bluuebunny/crossref_metadata_2025 huggingface dataset:
Low-energy dissociative recombination in small polyatomic molecules
Authors: Jungen Ch. , Pratt S. T.
Published: December 2010

Indirect dissociative recombination of low-energy electrons and molecular ions often occurs through capture into vibrationally excited Rydberg states. Properties of vibrational autoionization, the inverse of this capture mechanism, are used to develop some general ideas about the indirect recombination process, and these ideas are illustrated by examples from the literature. In particular, the Δv = −1 propensity rule for vibrational autoionization, i.e., that vibrational autoionization occurs by the minimum energetically allowed change in vibrational quantum numbers, leads to the prediction of thresholds in the dissociative recombination cross sections and rates at the corresponding vibrational thresholds. Capture into rotationally excited Rydberg states is also discussed in terms of recent low-temperature studies of the dissociative recombination of H3+.
Highly anisotropic sliding at TiN/Fe interfaces: A first principles study
Authors: Kádas K. , Eriksson O. , Skorodumova N. V.
Published: December 2010

By means of first principles density functional theory, we investigate the properties of the TiN(001)/fcc Fe(111) and TiN(001)/bcc Fe(110) interfaces. We demonstrate that along certain directions Fe slides with negligible energy barriers against TiN at both interfaces, whereas sliding along other directions is involved with significant energy barriers. The interface between bcc Fe and TiN has a low energy barrier for sliding along the [110] direction of the TiN lattice, as does sliding along the [010] direction at TiN(001)/fcc Fe(111). For fcc Fe on TiN, a large energy barrier is found for sliding along the [100] direction of the TiN lattice. We show that this phenomenon and the stability of these interfaces are determined by the interplay between N–Fe bonding and Ti–Fe antibonding interactions.
Evidence of a fully ballistic one-dimensional field-effect transistor: Experiment and simulation
Authors: Grémion E. , Niepce D. , Cavanna A. , Gennser U. , Jin Y.
Published: December 2010

We report the experimental demonstration of quantum point contact (QPC) field-effect transistor (FET) with a voltage gain greater than 1 at 4.2 K. Using Landauer–Büttiker approach in mesoscopic physics, simulation results show that this transistor is a fully ballistic one-dimensional FET, and the mechanism leading to a high gain is explained. This work provides therefore a general basis for devising future ballistic FETs.
Generation and optimization of electron currents along the walls of a conical target for fast ignition
Authors: Micheau S. , Debayle A. , d’Humières E. , Honrubia J. J. , Qiao B. , Zepf M. , Borghesi M. , Geissler M.
Published: December 2010

The interaction of an ultraintense laser pulse with a conical target is studied by means of numerical particle-in-cell simulations in the context of fast ignition. The divergence of the fast electron beam generated at the tip of the cone has been shown to be a crucial parameter for the efficient coupling of the ignition laser pulse to the precompressed fusion pellet. In this paper, we demonstrate that a focused hot electron beam is produced at the cone tip, provided that electron currents flowing along the surfaces of the cone sidewalls are efficiently generated. The influence of various interaction parameters over the formation of these wall currents is investigated. It is found that the strength of the electron flows is enhanced for high laser intensities, low density targets, and steep density gradients inside the cone. The hot electron energy distribution obeys a power law for energies of up to a few MeV, with the addition of a high-energy Maxwellian tail.
Self-mode-transition from laser wakefield accelerator to plasma wakefield accelerator of laser-driven plasma-based electron acceleration
Authors: Pae K. H. , Choi I. W. , Lee J.
Published: December 2010

Via three-dimensional particle-in-cell simulations, the self-mode-transition of a laser-driven electron acceleration from laser wakefield to plasma-wakefield acceleration is studied. In laser wakefield accelerator (LWFA) mode, an intense laser pulse creates a large amplitude wakefield resulting in high-energy electrons. Along with the laser pulse depletion, the electron bunch accelerated in the LWFA mode drives a plasma wakefield. Then, after the plasma wakefield accelerator mode is established, electrons are trapped and accelerated in the plasma wakefield. The mode transition process and the characteristics of the accelerated electron beam are presented.
Cantilever biosensor reader using a common-path, holographic optical interferometer
Authors: Pedersen Henrik C. , Jakobsen Michael L. , Hanson Steen G. , Dam-Hansen Carsten , Olesen Tom , Hansen Poul
Published: December 2010

We demonstrate an optical reader principle aimed at monitoring biologically induced deflections of microcantilevers often used in biosensor systems. The principle is based on a so-called common-path optical interferometer in which the two interfering optical beams are copropagating, which makes the system less sensitive to external disturbances. A detection limit of around 1 nm’s deflection is demonstrated.
Conformal GaP layers on Si wire arrays for solar energy applications
Authors: Tamboli Adele C. , Malhotra Manav , Kimball Gregory M. , Turner-Evans Daniel B. , Atwater Harry A.
Published: December 2010

We report conformal, epitaxial growth of GaP layers on arrays of Si microwires. Silicon wires grown using chlorosilane chemical vapor deposition were coated with GaP grown by metal-organic chemical vapor deposition. The crystalline quality of conformal, epitaxial GaP/Si wire arrays was assessed by transmission electron microscopy and x-ray diffraction. Hall measurements and photoluminescence show p- and n-type doping with high electron mobility and bright optical emission. GaP pn homojunction diodes on planar reference samples show photovoltaic response with an open circuit voltage of 660 mV.
Simple surface modification of poly(dimethylsiloxane) for DNA hybridization
Authors: Zhou Jinwen , Voelcker Nicolas H. , Ellis Amanda V.
Published: December 2010

Here, we present a simple chemical modification of poly(dimethylsiloxane) (PDMS) by curing a mixture of 2 wt% undecylenic acid (UDA) in PDMS prepolymer on a gold-coated glass slide. This gold slide had been previously pretreated with a self-assembled hydrophilic monolayer of 3-mercaptopropionic acid (MPA). During curing of the UDA/PDMS prepolymer, the hydrophilic UDA carboxyl moieties diffuses toward the hydrophilic MPA carboxyl moieties on the gold surface. This diffusion of the UDA within the PDMS prepolymer to the surface is a direct result of surface energy minimization. Once completely cured, the PDMS is peeled off the gold substrate, thereby exposing the interfacial carboxyl groups. These groups are then available for subsequent attachment of 5′-amino terminated DNA oligonucleotides via amide linkages. Our results show that the covalently tethered oligonucleotides can successfully capture fluorescein-labeled complementary oligonucleotides via hybridization, which are visualized using fluorescence microscopy.
Selective functionalization of halogens on zigzag graphene nanoribbons: A route to the separation of zigzag graphene nanoribbons
Authors: Lee Hoonkyung , Cohen Marvin L. , Louie Steven G.
Published: December 2010

Using the ab initio pseudopotential density functional method, we investigate the functionalization of halogen molecules into graphene-based nanostructures with zigzag and armchair edges. We find that halogen molecules adsorb through chemisorption on the zigzag edge carbon atoms with a binding energy of ∼1–5 eV, in sharp contrast to physisorption on the armchair edge and elsewhere where they adsorb with a binding energy of ∼0.07 eV. Our findings would be utilized for an approach to the separation of zigzag graphene nanoribbons with regular edges with the change of the solubility of the functionalized nanoribbons.
Ultrafast resistive switching in SrTiO3:Nb single crystal
Authors: Zhang X. T. , Yu Q. X. , Yao Y. P. , Li X. G.
Published: December 2010

The resistive switching effect of the SrTiO3:Nb (0.05wt %, 0.5 wt %, and 1 wt % Nb) single crystals contact with Ag and Pt, respectively, was studied by in situ monitoring the voltage drop (Vs) across the samples. For Ag/SrTiO3:Nb junction, the response time is as short as 5 ns, which is two orders of magnitude short than that of the Pt/SrTiO3:Nb junction. The effect of metal electrodes on the response time has been discussed, which is related to the barrier height of the junction.
Valence-band splittings in cubic and hexagonal AlN, GaN, and InN
Authors: Cláudio de Carvalho Luiz , Schleife André , Fuchs Frank , Bechstedt Friedhelm
Published: December 2010

Modern parameter-free band-structure calculations are applied to the uppermost valence bands near the Γ point. They are based on a nonlocal exchange-correlation starting point for the iteration of the quasiparticle equation and include spin-orbit interaction. The Ga 3d and In 4d electrons remarkably influence the valence-band splittings. Quasiparticle effects shrink the crystal-field splitting Δcf for GaN and increase the inverted Γ1−Γ5 distance for AlN. Beyond the quasicubic approximation, we find a small anisotropy of the spin-orbit splittings. While for AlN Δso does only weakly depend on the crystal structure, variations are found between zinc blende and wurtzite for GaN or InN.
Five-band bias-selectable integrated quantum well detector in an n-p-n architecture
Authors: Ariyawansa G. , Aytac Y. , Perera A. G. U. , Matsik S. G. , Buchanan M. , Wasilewski Z. R. , Liu H. C.
Published: December 2010

A detector with five bands covering visible to long-wave infrared is demonstrated using a GaAs-based n-p-n-architecture. The major elements are two back-to-back connected p-i-n photodiodes with InGaAs/GaAs and GaAs/AlGaAs-based quantum wells integrated within the n-regions. At 80 K, a preliminary detector shows two combinations of bands, each responding in three bands, covering the 0.6–0.8, 3–4, and 4–8 μm ranges and the 0.8–0.9, 0.9–1.0, and 9–13 μm ranges. A good selection of these two combinations based on the bias voltage polarity is observed. A similar four-band detector without any cross-talk between the bands is proposed using In0.53Ga0.47As/InP material system.
Conductance-dependent negative differential resistance in organic memory devices
Authors: You Y. T. , Wang M. L. , Xuxie H. N. , Wu B. , Sun Z. Y. , Hou X. Y.
Published: December 2010

Single-layer organic memories made of organic material with good conductance have been characterized. Asymmetrical bistable behaviors under biases of opposite polarities are observed for devices with asymmetric electrodes. It is experimentally confirmed that a close correlation exists between the conductivity of the organic layer and the asymmetric bistability of the device under opposite biases. Inserting a block layer or thickening the organic layer will result in negative differential resistance under positive biases, leading to reversible symmetrical bistability. The phenomena are ascribed to the presence of filamentary microconducting channels in the organic layer.
Nanoscale investigations of shift of individual interfaces in temperature induced processes of Ni–Si system by secondary neutral mass spectrometry
Authors: Lakatos A. , Langer G. A. , Csik A. , Cserhati C. , Kis-Varga M. , Daroczi L. , Katona G. L. , Erdélyi Z. , Erdelyi G. , Vad K. , Beke D. L.
Published: December 2010

We describe a method for measurement of nanoscale shift of interfaces in layered systems by a combination of secondary neutral mass spectrometry and profilometer. We demonstrate it by the example of the investigation of interface shifts during the solid state reaction in Ni/amorphous-Si system. The kinetics of the shrinkage of the initial nanocrystalline Ni film and the amorphous Si layer as well as the average growth kinetics of the product phases were determined at 503 K. The results show that nanoscale resolution can be reached and the method is promising for following solid state reactions in different thin film systems.
Intrinsic room temperature ferromagnetism in boron-doped ZnO
Authors: Xu X. G. , Yang H. L. , Wu Y. , Zhang D. L. , Wu S. Z. , Miao J. , Jiang Y. , Qin X. B. , Cao X. Z. , Wang B. Y.
Published: December 2010

We report room temperature ferromagnetism in boron-doped ZnO both experimentally and theoretically. The single phase Zn1−xBxO films deposited under high oxygen pressure by pulsed laser deposition show ferromagnetic behavior at room temperature. The saturation magnetization increases monotonically from 0 to 1.5 emu/cm3 with the increasing boron component x from 0% to 6.8%. The first-principles calculations demonstrate that the ferromagnetism in the B-doped ZnO originates from the induced magnetic moment of oxygen atoms in the nearest neighbor sites to B–Zn vacancy pairs. The calculated total magnetic moment shows an increasing trend with the boron component which is consistent with experiment.
Theoretical investigation of the spectrum and conversion efficiency of short wavelength extreme-ultraviolet light sources based on terbium plasmas
Authors: Sasaki Akira , Nishihara Katsunobu , Sunahara Atsushi , Furukawa Hiroyuki , Nishikawa Takeshi , Koike Fumihiro
Published: December 2010

The emission spectrum and conversion efficiency of laser-produced terbium plasmas are theoretically investigated on the basis of computational atomic data. The theoretically calculated spectrum reproduces the main peak of observed spectrum at λ=6.5 nm, which originates from 4d−4f transitions of near palladiumlike ions (Tb19+). A simple model of the isothermal expansion of terbium plasma suggests that efficient emission can be achieved by pumping the plasma with a laser pulse at an intensity of approximately one order of magnitude greater than that used with tin sources at λ=13.5 nm.
Significant elastic anisotropy in Ti1−xAlxN alloys
Authors: Tasnádi Ferenc , Abrikosov Igor A. , Rogström Lina , Almer Jonathan , Johansson Mats P. , Odén Magnus
Published: December 2010

Strong compositional-dependent elastic properties have been observed theoretically and experimentally in Ti1−xAlxN alloys. The elastic constant, C11, changes by more than 50% depending on the Al-content. Increasing the Al-content weakens the average bond strength in the local octahedral arrangements resulting in a more compliant material. On the other hand, it enhances the directional (covalent) nature of the nearest neighbor bonds that results in greater elastic anisotropy and higher sound velocities. The strong dependence of the elastic properties on the Al-content offers new insight into the detailed understanding of the spinodal decomposition and age hardening in Ti1−xAlxN alloys.
Effect of Zr addition on ZnSnO thin-film transistors using a solution process
Authors: Rim You Seung , Kim Dong Lim , Jeong Woong Hee , Kim Hyun Jae
Published: December 2010

Thin-film transistors (TFTs) with a ZrZnSnO (ZZTO) channel layer were fabricated using a solution process. As-prepared ZnSnO (ZTO) TFTs had a large off-current. However, as the content of Zr ions increased in ZTO, the threshold voltage shifted, and the off-current in the TFTs decreased. Because Zr has a lower standard electrode potential, it is more readily oxidized than Sn or Zn. Thus, Zr acted as an effective carrier suppressor in the ZTO system and a ZZTO TFT with a high mobility of a 4.02 cm2 V−1 s−1 and a large on/off ratio of over 106 was achieved.
On the mechanism for plasma hydrogenation of graphene
Authors: Jones J. D. , Hoffmann W. D. , Jesseph A. V. , Morris C. J. , Verbeck G. F. , Perez J. M.
Published: December 2010

We report that hydrogenation of mono-, bi-, and trilayer graphene samples via exposure to H2 plasma occurs as a result of electron irradiation of H2O adsorbates on the samples, rather than H species in the plasma as reported by [Elias et al., Science 323, 610 (2009)]. We propose that the hydrogenation mechanism is electron-impact fragmentation of H2O adsorbates into H+ ions. At incident electron energies >60 eV, we observe hydrogenation that is significantly more stable at temperatures >200 °C than previously reported.
Single picojoule pulse switching of magnetization in ferromagnetic (Ga,Mn)As
Authors: Reid A. H. M. , Astakhov G. V. , Kimel A. V. , Schott G. M. , Ossau W. , Brunner K. , Kirilyuk A. , Molenkamp L. W. , Rasing Th.
Published: December 2010

The recently demonstrated photoinduced reduction of the coercive field in (Ga,Mn)As is shown to display a pronounced increase in efficiency when triggered by short laser pulses. This is due to the relaxation timescale of the effect that is measured to be about 1.5 ns. In addition, a single 100-fs-pulse with only 80 pJ of energy is found to be sufficient to write a magnetic domain.
Characteristics of a high temperature vertical spin valve
Authors: Basu Debashish , Kum Hyun , Bhattacharya Pallab , Saha Dipankar
Published: December 2010

We demonstrate high temperature electrical spin injection and detection in degenerately p-doped GaAs in vertical spin valves using valence band electron tunneling. The maximum measured magnetoresistance at 10 and 300 K is 40% and ∼1%, respectively. Spin relaxation in these devices was found to be relatively insensitive to temperature (T) for T>125 K. The spin injection and detection efficiencies are mostly dominated by the ferromagnetic contact polarization and spin independent transport at the ferromagnet/semiconductor interface.
Experimental verification of the far-field subwavelength focusing with multiple concentric nanorings
Authors: Wang Tingting , Wang Xiao , Kuang Cuifang , Hao Xiang , Liu Xu
Published: December 2010

A structure for subwavelength focusing at optical frequencies based on multiple concentric air nanorings was proposed. Using the coherent illumination light at 532 nm, a sequence of two-dimensional intensity distribution was obtained. We experimentally demonstrated the smallest focal spot observed at a distance of 2.8 μm away from the output surface of the sample with the full width at half maximum of ∼320 nm (0.6λ) and a depth of focus of ∼2.4 μm (4.51λ).
Performance analysis of carbon-based tunnel field-effect transistors for high frequency and ultralow power applications
Authors: Yoon Youngki , Kim Sung Hwan , Salahuddin Sayeef
Published: December 2010

We perform atomistic simulations and energy-delay analysis on tunnel FETs (TFETs) based on partially unzipped carbon nanotubes (CNTs) and compare their performance against conventional homojunction CNT-TFETs. The device simulations show that the carbon heterojunctions could provide much larger on current compared to homojunction CNT-TFETs due to the effective small bandgap for the injected carriers, without paying a large penalty for off current and subthreshold swing. Subsequent energy-delay analysis shows that these heterojunctions could enable high performance operation and could prove favorable compared to a conventional Ge-source heterojunction TFET. Homojunction TFETs are found to be useful for low-frequency and low-power applications.
Investigation of terahertz sheet beam traveling wave tube amplifier with nanocomposite cathode
Authors: Shin Young-Min , Zhao Jinfeng , Barnett Larry R. , Luhmann Neville C.
Published: December 2010

Particle-in-cell simulations of a staggered double grating array traveling wave tube intended as a wideband amplifier for terahertz communications, sensing, and imaging applications showed that, for an electron beam power of 5 kW, it produces 150–275 W, corresponding to 3%–5.5% electronic efficiency, at 0.22 THz with over ∼30% bandwidth and with greater than 12 dB/cm growth rate. The circuit has been fabricated by both UV lithography and high precision computer-numerical-control machining with ∼2–3 μm dimensional tolerance and ∼50 nm surface roughness. A scandate nanocomposite (Sc2O3–W) cathode for the electron beam source has successfully emitted 120 A/cm2 (space charge limited) at 1150 °C and 50 A/cm2 at 1050 °C for 8000 h as required to produce the requisite high current density electron beam.
Structure, Stability, and Generation of CH3CNS
Authors: Krebsz Melinda , Hajgató Balázs , Bazsó Gábor , Tarczay György , Pasinszki Tibor
Published: December 2010

The unstable acetonitrile N-sulfide molecule CH3CNS has been photolytically generated in inert solid argon matrix from 3,4-dimethyl-1,2,5-thiadiazole by 254-nm UV irradiation, and studied by ultraviolet spectroscopy and mid-infrared spectroscopy. The molecule is stable in the matrix to 254-nm UV irradiation, but decomposes to CH3CN and a sulfur atom when broad-band UV irradiation is used. Chemiluminescence due to S2 formation from triplet sulfur atoms was detected on warming the matrix to ∼20–25 K. The ground-state structure and potential uni- and bimolecular reactions of CH3CNS are investigated using B3LYP, CCSD(T), and MR-AQCC quantum-chemical methods. CH3CNS is demonstrated to be stable under isolated conditions at room temperature, i.e. in the dilute gas phase or in an inert solid matrix, but unstable owing to bimolecular reactions, i.e. in the condensed phase.
UV-photoelectron Spectroscopy of Unhindered Germylenes and Carbon-arsenic Multiple-bonded Species
Authors: Chrostowska Anna , Dargelos Alain , Graciaa Alain
Published: December 2010

Ultraviolet photoelectron spectroscopy (UV-PES) is a well established technique that provides ionization energies of molecules in the gas phase. Flash vacuum thermolysis or vacuum gas-solid reactions coupled with UV-PES are especially suited for the generation and analysis of small amounts of short-lived species in real-time. These experimental data, supported by quantum chemical calculations for the consistency of the assignments of PES spectra, provide fundamental information about electronic structure and bonding that is obtained by no other technique. This paper aims to give some representative original examples chosen from Pau’s research group that illustrate the advantages and wide applicability of these techniques. These examples show the selected data and conclusions which focus on the reactivity of low-coordinated of Main Group IV and V elements. Germylenes and simplest carbon-arsenic multiple bonded species ware successfully characterized using UV photoelectron spectroscopy – a very powerful, direct characterization instrument.
Competition Between Azido Cleavage and Triplet Nitrene Formation in Azidomethylacetophenones
Authors: Ranaweera Ranaweera A. A. Upul , Zhao Yu , Muthukrishnan Sivaramakrishnan , Keller Christopher , Gudmundsdottir Anna D.
Published: December 2010

Photolysis of p- and m-azidomethylacetophenone (1a, 1b) in argon-saturated solutions yields predominantly imine 2a, 2b, whereas irradiation of 1a, 1b in oxygen-saturated solutions results in heterocycles 3a, 3b, aldehydes 4a, 4b and nitriles 5a, 5b. Density functional theory calculations place the energy of the first and second excited state of the triplet ketones (T1K and T2K) in 1a, 1b in close proximity to each other. The triplet transition state for cleaving the C–N bond in 1a, 1b to form azido and benzyl radicals 1aB, 1bB is located only 3 kcal mol–1 (1 kcal = 4.184 kJ) above T1K, indicating that azido cleavage is feasible. The calculations place the energy of the triplet azido group (TA) in 1a, 1b ∼25 kcal mol–1 below T1K; thus, this process is also easily accessible via energy transfer. Further, the transition state barrier for TA to expel N2 and form triplet nitrenes is less than 1 kcal mol–1 above TA in 1a, 1b. Laser flash photolysis of 1a, 1b reveals the formation of the triplet excited ketones of 1a, 1b, which decay to form benzyl radicals 1aB, 1bB and triplet alkylnitrenes. The triplet ketones and the benzyl radicals are quenched with molecular oxygen at rates close to diffusion, whereas the triplet nitrenes react more slowly with oxygen (∼5 × 105 M–1 s–1). We conclude that the triplet alkylnitrenes intercept the benzyl radicals to form 2 in argon-saturated solution, whereas the benzyl radicals are trapped to form 4 in oxygen-saturated solution; thus, the triplet nitrenes react with oxygen to form 3.
Thioketenes and Iminopropadienethiones RN=C=C=C=S from Isoxazolones
Authors: Kvaskoff David , Wentrup Curt
Published: December 2010

Isoxazolones 6 undergo thermal elimination of propene and isopropylthiol to produce thioketenes 7 at 500–600°C under flash vacuum thermolysis conditions. At 700–900°C further fragmentation occurs to produce iminopropadienethiones, RNCCCS 8. In addition, 3-alkylisoxazolones 6d–e rearrange to cyanothioketenes 10d–e. Compounds 7, 8, and 10 were characterized by Ar matrix IR spectroscopy and comparison with density functional theory-calculated spectra. Thioketenes 7 reacted with amines to afford thioamides 11. Reaction of aryliminopropadienethiones 8 with amines caused cyclization to 2-aminoquinoline-4(1H)-thiones 16.
Gold-Catalysis: Reactions of Organogold Compounds with Electrophiles
Authors: Hashmi A. Stephen K. , Ramamurthi Tanuja Dondeti , Todd Matthew H. , Tsang Althea S.-K. , Graf Katharina
Published: December 2010

Different arylgold(i), one alkynylgold(i), and one vinylgold(i) triphenylphosphane complexes were subjected to electrophilic halogenation reagents. With N-chlorosuccinimid, N-bromosuccinimid, and N-iodosuccinimid as well as the Barluenga reagent, selectively halogenated compounds were obtained. Trifluoroacetic acid, as a source of protons, leads to a clean protodeauration. With N-fluorobenzenesulfonimide or Selectfluor, exclusively a homocoupling was observed. For the precursor of the vinylgold(i) complex, a similar oxidative coupling could be induced by gold(iii) chloride. Reactions with silicon or tin electrophiles failed.
Electron Paramagnetic Resonance Spectroscopic Characterization of α,2- and α,4-Didehydrotoluene
Authors: Neuhaus Patrik , Henkel Stefan , Sander Wolfram
Published: December 2010

The elusive diradicals α,2- and α,4-didehydrotoluene 1 and 3, have been generated by photolysis of matrix-isolated 2-iodobenzyl iodide 7 and 4-iodobenzyl iodide 8, respectively. Diradical 3 could also be synthesized by flash vacuum thermolysis of 8, with subsequent trapping of the products in argon at 5 K. The diradicals in their triplet ground states were characterized by electron paramagnetic resonance spectroscopy. The triplet ground states were in accordance with previous theoretical calculations for these species.
Thermal Decomposition of N-Acyloxy-N-alkoxyamides - a New HERON Reaction
Authors: Johns Jennifer P. , van Losenoord Arjan , Mary Clément , Garcia Pierre , Pankhurst Damian S. , Rosser Adam A. , Glover Stephen A.
Published: December 2010

The HERON reaction has been observed in the thermal decompositions of N-acyloxy-N-alkoxyamides 1b, members of the class of anomeric amides. The N,N-bisoxo-substitution results in reduced amide resonance and this, combined with an nO–σ*NOAcyl anomeric destabilization of the N–OAcyl bond, results in their intramolecular rearrangement to anhydrides 42 and alkoxynitrenes 43 in competition with homolysis of the N–OAcyl bond to alkoxyamidyls 51. The primary HERON product alkoxynitrenes are scavenged by oxygen, giving a nitrate ester, in competition with a rearrangement to nitriles and dimerization to hyponitrites, leading, under the conditions, to alcohols and aldehydes. Persistent alkoxyamidyls most likely form a 1,3-diradical in a solvent-cage reaction, which cyclizes to 3,5-disubstituted-(5H)-1,4,2-dioxazoles 47. Substituent effects support this competition reaction.
Sustained Reduction in the Clinical Incidence of Methicillin-Resistant Staphylococcus aureus Colonization or Infection Associated with a Multifaceted Infection Control Intervention
Authors: Ellingson Katherine , Muder Robert R. , Jain Rajiv , Kleinbaum David , Feng Pei-Jean I. , Cunningham Candace , Squier Cheryl , Lloyd Jon , Edwards Jonathan , Gebski Val , Jernigan John
Published: December 2010

Objective.

To assess the impact and sustainability of a multifaceted intervention to prevent methicillin-resistant Staphylococcus aureus (MRSA) transmission implemented in 3 chronologically overlapping phases at 1 hospital.

Design.

Interrupted time-series analyses.

Setting.

A Veterans Affairs hospital in the northeastern United States.

Patients and Participants.

Individuals admitted to acute care units from October 1, 1999, through September 30, 2008. To calculate the monthly clinical incidence of MRSA colonization or infection, the number of MRSA-positive cultures obtained from a clinical site more than 48 hours after admission among patients with no MRSA-positive clinical cultures during the previous year was divided by patient-days at risk. Secondary outcomes included clinical incidence of methicillin-sensitive S. aureus colonization or infection and incidence of MRSA bloodstream infections.

Interventions.

The intervention—implemented in a surgical ward beginning October 2001, in a surgical intensive care unit beginning October 2003, and in all acute care units beginning July 2005—included systems and behavior change strategies to increase adherence to infection control precautions (eg, hand hygiene and active surveillance culturing for MRSA).

Results.

Hospital-wide, the clinical incidence of MRSA colonization or infection decreased after initiation of the intervention in 2001, compared with the period before intervention (P = .002), and decreased by 61% (P < .001) in the 7-year postintervention period. In the postintervention period, the hospital-wide incidence of MRSA bloodstream infection decreased by 50% (P = .02), and the proportion of S. aureus isolates that were methicillin resistant decreased by 30% (P < .001).

Conclusions.

Sustained decreases in hospital-wide clinical incidence of MRSA colonization or infection, incidence of MRSA bloodstream infection, and proportion of S. aureus isolates resistant to methicillin followed implementation of a multifaceted prevention program at one Veterans Affairs hospital. Findings suggest that interventions designed to prevent transmission can impact endemic antimicrobial resistance problems.
Clinical Incidence of Methicillin-Resistant Staphylococcus aureus (MRSA) Colonization or Infection as a Proxy Measure for MRSA Transmission in Acute Care Hospitals
Authors: Feng Pei-Jean I. , Kallen Alexander J. , Ellingson Katherine , Muder Robert , Jain Rajiv , Jernigan John A.
Published: December 2010

Background.

The incidence of methicillin-resistant Staphylococcus aureus (MRSA) colonization or infection has been used as a proxy measure for MRSA transmission, but incidence calculations vary depending on whether active surveillance culture (ASC) data are included.

Objective.

To evaluate the relationship between incidences of MRSA colonization or infection calculated with and without ASCs in intensive care units and non-intensive care units.

Setting.

A Veterans Affairs medical center.

Methods.

From microbiology records, incidences of MRSA colonization or infection were calculated with and without ASC data. Correlation coefficients were calculated for the 2 measures, and Poisson regression was used to model temporal trends. A Poisson interaction model was used to test for differences in incidence trends modeled with and without ASCs.

Results.

The incidence of MRSA colonization or infection calculated with ASCs was 4.9 times higher than that calculated without ASCs. Correlation coefficients for incidences with and without ASCs were 0.42 for intensive care units, 0.59 for non-intensive care units, and 0.48 hospital-wide. Trends over time for the hospital were similar with and without ASCs (incidence rate ratio with ASCs, 0.95 [95% confidence interval, 0.93-0.97]; incidence rate ratio without ASCs, 0.95 [95% confidence interval, 0.92-0.99]; P = .68). Without ASCs, 35% of prevalent cases were falsely classified as incident.

Conclusions.

At 1 Veterans Affairs medical center, the incidence of MRSA colonization or infection calculated solely on the basis of clinical culture results commonly misclassified incident cases and underestimated incidence, compared with measures that included ASCs; however, temporal changes were similar. These findings suggest that incidence measured without ASCs may not accurately reflect the magnitude of MRSA transmission but may be useful for monitoring transmission trends over time, a crucial element for evaluating the impact of prevention activities.
Major histocompatibility complex polymorphism: dynamics and consequences of parasite‐mediated local adaptation in fishes
Authors: Eizaguirre C. , Lenz T. L.
Published: December 2010

Parasitism is a common form of life and represents a strong selective pressure for host organisms. In response to this evolutionary pressure, vertebrates have developed genetically coded defences such as the major histocompatibility complex (MHC). Mechanisms of parasite‐mediated selection not only maintain outstanding polymorphism in these genes but have also been proposed to further promote host population divergence and ultimately speciation because it can drive evolution of local adaptation in which MHC genes play a crucial role. This review first highlights the dynamics and complexity of parasite‐mediated selection in natural systems, which not only depends on dominating parasite strategies and on the taxonomic diversity of the parasite community but also includes the differences in parasite communities between habitats and niches, creating divergent selection on locally adapted populations. Then the different ways in which MHC genes potentially allow vertebrates to respond to these dynamics and to adapt locally are outlined. Finally, it is proposed that varying selection strength in time and space may lead to variation in the strength of precopulatory reproductive isolation which has evolved to maintain local adaptation.
Risk of Japanese carriers of hyperphosphorylated paratarg‐7, the first autosomal‐dominantly inherited risk factor for hematological neoplasms, to develop monoclonal gammopathy of undetermined significance and multiple myeloma
Authors: Grass Sandra , Iida Shinsuke , Wikowicz Aleksandra , Preuss Klaus‐Dieter , Inagaki Atsushi , Shimizu Kazuyuki , Ziepert Marita , Ueda Ryuzo , Pfreundschuh Michael
Published: December 2010

Hyperphosphorylated paratarg‐7 (pP‐7) is a frequent target of paraproteins in German patients with monoclonal gammopathy of undetermined significance (MGUS)/multiple myeloma (MM). The frequency of MGUS/MM is lower in Japan than in Europe. As pP‐7, the first molecularly defined autosomal‐dominant risk factor for any hematological neoplasm, is inherited in a dominant fashion, we determined the incidence of the pP‐7 carrier state in a Japanese population, and compared the frequency of pP‐7‐specific paraproteins and the pP‐7 carrier state in Japanese and German patients with MGUS/MM. Peripheral blood from 111 Japanese patients with MGUS/MM and 278 healthy blood donors was analyzed for the pP‐7 carrier state by isoelectric focusing and for pP‐7‐specific antibodies by ELISA. The Japanese group was compared with 252 German MGUS/MM patients and 200 healthy controls. Five of 111 (4.5%) Japanese and 35/252 (13.9%) German IgA/IgG MGUS/MM patients had a pP‐7‐specific paraprotein (P = 0.009). The prevalence of healthy pP‐7 carriers in the Japanese study group was 1/278 (0.36%), whereas it was 4/200 in the German group (P = 0.166). The relative risk for pP‐7 carriers developing MGUS/MM had an odds ratio of 13.1 in the Japanese and 7.9 in the German group. In conclusion, the fraction of pP‐7 carriers with a pP‐7‐specific paraprotein is lower among Japanese than in German patients with MGUS/MM, but pP‐7 carriers in both ethnic groups have a high risk of developing MGUS/MM. (Cancer Sci 2011; 102: 565–568)
An HrpB‐dependent but type III‐independent extracellular aspartic protease is a virulence factor of Ralstonia solanacearum
Authors: JEONG YEONHWA , CHEONG HOON , CHOI OKHEE , KIM JUNG KYU , KANG YONGSUNG , KIM JINWOO , LEE SEUNGDON , KOH SERRY , MOON JAE SUN , HWANG INGYU
Published: December 2010

The host specificity of Ralstonia solanacearum, the causal organism of bacterial wilt on many solanaceous crops, is poorly understood. To identify a gene conferring host specificity of the bacterium, SL341 (virulent to hot pepper but avirulent to potato) and SL2029 (virulent to potato but avirulent to hot pepper) were chosen as representative strains. We identified a gene, rsa1, from SL2029 that confers avirulence to SL341 in hot pepper. The rsa1 gene encoding an 11.8‐kDa protein possessed the perfect consensus hrpII box motif upstream of the gene. Although the expression of rsa1 was activated by HrpB, a transcriptional activator for hrp gene expression, Rsa1 protein was secreted in an Hrp type III secretion‐independent manner. Rsa1 exhibited weak homology with an aspartic protease, cathepsin D, and possessed protease activity. Two specific aspartic protease inhibitors, pepstatin A and diazoacetyl‐d,l‐norleucine methyl ester, inhibited the protease activity of Rsa1. Substitution of two aspartic acid residues with alanine at positions 54 and 59 abolished protease activity. The SL2029 rsa1 mutant was much less virulent than the wild‐type strain, but did not induce disease symptoms in hot pepper. These data indicate that Rsa1 is an extracellular aspartic protease and plays an important role for the virulence of SL2029 in potato.
Fungal pathogenicity genes in the age of ‘omics’
Authors: VAN DE WOUW ANGELA P. , HOWLETT BARBARA J.
Published: December 2010

The identification of the fungal genes essential for disease underpins the development of disease control strategies. Improved technologies for gene identification and functional analyses, as well as a plethora of sequenced fungal genomes, have led to the characterization of hundreds of genes, denoted as pathogenicity genes, which are required by fungi to cause disease. We describe recent technologies applied to characterize the fungal genes involved in disease and focus on some genes that are likely to attract continuing research activity.
The wxacO gene of Xanthomonas citri ssp. citri encodes a protein with a role in lipopolysaccharide biosynthesis, biofilm formation, stress tolerance and virulence
Authors: LI JINYUN , WANG NIAN
Published: December 2010

Xanthomonas citri ssp. citri (Xcc) causes citrus canker, one of the most economically damaging diseases affecting citrus worldwide. Biofilm formation is important for the pathogen to survive epiphytically in planta prior to the induction of canker symptoms. In this study, two EZ‐Tn5 transposon mutants of Xcc strain 306, affected in biofilm formation, were isolated; subsequent analyses led to the identification of a novel gene locus XAC3596 (designated as wxacO), encoding a putative transmembrane protein, and the rfbC gene, encoding a truncated O‐antigen biosynthesis protein. Sodium dodecylsulphate‐polyacrylamide gel electrophoresis revealed that lipopolysaccharide (LPS) biosynthesis was affected in both wxacO and rfbC mutants. The wxacO mutant was impaired in the formation of a structured biofilm on glass or host plant leaves, as shown in confocal laser scanning microscopy analysis of strains containing a plasmid expressing the green fluorescent protein. Both wxacO and rfbC mutants were more sensitive than the wild‐type strain to different environmental stresses, and more susceptible to the antimicrobial peptide polymyxin B. The two mutants were attenuated in swimming motility, but not in flagellar formation. The mutants also showed reduced virulence and decreased growth on host leaves when spray inoculated. The affected phenotypes of the wxacO and rfbC mutants were complemented to wild‐type levels by the intact wxacO and rfbC genes, respectively. This report identifies a new gene influencing LPS production by Xcc. In addition, our results suggest that a structurally intact LPS is critical for survival in the phyllosphere and for the virulence of Xcc.
Hospitalized incidence and case fatality for upper gastrointestinal bleeding from 1999 to 2007: a record linkage study
Authors: Button L. A. , Roberts S. E. , Evans P. A. , Goldacre M. J. , Akbari A. , Dsilva R. , Macey S. , Williams J. G.
Published: December 2010

Aliment Pharmacol Ther 2011; 33: 64–76

Background  Upper gastrointestinal (GI) bleeding is the most common emergency managed by gastroenterologists.

Aim  To establish the hospitalized incidence and case fatality for upper GI bleeding, and to determine how they are associated with factors including day of admission, hospital size, social deprivation and distance from hospital.

Methods  Systematic record linkage of hospital in‐patient and mortality data for 24 421 admissions for upper GI bleeding among 22 299 people in Wales from 1999 to 2007.

Results  The hospitalized incidence of upper GI bleeding was 134 per 100 000. Case fatality was 10.0%. Incidence was stable from 1999 to 2007; case fatality fell from 11.4% in 1999–2000 to 8.6% in 2006–7. Incidence was associated significantly with social deprivation. Compared with weekday admissions, case fatality was 13% higher for weekend admissions and 41% higher for admissions on public holidays. There was little variation in case fatality according to social deprivation, hospital size or distance from hospital.

Conclusions  Incidence, but not case fatality, was associated significantly with social deprivation. The higher mortality for weekend and public holiday admissions could not be explained by measures of case mix and may indicate a possible impact of reduced staffing levels and delays to endoscopy at weekends in some hospitals.
The potential effect of exotic Pacific ratsRattus exulanson vectors of scrub typhus
Authors: Kuo Chi‐Chien , Wang Hsi‐Chieh , Huang Ching‐Lun
Published: December 2010

1. The role and influence of exotic species in indigenous vector‐borne diseases are important but remain understudied. Ascertaining whether disease vectors prefer exotic vs. native hosts has important implications for human health. Moreover, evaluating whether exotic hosts are intrinsically less susceptible to vectors, or whether vector loads can vary with environment, is instructive for possible disease dynamics in the face of range expansion of exotic species.Rattus exulanshas recently been recorded for the first time in eastern Taiwan, where scrub typhus is prevalent. We assessed the role ofR. exulansas a host for chiggers (larval trombiculid mites), and the degree to which vector loads ofR. exulansexhibited spatial variation.

2. We deployed live traps in two villages in Taiwan that differed in human population density and in the incidence of scrub typhus. We recovered and tallied chiggers from small mammals, and identified over one‐fifth of chiggers from each host to species. Chiggers were assayed forOrientia tsutsugamushi(OT) infection with nested‐PCR.

3. R. exulanswas the most common small mammal species captured (31·4% total captures), and supported about one‐fifth of total chiggers recovered.Leptotrombidium imphalumdominated the chigger assemblage of most native species (>90%), butGahrliepiaspp. was commonly found inR. exulans(39·1%). We detected OT in the genusLeptotrombidium(39%) but not in theGahrliepia. Prevalence and loads of chiggers inR. exulanswere about 5× and 17× higher, respectively, in the less densely populated village; a similar trend also occurred with nativeR. losea.

4. Synthesis and applications. Currently,R. exulansappears to play a relatively minor role in supporting chiggers. However, the fact that both prevalence and loads of chiggers inR. exulansvary greatly with environment, along with the abundance of most exotic species and the ecological flexibility ofR. exulans, implies a potential health risk as this species expands to areas with more chiggers. Our study suggests that a clearer understanding of interactions among native and exotic hosts and native parasite species can facilitate prediction of the impact of exotic hosts on the dynamics of vector‐borne diseases.
Nonspecific patterns of vector, host and avian malaria parasite associations in a central African rainforest
Authors: NJABO K. Y. , CORNEL A. J. , BONNEAUD C. , TOFFELMIER E. , SEHGAL R. N. M. , VALKIŪNAS G. , RUSSELL A. F. , SMITH T. B.
Published: December 2010

Malaria parasites use vertebrate hosts for asexual multiplication and Culicidae mosquitoes for sexual and asexual development, yet the literature on avian malaria remains biased towards examining the asexual stages of the life cycle in birds. To fully understand parasite evolution and mechanism of malaria transmission, knowledge of all three components of the vector‐host‐parasite system is essential. Little is known about avian parasite–vector associations in African rainforests where numerous species of birds are infected with avian haemosporidians of the genera Plasmodium and Haemoproteus. Here we applied high resolution melt qPCR‐based techniques and nested PCR to examine the occurrence and diversity of mitochondrial cytochrome b gene sequences of haemosporidian parasites in wild‐caught mosquitoes sampled across 12 sites in Cameroon. In all, 3134 mosquitoes representing 27 species were screened. Mosquitoes belonging to four genera (Aedes, Coquillettidia, Culex and Mansonia) were infected with twenty‐two parasite lineages (18 Plasmodium spp. and 4 Haemoproteus spp.). Presence of Plasmodium sporozoites in salivary glands of Coquillettidia aurites further established these mosquitoes as likely vectors. Occurrence of parasite lineages differed significantly among genera, as well as their probability of being infected with malaria across species and sites. Approximately one‐third of these lineages were previously detected in other avian host species from the region, indicating that vertebrate host sharing is a common feature and that avian Plasmodium spp. vector breadth does not always accompany vertebrate–host breadth. This study suggests extensive invertebrate host shifts in mosquito–parasite interactions and that avian Plasmodium species are most likely not tightly coevolved with vector species.
Telomere length measurement can distinguish pathogenic from non‐pathogenic variants in the shelterin component, TIN2
Authors: Vulliamy T , Beswick R , Kirwan MJ , Hossain U , Walne AJ , Dokal I
Published: December 2010

Vulliamy T, Beswick R, Kirwan MJ, Hossain U, Walne AJ, Dokal I. Telomere length measurement can distinguish pathogenic from non‐pathogenic variants in the shelterin component, TIN2.

Dyskeratosis congenita (DC) is a heterogeneous bone marrow failure syndrome with seven disease‐causing genes identified to date, six of which are linked to telomere maintenance. Mutations in one of these genes (TINF2), which encodes a component of the shelterin complex, are associated with particularly short telomeres. Among the 224 consecutive patients with different forms of bone marrow failure (46 with DC, 122 with aplastic anaemia and 57 with some features of DC), we have identified 16 new families with variants in exon 6 of the TINF2 gene, eight of which are novel. We observe that the phenotype associated with these mutations extends to a severe early presentation, not always classified as DC. In addition, we see that some of the variants identified are not associated with short telomeres and are also found in asymptomatic individuals. In the absence of any direct functional assay, the data indicates that the telomere length measurement can inform us as to which variants in TINF2 are pathogenic and which may be non‐pathogenic.