bluuebunny/crossref_metadata_2025 huggingface dataset:
Brittle Failure Assessment of a PWR-RPV for Operating Conditions and Loss of Coolant Accident
Authors: Siegele Dieter , Varfolomeyev Igor , Nagel Gerhard
Published: August 2008

The brittle failure assessment for the reactor pressure vessel (RPV) of a 1300MW pressurized water reactor was revised according to the state of the art. The RPV steel is 22 NiMoCr 37 (A 508 Cl. 2). The expected neutron fluence at the end of license (EOL) after 32years of full operation is Φ<2.3×1018neutrons∕cm2. The assessment followed a multibarrier concept to independently prove the exclusion of crack initiation, crack arrest, and exclusion of the load necessary to advance the arrested cracks through the RPV wall. Thermal and structural analyses of the RPV were performed both for the reactor shutdown with postulated upset conditions, as the most severe load case at operation, and for loss of coolant accident (LOCA) conditions. For LOCA transients, a leak size screening of different combinations of cold∕hot leg injection of emergency core cooling was performed, and the leading leak size was determined. A fracture mechanics based assessment was carried out for extended circumferential flaws in the weld joint between the RPV shell and the flange, as well as for axial flaws in the nozzle corner. These flaw geometries postulated at locations of the highest principal stresses and lowest temperatures under the respective transient conditions are representative for the brittle failure assessment of the whole vessel. For a normal operation, the maximum crack driving force takes place at high temperatures preceding the upset conditions. The transient follows a load path decreasing with temperature, producing a warm prestressing effect, which is considered in the assessment. Thus, a large safety margin against crack initiation can be demonstrated. At LOCA, the most severe conditions are determined for postulated cracks in the nozzle corner. Here, applying the constraint modified master curve, which takes account of the low stress triaxiality in the component, the exclusion of crack initiation is proven. Furthermore, two additional safety barriers are proven, the crack arrest after postulated crack initiation well within the allowable depth, as well as the preclusion of the load necessary to advance the arrested crack through the RPV wall.
The Combined Stress Intensity Factors of Multiple Longitudinally Coplanar Cracks in Autofrettaged Pressurized Tubes Influenced by the Bauschinger Effect
Authors: Levy C. , Perl M. , Kotagiri S.
Published: August 2008

The influence of the Bauschinger effect (BE) on the three dimensional, Mode I, combined stress intensity factor (SIF) distributions for arrays of longitudinal coplanar, surface cracks emanating from the bore of a fully or partially autofrettaged thick-walled cylinder is investigated. The combined SIFs, KIN, that depend on pressure effects and the “realistic”—Bauschinger effect dependent Autofrettage (BEDA), or, that depend on pressure effects and the “ideal”—Bauschinger effect independent autofrettage (BEIA), are obtained and compared for crack depth to wall thickness, a∕t=0.01–0.25; crack ellipticity, a∕c=0.5–1.5; crack spacing ratio, 2c∕d=0.25–0.75; and autofrettage level, e=30%, 60%, and 100%. The 3D analysis is performed via the finite element method and the submodeling technique, employing singular elements along the crack front. Both autofrettage residual stress fields, BEDA and BEIA, are simulated using an equivalent temperature field. The combined SIF, KIN, is found to vary along the crack front with the maximum determined by the crack ellipticity, crack depth, and crack spacing ratio. For a partially autofrettaged cylinder, the influence of the BE on the combined SIF, KIN, is substantially reduced as the level of overstrain becomes smaller. For some cases, when comparing like crack distributions, the KIN values obtained from the BEDA model are found to be as much as 100% higher than the KIN values that are computed using the BEIA model. A pressurized thick-walled cylinder with BEDA can be most critical when small cracks are farther apart. As crack depth increases, or when the spacing between cracks is smaller, the SIFs increase. Though the differences in the BEDA SIF, KIA, between e=100% and 60% are small (7–15%, in most cases), the increased level of autofrettage produces a 23–30% decrease in the combined SIF values, KIN. In certain cases, the BEIA model implies an infinite fatigue life, whereas the BEDA model for the same parameters implies a finite life. Therefore, it is important to perform a full 3D analysis to determine the real life cycle of the pressurized cylinder for materials that exhibit the BE.
Thermal Simulation of an Arbitrary Residual Stress Field in a Fully or Partially Autofrettaged Thick-Walled Spherical Pressure Vessel
Authors: Perl M.
Published: August 2008

The equivalent thermal load was previously shown to be the only feasible method by which the residual stresses due to autofrettage and its redistribution, as a result of cracking, can be implemented in a finite element (FE) analysis of a fully or partially autofrettaged thick-walled cylindrical pressure vessel. The present analysis involves developing a similar methodology for treating an autofrettaged thick-walled spherical pressure vessel. A general procedure for evaluating the equivalent temperature loading for simulating an arbitrary, analytical or numerical spherosymmetric autofrettage residual stress field in a spherical pressure vessel is developed. Once presented, the algorithm is applied to two distinct cases. In the first case, an analytical expression for the equivalent thermal loading is obtained for the ideal autofrettage stress field in a spherical shell. In the second case, the algorithm is applied to the discrete numerical values of a realistic autofrettage residual stress field incorporating the Bauschinger effect. As a result, a discrete equivalent temperature field is obtained. Furthermore, a FE analysis is performed for each of the above cases, applying the respective temperature field to the spherical vessel. The induced stress fields are evaluated for each case and then compared to the original stress. The FE results prove that the proposed procedure yields equivalent temperature fields that in turn simulate very accurately the residual stress fields for both the ideal and the realistic autofrettage cases.
Applying Neural Networks to the Solution of the Inverse Heat Conduction Problem in a Gun Barrel
Authors: Hwang Y. , Deng S.
Published: August 2008

The primary cause of gun barrel erosion is the heat generated by the shell as its travels along the barrel. Therefore, calculating the heat flux input to the gun bore is very important when investigating wear problems in the gun barrel and examining its thermomechanical properties. This paper employs the continuous-time analog Hopfield neural network (CHNN) to compute the temperature distribution in various forward heat conduction problems. An efficient technique is then proposed for the solution of inverse heat conduction problems using a three-layered backpropagation neural network (BPN). The weak generalization capacity of BPN networks when applied to the solution of nonlinear function approximations is improved by employing the Bayesian regularization algorithm. The CHNN scheme is used to calculate the temperature in a 155mm gun barrel and the trained BPN is then used to estimate the heat flux of the inner surface of the barrel. The results show that the proposed neural network analysis method successfully solves forward heat conduction problems and is capable of predicting the unknown parameters in inverse problems with an acceptable error.
Linear Stability Analysis and Application of a New Solution Method of the Elastodynamic Equations Suitable for a Unified Fluid-Structure-Interaction Approach
Authors: Giannopapa C. G. , Papadakis G.
Published: August 2008

In the conventional approach for fluid-structure-interaction problems, the fluid and solid components are treated separately and information is exchanged across their interface. According to the conventional terminology, the current numerical methods can be grouped in two major categories: partitioned methods and monolithic methods. Both methods use separate sets of equations for fluid and solid that have different unknown variables. A unified solution method has been presented in the previous work of Giannopapa and Papadakis (2004, “A New Formulation for Solids Suitable for a Unified Solution Method for Fluid-Structure Interaction Problems,” ASME PVP 2004, San Diego, CA, July, PVP Vol. 491–1, pp. 111–117), which is different from these methods. The new approach treats both fluid and solid as a single continuum; thus, the whole computational domain is treated as one entity discretized on a single grid. Its behavior is described by a single set of equations, which are solved fully implicitly. In this paper, the elastodynamic equations are reformulated so that they contain the same unknowns as the Navier–Stokes equations, namely, velocities and pressure. Two time marching and one spatial discretization scheme, widely used for fluid equations, are applied for the solution of the reformulated equations for solids. Using linear stability analysis, the accuracy and dissipation characteristics of the resulting difference equations are examined. The aforementioned schemes are applied to a transient structural problem (beam bending) and the results compare favorably with available analytic solutions and are consistent with the conclusions of the stability analysis. A parametric investigation using different meshes, time steps, and beam dimensions is also presented. For all cases examined, the numerical solution was stable and robust and therefore is suitable for the next stage of application to full fluid-structure-interaction problems.
Application of Models for Laminar to Turbulent Transition to Flow Around a Circular Cylinder
Authors: Reichel C. , Strohmeier K.
Published: August 2008

In many technical fields, for example, in heat exchanger design, circular cylinders are involved in fluid structure interaction problems. Therefore, correct fluid forces are needed. Direct numerical simulation or large eddy simulation are too time expensive, but great errors can occur if fluid forces are evaluated with mainstream statistical turbulence models. In this paper, several models are applied to flow around a circular cylinder in the Reynolds number range from 500 up to 106. Mainly 2D simulations are performed. Additionally, calculations are performed to evaluate the influence of three dimensional modeling. The incorrect prediction of laminar to turbulent transition is identified as the main reason for the misprediction of flow forces with common statistical turbulence models. It is demonstrated that improvements are possible with available transition models. Although no grid independence in spatial direction could be achieved, the results indicate that 3D calculations may abolish remaining deviations between calculated and measured force coefficients. (Most of the data contained within this paper have been presented at the 2005 ASME PVPD Conference in Denver, Colorado. Although the title of the paper has not been changed, some newer results have been added.)
Transient Fluid Forces on a Rigid Circular Cylinder Subjected to Small Amplitude Motions
Authors: Leblond Cédric , Melot Vincent , Sigrist Jean-François , Lainé Christian , Auvity Bruno , Peerhossaini Hassan
Published: August 2008

The present paper treats the transient fluid forces experienced by a rigid circular cylinder moving along a radial line in a fluid initially at rest. The body is subjected to a rapid displacement of relatively small amplitude in relation to its radius. Both infinite and cylindrically confined fluid domains are considered. Furthermore, non-negligible amplitude motions of the inner cylinder, and viscous and compressible fluid effects are addressed, successively. Different analytical methods and models are used to tackle each of these issues. For motions of non-negligible amplitude of the inner cylinder, a potential flow is assumed and the model, formulated as a two-dimensional boundary perturbation problem, is solved using a regular expansion up to second order. Subsequently, viscous and compressible effects are handled by assuming infinitesimal amplitude motions. The viscous fluid forces are formulated by solving a singular perturbation problem of the first order. Compressible fluid forces are then determined from the wave equation. A nonlinear formulation is obtained for the non-negligible amplitude motion. The viscous and compressible fluid forces, formulated in terms of convolution products, are linked to fluid history effects induced by wave propagation phenomena in the fluid domain. These models are expressed with dimensionless parameters and illustrated for a specific motion imposed on the inner cylinder. The different analytical models permit coverage of a broad range of motions. Hence, for a given geometry and imposed displacement, the appropriate fluid model can be identified and the resulting fluid forces rapidly estimated. The limits of these formulations are also discussed.
Effect of Groove Geometry on Weld-Induced Deformation in Full-Welded Ball Valve
Authors: Zeliang Xu
Published: August 2008

Welding groove geometry is one of the factors determining the structure’s weld-induced deformation. There are three types of welding groove geometry available for a full-welded ball valve. Multipass butt-welded plate experiments and finite element analysis were applied to determine which is the best of the valve. The experiments and analysis both show that the U-q groove is the best choice for the full-welded ball valve to get the smallest weld-induced deformation.
Rarefied gas flow through short tubes into vacuum
Authors: Varoutis S. , Valougeorgis D. , Sazhin O. , Sharipov F.
Published: August 2008

A rarefied gas flow into vacuum through a tube of finite length is investigated over the whole range of gas rarefaction by the direct simulation Monte Carlo method. The nonequilibrium effects at the inlet and outlet of the tube have been considered by including in the computational domain large volumes of the upstream and downstream reservoirs. Results for the dimensionless flow rate and for the flow field are presented for a wide range of the gas rarefaction and for various values of the length to radius ratio in the range from 0 to 10. The influence of the gas-surface interaction model, as well as the effect of the intermolecular potential model on the gas flow, is examined. A good agreement has been obtained between the present numerical results and the corresponding experimental ones available in the literature.
Luminescence enhancement of plasma-etched InAsP∕InGaAsP quantum wells
Authors: Cao Meng , Lao Yanfeng , Wu Huizhen , Liu Cheng , Xie Zhengsheng , Cao Chunfang , Wu Huizhen
Published: August 2008

Luminescence enhancement effects are observed in the plasma-etched InAs0.45P0.55/In0.68Ga0.32As0.45P0.55 quantum wells (QWs). Characterizations of photoluminescence, atomic force microscopy, and secondary-ion mass spectroscopy reveal that surface roughening due to ion bombardment onto surface and microstructure changes resulted from Ar+ ions tunneling into the material in the plasma etching process account for the PL enhancement phenomenon. The combination of plasma etching and selective lift-off of the InP cap layer of the InAs0.45P0.55∕In0.68Ga0.32As0.45P0.55 QW structures allows us to separate the two enhancement factors, which indicates the Ar+ ions tunneling into the crystal is the dominant factor that enhances the luminescence emission of InAs0.45P0.55∕In0.68Ga0.32As0.45P0.55 quantum wells.
Synthesis and characterization of Al2O3 and SiO2 films with fluoropolymer content using rf-plasma magnetron sputtering technique
Authors: Islam Mohammad , Inal Osman T.
Published: August 2008

Pure and molecularly mixed inorganic films for protection against atomic oxygen in lower earth orbit were prepared using radio-frequency (rf) plasma magnetron sputtering technique. Alumina (Al2O3) and silica (SiO2) films with average grain size in the range of 30–80nm and fully dense or dense columnar structure were synthesized under different conditions of pressure and power. Simultaneous oxide sputtering and plasma polymerization (PP) of hexafluoropropylene (HFP) led to the formation of molecularly mixed films with fluoropolymer content. The degree of plasma polymerization was strongly influenced by total chamber pressure and the argon to HFP molar ratio (nAr∕nM). An order of magnitude increase in pressure due to argon during codeposition changed the plasma-polymerization mechanism from radical-chain- to radical-radical-type processes. Subsequently, a shift from linear CH2 group based chain polymerization to highly disordered fluoropolymer content with branching and cross-linking was observed. Fourier transform infrared spectroscopy studies revealed chemical interaction between depositing SiO2 and PP-HFP through appearance of absorption bands characteristic of SiF stretching and expansion of SiO2 network. The relative amount and composition of plasma-polymerized fluoropolymer in such films can be controlled by changing argon to HFP flow ratio, total chamber pressure, and applied power. These films offer great potential for use as protective coatings in aerospace applications.
Atomic layer deposition of tin oxide films using tetrakis(dimethylamino) tin
Authors: Elam Jeffrey W. , Baker David A. , Hryn Alexander J. , Martinson Alex B. F. , Pellin Michael J. , Hupp Joseph T.
Published: August 2008

The authors present a new method for preparing thin films of SnO2 by atomic layer deposition (ALD) using alternating exposures to tetrakis(dimethylamino) tin and hydrogen peroxide. This method avoids problems of corrosion and agglomeration associated with the halogenated compound, SnCl4. Tin oxide films were successfully deposited on a variety of substrates using deposition temperatures of 50–300°C at an average growth rate of 1.2Å∕cycle. They use in situ quartz crystal microbalance and quadrupole mass spectrometry measurements to explore the mechanism for SnO2 ALD. Scanning electron microscopy of SnO2 films deposited on Si(100) show that the SnO2 films are smooth, conformal, and nearly featureless, while atomic force microscopy yields a surface roughness of only 0.84nm for a film with a thickness of 92nm. X-ray diffraction reveals that the SnO2 films are amorphous. Films deposited on glass yielded a resistivity of ∼0.3Ωcm and an optical transmission of 94% for a film thickness of 140nm. X-ray photoelectron spectroscopy measurements were consistent with residual dimethylamine ligands remaining in the film at deposition temperatures below 150°C. This method allows, for the first time, low temperature (50°C) growth of SnO2 films by ALD. Additionally, they show that this process is suitable for conformally coating high aspect ratio anodic alumina membranes.
Effect of growth temperature on the characteristics of ZnO films grown on Si(111) substrates by metal-organic chemical vapor deposition
Authors: Zhu Junjie , Yao Ran , Song Haiyan , Fu Zhuxi , Kuznetsov A. Yu. , Lee In-Hwan
Published: August 2008

ZnO films have been grown on Si(111) substrates by metal-organic chemical vapor deposition using diethylzinc and CO2 as precursors. The effects of growth temperature on growth rate, structure, and optical properties of the ZnO films were investigated in a temperature range between 450 and 700°C. As growth temperature increased, the growth mode changed from kinetics-limited to mass-transfer-limited, and finally, to desorption-limited mode. Using the Arrhenius equation, the activation energy for the kinetics-limited growth mode was estimated to be 105meV. The crystalline quality was also strongly dependent on growth temperature. With increasing growth temperature, the width of x-ray diffraction peaks decreases and the photoluminescence intensity enhances. Using CO2 as the oxygen source, we found that the optimal growth temperature was near 600°C.
Dimerization of titanyl phthalocyanine in thin films prepared by surface polymerization by ion-assisted deposition
Authors: Zachary Adam M. , Drabik Martin , Choi Yongsoo , Bolotin Igor L. , Biederman Hynek , Hanley Luke
Published: August 2008

Surface polymerization by ion-assisted deposition (SPIAD), the simultaneous dosing of hyperthermal ions while depositing an organic oligomer, was used to deposit titanyl phthalocyanine (TiOPc) thin films with 50 and 100 eV acetylene ions. The properties of the SPIAD TiOPc thin films are compared with films of the evaporated TiOPc monomer via examination of the electronic structure, ultraviolet-visible absorbance, and composition. Mass spectrometry, x-ray photoelectron spectroscopy, and other methods were used to determine the film composition, chemical bonding, and to examine the electronic structure. These results showed the formation of TiOPc dimers bound face to face. However, the overall phthalocyanine ring structure otherwise remained intact, except for small amounts of atmospheric oxidation at ion-induced radical sites.
Optical properties and electrical properties of heavily Al-doped ZnSe layers
Authors: Oh D. C. , Takai T. , Im I. H. , Park S. H. , Hanada T. , Yao T. , Song J. S. , Chang J. H. , Makino H. , Han C. S. , Koo K. H.
Published: August 2008

We have investigated optical properties and electrical properties of electrically degraded ZnSe layers by heavy Al doping, where their electron concentrations lie in the range of 7×1017–6×1018cm−3. Low-temperature photoluminescence exhibits two dominant radiative trap centers of 1.97eV (RD1) and 2.25eV (RD2), which are ascribed to VZn-related complex defects. Deep-level-transient spectroscopy shows two electron-trap centers at 0.16eV (ND1) and 0.80eV (ND2) below the conduction-band minimum. On the other hand, it is found that RD2 is dominant in relatively lightly doped ZnSe:Al layers below 7×1018cm−3 and RD1 is dominant in more heavily doped layers near 1×1019cm−3, while ND1 and ND2 are independent of Al doping concentration and their trap densities are estimated be below 3×1016cm−3. This indicates that RD1 and RD2 cause the carrier compensation in heavily doped ZnSe:Al layers. Their electron transport mechanism can be explained by ionized-impurity scattering mechanism.
Low temperature plasma etching for Si3N4 waveguide applications
Authors: Celo D. , Vandusen R. , Smy T. , Albert J. , Tarr N. G. , Waldron P. D.
Published: August 2008

Highly selective and anisotropic low temperature electron cyclotron resonance plasma etching process for silicon nitride optical rib waveguide devices compatible with integrated circuit technology is presented. Etching at low temperatures (−30°C) with SF6∕O2 chemistry in combination with a silicon dioxide hard mask achieved good anisotropy with the vertical sidewalls.
Research on metastable electron traps in the modified SOI materials induced by Si ion implantation
Authors: Zhang Enxia , Yu Zhishui , Cao Yanggen , Yang Hui , Zhang Zhengxuan , Wang Xi
Published: August 2008

Silicon-On-Insulator (SOI) materials were modified by Si ion implantation with different doses, as reported in this letter. The electrical performance was studied and the effect of a modification technique on the SOI materials was investigated. The characteristic, obtained by pseudo-metal-oxide-semiconductor (pseudo-MOS) method, showed that the drain ID current versus gate voltage VG(ID−VG) curves shifted along the axis of VG with the change of Si ion implantation doses. The results of electron paramagnetic resonance (EPR), x-ray photoelectron spectroscopy (XPS), and electronic test suggested that the parameters of implantation affect the electrical performance and that the metastable electron traps are introduced into the buried oxide layers of SOI materials.
Specific mechanism for strain relaxation dependent on crystallization route of LiNbO3 films on Al2O3(0001)
Authors: Akazawa Housei , Shimada Masaru
Published: August 2008

Distinct channels for relaxing strain were identified in epitaxial LiNbO3 thin films depending on whether the film was crystallized during or after sputter-deposition on an Al2O3(0001) substrate. When LiNbO3 continuously crystallizes during deposition, pseudomorphic growth continues with a build up of strain as the thickness increases. The primary process for relieving strain is achieved by dividing the crystal into small mosaic grains. Crystallization by postannealing amorphous films, in contrast, produces nearly dislocation-free, relaxed crystals with a wider domain of 100–200 nm. Introducing lattice disorder at antiphase positions that correspond to matching between 12 lattice units of LiNbO3 and 13 lattice units of Al2O3 in the a-direction limits the chemical interaction with the Al2O3 lattice within a short range and efficiently accommodates misfit strain. This results in atomic-scale grapho-epitaxy sustaining disordered lattice regions at the interface.
Oxidation and diffusion processes during annealing of AlCrVN hard coatings
Authors: Franz R. , Neidhardt J. , Mitterer C. , Schaffer B. , Hutter H. , Kaindl R. , Sartory B. , Tessadri R. , Lechthaler M. , Polcik P.
Published: August 2008

V-alloyed AlCrN hard coatings were deposited by reactive arc evaporation in an industrial-sized deposition system and subsequently annealed in ambient air at temperatures ranging from 550to700°C in order to study the formation mechanisms of the desired lubricious oxides. The oxidized samples were investigated by means of secondary ion mass spectrometry depth profiling, x-ray diffraction, Raman spectroscopy, and analytical transmission electron microscopy. Vanadium diffusion in the oxidized part of the coating leads to the formation of a V-rich top layer containing AlVO4 and the desired lubricious oxide V2O5 followed by a V-depleted inner oxide layer consisting of a mixed or nanocrystalline (Al,Cr,V)2O3 on top of the intact AlCrVN coating.
Latent Fingerprint Chemical Imaging by Mass Spectrometry
Authors: Ifa Demian R. , Manicke Nicholas E. , Dill Allison L. , Cooks R. Graham
Published: August 2008

Latent fingerprints (LFPs) potentially contain more forensic information than the simple identification of the subject; they may contain evidence of contacts with explosives or substances of abuse. Chemical information can also be useful in resolving overlapping LFPs from different individuals. We used desorption electrospray ionization mass spectrometry in an imaging mode to record compound-specific chemical fingerprints.
The Role of Excited-State Topology in Three-Body Dissociation of
sym
-Triazine
Authors: Savee John D. , Mozhayskiy Vadim A. , Mann Jennifer E. , Krylov Anna I. , Continetti Robert E.
Published: August 2008

Molecular fragmentation into three products poses an analytical challenge to theory and experiment alike. We used translational spectroscopy and high-level ab initio calculations to explore the highly debated three-body dissociation of
sym
-triazine to three hydrogen cyanide molecules. Dissociation was induced by charge exchange between the
sym
-triazine radical cation and cesium. Calculated state energies and electronic couplings suggest that reduction initially produces a population of
sym
-triazine partitioned between the 3s Rydberg and π* ←
n
electronically excited manifolds. Analysis of the topology of these manifolds, along with momentum correlation in the dissociation products, suggests that a conical intersection of two potential energy surfaces in the 3s Rydberg manifold leads to stepwise dissociation, whereas a four-fold glancing intersection in the π* ←
n
manifold leads to a symmetric concerted reaction.
Quantum Dynamics of Chemical Reactions
Authors: Clary David C.
Published: August 2008

Substantial recent progress has been made in developing theory to account for quantum effects on chemical reactions.
Large-Scale Molecular Dynamics Simulations of Self-Assembling Systems
Authors: Klein Michael L. , Shinoda Wataru
Published: August 2008

Relentless increases in the size and performance of multiprocessor computers, coupled with new algorithms and methods, have led to novel applications of simulations across chemistry. This Perspective focuses on the use of classical molecular dynamics and so-called coarse-grain models to explore phenomena involving self-assembly in complex fluids and biological systems.
Intermolecular Potentials
Authors: Stone Anthony J.
Published: August 2008

Computer simulations of molecular materials require a compact but accurate description of the energies of interacting molecules and the forces between them.
Insights into Current Limitations of Density Functional Theory
Authors: Cohen Aron J. , Mori-Sánchez Paula , Yang Weitao
Published: August 2008

Density functional theory of electronic structure is widely and successfully applied in simulations throughout engineering and sciences. However, for many predicted properties, there are spectacular failures that can be traced to the delocalization error and static correlation error of commonly used approximations. These errors can be characterized and understood through the perspective of fractional charges and fractional spins introduced recently. Reducing these errors will open new frontiers for applications of density functional theory.
A Conserved Mutation in an Ethylene Biosynthesis Enzyme Leads to Andromonoecy in Melons
Authors: Boualem Adnane , Fergany Mohamed , Fernandez Ronan , Troadec Christelle , Martin Antoine , Morin Halima , Sari Marie-Agnes , Collin Fabrice , Flowers Jonathan M. , Pitrat Michel , Purugganan Michael D. , Dogimont Catherine , Bendahmane Abdelhafid
Published: August 2008

Andromonoecy is a widespread sexual system in angiosperms characterized by plants carrying both male and bisexual flowers. In melon, this sexual form is controlled by the identity of the alleles at the
andromonoecious
(
a
) locus. Cloning of the
a
gene reveals that andromonoecy results from a mutation in the active site of 1-aminocyclopropane-1-carboxylic acid synthase. Expression of the active enzyme inhibits the development of the male organs and is not required for carpel development. A causal single-nucleotide polymorphism associated with andromonoecy was identified, which suggests that the
a
allele has been under recent positive selection and may be linked to the evolution of this sexual system.
Gas Disks to Gas Giants: Simulating the Birth of Planetary Systems
Authors: Thommes Edward W. , Matsumura Soko , Rasio Frederic A.
Published: August 2008

The ensemble of now more than 250 discovered planetary systems displays a wide range of masses, orbits and, in multiple systems, dynamical interactions. These represent the end point of a complex sequence of events, wherein an entire protostellar disk converts itself into a small number of planetary bodies. Here, we present self-consistent numerical simulations of this process, which produce results in agreement with some of the key trends observed in the properties of the exoplanets. Analogs to our own solar system do not appear to be common, originating from disks near the boundary between barren and (giant) planet-forming.
Dichotomous Dopaminergic Control of Striatal Synaptic Plasticity
Authors: Shen Weixing , Flajolet Marc , Greengard Paul , Surmeier D. James
Published: August 2008

At synapses between cortical pyramidal neurons and principal striatal medium spiny neurons (MSNs), postsynaptic D1 and D2 dopamine (DA) receptors are postulated to be necessary for the induction of long-term potentiation and depression, respectively—forms of plasticity thought to underlie associative learning. Because these receptors are restricted to two distinct MSN populations, this postulate demands that synaptic plasticity be unidirectional in each cell type. Using brain slices from DA receptor transgenic mice, we show that this is not the case. Rather, DA plays complementary roles in these two types of MSN to ensure that synaptic plasticity is bidirectional and Hebbian. In models of Parkinson's disease, this system is thrown out of balance, leading to unidirectional changes in plasticity that could underlie network pathology and symptoms.
Plague Through History
Authors: Stenseth Nils Chr.
Published: August 2008

Plague and the End of Antiquity
. The Pandemic of 541-750.
Lester K. Little, Ed.
. Cambridge University Press, Cambridge, in association with the American Academy in Rome, 2007. 380 pp. $85, £45. ISBN 9780521846394. Paper, $29.99, £15.99. ISBN 9780521718974.

Pestilential Complexities
. Understanding Medieval Plague.
Vivian Nutton, Ed.
. Wellcome Trust Centre for the History of Medicine at UCL, London, 2008. 138 pp. $72, £35, €52. ISBN 9780854841165.

The contributors to these volumes integrate findings from history, archeology, epidemiology, and molecular biology to provide multifaceted accounts of the plague and its effects on human history.
Comparison of Two Commercially Available Dengue Virus (DENV) NS1 Capture Enzyme-Linked Immunosorbent Assays Using a Single Clinical Sample for Diagnosis of Acute DENV Infection
Authors: Bessoff Kovi , Delorey Mark , Sun Wellington , Hunsperger Elizabeth
Published: August 2008

Dengue virus (DENV) nonstructural protein 1 (NS1) has shown promise as a novel diagnostic marker of acute DENV infection. Current techniques used to diagnose acute DENV infection, including virus isolation and reverse transcription-PCR (RT-PCR), are costly and difficult to perform, while traditional serological assays have low sensitivities during the acute stage of infection. Two commercially available NS1 antigen capture enzyme-linked immunosorbent assays (ELISAs), the Platelia dengue NS1Ag test (Bio-Rad Laboratories, Marnes La Coquette, France) and the Pan-E dengue early ELISA test (Panbio Diagnostics, Brisbane, Australia), were evaluated against a well-characterized panel of 208 real-time RT-PCR- and virus isolation-positive sera, as well as 45 real-time RT-PCR- and serologically negative sera from patients with other acute febrile illnesses. The overall sensitivities were 64.9% (95% confidence interval [CI95], 58.2 to 71.1%) for the Panbio test and 83.2% (CI95, 77.5 to 87.7%) for the Bio-Rad test, with interserotype variation, especially for DENV serotype 4. Predictive models were constructed to identify factors that had a significant influence on a test's outcome with respect to this panel of samples in order to identify the conditions in which the test will be most effective as a diagnostic tool. The immunoglobulin G titer was found to be the only covariate that significantly influenced results in the Bio-Rad test, while serotype and the day postonset were found to significantly influence results in the Panbio test. We concluded that the NS1 capture ELISA is a useful tool that can improve testing algorithms to diagnose DENV infection in single samples from acute and early convalescent cases.
Clonal Dissemination of
Staphylococcus epidermidis
in an Oncology Ward
Authors: Muldrew Kenneth L. , Tang Yi-Wei , Li Haijing , Stratton Charles W.
Published: August 2008

Coagulase-negative staphylococci (CoNS) are the main cause of catheter-related infections, especially among immunosuppressed and neutropenic patients, as well as a source of bacterial contamination in blood cultures. Using biochemical identification and pulsed-field gel electrophoresis (PFGE), we sought to identify possible clonal isolates of bacteremia in patients with central lines in an oncology ward (OW), with comparison to isolates that were recovered by venipuncture from an adult emergency room (ER). A total of 243 CoNS isolates were identified to species level from the OW (126) and ER (117), with
Staphylococcus epidermidis
isolates being the most common (OW, 79.4%; ER, 45.3%). PFGE demonstrated a predominant clone of
S. epidermidis
(major subtype A) which was 35.5 times more likely (odds ratio [OR] = 35.5; 95% confidence interval [CI] = 4.7 to 267.0;
P
< 0.00001) to be present in the OW versus the ER. These (CoNS or major subtype A) isolates were more frequently resistant to gentamicin (OR = 2.83; 95% CI = 1.23 to 6.53;
P
= 0.016) and less frequently resistant to trimethoprim-sulfamethoxazole (OR = 0.38; 95% CI = 0.18 to 0.80;
P
= 0.013). Subset analysis of
S. epidermidis
isolates 2 years after the study period showed the persistence of the clone of major subtype A within the OW. This study demonstrates the presence of a predominant clone among central line isolates from an OW that is not present in CoNS venipuncture isolates from an ER.
Two Different Panton-Valentine Leukocidin Phage Lineages Predominate in Japan
Authors: Ma Xiao Xue , Ito Teruyo , Kondo Yoko , Cho Moe , Yoshizawa Yukio , Kaneko Jun , Katai Atsuo , Higashiide Masato , Li Shanshuang , Hiramatsu Keiichi
Published: August 2008

We determined the entire nucleotide sequence of φSa2958-carrying Panton-Valentine leukocidin (PVL) gene, which was lysogenized in a sequence type 5 staphylococcal cassette chromosome
mec
(SCC
mec
) type II strain of methicillin-resistant
Staphylococcus aureus
(MRSA). Based on the nucleotide sequences of PVL phages, we developed PCRs to discriminate among five PVL phages, with a preliminary classification into two morphological groups (elongated-head type and icosahedral-head type) with four PCRs, including two PCRs for identifying the gene lineage between
lukS-PV
and the tail gene. The phages were then classified into five types by four PCRs identifying each phage-specific structure. With these PCRs, we examined the PVL phage types of 67 MRSA strains isolated in Japan from 1979 through 1985 and since 2000 and found that two morphologically distinct phages were predominant in Japan. The icosahedral-head-type phage, represented by the φ108PVL type, was identified for 39 of 53 strains isolated from 1979 through 1985. Of 26 other Japanese isolates, 25 belonged either definitively or presumably to elongated-head types as follows: 3 belonged to the φSa2958 type; 8 were determined to belong to an elongated-head type, but a determination of greater specificity was not made; and 14 belonged to a φSa2958-like phage of unknown type. We induced prophages by treatment with mitomycin C from six strains of the φSa2958 type or of φSa2958-like unknown-type phages; five of six strains carried intact PVL-carrying phages, which can infect other
S. aureus
strains and might generate novel PVL-positive strains of
S. aureus
. That various SCC
mec
elements were carried by different strains of the same phage type suggests that
S. aureus
strains might independently acquire PVL phages before they acquire various SCC
mec
elements.
High Rates of
Escherichia coli
Transmission between Livestock and Humans in Rural Uganda
Authors: Rwego Innocent B. , Gillespie Thomas R. , Isabirye-Basuta Gilbert , Goldberg Tony L.
Published: August 2008

Escherichia coli
is a zoonotic bacterium that is important to both public health and livestock economics. To date, most studies of zoonotic
E. coli
transmission have been conducted in developed nations with industrialized agricultural economies. In this study,
E. coli
bacteria were collected from people and livestock in two communities in rural western Uganda in order to investigate patterns of interspecific bacterial transmission in a developing rural economy characterized by very close human-livestock associations. Six hundred seventy-two
E. coli
isolates were genotyped using repetitive element-PCR (Rep-PCR) fingerprinting, and genetic distances between populations of bacteria from different hosts and locations were calculated. Genetic distances between human and livestock bacteria were generally very low, indicating high rates of bacterial gene flow among host species. Bacteria from humans and livestock in the same communities were virtually indistinguishable genetically. Data from surveys administered at the time of sample collection showed that people who did not regularly wash their hands before eating harbored bacteria approximately twice as similar genetically to bacteria of their livestock as did people who regularly washed their hands before eating. These results suggest that both rates of human-livestock interactions and patterns of human hygiene affect human-livestock bacterial transmission in this setting. This conclusion has implications not only for human and livestock health in subsistence-based agricultural economies but also for the emergence of zoonotic diseases out of such areas as a result of increasing globalization.
Association between Hypermutator Phenotype, Clinical Variables, Mucoid Phenotype, and Antimicrobial Resistance in
Pseudomonas aeruginosa
Authors: Waine David J. , Honeybourne David , Smith E. Grace , Whitehouse Joanna L. , Dowson Chris G.
Published: August 2008

The presence of hypermutator
Pseudomonas aeruginosa
was associated with poorer lung function in patients at the Adult West Midlands CF Unit. Mucoid isolates were more likely to be hypermutators. The presence of resistant mutant subpopulations was associated with hypermutator phenotype but was not good enough to be used as a test for this phenotype.
Comparison of GP5+/6+-PCR and SPF10-Line Blot Assays for Detection of High-Risk Human Papillomavirus in Samples from Women with Normal Cytology Results Who Develop Grade 3 Cervical Intraepithelial Neoplasia
Authors: Hesselink A. T. , van Ham M. A. P. C. , Heideman D. A. M. , Groothuismink Z. M. A. , Rozendaal L. , Berkhof J. , van Kemenade F. J. , Massuger L. A. F. G. , Melchers W. J. G. , Meijer C. J. L. M. , Snijders P. J. F.
Published: August 2008

Using a case control approach, we performed a two-way comparison study between GP5+/6+-PCR and HPV SPF10-Line Blot 25 (SPF10) assays for detection of 14 types of high-risk human papillomavirus (hrHPV) in samples from women with normal cytology results who had or developed grade 3 cervical intraepithelial neoplasia (CIN 3). Samples were pooled from two cohorts, i.e., women participating in population-based screening and women attending a gynecological outpatient clinic. Cases (n= 45) were women with histologically confirmed CIN 3 diagnosed within a median follow-up time of 2.7 (range, 0.2 to 7.9) years. Control samples were from women (n= 264) who had developed CIN 1 lesions at maximum (median follow-up at 5.8 [range, 0 to 10] years). Identical numbers of cases tested positive for 1 or more of the 14 hrHPV types by both systems (40/45; McNemar;P= 1.0). Conversely, SPF10scored significantly more controls as hrHPV positive than did GP5+/6+-PCR (95/264 versus 29/264; McNemar;P< 0.001). Consequently, women with normal cytology results and an hrHPV GP5+/6+-PCR-positive test exhibited a risk of CIN 3 that was 4.5 times higher (odds ratio [OR], 65; 95% confidence interval [95%CI], 24 to 178) than that seen for women with an hrHPV-positive SPF10test (OR, 14; 95%CI, 5 to 38)). Similar results were obtained after analysis of both cohorts separately. Discrepancy analysis by viral load assessment for the most common discordant hrHPV types (HPV16, -18, and -52) showed that samples which were SPF10positive only for these types had viral loads significantly lower than those for samples that were positive by both assays (analysis of variance;P≤ 0.006). Our data indicate that GP5+/6+-PCR has a better clinical performance than SPF10for women who are diagnosed with CIN 3 after prior normal cytology results. The extra positivity scored by SPF10mainly involved infections characterized by low viral loads that do not result in CIN 3.
Utility of the Germ Tube Test for Direct Identification of
Candida albicans
from Positive Blood Culture Bottles
Authors: Sheppard Donald C. , Locas Marie-Claude , Restieri Christiane , Laverdiere Michel
Published: August 2008

We compared the germ tube test for the direct identification of
Candida albicans
from positive blood culture bottles, with results obtained from subcultured colonies. The direct germ tube test was 87.1% sensitive and 100% specific for the identification of
C. albicans
when the results obtained from fungal colonies were compared.
Single Base Substitutions in the Capsid Region of the Norovirus Genome during Viral Shedding in Cases of Infection in Areas Where Norovirus Infection Is Endemic
Authors: Obara Mayumi , Hasegawa Sumiyo , Iwai Masae , Horimoto Eiji , Nakamura Kazuya , Kurata Takeshi , Saito Naohito , Oe Hiroshi , Takizawa Takenori
Published: August 2008

Norovirus (NoV) infections are the major cause of food- and waterborne nonbacterial gastroenteritis in Japan. Some individuals showed long-term excretion of the virus into feces in 29 outbreaks of acute nonbacterial gastroenteritis that occurred in Toyama Prefecture, Japan, in fiscal year 2006. In one of these cases, single base substitutions from A to G in the capsid region of the NoV genome were commonly detected in two individuals during virus shedding by direct sequencing of PCR products. The A-to-G substitution was accompanied by an N-to-S amino acid change. The population of clones that possessed A at the corresponding site was gradually replaced by those with G during the infectious course. Although other substitutions were observed in the complete open reading frame 2 sequence, they were not common in these two individuals. NoVs are capable of evolving in the gastroenteric tract.
Sendai Virus C Protein Plays a Role in Restricting PKR Activation by Limiting the Generation of Intracellular Double-Stranded RNA
Authors: Takeuchi Kenji , Komatsu Takayuki , Kitagawa Yoshinori , Sada Kiyonao , Gotoh Bin
Published: August 2008

Sendai virus (SeV) C protein is a multifunctional protein that plays important roles in regulating viral genome replication and transcription, antagonizing the host interferon system, suppressing virus-induced apoptosis, and facilitating virus assembly and budding. We here report a novel role of SeV C protein, the limitation of double-stranded RNA (dsRNA) generation for maintaining the rate of protein synthesis in infected cells. It was found that the intracellular protein synthesis rate was maintained even after wild-type (wt) SeV infection, but markedly suppressed following C-knockout SeV infection. This indicates the requirement of C protein for maintaining protein synthesis after infection. In contrast to wt SeV infection, C-knockout SeV infection caused phosphorylation of both the translation initiation factor eIF2α and dsRNA-dependent protein kinase (PKR). Phosphorylation of eIF2α occurred mainly due to the action of PKR, since knockdown of PKR by small interfering RNA limited eIF2α phosphorylation. C protein, however, could inhibit neither poly(I):poly(C)-activated nor Newcastle disease virus-induced phosphorylation of PKR and eIF2α, suggesting that C protein does not target common pathways leading to PKR activation. Immunofluorescent staining experiments with a monoclonal antibody specifically recognizing dsRNA revealed generation of a large amount of dsRNA in cells infected with C-knockout SeV but not wt SeV. The dsRNA generation as well as phosphorylation of PKR and eIF2α induced by C-knockout SeV was markedly suppressed in cells constitutively expressing C protein. Taken together, these results demonstrate that the SeV C protein limits generation of dsRNA, thereby keeping PKR inactive to maintain intracellular protein synthesis.