bluuebunny/crossref_metadata_2025 huggingface dataset:
Clinical Issues—January 2011
Authors: Blanchard Joan
Published: December 2010

Use of indwelling urinary catheters for perioperative patients

Key words: indwelling urinary catheter, urinary tract infection, Foley catheter.

Managing an Acinetobacter baumannii outbreak

Key words: Acinetobacter baumannii, opportunistic pathogen, health care‐associated infection, colonization pressure, bloodstream infection.

Frequently asked questions about meningitis

Key words: bacterial meningitis, viral meningitis, meningococcal infection, pneumococcal polysaccharide vaccine, meningococcal polysaccharide vaccine, pneumococcal conjugate vaccine.

Implementing droplet precautions

Key words: droplet precautions, personal protective equipment.
Clinical Update: Suspension Trauma
Authors: Pasquier Mathieu , Yersin Bertrand , Vallotton Laurent , Carron Pierre-Nicolas
Published: December 2010

Objective

Suspension trauma refers to the pathophysiologic syndrome that occurs when a victim is suspended motionless in a vertical position for an extended period of time. This can occur in sports that use a harness system as well as in various occupational activities including work on high wires or helicopter rescue operations. We reviewed the scientific evidence published to date in order to improve the prevention and treatment of suspension trauma.

Methods

Medline, PreMedline, the Cochrane Library, and Google Scholar were searched for relevant information about suspension trauma.

Results

Published data describing the pathophysiology of and the therapeutic approach to suspension trauma are sparse and consist mainly of case reports and a limited number of human experimental prospective studies. The pathophysiology of suspension trauma is related to hypovolemia induced by reduced venous return and by vagal stimulation. It is also influenced by the type of harness used. Chest harnesses may induce severe cardiorespiratory repercussions and have the lowest motionless suspension tolerance. Symptoms of suspension trauma include presyncope and can lead to a loss of consciousness.

Conclusions

Sports enthusiasts and workers who use a body harness system should never act alone and should not use a simple chest harness. If a victim shows symptoms of presyncope or is unconscious, he should be released from suspension as soon as is safely possible. There is no clear evidence to support the idea that the return to the horizontal position may contribute to the potential risk of rescue death.
Failure of a layer of buried surface hoar
Authors: Reiweger Ingrid , Schweizer Jürg
Published: December 2010

In order to study the formation of the initial failure leading to dry‐snow slab avalanche release, we performed loading experiments in a cold laboratory with natural samples including a layer of buried surface hoar. The experimental setup was such that the layered snow samples were loaded continuously for various tilt (slope) angles; loading rates varied between 1 and 20 Pa s−1. The stress at fracture decreased with increasing loading rate and increasing slope angle, i.e., increasing shear component of the load. The latter result means that the layer was stronger in compression than in shear which is attributed to the particularly anisotropic nature of layers of buried surface hoar. Particle image velocimetry revealed that almost 90% of the sample's global deformation was concentrated in the weak layer. For avalanche release our results imply that the shear component of deformation is of particular importance for failure initiation.
Earthquakes and plastic deformation of anhydrous slab mantle in double Wadati‐Benioff zones
Authors: Reynard Bruno , Nakajima Junichi , Kawakatsu Hitoshi
Published: December 2010

Double Wadati‐Benioff seismic zones (DSZ) with two parallel planes of seismicity separated by 15–30 km are a global feature of subduction zones in the 50–200 km depth range. Upper plane seismicity is generally attributed to dehydration of the oceanic crust but the origin of the lower seismicity plane is debated. Serpentine or hydrous‐phase dehydration embrittlement is a commonly advocated mechanism that implies significant slab mantle hydration. High‐resolution seismic tomography revealed low seismic velocities in the lower seismicity plane that are better explained by seismic anisotropy of anhydrous deformed peridotites than by serpentinization. Earthquakes correlate with anisotropic planar shear zones and favor a shear instability mechanism as the cause of lower plane seismicity without requiring the presence of water in the center of subducting slabs. The contribution of the subducted lithospheric mantle to the water budget of subduction zones is thus likely limited to the first 2–3 kilometers beneath oceanic crust.
Waves at the electron plasma frequency associated with solar wind magnetic holes: STEREO/Cluster observations
Authors: Briand C. , Soucek J. , Henri P. , Mangeney A.
Published: December 2010

Magnetic depressions are common structures of the interplanetary medium. These magnetic holes can be just isolated dips of the amplitude of the field or they can be associated with discontinuities in the field orientation (tangential or rotational). Electrostatic waves at the plasma frequency (Langmuir waves) are often observed in these magnetic structures. The aim of the present paper is to provide the main characteristics of these waves and to propose a mechanism to explain their formation. The study is based on a statistical analysis of observations performed by STEREO (between March 2007 and August 2009) and Cluster (between 2002 and 2005) when each mission was in the free solar wind. Complementary information is provided by the two missions through the different instrumental configurations. We first provide new characteristics of the waves (polarization, energy, spectrum, occurrence). We then show that the occurrence of Langmuir waves activity inside a hole is closely linked to the presence of a significant electron strahl outside the hole. Finally, we propose a scenario for the generation of the Langmuir waves inside the holes.
Seismic anisotropy and mantle flow beneath northeast China inferred from regional seismic networks
Authors: Li Juan , Niu Fenglin
Published: December 2010

Northeast China is situated partly on the Sino‐Korean craton and partly on a portion of the Inner Mongolia fold belt. Characterized by widespread Cenozoic intraplate volcanism and deformation caused by multiepisode extension, northeast China is an ideal place to study the underlying physical processes of rifting and active magmatism. We measured SKS wave splitting parameters from several regional networks of broadband stations recently deployed in northeast China. We employed a multievent signal‐to‐noise ratio (SNR) weighted method and obtained measurements of splitting parameters at 108 stations. These stations cover a variety of tectonic terranes, including the Songliao basin, the Jiamusi massif, the Inner Mongolia belt and the Yanshanian orogenic belt. Overall, the observed SKS splitting times are of low amplitude (∼0.8 s), indicating that the underlying mantle experienced relatively weak deformation in this region. The observed anisotropy varies consistently from place to place and exhibits an asymmetric pattern across the Songliao basin. At the southeast edge of the Songliao basin, the fast axis aligns nicely along the NW–SE direction, whereas the axis rotates slightly to NNW toward north beneath the Jiamusi massif. At the west edge of the basin where the north‐south gravity lineament (NSGL) is located, we found significant scatter in the fast‐axis direction. At the Yanshanian orogenic belt in the southwest corner of the basin, the fast axis aligns along the EW direction. The amplitude of the splitting time appears to be positively correlated with lithospheric thickness, suggesting that lithospheric deformation is the likely cause of the observed seismic anisotropy.
Source location of the 19 February 2008 Oregon bolide using seismic networks and infrasound arrays
Authors: Walker Kristoffer T. , Hedlin Michael A. H. , de Groot‐Hedlin Catherine , Vergoz Julien , Le Pichon Alexis , Drob Douglas P.
Published: December 2010

On 19 February 2008 a bolide traveled across the sky along a southern trajectory ending in a terminal burst above Oregon. The event was well recorded by the USArray, other seismic networks, four infrasound arrays, and several video cameras. We compare the results of locating the burst using these different sensor networks. Specifically, we reverse time migrate acoustic‐to‐seismic coupled signals recorded by the USArray out to 800 km range to image the source in 2‐D space and time. We also apply a grid search over source altitude and time, minimizing the misfit between observed and predicted arrival times using 3‐D ray tracing with a high‐resolution atmospheric velocity model. Our seismic and video results suggest a point source rather than a line source associated with a hypersonic trajectory. We compare the seismic source locations to those obtained by using different combinations of observed infrasound array signal back azimuths and arrival times. We find that all locations are consistent. However, the seismic location is more accurate than the infrasound locations due to the larger number of seismic sensors, a more favorable seismic source‐receiver geometry, and shorter ranges to the seismometers. For the infrasound array locations, correcting for the wind improved the accuracy, but implementing arrival times while increasing the precision reduced the accuracy presumably due to limitations of the source location method and/or atmospheric velocity model. We show that despite known complexities associated with acoustic‐to‐seismic coupling, aboveground infrasound sources can be located with dense seismic networks with remarkably high accuracy and precision.
Recurrent frontal slicks of a coastal ocean upwelling shadow
Authors: Ryan J. P. , Fischer A. M. , Kudela R. M. , McManus M. A. , Myers J. S. , Paduan J. D. , Ruhsam C. M. , Woodson C. B. , Zhang Y.
Published: December 2010

Marine ecosystems are greatly influenced by the structure and dynamics of fronts. In coastal upwelling systems, frontogenesis occurs frequently by upwelling and transport of cold water and warming in sheltered “upwelling shadow” retention sites. Monterey Bay, in the California Current upwelling system, hosts a dynamic upwelling shadow environment. Using a decade of satellite synthetic aperture radar (SAR) observations with ancillary remote sensing and in situ data, we describe recurrent surface slicks that develop along the seaward periphery of the Monterey Bay upwelling shadow, and we examine their relationships with fronts. Slick median dimensions, 17.5 km long and 0.8 km wide, describe their elongated structure. Although the typical pattern is a single slick, multiple slicks may concurrently develop in association with different types of fronts. Repeated volume surveys through a front, underlying a slick, revealed lateral mixing and interleaving of regional water types. Velocity fields from coastal HF radar show that slicks may coincide with a variety of surface circulation patterns, that they may extend contiguously across regions having very different surface velocity, and that they may be separated from the shear front of upwelling filaments by 5–10 km. Slicks occur in all seasons and may coincide with both upwelling and downwelling wind forcing. Surfactant accumulation in small‐scale convergence zones is indicated as the primary mechanism of slick formation, not ocean current shear or small‐scale air‐sea coupling. The results of this study emphasize the role of upwelling system fronts in creating small‐scale structure and dynamics that influence plankton ecology.
Frontal dynamics in a California Current System shallow front: 2. Mesoscale vertical velocity
Authors: Pallàs‐Sanz E. , Johnston T. M. S. , Rudnick D. L.
Published: December 2010

This is the second paper investigating the three‐dimensional dynamics from two consecutive, quasi‐synoptic surveys of a shallow front in the California Current System. The mesoscale vertical velocity (w) is obtained by solving a generalized ω equation using density and horizontal velocity observations. Highly nonlinear dynamics emerge from the ageostrophic forcing terms for w in an adiabatic generalized ω equation. The two main processes driving w are (1) wind‐induced cross‐frontal ageostrophic circulation (survey 1) and (2) ageostrophic kinematic deformation during frontogenesis (surveys 1 and 2). The horizontally averaged heat fluxes are positive in the whole water column with maxima at ∼50 m, which warms (cools) the upper (lower) water column and upwells (downwells) light (dense) water. Wind‐induced currents interact with the front, cooling the upper ocean and creating a divergent potential vorticity (PV) flux at the Ekman layer base which weakens the vertical heat and PV fluxes in survey 1. Vertical velocity extrema reach ∼10 m d−1 in both surveys. A diabatic ω equation is derived, which introduces an important new idea: the relation of the frictional w with the vertical diffusivity of the differential ageostrophic vorticity. This term is not found in the quasi‐geostrophic ω equation. By including vertical mixing, ∣w∣ is enhanced by a factor of 2 in the upper ∼100 m and reduced below. This effect is pronounced when the wind blows in the direction of the frontal jet, but it is sensitive to the vertical mixing parameterization.
Keynote: A renaissance for the point mutation: from legacy data to semantic web service
Authors: Baker Christopher
Published: December 2010

Experiments that construct or discover protein point-mutations and investigate their functional consequences represent one of the cornerstones of biomedical investigation. And yet, despite the importance of these annotations, the interpretation and reuse of knowledge about their impacts remains a formidable task. This is due to a number of reasons including (i) the publishing of salient mutation impact descriptions in unstructured text, (ii) the existence of numerous boutique databases of mutation information which can have many years of latency, and (iii) errors within manually populated mutation databases. In recent years the mining of mutations from scientific documents has emerged as a promising research theme resulting in automated methods for mutation extraction and denovo database creation. While such methods have shown good performance, this alone does not suffice in seamlessly integrating mutation annotations to other biological datatypes.In this talk I demonstrate the challenges and innovations that have resulted in the deployment of semantic services that supply text-extracted mutation impact annotations on demand. These include; mutation grounding algorithms linking extracted mutations to the correct position on wild type protein sequences, the grounding of mutated protein properties to GO Molecular Function, rule based extraction of mutation impacts and impact direction, conceptualization and population of mutation impact ontology, graphical composition of SPARQL queries using mutation specific metadata, visualization of mutation impact annotations on protein structures, dynamic annotation of PubMed abstracts containing mutations mentions using the Semantic Assistant framework , and lastly SADI web service deployment facilitating queries that leverage mutation impact annotations integrated with multiple semantic web services, namely queries that select for mutations that impact specific protein properties, mutations that impact specific metabolic or signaling pathways, drugs that target mutated proteins, and literature describing mutations on proteins with a given nsSNP.
TB domain proteins: evolutionary insights into the multifaceted roles of fibrillins and LTBPs
Authors: Robertson Ian , Jensen Sacha , Handford Penny
Published: December 2010

Fibrillins and LTBPs [latent TGFβ (transforming growth factor β)-binding proteins] perform vital and complex roles in the extracellular matrix and are relevant to a wide range of human diseases. These proteins share a signature ‘eight cysteine’ or ‘TB (TGFβ-binding protein-like)’ domain that is found nowhere else in the human proteome, and which has been shown to mediate a variety of protein–protein interactions. These include covalent binding of the TGFβ propeptide, and RGD-directed interactions with a repertoire of integrins. TB domains are found interspersed with long arrays of EGF (epidermal growth factor)-like domains, which occur more widely in extracellular proteins, and also mediate binding to a large number of proteins and proteoglycans. In the present paper, newly available protein sequence information from a variety of sources is reviewed and related to published findings on the structure and function of fibrillins and LTBPs. These sequences give valuable insight into the evolution of TB domain proteins and suggest that the fibrillin domain organization emerged first, over 600 million years ago, prior to the divergence of Cnidaria and Bilateria, after which it has remained remarkably unchanged. Comparison of sequence features and domain organization in such a diverse group of organisms also provides important insights into how fibrillins and LTBPs might perform their roles in the extracellular matrix.
For a PDK1 inhibitor, the substrate matters
Authors: Knight Zachary A.
Published: December 2010

More than 20 protein kinases are directly activated by 3-phosphoinositide-dependent kinase 1 (PDK1), which is a central component of the pathways that regulate cell growth, proliferation and survival. Despite the importance of PDK1 in cell signalling, highly selective PDK1 inhibitors have not been described. In this issue of the Biochemical Journal, Dario Alessi's group and their collaborators at GlaxoSmithKline report GSK2334470, a potent and selective PDK1 inhibitor. They show that this compound blocks the phosphorylation of known PDK1 substrates, but surprisingly find that the potency and kinetics of inhibition vary for different PDK1 targets. This substrate-specific inhibition has implications for the development of PDK1 inhibitors as drugs.
Angiotensin receptor blockers and angiogenesis: clinical and experimental evidence
Authors: Willis Lauren M. , El-Remessy Azza B. , Somanath Payaningal R. , Deremer David L. , Fagan Susan C.
Published: December 2010

Angiotensin II type 1 receptor antagonists [ARBs (angiotensin receptor blockers)] are indicated for BP (blood pressure)-lowering, renal protection and cardioprotection in patients unable to tolerate ACEIs (angiotensin-converting enzyme inhibitors). A recent meta-analysis revealed an association between ARBs and tumour development, possibly due to enhancement of angiogenesis. However, published evidence is conflicting on the effects of ARBs on angiogenesis or the expansion of the existing vascular network. ARBs have been shown to exert primarily anti-angiogenic effects in basic science studies of cancer, retinopathy, peripheral artery disease and some models of cardiovascular disease. In animal and cellular models of myocardial infarction and stroke, however, ARB administration has been associated with robust increases in vascular density and improved recovery. The aim of the present review is to examine the angiogenic effects of ARBs in animal and cellular models of relevant disease states, including proposed molecular mechanisms of action of ARBs and the clinical consequences of ARB use.
Supermatrix models, loop equations, and duality
Authors: Desrosiers Patrick , Eynard Bertrand
Published: December 2010

We study integrals over Hermitian supermatrices of arbitrary size p + q, which are parametrized by an external field X and a source Y of respective sizes m + n and p + q. We show that these integrals exhibit a simple topological expansion in powers of a formal parameter ℏ, which can be identified with 1/(p − q). The loop equation and the associated spectral curve are also obtained. The solutions to the loop equation are given in terms of the symplectic invariants introduced by Eynard and Orantin [Commun. Number Theory Phys. 1, 347 (2007)]. The symmetry property of the latter objects allows us to prove a duality that relates supermatrix models in which the role of X and Y are interchanged.
Effect of low energy ion irradiation on CdTe crystals: Luminescence enhancement
Authors: Olvera J. , Martínez O. , Avella M. , Plaza J. L. , de Dios S. , Diéguez E.
Published: December 2010

In this work we show that low energy ion sputtering is a very efficient technique as a cleaning process for CdTe substrates. We demonstrate, by using several techniques like grazing-angle x-ray diffraction, cathodoluminescence, microluminescence, and micro-Raman spectroscopy that the luminescent properties of CdTe substrates can be very much increased when CdTe surfaces are irradiated with low energy Argon ions. We postulate that this enhancement is mainly due to the removal of surface damage induced by the cutting and polishing processes. The formation of a low density of nonluminescent aggregates after the sputtering process has also been observed.
Natural charge spatial separation and quantum confinement of ZnO/GaN-core/shell nanowires
Authors: Wang Zhenhai , Fan Yingcai , Zhao Mingwen
Published: December 2010

We performed density-functional calculations to investigate the electronic structure of ZnO/GaN-core/shell heterostructured nanowires (NWs) orientating along ⟨0001⟩ direction. The built-in electric field arising from the charge redistribution at the {11¯00} interfaces and the band offsets were revealed. ZnO-core/GaN-shell NWs rather than GaN-core/ZnO-shell ones were predicted to exhibit natural charge spatial separation behaviors, which are understandable in terms of an effective mass model. The effects of quantum confinement on the band gaps and band offsets were also discussed.
Comprehensive analytical model for locally contacted rear surface passivated solar cells
Authors: Wolf Andreas , Biro Daniel , Nekarda Jan , Stumpp Stefan , Kimmerle Achim , Mack Sebastian , Preu Ralf
Published: December 2010

For optimum performance of solar cells featuring a locally contacted rear surface, the metallization fraction as well as the size and distribution of the local contacts are crucial, since Ohmic and recombination losses have to be balanced. In this work we present a set of equations which enable to calculate this trade off without the need of numerical simulations. Our model combines established analytical and empirical equations to predict the energy conversion efficiency of a locally contacted device. For experimental verification, we fabricate devices from float zone silicon wafers of different resistivity using the laser fired contact technology for forming the local rear contacts. The detailed characterization of test structures enables the determination of important physical parameters, such as the surface recombination velocity at the contacted area and the spreading resistance of the contacts. Our analytical model reproduces the experimental results very well and correctly predicts the optimum contact spacing without the use of free fitting parameters. We use our model to estimate the optimum bulk resistivity for locally contacted devices fabricated from conventional Czochralski-grown silicon material. These calculations use literature values for the stable minority carrier lifetime to account for the bulk recombination caused by the formation of boron-oxygen complexes under carrier injection.
Note: Zeeman splitting measurements in a high-temperature plasma
Authors: Golingo R. P. , Shumlak U. , Den Hartog D. J.
Published: December 2010

The Zeeman effect has been used for measurement of magnetic fields in low-temperature plasma, but the diagnostic technique is difficult to implement in a high-temperature plasma. This paper describes new instrumentation and methodology for simultaneous measurement of the entire Doppler-broadened left and right circularly polarized Zeeman spectra in high-temperature plasmas. Measurements are made using spectra emitted parallel to the magnetic field by carbon impurities in high-temperature plasma. The Doppler-broadened width is much larger than the magnitude of the Zeeman splitting, thus simultaneous recording of the two circularly polarized Zeeman line profiles is key to accurate measurement of the magnetic field in the ZaP Z-pinch plasma device. Spectral data are collected along multiple chords on both sides of the symmetry axis of the plasma. This enables determination of the location of the current axis of the Z-pinch and of lower-bound estimates of the local magnetic field at specific radial locations in the plasma.
Escape from the potential well: Competition between long jumps and long waiting times
Authors: Dybiec Bartłomiej
Published: December 2010

Within a concept of the fractional diffusion equation and subordination, the paper examines the influence of a competition between long waiting times and long jumps on the escape from the potential well. Applying analytical arguments and numerical methods, we demonstrate that the presence of long waiting times distributed according to a power-law distribution with a diverging mean leads to very general asymptotic properties of the survival probability. The observed survival probability asymptotically decays like a power law whose form is not affected by the value of the exponent characterizing the power law jump length distribution. It is demonstrated that this behavior is typical of and generic for systems exhibiting long waiting times. We also show that the survival probability has a universal character not only asymptotically, but also at small times. Finally, it is indicated which properties of the first passage time density are sensitive to the exact value of the exponent characterizing the jump length distribution.
Semianalytic model of electron pulse propagation: Magnetic lenses and rf pulse compression cavities
Authors: Berger Joel A. , Schroeder W. Andreas
Published: December 2010

The analytical Gaussian electron pulse propagation model of Michalik and Sipe [J. Appl. Phys. 99, 054908 (2006)] is extended to include the action of external forces on the pulse. The resultant ability to simulate efficiently the effect of electron optical elements (e.g., magnetic lenses and radio-frequency cavities) allows for the rapid assessment of electron pulse delivery systems in time-resolved ultrafast electron diffraction and microscopy experiments.
Single-shot microscopic electron imaging of intense femtosecond laser-produced plasmas
Authors: Inoue Shunsuke , Tokita Shigeki , Nishoji Toshihiko , Masuno Shinichiro , Otani Kazuto , Hashida Masaki , Sakabe Shuji
Published: December 2010

A simple technique for single-shot microscopic electron imaging was demonstrated for the study of intense femtosecond laser-produced plasmas. Passed through a permanent magnet lens designed for 110-keV electrons, hot electrons emitted from the plasma produced by a single laser pulse of 0.8 mJ with intensity of 3 × 1016 W/cm2 were successfully imaged. Analyzing this image, we found that electrons were emitted from an area of 3 μm in diameter. At higher laser intensity of 1018 W/cm2, distinct structures were observed in and near the focal spot of the laser; that is, the electrons were emitted from several separate spots. These results show that laser-plasma electron imaging is promising for studying the interactions of femtosecond lasers with high-density plasmas.
Impact of time and space evolution of ion tracks in nonvolatile memory cells approaching nanoscale
Authors: Cellere G. , Paccagnella A. , Murat M. , Barak J. , Akkerman A. , Harboe-Sorensen R. , Virtanen A. , Visconti A. , Bonanomi M.
Published: December 2010

Swift heavy ions impacting on matter lose energy through the creation of dense tracks of charges. The study of the space and time evolution of energy exchange allows understanding the single event effects behavior in advanced microelectronic devices. In particular, the shrinking of minimum feature size of most advanced memory devices makes them very interesting test vehicles to study these effects since the device and the track dimensions are comparable; hence, measured effects are directly correlated with the time and space evolution of the energy release. In this work we are studying the time and space evolution of ion tracks by using advanced non volatile memories and Monte Carlo simulations. Experimental results are very well explained by the theoretical calculations.
Understanding the optical spectroscopy of amphiphilic molecular rectifiers: A density functional approach
Authors: Tan Osbert , Clark S. J. , Szablewski M. , Cross G. H.
Published: December 2010

We present results of first principles density functional theory calculations of the electronic and atomic structural properties of model Z-type Langmuir–Blodgett (LB) layers comprising amphiphilic quinolinium tricyanoquinodimethanide (Q3CNQ) chromophores. We find that the chromophore electronic ground state is not as clearly “zwitterionic” as required by models to explain electrical rectification purportedly seen in such systems. The computed visible region transitions are not what have been assumed to be the intervalence charge transfer bands seen in the visible region of molecules in Z-type LB films. Our own LB deposition and spectroscopic studies suggest that almost all visible region features previously seen may be ascribed to aggregates. The calculated lowest energy electronic excitation between HOMO and LUMO levels, which is located in the near infrared region, has a transition moment aligned approximately 9° off the molecular long axis, and has a normalized oscillator strength of 1 order of magnitude higher than those of the visible region transitions. This most dominant feature has been neglected from discussions of Langmuir–Blodgett layer rectification but our own deposition studies show no sign of this feature, indicating that the structure of the modeled system differs from that of typical experimental structures. The model indicates that such idealized LB layer structures cannot confidently be invoked to explain their experimental optical or electrical properties.
The third order helicity of magnetic fields via link maps. II
Authors: Komendarczyk R.
Published: December 2010

In this sequel we extend the derivation of the third order helicity to magnetic fields supported on unlinked domains in three-space. The formula is expressed in terms of generators of the deRham cohomology of the configuration space of three points in \documentclass[12pt]{minimal}\begin{document}${\bb R}^3$\end{document}R3, which is a more practical domain from the perspective of applications. It also admits an ergodic interpretation as an average asymptotic Milnor \documentclass[12pt]{minimal}\begin{document}$\bar{\mu }_{123}$\end{document}μ¯123-invariant and allows us to obtain the \documentclass[12pt]{minimal}\begin{document}$L^2$\end{document}L2-energy bound for the magnetic field. As an intermediate step we derive an integral formula for Milnor \documentclass[12pt]{minimal}\begin{document}$\bar{\mu }_{123}$\end{document}μ¯123-invariant for parametrized Borromean links in \documentclass[12pt]{minimal}\begin{document}${\bb R}^3$\end{document}R3.
A planar refractive x-ray lens made of nanocrystalline diamond
Authors: Alianelli L. , Sawhney K. J. S. , Malik A. , Fox O. J. L. , May P. W. , Stevens R. , Loader I. M. , Wilson M. C.
Published: December 2010

Diamond has unique properties which make it the ideal material for use in synchrotron instrumentation. X-ray optics made of diamond are almost transparent, they possess strength, and are subject to very low thermal expansion; therefore they will be able to withstand the powerful beams generated by fourth-generation light sources without compromising brilliance. For this reason, several groups are attempting fabrication of refractive lenses and zone plates made of diamond. Lithography and, in general, microfabrication technology, are the ultimate tools for the innovation of synchrotron focusing optics. We propose to combine modern silicon microtechnology with advanced deposition methods to fabricate nanocrystalline-diamond lenses for third- and fourth-generation synchrotron sources. The fabrication method is described here and microfocusing synchrotron tests are illustrated.
Microwave spectra, structure, and dynamics of the weakly bound complex, N2 CO2
Authors: Frohman Daniel J. , Contreras Edwin S. , Firestone Ross S. , Novick Stewart E. , Klemperer William
Published: December 2010

The Fourier transform microwave spectra of the various isotopologs of the weakly bound complex of carbon dioxide with the most abundant molecule in the atmosphere, nitrogen, have been measured. The structure of the complex has been determined and evidence for the inversion of the N2 is presented. The molecule is T-shaped, with the OCO forming the cross of the T, a structure consistent with that deduced from a previous rotationally resolved infrared experiment. A significant wide-amplitude bending motion of the N2 is deduced from the values of the (nearly identical) nuclear quadrupole coupling constants of the nitrogen nuclei. The spectroscopic results are compared with high-quality ab initio calculations. We examine the consequences of the N2 CO2 complex formation in the atmosphere upon the greenhouse warming potential of carbon dioxide.
Phonon wave-packet simulations of Ar/Kr interfaces for thermal rectification
Authors: Roberts N. A. , Walker D. G.
Published: December 2010

The frequency and direction dependence of transmission coefficients at interfaces was investigated theoretically. The interfaces are formed by having two Lennard-Jones materials differing in mass and interatomic potential equally divided at the center of an fcc lattice system. A single frequency wave-packet is generated at one end of the system and allowed to propagate through the system until all interactions with the interface are complete. The transmission coefficient is then calculated by comparing the energy of the packet that is transmitted with the original wave-packet. Results show a difference in transmission when the wave-packet originates from opposite sides.
Multidimensional optical spectroscopy of a single molecule in a current-carrying state
Authors: Rahav S. , Mukamel S.
Published: December 2010

The nonlinear optical signals from an open system consisting of a molecule connected to metallic leads, in response to a sequence of impulsive pulses, are calculated using a superoperator formalism. Two detection schemes are considered: coherent stimulated emission and incoherent fluorescence. The two provide similar but not identical information. The necessary superoperator correlation functions are evaluated either by converting them to ordinary (Hilbert space) operators which are then expanded in many-body states, or by using Wick's theorem for superoperators to factorize them into nonequilibrium two point Green's functions. As an example we discuss a stimulated Raman process that shows resonances involving two different charge states of the molecule in the same signal.
Magnetically applied pressure-shear: A new method for direct measurement of strength at high pressure
Authors: Alexander C. S. , Asay J. R. , Haill T. A.
Published: December 2010

A new experimental technique to measure material shear strength at high pressures has been developed for use on magnetohydrodynamic (MHD) drive pulsed power platforms. By applying an external static magnetic field to the sample region, the MHD drive directly induces a shear stress wave in addition to the usual longitudinal stress wave. Strength is probed by passing this shear wave through a sample material where the transmissible shear stress is limited to the sample strength. The magnitude of the transmitted shear wave is measured via a transverse velocity interferometer system from which the sample strength is determined.
Influence of carrier concentration on piezoelectric potential in a bent ZnO nanorod
Authors: Shao Zhengzheng , Wen Liaoyong , Wu Dongmin , Zhang Xueao , Chang Shengli , Qin Shiqiao
Published: December 2010

The influence of carriers on the piezoelectric potential in a bent ZnO nanorod is investigated using finite difference method. The distributions of carriers and the electrical potential in the nanorod are obtained. The results shows that the positive piezoelectric potential in stretched side of the bent nanorod is significantly screened by the carriers and the negative potential in compressed side is well preserved when considering a moderate carrier concentration of 1×1017 cm−3. The calculation results agree with the experimental results that only negative pulses are observed in the nanogenerator experiment using the as-grown ZnO nanorods. Further investigation shows that when the carrier concentration is 1×1018 cm−3, the piezoelectric potential in the nanorod is almost completely screened by the redistributed carriers.
Influence of nuclear exchange on nonadiabatic electron processes in H$^+$++H$_2$2 collisions
Authors: Errea L. F. , Illescas Clara , Macías A. , Méndez L. , Pons B. , Rabadán I. , Riera A.
Published: December 2010

H \documentclass[12pt]{minimal}\begin{document}$^+$\end{document}++H \documentclass[12pt]{minimal}\begin{document}$_2$\end{document}2 collisions are studied by means of a semiclassical approach that explicitly accounts for nuclear rearrangement channels in nonadiabatic electron processes. A set of classical trajectories is used to describe the nuclear motion, while the electronic degrees of freedom are treated quantum mechanically in terms of a three-state expansion of the collision wavefunction. We describe electron capture and vibrational excitation, which can also involve nuclear exchange and dissociation, in the E = 2–1000 eV impact energy range. We compare dynamical results obtained with two parametrizations of the potential energy surface of H \documentclass[12pt]{minimal}\begin{document}$_3^+$\end{document}3+ ground electronic state. Total cross sections for E > 10 eV agree with previous results using a vibronic close-coupling expansion, and with experimental data for E < 10 eV. Additionally, some prototypical features of both nuclear and electron dynamics at low E are discussed.
The flux-flux correlation function for anharmonic barriers
Authors: Goussev Arseni , Schubert Roman , Waalkens Holger , Wiggins Stephen
Published: December 2010

The flux-flux correlation function formalism is a standard and widely used approach for the computation of reaction rates. In this paper we introduce a method to compute the classical and quantum flux-flux correlation functions for anharmonic barriers essentially analytically through the use of the classical and quantum normal forms. In the quantum case we show that for a general f degree-of-freedom system having an index one saddle the quantum normal form reduces the computation of the flux-flux correlation function to that of an effective one-dimensional anharmonic barrier. The example of the computation of the quantum flux-flux correlation function for a fourth order anharmonic barrier is worked out in detail, and we present an analytical expression for the quantum mechanical microcanonical flux-flux correlation function. We then give a discussion of the short-time and harmonic limits.
A high voltage pulse power supply for metal plasma immersion ion implantation and deposition
Authors: Salvadori M. C. , Teixeira F. S. , Araújo W. W. R. , Sgubin L. G. , Sochugov N. S. , Spirin R. E. , Brown I. G.
Published: December 2010

We describe the design and implementation of a high voltage pulse power supply (pulser) that supports the operation of a repetitively pulsed filtered vacuum arc plasma deposition facility in plasma immersion ion implantation and deposition (Mepiiid) mode. Negative pulses (micropulses) of up to 20 kV in magnitude and 20 A peak current are provided in gated pulse packets (macropulses) over a broad range of possible pulse width and duty cycle. Application of the system consisting of filtered vacuum arc and high voltage pulser is demonstrated by forming diamond-like carbon (DLC) thin films with and without substrate bias provided by the pulser. Significantly enhanced film/substrate adhesion is observed when the pulser is used to induce interface mixing between the DLC film and the underlying Si substrate.
Thermomechanical properties of Yb3+ doped laser crystals: Experiments and modeling
Authors: Petit Johan , Viana Bruno , Goldner Philippe , Roger Jean-Paul , Fournier Danièle
Published: December 2010

Thermal conductivity values of several laser materials were determined by photothermal measurements and compared to predicted values. The effect of the ytterbium doping concentration could be modeled using a simple cationic mass difference model. For ytterbium content corresponding to an absorption coefficient of 10 cm−1 (or 85% absorption of the pump power) Yb:GdVO4 (c-axis) and Yb:Gd3Ga5O12 laser materials present the highest measured thermal conductivity values of 8.1 W m−1 K−1 and 7.7 W m−1 K−1, respectively. Yb:Y3Al5O12, Yb:Lu3Al5O12, Yb:CaGdAlO4, and Yb:YAlO3 belong to the 6–7 W m−1 K−1 range while Yb:CaF2 and Yb:Lu2SiO5 are situated in the 5–6 W m−1 K−1 range. Other matrices such as Yb:SrLaGa3O7, Yb:CaGdAl3O7, Yb:SrGdGa3O7, and Yb:BaLaGa3O7 have thermal conductivity values lower than 5 W m−1 K−1. With the knowledge of the thermal conductivities and the determination of the thermal expansion coefficients, thermal shock parameters are evaluated for several ytterbium doped laser hosts.
Elastic strain and dopant activation in ion implanted strained Si nanowires
Authors: Minamisawa R. A. , Habicht S. , Buca D. , Carius R. , Trellenkamp S. , Bourdelle K. K. , Mantl S.
Published: December 2010

Strained Si nanowires (NWs) are attractive for deeply-scaled complementary metal-oxide-semiconductor devices due to the combination of enhanced carrier mobility and excellent electrostatic control as was demonstrated with trigate metal-oxide-semiconductor field effect transistors. The challenge in using strained Si NWs for devices is to preserve the elastic strain during the required processing steps. In this work we investigated the influence of fundamental processing steps like patterning and dopant ion implantation on the structural and transport properties of strained Si layers and NWs on silicon-on-insulator (SOI) substrates. NWs with widths down to 35 nm, fabricated on 25 nm strained SOI and implanted to doses ranging from 5×1014 to 2×1015 ions/cm2 were investigated. We show that strain conservation and a low sheet resistivity of 6.2×10−4 Ω cm, close to the layer resistivity, can only be obtained if the NWs are patterned on doped layers. For NWs directly implanted to doses above 1×1015 ions/cm2, complete strain relaxation and structural disorder by solid phase recrystallization were observed. In both cases, NWs with widths smaller than 55 nm exhibit an increased specific resistivity.
Limits for the vortex state spin torque oscillator in magnetic nanopillars: Micromagnetic simulations for a thin free layer
Authors: Aranda Gloria R. , Gonzalez Julian M. , del Val Juan J. , Guslienko Konstantin Y.
Published: December 2010

We report micromagnetic simulations of magnetization dynamics of a vortex state in the free layer of a circular nanopillar excited by the spin transfer torque effect of a perpendicular to the layer (dot) plane spin-polarized electrical current. The magnetization of the reference layer (polarizer) is assumed to be fixed. A new regime of the dynamic magnetization response to the current is reported: vortex expelling from the dot, subsequent in-plane magnetization oscillations in single domain state, and the vortex return with an opposite core polarization. We analyze conditions (limits of the vortex state as a nano-oscillator) to achieve steady magnetization oscillations corresponding to a gyrotropic motion of the vortex core in terms of the current intensity. These conditions are formulated via the critical currents and vary greatly with the magnetic damping parameter and the cell size used for micromagnetic simulations. The existing experiments on the current induced magnetization dynamics in nanopillars and nanocontacts are discussed.
Long-range order of Ni2+ and Mn4+ and ferromagnetism in multiferroic (Bi0.9La0.1)2NiMnO6 thin films
Authors: Langenberg E. , Rebled J. , Estradé S. , Daumont C. J. M. , Ventura J. , Coy L. E. , Polo M. C. , García-Cuenca M. V. , Ferrater C. , Noheda B. , Peiró F. , Varela M. , Fontcuberta J.
Published: December 2010

Epitaxial thin films of biferroic (Bi1−xLax)2NiMnO6 have been grown on SrTiO3 (001) substrates. High resolution electron microscopy, energy-loss spectroscopy and synchrotron radiation have been used to demonstrate that, under appropriate growth conditions, stoichiometric, and fully oxidized thin films with long-range order of Ni2+ and Mn4+ ions can be obtained, despite the presence of randomly distributed dissimilar cations (Bi, La) at the A-site. This ordering leads to Ni2+–O–Mn4+ ferromagnetic interactions and its preservation in thin films is key for implementation of these biferroic materials in practical devices.
The persistent luminescence and up conversion photostimulated luminescence properties of nondoped Mg2SnO4 material
Authors: Zhang Jiachi , Yu Minghui , Qin Qingsong , Zhou Hongliang , Zhou Meijiao , Xu Xuhui , Wang Yuhua
Published: December 2010

The nondoped Mg2SnO4 material with inverse spinel structure was synthesized by solid state reaction. This phosphor showed a broad green emission band covering 470–550 nm under 291 nm excitation, which was due to the recombination of F centers with holes. Stimulated by 980 nm infrared laser, the green photostimulated luminescence was first observed in a nondoped oxide. After ultraviolet irradiation, the green persistent luminescence of Mg2SnO4 could be seen in darkness for about 5 h. The decay curves revealed that the long persistent luminescence was governed by tunneling mechanism and it proved the presence of different trap clusters in Mg2SnO4. These trap clusters (such as [SnMg••–Oi″], [SnMg••–2e′], and [SnMg••–e″]) induced the trap levels with different depths in band gap and corresponded to the three components (at 110, 168, and 213 °C) of the thermoluminescence glow curve of Mg2SnO4. These trap levels with different depths were proved to be not independent. It revealed that the shallow traps (110 °C) and part of the deep traps (168 and 213 °C) were involved in the persistent luminescence. Meanwhile, all the shallow and deep traps were responsible for the photostimulated luminescence. Accordingly, the photoluminescence, persistent, and photostimulated luminescence mechanisms of the nondoped Mg2SnO4 material were first proposed.
Excitation of terahertz plasmons eigenmode of a parallel plane guiding system by an electron beam
Authors: Kumar Pawan , Kumar Manish , Tripathi V. K.
Published: December 2010

Two parallel semiconductor plates, separated by a short distance, support surface plasmon eigenmode with amplitude maxima at the inner surfaces of the plates and minimum at the center. A relativistic sheet electron beam propagating through the space between the planes resonantly excites the surface plasma wave (SPW). The frequency of the driven SPW decreases with the energy of the beam while the growth rate increases. At the beam current ≈168 A the growth rate of 5.93×108 rad/s is achieved at the frequency ≈0.51 THz of SPW for the 5 mm ŷ width and spacing between the two plates of ≈2.83 mm. The growth rate scales as 1/3 root of the electron beam current.