrays (QD-IBSC) exhibit a quantum efficiency (QE) that extends to below bandgap energies. However, the production of sub-bandgap photocurrent relies often on the thermal and/or tunneling escape of carriers from the QDs, which is incompatible with preservation of the output voltage. In this work, we test the effectiveness of introducing a thick GaAs spacer in addition to an InAlGaAs strain relief layer (SRL) over the QDs to reduce carrier escape. From an analysis of the QE at different temperatures, it is concluded that escape via tunneling can be completely blocked under short-circuit conditions, and that carriers confined in QDs with an InAlGaAs SRL exhibit a thermal escape activation energy over 100 meV larger than in the case of InAs QDs capped only with GaAs.
Structure and bonding in third-row main group dicarbides C2X (X=K–Br)
Authors: Rayón Víctor M. , Redondo Pilar , Barrientos Carmen , Largo Antonio
Published: September 2010

The molecular structures of third-row main group dicarbides C2X (X=K–Br) have been studied by theoretical methods. It is found that K, Ca, and Ga favor C2v-symmetric (T-shape) ground states, whereas As, Se, and Br have linear or quasilinear ground states. In the case of germanium. a very flat potential energy surface is found and an L-shape structure seems to be the ground state. Dissociation energies into X+C2 are relatively high. The main features of these compounds, in particular, the preference for linear or cyclic structures, have been rationalized in terms of the most relevant interactions between the third-row atom and dicarbon with the help of an energy decomposition analysis.
Enhancement of X129e polarization by off-resonant spin exchange optical pumping
Authors: Parnell S. R. , Deppe M. H. , Parra-Robles J. , Wild J. M.
Published: September 2010

A high power narrow line width (38 W, 0.09 nm full width at half maximum) external cavity diode laser is investigated for rubidium spin exchange optical pumping of X129e. This tunable photon source has a constant line width, independent of operating power or wavelength within a 1 nm tuning range. When using this laser, an increase in the X129e nuclear polarization is observed when optically pumping at a lower wavelength than the measured Rb electron D1 absorption. The exact detuning from D1 for the highest polarization is dependent upon the gas density. Furthermore, at high power and/or high Rb density, a reduction in the polarization occurs at the optimum wavelength as previously reported in spin exchange optical pumping studies of H3e which is consistent with high absorption close to the cell front face. These results are encouraging for moderate high throughput polarization of X129e in the midpressure range of (0.5–2.0 amagat).
Conductive path formation in glasses of phase change memory
Authors: Simon M. , Nardone M. , Karpov V. G. , Karpov I. V.
Published: September 2010

We present a model of data retention for phase change memory devices in which the active medium is a thin layer of chalcogenide glass. Data retention capability is compromised when a crystalline path is spontaneously formed in the glassy host, essentially shunting the device. We determine the probability and statistics of device failure for systems in which the crystalline volume fraction is below the critical volume fraction of percolation theory. In that regime, we show that rectilinear crystalline path formation is favored and we determine the criteria for when such paths dominate over the typical percolation cluster scenario. Our analytical approach, based on modeling the formation of such paths in terms of a half-space random walk, leads to closed form expressions that relate data retention characteristics to device parameters. The model is used to examine the effects of device geometry, temperature, and external fields. The temporal statistics of device reliability are also considered for several failure mechanisms. A computer simulation is employed that supports our derived relationships between failure probability and device parameters.
Electrical conduction mechanism in nonstoichiometric La3Ta0.5Ga5.5O14
Authors: Yaokawa Ritsuko , Uda Satoshi , Kimura Hiromitsu , Aota Katsumi
Published: September 2010

The electrical conduction mechanism in La3Ta0.5Ga5.5O14 (LTG) was studied from the standpoint of defect formation during growth caused by the nonstoichiometry of the crystal. Since the stoichiometric composition of LTG does not coincide with the congruent composition, single crystals grown from the stoichiometric melt under an atmosphere of O2/Ar in the oxygen partial pressure range from 0.005 to 1 atm was Ta-poor. Ta vacancies were formed during the growth, and their population was predominated by the growth-pO2. With increasing temperature up to 600 °C, the Ta vacancies were ionized to yield holes, and thus the electrical conductivity of the LTG crystal varied with temperature and growth-pO2. In contrast, Ga vacancies as a carrier source would form by Ga evaporation during growth under pO2 below 0.005 atm. The growth-pO2 dependence of the electrical conductivity was opposite to the case for Ta vacancies. For the case of sintered LTG with the exact stoichiometric composition, impurity defects dominated electrical conduction below 600 °C, where the impurity concentration was higher than the cation vacancies arising from the nonstoichiometry of the sintered LTG. Thus, electrical conductivity was almost independent of the sintering atmosphere of pO2. Above 700 °C, the dominant carrier in both single crystal and sintered LTG was ions related to oxygen defects formed by the anion Frenkel reaction.
Phase diagrams of binary mixtures of oppositely charged colloids
Authors: Bier Markus , van Roij René , Dijkstra Marjolein
Published: September 2010

Phase diagrams of binary mixtures of oppositely charged colloids are calculated theoretically. The proposed mean-field-like formalism interpolates between the limits of a hard-sphere system at high temperatures and the colloidal crystals which minimize Madelung-like energy sums at low temperatures. Comparison with computer simulations of an equimolar mixture of oppositely charged, equally sized spheres indicate semiquantitative accuracy of the proposed formalism. We calculate global phase diagrams of binary mixtures of equally sized spheres with opposite charges and equal charge magnitude in terms of temperature, pressure, and composition. The influence of the screening of the Coulomb interaction upon the topology of the phase diagram is discussed. Insight into the topology of the global phase diagram as a function of the system parameters leads to predictions on the preparation conditions for specific binary colloidal crystals.
Maximal rank of extremal marginal tracial states
Authors: Ohno Hiromichi
Published: September 2010

States on the coupled quantum system Mn(C)⊗Mn(C) whose restrictions to each subsystem are the normalized traces are called marginal tracial states. We investigate extremal marginal tracial states and compute their maximal rank. Diagonal marginal tracial states are also considered.
Mobility and metal–insulator transition of the two-dimensional electron gas in SiGe/Si/SiGe quantum wells
Authors: Gold A.
Published: September 2010

We consider the mobility of the interacting two-dimensional electron gas as realized in SiGe/Si/SiGe quantum wells. For zero temperature we calculate the mobility as function of the electron density for remote charged-impurity scattering and we take into account exchange-correlation effects and multiple-scattering effects. Multiple-scattering effects give rise to a metal–insulator transition at low electron density. Our calculation is in good agreement with experimental results obtained with remote doped SiGe/Si/SiGe quantum wells having electron densities near the metal–insulator transition. We discuss the critical density of the metal–insulator transition as function of the remote doping distance and make some predictions. The single-particle relaxation time and spin-polarization effects are also considered.
A low temperature anomaly observed in off-stoichiometric Ni–Mn–Ga system studied by higher harmonic ac-susceptibility measurements
Authors: Srivastava Saurabh Kumar , Srivastava Vijay Kumar , Joshi Anupam , Kamasa Pawel , Varga Lajos Károly , Khovaylo V. V. , Chatterjee Ratnamala
Published: September 2010

Results of fundamental and third order ac susceptibility measurements in a Ni49Mn29Ga22 single crystal demonstrate that higher harmonics of ac-susceptibility measurement is an excellent tool to identify transitions/anomalies originating from different magnetic substructures that remain undetected by usual dc susceptibility measurements. Anomaly observed at low temperature (∼150 K) has also been explored by differential scanning calorimetry, temperature dependent x-ray diffraction, and transmission electron microscopy measurements. The results demonstrate that the magnetic subsystem in Ni–Mn–Ga is unstable at low temperatures not only for metastable modulated crystal structure but also for very stable nonmodulated tetragonal structure.
A study of phase coexistence and temperature dependent monoclinic to tetragonal phase transition in the multiferroic (1−x)Pb(Fe1/2Nb1/2)O3−xPbTiO3 (x=0.08)
Authors: Singh Satendra Pal , Yoon Songhak , Baik Sunggi , Shin Namsoo , Pandey Dhananjai
Published: September 2010

The origin of coexistence of tetragonal and monoclinic phases in the morphotropic phase boundary (MPB) region of (1−x)Pb(Fe1/2Nb1/2)O3−xPbTiO3 has been investigated for x=0.08 by synchrotron x-ray powder diffraction in the 10–550 K range. It is shown that the phase coexistence observed at room temperature in the MPB region is essentially due to a first order phase transition between the low temperature monoclinic and high temperature tetragonal phases. This transition is shown to be accompanied with a phase coexistence over a very wide temperature range (ΔT∼200 K) across the room temperature.
Surface spin disorder effects in magnetite and poly(thiophene)-coated magnetite nanoparticles
Authors: Cótica Luiz F. , Santos Ivair A. , Girotto Emerson M. , Ferri Elidia V. , Coelho Adelino A.
Published: September 2010

Chemically synthesized magnetite and poly(thiophene)-coated magnetite nanoparticles and the correlations between their magnetic, structural, and microstructural properties are investigated. A typical superparamagnetic behavior was observed for faceted nanoparticle agglomerates of magnetite and nanocomposite. In nanocomposites, the polymer layer causes a sharp decrease in the spin disorder, which reduces the anisotropy constant significantly. This happens because the intimate contact between magnetite and poly(thiophene) leads to charge transfer from the polymer to the core via polaron interactions, causing a structural rearrangement of the nanoparticles and suppression of the spin movement at the surface. As this dynamic interaction can tune the core dimensions, the magnetic properties of nanocomposites can be tuned by controlling the core size through polymer coating. These characteristics can be exploited to design high-performance magnetically tunable nanodevices and applied in many areas of biomedicine (DNA separation, drug targeting, immune detection, and magnetic nanoparticle hyperthermia in cancer treatment).
Disentangling the role of linear transition dipole in band-edge emission from single CdSe/ZnS quantum dots: Combined linear anisotropy and defocused emission pattern imaging
Authors: Cyphersmith Austin , Early Kevin , Maksov Artem , Graham Jeremy , Wang Yikuan , Barnes Michael
Published: September 2010

Combined linear anisotropy and defocused wide-field fluorescence imaging of individual CdSe/ZnS quantum dots reveal an unambiguous contribution of a linear transition dipole polarized along the hexagonal (c-) symmetry axis of the nanocrystal which grows with increasing tilt angle of the c-axis with respect to the surface normal. These results offer some insights into quantum dot luminescence polarization dynamics, and provide a basis for unambiguously assigning the two Euler angles describing the c-axis orientation from defocused emission patterns for multidipole systems.
High-sensitivity detection of terahertz waves using nonlinear up-conversion in an organic 4-dimethylamino-N-methyl-4-stilbazolium tosylate crystal
Authors: Minamide Hiroaki , Zhang Jun , Guo Ruixiang , Miyamoto Katsuhiko , Ohno Seigo , Ito Hiromasa
Published: September 2010

We achieved high-sensitivity, rapid-response detection of terahertz (THz) waves using an organic nonlinear optical crystal, 4-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST). Nonlinear up-conversion in the crystal resulted in a shift of THz waves to near-infrared radiation at room temperature. A minimum THz-wave peak power of about 300 μW was measured at 19.2 THz by detecting the up-converted optical signal with an InGaAs-based photodetector. A noise equivalent power of about 6 nW/Hz1/2 was estimated in this experiment. Optimum conditions were obtained for THz-wave detection using a DAST crystal.
Anharmonic modal coupling in a bulk micromechanical resonator
Authors: Dunn Tyler , Wenzler Josef-Stefan , Mohanty Pritiraj
Published: September 2010

We present measurements of nonlinear coupling between various acoustic modes of a micromechanical resonator. Piezoelectric transduction allows measurement of both flexural and bulk longitudinal modes up to microwave frequencies, and we find that all modes of the device couple, regardless of type. This coupling thus provides a means of mechanical nonlinear signal processing across a wide range of frequencies. Through controlled simultaneous excitation, we quantify coupling strength by measuring the frequency shift in a detector mode in response to the known energy of a driven mode.
Theoretical investigation of Möbius strips formed from graphene
Authors: Wang Xianlong , Zheng Xiaohong , Ni Meiyan , Zou Liangjian , Zeng Zhi
Published: September 2010

First-principle calculations are performed on the formation of graphene Möbius strips and their shape evolution as a function of the strip width. Results show that Möbius strips formed from graphene nanoribbons with fixed length and different widths are stable. With the increase in the width, one planar triangular region appears, and finally, the strip evolves into three equilateral triangles stacked together. Physical properties such as deformation energy density, strain effects, and edge magnetism are discussed. As a result from the special topology, unlike zigzag-edged graphene nanoribbons, Möbius strips are ferromagnets with nonzero total magnetic moments observed at the edge.
Bound states for an induced electric dipole in the presence of an azimuthal magnetic field and a disclination
Authors: Bakke K.
Published: September 2010

Based on the Wei–Han–Wei setup [H. Wei, R. Han, and X. Wei, Phys. Rev. Lett. 75, 2071 (1995)], where a neutral particle with an induced electric dipole moment interacts with a configuration of crossed electric and magnetic fields, in this paper we study the bound states that arise when we change the Wei–Han–Wei field configuration and consider a field configuration of crossed azimuthal magnetic field and a radial electric field. Moreover, we consider here a spin-half neutral particle and the presence of a linear topological defect called disclination. We obtain the bound states in two distinct cases: in the first case, we consider that the wave function of the neutral particle is well-behaved at the origin and vanishes at the asymptotic limit; in the second case, we consider the neutral particle confined to a parabolic potential like a quantum dot.
Internal efficiency of InGaN light-emitting diodes: Beyond a quasiequilibrium model
Authors: Chow W. W. , Crawford M. H. , Tsao J. Y. , Kneissl M.
Published: September 2010

We propose a model to better investigate InGaN light-emitting diode (LED) internal efficiency by extending beyond the usual total carrier density rate equation approach. To illustrate its capability, the model is applied to study intrinsic performance differences between violet and green LEDs. The simulations show performance differences, at different current densities and temperatures, arising from variations in spontaneous emission and heat loss rates. By tracking the momentum-resolved carrier populations, these rate changes are, in turn, traced to differences in bandstructure and plasma heating. The latter leads to carrier distributions that deviate from the quasiequilibrium ones at lattice temperature.
On the existence of vortexlike solutions in the auroral F-region
Authors: Hamza A. M.
Published: September 2010

In this paper we construct a set of nonlinear coupled partial differential equations governing the evolution of plasma fluctuations as they occur in the ionospheric auroral F region. The nonlinear system of equations is shown to support a set of stationary vortexlike solutions. It is also shown that given stationary solutions, one is able to construct time-dependent solutions using an instanton ansatz.
Magnetocaloric effect in manganites: Metamagnetic transitions for magnetic refrigeration
Authors: Quintero M. , Sacanell J. , Ghivelder L. , Gomes A. M. , Leyva A. G. , Parisi F.
Published: September 2010

We present a study of the magnetocaloric effect in La5/8−yPryCa3/8MnO3 (y=0.3) and Pr0.5Ca0.09Sr0.41MnO3 manganites. The low temperature state of both systems is the result of a competition between the antiferromagnetic and ferromagnetic phases. The samples display magnetocaloric effect evidenced in an adiabatic temperature change during a metamagnetic transition from an antiferromagnetic to a ferromagnetic phase. As additional features, La5/8−yPryCa3/8MnO3 exhibits phase separation characterized by the coexistence of antiferromagnetic and ferromagnetic phases and Pr0.5Ca0.09Sr0.41MnO3 displays inverse magnetocaloric effect in which temperature decreases while applying an external magnetic field. In both cases, a significant part of the magnetocaloric effect appears from nonreversible processes. As the traditional thermodynamic description of the effect usually deals with reversible transitions, we developed an alternative way to calculate the adiabatic temperature change in terms of the change of the relative ferromagnetic fraction induced by magnetic field. To evaluate our model, we performed direct measurement of the sample’s adiabatic temperature change by means of a differential thermal analysis. An excellent agreement has been obtained between experimental and calculated data. These results show that metamagnetic transition in manganites play an important role in the study of magnetic refrigeration.
Electron-hole recombination properties of In0.5Ga0.5As/GaAs quantum dot solar cells and the influence on the open circuit voltage
Authors: Jolley Greg , Lu Hao Feng , Fu Lan , Tan Hark Hoe , Jagadish Chennupati
Published: September 2010

We report on a detailed analysis of the temperature dependent electrical properties of In0.5Ga0.5As/GaAs quantum dot solar cells. The effects leading to a reduction in the open circuit voltage are found to be the thermal injection of carriers from the n and p-type layers into the depletion region where they recombine with carriers occupying quantum dot states due to a thermal distribution. The departure of the device studied here from an ideal intermediate band solar cell is discussed.
ZnO nanowire and mesowire for logic inverter fabrication
Authors: Lee Young Tack , Im Seongil , Ha Ryong , Choi Heon-Jin
Published: September 2010

We report on a ZnO-based logic inverter utilizing two field effect transistors (FETs), whose respective channel has different wire-diameters under a top-gate dielectric of poly-4-vinylphenol. One FET with nanowire (160 nm) channel displayed an abrupt drain current (ID) increase and fast ID saturation near its positive threshold voltage (Vth) while the other FET with mesowire (770 nm) showed a thin-film transistor-like behavior and a negative Vth. When the nanowire and mesowire FETs were, respectively, used as a driver and a load, our inverter demonstrated an excellent voltage gain as high as 25 under a supply voltage of 20 V.
Dielectric thickness dependence of carrier mobility in graphene with HfO2 top dielectric
Authors: Fallahazad Babak , Kim Seyoung , Colombo Luigi , Tutuc Emanuel
Published: September 2010

We investigate the carrier mobility in monolayer and bilayer graphene with a top HfO2 dielectric, as a function of the HfO2 film thickness and temperature. The results show that the carrier mobility decreases during the deposition of the first 2–4 nm of top dielectric and remains constant for thicker layers. The carrier mobility shows a relatively weak dependence on temperature indicating that phonon scattering does not play a dominant role in controlling the carrier mobility. The data strongly suggest that fixed charged impurities located in close proximity to the graphene are responsible for the mobility degradation.
Enhancement of light power for strain-compensated hybrid InGaN/InGaN/MgZnO light-emitting diodes
Authors: Park Seoung-Hwan , Moon Yong-Tae , Lee Jeong Sik , Kwon Ho Ki , Park Joong Seo , Ahn Doyeol
Published: September 2010

Electronic and optical properties of strain-compensated InGaN/InGaN/MgZnO quantum well (QW) structures using a MgZnO substrate are investigated using the multiband effective mass theory. A strain-compensated InGaN/InGaN/MgZnO QW structure with a larger strain shows larger matrix element than that with a smaller strain. The spontaneous emission peak rapidly increases with increasing compressive strain because the matrix element is enhanced for the strain-compensated QW structure with a larger strain. In addition, we find that the strain-compensated QW structure with the larger Mg composition in the substrate has greater spontaneous emission peak than the strain-compensated QW structure with the smaller Mg composition in the substrate.
Three-dimensional sliced fluorescence imaging in bulbs
Authors: Chen Yu-wei , Chen Kuo-mei
Published: September 2010

To study dynamic behaviors of molecular photodissociation processes and photoinitiated inelastic and reactive collisions in a bulb environment, a three-dimensional sliced fluorescence imaging method has been developed. This experimental method combines the sliced fluorescence imaging techniques and a double resonance spectroscopic detection scheme to acquire the central slice of state-selected Newton spheres of scattering products. To illustrate the essence and simplicity of the present method, experimental images of state-selected CN photofragments from the ICN photodissociation are presented. For other chemically significant product species with a single fluorescent excited state, an infrared-optical double resonance detection scheme warrants the present technique a general method in the study of dynamic processes in bulbs.
Excitation pressure as a measure of the sensitivity of photosystem II to photoinactivation
Authors: Kornyeyev Dmytro , Logan Barry A. , Holaday A. Scott
Published: September 2010

The appearance of a new hypothesis implicating the oxygen-evolving complex as the dominant target of PSII photoinactivation (the ‘manganese cluster’ mechanism) suggests that the inactivation of PSII can be predicted on the basis of the total amount of incident photons, and challenges the role that electron transport and thermal dissipation of excitation energy play in mitigating PSII photoinactivation. This viewpoint article discusses evidence showing that minimising of the amount of energy reaching closed PSII reaction centres (i.e. the excitation pressure) is important for photoprotection. Examples are described where the parameters derived from excitation pressure correlate with the level of PSII photoinactivation, whereas the counting of incident photons does not. These examples confirm the role of electron transport and thermal energy dissipation as factors modulating PSII photoinactivation, and validate strategies that are aimed at understanding and improving PSII resistance to photoinactivation by analysis and manipulation of photoprotective processes. The authors conclude that an integrated model that incorporates various mechanisms of PSII photoinactivation and analysis of their contribution is needed. In addition, the role of UV light in naturally occurring PSII photoinactivation is evaluated. It is suggested that, when compared with visible light, the damaging effect of UV light may be limited under field conditions.