bluuebunny/crossref_metadata_2025 huggingface dataset:
Learning or Succeeding? Conflict Regulation With Mastery or Performance Goals
Authors: Darnon Céline , Butera Fabrizio
Published: August 2007

The present study aimed to integrate research on mastery and performance goals into research on sociocognitive conflict (confrontation involving divergent points of view). Participants interacted by discussing conflictual issues in a context enhancing either performance goals, mastery goals, or no goals. The amount of disagreement during the interaction was measured. Results indicated that disagreement predicted epistemic conflict regulation (focused on task comprehension) in the mastery goals condition, but relational conflict regulation (focused on affirmation of competence) in the performance goals condition. Results are discussed in terms of their contribution to the conflict regulation framework.
Conflict of Competences, Counterfactual Thinking, and Performance
Authors: Selimbegovic Leila , Quiamzade Alain , Chatard Armand , Mugny Gabriel , Fluri Daphné
Published: August 2007

Two studies were run to explore the relations between a conflict of competences (i.e., a situation in which two competent individuals present divergent solutions to the same task), counterfactual thinking, and performance. The first study shows that individuals who imagine themselves in a situation involving a conflict of competences generate more intensive subtractive than additive counterfactual thoughts. The second study tested the impact of a conflict of competences on performance in an anagram task. A condition involving a mere conflict of competences was compared to one involving a conflict of competences with additive counterfactuals (known to improve performance) and one involving a conflict of competences with subtractive counterfactuals (known to have no such effect on performance). As predicted, the performance of participants in the condition involving a mere conflict of competences and in that involving subtractive counterfactuals was inferior to that of participants in the condition involving additive counterfactuals.
When Negative Stereotypic Expectancies Turn Into Challenge or Threat: The Moderating Role of Regulatory Focus
Authors: Keller Johannes
Published: August 2007

The impact of negative stereotypic expectations on men’s verbal performance was investigated in an experimental study. The study was designed to test a theoretical perspective that relates self-regulatory processes as postulated in Regulatory Focus Theory (Higgins, 1998) to stereotypic expectancy effects on test performance as previously documented in research on stereotype threat. It is argued that negative stereotypic expectancies (e.g., “Men are bad at verbal tasks”) are more likely to result in a threat experience and poorer test performance when a prevention focus and in turn a special sensitivity to potential negative outcomes is activated whereas negative stereotypic expectancies are more likely to result in a challenge experience and better test performance when a promotion focus has been induced. The results indicate that expectancy effects on test performance are indeed moderated by the mode of self-regulation activated in the testing situation.
Stereotype Internalization, Math Perceptions, and Occupational Choices of Women With Counter-Stereotypical University Majors
Authors: Bonnot Virginie , Croizet Jean-Claude
Published: August 2007

Based on Eccles’ (1987) model of academic achievement-related decisions, we tested whether women, who are engaged in mathematical fields at university, have internalized, to some extent, the stereotype about women’s inferiority in math. The results indicate that men and women do not assess their ability self-concept, subjective value of math, or performance expectancies differently. However, women’s degree of stereotype endorsement has a negative impact on their ability self-concept and their performance expectancies, but does not affect their value of the math domain. Moreover, members of both genders envisage stereotypical careers after university graduation.
A Clinical-Psychological Approach to Suicidal Behavior in Depression from Moscow
Authors: Ponizovsky Alexander M
Published: August 2007

This contribution strives to familiarize Western readers with the theoretical concept of suicidal behavior which was developed at the Department of Suicidology of Moscow Psychiatric Research Institute and has been in use there for the last two decades. In describing this approach the paper concentrates on what differentiates it from traditional Western management without making value judgments about either approach. Such an account of the concept and its development will hopefully afford the reader an opportunity to arrive at his or her own conclusions regarding its clinical value.
A Study of Elderly Suicides in Hong Kong
Authors: Chi Iris , Yip Paul SF , Yu Gabriel KK , Halliday Peter
Published: August 2007

Hong Kong has one of the highest rates of suicide among the elderly in the world. Most of the existing suicide prevention programs have had very little effect on the elderly, who rarely utilize these programs. This study aims to help in understanding the problem, so that effective prevention can be provided to this high-risk group of suicidal people. Specifically, the study (1) describes the characteristics of the suicidal elderly, (2) investigates the reason(s) why the elderly are in distress and become suicidal, and (3) formulates a policy and service model to reach the elderly high-risk group.This research project involves secondary data analysis. Police records on elderly suicide cases in 1992 were scrutinized to find out the major reason(s) for fatal death in the elderly. Our study points out those districts that are more crowded and have fewer medical and social facilities tended to have higher suicide rates. Most of the deaths occurred at home or nearby, and the suicidal elderly were alone before their death. The majority of elderly suicide victims suffered from chronic diseases. Very few of them, however, were totally dependent: About 40% of the cases had consulted medical practitioners, and 27% had consulted psychiatrists within one month before their deaths. Close to 70% of the cases had indicated to family members or others their suicidal thoughts, and many of them had revealed numerous suicidal indications. Both policy and practice issues are discussed in light of the findings.
Euthanasia and Related Practices Worldwide
Authors: Kelleher † Michael J , Chambers Derek , Corcoran Paul , Keeley Helen S , Williamson Eileen
Published: August 2007

The present paper examines the occurrence of matters relating to the ending of life, including active euthanasia, which is, technically speaking, illegal worldwide. Interest in this most controversial area is drawn from many varied sources, from legal and medical practitioners to religious and moral ethicists. In some countries, public interest has been mobilized into organizations that attempt to influence legislation relating to euthanasia. Despite the obvious international importance of euthanasia, very little is known about the extent of its practice, whether passive or active, voluntary or involuntary. This examination is based on questionnaires completed by 49 national representatives of the International Association for Suicide Prevention (IASP), dealing with legal and religious aspects of euthanasia and physician-assisted suicide, as well as suicide. A dichotomy between the law and medical practices relating to the end of life was uncovered by the results of the survey. In 12 of the 49 countries active euthanasia is said to occur while a general acceptance of passive euthanasia was reported to be widespread. Clearly, definition is crucial in making the distinction between active and passive euthanasia; otherwise, the entire concept may become distorted, and legal acceptance may become more widespread with the effect of broadening the category of individuals to whom euthanasia becomes an available option. The “slippery slope” argument is briefly considered.
Why Has Suicide Increased in Young Males?
Authors: Hawton Keith
Published: August 2007

Several countries in the Western hemisphere have experienced a marked increase in suicide rates in young males in recent years. This article considers this phenomenon largely from the perspective of the United Kingdom, where rates of suicide in 15-24-year-old males nearly doubled in just over a decade. The possible reasons for this are considered, particularly in the context of relative stability of suicide rates in young females.
Suicidality in Borderline Personality Disorder
Authors: Kjellander Carole , Bongar Bruce , King Ashley
Published: August 2007

Recent research on the relationship between borderline personality disorder (BPD) and suicidal behavior is reviewed. Risk factors for attempted and completed suicide as well as the effect of the comorbidity of BPD with other Axis I and II disorders are considered. Explanations for suicidality in BPD are discussed. General assessment strategies are offered, along with treatment recommendations. Specifically, research has shown that borderline patients improve in the long-term, decreasing in suicidality, self-destructiveness, and interpersonal maladjustment, if survival is effectively managed during the turbulent years of youth. Clinical lore at times can lead clinicians to disregard the danger of suicide completion among chronically parasuicidal patients, which can prevent effective intervention during suicidal crises and result in unfortunate outcomes.
Observation of secondary ozone peaks near the tropopause over the Korean peninsula associated with stratosphere‐troposphere exchange
Authors: Hwang Seung‐Hyun , Kim Jhoon , Cho Gwang‐Rae
Published: August 2007

Vertical profiles of ozone partial pressure and temperature were obtained from ozonesonde measurements for 10 years from 1995 to 2004, over the midlatitude area at Pohang, Korea (36.02°N, 129.23°E), where stratosphere to troposphere exchange (STE) is very active. Secondary ozone peaks were observed in the upper troposphere/lower stratosphere at altitudes of about 14 km mostly in winter and spring. The 450 ozonesonde profiles were analyzed for this study together with satellite measurements from Halogen Occultation Experiment (HALOE) onboard the Upper Atmosphere Research Satellite (UARS). To compare with the satellite data sets, 188 HALOE data sets were archived over the period of 1993–2004 with extended locations for latitudes 32°N–40°N and longitudes of 120°E–135°E, which cover the Korean Peninsula region. The occurrence of secondary maxima in the upper troposphere is highly correlated with zonal wind speed and temperature enhancements. Most of these secondary peaks also were associated with stratosphere‐troposphere exchange processes. The backward trajectory model, Hybrid Single‐Particle Lagrangian Integrated Trajectory (HYSPLIT) from National Oceanic and Atmospheric Administration (NOAA) was used to examine these transport events further. The frequency of the secondary ozone peak appearance was found to increase at a rate of 1.4% yr−1 and 2.5% yr−1 for the past 10 years in this region on the basis of the ozonesonde and HALOE observations, respectively.
Major 20th century changes of carbonaceous aerosol components (EC, WinOC, DOC, HULIS, carboxylic acids, and cellulose) derived from Alpine ice cores
Authors: Legrand M. , Preunkert S. , Schock M. , Cerqueira M. , Kasper‐Giebl A. , Afonso J. , Pio C. , Gelencsér A. , Dombrowski‐Etchevers I.
Published: August 2007

An extended array of carbonaceous species including elemental carbon (EC), water insoluble organic carbon (WinOC) as well as dissolved organic carbon (DOC), humic‐like substances (HULIS), and single organic compounds like carboxylic acids, levoglucosan, and cellulose was investigated for the first time in Alpine snow deposits. These investigations were done on selected discrete ice cores sections extracted from Mount Rosa and Mount Blanc glaciers covering the 20th century and extending back to previous centuries. Here we focus on major changes in summer ice layers. Among carbonaceous components, EC reveals an outstanding increase with a sharp summer increase after World War II. This result is discussed against available past EC emission inventories in Europe which are thought to be mainly driven by emissions from road transport and residential sector. The long‐term trend of organic carbon (OC) aerosol preserved in ice, WinOC as well as water soluble organic carbon (WSOC), was successfully reconstructed using the suitable array of organic compounds we investigated in this study. It is shown that the level of OC preserved in ice has increased by a factor of 2 after 1950 likely as a result of the enhancement of the oxidative capacity of the atmosphere over the last decades producing more secondary organic atmospheric aerosol from biogenic gaseous precursors.
Modeling carbonaceous aerosol over Europe: Analysis of the CARBOSOL and EMEP EC/OC campaigns
Authors: Simpson D. , Yttri K. E. , Klimont Z. , Kupiainen K. , Caseiro A. , Gelencsér A. , Pio C. , Puxbaum H. , Legrand M.
Published: August 2007

In this paper the European Monitoring and Evaluation Programme (EMEP) MSC‐W model is used to assess our understanding of the sources of carbonaceous aerosol in Europe (organic carbon (OC), elemental carbon (EC), or their sum, total carbon (TC)). The modeling work makes use of new data from two extensive measurement campaigns in Europe, those of the CARBOSOL project and of the EMEP EC/OC campaign. As well as EC and OC measurements, we are able to compare with levoglucosan, a tracer of wood‐burning emissions, and with the source apportionment (SA) analysis of Gelencsér et al. (2007), which apportioned TC into primary versus secondary and fossil fuel versus biogenic origin. The model results suggest that emissions of primary EC and OC from fossil fuel sources are probably captured to better than a factor of two at most sites. Discrepancies for wintertime OC at some sites can likely be accounted for in terms of missing wood‐burning contributions. Two schemes for secondary organic aerosol (SOA) contribution are included in the model, and we show that model results for TC are very sensitive to the choice of scheme. In northern Europe the model seems to capture TC levels rather well with either SOA scheme, but in southern Europe the model strongly underpredicts TC. Comparison against the SA results shows severe underprediction of the SOA components. This modeling work confirms the difficulties of modeling SOA in Europe, but shows that primary emissions constitute a significant fraction of ambient TC.
Equatorial Kelvin waves as revealed by EOS Microwave Limb Sounder observations and European Centre for Medium‐Range Weather Forecasts analyses: Evidence for slow Kelvin waves of zonal wave number 3
Authors: Feng Liang , Harwood R. S. , Brugge R. , O'Neill A. , Froidevaux L. , Schwartz M. , Waters J. W.
Published: August 2007

Temperature and ozone observations from the Microwave Limb Sounder (MLS) on the EOS Aura satellite are used to study equatorial wave activity in the autumn of 2005. In contrast to previous observations for the same season in other years, the temperature anomalies in the middle and lower tropical stratosphere are found to be characterized by a strong wave‐like eastward progression with zonal wave number equal to 3. Extended empirical orthogonal function (EOF) analysis reveals that the wave 3 components detected in the temperature anomalies correspond to a slow Kelvin wave with a period of 8 days and a phase speed of 19 m/s. Fluctuations associated with this Kelvin wave mode are also apparent in ozone profiles. Moreover, as expected by linear theory, the ozone fluctuations observed in the lower stratosphere are in phase with the temperature perturbations, and peak around 20–30 hPa where the mean ozone mixing ratios have the steepest vertical gradient. A search for other Kelvin wave modes has also been made using both the MLS observations and the analyses from one experiment where MLS ozone profiles are assimilated into the European Centre for Medium‐Range Weather Forecasts (ECMWF) data assimilation system via a 6‐hourly 3D var scheme. Our results show that the characteristics of the wave activity detected in the ECMWF temperature and ozone analyses are in good agreement with MLS data.
Modeling stomatal and nonstomatal effects of water deficits on CO2 fixation in a semiarid grassland
Authors: Grant R. F. , Flanagan L. B.
Published: August 2007

The confidence with which we can model water deficit effects on grassland productivity is limited by uncertainty about the mechanisms, stomatal and nonstomatal, by which soil water deficits reduce CO2 uptake. We propose that these reductions can accurately be modeled from a combination of stomatal effects on gaseous CO2 diffusion and nonstomatal effects on biochemical CO2 fixation. These effects can be combined through a solution for the intercellular CO2 concentration (Ci) at which rates of diffusion and fixation are equal for each leaf surface in the canopy. In this model, both stomatal and nonstomatal effects are driven by a common indicator of plant water status calculated in a hydraulically‐driven scheme of soil‐plant‐atmosphere water transfer. As part of the ecosystem model ecosys, this combined model simulated concurrent declines in latent heat effluxes and CO2 influxes measured by eddy covariance during soil drying in a drought‐affected semiarid grassland. At the same time, the model simulated the declines in Ci at which CO2 fixation occurred during soil drying as calculated from seasonal measurements of phytomass δ13C. Alternative model formulations based on stomatal or nonstomatal effects alone simulated these declines in CO2 influxes and in Ci less accurately than did the formulation in which these effects were combined. We conclude that modeling water deficit effects on CO2 fixation requires the concurrent simulation of stomatal and nonstomatal effects. As part of a larger ecosystem model, this combined model can be used to assess climate effects on grassland productivity.
Slow slip events and seismic tremor at circum‐Pacific subduction zones
Authors: Schwartz Susan Y. , Rokosky Juliana M.
Published: August 2007

It has been known for a long time that slip accompanying earthquakes accounts for only a fraction of plate tectonic displacements. However, only recently has a fuller spectrum of strain release processes, including normal, slow, and silent earthquakes (or slow slip events) and continuous and episodic slip, been observed and generated by numerical simulations of the earthquake cycle. Despite a profusion of observations and modeling studies the physical mechanism of slow slip events remains elusive. The concurrence of seismic tremor with slow slip episodes in Cascadia and southwestern Japan provides insight into the process of slow slip. A perceived similarity between subduction zone and volcanic tremor has led to suggestions that slow slip involves fluid migration on or near the plate interface. Alternatively, evidence is accumulating to support the notion that tremor results from shear failure during slow slip. Global observations of the location, spatial extent, magnitude, duration, slip rate, and periodicity of these aseismic slip transients indicate significant variation that may be exploited to better understand their generation. Most slow slip events occur just downdip of the seismogenic zone, consistent with rate‐ and state‐dependent frictional modeling that requires unstable to stable transitional properties for slow slip generation. At a few convergent margins the occurrence of slow slip events within the seismogenic zone makes it highly likely that transitions in frictional properties exist there and are the loci of slow slip nucleation. Slow slip events perturb the surrounding stress field and may either increase or relieve stress on a fault, bringing it closer to or farther from earthquake failure, respectively. This paper presents a review of slow slip events and related seismic tremor observed at plate boundaries worldwide, with a focus on circum‐Pacific subduction zones. Trends in global observations of slow slip events suggest that (1) slow slip is a common phenomena observed at almost all subduction zones with instrumentation capable of recording it, (2) different frictional properties likely control fast versus slow slip, (3) the depth range of slow slip may be related to the thermal properties of the plate interface, and (4) the equivalent seismic moment of slow slip events is proportional to their duration (Moατ), different from the Moατ3 scaling observed for earthquakes.
Analysis of pumping‐induced unsaturated regions beneath a perennial river
Authors: Su Grace W. , Jasperse James , Seymour Donald , Constantz James , Zhou Quanlin
Published: August 2007

The presence of an unsaturated region beneath a streambed during groundwater pumping near streams can reduce the pumping capacity, change flow paths, and alter the types of biological transformations in the streambed sediments. A three‐dimensional, multiphase flow model of two horizontal collector wells along the Russian River near Forestville, California, was developed to investigate the impact of varying the ratio of the aquifer to streambed permeability on (1) the formation of an unsaturated region beneath the stream, (2) the pumping capacity, (3) stream water fluxes through the streambed, and (4) stream water traveltimes to the collector wells. The aquifer to streambed permeability ratio at which the unsaturated region was initially observed ranged from 10 to 100. The size of the unsaturated region beneath the streambed increased as the aquifer to streambed permeability ratio increased. The simulations also indicated that for a particular aquifer permeability, decreasing the streambed permeability by only a factor of 2–3 from the permeability where desaturation initially occurred resulted in reducing the pumping capacity. In some cases, the stream water fluxes increased as the streambed permeability decreased. However, the stream water residence times increased and the fraction of stream water that reached that the wells decreased as the streambed permeability decreased, indicating that a higher streambed flux does not necessarily correlate to greater recharge of stream water around the wells.
Ecohydrological controls on soil moisture and hydraulic conductivity within a pinyon‐juniper woodland
Authors: Lebron I. , Madsen M. D. , Chandler D. G. , Robinson D. A. , Wendroth O. , Belnap J.
Published: August 2007

The impact of pinyon‐juniper woodland encroachment on rangeland ecosystems is often associated with a reduction of streamflow and recharge and an increase in soil erosion. The objective of this study is to investigate vegetational control on seasonal soil hydrologic properties along a 15‐m transect in pinyon‐juniper woodland with biocrust. We demonstrate that the juniper tree controls soil water content (SWC) patterns directly under the canopy via interception, and beyond the canopy via shading in a preferred orientation, opposite to the prevailing wind direction. The juniper also controls the SWC and unsaturated hydraulic conductivity measured close to water saturation (K(h)) under the canopy by the creation of soil water repellency due to needle drop. We use this information to refine the hydrologic functional unit (HFU) concept into three interacting hydrologic units: canopy patches, intercanopy patches, and a transitional unit formed by intercanopy patches in the rain shadow of the juniper tree. Spatial autoregressive state‐space models show the close relationship between K(h) close to soil water saturation and SWC at medium and low levels, integrating a number of influences on hydraulic conductivity.
Geometric relationships of pristine Martian complex impact craters, and their implications to Mars geologic history
Authors: Boyce Joseph M. , Garbeil Harold
Published: August 2007

Based on the depths of pristine complex craters on Mars, we have estimated the final, post‐modification phase depth (dr) to diameter (D) function of Martian complex craters. We suggest that the dr/D function determined here holds globally for complex craters >∼12 km diameter. The global nature of this function may be due to the stability of slopes in the highly fractured rock that makes up the steep interior walls of post‐modification phase craters. The stability of such slopes should be controlled mainly by such factors as the nature of the fractures and not target strength. This function is an essential benchmark for studies that utilize crater geometry as their basis. For example, the function can be used in gradation history of Mars to predict the magnitude of degradation. For instance, an example 20‐km‐diameter, Middle/Early Noachian‐age crater that initially formed in the mid‐latitudes of Mars with a depth of 1800 m (instead of 1404 m as predicted by the fresh craters function) has lost ∼1450 m of its depth over its history, ∼350 m in the Noachian, ∼400 m during an intense episode of degradation at the end of the Noachian, and ∼700 m thereafter. No evidence of the period of intense degradation is found in the high‐latitudes, although those regions appear to have been affected by a process that reduced crater depth soon after they form.
Impact of Argo on analyses of the global ocean
Authors: Balmaseda M. , Anderson D. , Vidard A.
Published: August 2007

The impact of Argo on ECMWF operational ocean analyses has been assessed by conducting a set of observing system experiments spanning the period 2001–2006. The experiments evaluate the information content of Argo temperature and salinity data, gauged in terms of influence on the ocean state and the skill of seasonal forecasts. The salinity data from Argo is instrumental in correcting the salinity of the ECMWF analysis on a basin‐wide scale. The effect of Argo temperature is noticeable in the Indian, Atlantic and Southern Oceans. In the Pacific, the impact is modest, being confined to the South American coast. The information content of Argo combines well with the altimeter information in most regions. The impact of Argo on seasonal forecasts of sea surface temperature has been assessed for the period 2001–2006. The assimilation of Argo improves seasonal forecast skill in most areas, although the reduction of the error is small.
Relationship between trends in land precipitation and tropical SST gradient
Authors: Chung Chul Eddy , Ramanathan V.
Published: August 2007

Land precipitation trend from 1951 to 2002 shows widespread drying between 10°S to 20°N but the trend from 1977 to 2002 shows partial recovery. Based on general circulation model sensitivity studies, it is suggested that these features are driven largely by the meridional SST gradient trend in the tropics. Our idealized CCM3 experiments substantiate that land precipitation is more sensitive to meridional SST gradient than to an overall tropical warming. Various simulations produced for the IPCC 4th assessment report demonstrate that increasing CO2 increases SST in the entire tropics non‐uniformly and increases land precipitation only in certain latitude belts, again pointing to the importance of SST gradient change. Temporally varying aerosols in the IPCC simulations alter meridional SST gradient and land precipitation substantially. Anthropogenic aerosol direct solar forcing without its effects on SST is shown by the CCM3 to have weak but non‐negligible influence on land precipitation.
Connection between the decadal variability in the Southern Ocean circulation and the Southern Annular Mode
Authors: Yang Xiao‐Yi , Wang Dongxiao , Wang Jia , Huang Rui Xin
Published: August 2007

Previous studies demonstrated the remarkable upward trend of the Southern Annular Mode (SAM) and Southern Ocean wind stress in association with anthropogenic forcing. An oceanic reanalysis data set is used to investigate the response of the circulation in the Southern Ocean to the decadal variability of SAM. Our results indicate the strengthening and the poleward shift of the northward Ekman velocity as well as the Ekman pumping rate, which led to a corresponding strengthening trend in the Deacon Cell. This strengthening, in turn, intensified the meridional density gradient and the tilting of the isopycnal surfaces. On the interannual time scale, the Antarctic Circumpolar Currents (ACC) transport exhibits a positive correlation with SAM index as seen separately in observations. However, there is no significant trend in the total transport of ACC. Possible reasons are discussed.
Recent volume loss of British Columbian glaciers, Canada
Authors: Schiefer E. , Menounos B. , Wheate R.
Published: August 2007

We use the Shuttle Radar Topography Mission (SRTM) data and digital terrain models from aerial photography to quantify the change of glacier volume in British Columbia (BC), Canada for the period 1985–1999. We note substantial elevation bias in the SRTM elevations, typically on the order of −12 m km−1. The bias‐corrected thinning rate is −0.78 ± 0.19 m a−1 which yields an annual volume loss of 22.48 ± 5.53 km−3a−1. This rate of glacier volume loss is 65% of the estimate uncorrected for elevation bias (34.7 km−3a−1) and cautions against the use of uncorrected SRTM data for glacier change studies. Glacier recession in BC could account for ca. 0.67 ± 0.12 mm of sea level rise over the period 1985–1999 (0.05 ± 0.009 mm yr−1) or about 8.3% of the contribution from mountain glaciers and ice caps. The recent rate of glacier loss in the Coast Mountains (17.0 km−3a−1) is approximately double that observed for the previous two decades.
A new measure of entrainment zone structure
Authors: Brooks I. M. , Fowler A. M.
Published: August 2007

A wavelet covariance algorithm designed to objectively identify the upper and lower limits of the local transition zone between boundary layer and free troposphere is applied to the output fields from a series of Large Eddy Simulations of the convective atmospheric boundary layer. A new measure of entrainment zone structure is defined – the normalized difference between the standard deviations of the local transition zone limits; this is found to be a function of the convective Richardson number and a predictor of normalized entrainment rate. This provides a robust and objective means for determining the Richardson number from remote sensing observations, and the basis for determining the entrainment rate.
Competitive coexistence in stoichiometric chaos
Authors: Deng Bo , Loladze Irakli
Published: August 2007

Classical predator-prey models, such as Lotka-Volterra, track the abundance of prey, but ignore its quality. Yet, in the past decade, some new and occasionally counterintuitive effects of prey quality on food web dynamics emerged from both experiments and mathematical modeling. The underpinning of this work is the theory of ecological stoichiometry that is centered on the fact that each organism is a mixture of multiple chemical elements such as carbon (C), nitrogen (N), and phosphorus (P). The ratios of these elements can vary within and among species, providing simple ways to represent prey quality as its C:N or C:P ratios. When these ratios modeled to vary, as they frequently do in nature, seemingly paradoxical results can arise such as the extinction of a predator that has an abundant and accessible prey. Here, for the first time, we show analytically that the reduction in prey quality can give rise to chaotic oscillations. In particular, when competing predators differ in their sensitivity to prey quality then all species can coexist via chaotic fluctuations. The chaos generating mechanism is based on the existence of a junction-fold point on the nullcline surfaces of the species. Conditions on parameters are found for such a point, and the singular perturbation method and the kneading sequence analysis are used to demonstrate the existence of a period-doubling cascade to chaos as a result of the point.
Quadrupole, octopole, and hexadecapole electric moments of Σ, Π, Δ, and Φ electronic states: Cylindrically asymmetric charge density distributions in linear molecules with nonzero electronic angular momentum
Authors: Bruna Pablo J. , Grein Friedrich
Published: August 2007

The number of independent components, n, of traceless electric 2l-multipole moments is determined for C∞v molecules in Σ±, Π, Δ, and Φ electronic states (Λ=0,1,2,3). Each 2l pole is defined by a rank-l irreducible tensor with (2l+1) components Pm(l) proportional to the solid spherical harmonic rlYml(θ,φ). Here we focus our attention on 2l poles with l=2,3,4 (quadrupole Θ, octopole Ω, and hexadecapole Φ). An important conclusion of this study is that n can be 1 or 2 depending on both the multipole rank l and state quantum number Λ. For Σ±(Λ=0) states, all 2l poles have one independent parameter (n=1). For spatially degenerate states—Π, Δ, and Φ (Λ=1,2,3)—the general rule reads n=1 for l<2∣Λ∣ (when the 2l-pole rank lies below 2∣Λ∣) but n=2 for higher 2l poles with l⩾2∣Λ∣. The second nonzero term is the off-diagonal matrix element ⟨ψ+Λ∣P∣m∣=2Λ(l)∣ψ−Λ⟩. Thus, a Π(Λ=1) state has one dipole (μz) but two independent 2l poles for l⩾2—starting with the quadrupole [Θzz,(Θxx−Θyy)]. A Δ(Λ=2) state has n=1 for 2(1,2,3) poles (μz,Θzz,Ωzzz) but n=2 for higher 2(l⩾4) poles—from the hexadecapole Φ up. For Φ(Λ=3) states, it holds that n=1 for 21 to 25 poles but n=2 for all 2(l⩾6) poles. In short, what is usually stated in the literature—that n=1 for all possible 2l poles of linear molecules—only applies to Σ± states. For degenerate states with n=2, all Cartesian 2l-pole components (l⩾2∣Λ∣) can be expressed as linear combinations of two irreducible multipoles, Pm=0(l) and P∣m∣=2Λ(l) [parallel (z axis) and anisotropy (xy plane)]. Our predictions are exemplified by the Θ, Ω, and Φ moments calculated for Λ=0−3 states of selected diatomics (in parentheses): XΣ+2(CN), XΠ2(NO), aΠu3(C2), XΔ2(NiH), XΔ3(TiO), XΦ3(CoF), and XΦ4(TiF). States of Π symmetry are most affected by the deviation from axial symmetry.
Quantum effects in liquid water from an ab initio-based polarizable force field
Authors: Paesani Francesco , Iuchi Satoru , Voth Gregory A.
Published: August 2007

The importance of quantum effects as well as the accuracy of the ab initio-based polarizable TTM2.1-F force field in describing liquid water are quantitatively assessed by a detailed analysis of the temperature dependence of several thermodynamic and dynamical properties computed using the path-integral molecular dynamics and centroid molecular dynamics methods. The results show that quantum effects are not negligible even at relatively high temperatures, and their inclusion in simulations with the TTM2.1-F water model is necessary to achieve a more accurate description of the liquid properties. Comparison with the results reported in the literature for empirical, nonpolarizable force fields demonstrates that the effects of the nuclear quantization on the dielectric constant are dependent in part on how the electronic polarization is described in the underlying water model, while comparison with other ab initio-based force fields shows that the TTM2.1-F model provides an overall accurate description of liquid water. Analysis of the isotope effect on the dynamical properties does not display significant temperature dependence. This suggests that the contribution of quantum tunneling, which has been proposed as a possible cause for the different orientational dynamics observed for the HDO:H2O and HDO:D2O systems, appears to be small.
Siloxanes: A new class of candidate Bethe-Zel’dovich-Thompson fluids
Authors: Colonna P. , Guardone A. , Nannan N. R.
Published: August 2007

This paper presents a new class of Bethe-Zel’dovich-Thompson fluids, which are expected to exhibit nonclassical gasdynamic behavior in the single-phase vapor region. These are the linear and cyclic siloxanes, light silicon oils currently employed as working fluids in organic Rankine cycle turbines. State-of-the-art multiparameter equations of state are used to describe the thermodynamic properties of siloxanes and to compute the value of the fundamental derivative of gasdynamics Γ, whose negative sign is the herald of nonclassical gasdynamics. Siloxane fluids starting from D6 and cyclic siloxanes of greater complexity, and MD3M and linear siloxanes of greater complexity are predicted to exhibit a thermodynamic region in which Γ is negative and hence nonclassical wavefields are admissible. As an exemplary case, a nonclassical rarefaction shock wave propagating in fluid D6 is studied to demonstrate the possibility of using siloxane fluids in nonclassical gasdynamic applications and to experimentally verify the existence of nonclassical wavefields in the vapor phase. The sensitivity of the present results to the considered thermodynamic model of the fluid is also briefly discussed.
Vortex ring head-on collision with a heated vertical plate
Authors: Arévalo G. , Hernández R. H. , Nicot C. , Plaza F.
Published: August 2007

We report experimental results of the normal impact of a vortex ring in air on a vertical heated plate at constant temperature. We address the case in which the natural convection boundary layer is laminar and the vortex ring is stable. Vortex rings are created by pushing air through a circular exit orifice of a cavity, using a piston-cylinder system. The impinging vortex ring perturbs both the thermal and dynamical boundary layers where we measure the total heat flux exchanged by the heated plate and visualize the vortex motion during the impact. This unsteady impingement process is investigated for different vortex sizes and self-induced velocities, characterized by the Reynolds number of the ring. As a result, a localized heat transfer enhancement is originated by the ring impingement, which increases with the Reynolds number.
Correction of Lamb’s dissipation calculation for the effects of viscosity on capillary-gravity waves
Authors: Padrino J. C. , Joseph D. D.
Published: August 2007

Purely irrotational theories of the flow of a viscous liquid are applied to model the effect of viscosity on the decay and oscillation of capillary-gravity waves. In particular, the dissipation approximation used in this analysis gives rise to a viscous correction of the frequency of the oscillations which was not obtained by Lamb’s [H. Lamb, Hydrodynamics (Cambridge University Press, Cambridge, UK, 1932) (reprinted in 1993)] dissipation calculation. Moreover, our dissipation method goes beyond Lamb’s in the sense that it yields an eigenvalue relation valid for the entire continuous spectrum of wave numbers. Comparisons are presented between the purely irrotational theories and Lamb’s exact solution, showing good to reasonable agreement for long, progressive waves and for short, standing waves, even for very viscous liquids. The performance of the irrotational approximations deteriorates within an interval of wave numbers containing the cutoff where traveling waves become standing ones.
Amplified spontaneous emission and lasing properties of bisfluorene-cored dendrimers
Authors: Ribierre J. C. , Tsiminis G. , Richardson S. , Turnbull G. A. , Samuel I. D. W. , Barcena H. S. , Burn P. L.
Published: August 2007

A study of the amplified spontaneous emission (ASE) properties of three bisfluorene-cored dendrimers in the solid state is reported. The results show that the dendron type has a strong impact on the photoluminescence quantum yield and affects the ASE threshold, the optical gain, and loss coefficients. Optically pumped distributed feedback lasers operating in the blue spectral region were fabricated by spin coating the dendrimer films on top of a two-dimensional corrugated fused silica substrate. A best lasing threshold of 4.5μJ∕cm2 and a slope efficiency of 8.3% were obtained, which demonstrate the high potential of these materials for laser applications.
Low density solid ozone
Authors: Teolis B. D. , Famá M. , Baragiola R. A.
Published: August 2007

We report a very low density (∼0.5g∕cm3) structure of solid ozone. It is produced by irradiation of solid oxygen with 100keV protons at 20K followed by heating to sublime unconverted oxygen. Upon heating to 47K the porous ozone compacts to a density of ∼1.6g∕cm3 and crystallizes. We use a detailed analysis of the main infrared absorption band of the porous ozone to interpret previous research, where solid oxygen was irradiated by UV light and keV electrons.
Plasma formation and structural modification below the visible ablation threshold in fused silica upon femtosecond laser irradiation
Authors: Siegel J. , Puerto D. , Gawelda W. , Bachelier G. , Solis J. , Ehrentraut L. , Bonse J.
Published: August 2007

We have investigated the temporal and spatial evolution of the ablation process induced in fused silica upon irradiation with single 120fs laser pulses at 800nm. Time-resolved microscopy images of the surface reflectivity at 400nm reveal the existence of a transient plasma distribution with annular shape surrounding the visible ablation crater. The material in this annular zone shows an increased reflectivity after irradiation, consistent with a local refractive index increase of approximately 0.01. White light interferometry measurements indicate a shallow surface depression in this outer region, most likely due to material densification.
Modeling the resistance-temperature characteristic of a positive temperature coefficient thermistor, using experimentally determined permittivity data
Authors: Zubair M. A. , Leach C.
Published: August 2007

The resistivity-temperature [ρ(T)] and current-voltage [j(V)] characteristics of a (Ba,Ca)TiO3 based donor/acceptor codoped positive temperature coefficient of resistivity thermistor have been analyzed in the context of the double Schottky barrier (DSB) model, using experimentally measured permittivity data. The best fit between the modeled and experimental ρ(T) behavior occurred for a broad acceptor energy fluctuation width (Δ=0.35eV). Modeling the ρ(T) behavior below the Curie temperature required a nonvanishing surface charge, consistent with a residual potential barrier. j(V) characteristics showed satisfactory agreement with the DSB model at low applied voltages per grain boundary (Vgb⩽0.13–0.22eV).
Electron correlation in the GK state of the hydrogen molecule
Authors: Wang Jian , Wang Yu , Lv Shengliang , Ugalde Jesus M.
Published: August 2007

The second excited Σg+1 state of the hydrogen molecule, the so-called GK state, has a potential energy curve with double minima. At the united atom limit it converges to the 1s3d configuration of He. At large internuclear distances R, it dissociates to two separated atoms, one in the ground state and another in the 2p excited state. Radial pair density calculations and natural orbital analyses reveal unusual effect of electron correlation around the K minimum of the potential energy curve. As R>2.0a.u., a natural orbital of σu symmetry joins the two natural orbitals of σg symmetry at smaller R. The average interelectronic distance decreases as the internuclear distance increases from R=2.0to3.0a.u. Around R=3.0a.u. the singly peaked pair density curve splits into two peaks. The inner peak can be attributed to the formation of the ionic electron configuration (1s)2, where both 1s electrons are on the same nucleus. As the two 1s electrons run into different nuclei, one of the two 1s electrons is promoted to the 2p state, which results in the outer peak in the pair density curve. The Rydberg 1s2p configuration persists as the nuclei stretch, and becomes dominant at large R where four natural orbitals, two of σg and two of σu symmetry, become responsible.
Low current induced electroresistance in the polycrystalline La0.6Pb0.4MnO3 thin films
Authors: Singh Ajay , Aswal D. K. , Chowdhury P. , Padma N. , Gupta S. K. , Yakhmi J. V.
Published: August 2007

We report the temperature and current dependence of electroresistance (ER) in the polycrystalline (PC) La0.6Pb0.4MnO3 (LPMO) thin films with grain size 55 nm. ER is observed only below metal-insulator transition temperature (TIM). In the temperature range T<TIM, ER shows a sharp increase at low currents (<50 μA) followed by saturation. The experimental results can be understood in terms of modification of grain boundaries characteristics by spin polarized carriers. ER versus current behavior remains unaffected by the magnetic field, indicating that the mechanism governing ER and magnetoresistance are effectively decoupled. The sharp increase in ER at low currents suggests that PC LPMO films may have potential for application in low power devices operating at low temperatures.
Synthesis and thermoelectric properties of p-type Ba8Ga16ZnxGe30−x type-I clathrates
Authors: Deng Shukang , Tang Xinfeng , Zhang Qingjie
Published: August 2007

Zn-doping Ba8Ga16ZnxGe30−x (x=2.4, 2.6, 2.8, 3.0, 3.2) clathrates with different Zn contents were synthesized by combining the solid-state reaction with the spark plasma sintering method. The effects of Zn content on thermoelectric properties were investigated. The results show that all specimens exhibit p-type conduction characteristics. The electrical conductivity, the room-temperature carrier mobility, and the thermal conductivity decrease with increasing Zn content for Zn-doped Ba8Ga16ZnxGe30−x compounds, while the room-temperature carrier concentration Np increases with increasing Zn content. The carrier scattering mechanism is mainly ionized impurity mechanism in the low-temperature range (T<200 K), and gradually changes to an acoustical mechanism with the rising temperature. In all p-type Ba8Ga16ZnxGe30−x compounds, Ba8Ga16Zn3.2Ge26.8 exhibits the highest Seebeck coefficient with the value of 250 μV/K at 300 K and 307 μV/K around 700 K, respectively. The maximum ZT value of 0.38 is obtained at 790 K for Ba8Ga16Zn3.0Ge27.0.
Influence of source-drain electric field on mobility and charge transport in organic field-effect transistors
Authors: Hamadani B. H. , Richter C. A. , Gundlach D. J. , Kline R. J. , McCulloch I. , Heeney M.
Published: August 2007

We report on a strong field-dependent mobility in organic field-effect transistors fabricated by using poly(2,5-bis(3-tetradecylthiophene-2-yl)thieno[3,2-b]thiophene) (pBTTT-C14) as the active polymer layer. Charge transport and mobilities in devices annealed in the mesophase show a more pronounced dependence on channel length as compared with as-cast devices. Analysis reveals that the contact effects in both sets of devices are negligible from room temperature down to ≈100K. We show that this field dependence is consistent with a Poole-Frenkel model of mobility. Finally, the nonlinear transport data for short channel devices are modeled consistently in the Poole-Frenkel framework over a broad temperature range.
Phase transitions and ferroelectric properties in BiScO3-Bi(Zn1∕2Ti1∕2)O3-BaTiO3 solid solutions
Authors: Huang Chien-Chih , Cann David P. , Tan Xiaoli , Vittayakorn Naratip
Published: August 2007

Ceramics solid solutions within the ternary perovskite system Bi(Zn1∕2Ti1∕2)O3-BiScO3-BaTiO3 were synthesized via solid-state processing techniques. The crystal structure of sintered ceramics was analyzed by x-ray diffraction. A stable perovskite phase was obtained for all compositions with a BaTiO3 content greater than 50 mol %. Furthermore, a change in symmetry from pseudocubic to tetragonal was observed as the mole fraction of BaTiO3 increased. Dielectric measurements show a dielectric anomaly associated with a phase transformation over the temperature range of 30 °C–210 °C for all compositions. Examination of the polarization hysteresis behavior revealed weakly nonlinear hysteresis loops. With these data, ferroelectric phase diagrams were derived showing the transition between the pseudocubic relaxor behavior to the tetragonal normal ferroelectric behavior. This transition was also correlated with changes in the diffuseness parameter.