bluuebunny/crossref_metadata_2025 huggingface dataset:
Seasonal and solar activity variations of the Weddell Sea Anomaly observed in the TOPEX total electron content measurements
Authors: Jee G. , Burns A. G. , Kim Y.‐H. , Wang W.
Published: April 2009

The Weddell Sea Anomaly (WSA) in the ionosphere is characterized by higher plasma densities at night than during the day in the region near the Weddell Sea. According to previous studies on the WSA, it is known to occur mostly in southern summer and has not been reported in other seasons. We have utilized more than 13 years of TOPEX total electron content (TEC) measurements in order to study how the WSA varies with seasons and how it changes with solar activity. The TOPEX TEC data have been extensively utilized for climatological studies of the ionosphere because of their excellent spatial and temporal coverage. We investigate the seasonal and solar activity variations of the WSA using four seasonal cases (March equinox, June solstice, September equinox, and December solstice) and two solar activity conditions (F10.7 < 120 for solar minimum and F10.7 > 120 for solar maximum conditions) for geomagnetically quiet periods. Our analysis shows that (1) the WSA occurs only in the southern summer hemisphere for low F10.7, as in previous studies, but (2) the WSA occurs in all seasons except for winter when F10.7 is high; it is most prominent during the December solstice (southern summer) and still strong during both equinoxes. The TOPEX TEC maps in the midlatitude and high‐latitude ionosphere display significant global longitudinal variations for a given local time in the Southern Hemisphere, which varies with season and solar activity. The observed WSA appears to be an extreme manifestation of the longitudinal variations.
Effect of the satellite laser ranging network distribution on geocenter motion estimation
Authors: Collilieux X. , Altamimi Z. , Ray J. , van Dam T. , Wu X.
Published: April 2009

SLR network translations estimated between a quasi‐instantaneous station position set, theoretically expressed with respect to the center of mass of the Earth (CM), and a secular reference frame are the signature of the motion of the CM with respect to the Earth crust. Geocenter motion is defined here to be the motion of the CM with respect to the geometric center of the solid Earth surface (CF). SLR translational variations cannot be rigorously interpreted as identical to geocenter motion due to the sparse and nonuniform distribution of the SLR network. Their difference is called the network effect, which should be dominated at subdecadal timescales by loading signals. We have computed translation time series of the SLR network using two independent geophysically based loading models. One is a displacement model estimated from surface fluid data (Green's function approach), called forward model, and the other is a displacement model estimated from GPS and ocean bottom pressure (OBP) data, called inverse model. The translation models have been subtracted from their respective geocenter motion models computed from degree‐1 mass load coefficients in order to evaluate their network effect biases. Scatter due to the SLR network effect is at the level of 1.5 mm RMS. It could slightly shift the phase of the annual SLR geocenter motion estimate by less than 1 month and could affect X and Z annual geocenter motion amplitudes at the 1‐mm level, which is about one third of the expected signal. Two distinct methods are suggested to account for network effect when comparing SLR translations to geocenter motion models. The first is to add the network effect term predicted by a displacement model to the geocenter motion loading model. The second relies on an adequate combination of SLR and GPS products to estimate SLR translation that could be better compared with geocenter motion.
Mechanisms of deformation localization at the tips of shear fractures: Findings from analogue experiments and field evidence
Authors: Misra Santanu , Mandal Nibir , Dhar Rajib , Chakraborty Chandan
Published: April 2009

Using analogue experiments on polymethylmethaacrylate (PMMA) models, we investigated the process of deformation localization at the tips of preexisting planar shear cracks. Experiments show that this can take place in any of the following four principal mechanisms. Mechanism A: Brittle deformation is the dominant process and forms a pair of long tensile fractures at the crack tips. The tensile fractures propagate along the compression direction and transgress the entire model thickness, causing model failure at a small bulk strain (3%). Mechanism B: It involves both brittle and ductile (plastic) strain localization, where the tensile fractures grow to a limited length and incipient ductile zones appear at the tips. Mechanism C: Deformation localization is characterized by an association of macroscale shear bands and short, opened‐out tensile fissures (cf. wingfractures). Mechanism D: Ductile strain localizes in the form of a pair of shear bands at each tip. Fracture failure does not occur in this case. The transition from Mechanism A to Mechanism D is a continuous phenomenon in the experimental conditions, which we show as a function of initial crack angle (α angle between the crack and the far‐field compression direction) and crack length (l). Mechanism A tends to be replaced by Mechanism D with decreasing α (60° to 20°) and/or l. Using a finite element method (FEM), we calculated the maximum principal tensile stress (σ1max) and the maximum second stress invariant (I2max) of the stress field in the neighborhood of a sliding crack within a linearly elastic medium and analyzed the brittle‐ductile transitions observed in physical experiments. The calculations show that σ1max is directly proportional to l and attains a peak value for α = 45°, promoting Mechanism A. On the other hand, I2max occurs at α < 45°, favoring nucleation of ductile shear bands (Mechanism D). When α and l are increased simultaneously, σ1max takes its peak value at α = 60°. This analysis explains the dominance of Mechanism A for α > 45° in physical models with simultaneously varying crack length and orientation. We also demonstrate probable interactions between plastic strain localization and tensile fracturing at the crack tips. FEM results indicate that a plastic zone lowers the magnitude of tensile stress concentration at wing cracks and thereby dampen their growth when α < 45°. We finally complement our study with field examples.
Synoptic aspects of the summer monsoon of southern Oman and its global teleconnections
Authors: Charabi Yassine , Abdul‐Wahab Sabah A.
Published: April 2009

The interplay of El Nino–Southern Oscillation (ENSO) and the Indian Ocean dipole (IOD) can lead to different patterns of sea surface temperature and outgoing longwave radiation anomalies over the equatorial Indian Ocean with corresponding implications for the monsoon system. This paper investigates the extent to which the climatic mechanisms generated by the identified Indian Ocean dipole and the Equatorial Indian Ocean Oscillation affect the interannual variability of Southern Oman Summer Monsoon (SOSM) rainfall. For this purpose, the monsoon data were analyzed for the period of 1985–2005. Generally, the paper presented the possible relations of the interannual variation in SOSM with atmospheric convection and circulation over the equatorial Indian Ocean and ENSO. It could be advocated that the IOD and ENSO have complementarily affected the SOSM during the last four decades. The IOD exercised a substantial role, first, through its influence as a modulator of the SOSM and, second, through its impact on the correlation between the SOSM and ENSO. The results of the study indicated that the ENSO‐induced anomalous circulation over the Arabian Sea was either countered or supported by the IOD, depending on the state of the phase and the amplitude of the two.
Responses of stream nitrate and DOC loadings to hydrological forcing and climate change in an upland forest of the northeastern United States
Authors: Sebestyen Stephen D. , Boyer Elizabeth W. , Shanley James B.
Published: April 2009

In coming decades, higher annual temperatures, increased growing season length, and increased dormant season precipitation are expected across the northeastern United States in response to anthropogenic forcing of global climate. We synthesized long‐term stream hydrochemical data from the Sleepers River Research Watershed in Vermont, United States, to explore the relationship of catchment wetness to stream nitrate and DOC loadings. We modeled changes in growing season length and precipitation patterns to simulate future climate scenarios and to assess how stream nutrient loadings respond to climate change. Model results for the 2070–2099 time period suggest that stream nutrient loadings during both the dormant and growing seasons will respond to climate change. During a warmer climate, growing season stream fluxes (runoff +20%, nitrate +57%, and DOC +58%) increase as more precipitation (+28%) and quick flow (+39%) occur during a longer growing season (+43 days). During the dormant season, stream water and nutrient loadings decrease. Net annual stream runoff (+8%) and DOC loading (+9%) increases are commensurate with the magnitude of the average increase of net annual precipitation (+7%). Net annual stream water and DOC loadings are primarily affected by increased dormant season precipitation. In contrast, decreased annual loading of stream nitrate (−2%) reflects a larger effect of growing season controls on stream nitrate and the effects of lengthened growing seasons in a warmer climate. Our findings suggest that leaching of nitrate and DOC from catchment soils will be affected by anthropogenic climate forcing, thereby affecting the timing and magnitude of annual stream loadings in the northeastern United States.
Vertical and oblique ionospheric soundings over a very long multihop HF radio link from polar to midlatitudes: Results and relationships
Authors: Vilella C. , Miralles D. , Altadill D. , Acosta F. , Solé J. G. , Torta J. M. , Pijoan J. L.
Published: April 2009

A vertical incidence sounder (VIS) was installed at the Spanish Antarctic Base (62.7°S, 299.6°E) during the Antarctic summer survey 2004–2005. In addition, an oblique sounding (OS) system for HF communications between Antarctica and Spain (12,700 km) has been operated during the Antarctic summers since December 2003. OS results are compared to Rec533 model and to VIS data obtained from stations located along the radio path, including VIS stations at the emitter and receiver sites. The results presented in this paper show the potential of this infrastructure for ionospheric monitoring and research purposes at and from polar regions. The results also show that relevant information (e.g., maximum received frequency) of very long range radio links can be obtained from appropriate VIS stations along the path.
Surface mining and reclamation effects on flood response of watersheds in the central Appalachian Plateau region
Authors: Ferrari J. R. , Lookingbill T. R. , McCormick B. , Townsend P. A. , Eshleman K. N.
Published: April 2009

Surface mining of coal and subsequent reclamation represent the dominant land use change in the central Appalachian Plateau (CAP) region of the United States. Hydrologic impacts of surface mining have been studied at the plot scale, but effects at broader scales have not been explored adequately. Broad‐scale classification of reclaimed sites is difficult because standing vegetation makes them nearly indistinguishable from alternate land uses. We used a land cover data set that accurately maps surface mines for a 187‐km2 watershed within the CAP. These land cover data, as well as plot‐level data from within the watershed, are used with HSPF (Hydrologic Simulation Program‐Fortran) to estimate changes in flood response as a function of increased mining. Results show that the rate at which flood magnitude increases due to increased mining is linear, with greater rates observed for less frequent return intervals. These findings indicate that mine reclamation leaves the landscape in a condition more similar to urban areas rather than does simple deforestation, and call into question the effectiveness of reclamation in terms of returning mined areas to the hydrological state that existed before mining.
Modeling the impact of nano‐pores on mineralization in sedimentary rocks
Authors: Emmanuel Simon , Ague Jay J.
Published: April 2009

By limiting crystal size, nanometer‐scale pores in geological media can control the effective solubility of mineral phases. Since mineralization is determined by solubility, this mechanism, termed pore‐size controlled solubility (PCS), is potentially significant for the evolution of porosity and permeability during reactive transport. To demonstrate the potential impact in geological systems, we developed a new one‐dimensional numerical model, using a moving boundary condition, to describe the mineralization in the rock matrix adjacent to a pressure solution (stylolite) interface. In the model, the porous domain initially possesses a polymodal pore size distribution, although this is allowed to change in response to mineral precipitation, and the evolution of porosity and pore size distributions was simulated both for systems with constant mineral solubility and for systems in which solubility was pore size controlled. Consistent with field observations, total porosity decreases near the stylolite interface in all the simulations. However, in systems with constant solubility, nanometer‐scale pores close rapidly because of their high specific surface area; by contrast, when the PCS mechanism is included in the model, transient bimodal pore size distributions develop, with nano‐pores remaining open throughout the simulation. Our simulations suggest that the combination of the PCS mechanism with kinetic models for mineral precipitation can account for the bimodal pore size distributions observed in sedimentary carbonate rocks. Furthermore, while the mechanism is unlikely to affect rocks such as sandstones, PCS can impact carbonate and clay‐bearing sediments, which typically possess high levels of submicron porosity.
Overproduction of human interleukin‐2 in recombinant Escherichia coli BL21 high‐cell‐density culture by the determination and optimization of essential amino acids using a simple stoichiometric model
Authors: Yegane‐Sarkandy S. , Farnoud A. M. , Shojaosadati S. A. , Khalilzadeh R. , Sadeghyzadeh M. , Ranjbar B. , Babaeipour V.
Published: April 2009

In order to increase the productivity of human IL‐2 (interleukin‐2), a stoichiometric model has been used to determine the most essential amino acids and precise values of their amounts to be added to the culture during expression of human IL‐2 (as a model protein) by recombinant Escherichia coli BL21 (pET21a‐hil2). Experiments were performed to investigate the effect of chosen amino acids and their interactions on expression of human IL‐2. Glutamine, a mixture of leucine, aspartic acid and glycine, and a mixture of leucine, glutamine and aspartic acid, were the most effective for the expression of IL‐2. The most promising amino acids were then chosen for further experiments at three different levels to determine whether altering their stoichiometry can lead to better expression levels. The optimized value of glutamine in the flask was 0.316 g/l; a mixture of leucine, glutamine and aspartic acid at concentrations of 0.124, 0.316 and 0.212 g/l respectively and of leucine, aspartic acid and glycine in concentrations of 0.124, 0.212, 0.111 g/l respectively were chosen to be added to the flask. The effect of glutamine, as one of the amino acids most influencing the expression of IL‐2 in batch and fed‐batch high‐cell‐density cultures, was studied. The results revealed that the amount of expressed IL‐2 compared with the control culture increased from 81 to 195 mg/l in the shake flask, 403 to 594 mg/l in the fermentor and 5.15 to 10.01 g/l in the fermentor under fed‐batch cultivation.
Characterization of PRMT1 fromPlasmodium falciparum
Authors: Fan Qi , Miao Jun , Cui Long , Cui Liwang
Published: April 2009

Arginine methylation is a post-translational modification that affects many cellular processes in eukaryotes. The malaria parasite Plasmodium falciparum encodes three conserved PRMTs (protein arginine N-methyltransferases). We have determined that PfPRMT1 (P. falciparum PRMT1) has authentic type I PRMT activity to form monomethylarginines and asymmetric dimethylarginines. Compared with mammalian PRMT1s, PfPRMT1 possesses a distinctive N-terminal sequence that is ∼50 amino acids longer and is essential for enzyme activity. Recombinant PfPRMT1 methylated histones H4 and H2A and several conserved substrates involved in RNA metabolism, including fibrillarin, poly(A)-binding protein II, ribosomal protein S2 and a putative splicing factor. Using synthetic peptides and MS, we determined target arginines in several substrates and studied the enzyme kinetics. Whereas the kinetic parameters of recombinant PfPRMT1 on an H4 peptide and S-adenosylmethionine were similar to those of mammalian PRMT1s, PfPRMT1 had much higher substrate-turnover rates. In the histone H4 N-terminus, PfPRMT1 could methylate only Arg3, a mark for transcription activation. Western blotting detected dynamic dimethylation of H4-Arg3 during parasite development, suggesting that histone-arginine methylation may play a conserved role in chromatin-mediated gene regulation. Consistent with the presence of potential substrates in both the cytoplasm and nucleus, green fluorescent protein-tagged PfPRMT1 and untagged PfPRMT1 were localized in both cellular compartments, with the majority in the cytoplasm. in vitro assays showed that PfPRMT1 could be inhibited by several small-molecule inhibitors, with IC50-values in the sub-micromolar range. Most of these compounds also effectively inhibited parasite growth, suggesting that parasite PRMTs are promising targets for developing antiparasitic drugs.
Angiopoietin-2 promoter haplotypes confer an increased risk of stroke in a Chinese Han population
Authors: Chen Jingzhou , Yu Hui , Song Weihua , Sun Kai , Song Yan , Lou Kejia , Yang Tao , Zhang Yinhui , Hui Rutai
Published: April 2009

Angiopoietin-2 is an important mediator of angiogenesis, and we hypothesized that genetic variants of ANGPT2 (the gene encoding angiopoietin-2) would result in abnormal angiogenesis and contribute to stroke susceptibility. To test our hypothesis, we investigated the association of variants in the promoter of ANGPT2 with stroke in a multi-centre case-control study. We found that the C allele of rs3739390 conferred a 1.42-fold risk of lacunar infarction {adjusted OR (odds ratio), 1.42 [95% CI (confidence interval), 1.08–1.87]; P=0.012} and a 2.10-fold higher transcriptional activity than did the corresponding G allele rs3739390G. The haplotype G-G-T conferred a 1.54-fold risk of atherothrombotic stroke and a 1.64-fold risk for haemorrhagic stroke, whereas the haplotype G-C-C conferred approx. a 2.0-fold risk of each subtype of stroke. In conclusion, our results indicate that haplotypes in the promoter of ANGPT2 confer a high risk of stroke in a Chinese population.
Shape control of FePt nanocrystals
Authors: Poudyal Narayan , Chaubey Girija S. , Rong Chuan-bing , Liu J. Ping
Published: April 2009

FePt nanocrystals were prepared by simultaneous reduction of platinum acetylacetonate and thermal decomposition of iron pentacarbonyl in properly chosen solvents/surfactants. A variety of FePt nanocrystals, including nanowires, nanorods, nanocubes, and nanosized multipods, were successfully obtained. The shape control was realized by simply varying synthesis parameters. The as-synthesized nanocrystals, having chemically disordered fcc structure, are found to be superparamagnetic at room temperature and their ferromagnetic-superparamagnetic transition temperature is size dependent that increases with particle size. The as-synthesized FePt nanocrystals were transformed to the chemically ordered L10 structure upon heat treatment, which exhibits hard magnetic properties with coercivity as high as 25 kOe.
Magnetic anisotropy and spin wave relaxation in CoFe/PtMn/CoFe trilayer films
Authors: Ren Y. H. , Wu C. , Gong Y. , Pettiford C. , Sun N. X.
Published: April 2009

We investigated the magnetic anisotropic properties and the spin wave relaxation in trilayer films of CoFe/PtMn/CoFe grown on the seed layer Ru or NiFeCr with CoFe compositions being Co–16 at. % Fe. The measurements were taken in samples with the ferromagnetic layers of CoFe varying from 10 to 500 Å by the ferromagnetic resonance (FMR) technique. The magnetic anisotropic parameters were investigated by rotating the field aligned axis with respect to the spectral field in the configurations of both in plane and out of plane. We determine the effective in-plane anisotropy field of ∼0.005 T, the uniaxial out-of-plane anisotropy of ∼−0.3 T, and the exchange stiffness D of ∼512 meV Å2. Moreover, spin wave damping was estimated by analyzing the FMR linewidth and line shape as a function of the angle between the external field and easy axis and as a function of the thickness of the CoFe layers. We identify an extrinsic contribution of the damping parameter dominated by two-magnon scattering in addition to the intrinsic Gilbert term with a damping parameter, α=0.012. Further, we reveal that a significant linewidth broadening could also be caused by the overlap of the surface and the uniform spin wave excitations. The FMR lines show a strong dependence of the surface anisotropy contribution of free energy in trilayer films.
Multichannel microwave interferometer for the levitated dipole experiment
Authors: Boxer Alexander C. , Garnier Darren T. , Mauel Michael E.
Published: April 2009

A four-channel microwave interferometer (center frequency: 60 GHz) has been constructed to measure plasma density profiles in the levitated dipole experiment (LDX). The LDX interferometer has a unique design owing to the unique geometry of LDX. The main design features of the interferometer are: (1) the transmitted beam traverses the plasma entirely in O-mode; (2) the interferometer is a heterodyne system employing two free-running oscillators; (3) four signals of data are received from just on transmitted beam; (4) phase shifts are detected in quadrature. Calibration tests demonstrate that the interferometer measures phase shifts with an uncertainty of approximately 5°. Plasma densities in LDX corresponding to phase shifts of up to 5π are routinely and successfully measured.
Low temperature electrical transport properties of carbon matrix containing iron nanoparticles
Authors: Sajitha E. P. , Prasad V. , Subramanyam S. V.
Published: April 2009

We present a comparative study of the low temperature electrical transport properties of the carbon matrix containing iron nanoparticles and the films. The conductivity of the nanoparticles located just below the metal-insulator transition exhibits metallic behavior with a logarithmic temperature dependence over a large temperature interval. The zero-field conductivity and the negative magnetoresistance, showing a characteristic upturn at liquid helium temperature, are consistently explained by incorporating the Kondo relation and the two dimensional electron-electron interaction. The films, in contrast, exhibit a crossover of the conductivity from power-law dependence at high temperatures to an activated hopping law dependence in the low temperature region. The transition is attributed to changes in the energy dependence of the density of states near the Fermi level. The observed magnetoresistance is discussed in terms of quantum interference effect on a three-dimensional variable range hopping mechanism.
Optimization of selected molecular orbitals in group basis sets
Authors: Ferenczy György G. , Adams William H.
Published: April 2009

We derive a local basis equation which may be used to determine the orbitals of a group of electrons in a system when the orbitals of that group are represented by a group basis set, i.e., not the basis set one would normally use but a subset suited to a specific electronic group. The group orbitals determined by the local basis equation minimize the energy of a system when a group basis set is used and the orbitals of other groups are frozen. In contrast, under the constraint of a group basis set, the group orbitals satisfying the Huzinaga equation do not minimize the energy. In a test of the local basis equation on HCl, the group basis set included only 12 of the 21 functions in a basis set one might ordinarily use, but the calculated active orbital energies were within 0.001 hartree of the values obtained by solving the Hartree–Fock–Roothaan (HFR) equation using all 21 basis functions. The total energy found was just 0.003 hartree higher than the HFR value. The errors with the group basis set approximation to the Huzinaga equation were larger by over two orders of magnitude. Similar results were obtained for PCl3 with the group basis approximation. Retaining more basis functions allows an even higher accuracy as shown by the perfect reproduction of the HFR energy of HCl with 16 out of 21 basis functions in the valence basis set. When the core basis set was also truncated then no additional error was introduced in the calculations performed for HCl with various basis sets. The same calculations with fixed core orbitals taken from isolated heavy atoms added a small error of about 10−4 hartree. This offers a practical way to calculate wave functions with predetermined fixed core and reduced base valence orbitals at reduced computational costs. The local basis equation can also be used to combine the above approximations with the assignment of local basis sets to groups of localized valence molecular orbitals and to derive a priori localized orbitals. An appropriately chosen localization and basis set assignment allowed a reproduction of the energy of n-hexane with an error of 10−5 hartree, while the energy difference between its two conformers was reproduced with a similar accuracy for several combinations of localizations and basis set assignments. These calculations include localized orbitals extending to 4–5 heavy atoms and thus they require to solve reduced dimension secular equations. The dimensions are not expected to increase with increasing system size and thus the local basis equation may find use in linear scaling electronic structure calculations.
Global characteristics of zonal flows due to the effect of finite bandwidth in drift wave turbulence
Authors: Uzawa K. , Li Jiquan , Kishimoto Y.
Published: April 2009

The spectral effect of the zonal flow (ZF) on its generation is investigated based on the Charney–Hasegawa–Mima turbulence model. It is found that the effect of finite ZF bandwidth qualitatively changes the characteristics of ZF instability. A spatially localized (namely, global) nonlinear ZF state with an enhanced, unique growth rate for all spectral components is created under a given turbulent fluctuation. It is identified that such state originates from the successive cross couplings among Fourier components of the ZF and turbulence spectra through the sideband modulation. Furthermore, it is observed that the growth rate of the global ZF is determined not only by the spectral distribution and amplitudes of turbulent pumps as usual, but also statistically by the turbulence structure, namely, their probabilistic initial phase factors. A ten-wave coupling model of the ZF modulation instability involving the essential effect of the ZF spectrum is developed to clarify the basic features of the global nonlinear ZF state.
Use of nonaxisymmetric shaping in magnetic fusion
Authors: Boozer Allen H.
Published: April 2009

Nonaxisymmetric shaping of magnetic fusion plasmas extends the design space of nominally axisymmetric configurations, such as the tokamak, and defines fundamentally nonaxisymmetric configurations, called stellarators. Shaping is the primary design freedom to ensure suitable plasma equilibria for fusion applications. In fusion plasmas, the plasma pressure and current distributions are largely self-determined, and the only other determinant of plasma equilibria is the plasma shape. Since most of the freedom of shaping is in nonaxisymmetric shaping, understanding is needed. No fundamental demarcation exists between axisymmetric and quasiaxisymmetric tokamaks, so nonaxisymmetric shaping can be used to address issues that must be addressed for tokamaks to be an attractive fusion system. Stellarators offer design freedom beyond that available from extending the design space of nominally axisymmetric concepts. Stellarator experiments have demonstrated many benefits of nonaxisymmetric shaping, but the primary benefit is that sufficient freedom exists to design around many problems of fusion plasmas.
Effect of pressure on the magnetocaloric properties of nickel-rich Ni–Mn–Ga Heusler alloys
Authors: Mandal K. , Pal D. , Scheerbaum N. , Lyubina J. , Gutfleisch O.
Published: April 2009

Nickel-rich Ni–Mn–Ga Heusler alloys were prepared by arc melting and subsequent homogenization by annealing. A large magnetic entropy change was observed around 291 K in the alloy where martensite-austenite structural and ferro-para magnetic transitions almost coincide with each other. The effect of hydrostatic pressure of up to 8 kbar on magneto-structural transitions, magnetocaloric effect, and magnetic hysteresis was studied. The martensitic transition temperature as well as the Curie temperature TC was found to increase, whereas the magnetic entropy change |ΔSM| decreases slightly due to the application of hydrostatic pressure. The large hysteresis observed in M versus H curve at the ambient pressure almost vanishes due to the application of 8 kbar pressure.
Indentation of single-crystal silicon nanolines: Buckling and contact friction at nanoscales
Authors: Li Bin , Zhao Qiu , Huang Huai , Luo Zhiquan , Kang Min K. , Im Jang-Hi , Allen Richard A. , Cresswell Michael W. , Huang Rui , Ho Paul S.
Published: April 2009

High-quality single-crystal silicon nanolines (SiNLs) with a 24 nm linewidth and a height/width aspect ratio of 15 were fabricated. The mechanical properties of the SiNLs were characterized by nanoindentation tests with an atomic force microscope. The indentation load-displacement curves showed an instability with large displacement bursts at a critical load ranging from 9 to 30 μN. This phenomenon was attributed to a transition of the buckling mode of the SiNLs under indentation, which occurred preceding the final fracture of the nanolines. The mechanics of SiNLs under indentation was analyzed by finite element simulations, which revealed two different buckling modes depending on the contact friction at the nanoscale.
Formation of magnetic grains in ferroelectric Pb[Zr0.6Ti0.4]O3 ceramics doped with Fe3+ above the solubility limit
Authors: Kleebe Hans-Joachim , Lauterbach Stefan , Silvestroni Laura , Kungl Hans , Hoffmann Michael J. , Erdem Emre , Eichel Rüdiger-A.
Published: April 2009

The effect of excess iron-doping in piezoelectric lead-zirconate-titanate (PZT) on the microstructure was investigated by means of transmission electron microscopy in conjunction with electron diffraction and energy dispersive x-ray spectroscopy analysis. Electron paramagnetic resonance (EPR) spectroscopy has been used to characterize the site of the iron functional centers. A crystalline secondary magnetic phase formed upon sintering, magnetoplumbite (PbFe12O19), has been unequivocally identified. Furthermore, the phase assemblage observed in the Fe3+-doped PZT 60/40 sample could be correlated with an exchange-coupled resonance in the EPR spectra.
Sensitization of the photostimulable x-ray storage-phosphor CsBr:Eu2+ following room-temperature hydration
Authors: Appleby G. A. , Zimmermann J. , Hesse S. , Karg O. , von Seggern H.
Published: April 2009

The x-ray storage-phosphor CsBr:Eu2+ has been found to exhibit a strong increase in photostimulated-luminescence (PSL) intensity following hydration at room temperature. The sensitivity increases by a factor of 25 following a 60 min exposure to an atmosphere of 99% relative humidity, which is considered to be due to an incorporation of H2O molecules within the CsBr:Eu2+ matrix, which are orientated by and enhance the electric fields surrounding (Eu2+–O2−)-dipoles, increasing their charge trapping cross sections. Following irradiation the PSL increase is accompanied by the formation of mobile VK-centers, which decrease the F-center population by a recombination process, which appear as an intrinsic 360 nm emission from the CsBr matrix in low temperature thermoluminescence measurements.
Growth of single-crystal SiO2 clusters on Si(001) surface
Authors: Tanemura Tetsuo , Sato Seiichi , Kundu Manisha , Yamada Chikashi , Murata Yoshitada
Published: April 2009

Crystalline SiO2 clusters of nearly square shape were fabricated from amorphous silicon deposited on a clean Si(001) surface, where the deposited silicon was oxidized in the presence of atomic hydrogen and annealed in an O2 atmosphere. The side of these clusters was aligned along the [110] and [11¯0] azimuths of the Si(001) substrate. The crystallinity of the clusters was verified by grazing incidence x-ray diffraction and low-energy electron diffraction. The crystal structure of SiO2 clusters was estimated to be β-tridymite, whose [101¯0] and [0001] axes were parallel to the ⟨110⟩ axes of the substrate Si(001). When the Si(001) surface without deposited amorphous silicon was oxidized by the method described above, single-crystal SiO2 clusters were also prepared. However, the shape, the size, and the number density of the clusters were different from those of the clusters made from the amorphous silicon.
Duality and integrability: Electromagnetism, linearized gravity, and massless higher spin gauge fields as bi-Hamiltonian systems
Authors: Barnich Glenn , Troessaert Cédric
Published: April 2009

In the reduced phase space of electromagnetism, the generator of duality rotations in the usual Poisson bracket is shown to generate Maxwell’s equations in a second, much simpler Poisson bracket. This gives rise to a hierarchy of bi-Hamiltonian evolution equations in the standard way. The result can be extended to linearized Yang–Mills theory, linearized gravity, and massless higher spin gauge fields.
Periods and Feynman integrals
Authors: Bogner Christian , Weinzierl Stefan
Published: April 2009

We consider multiloop integrals in dimensional regularization and the corresponding Laurent series. We study the integral in the Euclidean region and where all ratios of invariants and masses have rational values. We prove that in this case all coefficients of the Laurent series are periods.
A high-performance tandem white organic light-emitting diode combining highly effective white-units and their interconnection layer
Authors: Wang Qi , Ding Junqiao , Zhang Zhiqiang , Ma Dongge , Cheng Yanxiang , Wang Lixiang , Wang Fosong
Published: April 2009

By utilizing 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline:Li/MoO3 as an effective charge generation layer (CGL), we extend our recently demonstrated single-emitting-layer white organic light-emitting diode (WOLED) to realize an extremely high-efficiency tandem WOLED. This stacked device achieves maximum forward viewing current efficiency of 110.9 cd/A and external quantum efficiency of 43.3% at 1 μA/cm2 and emits stable white light with Commission Internationale de L’Eclairage coordinates of (0.34, 0.41) at 16 V. It is noted that the combination of effective single units and CGL is key prerequisite for realizing high-performance tandem WOLEDs.
Simulation of inelastic electronic tunneling spectra of adsorbates from first principles
Authors: Ren Hao , Yang Jinlong , Luo Yi
Published: April 2009

We present first-principles simulations for inelastic electron tunneling spectra of molecules adsorbed on metal surface as measured in scanning tunneling microscopy experiments. Both elastic and inelastic tunneling processes are modeled in terms of Tersoff–Hamann approximation with a full vibration analysis at density functional theory levels. The calculated spectra of carbon oxide and acetylene molecules adsorbed on Cu(100) surface have well reproduced their experimental counterparts. The inelastic electron tunneling images of the observable vibration modes have been provided. The performance of gradient-corrected density functional is compared with that of local density functional.
The role of the Coriolis interaction on vector correlations in molecular predissociation: Excitation of isolated rotational lines
Authors: Kuznetsov Vladislav V. , Shternin Peter S. , Vasyutinskii Oleg S.
Published: April 2009

We present the full quantum mechanical expressions for the polarization differential cross sections of the photofragments produced in slow predissociation of a parent molecule via isolated rotational branches. Both radial and Coriolis nonadiabatic interactions between the molecular potential energy surfaces have been taken into account. The expressions describe the recoil angle distribution of the photofragments and the distributions of the photofragment angular momentum polarization (orientation and alignment) in terms of the anisotropy parameters of the ranks K=0,1,2. The explicit expressions for the anisotropy parameters are presented and analyzed which contain contributions from different possible photolysis mechanisms including incoherent, or coherent optical excitation of the parent molecule followed by the radial, or Coriolis nonadiabatic transitions to the dissociative states. The obtained expression for the zeroth-rank anisotropy parameter β is valid for any molecule and for an arbitrary value of the molecular total angular momentum J. The expressions for the orientation (K=1) and alignment (K=2) anisotropy parameters are given in the high-J limit in terms of the generalized dynamical functions which were analyzed for the case of photolysis of linear/diatomic molecules. As shown, the Coriolis nonadiabatic interaction results in several new photolysis mechanisms which can play an important role in the predissociation dynamics.
Modeling vibrational resonance in linear hydrocarbon chain with a mixed quantum-classical method
Authors: Gelman David , Schwartz Steven D.
Published: April 2009

The quantum dynamics of a vibrational excitation in a linear hydrocarbon model system is studied with a new mixed quantum-classical method. The method is suited to treat many-body systems consisting of a low dimensional quantum primary part coupled to a classical bath. The dynamics of the primary part is governed by the quantum corrected propagator, with the corrections defined in terms of matrix elements of zeroth order propagators. The corrections are taken to the classical limit by introducing the frozen Gaussian approximation for the bath degrees of freedom. The ability of the method to describe dynamics of multidimensional systems has been tested. The results obtained by the method have been compared to previous quantum simulations performed with the quasiadiabatic path integral method.
Apparatus for probing preignition behavior of hypergolic materials
Authors: Chowdhury Arindrajit , Bapat Chaitanya , Thynell Stefan T.
Published: April 2009

The determination of the condensed-phase preignition chemistry of hypergolic bipropellant pairs has been considerably challenging due to toxicity and reactivity of the used materials. In this work, we describe a new experimental technique for characterizing preignition behavior of hypergolic materials. Small quantities of the bipropellant pair are brought in contact under isothermal conditions, and spectral transmission measurements on the evolved products are performed using Fourier transform infrared spectroscopy. The gaseous products are subsequently quantified to yield species concentration profiles at various temperatures, hence facilitating the elucidation of the detailed condensed-phase chemical kinetics responsible for the ignition in the gas phase.
Effects of amorphous semiconductor thickness on top gate staggered organic field-effect transistors
Authors: Verilhac J. M. , Benwadih M. , Altazin S. , Jacob S. , Gwoziecki R. , Coppard R. , Serbutoviez C.
Published: April 2009

We have investigated the influence of the semiconductor thickness varying by almost two orders of magnitude on the transfer and output characteristics of top gate staggered organic field-effect transistors. We observe that the mobility in the saturation regime is almost constant in the thickness range studied. In contrast, the subthreshold slope and the threshold voltage are highly impacted by the semiconductor thickness, and in particular they showed a common optimum thickness value. On both sides of this optimum we observe a loss in performances, which are tentatively attributed to different mechanisms.
Relevance of length scales in exchange biased submicron dots
Authors: Li Zhi-Pan , Morales R. , Schuller Ivan K.
Published: April 2009

Strong dot-size dependence of the positive exchange bias onset with the cooling field was found in Ni/FeF2 exchange biased nanostructures. With increasing cooling field, the sign of the exchange bias field changes from negative to coexistence of positive and negative, and eventually to positive. As the structure size decreases, the lower limit of cooling fields necessary for only positive exchange bias also decreases and is one order of magnitude smaller than that of unpatterned films. This behavior is attributed to comparable Ni dot size with the antiferromagnet “domain” size estimated to be about 500 nm.
Morphology induced magnetoresistance enhancement of tunneling junctions with the Heusler electrode Co2Cr0.6Fe0.4Al
Authors: Herbort Christian , Jorge Elena Arbelo , Jourdan Martin
Published: April 2009

A large magnetoresistance is expected when half-metallic ferromagnets are used in magnetic tunneling junctions with polycrystalline AlOx barrier. We demonstrate by in situ tunneling microscopy how the atomically smooth morphology of Co2Cr0.6Fe0.4Al Heusler thin films results in unfavorable wetting properties of the Al layer, which forms the tunneling barrier after oxidation. The insertion of a very thin (2.5 Å) Mg layer at the Co2Cr0.6Fe0.4Al/Al interface changes the growth mode of the Al drastically. As a result the tunneling magnetoresistance (TMR) is clearly enhanced [Co2Cr0.6Fe0.4Al/AlOx/Co70Fe30 junction: TMR(4 K)=101%]. The corresponding Jullière spin polarization amounts to 67%, larger than previously reported values for this compound.
Poly(3-hexylthiophene)/ZnO hybrid pn junctions for microelectronics applications
Authors: Katsia E. , Huby N. , Tallarida G. , Kutrzeba-Kotowska B. , Perego M. , Ferrari S. , Krebs F. C. , Guziewicz E. , Godlewski M. , Osinniy V. , Luka G.
Published: April 2009

Hybrid poly(3-hexylthiophene)/ZnO devices are investigated as rectifying heterojunctions for microelectronics applications. A low-temperature atomic layer deposition of ZnO on top of poly(3-hexylthiophene) allows the fabrication of diodes featuring a rectification ratio of nearly 105 at ±4 V and a current density of 104 A/cm2. Electrical characteristics are discussed taking into account the chemical structure of the stack and the energy band diagram.
Counting graphene layers on glass via optical reflection microscopy
Authors: Gaskell P. E. , Skulason H. S. , Rodenchuk C. , Szkopek T.
Published: April 2009

We show that optical reflection microscopy is a reliable method to simultaneously locate and count graphene layers deposited on bulk, transparent substrates such as soda-lime glass. The visible contrast in optical reflection versus graphene layer number is resolvable on bulk substrates. A simple Fresnel theory based on the universal optical conductance of graphene layers accurately models optical reflection images taken at a wavelength of 550±5 nm. We directly count one to nine layers of graphene using reflection microscopy.
Separation of surface plasmon polariton from nonconfined cylindrical wave launched from single slits
Authors: Kihm H. W. , Kang J. H. , Kyoung J. S. , Lee K. G. , Seo M. A. , Ahn K. J.
Published: April 2009

We theoretically investigate the separation positions of surface plasmon polariton (SPP) from the cylindrical nonconfined diffracted light launched from a single slit. Through an analysis of the finite difference time domain calculations and the analytical solution of a line source on a metal surface, we find the wavelength dependent SPP separation positions defined as the lateral distance from the slit with two different criteria. These results show that the SPP separation positions can be approximated by a simple relationship given by the permittivity of the metal and by the wavelength regardless of how the criteria are chosen.
Ab initio molecular dynamics study of the hydrogen-deuterium exchange in bulk lithiumborohydride (LiBH4)
Authors: Ramzan M. , Ahuja R.
Published: April 2009

The hydrogen storage is still a challenge for mobile applications. The diffusion of hydrogen in solids is considered as a general model system but there is limited knowledge available for the dynamics of hydrogen in complex hydrides. In this letter, we present a systematic approach to study the hydrogen-deuterium exchange in bulk LiBH4 based on ab initio molecular dynamics. Our results predict the single hydrogen (deuterium) exchange in LiBH4, which supports the experimental results. The self-diffusion constant ⟨D⟩ of deuterium in LiBH4 is around 1.42×10−8 m2 s−1.
Electromagnetically induced transparency in acetylene molecules with counterpropagating beams in V and Λ schemes
Authors: Light P. S. , Benabid F. , Pearce G. J. , Couny F. , Bird D. M.
Published: April 2009

We report on the experimental observation of electromagnetically induced transparency in V and Λ energy level schemes using counterpropagating coupling and probe beam geometry. The observation was achieved using an acetylene photonic microcell. The conditions required for this observation are explored theoretically, and we show that the use of counterpropagating beams in electromagnetically induced transparency may have applications as a spectroscopic technique where velocity discrimination is desirable.
Impact of oxide defects on band offset at GeO2/Ge interface
Authors: Yang M. , Wu R. Q. , Chen Q. , Deng W. S. , Feng Y. P. , Chai J. W. , Pan J. S. , Wang S. J.
Published: April 2009

High quality GeO2 dielectrics were prepared on Ge(001) surface by direct atomic source oxidation. The band alignments have been studied by using high resolution x-ray photoemission spectroscopy. The valence and conduction band offsets at GeO2/Ge(001) interface are 4.59±0.03 and 0.54±0.03 eV, respectively. The calculated projected density of states indicate that the formation of germanium and oxygen vacancies at different oxidation stages might result in the reduction of valence band offsets, which clarified the varied experimental results of valence band offset [M. Perego et al., Appl. Phys. Lett. 90, 162115 (2007) and V. V. Afanas’ev and A. Stesmans, Appl. Phys. Lett. 84, 2319 (2004)].
Improvement of subthreshold current transport by contact interface modification in p-type organic field-effect transistors
Authors: Kano Masataka , Minari Takeo , Tsukagoshi Kazuhito
Published: April 2009

The charge injection efficiency of organic field-effect transistors (OFETs) is found to be a critical factor determining the subthreshold characteristics of these devices. OFETs fabricated using a wide band gap organic semiconductor and gold source/drain contacts display large threshold voltage and poor subthreshold characteristics. Insertion of a metal-oxide charge injection layer at the contact/semiconductor interface lower the injection barrier height, resulting in marked improvements in threshold voltage and subthreshold slope and strong suppression of the short-channel effect. The improved subthreshold characteristics are attributed to enhanced charge injection and the consequent promotion of charge accumulation.