bluuebunny/crossref_metadata_2025 huggingface dataset:
Two‐dimensional electrons at n‐GaAs/AlGaAs heterointerface under uniaxial compression
Authors: Minina N. Ya. , Bogdanov E. V. , Ilievsky A. A. , Polyansky A. V. , Kraak W. , Savin A. M. , Berman I. V.
Published: December 2006

It has been shown that under uniaxial compression P applied at low temperatures the transport properties of 2D electrons at a n‐(001)GaAs/Alx Ga1–x As heterointerface are governed mainly by the piezoelectric field. It arises across the structure in the [001] direction when the stress is applied in the [110] or [1$ \bar 1 $0] directions and causes the corresponding compensating redistribution of charges that increases the 2D electron concentration in a quantum well if P ‖[110] and decreases it if P ‖[1$ \bar 1 $0]. The anisotropy of the 2D electron mobility does not significantly change under uniaxial stress up to 3.5 kbar and does not indicate the change of the energy spectrum anisotropy that takes place in a 2D hole system under compression. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Threshold currents under pressure in InGaAsSb/AlGaAsSb laser diodes
Authors: Adamiec P. , Bohdan R. , Bercha A. , Dybala F. , Trzeciakowski W. , Rouillard Y. , Joullié A.
Published: December 2006

Threshold currents in quantum well InGaAsSb lasers grown on GaSb substrates have been measured in the temperature range from 170 up to 320 K at pressures up to 20 kbar. These measurements were aiming at the identification of major recombination channels in these devices: Auger recombination involving spin–orbit split‐off band and leakage of electrons to p‐claddings. The emission lines shifted with pressure 12 meV per kbar. Our results indicated that the expected resonance of Auger recombination for E g = Δ does not occur in the studied pressure/temperature range. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Pressure‐induced phase transition in Co‐doped ZnO
Authors: Mori Y. , Niiya N. , Mizuno T. , Nishii T. , Fujii A. , Fujii Y. , Takarabe K. , Wang Y. , Jiang J. Z.
Published: December 2006

High‐pressure X‐ray diffraction studies of Cox Zn1–x O (x = 0, 0.05, 0.10) were carried out with a synchrotron radiation source. The crystal parameters for three samples under pressure were refined by the Rietveld method. The bulk moduli for Cox Zn1–x O (x = 0, 0.05, 0.10) were determined by Birch's equation of state to be 144.9 ± 0.6, 143.4 ± 4.2, and 138.5 ± 1.9 GPa, and also the transition pressure from the wurtzite structure to the rocksalt structure were determined to be 8.2, 7.7, and 6.1 GPa, respectively. On increasing the Co‐doping into the ZnO, both the bulk moduli and transition pressures decrease, but the rates are quite different. The bulk modulus decreases by 4.8% with 10% Co‐doping but the transition pressure decreases by 25%. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Crystal stability and pressure‐induced phase transitions in scheelite AWO4 (A = Ca, Sr, Ba, Pb, Eu) binary oxides. I: A review of recent ab initio calculations, ADXRD, XANES, and Raman studies
Authors: López‐Solano J. , Rodríguez‐Hernández P. , Radescu S. , Mujica A. , Muñoz A. , Errandonea D. , Manjón F. J. , Pellicer‐Porres J. , Garro N. , Segura A. , Ferrer‐Roca Ch. , Kumar R. S. , Tschauner O. , Aquilanti G.
Published: December 2006

The structural properties of CaWO4, SrWO4, BaWO4, PbWO4, and EuWO4 scintillating crystals under pressure have been studied by X‐ray powder diffraction, X‐ray absorption near‐edge structure measurements, Raman spectroscopy, and ab initio density functional theory calculations. The results obtained from these studies will be reviewed here and their differences and similitudes discussed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
High pressure studies of the radial breathing modes in double‐wall carbon nanotubes
Authors: Arvanitidis J. , Christofilos D.
Published: December 2006

This work focuses on the high pressure Raman study of the radial breathing modes (RBMs) of bundled double‐wall carbon nanotubes (DWCNTs) using different excitation energies. The detailed examination of the Raman peaks attributed to the RBMs of the inner and outer tubes comprising the DWCNTs as a function of pressure provides a wealth of information concerning the pressure response of individual nanotubes as well as the inner‐outer tube (intratube) interactions. The outer tube acts as a protection shield for the inner tube whereas the latter increase the structural stability of the externals upon pressure application. More importantly, the pressure response of the inner tubes, expressed by the normalized pressure slopes Γi = (1/ωi) (∂ωi /∂P) vs. frequency of their RBMs, shows a remarkable grouping in quasi‐linear distributions wherein Γi increases with ω. This behavior is explained by assuming that the pressure response of an internal tube is crucially dependent on the intratube spacing and thus the structural characteristics of the encapsulating tube. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Kinetics of photo‐darkening and self‐bleaching in amorphous As2S3 and As2Se3 thin films
Authors: Munzar M. , Tichý L.
Published: December 2006

The kinetics of photo‐darkening of amorphous As2S3 and a‐As2Se3 thin films follows a single exponential, but the magnitude and the rate of the process is higher in case of As2S3. The kinetics of self‐bleaching (dark relaxation) in advance photo‐darkened state follows a stretched exponential (SRE) with different stretching parameter for a‐As2S3 and a‐As2Se3. Within the J. C. Phillips approach we suppose that photo‐darkening in amorphous As2S3 films is, to some extent, accompanied by changes in short‐range order interactions, while photo‐darkening of amorphous As2Se3 is accompanied rather by changes in Coulomb interactions. The self‐bleaching process reduced the magnitude of photo‐darkening up to 45% and 60% for amorphous As2S3 and As2Se3 films, respectively. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Differential effects of three species of Hypericum in an open field test
Authors: Diana Giovanni , Capasso Anna , Quaranta Emilia , Feo Vincenzo De
Published: December 2006

The effects of three species of Hypericum (H.) on mice motor activity were compared in an automated open field test. Methanol extracts of H. perforatum L., H. hircinum L. and H. perfoliatum L. were tested at doses ranging from 2.5 to 200 mg i.p. H. hircinum decreased locomotion at most dose levels. Moreover, a dose of 200 mg/kg of all three herbal species sharply decreased motor activity. Ten mg/kg of H. perforatum, a dose that is comparable to that endowed with antidepressant effects in humans, tended to increase exploration and stereotypic activity and to decrease immobility. The study suggests that there are differences in the neuropharmacological actions of the three plant extracts. However, common constituents might explain the reduced motor activity observed at high dose levels. Copyright © 2006 John Wiley & Sons, Ltd.
Application of the Mixed‐field‐environments concept in lifetime prediction of some ceramic components
Authors: Salmela Olli
Published: December 2006

In lifetime prediction, the effect of a certain use environment on the lifetime is taken into account by using an acceleration factor that is specific to that use environment. The fact that the product may be used in different countries with differing environmental conditions results in a set of acceleration factor values. Prior to this paper, the effect of multiple field environments has been taken into account by using an average value of the acceleration factors obtained for several use environments. As the magnitudes of the acceleration factors (each specific to a certain use environment) vary a lot, the use of the average value has resulted in unrealistic lifetime estimates. The unrealism related to the use of the average value can be avoided when using the mixture‐of‐distributions concept, since the true acceleration factor values, instead of an average value, can then be used. In this paper, the mixture‐of‐distributions concept is applied for the first time to evaluate the effect of multiple use environments (thermal cycling) on the lifetime of a component population. By using this concept, it is possible to evaluate all of the key figures of reliability for the whole population based on the fractions of the component population that are used in multiple, different use environments. This approach can be applied when allocating maintenance and spare parts for a product that is used worldwide. The mixture‐of‐distributions concept in lifetime prediction is demonstrated by analyzing the test results of some ceramic leadless chip carrier components. Acceleration factors in four alternative field environments are estimated by running thermo‐mechanical finite element analysis simulations. The lifetime performance of the whole component population used in certain alternative field environments is then evaluated by applying the mixture‐of‐distributions concept. Copyright © 2006 John Wiley & Sons, Ltd.
Ground‐based experimental platforms in gravitational biology and human physiology
Authors: Hemmersbach Ruth , von der Wiesche Melanie , Seibt Dieter
Published: December 2006

Scientists and technicians have been innovative in order to find experimental approaches to study the influence of gravity. Depending on the scientific question and the time course of events which are under investigation, different experimental platforms are available to provide conditions of altered gravitational stimulation on ground and to prepare space experimentsi.e.under real microgravity conditions. The application profile ranges from studies with molecules or single cells up to humans.
Fabrication of DNA micropatterns on the polycarbonate surface of compact discs
Authors: Wang Zhen , Li Rong-Xian
Published: December 2006

DNA micropatterns have been fabricated on the surface of Polycarbonate (PC) bases of compact discs, with the ultimate goal of using conventional CD technology for DNA analysis. To confirm the formation of -COOH groups on the PC surface upon UV/ozone treatment, contact angle titrations were carried out on the PC surfaces. The surface morphologies of PC surface were measured by Tapping-mode Atomic Force Microscopy (AFM). As the surface as “anchor” to attach the amine-modified ssDNA by covalent conjugates via amide bonds, the results of fluorescence spectroscopy showed that the fluorescein labeled complementary ssDNA can be used for detection the ssDNA immobilized on the patterned CD polycarbonate substrate.
Is dissociative amnesia a culture-bound syndrome? Findings from a survey of historical literature
Authors: POPE HARRISON G. , POLIAKOFF MICHAEL B. , PARKER MICHAEL P. , BOYNES MATTHEW , HUDSON JAMES I.
Published: December 2006

Background. Natural human psychological phenomena, such as depression, anxiety, delusions, hallucinations and dementia, are documented across the ages in both fictional and non-fictional works. We asked whether ‘dissociative amnesia’ was similarly documented throughout history.

Method. We advertised in three languages on more than 30 Internet web sites and discussion groups, and also in print, offering US$1000 to the first individual who could find a case of dissociative amnesia for a traumatic event in any fictional or non-fictional work before 1800.

Results. Our search generated more than 100 replies; it produced numerous examples of ordinary forgetfulness, infantile amnesia and biological amnesia throughout works in English, other European languages, Latin, Greek, Arabic, Sanskrit and Chinese before 1800, but no descriptions of individuals showing dissociative amnesia for a traumatic event.

Conclusions. If dissociative amnesia for traumatic events were a natural psychological phenomenon, an innate capacity of the brain, then throughout the millennia before 1800, individuals would presumably have witnessed such cases and portrayed them in non-fictional works or in fictional characters. The absence of cases before 1800 cannot reasonably be explained by arguing that our ancestors understood or described psychological phenomena so differently as to make them unrecognizable to modern readers because spontaneous complete amnesia for a major traumatic event, in an otherwise lucid individual, is so graphic that it would be recognizable even through a dense veil of cultural interpretation. Therefore, it appears that dissociative amnesia is not a natural neuropsychological phenomenon, but instead a culture-bound syndrome, dating from the nineteenth century.
Burden of community-onset bloodstream infection: a population-based assessment
Authors: LAUPLAND K. B. , GREGSON D. B. , FLEMONS W. W. , HAWKINS D. , ROSS T. , CHURCH D. L.
Published: December 2006

Although community-onset bloodstream infection (BSI) is recognized to be a major cause of morbidity and mortality, there is a paucity of population-based studies defining its overall burden. We conducted population-based laboratory surveillance for all community-onset BSI in the Calgary Health Region during 2000–2004. A total of 4467 episodes of community-onset BSI were identified for an overall annual incidence of 81·6/100 000. The three species,Escherichia coli,Staphylococcus aureus, andStreptococcus pneumoniaewere responsible for the majority of community-onset BSI; they occurred at annual rates of 25·8, 13·5, and 10·1/100 000, respectively. Overall 3445/4467 (77%) episodes resulted in hospital admission representing 0·7% of all admissions to major acute care hospitals. The subsequent hospital length of stay was a median of 9 (interquartile range, 5–15) days; the total days of acute hospitalization attributable to community-onset BSI was 51 146 days or 934 days/100 000 annually. Four hundred and sixty patients died in hospital for a case-fatality rate of 13%. Community-onset BSI is common and has a major patient and societal impact. These data support further efforts to reduce the burden of community-onset BSI.
Accuracy of ICD-9 coding for Clostridium difficile infections: a retrospective cohort
Authors: SCHEURER D. B. , HICKS L. S. , COOK E. F. , SCHNIPPER J. L.
Published: December 2006

Clostridium difficile (C. diff) is a major nosocomial problem. Epidemiological surveillance of the disease can be accomplished by microbiological or administrative data. Microbiological tracking is problematic since it does not always translate into clinical disease, and it is not always available. Tracking by administrative data is attractive, but ICD-9 code accuracy for C. diff is unknown. By using a large administrative database of hospitalized patients with C. diff (by ICD-9 code or cytotoxic assay), this study found that the sensitivity, specificity, positive, and negative predictive values of ICD-9 coding were 71%, 99%, 87%, and 96% respectively (using micro data as the gold standard). When only using symptomatic patients the sensitivity increased to 82% and when only using symptomatic patients whose test results were available at discharge, the sensitivity increased to 88%. C. diff ICD-9 codes closely approximate true C. diff infection, especially in symptomatic patients whose test results are available at the time of discharge, and can therefore be used as a reasonable alternative to microbiological data for tracking purposes.
Shear‐enhanced compaction and strain localization: Inelastic deformation and constitutive modeling of four porous sandstones
Authors: Baud Patrick , Vajdova Veronika , Wong Teng‐fong
Published: December 2006

We studied the mechanics of compactant failure in four sandstones associated with a broad range of failure modes in the brittle‐ductile transition. While Berea and Bentheim sandstones can fail by compaction localization, homogeneous cataclastic flow dominates failure modes in Adamswiller and Darley Dale sandstones at high effective pressures. We acquired new experimental data to complement previous studies, focusing on the strain hardening behavior in samples under drained conditions. The initial yield stresses were identified as the critical stresses at the onset of shear‐enhanced compaction, subsequent yield stresses were considered to depend on hardening given by plastic volumetric strain. The yield stresses were described by elliptical yield caps in the stress space, and we compared the cap evolution with two constitutive models: the critical state model and the cap model. Bentheim sandstone showed the best agreement with both models to relatively large strains. Darley Dale sandstone showed the best agreement with the associated flow rule as prescribed by the normality condition, which is implicitly assumed in both constitutive models. Shear‐enhanced compaction in Bentheim and Berea sandstones was appreciably more than that predicted for an associative flow rule, with the implication that a nonassociative model is necessary for capturing the inelastic and failure behavior of these sandstones over a broad range of effective pressures. With reference to the nonassociative model formulated by Rudnicki and Rice, bifurcation analysis would predict the transition of failure mode from shear band to compaction band and ultimately to cataclastic flow, in qualitative agreement with the experimental observations.
Relationship between hygroscopicity and cloud condensation nuclei activity for urban aerosols in Tokyo
Authors: Mochida Michihiro , Kuwata Mikinori , Miyakawa Takuma , Takegawa Nobuyuki , Kawamura Kimitaka , Kondo Yutaka
Published: December 2006

As described by the Köhler theory, the hygroscopicity of atmospheric aerosol particles is a key factor regulating their cloud condensation nuclei (CCN) activity. Here we investigated the relationship between hygroscopicity and CCN activity for urban aerosol particles using a hygroscopicity tandem differential mobility analyzer (HTDMA) coupled in series to a CCN counter. The HTDMA‐CCNC system was operated near the center of the Tokyo metropolitan area from 10 to 17 November 2004. For aerosol particles whose dry mobility diameters were 30–200 nm, the ratios of CCN to condensation nuclei (CN) at 0.22–1.3% supersaturation were obtained as a function of particle hygroscopicity at 83 and 89% RH. More‐hygroscopic particles were found to be more CCN active than less‐hygroscopic particles of the same size, indicating that hygroscopicity is a critical factor regulating CCN activity. The chemical compositions of particles were simultaneously measured using an aerosol mass spectrometer. They were found to relate closely to CCN activity as well as to the hygroscopicity. The measured CCN–hygroscopicity relationships were compared to those predicted by Köhler theory. The results suggest that CCN activity is possibly perturbed by changes in surface tension due to organics, dissolution/dissociation of water‐soluble organics under supersaturation conditions, or different nonideality of organics from inorganic salts. These factors associated with organics are potentially important for CCN activity and thus microphysical cloud processes in the atmosphere.
Magnetic properties of atmospheric particulate matter from automatic air sampler stations in Latium (Italy): Toward a definition of magnetic fingerprints for natural and anthropogenic PM10 sources
Authors: Sagnotti Leonardo , Macrì Patrizia , Egli Ramon , Mondino Manlio
Published: December 2006

Environmental problems linked to the concentration of atmospheric particulate matter with dimensions less than 10 μm (PM10) in urban settings have stimulated a variety of scientific researches. This study reports a systematic analysis of the magnetic properties of PM10 samples collected by six automatic stations installed for air quality monitoring through the Latium Region (Italy). We measured the low‐field magnetic susceptibility of daily air filters collected during the period July 2004 to July 2005. For each station, we derived an empirical linear correlation linking magnetic susceptibility to the concentration of PM10 produced by local sources (i.e., in absence of significant inputs of exogenous dust). An experimental approach is suggested for estimating the percentage of nonmagnetic PM10 transported from natural far‐sided sources (i.e., dust from North Africa and marine aerosols). Moreover, we carried out a variety of additional magnetic measurements to investigate the magnetic mineralogy of selected air filters spanning representative periods. The results indicate that the magnetic fraction of PM10 is composed by a mixture of low‐coercivity, magnetite‐like, ferrimagnetic particles with a wide spectrum of grain sizes, related to a variety of natural and anthropogenic sources. The natural component of PM10 has a characteristic magnetic signature that is indistinguishable from that of eolian dust. The anthropogenic PM10 fraction is mostly originated from circulating vehicles and is a mixture of prevailing fine superparamagnetic particles and subordinate large multidomain grains; the former are more directly related to exhaust, whereas the latter may be associated to abrasion of metallic parts.
Competition of magnetic and hydrodynamic forces on ellipsoidal particles under shear: Influence of the Earth's magnetic field on particle alignment in viscous media
Authors: Jezek Josef , Gilder Stuart A.
Published: December 2006

We present a model that describes the rotation of ellipsoidal magnetic particles in a viscous fluid under the influence of hydrodynamic and magnetic forces, with an aim to better understand how sediments acquire their remanent magnetizations. Analyses of the governing equations elucidate how magnetic particles will rotate for different values of leading parameters including particle shape, remanent and induced magnetic intensity, magnetic field intensity and direction, strain rate, shear direction, and viscosity. Numerical solution of the governing equations makes it possible to visualize the rotation path and the magnetic direction of a particle through time. Thus the model can discern the timescales and trajectories of magnetic particles rotating due to torque of the magnetic field couple while simultaneously entrained in a velocity gradient. For example, in a layer of viscosity 104 Pa s, prolate magnetite starting at any initial orientation and subjected to simple shear with a strain rate of 3.17 × 10−8 s−1 needs 4 months to rotate within 3° of the Earth's field direction. Under the same conditions, hydrodynamic forces will govern the orientation of oblate hematite whose moment will be perpetually randomly oriented with respect to the magnetic field direction. When applied to laboratory experiments, the viscous model successfully matches the observed data, particularly after accounting for mechanical interaction and flocculation effects. Magnetic anisotropies calculated from multiparticle systems of hematite yield typical sedimentary fabrics with relatively low percentages of anisotropy (<5%) and maximum principal axes that lie in the sedimentation plane.
How abundant is pedogenic magnetite? Abundance and grain size estimates for loessic soils based on rock magnetic analyses
Authors: Geiss Christoph E. , Zanner C. William
Published: December 2006

The upper soil horizons of many modern and ancient soils are enriched in fine‐grained pedogenic ferrimagnetic minerals. We use three grain‐size‐ and concentration‐dependent proxies (anhysteretic remanent magnetization/isothermal remanent magnetization ratios, coercivity spectra derived from alternating field demagnetization of saturation isothermal remanent magnetization and hysteresis properties) to quantify the abundance and grain size of the pedogenic magnetic component. Our analyses of modern loessic soils from the midwestern United States show that relatively small additions (2–10 vol % of the total ferrimagnetic component) of fine‐grained (coarse superparamagnetic to fine pseudosingle domain) magnetite or maghemite are sufficient to explain the changes in concentration and grain‐size‐dependent properties observed in the upper soil horizons. Furthermore, the pedogenic components of all studied sites display a narrow range of magnetic properties, which argues for a common origin of these particles over a wide range of climatic conditions.
Theoretical considerations on the anhysteretic remanent magnetization of interacting particles with uniaxial anisotropy
Authors: Egli R.
Published: December 2006

The anhysteretic remanent magnetization (ARM) is widely used in rock magnetism and paleomagnetism because of its sensitivity to the domain state of magnetic particles and the close analogy to natural remanent magnetizations. On the other hand, the ARM shares with other weak‐field magnetizations the property of being extremely sensitive to magnetostatic interactions. Therefore it is desirable to model the effects of interactions on natural assemblages of magnetic particles. Direct micromagnetic calculations of the ARM acquisition process are not practicable; therefore an analytical approach is used calculate the ARM susceptibility of a system of interacting single‐domain (SD) particles. The model is based on a statistical description of the interaction field. The equations obtained have been used to evaluate the dependence of the ARM on the packing fraction of the magnetic particles. The effect of interactions on the anisotropy of ARM (AARM) was evaluated as well. The AARM of densely packed particles is complex and depends critically on the microcoercivity. A physical interpretation of the AARM of highly interacting particles is therefore difficult.
Surface wind response to oceanic fronts
Authors: Song Qingtao , Cornillon Peter , Hara Tetsu
Published: December 2006

The response of surface winds to ocean fronts characterized by sharp gradients in both sea surface temperature (SST) and ocean currents was analyzed using scatterometer (NSCAT and QuikSCAT) wind data and Gulf Stream path positions in conjunction with simulations made with the Pennsylvania State University (PSU)‐National Center for Atmospheric Research (NCAR) Mesoscale Model (MM5). All match‐ups, between each scatterometer pass and the Gulf Stream path, were visually examined and only those for which the wind field was free of atmospheric fronts or large curvature over a reasonably straight segment of the Gulf Stream were selected. Ten match‐ups met these criteria for the period studied from 16 September 1996 to 29 June 1997 for NSCAT and from 24 July 1999 to 31 December 2000 for QuikSCAT. Changes in the modeled surface wind field across the front in each of the ten cases agree well with changes in the observed winds. Our findings suggest that the perturbation pressure gradient resulting from the thermal forcing by the front accounts for the decrease in wind speed when moving from warm to cold water and the increase observed in the converse. In the cases examined, the adjustment of the surface wind to the front occurred as a result of the vertical motion induced by horizontal divergence/convergence and advection in the marine atmospheric boundary layer (MABL). The dynamical forcing associated with strong surface currents is also shown to modify scatterometer‐derived winds. Finally the numerical simulations suggest that the dynamical and thermal effects are very nearly additive.
Trajectory prediction using HF radar surface currents: Monte Carlo simulations of prediction uncertainties
Authors: Ullman David S. , O'Donnell James , Kohut Josh , Fake Todd , Allen Arthur
Published: December 2006

An important aspect of particle trajectory modeling in the ocean is the assessment of the uncertainty in the final particle position. Monte Carlo particle trajectory simulations using surface currents derived from standard‐range and long‐range CODAR HF radar systems were performed using random‐walk and random‐flight models of the unresolved velocities. Velocity statistics for these models were derived from the covariance functions of differences between CODAR and drifter estimates of surface currents. Comparison of predicted trajectories and drifter tracks demonstrate that these predictions are superior to assuming the drifters stay at their initial position. Vertical shear between the effective depth of long‐range CODAR measurements (∼2.4 m) and that of drifters (0.65 m) causes the drifters to move more rapidly downwind than predicted. This bias is absent when standard‐range CODAR currents (effective depth ∼0.5 m) are used, implying that drifter leeway is not the cause of the bias. Particle trajectories were computed using CODAR data and the random‐flight model for 24‐hour intervals using a Monte Carlo approach to determine the 95% confidence interval of position predictions. Between 80% and 90% of real drifters were located within the predicted confidence interval, in reasonable agreement with the expected 95% success rate. In contrast, predictions using the random‐walk approach proved inconsistent with observations unless the diffusion coefficient was increased to approximately the random‐flight value. The consistency of the random‐flight uncertainty estimates and drifter data supports the use of our methodology for estimating model parameters from drifter‐CODAR velocity differences.
Active dust devils in Gusev crater, Mars: Observations from the Mars Exploration Rover Spirit
Authors: Greeley Ronald , Whelley Patrick L. , Arvidson Raymond E. , Cabrol Nathalie A. , Foley Daniel J. , Franklin Brenda J. , Geissler Paul G. , Golombek Matthew P. , Kuzmin Ruslan O. , Landis Geoffrey A. , Lemmon Mark T. , Neakrase Lynn D. V. , Squyres Steven W. , Thompson Shane D.
Published: December 2006

A full dust devil “season” was observed from Spirit from 10 March 2005 (sol 421, first active dust devil observed) to 12 December 2005 (sol 691, last dust devil seen); this corresponds to the period Ls 173.2° to 339.5°, or the southern spring and summer on Mars. Thermal Emission Spectrometer data suggest a correlation between high surface temperatures and a positive thermal gradient with active dust devils in Gusev and that Spirit landed in the waning stages of a dust devil season as temperatures decreased. 533 active dust devils were observed, enabling new characterizations; they ranged in diameter from 2 to 276 m, with most in the range of 10–20 m in diameter, and occurred from about 0930 to 1630 hours local true solar time (with the maximum forming around 1300 hours) and a peak occurrence in southern late spring (Ls ∼ 250°). Horizontal speeds of the dust devils ranged from <1 to 21 m/s, while vertical wind speeds within the dust devils ranged from 0.2 to 8.8 m/s. These data, when combined with estimates of the dust content within the dust devils, yield dust fluxes of 3.95 × 10−9 to 4.59−4 kg/m2/s. Analysis of the dust devil frequency distribution over the inferred dust devil zone within Gusev crater yields ∼50 active dust devils/km2/sol, suggesting a dust loading into the atmosphere of ∼19 kg/km2/sol. This value is less than one tenth the estimates by Cantor et al. (2001) for regional dust storms on Mars.
Straining of colloidal particles in saturated porous media
Authors: Xu Shangping , Gao Bin , Saiers James E.
Published: December 2006

Straining may influence the mobility of colloid‐sized particles within groundwater aquifers as well as within granular filters that are used in wastewater treatment. We conducted column transport experiments using latex microspheres as the colloids and quartz sand as the porous medium to investigate the response of colloid straining to changes in colloid diameter (dp) and sand grain diameter (dg). For these experiments the negatively charged microspheres were suspended in deionized water, and the quartz sand was thoroughly cleaned to minimize physicochemical deposition (attachment), which permitted the determination of straining in an unambiguous way. The measurements of strained (immobile phase) and effluent (aqueous phase) colloid concentrations could be described with a transport model that accounted for an exponential decline in straining rates with increasing concentrations of strained colloids. Best fit values of the model coefficient that quantified clean bed straining rates (ko) were negligibly small for dp/dg < 0.008 and, above this threshold, varied linearly with dp/dg. Our findings suggest that accurate inferences on the mobility of colloid‐sized particles will require consideration of the effects of straining when dp/dg exceeds 0.008.
Anisotropy factor of saturated and unsaturated soils
Authors: Assouline S. , Or D.
Published: December 2006

Variations in the degree of anisotropy in soil hydraulic conductivity with changes in water saturation (Se) may adversely impact predictability of flow and transport processes. The conceptual “layered cake” model was extended to consider effects of bulk density variations within a particular soil type. The anisotropy factor as function of matric potential A(ψ) exhibits different behavior for different soil textures. For example, A(ψ) for sand shows complex behavior with a local maximum just before A(ψ) drops to a minimum where sand becomes isotropic (A(ψ) = 1) near ψ = −1.0 bar. Experimentally determined relationships between soil bulk density and hydraulic properties show existence of strong correlation between A(Se) and the ratio of extreme hydraulic conductivity values K(Se)max/K(Se)min for each soil for the entire saturation range and across several soil types. The strong dependency of anisotropy factor on extreme values Kmax and Kmin was investigated for four simple and continuous probability density functions of bulk density. Additionally, simple analytical expressions for a binary system of alternating layers with Kmax and Kmin only were derived. An upper bound for A(Se) is obtained with equal weight for Kmax and Kmin (w = 0.5). The experimental data and model predictions agreed for certain values of weight assigned to either Kmax or Kmin (∼w = 0.02). Other approximations based on Kmax and Kmin provide simple estimates for anisotropy factor that could be related to shape of statistical distribution of hydraulic conductivity.
Effects of annealing on carrier lifetime in 4H-SiC
Authors: Jenny J. R. , Malta D. P. , Tsvetkov V. F. , Das M. K. , Hobgood H. McD. , Carter C. H. , Kumar R. J. , Borrego J. M. , Gutmann R. J. , Aavikko R.
Published: December 2006

We present results of a thermal anneal process that increases the minority carrier lifetime in SiC substrates to in excess of 3μs, compared to the starting as-grown substrates with lifetimes typically in the <10ns range. Measurement of lifetimes was conducted using microwave-photoconductive decay. Electron beam induced current measurements exhibited minority carrier diffusion lengths of up to 65μm, confirming the enhanced carrier lifetime of the annealed substrate material. Additionally, positron annihilation spectroscopy and deep level transient spectroscopic (DLTS) analysis of samples subjected to this anneal process indicated that a significant reduction of deep level defects, particularly Z1∕Z2, may account for the significantly enhanced lifetimes. The enhanced lifetime is coincident with a transformation of the original as-grown crystal into a strained or disordered lattice configuration as a result of the high temperature anneal process. The operational performance of p-i-n diodes employing drift layers fabricated from the annealed high-lifetime substrates confirmed conductivity modulation in the diodes consistent with ambipolar carrier lifetimes in the microsecond range.
Existence and computation of optimally localized coherent states
Authors: Holschneider Matthias , Teschke Gerd
Published: December 2006

This paper is concerned with localization properties of coherent states. Instead of classical uncertainty relations we consider “generalized” localization quantities. This is done by introducing measures on the reproducing kernel. In this context we may prove the existence of optimally localized states. Moreover, we provide a numerical scheme for deriving them.
On bipartite pure-state entanglement structure in terms of disentanglement
Authors: Herbut Fedor
Published: December 2006

Schrödinger’s disentanglement [E. Schrödinger, Proc. Cambridge Philos. Soc. 31, 555 (1935)], i.e., remote state decomposition, as a physical way to study entanglement, is carried one step further with respect to previous work in investigating the qualitative side of entanglement in any bipartite state vector. Remote measurement (or, equivalently, remote orthogonal state decomposition) from previous work is generalized to remote linearly independent complete state decomposition both in the nonselective and the selective versions. The results are displayed in terms of commutative square diagrams, which show the power and beauty of the physical meaning of the (antiunitary) correlation operator inherent in the given bipartite state vector. This operator, together with the subsystem states (reduced density operators), constitutes the so-called correlated subsystem picture. It is the central part of the antilinear representation of a bipartite state vector, and it is a kind of core of its entanglement structure. The generalization of previously elaborated disentanglement expounded in this article is a synthesis of the antilinear representation of bipartite state vectors, which is reviewed, and the relevant results of [Cassinelli et al., J. Math. Anal. Appl. 210, 472 (1997)] in mathematical analysis, which are summed up. Linearly independent bases (finite or infinite) are shown to be almost as useful in some quantum mechanical studies as orthonormal ones. Finally, it is shown that linearly independent remote pure-state preparation carries the highest probability of occurrence. This singles out linearly independent remote influence from all possible ones.
Theoretical modeling on the magnetization by electric field through product property
Authors: Huang Z.
Published: December 2006

Multilayer composites of piezoelectric and magnetostrictive materials can be designed to exhibit the magnetoelectric (ME) effect. This ME effect can be realized as an electric polarization induced by a magnetic field (called MEH effect) or a magnetization by an electric field (called MEE effect). Theoretical modeling of the MEE effect for 2-2 connectivity composites has been developed for three different boundary conditions for perfect coupling at the interface. The calculated MEE coefficients using material properties of piezoelectric lead zirconate titanate and magnetostrictive Terfenol-D are a few orders of magnitude larger than those of single phase ME materials and the calculated values are compared with experimental results in the literature.
Hydrostatic pressure dependence of polarization-induced interface charge in AlGaN∕GaN heterostructures determined by means of capacitance-voltage characterization
Authors: Franssen G. , Plesiewicz J. A. , Dmowski L. H. , Prystawko P. , Suski T. , Krupczyński W. , Jachymek R. , Perlin P. , Leszczyński M.
Published: December 2006

The hydrostatic pressure dependence of the polarization-induced interface charge in an AlGaN∕GaN heterostructure is investigated via capacitance-voltage (C-V) characterization of the two-dimensional electron gas (2DEG) at the heterojunction. The linear pressure coefficient of (3.3±0.4)×1011cm−2GPa−1 of the polarization-induced interface charge as obtained via C-V measurements of the investigated (28nmAl0.26Ga0.74N)∕GaN heterostructure agrees well with existing theoretical and experimental data (obtained via Hall-effect measurements). It is demonstrated that C-V characterization can be applied even when Hall-effect measurements of the 2DEG are inconclusive because of parallel conduction via the underlying GaN layer. In addition, we discuss the influence on the 2DEG concentration of interface trap states, which introduce a dependence of the measured 2DEG concentration on C-V test frequency. It is shown, however, that this effect does not influence the value of the pressure coefficient of the polarization-induced interface charge as determined via C-V characterization. Collaterally, the applicability of capacitance measurements of AlGaN∕GaN heterostructures for pressure sensing applications is confirmed.
Shape invariance through Crum transformation
Authors: Organista José Orlando , Nowakowski Marek , Rosu H. C.
Published: December 2006

We show in a rigorous way that Crum’s result regarding the equal eigenvalue spectrum of Sturm-Liouville problems can be obtained iteratively by successive Darboux transformations. Furthermore, it can be shown that all neighboring Darboux-transformed potentials of higher order, uk and uk+1, satisfy the condition of shape invariance provided the original potential u does so. Based on this result, we prove that under the condition of shape invariance, the nth iteration of the original Sturm-Liouville problem defined solely through the shape invariance is equal to the nth Crum transformation.
Measurements of the fluid and particle mobilities in strong electric fields
Authors: Kumar Anil , Elele Ezinwa , Yeksel Mike , Khusid Boris , Qiu Zhiyong , Acrivos Andreas
Published: December 2006

We present a method for measuring both the fluid and particle velocities in strong electric fields and carefully analyze the repeatability and reproducibility of the measurements. The experiments were conducted in 50-μm capillaries containing dilute aqueous suspensions of 4-μm polystyrene spheres subjected to dc as well as ac (5−50Hz) fields of strengths up to 1 and 0.6kV∕cm, respectively. These measurements indicate that the predictions of classical linear theories for electrokinetic phenomena apply well beyond the range of relatively weak electric fields for which these theories were developed. The results of our studies are critical for the quantification of microanalytical systems which make use of electrokinetic phenomena for the transport, control, and manipulation of fluids and particles.
Setup of a fluorescence lifetime and spectral correlated acquisition system for two-photon microscopy
Authors: Spriet Corentin , Trinel Dave , Laffray Sophie , Landry Marc , Vandenbunder Bernard , Heliot Laurent , Barbillat Jacques
Published: December 2006

In this article we present a complete laser scanning microscope designed for simultaneous spectral and lifetime measurements from every point of the specimen located within the field of view. The pulsed laser source used for two-photon excitation provides good spatial resolution with minimal invasivity. In addition, the detection module was optimized for minimal photon loss, allowing laser power minimization and further reduction of cells photodamage. Analysis of biological samples illustrates the performances of this configuration, particularly when applied to fluorescent resonance energy transfer (FRET) measurements. Indeed, multiparametric acquisition is particularly useful to discriminate between FRET and artifactual response due to acquisition invasivity or cell heterogeneity. Combined with adapted homemade driving software, this system is stable, portable, and optimized for living cell studies.
CO oxidation on electrically charged gold nanotips
Authors: McEwen J.-S. , Gaspard P.
Published: December 2006

We report a study of the oxidation of CO on a gold nanotip in the presence of high electrostatic fields. With the binding energies obtained using density functional theory as a function of the electric field, a simple field-dependent kinetic model based on the Langmuir-Hinshelwood mechanism is set up. We show that the dissociative adsorption of oxygen on gold happens only below a negative critical value of the electric field while the binding of CO on gold is enhanced for positive values. We explain the propagation of a wave observed in field ion microscopy experiments and predict that the oxidation of CO occurs on negatively charged gold clusters.
Laser spectroscopy of NiBr: New electronic states and hyperfine structure
Authors: Ye Jianjun , Leung J. W.-H. , Cheung A. S.-C.
Published: December 2006

Laser induced fluorescence spectrum of NiBr in the visible region between 604 and 666nm has been recorded and analyzed. Fourteen bands belonging to three electronic transition systems, namely, [15.1]Δ5∕22–XΠ3∕22, [15.1]Π3∕22–XΠ3∕22, and [14.0]Δ5∕22–XΠ3∕22 have been observed. Spectra of isotopic molecules were also observed and analyzed. Detailed analysis of the recorded spectra indicated that the two electronic states [15.1]Π3∕22 and [15.1]Δ5∕22 lie about 1cm−1 apart from each other and J-dependent perturbation due to spin-uncoupling interaction has been observed. Least squares fitting procedures involving deperturbation matrix elements were used to fit the observed line positions, which yielded accurate molecular constants for the [15.1]Π3∕22 and [15.1]Δ5∕22 states. In addition, the (1,0) band of the [15.1]Δ5∕22–XΠ3∕22 transition shows partially resolved hyperfine structure that was caused by the interaction of unpaired electron with the magnetic moment of the Br nucleus (nuclear spin of I=3∕2) in the excited state. The rapid decrease in hyperfine width as J increases suggests that the hyperfine coupling in the excited state conforms to Hund’s case (aβ) coupling scheme.
Improvement in electrical characteristics of high-k Al2O3 gate dielectric by field-assisted nitric oxidation
Authors: Chuang Kai-Chieh , Hwu Jenn-Gwo
Published: December 2006

The authors perform a simple technique for the improvements in both current density reliability of high-k Al2O3 gate dielectrics. An Al2O3 was prepared by chemical oxidation at an appropriate electrical field in nitric acid at room temperature then furnace annealed at 650°C in N2. The interface trap-induced capacitance was used to investigate the interfacial property between the gate dielectric Si substrate. On the other hand the stress induced leakage current (SILC) was measured for characterizing the property of bulk oxide. It was found that the electrical characteristics of bulk oxide including leakage breakdown field SILC, were much improved without sacrificing interfacial property. The improvement can be ascribed to the compensation oxidation process.
Electron heating mode transitions in dual frequency capacitive discharges
Authors: Turner M. M. , Chabert P.
Published: December 2006

The authors consider electron heating in the sheath regions of capacitive discharges excited by a combination of two frequencies, one much higher than the other. There is a common supposition that in such discharges the higher frequency is the dominant source of electron heating. In this letter, the authors discuss closed analytic expressions quantifying the Ohmic and collisionless electron heating in a dual frequency discharge. In both cases, the authors show that the lower frequency parameters strongly influence the heating effect. Moreover, this influence is parametrically different, so that the dominant heating mechanism may be changed by varying the low frequency current density.
Thickness-dependent magnetic domain change in epitaxial MnAs films on GaAs(001)
Authors: Ryu Kwang-Su , Kim JinBae , Lee YoungPak , Akinaga Hiro , Manago Takashi , Viswan Ravindranath , Shin Sung-Chul
Published: December 2006

The authors report the change of the magnetic domain structure, dependent on the film thickness of MnAs films epitaxially grown on GaAs(001), investigated by magnetic force microscopy. Interestingly, as the film thickness decreases, the domain structure within the ferromagnetic α-MnAs stripes changes from a head-on domain structure to a simple 180° one around a thickness of 250nm. This result is understood by the change in the demagnetizing factor of the ferromagnetic stripes with the film thickness.
Well-aligned in situ composites in directionally solidified Fe–Ni peritectic system
Authors: Su Yanqing , Luo Liangshun , Li Xinzhong , Guo Jingjie , Yang Huimin , Fu Hengzhi
Published: December 2006

Well-aligned in situ composites obtained in directionally solidified Fe–Ni peritectic system are formed by nonisothermal cellular coupled growth instead of isothermal coupled growth because of morphological instabilities. Peritectic coupled growth, with a plane interface like eutectic coupled growth, is always unstable due to the influence of peritectic reaction around the liquid/δ∕γ trijunctions. However, cellular nonisothermal peritectic coupled growth, in which one of the two solid phases bulges towards the liquid ahead of the other one, can reach a steady state and produce well-aligned in situ composites under proper growth conditions and sample composition.