bluuebunny/crossref_metadata_2025 huggingface dataset:
Morphological variability of greater yam (Dioscorea alataL.) in Malaysia
Authors: Hasan Sayed M. Zain , Ngadin Andrew A. , Shah Ramisah M. , Mohamad Norizan
Published: March 2008

An assessment of morphological variation among 70 accessions of greater yam (Dioscorea alataL.) collected throughout Malaysia was made. Data of 47 morphological variables measured from the accessions were subjected to multivariate analysis using principal component (PCA) and cluster analysis (CA). The PCA results indicated that the characters contributing largely to the species variability were those related to the shape, size and flesh colour of underground tubers; shape and colour of aerial tubers; position, shape, size and vein colour of the leaves; petiole colour; shoot growth rate; and number of days for shoots to germinate. The two-dimensional plot of the first two PCs showed a separation between accessions of purple tuber groups and those of white tuber groups, but was unable to distinguish accessions according to tuber shape groups, i.e. irregular, oblong and round, as revealed by visual observation. The dendrogram of CA revealed four major groups ofD. alatain Malaysia, which supported the PCA grouping. This study demonstrated thatD. alatain Malaysia consists of numerous genotypes revealing wide inter- and intra-group variability.
Energy balance and canopy conductance of a tropical semi‐deciduous forest of the southern Amazon Basin
Authors: Vourlitis George L. , de Souza Nogueira José , de Almeida Lobo Francisco , Sendall Kerrie M. , de Paulo Sérgio Roberto , Antunes Dias Carlos Alberto , Pinto Osvaldo Borges , de Andrade Nara Luísa Reis
Published: March 2008

Deforestation and climate change have the capacity to alter rainfall regimes, water availability, and surface‐atmosphere flux of water and energy of tropical forests, especially in ecotonal, semi‐deciduous tropical forests of the southern Amazon Basin, which have experienced rapid regional warming and deforestation over the last three decades. To reduce uncertainty regarding current and future energy and water flux, micrometeorological measurements of latent (Qe) and sensible heat flux (Qh) and canopy conductance (Gc) were combined with measurements of sap flux density (Fd) and maximum leaf conductance (gsmax) to characterize the seasonal controls on mass (H2O) and energy exchange of an ecotonal, semi‐deciduous forest in northern Mato Grosso, Brazil over the 2005‐2006 annual cycle. Average diel patterns and daily rates of energy flux and conductance declined during the dry season; however, the decline in Fd and Qe was smaller and/or more gradual than Gc and gsmax. Weekly averages of transpiration calculated from sap flow measurements during the dry‐wet season transition period were positively correlated (r2 = 0.47; p < 0.05; n = 11) with estimates of leaf area index (LAI) derived from the Modis‐Aqua satellite platform while estimates of evapotranspiration ET derived from eddy covariance were not, presumably because these estimates also include an evaporation component. Overall, our results suggest that access to deep water reserves can support high rates of Fd and Qe during the dry season, but because of high evaporative demand, declines in plant water potential lead to a corresponding decline in Gc. Furthermore, seasonal variations in LAI, that are likely to be controlled in part by plant water status and phenology, constrain tree and stand transpiration. Thus the consistency of Qe over the annual cycle appears to be the result of trade‐offs between water availability (rainfall, soil moisture, water potential), canopy structural properties (LAI), and meteorological conditions including vapor pressure deficit and net radiation.
Basement structure of the north‐western Yermak Plateau
Authors: Jokat W. , Geissler W. , Voss M.
Published: March 2008

The separation of Northeast Greenland and Svalbard was achieved by large strike slip movements in Cenozoic times. Evidence for these movements can be found onshore both on North Greenland and Svalbard. However, the role of the Yermak Plateau in this process is quite speculative. New multichannel seismic (10 km spacing) and aeromagnetic data (7.5 km spacing) across the north‐western part of the plateau show that the acoustic basement has a similar strike direction to that of the geological units onshore Svalbard. A prominent fault zone separates these most likely continental structures in the west from a more N‐S extended transitional crustal block in the eastern part of the plateau. This part of the plateau is characterized by strong magnetic anomalies at least indicating highly intruded and stretched continental or even oceanic crust. However, the seismic data show that the plateau‐like bathymetry is quite young. During most of its Cenozoic history the Yermak Plateau had a rough topography, similar to the topography onshore Svalbard. Thus, the paleo‐bathymetry might have played an important role for the water exchange between the Arctic Ocean and the North Atlantic prior to the opening of the Fram Strait, which is today the main pathway for the deep‐water masses.
Energetic neutral atom imaging of comets
Authors: Ekenbäck A. , Holmström M. , Barabash S. , Gunell H.
Published: March 2008

We present the first computer simulated images of energetic neutral atoms (ENAs) produced by charge exchange between solar wind protons and cometary neutrals. Proton bulk flow and temperature from MHD simulations are used along with a model of cometary neutral densities. The emission of hydrogen ENAs from the comet is then calculated using cross sections for the charge exchange collisions. The ENA production rate is integrated along lines of sight to produce an image of the fluxes. We find detection of hydrogen ENAs feasible and most favorable at solar zenith angles between 80 and 130 degrees.
Characteristics of electrostatic solitary waves in the Earth's foreshock region: Geotail observations
Authors: Shin K. , Kojima H. , Matsumoto H. , Mukai T.
Published: March 2008

We observed electrostatic solitary waves (ESW) in the Earth's foreshock region by the Geotail spacecraft. The foreshock region is classified into electron foreshock and ion foreshock regions, which are dominated by energetic electrons and superthermal ions, respectively. The Geotail waveform observations show the existence of ESW in both electron and ion foreshock regions. To understand the wave features of ESW, we examine the waveform and perform statistical analyses on the spatial distribution of the ESW. The results show that the occurrence and amplitude of ESW decrease as the distance from the bow shock transition increases. In the electron foreshock region, we find that ESW and electron beams are observed simultaneously. The plasma conditions are similar to those in the plasma sheet boundary layer (PSBL), in which ESW were first discovered by the Geotail spacecraft. In the ion foreshock region, ESW are simultaneously observed with superthermal ions reflected by the bow shock. We find two types of ESW in the ion foreshock region based on the orientation of their bipolar waveforms. We examine the angle between the magnetic field and the shock normal dependence of the occurrences of ESW in the ion foreshock region. The results show that ESW observed in the quasi‐parallel shock have characteristics that differ from those observed in the quasi‐perpendicular shock. From waveform and statistical analyses, the most plausible generation mechanism of the first type of ESW is the Buneman instability based on the superthermal ions and background electrons. A possible mechanism of the second type of ESW is the positive potential ESW propagating from the upstream region to the bow shock due to the reflection by the negative potentials or the negative potential ESW generated by the reflected superthermal ions.
Carbon isotopic characterization for the origin of excess methane in subsurface seawater
Authors: Sasakawa Motoki , Tsunogai Urumu , Kameyama Sohiko , Nakagawa Fumiko , Nojiri Yukihiro , Tsuda Atsushi
Published: March 2008

We collected samples of seawater, zooplankton, and sinking particles in the northwestern North Pacific to determine the source of excess CH4 over the saturation value in equilibrium with the atmospheric CH4 in the oxygenated open ocean, using stable carbon isotope as a tracer. We found that subsurface (∼100 m depth) seawater is supersaturated (up to 12%) with 13C‐enriched CH4 (up to −33.1‰) relative to surface seawater in equilibrium with the atmosphere (−47‰), suggesting that in situ addition of 13C‐enriched CH4 must be responsible for CH4 enrichment at depth. The δ13C of CH4 emitted from sinking particles (from −36.7 ± 1.2‰ to +5.9 ± 7.5‰) is within the range of that of excess CH4 in seawater, suggesting that the major source of subsurface excess CH4 is sinking particles. The unusually 13C‐enriched δ13C composition of CH4 emitted from sinking particles suggests that active microbial CH4 oxidation occurs within the oxic/anoxic boundary of these particles. On the basis of the Rayleigh equation, we estimated that at least 62% of CH4 produced within the anoxic center of sinking particles is oxidized within 100 m of the surface.
Satellite‐based estimate of the direct and indirect aerosol climate forcing
Authors: Quaas Johannes , Boucher Olivier , Bellouin Nicolas , Kinne Stefan
Published: March 2008

The main uncertainty in anthropogenic forcing of the Earth's climate stems from pollution aerosols, particularly their “indirect effect” whereby aerosols modify cloud properties. We develop a new methodology to derive a measurement‐based estimate using almost exclusively information from an Earth radiation budget instrument (CERES) and a radiometer (MODIS). We derive a statistical relationship between planetary albedo and cloud properties, and, further, between the cloud properties and column aerosol concentration. Combining these relationships with a data set of satellite‐derived anthropogenic aerosol fraction, we estimate an anthropogenic radiative forcing of −0.9 ± 0.4 Wm−2 for the aerosol direct effect and of −0.2 ± 0.1 Wm−2 for the cloud albedo effect. Because of uncertainties in both satellite data and the method, the uncertainty of this result is likely larger than the values given here which correspond only to the quantifiable error estimates. The results nevertheless indicate that current global climate models may overestimate the cloud albedo effect.
Improvements to the Community Land Model and their impact on the hydrological cycle
Authors: Oleson K. W. , Niu G.‐Y. , Yang Z.‐L. , Lawrence D. M. , Thornton P. E. , Lawrence P. J. , Stöckli R. , Dickinson R. E. , Bonan G. B. , Levis S. , Dai A. , Qian T.
Published: March 2008

The Community Land Model version 3 (CLM3) is the land component of the Community Climate System Model (CCSM). CLM3 has energy and water biases resulting from deficiencies in some of its canopy and soil parameterizations related to hydrological processes. Recent research by the community that utilizes CLM3 and the family of CCSM models has indicated several promising approaches to alleviating these biases. This paper describes the implementation of a selected set of these parameterizations and their effects on the simulated hydrological cycle. The modifications consist of surface data sets based on Moderate Resolution Imaging Spectroradiometer products, new parameterizations for canopy integration, canopy interception, frozen soil, soil water availability, and soil evaporation, a TOPMODEL‐based model for surface and subsurface runoff, a groundwater model for determining water table depth, and the introduction of a factor to simulate nitrogen limitation on plant productivity. The results from a set of offline simulations were compared with observed data for runoff, river discharge, soil moisture, and total water storage to assess the performance of the new model (referred to as CLM3.5). CLM3.5 exhibits significant improvements in its partitioning of global evapotranspiration (ET) which result in wetter soils, less plant water stress, increased transpiration and photosynthesis, and an improved annual cycle of total water storage. Phase and amplitude of the runoff annual cycle is generally improved. Dramatic improvements in vegetation biogeography result when CLM3.5 is coupled to a dynamic global vegetation model. Lower than observed soil moisture variability in the rooting zone is noted as a remaining deficiency.
Does Repression Exist? Memory, Pathogenic, Unconscious and Clinical Evidence
Authors: Rofé Yacov
Published: March 2008

The current dispute regarding the existence of repression has mainly focused on whether people remember or forget trauma. Repression, however, is a multidimensional construct, which, in addition to the memory aspect, consists of pathogenic effects on adjustment and the unconscious. Accordingly, in order to arrive at a more accurate decision regarding the existence of repression, studies relevant to all three areas are reviewed. Moreover, since psychoanalysis regards repression as a key factor in accounting for the development and treatment of neurotic disorders, relevant research from these two domains are also taken into account. This comprehensive evaluation reveals little empirical justification for maintaining the psychoanalytic concept of repression.
Writing as Thinking
Authors: Oatley Keith , Djikic Maja
Published: March 2008

Writing is analyzed as thinking that uses paper or other media to externalize and manipulate symbolic expressions. Mental operations of natural language can occur somewhat independently, and they communicate well with language that has been written, but for skilled writing these operations need elaborate installation in the mind. We explore four methods to see how expert writers externalize thoughts and interact with them: laboratory comparisons of novices and experts, interviews with accomplished writers (mostly of prose fiction), biographical analysis of Jane Austen's development as a writer, and consideration of Gustave Flaubert's notes and drafts. Writers can use paper to extend their thinking, and to create frameworks of cues that enable readers of a story to construct mental models that they may enter empathetically.
Offshore Middlemen: Transnational Intermediation in Technology Sourcing
Authors: Mahnke Volker , Wareham Jonathan , Bjorn-Andersen Niels
Published: March 2008

The tendency of acquiring information systems and other high technology services from international suppliers continues at unprecedented levels. The primary motivation for the offshore sourcing of technology and services continues to be labor cost arbitrage, and secondly, access to higher levels of expertise. Yet paradoxically, large gaps in technical proficiency, cultural values, and communication styles between client and vendor can undermine the overall success of the offshore relationship. This paper argues that a new breed of entities have emerged, brokering or intermediating offshore relations. The capabilities of such ‘middlemen’ include moderating disparities in expertise, culture, and communication styles that often deteriorate performance in offshore relationships. The paper presents a preliminary theoretical justification for the emergence of offshore intermediaries, describes how and why they develop boundary spanning capabilities, and offers a case study as initial evidence substantiating the function and processes in intermediating transnational offshoring relationships. Our theory development concludes with propositions concerning four major offshore intermediary capabilities: (i) intermediating cultural distance, (ii) intermediating cognitive distance, (iii) pre-contractual preparation and negotiation, and (iv) post-contractual operational management.
Operational Capabilities Development in Mediated Offshore Software Services Models
Authors: Jarvenpaa Sirkka L , Mao Ji-Ye
Published: March 2008

The paper expands theoretical and empirical understanding of capabilities development in the mediated offshore outsourcing model whereby a small or a medium-sized firm delivers offshore software services to a larger information technology firm that in turn contracts and interfaces with the actual end-client onshore firms. Such a mediated model has received little prior research attention, although it is common particularly among Chinese firms exporting services to Japan, the largest export market for Chinese software services. We conducted case studies in four China-based software companies to understand the mechanisms used to develop their operational capabilities. We focused on client-specific, process, and human resources capabilities that have been previously associated with vendor success. We found a range of learning mechanisms to build the capabilities in offshore firms. Results show that the development of human resources capabilities was most challenging in the mediated model; yet foundational for the development of the other capabilities. This paper contributes to the information systems literature by improving our understanding of the development of operational capabilities in small- and medium-sized Chinese firms that deploy the mediated model of offshore software services.
Pseudospectral time-dependent density functional theory
Authors: Ko Chaehyuk , Malick David K. , Braden Dale A. , Friesner Richard A. , Martínez Todd J.
Published: March 2008

Time-dependent density functional theory (TDDFT) is implemented within the Tamm-Dancoff approximation (TDA) using a pseudospectral approach to evaluate two-electron repulsion integrals. The pseudospectral approximation uses a split representation with both spectral basis functions and a physical space grid to achieve a reduction in the scaling behavior of electronic structure methods. We demonstrate here that exceptionally sparse grids may be used in the excitation energy calculation, following earlier work employing the pseudospectral approximation for determining correlation energies in wavefunction-based methods with similar conclusions. The pseudospectral TDA-TDDFT method is shown to be up to ten times faster than a conventional algorithm for hybrid functionals without sacrificing chemical accuracy.
Electronic spectrum of TaO and its hyperfine structure
Authors: Manke Kara J. , Vervoort Tyson R. , Kuwata Keith T. , Varberg Thomas D.
Published: March 2008

The BΦ5∕22−X1Δ3∕22(0,0) band at 778nm and the CΔ3∕22−X1Δ3∕22(0,0) band at 737nm of tantalum oxide (TaO) were recorded by laser excitation spectroscopy using a hollow cathode sputtering source to generate the molecules. The hyperfine structure arising from the Ta181 (I=7∕2) nucleus was measured at sub-Doppler resolution using the technique of intermodulated fluorescence spectroscopy. The hyperfine structure was assigned and fitted in order to derive accurate values for the magnetic dipole and electric quadrupole interactions. The magnetic hyperfine constant for the ground electronic state was also calculated using the density functional theory as h3∕2=625MHz, in good agreement with the experimental value of 647±10MHz. This result suggests that the XΔ2 ground state of TaO is well described by a pure δσ2 electronic configuration, where the unpaired electron is located in a Ta 5dδ orbital.
A fully relativistic method for calculation of nuclear magnetic shielding tensors with a restricted magnetically balanced basis in the framework of the matrix Dirac–Kohn–Sham equation
Authors: Komorovský Stanislav , Repiský Michal , Malkina Olga L. , Malkin Vladimir G. , Malkin Ondík Irina , Kaupp Martin
Published: March 2008

A new relativistic four-component density functional approach for calculations of NMR shielding tensors has been developed and implemented. It is founded on the matrix formulation of the Dirac–Kohn–Sham (DKS) method. Initially, unperturbed equations are solved with the use of a restricted kinetically balanced basis set for the small component. The second-order coupled perturbed DKS method is then based on the use of restricted magnetically balanced basis sets for the small component. Benchmark relativistic calculations have been carried out for the H1 and heavy-atom nuclear shielding tensors of the HX series (X=F,Cl,Br,I), where spin-orbit effects are known to be very pronounced. The restricted magnetically balanced basis set allows us to avoid additional approximations and/or strong basis set dependence which arises in some related approaches. The method provides an attractive alternative to existing approximate two-component methods with transformed Hamiltonians for relativistic calculations of chemical shifts and spin-spin coupling constants of heavy-atom systems. In particular, no picture-change effects arise in property calculations.
Efficient spin transfer torque in pseudo-spin-valve structure
Authors: Guo J. , Jalil M. B. A. , Tan S. G.
Published: March 2008

A generalized spin transport model is applied to a typical pseudo-spin-valve (PSV) structure, consisting of a Co1 (10nm)–Cu (6nm)–Co2 (3nm) trilayer with noncollinear magnetization. The model is based on the spin-drift-diffusion model, which considers both longitudinal and transverse components of spin accumulation and spin current across the PSV. The influence of a spin-selective interfacial resistance is incorporated by modifying the boundary conditions. The strength of the spin transfer torque is obtained by considering the transverse spin accumulation in the free layer. Our calculations predict a significant enhancement of spin torque and consequent reduction in the critical current density for current-induced magnetization switching by engineering the spin-dependent interfacial effects and optimizing the relative orientations of the anisotropy axes of the two ferromagnetic layers.
Magnetorefractive effect in annealed Co∕Cu∕Co∕Fe pseudo-spin-valve thin films
Authors: Wang Jian-Qing , Sidney Malak T. , Rokitowski Jared D. , Kim Nam H. , Wang Keqiang
Published: March 2008

Magnetic-field-induced changes in infrared transmission in magnetron sputtered Fe∕Co∕Cu∕Co pseudo-spin-valves (PSV’s) were studied for the magetorefractive effect (MRE). These PSV films deposited on Si (0001) were optimized by annealing at various temperatures (between 100 and 400°C). The optimized PSV films possessed abrupt low-field giant magnetoresistance (GMR) response at 15Oe and the switching field of the top hard magnetic layer was found to be sensitive to post treatments such as annealing and chemical exposure. The room temperature MRE spectra of a Fe (5nm)∕Co (5nm)∕Cu (3nm)∕Co (2nm) PSV were measured and the observed MRE was about 1% at 4μm, correlating well with the GMR effect.
All-atom level direct folding simulation of a ββα miniprotein
Authors: Jang Soonmin , Kim Eunae , Pak Youngshang
Published: March 2008

We performed ab initio folding simulation for a ββα peptide BBA5 (PDB code 1T8J) with a modified param99 force field using the generalized Born solvation model (param99MOD5/GBSA). For efficient conformational sampling, we extended a previously developed novel Q-replica exchange molecular dynamics (Q-REMD) into a multiplexed Q-REMD. Starting from a fully extended conformation, we were able to locate the nativelike structure in the global free minimum region at 280K. The current approach, which combines the more balanced force field with the efficient sampling scheme, demonstrates a clear advantage in direct folding simulation at all-atom level.
Electrical transport, heat capacity, and high-field magnetization study in intermetallic Ni2CeSn compound
Authors: Öner Yildirhan , Goruganti V. , Kamer O. , Guillot M. , Ross Joseph H.
Published: March 2008

Magnetization, heat capacity, and electrical resistivity measurements were performed on a Ni2CeSn compound (orthorhombic structure) in the temperature range of 2–300K. This compound is paramagnetic down to 6K. At higher temperatures above T=150K, the magnetic susceptibility obeys Curie–Weiss behavior yielding an effective magnetic moment μeff=2.56μB∕f.u., which is very close to that of the free Ce3+ ion (2.54μB) with a high negative Curie–Weiss temperature, ΘCW=−170K. As the temperature is decreased, the magnetic moment decreases gradually to 0.43μB∕f.u. at 4.2K. We also infer that, based on the high field (up to 23T) magnetization and the magnetic susceptibility data, a crystal-field splitting of cerium atoms becomes significant at temperatures below 150K. We used heat capacity and resistivity measurements to determine the crystal-field splitting of the Ce3+ magnetic sublevels. It is found that the ground magnetic state for the Ce3+ is a doublet of Jz=±1∕2 states, with a first excited quartet of Jz=±3∕2 and Jz=±5∕2 states separated by ∼107K. The resistivity exhibits a shallow minimum at about 11K, which may be due to the development of partial magnetic order based on these crystal-field-split states.
A mean-field model of extrinsic line broadening in ferromagnetic resonance
Authors: McMichael Robert D.
Published: March 2008

A model of ferromagnetic resonance in inhomogeneous films is described, which includes interactions in a mean-field approximation. The mean-field model yields linewidth values that span the range from intrinsic linewidth for strong interactions to fully broadened local resonance linewidths for weak interactions. For weak inhomogeneity, the mean-field model does not follow the quadratic dependence of broadening on inhomogeneity predicted by the two-magnon model. For weakly interacting regions with strong inhomogeneity, the mean-field model fills a gap in the modeling of ferromagnetic resonance spectra where only computationally intensive models have been available previously.
Magnetic and thermal effects of flying height control heater voltage on tunneling magnetoresistive heads
Authors: Jang Eunkyu
Published: March 2008

The resistance and signal amplitude of tunneling magnetoresistive (TMR) heads were investigated as a function of flying height control (FHC) heater voltage under nonflying condition. The resistance and signal amplitude measured with a quasistatic tester (QST) both during and after FHC heater voltage application are substantially different from the initial values. The change of resistance or amplitude is reversible up to 3.2V (∼204°C). However, there are permanent changes in TMR signal amplitude after voltage applications of 3.4V (∼225°C) and above. An additional test, where QST performances of heads were measured only after FHC voltage applications, was carried out to distinguish between magnetic fields from the FHC heater and from the QST. Still, there are significant changes in resistance and amplitude. Pin layer reversals by the FHC heater current were also observed.
Switching a magnetic antivortex core with ultrashort field pulses
Authors: Gliga S. , Hertel R. , Schneider C. M.
Published: March 2008

Antivortices are fundamental magnetic structures found alongside vortices in soft magnetic extended films and in patterned elements above a few micrometers in size. While the dynamic behavior of vortices has been the object of numerous studies, the magnetization dynamics of antivortices has not been studied as thoroughly. Using micromagnetic simulations, we investigate the dynamics of a single isolated antivortex in response to subnanosecond external field pulses. We find that these pulses can trigger the reversal of the antivortex core. This reversal mechanism is complementary to the one recently found in the vortex core switch. We also investigate the stability of the switching process in the isolated antivortex structure.
Investigation on a NiFe alloy with a coefficient of thermal expansion matching the one of silicon
Authors: Bedenbecker Matthias , Gatzen Hans H.
Published: March 2008

Thin-film materials with a high relative permeability μr play an important role in the design of magnetic microactuators. Since the relative permeability μr is affected by external parameters such as film thickness and internal stress, investigations were carried out to determine the influence of film stress caused by different coefficients of thermal expansion of substrate and magnetic film, especially in combination with an annealing process at high temperatures. When using a soft magnetic material with a coefficient of thermal expansion close to the one of the substrate, the stress can be minimized. A suitable combination is NiFe35∕65 and Si substrates. Investigations on the thermal match of the two materials, as well as the relative permeability μr, the coercivity Hc, and the saturation flux density BS, were carried out as functions of the deposition temperature tdep. The relative permeability increases from 200 to greater than 1000 at temperatures above 400°C, while the coercivity Hc decreases from 2000to1000A∕m.
Heusler alloy based current-perpendicular-to-the-plane giant magnetoresistance heads for high density magnetic recording
Authors: Nikolaev Konstantin , Anderson Paul , Kolbo Paul , Dimitrov Dimitar , Xue Song , Peng Xilin , Pokhil Taras , Cho Haeseok , Chen Yonghua
Published: March 2008

Narrow-track current-perpendicular-to-the-plane giant magnetoresistive heads containing Heusler alloy layer have been fabricated utilizing an abutted junction hard bias design. The head performance has been tested quasistatically and dynamically under high density recording conditions using a perpendicular magnetic recording media.
The effect of complex permeability and agglomeration on composite magnetic systems: A three-dimensional numerical analysis and comparison with analytical models
Authors: Drnovšek Boštjan , Bregar Vladimir B. , Pavlin Mojca
Published: March 2008

Magnetic permeability of a composite is investigated using three-dimensional numerical models for static and quasistatic case. To analyze the effect of agglomeration and imaginary part of intrinsic permeability on the effective permeability, inclusions with complex permeability and having random distribution or random distribution with agglomeration were used. Significant deviation of analytical effective medium and Maxwell–Garnett models from numerical results for imaginary part of permeability was observed. We obtained that agglomeration increases the real part of the effective permeability for higher volume fractions and higer intrinsic permeabilities. The effect of agglomeration is even more pronounced for the imaginary part of the effective permeability. Our results thus show that agglomeration and complex intrinsic permeability could explain experimentally observed effective permeability.
Threshold condition of dislocation loop emission from microvoids
Authors: Tszeng T. C.
Published: March 2008

This study examines the micromechanics of dislocation loop emission, aiming at determining the threshold condition associated with microvoid growth. The closed form of threshold stress is obtained for edge dislocation in the vicinity of cylindrical void in a general planar macroscopic stress state. The effects of surface energy and lattice friction are accounted for; the former is found to be significant. A prolate-to-oblate shape transition in uniaxial strain due to a higher driving force on slip plane transverse to the loading direction is observed. In the asymptotic condition of a large void, threshold condition is dictated by planar mean stress for general macroscopic stress state.
Dynamics of charge currents ballistically injected in GaAs by quantum interference
Authors: Zhao Hui , Loren Eric J. , Smirl Arthur L. , van Driel H. M.
Published: March 2008

The dynamics of charge currents ballistically injected in GaAs bulk and quantum wells are spatially and temporally resolved. The electrons and holes are injected with oppositely directed velocities without the use of accelerating fields by quantum interference between two photon absorption of a 200fs, 1430nm fundamental pulse and one photon absorption of the corresponding second harmonic pulse. The subsequent charge motion is followed with ∼200fs temporal and ∼1nm spatial resolution by using tightly focused optical differential transmission techniques that are dependent on the relative phase of the incident pump pulses. Initially, the electrons and holes ballistically separate by up to ∼20nm, and a space charge field forms, which decelerates the carriers. Within this ∼1ps regime, the momentum relaxes by electron-hole and phonon scatterings, and the space charge field restores the electrons and holes to a common position; on time scales long compared to 1ps, ambipolar diffusion and recombination complete the return of the system to equilibrium. A rigid shift (damped simple harmonic oscillator) model for the electron motion reproduces the key features in the data, and the procedure for extracting the spatiotemporal dynamics of the electrons is shown to be immune to energy relaxation effects and forgiving of nonlinear saturation.
Time shifts and correlations in synchronized chaos
Authors: Blakely Jonathan N. , Pruitt Matthew W. , Corron Ned J.
Published: March 2008

We introduce a new method for predicting characteristics of the synchronized state achieved by a wide class of unidirectional coupling schemes. Specifically, we derive a transfer function from the coupling model that provides estimates of the correlation between the drive and response waveforms, and of the time shift (i.e., lag or anticipation) of the synchronized state. To demonstrate the method, we apply it to a simulated system of coupled Rössler oscillators as well as to an experimental system of coupled chaotic electronic circuits. Finally, we show that the transfer function can be exploited to design novel coupling schemes that significantly improve the correlation and increase the maximum achievable time shift.
Propagation of an intense laser beam in a tapered plasma channel
Authors: Jha Pallavi , Singh Ram Gopal , Upadhyaya Ajay K. , Mishra Rohit K.
Published: March 2008

Propagation characteristics and modulation instability of an intense laser beam propagating in an axially tapered plasma channel, having a parabolic radial density profile, are studied. Using the source-dependent expansion technique, the evolution equation for the laser spot is set up and conditions for propagation of the laser beam with a constant spot size (matched beam) are obtained. Further, the dispersion relation and growth rate of modulation instability of the laser pulse as it propagates through linearly and quadratically tapered plasma channels, have been obtained.
Modeling of dielectric barrier discharge plasma actuator
Authors: Jayaraman Balaji , Cho Young-Chang , Shyy Wei
Published: March 2008

Glow discharge at atmospheric pressure using a dielectric barrier discharge can induce fluid flow and operate as an actuator for flow control. In this paper, we simulate the physics of a two-dimensional asymmetric actuator operating in helium gas using a high-fidelity first-principles-based numerical modeling approach to help improve our understanding of the physical mechanisms associated with such actuators. Fundamentally, there are two processes in the two half-cycles of the actuator operation, largely due to the difference in mobility between faster electrons and slower ions, and the geometric configurations of the actuator (insulator and electrodes). The first half-cycle is characterized by the deposition of the slower ion species on the insulator surface while the second half-cycle by the deposition of the electrons at a faster rate. A power-law dependence on the voltage for the resulting force is observed, which indicates that larger force can be generated by increasing the amplitude. Furthermore, one can enhance the effectiveness of the actuator by either increasing the peak value of the periodic force generation or by increasing the asymmetry between the voltage half-cycles or both. Overall, the increase in the lower electrode size, applied voltage, and dielectric constant tends to contribute to the first factor, and the decrease in frequency of applied voltage tends to contribute to the second factor. However, the complex interplay between the above factors determines the actuator performance.
Anisotropic cross-tie walls and their confinement in self-organized undulating Fe film
Authors: Fukunaga Kei-ichi , Sugawara Akira
Published: March 2008

The magnetic domain structure and domain wall width within a self-organized undulating Fe film are investigated by Lorentz microscopy and electron holography. SiO2 (15nm)∕Fe (20nm)∕SiO2 (15nm) trilayers were deposited onto NaCl(110) substrates faceted with (100) and (010) planes. The Fe films exhibited a ridge-and-valley structure with undulation period of approximately 30nm. Its in-plane uniaxial anisotropy with the easy axis parallel to the ridge is explained in terms of roughness-induced dipolar anisotropy. The wall type in the undulating Fe films was found to be a cross-tie wall. The vortices and antivortices in the cross-tie wall induce angular deviation of the moment as small as 20° from the easy-axis and effectively reduce the wall energy. The domain wall widths were determined to be 13±2 and 18±4nm by Lorentz microscopy and electron holography, respectively. The obtained widths, nearly half of the undulation period, were narrower than that observed for a flat Fe film. For comparison, the stable magnetization distribution and the internal structure of the walls were examined by numerical simulations based on the Landau–Lifshitz–Gilbert equation. The walls are found to be confined between adjacent ridges, i.e., within half an undulation period, due to the strong pinning of magnetization along the easy axis near the ridges, while the vortices and antivortices on the cross-tie walls are formed in the middle continuous part of the undulating film where angular deviation of the moment does not produce stray field.
Do the grain boundaries of β-In2S3 thin films have a role in sub-band-gap photosensitivity to 632.8nm?
Authors: Jayakrishnan R. , John Teny Theresa , Kartha C. Sudha , Vijayakumar K. P. , Jain Deepti , Chandra L. S. Sharath , Ganesan V.
Published: March 2008

Highly photoconducting β-In2S3 thin films with conducting grain boundaries were obtained, using “chemical spray pyrolysis” technique. By varying the atomic ratio of the precursor solution used for spray pyrolysis, the photoconductivity of these films could be tailored. Conducting grain boundaries were found only for samples with a specific stoichiometry and these films exhibited photoresponse to intrinsic and extrinsic excitation wavelengths in the range of 325–532nm. Postdeposition vacuum annealing of these films enhanced the grain boundary conductivity, caused the films to exhibit persistent photoconductivity for both intrinsic and extrinsic excitations and extended the extrinsic photoresponse to wavelengths beyond 632.8nm. Photoresponse to excitation wavelength of 632.8nm was observed in films with and without conducting grain boundaries which proved that the extrinsic photoresponse to this wavelength was an effect associated with the defect chemistry of the β-In2S3.
Imaging the real shape of nanoclusters in scanning force microscopy
Authors: Pakarinen Olli H. , Barth Clemens , Foster Adam S. , Henry Claude R.
Published: March 2008

A quantitative comparison between experiment and theory is given for the constant height mode imaging of metal nanoclusters in dynamic scanning force microscopy. We explain the fundamental mechanisms in the contrast formation with the help of the system Pd/MgO(001). The comparison shows that the shape and size of nanoclusters are precisely imaged due to the sharpness of the tip’s last nanometer. This quantitative comparison proves our previously proposed model for the contrast formation.
Measurement of x-ray free-electron-laser pulse energies by photoluminescence in nitrogen gas
Authors: Hau–Riege S. P. , Bionta R. M. , Ryutov D. D. , Krzywinski J.
Published: March 2008

We discuss the physics of a photoluminescence-based pulse-energy detector that will be used to characterize hard x-ray free-electron-laser pulses at the Linac Coherent Light Source. We tested the detector in a quasi-steady-state mode of operation at the conventional synchrotron light source Stanford positron electron assymetric ring 3 at the Stanford Synchrotron Radiation Laboratory. We also developed a Monte-Carlo model for the x-ray interaction with the nitrogen gas and the resulting ultraviolet signal and found good agreement with the experimental data. Remaining discrepancies can, to a large extent, be attributed to the varying luminescence behavior of different chamber wall materials.
Effect of reactive ion beam etching on the photoluminescence of CdTe epitaxial layers
Authors: Martinez-Pastor J. , Fuster D. , Abellán M. , Anguita J. , Sochinskii N. V.
Published: March 2008

We demonstrated the effect of reactive ion beam etching (RIBE) process on the PL properties of CdTe/sapphire metal organic vapor phase epitaxy layers. At optimum conditions, the RIBE attack does not make significant morphological changes but it results in an increase of the concentration of acceptor impurities. This was revealed by an increase of the overall photoluminescence (PL) intensity and, simultaneously, a decrease of the PL decay time, more important on the low energy side of PL spectrum due to the recombination of carriers in acceptor pairs.
Electron acceleration during guide field magnetic reconnection
Authors: Wan Weigang , Lapenta Giovanni , Delzanno Gian Luca , Egedal Jan
Published: March 2008

Particle-in-cell simulations of the guide field intermittent magnetic reconnection are performed to study electron acceleration and pitch angle distributions. During the growing stage of reconnection, the power-law distribution function for the high-energy electrons and the pitch angle distributions of the low-energy electrons are obtained and compare favorably with observations by the Wind spacecraft. Direct evidence is found for the secondary acceleration during the later reconnection stage. A correlation between the generation of energetic electrons and the induced reconnection electric field is found. Energetic electrons are accelerated first around the X line, and then in the region outside the diffusion region, when the reconnection electric field has a bipolar structure. The physical mechanisms of these accelerations are discussed. The in-plane electrostatic field that traps the low-energy electrons and causes the anisotropic pitch angle distributions has been observed.
Fragmentation of metastable SF6−∗ ions with microsecond lifetimes in competition with autodetachment
Authors: Graupner K. , Field T. A. , Mauracher A. , Scheier P. , Bacher A. , Denifl S. , Zappa F. , Märk T. D.
Published: March 2008

Fragmentation of metastable SF6−* ions formed in low energy electron attachment to SF6 has been investigated. The dissociation reaction SF6−*→SF5−+F has been observed ∼1.5–3.4μs and ∼17–32μs after electron attachment in a time-of-flight and a double focusing two sector field mass spectrometer, respectively. Metastable dissociation is observed with maximum intensity at ∼0.3eV between the SF6−* peak at zero and the SF5− peak at ∼0.4eV. The kinetic energy released in dissociation is low, with a most probable value of 18meV. The lifetime of SF6−* decreases as the electron energy increases, but it is not possible to fit this decrease with statistical Rice–Ramsperger–Kassel/quasiequilibrium theory. Metastable dissociation of SF6−* appears to compete with autodetachment of the electron at all electron energies.
Absolute calibration of image plates for electrons at energy between 100keV and 4MeV
Authors: Chen Hui , Back Norman L. , Bartal Teresa , Beg F. N. , Eder David C. , Link Anthony J. , MacPhee Andrew G. , Ping Yuan , Song Peter M. , Throop Alan , Van Woerkom Linn
Published: March 2008

We measured the absolute response of image plate (Fuji BAS SR2040) for electrons at energies between 100keV and 4MeV using an electron spectrometer. The electron source was produced from a short pulse laser irradiated on solid density targets. This paper presents the calibration results of image plate photon stimulated luminescence per electron at this energy range. The Monte Carlo radiation transport code MCNPX results are also presented for three representative incident angles onto the image plates and corresponding electron energy depositions at these angles. These provide a complete set of tools that allows extraction of our absolute calibration to other spectrometer setting at this electron energy range.
Effect of 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline outcoupling layer on electroluminescent performances in top-emitting organic light-emitting devices
Authors: Chen Shufen , Xie Wenfa , Meng Yanlong , Chen Ping , Zhao Yi , Liu Shiyong
Published: March 2008

The organic compound, 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) is used as a light outcoupling layer in top-emitting organic light-emitting devices with tris(8-hydroxyquinoline) aluminum emission layer. It is found that, in addition to the improvement of electroluminescent (EL) intensity and luminous efficiency with a factor of 1.6, the BCP capping layer causes a blueshift of EL spectra and a larger full width at half maximum (FWHM). A larger FWHM at the BCP capping layer of 50nm is attributed to the reduction of cathode reflectivity. In the meantime, the blueshift of EL spectra is caused by the increase of the reflective phase shift of the cathode when a thicker BCP layer is deposited. Moreover, our calculation demonstrates that the best EL coincides with a maximum magnification coefficient.
Magnetic properties of Bi0.5Sr0.5FexMn1−xO3 (⩽x⩽0.7)
Authors: Tzankov D. , Kovacheva D. , Krezhov K. , Puźniak R. , Wiśniewski A. , Sváb E. , Mikhov M.
Published: March 2008

Fe-substituted manganites Bi0.5Sr0.5FexMn1−xO3 (0⩽x⩽1.0) were synthesized by a solid-state reaction. X-ray powder diffraction and neutron diffraction investigations performed at room temperature show that the crystal structure is orthorhombic for x⩽ 0.3 and cubic for x>0.4. The unit cell volume increases with x. Magnetic properties were studied between 5 and 1000K in a magnetic field up to 16kOe for the compounds with x⩽0.7. A charge/orbital ordering feature was only observed in magnetization curves for the compound with no Fe. The magnetic state of the compounds with different Fe contents changes from paramagnetic to weak antiferromagnetic below the temperature TN varying in the range of 115–155K. Unusual thermomagnetic behavior in the paramagnetic region was observed, which could be related to a coexistence of antiferromagnetic and ferromagnetic fluctuations far above TN. The typical thermomagnetic zero field cooled/field cooled hysteresis below about 40K can be related to the formation of small ferromagnetic clusters below that temperature. The conductivity of the compounds, measured between 90 and 600K, is of the semiconducting type, and no magnetoresistant effect was observed for any of them in a field of 7kOe.
Properties of (Zn,Cr)Te semiconductor deposited at room temperature by magnetron sputtering
Authors: Wang W. G. , Han K. J. , Yee K. J. , Ni C. , Wen Q. , Zhang H. W. , Zhang Y. , Shah L. , Xiao John Q.
Published: March 2008

We report the fabrication of (Zn,Cr)Te films at room temperature by magnetron sputtering. Various structural and elemental characterizations revealed there was only a zinc blende phase from the ZnTe host and Cr atoms were distributed uniformly in these films. The magnetization measurement by superconducting quantum interference device magnetometer clearly showed that the samples were ferromagnetic at low temperatures with Curie temperature around 150K. The magnetic circular dichroism measurements confirmed that the observed ferromagnetism was originated from the interaction of substitutional Cr ions and ZnTe host. Transport measurement revealed typical semiconductor behaviors with the large negative magnetoresistance observed.
Multichannels high voltage programmable driver for piezoelectric transducer
Authors: Flaxer Eli
Published: March 2008

A complete design of a compact, high voltage, multichannel programmable waveform generator, using an 8bit microcontroller, 12bit digital to analog converter, and high voltage operation amplifier, is presented. The user can generate the waveform by several options: classic waveform, calculator, freehand drawing, and using excel or text file. All the waveform data are stored in a nonvolatile memory of the microcontroller. The generator can work as a stand-alone instrument or conjoined with a personal computer. We used this generator as a controller for piezoelectric inertial slider.