bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Reducing Gas on Swelling and Iron Whisker Formation during the Reduction of Iron Oxide Compact
Authors: Wang Haitao , Sohn Hong Yong
Published: June 2012

The effects of different types of reducing gas on swelling and iron whisker formation during the reduction of iron oxide compacts were investigated. The compacts sintered in air at 1273 K were reduced at 1173 K in different reducing atmospheres. The results indicated that catastrophic swelling can happen in CO but not when H2 is present in the reducing gas mixture. Scanning electron microscope (SEM) micrographs showed that catastrophic swelling was caused by a large amount of long iron whiskers formed during the reduction. The presence of N2 and CO2 in CO changed the amount of long iron whiskers and its distribution, which determined the extent of swelling.
An in situ vertebrate bioassay helps identify potential matrices for a predator‐based synthetic management tool
Authors: Parsons Michael H. , Blumstein Daniel T. , Dods Kenneth C.
Published: June 2012

To assist management and conservation needs, researchers have called for active kairomones to be elucidated and synthesized directly from animal exudates. However, the existing literature does not provide guidance on how to initiate this complex process. To our knowledge, composite synthetic predator scents that incorporate multiple compounds to accurately mimic the natural signal have not been produced. One approach to improve the accuracy of synthetics is to identify and recombine all major infochemicals within a benign solvent. Therefore, we tested 2 natural, pre‐existing matrices for their potential as vehicles for delivery of a predator scent, dingo (Canis lupus dingo) urine, which causes a startle reaction among western gray kangaroos (Macropus fuliginosus), and avoidance by European foxes (Vulpes vulpes). We compared 2 putative backbone matrices—aged (3‐yr old) dingo urine from a previously active lot, and 10% methanol—to a distilled water control. We used a novel fence‐crossing assay to observe kangaroo interactions with both solvents and a negative control. Our assay allowed us to control for high feeding motivation by testing compounds away from the food source. We determined that neither free‐ranging kangaroos nor European red foxes were adversely affected by either treatment matrix. Foxes were, however, attracted to the aged dingo urine, and were often observed scent‐rolling in the inactive substance. Our results suggest that dilute methanol could be a possible matrix for predator‐scent applications for kangaroos, while aged scents may act as an attractant for nontarget species, particularly canids. © 2012 The Wildlife Society.
Archive eggs: A research and management tool for avian conservation breeding
Authors: Smith Des H.V. , Moehrenschlager Axel , Christensen Nancy , Knapik Dwight , Gibson Keith , Converse Sarah J.
Published: June 2012

Worldwide, approximately 168 bird species are captive‐bred for reintroduction into the wild. Programs tend to be initiated for species with a high level of endangerment. Depressed hatching success can be a problem for such programs and has been linked to artificial incubation. The need for artificial incubation is driven by the practice of multiclutching to increase egg production or by uncertainty over the incubation abilities of captive birds. There has been little attempt to determine how artificial incubation differs from bird‐contact incubation. We describe a novel archive (data‐logger) egg and use it to compare temperature, humidity, and egg‐turning in 5 whooping crane (Grus americana) nests, 4 sandhill crane (G. canadensis) nests, and 3 models of artificial incubator; each of which are used to incubate eggs in whooping crane captive‐breeding programs. Mean incubation temperature was 31.7° C for whooping cranes and 32.83° C for sandhill cranes. This is well below that of the artificial incubators (which were set based on a protocol of 37.6° C). Humidity in crane nests varied considerably, but median humidity in all 3 artificial incubators was substantially different from that in the crane nests. Two artificial incubators failed to turn the eggs in a way that mimicked crane egg‐turning. Archive eggs are an effective tool for guiding the management of avian conservation breeding programs, and can be custom‐made for other species. They also have potential to be applied to research on wild populations. © 2012 The Wildlife Society.
Analysis of protein function in clinical C. albicans isolates
Authors: Gerami‐Nejad Maryam , Forche Anja , McClellan Mark , Berman Judith
Published: June 2012

Clinical isolates are prototrophic and hence are not amenable to genetic manipulation using nutritional markers. Here we describe a new set of plasmids carrying the NAT1 (nourseothricin) drug resistance marker (Shen et al., ), which can be used both in clinical isolates and in laboratory strains. We constructed novel plasmids containing HA–NAT1 or MYC–NAT1 cassettes to facilitate PCR‐mediated construction of strains with C‐terminal epitope‐tagged proteins and a NAT1–pMet3–GFP plasmid to enable conditional expression of proteins with or without the green fluorescent protein fused at the N‐terminus. Furthermore, for proteins that require both the endogenous N‐ and C‐termini for function, we have constructed a GF–NAT1–FP cassette carrying truncated alleles that facilitate insertion of an intact, single copy of GFP internal to the coding sequence. In addition, GFP–NAT1, RFP–NAT1 and M‐Cherry–NAT1 plasmids were constructed, expressing two differently labelled gene products for the study of protein co‐expression and co‐localization in vivo. Together, these vectors provide a useful set of genetic tools for studying diverse aspects of gene function in both clinical and laboratory strains of C. albicans. Copyright © 2012 John Wiley & Sons, Ltd.
The Educational Claims of Zoos: Where Do We Go from Here?
Authors: Moss Andrew , Esson Maggie
Published: June 2012

Zoos exude a certain self‐confidence regarding their roles as education providers. Indeed, the education outputs of zoos are, at face value, pretty impressive, with most investing in learning opportunities for leisure visitors, education groups and in some cases, as part of their in situ programs. However, these outputs are not necessarily reliable indicators of the educational achievements of zoos. Quantity does not necessarily equate to quality, just as outputs do not necessarily lead to outcomes. Zoo‐accreditation organizations such as the AZA and EAZA offer us clear insight into the strategic vision underpinning the education goals for zoo visitors; a heightened appreciation of the value of biodiversity and a connectedness with the natural world. Unsurprisingly, most zoos have educational goals that ally neatly with the vision of their respective accreditation body. Consequently, we are left with fairly narrow, top‐down educational goals. This does not necessarily sit well with what we know about the unpredictability of “free choice” learning in environments such as zoos and aquariums, or what is known about public science communication. Research that seeks to explore the impacts of zoo visits often focuses on evaluating performance based on educational goals and the findings are used as a means of providing evidence of institutional achievement. However, any visitor outcome that falls outside of this narrow range could well be missed by the research. In this article, we propose that research that takes unpredictable and unexpected outcomes into account is necessary and overdue. Zoo Biol. 32:13‐18, 2013. © 2012 Wiley Periodicals, Inc.
Thermodynamics of SU(N) Yang-Mills theories in 2 + 1 dimensions II — The deconfined phase
Authors: Caselle Michele , Castagnini Luca , Feo Alessandra , Gliozzi Ferdinando , Gürsoy Umut , Panero Marco , Schäfer Andreas
Published: June 2012

Abstract

We present a non-perturbative study of the equation of state in the deconfined phase of Yang-Mills theories in D = 2 + 1 dimensions. We introduce a holographic model, based on the improved holographic QCD model, from which we derive a non-trivial relation between the order of the deconfinement phase transition and the behavior of the trace of the energy-momentum tensor as a function of the temperature T. We compare the theoretical predictions of this holographic model with a new set of high-precision numerical results from lattice simulations of SU(N) theories with N = 2, 3, 4, 5 and 6 colors. The latter reveal that, similarly to the D = 3 + 1 case, the bulk equilibrium thermodynamic quantities (pressure, trace of the energy-momentum tensor, energy density and entropy density) exhibit nearly perfect proportionality to the number of gluons, and can be successfully compared with the holographic predictions in a broad range of temperatures. Finally, we also show that, again similarly to the D = 3 + 1 case, the trace of the energy-momentum tensor appears to be proportional to T
2 in a wide temperature range, starting from approximately 1.2 T

c
, where T

c
denotes the critical deconfinement temperature.
Higgs and non-universal gaugino masses: no SUSY signal expected yet?
Authors: Caron Sascha , Laamanen Jari , Niessen Irene , Strübig Antonia
Published: June 2012

Abstract

So far, no supersymmetric particles have been detected at the Large Hadron Collider (LHC). However, the recent Higgs results have interesting implications for the SUSY parameter space. In this paper, we study the consequences of an LHC Higgs signal for a model with non-universal gaugino masses in the context of SU(5) unification. The gaugino mass ratios associated with the higher representations produce viable spectra that are largely inaccessible to the current LHC and direct dark matter detection experiments. Thus, in light of the Higgs results, the non-observation of SUSY is no surprise.
Heterochrony: the Evolution of Development
Authors: McNamara Kenneth J.
Published: June 2012

Heterochrony can be defined as change to the timing or rate of development relative to the ancestor. Because organisms generally change in shape as well as increase in size during their development, any variation to the duration of growth or to the rate of growth of different parts of the organism can cause morphological changes in the descendant form. Heterochrony takes the form of both increased and decreased degrees of development, known as “peramorphosis” and “paedomorphosis,” respectively. These are the morphological consequences of the operation of processes that change the duration of the period of an individual’s growth, either starting or stopping it earlier or later than in the ancestor, or by extending or contracting the period of growth. Heterochrony operates both intra- and interspecifically and is the source of much intraspecific variation. It is often also the cause of sexual dimorphism. Selection of a sequence of species with a specific heterochronic trait can produce evolutionary trends in the form of pera- or paedomorphoclines. Many different life history traits arise from the operation of heterochronic processes, and these may sometimes be the targets of selection rather than morphological features themselves. It has been suggested that some significant steps in evolution, such as the evolution of vertebrates, were engendered by heterochrony. Human evolution was fuelled by heterochrony, with some traits, such as a large brain, being peramorphic, whereas others, such as reduced jaw size, are paedomorphic.
RETRACTED ARTICLE: Plasma Protein Adsorption to Zwitterionic Poly (Carboxybetaine Methacrylate) Modified Surfaces: Chain Chemistry and End-Group Effects on Protein Adsorption Kinetics, Adsorbed Amounts and Immunoblots
Authors: Abraham Sinoj , Bahniuk Markian S. , Unsworth Larry D.
Published: June 2012

Protein–surface interactions are crucial to the overall biocompatability of biomaterials, and are thought to be the impetus towards the adverse host responses such as blood coagulation and complement activation. Only a few studies hint at the ultra-low fouling potential of zwitterionic poly(carboxybetaine methacrylate) (PCBMA) grafted surfaces and, of those, very few systematically investigate their non-fouling behavior. In this work, single protein adsorption studies as well as protein adsorption from complex solutions (i.e. human plasma) were used to evaluate the non-fouling potential of PCBMA grafted silica wafers prepared by nitroxide-mediated free radical polymerization. PCBMAs used for surface grafting varied in charge separating spacer groups that influence the overall surface charges, and chain end-groups that influence the overall hydrophilicity, thereby, allows a better understanding of these effects towards the protein adsorption for these materials. In situ ellipsometry was used to quantify the adsorbed layer thickness and adsorption kinetics for the adsorption of four proteins from single protein buffer solutions, viz, lysozyme, α-lactalbumin, human serum albumin and fibrinogen. Total amount of protein adsorbed on surfaces differed as a function of surface properties and protein characteristics. Finally, immunoblots results showed that human plasma protein adsorption to these surfaces resulted, primarily, in the adsorption of human serum albumin, with total protein adsorbed amounts being the lowest for PCBMA-3 (TEMPO). It was apparent that surface charge and chain hydrophilicity directly influenced protein adsorption behavior of PCBMA systems and are promising materials for biomedical applications.
Time perspective and psychosocial positive functioning among Italian adolescents who binge eat and drink
Authors: Laghi Fiorenzo , Liga Francesca , Baumgartner Emma , Baiocco Roberto
Published: June 2012

Evidence of an association between binge eating and binge drinking and of related health consequences have stimulated investigators to examine and explore risk and protective factors plus the reasons why individuals engage in these risky behaviours (Benjamin & Wulfert, 2003; Ferriter & Ray, 2011). This study examined the relationship between binge drinking and eating, time perspective and psychological functioning. A cross‐sectional survey of 1350 17–19 year‐old adolescents was conducted. Findings suggested that adolescents engaged in both binge eating and binge drinking behaviours reported negative experiences in the past, and they showed a lower future orientation and a greater inclination to fatalism than did the other students Additionally, they were more likely to report lower feelings of satisfaction with life and self‐esteem than the others. The pattern of results allows to conclude that time perspective may be a salient dimension when exploring the psychosocial correlates of binge behaviours, particularly within adolescents.
Alendronate promotes plasmin‐mediated MMP‐9 inactivation by exposing cryptic plasmin degradation sites within the MMP‐9 catalytic domain
Authors: Farina Antonietta R. , Cappabianca Lucia , Di Ianni Natalia , Ruggeri Pierdomenico , Ragone Marzia , Merolle Stefania , Gulino Alberto , Mackay Andrew R.
Published: June 2012

Irreversible MMP‐9 inhibition is considered a significant therapeutic goal in inflammatory, vascular and tumour pathology. We report that divalent cation chelators Alendronate and EDTA not only directly inhibited MMP‐9 but also promoted irreversible plasmin‐mediated MMP‐9 inactivation by exposing cryptic plasmin‐degradation sites within the MMP‐9 catalytic‐domain and producing an inhibitory hemopexin–domain fragment. This effect was also observed using MDA‐MB‐231 breast cancer cells, which activated exogenous plasminogen to degrade endogenous proMMP‐9 in the presence of Alendronate or EDTA. Degradation‐mediated inactivation of proMMP‐9 occurred in the absence of transient activation, attesting to the incapacity of plasmin to directly activate proMMP‐9 and direct MMP‐9 inhibition by Alendronate and EDTA. Our study provides a novel rational for therapeutic Alendronate use in MMP‐9‐dependent pathology characterised by plasminogen activation.
Glycolytic cancer cells lacking 6‐phosphogluconate dehydrogenase metabolize glucose to induce senescence
Authors: Sukhatme Vikas P. , Chan Barden
Published: June 2012

We show that knockdown of 6‐phosphogluconate dehydrogenase (6PGD) of the pentose phosphate pathway (PPP) inhibits growth of lung cancer cells by senescence induction. This inhibition is not due to a defect in the oxidative PPP per se. NADPH and ribose phosphate production are normal in 6PGD knockdown cells and shutdown of PPP by knockdown of glucose‐6‐phosphate dehydrogenase (G6PD) has little effect on cell growth. Moreover, 6PGD knockdown cells can proliferate when the PPP is bypassed by using fructose instead of glucose in medium. Significantly, G6PD knockdown rescues proliferation of cells lacking 6PGD, suggesting an accumulation of growth inhibitory glucose metabolics in cells lacking 6PGD. Therefore, 6PGD inhibition may provide a novel strategy to treat glycolyic tumors such as lung cancer.
Six Sigma adoption: Operating performance impacts and contextual drivers of success
Authors: Swink Morgan , Jacobs Brian W.
Published: June 2012

We assess the operational impacts of Six Sigma program adoptions through an event study methodology, comparing financial data for 200 Six Sigma adopting firms against data for matched firms, which serve as control groups for the analyses. We employ various matching procedures using different combinations of pre‐adoption return on assets (ROA), industry, and size as matching criteria. By comparing performance outcomes across a hierarchy of operating metrics, we establish a pattern of Six Sigma adoption effects that provides strong evidence of a positive impact on ROA. Interestingly, these ROA improvements arise mostly from significant reductions in indirect costs; significant improvements in direct costs and asset productivity are not evident. We also find small improvements in sales growth due to Six Sigma adoption. Cross‐sectional analyses of the performance results reveal that distinctions in Six Sigma impacts across manufacturing and service firms are negligible. Interestingly, we find that the performance impact of Six Sigma adoption is negatively correlated to the firm's quality system maturity (indicated by prior ISO 9000 certification). Further analyses of manufacturing and service firms reveals that Six Sigma benefits are significantly correlated with intensity in manufacturing, and with financial performance before adoption in services. We discuss the implications of these findings for practice and for future research.
Holocene alluvial stratigraphy and response to climate change in the Roaring River valley, Front Range, Colorado, USA
Authors: Madole Richard F.
Published: June 2012

Stratigraphic analyses and radiocarbon geochronology of alluvial deposits exposed along the Roaring River, Colorado, lead to three principal conclusions: (1) the opinion that stream channels in the higher parts of the Front Range are relics of the Pleistocene and nonalluvial under the present climate, as argued in a water-rights trial USA v. Colorado, is untenable, (2) beds of clast-supported gravel alternate in vertical succession with beds of fine-grained sediment (sand, mud, and peat) in response to centennial-scale changes in snowmelt-driven peak discharges, and (3) alluvial strata provide information about Holocene climate history that complements the history provided by cirque moraines, periglacial deposits, and paleontological data. Most alluvial strata are of late Holocene age and record, among other things, that: (1) the largest peak flows since the end of the Pleistocene occurred during the late Holocene; (2) the occurrence of a mid- to late Holocene interval (~ 2450–1630(?) cal yr BP) of warmer climate, which is not clearly identified in palynological records; and (3) the Little Ice Age climate seems to have had little impact on stream channels, except perhaps for minor (~ 1 m) incision.
Spatiotemporal interpolation of elevation changes derived from satellite altimetry for Jakobshavn Isbræ, Greenland
Authors: Hurkmans R. T. W. L. , Bamber J. L. , Sørensen L. S. , Joughin I. R. , Davis C. H. , Krabill W. B.
Published: June 2012

Estimation of ice sheet mass balance from satellite altimetry requires interpolation of point‐scale elevation change (dH/dt) data over the area of interest. The largest dH/dtvalues occur over narrow, fast‐flowing outlet glaciers, where data coverage of current satellite altimetry is poorest. In those areas, straightforward interpolation of data is unlikely to reflect the true patterns ofdH/dt. Here, four interpolation methods are compared and evaluated over Jakobshavn Isbræ, an outlet glacier for which widespread airborne validation data are available from NASA's Airborne Topographic Mapper (ATM). The four methods are ordinary kriging (OK), kriging with external drift (KED), where the spatial pattern of surface velocity is used as a proxy for that of dH/dt, and their spatiotemporal equivalents (ST‐OK and ST‐KED). KED assumes a linear relationship between spatial gradients of velocity anddH/dt, which is confirmed for both negative (Pearson's correlation ρ < −0.85) and, to a lesser degree, positive (ρ = 0.73) dH/dtvalues. When compared to ATM data, KED and ST‐KED yield more realistic spatial patterns and higher thinning rates (over 20 m yr−1 as opposed to 7 m yr−1for OK). Spatiotemporal kriging smooths inter‐annual variability and improves interpolation in periods with sparse data coverage and we conclude, therefore, that ST‐KED produces the best results. Using this method increases volume loss estimates from Jakobshavn Isbræ by up to 20% compared to those obtained by OK. The proposed interpolation method will improve ice sheet mass balance reconstructions from existing and past satellite altimeter data sets, with generally poor sampling of outlet glaciers.
Modeling glacier thickness distribution and bed topography over entire mountain ranges with GlabTop: Application of a fast and robust approach
Authors: Linsbauer A. , Paul F. , Haeberli W.
Published: June 2012

The combination of glacier outlines with digital elevation models (DEMs) opens new dimensions for research on climate change impacts over entire mountain chains. Of particular interest is the modeling of glacier thickness distribution, where several new approaches were proposed recently. The tool applied herein, GlabTop (Glacier bed Topography) is a fast and robust approach to model thickness distribution and bed topography for large glacier samples using a Geographic Information System (GIS). The method is based on an empirical relation between average basal shear stress and elevation range of individual glaciers, calibrated with geometric information from paleoglaciers, and validated with radio echo soundings on contemporary glaciers. It represents an alternative and independent test possibility for approaches based on mass‐conservation and flow. As an example for using GlabTop in entire mountain ranges, we here present the modeled ice thickness distribution and bed topography for all Swiss glaciers along with a geomorphometric analysis of glacier characteristics and the overdeepenings found in the modeled glacier bed. These overdeepenings can be seen as potential sites for future lake formation and are thus highly relevant in connection with hydropower production and natural hazards. The thickest ice of the largest glaciers rests on weakly inclined bedrock at comparably low elevations, resulting in a limited potential for a terminus retreat to higher elevations. The calculated total glacier volume for all Swiss glaciers is 75 ± 22 km3 for 1973 and 65 ± 20 km3 in 1999. Considering an uncertainty range of ±30%, these results are in good agreement with estimates from other approaches.
Concentrated flow erodibility for physically based erosion models: Temporal variability in disturbed and undisturbed rangelands
Authors: Al‐Hamdan Osama Z. , Pierson Frederick B. , Nearing Mark A. , Williams C. Jason , Stone Jeffry J. , Kormos Patrick R. , Boll Jan , Weltz Mark A.
Published: June 2012

Current physically based overland flow erosion models for rangeland application do not separate disturbed and undisturbed conditions in modeling concentrated flow erosion. In this study, concentrated flow simulations on disturbed and undisturbed rangelands were used to estimate the erodibility and to evaluate the performance of linear and power law equations that describe the relationship between erosion rate and several hydraulic parameters. None of the hydraulic parameters consistently predicted the detachment capacity well for all sites, however, stream power performed better than most of other hydraulic parameters. Using power law functions did not improve the detachment relation with respect to that of the linear function. Concentrated flow erodibility increased significantly when a site was exposed to a disturbance such as fire or tree encroachment into sagebrush steppe. This study showed that burning increases erosion by amplifying the erosive power of overland flow through removing obstacles and by changing the soil properties affecting erodibility itself. However, the magnitude of fire impact varied among sites due to inherent differences in site characteristics and variability in burn severity. In most cases we observed concentrated flow erodibility had a high value at overland flow initiation and then started to decline with time due to reduction of sediment availability. Thus we developed an empirical function to predict erodibility variation within a runoff event as a function of cumulative unit discharge. Empirical equations were also developed to predict erodibility variation with time postdisturbance as a function of readily available vegetation cover and surface soil texture data.
Plume spreading in groundwater by stretching and folding
Authors: Mays David C. , Neupauer Roseanna M.
Published: June 2012

This paper proposes a new approach to the hydraulics of in situ groundwater remediation. In situ remediation promotes reactions between an injected treatment solution and the contaminated groundwater, but without a hydraulic mechanism to promote spreading, the laminar flows characteristic of porous media will keep the two fluids in approximately the same relative configuration as they travel through the aquifer, limiting the opportunity for reactions to occur. To address this fundamental limitation, this paper borrows a key result from the fluid mechanics literature: Spreading in laminar flows is optimized by chaotic advection. Previous studies have applied this result to groundwater remediation using the pulsed dipole model, but that model depends on reinjection of fluid, which presents a number of theoretical and practical limitations. Accordingly, this paper proposes a new conceptual model for plume spreading by chaotic advection, using an engineered sequence of extractions and injections of clean water at an array of wells, which generates plume spreading by stretching and folding the fluid interface between the injected treatment solution and the contaminated groundwater but does not require reinjection. The paper includes an overview of the analytical techniques—Poincaré sections, periodic points, stable and unstable manifolds, heteroclinic points, and Lyapunov exponents—used to demonstrate chaotic advection in the limiting case in which diffusion is negligible. Numerical simulations show that spreading by stretching and folding is complimentary to spreading resulting from aquifer heterogeneity.
Predicting tropical cyclone rapid intensification using the 37 GHz ring pattern identified from passive microwave measurements
Authors: Kieper Margaret E. , Jiang Haiyan
Published: June 2012

A distinctive satellite‐derived precipitative ring pattern around the tropical cyclone (TC) center is found to be related to rapid intensification (RI). The ring pattern appears on the Naval Research Laboratory (NRL) 37 GHz passive microwave composite color product as a cyan color ring. The probability of RI is evaluated for cases with this ring pattern by reviewing images of the NRL product for 84 TCs during 2003–2007 in the Atlantic basin using 6‐hourly National Hurricane Center (NHC) best track data. It is found that when combining the ring criterion with the Statistical Hurricane Prediction Scheme (SHIPS) RI Index (RII), the probability of RI almost doubled, indicating that both the ring and SHIPS RII contain independent information for RI prediction. A subjective technique for predicting RI is proposed using both the 37 GHz ring and the SHIPS RII. Both the probability of detection (POD) and the false alarm ratio (FAR) for the combined ring+SHIPS RII are lower than those for SHIPS RII alone (POD, 24% versus 77%, and FAR, 26% versus 66%) when treating every 6‐hr synoptic time as a separate case. Since the method was initially developed for RI event‐based forecasts, statistics based on 2003–2007 Atlantic RI events, which consist of a contiguous period where any 24‐hour subset shows at least a 30 kt intensity increase, are also generated. The method captures 21 out of these 28 events and produces 2 false alarms, producing a POD of 75% and a FAR of 9%.
On the space‐time distribution of major explosive volcanic eruptions on Earth
Authors: Palladino Danilo M. , Sottili Gianluca
Published: June 2012

Explosive volcanic activity on Earth is typically discontinuous in space and time. The occurrence of spatial/temporal eruption clusters due to mutual cause‐and‐effect relationships or external triggers (e.g., tectonic and/or tidal forcing) is still debated. To detect possible clustering of major explosive eruptions, we test the distribution of eruptions with Volcanic Explosivity Index (VEI) ≥ 4 from 1750 to present. The 143 documented VEI ≥ 4 events display a markedly non‐uniform frequency distribution, with the highest relative probability of eruption recurrence within 500 km distance from the preceding event. The analogous frequency pattern obtained from randomized data series of the same catalogue suggests that the observed eruption pattern is primarily imparted by the geodynamic distribution of volcanoes (mostly located along tectonically active linear belts), with no evidence of mutual or external influence. Our results highlight a counter‐intuitive array of major eruption loci as a consequence of the intrinsic worldwide asymmetry of explosive volcanism, with implications on hazard assessment.
Paleomagnetic secular variation at the Azores during the last 3 ka
Authors: Di Chiara Anita , Speranza Fabio , Porreca Massimiliano
Published: June 2012

We report on 33 new paleomagnetic directions obtained from 16 lava flows emplaced in the last 3 ka on São Miguel, the largest island of the Azores. The data provide 27 well‐dated directions from historical or 14C dated flows which, together with 6 directions previously gathered from the same flows by Johnson et al. (1998), yield the first paleomagnetic directional record of the last 3 ka from the Atlantic Ocean. Within‐flow directions are consistent, suggesting that inclination swings from 60° to 25° and declination changes between −10° to 20° reflect variations in the geomagnetic field over the last 3 ka. To a first approximation, the declination record is consistent with predictions from CALS3k.4 and gufm1 global field models. Conversely, inclination values are lower than model predictions at two different ages: 1) four sites from the 1652 AD flow yield I = 48° instead of I = 63° predicted by gufm1; 2) data from several flows nicely mimic the inclination minimum of 800–1400 AD, but inclination values are lower by ∼10° than CALS3k.4 model predictions. By interpolating a cubic spline fit on declination / inclination versus age data, we tentatively infer the directional evolution of the geomagnetic field at the Azores from 1000 BC to 1600 AD. The obtained curve shows three tracks in virtual overlap during the 1000–800 BC, 800–500 BC, and 400–700 AD time spans.
On the existence of stable seasonally varying Arctic sea ice in simple models
Authors: Moon W. , Wettlaufer J. S.
Published: June 2012

Within the framework of lower order thermodynamic theories for the climatic evolution of Arctic sea ice we isolate the conditions required for the existence of stable seasonally‐varying solutions, in which ice forms each winter and melts away each summer. This is done by constructing a two‐season model from the continuously evolving theory of Eisenman and Wettlaufer (2009) and showing that seasonally‐varying states are unstable under constant annual average short‐wave radiative forcing. However, dividing the summer season into two intervals (ice covered and ice free) provides sufficient freedom to stabilize seasonal ice. Simple perturbation theory shows that the condition for stability is determined by the timing of when the ice vanishes in summer and hence the relative magnitudes of the summer heat flux over the ocean versus over the ice. This scenario is examined within the context of greenhouse gas warming, as a function of which stability conditions are discerned.
Break detection of annual Swiss temperature series
Authors: Kuglitsch F. G. , Auchmann R. , Bleisch R. , Brönnimann S. , Martius O. , Stewart M.
Published: June 2012

Instrumental temperature series are often affected by artificial breaks (“break points”) due to (e.g.,) changes in station location, land‐use, or instrumentation. The Swiss climate observation network offers a high number and density of stations, many long and relatively complete daily to sub‐daily temperature series, and well‐documented station histories (i.e., metadata). However, for many climate observation networks outside of Switzerland, detailed station histories are missing, incomplete, or inaccessible. To correct these records, the use of reliable statistical break detection methods is necessary. Here, we apply three statistical break detection methods to high‐quality Swiss temperature series and use the available metadata to assess the methods. Due to the complex terrain in Switzerland, we are able to assess these methods under specific local conditions such as the Foehn or crest situations. We find that the temperature series of all stations are affected by artificial breaks (average = 1 break point / 48 years) with discrepancies in the abilities of the methods to detect breaks. However, by combining the three statistical methods, almost all of the detected break points are confirmed by metadata. In most cases, these break points are ascribed to a combination of factors in the station history.
Hydrologic connectivity increases denitrification in the hyporheic zone and restored floodplains of an agricultural stream
Authors: Roley Sarah S. , Tank Jennifer L. , Williams Maureen A.
Published: June 2012

Stream ecotones, specifically the lateral floodplain and subsurface hyporheic zone, can be important sites for nitrogen (N) removal via denitrification, but their role in streams with constructed floodplains has not been examined. We studied denitrification in the hyporheic zone and floodplains of an agriculturally influenced headwater stream in Indiana, USA, that had floodplains added as part of a “two‐stage ditch” restoration project. To examine the potential for N removal in the hyporheic zone, we seasonally measured denitrification rates and nitrate concentrations by depth into the stream sediments. We found that nitrate concentration and denitrification rates declined with depth into the hyporheic zone, but denitrification was still measureable to a depth of at least 20 cm. We also measured denitrification rates on the restored floodplains over the course of a flood (pre, during, and post‐inundation), and also compared denitrification rates between vegetated and non‐vegetated areas of the floodplain. We found that floodplain denitrification rates increased over the course of a floodplain inundation event, and that the presence of surface water increased denitrification rates when vegetation was present. Stream ecotones in midwestern, agriculturally influenced streams have substantial potential for N removal via denitrification, particularly when they are hydrologically connected with high‐nitrate surface water.
Monitoring groundwater‐surface water interaction using time‐series and time‐frequency analysis of transient three‐dimensional electrical resistivity changes
Authors: Johnson T. C. , Slater L. D. , Ntarlagiannis D. , Day‐Lewis F. D. , Elwaseif M.
Published: June 2012

Time‐lapse resistivity imaging is increasingly used to monitor hydrologic processes. Compared to conventional hydrologic measurements, surface time‐lapse resistivity provides superior spatial coverage in two or three dimensions, potentially high‐resolution information in time, and information in the absence of wells. However, interpretation of time‐lapse electrical tomograms is complicated by the ever‐increasing size and complexity of long‐term, three‐dimensional (3‐D) time series conductivity data sets. Here we use 3‐D surface time‐lapse electrical imaging to monitor subsurface electrical conductivity variations associated with stage‐driven groundwater‐surface water interactions along a stretch of the Columbia River adjacent to the Hanford 300 near Richland, Washington, USA. We reduce the resulting 3‐D conductivity time series using both time‐series and time‐frequency analyses to isolate a paleochannel causing enhanced groundwater‐surface water interactions. Correlation analysis on the time‐lapse imaging results concisely represents enhanced groundwater‐surface water interactions within the paleochannel, and provides information concerning groundwater flow velocities. Time‐frequency analysis using the Stockwell (S) transform provides additional information by identifying the stage periodicities driving groundwater‐surface water interactions due to upstream dam operations, and identifying segments in time‐frequency space when these interactions are most active. These results provide new insight into the distribution and timing of river water intrusion into the Hanford 300 Area, which has a governing influence on the behavior of a uranium plume left over from historical nuclear fuel processing operations.
Enhancement of magnetoelectric effect by combining different interfacial coupling mechanisms
Authors: Dai Jian-Qing , Song Yu-Min , Zhang Hu
Published: June 2012

First-principles calculations were used to investigate the interfacial electronic structure and magnetoelectric effect in the Fe/PbTiO3 heterointerface. We demonstrate that the large magnetoelectric effect in this system is determined by the combination of different magnetoelectric coupling mechanisms, i.e., the conjunction of interface bonding mechanism and the electrostatic screening of the spin-polarized carriers. The change of induced magnetic moments on interfacial Ti atoms is due to the variation of interface bonding when the ferroelectric polarization reverses, while the contribution to magnetoelectric coupling from interfacial Fe atoms is determined by the electrostatic screening of spin-polarized carriers. The combination of different interfacial magnetoelectric coupling mechanisms enhances the magnetoelectric coefficient at the Fe/PbTiO3 heterointerface to be several times larger in magnitude than that of individual magnetoelectric coupling mechanism. Our results indicate a new strategy to design multiferroic materials with large magnetoelectric effects.
First-principles investigation of electrical and magnetic properties of ZnO based diluted magnetic semiconductors codoped with H
Authors: Assadi M. H. N. , Zheng R. K. , Li S. , Ringer S. R.
Published: June 2012

Hydrogen (H) behavior in ZnO based diluted magnetic semiconductors (DMSs) was investigated theoretically. It was found that H exhibits diverse electronic and structural behavior across a range of different DMSs, depending on the doped transition metal element. For instance in the extensively debated Co doped ZnO system (ZnO:Co), H dopants do not introduce significant carrier concentrations at room temperature thus carrier mediated magnetism is not attainable by H codoping. In this case, magnetism can be manipulated by other mechanisms. In contrast, in the ZnO:V system, H is positively charged for the entire bandgap region, meaning carrier mediated magnetism may be possible.
On the density scaling of pVT data and transport properties for molecular and ionic liquids
Authors: López Enriqueta R. , Pensado Alfonso S. , Fernández Josefa , Harris Kenneth R.
Published: June 2012

In this work, a general equation of state (EOS) recently derived by Grzybowski et al. [Phys. Rev. E 83, 041505 (2011)] is applied to 51 molecular and ionic liquids in order to perform density scaling of pVT data employing the scaling exponent γEOS. It is found that the scaling is excellent in most cases examined. γEOS values range from 6.1 for ammonia to 13.3 for the ionic liquid [C4C1im][BF4]. These γEOS values are compared with results recently reported by us [E. R. López, A. S. Pensado, M. J. P. Comuñas, A. A. H. Pádua, J. Fernández, and K. R. Harris, J. Chem. Phys. 134, 144507 (2011)] for the scaling exponent γ obtained for several different transport properties, namely, the viscosity, self-diffusion coefficient, and electrical conductivity. For the majority of the compounds examined, γEOS > γ, but for hexane, heptane, octane, cyclopentane, cyclohexane, CCl4, dimethyl carbonate, m-xylene, and decalin, γEOS < γ. In addition, we find that the γEOS values are very much higher than those of γ for alcohols, pentaerythritol esters, and ionic liquids. For viscosities and the self-diffusion coefficient-temperature ratio, we have tested the relation linking EOS and dynamic scaling parameters, proposed by Paluch et al. [J. Phys. Chem. Lett. 1, 987–992 (2010)] and Grzybowski et al. [J. Chem. Phys. 133, 161101 (2010); Grzybowski et al. Phys. Rev. E 82, 013501 (2010)], that is, γ = (γEOS/ϕ) + γG, where ϕ is the stretching parameter of the modified Avramov relation for the density scaling of a transport property, and γG is the Grüneisen constant. This relationship is based on data for structural relaxation times near the glass transition temperature for seven molecular liquids, including glass formers, and a single ionic liquid. For all the compounds examined in our much larger database the ratio (γEOS/ϕ) is actually higher than γ, with the only exceptions of propylene carbonate and 1-methylnaphthalene. Therefore, it seems the relation proposed by Paluch et al. applies only in certain cases, and is really not generally applicable to liquid transport properties such as viscosities, self-diffusion coefficients or electrical conductivities when examined over broad ranges of temperature and pressure.
Study of field driven electroluminescence in colloidal quantum dot solids
Authors: Bozyigit Deniz , Wood Vanessa , Shirasaki Yasuhiro , Bulovic Vladimir
Published: June 2012

Semiconductor nanocrystals, or quantum dots (QDs), promise to drive advances in electronic light generation. It was recently shown that long range transport of charge, which is typically required for electric excitation and which is inherently limited in nanosized materials, can be avoided by developing devices that operate through local, field-assisted generation of charge. We investigate such devices that consist of a thin film of CdSe/ZnS core-shell QD placed between two dielectric layers and that exhibit electroluminescence under pulsed, high field excitation. Using electrical and spectroscopic measurements, we are able to elucidate the dynamics of charge within the QD layer and determine that charge trapping and field-induced luminescence quenching are the main limitations of device performance.
Anharmonic force field and vibrational dynamics of CH2F2 up to 5000 cm−1 studied by Fourier transform infrared spectroscopy and state-of-the-art ab initio calculations
Authors: Tasinato Nicola , Regini Giorgia , Stoppa Paolo , Charmet Andrea Pietropolli , Gambi Alberto
Published: June 2012

Difluoromethane (CH2F2, HFC-32) is a molecule used in refrigerant mixtures as a replacement of the more environmentally hazardous, ozone depleting, chlorofluorocarbons. On the other hand, presenting strong vibration-rotation bands in the 9 μm atmospheric window, it is a greenhouse gas which contributes to global warming. In the present work, the vibrational and ro-vibrational properties of CH2F2, providing basic data for its atmospheric modeling, are studied in detail by coupling medium resolution Fourier transform infrared spectroscopy to high-level electronic structure ab initio calculations. Experimentally a full quantum assignment and accurate integrated absorption cross sections are obtained up to 5000 cm−1. Ab initio calculations are carried out by using CCSD(T) theory and large basis sets of either the correlation consistent or atomic natural orbital hierarchies. By using vibrational perturbation theory to second order a complete set of vibrational and ro-vibrational parameters is derived from the ab initio quartic anharmonic force fields, which well compares with the spectroscopic constants retrieved experimentally. An excellent agreement between theory and experiment is achieved for vibrational energy levels and integrated absorption cross sections: transition frequencies up to four quanta of vibrational excitation are reproduced with a root mean square deviation (RMSD) of 7 cm−1 while intensities are predicted within few km mol−1 from the experiment. Basis set performances and core correlation effects are discussed throughout the paper. Particular attention is focused in the understanding of the anharmonic couplings which rule the vibrational dynamics of the |ν1⟩, |2ν8⟩, |2ν2⟩ three levels interacting system. The reliability of the potential energy and dipole moment surfaces in reproducing the vibrational eigenvalues and intensities as well as in modeling the vibrational and ro-vibrational mixings over the whole 400–5000 cm−1 region is also demonstrated by spectacular spectral simulations carried out by using the ro-vibrational Hamiltonian constants, and the relevant coupling terms, obtained from the perturbation treatment of the ab initio anharmonic force field. The present results suggest CH2F2 as a prototype molecule to test ab initio calculations and theoretical models.
Computed versus measured ion velocity distribution functions in a Hall effect thruster
Authors: Garrigues L. , Mazouffre S. , Bourgeois G.
Published: June 2012

We compare time-averaged and time-varying measured and computed ion velocity distribution functions in a Hall effect thruster for typical operating conditions. The ion properties are measured by means of laser induced fluorescence spectroscopy. Simulations of the plasma properties are performed with a two-dimensional hybrid model. In the electron fluid description of the hybrid model, the anomalous transport responsible for the electron diffusion across the magnetic field barrier is deduced from the experimental profile of the time-averaged electric field. The use of a steady state anomalous mobility profile allows the hybrid model to capture some properties like the time-averaged ion mean velocity. Yet, the model fails at reproducing the time evolution of the ion velocity. This fact reveals a complex underlying physics that necessitates to account for the electron dynamics over a short time-scale. This study also shows the necessity for electron temperature measurements. Moreover, the strength of the self-magnetic field due to the rotating Hall current is found negligible.