bluuebunny/crossref_metadata_2025 huggingface dataset:
The Economic and Potential Years of Life Lost from Suicide in Taiwan, 1997–2007
Authors: Law Chi-Kin , Yip Paul S. F. , Chen Ying-Yeh
Published: May 2011

Background: Taiwan has experienced a marked increase in the suicide rate in the last decade. However, the socioeconomic burden and impact to the community has not been adequately assessed. Aims: This study aimed to estimate the social and economic burden of premature mortality from suicide in Taiwan in 1997–2007. Methods: The suicide rate, potential years of life lost (PYLL), and present value of lifetime earnings (PVLE) by sex and age groups in 1997–2007 were calculated. The contribution of each suicide method to PYLL for each age group was also assessed. Results: Using the PYLL calculations, suicide had become the third leading cause of death in Taiwan in 2007, compared to its ninth position in terms of absolute numbers. Furthermore, the PYLL was associated with an estimated NTD (New Taiwan Dollars) 32.5 billion of lost earnings in 2007. The increase in PYLL and PVLE from suicide was highest in middle-aged men (aged 25–59 years). Charcoal burning suicide accounted for most of the increase in PYLL in the middle-aged group in the past decade. Conclusions: The loss of life in middle-aged males contributes disproportionately to the social and economic burden of suicide in Taiwan. Suicide intervention effort should target this high-risk population.
Detailed DEM analysis of a rockslide scar to characterize the basal sliding surface of active rockslides
Authors: Oppikofer Thierry , Jaboyedoff Michel , Pedrazzini Andrea , Derron Marc‐Henri , Blikra Lars Harald
Published: May 2011

The basal sliding surfaces in large rockslides are often composed of several surfaces and possess a complex geometry. The exact morphology and location in three dimensions of the sliding surface remains generally unknown, in spite of extensive field and subsurface investigations, such as those at the Åknes rockslide (western Norway). This knowledge is crucial for volume estimations, failure mechanisms, and numerical slope stability modeling. This paper focuses on the geomorphologic characterization of the basal sliding surface of a postglacial rockslide scar in the vicinity of Åknes. This scar displays a stepped basal sliding surface formed by dip slopes of the gneiss foliation linked together by steeply dipping fractures. A detailed characterization of the rockslide scar by means of high‐resolution digital elevation models permits statistical parameters of dip angle, spacing, persistence, and roughness of foliation surfaces and step fractures to be obtained. The characteristics are used for stochastic simulations of stepped basal sliding surfaces at the Åknes rockslide. These findings are compared with previous models based on geophysical investigations. This study discusses the investigation of rockslide scars and rock outcrops for a better understanding of potential rockslides. This work identifies possible basal sliding surface locations, which is a valuable input for volume estimates, design and location of monitoring instrumentation, and numerical slope stability modeling.
Evaluating changes and estimating seasonal precipitation for the Colorado River Basin using a stochastic nonparametric disaggregation technique
Authors: Kalra Ajay , Ahmad Sajjad
Published: May 2011

Precipitation estimation is an important and challenging task in hydrology because of high variability and changing climate. This research involves (1) analyzing changes (trend and step) in seasonal precipitation and (2) estimating seasonal precipitation by disaggregating water year precipitation using a k‐nearest neighbor (KNN) nonparametric technique for 29 climate divisions encompassing the Colorado River Basin. Water year precipitation data from 1900 to 2008 are subdivided into four seasons (i.e., autumn, winter, spring, and summer). Two statistical tests (Mann‐Kendall and Spearman's rho) are used to evaluate trend changes, and a rank sum test is used to identify the step change in seasonal precipitation. The results indicate a decrease in the upper basin and an increase in the lower basin winter precipitation resulting from an abrupt step change. The effect of El Niño–Southern Oscillations in relation to seasonal precipitation is also evaluated by removing the historic El Niño events. Decreasing winter and spring season precipitation trends for the upper basin are not linked to El Niño. Corroborating evidence of changes in seasonal precipitation is established by analyzing the trends in snow telemetry (SNOTEL) data and streamflow at the Lees Ferry gauge. KNN disaggregation results indicate satisfactory seasonal precipitation estimates during winter and spring seasons compared to autumn and summer seasons, and the superiority of KNN results is established when compared with the first‐order periodic autoregressive parametric approach. The analysis of seasonal changes and estimates of precipitation can help water managers to better manage the water resources in the Colorado River Basin.
Mixed methods for fitting the GEV distribution
Authors: Ailliot Pierre , Thompson Craig , Thomson Peter
Published: May 2011

The generalized extreme‐value (GEV) distribution is widely used for modeling and characterizing extremes. It is a flexible three‐parameter distribution that combines three extreme‐value distributions within a single framework: the Gumbel, Frechet, and Weibull. Common methods used for estimating the GEV parameters are the method of maximum likelihood and the method of L‐moments. This paper generalizes the mixed maximum likelihood and L‐moments GEV estimation procedures proposed by Morrison and Smith (2002) and derives the asymptotic properties of the resulting estimators. Analytic expressions are given for the asymptotic covariance matrices in a number of important cases, including the estimators proposed by Morrison and Smith (2002). These expressions are verified by simulation and the efficiencies of the various estimators established. The asymptotic results are compared to those obtained for small to medium‐size samples by simulation with the estimated parameters and quantiles assessed for accuracy and bias. Using simplified constraints for the support of the log likelihood, computational strategies and graphical tools are developed which lead to computationally efficient, numerically robust, estimation procedures suitable for automatic batch processing of many data sets. The methods are illustrated by application to annual maximum rainfall data at a large number of New Zealand locations. For Wellington, 24 h annual maximum rainfall over the period 1940–1999 is also considered within each phase of the Interdecadal Pacific Oscillation.
Time variant cross correlation to assess residence time of water and implication for hydraulics of a sink‐rise karst system
Authors: Bailly‐Comte V. , Martin Jonathan B. , Screaton E. J.
Published: May 2011

Transport rates and residence time in the subsurface are critical parameters for understanding water‐rock interactions for efficient contaminant remediation. This paper presents a methodology for assessing flow and transit time of water through hydrological systems, with specific applications to karst systems and implication for hydraulics of a conduit system surrounded by a porous and permeable intergranular matrix. A time variant cross‐correlation function analysis is applied to bivariate time series that characterize mass transfer, assuming a stationary system using sliding windows of various sizes. We apply the method to 1 year long temperature records in the Santa Fe River (north central Florida) measured at (1) the River Sink, where all the incoming surface water drains into a sinkhole, (2) Sweetwater Lake, where the river resurges into a 500 m long karst window, and (3) the River Rise, where the water discharges from a first‐magnitude karst spring. Results are compared with those obtained using specific conductivity. Estimated residence time ranges from less than 1 day during floods to more than 15 days during base flow within the 8000 m flow path between the River Sink and the River Rise. Results are used to characterize geometric, hydraulic, and hydrodynamic properties of this sink‐rise system with strong matrix‐conduit interactions. These properties are critical to the chemical and physical behavior of surface water–groundwater mixing. Our results also have direct implications for sampling strategies and hydrograph separation of many karst systems with different degrees and types of matrix porosity and permeability.
Wavelet‐based multiresolution analysis of Wivenhoe Dam water temperatures
Authors: Percival D. B. , Lennox S. M. , Wang Y.‐G. , Darnell R. E.
Published: May 2011

Water temperature measurements from Wivenhoe Dam offer a unique opportunity for studying fluctuations of temperatures in a subtropical dam as a function of time and depth. Cursory examination of the data indicate a complicated structure across both time and depth. We propose simplifying the task of describing these data by breaking the time series at each depth into physically meaningful components that individually capture daily, subannual, and annual (DSA) variations. Precise definitions for each component are formulated in terms of a wavelet‐based multiresolution analysis. The DSA components are approximately pairwise uncorrelated within a given depth and between different depths. They also satisfy an additive property in that their sum is exactly equal to the original time series. Each component is based upon a set of coefficients that decomposes the sample variance of each time series exactly across time and that can be used to study both time‐varying variances of water temperature at each depth and time‐varying correlations between temperatures at different depths. Each DSA component is amenable for studying a certain aspect of the relationship between the series at different depths. The daily component in general is weakly correlated between depths, including those that are adjacent to one another. The subannual component quantifies seasonal effects and in particular isolates phenomena associated with the thermocline, thus simplifying its study across time. The annual component can be used for a trend analysis. The descriptive analysis provided by the DSA decomposition is a useful precursor to a more formal statistical analysis.
Estimation of evaporation and sensible heat flux from open water using a large‐aperture scintillometer
Authors: McJannet D. L. , Cook F. J. , McGloin R. P. , McGowan H. A. , Burn S.
Published: May 2011

The use of scintillometers to determine sensible and latent heat flux is becoming increasingly common because of their ability to quantify convective fluxes over distances of hundreds of meters to several kilometers. The majority of investigations using scintillometry have focused on processes above land surfaces, but here we propose a new methodology for obtaining sensible and latent heat fluxes from a scintillometer deployed over open water. This methodology has been tested by comparison with eddy covariance measurements and through comparison with alternative scintillometer calculation approaches that are commonly used in the literature. The methodology is based on linearization of the Bowen ratio, which is a common assumption in models such as Penman's model and its derivatives. Comparison of latent heat flux estimates from the eddy covariance system and the scintillometer showed excellent agreement across a range of weather conditions and flux rates, giving a high level of confidence in scintillometry‐derived latent heat fluxes. The proposed approach produced better estimates than other scintillometry calculation methods because of the reliance of alternative methods on measurements of water temperature or water body heat storage, which are both notoriously hard to quantify. The proposed methodology requires less instrumentation than alternative scintillometer calculation approaches, and the spatial scales of required measurements are arguably more compatible. In addition to scintillometer measurements of the structure parameter of the refractive index of air, the only measurements required are atmospheric pressure, air temperature, humidity, and wind speed at one height over the water body.
E‐cadherin is crucial for embryonic stem cell pluripotency and can replace OCT4 during somatic cell reprogramming
Authors: Redmer Torben , Diecke Sebastian , Grigoryan Tamara , Quiroga‐Negreira Angel , Birchmeier Walter , Besser Daniel
Published: May 2011

We report new functions of the cell‐adhesion molecule E‐cadherin in murine pluripotent cells. E‐cadherin is highly expressed in mouse embryonic stem cells, and interference with E‐cadherin causes differentiation. During cellular reprogramming of mouse fibroblasts by OCT4, SOX2, KLF4 and c‐MYC, fully reprogrammed cells were exclusively observed in the E‐cadherin‐positive cell population and could not be obtained in the absence of E‐cadherin. Moreover, reprogrammed cells could be established by viral E‐cadherin in the absence of exogenous OCT4. Thus, reprogramming requires spatial cues that cross‐talk with essential transcription factors. The cell‐adhesion molecule E‐cadherin has important functions in pluripotency and reprogramming.
Novel role for the Lu/BCAM–spectrin interaction in actin cytoskeleton reorganization
Authors: Collec Emmanuel , Lecomte Marie-Christine , El Nemer Wassim , Colin Yves , Le Van Kim Caroline
Published: May 2011

Lu/BCAM (Lutheran/basal cell-adhesion molecule) is a laminin 511/521 receptor expressed in erythroid and endothelial cells, and in epithelial tissues. The RK573–574 (Arg573-Lys574) motif of the Lu/BCAM cytoplasmic domain interacts with αI-spectrin, the main component of the membrane skeleton in red blood cells. In the present paper we report that Lu/BCAM binds to the non-erythroid αII-spectrin via the RK573–574 motif. Alanine substitution of this motif abolished the Lu/BCAM–spectrin interaction, enhanced the half-life of Lu/BCAM at the MDCK (Madin–Darby canine kidney) cell surface, and increased Lu/BCAM-mediated cell adhesion and spreading on laminin 511/521. We have shown that the Lu/BCAM–spectrin interaction mediated actin reorganization during cell adhesion and spreading on laminin 511/521. This interaction was involved in a laminin 511/521-to-actin signalling pathway leading to stress fibre formation. This skeletal rearrangement was associated with an activation of the small GTP-binding protein RhoA, which depended on the integrity of the Lu/BCAM laminin 511/521-binding site. It also required a Lu/BCAM–αII-spectrin interaction, since its disruption decreased stress fibre formation and RhoA activation. We conclude that the Lu/BCAM–spectrin interaction is required for stress fibre formation during cell spreading on laminin 511/521, and that spectrin acts as a signal relay between laminin 511/521 and actin that is involved in actin dynamics.
Effects of DNA and protein size on substrate cleavage by human tyrosyl-DNA phosphodiesterase 1
Authors: Interthal Heidrun , Champoux James J.
Published: May 2011

TDP (tyrosyl-DNA phosphodiesterase) 1 catalyses the hydrolysis of phosphodiester linkages between a DNA 3′ phosphate and a tyrosine residue as well as a variety of other DNA 3′ substituents, and has been implicated in the repair of covalent complexes involving eukaryotic type IB topoisomerases. To better understand the substrate features that are recognized by TDP1, the size of either the DNA or protein component of the substrate was varied. Competition experiments and gel-shift analyses comparing a series of substrates with DNA lengths increasing from 6 to 28 nt indicated that, contrary to predictions based on the crystal structure of the protein, the apparent affinity for the substrate increased as the DNA length was increased over the entire range tested. It has been found previously that a substrate containing the full-length native form of human topoisomerase I protein is not cleaved by TDP1. Protein–oligonucleotide complexes containing either a 53 or 108 amino acid topoisomerase I-derived peptide were efficiently cleaved by TDP1, but similar to the full-length protein, a substrate containing a 333 amino acid topoisomerase I fragment was resistant to cleavage. Consistent with these results, evidence is presented that processing by the proteasome is required for TDP1 cleavage in vivo.
ATR signalling: more than meeting at the fork
Authors: Nam Edward A. , Cortez David
Published: May 2011

Preservation of genome integrity via the DNA-damage response is critical to prevent disease. ATR (ataxia telangiectasia mutated- and Rad3-related) is essential for life and functions as a master regulator of the DNA-damage response, especially during DNA replication. ATR controls and co-ordinates DNA replication origin firing, replication fork stability, cell cycle checkpoints and DNA repair. Since its identification 15 years ago, a model of ATR activation and signalling has emerged that involves localization to sites of DNA damage and activation through protein–protein interactions. Recent research has added an increasingly detailed understanding of the canonical ATR pathway, and an appreciation that the canonical model does not fully capture the complexity of ATR regulation. In the present article, we review the ATR signalling process, focusing on mechanistic findings garnered from the identification of new ATR-interacting proteins and substrates. We discuss how to incorporate these new insights into a model of ATR regulation and point out the significant gaps in our understanding of this essential genome-maintenance pathway.
Super toxins from a super bug: structure and function of Clostridium difficile toxins
Authors: Davies Abigail H. , Roberts April K. , Shone Clifford C. , Acharya K. Ravi
Published: May 2011

Clostridium difficile, a highly infectious bacterium, is the leading cause of antibiotic-associated pseudomembranous colitis. In 2009, the number of death certificates mentioning C. difficile infection in the U.K. was estimated at 3933 with 44% of certificates recording infection as the underlying cause of death. A number of virulence factors facilitate its pathogenicity, among which are two potent exotoxins; Toxins A and B. Both are large monoglucosyltransferases that catalyse the glucosylation, and hence inactivation, of Rho-GTPases (small regulatory proteins of the eukaryote actin cell cytoskeleton), leading to disorganization of the cytoskeleton and cell death. The roles of Toxins A and B in the context of C. difficile infection is unknown. In addition to these exotoxins, some strains of C. difficile produce an unrelated ADP-ribosylating binary toxin. This toxin consists of two independently produced components: an enzymatic component (CDTa) and the other, the transport component (CDTb) which facilitates translocation of CDTa into target cells. CDTa irreversibly ADP-ribosylates G-actin in target cells, which disrupts the F-actin:G-actin equilibrium leading to cell rounding and cell death. In the present review we provide a summary of the current structural understanding of these toxins and discuss how it may be used to identify potential targets for specific drug design.
Glucose-6-phosphate dehydrogenase–6-phosphogluconolactonase: a unique bifunctional enzyme from Plasmodium falciparum
Authors: Jortzik Esther , Mailu Boniface M. , Preuss Janina , Fischer Marina , Bode Lars , Rahlfs Stefan , Becker Katja
Published: May 2011

The survival of malaria parasites in human RBCs (red blood cells) depends on the pentose phosphate pathway, both in Plasmodium falciparum and its human host. G6PD (glucose-6-phosphate dehydrogenase) deficiency, the most common human enzyme deficiency, leads to a lack of NADPH in erythrocytes, and protects from malaria. In P. falciparum, G6PD is combined with the second enzyme of the pentose phosphate pathway to create a unique bifunctional enzyme named GluPho (glucose-6-phosphate dehydrogenase–6-phosphogluconolactonase). In the present paper, we report for the first time the cloning, heterologous overexpression, purification and kinetic characterization of both enzymatic activities of full-length PfGluPho (P. falciparum GluPho), and demonstrate striking structural and functional differences with the human enzymes. Detailed kinetic analyses indicate that PfGluPho functions on the basis of a rapid equilibrium random Bi Bi mechanism, where the binding of the second substrate depends on the first substrate. We furthermore show that PfGluPho is inhibited by S-glutathionylation. The availability of recombinant PfGluPho and the major differences to hG6PD (human G6PD) facilitate studies on PfGluPho as an excellent drug target candidate in the search for new antimalarial drugs.
A cryptic promoter in the LEE1 regulatory region of enterohaemorrhagic Escherichia coli: promoter specificity in AT-rich gene regulatory regions
Authors: Islam Md. Shahidul , Pallen Mark J. , Busby Stephen J. W.
Published: May 2011

Transcription of the LEE1 operon in the locus of enterocyte effacement of enterohaemorrhagic Escherichia coli is due to the P1 promoter. Mutational and biochemical analyses reveal the existence of an overlapping promoter, designated P1A, which can drive transcript initiation 10 bp upstream of the P1 promoter transcript start point. Because of the overlap between P1 and P1A, P1A activity is unmasked only when the P1 promoter is inactivated by mutation. In the present paper, we report that mutation of the P1–10 element is less effective in unmasking P1A promoter activity than mutation of the P1–35 element. This suggests that the P1 promoter −35 element, which corresponds to the consensus, can sequester RNA polymerase even when P1 is inactive and thereby prevent RNA polymerase from serving the P1A promoter. We propose that such promoter elements may play a role in enforcing specificity in bacterial regulatory regions that contain alternative possible promoters.
Remote hindlimb preconditioning and hepatoprotection: NO-table strides against liver ischaemia/reperfusion injury
Authors: Teoh Narci C.
Published: May 2011

Hepatic IR (ischaemia/reperfusion) injury is an important clinical problem complicating liver surgery and transplantation. IPC (ischaemic preconditioning) is a strategy whereby brief episodes of IR in an organ can induce an adaptive response to protect against subsequent prolonged IR injury. However, trauma to vessels supplying the target organ is unavoidable using the technique of direct IPC. One amenable strategy would be to apply the protective preconditioning stimulus to an organ distant or remote from the target organ of interest, a technique known as RIPC (remote IPC). In the present issue of Clinical Science, Abu-Amara and co-workers utilize hindlimb RIPC as a novel therapeutic strategy against liver IR injury and investigate the mechanistic contribution of NO to hepatoprotection by administering C-PTIO [2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide potassium salt], an NO scavenger. Their experiments set the stage for more definitive studies to demonstrate a discernible benefit for the utility of RIPC in liver surgery and transplantation.
Enhanced diamagnetic perturbations and electric currents observed downstream of the high power helicon
Authors: Roberson B. Race , Winglee Robert , Prager James
Published: May 2011

The high power helicon (HPH) is capable of producing a high density plasma (1017−1018 m−3) and directed ion energies greater than 20 eV that continue to increase tens of centimeters downstream of the thruster. In order to understand the coupling mechanism between the helicon antenna and the plasma outside the immediate source region, measurements were made in the plasma plume downstream from the thruster of the propagating wave magnetic field and the perturbation of the axial bulk field using a type ‘R’ helicon antenna. This magnetic field perturbation (ΔB) peaks at more than 15 G in strength downstream of the plasma source, and is 3–5 times larger than those previously reported from HPH. Taking the curl of this measured magnetic perturbation and assuming azimuthal symmetry suggests that this magnetic field is generated by a (predominantly) azimuthal current ring with a current density on the order of tens of kA m−2. At this current density the diamagnetic field is intense enough to cancel out the B0 axial magnetic field near the source region. The presence of the diamagnetic current is important as it demonstrates modification of the vacuum fields well beyond the source region and signifies the presence of a high density, collimated plasma stream. This diamagnetic current also modifies the propagation of the helicon wave, which facilitates a better understanding of coupling between the helicon wave and the resultant plasma acceleration.
Relativistic effects on the nuclear magnetic resonance shielding of FX (X = F, Cl, Br, I, and At) molecular systems
Authors: Gómez Sergio S. , Aucar Gustavo A.
Published: May 2011

We present ab inito full four-component and spin-free calculations of the NMR shielding parameter, σ, in the FX (X = F, Cl, Br, I and At) molecular systems. A different expression that overcomes the traditional non-relativistic (NR) approximation used to calculate the relationship between spin-rotation constants and the paramagnetic terms of σp are given. Large deviations from NR results are obtained for σ(X; X = I and At) and for σ(F; FAt). \documentclass[12pt]{minimal}\begin{document}$\sigma _{\parallel }^p$\end{document}σ∥p(I; FI) is zero within the NR approach but −447.4 parts per million from our calculations. The electronic origin of relativistic corrections are analyzed. All passive SO contributions are obtained as a difference between full four-component calculations and spin-free ones. Considering relativistic effects on the anisotropy, we obtain a deviation of 10% for I and 25% for At. \documentclass[12pt]{minimal}\begin{document}$\sigma _{\parallel }^{SO}$\end{document}σ∥SO(X) is always negative and \documentclass[12pt]{minimal}\begin{document}$\sigma _{\parallel }^{SF}$\end{document}σ∥SF(X) is always positive; the passive SO becomes larger than the SF one for X = Br, I, and At. Both \documentclass[12pt]{minimal}\begin{document}$\sigma _{\parallel }^{SO}$\end{document}σ∥SO(X) and \documentclass[12pt]{minimal}\begin{document}$\sigma _{\perp }^{SO}$\end{document}σ⊥SO(X) have a functional dependence such as a \documentclass[12pt]{minimal}\begin{document}${\rm Z}_X^b$\end{document}ZXb being the exponent 3.5 and 3.65, respectively. The passive SO contribution to the anisotropy has a similar functional dependence with an exponent of 3.60, meaning that its perpendicular component is larger than its corresponding parallel component.
Strong mobility degradation in ideal graphene nanoribbons due to phonon scattering
Authors: Betti A. , Fiori G. , Iannaccone G.
Published: May 2011

We investigate the low-field phonon-limited mobility in armchair graphene nanoribbons (GNRs) using full-band electron and phonon dispersion relations. We show that lateral confinement suppresses the intrinsic mobility of GNRs to values typical of common bulk semiconductors, and very far from the impressive experiments on two-dimensional graphene. 1 nm-wide suspended GNRs exhibit a mobility close to 500 cm2/V s at room temperature, whereas 1 nm-wide GNRs deposited on HfO2 exhibit a mobility of 60 cm2/V s due to surface phonons. We also show the occurrence of polaron formation, leading to band gap renormalization of ≈118 meV for 1-nm-wide armchair GNRs.
A local noncircular equilibrium model and its application to residual zonal flow calculations
Authors: Zhou Deng , Yu Weihong
Published: May 2011

A local up-down symmetric tokamak equilibrium model is proposed. The model, with constant plasma shape parameters, is a special case of the more general Miller’s local model [R. L. Miller et al., Phys. Plasmas 5, 973 (1998)]. Correspondingly, the equilibrium is determined only by a given reference flux surface, the local safety factor, the local pressure profile, and the profile of local toroidal field function. Although it is not complete, the model is particularly suitable for analytically investigating the effect of plasma shape factors on the radially localized plasma modes, like reversed shear Alfvenic eigenmodes, ballooning mode, etc. As an example of the application, the residual zonal flow in a shaped plasma is evaluated, and the result is in qualitative agreement with the previous investigations.
On plasma detachment in propulsive magnetic nozzles
Authors: Ahedo Eduardo , Merino Mario
Published: May 2011

Three detachment mechanisms proposed in the literature (via resistivity, via electron inertia, and via induced magnetic field) are analyzed with an axisymmetric model of the expansion of a small-beta, weakly collisional, near-sonic plasma in a diverging magnetic nozzle. The model assumes cold, partially magnetized ions and hot, isothermal, fully magnetized electrons. Different conditions of the plasma beam at the nozzle throat are considered. A central feature is that a positive thrust gain in the nozzle of a plasma thruster is intimately related to the azimuthal current in the plasma being diamagnetic. Then, and contrary to existing expectations, the three aforementioned detachment mechanisms are divergent, that is, the plasma beam diverges outwards of the guide nozzle, further hindering its axial expansion and the thrust efficiency. The rate of divergent detachment is quantified for the small-parameter range of the three mechanisms. Alternative mechanisms for a convergent detachment of the plasma beam are suggested.
Variational symplectic algorithm for guiding center dynamics in the inner magnetosphere
Authors: Li Jinxing , Qin Hong , Pu Zuyin , Xie Lun , Fu Suiyan
Published: May 2011

Charged particle dynamics in magnetosphere has temporal and spatial multiscale; therefore, numerical accuracy over a long integration time is required. A variational symplectic integrator (VSI) [H. Qin and X. Guan, Phys. Rev. Lett. 100, 035006 (2008) and H. Qin, X. Guan, and W. M. Tang, Phys. Plasmas 16, 042510 (2009)] for the guiding-center motion of charged particles in general magnetic field is applied to study the dynamics of charged particles in magnetosphere. Instead of discretizing the differential equations of the guiding-center motion, the action of the guiding-center motion is discretized and minimized to obtain the iteration rules for advancing the dynamics. The VSI conserves exactly a discrete Lagrangian symplectic structure and has better numerical properties over a long integration time, compared with standard integrators, such as the standard and adaptive fourth order Runge-Kutta (RK4) methods. Applying the VSI method to guiding-center dynamics in the inner magnetosphere, we can accurately calculate the particles’orbits for an arbitrary long simulating time with good conservation property. When a time-independent convection and corotation electric field is considered, the VSI method can give the accurate single particle orbit, while the RK4 method gives an incorrect orbit due to its intrinsic error accumulation over a long integrating time.
Fluctuation driven transport and stationary profiles
Authors: Kesner J. , Garnier D. T. , Mauel M. E.
Published: May 2011

Transport equations for particles and energy can be derived when the fluctuations conserve adiabatic invariants. The transport equations determine both stationary density and pressure profiles and the direction of the turbulence-driven fluxes which can be inward or outward. An inward turbulent pinch is predicted which creates stationary profiles and reverses direction depending on the density and temperature gradients. The transport fluxes are independent of the underlying drive that leads to plasma turbulence. For low frequency turbulence, the formulation remains correct when the collisional time scale is faster than the confinement time scale.
Steady solutions of inertial film flow along strongly undulated substrates
Authors: Nguyen P.-K. , Bontozoglou V.
Published: May 2011

Steady flow of a liquid film along sinusoidal, steeply corrugated walls is investigated by finite-element simulation of the 2D Navier-Stokes equations. Resonance between the wall and capillary-gravity waves travelling against the flow defines a critical Re and separates the flow into a subcritical and a supercritical regime. Steep corrugations trigger extensive flow separation in both regimes. However, the separation characteristics—most notably the limiting behavior for very thin and very thick films—vary because of the different significance of capillary forces in the two regimes. For very steep corrugations, two intersecting solution branches co-exist. The present computational predictions are compared favorably with independent experimental observations.
Velocity field analysis in an experimental cavitating mixing layer
Authors: Aeschlimann Vincent , Barre Stéphane , Djeridi Henda
Published: May 2011

The purpose of this experimental study was to analyze a two-dimensional cavitating shear layer. The global aim of this work was to improve understanding and modeling of cavitation phenomena, from a 2D turbulent shear flow to rocket engine turbopomp inducers. This 2D mixing layer flow provided us with a well documented test case to be used for comparisons between behavior with and without cavitation. Similarities and differences enabled us to characterize the effects of cavitation on flow dynamics. The experimental facility enabled us to set up a mixing layer configuration with different cavitation levels. The development of a velocity gradient was observed inside a liquid water flow using PIV–LIF (particle image velocimetry–laser induced fluorescence). Kelvin-Helmholtz instabilities developed at the interface and vaporizations and implosions of cavitating structures inside the vortices were observed. The mixing area grew linearly, showing a constant growth rate, for the range of cavitation levels studied. The spatial development of the mixing area seemed hardly to be affected by cavitation. Particularly, the self-similar behavior of the mean flow was preserved despite the presence of the vapor phase. Successive vaporizations and condensations of the fluid particles inside the turbulent area generated additional velocity fluctuations due to the strong density changes. Moreover, when cavitation developed, the Kelvin-Helmholtz vortex shape was modified, inducing a strong anisotropy (vortex distortion as ellipsoidal form) due to the vapor phase. The main results of this study clearly showed that the turbulence-cavitation relationship inside a mixing layer was not simply a change of compressibility properties of the fluid in the turbulent field, but a mutual interaction between large and small scales of the flow due to the presence of a two-phase flow.
Measurement of circular dichroism dynamics in a nanosecond temperature-jump experiment
Authors: Khuc Mai-Thu , Mendonça Lucille , Sharma Sapna , Solinas Xavier , Volk Martin , Hache François
Published: May 2011

The use of a fast temperature jump (T-jump) is a very powerful experiment aiming at studying protein denaturation dynamics. However, probing the secondary structure is a difficult challenge and rarely yields quantitative values. We present the technical implementation of far-UV circular dichroism in a nanosecond T-jump experiment and show that this experiment allows us to follow quantitatively the change in the helical fraction of a poly(glutamic acid) peptide during its thermal denaturation with 12 ns time resolution.
A proof of Clausius’ theorem for time reversible deterministic microscopic dynamics
Authors: Evans Denis J. , Williams Stephen R. , Searles Debra J.
Published: May 2011

In 1854 Clausius proved the famous theorem that bears his name by assuming the second “law” of thermodynamics. In the present paper we give a proof that requires no such assumption. Our proof rests on the laws of mechanics, a T-mixing property, an ergodic consistency condition, and on the axiom of causality. Our result relies on some recently derived theorems, such as the Evans-Searles and the Crooks fluctuation theorems and the recently discovered relaxation and dissipation theorems.
Disentangling the Mn moments on different sublattices in the half-metallic ferrimagnet Mn3−xCoxGa
Authors: Klaer P. , Jenkins C. A. , Alijani V. , Winterlik J. , Balke B. , Felser C. , Elmers H. J.
Published: May 2011

Ferrimagnetic Mn3−xCoxGa compounds have been investigated by magnetic circular dichroism in x-ray absorption (XMCD). Compounds with x>0.5 crystallize in the CuHg2Ti structure. A tetragonal distortion of the cubic structure occurs for x≤0.5. For the cubic phase, magnetometry reveals a linearly increasing magnetization of 2x Bohr magnetons per formula unit obeying the generalized Slater–Pauling rule. XMCD confirms the ferrimagnetic character with Mn atoms occupying two different sublattices with antiparallel spin orientation and different degrees of spin localization and identifies the region 0.6<x≤0.8 as most promising for a high spin polarization at the Fermi level. Individual Mn moments on inequivalent sites are compared to theoretical predictions.
A two-reflection divergent differentiating critical angle refractometer
Authors: Guo Wenping , Xia Min , Li Wei , Dai Jie , Yang Kecheng
Published: May 2011

A new critical angle refractometer (CAR) for high accuracy refractive index measurement of liquid has been developed. The instrument improves the accuracy by two reflections in an elongated parallelogram prism, and acquires the angular reflectivity without any angle scanning parts through introduction of a point source with a divergent beam and a charge coupled device. In addition, it employs a simple and robust measurement method that gets the critical angle by differentiating the angular reflectivity. Through investigating absorbing media with absorption index κ (the imaginary part of refractive index) from 0 to 10−2.1, the theoretical calculation shows that the proposed two-reflection CAR would outperform the traditional one-reflection CAR on lowering the principal error from the differentiation method and improving the ability of getting the critical angle. By testing two typical liquids–salt-water solution and milk, the preliminary experiment indicates that this two-reflection divergent differentiating critical angle refractometer is feasible and of high accuracy.
Ferromagnetic resonance of a single magnetic nanowire measured with an on-chip microwave interferometer
Authors: Zhang Hanqiao , Divan Ralu , Wang Pingshan
Published: May 2011

An on-chip microwave interferometer suitable for high-sensitivity nanoscale magnetic material characterization is proposed. The device cancels the background parasitic common mode noise automatically. The magnetization dynamics of a 240 nm wide, 5 μm long, and 70 nm thick single permalloy nanowire is investigated. Compared with a prototype device proposed previously, the proposed device has a more than 20 dB sensitivity improvement. Full wave three-dimensional simulation shows that the device has the capability of studying the fundamental physics of nanoscale magnetic devices.
Vacuum compatible sample positioning device for matrix assisted laser desorption/ionization Fourier transform ion cyclotron resonance mass spectrometry imaging
Authors: Aizikov Konstantin , Smith Donald F. , Chargin David A. , Ivanov Sergei , Lin Tzu-Yung , Heeren Ron M. A. , O’Connor Peter B.
Published: May 2011

The high mass accuracy and resolving power of Fourier transform ion cyclotron resonance mass spectrometers (FT-ICR MS) make them ideal mass detectors for mass spectrometry imaging (MSI), promising to provide unmatched molecular resolution capabilities. The intrinsic low tolerance of FT-ICR MS to RF interference, however, along with typically vertical positioning of the sample, and MSI acquisition speed requirements present numerous engineering challenges in creating robotics capable of achieving the spatial resolution to match. This work discusses a two-dimensional positioning stage designed to address these issues. The stage is capable of operating in ∼1 × 10–8 mbar vacuum. The range of motion is set to 100 mm × 100 mm to accommodate large samples, while the positioning accuracy is demonstrated to be less than 0.4 micron in both directions under vertical load over the entire range. This device was integrated into three different matrix assisted laser desorption/ionization (MALDI) FT-ICR instruments and showed no detectable RF noise. The “oversampling” MALDI-MSI experiments, under which the sample is completely ablated at each position, followed by the target movement of the distance smaller than the laser beam, conducted on the custom-built 7T FT-ICR MS demonstrate the stability and positional accuracy of the stage robotics which delivers high spatial resolution mass spectral images at a fraction of the laser spot diameter.
Very-high-strength (60-GPa) carbon nanotube fiber design based on molecular dynamics simulations
Authors: Cornwell Charles F. , Welch Charles R.
Published: May 2011

The mechanical properties of carbon nanotubes such as low density, high stiffness, and exceptional strength make them ideal candidates for reinforcement material in a wide range of high-performance composites. Molecular dynamics simulations are used to predict the tensile response of fibers composed of aligned carbon nanotubes with intermolecular bonds of interstitial carbon atoms. The effects of bond density and carbon nanotube length distribution on fiber strength and stiffness are investigated. The interstitial carbon bonds significantly increase load transfer between the carbon nanotubes over that obtained with van der Waals forces. The simulation results indicate that fibers with tensile strengths to 60 GPa could be produced by employing interstitial cross-link atoms. The elastic modulus of the fibers is also increased by the bonds.
Ab initio calculation of the potential of mean force for dissociation of aqueous Ca–Cl
Authors: Timko Jeff , De Castro Alexandra , Kuyucak Serdar
Published: May 2011

The potential of mean force for the dissociation of a Ca–Cl ion pair in water is calculated from ab initio molecular dynamics simulations. The constraint-force method is employed to enhance sampling over the entire range of the reaction coordinate (Ca–Cl distance) from 2.2 to 6.5 Å. Particular attention is paid to equilibration of the system as it is found that the potential of mean force is highly sensitive to the hydration number of the Ca2 + ion. The structure and polarization of hydration waters are examined in detail at three ion-ion separations of interest: the contact-ion position, the solvent-separated-ion position, and the transition state between them. The ab initio results are compared to the classical ones obtained using the CHARMM force field and the parameters of Dang and Smith. There are substantial differences between the polarization of hydration waters of Ca2 + and Cl− ions at all distances, which indicates that an accurate description of Ca–Cl dissociation with nonpolarizable force fields may not be feasible. The ab initio results presented here for the Ca–Cl ion pair complements our earlier results for Na–Cl, and together they provide useful benchmarks for polarizable force fields under construction.
Adiabatic quantum simulators
Authors: Biamonte J. D. , Bergholm V. , Whitfield J. D. , Fitzsimons J. , Aspuru-Guzik A.
Published: May 2011

In his famous 1981 talk, Feynman proposed that unlike classical computers, which would presumably experience an exponential slowdown when simulating quantum phenomena, a universal quantum simulator would not. An ideal quantum simulator would be controllable, and built using existing technology. In some cases, moving away from gate-model-based implementations of quantum computing may offer a more feasible solution for particular experimental implementations. Here we consider an adiabatic quantum simulator which simulates the ground state properties of sparse Hamiltonians consisting of one- and two-local interaction terms, using sparse Hamiltonians with at most three-local interactions. Properties of such Hamiltonians can be well approximated with Hamiltonians containing only two-local terms. The register holding the simulated ground state is brought adiabatically into interaction with a probe qubit, followed by a single diabatic gate operation on the probe which then undergoes free evolution until measured. This allows one to recover e.g. the ground state energy of the Hamiltonian being simulated. Given a ground state, this scheme can be used to verify the QMA-complete problem LOCAL HAMILTONIAN, and is therefore likely more powerful than classical computing.
Hidden temporal order unveiled in stock market volatility variance
Authors: Shapira Y. , Kenett D. Y. , Raviv Ohad , Ben-Jacob E.
Published: May 2011

When analyzed by standard statistical methods, the time series of the daily return of financial indices appear to behave as Markov random series with no apparent temporal order or memory. This empirical result seems to be counter intuitive since investor are influenced by both short and long term past market behaviors. Consequently much effort has been devoted to unveil hidden temporal order in the market dynamics. Here we show that temporal order is hidden in the series of the variance of the stocks volatility. First we show that the correlation between the variances of the daily returns and means of segments of these time series is very large and thus cannot be the output of random series, unless it has some temporal order in it. Next we show that while the temporal order does not show in the series of the daily return, rather in the variation of the corresponding volatility series. More specifically, we found that the behavior of the shuffled time series is equivalent to that of a random time series, while that of the original time series have large deviations from the expected random behavior, which is the result of temporal structure. We found the same generic behavior in 10 different stock markets from 7 different countries. We also present analysis of specially constructed sequences in order to better understand the origin of the observed temporal order in the market sequences. Each sequence was constructed from segments with equal number of elements taken from algebraic distributions of three different slopes.
Microwave discharge as a remote source of neutral oxygen atoms
Authors: Primc Gregor , Zaplotnik Rok , Vesel Alenka , Mozetic Miran
Published: May 2011

The late flowing afterglow of an oxygen plasma was used as a remote source of neutral oxygen atoms. Plasma was created via a microwave discharge in a narrow quartz glass tube with an inner diameter of 6 mm at powers between 50 W and 300 W. The tube was connected to a wider perpendicular tube with an inner diameter of 36 mm. The density of neutral oxygen atoms was measured in the wide tube about 70 cm from the discharge using a classical nickel catalytic probe. The oxygen atom density as a function of gas pressure had a well-defined maximum. The oxygen atom density can be as large as 11 × 1020 m-3. At the lowest power tested (50 W), the maximum was obtained at a pressure of about 30 Pa. However, at higher powers, the maximum shifted to higher pressures. As a result, at 300 W the maximum appeared at 60 Pa. The results can be explained through collision phenomena in gas phase and surfaces in both discharge and flowing afterglow regions, and strong pressure gradients along the narrow tube.