bluuebunny/crossref_metadata_2025 huggingface dataset:
Surface wave tomography of China from ambient seismic noise correlation
Authors: Zheng Sihua , Sun Xinlei , Song Xiaodong , Yang Yingjie , Ritzwoller Michael H.
Published: May 2008

We perform ambient noise tomography of China using data from the China National Seismic Network and surrounding global and regional stations. For most of the station pairs, we retrieve good Rayleigh waveforms from ambient noise correlations using 18 months of continuous data at all distance ranges across the entire region (over 5000 km) and for periods from 70 s down to about 8 s. We obtain Rayleigh wave group velocity dispersion measurements using a frequency‐time analysis method and invert for Rayleigh wave group velocity maps for periods from 8 s to 60 s. The tomographic maps display significant features that correlate with surface geology. Major basins, including Tarim, Junggar, Qadaim, Sichuan, Bohai‐Wan, and Songliao, are all well delineated by slow group velocities at shorter periods (10 to 20 s). The overall trend of crustal thickening from east to west is well represented by group velocity decreases from east to west at periods around 30 s.
Higher tropical SSTs strengthen the tropical upwelling via deep convection
Authors: Deckert R. , Dameris M.
Published: May 2008

Recent observations show a distinct cooling of the tropical lower stratosphere, and chemistry‐climate models (CCMs) suggest a link to a strengthening tropical upwelling, arguably related to increases in greenhouse gas concentrations from anthropogenic activity. The present study explores the strengthening of tropical upwelling by comparing ensemble realisations of two different transient scenarios with the CCM E39/C. Both scenarios share the same boundary conditions, including concentrations of ozone‐depleting substances, but differ in their climate forcing via prescribed sea surface temperatures (SSTs) and well‐mixed greenhouse gas concentrations. In the summer hemisphere tropics, higher SSTs amplify deep convection locally and hence the convective excitation of quasi‐stationary waves. These waves propagate upward through the region of easterly winds while dissipating, but still carry enough of the signal into the low‐latitude lower stratosphere to induce an anomalous low‐latitude Brewer‐Dobson (BD) cell. The transport change in turn increases the flux of ozone‐poor tropospheric air into the tropical lower stratosphere.
Pacific Subtropical Cell variability in the SODA 2.0.2/3 assimilation
Authors: Schott Friedrich A. , Stramma Lothar , Wang Weiqiang , Giese Benjamin S. , Zantopp Rainer
Published: May 2008

A new version of SODA, which covers the time period 1958–2005, is used to analyze decadal variability of the Pacific Subtropical Cell (STC) circulation. The analysis is based on transport time series across 9°S and 9°N. At the interannual time scale, STC convergence anomalies decrease during El Niños and increase during La Niñas through Sverdrup transport convergence changes. At decadal time scales, the assimilation shows a reduction of interior STC convergence of about 8 Sv from the 1960s to the 1990s and a subsequent rebound into the early 2000s by a similar amount, in agreement with the STC tendencies reported earlier from geostrophic section analysis, and associated with the occurrence and intensity of ENSO events among the decades analyzed. The results are compared with, and differ significantly from, those obtained by the German ECCO (GECCO) assimilation.
In vitro models of proarrhythmia
Authors: Lawrence C L , Pollard C E , Hammond T G , Valentin J‐P
Published: June 2008

Proarrhythmia models use electrophysiological markers to predict the risk of torsade de pointes (TdP) in patients. The set of variables used by each model to predict the torsadogenic propensity of a drug has been reported to correlate with clinical outcome; however, these reports should be interpreted cautiously as no model has been independently assessed. Each model is discussed along with its merits and shortcomings; none, as yet, having shown a predictive value that makes it clearly superior to the others. As predictive as these models may become, extrapolation of results directly to the clinic must be exercised with caution. The use of in silico models, from subcellular to whole system, is rapidly beginning to form the first line of screening activity in many drug discovery programmes, indicating that biological experimentation may become secondary to analysis by simulation. In vitro proarrhythmia models challenge current perceptions of appropriate surrogates for TdP in man and question existing non‐clinical strategies for assessing proarrhythmic risk. The rapid emergence of such models, compounded by the lack of a clear understanding of the key proarrhythmic mechanisms has resulted in a regulatory reluctance to embrace such models. The wider acceptance of proarrhythmia models is likely to occur when there is a clear understanding and agreement on the key proarrhythmia mechanisms. With greater acceptance and ongoing improvements, these models have the potential to unravel the complex mechanisms underlying TdP.

British Journal of Pharmacology (2008) 154, 1516–1522; doi:fn1; published online 2 June 2008
T‐cell antigen receptor triggering and lipid rafts: a matter of space and time scales
Authors: He Hai‐Tao , Marguet Didier
Published: June 2008

T‐cell antigen receptor triggering mechanisms and lipid rafts are of broad interest, but are also controversial topics. Here, we review some recent progress in these two research fields, which has been accomplished mostly in live cells and with the use of advanced technologies. We then discuss the potential relationship between membrane‐domain organization and T‐cell antigen receptor‐triggering mechanisms. On the basis of the relevant experimental observations, we argue that the key to achieving a better understanding of both processes is the ability to monitor the molecular dynamics and interactions taking place in the membrane of T cells at a spatial scale of tens to hundreds of nanometres, with a subsecond‐to‐second temporal resolution.
Have we become overly reliant on lipid rafts?
Authors: Kenworthy Anne K
Published: June 2008

During the past decade, the lipid‐raft hypothesis has focused attention on the role of membrane domains in controlling cellular functions. Among the best‐studied roles of lipid rafts is the regulation of T‐cell signalling. In particular, a model has emerged in which lipid rafts regulate protein–protein interactions during signalling in a cholesterol‐dependent manner. Does this model provide the best description of what is happening in living cell membranes? Alternatively, has our ability to evaluate this question critically become compromised by the influential nature of the lipid‐raft model itself? Here, this issue is explored in the context of two of the major tenets of the lipid‐raft model.
Measuring the Effects of Remifentanil on Cerebral Blood Flow and Arterial Arrival Time Using 3D Grase MRI with Pulsed Arterial Spin Labelling
Authors: Macintosh Bradley J , Pattinson Kyle TS , Gallichan Daniel , Ahmad Imran , Miller Karla L , Feinberg David A , Wise Richard G , Jezzard Peter
Published: May 2008

Arterial spin labelling (ASL) has proved to be a promising magnetic resonance imaging (MRI) technique to measure brain perfusion. In this study, volumetric three-dimensional (3D) gradient and spin echo (GRASE) ASL was used to produce cerebral blood flow (CBF) and arterial arrival time (AAT) maps during rest and during an infusion of remifentanil. Gradient and spin echo ASL perfusion-weighted images were collected at multiple inflow times (500 to 2,500 ms in increments of 250 ms) to accurately fit an ASL perfusion model. Fit estimates were assessed using z-statistics, allowing voxels with a poor fit to be excluded from subsequent analyses. Nonparametric permutation testing showed voxels with a significant difference in CBF and AAT between conditions across a group of healthy participants ( N = 10). Administration of remifentanil produced an increase in end-tidal CO2, an increase in CBF from 57 ± 12.0 to 77 ± 18.4 mL/100 g tissue per min and a reduction in AAT from 0.73 ± 0.073 to 0.64 ± 0.076 secs. Within grey matter, remifentanil produced a cerebrovascular response of 5.7 ± 1.60 %CBF per mm Hg. Significant differences between physiologic conditions were observed in both CBF and AAT maps, indicating that 3D GRASE-ASL has the sensitivity to study changes in physiology at a voxel level.
Differential Progression of Magnetization Transfer Imaging Changes Depending on Severity of Cerebral Hypoxic-Ischemic Injury
Authors: Tuor Ursula I , Meng Shuzhen , Qiao Min , Webster Nicole B , Crowley Shauna M , Dyck Richard H , Tomanek Boguslaw
Published: May 2008

We hypothesized that magnetic resonance magnetization transfer (MT) imaging would be sensitive for detecting cerebral ischemic injury in white matter of neonatal brain. We compared the progression of changes in T2 and the MT ratio (MTR) after cerebral hypoxic-ischemic insults of differing severity in neonatal rats. Magnetization transfer imaging parameters were first optimized, and then MTR and T2 maps were acquired at various times after a mild (rather selective white matter) or substantial insult produced by unilateral cerebral hypoxia—ischemia. Depending on insult severity, time after insult, and region (e.g., subcortical white matter or cortex), cerebral hypoxia—ischemia produced reductions in MTR and an increase in T2. The exception was acutely at 1 to 5 h at which time points MTR was reduced ipsilaterally in white matter, whereas T2 was not affected significantly. Progression of imaging changes differed in rats grouped according to whether gross damage was present after chronic recovery. Behavioral changes were generally associated with chronic reductions in MTR and gross brain damage. Magnetization transfer imaging was capable of early detection of hypoxic-ischemic injury and particularly sensitive for identifying the progression of cerebral injury in white matter. Magnetization transfer ratio has potential for assisting with early diagnosis and treatment assessment for infants affected by perinatal hypoxia—ischemia.
Comparison of Noninvasive Quantification Methods of in Vivo Vesicular Acetylcholine Transporter Using [123I]-IBVM SPECT Imaging
Authors: Barret O , Mazère J , Seibyl J , Allard M
Published: May 2008

Dementia with Lewy Body and Alzheimer's disease exhibit degeneration of the cholinergic neurons, and currently, the primary target of treatment is the cholinergic neurotransmitter system. [123I]-IBVM is a highly selective radioligand for in vivo visualization of the vesicular acetylcholine transporter (VAChT) using single photon emission computed tomography. This study compares different noninvasive methods using the occipital cortex as a reference region for the quantification of [123l]-IBVM binding in six older, healthy volunteers: two kinetic analyses based on one-tissue (1TCM) or two-tissue compartment model (2TCM), one linear and one multilinear analysis, and a simplified peak equilibrium analysis. Time—activity curves were well described by a 1TCM for all regions. The 2TCM converged reliably only in the striatum. Goodness of fit was not improved by using a 2TCM as compared with a 1TCM. The multilinear analysis gave binding potentials similar to the 1TCM while being more robust. The peak equilibrium method might prove to be a useful simplified analysis. The binding potentials obtained with reference region methods strongly correlated with results from invasive blood-sampling analysis. Noninvasive quantification of [123I]-IBVM data provides reliable estimates of VAChT binding, which is most valuable to study neurodegenerative diseases with specific cholinergic alteration.
Parents’ Needs Following Identification of Childhood Hearing Loss
Authors: Fitzpatrick Elizabeth , Angus Doug , Durieux-Smith Andrée , Graham Ian D. , Coyle Doug
Published: June 2008

Purpose

Appropriate support for families of children diagnosed with hearing impairment may have a direct impact on the success of early hearing detection and intervention programs in reducing the negative effects of permanent hearing loss. We conducted a qualitative study to explore parents’ needs after learning of their child’s hearing loss to better understand the important components of service delivery from families’ perspectives.

Method

Semistructured interviews were conducted with 17 families (21 parents) of preschool children in 4 centers in Ontario, Canada. Parents of children identified by neonatal screening as well as those identified through traditional referral routes participated. We asked parents to share their perceptions of the strengths and gaps in the care system.

Results

Although the majority of parents were satisfied with the range and quality of audiology and therapy services available, they identified gaps in the areas of service coordination, availability of information, and the integration of social service and parent support into the system. Access to audiology services appears to have been facilitated for children who were systematically screened.

Conclusions

The findings provide insights into the services most valued by families. These findings highlight the importance of eliciting parents’ perspectives in designing optimal care models for children and families.
Vowel Space Characteristics and Vowel Identification Accuracy
Authors: Neel Amy T.
Published: May 2008

Purpose

To examine the relation between vowel production characteristics and intelligibility.

Method

Acoustic characteristics of 10 vowels produced by 45 men and 48 women from the J. M. Hillenbrand, L. A. Getty, M. J. Clark, and K. Wheeler (1995) study were examined and compared with identification accuracy. Global (mean f0, F1, and F2; duration; and amount of formant movement) and fine-grained measures (vowel space area; mean distance among vowels; f0, F1, and F2 ranges; duration ratio between long and short vowels; and formant movement ratio between dynamic and static vowels) were used to predict identification scores. Acoustic measures of the most frequently confused pairs (/æ/–/ε/ and /ɑ/–/ʌ/) were compared.

Results

Global and fine-grained measures accounted for less than 1/4 of variance in identification scores: Vowel space area alone accounted for 9%–12% of variance. Differences in vowel identification were largely due to poor identification of /æ/, /ε/, /ɑ/, or /ʌ/. Well-identified vowels were distinctive in formant frequencies, duration, and amount of formant movement over time.

Conclusions

Distinctiveness among neighboring vowels is more important in determining vowel intelligibility than vowel space area. Acoustic comparison of confused vowels may be more useful in studying intelligibility of normal and disordered speech than in measuring vowel space area.
The Argument-Structure Complexity Effect in Children With Specific Language Impairment: Evidence From the Use of Grammatical Morphemes in French
Authors: Pizzioli Fabrizio , Schelstraete Marie-Anne
Published: May 2008

Purpose

The hypothesis that the linguistic deficit presented by children with specific language impairment (SLI) is caused by limited cognitive resources (e.g., S. Ellis Weismer & L. Hesketh, 1996) was tested against the hypothesis of a limitation in linguistic knowledge (e.g., M. L. Rice, K. Wexler, & P. Cleave, 1995).

Method

The study examined the influence of the argument-structure complexity of a target sentence on the production of grammatical morphemes in French children with SLI compared with younger children matched for grammatical level in production (GL) and children of the same chronological age (CA). A sentence production task was used where the target sentences varied in terms of argument complexity and length.

Results

The results indicated that children with SLI used articles and auxiliaries in obligatory contexts significantly less often than both the GL and CA control groups: More complex argument structures elicited the highest number of grammatical morpheme omissions; this effect was larger in children with SLI than in the GL group and was independent of the length of the sentences, which failed to show any influence on the production of grammatical morphemes.

Conclusion

These results support the hypothesis that grammatical-morpheme deficit in SLI depends at least in part on limited processing capacities.
Speech Disruptions in the Narratives of English-Speaking Children With Specific Language Impairment
Authors: Guo Ling-yu , Tomblin J. Bruce , Samelson Vicki
Published: May 2008

Purpose

This study examined the types, frequencies, and distribution of speech disruptions in the spoken narratives of children with specific language impairment (SLI) and their age-matched (CA) and language-matched (LA) peers.

Method

Twenty 4th-grade children with SLI, 20 typically developing CA children, and 20 younger typically developing LA children were included in this study. Speech disruptions (i.e., silent pauses and vocal hesitations) occurring in the narratives of these children were analyzed.

Results

Children with SLI exhibited speech disruption rates that were higher than those of their age-matched peers but not higher than those of their language-matched peers. The difference in disruption rates between the SLI and CA groups was restricted to silent pauses of 500–1000 ms. Moreover, children with SLI produced more speech disruptions than their peers before phrases but not before sentences, clauses, or words.

Conclusions

These findings suggest that there is a relationship between language ability and speech disruptions. Higher disruption rates at phrase boundaries in children with SLI than in their age-matched peers reflect lexical and syntactic deficits in children with SLI.
Characterizing the Growth Trajectories of Language-Impaired Children Between 7 and 11 Years of Age
Authors: Law James , Tomblin J. Bruce , Zhang Xuyang
Published: May 2008

Background

A number of different systems have been suggested for classifying language impairment in children but, to date, no one system has been widely accepted.

Method

This paper outlines an alternative system looking for distinct patterns of change in receptive language skills across time, involving a secondary analysis of children identified as having specific language impairment.

Participants

The participants were 184 children age-assessed at 3 time points—7, 8, and 11 years of age.

Results

The pattern of receptive language development is highly predictable. The dominant pattern of growth is consistent with declining rates of growth over time for all children. The primary way in which the children differ is with respect to their initial severity. The testing of the 2 classification systems revealed some statistically significant differences among the subtypes with regard to the shape of the growth rates, but the effect sizes associated with these differences were very small. Thus, it is possible to conclude that beyond the dominant pattern of growth, some subtypes of language impairment at 7 years of age showed only subtle differences in receptive language change across time. The results are discussed in terms of the sample selection and the age of the children who were studied.
Effects of Long-Term Training on Aided Speech-Recognition Performance in Noise in Older Adults
Authors: Burk Matthew H. , Humes Larry E.
Published: May 2008

Purpose

This study examined how repeated presentations of words in noise affected understanding of both trained and untrained words in noise (in isolation and in sentences).

Method

Eight older listeners with hearing impairment completed a word-based auditory training protocol lasting approximately 12 weeks. Training materials were presented in a closed-set condition with both orthographic and auditory feedback on a trial-to-trial basis. Performance on both trained and untrained lexically easy and hard words, as well as generalization to sentences, was measured. Listeners then returned for an additional 14 weeks to monitor retention of the trained materials.

Results

Training listeners on 1 set of words improved both their open- and closed-set recognition of the trained materials but did not improve performance on another set of untrained words. When training switched to the other set, performance for the new set of words improved significantly, whereas significant improvements on the previously trained words were maintained. Training generalized to unfamiliar talkers but did not generalize to untrained words or untrained keywords within running speech. Listeners were able to maintain improved performance over an extended period.

Conclusion

Older listeners were able to improve their word-recognition performance in noise on a set of 150 words with training.
The dispersive Alfvén wave in the time-stationary limit with a focus on collisional and warm-plasma effects
Authors: Finnegan S. M. , Koepke M. E. , Knudsen D. J.
Published: May 2008

A nonlinear, collisional, two-fluid model of uniform plasma convection across a field-aligned current (FAC) sheet, describing the stationary Alfvén (StA) wave, is presented. In a previous work, Knudsen showed that, for cold, collisionless plasma [D. J. Knudsen, J. Geophys. Res. 101, 10761 (1996)], the stationary inertial Alfvén (StIA) wave can accelerate electrons parallel to a background magnetic field and cause large, time-independent plasma-density variations having spatial periodicity in the direction of the convective flow over a broad range of spatial scales and energies. Knudsen suggested that these fundamental properties of the StIA wave may play a role in the formation of discrete auroral arcs. Here, Knudsen’s model has been generalized for warm, collisional plasma. From this generalization, it is shown that nonzero ion-neutral and electron-ion collisional resistivity significantly alters the perpendicular ac and dc structure of magnetic-field-aligned electron drift, and can either dissipate or enhance the field-aligned electron energy depending on the initial value of field-aligned electron drift velocity. It is also shown that nonzero values of plasma pressure increase the dominant Fourier component of perpendicular wavenumber.
Dynamics of turbulent transport dominated by the geodesic acoustic mode near the critical gradient regime
Authors: Miki Kazuhiro , Kishimoto Yasuaki , Li Jiquan , Miyato Naoaki
Published: June 2008

The effects of geodesic acoustic modes (GAMs) on the toroidal ion temperature gradient turbulence and associated transport near the critical gradient regime in tokamak plasma are investigated based on global Landau-fluid simulations and extended predator-prey modeling analyses. A new type of intermittent dynamics of transport accompanied with the emission and propagation of the GAMs, i.e., GAM intermittency [K. Miki et al., Phys. Rev. Lett. 99, 145003 (2007)], has been found. The intermittent bursts are triggered by the onset of spatially propagating GAMs when the turbulent energy exceeds a critical value. The GAMs suffer collisionless damping during the propagation and nonlocally transfer local turbulence energy to wide radial region. The stationary zonal flows gradually increase due to the accumulation of non-damped residual part over many periods of quasi-periodic intermittent bursts and eventually quench the turbulence, leading to a nonlinear upshift of the linear critical gradient; namely, the Dimits shift. This process is categorized as a new class of transient dynamics, referred to as growing intermittency. The Dimits shift is found to be established through this dynamical process. An extended minimal predator-prey model with collisionless damping of the GAMs is proposed, which qualitatively reproduce the main features of the growing intermittency and approximately predict its various time scales observed in the simulations.
Ambipolar stochastic particle diffusion and plasma rotation
Authors: Wingen A. , Spatschek K. H.
Published: May 2008

The motion of electrons and ions in stochastic magnetic fields is considered. The analysis starts from a Hamiltonian formulation of the drift motion including electric fields. For an efficient statistical evaluation of the resulting particle transport, a symplectic mapping technique is applied. Compared to previous considerations, the ion and electron test particle motion are investigated simultaneously, allowing calculations of the ambipolar electric field and its influence on stochastic transport. The predictions based on the relativistic drift model are applied to the magnetic perturbations in the TEXTOR-DED [A. Wingen et al., Nucl. Fusion 46, 941 (2006)]. The influence of the magnetic coil arrangement on the poloidal plasma rotation, caused by the generated radial electric field, is discussed.
Excitons in Si1−xGex nanocrystals: Ab initio calculations
Authors: de Oliveira E. L. , Albuquerque E. L. , de Sousa J. S. , Farias G. A.
Published: May 2008

The electronic structure of hydrogen-passivated Si1−xGex nanocrystals is investigated by means of ab initio calculations. Our calculated optical gaps and electron-hole binding energies decrease linearly with x, while the exciton exchange energy increases with x due to the increase of the spatial extent of the electron and hole wave functions. This also increases the electron-hole wave functions overlap, leading to recombination lifetimes that are very sensitive to the Ge content. Our results exhibited very good agreement with available theoretical data.
Giant magnetocaloric effect in Mn1−x(Ti0.5V0.5)xAs: Experiments and calculations
Authors: Balli M. , Fruchart D. , Gignoux D. , Dupuis C. , Kedous-Lebouc A. , Zach R.
Published: May 2008

In this paper, we present the giant magnetocaloric effect exhibited by the Mn1−x(Ti0.5V0.5)xAs compound with x=0.1. The ordering temperature decreases from 318K in the case of MnAs (x=0) to 266K in the case of Mn0.9Ti0.05V0.05As (x=0.1). A large magnetic entropy change −ΔSm attributed to a first order magnetic transition has been observed. For Mn0.9Ti0.05V0.05As, the maximum of −ΔSm occurs near TC=266K and is about 30J∕kgK for an applied field change of 2T, a value very close to that (∼31J∕kgK) measured in MnAs. For materials with a first order transition at TC, the observed magnetocaloric effect enhancement can be explained by magnetoelastic effects which are due to structural changes. A model based on the phenomenological approach of Bean and Rodbell [Phys. Rev. 126, 104 (1962)] has been developed in order to describe such a behavior. In this paper we apply this model to describe the giant magnetocaloric effect exhibited by Mn1−x(Ti0.5V0.5)xAs (x=0, 0.1) materials.
Impact of dithiol treatment and air annealing on the conductivity, mobility, and hole density in PbS colloidal quantum dot solids
Authors: Klem Ethan J. D. , Shukla Harnik , Hinds Sean , MacNeil Dean D. , Levina Larissa , Sargent Edward H.
Published: May 2008

Crosslinking molecules have recently been combined with colloidal quantum dots to build robust, closely packed, conductive solid-state devices. Ethanedithiol (EDT) has been used in PbS quantum dot photovoltaic devices to assist in film formation during fabrication. However, there is evidence that EDT influences the electronic properties of the colloidal quantum dot (CQD) films. We fabricate thin film field-effect transistors and find that EDT treatment increases the majority carrier mobility by a factor of 10. We attribute this increase to a reduction in interparticle spacing which we observe using transmission electron microscopy. However, this increase is accompanied by a decrease in the majority carrier concentration. Using x-ray photoelectron microscopy, we find that EDT reduces the extent of the surface oxidation which is acting as a p-type dopant in these materials. We find that by lightly reoxidizing, we can redope the CQD films and can do so without sacrificing mobility gains.
Magnetized plasma sheath with two species of positive ions
Authors: Hatami M. M. , Niknam A. R. , Shokri B. , Ghomi H.
Published: June 2008

The effects of the magnitude and direction of an oblique magnetic field and the effect of the ion densities ratio on a plasma sheath of electrons and two species of positive ions are investigated by using a three-fluid hydrodynamics model. These ions have different masses but the same ionization ratio (Z=1). It is shown that the density distribution and velocity of the lighter and heavier ion species begin to fluctuate under the action of the electrostatic and Lorentz forces when the ratio of electron Debye length to lighter ion species Larmor radius becomes greater than 1 and 3, respectively. Also, it is found that the velocity fluctuations of the lighter ion species are much higher than those of the heavier ion species. Furthermore, the obtained results due to the presence of the second ion (the heavier ion) are compared to the reported results of the magnetized plasma sheath including single positive ion species. In the presence of the second ion, it is shown that the velocity and density distribution of the lighter ion species in the magnetized plasma sheath decreases and increases, respectively.
Phase space modulation of laser produced protons with a double-foil target generation of quasimonoenergetic proton beams
Authors: Zheng Jun , Mima Kunioki , Sheng Zheng Ming , Li Yu Tong
Published: May 2008

It is shown by one-dimensional particle-in-cell simulation that quasimonoenergetic protons can be generated from a double-solid-foil target irradiated by two ultrashort intense laser pulses. In this approach, one uses the first laser pulse irradiating on the first foil to generate the energetic protons, and one uses the second laser pulse irradiating on the second foil to generate an electrostatic field, which modulates the energy spectrum of protons from the first foil. Quasimonoenergetic protons with tunable energy peaks can be obtained by controlling the time delay and intensity of the second pulse as well as the distance between the two foils. It is also found that a preplasma on the second foil increases the peak energy. The dependence of the proton beam quality on the laser and target parameters is also discussed.
Flow-flame interaction in a closed chamber
Authors: Akkerman V. B. , Bychkov V. V. , Bastiaans R. J. M. , de Goey L. P. H. , van Oijen J. A. , Eriksson L. E.
Published: May 2008

Numerous studies of flame interaction with a single vortex and recent simulations of burning in vortex arrays in open tubes demonstrated the same tendency for the turbulent burning rate ∝Urmsλ2∕3, where Urms is the root-mean-square velocity and λ is the vortex size. Here, it is demonstrated that this tendency is not universal for turbulent burning. Flame interaction with vortex arrays is investigated for the geometry of a closed burning chamber by using direct numerical simulations of the complete set of gas-dynamic combustion equations. Various initial conditions in the chamber are considered, including gas at rest and several systems of vortices of different intensities and sizes. It is found that the burning rate in a closed chamber (inverse burning time) depends strongly on the vortex intensity; at sufficiently high intensities it increases with Urms approximately linearly in agreement with the above tendency. On the contrary, dependence of the burning rate on the vortex size is nonmonotonic and qualitatively different from the law λ2∕3. It is shown that there is an optimal vortex size in a closed chamber, which provides the fastest total burning rate. In the present work, the optimal size is six times smaller than the chamber height.
Observation and calculation of the Cs2 2Δ1g3 and bΠu3 states
Authors: Xie Feng , Li Dan , Tyree Luke , Li Li , Sovkov Vladimir B. , Ivanov Valery S. , Magnier Sylvie , Marjatta Lyyra A.
Published: June 2008

The Cs2 2Δ1g3 and bΠ0u3 states have been observed by infrared-infrared double resonance spectroscopy for the first time. 221 2Δ1g3←AΣu+1←XΣg+1 double resonance lines have been assigned to transitions into the 2Δ1g3 v=6–13 vibrational levels. Resolved fluorescence into the bΠ0u3 v′=0–48 levels has been recorded. Molecular constants and potential energy curves are determined by the global fit of the entire set of the experimental data. Theoretical potential energy curves of the 2Δg3 and bΠu3 states have been determined in the framework of the pseudopotential method and are compared with the experimental results.
An investigation of the molecular geometry and electronic structure of nitryl chloride by a combination of rotational spectroscopy and ab initio calculations
Authors: Francis S. G. , Harvey J. N. , Walker N. R. , Legon A. C.
Published: May 2008

The ground-state rotational spectra of the six isotopomers O216N14Cl35, O216N14Cl37, O18O16N14Cl35, O218N14Cl35, O216N15Cl35, and O216N15Cl37 of nitryl chloride were observed with a pulsed-jet, Fourier-transform microwave spectrometer to give rotational constants, Cl and N14 nuclear quadrupole coupling, and spin-rotation coupling constants. These spectroscopic constants were interpreted to give r0, rs, and rm(2) versions of the molecular geometry and information about the electronic redistribution at N when nitryl chloride is formed from NO2 and a Cl atom. The rm(2) geometry has r(N–Cl)=1.8405(6)Å, r(N–O)=1.1929(2)Å, and the angle ON̂O=131.42(4)°, while the corresponding quantities for the rs geometry are 1.8489Å, 1.1940Å, and 131.73°, respectively. Electronic structure calculations at CCSD(T)∕cc-pVXZ (X=T, Q, or 5) levels of theory were carried out to give a re geometry, vibration-rotation corrections to equilibrium rotational constants, and values of the Cl35 and N14 nuclear hyperfine (quadrupole and spin-rotation) coupling constants in good agreement with experiment. The equilibrium geometry at the CCSD(T)/cc-pV5Z level of theory has r(N–Cl)=1.8441Å, r(N–O)=1.1925Å and the angle ON̂O=131.80°. The observed rotational constants were corrected for the vibration-rotation effects calculated ab initio to yield semiempirical equilibrium constants which were then fitted to give the following semiempirical equilibrium geometry: r(N–Cl)=1.8467(2)Å, r(N–O)=1.1916(1)Å, and the angle ON̂O=131.78(3)°.
Comparison of theoretical and experimental heat diffusivities in the DIII-D edge plasma
Authors: Stacey W. M.
Published: June 2008

Predictions of theoretical models for ion and electron heat diffusivity have been compared against experimentally inferred values of the heat diffusivity profile in the edge plasma of two H-modes and one L-mode discharge in DIII-D [J. Luxon, Nucl. Fusion 42, 614 (2002)]. Various widely used theoretical models based on neoclassical, ion temperature gradient modes, drift Alfvén modes and radiative thermal instability modes for ion transport, and based on paleoclassical, electron temperature gradient modes, trapped electron modes, and drift resistive ballooning modes for electron transport were investigated.
Density profiles and solvation forces for a Yukawa fluid in a slit pore
Authors: Karanikas S. , Dzubiella J. , Moncho-Jordá A. , Louis A. A.
Published: May 2008

The effect of varying wall-particle and particle-particle interactions on the density profiles near a single wall and the solvation forces between two walls immersed in a fluid of particles is investigated by grand canonical Monte Carlo simulations. Attractive and repulsive particle-particle and particle-wall interactions are modeled by a versatile hard-core Yukawa form. These simulation results are compared to theoretical calculations using the hypernetted chain integral equation technique, as well as with fundamental measure density functional theory (DFT), where particle-particle interactions are either treated as a first order perturbation using the radial distribution function or else with a DFT based on the direct-correlation function. All three theoretical approaches reproduce the main trends fairly well, but exhibit inconsistent accuracy, particularly for attractive particle-particle interactions. We show that the wall-particle and particle-particle attractions can couple together to induce a nonlinear enhancement of the adsorption and a related “repulsion through attraction” effect for the effective wall-wall forces. We also investigate the phenomenon of bridging, where an attractive wall-particle interaction induces strongly attractive solvation forces.
Thickness dependent lattice expansion in nanogranular Nb thin films
Authors: Hazra Dibyendu , Datta Subhadeep , Mondal Mintu , Ghatak Jay , Satyam P. V. , Gupta Anjan K.
Published: May 2008

We report on the dependence of the lattice parameter on thickness (t) and grain size (D) in nanogranular Nb thin films deposited on Si (100) substrates by using dc magnetron sputtering. The lattice parameter is found to exponentially increase with decreasing thickness as well as grain size. We analyze the lattice expansion in terms of the excess free volume in the grain boundaries, which is found to decrease with the grain size in large thickness limit. The thickness dependence of the lattice expansion and the grain size dependence of the excess free volume are discussed in terms of the oxygen content in the grain boundaries.
Effects of interface states and temperature on the C-V behavior of metal/insulator/AlGaN/GaN heterostructure capacitors
Authors: Miczek Marcin , Mizue Chihoko , Hashizume Tamotsu , Adamowicz Bogusława
Published: May 2008

The impact of states at the insulator/AlGaN interface on the capacitance-voltage (C-V) characteristics of a metal/insulator/AlGaN/GaN heterostructure (MISH) capacitor was examined using a numerical solver of a Poisson equation and taking into account the electron emission rate from the interface states. A parallel shift of the theoretical C-V curves, instead of the typical change in their slope, was found for a MISH device with a 25-nm-thick AlGaN layer when the SiNx/AlGaN interface state density Dit(E) was increased. We attribute this behavior to the position of the Fermi level at the SiNx/AlGaN interface below the AlGaN valence band maximum when the gate bias is near the threshold voltage and to the insensitivity of the deep interface traps to the gate voltage due to a low emission rate. A typical stretch out of the theoretical C-V curve was obtained only for a MISH structure with a very thin AlGaN layer at 300 °C. We analyzed the experimental C-V characteristics from a SiNx/Al2O3/AlGaN/GaN structure measured at room temperature and 300 °C, and extracted a part of Dit(E). The relatively low Dit (∼1011 eV−1 cm−2) in the upper bandgap indicates that the SiNx/Al2O3 bilayer is applicable as a gate insulator and as an AlGaN surface passivant in high-temperature, high-power AlGaN/GaN-based devices.
A stereographic projection path integral study of the coupling between the orientation and the bending degrees of freedom of water
Authors: Curotto E. , Freeman David L. , Doll J. D.
Published: May 2008

A Monte Carlo path integral method to study the coupling between the rotation and bending degrees of freedom for water is developed. It is demonstrated that soft internal degrees of freedom that are not stretching in nature can be mapped with stereographic projection coordinates. For water, the bending coordinate is orthogonal to the stereographic projection coordinates used to map its orientation. Methods are developed to compute the classical and quantum Jacobian terms so that the proper infinitely stiff spring constant limit is recovered in the classical limit, and so that the nonconstant nature of the Riemann Cartan curvature scalar is properly accounted in the quantum simulations. The theory is used to investigate the effects of the geometric coupling between the bending and the rotating degrees of freedom for the water monomer in an external field in the 250 to 500 K range. We detect no evidence of geometric coupling between the bending degree of freedom and the orientations.
Global time evolution of an axisymmetric vortex ring at low Reynolds numbers
Authors: Fukumoto Y. , Kaplanski F.
Published: June 2008

An initial-value problem of the Navier–Stokes equation is solved, at small Reynolds numbers, for evolution of an axisymmetric vortex ring. The traveling speed is written down in closed form over the whole time range, in terms of the generalized hypergeometric functions, for a vortex ring starting with infinitely thin core. We make a thorough asymptotic analysis of this solution. Three stages are identified, namely, initial, matured, and decaying stages. At the initial stage when the core is very thin, correction terms are found to Saffman’s early-time formula [Stud. Appl. Math. 449, 371 (1970)]. The augmented formula establishes a lower bound on traveling speed of vortex rings starting from delta-function cores and exhibits an excellent agreement with the numerical simulation, at a small Reynolds number, conducted by Stanaway et al. (NASA Technical Memorandum No. 101041, 1988). At the matured and decaying stages, the traveling speed is found to be closely fitted by Saffman’s matured-stage formula, over a very wide time range, by an adjustment of disposable parameters in his formula. The traveling distance as a function of time is also deduced in closed form, and a simple relation of the maximum distance traversed during the whole life, being finite, is found with the viscosity, the initial circulation, and the initial ring radius. The formation number for an optimal vortex ring, estimated based on our solution, compares well with the experiments and numerical simulations.
On the relation between centrifugal force and radial pressure gradient in flow inside curved and S-shaped ducts
Authors: Ng Y. T. , Luo S. C. , Lim T. T. , Ho Q. W.
Published: June 2008

Swirl flow in a curved duct and S-duct is governed by a centrifugal force and radial pressure gradient force between the sidewalls. In the present work, we introduce a dimensionless parameter that relates the ratio of these two forces and the duct’s center-line distance and show how the parameter is related to other more familiar dimensionless terms such as the pressure coefficient, Reynolds number, and Dean number. By using published data as well as our own measurements, it is shown that the data collapse reasonably well on a curve when the proposed parameter is plotted against dimensionless distance along the duct. The existence of collapsed curves for ducts of different curvature ratios indicates that the proposed parameter can be used to characterize the flow, although some scatter in the data exists, due to the presence of flow separation and streamwise vortices along the wall of the curved ducts. An attempt to suppress flow separation by using vortex generators in the S-duct leads to some improvement in the collapsed curve at the first bend of the duct. The results reported here are mainly focused on square and circular constant cross-sectioned 90° curved ducts and S-shaped ducts of different curvature ratios.
Electron effective mass and mobility in heavily doped n-GaAsN probed by Raman scattering
Authors: Ibáñez J. , Cuscó R. , Alarcón-Lladó E. , Artús L. , Patanè A. , Fowler D. , Eaves L. , Uesugi K. , Suemune I.
Published: May 2008

We investigate inelastic light scattering by longitudinal optic phonon-plasmon coupled modes (LOPCMs) in a series of heavily Se-doped, n-type GaAs1−xNx epilayers with x<0.4%. We perform a line shape analysis of the LOPCM spectra to estimate the optical effective mass, mopt∗, and the scattering time of the conduction electrons in GaAsN. We use these results to evaluate an effective carrier mobility for our samples. The values thus obtained, which we compare with measured electron Hall mobilities, indicate that the x-dependence of the mobility in GaAs1−xNx is dominated by the scattering time, rather than by the variation of the electron effective mass. The Raman analysis yields mopt∗ values that are lower than those obtained from the band anticrossing model.
Exchange bias and phase transformation in α-Fe2O3+NiO nanocomposites
Authors: Liu X. H. , Cui W. B. , Lv X. K. , Liu W. , Zhao X. G. , Li D. , Zhang Z. D.
Published: May 2008

The structure, phase components, and magnetic properties of antiferromagnetic coupled Fe2O3 and NiO nanocomposites have been investigated. A negative exchange bias field of about 2kOe and the anomalous shape of hysteresis loop are observed, which may be related to uncompensated and pinned antiferromagnetic spins at the interface between ferrimagnetic and antiferromagnetic phases in the powders. Furthermore, the exchange bias field varies with the strength of cooling field, and the exchange bias field HE of 0.76kOe is observed in antiferromagnetic-antiferromagnetic system.
Two dimensional simulation and modeling of the electrical behavior in nanocrystalline silicon thin-film transistors
Authors: Archontas N. , Georgoulas N. , Dimitriadis C. A. , Templier F. , Oudwan M. , Kamarinos G.
Published: May 2008

Nanocrystalline silicon thin-film transistors present technological interest in that they combine many of the advantages of amorphous with those of polycrystalline Si structures. Progress in practical implementation of this technology is hampered by limited understanding of the conduction mechanisms in these structures and of the underlying relationship between device behavior and process manufacturing parameters. These mechanisms are explored through detailed simulation that includes model calibration and correlation with experimental results, as well as parametric sensitivity evaluation of this class of devices over the entire range of applied voltage. Through fitting of the tests results, a unique set of density of states was identified that characterizes the particular technology used. The leakage current was attributed to the band to band tunneling and thermal generation-recombination mechanisms. For devices with channel length of less than 20μm, the kink effect was observed in the output characteristics for high drain voltages and the impact ionization coefficient was determined.
Tilt generation in step-graded InxGa1−xAs metamorphic pseudosubstrate on a singular GaAs substrate using a low-temperature grown InGaP interlayer
Authors: Ghanad Tavakoli Shahram , Hulko Oksana , Thompson David A.
Published: May 2008

Metamorphic pseudosubstrates of In0.42Ga0.58As were grown by molecular beam epitaxy using step-graded InxGa1−xAs buffer layers grown either directly on a (001) GaAs substrate or on a GaAs substrate overgrown with a layer of low-temperature grown In0.51Ga0.49P (LT-InGaP). The structures were examined using x-ray reciprocal space mapping to determine the characteristics of the pseudosubstrates and buffer layers. For the sample grown on the LT-InGaP layer, the pseudosubstrate exhibited an asymmetric tilt around [11¯0] toward the [110] direction. Weak-beam dark-field electron imaging shows an imbalance of misfit dislocations with opposite sign Burgers vector. An explanation for this tilt is given and it is suggested that it may be responsible for the improved quality of epitaxial layers grown on such pseudosubstrates.
Structural and optical properties of stacked self-assembled InAs∕InGaAs quantum dots on graded Si1−xGex∕Si substrate
Authors: Tanoto H. , Yoon S. F. , Ngo C. Y. , Loke W. K. , Dohrman C. , Fitzgerald E. A. , Narayanan B.
Published: June 2008

We have investigated the effects of InAs monolayer coverage on the structural and optical characteristics of stacked InAs quantum dot (QD) layers on graded Si1−xGex∕Si substrate. No preferential InAs QDs nucleation was observed along the cross-hatched lines on the graded Si1−xGex∕Si substrate. Employing alternate-beam molecular beam epitaxy, InAs QDs with areal density as high as 7×1010cm−2 was achieved. Temperature dependence of the InAs QDs optical properties is discussed. The InAs QDs show room-temperature photoluminescence at 1.3μm with full width at half-maximum of 65nm. The results are significant for potential realization of III-V QD devices on silicon-based platforms.