bluuebunny/crossref_metadata_2025 huggingface dataset:
An assessment of the tropical humidity‐temperature covariance using AIRS
Authors: Gambacorta A. , Barnet C. , Soden B. , Strow L.
Published: May 2008

We investigate the horizontal and vertical structure of the covariance between water vapor and temperature in the tropical troposphere, using satellite measurements from the Atmospheric InfraRed Sounder (AIRS). Our analysis reveals large spatial gradients in the local covariance between water vapor and temperature. Positive correlations dominate the tropical lower and upper troposphere, while regions of negative correlation are common in the tropical middle troposphere. While regressions of the tropical mean water vapor and temperature profiles reveal slopes of the same order of magnitude of the Clausius‐Clapeyron regime, the regression of local values can be up to an order of magnitude larger than the Clausius‐Clapeyron prediction. Results from the NOAA GFDL global circulation model are also shown for comparison.
Short‐term upper‐ocean variability in the central equatorial Indian Ocean during 2006 Indian Ocean Dipole event
Authors: Masumoto Yukio , Horii Takanori , Ueki Iwao , Hase Hideaki , Ando Kentaro , Mizuno Keisuke
Published: May 2008

Intensive observations, using an array of surface and subsurface moored buoys, are conducted around 80.5°E in the equatorial Indian Ocean during October/November 2006. An intriguing data set of atmospheric and oceanic variables during a peak phase of a positive Indian Ocean Dipole is obtained. The ocean observation data shows relatively shallow thermocline, which intensifies with time during the one‐month period, and eastward subsurface zonal flow under westward flowing surface current, generating unusually strong vertical shear above the thermocline. Intraseasonal meridional current variability is also observed. Upper‐ocean volume budget analysis indicates that a strong upwelling event, larger than 10 m/day, and associated upward movement of the isotherms below the thermocline occur for a few days in early November. These observed data demonstrates unusual conditions of the upper ocean during boreal autumn in 2006.
Adenosine Modulates ERK1/2, PI3K/Akt, and p38MAPK Activation in the Brain of the Anoxia-Tolerant Turtle Trachemys Scripta
Authors: Milton Sarah L , Dirk Lynda J , Kara Laurie F , Prentice Howard M
Published: May 2008

The fate of cells under anoxic or ischemic stress is determined by intracellular signaling pathways including the mitogen-activated protein kinases (MAPKs) and phosphatidylinositol 3-kinase (PI3K/Akt), which affect downstream members of the apoptotic cascade. The freshwater turtle Trachemys scripta is extremely tolerant of anoxia, surviving up to 48 h at room temperature and for weeks at 3°C in the complete absence of oxygen. We investigated the relationship between the neuroprotective purine adenosine, which increases greatly in the anoxic turtle brain, and MAPK and Akt activation during both short (1 h) and long-term (4 h) anoxia. ERK1/2 and Akt were significantly upregulated during the first hour of transition to full anoxia, but returned to baseline by 4 h anoxia. Conversely, p38MAPK levels were suppressed by a mean 71% at 1 h anoxia but also returned to baseline by 4 h anoxia. Systemic administration of the general adenosine receptor antagonist aminophylline abrogated the increases in both phosphorylated ERK1/2 and Akt, as well as the initial suppression of p38MAPK. The differential modulation of the MAPK/Akt pathways may be critical for neuronal protection during the initial transition to the hypometabolic state during anoxia, when physiologic stress is likely to be greatest.
Experimental and Theoretical Studies of Oxygen Gradients in Rat Pial Microvessels
Authors: Sharan Maithili , Vovenko Eugene P , Vadapalli Arjun , Popel Aleksander S , Pittman Roland N
Published: May 2008

Using modified oxygen needle microelectrodes and intravital videomicroscopy, measurements were made of tissue oxygen tension (PO2) profiles near cortical arterioles and transmural PO2 gradients in the pial arterioles of the rat. Under control conditions, the transmural PO2 gradient averaged 1.17 ± 0.06 mm Hg/μm (mean ± s.e., n = 40). Local arteriolar dilation resulted in a marked decrease in the transmural PO2 gradient to 0.68 ± 0.04 mm Hg/μm ( P < 0.001, n = 38). The major finding of this study is a dependence of the transmural PO2 gradient on the vascular tone of the pial arterioles. Using a model of oxygen transport in an arteriole and experimental PO2 profiles, values of radial perivascular and intravascular O2 fluxes were estimated. Our theoretical estimates show that oxygen flux values at the outer surface of the arteriolar wall are approximately 10−5mL O2/cm2 per sec, independent of the values of the arteriolar wall O2 consumption within a wide range of consumption values. This also means that PO2 transmural gradients for cerebral arterioles are within the limits of 1 to 2 mm Hg/μm. The data lead to the conclusion that O2 consumption of the arteriolar wall is within the range for the surrounding tissue and O2 consumption of the endothelial layer appears to have no substantial impact on the transmural PO2 gradient.
Quantification of Poly(ADP-Ribose)-Modified Proteins in Cerebrospinal Fluid from Infants and Children after Traumatic Brain Injury
Authors: Fink Ericka L , Lai Yichen , Zhang Xiaopeng , Janesko-Feldman Keri , Adelson P David , Szabó Csaba , Berger Rachel P , Sarnaik Ajit A , Kochanek Patrick M , Clark Robert SB
Published: May 2008

Poly-ADP-ribosylation (PAR) of proteins by poly(ADP-ribose) polymerases (PARP) occurs after experimental traumatic brain injury (TBI) and modulates neurologic outcome. Several promising pharmacological PARP inhibitors have been developed for use in humans, but there is currently no clinically relevant means of monitoring treatment effects. We therefore used an enzyme-linked immunosorbent assay to measure PAR-modified proteins in cerebrospinal fluid (CSF). Cerebrospinal fluid samples from 17 pediatric TBI patients and 15 controls were plated overnight and then incubated with polyclonal antibody against PAR. Histone-1, a PARP substrate, was incubated with active PARP, NAD, and nicked DNA, and served as the standard. Both peak and mean CSF PAR-modified proteins were increased in TBI patients versus controls. Peak CSF PAR-modified protein levels occurred on day 1 and levels remained increased on day 2 after TBI. Increases in peak CSF PAR-modified protein concentrations were independently associated with age and male sex, but not initial Glasgow Coma Scale score, Glasgow outcome score, or mechanism of injury. The increase in PAR-modified proteins in CSF after TBI may be because of increased PARP activation, decreased PAR degradation, or both. As PAR-modified protein concentration correlated with age and male sex, developmental and sex-dependent roles for PARP after TBI are implicated.
The Relationship Between Listener Comprehension and Intelligibility Scores for Speakers With Dysarthria
Authors: Hustad Katherine C.
Published: May 2008

Purpose

This study examined the relationship between listener comprehension and intelligibility scores for speakers with mild, moderate, severe, and profound dysarthria. Relationships were examined across all speakers and their listeners when severity effects were statistically controlled, within severity groups, and within individual speakers with dysarthria.

Method

Speech samples were collected from 12 speakers with dysarthria secondary to cerebral palsy. For each speaker, 12 different listeners completed 2 tasks (for a total of 144 listeners): One task involved making orthographic transcriptions, and 1 task involved answering comprehension questions. Transcriptions were scored for the number of words transcribed correctly. Responses to comprehension questions were scored on a 3-point scale according to their accuracy.

Results

Across all speakers, the Pearson product–moment correlation between comprehension and intelligibility scores was nonsignificant when the effects of severity were factored out and residual scores were examined. Within severity groups, the same relationship was significant only for the mild group. Within individual speaker groups, the relationship was nonsignificant for all but 2 speakers with dysarthria. Percentage of correct scores for listener comprehension was descriptively higher than percentage of correct intelligibility scores for all groups.

Conclusion

Findings suggest that transcription intelligibility scores do not accurately reflect listener comprehension scores. Measures of both intelligibility and listener comprehension may provide a more complete description of the information-bearing capability of dysarthric speech than either measure alone.
Laryngeal Muscles Are Spared in the Dystrophin DeficientmdxMouse
Authors: Thomas Lisa B. , Joseph Gayle L. , Adkins Tracey D. , Andrade Francisco H. , Stemple Joseph C.
Published: May 2008

Purpose

Duchenne muscular dystrophy (DMD)is caused by the loss of the cytoskeletal protein, dystrophin. The disease leads to severe and progressive skeletal muscle wasting. Interestingly, the disease spares some muscles. The purpose of the study was to determine the effects of dystrophin deficiency on 2 intrinsic laryngeal muscles, the posterior cricoarytenoid and the thyroarytenoid, in the mouse model.

Method

Larynges from dystrophin-deficientmdxand normal mice were examined histologically.

Results

Results demonstrate that despite the absence of dystrophin in themdxlaryngeal muscles, membrane damage, inflammation, necrosis, and regeneration were not detected in the assays performed.

Conclusions

The authors concluded that these muscles are 1 of only a few muscle groups spared in this model of dystrophin deficiency. The muscles may count on intrinsic and adaptive protective mechanisms to cope with the absence of dystrophin. Identifying these protective mechanisms may improve DMD management. The study also highlights the unique aspects of the selected laryngeal skeletal muscles and their dissimilarity to limb skeletal muscle.
Articulatory Movements During Vowels in Speakers With Dysarthria and Healthy Controls
Authors: Yunusova Yana , Weismer Gary , Westbury John R. , Lindstrom Mary J.
Published: May 2008

Purpose

This study compared movement characteristics of markers attached to the jaw, lower lip, tongue blade, and dorsum during production of selected English vowels by normal speakers and speakers with dysarthria due to amyotrophic lateral sclerosis (ALS) or Parkinson disease (PD). The study asked the following questions: (a) Are movement measures different for healthy controls and speakers with ALS or PD, and (b) Are articulatory profiles comparable for speakers with ALS and speakers with PD?

Method

Nineteen healthy controls and 15 speakers with dysarthria participated in this study. The severity of dysarthria varied across individuals and between the 2 disorder groups. The stimuli were 10 words (i.e.,
seed, feed, big, dish, too, shoo, bad, cat, box,
and
dog
) embedded into sentences read at a comfortable reading rate. Movement data were collected using the X-ray microbeam. Movement measures included distances, durations, and average speeds of vowel-related movement strokes.

Results

Differences were found (a) between speakers with ALS and healthy controls and (b) between speakers with ALS and PD, particularly in movement speed. Tongue movements in PD and ALS were more consistently different from healthy controls than jaw and lower lip movements. This study showed that the effects of neurologic disease on vowel production are often articulator-, vowel-, and context-specific.

Conclusions

Differences in severity between the speakers with PD and ALS may have accounted for some of the differences in movement characteristics between the groups. These factors need to be carefully considered when describing the nature of speech disorder and developing empirically based evaluation and treatment strategies for dysarthria.
The Influence of Fundamental Frequency and Sound Pressure Level Range on Breathing Patterns in Female Classical Singing
Authors: Collyer Sally , Thorpe C. William , Callaghan Jean , Davis Pamela J.
Published: May 2008

Purpose

This study investigated the influence of fundamental frequency (F0) and sound pressure level (SPL) range on respiratory behavior in classical singing.

Method

Five trained female singers performed an 8-s messa di voce (a crescendo and decrescendo on one F0) across their musical F0 range. Lung volume (LV) change was estimated, and chest-wall kinematic behavior (dimensional change in ribcage [RC] and abdominal [AB] wall) was recorded using triaxial magnetometry.

Results

The direction of F0 influence on LV excursion (LVE) varied among singers, but SPL range appeared to be less important than duration to LVE. LVE was generally evenly divided between crescendo and decrescendo. Kinematic patterns differed markedly among singers, despite task consistency, and RC and AB paradoxing was widespread.

Conclusion

Each singer maintained her characteristic kinematic pattern regardless of F0 or SPL range, although these did influence aspects of RC and AB behavior. Given the essential role of breathing in classical singing, further work is needed to understand how singers develop their highly individual respiratory strategies and the principles by which each singer’s breathing strategy can be optimized.
Efficacy of the Discreteness of Voicing Category (DOVC) Measure for Characterizing Voicing Errors in Children With Cochlear Implants: A Report
Authors: Bharadwaj Sneha V. , Graves Amanda G.
Published: May 2008

Purpose

This investigation explored the utility of an acoustic measure, called the discreteness of voicing category (DOVC), in identifying voicing errors in stop consonants produced by children with cochlear implants. Another objective was to examine the perceptual relevance of the DOVC measure and 2 commonly used voice onset time (VOT)-based measures, namely, mean VOT and ΔVOT (e.g., VOT /

/ − VOT /

/).

Method

Phonetic transcription and acoustic analyses were carried out on syllable–initial /

/ and /

/ produced by 10 children with cochlear implants. The DOVC was calculated as the difference between the shortest VOT value of a voiceless stop and the longest VOT value of a voiced stop across several productions of each.

Results

Phonetic transcription revealed that 4 of the 10 talkers demonstrated atypical voicing distinctions. Acoustic analyses indicated that the DOVC measure identified these same 4 talkers as producing atypical values, whereas mean VOT and ΔVOT identified a different set of talkers as demonstrating values outside the normal ranges.

Conclusion

Preliminary findings suggest that the DOVC measure corresponded with perceptual data better than the other acoustic measures examined in the present study. Data indicate that the DOVC measure may provide perceptually relevant information concerning the production of voicing distinctions.
Age-Related Changes to Speech Breathing With Increased Vocal Loudness
Authors: Huber Jessica E. , Spruill John
Published: May 2008

Purpose

The present study examines the effect of normal aging on respiratory support for speech when utterance length is controlled.

Method

Fifteen women (M= 71 years of age) and 10 men (M= 73 years of age) produced 2 sentences of different lengths in 4 loudness conditions while respiratory kinematics were measured. Measures included those related to lung volume and chest wall movements.

Results

Data from the older adults were compared with previously published data from 30 young adults. A significant Age × Sex effect was demonstrated. Older men produced speech at higher lung volumes than younger men. No significant differences existed between older and younger women. Older adults tended to use more abdominal movement in loud speech than younger adults, especially when talking in noise. Some of the mechanisms used by the older adults to support increased loudness in response to the cues differed from those used by the younger adults. Age-related differences were larger when participants produced the longer utterance as compared with the shorter one.

Conclusions

Reduced chest wall compliance, pulmonary elastic recoil, and laryngeal closure may explain the findings. These data can be used to help distinguish normal age-related changes from disease-related changes.
Why Do Preschool Language Abilities Correlate With Later Reading? A Twin Study
Authors: Harlaar Nicole , Hayiou-Thomas Marianna E. , Dale Philip S. , Plomin Robert
Published: May 2008

Purpose

Language acquisition is predictive of successful reading development, but the nature of this link is poorly understood.

Method

A sample of 7,179 twin pairs was assessed on parent–report measures of syntax and vocabulary at ages 2, 3, and 4 years and on teacher assessments of reading achievement (RA) at ages 7, 9, and 10 years. These measures were used to construct latent factors of early language ability (LA) and RA in structural equation model-fitting analyses.

Results

The phenotypic correlation between LA and RA (
r
= .40) was primarily due to shared environmental influences that contribute to familial resemblance. These environmental influences on LA and RA overlapped substantially (
r
C
= .62). Genetic influences made a significant but smaller contribution to the phenotypic correlation between LA and RA, and showed moderate overlap (
r
A
= .36). There was also evidence for a direct causal influence of LA on RA.

Conclusions

The association between early language and later reading is underpinned by common environmental and genetic influences. The effects of some risk factors on RA may be mediated by language. The results provide a foundation for more fine-grained studies that examine links between specific measures of language, reading, genes, and environments.
Estimating When and How Words Are Acquired: A Natural Experiment on the Development of the Mental Lexicon
Authors: Auer Edward T. , Bernstein Lynne E.
Published: May 2008

Purpose

Sensitivity of subjective estimates of age of acquisition (AOA) and acquisition channel (AC; printed, spoken, signed) to differences in word exposure within and between populations that differ dramatically in perceptual experience was examined.

Methods

Fifty participants with early-onset deafness and 50 participants with normal hearing rated 175 words in terms of subjective AOA and AC. Additional data were collected using a standardized test of reading and vocabulary.

Results

Participants with early-onset deafness rated words as learned later (
M
= 10 years) than did participants with normal hearing (
M
= 8.5 years),
F
(1, 99) = 28.59,
p
< .01. Group-averaged item ratings of AOA were highly correlated across the groups (
r
= .971) and with normative order of acquisition (deaf:
r
= .950, hearing:
r
= .946). The groups differed in their ratings of AC (hearing: printed = 30%, spoken = 70%, signed = 0%; deaf: printed = 45%, spoken = 38%, signed = 17%).

Conclusions

Subjective AOA and AC measures are sensitive to between- and within-group differences in word experience. The results demonstrate that these subjective measures can be applied as proxies for direct measures of lexical development in studies of lexical knowledge in adults with prelingual onset deafness.
Comodulation Masking Release (CMR) in Children and the Influence of Reading Status
Authors: Zettler Cynthia M. , Sevcik Rose A. , Morris Robin D. , Clarkson Marsha G.
Published: May 2008

Purpose

Research suggests that children with reading disabilities (RD) have difficulty processing temporal and spectral components of sounds. Comodulation masking release (CMR) measures a listener’s ability to use temporal and spectral information in noise to identify a signal. The purpose of this study was to determine whether children with RD had difficulty identifying a signal in CMR stimuli. Child and adult performance was compared to assess the development of CMR.

Method

Eighty-one 7- to 10-year-old children (30 with and 51 without RD) and 20 adults without RD listened to CMR stimuli through headphones. The difference between reference and modulated masker thresholds provided a measure of CMR.

Results

Hierarchical regression analyses indicated that reading status did not predict thresholds or CMR. An analysis of variance revealed significantly less CMR for children than for adults.

Conclusions

This research does not support the hypothesis that children with RD have difficulty processing temporal and spectral auditory information as measured by the CMR paradigm. In contrast with some previous research (K. Veloso, J. Hall, & J. Grose, 1990), this study suggests that CMR is continuing to develop beyond 10 years of age. Future research using a CMR paradigm with older children (10–16 years of age) would further illuminate the developmental picture of CMR.
Short-Term Word-Learning Rate in Children With Normal Hearing and Children With Hearing Loss in Limited and Extended High-Frequency Bandwidths
Authors: Pittman Andrea L.
Published: May 2008

Purpose

This study examined children’s word learning in limited and extended high-frequency bandwidth conditions. These conditions represent typical listening environments for children with hearing loss (HL) and children with normal hearing (NH), respectively.

Method

Thirty-six children with NH and 14 children with moderate-to-severe HL served as participants. All of the children were between 8 and 10 years of age and were assigned to either the limited or the extended bandwidth conditions. Five nonsense words were paired with 5 novel pictures. Word learning was assessed in a single session, multitrial, learning paradigm lasting approximately 15 min. Learning rate was defined as the number of exposures necessary to achieve 70% correct performance.

Results

Analysis of variance revealed a significant main effect for bandwidth but not for group. A Bandwidth × Group interaction was also not observed. In this short-term learning paradigm, the children in both groups required 3 times as many exposures to learn each new word in the limited bandwidth condition compared with the extended bandwidth condition.

Conclusion

These results suggest that children with HL may benefit from extended high-frequency amplification when learning new words and for other long-term auditory processes.
Factors Affecting the Benefits of High-Frequency Amplification
Authors: Horwitz Amy R. , Ahlstrom Jayne B. , Dubno Judy R.
Published: May 2008

Purpose

This study was designed to determine the extent to which high-frequency amplification helped or hindered speech recognition as a function of hearing loss, gain-frequency response, and background noise.

Method

Speech recognition was measured monaurally under headphones for nonsense syllables low-pass filtered in one-third-octave steps between 2.2 and 5.6 kHz. Adults with normal hearing and with high-frequency thresholds ranging from 40 to 80 dB HL listened to speech in quiet processed with an identical “nonindividualized” gain-frequency response. Hearing-impaired participants also listened to speech in quiet and noise processed with gain-frequency responses individually prescribed according to the National Acoustic Laboratories–Revised (NAL-R) formula.

Results

Mean speech recognition generally increased significantly with additional high-frequency speech bands. The one exception was that hearing-impaired participants’ recognition of speech processed by the nonindividualized response did not improve significantly with the addition of the highest frequency band. Significantly larger increases in scores with increasing bandwidth were observed for speech in noise than quiet.

Conclusions

Given that decreases in scores with additional high-frequency speech bands for individual participants were relatively small and few and did not increase with quiet thresholds, no evidence of a degree of hearing loss was found above which it was counterproductive to provide amplification.
Metallic switching of semiconducting single-walled carbon nanotubes with ZnO thin film
Authors: Wei Chung-Sheng , Su Chi-Chung , Chang Shuo-Hung
Published: May 2008

We demonstrate switching the p-type carbon nanotube field-effect transistors into the metallic behavior through deposition of the ZnO film. The ZnO film was deposited by rf sputtering and substrate heating during deposition. The change in the band structure of the ZnO coated single-walled carbon nanotube caused the switching. The analysis using x-ray diffraction spectrum, atomic force microscopy, and current measurements confirms the switching behavior. The method provides a new route for the application of carbon nanotubes in nanoelectronics.
Quasi-exactly solvable models based on special functions
Authors: Dolya S. N.
Published: May 2008

We suggest a systematic method of extension of quasiexactly solvable (QES) systems. We construct finite-dimensional subspaces on the basis of special functions (hypergeometric, Airy, Bessel ones) invariant with respect to the action of differential operators of the second order with polynomial coefficients. As an example of physical applications, we show that the known two-photon Rabi Hamiltonian becomes quasiexactly solvable at certain values of parameters when it can be expressed in terms of corresponding QES operators related to the hypergeometric function.
Reduced kinetic description of weakly-driven plasma waves
Authors: Lindberg R. R. , Charman A. E. , Wurtele J. S.
Published: May 2008

A model of kinetic effects in Langmuir wave dynamics is presented using a nonlinear distribution function that includes particle separatrix crossing and self-consistent electrostatic evolution. This model is based on the adiabatic motion of electrons in the wave to describe Bernstein–Greene–Kruskal-like Langmuir waves over a wide range of temperatures (0.1⩽kλD⩽0.4). The asymptotic distribution function yields a nonlinear frequency shift of the Langmuir wave that agrees well with Vlasov simulations, and can furthermore be used to determine the electrostatic energy required to develop the phase-mixed, asymptotic state. From this incoherent energy, energy conservation is employed to determine a simplified model of nonlinear Landau damping. The resulting nonlinear, dynamic frequency shift and damping are then used in an extended three-wave-type model of driven Langmuir waves and compared to Vlasov simulations in the context of backward Raman scattering.
On the physics of aerobreakup
Authors: Theofanous T. G. , Li G. J.
Published: May 2008

By using laser-induced fluorescence to visualize liquid drops that are suddenly exposed to supersonic gas streams, we show that the previously available experimental results, which are based on the shadowgraph method, allowed misinterpretations that have lead to inappropriate conceptualizations (and theory) of the physics that govern breakup at high Weber numbers (We>103)—instead of the Rayleigh–Taylor piercing, the dominant mechanism is shear-induced motion with a significant radial component and instabilities on the so-generated, stretched liquid sheet. At low Weber numbers (We<102), the new data reveal the quantitative features of multiwave piercing by Rayleigh–Taylor instabilities. The highly resolved images provide uniquely suitable benchmarks for direct numerical simulations of interfacial instabilities in general and of drop breakup in particular.
Convergence of folding free energy landscapes via application of enhanced sampling methods in a distributed computing environment
Authors: Huang Xuhui , Bowman Gregory R. , Pande Vijay S.
Published: May 2008

We have implemented the serial replica exchange method (SREM) and simulated tempering (ST) enhanced sampling algorithms in a global distributed computing environment. Here we examine the helix-coil transition of a 21 residue α-helical peptide in explicit solvent. For ST, we demonstrate the efficacy of a new method for determining initial weights allowing the system to perform a random walk in temperature space based on short trial simulations. These weights are updated throughout the production simulation by an adaptive weighting method. We give a detailed comparison of SREM, ST, as well as standard MD and find that SREM and ST give equivalent results in reasonable agreement with experimental data. In addition, we find that both enhanced sampling methods are much more efficient than standard MD simulations. The melting temperature of the Fs peptide with the AMBER99φ potential was calculated to be about 310K, which is in reasonable agreement with the experimental value of 334K. We also discuss other temperature dependent properties of the helix-coil transition. Although ST has certain advantages over SREM, both SREM and ST are shown to be powerful methods via distributed computing and will be applied extensively in future studies of complex bimolecular systems.
Local reactivity of O2 with Pt3 on Co3Pt and related backgrounds
Authors: Sotelo Juan C. , Seminario Jorge M.
Published: May 2008

We study the local reactivity of molecular oxygen with bimetallic substrates of a platinum trimer island supported on nanotips of CoPt, Pt, Co, Ni, and Fe. Because of the reduced interatomic distances and varying interaction strengths with the substrates, the supported island interaction with oxygen can be tuned from stronger to weaker relative to the interaction of a freestanding island with oxygen despite that there is no well-behaved trend with the binding energy of the island to the substrates.
An inherent structure view of liquid-vapor interfaces
Authors: Stillinger Frank H.
Published: May 2008

The formal statistical mechanical theory describing liquid-vapor interfaces at thermal equilibrium has been incomplete, owing partly to discrepancies between two primary views, the local free energy approach originated by van der Waals and the capillary wave approach initiated by Mandelstam. The former provides detailed prescriptions for interfacial density profiles and surface tensions, and has recently been tailored to conform to nonclassical critical phenomena. The latter postulates a crude discontinuous density profile that is geometrically delocalized by surface excitations, but which qualitatively incorporates basic gravitational effects that are missing in the van der Waals method. The present analysis provides a formalism within which both approaches can be reconciled. It draws upon the inherent structure mapping procedure to define an intrinsic liquid-vapor density profile which invokes no arbitrary parameters that are not already present in the many-particle potential energy function or its thermodynamics. By construction, this intrinsic profile plays a role conventionally given to a van der Waals interface profile, and although it is free of capillary waves it can serve as a starting point for evaluating the gravitational implications of those interfacial fluctuation effects.
Universal mathematical identities in density functional theory: Results from three different spin-resolved representations
Authors: Pérez P. , Chamorro E. , Ayers Paul W.
Published: May 2008

This paper supersedes previous theoretical approaches to conceptual DFT because it provides a unified and systematic approach to all of the commonly considered formulations of conceptual DFT, and even provides the essential mathematical framework for new formulations. Global, local, and nonlocal chemical reactivity indicators associated with the “closed-system representation” ([Nα,Nβ,να(r),νβ(r)]) of spin-polarized density functional theory (SP-DFT) are derived. The links between these indicators and the ones associated with the “open-system representation” ([μα,μβ,να(r),νβ(r)]) are derived, including the spin-resolved Berkowitz–Parr identity. The Legendre transform to the “density representation” ([ρα(r),ρβ(r)]) is performed, and the spin-resolved Harbola–Chattaraj–Cedillo–Parr identities linking the density representation to the closed-system and open-system representations are derived. Taken together, these results provide the framework for understanding chemical reactions from both the electron-following perspective (using either the closed-system or the open-system representation) and electron-preceding perspective (density representation). A powerful matrix-vector notation is developed; with this notation, identities in conceptual DFT become universal. Specifically, this notation allows the fundamental identities in conventional (spin-free) conceptual DFT, the [Nα,Nβ] representation, and the [N=Nα+Nβ,NS=Nα−Nβ] representation to be written in exactly the same forms. In cases where spin transfer and electron transfer are coupled (e.g., radical+molecule reactions), we believe that the [Nα,Nβ] representation may be more useful than the more common [N,NS] representation.
Ambipolar electrical spin injection and spin transport in organic semiconductors
Authors: Yunus M. , Ruden P. P. , Smith D. L.
Published: May 2008

We present a model to describe electrical injection of spin polarized electrons and holes from ferromagnetic contacts into a conjugated organic semiconductor. Transport in the semiconductor is treated by the spin dependent continuity equations coupled with Poisson’s equation. The recombination of injected electrons and holes is modeled as a Langevin process. The boundary conditions used to solve the continuity equations are formulated in terms of spin polarized particle currents at the boundaries. Injected spin currents are related to the charge currents via the transport parameters of the ferromagnetic contacts. Spin injection strongly depends on the contact polarization and the conductivity of the contact material. No approximations that limit the model to small current polarizations are made. In the case of conventional ferromagnetic metal contacts, the relatively weak polarization and high conductivity hinder spin polarized injection. Spin injection can be greatly enhanced if (spin dependent) tunneling is the limiting process, which may be described by spin dependent contact resistances. The dependence of the current polarization on these contact resistances is explored. On the other hand, if the injecting contacts are made from half-metallic materials with low conductivity, spin injection is strong even for thermionic injection and the spin current approaches the charge current.
Infrared luminescence and amplification properties of Bi-doped GeO2−Ga2O3−Al2O3 glasses
Authors: Zhou Shifeng , Dong Huafang , Zeng Heping , Hao Jianhua , Chen Jingxin , Qiu Jianrong
Published: May 2008

Bi, Ga, and Al codoped germanium glass was prepared and its optical properties were investigated by absorption, photoluminescence excitation (PLE), and photoluminescence spectra. Two active centers which occupy strong and weak crystal field environment are identified by using the PLE spectrum. The tunable and ultrabroadband luminescence properties are originated from electron transitions of these two active centers. Internal optical gain around 1300 and 1560 nm has been detected. The wavelength-dependent internal gains excited with 808 and 980 nm laser diodes show different characteristics, and the relative flat optical amplification can be realized by choosing 980 nm pumping.
Coexistence of direct and indirect band structures in arrays of InAs∕AlAs quantum dots
Authors: Shamirzaev Timur S. , Nenashev Alexey V. , Zhuravlev Konstantin S.
Published: May 2008

We report studies of energy structure of InAs self-assembled quantum dots (QDs) embedded in AlAs matrix by stationary and transient photoluminescence and calculations. Calculation reveals that the QDs have band alignment structure of type I. Photoluminescence demonstrates low-energy and high-energy bands with drastically different decay time related to carries recombination in QDs of different sizes. The experimental results evidence a direct-indirect transition of the QD conduction band structure with decreasing their size.
Production of cumulative jets by ablatively-driven implosion of hollow cones and wedges
Authors: Nikitin S. P. , Grun J. , Aglitskiy Y. , Manka C. , Zabetakis D. , Velikovich A. L. , Miller C.
Published: May 2008

Cumulative plasma jets formed by hollow cones imploded via laser ablation of their outer surfaces were observed. The velocity, shape, and density of the jets are measured with monochromatic 0.65keV x-ray imaging. Depending on cone geometry, cumulative jets with ion density ∼2×1020cm−3 and propagation velocities >10km∕s are formed. Similar results are observed when jets are formed by imploding wedges. Such jets can be used to simulate hydrodynamics of astrophysical jets interacting with stellar or interstellar matter.
Structural properties of dusty plasma in direct current and radio frequency gas discharges
Authors: Ramazanov T. S. , Dzhumagulova K. N. , Jumabekov A. N. , Dosbolayev M. K.
Published: May 2008

This paper presents radial distribution functions of dust particles obtained experimentally in dc and rf discharges. Pressure and interaction energy of dusty particles were calculated on the basis of these functions. The Langevin dynamics computer simulation for each experiment was performed. The comparisons with computer simulations are made.
Parametric conversion of a lower hybrid wave into a whistler in a plasma
Authors: Kumar Pawan , Tripathi V. K.
Published: May 2008

A large amplitude lower hybrid wave parametrically decays into a whistler wave and a low frequency lower hybrid wave in a plasma. The density perturbation due to the low frequency wave couples with the oscillatory velocity due to the pump wave to produce a nonlinear current, driving the whistler. The pump and whistler exert a low frequency ponderomotive force on electrons, driving the lower hybrid decay wave. The growth rate of the parametric instability scales linearly with the amplitude of the pump wave. It decreases with the electron cyclotron frequency. The process is relevant to beam plasma systems where lower hybrid waves are excited with greater ease and the whistler sideband wave can be seen outside the plasma as electromagnetic emission.
Modeling characteristics of nonequilibrium processes during breakdown of capacitive rf argon glow discharge
Authors: Deng Yongfeng , Han Xianwei , Shafiq-ur-Rehman  , Liu Yue
Published: May 2008

A self-consistent, diffusion-drift approximated fluid model including ion and electron continuity equations and an electron energy equation is presented for simulating the nonequilibrium characteristics during breakdown of argon rf glow discharge. The nonlinear partial differential equations of the model are solved numerically by using a so-called finite volume method. The numerical results indicate that there exist two different phases on the breakdown curves, i.e., the low p⋅d phase and high p⋅d phase. The breakdown voltage, analyzed for three different gaps, varies little in low p⋅d phase while in the high p⋅d phase, it increases linearly with pressure increase. Time evolution of Ohmic heating and energy loss during breakdown are presented in detail. Analysis yields that the heating mechanisms are the dominant factors in breakdown. Moreover, the steady discharge characteristics are also studied specifically under breakdown voltage of 10Torr. The charged particle densities are on the order of 1015∕m3 and the electron energy has two characteristic values at different rf phases.
Slowly oscillating modes in the passive scalar diffusion in stratified turbulence
Authors: Hanazaki Hideshi
Published: May 2008

Scalar fluxes in unsteady stratified turbulence are investigated when vertical mean gradients of both the density (active scalar) and the passive scalar exist. Analytical solutions by the rapid distortion theory show that there is a “slowly” oscillating mode in the passive scalar flux, whose oscillation period is twice as large as that of the density flux. For passive scalars with high Schmidt number Sc>2Pr∕(1+Pr) (Pr: Prandtl number of density), this slow mode with small initial decay becomes dominant, so that temporal oscillation of Kc (turbulent diffusion coefficient of the passive scalar) persists with larger amplitude than the density diffusion coefficient Kρ. On the other hand, at low Schmidt number Sc<2Pr∕(1+Pr)<2, slow mode suffers strong initial decay, so that Kc and Kρ decay at the similar rate. These results illustrate the importance of molecular diffusivity and unsteadiness in weak turbulence which would make significant difference between Kc and Kρ. A criterion for which the linear mechanisms become important is also derived. When the buoyancy Reynolds number Reb (=ϵ∕νN2, ϵ: energy dissipation rate; N: Brunt–Väisälä frequency) is smaller than Re(l0)[=u(l0)l0∕ν], i.e., the Reynolds number defined at the integral scale l0, turbulent energies, and fluxes would be affected by linear processes. This suggests that large value of Reb does not necessarily mean strong nonlinearity, and the differential diffusion previously observed in stratified turbulence for Reb≲103 could be due to linear processes.
Recent results for plasma antennas
Authors: Alexeff Igor , Anderson Ted , Farshi Esmaeil , Karnam Naresh , Pulasani Nanditha Reddy
Published: May 2008

Plasma antennas are just as effective as metal antennas. They can transmit, receive, and reflect radio waves just as well as metal antennas. In addition, plasma generated noise does not appear to be a problem.
Sound generation by head-on and oblique collisions of two vortex rings
Authors: Nakashima Yoshitaka
Published: May 2008

Sound generation by head-on and oblique collisions of two vortex rings with equal strength is investigated by a direct numerical simulation. The three-dimensional, unsteady, compressible Navier–Stokes equations are solved by a finite difference method, not only for a near-vortical field but also for a far-acoustic field. The theory of vortex sound is also applied to investigate the detailed relation between the vortex ring motion and the acoustic wave mode. Generation of two sound pressure waves, which are called the first and second pulses, is observed in the numerical results. The theoretical results show that, for the head-on collision, the generations of the first and second pulses are due to the variations of vorticity moment, associated with a decrease in the translational velocity of the vortex ring near the collision plane and its stretching motion, respectively. On the other hand, for the oblique collision, in addition to such generation mechanisms, the reconnection of vortex lines also affects the generation of the second pulse. The reconnection of vortex lines occurs more rapidly for a smaller collision angle, and therefore its contribution to the second pulse becomes large. In fact, in the oblique collision at a right angle, the generation of the second pulse is closely related to the reconnection of vortex lines, which can be seen by analyzing both the near and far fields. Furthermore, for a smaller collision angle, the reconnection of vortex lines leads to more rapid variation of the vorticity, which enhances asymmetric features of the second pulse exhibited by the octupole mode (third-order wave mode).
Molecular theory of barycentric velocity: Monatomic fluids
Authors: Eu Byung Chan
Published: May 2008

The notion of barycentric velocity appears in irreversible thermodynamics and fluid mechanics, in which it is a field variable obeying the hydrodynamic equations or, more specifically, the momentum balance equation, which is coupled to the rest of hydrodynamic equations. Therefore, its behavior is not known until the hydrodynamic equations are solved for the flow problem of interest. Unlike diffusion fluxes, heat fluxes, or stresses, it does not have its own constitutive relation similar to Fick’s law, Fourier’s law, and Newton’s law of viscosity. In this work, the constitutive equation is derived for it. In parallel to the phenomenological notion of barycentric velocity, the notion of mean fluid velocity appears in statistical mechanics of irreversible dynamic processes according to the theory of Irving and Kirkwood [J. Chem. Phys. 18, 817 (1950)], and plays the same role of the phenomenological counterpart. In this work, we investigate the statistical mechanical meanings of the mean fluid velocity of a fluid in flow beyond its formal connection with the barycentric velocity. We show that it consists of two components; the center-of-gravity velocity of the packet of fluid molecules, which may be identified with the barycentric velocity in the phenomenological theory, and the diffusive contribution of its collective modes relative to the center of gravity. If the fluid is uniform in space or if the packet of fluid mass is rigid, the diffusive component vanishes. The statistical mechanical (molecular theory) formula for the mean fluid velocity provides the constitutive relation for it in terms of density and temperature gradients present in the fluid in flow. The constitutive relation obtained for the mean fluid velocity can be an important component in the theory of transport processes in liquids. Its significance to fluid mechanics is briefly discussed.
Influence of the dendron chemical structure on the photophysical properties of bisfluorene-cored dendrimers
Authors: Ribierre J. C. , Ruseckas A. , Samuel I. D. W. , Barcena H. S. , Burn P. L.
Published: May 2008

A detailed study of the photophysics of a family of bisfluorene-cored dendrimers is reported. Polarized time-resolved fluorescence, singlet-singlet exciton annihilation and fluorescence quantum yield measurements were performed and used to understand how the dendron structure affects the light-emitting properties of the materials. The exciton diffusion rate is similar in all films studied. An increase in the nonradiative deactivation rate by nearly one order of magnitude is observed in films of dendrimers with stilbenyl and carbazolyl based dendrons as compared to solutions, whereas the dendrimers with biphenyl and diphenylethylenyl dendrons showed highly efficient emission (photoluminescence quantum yields of 90%) in both solution and the solid state. The results of the materials that show fluorescence quenching can be explained by the presence of quenching sites at a concentration of just a fraction of a percent of all macromolecules. A possible explanation of this quenching is hole transfer from the emissive chromophore to the dendron in a face-to-face geometry. These results are important for the design of efficient blue emitters for optoelectronic applications.
Determination of the rate constant for sulfur recombination by quasiclassical trajectory calculations
Authors: Du Shiyu , Francisco Joseph S. , Shepler Benjamin C. , Peterson Kirk A.
Published: May 2008

The sulfur recombination reaction has been thought of as one of the most important chemical reactions in the volcanic activities of the planet. It is also important in determining the propagation of elemental sulfur in the atmosphere. There have been two experimental attempts to determine the reaction rate of the S+S→S2 recombination, however their results differ by four orders of magnitude. In this work, we determine the rate constant of S+S→S2 from quasiclassical trajectory calculations. The third order rate constant at 298.15K predicted by the present calculations is 4.19×10−33cm6molecules−2s−1, which is in excellent agreement with the determination of Fair and Thrush [Trans. Faraday Soc. 65, 1208 (1969)]. The temperature dependent rate constant is determined to be 3.94×10−33exp[205.56(1∕T−1∕298.15)], which was determined from the temperature range of 100–500K.