bluuebunny/crossref_metadata_2025 huggingface dataset:
Substrate requirements of spawning Chinook salmon (Oncorhynchus tshawytscha) are dependent on local channel hydraulics
Authors: Moir H. J. , Pasternack G. B.
Published: July 2009

Micro‐scale (<0.1 channel widths) physical conditions within channels ultimately exert a strong control on habitat selection by fish species. Data are presented demonstrating that micro‐habitat requirements of spawning Chinook salmon (Oncorhynchus tshawytscha) are strongly inter‐related; fish utilized coarser substrate if associated with faster flow velocities. This was not observed to be controlled through a hydraulic sorting mechanism but, rather, related to the physical processes of spawning. Failure to consider the ‘elastic’ nature of Chinook salmon spawning requirements resulting from links between the physical parameters may have implications for river management practices such as restoration or setting environmental flows. Copyright © 2009 John Wiley & Sons, Ltd.
Turbo similarity searching: Effect of fingerprint and dataset on virtual‐screening performance
Authors: Gardiner Eleanor J. , Gillet Valerie J. , Haranczyk Maciej , Hert Jérôme , Holliday John D. , Malim Nurul , Patel Yogendra , Willett Peter
Published: July 2009

Turbo similarity searching uses information about the nearest neighbors in a conventional chemical similarity search to increase the effectiveness of virtual screening with a data fusion approach being used to combine the nearest‐neighbor information. A previous paper suggested that the approach was highly effective in operation; this paper further tests the approach using a range of different databases and of structural representations. Searches were carried out on three different databases of chemical structures, using seven different types of fingerprints, as well as molecular holograms, physicochemical properties, topological indices and reduced graphs. The results show that turbo similarity searching can indeed enhance retrieval but that this is normally achieved only if the similarity search that acts as its starting point has already achieved at least some reasonable level of search effectiveness. In other cases, a modified version of TSS that uses the nearest‐neighbor information for approximate machine learning can be used effectively. Though useful for qualitative (active/inactive) predictions of biological activity, turbo similarity searching does not appear to exhibit any predictive power when quantitative property data is available. Copyright © 2009 Wiley Periodicals, Inc. Statistical Analysis and Data Mining 2: 103‐114, 2009
Affordable loss: behavioral economic aspects of the plunge decision
Authors: Dew Nicholas , Sarasathy Saras , Read Stuart , Wiltbank Robert
Published: July 2009

Affordable loss involves decision makers estimating what they might be able to put at risk and determining what they are willing to lose in order to follow a course of action. Using the entrepreneur's new venture plunge decision, this article combines insights from behavioral economics to develop a detailed analysis of the affordable loss heuristic. Specifically, we develop propositions to explain how individuals: (1) decide what they can afford to lose; and (2) what they are willing to lose in order to plunge into entrepreneurship. The article also discusses the implications of affordable loss for the economics of strategic entrepreneurship. Copyright © 2009 Strategic Management Society.
Wind energy literature survey no. 13
Authors: Henriksen L. C.
Published: July 2009

As a service to readers, Wind Energy regularly conducts literature surveys and publishes lists of relevant articles drawn from recent issues of a large number of periodicals including: Journal of Wind Engineering & Industrial Aerodynamics, International Journal of Energy Research, Renewable Energy, Energy Sources, Journal of Solar Energy Engineering, American Institute of Aeronautics and Astronautics Journal, Electric Power Components and Systems, along with a number of periodicals published by the Institute of Electrical and Electronics Engineers, etc. The list is limited exclusively to journals not specifically devoted to wind energy and its applications. To assist the reader, the list is separated into broad categories. Although many papers fit several categories, each paper is listed only once under the category thought most appropriate. Please note that the inclusion in the list is not an endorsement of a paper's quality. Compiled by Lars Christian Henriksen, Wind Energy Department, Riso/ National Laboratory for Sustainable Energy, Technical University of Denmark, PO 49, DK‐4000 Roskilde, Denmark. Please e‐mail any suggestions to larh@risoe.dtu.dk.
Modelling of microstructural void evolution with configurational forces
Authors: Timmel M. , Kaliske M. , Kolling S.
Published: July 2009

We discuss the effect of material softening during cyclic loading. The decrease of stress is caused by a damage evolution in the microscale, e.g. due to micro‐void growth. For a numerical treatment of this material behaviour, phenomenological damage approaches are used in daily engineering practice. For a better understanding of the micromechanical process, multiscale methods are becoming increasingly important. The physical quantities which are responsible for the microstructural evolution associated with the damage process are transferred into the numerical model. In this context, the method of configurational forces is used to describe the geometrical changes of damaged areas. With the help of a homogenization technique, macro‐ and microscale are coupled. In consequence, each Gaussian point of the macromechanical finite element discretization represents a microstructure (representative volume element ‐ RVE), where the microscale evolves during the loading process according to observable damage phenomena. We present the general case of hyperelastic materials at finite strains.
Fracture mechanical behaviour of visco‐elastic materials: application to the so‐called dwell‐effect
Authors: Näser B. , Kaliske M. , Dal H. , Netzker Ch.
Published: July 2009

The material force approach is an efficient, elegant, and accepted means to compute the J‐integral as a fracture mechanical parameter for elastic and inelastic materials. With the formulation of a multiplicative split of the deformation gradient at hand, rate‐dependent (visco‐elastic) materials described for example by the physically based Bergström‐Boyce model can be investigated. For these investigations, the so‐called material volume forces have to be computed in order to separate the driving forces acting on the visco‐elastic zone around the crack tip from the driving forces acting on the crack tip itself, representing the crack driving force. To illustrate the effectiveness of this approach, the so‐called dwell‐effect of elastomeric materials is investigated.
Effects of inbreeding on reproductive success, performance, litter size, and survival in captive red wolves (Canis rufus)
Authors: Rabon David R. , Waddell William
Published: July 2009

Captive‐breeding programs have been widely used in the conservation of imperiled species, but the effects of inbreeding, frequently expressed in traits related to fitness, are nearly unavoidable in small populations with few founders. Following its planned extirpation in the wild, the endangered red wolf (Canis rufus) was preserved in captivity with just 14 founders. In this study, we evaluated the captive red wolf population for relationships between inbreeding and reproductive performance and fitness. Over 30 years of managed breeding, the level of inbreeding in the captive population has increased, and litter size has declined. Inbreeding levels were lower in sire and dam wolves that reproduced than in those that did not reproduce. However, there was no difference in the inbreeding level of actual litters and predicted litters. Litter size was negatively affected by offspring and paternal levels of inbreeding, but the effect of inbreeding on offspring survival was restricted to a positive influence. There was no apparent relationship between inbreeding and method of rearing offspring. The observable effects of inbreeding in the captive red wolf population currently do not appear to be a limiting factor in the conservation of the red wolf population. Additional studies exploring the extent of the effects of inbreeding will be required as inbreeding levels increase in the captive population. Zoo Biol 29:36–49, 2010. © 2009 Wiley‐Liss, Inc.
The impact of recent stressful experiences on HIV‐risk related behaviors
Authors: Wong Carolyn F. , Kipke Michele D. , Weiss George , McDavitt Bryce
Published: July 2009

Limited research has captured the wide varieties of distinct, but interrelated, life stressors that young men who have sex with men (YMSM) experience as emerging adults. We examined the way recent experiences of a diverse set of stressors predict illicit drug use, alcohol misuse, and inconsistent condom use (i.e., unprotected anal intercourse) among an ethnically diverse cohort of YMSM (N = 526). Results indicated that stress related to financial and health concerns were associated with increased risk for substance use, while health concerns and partner‐related stress were associated with sexual risk‐taking. Additional analyses indicated drug use and alcohol misuse did not significantly mediate the impact that stressors have on sexual risk. Findings show that stressors from different life domains can have impact on different HIV‐risk behavior. Results challenge the way diverse stressful life experiences are conceptualized for this population.
Akebia saponin D, a saponin component from Dipsacus asper Wall, protects PC 12 cells against amyloid‐β induced cytotoxicity
Authors: Zhou Yong‐Qiang , Yang Zhong‐Lin , Xu Lei , Li Ping , Hu Yu‐Zhu
Published: July 2009

According to Traditional Chinese Medicine, Alzheimer's disease (AD) is regarded as senile dementia, and the etiopathogenesis lies in kidney deficiency during aging. Dipsacus asper Wall (DAW), a well‐known traditional Chinese medicine for enhancing kidney activity, may possess the therapeutic effects against AD. Our objectives were to investigate the protective effects of DAW against the amyloid‐β peptide (Aβ)‐induced cytotoxicity and explore its major active components. Injury of PC 12 cells mediated by Aβ25–35 was adopted to assess the cytoprotective effects of DAW aqueous extract and various fractions. Salvianolic acid B, a polyphenol compound isolated from Salvia miltiorrhiza, was employed as a positive control agent due to its markedly protective effect against neurotoxicity of amyloid β. Five chemical fractions (i.e. alkaloids, essential oil, saponins, iridoid glucoside and polysaccharides) were prepared for activity test and analyzed by HPLC for active components identification. In addition, Akebia saponin D (the most important compound in DAW saponins) and hederagenin (the mother nucleus of akebia saponin D) were prepared for testing of their activity. DAW water extract, saponins fraction and akebia saponin D had the neuroprotective capacity to antagonize Aβ25–35‐induced cytotoxicity in PC 12 cells. In contrast, other fractions and hederagenin had no cytoprotective action. This research suggests that DAW may represent a potential treatment strategy for AD and akebia saponin D is one of its active components.
The CDK inhibitor, R‐roscovitine, promotes eosinophil apoptosis by down‐regulation of Mcl‐1
Authors: Duffin Rodger , Leitch Andrew E. , Sheldrake Tara A. , Hallett John M. , Meyer Colette , Fox Sarah , Alessandri Ana L. , Martin Morag C. , Brady Hugh J. , Teixeira Mauro M. , Dransfield Ian , Haslett Christopher , Rossi Adriano G.
Published: July 2009

Eosinophils are major players in inflammatory allergic diseases such as asthma, hay fever and eczema. Here we show that the cyclin‐dependent kinase inhibitor (CDKi) R‐roscovitine efficiently and rapidly induces human eosinophil apoptosis using flow cytometric analysis of annexin‐V/propidium iodide staining, morphological analysis by light microscopy, transmission electron microscopy and Western immunoblotting for caspase‐3 cleavage. We further dissect these observations by demonstrating that eosinophils treated with R‐roscovitine lose mitochondrial membrane potential and the key survival protein Mcl‐1 is down‐regulated. This novel finding of efficacious induction of eosinophil apoptosis by CDKi drugs has potential as a strategy for driving resolution of eosinophilic inflammation.
Cardiolipin‐enriched raft‐like microdomains are essential activating platforms for apoptotic signals on mitochondria
Authors: Sorice Maurizio , Manganelli Valeria , Matarrese Paola , Tinari Antonella , Misasi Roberta , Malorni Walter , Garofalo Tina
Published: July 2009

Cardiolipin (CL) has recently been shown to provide an anchor and an essential activating platform for caspase‐8 on mitochondria. We hypothesize that these platforms may correspond to “raft‐like” microdomains, which have demonstrated to be detectable on mitochondrial membrane of cells undergoing apoptosis. The role for CL in “raft‐like” microdomains could be to anchor caspase‐8 at contact sites between inner and outer membranes, facilitating its self‐activation, Bid cleavage and apoptosis execution. The role played by “raft‐like” microdomains in the apoptotic program could introduce a new task in the pathogenetic studies on human diseases associated with cardiolipin dismetabolism.
The BK channel accessory β1subunit determines alcohol‐induced cerebrovascular constriction
Authors: Bukiya Anna N. , Liu Jianxi , Dopico Alejandro M.
Published: July 2009

Ethanol‐induced inhibition of myocyte large conductance, calcium‐ and voltage‐gated potassium (BK) current causes cerebrovascular constriction, yet the molecular targets mediating EtOH action remain unknown. Using BK channel‐forming (cbv1) subunits from cerebral artery myocytes, we demonstrate that EtOH potentiates and inhibits current atlower and higher than ∼15 μM, respectively. By increasing cbv1's apparent‐sensitivity, accessory BK β1subunits shift the activation‐to‐inhibition crossover of EtOH action to <3 μM, with consequent inhibition of current under conditions found during myocyte contraction. Knocking‐downKCNMB1suppresses EtOH‐reduction of arterial myocyte BK current and vessel diameter. Therefore, BK β1is the molecular effector of alcohol‐induced BK current inhibition and cerebrovascular constriction.
Dietary selenium addition improves cerebrum and cerebellum impairments induced by methimazole in suckling rats
Authors: Ben Amara Ibtissem , Fetoui Hamadi , Guermazi Fadhel , Zeghal Najiba
Published: July 2009

The aim of this study is to investigate the improving effects of selenium (Se) on cerebrum and cerebellum impairments induced by methimazole (MMI) in suckling rats. Animals were randomly divided into four groups of six each: group I served as control which received standard diet; group II received only MMI (250 mg L−1, orally); group III received both MMI (250 mg L−1, orally) and Se (0.5 mg kg−1 of diet); group IV served as a positive control and received Se (0.5 mg kg−1 of diet) as sodium selenite (Na2SeO3). Treatments were started from the 14th day of pregnancy until day 14 after delivery. In the MMI‐treated group, plasma‐free thyroid hormone levels (FT3 and FT4), protein, DNA and RNA contents in cerebrum and cerebellum decreased when compared to control. Co‐treatment with Se ameliorated these parameters. In the MMI‐treated group, antioxidant enzyme activities (superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH‐Px) significantly decreased, while malonaldialdehyde (MDA) levels in cerebrum and cerebellum increased. Co‐administration of Se through the diet restored these parameters to near normal values. The biochemical modifications are correlated histologically with the abnormal development of an external granular layer, indicating a delay of granular cells migration towards the molecular layer in the MMI‐treated group. Our results showed that Se improved cerebrum and cerebellum MMI‐induced damages in suckling rats. Moreover, we concluded that Se is an important neuroprotective element that may be used as a dietary supplement against brain impairments.
Der Öffentliche Gesundheitsdienst als Prototyp staatlicher Gesundheitsfürsorge
Authors: Wildner Manfred , Zöllner Herbert , Zapf Andreas
Published: July 2009

Einleitung

Der moderne Staat des 21. Jahrhunderts gewährleistet mit seiner Rechtsordnung heute vor allem Freiheit und Solidarität in einer demokratischen Verfassung. Dabei steht er in einem Spannungsfeld von konkurrierenden Werten: Sicherheit und Freiheit, Ordnung und notwendige Veränderung, Herrschaftsausübung und Demokratie. Aufgabe des Staates ist es unter anderem, die Daseins-Risiken durch kluge Steuerung im Interesse des Allgemeinwohls gerade in den Bereichen, die ein Einzelner nicht bewältigen kann, abzufedern. Gleichzeitig soll er den Bürgerinnen und Bürgern politische Partizipation ermöglichen. Der Öffentliche Gesundheitsdienst (ÖGD) ist der Teil des öffentlichen Gesundheitswesens, welcher mit der Wahrnehmung öffentlich-rechtlicher Aufgaben auf dem Gebiet des Gesundheitswesens einschließlich der damit zusammenhängenden Untersuchungstätigkeit betraut ist. Diese Aufgaben beziehen sich im Wesentlichen auf die Bereiche Gesundheitsschutz, Gesundheitsförderung und Gesundheitsmanagement/Stewardship. Im Beitrag werden anhand von Beispielen unterschiedliche Arten der Wahrnehmung von Aufgaben des ÖGD veranschaulicht; des Weiteren werden einige Gedanken zur zukünftigen Entwicklung des ÖGD entwickelt.
ON A GLOBAL UPPER BOUND FOR JESSEN’S INEQUALITY
Authors: GAVREA B. , JAKŠETIĆ J. , PEČARIĆ J.
Published: July 2009

In two recent papers a global upper bound is derived for Jensen’s inequality for weighted finite sums. In this paper we generalize this result on positive normalized functionals.
CLOUD CAVITATION DYNAMICS
Authors: WILSON MILES , BLAKE JOHN R. , HAESE PETER M.
Published: July 2009

An analysis is developed for the behaviour of a cloud of cavitation bubbles during both the growth and collapse phases. The theory is based on a multipole method exploiting a modified variational principle developed by Miles [“Nonlinear surface waves in closed basins”, J. Fluid Mech.75 (1976) 418–448] for water waves. Calculations record that bubbles grow approximately spherically, but that a staggered collapse ensues, with the outermost bubbles in the cloud collapsing first of all, leading to a cascade of bubble collapses with very high pressures developed near the cloud centroid. A more complex phenomenon occurs for bubbles of variable radius with local zones of collapse, with a complex frequency spectrum associated with each individual bubble, leading to both local and global collective behaviour.
Model selection techniques for the frequency analysis of hydrological extremes
Authors: Laio Francesco , Di Baldassarre Giuliano , Montanari Alberto
Published: July 2009

The frequency analysis of hydrological extremes requires fitting a probability distribution to the observed data to suitably represent the frequency of occurrence of rare events. The choice of the model to be used for statistical inference is often based on subjective criteria, or it is considered a matter of probabilistic hypotheses testing. In contrast, specific tools for model selection, like the well‐known Akaike information criterion (AIC) and the Bayesian information criterion (BIC), are seldom used in hydrological applications. The objective of this study is to verify whether the AIC and BIC work correctly when they are applied to identifying the probability distribution of hydrological extremes, i.e., when the available samples are small and the parent distribution is highly asymmetric. An additional model selection criterion, based on the Anderson‐Darling goodness‐of‐fit test statistic, is here proposed, and the performances of the three methods are compared through an extensive numerical analysis. The capability of the three criteria to recognize the correct parent distribution from the available data samples varies from case to case, and it is rather good in some cases (in particular when the parent is a two‐parameter distribution) and unsatisfactory in others. An application to flood peak time series from 1000 catchments located in the United Kingdom provides some further information on the qualities and drawbacks of the considered criteria. From the numerical simulations and data‐based analyses it can be concluded that the three model selection techniques considered here produce results of comparable quality.
Effects of elevated pCO2 on dissolution of coral carbonates by microbial euendoliths
Authors: Tribollet A. , Godinot C. , Atkinson M. , Langdon C.
Published: July 2009

Eight‐month‐old blocks of the coral Porites lobata colonized by natural Hawaiian euendolithic and epilithic communities were experimentally exposed to two different aqueous pCO2 treatments, 400 ppmv and 750 ppmv, for 3 months. The chlorophyte Ostreobium quekettii dominated communities at the start and at the end of the experiment (65–90%). There were no significant differences in the relative abundance of euendolithic species, nor were there any differences in bioeroded area at the surface of blocks (27%) between pCO2 treatments. The depth of penetration of filaments of O. quekettii was, however, significantly higher under 750 ppmv (1.4 mm) than under 400 ppmv (1 mm). Consequently, rates of carbonate dissolution measured under elevated pCO2 were 48% higher than under ambient pCO2 (0.46 kg CaCO3 dissolved m−2 a−1 versus 0.31 kg m−2 a−1). Thus, biogenic dissolution of carbonates by euendoliths in coral reefs may be a dominant mechanism of carbonate dissolution in a more acidic ocean.
Toward a consistency cross‐check of eddy covariance flux–based and biometric estimates of ecosystem carbon balance
Authors: Luyssaert S. , Reichstein M. , Schulze E.‐D. , Janssens I. A. , Law B. E. , Papale D. , Dragoni D. , Goulden M. L. , Granier A. , Kutsch W. L. , Linder S. , Matteucci G. , Moors E. , Munger J. W. , Pilegaard K. , Saunders M. , Falge E. M.
Published: July 2009

Quantification of an ecosystem's carbon balance and its components is pivotal for understanding both ecosystem functioning and global cycling. Several methods are being applied in parallel to estimate the different components of the CO2 balance. However, different methods are subject to different sources of error. Therefore, it is necessary that site level component estimates are cross‐checked against each other before being reported. Here we present a two‐step approach for testing the accuracy and consistency of eddy covariance–based gross primary production (GPP) and ecosystem respiration (Re) estimates with biometric measurements of net primary production (NPP), autotrophic (Ra) and heterotrophic (Rh) respiration. The test starts with closing the CO2 balance to account for reasonable errors in each of the component fluxes. Failure to do so within the constraints will classify the flux estimates on the site level as inconsistent. If the CO2 balance can be closed, the test continues by comparing the closed site level Ra/GPP with the Rh/GPP ratio. The consistency of these ratios is then judged against expert knowledge. Flux estimates of sites that pass both steps are considered consistent. An inconsistent ratio is not necessarily incorrect but provides a signal for careful data screening that may require further analysis to identify the possible biological reasons of the unexpected ratios. We reviewed the literature and found 16 sites, out of a total of 529 research forest sites, that met the data requirements for the consistency test. Thirteen of these sites passed both steps of the consistency cross‐check. Subsequently, flux ratios (NPP/GPP, Rh/NPP, Rh/Re, and Re/GPP) were calculated for the consistent sites. Similar ratios were observed at sites which lacked information to check consistency, indicating that the flux data that are currently used for validating models and testing ecological hypotheses are largely consistent across a wide range of site productivities. Confidence in the output of flux networks could be further enhanced if the required fluxes are independently estimated at all sites for multiple years and harmonized methods are used.
Asymmetric shear flow effects on magnetic field configuration within oppositely directed solar wind reconnection exhausts
Authors: Eriksson S. , Gosling J. T. , Phan T. D. , Blush L. M. , Simunac K. D. C. , Krauss‐Varban D. , Szabo A. , Luhmann J. G. , Russell C. T. , Galvin A. B. , Acuña M. H.
Published: July 2009

We present observations of the nearly oppositely directed solar wind reconnection jets from the same reconnection X line that swept by the Wind and STEREO‐A spacecraft on 11 March 2007. The event was characterized by an external plasma density asymmetry and a jet‐aligned shear flow across the exhausts. A well‐defined pair of asymmetric current sheets bounded both outflow regions. The observed current sheet asymmetries and differences in the magnitude of the antiparallel magnetic field components within the two exhausts were consistent with the sense of the shear flow and the predictions from two‐dimensional MHD simulations of reconnection outflows for the Earth's asymmetric flank magnetopause.
Chalk‐Ex—Fate of CaCO3 particles in the mixed layer: Evolution of patch optical properties
Authors: Balch W. M. , Plueddeman A. J. , Bowler B. C. , Drapeau D. T.
Published: July 2009

The fate of particles in the mixed layer is of great relevance to the global carbon cycle as well as to the propagation of light in the sea. We conducted four manipulative field experiments called “Chalk‐Ex” in which known quantities of uniform, calcium carbonate particles were injected into the surface mixed layer. Since the production term for these patches was known to high precision, the experimental design allowed us to focus on terms associated with particle loss. The mass of chalk in the patches was evaluated using the well‐calibrated light‐scattering properties of the chalk plus measurements from a variety of optical measurements and platforms. Patches were surveyed with a temporal resolution of hours over spatial scales of tens of kilometers. Our results demonstrated exponential loss of the chalk particles with time from the patches. There was little evidence for rapid sinking of the chalk. Instead, horizontal eddy diffusion appeared to be the major factor affecting the dispersion of the chalk to concentrations below the limits of detection. There was unequivocal evidence of subduction of the chalk along isopycnals and subsequent formation of thin layers. Shear dispersion is the most likely mechanism to explain these results. Calculations of horizontal eddy diffusivity were consistent with other mixed layer patch experiments. Our results provide insight into the importance of physics in the formation of subsurface particle maxima in the sea, as well as the importance of rapid coccolith production and critical patch size for maintenance of natural coccolithophore blooms in nature.
Coupled core‐mantle thermal evolution of early Mars
Authors: Ke Y. , Solomatov V. S.
Published: July 2009

Several arguments point out that at the end of planetary accretion, the core of Mars was likely to be much hotter than its mantle, resulting in the formation of a completely or partially molten thermal boundary layer at the base of the mantle. Here we address the following questions: How did the superheated core cool and what role did it play in the early mantle dynamics of Mars? We divide the coupled core‐mantle evolution of early Mars into two stages. During the first stage, vigorous convection within the molten boundary layer removes the heat from the core so that the boundary layer expands up. As the boundary layer gets thicker, the temperature of the layer decreases. Eventually, the temperature of the molten boundary layer drops down to the temperature for the rheological transition (melt fraction ∼40%) within 100 years. This stage is described by a parameterized convection approach. The second stage is modeled in spherical shell geometry using the fully three‐dimensional finite element code CitcomS. A single plume (“superplume”) forms by the instability of the thermal boundary layer. The superplume stage lasts much longer, on the scale of millions to hundreds of millions of years, depending on the mantle viscosity. During both stages of evolution the heat flux can easily satisfy the requirements for the dynamo.
Shape optimization of the total scattering cross section for cylindrical scatterers
Authors: Jacobsson Per , Rylander Thomas
Published: July 2009

We propose and test a gradient‐based shape optimization algorithm for the total scattering cross section of infinitely long cylinders, by means of changing the shape of the cylinder's cross section. On the basis of the optical theorem, we derive sensitivity expressions for both dielectric and metal cylinders given an incident plane wave, where the wave vector is perpendicular to the cylinder axis. Both the transverse electric (TE) case and the transverse magnetic case are considered. The sensitivity expressions are based on the continuum form of Maxwell's equations, and they provide the sensitivity with respect to an arbitrary number of shape parameters in terms of the field solution of the original scattering problem and an adjoint scattering problem. These results are used to construct a gradient‐based optimization algorithm that we exploit for the reduction of the total scattering cross section in the TE case for metal cylinders, e.g., struts used in reflector antennas. We present optimized cross sections that are oblong in the direction of the incident wave vector, and some of these designs feature corrugations that are parallel to the cylinder axis. We show designs with asymmetric cross sections that yield a low monostatic scattering cross section for certain directions in combination with a low total scattering cross section, which can be used to reduce the noise temperature contributions from the upper strut in an inverted Y tripod reflector antenna.
Real‐time specification of HF propagation support based on a global assimilative model of the ionosphere
Authors: McNamara Leo F. , Baker Craig R. , Borer William S.
Published: July 2009

An HF propagation program, HFNowcast, has been developed that takes advantage of the availability of a real‐time global model of the ionosphere to specify in real time the range of frequencies that would be supported on a given HF communications circuit. HFNowcast determines the range of frequency support for a specified circuit, from the lowest usable F layer frequency (FLUF) to the highest (FMUF), together with the E layer ELUF and EMUF. The lack of real‐time observations of HF absorption and HF noise at the receiver means that it is not possible to provide real‐time specifications of the signal‐to‐noise ratio (SNR), the key parameter for HF communications. The global model (developed by Utah State University (USU)) includes particle E precipitation at high dip latitudes during the night, which often precludes the determination of foF2 and M(3000)F2 and thus the simple determination of propagation support in those regions. The FMUF is therefore derived by first calculating the vertical incidence ionogram at the control point(s) and then transforming that ionogram to the oblique incidence (OI) ionogram for the given circuit/hop length. HFNowcast has been validated favorably against several months of oblique propagation observations on midlatitude circuits, although its day‐to‐day variability does not match the observations very well, and it tends to underestimate the FMUFs. The systematic differences between the predictions and observations can be attributed directly to limitations of the current version of the USU model of the ionosphere.
Characteristics of deep GPS signal fading due to ionospheric scintillation for aviation receiver design
Authors: Seo Jiwon , Walter Todd , Chiou Tsung‐Yu , Enge Per
Published: July 2009

Deep and frequent fading of Global Positioning System (GPS) signals caused by ionospheric scintillation is a major concern for aircraft navigation using GPS in the equatorial region during solar maximum. Aviation receivers use both code and carrier measurements to calculate position solutions. Deep signal fading can break a receiver's carrier tracking lock to a satellite channel. The lost channel cannot be used for position calculation until the receiver reacquires the channel and reestablishes tracking. A solar maximum data set analyzed in this paper demonstrates frequent deep signal fading of almost all satellites in view. This could significantly reduce the number of simultaneous tracked satellites and consequently decrease navigation availability. Forty‐five minutes of strong scintillation, which was the worst scintillation period of a 9 day campaign at Ascension Island in 2001, are analyzed in this paper. The importance of short reacquisition time of the receiver is described. In order to design an aviation receiver with short reacquisition time under frequent deep signal fading, the characteristics of signal fading should be well understood. Fading duration and the time between deep fades are two important characteristics for GPS navigation. This paper presents a fading duration model based on real scintillation data. The time between deep fades observed in this data shows very frequent deep fades which can significantly reduce benefit of carrier smoothing filters of aviation receivers.
Blocking precursors to stratospheric sudden warming events
Authors: Martius O. , Polvani L. M. , Davies H. C.
Published: July 2009

The primary causes for the onset of major, midwinter, stratospheric sudden warming events remain unclear. In this paper, we report that 25 of the 27 events objectively identified in the ERA‐40 dataset for the period 1957–2001 are preceded by blocking patterns in the troposphere. The spatial characteristics of tropospheric blocks prior to sudden warming events are strongly correlated with the type of sudden warming event that follows. Vortex displacement events are nearly always preceded by blocking over the Atlantic basin only, whereas vortex splitting events are preceded by blocking events occurring in the Pacific basin or in both basins contemporaneously. The differences in the geographical blocking distribution prior to sudden warming events are mirrored in the patterns of planetary waves that are responsible for producing events of either type. The evidence presented here, suggests that tropospheric blocking plays an important role in determining the onset and the type of warmings.
Routing of western Canadian Plains runoff during the 8.2 ka cold event
Authors: Carlson Anders E. , Clark Peter U. , Haley Brian A. , Klinkhammer Gary P.
Published: July 2009

The collapse of the Laurentide Ice Sheet over Hudson Bay ∼8.47 ka allowed the rapid drainage of glacial Lake Agassiz into the Labrador Sea, an event identified as causing a reduction in Atlantic meridional overturning circulation (AMOC) and the 8.2 ka cold event. Atmosphere‐ocean models simulations based on this forcing, however, fail to reproduce several characteristics of this event, particularly its duration. Here we use planktonic foraminifera U/Ca records to document the routing of western Canadian Plains runoff that accompanied ice‐sheet collapse. Geochemical modeling of the ∼7 nmol/mol increase in U/Ca at the opening of Hudson Bay indicates an increase in freshwater discharge of 0.13 ± 0.03 Sverdrups (106 m3 s−1) from routing, a sufficient magnitude to cause an AMOC reduction. We suggest that this routing event suppressed AMOC strength for several centuries after the drainage of Lake Agassiz, explaining multi‐centennial climate anomalies associated with the 8.2 ka cold event.
Survey of upper band chorus and ECH waves: Implications for the diffuse aurora
Authors: Meredith Nigel P. , Horne Richard B. , Thorne Richard M. , Anderson Roger R.
Published: July 2009

The origin of the diffuse aurora has been a source of controversy for many years. More recently, the question has taken a new significance in view of the associated changes in atmospheric chemistry which may affect the middle atmosphere. Here, we use CRRES data to assess the importance of upper band chorus and electron cyclotron harmonic (ECH) waves in the production of the diffuse aurora. Both wave modes increase with increasing geomagnetic activity, suggesting they are related to periods of enhanced convection and/or substorm activity. They are confined to the near‐equatorial region, which excludes the prenoon sector from the wave survey. During active conditions, intense ECH waves and upper band chorus, with amplitudes exceeding 1 mV m−1, are observed in the region 4 < L< 7 from 2100 to 0600 MLT approximately 20% and 6% of the time, respectively. This suggests that both wave modes can put electrons on strong diffusion, but only during active conditions and not at all local times. Scattering rates fall below the strong diffusion limit at other times when the wave amplitudes are weaker. Fluxes of low energy electrons (100 eV < E < 30 keV) also increase with increasing geomagnetic activity in approximately the same region of geospace as the waves, suggesting that these electrons are responsible for the generation of the waves. The patterns of the upper band chorus, ECH waves, and low‐energy electrons are similar to the global morphology of the diffuse aurora, suggesting that both wave modes play significant roles in the production of the diffuse aurora.
Structural basis for recruitment of BRCA2 by PALB2
Authors: Oliver Antony W , Swift Sally , Lord Christopher J , Ashworth Alan , Pearl Laurence H
Published: July 2009

The breast cancer 2, early onset protein (BRCA2) is central to the repair of DNA damage by homologous recombination. BRCA2 recruits the recombinase RAD51 to sites of damage, regulates its assembly into nucleoprotein filaments and thereby promotes homologous recombination. Localization of BRCA2 to nuclear foci requires its association with the partner and localizer of BRCA2 (PALB2), mutations in which are associated with cancer predisposition, as well as subtype N of Fanconi anaemia. We have determined the structure of the PALB2 carboxy‐terminal β‐propeller domain in complex with a BRCA2 peptide. The structure shows the molecular determinants of this important protein–protein interaction and explains the effects of both cancer‐associated truncating mutants in PALB2 and missense mutations in the amino‐terminal region of BRCA2.
Insights into SAGA function during gene expression
Authors: Rodríguez‐Navarro Susana
Published: July 2009

Histone modifications are a crucial source of epigenetic control. SAGA (Spt–Ada–Gcn5 acetyltransferase) is a chromatin‐modifying complex that contains two distinct enzymatic activities, Gcn5 and Ubp8, through which it acetylates and deubiquitinates histone residues, respectively, thereby enforcing a pattern of modifications that is decisive in regulating gene expression. Here, I discuss the latest contributions to understanding the roles of the SAGA complex, highlighting the characterization of the SAGA‐deubiquitination module, and emphasizing the functions newly ascribed to SAGA during transcription elongation and messenger‐RNA export. These findings suggest that a crosstalk exists between chromatin remodelling, transcription and messenger‐RNA export, which could constitute a checkpoint for accurate gene expression. I focus particularly on the new components of human SAGA, which was recently discovered and confirms the conservation of the SAGA complex throughout evolution.
On the role of vibrational anharmonicities in a two-qubit system
Authors: Gu Yingying , Babikov Dmitri
Published: July 2009

Anharmonicities of vibrational modes allow controlling state-to-state transitions and encoding quantum information bits into vibrational eigenstates. Resonances between different transitions hinder the control. In this paper all resonances that can occur in a two-qubit system are identified and studied. Computational experiments are carried out using optimal control theory and numerical propagation of vibrational wave packets. Useful insight is obtained into the mechanisms of negative effect of these resonances onto the control tasks. A set of general criteria is derived for evaluation of candidate molecules for practical realization of vibrational two-qubit system. Several simple strategies for avoiding such resonances by choosing suitable vibrational characteristics (mode frequencies and anharmonicities) are proposed.
Kinetic Monte Carlo simulations of surface growth during plasma deposition of silicon thin films
Authors: Pandey Sumeet C. , Singh Tejinder , Maroudas Dimitrios
Published: July 2009

Based on an atomically detailed surface growth model, we have performed kinetic Monte Carlo (KMC) simulations to determine the surface chemical composition of plasma deposited hydrogenated amorphous silicon (a-Si:H) thin films as a function of substrate temperature. Our surface growth kinetic model consists of a combination of various surface rate processes, including silyl (SiH3) radical chemisorption onto surface dangling bonds or insertion into Si–Si surface bonds, SiH3 physisorption, SiH3 surface diffusion, abstraction of surface H by SiH3 radicals, surface hydride dissociation reactions, as well as desorption of SiH3, SiH4, and Si2H6 species into the gas phase. Transition rates for the adsorption, surface reaction and diffusion, and desorption processes accounted for in the KMC simulations are based on first-principles density-functional-theory computations of the corresponding optimal pathways on the H-terminated Si(001)-(2×1) surface. Results are reported for two types of KMC simulations. The first employs a fully ab initio database of activation energy barriers for the surface rate processes involved and is appropriate for modeling the early stages of growth. The second uses approximate rates for all the relevant processes to account properly for the effects on the activation energetics of interactions between species adsorbed at neighboring surface sites and is appropriate to model later stages of growth toward a steady state of the surface composition. The KMC predictions for the temperature dependence of the surface concentration of SiHx(s) (x=1,2,3) species, the surface hydrogen content, and the surface dangling-bond coverage are compared to experimental measurements on a-Si:H films deposited under operating conditions for which the SiH3 radical is the dominant deposition precursor. The predictions of both KMC simulation types are consistent with the reported experimental data, which are based on in situ attenuated total reflection Fourier transformed infrared spectroscopy.
Characterizations of strip-line microwave micro atmospheric plasma and its application to neutralization
Authors: Ogata Ken , Terashima Kazuo
Published: July 2009

In this work, we estimate the plasma parameters of strip-line microwave micro atmospheric plasma (SMMAP) such as rotational temperature (Tr) both from OH and N2 rotational transitions (610–770 and 770–980 K in Ar, respectively), electron density (Ne) from Stark broadening (about 1013/cm3 in mixture of Ar and H2), and the distribution of electric field before ignition of SMMAP (5×104 V/m at maximum, and applied voltage less than 5 V). Since the lower applied voltage of SMMAP might enable us to conduct efficient processing without electrostatic damage (ESD), we applied jet-type SMMAP to neutralization. The result of neutralization showed that it can reduce surface charge from ±1000 to ±100 V for 0.2 s at 10 W with Ar gas flow within 4 V offset voltage, which provides efficient plasma processing without ESD.
Design of a high-pressure circulating pump for viscous liquids
Authors: Seifried Bernhard , Temelli Feral
Published: July 2009

The design of a reciprocating dual action piston pump capable of circulating viscous fluids at pressures of up to 34 MPa (5000 psi) and temperatures up to 80 °C is described. The piston of this pump is driven by a pair of solenoids energized alternatively by a 12 V direct current power supply controlled by an electronic controller facilitating continuously adjustable flow rates. The body of this seal-less pump is constructed using off-the-shelf parts eliminating the need for custom made parts. Both the electronic controller and the pump can be assembled relatively easily. Pump performance has been evaluated at room temperature (22 °C) and atmospheric pressure using liquids with low and moderately high viscosities, such as ethanol and corn oil, respectively. At ambient conditions, the pump delivered continuous flow of ethanol and corn oil at a flow rate of up to 170 and 17 cm3/min, respectively. For pumping viscous fluids comparable to corn oil, an optimum reciprocation frequency was ascertained to maximize flow rate. For low viscosity liquids such as ethanol, a linear relationship between the flow rate and reciprocation frequency was determined up to the maximum reciprocation frequency of the pump. Since its fabrication, the pump has been used in our laboratory for circulating triglycerides in contact with supercritical carbon dioxide at pressures of up to 25 MPa (3600 psi) and temperatures up to 70 °C on a daily basis for a total of more than 1500 h of operation functioning trouble free.
Magnetization reversal in amorphous Fe/Dy multilayers: A Monte Carlo study
Authors: Talbot Etienne , Ledue Denis , Berche Pierre-Emmanuel
Published: July 2009

The Monte Carlo method in the canonical ensemble is used to investigate magnetization reversal in multilayers of amorphous transition metal and rare earth elements. Our study is based on a model containing diluted clusters which exhibit an effective uniaxial anisotropy in competition with random magnetic anisotropy in the matrix. We simulate hysteresis loops for an abrupt profile and a diffuse one obtained from atom probe tomography analyses. Our results give evidence that the atom probe tomography profile favors perpendicular magnetic anisotropy in agreement with magnetic measurements. Moreover, the hysteresis loops calculated at several temperatures qualitatively agree with the experimental ones.
Plasma equilibrium in a magnetic field with stochastic regions
Authors: Krommes John A. , Reiman Allan H.
Published: July 2009

The nature of plasma equilibrium in a magnetic field with stochastic regions is examined. It is shown that the magnetic differential equation that determines the equilibrium Pfirsch–Schlüter currents can be cast in a form similar to various nonlinear equations for a turbulent plasma, allowing application of the mathematical methods of statistical turbulence theory. An analytically tractable model, previously studied in the context of resonance-broadening theory, is applied with particular attention paid to the periodicity constraints required in toroidal configurations. It is shown that even a very weak radial diffusion of the magnetic field lines can have a significant effect on the equilibrium in the neighborhood of the rational surfaces, strongly modifying the near-resonant Pfirsch–Schlüter currents. Implications for the numerical calculation of three-dimensional equilibria are discussed.
Soft x-ray appearance potential spectroscopy study of NiO and CoO single crystal surfaces
Authors: Fukuda Y. , Mochizuki S. , Sanada N.
Published: July 2009

Soft x-ray appearance potential spectroscopy (SXAPS) spectra of Ni 2p, Co 2p, and O 1s for NiO and CoO single crystal surfaces have been measured. Two peaks and a shoulder along with two core lines due to 2p3/2 and 2p1/2 are found for a Ni 2p raw spectrum. A Ni 2p metallic edge was observed for the NiO surface sputtered by Ar ions. An O 1s spectrum of NiO exhibits a broad peak between about 522 and 550 eV and the self-deconvoluted spectrum shows five peaks. For the Co 2p spectrum, two core lines due to 2p3/2 and 2p1/2 along with a shoulder are found and the self-deconvoluted spectrum exhibits four peaks. The broad peak is also seen between about 525 and 555 eV for the O 1s spectrum of CoO and the self-deconvoluted spectrum shows four peaks. The features of the self-deconvoluted SXAPS spectra of Ni 2p, Co 2p, and O 1s for NiO and CoO are found to resemble those of the corresponding near edge x-ray absorption fine structure (NEXAFS). The origin of the peaks is discussed to compare the present work with the previous theoretical calculations for the NEXAFS spectra.