bluuebunny/crossref_metadata_2025 huggingface dataset:
Global chemical transport model study of ozone response to changes in chemical kinetics and biogenic volatile organic compounds emissions due to increasing temperatures: Sensitivities to isoprene nitrate chemistry and grid resolution
Authors: Ito Akinori , Sillman Sanford , Penner Joyce E.
Published: April 2009

Global modeling studies show a wide variability in the response of the O3 budget to climate change as projected by applying Intergovernmental Panel on Climate Change scenarios in climate models. We employ sensitivity studies to elucidate the major uncertainties in the response of tropospheric O3 to perturbations in biogenic volatile organic compounds (BVOC) emissions and reaction rate coefficients due to changes in temperature. The change in global O3 burden due to an increase in BVOC emissions associated with a +5 K depends critically on the assumed treatment for the fraction of NOx recycled (0–100%) from isoprene nitrate (+9 to +34 Tg), in contrast to the chemical reaction rate coefficients response (−8 to −9 Tg). The model O3 burden shows sensitivity (40 Tg) to the NOx recycling efficiencies (0–100%) similar to the burden's sensitivity to the grid resolution (4° × 5°–1° × 1°). The correlation of O3 with total alkyl nitrates (ΣANs) in the surface air at a California forest site shows sensitivity to the NOx recycling (40–100%) similar to the correlation's sensitivity to the horizontal resolution (4° × 5°–1° × 1°). The results of the sensitivity simulations imply that the slope of O3 to ΣANs might be used to constrain the yield of isoprene nitrate and NOx recycling fraction, but better agreement could be achieved by using a higher‐resolution model with even higher NOx recycling from isoprene nitrate. Our results suggest that the reduction of NOx recycling from isoprene nitrate be set apart from that due to the effect of the grid resolution in the chemical transport model.
How well do IPCC‐AR4/CMIP3 climate models simulate global dimming/brightening and twentieth‐century daytime and nighttime warming?
Authors: Wild Martin
Published: April 2009

Observations indicate that greenhouse induced twentieth‐century warming has been strongly modulated by variations in surface solar radiation. Between the 1950s and 1980s, declining surface solar radiation (“global dimming”) likely caused a dampening of global warming, whereas increasing surface solar radiation (“brightening”) may have contributed to the rapid warming in the last 2 decades, and possibly also in the first half of the twentieth century. This is also reflected in the decadal evolution of diurnal temperature range, which is highly correlated with surface solar radiation, and which shows a distinct transition from a strong decrease between the 1950s and 1980s, toward a leveling off thereafter. The present study investigates to what extent these effects are simulated in the latest generation of global climate models used in the fourth Intergovernmental Panel on Climate Change (IPCC) assessment report (AR4) (phase 3 of the Coupled Model Intercomparison Project (CMIP3) models). While these models reproduce the overall twentieth century warming over global land surfaces well, they underestimate the decadal variations in the warming and particularly also in diurnal temperature range, indicative of a lack of decadal variations in surface solar radiation in the models.
Water vapor abundance near the surface of Venus from Venus Express/VIRTIS observations
Authors: Bézard Bruno , Tsang Constantine C. C. , Carlson Robert W. , Piccioni Giuseppe , Marcq Emmanuel , Drossart Pierre
Published: April 2009

Nightside observations of the 1.18‐μm atmospheric window by the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) aboard the Venus Express spacecraft were analyzed to measure and map the water vapor abundance in the lower atmosphere. Thermal emission in this window originates partly from the surface and partly from the first scale height (0–15 km) of the atmosphere. Constraints on the CO2 continuum absorption, which is the dominant source of gaseous opacity in the window, were obtained from the variation of the 1.185‐μm intensity with surface elevation. An absorption coefficient of 1 ± 0.4 × 10−9 cm−1 amagat−2 best fits the observed variation. We retrieved a water vapor mole fraction of 44 ± 9 ppm from various selections of VIRTIS spectra in the southern hemisphere, in agreement with previous analyses of the nightside emission. This value is somewhat larger than that previously determined at higher altitudes from the 2.3‐ and 1.74‐μm nightside windows, but the error bars still allow a constant with height H2O mole fraction from the surface up to 40 km. Using the intensity ratio in the two wings of the 1.18‐μm window as a proxy, we searched for horizontal variations of the H2O abundance in various VIRTIS observational sequences. We derived stringent upper limits for any possible latitudinal variations on the night side: ±1.5% in the range 60°S–25°N and ±3% for the broader range 80°S–25°N. The lack of detectable latitudinal variations is consistent with a constant with height water profile in the lower atmosphere and probably precludes any strong concentration gradient near the surface.
Non‐dipolar solar wind structure observed in the cycle 23/24 minimum
Authors: Tokumaru M. , Kojima M. , Fujiki K. , Hayashi K.
Published: May 2009

Interplanetary scintillation (IPS) observations made in the Cycle 23/24 minimum using the Solar‐Terrestrial Environment Laboratory (STEL) multi‐station system indicated that during intervals the solar wind had a significantly non‐dipolar structure that consisted of fast wind components at the poles and the equator and slower wind components in between. The solar wind structure revealed from the IPS observations was consistent with a marked increase in the occurrence of fast winds observed in situ near the earth. The poleward boundary of the slow wind region observed during this minimum was ±30 north and south. In addition, our IPS observations revealed that the organization of the 3‐dimensional solar wind was highly variable during 2007–2008. These features greatly differ from those observed during the previous minima. This fact may be attributed to the weak magnetic field intensity at the poles during the Cycle 23/24 minimum.
Photochemistry of OIO: Laboratory study and atmospheric implications
Authors: Gómez Martín Juan C. , Ashworth Stephen H. , Mahajan Anoop S. , Plane John M. C.
Published: April 2009

Iodine chemistry influences the oxidizing capacity of the atmosphere, principally by depleting ozone, and induces the formation of new particles in the marine boundary layer. The photochemistry of iodine dioxide (OIO) plays a key role in both these processes. Here we report that OIO photolyses in the visible (480–650 nm), yielding iodine atoms with a quantum efficiency of unity (1.07 ± 0.15). As a result, much smaller sources of iodine precursors are required to cause significant ozone depletion, which has important implications for the marine boundary layer ozone budget.
Constraints on shear wave attenuation in the Earth's inner core from an observation of PKJKP
Authors: Cao A. , Romanowicz B.
Published: April 2009

Based on the high quality broadband data from Gräfenberg array in Germany, we recently detected a reliable PKJKP phase, for which four kinds of evidence (travel time, slowness, back‐azimuth, and comparison with a pseudo‐liquid inner core model) were simultaneously provided. Also, for the first time, a clear waveform of PKJKP was observed. This gives us an unprecedented opportunity to put constraints on the shear wave attenuation in the earth's inner core using body waves. In order to minimize the potential influence of dispersion and phase shift caused by mantle heterogeneity, we adopt an envelope modeling approach. Our results show that the estimated Qβ from the shear phase PKJKP is significantly larger (∼315 ± 150) than that from normal mode observations. Because PKJKP samples the deep inner core, this indicates an increase of Qβ with depth in the inner core, in agreement with what is generally observed for Qα.
Abundance, composition, diversity and novelty of soil Proteobacteria
Authors: Spain Anne M , Krumholz Lee R , Elshahed Mostafa S
Published: April 2009

Small subunit (16S) rRNA gene surveys generating near full-length 16S rRNA clones offer a unique opportunity for in-depth phylogenetic analysis to highlight the breadth of diversity within various major bacterial phyla encountered in soil. This study offers a detailed phylogenetic analysis of the Proteobacteria-affiliated clones identified from 13 001 nearly full-length 16S rRNA gene clones derived from Oklahoma tall-grass prairie soil. Proteobacteria was the most abundant phylum in the community, and comprised 25% of the total clones. The most abundant and diverse class within the Proteobacteria was Alphaproteobacteria, followed by the Delta-, Beta- and Gammaproteobacteria. Members of the Epsilon- and Zetaproteobacteria were not detected in the dataset. Our analysis identified 15 novel order-level and 48 novel family-level Proteobacteria lineages. In addition, we show that the majority of Proteobacteria clones in the dataset belong to orders and families containing no described cultivated representatives (50% and 65%, respectively). An examination of the ecological distribution of the six most abundant Proteobacteria lineages in this dataset with no characterized pure culture representatives provided important information regarding their global distribution and environmental preferences. This level of novel phylogenetic diversity indicates that our understanding of the functions of soil microorganisms, even those belonging to phyla with numerous and diverse well-characterized cultured representatives such as the Proteobacteria, remains far from adequate.
Genetic and Environmental Contributions to Phenotypic Components of Metabolic Syndrome: A Population‐based Twin Study
Authors: Zhang Shanchun , Liu Xin , Yu Yunxian , Hong Xiumei , Christoffel Katherine K. , Wang Binyan , Tsai Hui‐Ju , Li Zhiping , Liu Xue , Tang Genfu , Xing Houxun , Brickman Wendy J. , Zimmerman Donald , Xu Xiping , Wang Xiaobin
Published: April 2009

The increasing prevalence of metabolic syndrome (MS) poses a serious public‐health problem worldwide. Effective prevention and intervention require improved understanding of the factors that contribute to MS. We analyzed data on a large twin cohort to estimate genetic and environmental contributions to MS and to major MS components and their intercorrelations: waist circumference (WC), systolic (SBP) and diastolic blood pressure (DBP), fasting plasma glucose (FPG), triglycerides (TGs), and high‐density lipoprotein–cholesterol (HDL‐C). We applied structural equation modeling to determine genetic and environmental structure of MS and its major components, using 1,617 adult female twin pairs recruited from rural China. The heritability estimate for MS was 0.42 (95% confidence interval (CI): 0.00–0.83) in this sample with low MS prevalence (4.4%). For MS components, heritability estimates were statistically significant and ranged from 0.13 to 0.64 highest for WC, followed by TG, SBP, DBP, HDL‐C, and FPG. HDL‐C was mainly influenced by common environmental factors (0.62, 95% CI: 0.58–0.62), whereas the other five MS components were largely influenced by unique environmental factors (0.32–0.44). Bivariate Cholesky decomposition analysis indicated that the clinical clustering of MS components may be explained by shared genetic and/or environmental factors. Our study underscores the importance of examining MS components as intercorrelated traits, and to carefully consider environmental and genetic factors in studying MS etiology.
Randomized Trial of a Behavioral Weight Loss Intervention for Low‐income Women: The Weight Wise Program
Authors: Samuel‐Hodge Carmen D. , Johnston Larry F. , Gizlice Ziya , Garcia Beverly A. , Lindsley Sara C. , Bramble Kathy P. , Hardy Trisha E. , Ammerman Alice S. , Poindexter Patricia A. , Will Julie C. , Keyserling Thomas C.
Published: April 2009

Low‐income women in the United States have the highest rates of obesity, yet they are seldom included in weight loss trials. To address this research gap, components of two evidence‐based weight loss interventions were adapted to create a 16‐week intervention for low‐income women (Weight Wise Program), which was evaluated in a randomized trial with the primary outcome of weight loss at 5‐month follow‐up. Participants were low‐income women (40–64 years) with a BMI of 25–45. Of 143 participants, 72 were randomized to the Weight Wise Program (WWP) and 71 to the Control Group (CG). Five‐month follow‐up data were obtained from 64 (89%) WWP and 62 (87%) CG participants. With baseline values carried forward for missing data, WWP participants had a weight change of −3.7 kg compared to 0.7 kg in the CG (4.4 kg difference, 95% confidence interval (CI), 3.2–5.5, P < 0.001). For systolic blood pressure (SBP), change in the WWP was −6.5 mm Hg compared to −0.4 mm Hg among controls (6.2 mm Hg difference, 95% CI, 1.7–10.6, P = 0.007); for diastolic BP (DBP), changes were −4.1 mm Hg for WWP compared to −1.3 mm Hg for controls (2.8 mm Hg difference, 95% CI, 0.0–5.5, P = 0.05). Of the 72 WWP participants, 64, 47, and 19% lost at least 3, 5, and 7% of their initial body weight, respectively. In conclusion, the WWP was associated with statistically significant and clinically important short‐term weight loss.
Fat and Water 1H MRI to Investigate Effects of Leptin in Obese Mice
Authors: James Judy R. , Hertel JeAnne L. , Babsky Andriy M. , Hekmatyar S.K. , Heiman Mark L. , Jackson Charles V. , Bansal Navin
Published: April 2009

Leptin is known to be associated with regulation of body weight and fat content. The effects of exogenous leptin on abdominal visceral (VS) and subcutaneous (SC) fat volume and hepatic fat‐to‐water ratio in leptin‐deficient obese mice were investigated by 1H magnetic resonance imaging (MRI). Chemical shift‐selected fat and water 1H MRI of control and leptin‐treated mice were obtained 1 day before treatment and after 7 days of treatment (0.3 mg/kg/day). Hepatic fat‐to‐water ratio and VS fat volume decreased significantly with treatment, whereas SC fat volume did not change. Noninvasive measurement of fat and water content in different body regions using MRI should prove useful for evaluating new drugs for the treatment of obesity and other metabolic disorders.
Epidemiology of Speech and Language Impairment in a Nationally Representative Sample of 4- to 5-Year-Old Children
Authors: McLeod Sharynne , Harrison Linda J.
Published: April 2009

Purpose

To draw on multiple sources of information to determine prevalence of speech and language impairment in young Australian children.

Method

Information about 4,983 children (ages 4–5 years) from Growing Up in Australia: The Longitudinal Study of Australian Children (Australian Institute of Family Studies, 2007) was obtained via parent interviews and questionnaires, teacher questionnaires, and direct assessment. Data were statistically weighted to the Australian population of 253,202 children in the target age group.

Results

Parent-reported prevalence: 25.2% had concerns about how their child talked and made speech sounds (11.8% “concerned”; 13.4% “a little concerned”), and 9.5% had concerns about how their child understood language (4.4% “concerned”; 5.1% “a little concerned”). Parents who reported concerns identified “speech not clear to others” as the most frequent area of difficulty (12.0%).Teacher-reported prevalence: 22.3% of children were considered to be less competent than others in their expressive language ability (6.7% “much less competent”; 15.6% “less competent”); 16.9% were considered to be less competent than others in their receptive language ability (4.0% “much less competent”; 12.9% “less competent”). The match between parent and teacher identification was higher for expressive speech and language concern than for receptive language.Direct assessment: 13.0% of children were 1–2SDs below the mean on the Adapted Peabody Picture Vocabulary Test–III (S. Rothman, 2003), and a further 1.7% were > 2SDs below the mean. Parent and teacher reports were significantly correlated with scores obtained via direct assessment.Period prevalence: Parents and teachers reported that 14.5% of children had accessed speech-language pathologist (SLP) services. 2.2% indicated that they needed but could not access an SLP.

Conclusion

Multiple indicators of speech and language impairment in diverse contexts confirmed the high prevalence of this condition in early childhood and a concomitant need for SLP services.
School-Age Children Talk About Chess: Does Knowledge Drive Syntactic Complexity?
Authors: Nippold Marilyn A.
Published: April 2009

Purpose

This study examined language productivity and syntactic complexity in school-age children in relation to their knowledge of the topic of discussion—the game of chess.

Method

Children (
N
= 32; mean age = 10;11 [years;months]) who played chess volunteered to be interviewed by an adult examiner who had little or no experience playing chess. Children’s chess knowledge and experience was assessed, and each child was classified as a novice or an expert player. Each child participated in 3 speaking tasks: General Conversation, Chess Conversation, and Chess Explanation. Interviews were audiorecorded, transcribed into Systematic Analysis of Language Transcripts (J. F. Miller & R. Chapman, 2003), segmented into T-units, and coded for finite clauses. Each speaking task was analyzed for total T-units; mean length of T-unit; clausal density; and nominal, relative, and adverbial clause use.

Results

Total T-units, mean length of T-unit, clausal density, and the use of each type of subordinate clause was substantially higher in the Chess Explanation task compared with the Chess Conversation task or the General Conversation task. Compared with the novices, the experts knew more about chess, had played longer, and were stronger players. Nevertheless, the novices and experts did not differ on any of the language factors for any of the speaking tasks.

Conclusions

Language productivity and syntactic complexity in school-age children are strongly influenced by the speaking task. When children are presented with a motivating and challenging topic, they rise to the occasion to explain the finer details of it to a naïve adult.
Enhancement of emission from CdSe quantum dots induced by propagating surface plasmon polaritons
Authors: Lin T. J. , Chuang W. J. , Cheng Soofin , Chen Y. F.
Published: April 2009

The influence on the emission property of CdSe quantum dots arising from propagating surface plasmon polaritons based on interconnected periodic gold nanoarrays with a large area of 1 cm2 is reported. Variation in the structural parameters allows us to tune the surface plasmon resonance to the emission band of quantum dots, which can result in an enhancement up to 54 times in the external quantum efficiency. Our strategy for the enhancement of luminescence efficiency from semiconductor quantum dots should be useful for the creation of high efficiency solid state emitters.
Energy conservation in collision broadening over a sequence of scattering events in semiclassical Monte Carlo simulation
Authors: Aksamija Z. , Ravaioli U.
Published: April 2009

In this paper, we discuss energy conservation when collisional broadening is considered, and a Lorentzian lineshape assumed, in a Monte Carlo simulation of electron transport. We show that collisional broadening with a Lorentzian distribution does not lead to energy conservation on the average over many electron-phonon collision events. We compute the expected value of departure from energy conservation for a realistic silicon bandstructure, and compare it to results from full-band Monte Carlo simulation to show good agreement. Finally, we propose a corrected distribution approach, where the Lorentzian distribution is divided by the density-of-states curve to obtain a distribution which is able to conserve energy in the average over many electron-phonon collisions.
Dielectric breakdown and inelastic electron tunneling spectroscopy of top and bottom pinned Co–Fe–B/MgO/Co–Fe–B magnetic tunnel junctions
Authors: Khan Ayaz Arif , Schmalhorst J. , Thomas A. , Drewello V. , Reiss G.
Published: April 2009

The time dependent dielectric breakdown in Co–Fe–B/MgO/Co–Fe–B magnetic tunnel junctions was investigated by voltage ramp experiments. The measurements were done for two types of junctions: one set of junctions had exchange biased (pinned) bottom electrodes and one set had exchange biased (pinned) top electrodes with an additional artificial ferrimagnet. We found a significant polarity dependence in the dielectric breakdown: top as well as bottom pinned tunnel junctions showed higher breakdown voltage when the top electrode was biased positively compared to negative bias. In contrast to this the differential resistance (dV/dI)−V spectra revealed an asymmetry for the top pinned junctions which was reversed in comparison to the bottom pinned system. This indicates that both asymmetries have different origins. Additionally the bottom pinned junctions showed in general slightly lower breakdown voltages and stronger magnon excitation in the inelastic electron tunneling (d2I/dV2)−V spectra than the top pinned junctions. Possible reasons for these correlations are discussed.
Particle-in-cell with Monte Carlo collision modeling of the electron and negative hydrogen ion transport across a localized transverse magnetic field
Authors: Kolev St. , Hagelaar G. J. M. , Boeuf J. P.
Published: April 2009

The control of the electron temperature and charged particle transport in negative hydrogen ion sources has a crucial role for the performance of the system. It is usually achieved by the use of a magnetic filter—localized transverse magnetic field, which reduces the electron temperature and enhances the negative ion yield. There are several works in literature on modeling of the magnetic filter effects based on fluid and kinetic modeling, which, however, suggest rather different mechanisms responsible for the electron cooling and particle transport through the filter. Here a kinetic modeling of the problem based on the particle-in-cell with Monte Carlo collisions method is presented. The charged particle transport across a magnetic filter is studied in hydrogen plasmas with and without including volume production of negative ions, in a one-dimensional Cartesian geometry. The simulation shows a classical (collisional) electron diffusion across the magnetic filter with reduction in the electron temperature but no selective effect in electron energy is observed (Coulomb collisions are not considered). When a bias voltage is applied, the plasma is split into an upstream electropositive and a downstream electronegative regions. Different configurations with respect to bias voltage and magnetic field strength are examined and discussed. Although the bias voltage allows negative ion extraction, the results show that volume production of negative ions in the downstream region is not really enhanced by the magnetic filter.
Analysis of the radial transport of tracers in a turbulence simulation
Authors: Sánchez Burillo G. , van Milligen B. Ph. , Thyagaraja A.
Published: April 2009

It has been suggested that radial transport in turbulent plasmas may be nonlocal and non-Markovian. In this paper the transport of test particles in the global, electromagnetic, three-dimensional code CUTIE [A. Thyagaraja et al., Phys. Plasmas 12, 090907 (2005)] is characterized. This code includes a nonlinear feedback mechanism between the meso- and macroscales that are expected to lead to some degree of self-organization that should be reflected in the trajectories of the tracer particles. Several techniques are used to analyze these trajectories, and indeed long-range spatial and temporal correlations are detected, indicating that effective global radial transport in CUTIE does not satisfy the traditional paradigm of diffusive transport. Part of this result can be explained from the existence of propagating ballistic events, and another part from a dependence of local transport properties on the safety factor: local transport is found to depend sensitively on the position relative to specific rational surfaces.
Mechanism and dynamics of the reaction of XeF2 with fluorinated Si(100): Possible role of gas phase dissociation of a surface reaction product in plasmaless etching
Authors: Hefty R. C. , Holt J. R. , Tate M. R. , Ceyer S. T.
Published: April 2009

Xenon difluoride is observed to react with Si–Si σ-dimer and σ-lattice bonds of Si(100)2×1 at 150 K by single and two atom abstraction at F coverages above 1 ML. As in the limit of zero F coverage, a measurable fraction of the scattered, gas phase product of single atom abstraction, XeF, is sufficiently internally excited to dissociate into F and Xe atoms before detection. Using the XeF internal energy and orientation distributions determined in the limit of zero coverage, the laws of conservation of momentum, energy, and mass are applied to the measured F velocity and angular distributions at higher coverage to simulate the Xe atom velocity and angular distributions and their intensities at higher coverage. The simulation predicts the observed Xe atom velocity and angular distributions at high coverage reasonably well, largely because the exothermicity channeled to XeF remains approximately constant as the coverage increases. This constancy is an opportune consequence of the trade-off between the attractiveness of the potential energy surface as the coverage is increased and the dynamics of the XeF product along the potential surface. The energy, momentum, and mass conservation analysis is also used to distinguish between Xe atoms that arise from XeF gas phase dissociation and Xe atoms that are produced by two atom abstraction. This distinction enables the calculation of percentages of the single and two atom abstraction pathways, as well as the percentages of the two pathways available to the Xe atom produced by two atom abstraction, inelastic scattering, and desorption. Finally, the simulation reveals that between 9% and 12% of F atoms produced by gas phase dissociation of XeF are scattered back toward the surface. These F atoms likely react readily with Si to form the higher fluorides that ultimately lead to etching. Gas phase dissociation of the scattered product of a surface reaction is a novel mechanism to explain the unique reactivity of XeF2 to etch Si in the absence of a plasma.
Advanced photoelectric effect experiment beamline at Elettra: A surface science laboratory coupled with Synchrotron Radiation
Authors: Panaccione G. , Vobornik I. , Fujii J. , Krizmancic D. , Annese E. , Giovanelli L. , Maccherozzi F. , Salvador F. , De Luisa A. , Benedetti D. , Gruden A. , Bertoch P. , Polack F. , Cocco D. , Sostero G. , Diviacco B. , Hochstrasser M. , Maier U. , Pescia D. , Back C. H. , Greber T. , Osterwalder J. , Galaktionov M. , Sancrotti M. , Rossi G.
Published: April 2009

We report the main characteristics of the advanced photoelectric effect experiments beamline, operational at Elettra storage ring, featuring a fully independent double branch scheme obtained by the use of chicane undulators and able to keep polarization control in both linear and circular mode. The paper describes the novel technical solutions adopted, namely, (a) the design of a quasiperiodic undulator resulting in optimized suppression of higher harmonics over a large photon energy range (10–100 eV), (b) the thermal stability of optics under high heat load via cryocoolers, and (c) the end station interconnected setup allowing full access to off-beam and on-beam facilities and, at the same time, the integration of users’ specialized sample growth chambers or modules.
Microcanonical rates, gap times, and phase space dividing surfaces
Authors: Ezra Gregory S. , Waalkens Holger , Wiggins Stephen
Published: April 2009

The general approach to classical unimolecular reaction rates due to Thiele is revisited in light of recent advances in the phase space formulation of transition state theory for multidimensional systems. Key concepts, such as the phase space dividing surface separating reactants from products, the average gap time, and the volume of phase space associated with reactive trajectories, are both rigorously defined and readily computed within the phase space approach. We analyze in detail the gap time distribution and associated reactant lifetime distribution for the isomerization reaction HCN⇌CNH, previously studied using the methods of phase space transition state theory. Both algebraic (power law) and exponential decay regimes have been identified. Statistical estimates of the isomerization rate are compared with the numerically determined decay rate. Correcting the RRKM estimate to account for the measure of the reactant phase space region occupied by trapped trajectories results in a drastic overestimate of the isomerization rate. Compensating but as yet not fully understood trapping mechanisms in the reactant region serve to slow the escape rate sufficiently that the uncorrected RRKM estimate turns out to be reasonably accurate, at least at the particular energy studied. Examination of the decay properties of subensembles of trajectories that exit the HCN well through either of two available symmetry related product channels shows that the complete trajectory ensemble effectively attains the full symmetry of the system phase space on a short time scale t≲0.5 ps, after which the product branching ratio is 1:1, the “statistical” value. At intermediate times, this statistical product ratio is accompanied by nonexponential (nonstatistical) decay. We point out close parallels between the dynamical behavior inferred from the gap time distribution for HCN and nonstatistical behavior recently identified in reactions of some organic molecules.
Tensor cross sections and collisional depolarization of OH(X 2Π) in collisions with helium
Authors: Dagdigian Paul J. , Alexander Millard H.
Published: April 2009

Tensor cross sections for collisions of OH(X 2Π) with helium are computed using accurate ab initio potential energy surfaces computed by Lee et al. We use these cross sections to predict rate constants for collisional depolarization of specific rotational fine-structure levels of OH(X 2Π) in collisions with helium. Good agreement is found with the results of the two-color polarization spectroscopy experiments of Paterson et al. [J. Chem. Phys. 129, 074304 (2008)]. By examination of partial cross sections, the range of impact parameters at which collisional depolarization occurs is shown to be similar to that for rotationally inelastic collisions.
Theoretical investigation of methane under pressure
Authors: Spanu Leonardo , Donadio Davide , Hohl Detlef , Galli Giulia
Published: April 2009

We present computer simulations of liquid and solid phases of condensed methane at pressures below 25 GPa, between 150 and 300 K, where no appreciable molecular dissociation occurs. We used molecular dynamics (MD) and metadynamics techniques and empirical potentials in the rigid molecule approximation, whose validity was confirmed a posteriori by carrying out ab initio MD simulations for selected pressure and temperature conditions. Our results for the melting line are in satisfactory agreement with existing measurements. We find that the fcc crystal transforms into a hcp structure with four molecules per unit cell (B phase) at about 10 GPa and 150 K, and that the B phase transforms into a monoclinic high pressure phase above 20 GPa. Our results for solid/solid phase transitions are consistent with those of Raman studies but the phase boundaries estimated in our calculations are at higher pressure than those inferred from spectroscopic data.
All-solution based device engineering of multilayer polymeric photodiodes: Minimizing dark current
Authors: Keivanidis Panagiotis E. , Khong Siong-Hee , Ho Peter K. H. , Greenham Neil C. , Friend Richard H.
Published: April 2009

We present photodiodes fabricated with several layers of semiconducting polymers, designed to show low dark current under reverse bias operation. Dark current minimization is achieved through the presence of additional polymer layers that reduce charge carrier injection in reverse bias, when in contact with the device electrodes. All polymer layers are deposited via spin coating and are photocross-linked for allowing further polymer layer deposition, by using a bis-fluorinated phenyl-azide photocross-linking agent. Dark current density values as low as 40 pA/mm2 are achieved with a corresponding external quantum efficiency (EQE) of 20% at a reverse bias of −0.5 V when an electron-blocking layer is used. Dark current is further reduced when both an electron- and a hole-blocking layer are used but the EQE falls significantly.
Purely hopping conduction in c-axis oriented LiNbO3 thin films
Authors: Shandilya Swati , Tomar Monika , Sreenivas K. , Gupta Vinay
Published: May 2009

Dielectric constant and ac conductivity of highly c-axis oriented LiNbO3 thin film grown by pulsed laser deposition were studied in a metal-insulator-metal configuration over a wide temperature (200 to 450 K) and frequency (100 Hz to 1 MHz) range. The preferred oriented Al (1%) doped ZnO film with electrical conductivity 1.1×103 Ω−1 cm−1 was deposited for dual purpose: (1) to serve as nucleating center for LiNbO3 crystallites along preferred c-axis growth direction, and (2) to act as a suitable bottom electrode for electrical studies. The room temperature dc conductivity (σdc) of LiNbO3 film was about 5.34×10−10 Ω−1 cm−1 with activation energy ∼0.3 eV, indicating extrinsic conduction. The ac conductivity σac was found to be much higher in comparison to σdc in the low temperature region (<300 K) and exhibits a power law behavior due to the hopping of charge carriers. In higher temperature region (>300 K), σac shows a weak frequency dependence, whereas dielectric constant exhibits a strong frequency dispersion. The dielectric dispersion data has been discussed in the light of theoretical models based on Debye type mixed conduction and purely hopping conduction. The dominant conduction in c-axis oriented LiNbO3 thin film is attributed to the purely hopping where both σdc and σac arise due to same mechanism.
Multilevel conductance switching in organic memory devices based on AlQ3 and Al/Al2O3 core-shell nanoparticles
Authors: Reddy V. S. , Karak S. , Dhar A.
Published: April 2009

Multilevel conductance switching in organic memory devices based on AlQ3 and Al/Al2O3 core-shell nanoparticles is demonstrated. The effect of middle Al layer thickness and the size of the nanoparticles on device performance are investigated. The high-resolution transmission electron micrographs revealed the formation of core-shell nanoparticles. The device has shown a series of conductance states. These states are nonvolatile in nature and can be accessed by applying proper programming voltage above a threshold voltage. Field-induced transfer of charge carriers between AlQ3 and aluminum core is proposed to be responsible for conductance switching.
Construction of an integrated Raman- and angular-scattering microscope
Authors: Smith Zachary J. , Berger Andrew J.
Published: April 2009

We report on the construction of a multimodal microscope platform capable of gathering both elastically and inelastically scattered light from a 38 μm2 region in both epi- and transillumination geometries. Simultaneous monitoring of elastic and inelastic scattering from a microscopic region allows noninvasive characterization of the chemistry and morphology of a living sample without the need for exogenous dyes or labels, thus allowing measurements to be made longitudinally in time on the same sample as it evolves naturally. A sample is illuminated either from above or below with a focused 785 nm TEM00 mode laser beam, with elastic and inelastic scattering collected by two separate measurement arms. The measurements may be made either simultaneously, if identical illumination geometries are used, or sequentially, if the two modalities utilize opposing illumination paths. In the inelastic arm, Stokes-shifted light is dispersed by a spectrograph onto a charge-coupled device (CCD) array. In the elastic scattering collection arm, a relay system images the microscope’s back aperture onto a CCD array. Postprocessing of the inelastic scattering to remove fluorescence signals yields high quality Raman spectra that report on the sample’s chemical makeup. Comparison of the elastically scattered pupil images to generalized Lorenz–Mie theory yields estimated size distributions of scatterers within the sample.
Dielectric properties of KTa0.6Nb0.4O3 thin films on alumina substrates prepared by chemical solution deposition
Authors: Glinšek S. , Malič B. , Kutnjak Z. , Wang H. , Krupka J. , Kosec M.
Published: April 2009

Dielectric properties of KTa0.6Nb0.4O3 thin films on polycrystalline alumina substrates prepared by chemical solution deposition were investigated. Dielectric measurements were performed in radio frequency range by patterning planar capacitors on the film surface and in microwave frequency range by split-post dielectric resonator method. The relaxorlike behavior of dielectric properties, which has not been determined in K(Ta, Nb)O3 thin films previously, was unambiguously confirmed by the fit to the Vogel–Fulcher law. The room temperature values of permittivity and dielectric losses, measured at 10 kHz, are 2430 and 0.08, respectively. The corresponding values, measured at 14.5 GHz, are 590 and 0.52.
A simple cross-correlation technique between infrared and hard x-ray pulses
Authors: Krässig Bertold , Dunford R. W. , Kanter E. P. , Landahl E. C. , Southworth S. H. , Young L.
Published: April 2009

We report a gas phase technique to establish the temporal overlap of ultrafast infrared laser and hard x-ray pulses. We use tunnel ionization of a closed shell atom in the strong field at the focus of an infrared laser beam to open a distinct x-ray absorption resonance channel with a clear fluorescence signature. The technique has an intrinsic response of a few femtoseconds and is nondestructive to the two beams. It provides a step-functionlike cross-correlation result. The details of the transient provide a diagnostic of the temporal overlap of the two pulses.
The structure of diaminodurene and the dynamics of the methyl groups
Authors: Sobczyk L. , Prager M. , Sawka-Dobrowolska W. , Bator G. , Pawlukojć A. , Grech E. , van Eijck L. , Ivanov A. , Rols S. , Wuttke J. , Unruh T.
Published: April 2009

Diaminodurene crystallizes in the orthorhombic space group Pbca, with eight molecules in the unit cell. Four inequivalent methyl groups with different environments exist in a molecule. The amino groups are also different, which is well reflected in infrared spectra. Two tunneling modes are resolved at 23.7 and 7.0 μeV at 4.5 K. Their intensities are consistent with the presence of two further unresolved tunneling modes. Quasielastic spectra are composed of three Lorentzians of equal intensities. The two low activation energies and tunnel modes are modeled into consistent rotational potentials. The third activation energy and a librational band are used to guess the strength of the two stronger rotational potentials. The internal modes related to the torsional/librational vibrations mix with ring torsions in the range of 70–220 cm−1. This way the tunnel modes couple to ring torsions whose energy determines the broadening of both tunnel bands. The calculations for free molecules yield mode frequencies a little bit lower than the experimental inelastic neutron scattering (INS) values. Application of theoretical methods elaborated for the crystalline state leads to a satisfactory consistency. It is also valid for bending modes of NH2 groups, which in the solid state show much higher frequencies than in the gas phase, as expected.
Fabry–Pérot resonators for surface plasmon polaritons probed by cathodoluminescence
Authors: Kuttge M. , Vesseur E. J. R. , Polman A.
Published: May 2009

Surface plasmon polariton Fabry–Pérot resonators were made in single-crystalline gold by focused ion beam milling of two parallel 100 nm deep grooves. The plasmonic cavity modes were spatially and spectrally resolved using cathodoluminescence spectroscopy. Mode numbers up to n=10 were observed. The cavity quality factor Q depends strongly on groove depth; the highest Q=21 was found for groove depth of 100 nm at λ=690 nm. The data are consistent with finite-difference time domain calculations that show that the wavelength of maximum reflectivity is strongly correlated with groove depth.
Plasma currents induced by resonant magnetic field perturbations in tokamaks
Authors: Reiser D. , Chandra D.
Published: April 2009

The plasma response on externally applied resonant magnetic field perturbations is studied by means of numerical simulations. It is shown that dependent on collisionality and perturbation strength, plasma currents build up which can compensate the external field. These plasma currents are accompanied by out-of-phase currents and poloidal flows at the resonant surfaces. With an increasing perturbation field the screening of the externally applied field decreases and at a certain level, the vacuum field approximation holds for the total magnetic field.
Determination and comparison of kinetic parameters of low density biomass fuels
Authors: Kalita P. , Mohan G. , Pradeep Kumar G. , Mahanta P.
Published: April 2009

Biomass has great potential as a clean, renewable feedstock for producing modern energy carriers. Low density biomass, such as rice husk, sawdust, bamboo dust, etc., can provide a continuous supply of liquid and gaseous fuels through thermochemical conversion processes. In the present study, kinetics of the thermal decomposition of three biomasses such as rice husk, sawdust, and bamboo dust were evaluated under air atmosphere from ambient temperature to 1000 °C at a heating rate of 10 °C min−1. Two distinct reaction zones were observed for all the three biomasses. From the thermogravimetric (TG) and differential TG curves, the activation energies, pre-exponential factors, and order of reaction were determined for both the reaction zones. Experimental results were validated numerically and these results are found to be very close to the numerical results. As observed, thermal decomposition rates in the first reaction zone were found to be significantly higher than those in the second reaction zone.
A phase relation study of Ba–Y–Cu–O coated-conductor films using the combinatorial approach
Authors: Wong-Ng W. , Otani M. , Levin I. , Schenck P. , Yang Z. , Liu G. , Cook L. P. , Feenstra R. , Zhang W. , Rupich M. W.
Published: April 2009

Phase relationships in bulk and thin film Ba–Y–Cu–O high-Tc superconductor system were determined at processing conditions relevant for industrial production of coated conductors. Our results demonstrated that the absence of BaY2CuO5 (which has a critical effect on flux pinning) at 735 °C—a typical temperature employed in production of coated conductors—in thin films processed in situ from the BaF2 precursor is caused by the sluggish reaction kinetics rather than by the presence of fluorine in the system. Thermodynamic calculations combined with annealing experiments confirmed that BaY2CuO5 is thermodynamically stable but forms at temperatures higher than 735 °C.
Electric discharge caused by expanding armatures in flux compression generators
Authors: Shkuratov Sergey I. , Baird Jason , Talantsev Evgueni F. , Altgilbers Larry L.
Published: April 2009

In this letter, we experimentally demonstrate that explosively driven expansion of metallic armature of the magnetic flux compression generator (FCG) plays a dominant role in the formation of plasma and electric discharge initiation inside the FCG.
High sensitivity interdigited capacitive sensors using branched treelike carbon nanotubes on silicon membranes
Authors: Abdi Y. , Ebrahimi A. , Mohajerzadeh S. , Fathipour M.
Published: April 2009

Branched treelike carbon nanotubes on silicon substrate have been exploited for the realization of high sensitivity interdigital capacitive pressure sensors. The interdigital structure has been realized using a micromachining technique on silicon membranes, whereas the growth of nanotubes has been achieved using a direct-current plasma enhanced chemical vapor deposition method. A sequential growth and hydrogenation has led to the formation of multiple branched structures of nanotubes. The growth in an interdigital manner results in a high overlap between neighboring fingers and consequently a magnified response to mechanical variations in the membrane as a result of applying an external pressure is observed. An oscillatory behavior has been observed which may be attributed to the vibration of nanotubes on thinned membranes.
Identification of a C-terminus domain critical for the sensitivity of Kir2.1 to cholesterol
Authors: Epshtein Yulia , Chopra Arun P. , Rosenhouse-Dantsker Avia , Kowalsky Gregory B. , Logothetis Diomedes E. , Levitan Irena
Published: April 2009

A variety of ion channels are regulated by cholesterol, a major lipid component of the plasma membrane whose excess is associated with multiple pathological conditions. However, the mechanism underlying cholesterol sensitivity of ion channels is unknown. We have recently shown that an increase in membrane cholesterol suppresses inwardly rectifying K
+
(Kir2) channels that are responsible for maintaining membrane potential in a variety of cell types. Here we show that cholesterol sensitivity of Kir2 channels depends on a specific region of the C terminus of the cytosolic domain of the channel, the CD loop. Within this loop, the L222I mutation in Kir2.1 abrogates the sensitivity of the channel to cholesterol whereas a reverse mutation in the corresponding position in Kir2.3, I214L, has the opposite effect, increasing cholesterol sensitivity. Furthermore, the L222I mutation has a dominant negative effect on cholesterol sensitivity of Kir2.1 WT. Mutations of 2 additional residues in the CD loop in Kir2.1, N216D and K219Q, partially affect the sensitivity of the channel to cholesterol. Yet, whereas these mutations have been shown to affect activation of the channel by the membrane phospholipid phosphatidylinositol 4,5-bisphosphate [PI(
4
,
5
)P
2
], other mutations outside the CD loop that have been previously shown to affect activation of the channel by PI(
4
,
5
)P
2
had no effect on cholesterol sensitivity. Mutations of the lipid-facing residues of the outer transmembrane helix also had no effect. These findings provide insights into the structural determinants of the sensitivity of Kir2 channels to cholesterol, and introduce the critical role of the cytosolic domain in cholesterol dependent channel regulation.
Steroid receptor coactivator-1 is necessary for regulation of corticotropin-releasing hormone by chronic stress and glucocorticoids
Authors: Lachize Servane , Apostolakis Ede M. , van der Laan Siem , Tijssen Ans M. I. , Xu Jianming , de Kloet E. Ronald , Meijer Onno C.
Published: April 2009

Adaptation to stress in vertebrates occurs via activation of hormonal and neuronal signaling cascades in which corticotropin-releasing hormone (CRH) plays a central role. Expression of brain CRH is subject to strong, brain-region specific regulation by glucocorticoid hormones and neurogenic intracellular signals. We hypothesized that Steroid Receptor Coactivator 1 (SRC-1), a transcriptional coregulator of the glucocorticoid receptor, is involved in the sensitivity of CRH regulation by stress-related factors. In the brains of SRC-1 knockout mice we found basal CRH mRNA levels to be lower in the central nucleus of the amygdala. Hypothalamic CRH up-regulation after chronic (but not acute) stress, as well as region-dependent up- and down-regulation induced by synthetic glucocorticoids, were significantly attenuated compared with wild type. The impaired induction of the
crh
gene by neurogenic signals was corroborated in AtT-20 cells, where siRNA and overexpression experiments showed that SRC-1 is necessary for full induction of a CRH promoter reporter gene by forskolin, suggestive of involvement of transcription factor CREB. In conclusion, SRC-1 is involved in positive and negative regulation of the
crh
gene, and an important factor for the adaptive capacity of stress.