bluuebunny/crossref_metadata_2025 huggingface dataset:
A Novel Displacement Gradient Boundary Element Method for Elastic Stress Analysis With High Accuracy
Authors: Okada H. , Rajiyah H. , Atluri S. N.
Published: July 2009

The boundary element method (BEM) in current usage, is based on the displacement boundary integral equation. The current practice of computing stresses in the BEM involves the use of a two-tier approach: (i) numerical differentiation of the displacement field at the boundary, and (ii) analytical differentiation of the displacement integral equation at the source point in the interior. A new direct integral equation for the displacement gradient is proposed here, to obviate this two-tier approach. The new direct boundary integral equation for displacement gradients has a lower order singularity than in the standard formulation, and is quite tractable from a numerical view point. Numerical results are presented to illustrate the advantages of the present approach.
Small Scale Contact Conditions for the Linear-Elastic Interface Crack
Authors: Anderson Peter M.
Published: July 2009

Conditions are discussed for which the contact zone at the tip of a two-dimensional interface crack between anisotropic elastic materials is small. For such “small scale contact” conditions combined with small scale yielding conditions, a stress concentration vector uniquely characterizes the near tip field, and may be used as a crack growth parameter. Representative calculations for an interface crack on a representative Cu grain boundary show small contact conditions to prevail, except possibly under large shearing loads.
Coordinate Reduction in the Dynamics of Constrained Multibody Systems—A New Approach
Authors: Ider S. K. , Amirouche F. M. L.
Published: July 2009

In this paper a new theorem for the generation of a basis for the null space of a rectangular matrix, with m linearly independent rows and n (n > m) columns is presented. The method is based on Gaussian row operations to transform the constraint Jacobian matrix to an uptriangular matrix. The Gram-Schmidt process is then utilized to identify basis vectors orthogonal to the uptriangular matrix. A complement orthogonal array which forms the basis for the null space for which the algebraic constraint equations are satisfied is then formulated. An illustration of the theorem application to constrained dynamical systems for both Lagrange and Kane’s equations is given. A numerical computer algorithm based on Kane’s equations with embedded constraints is also presented. The method proposed is well conditioned and computationally efficient and inexpensive.
Hopf Bifurcation in the Presence of Both Parametric and External Stochastic Excitations
Authors: Sri Namachchivaya N.
Published: July 2009

In this paper the effect of small parametric and external stochastic perturbations on a two-dimensional system exhibiting Hopf bifurcation is discussed in detail. It is shown that even small fluctuations in parameters can have an important effect when the system is in the neighborhood of bifurcation points. The Markov diffusion approximation is used to obtain analytical results relating to the statistical properties of the stochastic response. Both moment and sample stability conditions along with the stationary moments are obtained. For the nonlinear system, stationary and transient probability densities are found along with their stationary moments. It was found that in nonlinear systems, a shift of the bifurcation point takes place due to the presence of parametric noise.
Rigid Body Collisions
Authors: Brach Raymond M.
Published: July 2009

A general approach is presented for solving the problem of the collision of two rigid bodies at a point. The approach overcomes the difficulties encountered by others on the treatment of contact velocity reversals and negative energy losses. A classical problem is solved; the initial velocities are presumed known and the final velocities unknown. The interaction process between the two bodies is modeled using two coefficients. These are the classical coefficient of restitution, e, and the ratio, μ, of tangential to normal impulses. The latter quantity can be a coefficient of friction as a special case. The paper reveals that these coefficients have a much broader intepretation than previously recognized in the solution of collision problems. The appropriate choice of values for μ is related to the energy loss of the collision. It is shown that μ is bounded by values which correspond to no sliding at separation and conservation of energy. Another bound on μ combined with limits on the coefficient e, provides an overall bound on the energy loss of a collision. Examples from existing mechanics literature are solved to illustrate the significance of the coefficients and their relationship to the energy loss of collisions.
The Onset of Chaos in a Two-Degree-of-Freedom Impacting System
Authors: Shaw Jinsiang , Shaw Steven W.
Published: July 2009

The dynamic response of a two-degree-of-freedom impacting system is considered. The system consists of an inverted pendulum with motion limiting stops attached to a sinusoidally excited mass-spring system. Two types of periodic response for this system are analyzed in detail; existence, stability, and bifurcations of these motions can be explicitly computed using a piecewise linear model. The appearance and loss of stability of very long period subharmonics is shown to coincide with a global bifurcation in which chaotic motions, in the form of Smale horseshoes, arise. Application of this device as an impact damper is also briefly discussed.
Almost-Sure Stability of Some Linear Stochastic Systems
Authors: Ariaratnam S. T. , Ly B. L.
Published: July 2009

The almost-sure stability of linear second-order systems which are parametrically excited by ergodic, “nonwhite,” random processes is studied by an extension of the method of Infante. In this approach, a positive-definite quadratic function of the form V = x′Px is assumed and a family of stability boundaries depending on the elements of the matrix P is obtained. An envelope of these boundaries is then solved for by optimizing the stability boundary with respect to the elements of P. It is found that the optimum matrix P in general depends not only on the system constants but also on the excitation intensities. This approach is, in principle, applicable to study systems involving two or more random processes. The results reported in previous investigations are obtained as special cases of the present study.
Dynamic Shear Band Development in Plane Strain
Authors: Needleman A.
Published: July 2009

Plane strain compression of a rectangular block is used as a model problem to investigate the dynamics of shear band development from an internal inhomogeneity. The material is characterized as a von Mises elastic-viscoplastic solid, with a hardness function that exhibits a local maximum. Regardless of whether the material is hardening or softening, plastic strain development involves the evolution of fingerlike contours emanating from the inhomogeneity at 45 deg to the compression axis. Once a given strain contour crosses the specimen, it fans out about its initial direction of propagation. For a softening solid, this fanning out ceases for some strain level greater than the strain at the hardness maximum and further straining takes place in an ever narrowing band. Many of the qualitative features of shear band development under dynamic loading conditions are the same as under quasistatic loading conditions, but a significant retardation of shear band development due to inertial effects is found.
A Mesomechanical Model for Brittle Deformation Processes: Part II
Authors: Sumarac Dragoslav , Krajcinovic Dusan
Published: July 2009

The approximate, closed-form solutions for the inelastic strain and compliances are derived for some simple plane stress and plane strain cases. The computations are performed for a model-ignoring crack interaction as well as for the case of the self-consistent model.
Magnetic Fields Generated by a Mechanical Singularity in a Magnetized Elastic Half Plane
Authors: Yeh Chau-Shioung
Published: July 2009

The induced magnetic fields generated by a line mechanical singularity in a magnetized elastic half plane are investigated in this paper. One version of linear theory for soft ferromagnetic elastic solids which has been developed by Pao and Yeh (1973) is adopted to analyze the plane strain problem undertaken. By applying the Fourier transform technique, the exact solutions for the generated magnetic inductions due to various mechanical singularities such as a single force, a dipole, and single couple are obtained in a closed form. The distributions of the generated inductions on the surface are shown with figures.
On the Flexure of a Partially Embedded Bar Under Lateral Loads
Authors: Pak Ronald Y. S.
Published: July 2009

This investigation is concerned with a laterally-loaded bar which is partially embedded in a three-dimensional elastic half space. The loading is assumed to be applied at the unembedded end of the bar and may, in general, be a combination of horizontal shear forces and moments. On the adoption of a one-dimensional theory for the bar and the classical theory of elasticity for the semi-infinite solid, the structure-medium interaction problem is reduced to a Fredholm integral equation of the second kind whose solution is then computed. Selected results are presented to illustrate various features of the solution. A set of compliance charts is also included.
Pseudodissipative Systems II: Stability of Reduced Equilibria
Authors: Walker J. A.
Published: July 2009

In terms of the Lagrange formulation of dynamics, ignorable coordinates are defined for the class of “pseudodissipative” mechanical systems. Reduced equilibria (steady motions) of such systems are defined and studied with regard to their stability properties. We obtain broad results and results readily applicable to specific technical problems.
Adiabatic Shear Banding in Plane Strain Problems
Authors: Batra R. C. , Liu De-Shin
Published: July 2009

Plane strain thermomechanical deformations of a viscoplastic body are studied with the objective of analyzing the localization of deformation into narrow bands of intense straining. Two different loadings, namely, the top and bottom surfaces subjected to a prescribed tangential velocity, and these two surfaces subjected to a preassigned normal velocity, are considered. In each case a material defect, flaw, or inhomogeneity is modeled by introducing a temperature bump at the center of the specimen. The solution of the initial boundary value problem by the Galerkin-Adams method reveals that the deformation eventually localizes into a narrow band aligned along the direction of the maximum shearing strain. For both problems, bands of intense shearing appear to diffuse out from the center of the specimen.
Dynamic Modulus of Poroelastic Materials
Authors: Okuno A. , Kingsbury H. B.
Published: July 2009

A simple mathematical formula is proposed to predict the fluid damping effects in poroelastic materials. Biot’s poroelasticity equations are solved to obtain the response of poroelastic materials undergoing harmonic tension-compression and bending deformation. Complex moduli of poroelastic material are explored from the response functions on basis of mathematical models. It is shown that the effects of material parameters, geometrical parameters, and flow boundary conditions on the fluid damping are predicted by simple mathematical formulas. Numerical results are presented and compared with those of other researchers.
Environmentally-Induced Expansion of Heterogeneous Media
Authors: Schulgasser Kalman
Published: July 2009

Relationships between effective expansion behavior and effective elastic constants for composite materials have been known for many years. In the present work composites are considered for which more than one environmental variable (e.g., temperature and relative humidity) cause expansions. A simple direct method to relate effective expansions due to different causes is developed. It is shown that most of the previous elasticity-expansion behavior results are gotten as corollaries, and the applicability of these relationships is broadened.
Line Inclusions in Anisotropic Elastic Solids
Authors: Li Qianqian , Ting T. C. T.
Published: July 2009

A line inclusion located at x2 = 0, |x1| < 1 in the anisotropic elastic medium of infinite extent under uniform loading at infinity is considered. Stroh’s formalism is used to find the displacement and stress fields. The inclusion can be rigid or elastic. Conditions on the loading under which the line inclusion does not disturb the homogeneous field are derived. For the rigid inclusion, a real form solution is obtained for the stress and displacement along x2 = 0. When the inclusion is elastic (and anisotropic), a pair of singular Fredholm integral equations of the second kind is derived for the difference in the stress on both surfaces of the inclusion. The pair can be decoupled and asymptotic solutions of the integral equation are obtained when λ, which represents the relative rigidity of the matrix to the inclusion, is small. For the general cases, the integral equation is solved by a numerical discretization. Excellent agreements between the asymptotic and numerical solutions are observed for small λ.
Interfacial Stresses in Bimetal Thermostats
Authors: Suhir E.
Published: July 2009

The magnitude and the distribution of the interfacial stresses in thermostat-like structures are determined on the basis of an elementary beam theory, with consideration of both the longitudinal and the transverse (“through-thickness”) interfacial compliances of the thermostat strips. The suggested approach is applicable, generally speaking, to any elongated lap shear assembly, subjected to thermal or external loading.
A Boundary Integral Equation Formulation in Derivative Unknowns for Two-Dimensional Potential Problems
Authors: Choi Joo Ho , Kwak Byung Man
Published: July 2009

A boundary integral equation called Derivative BIE is developed for two-dimensional potential problems in terms of tangential and normal derivatives of the potential on the boundary, by integrating by parts the Cauchy formula. The potential values on the boundary can be calculated by integration after the solution is obtained. The primary unknowns in this formulation can be of direct interest in a shape design sensitivity analysis where the tangential derivatives of the potential are also required. The method is applied to several test problems, and the results show better accuracy than those by the conventional boundary element method, not only for the derivatives of the potential but also for the potential itself.
Elastoplastic Buckling of Annular Plates in Pure Shear
Authors: Ore E. , Durban D.
Published: July 2009

A linear buckling analysis is presented for annular elastoplastic plates under shear loads. The standard plate buckling equations are used in conjunction with the small strain J2 flow and deformation theories of plasticity. The main numerical finding is that deformation theory predicts critical loads which are considerably below the predictions obtained with the flow theory. Furthermore, comparison with experimental data for different metals shows a good agreement with the deformation theory results over a wide range of geometries. The limiting buckling problem of a long narrow panel under shear stresses is treated separately. This problem admits an exact solution and it is shown that the critical loads for the panel are approached asymtotically by the annular plate results. Contact is made with earlier studies on the buckling of elastic-orthotropic and elastoplastic shear panels.
Effect of Correlation on the Almost-Sure Asymptotic Stability of Second-Order Linear Stochastic Systems
Authors: Ariaratnam S. T. , Xie Wei Chau
Published: July 2009

A method of obtaining a sufficient almost-sure (a.s.) asymptotic stability condition for second-order, linear systems with both ergodic damping and stiffness coefficients is presented. The probabilistic property of the correlation between the damping and stiffness coefficients is taken into account. A sufficient condition for a.s. asymptotic stability is derived and numerical results are presented for the case of Gaussian noise coefficients. Results obtained in some of the previous investigations are included in the present study as special cases.
Determining Lyapunov Exponents by Means of Interpolated Mapping
Authors: Tongue Benson H. , Smith David
Published: July 2009

The method of Interpolated Mapping is extended to encompass the calculation of transient system behavior, specifically the efficient determination of the Lyapunov exponents for a simple nonlinear system. Both the continuous Lyapunov exponents as well as the corresponding Lyapunov exponents of the Poincare´ map for a forced Duffing’s oscillator are found. The use of Interpolated Mapping is compared to straightforward numerical integration and is shown to offer distinct computational advantages.
Improvement of a Nonparametric Identification Procedure Used in Nonlinear Dynamics
Authors: Argoul P. , Jezequel L.
Published: July 2009

The advantage of nonparametric identification methods based on the use of approximations of the restoring forces is that they do not require the a priori knowledge of a model for the nonlinear behavior of the structure. However, the main difficulty encountered with this type of methods is the fitting of nonlinear forces in the force-state mapping fields where there are not sufficient experimental data. In this paper, an improvement of the regression technique in conjunction with the use of two-dimensional Chebyshev orthogonal polynomials by introducing an interative computation process is presented. It is shown that the proposed method can properly identify the discretized model even in the case of high cross-product displacement-velocity terms and that this method can be used for structures presenting important nonlinear modal coupling.
Analysis of Thermal Stresses in a Ceramic-to-Metal Cylindrical Joint With a Homogeneous Elastic Medium
Authors: Kimura Osamu , Kawashima Toshio
Published: July 2009

It is well known that large thermal stresses arise in a ceramic-to-metal joint because of thermal expansion mismatch. Therefore, to avoid fracture of a joint, it has been recommended a joint in which thermal expansion coefficient of a ceramic member is smaller than that of a metal member. The joint is called a “compressive” joint, because it was believed that only compressive stresses occur in the ceramic member. Since ceramic is about ten times as strong in compression as in tension, this joint is considered stronger than a tensile joint. A finite element calculation (FEC), however, has shown that a large tensile stress is generated even in ceramic part of a compressive joint. The aim of this study is to clarify stress distribution in a compressive joint by solving analytically the stress equation of the joint. For convenience, we deal with a special joint in which the elastic constants of the ceramic member are assumed to be the same as those of the metal member. The result of the analysis gives the same stress distribution obtained by FEC, and its value of the tensile stress agrees fairly well with that of FEC.
Cavities vis-a`-vis Rigid Inclusions and Some Related General Results in Plane Elasticity
Authors: Dundurs John
Published: July 2009

There is a strange feature of plane elasticity that seems to have gone unnoticed: The stresses in a body that contains rigid inclusions and is loaded by specified surface tractions depend on the Poisson ratio of the material. If the Poisson ratio in this stress field is set equal to +1 for plane strain, or +∞ for plane stress, the rigid inclusions become cavities for elastic constants within the physical range. The paper pursues this circumstance, and in doing so also produces several useful by-products that are connected with the stretching and curvature change of a boundary.
Analysis of Branched Interface Cracks Between Dissimilar Anisotropic Media
Authors: Miller G. R. , Stock W. L.
Published: July 2009

A solution is presented for the problem of a crack branching off the interface between two dissimilar anisotropic materials. A Green’s function solution is developed using the complex potentials of Lekhnitskii (1981) allowing the branched crack problem to be expressed in terms of coupled singular integral equations. Numerical results for the stress intensity factors at the branch crack tip are presented for some special cases, including the no-interface case which is compared to the isotropic no-interface results of Lo (1978).
Three-Dimensional Analysis of Cracking Through the Boundary of a Two-Phase Material
Authors: Hanson M. T. , Lin W. , Keer L. M.
Published: July 2009

The penetration through a two-phase boundary by a biplanar (kinked) crack of arbitrary shape is considered in this paper. The two-phase boundary is modeled as the interface between two perfectly-bonded elastic, isotropic, homogeneous half spaces with different elastic constants. The planar crack on either side of the interface may be arbitrarily orientated with respect to the interface boundary. The body-force method is used to derive a set of coupled two-dimensional singular integral equations which are solved numerically. The solution yields the three crack opening displacements as well as the three modes of stress intensity factors along the crack contour. Numerical results are given for a penny-shaped crack symmetrically oriented with respect to the interface. Mode I stress intensity factors are given for the biplanar crack that experiences a kink when passing through the interface.
Inelastic Response of an Infinite Cylindrical Shell to Transient Acoustic Waves
Authors: Geers Thomas L. , Yen Chi-Lin
Published: July 2009

The geometrically and constitutively nonlinear response of an infinite, circular, cylindrical shell submerged in an infinite fluid medium to a transverse, transient acoustic wave is analyzed. Circumferential Fourier series solutions are obtained through the numerical integration of coupled ordinary differential equations and convolution integrals. Numerical results are presented in the form of response histories, response snapshots, and iso-damage curves for incident waves of rectangular pressure profile. Response solutions obtained with the first-order doubly asymptotic approximation are compared with their “exact” counterparts. It is found that doubly asymptotic approximations are unsuitable for two-dimensional, shock-response analysis of yielding submerged structures.
Stability of a Semi-Active Impact Damper: Part II—Periodic Solutions
Authors: Karyeaclis M. P. , Caughey T. K.
Published: July 2009

All solutions of the semi-active impact damper described in Part I were shown to be bounded when the excitation is bounded. In this part, the existence of periodic solutions is investigated. Emphasis is placed on two impacts/cycle periodic solutions. Exact symmetric and nonsymmetric harmonic solutions are derived analytically and the region of asymptotic stability is determined.
The Oscillation of Slender Elliptical Inviscid and Newtonian Jets: Effects of Surface Tension, Inertia, Viscosity, and Gravity
Authors: Bechtel S. E.
Published: July 2009

The motion of inviscid and Newtonian jets issuing from elliptical orifices is analyzed. The analysis is not confined to small departures of the jet free surface from a circular cylindrical mean surface, but rather is fully nonlinear. Two types of behavior are predicted: (1) In the presence of surface tension the major axis of the elliptical jet cross-section alternates between perpendicular directions with distance down the jet. In this case the system is described as a single-degree-of-freedom nonlinear oscillator, conservative for the inviscid elliptical jet in the absence of gravity, and nonconservative for the Newtonian jet. (2) When surface tension is neglected, the transformation occurs only once, after which the jet flattens into a sheet perpendicular to the major axis of the orifice. The effect of gravity is discussed both for downward flowing jets and fountains.
New Treatment Option for Second-Stage African Sleeping Sickness: In Vitro and In Vivo Efficacy of Aza Analogs of DB289
Authors: Wenzler Tanja , Boykin David W. , Ismail Mohamed A. , Hall James Edwin , Tidwell Richard R. , Brun Reto
Published: July 2009

African sleeping sickness is a fatal parasitic disease, and all drugs currently in use for treatment have strong liabilities. It is essential to find new, effective, and less toxic drugs, ideally with oral application, to control the disease. In this study, the aromatic diamidine DB75 (furamidine) and two aza analogs, DB820 and DB829 (CPD-0801), as well as their methoxyamidine prodrugs and amidoxime metabolites, were evaluated against African trypanosomes. The active parent diamidines showed similar in vitro profiles against different
Trypanosoma brucei
strains, melarsoprol- and pentamidine-resistant lines, and a P2 transporter knockout strain (AT1KO), with DB75 as the most trypanocidal molecule. In the
T. b. rhodesiense
strain STIB900 acute mouse model, the aza analogs DB820 and DB829 demonstrated activities superior to that of DB75. The aza prodrugs DB844 and DB868, as well as two metabolites of DB844, were orally more potent in the
T. b. brucei
strain GVR35 mouse central nervous system (CNS) model than DB289 (pafuramidine maleate). Unexpectedly, the parent diamidine DB829 showed high activity in the mouse CNS model by the intraperitoneal route. In conclusion, DB868 with oral and DB829 with parenteral application are potential candidates for further development of a second-stage African sleeping sickness drug.
Activity of Telavancin against Staphylococci and Enterococci Determined by MIC and Resistance Selection Studies
Authors: Kosowska-Shick Klaudia , Clark Catherine , Pankuch Glenn A. , McGhee Pamela , Dewasse Bonifacio , Beachel Linda , Appelbaum Peter C.
Published: July 2009

This study used CLSI broth microdilution to test the activity of telavancin and comparator antimicrobial agents against 67 methicillin (meticillin)-resistantStaphylococcus aureus(MRSA) isolates. Twenty-six vancomycin-intermediateS. aureus(VISA) strains were among the isolates tested; all strains were susceptible to telavancin at ≤1 μg/ml, whereas 12/26 (46%) of these isolates were nonsusceptible to daptomycin at the same concentration. All strains were susceptible to quinupristin-dalfopristin, while resistance was found to all other drugs tested. Telavancin demonstrated potent activity against all vancomycin-susceptible isolates as well as against heterogeneously VISA and VISA resistance phenotypes. In multistep resistance selection studies, telavancin yielded one stable mutant after 43 days in one MRSA strain out of the 10 MRSA strains tested with the MIC rising eightfold from 0.25 μg/ml (parent) to 2 μg/ml. MICs for this clone did not increase further when passages were continued for the maximum 50 days. In contrast, daptomycin selected stable resistant clones (MIC increase of >4×) after 14 to 35 days in 4 of 10 MRSA strains with MICs increasing from 1 to 2 μg/ml (parents) to 4 to 8 μg/ml (resistant clones). Sequencing analysis of daptomycin resistance determinants revealed point mutations in themprFgenes of all four stable daptomycin-resistant clones. Teicoplanin gave rise to resistant clones after 14 to 21 days in 2 of 10 MRSA strains with MICs rising from 1 to 2 μg/ml (parents) to 4 to 16 μg/ml (stable resistant clones). Linezolid selected stable resistant clones after 22 to 48 days in 2 of 10 MRSA strains with MICs rising from 2 to 4 μg/ml (parents) to 32 μg/ml (resistant clones). Vancomycin yielded no resistant clones in 10 MRSA strains tested; however, MICs increased two- to fourfold from 1 to 8 μg/ml to 2 to 16 μg/ml after 50 days. No cross-resistance was found with any clone/antimicrobial combination. The two enterococci developed resistance to daptomycin, and one developed resistance to linezolid. Single-step mutation frequencies for telavancin (<4.0 × 10−11to <2.9 × 10−10at 2× MIC) were lower than the spontaneous mutation frequencies obtained with the comparators.
Dosing Regimens of Cotrimoxazole (Trimethoprim-Sulfamethoxazole) for Melioidosis
Authors: Cheng Allen C. , McBryde Emma S. , Wuthiekanun Vanaporn , Chierakul Wirongrong , Amornchai Premjit , Day Nicholas P. J. , White Nicholas J. , Peacock Sharon J.
Published: July 2009

Melioidosis is an infectious disease with a propensity for relapse, despite prolonged antibiotic eradication therapy for 12 to 20 weeks. A pharmacokinetic (PK) simulation study was performed to determine the optimal dosing of cotrimoxazole (trimethoprim-sulfamethoxazole [TMP-SMX]) used in current eradication regimens in Thailand and Australia. Data for bioavailability, protein binding, and coefficients of absorption and elimination were taken from published literature. Apparent volumes of distribution were correlated with body mass and were estimated separately for Thai and Australian populations. In vitro experiments demonstrated concentration-dependent killing. In Australia, the currently used eradication regimen (320 [TMP]/1,600 [SMX] mg every 12 h [q12h]) was predicted to achieve the PK-pharmacodynamic (PD) target (an area under the concentration-time curve from 0 to 24 h/MIC ratio of >25 for both TMP and SMX) for strains with the MIC
90
of Australian strains (≤1/19 mg/liter). In Thailand, the former regimen of 160/800 mg q12h would not be expected to attain the target for strains with an MIC of ≥1/19 mg/liter, but the recently implemented weight-based regimen (<40 kg [body weight], 160/800 mg q12h; 40 to 60 kg, 240/1,200 mg q12h; >60 kg, 320/1,600 mg q12h) would be expected to achieve adequate concentrations for strains with an MIC of ≤1/19 mg/liter. The results were sensitive to the variance of the PK parameters. Prospective PK-PD studies of Asian populations are needed to optimize TMP-SMX dosing in melioidosis.
NontypeableHaemophilus influenzaeClearance by Alveolar Macrophages Is Impaired by Exposure to Cigarette Smoke
Authors: Martí-Lliteras Pau , Regueiro Verónica , Morey Pau , Hood Derek W. , Saus Carles , Sauleda Jaume , Agustí Alvar G. N. , Bengoechea José Antonio , Garmendia Junkal
Published: July 2009

NontypeableHaemophilus influenzae(NTHI) is an opportunistic gram-negative pathogen that causes respiratory infections and is associated with progression of respiratory diseases. Cigarette smoke is a main risk factor for development of respiratory infections and chronic respiratory diseases. Glucocorticoids, which are anti-inflammatory drugs, are still the most common therapy for these diseases. Alveolar macrophages are professional phagocytes that reside in the lung and are responsible for clearing infections by the action of their phagolysosomal machinery and promotion of local inflammation. In this study, we dissected the interaction between NTHI and alveolar macrophages and the effect of cigarette smoke on this interaction. We showed that alveolar macrophages clear NTHI infections by adhesion, phagocytosis, and phagolysosomal processing of the pathogen. Bacterial uptake requires host actin polymerization, the integrity of plasma membrane lipid rafts, and activation of the phosphatidylinositol 3-kinase (PI3K) signaling cascade. Parallel to bacterial clearance, macrophages secrete tumor necrosis factor alpha (TNF-α) upon NTHI infection. In contrast, exposure to cigarette smoke extract (CSE) impaired alveolar macrophage phagocytosis, although NTHI-induced TNF-α secretion was not abrogated. Mechanistically, our data showed that CSE reduced PI3K signaling activation triggered by NTHI. Treatment of CSE-exposed cells with the glucocorticoid dexamethasone reduced the amount of TNF-α secreted upon NTHI infection but did not compensate for CSE-dependent phagocytic impairment. The deleterious effect of cigarette smoke was observed in macrophage cell lines and in human alveolar macrophages obtained from smokers and from patients with chronic obstructive pulmonary disease.
Spores as Infectious Propagules ofCryptococcus neoformans
Authors: Velagapudi Rajesh , Hsueh Yen-Ping , Geunes-Boyer Scarlett , Wright Jo Rae , Heitman Joseph
Published: July 2009

Cryptococcus neoformansandCryptococcus gattiiare closely related pathogenic fungi that cause pneumonia and meningitis in both immunocompromised and immunocompetent hosts and are a significant global infectious disease risk. Both species are found in the environment and are acquired via inhalation, leading to an initial pulmonary infection. The infectious propagule is unknown but is hypothesized to be small desiccated yeast cells or spores produced by sexual reproduction (opposite- or same-sex mating). Here we characterize the morphology, germination properties, and virulence of spores. A comparative morphological analysis of hyphae and spores produced by opposite-sex mating, same-sex mating, and self-fertile diploid strains was conducted by scanning electron microscopy, yielding insight into hyphal/basidial morphology and spore size, structure, and surface properties. Spores isolated by microdissection were found to readily germinate even on water agarose medium. Thus, nutritional signals do not appear to be required to stimulate spore germination, and as-yet-unknown environmental factors may normally constrain germination in nature. As few as 500 CFU of a spore-enriched infectious inoculum (∼95% spores) of serotype AC. neoformansvar.grubiiwere fully virulent (100% lethal infection) in both a murine inhalation virulence model and the invertebrate model hostGalleria mellonella. In contrast to a previous report onC. neoformansvar.neoformans, spores ofC. neoformansvar.grubiiwere not more infectious than yeast cells. Molecular analysis of isolates recovered from tissues of infected mice (lung, spleen, and brain) provides evidence for infection and dissemination by recombinant spore products. These studies provide a detailed morphological and physiological analysis of the spore and document that spores can serve as infectious propagules.
EMISSION AND INTENSITY MODULATION OF TERAHERTZ ELECTROMAGNETIC RADIATION UTILIZING 2-DIMENSIONAL PLASMONS IN DUAL-GRATING-GATE HEMT'S
Authors: OTSUJI TAIICHI , NISHIMURA TAKUYA , TSUDA YUKI , MEZIANI YAHYA MOUBARAK , SUEMITSU TETSUYA , SANO EIICHI
Published: July 2009

Two dimensional plasmons in submicron transistors have attracted much attention due to their nature of promoting emission/detection of electromagnetic radiation in the terahertz range. We have recently proposed and fabricated a highly efficient, broadband plasmon-resonant terahertz emitter. The device incorporates doubly interdigitated grating gates and a vertical cavity into a high electron mobility transistor. The device operates in various modes: (1) DC-current-driven self oscillation, (2) CW-laser excited terahertz emission, (3) two-photon injection-locked difference-frequency terahertz emission, and (4) impulsive laser excited terahertz emission. Furthermore, the device can operate in completely different functionalities including ultrahigh-speed intensity modulation for terahertz carrier waves. This paper reviews recent advances on plasma wave devices.
THE EFFECTS OF INCREASING AlN MOLE FRACTION ON THE PERFORMANCE OF AlGaN ACTIVE REGIONS CONTAINING NANOMETER SCALE COMPOSITIONALLY INHOMOGENEITIES
Authors: SAMPATH A.V. , REED M.L , MOE C. , GARRETT G.A. , READINGER E.D. , SARNEY W.L , SHEN H. , WRABACK M. , CHUA C. , JOHNSON N.M.
Published: July 2009

In this paper we report on the characterization of n - Al 0.51 Ga 0.49 N active regions and the fabrication of ultraviolet LEDs that contain self-assembled, nanometer-scale compositional inhomogeneities ( NCI - AlGaN ) with emission at ~290 nm. These active regions exhibit reduced integrated photoluminescence intensity and PL lifetime relative to 320 nm NCI - AlGaN active regions that have significantly lower AlN mole fraction, despite having more than an order of magnitude fewer threading dislocations, as measured by transmission electron microscopy. This behavior is attributed to nonradiative recombination associated with the presence of a larger density of point defects in the higher Al content samples. The point defects are ameliorated somewhat by the lower density of NCI AlGaN regions in the higher Al content samples, which leads to a larger concentration of carriers in the NCI and concomitant reduced radiative lifetime that may account for the high observed peak IQE (~ 25%). Prototype flip chip double heterostructure-NCI- ultraviolet light emitting diodes operating at 292 nm have been fabricated that employ a 50% NCI - AlGaN active region.
THE FIRST 70NM 6-INCH GaAs PHEMT MMIC PROCESS
Authors: KARIMY H. , GUNTER L. , DUGAS D. , CHAO P.C. , KONG W. , YANG S. , SEEKELL P. , DUH K.H.G. , LOMBARDI J. , MT PLEASANT L.
Published: July 2009

BAE Systems has developed a high power, high yield 70nm 6" 2-mil PHEMT MMIC process for frequencies up to 100GHz. Utilizing T -gate technology and 2-mil substrates, we have created a millimeter wave technology that produces excellent performance from Ka -band through W -bands. The device DC and RF characteristics have excellent uniformity across the wafer. In this paper, we report the 70nm device fabrication on 6-inch wafers and compare the DC and RF characteristics with its mature 0.1µm counterpart.
HIGH CURRENT DENSITY/HIGH VOLTAGE AlGaN/GaN HFETs ON SAPPHIRE
Authors: SHI JUNXIA , POPHRISTIC M. , EASTMAN L. F.
Published: July 2009

AlGaN / GaN heterojunction field effect transistors (HFETs) on sapphire substrates for power-switching applications have been fabricated. Design parameters such as source-gate spacing (Lsg), gate length (Lg), and gate width (Wg) have been varied to check their effects on the device performances. For a gate-drain spacing (Lgd) of 10µm, a specific on-resistance (ARon) of 1.35mΩ-cm2 and off-state breakdown voltage (BV) of 770V was achieved, which is close to the 4- H SiC theoretical limit.
GaN TRANSISTORS FOR POWER SWITCHING AND MILLIMETER-WAVE APPLICATIONS
Authors: UEDA TETSUZO , UEMOTO YASUHIRO , TANAKA TSUYOSHI , UEDA DAISUKE
Published: July 2009

We review our state-of-the-art GaN -based device technologies for power switching at low frequencies and for future millimeter-wave communication systems. These two applications are emerging in addition to the power amplifiers at microwave frequencies which have been already commercialized for cellular base stations. Technical issues of the power switching GaN device include lowering the fabrication cost, normally-off operation and further increase of the breakdown voltages extracting full potential of GaN -based materials. We establish flat and crack-free epitaxial growth of GaN on Si which can reduce the chip cost. Our novel device structure called Gate Injection Transistor (GIT) achieves normally-off operation with high enough drain current utilizing conductivity modulation. Here we also present the world highest breakdown voltage of 10400V in AlGaN / GaN HFETs. In this paper, we also present high frequency GaN -based devices for millimeter-wave applications. Short-gate MIS-HFETs using in-situ SiN as gate insulators achieve high fmax up to 203GHz. Successful integration of low-loss microstrip lines with via-holes onto sapphire enables compact 3-stage K -band amplifier MMIC of which the small-signal gain is as high as 22dB at 26GHz. The presented devices are promising for the two future emerging applications demonstrating high enough potential of GaN -based transistors.
4-NM AlN BARRIER ALL BINARY HFET WITH SiNx GATE DIELECTRIC
Authors: ZIMMERMANN TOM , CAO YU , JENA DEBDEEP , XING HUILI GRACE , SAUNIER PAUL
Published: July 2009

Undoped AlN / GaN heterostructures, grown on sapphire by molecular beam epitaxy, exhibit very low sheet resistances, ~ 150 Ohm/sq, resulting from the 2-dimensional electron gas situated underneath a 4 nm thin AlN barrier. This extraordinarily low sheet resistance is a result of high carrier mobility and concentration (~ 1200 cm2/Vs and ~ 3.5×1013 cm-2 at room temperature), which is ~ 3 × smaller than that of the conventional AlGaN / GaN heterojunction field effect transistor (HFET) structures. Using a 5 nm SiN x deposited by plasma enhanced chemical vapor deposition as gate-dielectric, HFETs were fabricated using these all binary AlN / GaN heterostructures and the gate tunneling current was found to be efficiently suppressed. Output current densities of 1.7 A/mm and 2.1 A/mm, intrinsic transconductance of 455 mS/mm and 785 mS/mm, were achieved for 2 µm and 250 nm gate-length devices, respectively. Current gain cut-off frequency fT of 3.5 GHz and 60 GHz were measured on 2 µm and 250 nm gate-length devices, limited by the high ohmic contact resistance as well as the relatively long gate length in comparison to the electron mean free path under high electric fields.
BI-DIRECTIONAL SCALABLE SOLID-STATE CIRCUIT BREAKERS FOR HYBRID-ELECTRIC VEHICLES
Authors: URCIUOLI D. P. , VELIADIS VICTOR
Published: July 2009

Power electronics in hybrid-electric military ground vehicles require fast fault isolation, and benefit additionally from bi-directional fault isolation. To prevent system damage or failure, maximum fault current interrupt speeds in tens to hundreds of microseconds are necessary. While inherently providing bi-directional fault isolation, mechanical contactors and circuit breakers do not provide adequate actuation speeds, and suffer severe degradation during repeated fault isolation. Instead, it is desired to use a scalable array of solid-state devices as a solid-state circuit breaker (SSCB) having a collectively low conduction loss to provide large current handling capability and fast transition speed for current interruption. Although, both silicon-carbide (SiC) JFET and SiC MOSFET devices having high breakdown voltages and low drain-to-source resistances have been developed, neither device structure alone is capable of reverse blocking at full voltage. Limitations exist for using a dual common-source structure for either device type. Small-scale SSCB experiments were conducted using 0.03 cm2 normally-on SiC VJFETs. Based on results of these tests, a normally-on VJFET device modification is made, and a proposed symmetric SiC JFET is considered for this application.
CRYSTALLIZATION AND MAGNETO-TRANSPORT CHARACTERISTICS IN MOD YBa2Cu3O7-δ FILMS
Authors: GAO BO , YING LILIANG , LIU JINLEI , LU YUMING , LIU ZHIYONG , CAI CHUANBING , HÜHNE RUBEN , HOLZAPFEL BERNHARD
Published: July 2009

YBa 2 Cu 3 O 7-δ (YBCO) films are prepared on the substrate of single crystal LaAlO 3 (LAO) by using metal trifluoroacetates deposition (TFA-MOD). The phase evolvement, magneto-transport and flux pinning characteristics in MOD - YBCO films are studied. It is revealed that Ba - Cu - O and Y - Cu - O precipitates are formed and can be controlled by optimum crystallization process. The field dependence of Jc ( H // c ) shows that the accommodation field Hacc decreases exponentially with increasing temperature and the power-law relationship holds in the medium fields with an exponent α of about 0.67, nearly independent of temperatures. Compared with the samples grown by pulsed laser deposition, MOD films have larger Hacc at higher temperatures (> 50 K) indicating that the value of the exponent α is affected by the precipitates entrapped in the YBCO matrix.
EFFECT OF SINTERING TIME ON SUPERCONDUCTIVITY IN MgB2
Authors: ZHANG Y. , ZHOU S. H. , LU C. , CHUNG K. C. , DOU S. X.
Published: July 2009

We studied the effect of sintering time on microstrain, critical current density ( J c ), and resistivity (ρ) in MgB 2 bulks. All samples were fabricated by solid state reaction and sintered within a time range of 30 minutes – 60 hours. It has been found that microstrain increases as the sintering time increases, while the connectivity decreases with sintering time from 30 minutes to 20 hours, and then increases to 60 hours. Both the irreversibility field, H irr , and the upper critical field, H c 2, were increased with microstrain. This indicates that the disorder significantly affects H irr and H c 2. The sample with the sintering time of 30 minutes exhibited the highest J c at all fields, due to its having the highest connectivity. When the sample is sintered for a very long time (60 hours), J c at high fields can be improved. This is mainly attributed to increased H c 2.
COMPARATIVE STUDY OF MAGNETIC BEHAVIOR OF RuSr2RE1.5Ce0.5Cu2O10-δ WHERE RE = Eu AND Sm
Authors: NIGAM R. , PAN A. V. , DOU S. X.
Published: July 2009

Systematic investigation of structural, magnetic and transport properties of RuSr 2 RE 2-x Ce x Cu 2 O 10 with RE being Sm and Eu has been performed. We present the experimental evidence that the synthesis of RuSr 2 Eu 1.5 Ce 0.5 Cu 2 O 10 under non-optimised heat treatment conditions may results in the formation of secondary RuSr 2 EuCu 2 O 8 phase. In contrast, similar preparation conditions for RuSr 2 Sm 1.5 Ce 0.5 Cu 2 O 10 samples lead to the pure phase. Consequently, RuSr 2 Eu 1.5 Ce 0.5 Cu 2 O 10 samples exhibit a small peak around 125 K in the temperature dependence of dc magnetization, pronounced irreversibility between zero-field cooled and field cooled curves at temperatures higher than the peak temperature, and the bell shaped behavior of the coercive field as the function of temperature above Curie's temperature. These anomalous features, which may arise due to the superposition effect of the main and secondary phases, which are both magnetic, are completely absent for RuSr 2 Sm 1.5 Ce 0.5 Cu 2 O 10 sample, which does not consist of the secondary phase.
STUDY OF MICROSTRUCTURE OF HYDROCARBON DOPED MgB2 WIRES BY TRANSMISSION ON ELECTRON MICROSCOPY
Authors: KANG SEONG GU , CHUNG JUN-KI , PARK SUNG CHANG , JEONG DAE GIL , KIM CHEOL JIN
Published: July 2009

The microstructure of the MgB 2 wires with hydrocarbon, pyrene (C16H10) addition has been investigated by transmission electron microscopy (TEM) equipped with energy-dispersive X-ray spectroscopy (EDX). In our study, MgB 2 wires have been fabricated through powder-in-tube (PIT) process using pure Fe as sheath material and sintered at 600°C ~800°C for 30min to 4 hrs under high purity argon gas. TEM and EDS analyses were conducted on the specimens prepared by tripod polishing and ion milling method. The structural features such as second phases, interface and defects were investigated by electron microscopy.
CHARACTERISTICS OF MgB2 THIN FILMS SYNTHESIZED BY CO-EVAPORATION METHOD
Authors: PARK SUNG CHANG , CHUNG JUN-KI , KANG SEONG GU , LIM YEONG JIN , KIM CHEOL JIN , KIM CHAN-JOONG
Published: July 2009

MgB 2 thin films have been synthesized by co -evaporation method by controlling the relative deposition rates of B and Mg on sapphire ( Al 2 O 3) substrate. Before the co -evaporation of Mg and B , the deposition rates of each element have been measured separately with various substrate temperatures. As the substrate temperature increased above the optimum growth condition, Mg started to evaporate from the already reacted MgB 2 and form MgB 12 as a second phase, which resulted in the tendency decreasing the critical temperature. Superconducting properties have been measured by PPMS and the microstructural features have been characterized with XRD, SEM and EDS.
SYNTHESIS AND CHARACTERIZATION OF MgB2 FILMS DEPOSITED BY ULTRASONIC SPRAY PYROLYSIS
Authors: CHUNG JUN-KI , KIM WON-JEONG , LIM YEONG-JIN , PARK SUNG-CHANG , KIM CHEOL-JIN
Published: July 2009

The MgB 2 films have been prepared on the c-cut sapphire substrates by ultrasonic spray pyrolysis (USP) technique using Boric acid and Magnesium acetate tetrahydrate dissolved into distillated water and ethanol as starting materials. The overall concentrations were fixed at 0.1mol/L. During the deposition, 96% Ar - 4% H 2 was used as carrier gas. The reaction temperatures were 850 °C, 900 °C and 950 °C . The deposited MgB 2 films showed strongly (1 0 1) plane orientation. In the sample deposited at 950 °C for 5min, MgB 2 film showed a homogeneous surface, with good grain connectivity. The critical temperature (Tc) was observed to be 31.5 K. The crystal structural and microstructural properties of the MgB 2 films prepared by USP were observed to be strongly dependent on the reacting temperature.