bluuebunny/crossref_metadata_2025 huggingface dataset:
Control, collaboration, and productivity in international joint ventures: theory and evidence
Authors: Li Jing , Zhou Changhui , Zajac Edward J.
Published: April 2009

This study analyzes the following unresolved questions: In international joint ventures (IJVs) in a developing country, how could different IJV structures address control and collaboration considerations, and what is the likely effect of such different structures on IJV productivity? Theoretically, we suggest that the ambiguity surrounding these questions reflects the tendency of researchers to view control and collaboration as opposing objectives, studying one or the other; in contrast, we provide a more integrative perspective that blends the two objectives, focusing on common underlying issues relating to enhancing partner commitment, ensuring partner knowledge contributions, and reducing partner risks. We address the most salient design consideration for IJV partners, that is, IJV ownership structure, to posit that joint consideration of the control benefit of a higher foreign ownership level in IJVs and the collaboration benefit of a more balanced IJV ownership structure results in an expected inverted U‐curve relationship between foreign ownership and IJV productivity. Additionally, we posit and test how three environmental contingencies, by affecting the need for control and collaboration in IJVs, would further influence the specific shape of the inverted U‐curve relationship. We find strong support for our theory using an extensive longitudinal dataset of over 5,000 IJVs in China from 1999–2003. We discuss the value of our approach and findings both for researchers and for IJV partners seeking the dual benefits of control and collaboration. Copyright © 2009 John Wiley & Sons, Ltd.
Thermally Activated Photoluminescence in Lead Selenide Colloidal Quantum Dots
Authors: Kigel Ariel , Brumer Maya , Maikov Georgy I. , Sashchiuk Aldona , Lifshitz Efrat
Published: April 2009

The thermal activation processes in PbSe colloidal quantum dots and their influence on the ground‐state exciton emission are discussed. Activation of a dark exciton occurs at 1.4–7 K, assisted by an acoustic phonon coupling. Activation of a bright exciton occurs at 100–200 K, which appears as a sudden change in the photoluminescence band intensity, energy, and full width at half maximum. This activation overcomes the dark–bright‐state splitting, when the activation temperature increases with the decrease of the dots' size. The dark exciton lifetime is found to be ≈6–12 µs at 1.4 K, while the bright exciton lifetime at 300 K evaluated as 450 ns varies slightly with the change in the size of the dots. In addition, the emission quantum yield of these dots, measured at a variety of temperatures when dissolved in various solvents, reveals information about the influence of the environment on the recombination processes.
Activin A Is Essential for Neurogenesis Following Neurodegeneration
Authors: Abdipranoto-Cowley Andrea , Park Jin Sung , Croucher David , Daniel James , Henshall Susan , Galbraith Sally , Mervin Kyle , Vissel Bryce
Published: April 2009

It has long been proposed that excitotoxicity contributes to nerve cell death in neurodegenerative diseases. Activin A, a member of the transforming growth factor-β superfamily, is expressed by neurons following excitotoxicity. We show for the first time that this activin A expression is essential for neurogenesis to proceed following neurodegeneration. We found that intraventricular infusion of activin A increased the number of newborn neurons in the dentate gyrus, CA3, and CA1 layers of the normal adult hippocampus and also, following lipopolysaccharide administration, had a potent inhibitory effect on gliosis in vivo and on microglial proliferation in vivo and in vitro. Consistent with the role of activin A in regulating central nervous system inflammation and neurogenesis, intraventricular infusion of follistatin, an activin A antagonist, profoundly impaired neurogenesis and increased the number of microglia and reactive astrocytes following onset of kainic acid-induced neurodegeneration. These results show that inhibiting endogenous activin A is permissive for a potent underlying inflammatory response to neurodegeneration. We demonstrate that the anti-inflammatory actions of activin A account for its neurogenic effects following neurodegeneration because co-administration of nonsteroidal anti-inflammatory drugs reversed follistatin's inhibitory effects on neurogenesis in vivo. Our work indicates that activin A, perhaps working in conjunction with other transforming growth factor-β superfamily molecules, is essential for neurogenesis in the adult central nervous system following excitotoxic neurodegeneration and suggests that neurons can regulate regeneration by suppressing the inflammatory response, a finding with implications for understanding and treating acute and chronic neurodegenerative diseases.

Disclosure of potential conflicts of interest is found at the end of this article.
Maintenance of Undifferentiated State and Self-Renewal of Embryonic Neural Stem Cells by Polycomb Protein Ring1B
Authors: Román-Trufero Mónica , Méndez-Gómez Héctor R. , Pérez Claudia , Hijikata Atsushi , Fujimura Yu-ichi , Endo Takaho , Koseki Haruhiko , Vicario-Abejón Carlos , Vidal Miguel
Published: April 2009

Cell lineages generated during development and tissue maintenance are derived from self-renewing stem cells by differentiation of their committed progeny. Recent studies suggest that epigenetic mechanisms, and in particular the Polycomb group (PcG) of genes, play important roles in controlling stem cell self-renewal. Here, we address PcG regulation of stem cell self-renewal and differentiation through inactivation of Ring1B, a histone H2A E3 monoubiquitin ligase, in embryonic neural stem cells (NSCs) from the olfactory bulb of a conditional mouse mutant line. We show that neural stem/progenitor cell proliferation in vivo and in neurosphere assays is impaired, lacking Ring1B, and their self-renewal and multipotential abilities, assessed as sphere formation and differentiation from single cells, are severely affected. We also observed unscheduled neuronal, but not glial, differentiation of mutant stem/progenitor cells under proliferating conditions, an alteration enhanced in cells also lacking Ring1A, the Ring1B paralog, some of which turned into morphologically identifiable neurons. mRNA analysis of mutant cells showed upregulation of some neuronal differentiation–related transcription factors and the cell proliferation inhibitor Cdkn1a/p21, as well as downregulation of effectors of the Notch signaling pathway, a known inhibitor of neuronal differentiation of stem/progenitor cells. In addition, differentiation studies of Ring1B-deficient progenitors showed decreased oligodendrocyte formation in vitro and enhanced neurogenesis and reduced gliogenesis in vivo. These data suggest a role for Ring1B in maintenance of the undifferentiated state of embryonic neural stem/progenitor cells. They also suggest that Ring1B may modulate the differentiation potential of NSCs to neurons and glia.

Disclosure of potential conflicts of interest is found at the end of this article.
ES Cell Cycle Progression and Differentiation Require the Action of the Histone Methyltransferase Dot1L
Authors: Barry Evan R. , Krueger Winfried , Jakuba Caroline M. , Veilleux Eric , Ambrosi Dominic J. , Nelson Craig E. , Rasmussen Theodore P.
Published: April 2009

Mouse embryonic stem cells (ESCs) proliferate with rapid cell cycle kinetics but without loss of pluripotency. The histone methyltransferase Dot1L is responsible for methylation of histone H3 at lysine 79 (H3K79me). We investigated whether ESCs require Dot1L for proper stem cell behavior. ESCs deficient in Dot1L tolerate a nearly complete loss of H3K79 methylation without a substantial impact on proliferation or morphology. However, shortly after differentiation is induced, Dot1L-deficient cells cease proliferating and arrest in G2/M-phase of the cell cycle, with increased levels of aneuploidy. In addition, many aberrant mitotic spindles occur in Dot1L-deficient cells. Surprisingly, these mitotic and cell cycle defects fail to trigger apoptosis, indicating that mouse ESCs lack stringent cell cycle checkpoint control during initial stages of differentiation. Transcriptome analysis indicates that Dot1L deficiency causes the misregulation of a select set of genes, including many with known roles in cell cycle control and cellular proliferation as well as markers of endoderm differentiation. The data indicate a requirement for Dot1L function for early stages of ESC differentiation where Dot1L is necessary for faithful execution of mitosis and proper transcription of many genes throughout the genome.

Disclosure of potential conflicts of interest is found at the end of this article.
Modelling the response function of energy dispersive X‐ray spectrometers with silicon detectors
Authors: Scholze F. , Procop M.
Published: April 2009

A new, analytical description of the physical processes determining the spectral response of an energy dispersive X‐ray spectrometer with a silicon detector (Si(Li) or silicon drift detector (SDD)) is presented. The model considers the detector statistical noise, the electronic noise, the incomplete charge collection (ICC) that gives rise to the peak tailing, the escape effect, the fluorescence of the front contact or the dead layer and hot photoelectrons that cause the shelf. Only five free parameters are necessary to model the response function: the electronic noise, three parameters describing the shape of the charge collection efficiency beneath the front contact and the thickness of the detector front layer. Once the five parameters are adjusted to have agreement between a measured and a calculated response function, the response function can be calculated for any other photon energy in the range from 0.1 keV to 30 keV.

The algorithm is implemented in IDL and MATLAB and is available also as MATLAB stand‐alone program. It enables the determination of the optimum parameter set by fitting a calculated response function to a measured one for monochromatic radiation. A (m,n)‐type matrix can be calculated whereby m represents the number of channels for the response function and n the number of photon energies in the selected range. The matrix can be used to convolute a calculated spectrum for comparison with a measured one.

The calculated response functions are in agreement with the pulse height distributions measured with monochromatic synchrotron radiation in the energy range from 0.1 keV to 10 keV for three spectrometers with detector crystals different in construction. It is shown that the improved description of the detector response enables the detection of minor components of characteristic lines in fluorescence spectra, which have been attributed earlier to the detector. Copyright © 2009 John Wiley & Sons, Ltd.
Hexakis(cyanogen)zinc(II) Hexafluoridoarsenate – Synthesis, Structure and a Raman Spectroscopic Study of an Octahedral Homoleptic Cyanogen Complex
Authors: Beck Johannes , Zink Marcus
Published: April 2009

[Zn(NCCN)6][AsF6]2 (1) was prepared either by dissolving [Zn(SO2)6](Te6)[AsF6]6 in a SO2/(CN)2 mixture, or by the reaction of [Zn(AsF6)2(SO2)x] dissolved in liquid SO2 and cyanogen. The respective nickel complex [Ni(NCCN)x][AsF6]2 (2) was obtained from [Ni(AsF6)2(SO2)x] or from [Ni(SO2)6](Te6)[AsF6]6. Both, 1 and 2 were obtained in quantitative yield. Compound 1 crystallizes isopointally to [Ni(NCCH3)6][SbF6]2 (Leban 1987), [Fe(NCCH3)6][SbF6]2 (Brennessel 2001), [Zn(NCCH3)6][AsF6]2 (Passmore 2006) and contains only slightly distorted octahedral [Zn(NCCN)6]2+ cations and [AsF6]– anions. The linearity of the NC–CN molecules is preserved in the complexes. Raman spectra of 1 and 2 are presented and compared with the literature data. The almost identical spectra allow for the assumption that the nickel complex (2) is isostructural to the zinc complex (1).
Study of Natural Halloysite from the Dragon Mine, Utah (USA)
Authors: García Francisco J. , García Rodríguez Sergio , Kalytta Andreas , Reller Armin
Published: April 2009

A natural sample from the Dragon Mine, Tintic District, Silver City, Utah (USA), has been characterised. It contains a mixture of halloysite and alunite. The former shows the characteristic tubularly shaped particles while the latter is found to crystallise in platy particles. The crystal structure of halloysite is stable up to 400–450 °C and before decomposition some crystallisation is observed. Amorphisation is observed with further increasing the annealing temperature. However, the halloysite particles conserve the original morphology (tubes) up to 900 °C. The size distribution of the tubes is found to be quite broad. This is argued to be responsible for the poor measured surface area.
Synthesis of Chloroalkoxy eicosanoic and docosanoic acids from meadowfoam fatty acids by oxidation with aqueous sodium hypochlorite
Authors: Mund Melissa S. , Isbell Terry A.
Published: April 2009

Chloroalkoxy substituted C20 and C22 fatty acids can be synthesized from the unsaturated fatty acids in meadow‐foam oil by reaction of the fatty acids with primary or secondary alcohols and an aqueous sodium hypochlorite solution (commercial bleach). The reactions are conducted at room temperature for 3 h. Chlorohydroxy fatty acid derivatives are formed as by‐products owing to the presence of water in the reaction mixture. Chlorinated δ‐lactones are also produced by direct reaction of sodium hypochlorite with the Δ5 unsaturated fatty acids present in meadowfoam or by ring closure of the 6‐chloro‐5‐hydroxy fatty acids. The product yield of chloroalkoxy fatty acids is dependent on the nature and volume of the alcohol used in the reaction, as well as the concentration and pH of the sodium hypochlorite solution. Primary alcohols such as methanol and butanol produce maximal yields (50–60%) of chloroalkoxy fatty acids whereas the secondary alcohol 2‐propanol gives a 30% yield. Chloroalkoxy fatty acid yields can be increased to 75–80% by elimination of water from the reaction mixture through a procedure that partitions sodium hypochlorite from water into hexane/ethyl acetate mixtures. All of the reaction products were fully characterized using nuclear magnetic resonance and gas chromatography‐mass spectrometry.
Molecular and functional characterization of adipokinetic hormone receptor and its peptide ligands in Bombyx mori
Authors: Zhu Chenggang , Huang Haishan , Hua Rongsheng , Li Guo , Yang Dong , Luo Jiansong , Zhang Cunxin , Shi Liangen , Benovic Jeffrey L. , Zhou Naiming
Published: April 2009

Neuropeptides of the adipokinetic hormone (AKH) family are among the best studied hormone peptides, but its signaling pathways remain to be elucidated. In this study, we molecularly characterized the signaling of Bombyx AKH receptor (AKHR) and its peptide ligands in HEK293 cells. In HEK293 cells stably expressing AKHR, AKH1 stimulation not only led to a ligand concentration dependent mobilization of intracellular Ca2+ and cAMP accumulation, but also elicited transient activation of extracellular signal‐regulated kinase 1/2 (ERK1/2) pathway. We observed that AKH receptor was rapidly internalized after AKH1 stimulation. We further demonstrated that AKH2 exhibited high activities in cAMP accumulation and ERK1/2 activation on AKHR comparable to AKH1, whereas AKH3 was much less effective.
EXISTENCE AND STABILITY OF PERIODIC SOLUTIONS OF A RAYLEIGH TYPE EQUATION
Authors: WANG YONG , DAI XIAN-ZHI
Published: April 2009

In this work, we shall be concerned with the following forced Rayleigh type equation: Under certain assumptions, some criteria for guaranteeing the existence, uniqueness and asymptotic stability (in the Lyapunov sense) of periodic solutions of this equation are presented by applying the Manásevich–Mawhin continuation theorem, Floquet theory, Lyapunov stability theory and some analysis techniques. Moreover, an example is provided to demonstrate the applications of our results.
Subject-verb order in spoken Arabic: Morpholexical and event-based factors
Authors: Owens Jonathan , Dodsworth Robin , Rockwood Trent
Published: April 2009

This article explores the relationship between the global functions of variable subject-verb order and morpholexical class of subjects in the spoken Arabic of the Arabian peninsula. Using corpus-based methods, it is shown that lexical class—pronoun, pronominal, noun—definiteness, and the discourse-defined lexical specificity of a noun all correlate significantly with subject-verb or verb-subject word order. The global function of the two orders is explored using an array of measures to show that verb-subject order prototypically presents events, while subject-verb signals available referentiality. Using the quantitatively based study of Anthony Naro and Sebastiao Votre ([1999]. Discourse motivations for linguistic regularities: Verb/subject order in spoken Brazilian Portuguese.Probus11:75–100.) on Brazilian Portuguese as a point of comparison, a typological framework is developed for understanding languages with variable subject-verb order.
Universal and dialect-specific pathways of acquisition: Caregivers, children, and t/d deletion
Authors: Smith Jennifer , Durham Mercedes , Fortune Liane
Published: April 2009

T/d deletion is one of the most widely studied variables in sociolinguistic research, and findings demonstrate universal morphological and phonological constraints across a range of dialects. Research into the acquisition of this variable suggests that articulatory constraints are learned first, followed by grammatical, and finally stylistic and social constraints. Dialect-specific constraints are also found, implicating the caregiver in the process of acquisition. In this article, we contribute to this research on the acquisition of t/d through the examination of the speech of preschool children in interaction with their primary caregivers in a community in Scotland. Our results mirror previous results on how and when particular constraints are acquired, providing further evidence for universal order of acquisition of this form. We also demonstrate dialect-specific constraints on use that can be mapped directly to caregiver speech. This provides additional evidence on how variable forms are transmitted from parent to child in these early stages.
Neuentwicklung und Validierung eines szenariobasierten Verfahrens zur Erfassung der Neigung zu sexueller Aggression
Authors: Eyssel Friederike , Bohner Gerd , Süssenbach Philipp , Schreiber Paul
Published: April 2009

Zusammenfassung. Die Vergewaltigungsneigung (VN) wird oft mittels szenariobasierter Verfahren (SBV) erfasst, bei denen Befragte angeben, ob sie ebenso gehandelt hätten wie ein Protagonist, der sexuell gewalttätiges Verhalten zeigt. Die vorliegende Arbeit stellt die Weiterentwicklung eines SBV vor, mit dem sich eine generelle Neigung zu sexueller Aggression erfassen lässt. Männliche Studierende (N = 100) bearbeiteten sowohl Gewaltszenarien als auch Fragebogenskalen zur Konstruktvalidierung. Das neue Verfahren korrelierte hypothesengemäß hoch positiv mit einem etablierten SBV, wies jedoch einen höheren Mittelwert und eine weniger schiefe Verteilung auf. Es war unabhängig von sozialer Erwünschtheit und korrelierte positiv mit Vergewaltigungsmythenakzeptanz, feindseligem Sexismus und selbstberichteter sexueller Aggression. Auch die Ergebnisse einer zweiten Studie (N = 60) bestätigen die Konstruktvalidität des neuen SBV.
Wohlbefindensforschung im Kindes- und Jugendalter
Authors: Nitzko Sina , Seiffge-Krenke Inge
Published: April 2009

Zusammenfassung. In diesem Beitrag werden einführend die Konstrukte subjektives Wohlbefinden und gesundheitsbezogene Lebensqualität näher beleuchtet. Des Weiteren wird ein Überblick über Korrelate des Wohlbefindens gegeben. Unter Berücksichtigung der Entwicklungsdynamik sowie von Alters- und Geschlechtsunterschieden wird die Bedeutung sozialer Beziehungen für Wohlbefinden bzw. Wohlbefindensbeeinträchtigungen aufgezeigt. Thematisiert werden zudem Zusammenhänge zwischen dem sich entwickelnden Körperkonzept und dem Wohlbefinden. Auffällig ist die gesteigerte Unzufriedenheit mit Gewicht und Figur, die sich bei weiblichen Heranwachsenden zeigt. Auch im Zusammenhang mit Risikoverhaltensweisen wie Alkohol- und Nikotinkonsum, die gehäuft im Jugendalter in Erscheinung treten, werden Konsequenzen für das Wohlbefinden aufgezeigt. Abschließend werden entwicklungsbezogene Prinzipien vorgestellt, welche bezüglich der Erarbeitung von Präventions- und Gesundheitsförderungsmaßnahmen in Kindheit und Jugend Berücksichtigung finden sollten.
Developments in hydrometric network design: A review
Authors: Mishra Ashok K. , Coulibaly Paulin
Published: April 2009

Hydrometric network design for surface water monitoring is employed to address a wide range of environmental and water resources problems. Historical overview of hydrometric network design is provided along with a discussion on new developments and challenges in the design of optimal hydrometric networks. This review starts with precise examples of decline in hydrometric network density, then highlights the increasing requirement of optimal network design in a context of climate and land use changes. An extensive survey of methodological development in hydrometric network design is provided along with discussion on the issue of uncertainty in hydrometric network design and the evolution in data collection techniques and technology. Finally, some conclusions are drawn on the future of hydrometric network design.
Numerically reproduced internal wave spectra in the deep ocean
Authors: Sugiyama Yoshifumi , Niwa Yoshihiro , Hibiya Toshiyuki
Published: April 2009

A vertically two‐dimensional internal wave field is forced equally at the near‐inertial frequency and the semidiurnal tidal frequency both at the lowest vertical wavenumber. These correspond to wind forcing and internal tide forcing, the main energy sources for the internal wave field. After 5 years of spin‐up, a quasi‐stationary internal wave field with characteristics of the Garrett‐Munk‐like spectrum is successfully reproduced. Furthermore, we carry out additional experiments by changing the strength of the semidiurnal tidal forcing relative to the near‐inertial forcing. It is demonstrated that the Garrett‐Munk‐like spectrum is created and maintained only when energy is supplied both from the near‐inertial forcing and the semidiurnal tidal forcing. So long as both energy sources are available, nonlinear interactions among internal waves occur such that the resulting internal wave spectrum becomes close to the Garrett‐Munk‐like spectrum irrespective of the ratio of the near‐inertial forcing to the semidiurnal tidal forcing.
Dipolarization fronts as a signature of transient reconnection in the magnetotail
Authors: Sitnov M. I. , Swisdak M. , Divin A. V.
Published: April 2009

Dipolarization fronts (DFs), characterized by a strong and steep increase of the tail magnetic field component Bz normal to the neutral plane and preceded by a much less negative dip of Bz, are reported in many observations of bursty bulk flows and substorm activations throughout the whole Earth's magnetotail. It is shown that similar structures appear in full‐particle simulations with open boundaries in a transient regime before the steady reconnection in the original Harris current sheet driven out of the equilibrium by the initial X‐line perturbation is established. Being secondary reconnection structures propagating with the Alfvén speed, DFs are different from the magnetic field pileup regions reported in earlier simulations with closed boundaries. They also differ from the secondary plasmoids with bipolar Bz changes reported in earlier fluid simulations and particle simulations with open boundaries. In spite of their transient nature, DFs are found to form when the force balance is already restored in the system, which justifies their interpretation as a nonlinear stage of the tearing instability developing in two magnetotail‐like structures on the left and on the right of the initial central X‐line. Both electrons and ions are magnetized at the front of the dipolarization wave. In contrast, in its trail, ions are unmagnetized and move slower compared to the E × B drift, whereas electrons either follow that drift being completely magnetized or move faster, forming super‐Alfvénic jets. In spite of the different motions of electrons and ions, the growth of the front is not accompanied by the corresponding growth of the electrostatic field and the energy dissipation in fronts is dominated by ions.
Oxygenated fraction and mass of organic aerosol from direct emission and atmospheric processing measured on the R/V Ronald Brown during TEXAQS/GoMACCS 2006
Authors: Russell L. M. , Takahama S. , Liu S. , Hawkins L. N. , Covert D. S. , Quinn P. K. , Bates T. S.
Published: April 2009

Submicron particles collected on Teflon filters aboard the R/V Ronald Brown during the Texas Air Quality Study and Gulf of Mexico Atmospheric Composition and Climate Study (TexAQS/GoMACCS) 2006 in and around the port of Houston, Texas, were measured by Fourier transform infrared (FTIR) and X‐ray fluorescence for organic functional groups and elemental composition. Organic mass (OM) concentrations (1–25 μg m−3) for ambient particle samples measured by FTIR showed good agreement with measurements made with an aerosol mass spectrometer. The fractions of organic mass identified as alkane and carboxylic acid groups were 47% and 32%, respectively. Three different types of air masses were identified on the basis of the air mass origin and the radon concentration, with significantly higher carboxylic acid group mass fractions in air masses from the north (35%) than the south (29%) or Gulf of Mexico (26%). Positive matrix factorization analysis attributed carboxylic acid fractions of 30–35% to factors with mild or strong correlations (r > 0.5) to elemental signatures of oil combustion and 9–24% to wood smoke, indicating that part of the carboxylic acid fraction of OM was formed by the same sources that controlled the metal emissions, namely the oil and wood combustion activities. The implication is that a substantial part of the measured carboxylic acid contribution was formed independently of traditionally “secondary” processes, which would be affected by atmospheric (both photochemical and meteorological) conditions and other emission sources. The carboxylic acid group fractions in the Gulf of Mexico and south air masses (GAM and SAM, respectively) were largely oil combustion emissions from ships as well as background marine sources, with only limited recent land influences (based on radon concentrations). Alcohol groups accounted for 14% of OM (mostly associated with oil combustion emissions and background sources), and amine groups accounted for 4% of OM in all air masses. Organosulfate groups were found in GAM and SAM, accounting for 1% and 3% of OM, respectively. Two thirds of the OM and oxygen‐to‐carbon (O/C) measured could be attributed to oil and wood combustion sources on the basis of mild or strong correlations to coemitted, nonvolatile trace metals, with the remaining one third being associated with atmospherically processed organic aerosol. The cloud condensation nuclei (CCN) fraction (normalized by total condensation nuclei) had weak correlations to the alcohol and amine group fractions and mild correlation with O/C, also varying inversely with alkane group fraction. The chemical components that influenced f(RH) were sulfate, organic, and nitrate fraction, but this contrast is consistent with the size‐distribution dependence of CCN counters and nephelometers.
Combining site and regional flood information using a Bayesian Monte Carlo approach
Authors: Micevski Tom , Kuczera George
Published: April 2009

Regression‐based methods are widely used in flood regionalization. Since the generalized least squares (GLS) regression model properly accounts for both model and sampling errors, realistic estimates of uncertainty can be obtained. This study presents a general Bayesian approach for inferring the GLS regional regression model and for combining with any available site information to obtain the most accurate flood quantiles. A robust block Metropolis scheme is developed to sample the posterior distribution of the GLS regression model parameters. A particular feature of the sampler is the use of a uniform proposal for the regional model error variance to avoid convergence difficulties. A simple but general procedure, based on importance sampling, is developed to combine any kind of site information with regional information. The benefit of this approach is that all available information is fully exploited, and uncertainty is rigorously quantified as well as being minimized. Two case studies are presented. A synthetic case study illustrates the complex nature of the posterior distribution for the regional model error variance with its shape dependent on how much sampling error dominates the total error in the regional GLS model. A second case study involving 24 sites from the east coast of Australia is presented for the log Pearson III model. It demonstrates the significant benefit of combining site and regional information and the quantification of uncertainty.
Control of the activity of WW‐HECT domain E3 ubiquitin ligases by NDFIP proteins
Authors: Mund Thomas , Pelham Hugh R B
Published: April 2009

HECT domain E3 ubiquitin ligases of the NEDD4 family control many cellular processes, but their regulation is poorly understood. They contain multiple WW domains that recognize PY elements. Here, we show that the small PY‐containing membrane proteins, NDFIP1 and NDFIP2 (NEDD4 family‐interacting proteins), activate the catalytic activity of ITCH and of several other HECT ligases by binding to them. This releases them from an autoinhibitory intramolecular interaction, which seems to be characteristic of these enzymes. Activation of ITCH requires multiple PY–WW interactions, but little else. Binding of NDFIP proteins is highly dynamic, potentially allowing activated ligases to access other PY‐containing substrates. In agreement with this, NDFIP proteins promote ubiquitination in vivo both of Jun proteins, which have a PY motif, and of endophilin, which does not.
RNA‐directed DNA methylation requires an AGO4‐interacting member of the SPT5 elongation factor family
Authors: Bies‐Etheve Natacha , Pontier Dominique , Lahmy Sylvie , Picart Claire , Vega Danielle , Cooke Richard , Lagrange Thierry
Published: April 2009

Recent studies have identified a conserved WG/GW‐containing motif, known as the Argonaute (AGO) hook, which is involved in the recruitment of AGOs to distinct components of the eukaryotic RNA silencing pathways. By using this motif as a model to detect new components in plant RNA silencing pathways, we identified SPT5‐like, a plant‐specific AGO4‐interacting member of the nuclear SPT5 (Suppressor of Ty insertion 5) RNA polymerase (RNAP) elongation factor family that is characterized by the presence of a carboxy‐terminal extension with more than 40 WG/GW motifs. Knockout SPT5‐like mutants show a decrease in the accumulation of several 24‐nt RNAs and hypomethylation at different loci revealing an implication in RNA‐directed DNA methylation (RdDM). Here, we propose that SPT5‐like emerged in plants as a facultative RNAP elongation factor. Its plant‐specific origin and role in RdDM might reflect functional interactions with plant‐specific RNA Pols required for RdDM.
Synthesis and characterization of metastable nanocrystalline cobalt
Authors: Osorio-Cantillo C. , Perales-Perez O.
Published: April 2009

Applications of elemental cobalt are consequence of its phase-dependent magnetic properties; the anisotropic high-coercivity hcp-Co phase is preferred for permanent magnet applications, while the more symmetric low coercivity fcc- and pseudocubic ε-Co can be used in soft magnetic applications involving power electronics and magnetic write heads. The present work addresses the synthesis and characterization of nanocrystalline cobalt particles produced through a modified polyol-based approach conducive to the formation of fcc-, hcp-, or ε-Co phases. Metastable ε-Co and hcp-Co were exclusively formed in the presence of trimethylene glycol. In turn, fcc-Co or mixture of fcc/hcp-Co phases were produced in tetraethylene glycol. The average crystallite size in all cases ranged between 10 and 13 nm. Magnetic measurements confirmed the strong influence of synthesis conditions on crystal structure and hence on magnetic properties of nanocrystalline cobalt. The coercivity of the products varied from 338 to 550 Oe depending on the presence of the different cobalt structures.
Issues on the pulse-width dependence and the shape of acoustic radiation induced static displacement pulses in solids
Authors: Narasimha Karthik Thimmavajjula , Kannan Elankumaran , Balasubramaniam Krishnan
Published: April 2009

Recent experimental results showing the pulse width independence and the flat topped shape of static displacement generated during finite amplitude sinusoidal ultrasonic tone burst propagation in solids and the contradicting previous results reported in the literature are considered. The pulse width independence is analytically confirmed and the flat topped shape is explained by considering the progressive spatial and time domain shapes of the static strain and displacement pulses. A numerical simulation of the finite amplitude longitudinal ultrasonic wave propagation in solids has been performed to further verify the pulse width independence of the static displacement pulse.
Raman analysis of longitudinal optical phonon-plasmon coupled modes of aligned ZnO nanorods
Authors: Cheng An-Jen , Tzeng Yonhua , Xu Hui , Alur Siddharth , Wang Yaqi , Park Minseo , Wu Tsung-hsueh , Shannon Curtis , Kim Dong-Joo , Wang Dake
Published: April 2009

The electronic properties of vertically aligned ZnO nanorods have been investigated using micro-Raman spectroscopy. The concentration and mobility of the charge carriers were determined via Raman line shape analysis using longitudinal-optical-phonon-plasmon coupled mode. The local laser heating and the stress effects have been considered when analyzing the Raman spectra. The mobility and carrier concentration of the aligned ZnO nanorods are 84.8cm2∕Vs and 3.8×1017cm−3, respectively. As a comparison, the mobility and carrier concentration of the undoped bulk ZnO were also obtained from the Raman line shape analysis. The mobility of the aligned ZnO nanorods is about 20% lower than that of the undoped bulk ZnO, which can be attributed to enhanced surface scattering due to the reduction in dimension.
Nonlinear Landau damping of transverse electromagnetic waves in dusty plasmas
Authors: Tsintsadze N. L. , Chaudhary Rozina , Shah H. A. , Murtaza G.
Published: April 2009

High-frequency transverse electromagnetic waves in a collisionless isotropic dusty plasma damp via nonlinear Landau damping. Taking into account the latter we have obtained a generalized set of Zakharov equations with local and nonlocal terms. Then from this coupled set of Zakharov equations a kinetic nonlinear Schrödinger equation with local and nonlocal nonlinearities is derived for special cases. It is shown that the modulation of the amplitude of the electromagnetic waves leads to the modulation instability through the nonlinear Landau damping term. The maximum growth rate is obtained for the special case when the group velocity of electromagnetic waves is close to the dust acoustic velocity.
Ponderomotive acceleration of electrons by a laser pulse in magnetized plasma
Authors: Sharma Anamika , Tripathi V. K.
Published: April 2009

Electron acceleration by a circularly polarized Gaussian laser pulse in magnetized plasma is investigated in the limit of frozen refractive index. The electron acceleration depends on the ratio of laser frequency to electron cyclotron frequency, amplitude of the laser pulse and plasma density. Near Doppler shifted cyclotron resonance the electron acquires maximum energy. In this scheme, 0.10 MeV electrons can be effectively accelerated to 1–100 MeV using moderate intensity laser pulse.
High performance diffuse reflectance circular dichroism spectrophotometer
Authors: Harada Takunori , Miyoshi Yuichi , Kuroda Reiko
Published: April 2009

A new dual-purpose transmittance circular dichroism (CD) and diffuse reflectance CD (DRCD) universal chiroptical spectrophotometer (UCS-3, J-800KCMFII) was successfully developed to have the capability of measuring DRCD spectra down to 190 nm with high efficiency, based on UCS-2: J-800KCMF. Optical components newly used in UCS-3 are the integrating sphere of optimum size and material to achieve high performance particularly in the shorter wavelength region, a baffle installed to reduce the first specular reflection signals, and a condenser lens to increase light intensity per area for small samples. As a result, UCS-3 has become a very powerful instrument to measure DRCD spectra of powdered samples in situ, with approximately 20 times sensitivity of existing UCS-2. We could show that to achieve similar quality DRCD spectra, only 50 μg of (S)-(+)-1,1′-binaphthyl-2,2′-diyl hydrogen phosphate is required on UCS-3, as compared with 1.12 mg for UCS-2.
An investigation of some effects of drifts and magnetic field direction in the scrape-off layer and divertor of tokamak plasmas
Authors: Stacey W. M.
Published: April 2009

Various effects of particle drifts in the scrape-off layer (SOL) and divertor of tokamaks have been calculated. The predictions are consistent with several experimentally observed phenomena, e.g., the double reversal of parallel ion velocity in the SOL and the enhanced core penetration of argon injected into the divertor when the grad-B ion drift is into, rather than away from, the divertor. Other interesting phenomena, such as the structure of the parallel current flowing in the SOL and the reversal of the sign of the electrostatic potential in the SOL when the toroidal field direction is reversed, are also predicted.
Al doped graphene: A promising material for hydrogen storage at room temperature
Authors: Ao Z. M. , Jiang Q. , Zhang R. Q. , Tan T. T. , Li S.
Published: April 2009

A promising material for hydrogen storage at room temperature–Al doped graphene is proposed theoretically by using density functional theory calculation. Hydrogen storage capacity of 5.13 wt % is predicted at T=300 K and P=0.1 GPa with an adsorption energy Eb=−0.260 eV/H2. This is close to the target specified by U.S. Department of Energy with a storage capacity of 6 wt % and a binding energy of −0.2 to −0.4 eV/H2 at ambient temperature and modest pressure for commercial applications. It is believed that the doped Al alters the electronic structures of both C and H2. The bands of H2 overlapping with those of Al and C simultaneously are the underlying mechanism of hydrogen storage capacity enhancement.
Reversal magnetoresistance effect in ferromagnet/superconductor/ferromagnet/antiferromagnet heterostructure
Authors: Peng Lin , Cai Chuanbing , Chen Changzhao , Fan Feng , Wang Xiaoqi , Liu Zhiyong
Published: April 2009

The oxide heterostructure consisting of La0.7Sr0.3MnO3/YBa2Cu3O7-δ/La0.7Sr0.3MnO3/La0.33Ca0.67MnO3 is fabricated by using the technique of pulsed laser deposition. The magnetoresistance (MR) for the system is investigated in the region of mixed vortex state near the onset temperature of superconducting transition. The present experimental results indicate a reversal variation in MR that is observed with increasing temperature in the system, implying the competition between a positive MR of YBa2Cu3O7-δ and a negative MR of La0.7Sr0.3MnO3. Furthermore, our analysis further suggests that the large MR peaks are mainly caused by spin-dependent interface scattering, which depends on the relative orientation of magnetization in two ferromagnetic layers. And it is proved that the superconductivity is an essential factor for the large positive MR in the artificial heterostructure system.
Quantum well intermixing of a quantum well structure grown on an InAsP metamorphic pseudosubstrate on InP
Authors: Hulko O. , Thompson D. A. , Robinson B. J. , Simmons J. G.
Published: April 2009

InGaAsP quantum well (QW) structures, with ∼1% compressive strain, have been grown on an InAs0.21P0.79 metamorphic substrate layer (MSL) deposited on an InP substrate. For comparison, a similar QW structure is grown directly on InP. A consequence of growth on the MSL is to move the QW and barrier compositions outside the spinodal isotherm resulting in a significant reduction in phase separation. This is shown to increase the photoluminescence wavelength and improve its quality in terms of linewidth and intensity. Thermally induced QW intermixing (QWI) has also been carried out on these structures both with and without a low-temperature InP capping layer. The defects present in the underlying metamorphic buffer layers are shown to have no effect on the QWI process. However, the samples with the MSL are shown to exhibit more intermixing either due to a higher diffusion or greater P–As exchange probability in the different composition QW and barrier layers compared to the QW structure grown without the MSL, and possibly influenced by the large reduction in phase separation.
Spin-resolved photoemission of a ferromagnetic Mn5Ge3(0001) epilayer on Ge(111)
Authors: Dedkov Yu. S. , Holder M. , Mayer G. , Fonin M. , Preobrajenski A. B.
Published: April 2009

Here we present a study of the electronic structure of epitaxial ferromagnetic Mn5Ge3(0001) films on Ge(111) by means of x-ray absorption spectroscopy, x-ray photoelectron spectroscopy, and spin-resolved photoelectron spectroscopy. Spin-polarization (P) value of +(15±5)% at the Fermi energy (EF) is measured with a photon energy of hν=21.2 eV. Our findings are in contrast to recent band structure calculations, predicting P=−41% at EF for the ferromagnetic bulk Mn5Ge3.
Reformulation of microscopic balance equations for multiscale materials modeling
Authors: Chen Youping
Published: April 2009

In this paper we present a new formalism that analytically links atomic variables to continuously distributed local properties and that leads to a concurrent two-level representation of balance laws for atomistic systems with general lattice structure. The new component of this formulation is an explicit decomposition of associated fluxes in multiatomic lattices into components representing the distortions of lattice cells and the rearrangement of atoms within the lattice cells. New formulation of balance laws is obtained in a form that is suitable for a direct atomistic analysis at fine scale to a continuum analysis in coarse scales. The results of this work will provide a new continuum field representation of classical N-body dynamics that can fully reproduce phonon dispersion relations of multiatomic crystalline materials and will enable coupled atomistic and continuum simulations within a single theoretical framework.
Ultrafast relaxation and optical saturation of intraband absorption of GaN/AlN quantum dots
Authors: Nevou L. , Mangeney J. , Tchernycheva M. , Julien F. H. , Guillot F. , Monroy E.
Published: April 2009

We report on the measurements of ultrafast relaxation and absorption saturation of the s-pz intraband transition at λ=1.55 μm in GaN/AlN quantum dot superlattice. The recovery time of the intraband absorption is assessed using degenerate pump-probe experiments at room temperature. Measurements reveal a multiexponential decay of the differential transmission with an ultrafast (∼160 fs) and a slower (∼1.5 ps) time constant attributed to the excited state lifetime and to the thermalization time in the ground state, respectively. The saturation intensity of the intraband absorption (<140 MW/cm2) is one order of magnitude smaller than the value measured in nitride quantum wells.
The effect of dielectric friction on the rate of charge separation in type II ZnSe/CdS semiconductor nanorods
Authors: Hewa-Kasakarage Nishshanka N. , El-Khoury Patrick Z. , Schmall Nickolas , Kirsanova Maria , Nemchinov Alexander , Tarnovsky Alexander N. , Bezryadin Alexey , Zamkov Mikhail
Published: April 2009

The effect of dielectric friction on the rate of charge separation in type II ZnSe/CdS semiconductor nanorods has been investigated using picosecond transient absorption spectroscopy. The spatial separation of an excited electron-hole pair was estimated from the redshift in band edge absorption corresponding to the decrease in the exciton binding energy. The present study identifies a considerable effect of the solvent polarity on the rate of charge separation in semiconductor heterostructures, which should be taken into account when selecting nanorod caging media, such as solvents or polymer matrices.
Soil responses to fire in Mediterranean forest landscapes in relation to the previous stage of land abandonment
Authors: Llovet Joan , Ruiz-Valera Manuel , Josa Ramon , Vallejo V. Ramon
Published: April 2009

The current paper presents a study on the interaction between land abandonment and soil responses to fire in old agricultural terraced landscapes. The study area, located near the Guadalest reservoir (E Spain), was partially affected by a forest fire in August 1998. We monitored burned and unburned areas as well as two pre-fire stand ages since agricultural abandonment: 8–15 years (dry grassland with young Pinus halepensis) and >35 years (mature pine forest). We analysed soil surface structure, water repellency and infiltrability, and we monitored plant response, runoff and sediment production for a period of 7 years after the fire. Aggregate stability increased with both time-since-abandonment and fire. Water repellency increased with land abandonment but was not affected by fire. Unburned erosion plots produced almost no runoff, even during heavy rainstorms. Fire scarcely modified runoff and erosion rates in recently abandoned terraces. A dry period following fire restricted plant recovery in burned pine forest. Burned forest plots registered runoff and sediment yields one to four orders of magnitude higher than unburned forest plots. In burned pine forest, the maximum sediment production was registered 3 years after the fire, when rainstorms took place and plant cover was still low. Old agricultural terraces colonised by pines were found to be both vulnerable to degradation as a consequence of fire and highly dependent on post-fire rain for their recovery.
Public perspectives of fire, fuels and the Forest Service in the Great Lakes Region: a survey of citizen - agency communication and trust
Authors: Shindler Bruce A. , Toman Eric , McCaffrey Sarah M.
Published: April 2009

Relative to the western United States, where fire and fuel management programs have received greater emphasis, few community-based studies have focused on the Great Lakes region. The present paper describes public opinion research from counties surrounding National Forests in Wisconsin, Minnesota and Michigan. Survey data address citizen perspectives on (1) fuel reduction practices and related risks, (2) confidence in the US Forest Service to effectively implement treatments, and (3) interactions between the agency and forest communities. Substantial support for prescribed fire and thinning treatments is evident, with few participants believing these practices should not be considered or are unnecessary. However, ratings of agency actions were weak at all three study sites; in particular, there is some skepticism that managers can safely implement prescribed fire programs. Overall, Minnesota residents had fewer concerns whereas Michigan respondents were more cautious. These results are discussed and compared with findings from the western US.