bluuebunny/crossref_metadata_2025 huggingface dataset:
Receptivity, instability and breakdown of Görtler flow
Authors: SCHRADER LARS-UVE , BRANDT LUCA , ZAKI TAMER A.
Published: July 2011

Receptivity, disturbance growth and breakdown to turbulence in Görtler flow are studied by spatial direct numerical simulation (DNS). The boundary layer is exposed to free-stream vortical modes and localized wall roughness. We propose a normalization of the roughness-induced receptivity coefficient by the square root of the Görtler number. This scaling removes the dependence of the receptivity coefficient on wall curvature. It is found that vortical modes are more efficient at generating Görtler vortices than localized roughness. The boundary layer is most receptive to zero- and low-frequency free-stream vortices, exciting steady and slowly travelling Görtler modes. The associated receptivity mechanism is linear and involves the generation of boundary-layer streaks, which soon evolve into unstable Görtler vortices. This connection between transient and exponential amplification is absent on flat plates and promotes transition to turbulence on curved walls. We demonstrate that the Görtler boundary layer is also receptive to high-frequency free-stream vorticity, which triggers steady Görtler rolls via a nonlinear receptivity mechanism. In addition to the receptivity study, we have carried out DNS of boundary-layer transition due to broadband free-stream turbulence with different intensities and frequency spectra. It is found that nonlinear receptivity dominates over the linear mechanism unless the free-stream fluctuations are concentrated in the low-frequency range. In the latter case, transition is accelerated due to the presence of travelling Görtler modes.
Acceptance and commitment therapy as guided self-help for psychological distress and positive mental health: a randomized controlled trial
Authors: Fledderus M. , Bohlmeijer E. T. , Pieterse M. E. , Schreurs K. M. G.
Published: July 2011

Background

In order to reduce the high prevalence of depression, early interventions for people at risk of depression are warranted. This study evaluated the effectiveness of an early guided self-help programme based on acceptance and commitment therapy (ACT) for reducing depressive symptomatology.

Method

Participants with mild to moderate depressive symptomatology were recruited from the general population and randomized to the self-help programme with extensive email support (n=125), the self-help programme with minimal email support (n=125) or to a waiting list control group (n=126). Participants completed measures before and after the intervention to assess depression, anxiety, fatigue, experiential avoidance, positive mental health and mindfulness. Participants in the experimental conditions also completed these measures at a 3-month follow-up.

Results

In the experimental conditions significant reductions in depression, anxiety, fatigue, experiential avoidance and improvements in positive mental health and mindfulness were found, compared with the waiting list condition (effect sizes Cohen's d=0.51–1.00). These effects were sustained at the 3-month follow-up. There were no significant differences between the experimental conditions on the outcome measures.

Conclusions

The ACT-based self-help programme with minimal email support is effective for people with mild to moderate depressive symptomatology.
Amygdala to hippocampal volume ratio is associated with negative memory bias in healthy subjects
Authors: Gerritsen L. , Rijpkema M. , van Oostrom I. , Buitelaar J. , Franke B. , Fernández G. , Tendolkar I.
Published: July 2011

Background

Negative memory bias is thought to be one of the main cognitive risk and maintenance factors for depression, but its neural substrates are largely unknown. Here, we studied whether memory bias is related to amygdala and hippocampal volume, two structures that are critical for emotional memory processes and that show consistent volume alterations in depression.

Method

Structural magnetic resonance imaging (MRI) was carried out in 272 healthy participants (62% female, 18–50 years old). All images were acquired on 1.5 T Siemens MRI scanners. Automatic segmentation of amygdala and hippocampus was performed using the FIRST module of FSL. Negative memory bias was assessed by the self-referent encoding/evaluation test.

Results

Negative memory bias was associated with larger amygdala (p=0.042) and smaller hippocampal (p=0.029) volumes. In additional analyses, we found that, compared with the associations found with hippocampus and amygdala volume separately, a stronger association was found between negative memory bias and the ratio of amygdala:hippocampus volume (p=0.021).

Conclusions

In non-depressed subjects we found that larger amygdala and smaller hippocampal volumes are associated with negative memory bias. This suggests that an increased amygdala:hippocampus volume ratio plays a role in cognitive vulnerability often seen in individuals with high risk for depression and that these structural brain differences may pre-date the onset of depression.
Energy dissipation of ion beam in two-component plasma in the presence of laser irradiation
Authors: Hu Zhang-Hu , Song Yuan-Hong , Mišković Z.L. , Wang You-Nian
Published: July 2011

We use a two-dimensional particle-in-cell simulation to investigate the dynamic polarization and stopping power for an ion beam propagating through a two-component plasma, which is simultaneously irradiated by a strong laser pulse. Compared to the laser-free case, we observe a reduction in the instantaneous stopping power that initially follows the shape of the laser pulse and becomes particularly large as the laser frequency approaches the plasma electron frequency. We attribute this large reduction in the ion stopping power to an increase in plasma temperature due to the energy absorbed in the plasma from the laser pulse through the process of wave heating. In addition, dynamic polarization of the plasma by the ion is found to be strongly modulated by the laser field.
Nonlinear absorption of intense short pulse laser over a metal surface embedded with nanoparticles
Authors: Kumar Ashok , Verma A. L.
Published: July 2011

The anomalous absorption of laser, incident at an arbitrary angle of incidence on a metal surface embedded with nanoparticles, is studied. The electrons inside a nanoparticle resonantly absorb laser energy when the laser frequency equals the frequency of surface charge oscillations of the nanoparticle. A monolayer of nanoparticles of radius rnp0 ≈ 50 A with inter-particle separation d ~ 10rnp0 can cause up to 40% reduction of the reflection of p-polarized laser light. The absorption coefficient increases with the angle of incidence and has a sharp peak at a resonant frequency width of about 1%. At high laser power, even if the nanoparticles are initially off resonant with the laser, the particle heating and subsequent expansion reduces the resonance frequency, and the resonance absorption is realized after a time delay. The delay is found to be directly proportional to the cluster size and inversely proportional to the laser intensities.
An inverse optimization approach for determining weights of joint displacement objective function for upper body kinematic posture prediction
Authors: Zou Qiuling , Zhang Qinghong , Yang Jingzhou (James) , Gragg Jared
Published: July 2011

Human posture prediction can often be formulated as a nonlinear multiobjective optimization (MOO) problem. The joint displacement function is considered as a benchmark of human performance measures. When the joint displacement function is used as the objective function, posture prediction is a MOO problem. The weighted-sum method is commonly used to find a Pareto solution of this MOO problem. Within the joint displacement function, the relative value of the weights associated with each joint represents the relative importance of that joint. Usually, weights are determined by trial and error approaches. This paper presents a systematic approach via an inverse optimization approach to determine the weights for the joint displacement function in posture prediction. This inverse optimization problem can be formulated as a bi-level optimization problem. The design variables are joint angles and weights. The cost function is the summation of the differences between two set of joint angles (the design variables and the realistic posture). Constraints include (1) normalized weights within limits and (2) an inner optimization problem to solve for joint angles (predicted posture). Additional constraints such as weight limits and weight linear equality constraints, obtained through observations, are also implemented in the formulation to test the method. A 24 degree of freedom human upper body model is used to study the formulation and visualize the prediction. An in-house motion capture system is used to obtain the realistic posture. Four different percentiles of subjects are selected to run the experiment. The set of weights for the general seated posture prediction is obtained by averaging all weights for all subjects and all tasks. On the basis of obtained set of weights, the predicted postures match the experimental results well.
Toward safe and stable time-delayed mobile robot teleoperation through sampling-based path planning
Authors: Nieto Jorge , Slawiñski Emanuel , Mut Vicente , Wagner Bernardo
Published: July 2011

This work proposes a teleoperation architecture for mobile robots in partially unknown environments under the presence of variable time delay. The system is provided with artificial intelligence represented by a probabilistic path planner that, in combination with a prediction module, assists the operator while guaranteeing a collision-free motion. For this purpose, a certain level of autonomy is given to the system. The structure was tested in indoor environments for different kinds of operators. A maximum time delay of 2s was successfully coped with.
High-accuracy global localization filter for three-dimensional environments
Authors: Martín Fernando , Moreno Luis , Garrido Santiago , Blanco Dolores
Published: July 2011

The localization problem in mobile robotics can be defined as the search of the robot's coordinates in a known environment. If there is no information about the initial location, we are talking about global localization. In this work, we have developed an algorithm that solves this problem in a three-dimensional (3D) environment using evolutionary computation concepts. The method has been called RELF-3D and has many features that make it very robust and reliable: thresholding and discarding mechanisms, different cost functions, effective convergence criteria, and so on. The resulting global localization module has been tested in numerous experiments and the most important improvement obtained is the accuracy of the method, allowing its application in manipulation tasks.
The role of gesture in designing
Authors: Visser Willemien , Maher Mary Lou
Published: July 2011

This paper introduces the special issue of AI EDAM on the role of gesture in designing. It starts with the context of the papers submitted and a summary of the papers accepted. We then introduce gesture studies, one of the two main domains with which this Special Issue is concerned. We do not introduce design research: we suppose the readers of AI EDAM are familiar with this domain. After this general introduction to the domain of gesture studies, we provide an overview of gestures in design, that is, the research environment of the papers in this Special Issue. We then discuss some dimensions on which these papers differ, as well as some on which they are related.
Using speech to identify gesture pen strokes in collaborative, multimodal device descriptions
Authors: Herold James , Stahovich Thomas F.
Published: July 2011

One challenge in building collaborative design tools that use speech and sketch input is distinguishing gesture pen strokes from those representing device structure, that is, object strokes. In previous work, we developed a gesture/object classifier that uses features computed from the pen strokes and the speech aligned with them. Experiments indicated that the speech features were the most important for distinguishing gestures, thus indicating the critical importance of the speech–sketch alignment. Consequently, we have developed a new alignment technique that employs a two-step process: the speech is first explicitly segmented (primarily into clauses), then the segments are aligned with the pen strokes. Our speech segmentation step is unique in that it uses sketch features for locating segment boundaries in multimodal dialog. In addition, it uses a single classifier to directly combine word-based, prosodic (pause), and sketch-based features. In the second step, segments are initially aligned with strokes based on temporal correlation, and then classifiers are used to detect and correct two common alignment errors. Our two-step technique has proven to be substantially more accurate at alignment than the existing technique that lacked explicit segmentation. It is more important that, for nearly all cases, our new technique results in greater gesture classification accuracy than the existing technique, and performed nearly as well as the benchmark manual speech–sketch alignment.
Emergency oral rabies vaccination of foxes in Italy in 2009–2010: identification of residual rabies foci at higher altitudes in the Alps
Authors: MULATTI P. , MÜLLER T. , BONFANTI L. , MARANGON S.
Published: July 2011

Following a resurgence of fox rabies in northeastern Italy in 2008–2009, two emergency oral rabies vaccination (ORV) campaigns were performed in the Alpine mountain ranges in 2009 and 2010 using aerial distribution to prevent the disease from spreading further inland. Vaccine baits were distributed only below the freezing point altitude, 1000 m above sea level (a.s.l.) in December 2009–January 2010 and 1500 m a.s.l. in April–May 2010, to avoid repeated freeze–thaw cycles. Spatial analysis unexpectedly identified fox rabies hotspots above the threshold altitudes, probably representing local residual rabies foci which may have contributed to maintaining the infectious cycle in areas not vaccinated at higher altitudes. Based on the results obtained, in May 2010, the second ORV campaign was extended to include threshold altitudes of up to 2300 m a.s.l. to eliminate residual foci. The observations made may help in the formulation of ORV strategies in countries sharing similar topographical features.
Training Parents of Overweight Children in Parenting Skills: A 12-Month Evaluation
Authors: Moens Ellen , Braet Caroline
Published: July 2011

Background:The origins of childhood obesity invariably need to be looked at within a family context and several reviews have concluded in favour of parental involvement in the treatment of paediatric obesity. However, there is little consensus on the format, and next to weight outcomes behavioural outcomes also merit more attention when assessing program effectiveness.Method:In this pilot study, a total of 50 families with overweight children (aged 6–12) were randomly allocated to a parent-led intervention group (cognitive behavioural training) or to a waiting list control group (Study 1). Afterwards, the parents of the waitlist control group also followed the intervention. All children were included in a follow-up study and were compared with a reference group (Study 2).Results:The intervention group as well as the waitlist group (who had not yet received treatment) showed a decrease in adjusted BMI over a 6-month period, although the decrease was only significant for the intervention group (Study 1). All children showed a decrease of 7% in adjusted BMI from pre to one-year follow-up measurement (Study 2), while the reference group showed an increase in adjusted BMI over that period. Parents reported significant positive changes in children's eating behaviour and a significant positive increase in familial health principles.Conclusions:Weight and behavioural outcomes suggest potential for intervention effectiveness. Long-term follow-up is needed to reveal residual benefits of enhanced parenting skills on environmental lifestyle changes.
Effects of first and second language on segmentation of non-native speech
Authors: HANULÍKOVÁ ADRIANA , MITTERER HOLGER , MCQUEEN JAMES M.
Published: July 2011

Do Slovak–German bilinguals apply native Slovak phonological and lexical knowledge when segmenting German speech? When Slovaks listen to their native language, segmentation is impaired when fixed-stress cues are absent (Hanulíková, McQueen & Mitterer, 2010), and, following the Possible-Word Constraint (PWC; Norris, McQueen, Cutler & Butterfield, 1997), lexical candidates are disfavored if segmentation leads to vowelless residues, unless those residues are existing Slovak words. In the present study, fixed-stress cues on German target words were again absent. Nevertheless, in support of the PWC, both German and Slovak listeners recognized German words (e.g.,Rose“rose”) faster in syllable contexts(suckrose)than in single-consonant contexts(krose,trose). But only the Slovak listeners recognized, for example,Rosefaster inkrosethan introse(kis a Slovak word,tis not). It appears that non-native listeners can suppress native stress segmentation procedures, but that they suffer from prevailing interference from native lexical knowledge.
Concurrent and construct validity of Mediterranean diet scores as assessed by an FFQ
Authors: Benítez-Arciniega Alejandra A , Mendez Michelle A , Baena-Díez Jose M , Rovira Martori Maria-Asunción , Soler Cristina , Marrugat Jaume , Covas Maria-Isabel , Sanz Hector , Llopis Alba , Schröder Helmut
Published: July 2011

Objective

The aim of the present study was to assess the concurrent and construct validity of two diet-quality indices, a modified Mediterranean diet score (mMDS) and a Mediterranean-like diet score (MLDS) additionally incorporating unhealthy food choices, as determined by an FFQ.

Design

A validation study assessing FFQ intake estimates compared with ten or more unannounced 24 h recalls. Pearson's correlation coefficients, intraclass correlation coefficients (ICC), Bland–Altman plots and the limits of agreement method were used to assess the between-method agreement of scores. Construct validity was shown using associations between nutrient intakes derived from multiple 24 h recalls and the mMDS and MLDS derived from the FFQ.

Setting

Gerona, Spain.

Subjects

A total of 107 consecutively selected participants from a population-based cross-sectional survey.

Results

Pearson's correlations for the energy-adjusted mMDS and MLDS compared with multiple recalls were 0·48 and 0·62, respectively. The average FFQ energy-adjusted mMDS and MLDS were 102 % and 98 % of the recall-based mMDS and MLDS estimates, respectively. The FFQ under- and overestimated dietary recall estimates of the energy-adjusted MLDS by 28 % and 25 %, respectively, with slightly wider boundaries for the mMDS (31 % and 34 %). The ICC, which assesses absolute agreement, was similar to Pearson's correlations (mMDS = 0·48 and MLDS = 0·61). The mean differences between methods were similar across the range of average ratings for both scores, indicating the absence of bias. The FFQ-derived mMDS and MLDS correlated in the anticipated directions with intakes of eleven (73·3 %) and thirteen of fifteen nutrients (86·7 %), respectively.

Conclusions

The FFQ provides valid estimates of diet quality as assessed by the mMDS and MLDS.
Age-Dependent Expression of Collagen Receptors and Deformation of Type I Collagen Substrates by Rat Cardiac Fibroblasts
Authors: Wilson Christopher G. , Stone John W. , Fowlkes Vennece , Morales Mary O. , Murphy Catherine J. , Baxter Sarah C. , Goldsmith Edie C.
Published: July 2011

Little is known about how age influences the ways in which cardiac fibroblasts interact with the extracellular matrix. We investigated the deformation of collagen substrates by neonatal and adult rat cardiac fibroblasts in monolayer and three-dimensional (3D) cultures, and quantified the expression of three collagen receptors [discoidin domain receptor (DDR)1, DDR2, and β1 integrin] and the contractile protein alpha smooth muscle actin (α-SMA) in these cells. We report that adult fibroblasts contracted 3D collagen substrates significantly less than their neonate counterparts, whereas no differences were observed in monolayer cultures. Adult cells had lower expression of β1 integrin and α-SMA than neonate cultures, and we detected significant correlations between the expression of α-SMA and each of the collagen receptors in neonate cells but not in adult cells. Consistent with recent work demonstrating age-dependent interactions with myocytes, our results indicate that interactions between cardiac fibroblasts and the extracellular matrix change with age.
Quantitative Electron Microscopy of Cellulose Nanofibril Structures from Eucalyptus and Pinus radiata Kraft Pulp Fibers
Authors: Chinga-Carrasco Gary , Yu Yingda , Diserud Ola
Published: July 2011

This work comprises the structural characterization of Eucalyptus and Pinus radiata pulp fibers and their corresponding fibrillated materials, based on quantitative electron microscopy techniques. Compared to hardwood fibers, the softwood fibers have a relatively open structure of the fiber wall outer layers. The fibrillation of the fibers was performed mechanically and chemi-mechanically. In the chemi-mechanical process, the pulp fibers were subjected to a TEMPO-mediated oxidation to facilitate the homogenization. Films were made of the fibrillated materials to evaluate some structural properties. The thicknesses and roughnesses of the films were evaluated with standardized methods and with scanning electron microscopy (SEM), in backscattered electron imaging mode. Field-emission SEM (FE-SEM) and transmission electron microscopy (TEM) were performed to quantify the nanofibril morphology. In this study, we give additional and significant evidences about the suitability of electron microscopy techniques for quantification of nanofibril structures. In addition, we conclude that standard methods are not suitable for estimating the thickness of films having relatively rough surfaces. The results revealed significant differences with respect to the morphology of the fibrillated material. The differences are due to the starting raw material and to the procedure applied for the fibrillation.
Introduction to Stem Cell Special Section
Authors: Schatten Heide
Published: July 2011

The prospect of utilizing stem cells for clinical applications has generated an enormous amount of enthusiasm in the stem cell research community and has led to a wealth of new data that offer the possibility for practical applications into clinical translation. Recent advances in stem cell imaging has contributed greatly to the ultimate goal to identify and culture specific cell types for regeneration of tissue that had been affected by disease such as Parkinson's, Alzheimer's, heart disease, muscle diseases, and others.
Inflammation and wound healing: the role of the macrophage
Authors: Koh Timothy J. , DiPietro Luisa Ann
Published: July 2011

The macrophage is a prominent inflammatory cell in wounds, but its role in healing remains incompletely understood. Macrophages have many functions in wounds, including host defence, the promotion and resolution of inflammation, the removal of apoptotic cells, and the support of cell proliferation and tissue restoration following injury. Recent studies suggest that macrophages exist in several different phenotypic states within the healing wound and that the influence of these cells on each stage of repair varies with the specific phenotype. Although the macrophage is beneficial to the repair of normally healing wounds, this pleotropic cell type may promote excessive inflammation or fibrosis under certain circumstances. Emerging evidence suggests that macrophage dysfunction is a component of the pathogenesis of nonhealing and poorly healing wounds. As a result of advances in the understanding of this multifunctional cell, the macrophage continues to be an attractive therapeutic target, both to reduce fibrosis and scarring, and to improve healing of chronic wounds.
The accountability of power: Democracy and governance in modern times
Authors: Hupe Peter , Edwards Arthur
Published: July 2011

In modern governing, a variety of actors in the public domain daily make decisions with consequences for the common good, but how these actors are held accountable to political representatives is not always clear. While representative democracy in most societies still functions as the traditional standard, deficits in democratic control are perceived. There is an exercise ofpower-without-corresponding-representation. At the same time modern citizens appear hard to engage in politics.Representation-without-corresponding-participationalso appears. We address this dual problem, one of accountability and one of legitimacy, in terms of political theory. Various strategies are explored, indicating that some of them contribute to bringing democracy up to date more than others. In particular, it seems fundamental to rethink contemporary democracy by connecting it with the multi-dimensional character of governance. Functional participation by modern citizens can enhance the legitimacy of the exercise of power by making the latter accountable in a multi-local way.
Dissolved methane distribution in the South Pacific and the Southern Ocean in austral summer
Authors: Yoshida Osamu , Inoue Hisayuki Y. , Watanabe Shuichi , Suzuki Koji , Noriki Shinichiro
Published: July 2011

Oceanic methane (CH4) was examined in the South Pacific and the Southern Ocean from December 2001 to February 2002. From the oligotrophic South Pacific (10°S) to the Subtropical Front (STF), we observed the maximum concentrations of CH4 in the subsurface layer which ranged from 2.7 to 3.9 nmol kg−1. South of the STF, higher levels of CH4 were often detected in both the surface and the subsurface layers. Elevated surface CH4 concentrations (3.4–6.1 nmol kg−1) south of the STF tended to be higher than those north of the STF. Higher CH4 were often concomitant with an increase in chlorophyll a levels in the Seasonal Ice Zone (SIZ). Considering that phytoplankton does not generate methane directly, the high CH4 production probably resulted from the grazing processes of Antarctic krill and/or zooplankton fed on phytoplankton and the subsequent microbial methanogenesis in addition to the aerobic CH4 production in the water column. Present results showed a good relation between surface CH4 data (<50 m) and σθ between 10°S and the Polar Front (PF), which allow us to provide interpolation/extrapolation schemes for CH4 concentration and sea‐air CH4 flux in the wide area ([CH4] = 0.15 σθ − 0.98 (RMS = 0.21 nmol kg−1, r = 0.68, n = 49, p < 0.001). The sea‐air fluxes estimated during our survey were from 2.4 to 4.9 mol CH4 km−2 d−1 between 10°S and the PF (54°S), and from 0.8 to 2.3 mol CH4 km−2 d−1 south of the PF, where the sea‐air CH4 flux was largely affected by the wind speed.
Revisiting linearized one‐dimensional tidal propagation
Authors: Toffolon Marco , Savenije Hubert H. G.
Published: July 2011

In this paper we extend the validity of the classical linear solution for tidal hydrodynamics including the effects of width and depth convergence. Reworking such a solution in the light of externally defined, dimensionless parameters we are able to provide simple relationships to predict the most relevant features of the tidal wave at the estuary mouth (velocity amplitude, phase lag, wavelength, and damping) and to reproduce the main dynamics of tidal wave propagation along finite and infinite length channels. We also highlight the need for an accurate treatment of the linearized bed shear stress by exploiting an iterative procedure, and we show the improvement that can be reached by subdividing the entire estuary in shorter reaches. Different versions of the analytical solution are compared with numerical results, highlighting the strengths and weaknesses of the linear model.
Global monthly water stress: 1. Water balance and water availability
Authors: van Beek L. P. H. , Wada Yoshihide , Bierkens Marc F. P.
Published: July 2011

Surface fresh water (i.e., blue water) is a vital and indispensable resource for human water use in the agricultural, industrial, and domestic sectors. In this paper, global water availability is calculated by forcing the global hydrological model PCR‐GLOBWB with daily global meteorological fields for the period 1958–2001. To represent blue water availability, a prognostic reservoir operation scheme was included in order to produce monthly time series of global river discharge modulated by reservoir operations. To specify green water availability for irrigated areas, actual transpiration from the model was used. Thus, the computed water availability reflects the climatic variability over 1958–2001 and is contrasted against the monthly water demand using the year 2000 as a benchmark in the companion paper. As the water that is withdrawn to meet demand directly interferes with blue water availability along the drainage network, this paper evaluates model performance for three regimes reflecting different degrees of human interference: natural discharge, discharge regulated by reservoirs, and modified discharge. In the case of modified discharge, the net blue water demand for the year 2000 is subtracted directly from the regulated discharge, taking water demand equal to consumptive water use. Results show that model simulations of monthly river discharge compare well with observations from most of the large rivers. Exceptions are basins subject to large extractions for irrigation purposes, where simulated discharge exceeds the observations even when water demand is taken into account. Including the prognostic reservoir operation scheme results in mixed performance, with a poorer approximation of peak flows but with a marginally better simulation of low flows and persistence. A comparison of simulated actual evapotranspiration with that from the ERA‐40 reanalysis as a proxy for observed rates shows similar patterns over nonirrigated areas but substantial deviations over major irrigated areas. As expected, assimilated actual evapotranspiration over these areas includes water from alternative sources, whereas the simulations with PCR‐GLOBWB are limited by soil moisture, i.e., green water availability. On the basis of this evidence we conclude that the simulation provides adequate fields of water availability to assess water stress at the monthly scale, for which a separate validation is provided in the companion paper.
Global monthly water stress: 2. Water demand and severity of water stress
Authors: Wada Yoshihide , van Beek L. P. H. , Viviroli Daniel , Dürr Hans H. , Weingartner Rolf , Bierkens Marc F. P.
Published: July 2011

This paper assesses global water stress at a finer temporal scale compared to conventional assessments. To calculate time series of global water stress at a monthly time scale, global water availability, as obtained from simulations of monthly river discharge from the companion paper, is confronted with global monthly water demand. Water demand is defined here as the volume of water required by users to satisfy their needs. Water demand is calculated for the benchmark year of 2000 and contrasted against blue water availability, reflecting climatic variability over the period 1958–2001. Despite the use of the single benchmark year with monthly variations in water demand, simulated water stress agrees well with long‐term records of observed water shortage in temperate, (sub)tropical, and (semi)arid countries, indicating that on shorter (i.e., decadal) time scales, climatic variability is often the main determinant of water stress. With the monthly resolution the number of people experiencing water scarcity increases by more than 40% compared to conventional annual assessments that do not account for seasonality and interannual variability. The results show that blue water stress is often intense and frequent in densely populated regions (e.g., India, United States, Spain, and northeastern China). By this method, regions vulnerable to infrequent but detrimental water stress could be equally identified (e.g., southeastern United Kingdom and northwestern Russia).
The value of glacier mass balance, satellite snow cover images, and hourly discharge for improving the performance of a physically based distributed hydrological model
Authors: Finger David , Pellicciotti Francesca , Konz Markus , Rimkus Stefan , Burlando Paolo
Published: July 2011

Physically based hydrological models describe natural processes more accurately than conceptual models but require extensive data sets to produce accurate results. To identify the value of different data sets for improving the performance of the distributed hydrological model TOPKAPI we combine a multivariable validation technique with Monte Carlo simulations. The study is carried out in the snow and ice‐dominated Rhonegletscher basin, as these types of mountainous basins are generally the most critical with respect to data availability and sensitivity to climate fluctuations. Each observational data set is used individually and in combination with the other data sets to determine a subset of best parameter combinations out of 10,000 Monte Carlos runs performed with randomly generated parameter sets. We validate model results against discharge, glacier mass balance, and satellite snow cover images for a 14 year time period (1994–2007). While the use of all data sets combined provides the best overall model performance (defined by the concurrent best agreement of simulated discharge, snow cover and mass balance with their respective measurements), the use of one or two variables for constraining the model results in poorer performance. Using only one data set for constraining the model glacier mass balance proved to be the most efficient observation leading to the best overall model performance. Our main result is that a combination of discharge and satellite snow cover images is best for improving model performance, since the volumetric information of discharge data and the spatial information of snow cover images are complementary.
Significant nonadiabatic effects in the C + CH reaction dynamics
Authors: Yang Huan , Hankel Marlies , Zheng Yujun , Varandas Antonio J. C.
Published: July 2011

Rigorous quantum nonadiabatic calculations are carried out on the two coupled electronic states (12A′ and 22A′) for the C + CH reaction. For all calculations, the initial wave packet was started from the entrance channel of the 12A′ state and the initial state of the CH reactant was kept in its ground rovibrational state. Reaction probabilities for total angular momenta J from 0 to 160 are calculated to obtain the integral cross section over an energy range from 0.005 to 0.8 eV collision energy. Significant nonadiabatic effects are found in the reaction dynamics. The branching ratio of the ground state and excited state of C2 produced is around 0.6, varying slightly with the collision energy. Also, a value of 2.52 × 10−11 cm3 molecule−1 s−1 for the state selected rate constant k (v = 0, j = 0) at 300 K is obtained, which may be seen as a reference in the future chemical models of interstellar clouds.
Atomic and molecular spectra of normal liquid 4He excited by corona discharges
Authors: Li Z.-L. , Bonifaci N. , Denat A. , Atrazhev V. M. , Shakhatov V. A. , Haeften K. von
Published: July 2011

Liquid 4He at 4.2 K and different pressures up to 8 MPa is excited by positive and negative corona discharges. Emission of He I atomic lines and He2 molecular bands is observed. In negative corona, the line spectrum has distinct blue-shift and broadening, which becomes stronger with increasing pressure. The rotational structure of the molecular bands is resolved at pressures of 0.1–0.2 MPa. A blue shift of the Q-branch maximum with pressure is observed. A rotational temperature of 900 K is estimated from the d3Σu+ − b3Πg molecular band emission. Positive corona was produced on a point anode with smaller electrode radius and higher voltages than for the negative corona. The electric currents for the negative and positive corona are similar. The radiation from the positive corona discharges has spectral features which differ qualitatively from the negative corona discharges. The spectra with a positive corona have marked asymmetries with greater intensities in the longer wavelength (red) wings.
Stark-induced adiabatic Raman passage for preparing polarized molecules
Authors: Mukherjee Nandini , Zare Richard N.
Published: July 2011

We propose a method based on Stark-induced adiabatic Raman passage (SARP) for preparing vibrationally excited molecules with known orientation and alignment for future dynamical stereochemistry studies. This method utilizes the (J, M)-state dependent dynamic Stark shifts of rovibrational levels induced by delayed but overlapping pump and Stokes pulses of unequal intensities. Under collision-free conditions, our calculations show that we can achieve complete population transfer to an excited vibrational level (v > 0) of the H2 molecule in its ground electronic state. Specifically, the H2 (v = 1, J = 2, M = 0) level can be prepared with complete population transfer from the (v = 0, J = 0, M = 0) level using the S(0) branch of the Raman transition with visible pump and Stoke laser pulses, each polarized parallel to the $\hat z$ẑ axis (uniaxial π − π Raman pumping). Similarly, H2 (v = 1, J = 2, M = ±2) can be prepared using SARP with a left circularly polarized pump and a right circularly (or vice versa) polarized Stokes wave propagating along the $\hat z$ẑ axis (σ± − σ∓ Raman pumping). This technique requires phase coherent nanosecond pulses with unequal intensity between the pump and the Stokes pulses, one being four or more times greater than the other. A peak intensity of ∼16 GW/cm2 for the stronger pulse is required to generate the desirable sweep of the Raman resonance frequency. These conditions may be fulfilled using red and green laser pulses with the duration of a few nanoseconds and optical energies of ∼12 and 60 mJ within a focused beam of diameter ∼0.25 mm. Additionally, complete population transfer to the v = 4 vibrational level is predicted to be possible using SARP with a 355-nm pump and a near infrared Stokes laser with accessible pulse energies.
New method of accurate estimation of the electron–phonon coupling constants in fractionally charged incommensurate electronic states in molecular systems
Authors: Kato Takashi
Published: July 2011

The electron–phonon interactions in the fractionally positively charged incommensurate tetrathiafulvalene (TTF) molecular systems are investigated. In particular, since there are fractionally positive charges per TTF molecule, it is very difficult to estimate the vibronic and electron–phonon coupling constants, and thus there have been no reports of the exact calculations in the electron–phonon coupling constants in such fractionally positively charged incommensurate systems. Therefore, in this paper, we suggest new method of accurate estimation of the electron–phonon coupling constants in the fractionally positively charged systems. Total electron–phonon coupling constants for the monocation (l+100) of TTF is compared with that for the monoanion (l−100) of tetracyanoquinodimethanide (TCNQ). Furthermore, logarithmically averaged phonon frequency for the monocation (νln , +1.00) of TTF is compared with that for the monoanion (νln , −1.00) of TCNQ. The C–C and C–S stretching mode of 1599 cm−1 and the C–S–C and C–C–S bending mode of 472 cm−1 strongly couple to the b3u highest occupied molecular orbital (HOMO) in TTF molecule. The l+100 value for TTF molecule is estimated to be 0.274 eV, and the νln , +1.00 value for TTF molecule is estimated to be 926 cm−1. The density of states at the Fermi level (NNM, crystal(εF)+0.59, +0.59) values for TTF0.59+, which are essential physical values in order to investigate the mechanisms of the non-Ohmic current–voltage characteristics excellently suggested by Cohen and Heeger et al., are also estimated. By comparing the NNM, crystal(εF)+0.59, +0.59 values estimated by us with those estimated from the experimental results of the Pauli susceptibility and the current–voltage characteristics in TTF0.59+ suggested by Cohen and Heeger et al., and from the band calculations, we show that the l+0.59, νln , +1.00, RE+0.59, and NNM, crystal(εF)+0.59, +0.59 values estimated by our new calculation method are very accurate and reliable.
A microscopic two-band model for the electron-hole asymmetry in high-T
c superconductors and reentering behavior
Authors: Bru J.-B. , Pedra W. de Siqueira , Dömel A.-S.
Published: July 2011

To our knowledge there is no rigorously analyzed microscopic model explaining the electron-hole asymmetry of the critical temperature seen in high-Tc cuprate superconductors – at least no model not breaking artificially this symmetry. We present here a microscopic two-band model based on the structure of energetic levels of holes in CuO2 conducting layers of cuprates. In particular, our Hamiltonian does not contain ad hoc terms implying – explicitly – different masses for electrons and holes. We prove that two energetically near-lying interacting bands can explain the electron-hole asymmetry. Indeed, we rigorously analyze the phase diagram of the model and show that the critical temperatures for fermion densities below half-filling can manifest a very different behavior as compared to the case of densities above half-filling. This fact results from the inter-band interaction and intra-band Coulomb repulsion in interplay with thermal fluctuations between two energetic levels. So, if the energy difference between bands is too big (as compared to the energy scale defined by the critical temperatures of superconductivity) then the asymmetry disappears. Moreover, the critical temperature turns out to be a non-monotonic function of the fermion density and the phase diagram of our model shows “superconducting domes” as in high-Tc cuprate superconductors. This explains why the maximal critical temperature is attained at donor densities away from the maximal one. Outside the superconducting phase and for fermion densities near half-filling the thermodynamics governed by our Hamiltonian corresponds, as in real high-Tc materials, to a Mott-insulating phase. The nature of the inter-band interaction can be electrostatic (screened Coulomb interaction), magnetic (for instance, some Heisenberg-type one-site spin–spin interaction), or a mixture of both. If the inter-band interaction is predominately magnetic then – additionally to the electron-hole asymmetry – we observe a reentering behavior meaning that the superconducting phase can only occur in a finite interval of temperatures. This phenomenon is rather rare, but has also been observed in the so-called magnetic superconductors. The mathematical results here are direct consequences of [J.-B. Bru and W. de Siqueira Pedra, Rev. Math. Phys. 22, 233 (2010)] which is reviewed in the introduction.
Scanning Fabry-Pérot interferometer with largely tuneable free spectral range for high resolution spectroscopy of single quantum dots
Authors: Abbarchi Marco , Kuroda Takashi , Duval Romain , Mano Takaaki , Sakoda Kazuaki
Published: July 2011

We report on the implementation of a scanning Fabry-Pérot interferometer for photoluminescence spectroscopy investigation. We choose a conveniently small reflectivity of the two planar semitransparent mirrors which, in spite of a moderate cavity finesse, ensures a good mechanical stability over a long time. We also exploit the large tuneability of the cavity length (i.e., of the free spectral range) for changing the spectral resolution over two order of magnitude (from ∼300 μeV to ∼4 μeV in full width at half maximum). Such a characteristic easily allows to scan both sharp and broad luminescence bands. We test our Fabry-Pérot interferometer on sharp photoluminescence lines resulting from excitonic recombination in self-assembled GaAs quantum dots. We demonstrate the ability of our system to resolve linewidth as small as 4 μeV.
Collective translational motions and cage relaxations in molecular ionic liquids
Authors: Schröder Christian
Published: July 2011

In this computational study, the collective translational motions of 1-ethyl-3-methylimidazolium triflate, characterized by its current correlation function and its collective dipolar displacement, are interpreted in terms of an ion cage around a central ion. Thereby, a coincidence of the relevant time constants is observed. Furthermore, the ion cage is long living and its composition is rather heterogeneous. Besides high numbers of counter ions, several ions of like charge populate the first shell around a central ion. In contrast to the strong influence of the local environment on the collective translational motion, rotations are strictly collective. In other words, a local picture falls short of describing the overall antiparallel alignment of ionic dipoles. A further issue of this work is the interpretation of the initial region of the collective dipolar displacement. It can be related to all collective translational processes showing up in the computational dielectric spectrum. In particular, slow translational processes which are invisible in the current correlation function can be detected. The inclusion of these slow processes allow for an excellent computational reconstruction of the experimental spectrum of the generalized dielectric constant.
Frequency and gate voltage effects on the dielectric properties and electrical conductivity of Al/SiO2/p-Si metal-insulator-semiconductor Schottky diodes
Authors: Yıldız D. E. , Dökme İ.
Published: July 2011

The dielectric properties and electrical conductivity of Al/SiO2/p-Si (MIS) Schottky diodes (SDs) in the frequency range of 10 kHz to 10 MHz and the gate voltage range of −2 to 6 V have been investigated in detail using experimental C-V and G/w-V measurements. Experimental results indicated that the voltage dependence of the real part of the dielectric constant (ɛ′) and loss tangent (tan δ) characteristics have a peak at each frequency. The values of ɛ′ increase with decreasing frequency and tend to be frequency independent in the negative voltage region. However, the values of the dielectric loss (ɛ″) increase with decreasing frequency at each voltage. In contrast, ɛ′ and ɛ″ are almost found to decrease, and the ac electrical conductivity (σac) and the real part of the electric modulus (M′) increase, with increasing frequency. In addition, the imaginary part of the electric modulus (M″) showed a peak that shifts to a higher frequency with increasing applied voltage. It can be concluded that interfacial polarization can more easily occur at low frequencies, and consequently the majority of interface states at the Si–SiO2 interface contribute to the deviation of the dielectric properties of Al/SiO2/p-Si (MIS) SDs.
Dynamic nuclear self-polarization with circularly polarized light
Authors: Koizumi M. , Goto J. , Matsuki S.
Published: July 2011

Lattice nuclei of III-V type semiconductors can be self-polarized through the contact hyperfine interaction with artificially excited conduction electrons at extremely low temperatures. In the self-polarization process, a positive feedback between the nuclear magnetization and the expansion of the energy splitting of the conduction electron states due to this nuclear magnetization takes an essential role. Extending the original theoretical work on the self-polarization with linearly polarized (LP) light by Dyakonov and Perel,1 we examined the effect of the circularly polarized (CP) light on the phenomenon of the nuclear self-polarization. While no polarization is obtained with LP light above the critical temperature, the nuclear polarization is enhanced also above the critical temperatures with CP light. More important finding in the application of CP light is that the direction of the nuclear polarization can be controlled by the orientation of the excited conduction-electron polarization, which is easily manipulated by changing the degree of polarization of the excitation light. Related to this polarization change, it is also remarked that the nuclear polarization shows a hysteresis phenomenon below the critical temperature when the degree of the electron polarization is swept up and down.