bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamics of a high-Reynolds-number bubble rising within a thin gap
Authors: Roig Véronique , Roudet Matthieu , Risso Frédéric , Billet Anne-Marie
Published: August 2012

We report an experimental analysis of path and shape oscillations of an air bubble of diameter $d$ rising in water at high Reynolds number $\mathit{Re}$ in a vertical Hele-Shaw cell of width $h$. Liquid velocity perturbations induced by the relative movement have also been investigated to analyse the coupling between the bubble motion and the wake dynamics. The confinement ratio $h/ d$ is less than unity so that the bubble is flattened between the walls of the cell. As the bubble diameter is increased, the Archimedes and the Bond numbers increase within the ranges $10\leq \mathit{Ar}\leq 1{0}^{4} $ and $6\ensuremath{\times} 1{0}^{\ensuremath{-} 3} \leq Bo\leq 140$. Mean shapes become more and more elongated. They first evolve from in-plane circles to ellipses, then to complicated shapes without fore–aft symmetry and finally to semi-circular-capped bubbles. The scaling law $\mathit{Re}= 0. 5\mathit{Ar}$ is valid for a large range of $\mathit{Ar}$, however, indicating that the liquid films between the bubble and the walls do not contribute significantly to the drag force exerted on the bubble. The coupling between wake dynamics, bubble path and shape oscillations evolves and a succession of different regimes of oscillations is observed. The rectilinear bubble motion becomes unstable from a critical value ${\mathit{Ar}}_{1} $ through an Hopf bifurcation while the bubble shape is still circular. The amplitude of path oscillations first grows as $\mathit{Ar}$ increases above ${\mathit{Ar}}_{1} $ but then surprisingly decreases beyond a second Archimedes number ${\mathit{Ar}}_{2} $. This phenomenon, observed for steady ellipsoidal shape with moderate eccentricity, can be explained by the rapid attenuation of bubble wakes caused by the confinement. Shape oscillations around a significantly elongated mean shape start for $\mathit{Ar}\geq {\mathit{Ar}}_{3} $. The wake structure progressively evolves due to changes in the bubble shape. After the break-up of the fore–aft symmetry, a fourth regime involving complicated shape oscillations is then observed for $\mathit{Ar}\geq {\mathit{Ar}}_{4} $. Vortex shedding disappears and unsteady attached vortices coupled to shape oscillations trigger path oscillations of moderate amplitude. Path and shape oscillations finally decrease when $\mathit{Ar}$ is further increased. For $\mathit{Ar}\geq {\mathit{Ar}}_{5} $, capped bubbles followed by a steady wake rise on a straight path.
Three-dimensional vortex structure on a rotating wing
Authors: Ozen Cem A. , Rockwell D.
Published: August 2012

The three-dimensional structure of the leading-edge vortex on a rotating wing is addressed using a technique of particle image velocimetry. Organized patterns of chordwise-oriented vorticity, which exist within the vortex, arise from the spanwise flow along the surface of the wing, which can attain a velocity the same order as the velocity of the wing at its radius of gyration. These patterns are related to the strength (circulation) and coherence of the tip and root vortices. The associated distributions of spanwise-oriented vorticity along the leading-edge vortex are characterized in relation to the vorticity flux and downwash along the wing.
ALGORITHMS TO IDENTIFY ABUNDANTp-SINGULAR ELEMENTS IN FINITE CLASSICAL GROUPS
Authors: NIEMEYER ALICE C. , POPIEL TOMASZ , PRAEGER CHERYL E.
Published: August 2012

LetGbe a finited-dimensional classical group andpa prime divisor of ∣G∣ distinct from the characteristic of the natural representation. We consider a subfamily ofp-singular elements inG(elements with order divisible byp) that leave invariant a subspaceXof the naturalG-module of dimension greater thand/2 and either act irreducibly onXor preserve a particular decomposition ofXinto two equal-dimensional irreducible subspaces. We proved in a recent paper that the proportion inGof these so-calledp-abundantelements is at least an absolute constant multiple of the best currently known lower bound for the proportion of allp-singular elements. From a computational point of view, thep-abundant elements generalise another class ofp-singular elements which underpin recognition algorithms for finite classical groups, and it is our hope thatp-abundant elements might lead to improved versions of these algorithms. As a step towards this, here we present efficient algorithms to test whether a given element isp-abundant, both for a known primepand for the case wherepis not knowna priori.
CLASSIFICATION OF QUIVER HOPF ALGEBRAS AND POINTED HOPF ALGEBRAS OF TYPE ONE
Authors: ZHANG SHOUCHUAN , CHEN HUI-XIANG , ZHANG YAO-ZHONG
Published: August 2012

Quiver Hopf algebras are classified by means of ramification systems with irreducible representations. This leads to the classification of Nichols algebras over group algebras and pointed Hopf algebras of type one.
Constructing Commonality: Standardization and Modernization in Chinese Nation-Building
Authors: Kipnis Andrew B.
Published: August 2012

This essay examines the importance of Chinese nation-building in the contemporary era. Defining nation-building in terms of processes that help to bridge local differences especially but not only when also distinguishing China from the rest the world, I argue that a focus on globalization has masked the importance of Chinese nation-building to contemporary social change. I analyze three very different societal arenas in which national forms of commonality are being constructed: the consolidation of the education system, the expansion of the urban built environment, and the spread of the Chinese Internet. Though each arena illustrates a very different aspect of the nation-building process, they all result in an increased degree of commonality in lived experience and communicative practice across China.
Folate, colorectal cancer and the involvement of DNA methylation
Authors: Williams Elizabeth A.
Published: August 2012

Diet is a major factor in the aetiology of colorectal cancer (CRC). Epidemiological evidence suggests that folate confers a modest protection against CRC risk. However, the relationship is complex, and evidence from human intervention trials and animal studies suggests that a high-dose of folic acid supplementation may enhance the risk of colorectal carcinogenesis in certain circumstances. The molecular mechanisms underlying the apparent dual modulatory effect of folate on colorectal carcinogenesis are not fully understood. Folate is central to C1metabolism and is needed for both DNA synthesis and DNA methylation, providing plausible biological mechanisms through which folate could modulate cancer risk. Aberrant DNA methylation is an early event in colorectal carcinogenesis and is typically associated with the transcriptional silencing of tumour suppressor genes. Folate is required for the production of S-adenosyl methionine, which serves as a methyl donor for DNA methylation events; thereby folate availability is proposed to modulate DNA methylation status. The evidence for an effect of folate on DNA methylation in the human colon is limited, but a modulation of DNA methylation in response to folate has been demonstrated. More research is required to clarify the optimum intake of folate for CRC prevention and to elucidate the effect of folate availability on DNA methylation and the associated impact on CRC biology.
The rapid development of birdwatching in mainland China: a new force for bird study and conservation
Authors: MA ZHIJUN , CHENG YIXIN , WANG JUNYAN , FU XINGHUA
Published: August 2012

Birdwatching is a popular activity in western countries where it has helped to integrate research into birds, bird conservation, and socio-economic development. We analysed the development of birdwatching in mainland China and its roles in bird study and conservation using a standard questionnaire and interviews. Birdwatching in mainland China began only recently (in the 1990s). The increased numbers of foreign birdwatchers visiting China promoted birdwatching there. As of 2010, a total of 36 local birdwatching societies had been established, and the number of birdwatchers exceeds 20,000. The development of birdwatching has been positively correlated with local economic conditions–that is, the number of birdwatchers is much greater in economically developed areas than in relatively undeveloped areas. Birdwatchers have not only contributed to a greater understanding of the population status of birds in China but also promoted bird conservation at the local level. Although China’s conservation policies are currently formulated and implemented in a top-down manner via government regulation, with little contribution from local individuals, the rapid development of birdwatching reflects an improved understanding of conservation by local communities and growing participation in conservation initiatives by local people and organisations. We predict that with the continued development of China’s economy, birdwatching will further develop and play an increasing role in China’s conservation policies and practices. This is important as China is a country with a high rate of endemism and many globally-threatened species
Opportunities for reversible inhibitors of monoamine oxidase-A (RIMAs) in the treatment of depression
Authors: Lum Christopher T. , Stahl Stephen M.
Published: August 2012

Treatment-resistant depression (TRD) may be implicated in 33–57% of depression cases. The currently available effective treatments include electroconvulsive therapy (ECT) or augmentation of serotonin selective reuptake inhibitors (SSRIs) with antipsychotics. ECT and antipsychotics are both associated with safety and tolerability concerns. Depression is hypothesized to result from a dysregulation of monoamine neurotransmitters, although the source of the dysregulation has been unclear. However, recent studies have revealed that an enzyme that degrades the neurotransmitters, known as monamine oxidase-A (MAO-A), may be overactive in patients with depression. Thus, treatments for depression that modulate MAO-A could act upstream relative to current antidepressant treatments. Monoamine oxidase inhibitors (MAOIs) can be highly effective therapeutic agents for depression and some anxiety disorders. Some evidence suggests that MAOIs may act by reversing excessive neurotransmitter depletion within the neuron and the synapse. MAOIs tend to be underutilized in clinical practice, due in part to misinformation and mythology about their dietary and drug interactions. The new class of reversible monoamine oxidase inhibitors (RIMAs) has shown efficacy in depression, with safety and tolerability comparable to SSRIs. This article discusses recent progress in RIMAs toward the treatment of TRD. Dietary and drug interactions of MAOIs will be covered, as well as guidelines for integrating these agents into clinical practice.
Nitrogen fixation and identification of potential diazotrophs in the Canadian Arctic
Authors: Blais Marjolaine , Tremblay Jean‐Éric , Jungblut Anne D. , Gagnon Jonathan , Martin Johannie , Thaler Mary , Lovejoy Connie
Published: August 2012

Global gaseous nitrogen (N2) fixation rates may be underestimated and data is lacking from many regions without conspicuous diazotrophic cyanobacteria, such as cold oceans. We estimated N2 fixation rates at diverse sites in the Canadian Arctic, including the mouth of the Mackenzie River, the offshore Beaufort Sea, Lancaster Sound, Baffin Bay and a river influenced fjord. We also identified potential diazotrophic communities using a targeted survey of the nifH gene. Nitrogen fixation rates ranged from 0.02 nmol N L−1 d−1 in Baffin Bay to 4.45 nmol N L−1 d−1 in the Mackenzie River plume. Sequences recovered from the nifH gene survey belonged mainly to Cluster III, a group of nifH sequences associated with diverse microorganisms, with some α‐ andγ‐proteobacterianifH genes at most sites. Cyanobacteria nifH genes with best matches to Nostocales, which are common in Arctic freshwaters, were recovered from the marine Beaufort Sea. The geographic pattern of N2 fixation rates and nifHgene identities suggest that the Mackenzie River is the source of a diazotrophic community that contributes new nitrogen to the nitrogen‐depleted surface waters of the Beaufort Sea. This first record of N2 fixation at high latitudes refines our understanding of the global nitrogen budget.
Drought research and monitoring program is focus of congressional hearing
Authors: Showstack Randy
Published: August 2012

With more than 70% of the United States currently classified as being anywhere from abnormally dry to experiencing exceptional drought—according to the U.S. Drought Monitor, a consensus product of U.S. federal and academic scientists—witnesses at a 25 July U.S. House of Representatives committee hearing expressed concern about the impact of the drought and voiced strong support for reauthorizing the National Integrated Drought Information System (NIDIS). Republican and Democratic members of the House Science, Space, and Technology Committee also expressed their support for NIDIS, which is part of the National Oceanic and Atmospheric Administration's (NOAA) Climate Program Office and is currently authorized through 2012. However, members of Congress expressed differing perspectives about the potential relationship between climate change and extreme events such as drought.
Cornelius Schiller (1961–2012)
Authors: Rosenlof Karen , Müller Rolf
Published: August 2012

Cornelius Schiller, an international leader in high‐altitude water vapor measurements and quality assessment who took charge of several research campaigns and mentored many young scientists, passed away on 3 March 2012 in Neuss, Germany, after a battle with cancer. He was 50 years old. Cornelius spent his childhood and most of his life in the Niederrhein region of Germany, close to Düsseldorf. He studied physics at the University of Bonn, and his developing interest in the physics and chemistry of the atmosphere led him to work with Dieter Ehhalt at the Forschungszentrum Jülich (Research Centre Jülich) in Germany. Cornelius' career started shortly after the discovery of the ozone hole, and he had the opportunity to participate in the first large‐scale ozone measurement campaign in the Arctic, known as the Airborne Arctic Stratospheric Expedition, during January and February 1989; he contributed airborne observations of ozone‐depleting chlorine and bromine substances.
Is pretenure interdisciplinary research a career risk?
Authors: Fischer E. V. , Mackey K. R. M. , Cusack D. F. , DeSantis L. R. G. , Hartzell‐Nichols L. , Lutz J. A. , Melbourne‐Thomas J. , Meyer R. , Riveros‐Iregui D. A. , Sorte C. J. B. , Taylor J. R. , White S. A.
Published: August 2012

Despite initiatives to promote interdisciplinary research, early‐career academics continue to perceive professional risks to working at the interface between traditional disciplines. Unexpectedly, the inherent practical challenges of interdisciplinary scholarship, such as new methodologies and lexicons, are not the chief source of the perceived risk. The perception of risk is pervasive across disciplines, and it persists despite efforts to support career development for individuals with common interests [Mitchell and Weiler, 2011]. Suggestions that interdisciplinary work can go unrewarded in academia [Clark et al., 2011] foster a concern that targeting interdisciplinary questions, such as those presented by climate change, will pose problems for acquiring and succeeding in a tenure‐track position. If self‐preservation limits the questions posed by early‐career academics, a perceived career risk is as damaging as a real one to new transdisciplinary initiatives. Thus, institutions should address the source of this perception whether real or specious.
Abrupt climate change: Mechanisms, patterns, and impacts
Authors: Schultz Colin
Published: August 2012

In the span of only a few decades, the global temperature can soar by more than a dozen degrees Celsius, a feat that 20 years ago was considered improbable, if not impossible. But recent research in the nascent field of rapid climate change has upended the dominant views of decades past. Focusing primarily on events during and after the most recent glaciation, from 80,000 years ago, the AGU monograph Abrupt Climate Change: Mechanisms, Patterns, and Impacts, edited by Harunur Rashid, Leonid Polyak, and Ellen Mosley‐Thompson, explores the transient climate transitions that were only recently uncovered in climate proxies around the world. In this interview, Eos talks to Harunur Rashid about piecing together ancient climes, the effect of abrupt change on historical civilizations, and why younger researchers may be more worried about modern warming than their teachers.
New model to estimate water in the Earth's mantle
Authors: Bhattacharya Atreyee
Published: August 2012

The Earth's mantle could be holding as much water as the ocean and atmosphere combined—but in the form of defects in dry minerals, such as olivine, that make up a large fraction of the mantle. Water in mantle minerals weakens chemical bonds, affecting physical and chemical properties of the mantle, particularly viscosity and electrical conductivity. Scientists continue to debate not just the amount of water but also its distribution in the mantle. Seismic velocity profiles, typically used to map the water content of the mantle, are, in fact, not sensitive to the amount of water. An increase of 1% by weight of water in mantle minerals, i.e., from “dry” to “very wet” conditions, reduces seismic velocities by at most 1%, which is often below the detection limit. On the other hand, an increase in water content by only 0.01%, from “dry” to “damp” conditions increases electrical conductivity in mantle minerals by an order of magnitude or more, making electrical conductivity a more sensitive tool to estimate the water content of mantle minerals.
Significant changes to ENSO strength and impacts in the twenty‐first century: Results from CMIP5
Authors: Stevenson S. L.
Published: August 2012

Changes to the El Niño/Southern Oscillation (ENSO) and its atmospheric teleconnections under climate change are investigated using simulations conducted for the Coupled Model Intercomparison Project (CMIP5). The overall response to CO2increases is determined using 27 models, and the ENSO amplitude change based on the multi‐model mean is indistinguishable from zero. However, changes between ensembles run with a given model are sometimes significant: for four of the eleven models having ensemble sizes larger than three, the 21st century change to ENSO amplitude is statistically significant. In these four models, changes to SST and wind stress do not differ substantially from those in the models with no ENSO response, indicating that mean changes are not predictive of the ENSO sensitivity to climate change. Also, ocean vertical stratification is less (more) sensitive to CO2in models where ENSO strengthens (weakens), likely due to a regulation of the subsurface temperature structure by ENSO‐related poleward heat transport. Atmospheric teleconnections also show differences between models where ENSO amplitude does and does not respond to climate change; in the former case El Niño/La Niña‐related sea level pressure anomalies strengthen with CO2, and in the latter they weaken and shift polewards and eastwards. These results illustrate the need for large ensembles to isolate significant ENSO climate change responses, and for future work on diagnosing the dynamical causes of inter‐model teleconnection differences.
Electrical discharges as a possible source of methane on Mars: Lab simulation
Authors: Robledo‐Martinez A. , Sobral H. , Ruiz‐Meza A.
Published: August 2012

At a concentration of 10–50 ppbv, methane is suggested to be a trace element in the Martian atmosphere. The sharp variations in its concentration observed are difficult to explain using current theories for sources and sinks (be it biotic or abiotic). Here we propose, and demonstrate with a lab simulation, a new production mechanism for methane based on the effect of electrical discharges over iced surfaces. The discharges, caused by electrification of dust devils and sand storms, ionize gaseous CO2 and water molecules and their byproducts recombine to produce methane. Our experimental results show that pulsed electrical discharges over ice samples in a synthetic Martian atmosphere produce about 1.41×1016molecules of methane per joule of applied energy. The results of the electrical discharge experiment were compared with photolysis induced with UV laser radiation and it was found that both produce methane although the efficiency of photolysis is one‐third of that of the discharge.
A numerical simulation of a negative solar wind impulse: Revisited
Authors: Fujita S. , Yamagishi H. , Murata Ken T. , Den M. , Tanaka T.
Published: August 2012

Response of the magnetosphere‐ionosphere system to a negative impulse of the solar wind dynamic pressure (the negative SI) is studied again with foci of the following three points; multiple convection oscillations, mirror‐image relationship between the negative and positive SIs, and appearance of the overshielding potential. When the negative impulse impinges on the magnetopause, the Region 1 (R1)‐type field‐aligned current (FAC) and R2‐type FAC appears alternatively in the dayside polar ionosphere (∼70°, ∼10 hLT and 14 hLT). These ionospheric current systems shift nightward and poleward. This alternative appearance of FACs invokes positive and negative ionospheric potential patterns switching alternatively. It is revealed that the negative SI is accompanied with multiple convection oscillations repeating more than the positive SI. We also notice that the magnetospheric current system producing the preliminary impulse (PI) of the intensive negative SI is a mirror‐image of that of the positive SI. The multiple convection oscillations and the mirror‐image relationship were not discussed by Fujita et al. (2004) who studied a moderate‐amplitude negative SI. In addition, the R2‐type FACs induced by the negative and positive SIs tend to yield the overshielding electric potential in the ionosphere. The shielding potential invoked by the SIs has shorter duration than that for the northward turn of the interplanetary magnetic field. The duration is longer for the negative SI than for the positive SI.
Sensitivity of aerosol indirect effects to cloud nucleation and autoconversion parameterizations in short‐range weather forecasts during the May 2003 aerosol IOP
Authors: Chuang Catherine C. , Kelly James T. , Boyle James S. , Xie Shaocheng
Published: August 2012

Aerosol‐cloud interactions begin with the direct involvement of aerosols in cloud nucleation followed by its indirect contribution to the formation of precipitation through autoconversion. Since the treatments of cloud microphysics in climate models are highly parameterized, a thorough study is needed to examine the range of simulations associated with different parameterizations of aerosol‐cloud interactions. Unlike previous studies focused on climate‐mode simulations, our interest is in short‐range model response before the development of model bias and the compensation of multiple feedback mechanisms. In this study, we modified CAM4 to explore model sensitivity to treatments of cloud nucleation and autoconversion over the Atmospheric Radiation Measurement Southern Great Plains (SGP) facility during the May 2003 Aerosol Intensive Operations Period (IOP) under the Cloud‐Associated Parameterizations Testbed framework. Simulated liquid water path and low cloud fraction were sensitive to the choice of parameterization; however, change of modeled precipitation was insignificant with varying parameterization in short‐range (∼3 day) simulation. In general, simulated cloud properties were more sensitive to the treatment of autoconversion than nucleation. Calculations of sulfate indirect effects indicate that the change of shortwave fluxes from cloud lifetime effect is much more sensitive to cloud parameterizations than cloud albedo effect. Microphysical feedbacks complicate the local response of the climate system and can yield a positive 2nd indirect sulfate forcing that counters the expectation that increases in aerosol concentration decrease the shortwave fluxes. As a result, the calculated total sulfate indirect forcing over SGP varies widely ranging from −0.1 to −2.1 W m−2 during the IOP.
Young Indians' Views of the Acceptability of Physician-Assisted Suicide
Authors: Kamble Shanmukh V. , Sorum Paul C. , Mullet Etienne
Published: August 2012

The acceptability by people in India of physician-assisted suicide was examined. Two hundred ninety-three Indian university students judged acceptability of PAS in 36 scenarios composed of all combinations of four factors: (a) the patient's age, (b) the level of incurability of the illness, (c) the type of suffering, and (d) the extent to which the patient requests a life-ending procedure. Three clusters of participants were found. For 29%, PAS was mainly unacceptable but less so if the patient was older or requested it. For 29%, it was mainly acceptable but less so if the patient was younger or did not request it. For 42%, it was clearly unacceptable if the patient was young but was clearly acceptable if patient was elderly, and more so if the patient requested it. The patient's age was the main determinant of acceptability, which is in accordance with the Hindu philosophy of reincarnation.
High-resolution spectroscopy for Doppler-broadening ion temperature measurements of implosions at the National Ignition Facility
Authors: Koch J. A. , Stewart R. E. , Beiersdorfer P. , Shepherd R. , Schneider M. B. , Miles A. R. , Scott H. A. , Smalyuk V. A. , Hsing W. W.
Published: August 2012

Future implosion experiments at the national ignition facility (NIF) will endeavor to simultaneously measure electron and ion temperatures with temporal and spatial resolution in order to explore non-equilibrium temperature distributions and their relaxation toward equilibrium. In anticipation of these experiments, and with understanding of the constraints of the NIF facility environment, we have explored the use of Doppler broadening of mid-Z dopant emission lines, such as krypton He-α at 13 keV, as a diagnostic of time- and potentially space-resolved ion temperature. We have investigated a number of options analytically and with numerical raytracing, and we have identified several promising candidate spectrometer designs that meet the expected requirements of spectral and temporal resolution and data signal-to-noise ratio for gas-filled exploding pusher implosions, while providing maximum flexibility for use on a variety of experiments that potentially include burning plasma.
Surface acoustic waves in pillars-based two-dimensional phononic structures with different lattice symmetries
Authors: Khelif Abdelkrim , Achaoui Younes , Aoubiza Boujemaa
Published: August 2012

The theoretical study deals with the propagation of surface acoustic waves in two-dimensional arrays of resonant elements with different symmetry lattices. The resonant elements are cylindrical pillars on the surface of a semi-infinite substrate. The obtained band structures show the interaction of the pillars acoustic resonances with the semi-infinite medium which form additional band gaps that are decoupled from Bragg gaps. Especially, the frequency position of the lowest band gap is invariant with respect to lattice symmetries. Thereby, this position is independent of the lattice pitch, which is unexpected in band gaps based on Bragg interferences. However, the role of the period remains important for defining the non-radiative region limited by the slowest bulk mode and influencing the existence of the guided modes. Numerical simulations are based on the efficient finite element method and considered silicon pillars on a silicon substrate.
Photoluminescent and gas-sensing properties of ZnO nanowires prepared by an ionic liquid assisted vapor transfer approach
Authors: Subannajui Kittitat , Wongchoosuk Chatchawal , Ramgir Niranjan , Wang Chunyu , Yang Yang , Hartel Andreas , Cimalla Volker , Zacharias Margit
Published: August 2012

In this work, the ionic liquid assisted technique was used to control the growth characteristic of ZnO nanowires (NWs). The major change after adding ionic liquid into the growth system was the change in NW growth orientation, which was shifted from polar c- to non-polar a-orientation. Room temperature photoluminescence demonstrates a big reduction of the green luminescence which implies an annihilation of deep level emission. We propose two possible mechanisms responsible for the reduction of the green emission: The first mechanism is the passivation of ZnO NWs surface by fractions of ionic liquid employed for the growth, which further reduces the green emission. The second mechanism is the reduction of the defect density by changing the growth orientation. By using a semi-empirical Austin Model 1 method, the formation energy of oxygen vacancies in c- and a-oriented ZnO NWs has been simulated and compared. Accordingly, the gas-sensor constructed from ionic liquid assisted ZnO nanowires does not response when exposed to CO. This inert sensitivity is caused by the suppressed adsorption of CO molecules due to the presence of the passivation layer. The study presented here provides a new insight of how the recombination appears at the surface of ZnO NWs.
An evaluation of high energy bremsstrahlung background in point-projection x-ray radiography experiments
Authors: Krauland C. M. , Jarrott L. C. , Drake R. P. , Keiter P. A. , Kuranz C. C. , Westover B. , Sawada H. , Kaczala D. N. , Bonofiglo P.
Published: August 2012

Backlit pinhole x-ray radiography has provided high-resolution images in many recent high-energy-density laser experiments. Its aim is to image the object of interest with a roughly monochromatic Kα source. However, despite the high intrinsic brightness achieved by the technique, data on x-ray film have shown a signal to background ratio near one, with data on image plates producing a higher background. This has been attributed, without direct evidence, to the interaction of suprathermal electrons with the (high Z) pinhole substrate. We present here the first direct measurement of the hard x-rays produced by such a backlighter target and a test of an approach to reducing the background. Specifically, a thick, low-Z layer was added on the side of the substrate toward the detector, intended to stop the energetic electrons and produce smaller emissions. Results from the Omega-60 laser experiment showed that the oft-seen background signal is in the range of 60–80 keV, a plausible energy range for energetic electrons produced in the laser-irradiated plasma. It also showed a comparable level of background signal in both types of targets. The work presented here includes target design and motivating theory, as well as the unexpected findings about x-ray background production.
Comparisons of NIF convergent ablation simulations with radiograph data
Authors: Olson R. E. , Hicks D. G. , Meezan N. B. , Koch J. A. , Landen O. L.
Published: August 2012

A technique for comparing simulation results directly with radiograph data from backlit capsule implosion experiments will be discussed. Forward Abel transforms are applied to the kappa*rho profiles of the simulation. These provide the transmission ratio (optical depth) profiles of the simulation. Gaussian and top hat blurs are applied to the simulated transmission ratio profiles in order to account for the motion blurring and imaging slit resolution of the experimental measurement. Comparisons between the simulated transmission ratios and the radiograph data lineouts are iterated until a reasonable backlighter profile is obtained. This backlighter profile is combined with the blurred, simulated transmission ratios to obtain simulated intensity profiles that can be directly compared with the radiograph data. Examples will be shown from recent convergent ablation (backlit implosion) experiments at the NIF.
Liquid-vapor phase diagram and cluster formation of two-dimensional ionic fluids
Authors: Méndez-Maldonado Gloria Arlette , González-Melchor Minerva , Alejandre José
Published: August 2012

Direct molecular dynamics simulations on interfaces at constant temperature are performed to obtain the liquid-vapor phase diagram of the two-dimensional soft primitive model, an equimolar mixture of equal size spheres carrying opposite charges. Constant temperature and pressure simulations are also carried out to check consistency with interface simulations results. In addition, an analysis of the cluster formation of mixtures of particles with charge asymmetry in the range 1:1 to 1:36 at low and high densities is performed. The number of free ions, when plotted as a function of the positive ion charge, Z+, has an oscillatory behavior and is independent of the density. The formation of aggregates is analyzed in terms of the attraction and repulsion between ions.
High-Schmidt-number mass transport mechanisms from a turbulent flow to absorbing sediments
Authors: Scalo Carlo , Piomelli Ugo , Boegman Leon
Published: August 2012

We have investigated the mechanisms involved in dissolved oxygen (DO) transfer from a turbulent flow to an underlying organic sediment bed populated with DO-absorbing bacteria. Our numerical study relies on a previously developed and tested computational tool that couples a bio-geochemical model for the sediment layer and large-eddy simulation for transport on the water side. Simulations have been carried out in an open channel configuration for different Reynolds numbers (Reτ = 180–1000), Schmidt numbers (Sc = 400–1000), and bacterial populations (χ* = 100–700 mg l−1). We show that the average oxygen flux across the sediment-water interface (SWI) changes with Reτ and Sc, in good agreement with classic heat-and-mass-transfer parametrizations. Time correlations at the SWI show that intermittent peaks in the wall-shear stress initiate the mass transfer and modulate its distribution in space and time. The diffusive sublayer acts as a de-noising filter with respect to the overlying turbulence; the instantaneous mass flux is not affected by low-amplitude background fluctuations in the wall-shear stress but, on the other hand, it is receptive to energetic and coherent near-wall transport events, in agreement with the surface renewal theory. The three transport processes involved in DO depletion (turbulent transport, molecular transport across the diffusive sublayer, and absorption in the organic sediment layer) exhibit distinct temporal and spatial scales. The rapidly evolving near-wall high-speed streaks transport patches of fluid to the edge of the diffusive sublayer, leaving slowly regenerating elongated patches of positive DO concentration fluctuations and mass flux at the SWI. The sediment surface retains the signature of the overlying turbulent transport over long time scales, allowed by the slow bacterial absorption.
Merged-beams for slow molecular collision experiments
Authors: Wei Qi , Lyuksyutov Igor , Herschbach Dudley
Published: August 2012

Molecular collisions can be studied at very low relative kinetic energies, in the milliKelvin range, by merging codirectional beams with much higher translational energies, extending even to the kiloKelvin range, provided that the beam speeds can be closely matched. This technique provides far more intensity and wider chemical scope than methods that require slowing both collision partners. Previously, at far higher energies, merged beams have been widely used with ions and/or neutrals formed by charge transfer. Here, we assess for neutral, thermal molecular beams the range and resolution of collision energy that now appears attainable, determined chiefly by velocity spreads within the merged beams. Our treatment deals both with velocity distributions familiar for molecular beams formed by effusion or supersonic expansion, and an unorthodox variant produced by a rotating supersonic source capable of scanning the lab beam velocity over a wide range.
Monte Carlo modeling of surface excitation in reflection electron energy loss spectroscopy spectrum for rough surfaces
Authors: Da B. , Mao S. F. , Zhang G. H. , Wang X. P. , Ding Z. J.
Published: August 2012

It has been experimentally found that the surface roughness influences strongly the surface and bulk plasmon excitation by glancing-angle reflection electron energy loss spectroscopy (REELS). However, there is still little theoretical work dealing with the surface roughness effect in REELS. Such a work is required to predict REELS spectra accurately, providing an understanding of the experimental phenomena observed. In this study, we use a finite element triangle mesh method build in a fully 3D rough surface model based on the surface topography measured by atomic force microscopy. Then REELS spectra for these rough surfaces are theoretically simulated by using Monte Carlo simulation including surface plasmon excitation and bulk plasmon excitation. The simulation results for Al sample with different surface roughnesses agree well with experimental data. Based on the analysis of the maximum depth of backscattered electrons and the depth distribution of surface bulk excitation under different conditions of roughness, the influence of surface roughness to the surface excitation in REELS spectra can be well understood.
Quantifying the rebinding effect in multivalent chemical ligand-receptor systems
Authors: Weber Marcus , Bujotzek Alexander , Haag Rainer
Published: August 2012

Multivalent ligand-receptor systems often show an enhancement in binding compared to the constituent monovalent systems. This “cooperativity effect” is often attributed to the favorable spatial preorganisation of the ligands by the connecting spacer that leads to a reduction of entropy loss at ligand binding. A different factor that has been proposed to contribute to the cooperativity effect is “rebinding”: As soon as a single ligand-receptor complex dissociates, the presence of another ligand “on coat-tails” will increase the probability of another binding event, which in turn will drive the system to a state where all ligands are bound. In this article, we derive a first quantitative description of the rebinding effect. In order to model the inherent memory effect of a spacer-connected system, we pursue a mathematical approach based on Markov state models and conformation dynamics. The theoretical investigations are illustrated by studying different prototypic ligand-receptor systems.
Dynamic heterogeneity in the glass-like monoclinic phases of CBrnCl4−n, n = 0,1,2
Authors: Zuriaga M. J. , Perez S. C. , Pardo L. C. , Tamarit J. Ll.
Published: August 2012

Glassy dynamics of rigid molecules is still a matter of controversy: the physics behind the relaxation process at time scales faster than that ruled by the viscosity, the so called Johari-Goldstein process, is not known. In this work we unravel the mechanism of such a process by using a simple molecular model in which the centers of mass of the molecules are forming an ordered lattice, and molecular reorientation is performed by jumps between equilibrium orientations. We have studied the dynamics of simple quasi-tetrahedral molecules CBrnCl4−n, n = 0, 1, 2, in their monoclinic phases by means of dielectric spectroscopy and nuclear quadrupole resonance: the first technique allows to measure in a broad time scale but it is insensitive to molecular particularities, while the second has a restricted time window but senses the movement of each chlorine atom separately. The dynamic picture emerging from these techniques is that the secondary relaxation process is related to the different molecular surroundings around each nonequivalent atom of the molecule. Dynamical heterogeneities thus seem to be the cause of the secondary relaxation in this simple model of glass.
Water confined between sheets of mackinawite FeS minerals
Authors: Wittekindt Carsten , Marx Dominik
Published: August 2012

Wet iron-sulfur minerals have been shown to be ideal environments to allow for simple chemical reactions to occur in nature, for instance, in the framework of prebiotic chemistry. Yet, not much is known about such water/mineral interfaces beyond those involving pyrite, FeS2, which is, however, chemically rather inert. In contrast, mackinawite is chemically reactive and consists of a layered crystal structure comprising FeS sheets that can be easily cleaved. Here, the properties of water confined between such sheets in lamella-like setups is investigated in the spirit of surface science model systems. The properties of this intercalated water are found to depend significantly on the interlayer distance and change from “arrested water” (in the limit of small interlayer distances) to liquid-like behavior.
Quantum dynamics of solid Ne upon photo-excitation of a NO impurity: A Gaussian wave packet approach
Authors: Unn-Toc W. , Uranga-Piña Ll. , Meier C. , Halberstadt N. , Rubayo-Soneira J.
Published: August 2012

A high-dimensional quantum wave packet approach based on Gaussian wave packets in Cartesian coordinates is presented. In this method, the high-dimensional wave packet is expressed as a product of time-dependent complex Gaussian functions, which describe the motion of individual atoms. It is applied to the ultrafast geometrical rearrangement dynamics of NO doped cryogenic Ne matrices after femtosecond laser pulse excitation. The static deformation of the solid due to the impurity as well as the dynamical response after femtosecond excitation are analyzed and compared to reduced dimensionality studies. The advantages and limitations of this method are analyzed in the perspective of future applications to other quantum solids.
Capacity of multiple-input multiple-output quantum depolarizing channels
Authors: Xiao Hailin , Ouyang Shan
Published: August 2012

Decoherence-free subspaces (DFS) are to utilize the symmetric properties of the interaction between the system and environment so that they can be tolerant against the effect of decoherence. In this paper, we propose multiple-input multiple-output (MIMO) scheme to drive a finite-dimensional quantum system into DFS. For quantum system, the scheme is not only immune to dephasing but also feasible with currently available technology. Motivated by Shannon mutual information, we derive the capacity of MIMO quantum depolarizing channels.
Development of multi-channel Doppler spectroscopic measurement system using 8 × 8 multianode photomultiplier tube assembly
Authors: Kamio S. , Suzuki N. , Cao Q. H. , Watanabe T. G. , Abe K. , Sakumura M. , Ishiguchi K. , Imazawa R. , Yamada T. , Inomoto M. , Takase Y. , Ono Y.
Published: August 2012

Using an 8 × 8 channel photomultiplier tube assembly and a single Czerny-Turner monochromator, we have developed a novel Doppler spectroscopic system which can measure the time evolutions of spectral distribution of plasma emission from eight different lines of sight simultaneously. An optical lens system is employed to couple the output of the monochromator with the detector assembly, resulting in small cross-talks less than 5% in spatial distribution together with large magnification of up to 50 in wavelength direction. The suggested system yields cost-effective polychromatic measurements of eight spatial channels with uniform optical and electrical characteristics.
Preparation of an exponentially rising optical pulse for efficient excitation of single atoms in free space
Authors: Dao Hoang Lan , Aljunid Syed Abdullah , Maslennikov Gleb , Kurtsiefer Christian
Published: August 2012

We report on a simple method to prepare optical pulses with exponentially rising envelope on the time scale of a few ns. The scheme is based on the exponential transfer function of a fast transistor, which generates an exponentially rising envelope that is transferred first on a radio frequency carrier, and then on a coherent cw laser beam with an electro-optical phase modulator. The temporally shaped sideband is then extracted with an optical resonator and can be used to efficiently excite a single 87Rb atom.
Two-dimensional plasma expansion in a magnetic nozzle: Separation due to electron inertia
Authors: Ahedo Eduardo , Merino Mario
Published: August 2012

A previous axisymmetric model of the supersonic expansion of a collisionless, hot plasma in a divergent magnetic nozzle is extended here in order to include electron-inertia effects. Up to dominant order on all components of the electron velocity, electron momentum equations still reduce to three conservation laws. Electron inertia leads to outward electron separation from the magnetic streamtubes. The progressive plasma filling of the adjacent vacuum region is consistent with electron-inertia being part of finite electron Larmor radius effects, which increase downstream and eventually demagnetize the plasma. Current ambipolarity is not fulfilled and ion separation can be either outwards or inwards of magnetic streamtubes, depending on their magnetization. Electron separation penalizes slightly the plume efficiency and is larger for plasma beams injected with large pressure gradients. An alternative nonzero electron-inertia model [E. Hooper, J. Propul. Power 9, 757 (1993)] based on cold plasmas and current ambipolarity, which predicts inwards electron separation, is discussed critically. A possible competition of the gyroviscous force with electron-inertia effects is commented briefly.
Properties of convective cells generated in magnetized toroidal plasmas
Authors: Theiler C. , Loizu J. , Furno I. , Fasoli A. , Ricci P.
Published: August 2012

Convective cells for turbulence control, generated by means of biased electrodes, are investigated in the simple magnetized toroidal plasmas of TORPEX. A two-dimensional array of 24 electrodes is installed on a metal limiter to test different biasing schemes. This allows influencing significantly both radial and vertical blob velocities. It is shown that these changes agree quantitatively with the flows deduced from the time averaged potential perturbations induced by the biasing. Detailed measurements along and across the magnetic field provide a rather clear picture of the effect of biasing on time averaged profiles. The biased electrodes produce perturbations of the plasma potential and density profiles that are fairly uniform along the magnetic field. Background flows influence the location where potential variations are induced. The magnitude of the achievable potential variations in the plasma is strongly limited by cross-field currents and saturates at large bias voltages once the electrodes draw electron saturation current. A quantitative discussion on the origin of cross-field currents is presented, considering contributions related with diamagnetic drifts, ion inertia, collisions with neutrals, and viscosity.
Thermoelectric properties and Kondo behavior in indium incorporated p-type Ce0.9Fe3.5Ni0.5Sb12 skutterudites
Authors: Puneet Pooja , He Jian , Zhu Song , Tritt Terry M.
Published: August 2012

Herein, we report the effects of indium (In) incorporation upon the thermoelectric and magnetic properties of Ni doped Fe-based filled skutterudites (InxCe0.9Fe3.5Ni0.5Sb12 with x = 0, 0.1, and 0.5). We find that secondary phases (such as InSb) can be formed upon surpassing the filling fraction limit and these in turn result in improved thermoelectric properties. A maximum dimensionless figure of merit, ZT ≈ 0.9 at ∼650 K was obtained for the sample with the nominal composition In0.1Ce0.9Fe3.5Ni0.5Sb12. Interestingly, we also observe Kondo-like behavior and evidence of the crystal field effect in these samples. The low-temperature (T < 100 K) thermopower and electrical resistivity of our samples exhibit Kondo-like behavior while their corresponding magnetic susceptibility suggests that the Ce3+ ions are influenced by the cubic crystal symmetry of the skutterudites class of materials, thus resulting in the crystal field effect. Lastly, the magnetic susceptibility data can be interpreted in the context of a second-order perturbation model.