bluuebunny/crossref_metadata_2025 huggingface dataset:
Cognitive Processes during Acute Psychosis: The Role of Heightened Responsibility and Catastrophic Misinterpretations
Authors: Luzón Olga , Harrop Chris , Nolan Fiona
Published: June 2009

Background:This study investigated the role of cognitive mechanisms underlying obsessive compulsive and panic disorders in psychosis, and in particular, their possible contributions to acute psychosis.Method:A total of 90 participants were recruited comprising three equal-size groups, including two clinical groups (acute and stable) and one non-clinical matched control group. Symptom severity and distress was assessed using the PSYRATS, and questionnaire measures of anxiety and obsessive beliefs were administered to all participants.Results:Individuals with a diagnosis of psychosis reported significantly higher levels of obsessional beliefs and anxiety sensitivity than the non-clinical group. Furthermore, acutely psychotic patients reported a significantly higher sense of responsibility and catastrophic misinterpretation than the stable psychiatric controls, and than samples of OCD and GAD patients.Conclusions:Results suggest that these anxiety processes are particularly important during acute psychotic episodes, beyond the reported comorbidity. The theoretical and clinical implications of these findings, the limitations of the methodology employed, and suggestions for future research are discussed.
Nutrition and health education intervention for student volunteers: topic-wise assessment of impact using a non-parametric test
Authors: Vijayapushpam T , Antony Grace Maria , Subba Rao GM , Raghunatha Rao D
Published: June 2009

Objective

To assess the impact of a classroom-based nutrition and health education intervention among student community volunteers in improving their knowledge on individual topics.

Design

Prospective follow-up study. Topic-wise knowledge change among student volunteers on individual topics (twenty-one questions related to nutrition and health, eight questions related to infectious diseases and two questions related to obesity and hypertension) pertaining to nutrition and health was evaluated at baseline and after intervention, using the McNemar test.

Setting

Six different colleges affiliated to Osmania University, Andhra Pradesh, India.

Subjects

Six hundred and eighty-seven student volunteers under the National Service Scheme, of both genders, average age 19 years.

Results

A significant mean improvement of 11·36 (sd 8·49, P < 0·001) was observed in the overall nutrition and health knowledge scores of the student volunteers after the education intervention. The McNemar test showed that knowledge on individual topics related to energy, proteins, fats, adolescent phase, obesity, some lifestyle diseases and infectious diseases improved significantly (P < 0·01). No significant (P > 0·05) improvement was observed in knowledge on the nutritional content of milk and sprouted grams, hypertension, HIV/AIDS, ELISA and malaria.

Conclusions

Topics on which our educational intervention could not bring about significant knowledge improvement have been identified and suitable modifications can be carried out to strengthen them.
An investigation of the ways in which public health nutrition policy and practices can address climate change
Authors: Sulda Heidi , Coveney John , Bentley Michael
Published: June 2009

Objective

To develop a framework to guide action in the public health nutrition workforce to develop policies and practices addressing factors contributing to climate change.

Design

Action/consultative research.

Setting

Interviews – South Australia, questionnaire – Australia.

Subjects

Interviews – key informants (n 6) were from various government, academic and non-government positions, invited through email. Questionnaire – participants were members of the public health nutrition workforce (n 186), recruited to the study through emails from public health nutrition contacts for each State in Australia (with the exception of South Australia).

Results

Support by participants for climate change as a valid role for dietitians and nutritionists was high (78 %). However, climate change was ranked low against other public health nutrition priorities. Support of participants to conduct programmes to address climate change from professional and work organisations was low. The final framework developed included elements of advocacy/lobbying, policy, professional recognition/support, organisational support, knowledge/skills, partnerships and programmes.

Conclusions

This research demonstrates a need for public health nutrition to address climate change, which requires support by organisations, policy, improved knowledge and increased professional development opportunities.
Factors associated with overweight in children in Rasht, Iran: gender, maternal education, skipping breakfast and parental obesity
Authors: Maddah Moshen , Nikooyeh Bahareh
Published: June 2009

Objective

The present study aimed to investigate the determinants of overweight and obesity among 6- to 11-year-old schoolchildren in Rasht, Iran.

Design

Cross-sectional survey. Data on age, weekly frequency of skipping breakfast, physical activity and hours of television viewing were collected. Information on birth weight, parental age, parental educational levels, parental weight and height, and mother’s employment status were gathered through self-administrated questionnaires given to the parents.

Setting

Elementary schools in Rasht.

Subjects

A total of 6635 children (3551 boys and 3084 girls) attending elementary schools in Rasht were studied.

Results

The overall prevalence of overweight was 11·5 % and 15·0 % for boys and girls, respectively; while the overall prevalence of obesity was 5·0 % and 5·9 %, respectively. Children with more educated mothers had a higher prevalence of overweight than children with less educated mothers. Logistic regression analysis showed that children with overweight/obese parents, children with more educated mothers and children who often skipped breakfast were more prone to overweight and obesity.

Conclusions

These data suggest that overweight and obesity is a public health concern in this age group in Rasht. The observed sex and social differences in the prevalence of overweight and obesity call for policy makers’ attention.
Adolescent Risk Behavior in Italy and The Netherlands
Authors: Ciairano Silvia , Kliewer Wendy , Rabaglietti Emanuela
Published: June 2009

Jessor et al.’s (2003) model of relationships among protective factors (models protection, controls protection, support protection), risk factors (models risk, opportunity risk, vulnerability risk), and adolescent risk behavior (delinquency, problem drinking, marijuana use, tobacco use, sexual activity) was investigated in adolescent samples of both genders from Italy (n = 488, M age = 17 years) and the Netherlands (n = 480, M age = 17 years). After accounting for sociodemographic variables, risk and protective factors and their interactions accounted for 46–52% of additional variation in risk behavior. Although levels of risk, protection, and risk behavior differed by country and by sex, the association of risk and protective factors with risk behavior was similar for Italian and Dutch youth and for boys and girls. Controls protection (e.g., intolerance of deviancy, parental control and disapproval, friends’ disapproval) and models of risk (family and peer models of risk behavior) had the strongest associations with adjustment. Additionally, controls protection moderated the influence of models risk among the Italians while support protection buffered vulnerability risk among the Dutch. These data support the utility of the explanatory model in these national contexts.
Is Acknowledgment of Trauma a Protective Factor?
Authors: Maercker Andreas , Povilonyte Marija , Lianova Raichat , Pöhlmann Karin
Published: June 2009

We assessed victims’ status and its relation to self-perceived “social acknowledgment as a victim or survivor” ( Maercker & Müller, 2004 ) in a sample of Chechen refugees living in camps in Ingushetia. A total of 61 Chechen refugees were surveyed using a war-related trauma checklist, the Impact of Event Scale-Revised, and the Disclosure of Trauma Questionnaire. Rates of potentially traumatic events and posttraumatic stress disorder (PTSD) appeared to be very high in this sample: 100% reported one or more potentially traumatic events and over 75% were estimated to have PTSD. As expected, social acknowledgment as a victim or survivor was negatively related to PTSD symptoms. We discuss the possible causal direction of this finding. Our cross-sectional study provides further evidence that social acknowledgment should be regarded as a protective or resource factor in the aftermath of trauma.
Substorm entropies
Authors: Wing Simon , Johnson Jay R.
Published: June 2009

The specific entropy (s = p/ργ) and total entropy (S = p1/γV) of the plasma sheet during substorms are investigated with DMSP observations using a method that assumes ion isotropy (as also assumed in the derivation of S = p1/γV) and empirical magnetic field models that capture the expected characteristics of substorm phases. Earthward reductions of S are found during quasi‐steady periods (e.g., growth phase) as well as during the transition from growth to expansion phases. During quasi‐steady periods, (1) S and flux tube content (N) decrease moderately at midtail, but more steeply at the inner edge of the plasma sheet, and (2) s appears roughly conserved in the X or convection direction, but closer to Earth, there is a duskward heat flux. Both 1 and 2 suggest that curvature/gradient drifts can play a significant role in the S and N losses. On the other hand, during the transition from growth to expansion phases, S is reduced by an order of magnitude earthward of 20 RE, which can be attributed mainly to the reduction in V from the dipolarization after onset, but s is roughly conserved. This result is consistent with a mechanism that reduces the flux tube volume/content without significantly altering s. Recent magnetohydrodynamic/particle‐in‐cell simulations of magnetic reconnection indicate that s tends to be conserved except in the small dissipation region, but the change in the field line topology for a reconnected field line can lead to a reduction in S with the remainder contained in a plasmoid that forms tailward of the X line.
Viscous constitutive relations of solid‐liquid composites in terms of grain boundary contiguity: 3. Causes and consequences of viscous anisotropy
Authors: Takei Yasuko , Holtzman Benjamin K.
Published: June 2009

The viscous constitutive relations of partially molten rocks developed here show that an anisotropy in grain‐scale melt distribution can lead to a strong anisotropy in the viscosity of the solid framework. With anisotropic viscosity, a direct coupling between shear and isotropic components of stress occurs, and hence, the role of shear deformation in melt migration significantly increases. We demonstrate the significant effects of viscous anisotropy on melt migration dynamics by solving the solid‐liquid two‐phase dynamics for two simple cases. First, in rotary shear deformation, an anisotropy creates a driving force for melt migration up stress gradients in the solid matrix, which does not exist with isotropic viscosity. Second, in uniform simple shear deformation, melt segregates spontaneously into low‐angle bands due to anisotropic melt alignment, in close agreement with experimental observations. Our results indicate that stress‐induced melt alignment at the grain scale drives further melt redistribution over distances much longer than the grain scale. The development of such “multiscale anisotropy” is demonstrated by “forward” or ab initio approaches based on the equations of two‐phase dynamics, in which the viscous constitutive relation is based on observed microstructure and realistic rheology. When applied to a simple approximation of flow in the mantle beneath ridge and subduction zone, the anisotropic constitutive relation significantly affects melt migration patterns.
Seismic wave attenuation in carbonates
Authors: Adam L. , Batzle M. , Lewallen K. T. , van Wijk K.
Published: June 2009

The effect of pore fluids on seismic wave attenuation in carbonate rocks is important for interpreting remote sensing observations of carbonate reservoirs undergoing enhanced oil recovery. Here we measure the elastic moduli and attenuation in the laboratory for five carbonate samples with 20% to 30% porosity and permeability between 0.03 and 58.1 mdarcy. Contrary to most observations in sandstones, bulk compressibility losses dominate over shear wave losses for dry samples and samples fully saturated with either liquid butane or brine. This observation holds for four out of five samples at seismic (10–1000 Hz) and ultrasonic frequencies (0.8 MHz) and reservoir pressures. Attenuation modeled from the modulus data using Cole‐Cole relations agrees in that the bulk losses are greater than the shear losses. On average, attenuation increases by 250% when brine substitutes a light hydrocarbon in these carbonate rocks. For some of our samples, attenuation is frequency‐dependent, but in the typical exploration frequency range (10–100 Hz), attenuation is practically constant for the measured samples.
A numerical study of circulation in a coastal reef‐lagoon system
Authors: Lowe Ryan J. , Falter James L. , Monismith Stephen G. , Atkinson Marlin J.
Published: June 2009

A coupled wave‐circulation numerical model was used to simulate the distribution of wave energy, as well as the circulation induced by wave breaking, wind, and tidal forcing, within a coral reef system in Kaneohe Bay, Oahu, Hawaii. Modeled wave, current, and wave setup fields were compared with field measurements collected on the forereef, reef flat, and reef channels and in the lagoon over a 4‐week period. The predicted wave height transformation across the reef‐lagoon system was in good agreement with field observations, using single‐parameter (spatially uniform) values to describe both wave‐breaking and frictional dissipation. The spatial distribution of the resulting wave setup field drove a persistent wave‐driven flow across the reef flat that returned to the ocean through two deeper channels in the reef. Both the magnitude and direction of these currents were well described using a spatially uniform hydraulic roughness length scale. Notably, the model lends support to field observations that setup within the coastally bounded lagoon was a substantial fraction of the maximum setup on the reef (∼60–80%), which generated relatively weak cross‐reef wave‐driven flows (∼10–20 cm s−1) compared with reefs having mostly unbounded lagoons (e.g., many atolls and barrier reefs). Numerical experiments conducted using Lagrangian particle tracking revealed that residence times within Kaneohe Bay are extremely heterogeneous, typically ranging from <1 day on the reef to >1 month within its sheltered southern lagoon.
Characterization of dense focal plane array feeds for parabolic reflectors in achieving closely overlapping or widely separated multiple beams
Authors: Ng Mou Kehn M. , Shafai L.
Published: June 2009

In the advent of modern mobile satellite communications requiring rapid and adaptive multiple beams, this work studies the ability of reflector antennas fed by dense focal plane arrays (FPA) in achieving arbitrarily shaped and sized footprints to meet the demands. In this paper, the efficiencies of single off‐axis as well as multiple beams of FPA‐fed paraboloids are investigated. The offset FPA considered here comprises hard rectangular waveguides. The focal plane field, which the FPA samples, is synthesized by integration of the physical optics induced electric currents over the reflector surface caused by the off‐axis incident plane wave arriving at that incidence angle of interest. Full mutual coupling analysis has been performed in the FPA sampling, thereby taking into account mutual coupling losses in the arrays. The fields over the tilted elliptical aperture of off‐axis beams needed for calculation of the aperture efficiency are obtained by projecting the usual focal plane fields to this tilted aperture using geometrical optics. Results show that the total efficiency of the offset FPA‐fed reflector decreases with increasing beam angle and increases with larger number of FPA elements. It is also found that the maximum directive gain of the reflector radiation patterns falls noticeably with beam angle when the FPA population is low, but the directivity can be maintained well when an adequate number of FPA elements are used. Multiple beams that are either closely overlapping or widely separated are also successfully investigated.
Storm sudden commencement and its effect on high‐latitude HF communication links
Authors: Ritchie S. E. , Honary F.
Published: June 2009

Following particle precipitation at high latitudes that occurs as a result of geomagnetic disturbances, the electron density of the E region of the ionosphere undergoes substantial variation. These variations modify the E layer propagation characteristics which adversely affect HF propagation paths both unexpectedly and in many cases for long periods of time. This paper presents two case studies of how the enhancement of E region electron density immediately following storm sudden commencement affects high‐latitude HF communications links in and through the auroral zone. Using data gathered from ionosondes, incoherent scatter radar and an oblique sounder, the Advanced Composition Explorer Satellite, and riometers and magnetometers, the physical effects of particle precipitation on the ionospheric E layer and the resulting effect on HF links is revealed. Both case studies show that besides the expected occurrence of severe short‐term absorption and the reduction in the critical frequency of the F layer caused by a redistribution of the electron density in the upper layers of the ionosphere, there is the likelihood a sporadic E layer will form and/or be enhanced because of significant and sustained particle precipitation. When the critical frequency of the sporadic E layer increases above the norm and in cases exceeds the critical frequency of the F layer, there are severe implications for many HF radio communication systems used at high latitudes unless corrective action is taken.
Delta progradation driven by an advancing sediment source: Coupled theory and experiment describing the evolution of elongated deltas
Authors: Kim Wonsuck , Dai Albert , Muto Tetsuji , Parker Gary
Published: June 2009

Most of the models of alluvial fan and delta morphodynamics to date have used one of two assumptions concerning the upstream boundary condition: (1) a fixed sediment feed point at the vertex or (2) a feed point corresponding to a bedrock‐alluvial transition that, e.g., migrates upstream under conditions of constant base level. Here, however, we present both experimental and numerical results pertaining to a new configuration, i.e., one in which the sediment feed point migrates downstream. The research is motivated by the operation of the tailings pond of a mine in which a delta forms. The mine operators must frequently move the outfalls of their slurry pipelines downstream to avoid their burial under sediment as the delta aggrades. This downstream migration results in a characteristic delta configuration. Under the right conditions, as the tailings delta progrades downstream, it does not have time to fill all the available space in the lateral direction, thus leaving unfilled open water on either side. The result is the formation of an elongated delta. Here we use both experiments and numerical modeling to characterize the control of the feed point migration rate on the lateral extent of the prograding deltas. We use these results to obtain a partial explanation of natural elongated deltas. In the case of such deltas, the downstream progradation of natural levees provides an analog to the downstream migration of the outfall of a slurry pipeline.
Pick‐up ions and the 2–3 kHz radio emissions
Authors: Mitchell J. J. , Cairns Iver H. , Heerikhuisen J.
Published: June 2009

The 2–3 kHz radio emissions observed by the Voyager spacecraft are thought to turn on where pick‐up ions drive lower‐hybrid waves. Previous work focused on pick‐up ions born via charge exchange with neutrals from the inner heliosheath. However, Boltzmann simulations show that inner heliosheath neutrals have significantly lower speeds after crossing the heliopause compared with fluid simulations. We calculate the pick‐up ion distributions resulting from charge exchange with various neutral species, finding that neutrals born in the supersonic solar wind give a ring‐beam distribution, but inner heliosheath neutrals do not. The emission theory survives with supersonic solar wind neutrals as the pick‐up ion source. This leads to increases in the ring‐beam and electron tail speeds, available lower‐hybrid wave energy, and radio flux. Larger ring speeds increase the necessary magnetic field to ≳0.2 nT, constraining the source location, and predicting magnetic field strengths agreeing with heliosphere and interstellar medium models.
Testing the influence of small crystals on ice size spectra using Doppler lidar observations
Authors: Westbrook C. D. , Illingworth A. J.
Published: June 2009

Analysis of the vertical velocity of ice crystals observed with a 1.5μm Doppler lidar from a continuous sample of stratiform ice clouds over 17 months show that the distribution of Doppler velocity varies strongly with temperature, with mean velocities of 0.2ms−1 at −40°C, increasing to 0.6ms−1 at −10°C due to particle growth and broadening of the size spectrum. We examine the likely influence of crystals smaller than 60μm by forward modelling their effect on the area‐weighted fall speed, and comparing the results to the lidar observations. The comparison strongly suggests that the concentration of small crystals in most clouds is much lower than measured in‐situ by some cloud droplet probes. We argue that the discrepancy is likely due to shattering of large crystals on the probe inlet, and that numerous small particles should not be included in numerical weather and climate model parameterizations.
Pairwise energy gain‐loss feature of solar wind protons in the near‐Moon wake
Authors: Nishino M. N. , Maezawa K. , Fujimoto M. , Saito Y. , Yokota S. , Asamura K. , Tanaka T. , Tsunakawa H. , Matsushima M. , Takahashi F. , Terasawa T. , Shibuya H. , Shimizu H.
Published: June 2009

We study solar wind (SW) intrusion into the near‐Moon wake using SELENE (KAGUYA) data. It has been known that SW protons are gradually accelerated toward the wake center along magnetic field in the distant lunar wake, while SW intrusion into the near‐Moon wake has never been measured. We show that the SW protons come into the lunar wake at ∼100 km altitude in the direction perpendicular to the magnetic field, as they gain kinetic energy in one hemisphere while lose in the other hemisphere. Particle trajectory calculations and theoretical treatment demonstrate that proton Larmor motions and inward electric field around the wake boundary result in energy gain and loss of the SW protons. Our result shows emergence of proton particle dynamics around the near‐Moon space, and suggests that the SW protons may relatively easily access the low‐latitude and low‐altitude region on the lunar night side.
Validation of community models: Identifying events in space weather model timelines
Authors: MacNeice Peter
Published: June 2009

I develop and document a set of procedures which test the quality of predictions of solar wind speed and polarity of the interplanetary magnetic field (IMF) made by coupled models of the ambient solar corona and heliosphere. The Wang‐Sheeley‐Arge (WSA) model is used to illustrate the application of these validation procedures. I present an algorithm which detects transitions of the solar wind from slow to high speed. I also present an algorithm which processes the measured polarity of the outward directed component of the IMF. This removes high‐frequency variations to expose the longer‐scale changes that reflect IMF sector changes. I apply these algorithms to WSA model predictions made using a small set of photospheric synoptic magnetograms obtained by the Global Oscillation Network Group as input to the model. The results of this preliminary validation of the WSA model (version 1.6) are summarized.
Why is effective treatment of asthma so difficult? An integrated systems biology hypothesis of asthma
Authors: Voelkel Norbert F , Spiegel Sarah
Published: June 2009

A hypothesis is presented that asthma is not only an airway disease, but that the disease involves the entire lung, and that the chronicity of asthma and asthma exacerbations can perhaps be explained if one considers asthma as a systemic disease. Increased lung—not only airway—vascularity may be the result of the action of angiogenesis factors, such as vascular endothelial growth factor (VEGF) and sphingosine‐1‐phosphate (S1P). A bone‐marrow lung axis can be postulated as one element of the systemic nature of the asthma syndrome, in which the inflamed lung emits chemotactic signals, which the bone marrow responds to by releasing cells that contribute to lung angiogenesis. A molecular model of the pathobiology of asthma can be built by connecting hypoxia‐inducible transcription factor‐1 alpha, VEGF S1P, and bone‐marrow precursor cell mobilization and acknowledging that angiogenesis is part of the inflammatory response.
Noninvasive Assessment of the Brain Redox Status after Transient Middle Cerebral Artery Occlusion Using Overhauser-Enhanced Magnetic Resonance Imaging
Authors: Yamato Mayumi , Shiba Takeshi , Yamada Ken-ichi , Watanabe Toshiaki , Utsumi Hideo
Published: June 2009

Oxidative stress has been implicated in the cell death that occurs after ischemia–reperfusion of the brain, which causes the production of reactive oxygen species and a decrease in antioxidants, leading to mitochondrial dysfunction. However, the invasive methods used to collect much of this evidence are themselves stress inducing, which could skew the results. In this study, we aimed at demonstrating brain redox alterations after ischemia–reperfusion noninvasively, using Overhauser-enhanced magnetic resonance imaging. The reduction rate of 3-methoxycarbonyl-2,2,5,5-tetramethylpyrrolidine-l-oxyl (methoxycarbonyl-PROXYL), a redox-sensitive contrast agent, was used as an index of the redox status in vivo. No changes were observed in the antioxidant concentration, the mitochondrial complex activity, or in the redox status image intensity after 3 h of reperfusion, following transient middle cerebral artery occlusion; however, after 24 h of reperfusion, the methoxycarbonyl-PROXYL reduction rate, calculated from continuous images, had decreased significantly. Concordantly, biochemical assays showed that the concentration of ascorbic acid in the ischemic hemisphere and the activity of mitochondrial complex II had also decreased. Thus, the noninvasive imaging of the brain redox alterations faithfully reflected changes in antioxidant levels and in mitochondrial complex II activity after ischemia–reperfusion.
Cardiac Arrest and Cardiopulmonary Resuscitation Dysregulates the Hypothalamic–Pituitary–Adrenal Axis
Authors: Neigh Gretchen N , Karelina Kate , Zhang Ning , Glasper Erica R , Owens Michael J , Plotsky Paul M , Nemeroff Charles B , DeVries A Courtney
Published: June 2009

Cardiac arrest and cardiopulmonary resuscitation (CA/CPR) increase the risk for affective disorders in human survivors. Postischemic anxiety- and depressive-like behaviors have been documented in animal models of CA/CPR; however, the stability of post-CA/CPR anxiety-like behavior over time and the underlying physiologic mechanisms remain unknown. The hypothalamic–pituitary–adrenal (HPA) axis and the corticotropin releasing factor (CRF) system may mediate the pathophysiology of anxiety and depression; therefore, this study measured CA/CPR-induced changes in CRF receptor binding and HPA axis negative feedback. Mice were exposed to CA/CPR or SHAM surgery and assessed 7 or 21 days later. Consistent with earlier demonstrations of anxiety-like behavior 7 days after CA/CPR, increased anxiety-like behavior in the open field was also present 21 days after CA/CPR. On postoperative day 7, CA/CPR was associated with an increase in basal serum corticosterone concentration relative to SHAM, but this difference resolved by postoperative day 21. The Dexamethasone Suppression Test showed that the CA/CPR group had enhanced negative feedback compared with SHAM controls at postoperative day 21. Furthermore, there was a gradual increase in CRF1 receptor binding in the paraventricular nucleus of the hypothalamus and bed nucleus of the stria terminalis, as well as a transient decrease of both CRF1 and CRF2A receptors in the dorsal hippocampus. Therefore, sustained changes in activity of the HPA axis and the CRF system after CA/CPR may contribute to the postischemic increase in affective disorders.
Temperature dependent carrier lifetime studies on Ti-doped multicrystalline silicon
Authors: Paudyal B. B. , McIntosh K. R. , Macdonald D. H.
Published: June 2009

Carrier lifetime measurements were performed on deliberately Ti-doped multicrystalline silicon wafers using a temperature controlled photoconductance device. The dominant recombination center was found to be the double-donor level associated with interstitial titanium. The interstitial Ti concentrations in multicrystalline silicon wafers were determined by measuring the Shockley–Read–Hall time constant for holes and using the known values of the thermal velocity and capture cross section for holes of the double-donor level at different temperatures. The measured values of the Ti concentration were then used to determine the electron capture cross section of the double-donor level over the temperature range of 140–270 °C via the measured values of the Shockley–Read–Hall time constant for electrons and the known thermal velocity. Multiphonon emission was found to be the most likely capture mechanism for this temperature range for electron capture into the double-donor level of Ti in silicon. The effective segregation coefficient for Ti was estimated by fitting Scheil’s equation to the measured values of the Ti concentrations and their respective vertical positions in the ingot. If all Ti were present as the interstitial double-donor, a lower limit of 1.8×10−6 can be ascribed to the segregation coefficient, which is very close to the equilibrium value.
Control of 2ω (527 nm) stimulated Raman scattering in a steep density gradient plasma
Authors: Moody J. D. , Divol L. , Froula D. H. , Glenzer S. H. , Gregori G. , Kirkwood R. K. , Mackinnon A. , Meezan N. , Niemann C. , Suter L. J. , Bahr R. , Seka W.
Published: June 2009

Experiments show that application of laser smoothing schemes including smoothing by spectral dispersion and polarization smoothing effectively suppresses stimulated Raman scattering from a 2ω (527 nm) laser beam in a low average-gain plasma with a steep density gradient. Full-wave simulations reproduce the observed trends in the data and show that the scattering reduction is an indirect result of suppressing active filamentation.
Interface properties of a Li3PO4/Al cathode in organic light emitting diodes
Authors: Gassmann Andrea , Melzer Christian , Mankel Eric , Jaegermann Wolfram , von Seggern Heinz
Published: June 2009

Recently Li3PO4/Al has been introduced as an alternative cathode for the commonly used LiF/Al system for organic light emitting diodes (OLEDs) due to its competitive electron injection properties. In the present article the interfaces of the organic semiconductor with the Li3PO4/Al bilayer cathode are investigated using photoelectron spectroscopy to elucidate the origin behind the efficient electron injection. Therefore, a thick Li3PO4 layer was vacuum deposited onto an indium tin oxide substrate and characterized in order to learn about the stoichiometry of evaporated Li3PO4. During evaporation Li3PO4 decomposes, forming a layer consisting of P2O5 and LiPO3. In a second step the interface between Li3PO4 and Alq3 [tris(8-hydroxyquinoline) aluminum] was investigated, whereupon Li3PO4 coverage Alq3 molecules decompose, forming aluminum oxide or aluminum phosphate leaving 8-quinolinol molecules behind. A similar reaction occurs at the Li3PO4/Al interface where again an oxidation of the metallic aluminum points toward the formation of aluminum oxide or phosphate. A work function lowering of up to 180 meV observed once Al was covered by Li3PO4 is likely to be caused by the polar nature of all generated or deposited species. A simple estimate of the surface potential drop caused by those dipoles can account for the work function lowering and explain the highly efficient electron injection property of the Li3PO4/Al cathode in an OLED.
Thermoelectric properties of Bi–Te films with controlled structure and morphology
Authors: Li Bassi A. , Bailini A. , Casari C. S. , Donati F. , Mantegazza A. , Passoni M. , Russo V. , Bottani C. E.
Published: June 2009

A study of the thermoelectric transport properties of Bi–Te thin films with different structures and morphologies is here presented. Films were grown by pulsed laser deposition (PLD), which permits to control the composition, phase and crystallinity of the deposited material, and the morphology at the micrometer/nanometer scale. The carrier density and mobility at room temperature and the in plane electrical resistivity and Seebeck coefficient in the temperature range 300–400 K have been measured both for films characterized by a compact morphology and by the presence of different phases (Bi2Te3, BiTe, and Bi4Te3) and for Bi2Te3 films with different morphologies at the micrometer/nanometer scale (from a compact structure to a less connected assembly of randomly oriented crystalline grains). The correlation among thermoelectric and structural properties has been investigated, showing the potential of PLD to produce n-type Bi–Te thin films with desired properties for peculiar applications. Films with a layered Bi2Te3 structure show the best properties, with Seebeck coefficient in the range from −175 to −250 μV/K and power factor in the range 20–45 μW/cm K2, with expected ZT values greater than 1.5. Also films composed by partially randomly oriented submicrometer crystals look promising, since the smaller power factor (∼10 μW/cm K2) can in principle be compensated by a strong reduction of the phonon thermal conductivity via proper engineering of grain boundaries.
Influence of structural defects on carrier lifetime in 4H-SiC epitaxial layers: Optical lifetime mapping
Authors: Hassan J. , Bergman J. P.
Published: June 2009

The influence of structural defects on carrier lifetime in 4H-SiC epilayers has been studied using high spatial resolution optically detected lifetime measurements. Full wafers mappings with 200 μm spatial resolution revealed the carrier lifetime variations that can be associated with structural defects replicated from the substrate and variations in the epitaxial growth conditions due to the susceptor design. High resolution mappings over smaller regions with lateral step size down to 20 μm, revealed local carrier lifetime reductions associated with different structural defects in the epitaxial layers. Identified defects that influence the carrier lifetime are the carrot defects and different types of in-grown stacking faults. Also clusters of threading screw dislocations in the epilayer probably originating from the dissociation of micropipe in the substrate are found to effectively reduce the carrier lifetime. Furthermore, optically detected lifetime mapping has been demonstrated as a nondestructive technique which allows nonvisible structural defects to be detected in as-grown epilayers.
A two-photon pumped polyfluorene laser
Authors: Tsiminis Georgios , Ruseckas Arvydas , Samuel Ifor D. W. , Turnbull Graham A.
Published: June 2009

A tunable two-photon pumped solid-state laser based on polyfluorene is reported. A detailed investigation of the two-photon absorption in polyfluorene for both nanosecond and femtosecond time regimes in solution, and solid-state allows the determination of the most favorable conditions for lasing. Tunable distributed feedback lasers are made by spin coating from a polyfluorene solution on corrugated silica substrates and lasing is achieved under two-photon excitation at 640 nm with an absorbed energy density at lasing threshold of 1.3 mJ/cm2. These results highlight an alternative pumping scheme for blue organic semiconductor lasers.
Pumping of atomic alkali lasers by photoexcitation of a resonance line blue satellite and alkali-rare gas excimer dissociation
Authors: Readle J. D. , Wagner C. J. , Verdeyen J. T. , Spinka T. M. , Carroll D. L. , Eden J. G.
Published: June 2009

Photoassociation of alkali-rare gas atomic collision pairs provides an alternative approach to optically pumping atomic alkali lasers. Lasing on the 6 P21/2→6 S21/2 (D1) transition of Cs has been observed when the blue satellite of the 6 P23/2←6 S21/2 (D2) transition, peaking at ∼837 nm for mixtures of Cs vapor, Ar, and ethane, is pumped by a pulsed dye laser. For 50% output coupling, laser threshold with respect to absorbed pump energy is ∼40 μJ at T=435 K and the slope efficiency approaches 10%. The measured spectral breadth for the blue satellite (≳5 nm at 410 K) will accommodate cw pumping of the Cs laser with conventional semiconductor lasers.
Improvement of the phase diagram for the pseudobinary PbNb2O6–BaNb2O6 system
Authors: Venet M. , Zabotto F. L. , Eiras J. A. , Garcia D.
Published: June 2009

Characteristics of phase transitions of lead barium niobate compositions around the morphotropic phase boundary were investigated. Using structural characterizations, it was found that the morphotropic phase boundary extends toward a wide composition range, in which both tetragonal (4mm) and orthorhombic (m2m) tungsten bronze phases coexist. In addition, on heating, two phase transitions were observed for all the studied compositions. First, the fraction with m2m symmetry phase transforms into the 4mm symmetry one and, second, the 4mm symmetry phase, which represents the whole material, transforms into the paraelectric phase (4/mmm symmetry). The phase transition temperatures were determined from dielectric characterizations. These results helped to improve the phase diagram of the pseudobinary PbNb2O6–BaNb2O6 system around the morphotropic phase boundary region.
Traveling wave dielectrophoresis micropump based on the dispersion of a capacitive electrode layer
Authors: Marczak Marcin , Diesinger Heinrich
Published: June 2009

A traveling wave dielectrophoresis microfluid pump based on structural dispersion is demonstrated. The phase shift between medium polarization and applied propagating field, necessary to generate asynchronous propagative forces in dielectrophoresis, is generated by an RC circuit consisting of the electrode insulator and the liquid conductivity. Since the device characteristics involve only bulk properties, the micropump does not require conductivity gradient or double layers, unlike existing micropumps using electro-osmosis and electrohydrodynamic shear forces. Its frequency of maximum pumping force can be made considerably lower than the dielectric relaxation frequency of the liquid. By decomposing the traveling wave electrode array into a rudimentary RC model, coincidence is found between optimized pumping conditions and crossover of the impedance measured between electrode combs. By using impedance spectroscopy alternately with pumping, the frequency of the applied signal can be matched in real-time to the complex dielectric constant of the liquid to keep the pumping force maximized.
Field emission enhancement in ultrananocrystalline diamond films by in situ heating during single or multienergy ion implantation processes
Authors: Joseph P. T. , Tai N. H. , Chen C. H. , Niu H. , Cheng H. F. , Palnitkar U. A. , Lin I. N.
Published: June 2009

The single or multienergy nitrogen (N) ion implantation (MENII) processes with a dose (4×1014 ions/cm2) just below the critical dose (1×1015 ions/cm2) for the structural transformation of ultrananocrystalline diamond (UNCD) films were observed to significantly improve the electron field emission (EFE) properties. The single energy N ion implantation at 300 °C has shown better field emission properties with turn-on field (E0) of 7.1 V/μm, as compared to room temperature implanted sample at similar conditions (E0=8.0 V/μm) or the pristine UNCD film (E0=13.9 V/μm). On the other hand, the MENII with a specific sequence of implantation pronouncedly showed different effect on altering the EFE properties for UNCD films, and the implantation at 300 °C further enhanced the EFE behavior. The best EFE characteristics achieved for the UNCD film treated with the implantation process are E0=4.5 V/μm and current density of (Je)=2.0 mA/cm2 (at 24.5 V/μm). The prime factors for improving the EFE properties are presumed to be the grain boundary incorporation and activation of the implanted N and the healing of induced defects, which are explained based on surface charge transfer doping mechanism.
Correction for dispersion and Coulombic interactions in molecular clusters with density functional derived methods: Application to polycyclic aromatic hydrocarbon clusters
Authors: Rapacioli Mathias , Spiegelman Fernand , Talbi Dahbia , Mineva Tzonka , Goursot Annick , Heine Thomas , Seifert Gotthard
Published: June 2009

The density functional based tight binding (DFTB) is a semiempirical method derived from the density functional theory (DFT). It inherits therefore its problems in treating van der Waals clusters. A major error comes from dispersion forces, which are poorly described by commonly used DFT functionals, but which can be accounted for by an a posteriori treatment DFT-D. This correction is used for DFTB. The self-consistent charge (SCC) DFTB is built on Mulliken charges which are known to give a poor representation of Coulombic intermolecular potential. We propose to calculate this potential using the class IV/charge model 3 definition of atomic charges. The self-consistent calculation of these charges is introduced in the SCC procedure and corresponding nuclear forces are derived. Benzene dimer is then studied as a benchmark system with this corrected DFTB (c-DFTB-D) method, but also, for comparison, with the DFT-D. Both methods give similar results and are in agreement with references calculations (CCSD(T) and symmetry adapted perturbation theory) calculations. As a first application, pyrene dimer is studied with the c-DFTB-D and DFT-D methods. For coronene clusters, only the c-DFTB-D approach is used, which finds the sandwich configurations to be more stable than the T-shaped ones.
Energy transfer in nanowire solar cells with photon-harvesting shells
Authors: Peters C. H. , Guichard A. R. , Hryciw A. C. , Brongersma M. L. , McGehee M. D.
Published: June 2009

The concept of a nanowire solar cell with photon-harvesting shells is presented. In this architecture, organic molecules which absorb strongly in the near infrared where silicon absorbs weakly are coupled to silicon nanowires (SiNWs). This enables an array of 7-μm-long nanowires with a diameter of 50 nm to absorb over 85% of the photons above the bandgap of silicon. The organic molecules are bonded to the surface of the SiNWs forming a thin shell. They absorb the low-energy photons and subsequently transfer the energy to the SiNWs via Förster resonant energy transfer, creating free electrons and holes within the SiNWs. The carriers are then separated at a radial p-n junction in a nanowire and extracted at the respective electrodes. The shortness of the nanowires is expected to lower the dark current due to the decrease in p-n junction surface area, which scales linearly with wire length. The theoretical power conversion efficiency is 15%. To demonstrate this concept, we measure a 60% increase in photocurrent from a planar silicon-on-insulator diode when a 5 nm layer of poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene is applied to the surface of the silicon. This increase is in excellent agreement with theoretical predictions.
Neoclassical equilibrium in gyrokinetic simulations
Authors: Garbet X. , Dif-Pradalier G. , Nguyen C. , Sarazin Y. , Grandgirard V. , Ghendrih Ph.
Published: June 2009

This paper presents a set of model collision operators, which reproduce the neoclassical equilibrium and comply with the constraints of a full-f global gyrokinetic code. The assessment of these operators is based on an entropy variational principle, which allows one to perform a fast calculation of the neoclassical diffusivity and poloidal velocity. It is shown that the force balance equation is recovered at lowest order in the expansion parameter, the normalized gyroradius, hence allowing one to calculate correctly the radial electric field. Also, the conventional neoclassical transport and the poloidal velocity are reproduced in the plateau and banana regimes. The advantages and drawbacks of the various model operators are discussed in view of the requirements for neoclassical and turbulent transport.
Optimization of an organic memristor as an adaptive memory element
Authors: Berzina Tatiana , Smerieri Anteo , Bernabò Marco , Pucci Andrea , Ruggeri Giacomo , Erokhin Victor , Fontana M. P.
Published: June 2009

The combination of memory and signal handling characteristics of a memristor makes it a promising candidate for adaptive bioinspired information processing systems. This poses stringent requirements on the basic device, such as stability and reproducibility over a large number of training/learning cycles, and a large anisotropy in the fundamental control material parameter, in our case the electrical conductivity. In this work we report results on the improved performance of electrochemically controlled polymeric memristors, where optimization of a conducting polymer (polyaniline) in the active channel and better environmental control of fabrication methods led to a large increase both in the absolute values of the conductivity in the partially oxydized state of polyaniline and of the on-off conductivity ratio. These improvements are crucial for the application of the organic memristor to adaptive complex signal handling networks.
The effect of grooved surface on dielectric multipactor
Authors: Chang C. , Huang H. J. , Liu G. Z. , Chen C. H. , Hou Q. , Fang J. Y. , Zhu X. X. , Zhang Y. P.
Published: June 2009

The effect of periodic rectangular grooves on vacuum multipactor has been theoretically and experimentally investigated. Dynamic calculation is applied to research the electron trajectory and impact energy under groove surface. Two-dimensional electromagnetic particle-in-cell simulation is used to analyze and compare multipactor scenario, statistic energy, and secondary emission yield on the flat surface with that on the corrugated surface. It has been found by computational and simulative analysis that grooved surface can explicitly suppress multipactor in the developmental stage of multipactor. S-band high power microwave (HPM) dielectric breakdown experiment under vacuum, with microsecond pulse length was conducted. It was confirmed by experiment that periodic grooves perpendicular to the major electric field can effectively increase transmitted power.