bluuebunny/crossref_metadata_2025 huggingface dataset:
An analysis of coupling between a whispering gallery mode laser in an elliptical microring and the dominant mode in the coaxially oriented elliptical optical fiber
Authors: Baktur Reyhan , Pearson L. Wilson , Ballato John
Published: January 2010

The problem of coupling a whispering gallery mode laser into an optical fiber is considered. The whispering gallery mode laser is generated in a polymer microring formed coaxially on the optical fiber. The focus of this paper is to determine factors that influence the coupling between the laser and the fiber around which it is formed. The coupling mechanism is analyzed and it is found that when the microring and the fiber are of elliptical cross section, there exists controllable coupling between the laser and propagation mode in the fiber. The coupling between laser mode and fiber mode is due to characteristics of Mathieu functions that describe the fields in elliptical waveguides. It is shown that the coupling between the laser and the dominant mode in the fiber can be optimized by the designing the dimension of microring, the eccentricity of the elliptical cross section, and the material contrast between fiber and microring.
Microstructure evolution in carbon-ion implanted sapphire
Authors: Orwa J. O. , Peng J. L. , McCallum J. C. , Jamieson D. N. , Rubanov S. , Prawer S.
Published: January 2010

Carbon ions of MeV energy were implanted into sapphire to fluences of 1×1017 or 2×1017cm−2 and thermally annealed in forming gas (4% H in Ar) for 1h. Secondary ion mass spectroscopy results obtained from the lower dose implant showed retention of implanted carbon and accumulation of H near the end of range in the C implanted and annealed sample. Three distinct regions were identified by transmission electron microscopy of the implanted region in the higher dose implant. First, in the near surface region, was a low damage region (L1) composed of crystalline sapphire and a high density of plateletlike defects. Underneath this was a thin, highly damaged and amorphized region (L2) near the end of range in which a mixture of i-carbon and nanodiamond phases are present. Finally, there was a pristine, undamaged sapphire region (L3) beyond the end of range. In the annealed sample some evidence of the presence of diamond nanoclusters was found deep within the implanted layer near the projected range of the C ions. These results are compared with our previous work on carbon implanted quartz in which nanodiamond phases were formed only a few tens of nanometers from the surface, a considerable distance from the projected range of the ions, suggesting that significant out diffusion of the implanted carbon had occurred.
Spectroscopic ellipsometry of wurtzite ZnO and GaN: Examination of a special case
Authors: Shokhovets S. , Spieß L. , Gobsch G.
Published: January 2010

We examine the special case of spectroscopic ellipsometry measurements in the vicinity of the fundamental absorption edge of wurtzite ZnO and GaN when the optic axis is perpendicular to the sample surface. It is demonstrated, both by calculations and direct experimental data, that the isotropic dielectric function (DF) derived by means of the isotropic model does not lie between the ordinary and extraordinary DFs and is not their mixture. In general, the isotropic DF also cannot be considered as being approximately identical to the ordinary DF. We observe that their difference may become significant and, in addition, shows a complicated spectral behavior, especially in a range of excitonic absorption. The discrepancy between the isotropic and ordinary DFs of ZnO exceeds 15% at room temperature. For GaN, this effect is considerably smaller. However, the discrepancy might not be neglected if the temperature is sufficiently low.
A statistical model of magnetic islands in a current layer
Authors: Fermo R. L. , Drake J. F. , Swisdak M.
Published: January 2010

This letter describes a statistical model of the dynamics of magnetic islands in very large current layers that develop in space plasma. Two parameters characterize the island distribution: the flux ψ contained in the island and the area A it encloses. The integrodifferential evolution equation for this distribution function is based on rules that govern the small-scale generation of secondary islands, the rates of island growth, and island merging. The numerical solutions of this equation produce island distributions relevant to the magnetosphere and solar corona. The solution of a differential equation for large islands explicitly shows the role merging plays in island growth.
Low-field magnetic characterization of ferromagnets using a minor-loop scaling law
Authors: Kobayashi Satoru , Takahashi Seiki , Shishido Toetsu , Kamada Yasuhiro , Kikuchi Hiroaki
Published: January 2010

A scaling power law relating hysteresis loss and remanence in minor hysteresis loops is proposed for the low-field magnetic characterization of ferromagnetic materials. We demonstrate that the law holds true for very low to an intermediate level of magnetization, associated with a universal exponent of ≈1.35, irrespective of types of ferromagnets and temperature, unlike the Steinmetz law with limited applicability. The coefficient in the scaling law shows almost the same behavior as coercivity and can be used for the evaluation of the magnetic quality of materials for which the Steinmetz law cannot be applied and/or low measurement field is necessary.
Chemical reactivity of aromatic hydrocarbons and operational degradation of organic light-emitting diodes
Authors: Kondakov Denis Y. , Brown Christopher T. , Pawlik Thomas D. , Jarikov Viktor V.
Published: January 2010

We report the study of the chemical reactivity of representative hydrocarbon organic light-emitting diode (OLED) materials—fully aromatic derivatives of anthracene and tetracene in the OLED environment. In addition to the participation in free-radical chemistry initiated by homolytic bond dissociation reactions of arylamines, the hydrocarbons appear to initiate and undergo dehydrogenation reactions following the electronic excitation caused by the recombination of charge carriers or by the absorption of a photon. A chemical product of the intramolecular dehydrogenation reaction, cyclization, was identified in photoexcited films of representative anthracene derivative and detected in electrically degraded OLEDs utilizing this material in the emissive layer. Other analogous intra- and intermolecular dehydrogenation reactions initiated by the excited states of hydrocarbons are also expected to occur in operating OLEDs. The stepwise transfers of hydrogen atoms or ions to neighboring molecules are likely to yield, at least in part, neutral or ionic forms of performance-damaging species—nonradiative recombination centers and luminescence quenchers. A comparison of the luminescence losses and quantities of the identified degradation product in OLEDs and photoexcited films suggests that the dehydrogenation mechanism plays a minor but not negligible part in the operational degradation of modern OLEDs utilizing hydrocarbons as emissive layer hosts.
Renewable energy of waste heat recovery system for automobiles
Authors: Hsu Cheng-Ting , Yao Da-Jeng , Ye Ke-Jyun , Yu Ben
Published: January 2010

A system to recover waste heat comprised of eight thermoelectric generators (TEGs) to convert heat from the exhaust pipe of an automobile to electrical energy has been constructed. Simulations and experiments for the thermoelectric module in this system are undertaken to assess the feasibility of these applications. In order to estimate the temperature difference between thermoelectric elements, a network of thermal resistors is constructed. The results assist in predicting power output of TEG module more precisely. Three configurations of heat sinks, which are comprised of 10, 22, and 44 fins, are applied in this simulation. The results of the simulations show the average thermal resistance of these heat sinks in each section of the system with varied velocity of external flow. As the performance of a TEG module is influenced by an applied pressure through the effect of the thermal contact resistance, we clamp the TE module to our experimental apparatus; the relation between power output and pressure applied in this case is presented. Besides simulations, the system is designed and assembled. Measurements followed the connection of the system to the middle of an exhaust pipe. Through these simulations and experiments, the power generated with a commercial TEG is presented. The results establish the fundamental development of materials that enhance the TEG efficiency for vehicles.
Damping mechanisms in alumina borate whisker-reinforced-aluminum matrix composites with or without SnO2 coatings
Authors: Hu J. , Wang X. F. , Zheng Z. Z.
Published: January 2010

SnO 2 was successfully coated on the surface of alumina borate whiskers. The pure aluminum matrix composites reinforced with a SnO2-coated alumina borate whisker were fabricated by squeeze casting. The effects of coating contents on the damping properties of the coated composites at various temperatures, frequencies, and strain amplitudes were examined. The microstructures of the coated composites were also investigated through transmission electron microscopy observations. These results indicate that the introduction of Sn at the interface between whisker and matrix in the coated composites during the squeeze casting process alters not only the interface structures but also the dislocation status of the matrices in the vicinity of the interface. The results of damping characterization indicate that the damping capacities of the coated composites strongly depend on the coating contents and strain amplitudes. A damping peak at low temperatures appeared not only in the coated composites but also in the noncoated one, which is related to dislocation motion and interfacial slip caused by Sn. A damping peak at high temperatures appeared only in the coated composites, and the damping mechanisms at high temperature change with the increase in strain amplitudes. Sn played an important role on the damping mechanisms of the coated composites all along.
Ultrahigh vacuum/high-pressure flow reactor for surface x-ray diffraction and grazing incidence small angle x-ray scattering studies close to conditions for industrial catalysis
Authors: van Rijn R. , Ackermann M. D. , Balmes O. , Dufrane T. , Geluk A. , Gonzalez H. , Isern H. , de Kuyper E. , Petit L. , Sole V. A. , Wermeille D. , Felici R. , Frenken J. W. M.
Published: January 2010

A versatile instrument for the in situ study of catalyst surfaces by surface x-ray diffraction and grazing incidence small angle x-ray scattering in a 13 ml flow reactor combined with reaction product analysis by mass spectrometry has been developed. The instrument bridges the so-called “pressure gap” and “materials gap” at the same time, within one experimental setup. It allows for the preparation and study of catalytically active single crystal surfaces and is also equipped with an evaporator for the deposition of thin, pure metal films, necessary for the formation of small metal particles on oxide supports. Reactions can be studied in flow mode and batch mode in a pressure range of 100–1200 mbar and temperatures up to 950 K. The setup provides a unique combination of sample preparation, characterization, and in situ experiments where the structure and reactivity of both single crystals and supported nanoparticles can be simultaneously determined.
Atomic and molecular effects on spherically convergent ion flow. I. Single atomic species
Authors: Emmert G. A. , Santarius J. F.
Published: January 2010

A formalism for analyzing the effect of ion-neutral gas interactions on the flow of ions between nearly transparent electrodes in spherical geometry has been developed for atomic ions in a weakly ionized plasma, so that the important atomic effects are charge exchange and ion impact ionization. The formalism is applied to spherical, gridded, inertial-electrostatic confinement (IEC) devices. The formalism yields detailed information about the energy spectra of the ions and fast neutral atoms, and the resulting fusion rate for H3e ions in a background H3e gas. The results are illustrated with an example calculation for the Wisconsin IEC device operating on H3e.
Step bunching in the absence of an Ehrlich–Schwoebel barrier during nanowire growth
Authors: Golovin A. A. , Davis S. H. , Voorhees P. W.
Published: January 2010

Step bunching at a growing crystal surface is usually attributed to the presence of the Ehrlich–Schwoebel (ES) effect caused by the asymmetry of the attachment kinetics at a step. Here, we show that, contrary to the case of rectilinear motion, step bunches at the solid-liquid interface of a nanowire grown by the vapor-liquid-solid process can form even in the absence of the ES effect. It is found that two circular steps propagating from the edge of the nanowire inward form a bunch if the initial distance between the steps is less than a critical value. This effect is caused by the interaction of steps with each other via the diffusion field in the bulk of the liquid catalytic particle. The normal ES effect promotes the bunching, while the anomalous ES effect delays it.
Photoluminescence of rare earth3+ doped uniaxially aligned HfO2 nanotubes prepared by sputtering with electrospun polyvinylpyrolidone nanofibers as templates
Authors: Liu L. X. , Ma Z. W. , Xie Y. Z. , Su Y. R. , Zhao H. T. , Zhou M. , Zhou J. Y. , Li J. , Xie E. Q.
Published: January 2010

Rare earth (RE) ions (Eu3+,Tb3+) doped uniaxially aligned HfO2 nanotubes were prepared by radio frequency sputtering with electrospun polyvinylpyrolidone (PVP) nanofiber templates. The as-sputtered samples were annealed at different temperatures (500–1000 °C) in O2 ambient in order to remove their PVP cores and make the HfO2 shells well crystallized. Morphologies and crystal configuration of the samples were investigated by optical microscope, scanning electron microscopy, transmission electron microscopy, x–ray diffraction, and Raman spectroscopy. The nanotubes have uniform intact structure with an average diameter of 200 nm and a wall thickness of about 25 nm. Photoluminescence (PL) properties of the RE doped nanotubes have been studied in detail. The emission peaks of the aligned HfO2:Eu and HfO2:Tb nanotubes could correspond to the D50→F7J (J=0–2) transitions of Eu3+ and the D54→F7J (J=3–6) transitions of Tb3+, respectively. The PL intensities of the HfO2:RE3+ nanotubes were higher by several orders of magnitude than that of the films. This enhancement in the PL could be ascribed to the high density of surface states of HfO2:RE3+ nanotubes.
Schlieren technique applied to the arc temperature measurement in a high energy density cutting torch
Authors: Prevosto L. , Artana G. , Mancinelli B. , Kelly H.
Published: January 2010

Plasma temperature and radial density profiles of the plasma species in a high energy density cutting arc have been obtained by using a quantitative schlieren technique. A Z-type two-mirror schlieren system was used in this research. Due to its great sensibility such technique allows measuring plasma composition and temperature from the arc axis to the surrounding medium by processing the gray-level contrast values of digital schlieren images recorded at the observation plane for a given position of a transverse knife located at the exit focal plane of the system. The technique has provided a good visualization of the plasma flow emerging from the nozzle and its interactions with the surrounding medium and the anode. The obtained temperature values are in good agreement with those values previously obtained by the authors on the same torch using Langmuir probes.
Analysis of transient electron energy in a micro dielectric barrier discharge for a high performance plasma display panel
Authors: Uchida Giichiro , Uchida Satoshi , Kajiyama Hiroshi , Shinoda Tsutae
Published: January 2010

We present here analysis of electron energy of a micro dielectric barrier discharge (micro-DBD) for alternating-current plasma display panel (ac-PDP) with Ne/Xe gas mixture by using the optical emission spectroscopy (OES). The OES method is quite useful to evaluate a variety of electron energy in a high pressure DBD ignited in a PDP small cell. Experiment shows that the ratio of Ne emission intensity (INe) relative to Xe emission intensity (IXe) drastically decreases with time. This temporal profile is well consistent with dynamic behavior of electron temperature in a micro-DBD, calculated in one-dimensional fluid model. INe/IXe also decreases with an increase in Xe gas pressure and a decrease in applied voltage especially in the initial stage of discharge, and these reflect the basic features of electron temperature in a micro-DBD. The influences of plasma parameters such as electron temperature on luminous efficacy are also theoretically analyzed using one-dimensional fluid model. The low electron temperature, which is attained at high Xe gas pressure, realizes the efficient Xe excitation for vacuum ultraviolet radiation. The high Xe-pressure condition also induces the rapid growth of discharge and consequent high plasma density, resulting in high electron heating efficiency.
Improving the d33 and g33 properties of 0-3 piezoelectric composites by dielectrophoresis
Authors: van den Ende D. A. , Bory B. F. , Groen W. A. , van der Zwaag S.
Published: January 2010

Composites of piezoelectric particles in a polymer matrix with enhanced properties in the poling direction were prepared by dielectrophoretic alignment of the particles. The effect of processing parameters such as the amplitude and frequency of the applied electric field and the viscosity of the matrix on the dielectric and piezoelectric properties of the cured composite were demonstrated for a composite with a PZT volume fraction of 0.2. The amount of structuring could be correlated to the dielectric and piezoelectric properties of the composite through the P2¯ order parameter for the average particle chain orientation, which was derived from image analysis of the microstructure. The piezoelectric properties of the aligned composites can be described with a new model for composites containing particles arranged into chains. The model predictions are in good agreement with the experimental results.
Thermoreflectance dependence on Fermi surface electron number density perturbations
Authors: Hopkins Patrick E.
Published: January 2010

The effects of an optical excitation on the thermoreflectance spectra of a solid are studied. A photonic excitation with sufficient energy will cause a perturbation in the electron number density around the Fermi surface. As the number density changes, so do the plasma frequency and carrier scattering rates, creating a change in the thermoreflectance response. Not accounting for the appropriate electron number density around the Fermi level after an optical excitation leads to an underestimate of electron scattering rates.
Combination of a Knudsen effusion cell with a quartz crystal microbalance: In situ measurement of molecular evaporation rates with a fully functional deposition source
Authors: Gutzler Rico , Heckl Wolfgang M. , Lackinger Markus
Published: January 2010

We describe a straightforward, reliable, and inexpensive design of a Knudsen type molecular effusion cell capable of measuring molecular evaporation rates in situ. This is accomplished by means of a quartz crystal microbalance integrated into the shutter of the effusion cell. The presented layout facilitates both the measurement of effusion rates under ultrahigh vacuum conditions without the need for a separate experimental setup and the growth of surface supported molecular layers and nanostructures. As an important prerequisite for reproducible deposition of molecular films with defined coverages ranging from submonolayers up to multilayers, the Knudsen cell features a stable deposition rate for crucible temperatures between 50 and 500 °C. Experimental determination of deposition rates for different crucible temperatures allows to approximate sublimation enthalpies of the evaporant based on the Clausius–Clapeyron equation.
Defects analysis at the nanometric scale in Ca3Co4O9 thin films
Authors: Moubah R. , Colis S. , Ulhaq-Bouillet C. , Dinia A.
Published: January 2010

We report on the nature and origin of structural defects at a nanometric scale in incommensurate Ca3Co4O9 thin films deposited by pulsed laser ablation on Al2O3(001) substrates. X-ray diffraction suggests that the deposited films have a well defined texture and that are free of spurious phases. However, cross section scanning high resolution transmission electron microscopy observations show the presence of regions with different kinds of stacking. Such regions present different chemical compositions from that of Ca3Co4O9 and are not detectable in diffraction mode. The local chemical analysis and the interplane distance measurement suggest that these defects correspond to the formation of the CaCo2O4 spurious phase. This phase has a similar structure and close lattice parameters with those of Ca3Co4O9. The origin of the formation of CaCo2O4 is discussed in terms of (i) strains due to the substrate which tend to suppress the incommensurability of the system, and (ii) local chemical nonstoichiometry.
Visualization of the cation migration in ionic polymer-metal composite under an electric field
Authors: Park Il-Seok , Kim Sang-Mun , Pugal Deivid , Huang Liming , Tam-Chang Suk-Wah , Kim Kwang J.
Published: January 2010

Ionic polymer-metal composites (IPMCs) exhibit a large dynamic bending deformation due to the redistribution of counter-ions inside the polymer. It has not been possible to get the high resolution data of the cation migration. The images obtained so far have only validated the versatile actuation model. The actuation model states that the electrically induced cation movement contributes to the volumetric stress change in the membrane. In this work, a visualization of the cation migration using the fluorescent microscopy is created. The results demonstrated in this letter help to understand the underlying mechanism of the IPMC transduction.
Note: A simple, convenient, and reliable method to prepare gold scanning tunneling microscope tips
Authors: Qian Guoguang , Saha Swatilekha , Lewis K. M.
Published: January 2010

A simple method to prepare gold tips for scanning tunneling microscopy has been introduced. In this method, electrochemical etching without a hazardous electrolyte was employed. The setup uses basic laboratory instrumentation to control the etching process. This avoids purchasing complicated, expensive, and dedicated equipment for tip preparation. A procedure to optimize the etching parameters by setting the current limit is described. Etched tips were checked with both optical and scanning electron microscopy.
Giant tunnel electroresistance with PbTiO3 ferroelectric tunnel barriers
Authors: Crassous A. , Garcia V , Bouzehouane K. , Fusil S. , Vlooswijk A. H. G. , Rispens G. , Noheda B , Bibes M. , Barthélémy A.
Published: January 2010

The persistency of ferroelectricity in ultrathin films allows their use as tunnel barriers. Ferroelectric tunnel junctions are used to explore the tunneling electroresistance effect—a change in the electrical resistance associated with polarization reversal in the ferroelectric barrier layer—resulting from the interplay between ferroelectricity and quantum-mechanical tunneling. Here, we use piezoresponse force microscopy and conductive-tip atomic force microscopy at room temperature to demonstrate the resistive readout of the polarization state through its influence on the tunnel current in PbTiO3 ultrathin ferroelectric films. The tunnel electroresistance reaches values of 50 000% through a 3.6 nm PbTiO3 film.
Ordered microdroplet formations of thin ferrofluid layer breakups
Authors: Chen Ching-Yao , Li C.-S.
Published: January 2010

The ordered breakup pattern of a thin layer of ferrofluid drop subjected to a uniform perpendicular field is experimentally investigated. The results confirm a universal pattern formation containing numerous breaking droplets of a uniform size, which is independent of the initial area of ferrofluid drop and the propagating directions of the formation waves. Two quantitative observations regarding the size and number of breaking droplets are concluded. Both the experiments and theoretical analysis show the correlation between the diameter of breaking droplets (d) and magnetization strength (M) can be characterized as d∝1/M2. The uniform size of breaking droplets under a constant field strength results in a linear proportionality between the number of breaking droplets (N) and the initial area of ferrofluid drop (A) as N∝A, which is verified by the experiments.
Jensen–Tsallis divergence and atomic dissimilarity for position and momentum space electron densities
Authors: Antolín J. , López-Rosa S. , Angulo J. C. , Esquivel R. O.
Published: January 2010

Quantifying the dissimilarity among two or more many-electron systems by means of their one-particle densities is a hot topic within the physical applications of the information theory. This is a relevant achievement of the so-called “divergence measures,” for which several definitions have been considered, each one with its own advantages and difficulties. Nevertheless, all of them are considered in order to disclose the differences among the involved systems, neutral atoms in the present work, according to their densities in the position and momentum spaces. The pioneering Jensen–Shannon divergence (JSD) constitutes a particular case of the one-parameter Jensen–Tsallis divergence (JTD). The analysis here provided for the JTD of atomic systems generalizes and improves some previous results on the JSD one. Such an improvement mainly arises from the capability of JTD to modify, by means of its characteristic parameter, the relative contribution of relevant specific regions of the atomic densities in both conjugated spaces.
Photoelectron imaging of small silicon cluster anions, Sin− (n=2–7)
Authors: Peppernick Samuel J. , Gunaratne K. D. Dasitha , Sayres Scott G. , Castleman A. W.
Published: January 2010

Photoelectron imaging experiments were conducted on small silicon cluster anions, Sin− (n=2–7), acquired at a photon energy of 3.49 eV (355 nm). Electronic transitions arising from the anion ground states are observed, and the evaluated vertical detachment energies agree well with previous measurements and theoretical calculations. The anisotropy β parameters have also been determined for each unique feature appearing in the photoelectron angular distributions at the employed photon energy. Separate calculations using density functional theory are also undertaken to determine the relative atomic orbital contributions constructing the interrogated highest occupied and low-lying molecular orbitals of a specific cluster. A method to interpret the observed cluster angular distributions, term the β-wave approach, is then implemented which provides quantitative predictions of the anisotropy β parameter for partial wave emission from molecular orbitals partitioned by varying contributions of atomic orbital angular momenta. Highlighted in the β-wave analysis is the ability of discriminating between disparate molecular orbitals from two nearly isoenergetic structural isomers of opposing point group symmetry for the Si4− and Si6− cluster ions, respectively.
An enzyme with self-control
Authors: Leslie Mitch
Published: January 2010

To keep itself in check, Plk4 encourages its own removal.
FYCO1 is a Rab7 effector that binds to LC3 and PI3P to mediate microtubule plus end–directed vesicle transport
Authors: Pankiv Serhiy , Alemu Endalkachew A. , Brech Andreas , Bruun Jack-Ansgar , Lamark Trond , Øvervatn Aud , Bjørkøy Geir , Johansen Terje
Published: January 2010

Autophagy is the main eukaryotic degradation pathway for long-lived proteins, protein aggregates, and cytosolic organelles. Although the protein machinery involved in the biogenesis of autophagic vesicles is well described, very little is known about the mechanism of cytosolic transport of autophagosomes. In this study, we have identified an adaptor protein complex, formed by the two autophagic membrane-associated proteins LC3 and Rab7 and the novel FYVE and coiled-coil (CC) domain–containing protein FYCO1, that promotes microtubule (MT) plus end–directed transport of autophagic vesicles. We have characterized the LC3-, Rab7-, and phosphatidylinositol-3-phosphate–binding domains in FYCO1 and mapped part of the CC region essential for MT plus end–directed transport. We also propose a mechanism for selective autophagosomal membrane recruitment of FYCO1.
Stringent requirement for HRD1, SEL1L, and OS-9/XTP3-B for disposal of ERAD-LS substrates
Authors: Bernasconi Riccardo , Galli Carmela , Calanca Verena , Nakajima Toshihiro , Molinari Maurizio
Published: January 2010

Sophisticated quality control mechanisms prolong retention of protein-folding intermediates in the endoplasmic reticulum (ER) until maturation while sorting out terminally misfolded polypeptides for ER-associated degradation (ERAD). The presence of structural lesions in the luminal, transmembrane, or cytosolic domains determines the classification of misfolded polypeptides as ERAD-L, -M, or -C substrates and results in selection of distinct degradation pathways. In this study, we show that disposal of soluble (nontransmembrane) polypeptides with luminal lesions (ERAD-LS substrates) is strictly dependent on the E3 ubiquitin ligase HRD1, the associated cargo receptor SEL1L, and two interchangeable ERAD lectins, OS-9 and XTP3-B. These ERAD factors become dispensable for degradation of the same polypeptides when membrane tethered (ERAD-LM substrates). Our data reveal that, in contrast to budding yeast, tethering of mammalian ERAD-L substrates to the membrane changes selection of the degradation pathway.
Polo-like kinase 4 kinase activity limits centrosome overduplication by autoregulating its own stability
Authors: Holland Andrew J. , Lan Weijie , Niessen Sherry , Hoover Heather , Cleveland Don W.
Published: January 2010

Accurate control of the number of centrosomes, the major microtubule-organizing centers of animal cells, is critical for the maintenance of genome integrity. Abnormalities in centrosome number can promote errors in spindle formation that lead to subsequent chromosome missegregation, and extra centrosomes are found in many cancers. Centrosomes are comprised of a pair of centrioles surrounded by amorphous pericentriolar material, and centrosome duplication is controlled by centriole replication. Polo-like kinase 4 (Plk4) plays a key role in initiating centriole duplication, and overexpression of Plk4 promotes centriole overduplication and the formation of extra centrosomes. Using chemical genetics, we show that kinase-active Plk4 is inherently unstable and targeted for degradation. Plk4 is shown to multiply self-phosphorylate within a 24–amino acid phosphodegron. Phosphorylation of multiple sites is required for Plk4 instability, indicating a requirement for a threshold level of Plk4 kinase activity to promote its own destruction. We propose that kinase-mediated, autoregulated instability of Plk4 self-limits Plk4 activity so as to prevent centrosome amplification.
Hyperpolarization-activated inward leakage currents caused by deletion or mutation of carboxy-terminal tyrosines of the Na+/K+-ATPase α subunit
Authors: Meier Susan , Tavraz Neslihan N. , Dürr Katharina L. , Friedrich Thomas
Published: January 2010

The Na+/K+-ATPase mediates electrogenic transport by exporting three Na+ ions in exchange for two K+ ions across the cell membrane per adenosine triphosphate molecule. The location of two Rb+ ions in the crystal structures of the Na+/K+-ATPase has defined two “common” cation binding sites, I and II, which accommodate Na+ or K+ ions during transport. The configuration of site III is still unknown, but the crystal structure has suggested a critical role of the carboxy-terminal KETYY motif for the formation of this “unique” Na+ binding site. Our two-electrode voltage clamp experiments on Xenopus oocytes show that deletion of two tyrosines at the carboxy terminus of the human Na+/K+-ATPase α2 subunit decreases the affinity for extracellular and intracellular Na+, in agreement with previous biochemical studies. Apparently, the ΔYY deletion changes Na+ affinity at site III but leaves the common sites unaffected, whereas the more extensive ΔKETYY deletion affects the unique site and the common sites as well. In the absence of extracellular K+, the ΔYY construct mediated ouabain-sensitive, hyperpolarization-activated inward currents, which were Na+ dependent and increased with acidification. Furthermore, the voltage dependence of rate constants from transient currents under Na+/Na+ exchange conditions was reversed, and the amounts of charge transported upon voltage pulses from a certain holding potential to hyperpolarizing potentials and back were unequal. These findings are incompatible with a reversible and exclusively extracellular Na+ release/binding mechanism. In analogy to the mechanism proposed for the H+ leak currents of the wild-type Na+/K+-ATPase, we suggest that the ΔYY deletion lowers the energy barrier for the intracellular Na+ occlusion reaction, thus destabilizing the Na+-occluded state and enabling inward leak currents. The leakage currents are prevented by aromatic amino acids at the carboxy terminus. Thus, the carboxy terminus of the Na+/K+-ATPase α subunit represents a structural and functional relay between Na+ binding site III and the intracellular cation occlusion gate.
Intrinsic versus extrinsic voltage sensitivity of blocker interaction with an ion channel pore
Authors: Martínez-François Juan Ramón , Lu Zhe
Published: January 2010

Many physiological and synthetic agents act by occluding the ion conduction pore of ion channels. A hallmark of charged blockers is that their apparent affinity for the pore usually varies with membrane voltage. Two models have been proposed to explain this voltage sensitivity. One model assumes that the charged blocker itself directly senses the transmembrane electric field, i.e., that blocker binding is intrinsically voltage dependent. In the alternative model, the blocker does not directly interact with the electric field; instead, blocker binding acquires voltage dependence solely through the concurrent movement of permeant ions across the field. This latter model may better explain voltage dependence of channel block by large organic compounds that are too bulky to fit into the narrow (usually ion-selective) part of the pore where the electric field is steep. To date, no systematic investigation has been performed to distinguish between these voltage-dependent mechanisms of channel block. The most fundamental characteristic of the extrinsic mechanism, i.e., that block can be rendered voltage independent, remains to be established and formally analyzed for the case of organic blockers. Here, we observe that the voltage dependence of block of a cyclic nucleotide–gated channel by a series of intracellular quaternary ammonium blockers, which are too bulky to traverse the narrow ion selectivity filter, gradually vanishes with extreme depolarization, a predicted feature of the extrinsic voltage dependence model. In contrast, the voltage dependence of block by an amine blocker, which has a smaller “diameter” and can therefore penetrate into the selectivity filter, follows a Boltzmann function, a predicted feature of the intrinsic voltage dependence model. Additionally, a blocker generates (at least) two blocked states, which, if related serially, may preclude meaningful application of a commonly used approach for investigating channel gating, namely, inferring the properties of the activation gate from the kinetics of channel block.
Kinetics of M1 muscarinic receptor and G protein signaling to phospholipase C in living cells
Authors: Falkenburger Björn H. , Jensen Jill B. , Hille Bertil
Published: January 2010

G protein–coupled receptors (GPCRs) mediate responses to external stimuli in various cell types. Early events, such as the binding of ligand and G proteins to the receptor, nucleotide exchange (NX), and GTPase activity at the Gα subunit, are common for many different GPCRs. For Gq-coupled M1 muscarinic (acetylcholine) receptors (M1Rs), we recently measured time courses of intermediate steps in the signaling cascade using Förster resonance energy transfer (FRET). The expression of FRET probes changes the density of signaling molecules. To provide a full quantitative description of M1R signaling that includes a simulation of kinetics in native (tsA201) cells, we now determine the density of FRET probes and construct a kinetic model of M1R signaling through Gq to activation of phospholipase C (PLC). Downstream effects on the trace membrane lipid phosphatidylinositol 4,5-bisphosphate (PIP2) and PIP2-dependent KCNQ2/3 current are considered in our companion paper in this issue (Falkenburger et al. 2010. J. Gen. Physiol. doi:10.1085/jgp.200910345). By calibrating their fluorescence intensity, we found that we selected transfected cells for our experiments with ∼3,000 fluorescently labeled receptors, G proteins, or PLC molecules per µm2 of plasma membrane. Endogenous levels are much lower, 1–40 per µm2. Our kinetic model reproduces the time courses and concentration–response relationships measured by FRET and explains observed delays. It predicts affinities and rate constants that align well with literature values. In native tsA201 cells, much of the delay between ligand binding and PLC activation reflects slow binding of G proteins to receptors. With M1R and Gβ FRET probes overexpressed, 10% of receptors have G proteins bound at rest, rising to 73% in the presence of agonist. In agreement with previous work, the model suggests that binding of PLC to Gαq greatly speeds up NX and GTPase activity, and that PLC is maintained in the active state by cycles of rapid GTP hydrolysis and NX on Gαq subunits bound to PLC.
Kinetics of PIP2 metabolism and KCNQ2/3 channel regulation studied with a voltage-sensitive phosphatase in living cells
Authors: Falkenburger Björn H. , Jensen Jill B. , Hille Bertil
Published: January 2010

The signaling phosphoinositide phosphatidylinositol 4,5-bisphosphate (PIP2) is synthesized in two steps from phosphatidylinositol by lipid kinases. It then interacts with KCNQ channels and with pleckstrin homology (PH) domains among many other physiological protein targets. We measured and developed a quantitative description of these metabolic and protein interaction steps by perturbing the PIP2 pool with a voltage-sensitive phosphatase (VSP). VSP can remove the 5-phosphate of PIP2 with a time constant of τ <300 ms and fully inhibits KCNQ currents in a similar time. PIP2 was then resynthesized from phosphatidylinositol 4-phosphate (PIP) quickly, τ = 11 s. In contrast, resynthesis of PIP2 after activation of phospholipase C by muscarinic receptors took ∼130 s. These kinetic experiments showed that (1) PIP2 activation of KCNQ channels obeys a cooperative square law, (2) the PIP2 residence time on channels is <10 ms and the exchange time on PH domains is similarly fast, and (3) the step synthesizing PIP2 by PIP 5-kinase is fast and limited primarily by a step(s) that replenishes the pool of plasma membrane PI(4)P. We extend the kinetic model for signaling from M1 muscarinic receptors, presented in our companion paper in this issue (Falkenburger et al. 2010. J. Gen. Physiol. doi:10.1085/jgp.200910344), with this new information on PIP2 synthesis and KCNQ interaction.
Multicenter Study of Surveillance for Hospital-Onset Clostridium difficile Infection by the Use of ICD-9-CM Diagnosis Codes
Authors: Dubberke Erik R. , Butler Anne M. , Yokoe Deborah S. , Mayer Jeanmarie , Hota Bala , Mangino Julie E. , Khan Yosef M. , Popovich Kyle J. , Stevenson Kurt B. , McDonald L. Clifford , Olsen Margaret A. , Fraser Victoria J. ,   Prevention Epicenters Program of the Centers for Disease Control and Prevention
Published: January 2010

Objective.

To compare incidence of hospital-onset Clostridium difficile infection (CDI) measured by the use of International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) discharge diagnosis codes with rates measured by the use of electronically available C. difficile toxin assay results.

Methods.

Cases of hospital-onset CDI were identified at 5 US hospitals during the period from July 2000 through June 2006 with the use of 2 surveillance definitions: positive toxin assay results (gold standard) and secondary ICD-9-CM discharge diagnosis codes for CDI. The x2 test was used to compare incidence, linear regression models were used to analyze trends, and the test of equality was used to compare slopes.

Results.

Of 8,670 cases of hospital-onset CDI, 38% were identified by the use of both toxin assay results and the ICD-9-CM code, 16% by the use of toxin assay results alone, and 45% by the use of the ICD-9-CM code alone. Nearly half (47%) of cases of CDI identified by the use of a secondary diagnosis code alone were community-onset CDI according to the results of the toxin assay. The rate of hospital-onset CDI found by use of ICD-9-CM codes was significantly higher than the rate found by use of toxin assay results overall (P<.001), as well as individually at 3 of the 5 hospitals (P<.001 for all). The agreement between toxin assay results and the presence of a secondary ICD-9-CM diagnosis code for CDI was moderate, with an overall k value of 0.509 and hospital-specific k values of 0.489–0.570. Overall, the annual increase in CDI incidence was significantly greater for rates determined by the use of ICD-9-CM codes than for rates determined by the use of toxin assay results (P = .006).

Conclusions.

Although the ICD-9-CM code for CDI seems to be adequate for measuring the overall CDI burden, use of the ICD-9-CM discharge diagnosis code for CDI, without present-on-admission code assignment, is not an acceptable surrogate for surveillance for hospital-onset CDI.
Distribution of Airborne Influenza Virus and Respiratory Syncytial Virus in an Urgent Care Medical Clinic
Authors: Lindsley William G. , Blachere Francoise M. , Davis Kristina A. , Pearce Terri A. , Fisher Melanie A. , Khakoo Rashida , Davis Stephen M. , Rogers Mark E. , Thewlis Robert E. , Posada Jose A. , Redrow John B. , Celik Ismail B. , Chen Bean T. , Beezhold Donald H.
Published: January 2010

Background . Considerable controversy exists with regard to whether influenza virus and respiratory syncytial virus (RSV) are spread by the inhalation of infectious airborne particles and about the importance of this route, compared with droplet or contact transmission.

Methods . Airborne particles were collected in an urgent care clinic with use of stationary and personal aerosol samplers. The amounts of airborne influenza A, influenza B, and RSV RNA were determined using real-time quantitative polymerase chain reaction. Health care workers and patients participating in the study were tested for influenza.

Results . Seventeen percent of the stationary samplers contained influenza A RNA, 1% contained influenza B RNA, and 32% contained RSV RNA. Nineteen percent of the personal samplers contained influenza A RNA, none contained influenza B RNA, and 38% contained RSV RNA. The number of samplers containing influenza RNA correlated well with the number and location of patients with influenza (r=0.77). Forty-two percent of the influenza A RNA was in particles ⩽4.1 µm in aerodynamic diameter, and 9% of the RSV RNA was in particles ⩽4.1 µm.

Conclusions . Airborne particles containing influenza and RSV RNA were detected throughout a health care facility. The particles were small enough to remain airborne for an extended time and to be inhaled deeply into the respiratory tract. These results support the possibility that influenza and RSV can be transmitted by the airborne route and suggest that further investigation of the potential of these particles to transmit infection is warranted.
Comparison of the Duration of Antimicrobial Activity of 2 Different Antimicrobial Central Venous Catheters
Authors: Matheos Theofilos , Walz J. Matthias , Adams Janice P. , Johnson Karen , Longtine Karen , Longtine Jaclyn , O'Neill Melissa , Heard Stephen O.
Published: January 2010

We compared the duration of antimicrobial effectiveness of 2 different antimicrobial catheters. The baseline activity of minocycline-rifampin catheters was greater than that of silver-platinum-carbon catheters against Staphylococcus aureus, Staphylococcus epidermidis, and Enterococcus faecalis. The antimicrobial activity of the minocycline-rifampin catheters against these pathogens persisted for up to 12 days, while that of the silver-platinum-carbon catheters was depleted by day 10 (P< .05).
PopW of Ralstonia solanacearum, a new two‐domain harpin targeting the plant cell wall
Authors: LI JIAN‐GANG , LIU HONG‐XIA , CAO JING , CHEN LI‐FENG , GU CHUN , ALLEN CAITILYN , GUO JIAN‐HUA
Published: January 2010

Harpins are extracellular glycine‐rich proteins eliciting a hypersensitive response (HR). In this study, we identified a new harpin, PopW, from Ralstonia solanacearum strain ZJ3721. This 380‐amino‐acid protein is acidic, rich in glycine and serine, and lacks cysteine. When infiltrated into the leaves of tobacco (non‐host), PopW induced a rapid tissue collapse via a heat‐stable but protease‐sensitive HR‐eliciting activity. PopW has an N‐terminal harpin domain (residues 1–159) and a C‐terminal pectate lyase (PL) domain (residues 160–366); its HR‐eliciting activity depends on its N‐terminal domain. Analyses of subcellular localization and plasmolysis demonstrated that PopW targeted the onion cell wall. This was further confirmed by its ability to specifically bind to calcium pectate, a major component of the plant cell wall. However, PopW had no detectable PL activity. Western blotting revealed that PopW was secreted by the type III secretion system in an hrpB‐dependent manner. Gene sequencing indicated that popW is conserved among 20 diverse strains of R. solanacearum. A popW‐deficient mutant retained the ability of wild‐type strain ZJ3721 to elicit HR in tobacco and to cause wilt disease in tomato (a host). We conclude that PopW is a new cell wall‐associated, hrpB‐dependent, two‐domain harpin that is conserved across the R. solanacearum species complex.
Effects of plant structure on butterfly diversity in Mt. Marsabit Forest – northern Kenya
Authors: Humpden Nyamweya N. , Nathan Gichuki N.
Published: January 2010

Butterflies, like most forest dependent animals are good ecological indicators of the health of the forests they dwell. For example, butterfly species richness decreases after a forest disturbance and fragmentation but a few species may subsequently invade the forest fragment and boost the species richness. Studies were conducted to determine the effects of human activity and seasonal changes on butterfly species in the affected new habitats. Results showed that both seasonal and habitat changes significantly affect the butterfly abundance (P = 0.0001). Similarly, there was significant correlation between plant diversity and butterfly diversity in wet season (r = 0.854) and dry season (r = 0.855). The significance of these studies as a useful tool for sustainable forest use and conservation is discussed.