bluuebunny/crossref_metadata_2025 huggingface dataset:
Rain‐vapor interaction and vapor source identification using stable isotopes from semiarid western India
Authors: Deshpande R. D. , Maurya A. S. , Kumar Bhishm , Sarkar A. , Gupta S. K.
Published: December 2010

Results of a 4 year (2005–2008) study of stable isotopic composition of daily rain and ground‐level vapor (GLV) at a semiarid station in western India are reported. The GLV samples were collected by complete cryogenic trapping. The sampling was mostly limited to the rainy season (June, July, August, and September) and about a month before and after. The maximum number of samples was collected during the year 2007. The GLV has a steady baseline δ18O and δD composition without distinguishable seasonal differences. The d‐excess of GLV indicates that its isotopic composition has a significant contribution from kinetic evaporation of nonlocal water sources. During a rain event, GLV rapidly interacts with raindrops and tends to move toward isotopic equilibrium. On cessation of rain, the δ18O and δD of GLV quickly return to the typical baseline values. Therefore, use of isotopic composition of monthly rainfall for estimating average monthly isotopic composition of GLV can lead to erroneous results. Within a rainy season, certain large rain events have depleted δ18O and δD values compared to other equally large rain events with significantly enriched δ18O and δD. These isotopic differences are apparently not related to amount of rainfall. Variable magnitude of evaporation from falling raindrops and/or cloud liquid water fraction cannot explain the observed differences. Instead, it is shown that varying source regions (Arabian Sea or Bay of Bengal) and cloud top temperature may be responsible for observed differences.
Observations of stepping mechanisms in a rocket‐and‐wire triggered lightning flash
Authors: Biagi C. J. , Uman M. A. , Hill J. D. , Jordan D. M. , Rakov V. A. , Dwyer J.
Published: December 2010

We present 10 high‐speed video images that depict the bottom 150 m of a downward‐negative, dart‐stepped leader in a rocket‐and‐wire triggered flash, recorded at 240 kiloframes per second (4.17 μs frame integration time), along with correlated measurements of the X‐ray emission at 50 m, electric field derivative (dE/dt) at 80 m, and the rocket‐launch‐tower current beneath the leader. We observed discrete segments of secondary channel that exhibited luminosity above that of the surrounding corona streamers and were distinctly separate and beneath the downward‐extending leader channel. These segments appear similar to the space stems or space leaders that have been imaged in long negative laboratory sparks. Multiple simultaneous pulses in X‐ray emission, dE/dt, and launch tower current were recorded during the time that the leader steps were imaged. The leader extended at an average downward speed between 2.7 × 106 and 3.4 × 106 m s−1.
Functional relationships between vegetation, channel morphology, and flow efficiency in an alluvial (anabranching) river
Authors: Jansen John D. , Nanson Gerald C.
Published: December 2010

Water and sediment flux interactions are examined in Magela Creek, an alluvial (anabranching) sand bed river in the northern Australian tropics. Dense riparian vegetation stabilizes the channels and floodplains thereby preventing erosional instability at flow depths up to 6.2 times bankfull and discharges up to 15 times bankfull. Narrow anabranching channels characterize >92% of the alluvial reach and transport bed load more efficiently than short reaches of wide single‐channels, yet overall 29 ± 12% of the bed load is sequestered and the average vertical accretion rate is 0.41 ± 0.17 mm yr−1 along the 12 km study reach. The most effective discharge for transporting sediment (40–45 m3 s−1) is consistent at all 5 stations (10 channels) examined and is equivalent to the channel‐forming discharge. It has an average recurrence interval of 1.01 years, occurs for an exceptionally long portion (13–15%) of the annual flow duration, and averages a remarkable 2.1 times bankfull. The high flow efficiency (i.e., bed load transport rate to stream power ratio) of the anabranches is facilitated by low width/depth channels with banks reinforced by vegetation. Colonnades of bank top trees confine high‐velocity flows overbed (i.e., over the channel bed) at stages well above bankfull. At even larger overbank flows, momentum exchange between the channels and forested floodplains restrains overbed velocities, in some cases causing them to decline, thereby limiting erosion. Magela Creek exhibits a complicated set of planform, cross‐sectional and vegetative adjustments that boost overbed velocities and enhance bed load yield in multiple channels while restraining velocities and erosion at the largest discharges.
Experimental and numerical investigations on degradation of channel bed of cohesive sediment mixtures
Authors: Kothyari Umesh C. , Jain Rajesh K.
Published: December 2010

Experimental observations on a degradation profile of channel beds consisting of cohesive sediment mixtures are presented. The sediment used for the experimentation consisted of fine gravel mixed with clay in varying proportions (10%–50% by weight) and fine gravel and fine sand in equal proportions mixed with varying proportions of clay (10%–50% by weight). The clay percentage in bed material and unconfined compressive strength of channel bed were found to be the main factors controlling the depth of degradation of channel bed of cohesive sediment mixtures, as degradation depth reduces considerably with an increase in clay percentage and unconfined compressive strength of sediment bed. An algorithm is also proposed to compute transient bed and water surface profiles in a channel bed made up of such cohesive sediment mixtures. For this purpose the predictor‐corrector‐based, essentially nonoscillatory finite difference numerical scheme is utilized for the solution of governing equations through the use of appropriate initial and boundary conditions. The recently proposed relationships by the authors for bed and suspended load transport of cohesive sediment mixtures were used as the auxiliary equations in the proposed algorithm. The observations on degradation of channel beds consisting of such cohesive sediment mixtures have not been reported so far in the literature to the best of our knowledge.
Numerical Monte Carlo analysis of the influence of pore‐scale dispersion on macrodispersion in 2‐D heterogeneous porous media
Authors: Beaudoin Anthony , de Dreuzy Jean‐Raynald , Erhel Jocelyne
Published: December 2010

We investigate the influences of pore‐scale dispersion and of larger‐scale permeability heterogeneities on the macrodispersion without the molecular diffusion. Permeability follows a lognormal exponentially correlated distribution characterized by its correlation length λ and its lognormal variance σ2. Macrodispersion is evaluated numerically by using parallel simulations on grids of characteristic size ranging from 200λ to 1600λ. We note αL and αT the pore‐scale longitudinal and transversal dispersivities. For αL/λ < 10−2 and αT/λ < 10−3, the influence of pore‐scale dispersion on the macrodispersion is smaller than 5% of the macrodispersion due only to permeability heterogeneities. Larger dispersivities (αL/λ ≥ 10−2 or αT/λ ≥ 10−3) induce larger effects than those obtained by the semianalytical expression of Salandin and Fiorotto (1998) for σ2 > 1. The effects of local dispersion on the longitudinal macrodispersion remain limited to 25% at most of the macrodispersion due only to permeability heterogeneities. For σ2 > 1, isotropic local dispersion induces a reduction of the longitudinal macrodispersion, whereas anisotropic local dispersion lets it increase. The longitudinal and transverse local dispersions induce opposite effects on the longitudinal macrodispersion, which are respectively an increase and a reduction. The transverse macrodispersion null without local dispersion or molecular diffusion becomes strictly positive with local dispersion. Because of the velocity field heterogeneities, it is amplified by a factor of 2 to 50 from the grid scale to the macro scale. The transverse dispersion is triggered by both longitudinal and transverse local dispersions. A reduction of a factor of 2 of the transverse local dispersion at fixed longitudinal local dispersion yields only a reduction of a factor of 4 at most of the transverse macrodispersion for σ2 ≥ 2.25.
Positive Psychology, Happiness, and Virtue: The Troublesome Conceptual Issues
Authors: Kristjánsson Kristján
Published: December 2010

This article subjects the recently prominent theory of positive psychology to critical conceptual scrutiny, with emphasis on its general take on happiness, virtue, and positive emotion. It is argued that positive psychology suffers from internal divisions (such as divergent views of its proponents on what happiness is), ambiguities (e.g., regarding the possibility of nonvirtuous happiness), ambivalence (concerning self-realism vs. anti-self-realism), and at least one serious misconception (the assumption that any view that makes overall evaluative judgments thereby prescribes). Nevertheless, many of the charges commonly urged against positive psychology, in particular by Aristotelian theorists, do not stick, and we may be well advised to give it the benefit of our doubt.
The Future of an Applied Evolutionary Psychology for Human Partnerships
Authors: Roberts S. Craig , Miner Emily J. , Shackelford Todd K.
Published: December 2010

There has been significant recent progress in our understanding of human mate choice. We outline several frontiers of rapid cultural change which may increasingly directly affect individual self-evaluation in the mating market, formation and maintenance of long-term partnerships, and potentially reproductive outcome and child health. Specifically, we review evidence for the effects of (1) increasing exposure to mass media, (2) the advent of novel ways to meet potential partners, and (3) cultural influences which may disrupt or alter the expression of evolved mate preferences. We comment on the potential for these effects to influence self-perception and partner-perception, with downstream effects on relationship satisfaction and stability. A common theme emerges, which is that these effects may contribute to relationship dissatisfaction and dissolution, with negative implications for societal change. We then address how we envisage evolutionary psychology research may focus on and offer informed approaches to ameliorate these effects in the future. We picture the development of a field of applied evolutionary psychology, and we suggest that this will increasingly become a central focus for many researchers.
Information Avoidance: Who, What, When, and Why
Authors: Sweeny Kate , Melnyk Darya , Miller Wendi , Shepperd James A.
Published: December 2010

Although acquiring information can provide numerous benefits, people often opt to remain ignorant. We define information avoidance as any behavior designed to prevent or delay the acquisition of available but potentially unwanted information. We review the various literatures that examine information avoidance and provide a unique framework to integrate the contributions of these disparate areas of research. We first define information avoidance and distinguish it from related phenomena. We then discuss the motivations that prompt information avoidance and the factors that moderate the likelihood of avoidance. Finally, we discuss individual differences that predict preferences for information avoidance. We conclude by evaluating the current state of research on information avoidance and discussing directions for future research.
New Horizons in the Evolutionary Science of the Human Family
Authors: Gorelik Gregory , Shackelford Todd K. , Salmon Catherine A.
Published: December 2010

Familial relationships cannot be properly understood outside of an evolutionary framework. Pseudoscientific and traditional modes of thought have steered us away from an accurate account of ourselves and our kin. Recent theoretical and empirical advances in the evolutionary sciences, such as the theories of inclusive fitness, parental investment, and parent-offspring conflict, have aided our understanding of familial conflict and cooperation. We suggest that a gene's eye perspective of human families can likewise illuminate much of human psychology and behavior by contrasting individual interests with genetic interests. Furthermore, theoretical and empirical work on genetic imprinting and extended phenotypic action-at-a-distance have unveiled the extent to which co-evolutionary arms races and manipulation lie at the heart of familial interactions and psychological disorders. We posit that human cultural trends and morals can ultimately be grounded on an evolutionary foundation: not only do human laws and institutions reflect group-level manifestations of gene-level cooperative adaptations, but also they may reflect gene-level manipulative adaptations. An awareness of evolutionary dynamics can advance human well-being and unveil the hidden mechanisms beneath all human and nonhuman relationships.
A cell autonomous role for the Notch ligand Delta‐like 3 in αβ T‐cell development
Authors: Hoyne Gerard F , Chapman Gavin , Sontani Yovina , Pursglove Sharon E , Dunwoodie Sally L
Published: December 2010

Notch signalling is critical to help direct T‐cell lineage commitment in early T‐cell progenitors and in the development of αβ T‐cells. Epithelial and stromal cell populations in the thymus express the Notch DSL (Delta, Serrate and Lag2)ligands Delta‐like 1 (Dll1), Delta‐like 4 (Dll4), Jagged 1 and Jagged 2, and induce Notch signalling in thymocytes that express the Notch receptor. At present there is nothing known about the role of the Delta‐like 3 (Dll3) ligand in the immune system. Here we describe a novel cell autonomous role for Dll3 in αβ T‐cell development. We show that Dll3 cannot activate Notch when expressed in trans but like other Notch ligands it can inhibit Notch signalling when expressed in cis with the receptor. The loss of Dll3 leads to an increase in Hes5 expression in double positive thymocytes and their increased production of mature CD4+ and CD8+ T cells. Studies using competitive irradiation chimeras proved that Dll3 acts in a cell autonomous manner to regulate positive selection but not negative selection of autoreactive T cells. Our results indicate that Dll3 has a unique function during T‐cell development that is distinct from the role played by the other DSL ligands of Notch and is in keeping with other recent studies indicating that Dll1 and Dll3 ligands have non‐overlapping roles during embryonic development.
Analysis of Cancer Omics Data In A Semantic Web Framework
Authors: Holford Matthew , McCusker James , Cheung Kei , Krauthammer Michael
Published: December 2010

Our work concerns the elucidation of the cancer (epi)genome, transcriptome and proteome to better understand the complex interplay between a cancel cell's molecular state and its response to anti-cancer therapy. To study the problem, we have previously focused on data warehousing technologies and statistical data integration. In this paper, we present recent work on extending our analytical capabilities using Semantic Web technology. A key new component presented here is a SPARQL endpoint to our existing data warehouse. This endpoint allows the merging of observed quantitative data with existing data from semantic knowledge sources such as Gene Ontology (GO). We show how such variegated quantitative and functional data can be integrated and accessed in a universal manner using Semantic Web tools. We also demonstrate how Description Lobic (DL) reasoning can be used to infer previously unstated conclusions from existing knowledge bases. As proof of concept, we illustrate the ability of our setup to answer complex queries on resistance of cancer cells to Decitabine, a demethylating agent.
Air Pollution and Atherosclerosis: Epidemiologic Studies
Authors: Van Hee V. C. , Kaufman J. D.
Published: December 2010

A large and growing body of epidemiologic studies has demonstrated increased cardiovascular morbidity and mortality associated with increased air pollution levels, but the pathogenesis of air pollution-related deaths remains uncertain. Although both acute elevations in particulate matter air pollution (PM) and increased long-term average PM or traffic-related pollutants more generally have been associated with overall cardiovascular mortality and events such as myocardial infarction and sudden cardiac death, it is not known whether pollutants only acutely trigger cardiovascular events or they also induce slow progression of atherosclerotic disease burden. Toxicologic studies show that inhalation of fine particles accelerates atherosclerosis in animals, but the human epidemiologic studies characterizing the role of PM in atherosclerosis have only begun to examine this hypothesis in detail. Most human epidemiologic studies have focused on outcomes (such as mortality and acute myocardial infarction) that do not distinguish the extent of atherosclerotic burden in exposed individuals, and therefore cannot assess whether long-term air pollution exposure is associated with an increase in atherosclerotic disease burden or simply triggering of acute cardiovascular events. To date, few epidemiologic studies have directly addressed the relationship between air pollution and atherosclerotic disease; however, there is growing epidemiologic evidence that chronic air pollution exposures lead to acceleration or initiation of the atherogenesis.
Hypertension and Vascular Toxicity of PM
Authors: Ying Z. , Rajagopalan S.
Published: December 2010

A growing body of data implicates particulate matter air pollution (PM) as an important factor in the pathogenesis of cardiovascular disease. PM influences susceptibility to adverse cardiovascular events and may be particularly harmful in individuals with pre-existing cardiovascular disease (CVD) risk factors such as diabetics, hypertensives and smokers. The synergistic interaction of PM with other conventional risk factors is internally consistent with our current understanding of how risk factors mediate complex diseases such as hypertension, whereby the pathways involved in mediating the adverse effects often converge on final common mechanisms. A number of studies have now demonstrated rapid effects of inhaled particulates on cardiovascular variables such as vascular tone and function, arguing for mechanisms transducing PM signals within minutes to hours. There is also good evidence to suggest sub-acute and chronic effects of PM with persuasive lines of evidence to support a role for reactive oxygen species (ROS) dependent mechanisms. The extent of these effects depend on the source, composition and duration of exposure to PM and the underlying susceptibility of the individual or the animal. Our understanding of the locus of generation of these mediators (lung versus extra-pulmonary), the source(s), time course of release and the relative contribution to various vascular effects continues to evolve. In this section we will discuss recent studies that have enhanced our understanding of PM-mediated vascular effects with a focus on hypertension, and we will discuss the relative biological significance of these findings.
Environmental Pollutants and Heart Failure
Authors: Prabhu S. D.
Published: December 2010

This chapter reviews the available studies linking pollution and heart failure. Heart failure is a common disorder that carries a high mortality. As such, it is of high significance from the standpoint of both cardiovascular health and health care costs. Epidemiological studies have demonstrated that both short-term and long-term exposure to air pollution can have adverse effects on disease exacerbations, progression and mortality in subjects with heart failure. Although several biological mechanisms have been put forth to explain these associations, the pathophysiological responses unique to individual particulate and gaseous constituents of urban air pollution remain incompletely defined. Aldehydes are important organic components of both particulate matter and the pollutant mix derived from other environmental sources. To define the effects of aldehyde exposure, we performed animal studies evaluating the cardiac effects of acrolein, a prototypical reactive α,β-unsaturated aldehyde classified by the Environmental Protection Agency as a high priority air and water toxic. These experiments indicated that acrolein, at concentrations observed clinically in human disease or within the range of estimated oral exposure, can induce myocardial dysfunction, augment the sensitivity of the heart to ischemic injury, and trigger pathological ventricular remodeling. Therefore, analogous exposure to acrolein and related aldehydes via inhalation may also contribute importantly to pollution-associated cardiovascular dysfunction and heart failure risk. The further recognition and identification of environmental factors that precipitate and/or exacerbate heart failure is of paramount importance for both individual and public health.
Air Pollution and Ischemic Heart Disease
Authors: Peters A.
Published: December 2010

Both episodic and long-term exposures to particulate air pollution are associated with an increased risk of ischemic heart disease. Time-series studies show an association between exposure to particulate air pollution and the exacerbation of ischemic heart disease on days of high pollution. Long-term effects of chronic exposure to polluted air are documented by several prospective cohort studies. These studies show that long-term exposure to ambient PM2.5 is associated with an increase in risk for atherosclerosis and traffic-related pollutants such as ultrafine particles. Several studies suggest that the cardiovascular effects of air pollution may be related to increases in blood coagulation and inflammation. Based on day-to-day fluctuation of particles, evidence for induction of ischemia by PM has been reported in patients with coronary artery disease. There seems to be immediate responses to particulate matter when assessed by personal measurements or within experimental settings. The link between acute changes in intermediate phenotypes of cardiovascular disease and chronic elevated risks are also subject of current research. The exact particle properties responsible for these associations are currently being investigated, but traffic-related particles seem to be the likely culprits. Exposure to traffic particles has been associated with the sudden onset of myocardial infarction. We have found an increase in the onset of myocardial infarction one hour after time spent in traffic. Incident coronary artery disease has also been linked to traffic density and it has been shown that traffic-related exposure is associated with an increase in measures of coronary atherosclerosis. Animal studies with ultrafine particles demonstrate that traffic might be especially potent in inducing atherosclerosis in experimental settings. Collectively, this evidence supports the view that exposure to traffic pollutants could have adverse effects on ischemic heart disease. Links between other forms of cardiovascular diseases also exist. The effects of traffic-generated pollutants on susceptible subgroups based on either genetic susceptibility or other co-morbidities are currently being investigated.
Vehicular Emissions and Cardiovascular Disease
Authors: Campen M. , Lund A.
Published: December 2010

Exposure to traffic-related air pollution is a ubiquitous, daily occurrence throughout the world. Evidence is emerging that implicates a causal role for traffic-related contaminants in promoting the incidence of cardiovascular morbidity and mortality. Our current understanding of the relationships between vehicular emissions and public health is muddled by the complexities of the combustion mixture chemistry, pathological mechanisms, and exposure dynamics. Controlled clinical and toxicological exposure studies have observed adverse cardiovascular effects from diesel and gasoline engine emissions. These effects include endothelial dysfunction, electrocardiographic abnormalities, and vascular inflammation and oxidative stress. The contribution of causal components or the potential interactions among the gases and particulates in vehicular emissions has not been clearly delineated. This chapter discusses recent work studying the impact of vehicular pollution on cardiovascular health.
Metals in Environmental Cardiovascular Diseases
Authors: Barchowsky A.
Published: December 2010

Metals are essential to cardiovascular function and health, but their toxicities are among the oldest known. Their role in promoting cardiovascular diseases and their mechanisms for affects in heart and vascular tissues are often unrealized or controversial. Exposure to metals is widespread and may produce greater effects in susceptible populations or when exposures occur during development. There is increased appreciation that environmental exposures to metals or exposures even at occupational or therapeutic levels may have more subtle effects in causing or modifying disease. Uncertainty in understanding mechanisms of metal action often comes from the approach of using high dose toxicity studies that determine acute toxicities non-human mammals to identify pathogenic etiology in humans who often experience much lower chronic exposures. Mechanisms of metals or metalloid action are often thought to be caused by disrupting the normal signaling of selective ion channels, mediated by random interactions with peptide or protein sulfhydryls, or similarly produced by random oxidant injury. While this may be true for the highest levels of exposure, recent epidemiological studies and studies in genetic rodent models indicate that pathogenic effects of metals on cell signaling are not random. Not all of the effects are accounted for by direct competition with endogenous ions or oxidant-mediated processes. Resolving the molecular understanding of these pathogenic effects and toxicities is complicated by complex differential concentration- and time-dependent actions of metals in different cell types, as well as a high degree of interactions between metals in common mixed exposures. This chapter presents toxic effects of metals in the heart and blood vessels with an emphasis on the cellular and molecular actions underlying disease and clinically significant toxicities that are directly linked to human exposures to metals.
Environmental Aldehydes and Cardiovascular Disease
Authors: Conklin D. J. , Haberzettl P. , Lee J. , Srivastava S.
Published: December 2010

Aldehydes are ubiquitous carbonyl-containing compounds and toxic levels are reached in the environment as a primary result of anthropogenic input. Combustion of organic substrates generates high levels of a number of diverse aldehydes, in part, as a function of combustion temperature or pyrolysis. Burning of fuels (e.g., coal diesel, and gasoline) generates reactive aldehydes in the environment, and likewise, aldehydes are made during cooking especially in the presence of overheated cooking oils. Human exposure to environmental aldehydes encompasses air, water and food sources. Many studies show that the cardiovascular system is exquisitely sensitive to aldehyde exposure, especially exposure to α-βunsaturated aldehydes, such as acrolein and 4-hydroxy-trans-2-nonenal (HNE). Interestingly, these aldehydes also are generated endogenously during lipid peroxidation and inflammation, and are associated with pathogenesis in chronic diseases (e.g., atherosclerosis, Alzheimer's disease). Fortunately not all environmental aldehydes appear to be toxic in the cardiovascular system and several could be beneficial, such as aromatic aldehydes ppresent in foods and flavorings including benzaldehyde (oil of almond) and cinnamaldehyde (cinnamon). These food-derived aldehydes have low toxicity in cardiovascular tissues, directly stimulate blood vessel relaxation, and are anti-inflammatory, which perhaps promotes decreased cardiovascular disease risk. While many of the mechanisms by which aldehydes exert effects in cardiovascular tissues remain unknown, studies indicate unsaturated aldehydes have proclivity to form protein-acrolein adducts via cysteine and lysine residues. Could this mechanism (e.g., protein-aldehyde adducts→ER stress→unfolded protein response) account for the association between environmental aldehyde exposure and increased cardiovascular disease risk? Alternatively, unsaturated aldehydes can stimulate the transient receptor potential channel (e.g., TRPA1) leading to increased cellular calcium. Collectively, the cardiovascular system possesses a large cadre of enzymes designed to metabolize and detoxify aldehydes for rapid clearance. Alterations in the level or efficiency of metabolite removal (e.g., GST gene polymorphisms) similarly provide a mechanistic explanation for altered individual susceptibility to aldehyde exposure. Future studies will endeavor to explore the role of aldehyde action and metabolism in human cardiovascular health.
Turbulent velocity spectra in superfluid flows
Authors: Salort J. , Baudet C. , Castaing B. , Chabaud B. , Daviaud F. , Didelot T. , Diribarne P. , Dubrulle B. , Gagne Y. , Gauthier F. , Girard A. , Hébral B. , Rousset B. , Thibault P. , Roche P.-E.
Published: December 2010

We present velocity spectra measured in three cryogenic liquid H4e steady flows: grid and wake flows in a pressurized wind tunnel capable of achieving mean velocities up to 5 m/s at temperatures above and below the superfluid transition, down to 1.7 K, and a “chunk” turbulence flow at 1.55 K, capable of sustaining mean superfluid velocities up to 1.3 m/s. Depending on the flows, the stagnation pressure probes used for anemometry are resolving from one to two decades of the inertial regime of the turbulent cascade. We do not find any evidence that the second-order statistics of turbulence below the superfluid transition differ from the ones of classical turbulence, above the transition.
Ultra-low-noise preamplifier for condenser microphones
Authors: Starecki Tomasz
Published: December 2010

The paper presents the design of a low-noise preamplifier dedicated for condenser measurement microphones used in high sensitivity applications, in which amplifier noise is the main factor limiting sensitivity of the measurements. In measurement microphone preamplifiers, the dominant source of noise at lower frequencies is the bias resistance of the input stage. In the presented solution, resistors were connected to the input stage by means of switches. The switches are opened during measurements, which disconnects the resistors from the input stage and results in noise reduction. Closing the switches allows for fast charging of the microphone capacitance. At low frequencies the noise of the designed preamplifier is a few times lower in comparison to similar, commercially available instruments.
Structure and adsorption of water in nonuniform cylindrical nanopores
Authors: Torrie G. M. , Lakatos G. , Patey G. N.
Published: December 2010

Grand canonical Monte Carlo simulations are used to examine the adsorption and structure of water in the interior of cylindrical nanopores in which the axial symmetry is broken either by varying the radius as a function of position along the pore axis or by introducing regions where the characteristic strength of the water–nanopore interaction is reduced. Using the extended simple point charge (SPC/E) model for water, nanopores with a uniform radius of 6.0 Å are found to fill with water at chemical potentials approximately 0.5 kJ/mol higher than the chemical potential of the saturated vapor. The water in these filled pores exists in either a weakly structured fluidlike state or a highly structured uniformly polarized state composed of a series of stacked water clusters with pentagonal cross sections. This highly structured state can be disrupted by creating hydrophobic regions on the surface of the nanopore, and the degree of disruption can be systematically controlled by adjusting the size of the hydrophobic regions. In particular, hydrophobic banded regions with lengths larger than 9.2 Å result in a complete loss of structure and the formation of a liquid–vapor coexistence in the tube interior. Similarly, the introduction of spatial variation in the nanopore radius can produce two condensation transitions at distinct points along the filling isotherm.
Structural and dynamical analysis of monodisperse and polydisperse colloidal systems
Authors: Yiannourakou Marianna , Economou Ioannis G. , Bitsanis Ioannis A.
Published: December 2010

We present a semigrand ensemble Monte Carlo and Brownian dynamics simulation study of structural and dynamical properties of polydisperse soft spheres interacting via purely repulsive power-law potentials with a varying degree of “softness.” Comparisons focus on crystal and amorphous phases at their coexistence points. It is shown through detailed structural analysis that as potential interactions soften, the “quality of crystallinity” of both monodisperse and polydisperse systems deteriorates. In general, polydisperse crystalline phases are characterized by a more ordered structure than the corresponding monodisperse ones (i.e., for the same potential softness). This counter-intuitive feature originates partly from the fact that particles of different sizes may be accommodated more flexibly in a crystal structure and from the reality that coexistence (osmotic) pressure is substantially higher for polydisperse systems. These trends diminish for softer potentials. Potential softness eventually produces substitutionally disordered crystals. However, substitutional order is apparent for the hard-spherelike interactions. Diffusionwise, crystals appear quite robust with a slight difference in the vibrational amplitudes of small and large particles. This difference, again, diminishes with potential softness. Overcrowding in amorphous polydisperse suspensions causes “delayed” diffusion at intermediate times.
The van Hove distribution function for Brownian hard spheres: Dynamical test particle theory and computer simulations for bulk dynamics
Authors: Hopkins Paul , Fortini Andrea , Archer Andrew J. , Schmidt Matthias
Published: December 2010

We describe a test particle approach based on dynamical density functional theory (DDFT) for studying the correlated time evolution of the particles that constitute a fluid. Our theory provides a means of calculating the van Hove distribution function by treating its self and distinct parts as the two components of a binary fluid mixture, with the “self ” component having only one particle, the “distinct” component consisting of all the other particles, and using DDFT to calculate the time evolution of the density profiles for the two components. We apply this approach to a bulk fluid of Brownian hard spheres and compare to results for the van Hove function and the intermediate scattering function from Brownian dynamics computer simulations. We find good agreement at low and intermediate densities using the very simple Ramakrishnan–Yussouff [Phys. Rev. B 19, 2775 (1979)] approximation for the excess free energy functional. Since the DDFT is based on the equilibrium Helmholtz free energy functional, we can probe a free energy landscape that underlies the dynamics. Within the mean-field approximation we find that as the particle density increases, this landscape develops a minimum, while an exact treatment of a model confined situation shows that for an ergodic fluid this landscape should be monotonic. We discuss possible implications for slow, glassy, and arrested dynamics at high densities.
Energy-gap opening and quenching in graphene under periodic external potentials
Authors: Zhang Aihua , Dai Zhenxiang , Shi Lei , Feng Yuan Ping , Zhang Chun
Published: December 2010

We investigated the effects of periodic external potentials on properties of charge carriers in graphene using both the first-principles method based on density functional theory (DFT) and a theoretical approach based on a generalized effective spinor Hamiltonian. DFT calculations were done in a modified Kohn–Sham procedure that includes the effects of the periodic external potential. Unexpected energy band gap opening and quenching were predicted for the graphene superlattice with two symmetrical sublattices and those with two unsymmetrical sublattices, respectively. Theoretical analysis based on the spinor Hamiltonian showed that the correlations between pseudospins of Dirac fermions in graphene and the applied external potential, and the potential-induced intervalley scattering, play important roles in energy-gap opening and quenching.
Structural characterization for L1-ordered FePt films with (001) texture by x-ray diffraction
Authors: Yamane H. , Narisawa T. , Hasegawa T. , Ishio S.
Published: December 2010

The nanostructure of L10-ordered FePt films with a [001] orientation prepared by both an epitaxial growth and nonepitaxial method was characterized by fitting X-ray diffraction profiles. Good fitting results for both types of films were obtained by considering the structural inter-and intragrain disorders in a calculation model. The distributions of the long range order and film thicknesses were considered to be part of the structural disorder among the grains. The fluctuation of the lattice spacing and the depth of x-ray interference along the surface normal were also taken into account to explain the structural disorder within the grain. The epitaxial FePt films grown on the MgO(100) underlayer were gradually transformed from a disordered A1 phase to an ordered L10 phase with increasing deposition temperature. A thinner film of 5 nm indicated a relatively low long range order with the fluctuation of lattice spacing. This is attributed to a large mismatch between the lattice of the initial growth layer and the MgO underlayer. On the other hand, for nonepitaxial FePt films prepared by SiO2 doping and rapid thermal post-annealing, high [001]-oriented L10 grains without the distribution of long range order were obtained at an initial transformation stage at a low annealing temperature, and the L10 grains grew along the film surface with increasing temperature. The fluctuation of lattice spacing was independent of the crystallite height in the nonepitaxial films, whereas the structural disorders such as the lattice fluctuation and chemical disorder in epitaxial films increased with a decrease in the crystallite height.
Increase in the Tb3+ green emission in SiO2–LaF3 nano-glass-ceramics by codoping with Dy3+ ions
Authors: Velázquez J. J. , Rodríguez V. D. , Yanes A. C. , del-Castillo J. , Méndez-Ramos J.
Published: December 2010

95 SiO 2 – 5 LaF 3 sol-gel derived nano-glass-ceramics single doped with 0.1Dy3+ or 0.1Tb3+ mol % and codoped with 0.1Dy3+ and xTb3+ (x=0.1,0.3) mol % were successfully obtained. XRD and HRTEM measurements confirm the precipitation of LaF3 nanocrystals during the ceramming process, with mean size ranging from 10 to 20 nm and increasing with the thermal treatment temperature. About 75% of lanthanide ions are partitioned into LaF3 nanocrystals, as calculated from luminescence decays. The effect of increasing the Tb3+ concentration and also of codoping with Dy3+ in the Tb3+ green emission from the D54 level have been studied. The energy transfer mechanisms between Tb3+ ions and also between Tb3+–Dy3+ ions, which favor the green emission, have been analyzed.
InAlN/GaN Bragg reflectors grown by plasma-assisted molecular beam epitaxy
Authors: Gačević Ž. , Fernández-Garrido S. , Hosseini D. , Estradé S. , Peiró F. , Calleja E.
Published: December 2010

We report on molecular beam epitaxy growth and characterization of ten-period lattice-matched InAlN/GaN distributed Bragg reflectors (DBRs), with peak reflectivity centered around 400 nm. Thanks to the well tuned ternary alloy composition, crack-free surfaces have been obtained, as confirmed by both optical and transmission electron microscopy (TEM). Their good periodicity and well-defined interfaces have been confirmed by both x-ray diffraction and TEM measurements. Peak reflectivity values as high as 60% with stop bands of 30 nm have been demonstrated. Optical measurements revealed that discrepancy between the obtained (60%) and the theoretically expected (∼75%) reflectivity is a consequence of significant residual absorption (∼35%). TEM measurements revealed the coexistence of zinc-blende and wurtzite phases, as well as planar defects, mainly in GaN. These defects are suggested as the potential source of the undesired absorption and/or scattering effects that lowered the DBRs’ peak reflectivity.
Effect of n-p-n heterostructures on interface recombination and semiconductor laser cooling
Authors: Rupper G. , Kwong N. H. , Binder R. , Li Ch.-Y. , Sheik-Bahae M.
Published: December 2010

The design of doped n-p-n semiconductor heterostructures has a significant influence on the structures’ nonradiative decay and can also affect their photoluminescence characteristics. Such structures have recently been explored in the context of semiconductor laser cooling. We present a theoretical analysis of optically excited n-p-n structures, focusing mainly on the influence of the layer thicknesses and doping concentrations on nonradiative interface recombination. We find that high levels of n-doping (1019 cm−3) can reduce the minority-carrier density at the interface and increase the nonradiative lifetime. We calculate time-dependent luminescence decay and find them to be in good agreement with experiment for temperatures >120 K, which is the temperature range in which our model assumptions are expected to be valid. A theoretical analysis of the cooling characteristics of n-p-n structures elucidates the interplay of nonradiative, radiative, and Auger recombination processes. We show that at high optical excitation densities, which are necessary for cooling, the undesired nonradiative interface recombination rates for moderate (1017 cm−3) n-doping concentrations are drastically increased, which may be a major hindrance in the observation of laser cooling of semiconductors. On the other hand, high n-doping concentrations are found to alleviate the problem of increased nonradiative rates at high excitation densities, and for the model parameters used in the calculation we find positive cooling efficiencies over a wide range of excitation densities.
XeF
2
-induced removal of SiO2 near Si surfaces at 300 K: An unexpected proximity effect.
Authors: Veyan J.-F. , Halls M. D. , Rangan S. , Aureau D. , Yan X.-M. , Chabal Y. J.
Published: December 2010

XeF 2 interaction with SiO2/Si stacks has been investigated to understand the role of Si in proximity of SiO2 during XeF2 exposures of Si/SiO2 stacks. In situ Fourier transform infrared absorption spectroscopy, using a custom-made reaction cell compatible with high XeF2 pressures, reveals that, while pure SiO2 is not etched by XeF2, the oxide in SiO2/Si stacks is effectively removed when XeF2 has access to the silicon, i.e., when the Si in close proximity to the oxide is etched. Thick oxides (∼1–2 μm) are removed if sample edges are accessible, while thinner oxides (50–100 nm) are removed without requiring edge access. This unexpected SiO2 removal is found to be due to the formation of reactive fluorine species (XeF and F) evolved by the reaction of XeF2 with Si, which can, subsequently, etch SiO2. Calculations based on density functional theory provide critical insight into the underlying energetics and reaction pathways controlling XeF2 etching of both Si and SiO2.
Magnetic domain-wall depinning with reduced current density by short pulse rise time
Authors: Langner Hauke H. , Bocklage Lars , Krüger Benjamin , Matsuyama Toru , Meier Guido
Published: December 2010

The depinning probability of magnetic domain walls at constrictions by current pulses depends on the external magnetic field and on the temporal shape of current pulses. We investigate the depinning of domain walls in permalloy nanowires in dependence of the rise time of a current pulse. We observe a change in the depinning probability when varying the pulse rise time and the pulse amplitude at a constant magnetic field. The experiments reveal that the current density for domain-wall depinning can be strongly reduced by current pulses with short rise times.
A formula for the wall-amplified added mass coefficient for a solid sphere in normal approach to a wall and its application for such motion at low Reynolds number
Authors: Yang F.-L.
Published: December 2010

This work re-examines the potential flow theory for a sphere in normal approach to a wall, based on the classical results derived by Lamb [Hydrodynamics (Dover, New York, 1932)] and Milne-Thomson [Theoretical Hydrodynamics, 5th ed. (Dover, New York, 1968)]. These authors generated an expression in which the kinetic energy for a sphere in an unbounded fluid is augmented by a wall correction function in terms of an infinite series that depends on the scaled center-to-wall distance, h∗=h/a, with a denoting the sphere radius. By truncating the series at the order of h∗−3, the resulting one-term correction function, 3/8h∗−3, is widely employed to approximate the wall-amplified added mass coefficient, CAM(h∗), in multiphase flow research. Nonetheless, this work shows that this one-term correction deviates greatly from corrections including higher order terms when the interstitial gap drops below the half sphere radius. Thus, an explicit formula is developed, for all h∗, using a near-wall Padé approximation, an intermediate bridging function, and a far-field approximation. This proposed formula provides an efficient and reasonable approximation to the infinite series and thus may serve as an improved wall correction function as compared to the one-term formula. The developed formula is applied to compute the unsteady approach of a nonrotating sphere toward a wall in a viscous fluid at low Reynolds number condition. In addition to Brenner’s wall correction on the quasisteady viscous force [H. Brenner, “The slow motion of a sphere through a viscous fluid towards a plane surface,” Chem. Eng. Sci. 16, 242 (1961)], the current formula is employed to modify both the added mass coefficient, from 1/2, and the history force. This latter force is modified by integrating the wall-modified potential flow theory with the boundary layer theory. If the one-term correction is used in the equation of motion, underestimation of the sphere motion and the force magnitudes are observed. Lastly, the limiting value of the infinite series derived by Lamb and Milne-Thomson as h→a is analytically evaluated, leading to a result in terms of the generalized zeta function, ζ(3,1). When this limiting value is compared to the one-term correction at h=a, a 38% deficiency of the wall-augmented kinetic energy is revealed, resulting in an underestimated CAM(h∗) that plays a crucial role in presenting the near-wall normal approach.
Strongly enhanced photon collection from diamond defect centers under microfabricated integrated solid immersion lenses
Authors: Hadden J. P. , Harrison J. P. , Stanley-Clarke A. C. , Marseglia L. , Ho Y.-L. D. , Patton B. R. , O’Brien J. L. , Rarity J. G.
Published: December 2010

The efficiency of photon collection from optically active defect centers in bulk diamond is greatly reduced by refraction at the diamond-air interface. We report on the fabrication and measurement of a geometrical solution to the problem; integrated solid immersion lenses (SILs) etched directly into the surface of diamond. An increase of a factor of 10 was observed in the saturated count-rate from a single negatively charged nitrogen-vacancy (NV−) within a 5 μm diameter SIL compared with NV−’s under a planar surface in the same crystal. Such a system is potentially scalable and easily adaptable to other defect centers in bulk diamond.
Monolithic diamond optics for single photon detection
Authors: Siyushev P. , Kaiser F. , Jacques V. , Gerhardt I. , Bischof S. , Fedder H. , Dodson J. , Markham M. , Twitchen D. , Jelezko F. , Wrachtrup J.
Published: December 2010

In this work, we experimentally demonstrate a novel and simple approach that uses off-the-shelf optical elements to enhance the collection efficiency from a single emitter. The key component is a solid immersion lens made of diamond, the host material for single color centers. We improve the excitation and detection of single emitters by one order of magnitude, as predicted by theory.