bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonlinear Behavior and Critical State of a Penny-Shaped Dielectric Crack in a Piezoelectric Solid
Authors: Chiang Chun-Ron , Weng George J.
Published: September 2007

By means of the Hankel transform and dual-integral equations, the nonlinear response of a penny-shaped dielectric crack with a permittivity κ0 in a transversely isotropic piezoelectric ceramic is solved under the applied tensile stress σzA and electric displacement DzA. The solution is given through the universal relation, Dc∕σzA=KD∕KI=MD∕Mσ, regardless of the electric boundary conditions of the crack, where Dc is the effective electric displacement of the crack medium, and KD and KI are the electric displacement and the stress intensity factors, respectively. The proportional constant MD∕Mσ has been derived and found to have the characteristics: (i) for an impermeable crack it is equal to DzA∕σzA; (ii) for a permeable one it is only a function of the ceramic property; and (iii) for a dielectric crack with a finite κ0 it depends on the ceramic property, the κ0 itself, and the applied σzA and DzA. The latter dependence makes the response of the dielectric crack nonlinear. This nonlinear response is found to be further controlled by a critical state (σc,DzA), through which all the Dc versus σzA curves must pass, regardless of the value of κ0. When σzA<σc, the response of an impermeable crack serves as an upper bound, whereas that of the permeable one serves as the lower bound, and when σzA>σc the situation is exactly reversed. The response of a dielectric crack with any κ0 always lies within these bounds. Under a negative DzA, our solutions further reveal the existence of a critical κ*, given by κ*=−RDzA, and a critical D*, given by D*=−κ0∕R (R depends only on the ceramic property), such that when κ0>κ* or when ∣DzA∣<∣D*∣, the effective Dc will still remain positive in spite of the negative DzA.
Effects of Temperature Changes on the Mechanical and Ballistic Responses in Biathlon Shooting
Authors: Grebot Christelle , Burtheret Alain
Published: September 2007

Background: Biathlon is a nordic sport that combines cross-country skiing with rifle marksmanship. It was reported that standing shooting was significantly affected because skiing exercise usually decreased the postural control of biathletes and increased the shooting time. Another hypothesis that may explain the decrease of one’s shooting accuracy after a cession of cross-country skiing could be linked with mechanical factors. The goal of the present study was to examine the influence of negative temperatures on the trigger mechanism and on the ballistic responses of the bullet. Method of approach: In order to determine the possible variations of the force required for triggering, five biathlon rifles were equipped with strain gauges fixed on the trigger. A thermostat vessel was used to control the temperature changes at room temperature (+20°C)(+68°F) until −20°C(−4°F). Concerning the ballistic measurements, eight series of five shots were performed at +20°C(+68°F), at −3°C(+26.6°F), at −10°C(+14°F), and at −20°C(−4°F). The shooting precision was assessed by determining the group diameter (GD) and the shooting score (Sc). Results: The results showed that from +20°C(+68°F) until −8°C(+17.6°F), the triggering force was equal to 5N(1.12lb), whereas at −20°C(−4°F), a triggering force of 8N(1.8lb) was required. The increase of the triggering force that was found under −8°C(+17.6°F) could be caused by the difference between the coefficients of expansion of the different materials constituting the trigger mechanism. Concerning the ballistic measurements, GD at room temperature was significantly lower (P<0.05) than −3°C(+26.6°F), −10°C(+14°F), and −20°C(−4°F). Furthermore, Sc was significantly better at +20°C(+68°F)(P<0.05) compared to −3°C(+26.6°F), −10°C(+14°F), and −20°C(−4°F) conditions. Conclusion: It can be supposed that the degradation of GD and Sc could be due to the formation of frost in the barrel and by the difference of the expansion coefficient of the bullet-barrel materials. Consequently, both mechanical responses could partly explain the shooting accuracy impairment observed in negative temperature shooting conditions.
Fluid–Structure
Interaction Effects in the Dynamic Response of Free-Standing Plates to Uniform Shock
Loading
Authors: Kambouchev Nayden , Radovitzky Raul , Noels Ludovic
Published: September 2007

The problem of uniform shocks interacting with free-standing plates is studied analytically and numerically for arbitrary shock intensity and plate mass. The analysis is of interest in the design and interpretation of fluid–structure interaction (FSI) experiments in shock tubes. In contrast to previous work corresponding to the case of incident blast profiles of exponential distribution, all asymptotic limits obtained here are exact. The contributions include the extension of Taylor’s FSI analysis for acoustic waves, the exact analysis of the asymptotic limits of very heavy and very light plates for arbitrary shock intensity, and a general formula for the transmitted impulse in the intermediate plate mass range. One of the implications is that the impulse transmitted to the plate can be expressed univocally in terms of a single nondimensional compressible FSI parameter.
Designing Optimal Volume Fractions For Functionally Graded Materials With Temperature-Dependent Material Properties
Authors: Bobaru Florin
Published: September 2007

We present a numerical approach for material optimization of metal-ceramic functionally graded materials (FGMs) with temperature-dependent material properties. We solve the non-linear heterogeneous thermoelasticity equations in 2D under plane strain conditions and consider examples in which the material composition varies along the radial direction of a hollow cylinder under thermomechanical loading. A space of shape-preserving splines is used to search for the optimal volume fraction function which minimizes stresses or minimizes mass under stress constraints. The control points (design variables) that define the volume fraction spline function are independent of the grid used in the numerical solution of the thermoelastic problem. We introduce new temperature-dependent objective functions and constraints. The rule of mixture and the modified Mori-Tanaka with the fuzzy inference scheme are used to compute effective properties for the material mixtures. The different micromechanics models lead to optimal solutions that are similar qualitatively. To compute the temperature-dependent critical stresses for the mixture, we use, for lack of experimental data, the rule-of-mixture. When a scalar stress measure is minimized, we obtain optimal volume fraction functions that feature multiple graded regions alternating with non-graded layers, or even non-monotonic profiles. The dominant factor for the existence of such local minimizers is the non-linear dependence of the critical stresses of the ceramic component on temperature. These results show that, in certain cases, using power-law type functions to represent the material gradation in FGMs is too restrictive.
Thermoelastic Dynamic Instability (TEDI) in Frictional Sliding of a Half-Space Against a Rigid Non-Conducting Wall
Authors: Afferrante L. , Ciavarella M.
Published: September 2007

In the sliding of half-spaces with constant friction coefficient, two classes of instabilities are well known: thermoelastic instability (TEI), which occurs for sufficiently long wavelengths and Dynamic Instability (DI), which happens at sufficiently high friction coefficient, and whose growth factor increases linearly with wave number. Although the two phenomena look therefore quite distinct, their coupling is discussed here for an elastic and conducting half-space sliding against a rigid and non-conducting wall. The coupling between thermal and dynamic effects is not always negligible. In fact, surprisingly, new areas of instability are found, called thermoelastic dynamic instabilities (TEDI), similar to TEI at high speeds and DI at low speeds. TEDI lowers the critical speed and friction coefficient in many conditions even to zero. At low speeds, TEDI is ill-posed as DI at small wavelengths, and hence a regularized friction law like the Rice-Ruina one would probably be needed to correct the results.
The Girsanov
Linearization Method for Stochastically Driven Nonlinear
Oscillators
Authors: Saha Nilanjan , Roy D.
Published: September 2007

For most practical purposes, the focus is often on obtaining statistical moments of the response of stochastically driven oscillators than on the determination of pathwise response histories. In the absence of analytical solutions of most nonlinear and higher-dimensional systems, Monte Carlo simulations with the aid of direct numerical integration remain the only viable route to estimate the statistical moments. Unfortunately, unlike the case of deterministic oscillators, available numerical integration schemes for stochastically driven oscillators have significantly poorer numerical accuracy. These schemes are generally derived through stochastic Taylor expansions and the limited accuracy results from difficulties in evaluating the multiple stochastic integrals. As a numerically superior and semi-analytic alternative, a weak linearization technique based on Girsanov transformation of probability measures is proposed for nonlinear oscillators driven by additive white-noise processes. The nonlinear part of the drift vector is appropriately decomposed and replaced, resulting in an exactly solvable linear system. The error in replacing the nonlinear terms is then corrected through the Radon-Nikodym derivative following a Girsanov transformation of probability measures. Since the Radon-Nikodym derivative is expressible in terms of a stochastic exponential of the linearized solution and computable with high accuracy, one can potentially achieve a remarkably high numerical accuracy. Although the Girsanov linearization method is applicable to a large class of oscillators, including those with nondifferentiable vector fields, the method is presently illustrated through applications to a few single- and multi-degree-of-freedom oscillators with polynomial nonlinearity.
Stress–Strain Relationship for Metal Hollow Sphere Materials as a Function of Their Relative Density
Authors: Karagiozova D. , Yu T. X. , Gao Z. Y.
Published: September 2007

The stress–strain relationship for uniaxial compression of a metal hollow sphere material in large strains is obtained using a simplified model for the spheres’ deformation within a 3D block assuming a hexagonal packing pattern. The yield strength and material strain hardening are obtained as functions of the relative density in two characteristic loading directions. The expression for the stress–strain relationship consisting of quadratic and linear terms with respect to the relative density is linked to the partitioning of the deformation energy during compression. The theoretical predictions are compared with limited test results on mild steel hollow sphere material and finite element simulation results obtained by our group.
Integral Representation of Energy Release Rate in Graded Materials
Authors: Jin Z.-H. , Sun C. T.
Published: September 2007

It is well known that, for homogeneous materials, the path-independent J contour integral is the (potential) energy release rate. For general nonhomogeneous, or graded materials, such a contour integral as the energy release rate does not exist. This work presents a rigorous derivation of the extended J integral for general graded materials from the potential energy variation with crack extension. Effects of crack shielding and amplification due to a graded interlayer in an elastic-plastic material system are discussed in terms of this integral.
On the Normal Component of Centralized Frictionless Collision Sequences
Authors: Mosterman Pieter J.
Published: September 2007

A typical assumption for rigid body collisions with multiple impact points is that all collisions occur simultaneously and are synchronized in their compression/expansion behavior, a useful assumption given the microscopic time scale at which collisions occur. In the case in which collisions are dependent upon one another, however, there is interaction between and within compression and expansion phases. Instead of treating the collisions as separate consecutive impacts or by activating all constraints at the same time, a rule is presented that orders the collisions as a sequence of interacting events at a point in time to handle the normal component of the collisions.
Dynamic Stress of a Circular Cavity Buried in a Semi-Infinite Functionally Graded Material Subjected to Shear Waves
Authors: Fang Xue-qian , Hu Chao , Du Shan-yi
Published: September 2007

The multiple scattering of shear waves and dynamic stress in a semi-infinite functionally graded material with a circular cavity is investigated, and the analytical solution of this problem is derived. The analytical solutions of wave fields are expressed by employing the wave function expansion method, and the expanded mode coefficients are determined by satisfying the boundary condition of the cavity. The image method is used to satisfy the traction-free boundary condition of the material structure. As an example, the numerical solution of the dynamic stress concentration factors around the cavity is also presented. The effects of the buried depth of the cavity, the incident wave number, and the nonhomogeneity parameter of materials on the dynamic stress concentration factors are analyzed. Analyses show that when the nonhomogeneity parameter of materials is <0, it has less influence on the maximum dynamic stress around the cavity; however, it has greater influence on the distribution of dynamic stress around the cavity. When the nonhomogeneity parameter of materials is >0, it has greater influence on both the maximum dynamic stress and the distribution of dynamic stress around the cavity, especially in the case that the buried depth is comparatively small.
A Note on the Principle of Maximum Dissipation Rate
Authors: Fischer F. D. , Svoboda J.
Published: September 2007

The Principle of Maximum Dissipation Rate (PMD) can be exploited to derive homogeneous kinetic rate laws for the internal variables. A “normality structure” expressing the rates of the internal variables as normal to convex functions (entropy production rate, dissipation function as flow potentials) in the space of the conjugate thermodynamic forces is a direct consequence of the PMD. This paper can be considered as a note to Yang et al., 2005, ASME J. Appl. Mech., 72, pp. 322–329.
Analysis of One-Dimensional and Two-Dimensional Thin Film “Pull-in” Phenomena Under the Influence of an Electrostatic Potential
Authors: Duan Gang , Wan Kai-Tak
Published: September 2007

A thin one-dimensional rectangular or two-dimensional axisymmetric film is clamped at the perimeter. An electrostatic potential (V0*) applied to a pad directly underneath the film leads to a “pull-in” phenomenon. The electromagnetic energy stored in the capacitive film-pad dielectric gap is decoupled from the mechanical deformation of the film using the Dugdale-Barenblatt-Maugis cohesive zone approximation. The ratio of film-pad gap (g) to film thickness (h), or, γ=g∕h, is found to play a crucial role in the electromechanical behavior of the film. Solution spanning a wide range of γ is found such that V0*∝γ3∕2 for γ<0.5 and V0*∝γ5∕2 for γ>5. The new model leads to new design criteria for MEMS-RF-switches.
Parametric Formulation of the Finite-Volume Theory for Functionally Graded Materials—Part I: Analysis
Authors: Cavalcante Marcio A. A. , Marques Severino P. C. , Pindera Marek-Jerzy
Published: September 2007

The recently reconstructed higher-order theory for functionally graded materials is further enhanced by incorporating arbitrary quadrilateral subcell analysis capability through a parametric formulation. This capability significantly improves the efficiency of modeling continuous inclusions with arbitrarily-shaped cross sections of a graded material’s microstructure previously approximated using discretization based on rectangular subcells, as well as modeling of structural components with curved boundaries. Part I of this paper describes the development of the local conductivity and stiffness matrices for a quadrilateral subcell which are then assembled into global matrices in an efficient manner following the finite-element assembly procedure. Part II verifies the parametric formulation through comparison with analytical solutions for homogeneous curved structural components and graded components where grading is modeled using piecewise uniform thermoelastic moduli assigned to each discretized region. Results for a heterogeneous microstructure in the form of a single inclusion embedded in a matrix phase are also generated and compared with the exact analytical solution, as well as with the results obtained using the original reconstructed theory based on rectangular discretization and finite-element analysis.
Parametric Formulation of the Finite-Volume Theory for Functionally Graded Materials—Part II: Numerical Results
Authors: Cavalcante Marcio A. A. , Marques Severino P. C. , Pindera Marek-Jerzy
Published: September 2007

In Part I of this communication, the finite-volume theory for functionally graded materials was further extended to enable efficient analysis of structural components with curved boundaries, as well as efficient modeling of continuous inclusions with arbitrarily-shaped cross sections of a graded material’s microstructure, previously approximated using discretizations by rectangular subcells. This was accomplished through a parametric formulation based on mapping of a reference square subcell onto a quadrilateral subcell resident in the actual microstructure. In Part II, the parametric formulation is verified through comparison with analytical solutions for homogeneous and graded curved structural components subjected to transient thermal and steady-state thermomechanical loading. Grading is modeled using piecewise uniform thermoelastic moduli assigned to each discretized region. Results for a heterogeneous microstructure in the form of a single inclusion embedded in the matrix phase of large dimensions are also generated and compared with the exact analytical solution, as well as with the results obtained using the standard version of the finite-volume theory based on rectangular discretization and the finite-element method. It is demonstrated that the parametric finite-volume theory is a very competitive alternative to the finite-element method based on the quality of results and execution time.
The Parametric Resonance Instability in a Drilling Process
Authors: Huang Bo-Wun , Kuang Jao-Hwa
Published: September 2007

This study investigates dynamic instability in a high-speed drilling process. A pretwisted beam is used to simulate the drill. The time-dependent nature of the thrust force and the drilling depth is considered in the equation of motion of the drill. A moving Winkler-type elastic foundation assumption is applied to the drill tip to approximate the time-varying boundary conditions in the drilling process. Galerkin’s method is used to formulate the characteristic equation in a discrete form. The variation of the instability regions of the drill system is solved and analyzed by employing the multiple-scales perturbation method. The numerical results indicate that the unstable regions suddenly enlarge and shift toward a lower frequency when the drill first contacts the work piece. The effects of the rotational speed, pretwisted angle, and thrust force of the drill on the variation of the dynamic instability in high-speed drilling are also studied and are found to be highly influential.
Normality Structures With Thermodynamic Equilibrium Points
Authors: Yang Q. , Wang R. K. , Xue L. J.
Published: September 2007

Enriched by the nonlinear Onsager reciprocal relations and thermodynamic equilibrium points (Onsager, Phys. Rev., 37, pp. 405–406; 38, pp. 2265–2279), an extended normality structure by Rice (1971, J. Mech. Phys. Solids, 19, pp. 433–455) is established in this paper as a unified nonlinear thermodynamic theory of solids. It is revealed that the normality structure stems from the microscale irrotational thermodynamic fluxes. Within the extended normality structure, this paper focuses on the microscale thermodynamic mechanisms and significance of the convexity of flow potentials and yield surfaces. It is shown that the flow potential is convex if the conjugate force increment cannot not oppose the increment of the rates of local internal variables. For the Rice fluxes, the convexity condition reduces to the local rates being monotonic increasing functions with respect to their conjugate forces. The convexity of the flow potential provides the thermodynamic system a capability against the disturbance of the thermodynamic equilibrium point. It is proposed for time-independent behavior that the set of plastically admissible stresses determined by yield conditions corresponds to the set of thermodynamic equilibrium points. Based on that viewpoint, the intrinsic dissipation inequality is just the thermodynamic counterpart of the principle of maximum plastic dissipation and requires the convexity of the yield surfaces.
Computational Examination of the Effect of Material Inhomogeneity on the Necking of Stent Struts Under Tensile Loading
Authors: McGarry J. P. , O’Donnell B. P. , McHugh P. E. , O’Cearbhaill E. , McMeeking R. M.
Published: September 2007

This study presents a computational investigation of tensile behavior and, in particular, necking due to material inhomogeniety of cardiovascular stent struts under conditions of tensile loading. Polycrystalline strut microstructures are modelled using crystal plasticity theory. Two different idealized morphologies are considered for three-dimensional models, with cylindrical grains and with rhombic-dodecahedron grains. Results are compared to two-dimensional models with hexagonal grains. For all cases, it is found that necking initiates at a significantly higher strain than that at UTS (ultimate tensile stress). Two-dimensional models are shown to exhibit an unrealistically high dependence of necking strain on randomly generated grain orientations. Three-dimensional models with cylindrical grains yield a significantly higher necking strain than models with rhombic-dodecahedron grains. It is shown that necking is characterized by a dramatic increase in stress triaxiality at the center of the neck. Finally, the ratios of UTS to necking stress computed in this study are found to compare well to values predicted by existing bifurcation models.
Dynamic Failure Behavior of Polycrystalline Alumina Under Impact Loading
Authors: Yao Guowen , Liu Zhanfang
Published: September 2007

Plate impact experiments and impact recovery experiments were performed on 92.93wt.% aluminas using a 100mmdia compressed-gas gun. Free surface velocity histories were traced by a velocity interferometry system for any reflector (VISAR) velocity interferometer. There is a recompression signal in free surface velocity, which shows evidence of a failure wave in impacted alumina. The failure wave velocities are 1.27km∕s and 1.46km∕s at stresses of 7.54GPa and 8.56GPa, respectively. It drops to 0.21km∕s after the material released. SEM analysis of recovered samples showed the transit of intergranular microcracks to transgranular microcracks with increasing shock loading. A failure wave in impacted ceramics is a continuous fracture zone, which may be associated with the damage accumulation process during the propagation of shock waves. Then a progressive fracture model was proposed to describe the failure wave formation and propagation in shocked ceramics. The governing equation of the failure wave is characterized by inelastic bulk strain with material damage and fracture. Numerical simulation of the free surface velocity was performed in good agreement with the plate impact experiments. And the longitudinal, lateral, and shear stress histories upon the arrival of the failure wave were predicted, which present the diminished shear strength and lost spall strength in the failed layer.
Elastic Fields Around the Cohesive Zone of a Mode III Crack Perpendicular to a Bimaterial Interface
Authors: Zhang W. , Deng X.
Published: September 2007

Asymptotic stress and displacement fields near the cohesive zone ahead of a semi-infinite Mode III crack normal to a bimaterial interface are derived using elliptic coordinates.
Series Solution of Three-Dimensional Unsteady Laminar Viscous Flow Due to a Stretching Surface in a Rotating Fluid
Authors: Tan Yue , Liao Shi-Jun
Published: September 2007

An analytic technique, namely the homotopy analysis method, is applied to solve the Navier–Stokes equations governing unsteady viscous flows due to a suddenly stretching surface in a rotating fluid. Unlike perturbation methods, the current approach does not depend upon any small parameters at all. Besides contrary to all other analytic techniques, it provides us with a simple way to ensure the convergence of solution series. In contrast to perturbation approximations which have about 40% average errors for the considered problem, our series solutions agree well with numerical results in the whole time region 0⩽t<+∞. Explicit analytic expressions of the skin friction coefficients are given, which agree well with numerical results in the whole time region 0⩽t<+∞. This analytic approach can be applied to solve some complicated three-dimensional unsteady viscous flows governed by the Navier–Stokes equations.
Lateral Motion of an Axially Moving Tape on a Cylindrical Guide Surface
Authors: Raeymaekers Bart , Talke Frank E.
Published: September 2007

The lateral motion of a tape moving axially over a cylindrical guide surface is investigated. The effects of lateral bending stiffness and friction force are studied and the attenuation of lateral tape motion as a function of the guide radius and friction coefficient is determined. Good agreement between numerical predictions and experimental results is observed.
Regulation of a Novel
Acidithiobacillus caldus
Gene Cluster Involved in Metabolism of Reduced Inorganic Sulfur Compounds
Authors: Rzhepishevska Olena I. , Valdés Jorge , Marcinkeviciene Liucija , Gallardo Camelia Algora , Meskys Rolandas , Bonnefoy Violaine , Holmes David S. , Dopson Mark
Published: September 2007

Acidithiobacillus caldus
has been proposed to play a role in the oxidation of reduced inorganic sulfur compounds (RISCs) produced in industrial biomining of sulfidic minerals. Here, we describe the regulation of a new cluster containing the gene encoding tetrathionate hydrolase (
tetH
), a key enzyme in the RISC metabolism of this bacterium. The cluster contains five cotranscribed genes, IS
ac1
,
rsrR
,
rsrS
,
tetH
, and
doxD
, coding for a transposase, a two-component response regulator (RsrR and RsrS), tetrathionate hydrolase, and DoxD, respectively. As shown by quantitative PCR,
rsrR
,
tetH
, and
doxD
are upregulated to different degrees in the presence of tetrathionate. Western blot analysis also indicates upregulation of TetH in the presence of tetrathionate, thiosulfate, and pyrite. The
tetH
cluster is predicted to have two promoters, both of which are functional in
Escherichia coli
and one of which was mapped by primer extension. A pyrrolo-quinoline quinone binding domain in TetH was predicted by bioinformatic analysis, and the presence of an
o
-quinone moiety was experimentally verified, suggesting a mechanism for tetrathionate oxidation.
Direct Effect of Human Immunodeficiency Virus Protease Inhibitors on Neutrophil Function and Apoptosis via Calpain Inhibition
Authors: Hadad Nurit , Levy Rachel , Schlaeffer Francisc , Riesenberg Klaris
Published: September 2007

Impairment of neutrophil functions and high levels of apoptotic neutrophils have been reported in human immunodeficiency virus (HIV) patients. The aim of the present study was to investigate the direct in vitro effects of the different HIV protease inhibitors (PIs) on neutrophil functions and apoptosis and to explore their mechanisms of action. The effects of nelfinavir (NFV), saquinavir (SQV), lopinavir (LPV), ritonavir (RTV), and amprenavir (APV) in the range of 5 to 100 μg/ml on neutrophil function, apoptosis, and μ-calpain activity were studied. The neutrophil functions studied included superoxide production stimulated by 5 ng/ml phorbol myristate acetate, 5 × 10−7MN-formyl-methionyl-leucyl-phenylalanine, and 1 mg/ml opsonized zymosan; specific chemotaxis; random migration; and phagocytosis. Apoptosis was determined by DNA fragmentation, fluorescein isothiocyanate-annexin V binding, and nuclear morphology. All three neutrophil functions, as well as apoptosis, were similarly affected by the PIs. SQV and NFV caused marked inhibition and LPV and RTV caused moderate inhibition, while APV had a minor effect. μ-Calpain activity was not affected by the PIs in neutrophil lysate but was inhibited after its translocation to the membranes after cell stimulation. SQV, which was the most potent inhibitor of neutrophil functions and apoptosis, caused significant inhibition of calpain activity, while APV had no effect. The similar patterns of inhibition of neutrophil functions and apoptosis by the PIs, which coincided with inhibition of calpain activity, suggest the involvement of calpain activity in the regulation of these processes.
Rapid Method for Detection of Influenza A and B Virus Antigens by Use of a Two-Photon Excitation Assay Technique and Dry-Chemistry Reagents
Authors: Koskinen Janne O. , Vainionpää Raija , Meltola Niko J. , Soukka Jori , Hänninen Pekka E. , Soini Aleksi E.
Published: September 2007

New separation-free assay methods for the rapid detection of influenza A and B virus antigens are presented. The methods employ dry-chemistry reagents and the recently developed two-photon excitation (TPX) fluorescence detection technology. According to the assay scheme, virus antigens are sandwiched by capture antibody onto polymer microspheres and fluorescently labeled antibody conjugate. Consequently, fluorescent immunocomplexes are formed on the surface of microspheres in proportion to the concentration of the analyte in the sample. The fluorescence signal from individual microspheres is measured, separation free, by means of two-photon excited fluorescence detection. In order to demonstrate the applicability of the new assay technique for virus antigen detection, methods for influenza A and B viruses were constructed. The assay method for influenza A virus applied a molecular fluorescent label, whereas the method for influenza B virus required a nanoparticle fluorescent reporter to reach sufficient clinical sensitivity. The new methods utilize a dry-chemistry approach, where all assay-specific reagents are dispensed into assay wells already in the manufacturing process of the test kits. The performance of the assay methods was tested with nasopharyngeal specimens using a time-resolved fluoroimmunoassay as a reference method. The results suggest that the new technique enables the rapid detection of influenza virus antigens with sensitivity and specificity comparable to that of the reference method. The dose-response curves showed linear responses with slopes equal to unity and dynamic assay ranges of 3 orders of magnitude. Applicability of the novel TPX technique for rapid multianalyte testing of respiratory infections is discussed.
Molecular Characterization of Human Immunodeficiency Virus Type 1 (HIV-1) and HIV-2 in Yaoundé, Cameroon: Evidence of Major Drug Resistance Mutations in Newly Diagnosed Patients Infected with Subtypes Other than Subtype B
Authors: Ndembi Nicaise , Abraha Awet , Pilch Heather , Ichimura Hiroshi , Mbanya Dora , Kaptue Lazare , Salata Robert , Arts Eric J.
Published: September 2007

Prior to current studies on the emergence of drug resistance with the introduction of antiretroviral therapy (ART) in Cameroon, we performed genotypic analysis on samples from drug-naïve, human immunodeficiency virus (HIV)-infected individuals in this country. Of the 79 HIV type 1 (HIV-1)polsequences analyzed from Cameroonian samples, 3 (3.8%) were identified as HIV-1 group O, 1 (1.2%) was identified as an HIV-2 intergroup B/A recombinant, and the remaining 75 (95.0%) were identified as HIV-1 group M. Group M isolates were further classified as subtypes A1 (n= 4), D (n= 4), F2 (n= 6), G (n= 12), H (n= 2), and K (n= 1) and as circulating recombinant forms CRF02_AG (n= 41), CRF11_cpx (n= 1), and CRF13_cpx (n= 2). Twopolsequences were identified as unique recombinant forms of CRF02_AG/F2 (n= 2). M46L (n= 2), a major resistance mutation associated with resistance to protease inhibitors, was observed in 2/75 (2.6%) group M samples. Single mutations associated with resistance to nucleoside reverse transcriptase inhibitors (T215Y/F [n= 3]) and nonnucleoside reverse transcriptase inhibitors (V108I [n= 1], L100I [n= 1], and Y181C [n= 2]) were observed in 7 of 75 (9.3%) group M samples. None of the patients had any history of ART exposure. Population surveillance of transmitted HIV drug resistance is required and should be included to aid in the development of appropriate guidelines.
Monitoring of Polyomavirus BK Virus Viruria and Viremia in Renal Allograft Recipients by Use of a Quantitative Real-Time PCR Assay: One-Year Prospective Study
Authors: Pang Xiaoli L. , Doucette Karen , LeBlanc Barbara , Cockfield Sandra M. , Preiksaitis Jutta K.
Published: September 2007

We have developed a real-time quantitative PCR (rt-QPCR) assay to detect and kinetically monitor BK virus viruria and viremia in renal transplant recipients (RTRs). A total of 607 urine and 223 plasma samples were collected from 203 individuals including those with BK virus-associated nephropathy (BKVAN) (
n
= 8), those undergoing routine posttransplant surveillance (SV) (
n
= 155), those with nontransplant chronic kidney disease (NT-CKD) (
n
= 20), and healthy living kidney donors (LD) (
n
= 20). The rt-QPCR assay was found to be highly sensitive and specific, with a wide dynamic range (2.4 to 11 log
10
copies/ml) and very good precision (coefficient of variation, ∼5.9%). There was a significant difference in the prevalences of viruria and viremia between the BKVAN (100% and 100%) and SV (23% and 3.9%) groups (
P
< 0.001). No viruria or viremia was detected in LD or in NT-CKD patients. The median (range) peak levels of BK virus viruria and viremia, in log
10
copies/ml, were 10.26 (9.04 to 10.83) and 4.83 (3.65 to 5.86) for the BKVAN group versus 0 (0 to 10.83) and 0 (0 to 5.65) for the SV group, respectively (
P
< 0.001). When the BK virus load in the urine was <7.0 log
10
copies/ml, no BK virus viremia was detected. When the BK virus load in the urine reached 7.0, 8.0, 9.0, and ≥10.0 log
10
copies/ml, the corresponding detection of BK virus viremia increased to 20, 33, 50, and 100%, respectively. We propose monitoring of BK virus viruria in RTRs, with plasma BK virus load testing reserved for those with viruria levels of ≥7.0 log
10
copies/ml.
Novel Approach for Genotyping Varicella-Zoster Virus Strains from Germany
Authors: Schmidt-Chanasit Jonas , Stürmer Martin , Hahn Anke , Schäd Susanne G. , Gross Gerd , Ulrich Rainer G. , Heckel Gerald , Doerr Hans Wilhelm
Published: September 2007

In this study, we present a novel genotyping scheme to classify German wild-type varicella-zoster virus (VZV) strains and to differentiate them from the Oka vaccine strain (genotype B). This approach is based on analysis of four loci in open reading frames (ORFs) 51 to 58, encompassing a total length of 1,990 bp. The new genotyping scheme produced identical clusters in phylogenetic analyses compared to full-genome sequences from well-characterized VZV strains. Based on genotype A, D, B, and C reference strains, a dichotomous identification key (DIK) was developed and applied for VZV strains obtained from vesicle fluid and liquor samples originating from 42 patients suffering from varicella or zoster between 2003 and 2006. Sequencing of regions in ORFs 51, 52, 53, 56, 57, and 58 identified 18 single-nucleotide polymorphisms (SNPs), including two novel ones, SNP 89727 and SNP 92792 in ORF51 and ORF52, respectively. The DIK as well as phylogenetic analysis by Bayesian inference showed that 14 VZV strains belonged to genotype A, and 28 VZV strains were classified as genotype D. Neither Japanese (vaccine)-like B strains nor recombinant-like C strains were found within the samples from Germany. The novel genotyping scheme and the DIK were demonstrated to be practical and simple and allow the highly efficient replication of phylogenetic patterns in VZV initially derived from full-genome DNA sequence analyses. Therefore, this approach may allow us to draw a more comprehensive picture of wild-type VZV strains circulating in Germany and Central Europe by high-throughput procedures in the future.
Evaluation of MChip with Historic Subtype H1N1 Influenza A Viruses, Including the 1918 “Spanish Flu” Strain
Authors: Moore Chad L. , Smagala James A. , Smith Catherine B. , Dawson Erica D. , Cox Nancy J. , Kuchta Robert D. , Rowlen Kathy L.
Published: September 2007

The robustness of a recently developed diagnostic microarray for influenza, the MChip, was evaluated with 16 historic subtype H1N1 influenza A viruses (A/H1N1), including A/Brevig Mission/1/1918. The matrix gene segments from all 16 viruses were successfully detected on the array. An artificial neural network trained with temporally related A/H1N1 viruses identified A/Brevig Mission/1/1918 as influenza virus A/H1N1 with 94% probability.
Antimicrobial Susceptibility and Genetic Characteristics of
Streptococcus pneumoniae
Isolates Indicating Possible Nosocomial Transmission Routes in a Community Hospital in Japan
Authors: Qin Liang , Masaki Hironori , Watanabe Kiwao , Furumoto Akitsugu , Watanabe Hiroshi
Published: September 2007

A clinical study was designed to study
Streptococcus pneumoniae
isolates recovered from a community hospital in Japan from April 2001 to November 2002. A total of 73 isolates were defined as derived from inpatient, outpatient, and hospital staff groups. The MIC results showed that 20 strains (27.4%) were susceptible to penicillin G, 39 strains (53.4%) had intermediate resistance, and 14 strains (19.2%) had full resistance. Low susceptibility to macrolides was also detected: 32.9%, 32.9%, and 34.2% of all strains were resistant to erythromycin, clarithromycin, and azithromycin, respectively. Thirty strains (41%) were resistant to at least two different kinds of antibiotics. Nineteen disparate serotypes were detected besides two nontypeable strains, and the predominant serotypes were 19F and 23F. Pulsed-field gel electrophoresis (PFGE) pattern A was dominant in the serotype 19F group; this pattern was similar to that of the international clone Taiwan 19F. A total of 10 different patterns were detected in the 23F group and were distinguishable from those of the international clones Spain 23F and Taiwan 23F. Pattern b strains were identified in the same ward, and pattern d strains were found both in patients with nosocomial pneumococcal infections (NPI) and in outpatients. In conclusion, drug-resistant
S. pneumoniae
was spreading rapidly, especially isolates of the serotype 19F and 23F groups. PFGE data revealed interpatient transmission and suggested that there might be some association between NPI patient strains and outpatient strains.
Concordance between
Neisseria gonorrhoeae
Genotypes Recovered from Known Sexual Contacts
Authors: Bilek Nicole , Martin Iona M. , Bell Gill , Kinghorn George R. , Ison Catherine A. , Spratt Brian G.
Published: September 2007

Neisseria gonorrhoeae
multiantigen sequence typing (NG-MAST) is a highly discriminatory molecular typing procedure that provides precise and unambiguous strain characterization. Since molecular typing can complement contact tracing for reconstructing gonorrhea sexual networks, the concordance between the NG-MAST genotypes of pairs of
N. gonorrhoeae
isolates from recent sexual contacts was examined. Among 72 pairs of gonococci from recent sexual contacts, the genotypes of each pair were concordant in 65 cases (90.3%). In two further pairs, the isolates from sexual contacts differed by only a single nonsynonymous substitution in the porin gene, and in both of these pairs, the isolates were the same by
opa
typing. The other five nonconcordant pairs of isolates were clearly different strains.
opa
typing data were available for 51 of the pairs of isolates from sexual contacts, and concordant
opa
types were obtained in 38 cases (74.5%). NG-MAST should therefore be better than
opa
typing at identifying recent sexual contacts and has the important advantage over
opa
typing of being a more precise method of strain characterization.
Multiple-Locus Variable-Number Tandem-Repeat Analysis for Rapid Typing of
Candida glabrata
Authors: Grenouillet Frédéric , Millon Laurence , Bart Jean-Mathieu , Roussel Sandrine , Biot Isabelle , Didier Emeline , Ong Anne-Sophie , Piarroux Renaud
Published: September 2007

A multiple-locus variable-number tandem-repeat analysis (MLVA) using six microsatellite markers was assessed in 127
Candida glabrata
isolates. Thirty-seven different genotypes, stable both in vitro and in vivo, were observed. The highest discriminatory power (
D
= 0.902) was reached by using only four markers. MLVA seems to be relevant for
C. glabrata
typing.
Multiplexed Reverse Transcriptase PCR Assay for Identification of Viral Respiratory Pathogens at the Point of Care
Authors: Létant Sonia E. , Ortiz Josue I. , Bentley Tammero Lance F. , Birch James M. , Derlet Robert W. , Cohen Stuart , Manning Dannelle , McBride Mary T.
Published: September 2007

We have developed a nucleic acid-based assay that is rapid, sensitive, and specific and can be used for the simultaneous detection of five common human respiratory pathogens, including influenza virus A, influenza virus B, parainfluenza virus types 1 and 3, respiratory syncytial virus (RSV), and adenovirus groups B, C, and E. Typically, diagnosis on an unextracted clinical sample can be provided in less than 3 h, including sample collection, preparation, and processing, as well as data analysis. Such a multiplexed panel would enable rapid broad-spectrum pathogen testing on nasal swabs and therefore allow implementation of infection control measures and the timely administration of antiviral therapies. We present here a summary of the assay performance in terms of sensitivity and specificity. The limits of detection are provided for each targeted respiratory pathogen, and result comparisons were performed on clinical samples, our goal being to compare the sensitivity and specificity of the multiplexed assay to the combination of immunofluorescence and shell vial culture currently implemented at the University of California-Davis Medical Center hospital. Overall, the use of the multiplexed reverse transcription-PCR assay reduced the rate of false-negative results by 4% and reduced the rate of false-positive results by up to 10%. The assay correctly identified 99.3% of the clinical negatives and 97% of the adenovirus, 95% of the RSV, 92% of the influenza virus B, and 77% of the influenza virus A samples without any extraction performed on the clinical samples. The data also showed that extraction will be needed for parainfluenza virus, which was only identified correctly 24% of the time on unextracted samples.
Interleukin-7 Enhances Proliferation Responses to T-Cell Receptor Stimulation in Naïve CD4
+
T Cells from Human Immunodeficiency Virus-Infected Persons
Authors: Bazdar Douglas A. , Sieg Scott F.
Published: September 2007

Proliferation responses of naïve CD4
+
T cells to T-cell receptor and interleukin-7 (IL-7) stimulation were evaluated by using cells from human immunodeficiency virus-positive (HIV
+
) donors. IL-7 enhanced responses to T-cell receptor stimulation, and the magnitude of this enhancement was similar in cells from healthy controls and from HIV
+
subjects. The overall response to T-cell receptor stimulation alone or in combination with IL-7, however, was diminished among viremic HIV
+
donors and occurred independent of antigen-presenting cells. Frequencies of CD127
+
cells were related to the magnitudes of proliferation enhancement that were mediated by IL-7. Thus, IL-7 enhances but does not fully restore the function of naïve CD4
+
T cells from HIV-infected persons.
Identification of the DNA Sequence Interacting with Kaposi's Sarcoma-Associated Herpesvirus Viral Interferon Regulatory Factor 1
Authors: Park Junsoo , Lee Myung-Shin , Yoo Seung-Min , Jeong Kwi Wan , Lee Daeyoup , Choe Joonho , Seo Taegun
Published: September 2007

Kaposi's sarcoma-associated herpesvirus (KSHV) is the etiological agent of Kaposi's sarcoma. The open reading frame (K9) of KSHV encodes viral interferon regulatory factor 1 (vIRF1), which functions as a repressor of interferon-mediated signal transduction. The amino-terminal region of vIRF1 displays significant homology to the DNA-binding domain of cellular interferon regulatory factors, supporting the theory that the protein interacts with specific DNA sequences. Here, we identify the consensus sequence of vIRF1-binding sites from a pool of random oligonucleotides. Moreover, our data show that vIRF1 interacts with the K3:viral dihydrofolate reductase:viral interleukin 6 promoter region in the KSHV genome.
Interferons and Ribavirin Effectively Inhibit Norwalk Virus Replication in Replicon-Bearing Cells
Authors: Chang Kyeong-Ok , George David W.
Published: September 2007

The development of effective therapies for noroviral gastroenteritis has been hampered by the absence of a cell culture system. Recently, we reported the generation of Norwalk virus (NV) replicon-bearing cells in BHK21 and Huh-7 cells and demonstrated that alpha interferon (IFN-α) effectively inhibited the replication of NV in these cells. In continuing studies for screening potential antinoroviral agents, we tested IFN-γ and ribavirin for their effects on NV replication in the cells. Like IFN-α, IFN-γ inhibited the replication of NV in the replicon-bearing cells, showing the reduction of the NV genome and proteins in a dose-dependent manner. The effective dose for reducing 50% (ED
50
) of the NV genome and protein was calculated to be approximately 40 units/ml. When ribavirin was applied to the cells, it effectively reduced the NV genome and protein with the ED
50
calculated as approximately 40 μM. The combination of IFN-α and ribavirin showed additive effects on the inhibition of NV replication. With the addition of guanosine to the ribavirin treatment, moderately reversed antiviral effects were observed, suggesting that the ribavirin effect may be associated with the depletion of GTP in the cells. Sequencing analysis of the conserved polymerase regions of NV in the ribavirin-treated (100 μM) and nontreated groups showed that the mutation rates were similar and indicated that ribavirin did not induce catastrophic mutations. The NV replicon-bearing cells provide an excellent tool for screening potential antinoroviral agents, and our results indicated that IFNs and ribavirin may be good therapeutic options for noroviral gastroenteritis.