bluuebunny/crossref_metadata_2025 huggingface dataset:
Ice and ocean processes in the Bellingshausen Sea, Antarctica
Authors: Holland Paul R. , Jenkins Adrian , Holland David M.
Published: May 2010

In the vicinity of the Antarctic Peninsula observations show diminishing sea ice and a rapid warming of atmosphere and ocean. These changes have led to the collapse of ice shelves and retreat, acceleration, and thinning of inland ice. However, ocean observations in the center of the nearby Bellingshausen Sea are spatially and temporally coarse. In this study, ocean and sea ice models forced by atmospheric reanalyses are used to investigate this data gap by simulating processes in the Bellingshausen Sea for the years 1979–2007. The model suggests flow features in the region and predicts the basal melting of local ice shelves. Modeled ocean conditions are found to be less variable than in the nearby Amundsen Sea, which is situated closer to foci of annual and interannual atmospheric variability. Melt rates beneath George VI Ice Shelf are investigated in detail, concluding that the ice shelf may have been melting out of balance (and therefore thinning) for decades. The melt rate contains significant interannual variability that the model links to variation in sea ice conditions offshore of the southern end of the ice shelf. This stands in contrast to the Amundsen Sea, where models suggest that ice shelf melting is controlled by variable transport of Circumpolar Deep Water onto the continental shelf.
Economic consequences of optimized water management for a prolonged, severe drought in California
Authors: Harou Julien J. , Medellín‐Azuara Josué , Zhu Tingju , Tanaka Stacy K. , Lund Jay R. , Stine Scott , Olivares Marcelo A. , Jenkins Marion W.
Published: May 2010

If abrupt climate change has occurred in the past and may be more likely under human forcing, it is relevant to look at the adaptability of current infrastructure systems to severe conditions of the recent past. Geologic evidence suggests two extreme droughts in California during the last few thousand years, each 120–200 years long, with mean annual streamflows 40%–60% of the historical mean. This study synthesized a 72 year drought with half of mean historical inflows using random sampling of historical dry years. One synthetic hydrological record is used, and sensitivity to different interpretations of the paleorecord is not evaluated. Economic effects and potential adaptation of California's water supply system in 2020 to this drought is explored using a hydroeconomic optimization model. The model considers how California could respond to such an extreme drought using water trading and provides best‐case estimates of economic costs and effects on water operations and demands. Results illustrate the ability of extensive, intertied, and flexible water systems with heterogeneous water demands to respond to severe stress. The study follows a different approach to climate change impact studies, focusing on past climate changes from the paleorecord rather than downscaled general circulation model results to provide plausible hydrologic scenarios. Adaptations suggested for the sustained drought are similar for dry forms of climate warming in California and are expensive but not catastrophic for the overall economy but would impose severe burdens on the agricultural sector and environmental water uses.
Possible strain partitioning structure between the Kumano fore‐arc basin and the slope of the Nankai Trough accretionary prism
Authors: Martin Kylara M. , Gulick Sean P. S. , Bangs Nathan L. B. , Moore Gregory F. , Ashi Juichiro , Park Jin‐Oh , Kuramoto Shin'ichi , Taira Asahiko
Published: May 2010

A 12 km wide, 56 km long, three‐dimensional (3‐D) seismic volume acquired over the Nankai Trough offshore the Kii Peninsula, Japan, images the accretionary prism, fore‐arc basin, and subducting Philippine Sea Plate. We have analyzed an unusual, trench‐parallel depression (a “notch”) along the seaward edge of the fore‐arc Kumano Basin, just landward of the megasplay fault system. This bathymetric feature varies along strike, from a single, steep‐walled, ∼3.5 km wide notch in the northeast to a broader, ∼5 km wide zone with several shallower linear depressions in the southwest. Below the notch we found both vertical faults and faults which dip toward the central axis of the depression. Dipping faults appear to have normal offset, consistent with the extension required to form a bathymetric low. Some of these dipping faults may join the central vertical fault(s) at depth, creating apparent flower structures. Offset on the vertical faults is difficult to determine, but the along‐strike geometry of these faults makes predominantly normal or thrust motion unlikely. We conclude, therefore, that the notch feature is the bathymetric expression of a transtensional fault system. By considering only the along‐strike variability of the megasplay fault, we could not explain a transform feature at the scale of the notch. Strike‐slip faulting at the seaward edge of fore‐arc basins is also observed in Sumatra and is there attributed to strain partitioning due to oblique convergence. The wedge and décollement strength variations which control the location of the fore‐arc basins may therefore play a role in the position where an along‐strike component of strain is localized. While the obliquity of convergence in the Nankai Trough is comparatively small (∼15°), we believe it generated the Kumano Basin Edge Fault Zone, which has implications for interpreting local measured stress orientations and suggests potential locations for strain‐partitioning‐related deformation in other subduction zones.
Relationships of coastal nocturnal boundary layer winds and turbulence to Houston ozone concentrations during TexAQS 2006
Authors: Tucker Sara C. , Banta Robert M. , Langford Andrew O. , Senff Christoph J. , Brewer W. Alan , Williams Eric J. , Lerner Brian M. , Osthoff Hans D. , Hardesty R. Michael
Published: May 2010

Measurements made with a ship‐based Doppler wind lidar during the summertime 2006 Texas Air Quality Study are used to study the relationship between lower‐tropospheric vertical structure and winds and ozone (O3) concentrations in Houston, Texas, under two different flow regimes. We observed that strong southerly flow regimes, dominated by the subtropical anticyclone (Bermuda high) off the Atlantic coast of the United States, resulted in strong (i.e., high wind speed) onshore nocturnal low‐level jets (LLJ) and low O3 and oxidant Ox (where Ox = O3 + NO2) concentrations at night and the following afternoon. In contrast, periods dominated by northerly or easterly flow resulted in relatively weak (low wind speed), but still onshore, nocturnal LLJs associated with higher concurrent and next‐day concentrations of O3 and Ox. We present lidar data from 24 h example periods for each of these conditions and demonstrate how each type of flow regime is related to in situ ship‐based ozone measurements. We expanded the study to include all days during the study when the ship was near Houston, to demonstrate how the strength of the meridional winds aloft show a better relationship to concurrent ship‐measured Ox concentrations than the winds near the surface do. We found a strong relationship between a parameterization of the observed nocturnal jets, which reflect the synoptic conditions, to peak hourly O3 measured the next day at the ship and averaged throughout the Houston/Galveston/Brazoria continuous ambient monitoring stations monitoring network, indicating potential applications for planning air quality.
The influence of tectonic regimes on the earthquake size distribution: A case study for Italy
Authors: Gulia Laura , Wiemer Stefan
Published: May 2010

We explore the hypothesis that the relative size distribution of earthquakes, or b‐value, systematically depends on the style‐of‐faulting of seismotectonic zones. Because the b‐value has been shown to be inversely proportional to stress, we expect to find b(thrust) < b(strike‐slip) < b(normal). We test this expectation for the case of Italy. We first of all build a seismotectonic zonation model, consisting of 10 distinct tectonic zones. The faulting style of each zone is then characterized by the summed moment tensor of first‐motion and full‐waveform based focal mechanism. We calculate the b‐value for each zone: the lowest values are obtained for reverse zones (0.75–0.81), highest for the normal (1.09), followed by the strike‐slips (0.9–0.92). Our results suggest that b‐values, which are a critical parameter in all seismic hazard assessments, should be set according to the local faulting regimes. In addition, seismotectonic zonation models should take b‐value variations as one input.
Regular Multicomponent Exercise Increases Physical Fitness and Muscle Protein Anabolism in Frail, Obese, Older Adults
Authors: Villareal Dennis T. , Smith Gordon I. , Sinacore David R. , Shah Krupa , Mittendorfer Bettina
Published: May 2010

Aging is associated with a decline in strength, endurance, balance, and mobility. Obesity worsens the age‐related impairment in physical function and often leads to frailty. The American College of Sports Medicine recommends a multicomponent (strength, endurance, flexibility, and balance) exercise program to maintain physical fitness. However, the effect of such an exercise program on physical fitness in frail, obese older adults is not known. We therefore determined the effect of a 3‐month long multicomponent exercise training program, on endurance (peak aerobic capacity (VO2 peak)), muscle strength, muscle mass, and the rate of muscle protein synthesis (basal rate and anabolic response to feeding) in nine 65‐ to 80‐year‐old, moderately frail, obese older adults. After 3 months of training, fat mass decreased (P < 0.05) whereas fat‐free mass (FFM), appendicular lean body mass, strength, and VO2 peak increased (all P < 0.05). Regular strength and endurance exercise increased the mixed muscle protein fractional synthesis rate (FSR) but had no effect on the feeding‐induced increase in muscle protein FSR (∼0.02%/h increase from basal values both before and after exercise training; effect of feeding: P = 0.02; effect of training: P = 0.047; no interaction: P = 0.84). We conclude that: (i) a multicomponent exercise training program has beneficial effects on muscle mass and physical function and should therefore be recommended to frail, obese older adults, and (ii) regular multicomponent exercise increases the basal rate of muscle protein synthesis without affecting the magnitude of the muscle protein anabolic response to feeding.
Functional properties of BaTiO3–Ni0.5Zn0.5Fe2O4 magnetoelectric ceramics prepared from powders with core-shell structure
Authors: Curecheriu L. P. , Buscaglia M. T. , Buscaglia V. , Mitoseriu L. , Postolache P. , Ianculescu A. , Nanni P.
Published: May 2010

In the present work, diphasic ceramic composites with core-shell nanostructures formed by Ni0.50Zn0.50Fe2O4 core and BaTiO3 shell were investigated. Their properties were compared with those of composites prepared by coprecipitation. The core-shell structure was confirmed by microstructural powder analysis. Homogeneous microstructures with a good phase mixing and percolated dielectric phase by the magnetic one were obtained from coprecipitated powders. Less homogeneous microstructures resulted in ceramics produced from the powder prepared by core-shell method, with isolated small ferrite grains besides large ferrite aggregates embedded into the BaTiO3 matrix. Both the ferroelectric and magnetic phases preserve their basic properties in bulk composite form. However, important differences in the dielectric relaxation and conduction mechanisms were found as result of the microstructural difference. Extrinsic contributions play important roles in modifying the electric properties in both ceramics, causing space charge effect, Maxwell–Wagner relaxations and hopping conductivity, mainly due to the ferrite low resistivity phase. The conductivity and dielectric modulus spectra analysis allowed to identify different polaron contributions associated with the microstructural differences. It results that by using the core-shell method, improved dielectric properties and limited hopping contributions can be realized.
Graphene buffer layer on Si-terminated SiC studied with an empirical interatomic potential
Authors: Lampin Evelyne , Priester Catherine , Krzeminski Christophe , Magaud Laurence
Published: May 2010

The atomistic structure of the graphene buffer layer on Si-terminated SiC is investigated using a modified version of the environment-dependent interatomic potential. The determination of the equilibrium state by the conjuguate gradients method suffers from a complex multiple-minima energy surface. The initial configuration is therefore modified to set the system in specific valleys of the energy surface. The solution of minimal energy forms a hexagonal pattern composed of stuck regions separated by unbonded rods that release the misfit with the SiC surface. The structure presents the experimental symmetries and a global agreement with an ab initio calculation. It is therefore expected that the interatomic potential could be used in classical molecular dynamics calculations to study the graphene growth.
Addendum to “Fundamental questions relating to ion conduction in disordered solids”
Authors: Macdonald J. Ross
Published: May 2010

The extensive review cited in the title discusses “a number of basic scientific questions relating to ion conduction in homogeneously disordered solids” [J. C. Dyre et al., Rep. Prog. Phys. 72, 046501 (2009)]. Although it suggests answers to some of the questions raised, its main purpose is “to draw attention to the fact that this field of research still presents several fundamental challenges.” This work succeeds admirably in that goal, but it does not contain reference to and discussion of some relevant published work related to the fundamental questions it discusses. It is therefore the purpose of this work to add additional information about some of these subjects, including new insights about the Barton, Nakajima, and Namikawa relation. Although most of this information is based on published papers, its omission from the cited review is an indication that it is not widely known and is therefore worth discussing.
Structures and phonon properties of nanoscale fractional graphitic structures in amorphous carbon determined by molecular simulations
Authors: Kumagai Tomohisa , Choi Junho , Izumi Satoshi , Kato Takahisa
Published: May 2010

Although amorphous carbon (a-C) materials are being widely used, relaxed atomic structures of a-C have not yet been investigated in detail. In this study, a-C structures were relaxed in molecular simulations, and their structural properties and phonon properties were investigated. As a result, several nanoscale fractional graphitic structures were observed in the annealed a-C structures. Further, it was found that the fractional graphitic structures caused a peak in the fractional phonon density of states of the annealed a-C structures, which corresponded to the D peak. The main phonon mode in the fractional graphitic structure with phonon frequencies of the D peak position and that of the G peak position were the distortion mode of six-membered rings, and the stretching mode of the bonds between threefold coordinated atoms, respectively. Both the distortion mode of six-membered rings and the bond-stretching mode were observed in phonon frequencies between the D peak position and the G peak position.
Detrapping dynamics in Al2O3 metal-oxide-semiconductor
Authors: Rao Rosario , Irrera Fernanda
Published: May 2010

In this paper, we use a two-pulse C-V technique to study detrapping in Al2O3 metal-oxide-semiconductor at extremely short (and long) times. The investigated timescale spanned from hundreds of microseconds to ten minutes. The flat band voltage instability was studied systematically and a phenomenological model was written which accounts for logarithmic dependence on time, and linear dependence on the film thickness and the accelerating voltage. A main goal of the work is to demonstrate that this technique is a tool for the investigation of fast electrical transients in high-k films on timescale which are not accessible with conventional steady-state techniques.
Critical view on energy transfer, site symmetry, improvement in luminescence of Eu3+, Dy3+ doped YVO4 by core-shell formation
Authors: Singh L. Robindro , Ningthoujam R. S.
Published: May 2010

Nanoparticles of Dy3+ and Eu3+ doped YVO4 (core) have been prepared by urea-hydrolysis in ethylene glycol medium and further heated at 500 and 900 °C to grow particles as well as remove unwanted hydrocarbon/H2O, which acts as quencher in luminescence. Samples show emission peaks at 488 (blue), 537 (green), 572 (yellow), 592 (orange), and 617 nm (red). The emission intensity decreases when excitation wavelength changes from 300 [V–O charge transfer band (CTB)] to 255 nm (Eu/Dy–O CTB) and then to 355/395 nm (direct excitations of Dy3+/Eu3+). This is attributed to energy transfer from V–O to Eu3+/Dy3+, Eu/Dy–O to Eu3+/Dy3+. Energy transfer from Dy3+ to Eu3+ is more than that from Eu3+ to Dy3+. With heat-treatment temperature increases from 500 to 900 °C, emission intensity is improved due to the extent of decrease in nonraditive transition probability arising from surface. To the best of authors’ knowledge, local/site symmetry of Eu3+ and Dy3+ in same host is not detail discussed in literature. In the same host, asymmetric ratio of electric dipole allowed transition to magnetic dipole transition in both ions should be same but this was not happen. This study will give the origin of this. After covering core-nanoparticles with undoped YVO4 shell, luminescence intensity is further improved due to the extent of reduction in surface Eu3+/Dy3+ of particles and cross-relaxation reduction among Eu3+/Dy3+ ions.
Comparison of inelastic and quasielastic scattering effects on nonlinear electron transport in quantum wires
Authors: Huang Danhong , Gumbs Godfrey
Published: May 2010

When impurity and phonon scattering coexist, the Boltzmann equation has been solved accurately for nonlinear electron transport in a quantum wire. Based on the calculated nonequilibrium distribution of electrons in momentum space, the scattering effects on both the nondifferential (for a fixed dc field) and differential (for a fixed temperature) mobilities of electrons as functions of temperature and dc field have been demonstrated. The nondifferential mobility of electrons is switched from a linearly increasing function of temperature to a paraboliclike temperature dependence as the quantum wire is tuned from an impurity-dominated system to a phonon-dominated one, as described by Fang et al. [Phys. Rev. B 78, 205403 (2008)]. In addition, a maximum has been obtained in the dc field dependence of the differential mobility of electrons. The low-field differential mobility is dominated by the impurity scattering, whereas the high-field differential mobility is limited by the phonon scattering as described by Hauser et al. [Semicond. Sci. Technol. 9, 951 (1994)]. Once a quantum wire is dominated by quasielastic scattering, the peak of the momentum-space distribution function becomes sharpened and both tails of the equilibrium electron distribution centered at the Fermi edges are raised by the dc field after a redistribution of the electrons is fulfilled in a symmetric way in the low-field regime. If a quantum wire is dominated by inelastic scattering, on the other hand, the peak of the momentum-space distribution function is unchanged while both shoulders centered at the Fermi edges shift leftward correspondingly with increasing dc field through an asymmetric redistribution of the electrons even in low-field regime as described by Wirner et al. [Phys. Rev. Lett. 70, 2609 (1993)].
Direct observations of Ge2Sb2Te5 recording marks in the phase-change disk
Authors: Naito Muneyuki , Ishimaru Manabu , Hirotsu Yoshihiko , Kojima Rie , Yamada Noboru
Published: May 2010

Atomistic structures of the Ge2Sb2Te5 thin film in the real phase-change disk have been investigated using transmission electron microscopy (TEM). As-deposited amorphous Ge2Sb2Te5 films were laser-irradiated for initialization (crystallization) and recording. Cross-sectional TEM observations revealed that the recording mark was fully amorphized by laser irradiation. A slight difference between the as-deposited and the laser irradiation-induced amorphous Ge2Sb2Te5 was observed in the intensity profile of nanobeam electron diffraction patterns and atomic pair distribution functions. This difference was attributed to structural relaxation of amorphous Ge2Sb2Te5, which gives rise to the alteration of chemical order.
Piezoelectric polarization of semipolar and polar GaInN quantum wells grown on strained GaN templates
Authors: Feneberg Martin , Thonke Klaus , Wunderer Thomas , Lipski Frank , Scholz Ferdinand
Published: May 2010

Piezoelectric polarization in GaInN/GaN quantum well (QW) structures is not only dependent on the strain in the pseudomorphically grown QWs but also severely influenced by the strain already present in the underlying template. Here, we investigate the influence of template strain on the piezoelectric polarization of QWs grown in the polar [0001] and in semipolar off-[0001] directions. We find that an efficient strain-engineering can be used to decrease polarization fields or even cancel them out completely. Even a change of sign of the built-in polarization fields within QWs can be achieved in certain strain-situations. Our results shed light on recent ambiguous results concerning the piezoelectric tensor component e15 and are able to explain unexpected differences in device performance of polar and semipolar QW devices.
Growth of ZnSe(1−x)Tex epilayers by isothermal closed space sublimation
Authors: Larramendi Erick M. , Gutiérrez Z-B Karla , Arens Christof , Woggon Ulrike , Schikora Detlef , Lischka Klaus
Published: May 2010

ZnSe ( 1 − x ) Te x  (x∼0.06) epilayers were grown on GaAs(001) substrates at 350 °C by isothermal closed space sublimation (ICSS) technique. The epitaxial growth was performed in low-pressure helium atmosphere (∼0.1 mbar) by sequential exposures of the substrate to vapors of a solid solution of selenium-tellurium and elemental zinc. The use of a mixed source is proposed in order to regulate the partial vapor pressure of the constituents by composition. Strain and composition of the ZnSe(1−x)Tex epilayers were extracted from high resolution x-ray reciprocal space mapping. Structural investigations show a reasonably good crystalline quality of the epilayers. Good reproducibility of composition and control of thickness were obtained although atomic layer epitaxy regimen was not achieved. A growth rate of 1.3 monolayers/cycle was ascribed to multilayer adsorption and the existence of an efficient transport of SeTe in graphite under thermodynamic conditions of ICSS. Both Raman and photoluminescence characterizations suggest the existence of random alloy epilayers with larger composition disorder in the mesoscopic scale than those obtained by molecular beam epitaxy.
Luminescence and Raman studies of YNbO4 phosphors doped by Eu3+, Ga3+, and Al3+
Authors: Nazarov Mihail , Kim Young Jin , Lee Eun Young , Min Kyoung-In , Jeong Mun Seok , Lee Su Woong , Noh Do Young
Published: May 2010

Efficient phosphors based on YNbO4 and doped by Eu3+, Ga3+, and Al3+ were synthesized with different fluxes under different thermal conditions and investigated under x-ray excitation and Raman spectroscopy. The samples codoped by Al3+ and Ga3+ show higher intensity under x-ray excitation in comparison with YNbO4:Eu3+ phosphors. The model of redistribution energy transfer from D51 level to F7J is proposed. Monoclinic fergusonite crystal structure and excellent luminescent properties under x-ray excitation allow recommend these phosphors as good candidates for different applications.
Structural and magnetic properties of magnetron sputtered Ni–Mn–Sn ferromagnetic shape memory alloy thin films
Authors: Vishnoi Ritu , Kaur Davinder
Published: May 2010

In the present study, structural and magnetic properties of Mn-rich, off-stoichiometric, nanocrystalline Ni–Mn–Sn ferromagnetic shape memory alloy thin films, grown on Si (100) substrates at 550 °C by dc magnetron sputtering have been systematically investigated. The crystallization, surface morphology, and structural features were studied using x-ray diffraction, atomic force microscopy, and field emission scanning electron microscopy. The structural transition from austenite to martensite was observed with an increase of Mn content. Austenitic phase with mixed L21/A2+B2 structure has been observed at room temperature in Ni52.6Mn23.7Sn23.6 (S1) and Ni51.5Mn26.1Sn22.2 (S2) films, while those with composition of Ni58.9Mn28.0Sn13.0 (S3) and Ni58.3Mn29.0Sn12.6 (S4) show martensitic phase with 14M modulated monoclinic structures. Field induced martensite-austenite transformation has been observed in magnetization studies using superconducting quantum interference device magnetometer. Temperature dependent magnetization measurements demonstrate the influence of magnetic field on the structural phase transition temperature. The investigations reveal an increase of martensitic transformation temperature (TM) with corresponding increase in substitution of Mn. The films exhibit ferromagnetic behavior at low temperatures below Curie temperature (TC). The decrease in saturation moment with increasing Mn content, indicates the existence of antiferromagnetic correlations within ferromagnetic matrix.
High performance resonance Raman spectroscopy using volume Bragg gratings as tunable light filters
Authors: Paillet Matthieu , Meunier François , Verhaegen Marc , Blais-Ouellette Sébastien , Martel Richard
Published: May 2010

We designed a near infrared tunable resonance Raman spectroscopy system based on a tandem of thick volume Bragg gratings (VBGs). VBGs are here the constituents of two light filtering units: a tunable laser line filter (LLF) and a tunable notch filter (NF). When adapted in a micro-Raman setup with a single stage monochromator (1800 gr/mm grating), the tandem of LLF and NF allowed measurements of Raman signals down to ±20 cm−1. The good performance and fast tunability of the VBG Raman system was demonstrated on a sulfur powder and on a bulk single-walled carbon nanotube sample through a series of 22 Stokes and anti-Stokes spectra recorded at excitation wavelengths between 800 and 990 nm. The main drawbacks of the setup are the limited spectral range to the near infrared and the small angular acceptance of the filters (≈1 mrad), which causes mainly attenuation problems with the NF. The impact of the main limitations is discussed and solutions are provided.
Leakage behavior and conduction mechanisms of Ba(Ti0.85Sn0.15)O3/Bi1.5Zn1.0Nb1.5O7 heterostructures
Authors: Wang S. J. , Miao S. , Reaney I. M. , Lai M. O. , Lu L.
Published: May 2010

Polycrystalline Ba(Ti0.85Sn0.15)O3/Bi1.5Zn1.0Nb1.5O7 (BTS/BZN) heterostructure thin films were deposited on LaNiO3/SiO2/Si substrates by pulsed laser deposition. The leakage mechanisms of the BTS/BZN heterostructure thin films were studied in the temperature range from 303 to 403 K. At a high electric field (>100 kV/cm) and a positive bias, the leakage is dominated by space-charge-limited-current, while Fowler–Nordheim tunneling is the main reason for conduction under a negative bias. At a low electric field, the leakage current is controlled by the Ohmic contact.
Field and current-induced magnetization reversal studied through spatially resolved point-contacts
Authors: Saxegaard Magne , Yang DeZheng , Wahlström Erik , Bručas Rimantas , Hanson Maj
Published: May 2010

We present results from scanning tunneling microscopy based point-contact measurements of the local resistance in octagon shaped, Co(20 nm)/Cu(5 nm)/Fe19Ni81(2.5 nm) spin-valve rings. Through this technique one can detect the magnetoresistance with spatial resolution, and link it to magnetic domain wall motion within the ring. Measurements with varying currents indicate current-induced effects leading to offsets in the magnetic fields required for magnetic switching. The offsets can be attributed to current-induced spin-transfer torque effects for the thin Fe19Ni81 layer and to Oersted field effects for the thick Co layer.
Optimization of carriers by self-doping in Cu0.5Tl0.5Ba2Ca2Cu3−yMyO10−δ superconductor
Authors: Mumtaz M. , Khan Nawazish A. , Khan Sajid
Published: May 2010

The elements of fourth group (IV-A) of the periodic table have been doped in Cu0.5Tl0.5Ba2Ca2Cu3−yMyO10−δ (M=Si, Ge, Sn, and y=0, 1) samples to explore any possible electron-phonon interaction mechanism in oxide high temperature superconductors. We have observed that doped atoms with masses significantly different from that of Cu atom suppress the superconducting properties of the final compound. The postannealing experiments in flowing oxygen were also carried out to optimize the carriers density in the unit cell. After postannealing in oxygen the superconducting properties of all the samples are improved, which is most likely due to the optimization of carriers density in the material. It is observed from Fourier transform infrared absorption measurements that the CuO2 planar mode is hardened with the doping of Si, whereas, it is softened with the incorporation of Ge and Sn in the unit cell. The apical oxygen modes are softened with Si doping but these modes are hardened with the incorporation of Ge and Sn. It is most likely that the density of phonons is significantly altered due to increased anharmonic oscillations produced by heavier and lighter atoms in MO2/CuO2 (i.e., M=Sn,Si) planes, which suppress the phonon population from a desired level and hence the superconductivity. The shift in oxygen phonon modes after postannealing is most probably linked to the change in oxidation state of thallium.
Comment on “Phenomenological theory of laser-plasma interaction in ‘bubble' regime” [Phys. Plasmas 11, 5256 (2004)]
Authors: Rahmatollahpur Sh.
Published: May 2010

A reliable analytical expression for the maximum energy (γmax) of the accelerated electrons in the bubble regime is derived. The presented equation is more consistent than the previous equation derived by Kostyukov et al. [Phys. Plasmas 11, 5256 (2004)]. The (γmax) derived by I. Kostyukov et al. was two time larger than γmax observed in the particle in the cell (PIC) simulations. This new equation explains the monoenergetic electron energy more accurately in the relativistic regime and is in consistence with the observed PIC simulations.
Response to “Comment on ‘Phenomenological theory of laser-plasma interaction in “bubble” regime' ” [Phys. Plasmas 17, 054703 (2010)]
Authors: Kostyukov I. , Pukhov A.
Published: May 2010

The result obtained in the Comment is incorrect whereas the result obtained in our paper [I. Kostyukov, A. Pukhov, and S. Kiselev, Phys. Plasmas 11, 5256 (2004)] is correct.
Shear wave vortex solution in a strongly coupled dusty plasma
Authors: Janaki M. S. , Chakrabarti N.
Published: May 2010

The properties of electrostatic transverse shear waves in a strongly coupled dusty plasma are examined using the nonlinear version of the generalized hydrodynamic equation. In the kinetic limit, it is shown that strongly coupled plasmas support localized dipolar vortexlike solutions with amplitude modulated periodically.
To the theory of high-power gyrotrons with uptapered resonators
Authors: Dumbrajs O. , Nusinovich G. S.
Published: May 2010

In high-power gyrotrons it is desirable to combine an optimal resonator length with the optimal value of the resonator quality factor. In resonators with the constant radius of the central part, the possibilities of this combination are limited because the quality factor of the resonator sharply increases with its length. Therefore the attempts to increase the length for maximizing the efficiency leads to such increase in the quality factor which makes the optimal current too small. Resonators with slightly uptapered profiles offer more flexibility in this regard. In such resonators, one can separate optimization of the interaction length from optimization of the quality factor because the quality factor determined by diffractive losses can be reduced by increasing the angle of uptapering. In the present paper, these issues are analyzed by studying as a typical high-power 17 GHz gyrotron which is currently under development in Europe for ITER (http://en.wikipedia.org/wiki/ITER). The effect of a slight uptapering of the resonator wall on the efficiency enhancement and the purity of the radiation spectrum in the process of the gyrotron start-up and power modulation are studied. Results show that optimal modification of the shape of a slightly uptapered resonator may result in increasing the gyrotron power from 1052 to 1360 kW.
Modeling of injection characteristics of polar and nonpolar III-nitride multiple quantum well structures
Authors: Kisin Mikhail V. , El-Ghoroury Hussein S.
Published: May 2010

Carrier confinement and injection characteristics of polar and nonpolar III-nitride quantum well (QW) light-emitting diode or laser diode structures are compared. We demonstrate that strongly inhomogeneous QW injection in multiple-QW (MQW) active region is one of the possible reasons holding back the advance of nonpolar laser structures. In polar structures, strong interface polarization charges induce the nonuniform carrier distribution among the active QWs so that the extreme p-side QW always dominates the optical emission. On the contrary, in nonpolar MQW structures, the inhomogeneity of QW populations is supported mainly by QW residual charges and the prevailing QW is the one closest to the n-side of the diode. For both polar and nonpolar structures, the QW injection inhomogeneity is strongly affected by the QW carrier confinement and becomes more pronounced in longer wavelength emitters with deeper active QWs. We show that in nonpolar structures indium incorporation into optical waveguide layers improves the uniformity of QW injection. On the contrary, QW injection in polar structures remains inhomogeneous even at high-indium waveguide layer compositions. We show, however, that polarization-matched design of the electron-blocking layer can noticeably improve the injection uniformity in polar MQW structure and enhance the structure internal quantum efficiency.
Substitutional and clustered B in ion implanted Ge: Strain determination
Authors: Bisognin G. , Vangelista S. , Berti M. , Impellizzeri G. , Grimaldi M. G.
Published: May 2010

The lattice strain induced both by substitutional and clustered B in B-implanted Ge samples has been investigated by means of high resolution x-ray diffraction (HRXRD). The main results can be summarized as follows: while substitutional (i.e., electrically active) B exhibits a negative strain, clustered (i.e., electrically inactive) B reverses the lattice strain from negative to positive values, the latter being much higher with respect to those found for clustered B in Si. In particular, the lattice volume modification for each B atom (ΔV) induced by substitutional (ΔVSub) and clustered (ΔVCl) B is ΔVSub=−12.4 Å3 and ΔVCl=+14.8 Å3, respectively. These unexpected results demonstrate the ability of HRXRD to quantitatively detect the amount of electrically inactive (and active) B.
Accurate ab initio calculations of the ground states of FeC, FeC+, and FeC−
Authors: Tzeli Demeter , Mavridis Aristides
Published: May 2010

For the ground states of the diatomic carbide FeC(X Δ3) and its ions, FeC+(X Δ2) and FeC−(X Δ2), we report on accurate multireference variational ab initio results employing augmented correlation consistent basis sets of quintuple cardinality. The dissociation energies and bond lengths are found to be D00=87±1, 95.2, and 84±1 kcal/mol at re=1.581, 1.556, and 1.660 Å for FeC, FeC+, and FeC−, respectively. All our final numbers are in agreement with the available experimental data.
Large-area graphene on polymer film for flexible and transparent anode in field emission device
Authors: Verma Ved Prakash , Das Santanu , Lahiri Indranil , Choi Wonbong
Published: May 2010

We present the fabrication and electrical characterization of large graphene structure on polyethylene terephthalate (PET) flexible substrate. Graphene film was grown on Cu foil by thermal chemical vapor deposition and transferred to PET by using hot press lamination. The graphene/PET film shows high quality, flexible transparent conductive structure with unique electrical-mechanical properties; ∼88.80% light transmittance and ∼1.1742 kΩ/sq sheet resistance. We demonstrate application of graphene/PET film as flexible and transparent electrode for field emission displays. Our proposed techniques can be tailored for any flexible substrate and large scale production, which could open up exciting device applications in foldable electronics.
Temperature-dependent leakage current characteristics of Pr and Mn cosubstituted BiFeO3 thin films
Authors: Wen Zheng , Shen Xuan , Wu Jingxian , Wu Di , Li Aidong , Yang Bin , Wang Zhu , Chen Hengzhi , Wang Junling
Published: May 2010

Leakage current characteristics of (Bi0.86Pr0.14)(Fe0.95Mn0.05)O3 (BPFMO) thin films are studied at various temperatures from 293 down to 93 K. Space charge limited current and Poole–Frenkel (PF) emission are found to be the dominant mechanism in the low and the high electric fields, respectively. The trap ionization energy at zero-field in BPFMO films is deduced to be around 0.29 eV, which indicates the existence of shallow traps. A negative differential resistivity behavior is observed before the onset of PF emission at 93 K, which is discussed in terms of the competition between electron trapping and field-assisted thermal emission.
Metal-specific and NADPH oxidase dependent changes in lipoxygenase and NADPH oxidase gene expression in Arabidopsis thaliana exposed to cadmium or excess copper
Authors: Remans Tony , Opdenakker Kelly , Smeets Karen , Mathijsen Dennis , Vangronsveld Jaco , Cuypers Ann
Published: May 2010

Reactive oxygen species produced by NADPH oxidase and oxylipins derived from lipoxygenase activity can signal various stress conditions and have been implicated when plants are exposed to heavy metals. Transcriptional profiling of the 10 NADPH oxidase and 6 lipoxygenase genes was performed after exposure of Arabidopsis thaliana wild-type and NADPH oxidase mutants to 5 µM CdSO4 or 2 µM CuSO4 for 24 h. Under these short exposures to environmentally realistic concentrations of Cd or Cu, plants modulate signalling networks that regulate the onset of adaptive responses. Metal-specific NADPH oxidase genes were upregulated by Cd but downregulated by Cu, and metal-specific lipoxygenase gene expression was observed only after Cu exposure. Genes that are responsive to both metals were upregulated and may be responsive to general oxidative stress. For all metal-responsive genes except RBOHD, distinct responses were observed between leaves and roots, which may be due to different stress intensities and signalling mechanisms. Mutation of NADPH oxidase genes had opposing effects on gene expression after Cd or Cu exposure. Upregulation of LOX1 and LOX6 in the roots after exposure to Cd depended on NADPH oxidase gene expression, whereas LOX3 and LOX6 expression was induced more strongly in NADPH oxidase mutants after Cu exposure. Furthermore, NADPH oxidases regulated their own expression level and that of other members of the gene family when exposed to Cd or Cu. The results suggest interplay between reactive oxygen species and oxylipin signalling under Cd or Cu stress, and are useful as a basis for genetic studies to unravel metal-specific signalling mechanisms.
Submergence tolerance in Hordeum marinum: dissolved CO2 determines underwater photosynthesis and growth
Authors: Pedersen Ole , Malik Al I. , Colmer Timothy D.
Published: May 2010

Floodwaters differ markedly in dissolved CO2, yet the effects of CO2 on submergence responses of terrestrial plants have rarely been examined. The influence of dissolved CO2 on underwater photosynthesis and growth was evaluated for three accessions of the wetland plant Hordeum marinum Huds. All three accessions tolerated complete submergence, but only when in CO2 enriched floodwater. Plants submerged for 7 days in water at air equilibrium (18 µM CO2) suffered loss of biomass, whereas those with 200 µM CO2 continued to grow. Higher underwater net photosynthesis at 200 µM CO2 increased by 2.7- to 3.2-fold sugar concentrations in roots of submerged plants, compared with at air equilibrium CO2. Leaf gas films enhancing gas exchange with floodwater, lack of a shoot elongation response conserving tissue sugars and high tissue porosity (24–31% in roots) facilitating internal O2 movement, would all contribute to submergence tolerance in H. marinum. The present study demonstrates that dissolved CO2 levels can determine submergence tolerance of terrestrial plants. So, submergence experiments should be conducted with defined CO2 concentrations and enrichment might be needed to simulate natural environments and, thus, provide relevant plant responses.
Leaf hydraulic architecture and water relations of three ferns from contrasting light habitats
Authors: Lo Gullo Maria A. , Raimondo Fabio , Crisafulli Alessandro , Salleo Sebastiano , Nardini Andrea
Published: May 2010

Leaf hydraulic architecture and water relations of three fern species were measured. The species selected were adapted either to deeply shaded (Woodwardia radicans), moderately shaded (Dryopteris affinis) or moderately sunny (Polystichum setiferum) habitats, as confirmed by microclimatic measurements performed in the field. Leaf water potential (Ψleaf) was lower and leaf conductance to water vapour (gL) was higher in P. setiferum than in the shade-adapted ferns. Leaf osmotic potential and water potential at the turgor loss point were lower in the sun-adapted species than in the other ferns. Leaf hydraulic resistance (Rleaf) was lowest in P. setiferum and Rleaf was correlated with gL across species. Low Rleaf was coordinated with low rachis hydraulic resistance (Rrachis). Low values of Rrachis in P. setiferum were not due to the presence of wide xylem conduits as checked on the basis of anatomical measurements, but to increased radial permeability of vascular bundles. This was a consequence of the absence of endodermis surrounding the vascular bundles in P. setiferum, which was observed in the rachis of shade-adapted species. We conclude that hydraulic adjustment of fern fronds is a key component of adaptation of pteridophytes to contrasting light habitats.
Plants versus pathogens: an evolutionary arms race
Authors: Anderson Jonathan P. , Gleason Cynthia A. , Foley Rhonda C. , Thrall Peter H. , Burdon Jeremy B. , Singh Karam B.
Published: May 2010

The analysis of plant–pathogen interactions is a rapidly moving research field and one that is very important for productive agricultural systems. The focus of this review is on the evolution of plant defence responses and the coevolution of their pathogens, primarily from a molecular-genetic perspective. It explores the evolution of the major types of plant defence responses including pathogen associated molecular patterns and effector triggered immunity as well as the forces driving pathogen evolution, such as the mechanisms by which pathogen lineages and species evolve. Advances in our understanding of plant defence signalling, stomatal regulation, R gene–effector interactions and host specific toxins are used to highlight recent insights into the coevolutionary arms race between pathogens and plants. Finally, the review considers the intriguing question of how plants have evolved the ability to distinguish friends such as rhizobia and mycorrhiza from their many foes.
Stabilizing capping motif for β-hairpins and sheets
Authors: Kier Brandon L. , Shu Irene , Eidenschink Lisa A. , Andersen Niels H.
Published: May 2010

Although much has been learned about the design of models of β-sheets during the last decade, modest fold stabilities in water and terminal fraying remain a feature of most β-hairpin peptides. In the case of hairpin capping, nature did not provide guidance for solving the problem. Some observations from prior turn capping designs, with further optimization, have provided a generally applicable, “unnatural” beta cap motif (alkanoyl-Trp at the N terminus and Trp-Thr-Gly at the C terminus) that provides a net contribution of 6 + kJ/mol to β-hairpin stability, surpassing all other interactions that stabilize β-hairpins including the covalent disulfide bond. The motif, made up entirely of natural residues, is specific to the termini of antiparallel β-strands and reduces fraying at the ends of hairpins and other β-sheet models. Utilizing this motif, 10- to 22-residue peptide scaffolds of defined stereochemistry that are greater than 98% folded in water have been prepared. The β-cap can also be used to staple together short antiparallel β-strands connected by a long flexible loop.
Heme biosynthesis is coupled to electron transport chains for energy generation
Authors: Möbius Kalle , Arias-Cartin Rodrigo , Breckau Daniela , Hännig Anna-Lena , Riedmann Katrin , Biedendieck Rebekka , Schröder Susanne , Becher Dörte , Magalon Axel , Moser Jürgen , Jahn Martina , Jahn Dieter
Published: May 2010

Cellular energy generation uses membrane-localized electron transfer chains for ATP synthesis. Formed ATP in turn is consumed for the biosynthesis of cellular building blocks. In contrast, heme cofactor biosynthesis was found driving ATP generation via electron transport after initial ATP consumption. The FMN enzyme protoporphyrinogen IX oxidase (HemG) of
Escherichia coli
abstracts six electrons from its substrate and transfers them via ubiquinone, cytochrome
bo
3
(Cyo) and cytochrome
bd
(Cyd) oxidase to oxygen. Under anaerobic conditions electrons are transferred via menaquinone, fumarate (Frd) and nitrate reductase (Nar). Cyo, Cyd and Nar contribute to the proton motive force that drives ATP formation. Four electron transport chains from HemG via diverse quinones to Cyo, Cyd, Nar, and Frd were reconstituted in vitro from purified components. Characterization of
E. coli
mutants deficient in
nar
,
frd
,
cyo
,
cyd
provided in vivo evidence for a detailed model of heme biosynthesis coupled energy generation.
RNA silencing in plants and its suppression by plant viruses.
Authors: Kon T. , Ikegami M.
Published: May 2010

RNA silencing is a sequence-specific degradation of RNA and a means of regulation of gene expression via small RNA molecules. In plants, this process is commonly referred to as post-transcriptional gene silencing (PTGS). PTGS is characterized by accumulation of small-interfering RNAs (siRNAs) and microRNAs (miRNAs), degradation of target mRNAs and methylation of homologous gene sequences. In addition to gene regulation, PTGS also plays an important role as an immunity system in plants, which acts against diverse molecular parasites or foreign genetic elements including transposons, transgenes, viruses and viroids. Most plant viruses have evolved the capacity to counteract this defence response by encoding suppressors of PTGS. Viral suppressors are highly diverse in sequence and act at distinct steps in PTGS. Furthermore, the relative ability of viral suppressors to interfere with PTGS in plants can be associated with pathogenicity. In this review, we focus on recent advances in understanding RNA silencing and its suppression by plant viruses.