bluuebunny/crossref_metadata_2025 huggingface dataset:
Validation of Turkish and English Versions of the Schizotypal Personality Questionnaire-B
Authors: Aycicegi Ayse , Dinn Wayne M. , Harris Catherine L.
Published: February 2005

Abstract. We present normative data for a Turkish translation of the Schizotypal Personality Questionnaire-B (SPQ-B). The SPQ-B is a brief, self-report screening instrument developed by Raine and Benishay (1995) and is used to evaluate respondents for the presence of schizotypal personality features. We describe the internal consistency and test-retest reliability of the Turkish instrument and report intercorrelations among subfactors and total SPQ-B score. For comparison purposes, we present normative data for the SPQ-B (English version) from two studies examining schizotypy among nonclinical student samples in the United States. We report α coefficients and assess the convergent validity of the SPQ-B by examining the relationship between scores on the SPQ-B and performance on two existing measures of schizotypy and schizophrenic-spectrum personality disorders. Central tendency, distribution of scores, factor structure, and intercorrelations in both Turkish and US samples were similar, suggesting that our Turkish translation of the SPQ-B is a culturally valid instrument.
Factorial Structure of the Quality of Life Questionnaire in a Spanish Sample of Visually Disabled Adults1
Authors: Verdugo Miguel Angel , Prieto Gerardo , Caballo Cristina , Peláez Ana
Published: February 2005

Abstract. This study presents a new Spanish version of the Quality of Life Questionnaire (QOL.Q; Schalock & Keith, 1993a ) for use with adults with visual disability. The QOL.Q was originally developed in English and designed to measure four dimensions of quality of life in populations with mental retardation. The purpose of this paper is to study some psychometric properties of the Spanish translation for a population with visual disabilities. Confirmatory factor analysis (CFA) has been used to check whether the factorial structure of the Spanish version of the questionnaire was similar to the original version. The questionnaire was applied to a sample of 364 adults with visual disability. As the results indicated that the data was not appropriate for the aforementioned structure, an Exploratory factor analysis was carried out with the aim of determining which factorial structure would be most appropriate. As a result, the Spanish version of the questionnaire consists of 24 items assigned to three subscales: Competence (8), Satisfaction (10), and Self-determination (6). A new CFA permitted the testing of the appropriate fit between the responses and the new proposed model. Psychometric analyses of these subscales seem to indicate good measurement properties of the new scale.
Joint Correspondence Analysis (JCA) by Maximum Likelihood
Authors: Vermunt Jeroen K. , Anderson Carolyn J.
Published: February 2005

Abstract. Parameter estimation in joint correspondence analysis (JCA) is typically performed by weighted least squares using the Burt matrix as the data matrix. In this paper, we show how to estimate the JCA model by means of maximum likelihood. For that purpose, JCA is defined as a model for the full K-way distribution by generalizing the correspondence analysis model for three-way tables proposed by Choulakian (1988a , 1988b ). The advantage of placing JCA in a more formal statistical framework is that standard chi-squared tests can be applied to assess the goodness-of-fit of unrestricted and restricted models.
A Hierarchy of Multinomial Models for Multidimensional Source Monitoring
Authors: Meiser Thorsten
Published: February 2005

Abstract. Several models have been proposed for the measurement of cognitive processes in source monitoring. They are specified within the statistical framework of multinomial processing tree models and differ in their assumptions on the storage and retrieval of multidimensional source information. In the present article, a hierarchical relationship is demonstrated between multinomial models for crossed source information ( Meiser & Bröder, 2002 ), for partial source memory ( Dodson, Holland, & Shimamura, 1998 ) and for several sources ( Batchelder, Hu, & Riefer, 1994 ). The hierarchical relationship allows model comparisons and facilitates the specification of identifiability conditions. Conditions for global identifiability are discussed, and model comparisons are illustrated by reanalyses and by a new experiment on the storage and retrieval of multidimensional source information.
Comparison of the Performance of Nonparametric and Parametric MANOVA Test Statistics when Assumptions Are Violated
Authors: Finch Holmes
Published: February 2005

Abstract. Multivariate analysis of variance (MANOVA) is a useful tool for social scientists because it allows for the comparison of response-variable means across multiple groups. MANOVA requires that the observations are independent, the response variables are multivariate normally distributed, and the covariance matrix of the response variables is homogeneous across groups. When the assumptions of normality and homogeneous covariance matrices are not met, past research has shown that the type I error rate of the standard MANOVA test statistics can be inflated while their power can be attenuated. The current study compares the performance of a nonparametric alternative to one of the standard parametric test statistics when these two assumptions are not met. Results show that when the assumption of homogeneous covariance matrices is not met, the nonparametric approach has a lower type I error rate and higher power than the most robust parametric statistic. When the assumption of normality is untenable, the parametric statistic is robust, and slightly outperforms the nonparametric statistic in terms of type I error rate and power.
Local Contextual Cuing in Visual Search
Authors: Hoffmann Joachim , Sebald Albrecht
Published: February 2005

Abstract. Previous research has indicated that covariations between the global layout of search displays and target locations result in contextual cuing: the global context guides attention to probable target locations. The present experiments extend these findings by showing that local redundancies also facilitate visual search. Participants searched for randomly located targets in invariant homogenous displays, i.e., the global context provided information neither about the location nor about the identity of the target. The only redundancy referred to spatial relations between the targets and certain distractors: Two of the distractors were frequently presented next to the targets. In four of five experiments, targets with frequent flankers were detected faster than targets with rare flankers. The data suggest that this local contextual cuing does not depend on awareness of the redundant local topography but needs the redundantly related stimuli to be attended to.
The Odd-Even Effect in Addition
Authors: Vandorpe Stefaan , De Rammelaere Stijn , Vandierendonck André
Published: February 2005

Abstract. The odd-even effect is a well documented finding in the literature on mental arithmetic, at least for multiplication. It implies that false answers with the same parity as the correct answer are rejected more slowly than false answers with a different parity. For addition, this effect is not so well documented. The study by Krueger and Hallford (1984 ) is the only one that investigated odd-even effects for addition. However, they did not investigate odd-even effects per problem, even though there are indications that problem type can modulate odd-even effects for multiplication ( Lemaire & Reder, 1999 ). Therefore, we wanted to get more insight into odd-even effects for addition by investigating odd-even effects per problem type. Our results extended the findings of Krueger and Hallford. First of all, we found an interaction between split and problem type. The most important and new result of present study, however, was a strong parity effect for E + E problems. We discuss our results in terms of two alternative explanations for odd-even effects, namely use of a parity rule on the one hand and familiarity with even outcomes on the other.
Inconsistent Probability Estimates of a Hypothesis
Authors: Bonini Nicolao , Gonzalez Michel
Published: February 2005

Abstract. This paper studies consistency in the judged probability of a target hypothesis in lists of mutually exclusive nonexhaustive hypotheses. Specifically, it controls the role played by the support of displayed competing hypotheses and the relatedness between the target hypothesis and its alternatives. Three experiments are reported. In all experiments, groups of people were presented with a list of mutually exclusive nonexhaustive causes of a person’s death. In the first two experiments, they were asked to judge the probability of each cause as that of the person’s decease. In the third experiment, people were asked for a frequency estimation task. Target causes were presented in all lists. Several other alternative causes to the target ones differed across the lists. Findings show that the judged probability/frequency of a target cause changes as a function of the support of the displayed competing causes. Specifically, it is higher when its competing displayed causes have low rather than high support. Findings are consistent with the contrastive support hypothesis within the support theory.
Remotely‐sensed chl a at the Chesapeake Bay mouth is correlated with annual freshwater flow to Chesapeake Bay
Authors: Acker James G. , Harding Lawrence W. , Leptoukh Gregory , Zhu Tong , Shen Suhung
Published: February 2005

High freshwater flow delivers excess nutrients to Chesapeake Bay, leading to increased phytoplankton biomass, turbidity, and eutrophication. Low flow in 2002 was associated with a persistent drought that terminated abruptly in autumn 2002, followed by extremely high flow in 2003. This large difference in flow caused improved water quality in 2002 as nutrient loading subsided, and degraded water quality in 2003 with increased loading associated with high flow. We analyzed remotely sensed chlorophyll (chl a) data using an online data analysis tool to quantify the effect of sequential low and high freshwater flow on phytoplankton biomass near the mouth of the Bay. Chl a in the study area was significantly higher in 2003 than in 2002, consistent with strong forcing by freshwater flow and nutrient loading in the nutrient‐limited region of the Bay.
Improvements in cloud identification over snow/ice surfaces from ERBE to CERES
Authors: Sun Moguo , Cess Robert D.
Published: February 2005

The procedure used in the Earth Radiation Budget Experiment for identifying the presence of clouds over snow/ice surfaces is known to have shortcomings, and this is corroborated through use of surface insolation measurements at the South Pole as an independent means of identifying clouds. These surface insolation measurements are then used to validate the more detailed cloud identification scheme used in the follow‐up Clouds and the Earth's Radiant Energy System (CERES), and this validation is extended to the polar night through use of CERES measurements of the outgoing longwave radiation.
Thermospheric densities derived from spacecraft orbits: Accurate processing of two‐line element sets
Authors: Picone J. M. , Emmert J. T. , Lean J. L.
Published: February 2005

This paper presents a new, fast, and accurate method for retrieving the total mass density of the upper atmosphere from routinely compiled trajectories of objects in low Earth orbit. Comparison to density values from state‐of‐the‐art precision orbit determination calculations on routine tracking observations shows our results to be of comparable accuracy at vastly lower computational and administrative costs, a result both unprecedented and unforeseen. This means that the difficulty of obtaining raw observational data and precision orbit determination software is no longer an obstacle to the scientific analysis of orbits. The accessibility of orbital elements and the speed and accuracy of the new method enable the use of a vast and growing archive of global data for analysis of thermospheric evolution and responses to solar, and possibly geomagnetic, forcing. The new procedure defines precisely the effective density values that may be extracted from orbit data; these values are explicitly independent of any atmospheric model. The discussion also contrasts the new approach with past analytic methods and with standard precision orbit techniques.
On the aggregate‐scale partitioning of solar radiation in Arctic sea ice during the Surface Heat Budget of the Arctic Ocean (SHEBA) field experiment
Authors: Perovich Donald K.
Published: February 2005

The partitioning of the incident solar irradiance among reflection to the atmosphere, absorption in the snow and ice, and transmission to the ocean is a critical component of the summer melt cycle of Arctic sea ice. Observations from a year‐long field experiment (Surface Heat Budget of the Arctic Ocean (SHEBA)) showed that of the solar radiation incident between 1 April and 5 October 1998, 68% was reflected to the atmosphere, 24% was absorbed in the snow and ice, and 8% was transmitted to the ocean. The amount of energy reflected to the atmosphere was greatest in May, when the surface albedo and the incident irradiance were large. The energy absorbed in the snow and ice increased slowly in April and May in conjunction with the increase in incident solar irradiance, followed by a sharp increase in June associated with the onset of melt. In spring, virtually none of the solar energy incident on snow‐covered sea ice is transmitted to the ocean compared to over 90% of that incident on leads. The energy transmitted to the ocean reached a maximum near the end of the melt season in mid‐August when the albedo and ice thickness were at minima and lead and pond fractions were at maxima. While much of the solar energy transmitted to the ocean was through leads, substantial portions were also transmitted through bare ice (23%) and ponded ice (16%). During the melt season, the combined energy transmitted through bare ice and ponds was equivalent to that through leads. This marked a significant change in the interaction of solar energy with the sea ice cover, with substantial amounts of solar energy transmitted to the ocean through the thin summer ice cover of SHEBA compared to the thicker ice studied in 1975 (Arctic Ice Dynamics Joint Experiment (AIDJEX)).
Estimating spatially variable representative elementary scales in fractured architecture using hydraulic head observations
Authors: Wellman Tristan P. , Poeter Eileen P.
Published: February 2005

Water resources within large‐scale fractured aquifers are typically evaluated using continuum models. While any arbitrary scale of continuum can be imposed to represent fracture architecture, using the representative elementary volume eliminates errors that result from estimating network connectivity. In traditional theory, representative elementary scales (RES) are equal in magnitude and geometry throughout a domain and are normally determined using a structural indicator such as porosity or effective hydraulic conductivity. We present a fluid‐based methodology, analyzing scale‐dependent energy variation, to estimate RES using relatively low cost, readily available hydraulic head data. Hydraulic head predictions of RES (HYRES) reveal a spatial variation in elementary scale consistent with the flow field and fracture architecture. Porosity predictions of RES (PORRES) incorporate the structural effect of disconnected fracture regions but do not account for fluid behavior. RES estimated from hydraulic conductivity (KRES) are sensitive to fracture connectivity, which controls fluid movement, but are difficult to quantify because of scale and spatial variability. HYRES may be the superior approach for evaluating water resources because it is sensitive to fracture connectivity and avoids complications with scale and spatially dependent averaging. Our method is sensitive to fracture density, clustering, connectivity, and flow direction, but is insensitive to the magnitude of hydraulic gradient. HYRES is a novel approach to estimating spatially variable RES that improves water resource evaluation and flow characterization in fractured aquifers.
Mechanisms of inverse agonist action at D2 dopamine receptors
Authors: Roberts David J , Strange Philip G
Published: February 2005

Mechanisms of inverse agonist action at the D2(short) dopamine receptor have been examined.

Discrimination of G‐protein‐coupled and ‐uncoupled forms of the receptor by inverse agonists was examined in competition ligand‐binding studies versus the agonist [3H]NPA at a concentration labelling both G‐protein‐coupled and ‐uncoupled receptors.

Competition of inverse agonists versus [3H]NPA gave data that were fitted best by a two‐binding site model in the absence of GTP but by a one‐binding site model in the presence of GTP. Ki values were derived from the competition data for binding of the inverse agonists to G‐protein‐uncoupled and ‐coupled receptors. Kcoupled and Kuncoupled were statistically different for the set of compounds tested (ANOVA) but the individual values were different in a post hoc test only for (+)‐butaclamol.

These observations were supported by simulations of these competition experiments according to the extended ternary complex model.

Inverse agonist efficacy of the ligands was assessed from their ability to reduce agonist‐independent [35S]GTPγS binding to varying degrees in concentration–response curves. Inverse agonism by (+)‐butaclamol and spiperone occurred at higher potency when GDP was added to assays, whereas the potency of (−)‐sulpiride was unaffected.

These data show that some inverse agonists ((+)‐butaclamol, spiperone) achieve inverse agonism by stabilising the uncoupled form of the receptor at the expense of the coupled form. For other compounds tested, we were unable to define the mechanism.

British Journal of Pharmacology (2005) 145, 34–42. doi:10.1038/sj.bjp.0706073
Purinergic modulation of cardiovascular function in the rat locus coeruleus
Authors: Yao Song T , Lawrence Andrew J
Published: February 2005

The purpose of the present study was to determine whether purines exerted a physiological role in central cardiovascular modulation at the level of the locus coeruleus (LC).

In pentobarbitone‐anaesthetised Wistar–Kyoto rats, unilateral microinjection of ATP or α,β‐methyleneATP into the LC elicited dose‐related decreases in blood pressure and heart rate. Unilateral microinjection of the P2 purinoceptor antagonists suramin and PPADS, caused pressor and tachycardic responses. Administration of the selective P2X1 receptor antagonist NF‐279 had no effect. While both ATP and L‐glutamate (L‐GLU) resulted in depressor responses after intra‐LC microinjection, following intra‐LC microinjection of P2 purinoceptor antagonists into the LC, the effects of subsequent administration of either ATP or L‐GLU were functionally reversed, such that a pressor response ensued.

Microinjection of noradrenaline into the LC caused an increase in blood pressure and heart rate; however, the α2‐adrenoceptor antagonist idazoxan had no cardiovascular effects, but did prevent the pressor response to PPADS or suramin. In addition, coinjection of idazoxan with either suramin or PPADS abolished the ATP and L‐GLU mediated pressor responses observed following either suramin or PPADS administration.

The present data suggest that firstly, purines are capable of acting within the LC to ultimately modulate the cardiovascular system and secondly, that there is apparently a functional interaction between tonically active purinergic and noradrenergic systems within the LC of the rat.

British Journal of Pharmacology (2005) 145, 342–352. doi:10.1038/sj.bjp.0706179
Analysis of copper-rich precipitates in silicon: Chemical state, gettering, and impact on multicrystalline silicon solar cell material
Authors: Buonassisi Tonio , Marcus Matthew A. , Istratov Andrei A. , Heuer Matthias , Ciszek Theodore F. , Lai Barry , Cai Zhonghou , Weber Eicke R.
Published: February 2005

In this study, synchrotron-based x-ray absorption microspectroscopy (μ-XAS) is applied to identify the chemical states of copper-rich clusters within a variety of silicon materials, including as-grown cast multicrystalline silicon solar cell material with high oxygen concentration and other silicon materials with varying degrees of oxygen concentration and copper contamination pathways. In all samples, copper silicide (Cu3Si) is the only phase of copper identified. It is noted from thermodynamic considerations that unlike certain metal species, copper tends to form a silicide and not an oxidized compound because of the strong silicon–oxygen bonding energy; consequently the likelihood of encountering an oxidized copper particle in silicon is small, in agreement with experimental data. In light of these results, the effectiveness of aluminum gettering for the removal of copper from bulk silicon is quantified via x-ray fluorescence microscopy, and a segregation coefficient is determined from experimental data to be at least (1–2)×103. Additionally, μ-XAS data directly demonstrate that the segregation mechanism of Cu in Al is the higher solubility of Cu in the liquid phase. In light of these results, possible limitations for the complete removal of Cu from bulk mc-Si are discussed.
Transmission of steady and oscillatory fluid shear stress across epithelial and endothelial surface structures
Authors: Han Yuefeng , Ganatos Peter , Weinbaum Sheldon
Published: February 2005

The glycocalyx on the apical surface of vascular endothelial cells and the microvilli and cilia on kidney epithelial cells have been modeled as surface layers with a hexagonal arrangement of structural elements. These elements have been proposed to serve a mechanosensory function in the initiation of intracellular signaling by fluid shear stress. In this paper we examine the response of these surface layers when steady or oscillating shear is applied at their outer edge. In the case of steady shear, our results show that the deflection of the structural elements is proportional to the product of the applied shear stress and their length L and inversely proportional to the natural damped vibration frequency of the structural element ωc. A fluid velocity boundary layer develops at the outer edge of the surface layers when the dimensionless Brinkman parameter α=L∕KP, where KP is the Darcy permeability, is asymptotically large. In the case of oscillating shear, we find that the motions of both the fluid and structural elements are in a quasisteady state at physiological conditions. No attenuation or phase shift of the torque is induced by the hydrodynamic drag when the applied frequency ω<ωc or ωr(=ω∕ωc)<1. However, the velocity at the tips of the structural element is π∕2 out of phase with the applied shear in this frequency range, due to the elastic recoil of the element. Furthermore, the fluid velocity at the tips can also be out of phase with the applied shear at large α if the closely spaced structural elements of the glycocalyx on endothelial cells or microvilli on proximal tubule cells transport substantial fluid with them.
Radio frequency sheath formation and excitation around a stepped electrode
Authors: Barnat E. V. , Hebner G. A.
Published: February 2005

Plasma and sheath structure around a rf excited stepped electrode is investigated. Laser-induced fluorescence dip spectroscopy is used to spatially resolve sheath fields in an argon discharge while optical emission and laser-induced fluorescence are used to measure the spatial structure of the surrounding discharge for various discharge conditions and step-junction configurations. The presence of the step perturbs the spatial structure of the fields around the step as well as the excitation in the region above the step.
Heat-affected zone and ablation rate of copper ablated with femtosecond laser
Authors: Hirayama Yoichi , Obara Minoru
Published: February 2005

We describe the experimental and molecular dynamics simulation study of crystalline copper (Cu) ablation using femtosecond lasers. This study is focused on the heat-affected zone after femtosecond laser ablation and the laser ablation rate. As a result of the x-ray diffraction measurement on the ablated surface, the crystallinity of the surface is partially changed from a crystal structure into an amorphous one. At the laser fluences below the ablation threshold, the entire laser energy coupled to the Cu target is absorbed, while during the fluence regime over the threshold fluence, the ablation rate depends on the absorption coefficient, and the residual energy which is not used for the ablation, is left in the Cu substrate. The heat-affected zone at the fluences below the threshold is estimated to be greater than that over the threshold fluence. In addition, the laser ablation of Cu is theoretically investigated by a two-temperature model and molecular dynamics (MD) simulation to explain the heat-affected zone and ablation rate. The MD simulation takes into account the electron temperature and thermal diffusion length calculated by the two-temperature model. Variation in the lattice temperature with time and depth is calculated by the MD simulation coupled with the two-temperature model. The experimental ablation rate and the heat-affected zone are theoretically well explained.
Structures of Mo2Oy− and Mo2Oy (y=2, 3, and 4) studied by anion photoelectron spectroscopy and density functional theory calculations
Authors: Yoder Bruce L. , Maze Joshua T. , Raghavachari Krishnan , Jarrold Caroline Chick
Published: February 2005

The competitive structural isomers of the Mo2Oy−∕Mo2Oy (y=2, 3, and 4) clusters are investigated using a combination of anion photoelectron (PE) spectroscopy and density functional theory calculations. The PE spectrum and calculations for MoO3−∕MoO3 are also presented to show the level of agreement to be expected between the spectra and calculations. For MoO3− and MoO3, the calculations predict symmetric C3v structures, an adiabatic electron affinity of 3.34 eV, which is above the observed value 3.17(2) eV. However, there is good agreement between observed and calculated vibrational frequencies and band profiles. The PE spectra of Mo2O2− and Mo2O3− are broad and congested, with partially resolved vibrational structure on the lowest energy bands observed in the spectra. The electron affinities (EAas) of the corresponding clusters are 2.24(2) and 2.33(7) eV, respectively. Based on the calculations, the most stable structure of Mo2O2− is Y shaped, with the two Mo atoms directly bonded. Assignment of the Mo2O3− spectrum is less definitive, but a O–Mo–O–Mo–O structure is more consistent with overall electronic structure observed in the spectrum. The PE spectrum of Mo2O4− shows cleanly resolved vibrational structure and electronic bands, and the EA of the corresponding Mo2O4 is determined to be 2.13(4) eV. The structure most consistent with the observed spectrum has two oxygen bridge bonds between the Mo atoms.
Hydrophobic effects on partial molar volume
Authors: Imai Takashi , Hirata Fumio
Published: February 2005

The hydrophobic effects on partial molar volume (PMV) are investigated as a PMV change in the transfer of a benzenelike nonpolar solute from the nonpolar solvent to water, using an integral equation theory of liquids. The volume change is divided into two effects. One is the “packing” effect in the transfer from the nonpolar solvent to hypothetical “nonpolar water” without hydrogen bonding networks. The other is the “iceberg” effect in the transfer from nonpolar water to water. The results indicate that the packing effect is negative and a half compensated by the positive iceberg effect. The packing effect is explained by the difference in the solvent compressibility. Further investigation shows that the sign and magnitude of the volume change depend on the solute size and the solvent compressibility. The finding gives a significant implication that the exposure of a hydrophobic residue caused by protein denaturation can either increase or decrease the PMV of protein depending on the size of the residue and the fluctuation of its surroundings.
Noncontact thermal characterization of multiwall carbon nanotubes
Authors: Wang Xinwei , Zhong Zhanrong , Xu Jun
Published: February 2005

In this work, a photothermal experiment is designed and conducted to characterize the thermal transport in carbon nanotubes (CNTs) along the axial direction exclusively. We characterize the thermal contact resistance between CNTs and the substrate. The measured value demonstrates a sound thermal contact between them. Our experimental result reveals a low thermal conductivity of the CNTs along their axial direction. The unique structure of the CNTs characterized in our work indicates that the thermal transport in the axial direction is across the carbon atomic layers. This explains why the measured thermal conductivity is much lower than theoretical predictions, in which the thermal conductivity is along the atomic layer direction. In addition, our transmission electron microscope observation of the CNTs reveals poor structural qualities, which can strongly enhance phonon scattering and reduce the thermal conductivity.
Bounds and estimates for transport coefficients of random and porous media with high contrasts
Authors: Berryman James G.
Published: February 2005

Bounds on transport coefficients of random polycrystals of laminates are presented, including the well-known Hashin–Shtrikman bounds and some rigorous bounds involving two formation factors for a two-component porous medium. A class of self-consistent estimators is then formulated based on the observed analytical structure both of these bounds and also of earlier self-consistent estimates [of the coherent potential approximation (CPA) or CPA-type]. A numerical study is made, assuming first that the internal structure (i.e., the laminated grain structure) is not known, and then that it is known. The purpose of this aspect of the study is to attempt to quantify the differences in the predictions of properties of a system being modeled when such organized internal structure is present in the medium but detailed spatial correlation information may or (more commonly) may not be available. Some methods of estimating formation factors from data are also presented and then applied to a high-contrast fluid-permeability numerical simulation data set. Hashin–Shtrikman bounds are found to be very accurate estimates for low contrast heterogeneous media. But formation factor lower bounds are superior estimates for high contrast situations. Other related bounds by Bergman that interpolate between the Hashin–Shitrikman bounds and the formation factor bounds are also briefly discussed. The self-consistent estimators developed here also tend to agree better with data than either the bounds or the CPA estimates, which themselves tend to overestimate values for high-contrast conducting composites.
Sensitivity of spectral variational multiscale methods for large-eddy simulation of isotropic turbulence
Authors: Sagaut P. , Levasseur V.
Published: February 2005

Subgrid closures in the Fourier space belonging to the variational multiscale method proposed by Hughes are investigated in the case of the incompressible freely evolving isotropic turbulence in the limit of an infinite Reynolds number. Sensitivity to the closure used at small scales is shown to be high, and different hybrid spectral closures proposed in the present study which explicitly account for the computed kinetic energy spectrum shape yield good results. The original formulation of the method is observed to suffer from an unphysical energy pile-up in the large scales, which arises from the fact that the kinetic energy transfers associated with distant triadic interactions are neglected. The use of a nonorthogonal operator to define the resolved large and small scales is proved to alleviate this problem, yielding an accurate and robust spectral variational multiscale methods for high Reynolds number flows.
A numerical study of the alpha model for two-dimensional magnetohydrodynamic turbulent flows
Authors: Mininni Pablo D. , Montgomery David C. , Pouquet Annick G.
Published: February 2005

We explore some consequences of the “alpha model,” also called the “Lagrangian-averaged” model, for two-dimensional incompressible magnetohydrodynamic (MHD) turbulence. This model is an extension of the smoothing procedure in fluid dynamics, which filters velocity fields locally while leaving their associated vorticities unsmoothed, and has proved useful for high Reynolds number turbulence computations. We consider several known effects (selective decay, dynamic alignment, inverse cascades, and the probability distribution functions of fluctuating turbulent quantities) in magnetofluid turbulence and compare the results of numerical solutions of the primitive MHD equations with their alpha-model counterparts’ performance for the same flows, in regimes where available resolution is adequate to explore both. The hope is to justify the use of the alpha model in regimes that lie outside currently available resolution, as will be the case in particular in three-dimensional geometry or for magnetic Prandtl numbers differing significantly from unity. We focus our investigation, using direct numerical simulations with a standard and fully parallelized pseudospectral method and periodic boundary conditions in two space dimensions, on the role that such a modeling of the small scales using the Lagrangian-averaged framework plays in the large-scale dynamics of MHD turbulence. Several flows are examined, and for all of them one can conclude that the statistical properties of the large-scale spectra are recovered, whereas small-scale detailed phase information (such as, e.g., the location of structures) is lost.
Turbulence in dilute polymer solutions
Authors: Liberzon A. , Guala M. , Lüthi B. , Kinzelbach W. , Tsinober A.
Published: February 2005

The work reported below is a comparative study of the properties of turbulence with weak mean flow in a Newtonian fluid and in a dilute polymer solution with an emphasis on the small scale phenomena. The main tool used is a three-dimensional particle tracking system allowing to measure and follow in a Lagrangian manner the field of velocities, as well as velocity derivatives, and thus vorticity, strain, and a variety of related and dynamically significant quantities. The comparison of data from the two flows allows to directly observe the influence of polymers on these quantities as well as the evolution of material elements in the presence of polymers.
Novel method for selective probing of ground-state rotational dynamics of solutes in solvents
Authors: Truong Thai V. , Shen Y. R.
Published: February 2005

We introduce an optical pump/probe method that allows selective measurement of ground-state rotational dynamics of solutes in liquids. It relies on employing two successive pump pulses that are adjusted to create an optical anisotropy due to the orientational distribution of only the ground-state solute molecules. Measurement on a dye-solvent system shows a large difference between the rotational diffusion rates of the ground state and the excited state of the dye molecules due to different solute–solvent interactions.
TCSPC upgrade of a confocal FCS microscope
Authors: Benda Aleš , Hof Martin , Wahl Michael , Patting Matthias , Erdmann Rainer , Kapusta Peter
Published: February 2005

We extended the measurement capabilities of the Carl Zeiss ConfoCor 1 FCS microscope by (a) using pulsed picosecond diode lasers instead of a continuous wave (CW) laser excitation, (b) introducing a fast single photon avalanche diode detector, and (c) exploiting the capabilities of the PicoQuant TimeHarp 200 board. When the time-tagged time-resolved (TTTR) mode of the TimeHarp is utilized, the complete fluorescence dynamics are recorded. That is, the time-evolution of the fluctuations and the fluorescence decay kinetics are captured simultaneously. Recording individual photon events (without on-the-fly data reduction like in hardware correlators) preserves the full information content of the measurement for virtually unlimited data analysis tasks and provides a much more detailed view of processes happening in the detection volume. For example, autocorrelation functions of dyes in a mixture can be separated and/or their cross-correlation can be investigated. These virtual two-channel measurements are performed utilizing a single detection channel setup. The time-resolved FCS is a powerful tool in biological studies and is demonstrated here on unilamellar vesicles giving clear evidence for Bodipy dye exchange between them. The described upgrade scenario is applicable to other confocal microscopes as well. In principle, any FCS system so far utilizing conventional CW lasers can benefit from pulsed excitation and the original functionality of the setup is fully preserved.
Piezoelectric–piezomagnetic multilayer with simultaneously negative permeability and permittivity
Authors: Liu H. , Zhu S. N. , Zhu Y. Y. , Chen Y. F. , Ming N. B. , Zhang X.
Published: February 2005

We study the propagation of an electromagnetic (EM) wave in piezoelectric–piezomagnetic multilayers, in which the incident EM wave excites high frequency acoustic waves and couples strongly with them through piezoelectric and piezomagnetic effects, creating dielectric polariton and magnetic polariton simultaneously. The dispersion abnormality appears at some frequency ranges where simultaneous negative permittivity and permeability can be achieved. Theoretical analysis and numerical simulation proved that this structure forms a kind of “left-handed” material.
Optoelectronic properties of three-dimensional ZnO hybrid structure
Authors: Jeong Min-Chang , Oh Byeong-Yun , Lee Woong , Myoung Jae-Min
Published: February 2005

Three-dimensional (3D) ZnO hybrid structure was fabricated by growing a ZnO buffer layer, a ZnO nanowire array, and a ZnO film continuously through the control of supersaturation conditions. Lower and upper ends of vertically aligned nanowires in this hybrid structure formed seamless interfacial contacts with the buffer layer and the film for current conduction. Photocurrent was generated only when the ultraviolet (UV) light (λ=350nm) was irradiated. This structure also exhibited different atmosphere-dependent responses to the UV light. The optoelectronic properties of the 3D structure are attributed to the photogenerated carriers and the surface reaction of negatively charged oxygen species in ZnO nanowires.
Two-dimensional micromanipulation using liquid crystals
Authors: Mieda Yoshitaka , Furutani Katsushi
Published: February 2005

We developed a two-dimensional micromanipulation method using liquid crystals. The combination of the backflow effect in the twisted nematic cell and the electrostatic force for the naturally charged microparticles causes the net movement. By adjusting the polarity and the duty ratio of the rectangular voltage, the particles can be driven two-dimensionally and bidirectionally. The velocity of the particles depended on the duty ratio, amplitude, and frequency of the applied voltage.
Transport and magnetic Jc of MgB2 strands and small helical coils
Authors: Sumption M. D. , Bhatia M. , Rindfleisch M. , Tomsic M. , Collings E. W.
Published: February 2005

The critical current densities of MgB2 monofilamentary strands with and without SiC additions were measured at 4.2 K. Additionally, magnetic Jc at B=1T was measured from 4.2 to 40 K. Various heat treatment times and temperatures were investigated for both short samples and small helical coils. SiC additions were seen to improve high field transport Jc at 4.2 K, but improvements were not evident at 1 T at any temperature. Transport results were relatively insensitive to heat treatment times and temperatures for both short samples and coils in the 700–900 °C range.
Sensitivity of exciton spin relaxation in quantum dots to confining potential
Authors: Mackowski S. , Gurung T. , Jackson H. E. , Smith L. M. , Heiss W. , Kossut J. , Karczewski G.
Published: February 2005

We observe a strong dependence of the exciton spin relaxation in CdTe quantum dots on the average dot size and the depth of the confining potential. After rapid thermal annealing, which increases the average dot size and leads to weaker confinement, we measure the spin relaxation time of the quantum dot excitons to be 1.5ns, as compared to 4.8ns found previously for the as-grown CdTe quantum dots. The annealed CdTe quantum dots exhibit also smaller values of the absolute polarization of the quantum dot emission. This dramatic enhancement of the spin scattering efficiency upon annealing is attributed to increased mixing between different spin states in larger CdTe quantum dots.
2-ps passively mode-locked Nd:YVO4 laser using an output-coupling-type semiconductor saturable absorber mirror
Authors: Fan Ya-Xian , He Jing-Liang , Wang Yong-Gang , Liu Sheng , Wang Hui-Tian , Ma Xiao-Yu
Published: February 2005

We have demonstrated stable self-starting passive mode-locking in a diode-end-pumped Nd:YVO4 laser using a semiconductor saturable absorber mirror (SESAM). An In0.25Ga0.75As single quantum-well SESAM, which was grown by the metalorganic chemical-vapor deposition technique at low temperature, acts as a passive mode-locking device and an output coupler at the same time. Continuous-wave mode-locked transform-limited pulses were obtained at 1064 nm with a pulse duration of 2.1 ps and an average output power of 1.28 W at a repetition rate of 96.5 MHz.
Monte Carlo simulation of the effects of vacuum-ultraviolet radiation on dielectric materials
Authors: Upadhyaya G. S. , Shohet J. L. , Lauer J. L.
Published: February 2005

Radiation-induced damage during plasma processing of semiconductor materials can adversely affect device reliability. However, it has been shown that vacuum ultraviolet (VUV) radiation (8–20 eV) can beneficially deplete previously deposited charge on the surface of dielectrics by temporarily increasing their conductivity. Incident VUV photons can cause photoemission and form electron-hole pairs in the dielectric thus producing the desired increased conductivity. To verify this, statistical information obtained from a Monte Carlo simulation is used to model VUV exposure of dielectrics. The simulation calculates the surface potential on the dielectric produced by electron photoemission, which compares favorably with experimental surface-potential measurements made using a Kelvin probe.
Vortex-like surface wave and its role in the transient phenomena of meta-material focusing
Authors: Zhou Lei , Chan C. T.
Published: February 2005

We show that a slab of meta-material (with ε=μ=−1+iΔ) possesses a vortex-like surface wave with no ability to transport energy, whose nature is completely different from a localized mode or a standing wave. Through computations based on a rigorous time-dependent Green’s function approach, we demonstrate that such a mode inevitably generates characteristic image oscillations in two-dimensional focusing with even a monochromatic source, which were observed in many numerical simulations, but such oscillations are weak in three-dimensional focusing.
Increased atomic hydrogen flux from a cascaded arc plasma source by changing the nozzle geometry
Authors: Vankan P. , Engeln R. , Schram D. C.
Published: February 2005

A very high flux of hydrogen atoms with energies in the eV range has been obtained by using a thermal plasma source and by optimization of the nozzle exit geometry. It proves that the flux of hydrogen atoms emerging from a cascaded arc plasma source depends strongly on the geometry of the nozzle. By decreasing the nozzle length by a factor 2, the atomic hydrogen flux is increased by a factor of 13, and a further increase of a factor of 2.5 can be obtained by increasing the nozzle diameter. The resulting atomic hydrogen flux is 1.2×1021s−1, corresponding to a dissociation degree of over 30%. It is argued that the main loss channel for atomic hydrogen is surface recombination, and that by using nozzle geometries that reduce the surface loss, the atomic flux is increased.
Real space imaging of the microscopic origins of the ultrahigh dielectric constant in polycrystalline CaCu3Ti4O12
Authors: Kalinin S. V. , Shin J. , Veith G. M. , Baddorf A. P. , Lobanov M. V. , Runge H. , Greenblatt M.
Published: February 2005

The origins of an ultrahigh dielectric constant in polycrystalline CaCu3Ti4O12 (CCTO) were studied using the combination of impedance spectroscopy, electron microscopy, and scanning probe microscopy (SPM). Impedance spectra indicate that the transport properties in the 0.1Hz–1MHz frequency range are dominated by a single parallel resistive-capacitive (RC) element with a characteristic relaxation frequency of 16Hz. dc potential distributions measurements by SPM illustrate that significant potential drops occur at the grain boundaries, which thus can be unambiguously identified as the dominant RC element. High frequency ac amplitude and phase distributions illustrate very weak grain boundary contrast in SPM, indicative of strong capacitive coupling across the interfaces. These results demonstrate that the ultrahigh dielectric constant reported for polycrystalline CCTO materials is related to grain-boundary behavior.
Low-voltage operation of a pentacene field-effect transistor with a polymer electrolyte gate dielectric
Authors: Panzer Matthew J. , Newman Christopher R. , Frisbie C. Daniel
Published: February 2005

Large operating voltages are often required to switch organic field-effect transistors (OFETs) on and off because commonly used gate dielectric layers provide low capacitive coupling between the gate electrode and the semiconductor. We present here a pentacene OFET gated by a solution-deposited polymer electrolyte film in which the current was modulated over four orders of magnitude using gate voltages less than 2V. A subthreshold slope of 180mV per decade of current was observed during transistor turn on at a source-drain bias of −1V; the estimated dielectric layer specific capacitance was 5μF∕cm2. Sweep rate-dependent hysteresis may be attributed to a combination of ion migration and charge carrier trapping effects. Strategies to improve switching speeds for polymer electrolyte-gated OFETs are also discussed.
Strained silicon thin-film transistors fabricated on glass
Authors: Lee J. J. , Maa J. S. , Tweet D. J. , Hsu S. T.
Published: February 2005

Strained-Si thin-film transistors were fabricated on glass substrate by direct transfer of a 35nm strained Si film onto glass. The strained Si films were originally grown on a relaxed SiGe layer on Si substrate. The tensile strain for the strained Si on glass (SSOG) was found to be 0.80%±0.02%. The effective electron mobility of the fabricated NMOS TFTs is 820cm2∕Vs. These devices show low interface charge densities at the bonding interface and at the gate oxide interface, as confirmed by the low subthreshold swing of 77mV∕dec for the 0.5μm SSOG device.
Improved stability of organic electroluminescent devices by doping styrylamines in hole or electron transporting layer
Authors: Lee Meng-Ting , Liao Chi-Hung , Tsai Chih-Hung , Chen Chin H.
Published: February 2005

The stability of green organic electroluminescent devices has been improved by doping styrylamine derivate, p-bis(p-N,N-diphenyl-aminostyryl)benzene (DSA-Ph) in hole or electron transporting layer. Compared with the undoped device, the stability of the electron transporting layer has increased by a factor of 1.8 without affecting the electroluminescence efficiency of 11cd∕A and color (CIEx,y=0.34, 0.62). The enhanced stability is believed to derive from the hole trapping nature of DSA-Ph which can reduce the residual hole carriers in tris(8-hydroquinolinato)aluminum (Alq3) and suppress the formation of fluorescent quencher of Alq3 cationic species.