bluuebunny/crossref_metadata_2025 huggingface dataset:
Material Compatibility in Interfacial Transient Thermal Fracture of Ceramic-to-Metal Bonds
Authors: Kokini Klod
Published: July 2009

The effect of changing thermal expansion coefficients and thermal properties on the deformations and strain energy release rates of cracks at the interface between a ceramic-to-metal bond subjected to a transient thermal load is examined. The configurations of a two-dimensional edge and center through-cracks are analyzed. The effects of the thickness of the ceramic are considered. The results show that equating the thermal expansion coefficients of the two materials can lead to an increase in the strain energy release rate. A simple two-bar model is used to provide a qualitative explanation for the results.
A Surface Crack in Shells Under Mixed-Mode Loading Conditions
Authors: Joseph P. F. , Erdogan F.
Published: July 2009

The problem of a shallow shell containing a surface crack and subjected to general loading conditions is considered. It is shown that, as in the three-dimensional elasticity formulation, the mode I state can be separated whereas modes II and III remain coupled. A line spring model is developed to formulate the part-through crack problem under mixed-mode conditions. A shallow shell of arbitrary curvature having a part-through crack located on the outer or the inner surface of the shell is then considered. Reissner’s transverse shear theory is used to formulate the problem by assuming that the shell is subjected to all five moment and stress resultants. The uncoupled antisymmetric problem is solved for cylindrical and toroidal shells having a surface crack in various orientations and the primary and the secondary stress intensity factors are given. The results show that, unlike the through crack problems, in surface cracks the effect of shell curvature on the stress intensity factors is relatively insignificant.
Sound Radiation From Beams Under the Action of Moving Line Forces
Authors: Keltie R. F. , Peng H.
Published: July 2009

The topic of sound radiation from beams under the action of harmonic line forces moving at subsonic speeds is studied. The nondimensional sound power is formulated through integration of the surface acoustic intensity distribution over the entire beam. Asymptotic expressions for the sound power in the low frequency region are derived depending upon the characteristics of the fluid loading and the spatial extent of the applied forces. Numerical integrations have been performed to determine the effects on the radiated sound power of the Mach number, M, the acoustic length of line force, KoL, and the wavenumber ratio, γ. The results show that for beams under heavy fluid loading, the effect of the speed of the moving force is not pronounced, while for beams under light fluid loading, the unique coincidence radiation peak at γ ∼ 1 for a stationary force (M = 0̸) is split into two coincidence peaks (located in the frequency regions γ<1 and γ>1 respectively) due to the effects of the Doppler shift. The values of KoL that suppress the coincidence peaks are also changed due to the motion of the line force.
Axisymmetric Free Vibrations of a Transversely Isotropic Finite Cylindrical Rod
Authors: Lusher C. P. , Hardy W. N.
Published: July 2009

The frequencies of free vibration and mode shapes are calculated for axisymmetric modes of an elastic cylinder of finite length having hexagonal symmetry with the crystallographic c-axis coincident with the axis of the cylinder (a transversely isotropic finite cylindrical rod). A series solution is used which satisfies term-by-term the differential equations of linear elasticity and the boundary conditions on the shear stress; the boundary conditions on the normal stresses are satisfied by using an orthogonalization procedure. As an example, the method is applied to sapphire, with one of the six elastic constants (c14) taken to be zero. The other five elastic constants are those of the hexagonal system. The calculated acoustic vibration frequencies agree to better than 1 percent with measurements made on sapphire at room temperature, for a cylinder of half-height to radius ratio ∼ 1.
Ultrasonic Wave Reflection From Liquid-Coupled Orthotropic Plates With Application to Fibrous Composites
Authors: Nayfeh Adnan H. , Chimenti D. E.
Published: July 2009

We present a unified analytical treatment supported by extensive experimental data of the interaction of ultrasonic waves with arbitrarily-oriented orthotropic elastic plates. The plates are assumed to be immersed in a fluid and subjected to incident acoustic beams at arbitrary polar and azimuthal angles. Reflection and transmission coefficients are derived from which all propagation characteristics are identified. Highly complex reflection behavior, expressed as phase velocity-frequency dispersion, is observed. Extensive experimental data has been collected in ultrasonic reflection measurements on a plate of T300/Ciba-Geigy 914 composite, selected as a model system to test the theory. Comparisons between theory and experiment show good agreement at several azimuthal angles between 0 deg and 90 deg.
Optimal Control of Nonlinear Structures
Authors: Yang J. N. , Long F. X. , Wong D.
Published: July 2009

Three optimal control algorithms are proposed for reducing oscillations of flexible nonlinear structures subjected to general stochastic dynamic loads, such as earthquakes, waves, winds, etc. The optimal control forces are determined analytically by minimizing a time-dependent quadratic performance index, and nonlinear equations of motion are solved using the Wilson-θ numerical procedures. The optimal control algorithms developed for applications to nonlinear structures are referred to as the instantaneous optimal control algorithms, including the instantaneous optimal open-loop control algorithm, instantaneous optimal closed-loop control algorithm, and instantaneous optimal closed-open-loop control algorithm. These optimal algorithms are computationally efficient and suitable for on-line implementation of active control systems to realistic nonlinear structures. Numerical examples are worked out to demonstrate the applications of these optimal control algorithms to nonlinear structures. In particular, control of structures undergoing inelastic deformations under strong earthquake excitations are illustrated. The advantage of using combined passive/active control systems is also demonstrated.
On the Dynamics of Large Systems With Localized Nonlinearities
Authors: Hagedorn P. , Schramm W.
Published: July 2009

In this paper, a certain class of dynamical systems is discussed, which can be decomposed into a large linear subsystem and one or more nonlinear subsystems. For this class of nonlinear systems the dynamic behavior is represented in the time domain by means of an integral equation. A simple numerical procedure for the solution of this integral equation is given. It is also shown how the decomposition of the system can be used in measuring the frequency response of the large linear subsystem, without actually separating it from the nonlinear subsystems. An elastostatic analogy is used to illustrate the ideas and a numerical example is given for a dynamic system.
An Exact Periodic Solution of a Hydromagnetic Flow in a Horizontal Channel
Authors: Vajravelu K.
Published: July 2009

An exact periodic solution for the hydromagnetic unsteady flow of an incompressible fluid with constant properties is obtained. The hydrodynamic (HD) and the hydromagnetic (HM) cases are studied. The flow field here is a generalization of the well-known Couette flow, in which one wall is at rest and the other wall oscillates in its own plane about a constant mean velocity. In order to have some suggestions about the approximate solutions, the exact solution is compared with its own approximate form.
Self-Equilibrated Singular Solutions of a Complete Spherical Shell: Classical Theory Approach
Authors: Simos Nikolaos , Sadegh Ali M.
Published: July 2009

The elastic response of a complete spherical shell under the influence of concentrated loads (normal point loads, concentrated tangential loads, and concentrated surface moments) which apply in a self-equilibrating fashion is obtained. The mathematical analysis incorporates the classical uncoupled system of equations for the transverse displacement W and a stress function F. The solution formulae for all three types of singular loading are in closed form and they are expressed in terms of complex Legendre and other elementary functions. The two latter portions of the analysis are associated with a multivalued stress function F which leads to a single-valued stress and displacement formulae. The intricacies of the solutions and their singular character are also discussed. Lastly, some representative shell problems are evaluated.
Axial Crushing of Multicorner Sheet Metal Columns
Authors: Abramowicz W. , Wierzbicki T.
Published: July 2009

A method is developed for predicting crush behavior of multicorner prismatic columns subjected to an axial compressive load. The corner element of an arbitrary angle is analyzed first using rigorous methods of structural plasticity with finite deformations and rotations. On that basis, crush predictions are made for multicorner columns with an even number of corners. Static crush tests on square, hexagonal, and rhomboidal thin-walled columns are also reported here. Good correlation between the theory and experiments was obtained for the magnitude of a mean crushing force and kinematic parameters describing the process of progressive folding.
On Standard Eigenvalues of Variable-Coefficient Heat and Rod Equations
Authors: Gottlieb H. P. W.
Published: July 2009

Forms of the variable-heat-conductivity coefficient function in the one-dimensional heat equation are determined which yield a standard harmonic eigenvalue sequence as in the case of homogeneity. The continuous case is found to correspond to a four-thirds power law dependence on coordinate. For the stepped case, the condition on the ratio of segmental heat conductivities in terms of the junction location is presented.
Statistical Identification of Nonlinear Random Vibration Systems
Authors: Ozaki Tohru
Published: July 2009

A statistical method for the identification of nonlinear random vibration systems is presented. The first step in the identification process is to obtain a discrete time version of a random vibration model using a local linearization approach. It is shown that the discrete time version thus obtained may be utilized in the identification of original random vibration model. The method is applied to some real ship engineering data.
Vibration of Beams and Plate Strips With Three-Dimensional Flexibility
Authors: Stein Manuel
Published: July 2009

Studies making use of higher vibration modes and frequencies have indicated a need for a more accurate beam theory. Equations of motion are developed here that give a more accurate representation of the dynamic behaivor of a beam than conventional beam theory. Results are obtained using these equations for the natural vibrations of simply-supported aluminum beams of rectangular cross-sections. These results are compared to results from conventional beam theory, and they are examined to identify where various effects are important.
A Constitutive Model for Jointed Rock Mass With Orthogonal Sets of Joints
Authors: Chen E. P.
Published: July 2009

The development and numerical implementation of a constitutive model for jointed rock media is the subject of investigation in this paper. The constitutive model is based on the continuum assumption of strain-partitioning among the elastic rock matrix and joint sets with nonlinear normal and shear responses. Rate equations for the stress-strain response of the jointed media have been formulated. A numerical incremental solution scheme to these equations has been developed. It has been implemented into the finite element code JAC as an additional material model. Several sample problems have been solved for demonstration purposes. Interpretation and discussion of these results are presented.
Melting From a Horizontal Rotating Disk
Authors: Wang C. Y.
Published: July 2009

Melting of a disk is facilitated by rotation. The problem is governed by a nondimensional parameter α which represents the relative importance of injection (melt) rate and rotation times viscosity. The nonlinear governing equations are solved by perturbations for small α and numerical integration for arbitrary α. Torque and heat transfer rates are found. The solution is one of the rare exact similarity solutions of the Navier-Stokes equations.
A Test Specimen for Determining the Fracture Resistance of Bimaterial Interfaces
Authors: Charalambides P. G. , Lund J. , Evans A. G. , McMeeking R. M.
Published: July 2009

A test specimen capable of measuring the fracture resistance of bimaterial interfaces has been devised. A finite element approach has been used to characterize trends in the stress intensities and center point displacement with specimen dimensions, elastic properties, and crack length. The utility of the specimen has been demonstrated by conducting experiments on the model system, Al/PMMA.
A Theoretical and Experimental Study of a Curved Strip Compressed by a Flat Plate
Authors: Iseki H. , Sowerby R. , Bhattacharyya D. , Gatt P.
Published: July 2009

The quasi-static loading of a curved strip compressed by a flat, rigid plate is considered, with particular reference to large deformations and the ensuing buckling behavior. Experiments were performed on curved strips of constant width but of different thickness. The strips were initially deformed to a fixed radius of curvature and stress relieved before pinning the ends. The span was held constant at about 305 mm. The deformation characteristics have been analyzed using an incremental finite element technique. Particular attention has been paid to modeling the situation when a node contacts the plate and the condition for separation of the strip from the plate. The predicted loads and deformation modes agreed well with experimental results from tests on steel and aluminum specimens. The experimental and theoretical procedures are pertinent to the study of dent resistance of sheet metal stampings, particularly automotive panels.
Kinking of a Crack Out of an Interface
Authors: He Ming-Yuan , Hutchinson John W.
Published: July 2009

Kinking of a plane strain crack out of the interface between two dissimilar isotropic elastic solids is analyzed. The focus is on the initiation of kinking and thus the segment of the crack leaving the interface is imagined to be short compared to the segment in the interface. Accordingly, the analysis provides the stress intensity factors and energy release rate of the kinked crack in terms of the corresponding quantities for the interface crack prior to kinking. Roughly speaking, the energy release rate is enhanced if the crack heads into the more compliant material and is diminished if it kinks into the stiff material. The results suggest a tendency for a crack to be trapped in the interface irrespective of the loading when the compliant material is tough and the stiff material is at least as tough as the interface.
When is a Moment Conservative?
Authors: Christoffersen Jes
Published: July 2009

A simple, yet fully-general condition under which moment loading is conservative is presented. The condition is stated in terms of a Maxwell-type reciprocity relation between infinitesimal rotations and an appropriately defined differential of the moment. The usefulness of this concept is illustrated by examples concerning torsional instability of shafts.
Cavity Formation at the Center of a Composite Incompressible Nonlinearly Elastic Sphere
Authors: Horgan C. O. , Pence T. J.
Published: July 2009

In this paper, the effect of material inhomogeneity on void formation and growth in incompressible nonlinearly elastic solids is examined. A bifurcation problem is considered for a solid composite sphere composed of two arbitrary homogeneous isotropic incompressible elastic materials perfectly bonded across a spherical interface. Under a uniform radial tensile dead load, a branch of radially symmetric configurations involving a traction-free internal cavity centered at the origin bifurcates from the undeformed configuration. In contrast to the situation for a homogeneous neo-Hookean sphere, bifurcation here may occur either locally to the right or to the left. In the latter case, the cavity has finite radius on first appearance. This discontinuous change in stable equilibrium configurations is reminiscent of the snap-through buckling phenomenon observed in certain structural mechanics problems. Explicit conditions determining the type of bifurcation are established for the general composite sphere. An analysis of the stress distribution is carried out and the effect of cavitation at the center on possible interface debonding is explored for the special case when the constituent materials are both neo-Hookean. It is shown that, in a quasi-static loading process, cavitation has the effect of preventing debonding at the interface.
Void Growth in Elastic-Plastic Materials
Authors: Hom C. L. , McMeeking R. M.
Published: July 2009

Three-dimensional finite element computations have been done to study the growth of initially spherical voids in periodic cubic arrays. The numerical method is based on finite strain theory and the computations account for the interaction between neighboring voids. The void arrays are subjected to macroscopically uniform fields of uniaxial tension, pure shear, and high triaxial stress. The macroscopic stress-strain behavior and the change in void volume were obtained for two initial void volume fractions. The calculations show that void shape, void interaction, and loss of load carrying capacity depend strongly on the triaxiality of the stress field. The results of the finite element computation were compared with several dilatant plasticity continuum models for porous materials. None of the models agrees completely with the finite element calculations. Agreement of the finite element results with any particular constitutive model depended on the level of macroscopic strain and the triaxiality of the remote uniform stress field.
A New Boundary Equation Solution to the Plate Problem
Authors: Katsikadelis J. T. , Armena`kas A. E.
Published: July 2009

A new boundary equation method is presented for analyzing plates of arbitrary geometry. The plates may have holes and may be subjected to any type of boundary conditions. The boundary value problem for the plate is formulated in terms of two differential and two integral coupled boundary equations which are solved numerically by discretizing the boundary. The differential equations are solved using the finite difference method while the integral equations are solved using the boundary element method. The main advantages of this new method are that the kernels of the boundary integral equations are simple and do not have hyper-singularities. Moreover, the same set of equations is employed for all types of boundary conditions. Furthermore, the use of intrinsic coordinates facilitates the modeling of plates with curvilinear boundaries. The numerical results demonstrate the accuracy and the efficiency of the method.
Transient Thermal Stresses in Cylindrically Orthotropic Composite Tubes
Authors: Kardomateas G. A.
Published: July 2009

A solution is given for the stresses and displacements in an orthotropic, hollow circular cylinder, due to an imposed constant temperature on the one surface and heat convection into a medium of a different constant temperature at the other surface. Temperature-independent material properties are assumed and a displacement approach is used. Results for the variation of stresses with time and through the thickness are presented.
The Extensible Cable as a Limiting Case of a Very Flexible Rod
Authors: Huddleston J. V.
Published: July 2009

For an extensible cable with a free end, the exact nonlinear differential equations that describe the final shape of the cable present difficulties when one tries to integrate them to find the angle of inclination in the vicinity of that free end. To circumvent these difficulties, a method is proposed wherein the cable is replaced by a flexible rod. The moment of inertia of the cross-section of the rod is then allowed to approach zero while the cross-sectional area and the length of the rod remain finite. In that process, the rod approaches the cable as a limiting case, but since the rod has a proper differential equation on the inclination, no singularity occurs. To establish the validity of the method, two cases without a free end are considered first. For these, cable solutions previously obtained by the author are used for comparison. After that, the method is used to solve two cases involving a cable with a free end. In each of these two cases, the cable is suspended in a moving fluid, but they differ in the assumptions made about the drag force. The results obtained appear reasonable and suggest that this method, tantamount to removing the idealization of perfect flexibility from the cable, shows promise as a method of analyzing cables with a free end.
Nonlinear Modeling of Flexible Multibody Systems Dynamics Subjected to Variable Constraints
Authors: Ider S. K. , Amirouche F. M. L.
Published: July 2009

This paper presents the geometric stiffening effects and the complete nonlinear interaction between elastic and rigid body motion in the study of constrained multibody dynamics. A recursive formulation (or direct path approach) of the equations of motion based on Kane’s equations, finite element method and modal analysis techniques is presented. An extended matrix formulation of the partial angular velocities and partial velocities for flexible (elastic) bodies is also developed and forms the basis for our analysis. Closed loops and kinematical constraints (specified motions) are allowed and their corresponding Jacobian matrices are fully developed. The constraint equations are appended onto the governing equations of motion by representing them in a minimum dimension form using an innovative method called the Pseudo-Uptriangular Decomposition method. Examples are presented to illustrate the method and procedures proposed.
Formulation of a Basic Building Block Model for Interaction of High Speed Vehicles on Flexible Structures
Authors: Vu-Quoc L. , Olsson M.
Published: July 2009

In traditional analyses of vehicle/structure interaction, especially when there are constraints between vehicle masses and the structure, vehicle nominal motion is prescribed a priori, and therefore unaffected by the structure flexibility. In this paper, a concept of nominal motion is defined, and a methodology is proposed in which the above restriction is removed, allowing the vehicle nominal motion to become unknown, and encompassing the traditional approach as a particular case. General nonlinear equations of motion of a building block model, applicable to both wheel-on-rail and magnetically levitated vehicles, are derived. These equations are simplified to a set of mildly nonlinear equations upon introducing additional assumptions — essentially on small structural deformation. An example is given to illustrate the present formulation.
The Elastic Response of Creep Damaged Materials
Authors: Rides M. , Cocks A. C. F. , Hayhurst D. R.
Published: July 2009

A series of stress change experiments on a batch of tough pitch copper are presented which were devised to evaluate the variation of Young’s modulus with creep damage. Kachanov’s model is used to describe the creep response and a model orginally proposed by Chaboche (1979) is found to adequately represent the elastic response of the material. A simple two-bar structure is analyzed to assess the effect of including the variation of elastic properties with creep damage in structural analysis. In most practical situations the added complexity involved in incorporating this effect does not strongly affect the structural response.
On the Inversion of Residual Stresses From Surface Displacements
Authors: Gao Zhanjun , Mura T.
Published: July 2009

When plastic damage regions are accumulated in a material, there exist residual displacements on the surface of the material after all the loadings are removed. The residual displacements are defined as the difference between before and after loading, and can be measured experimentally without destruction of the material. This paper addresses the problem of evaluating the residual stress field caused by the accumulation of the plastic damage regions in a subdomain of the material. The problem is formulated as a system of integral equations relating the surface displacements to the unknown plastic strains. The damage domain, which appears as the domain of integration of the integral equations, is also unknown. Determination of the shape of the damage domain, together with the plastic strains, is a very complicated nonlinear problem. In addition to the residual surface displacement data, it requires more information about the loading history or other restrictive assumptions. However, the residual stress field in the vicinity of the damage domain is obtained after the equivalent damage domain and the equivalent plastic strains are introduced. The problem is an inverse problem, which is substantially different from the conventional forward analysis of structural mechanics. Special attention is given to the uniqueness and stability of the solution.
Three-Dimensional Transient Interlaminar Thermal Stresses in Angle-Ply Composites
Authors: Wang Yuan Ruo , Chou Tsu-Wei
Published: July 2009

This paper studies the three-dimensional transient interlaminar thermal stresses in elastic, angle-ply laminated composites due to sudden changes in the thermal boundary conditions. The transient temperature field and transient interlaminar thermal stresses of the laminate are obtained by solving the heat conduction equation and by a zeroth-order perturbation analysis of the equilibrium equations, respectively. Numerical results for a four-layer angle-ply laminate have shown that the interlaminar normal stress near the free edge is significantly higher than that in the interior region and it increases rapidly with the fiber volume fraction.
Moderately Thick Angle-Ply Cylindrical Shells Under Internal Pressure
Authors: Abu-Arja Kamal R. , Chaudhuri Reaz A.
Published: July 2009

Heretofore unavailable closed-form solutions are obtained for unbalanced symmetric as well as balanced unsymmetric angle-ply, moderately thick cylindrical shells subjected to axially varying (axisymmetric) internal pressure loading, under the framework of constant shear-angle theory (CST) or first-order shear deformation theory (FSDT), for any boundary condition. The solutions are obtained for four CST-based kinematic relations, which are extensions of the classical shell theories due to Donnell, Love-Timoshenko, Love-Riessner, and Sanders. The available CLT (classical lamination theory)-based solutions can be obtained from the present solutions in the limiting case of the two transverse shear moduli tending to infinity. Numerical results have been presented for two layer and three layer angle-ply cylindrical shells with simply-supported edges and have been compared with the corresponding CLT-based analytical solutions and also the LCST (layerwise constant shear angle theory)-based finite element solutions.
Some Axisymmetric Problems for Layered Elastic Media: Part I—Multiple Region Contact Solutions for Simply-Connected Indenters
Authors: Shield T. W. , Bogy D. B.
Published: July 2009

The contact of a flat, simply-connected axisymmetric indenter with a layered elastic half space is examined. The problem is mathematically formulated using integral transforms to derive singular integral equations for the contact pressure. The solution of these equations is obtained by expansion in orthogonal polynomials. The solution predicts complete contact between the indenter and the surface of the layered half space only for a restricted range of the material and geometrical parameters. Outside of this range, solutions exist with multiple contact regions. A parameter space is divided into zones for single and multiple contact solutions and comparisons are made with the solutions for the analogous plane-strain problem.
Rolling Contact With Friction and Non-Hertzian Pressure Distribution
Authors: Liu C. , Paul B.
Published: July 2009

A numerical technique has been developed to deal with three-dimensional rolling contact problems with an arbitrary contact region under an arbitrary pressure. Results of this technique are checked against existing solutions for cases of Hertzian contact. A solution for a case of non-Hertzian contact is also presented. This numerical technique works satisfactorily for cases with small spin creepage. For cases of large spin creepage, we utilize a recent work (by the authors) for the limiting case of fully developed sliding contact.
Viscoelastic Winding Mechanics
Authors: Lin J. Y. , Westmann R. A.
Published: July 2009

The viscoelastic analysis of tape systems composed of rate-dependent materials is presented. Histories for winding, winding-pause, and winding-pause-unwinding are considered. The winding problem is reduced to determining the appropriate Green’s function by numerical solution of a Volterra integral equation of the second kind. This Green’s function and integral superposition permits the evaluation of the stress and displacement fields in the tape system for any winding history. Viscoelastic unwinding is treated by the superposition of two-states — one determined from the initial condition of the tape when unwinding begins and the second state given in terms of an arbitrary external pressure evaluated by solving an integral equation. Numerical results are presented for several histories and representative material properties.
On the Approximation of a Deflection Curve by Force Actuators With Variable Spacing
Authors: Natarajan K. , Dumont G. A. , Davies M. S.
Published: July 2009

In this paper we discuss a suboptimal method of approximating a desired deflection curve of a simple beam by a given number of force actuators. The spacing between the actuators is allowed to vary as a function of the deflection curve. The method is applied to an example of approximation of a deflection curve of the slice lip on a paper machine headbox for the control of the basis weight profile of paper. The approximation error with variable spacing is compared with that obtained when the spacing is not varied (uniformly-spaced actuators). Significant reduction in error is observed.
Free Wave Propagation in Plates of General Anisotropic Media
Authors: Nayfeh Adnan H. , Chimenti D. E.
Published: July 2009

We develop the analysis for the propagation of free waves in a general anisotropic plate. We begin with a formal analysis of waves in a plate belonging to the triclinic symmetry group. The calculation is then carried forward for the slightly more specialized case of a monoclinic plate. We derive the secular equation for this case in closed form and isolate the mathematical conditions for symmetric and antisymmetric wave mode propagation in completely separate terms. Material systems of higher symmetry, such as orthotropic, transversely isotropic, cubic, and isotropic are contained implicitly in our analysis. We also demonstrate that the particle motions for Lamb and SH modes uncouple if propagation occurs along an in-plane axis of symmetry. We present numerical free-wave dispersion results drawn from concrete examples of materials belonging to several of these symmetry groups.
An Experimental Investigation of Complicated Responses of a Two-Degree-of-Freedom Structure
Authors: Nayfeh A. H. , Balachandran B. , Colbert M. A. , Nayfeh M. A.
Published: July 2009

Recent theoretical studies indicate that whereas large excitation amplitudes are needed to produce chaotic motions in single-degree-of-freedom systems, extremely small excitation levels can produce chaotic motions in multi-degree-of-freedom systems if they possess autoparametric resonances. To verify these results, we conducted an experimental study of the response of a two-degree-of-freedom structure with quadratic nonlinearities and a two-to-one internal resonance to a primary resonant excitation of the second mode. The responses were analyzed using hardware and software developed for performing time-dependent modal decomposition. We observed periodic, quasi-periodic, and chaotic responses, as predicted by theory. Conditions were found under which extremely small excitation levels produced chaotic motions.
Mode III Crack Tip Plastic Zone Solution for Work Hardening Solid Using Dislocation Motion
Authors: Weertman J.
Published: July 2009

The stress and strain field solutions for the stationary mode III crack in small-scale yielding is obtained from a direct physical picture in which the plastic strain is produced by the motion of infinitesimal dislocations. The analysis is based on a shifting center, cylindrical coordinate system. The nonredundant dislocation density is determined. The ratio of nonredundant to redundant dislocation density within the plastic zone may be a useful measure for placing cracks into a brittle class, a ductile class and semibrittle to semiductile classes.
New Variant of CTX-M-Type Extended-Spectrum β-Lactamases, CTX-M-71, with a Gly238Cys Substitution in a
K
lebsiella pneumoniae
Isolate from Bulgaria
Authors: Schneider Ines , Queenan Anne Marie , Markovska Rumyana , Markova Boyka , Keuleyan Emma , Bauernfeind Adolf
Published: July 2009

A single
K
lebsiella pneumoniae
strain isolated in a Bulgarian hospital was found to produce CTX-M-71, a new CTX-M variant characterized by one amino acid substitution from glycine to cysteine at position 238 in comparison to CTX-M-15. This exchange decreased the hydrolytic activity of the β-lactamase for cefotaxime, ceftazidime, and cefepime.
D27-pLpxL, an Avirulent Strain of
Yersinia pestis
, Primes T Cells That Protect against Pneumonic Plague
Authors: Szaba Frank M. , Kummer Lawrence W. , Wilhelm Lindsey B. , Lin Jr-Shiuan , Parent Michelle A. , Montminy-Paquette Sara W. , Lien Egil , Johnson Lawrence L. , Smiley Stephen T.
Published: July 2009

Vaccinating with live, conditionally attenuated, pigmentation (Pgm)-deficient
Yersinia pestis
primes T cells that protect mice against pneumonic plague. However, Pgm-deficient strains are not considered safe for human use because they retain substantial virulence in animal models.
Y. pestis
strains engineered to express
Escherichia coli
LpxL are avirulent owing to constitutive production of lipopolysaccharide with increased Toll-like receptor 4-activating ability. We generated an LpxL-expressing Pgm-deficient strain (D27-pLpxL) and demonstrate here that this avirulent strain retains the capacity to prime protective T cells. Compared with unvaccinated controls, mice immunized intranasally with live D27-pLpxL exhibit a decreased bacterial burden and increased survival when challenged intranasally with virulent
Y. pestis
. T cells provide a substantial degree of this protection, as vaccine efficacy is maintained in B-cell-deficient μMT mice unless those animals are depleted of CD4 and CD8 T cells at the time of challenge. Upon challenge with
Y. pestis
, pulmonary T-cell numbers decline in naive mice, whereas immunized mice show increased numbers of CD44
high
CD43
high
effector T cells and T cells primed to produce tumor necrosis factor alpha and gamma interferon; neutralizing these cytokines at the time of challenge abrogates protection. Immunization does not prevent dissemination of
Y. pestis
from the lung but limits bacterial growth and pathology in visceral tissue, apparently by facilitating formation of granuloma-like structures. This study describes a new model for studying T-cell-mediated protection against pneumonic plague and demonstrates the capacity for live, highly attenuated,
Y. pestis
vaccine strains to prime protective memory T-cell responses safely.
Nod1/Nod2-Mediated Recognition Plays a Critical Role in Induction of Adaptive Immunity to Anthrax after Aerosol Exposure
Authors: Loving Crystal L. , Osorio Manuel , Kim Yun-Gi , Nuñez Gabriel , Hughes Molly A. , Merkel Tod J.
Published: July 2009

Toll-like receptors and Nod-like receptors (NLR) play an important role in sensing invading microorganisms for pathogen clearance and eliciting adaptive immunity for protection against rechallenge. Nod1 and Nod2, members of the NLR family, are capable of detecting bacterial peptidoglycan motifs in the host cytosol for triggering proinflammatory cytokine production. In the current study, we sought to determine if Nod1/Nod2 are involved in sensing
Bacillus anthracis
infection and eliciting protective immune responses. Using mice deficient in both Nod1 and Nod2 proteins, we showed that Nod1/Nod2 are involved in detecting
B. anthracis
for production of tumor necrosis factor alpha, interleukin-1α (IL-1α), IL-1β, CCL5, IL-6, and KC. Proinflammatory responses were higher when cells were exposed to viable spores than when they were exposed to irradiated spores, indicating that recognition of vegetative bacilli through Nod1/Nod2 is significant. We also identify a critical role for Nod1/Nod2 in priming responses after
B. anthracis
aerosol exposure, as mice deficient in Nod1/Nod2 were impaired in their ability to mount an anamnestic antibody response and were more susceptible to secondary lethal challenge than wild-type mice.
Quantitative Comparison of Active and Latent Tuberculosis in the Cynomolgus Macaque Model
Authors: Lin Philana Ling , Rodgers Mark , Smith Le'kneitah , Bigbee Matthew , Myers Amy , Bigbee Carolyn , Chiosea Ion , Capuano Saverio V. , Fuhrman Carl , Klein Edwin , Flynn JoAnne L.
Published: July 2009

We previously described that low-dose
Mycobacterium tuberculosis
infection in cynomolgus macaques results in a spectrum of disease similar to that of human infection: primary disease, latent infection, and reactivation tuberculosis (S. V. Capuano III, D. A. Croix, S. Pawar, A. Zinovik, A. Myers, P. L. Lin, S. Bissel, C. Fuhrman, E. Klein, and J. L. Flynn, Infect. Immun.
71:
5831-5844, 2003). This is the only established model of latent infection, and it provides a unique opportunity to understand host and pathogen differences across of range of disease states. Here, we provide a more extensive and detailed characterization of the gross pathology, microscopic histopathology, and immunologic characteristics of monkeys in each clinical disease category. The data underscore the similarities between human and nonhuman primate
M. tuberculosis
infection. Furthermore, we describe novel methods of quantifying gross pathology and bacterial burden that distinguish between active disease and latent infection, and we extend the usefulness of this model for comparative studies. Early in infection, an abnormal chest X ray,
M. tuberculosis
growth by gastric aspirate, and increased mycobacterium-specific gamma interferon (IFN-γ) in peripheral blood mononuclear cells (PBMCs) and bronchoalveolar lavage (BAL) cells were associated with the development of active disease. At necropsy, disease was quantified with respect to pathology and bacterial numbers. Microscopically, a spectrum of granuloma types are seen and differ with disease type. At necropsy, monkeys with active disease had more lung T cells and more IFN-γ from PBMC, BAL, and mediastinal lymph nodes than monkeys with latent infection. Finally, we have observed a spectrum of disease not only in monkeys with active disease but also in those with latent infection that provides insight into human latent tuberculosis.
Burkholderia pseudomalleiIsocitrate Lyase Is a Persistence Factor in Pulmonary Melioidosis: Implications for the Development of Isocitrate Lyase Inhibitors as Novel Antimicrobials
Authors: van Schaik Erin J. , Tom Marina , Woods Donald E.
Published: July 2009

Burkholderia pseudomallei, the causative agent of melioidosis, has often been called the great “mimicker,” and clinical disease due to this organism may include acute, chronic, and latent pulmonary infections. Interestingly, chronic pulmonary melioidosis is often mistaken for tuberculosis, and this can have significant consequences, as the treatments for these two infections are radically different. The recurrent misdiagnosis of melioidosis for tuberculosis has caused many to speculate that these two bacterial pathogens use similar pathways to produce latent infections. Here we show that isocitrate lyase is a persistence factor forB. pseudomallei, and inhibiting the activity of this enzyme during experimental chronicB. pseudomalleilung infection forces the infection into an acute state, which can then be treated with antibiotics. We found that if antibiotics are not provided in combination with isocitrate lyase inhibitors, the resultingB. pseudomalleiinfection overwhelms the host, resulting in death. These results suggest that the inhibition of isocitrate lyase activity does not necessarily attenuate virulence as previously observed forMycobacterium tuberculosisinfections but does force the bacteria into a replicating state where antibiotics are effective. Therefore, isocitrate lyase inhibitors could be developed for chronicB. pseudomalleiinfections but only for use in combination with effective antibiotics.
SIMULATION OF TERAHERTZ WAVE TRANSMISSION THROUGH AN ARRAY OF SUBWAVELENGTH METALLIC SLITS
Authors: HE XIAO-YONG , ZHANG QING-XIAO
Published: July 2009

The transmission properties of terahertz wave through subwavelength metallic slits have been investigated using a quasianalytical modal expansion method. The effects of slit widths, periodic length and incident angle on the transmission spectrum and scattering phase are given and dicussed. The results demonstrate that the transmittance increases with the increasing of the ratio of width to slit period. As the incident angle increases, the transmittance increases and shows more peaks.
Bis(aryloxo) derivatives of tin(IV) porphyrins: synthesis, spectroscopy and redox activity
Authors: Reddy D. Raghunath , Maiya Bhaskar G.
Published: July 2009

Spectroscopic, electrochemical and fluorescence properties of five octahedral tin(IV) porphyrins ([( TpTP ) Sn ( O -m,p- C 6 H 3( CH 3)2)2] (1), [( TpTP ) Sn ( O -p- C 6 H 4( CH 3))2] (2), [( TpTP ) Sn ( O - C 6 H 5)2] (3), [( TpTP ) Sn ( O -p- C 6 H 4 O -o,p- C 6 H 3( NO 2)2)2] (4) and [( TpTP ) Sn ( O -p- C 6 H 4( NO 2))2] (5)) bearing electron donating/electron withdrawing aryloxo subunits as the axial ligands are investigated in detail. These complexes have been synthesized by the reaction of 5,10,15,20-tetra(4-methylphenyl)porphyrinato tin(IV) dihydroxide ([( TpTP ) Sn ( OH )2]) and either 3, 4-dimethylphenol, p-cresol, phenol, 4-(2,4-dinitrophenoxy)phenol or p-nitrophenol and were isolated in good-to-moderate yields. Analysis of the spectral data (FAB mass, IR, UV-vis and 1H NMR) of 1 - 5 suggests that the two trans axial aryloxo ligands are strongly bound in a symmetric manner at the tin center in these complexes. Specifically, the general symmetry observed in the 1H NMR spectra and the ring current effect experienced by the protons present on the axial ligands are revealing in this regard. Each porphyrin ring undergoes two successive, reversible/quasi-reversible, one-electron reductions in CH 2 Cl 2, 0.1 M TBAP. The bound nitroaromatic axial ligands of complexes 4 and 5 could also be reduced under the same set of experimental conditions. The wavelengths of maximum emission, the singlet energies and the Stokes’ shifts observed in the fluorescence spectra of 1 - 5 are close to the corresponding parameters of the reference porphyrin, [( TpTP ) Sn ( OH )2]. On the other hand, fluorescence intensities of complexes 1 - 4 are quenched in comparison with that of [( TpTP ) Sn ( OH )2] in three different solvents. A detailed analysis of the emission and redox potential data indicates that a photoinduced electron transfer from the axial aromatic subunit to singlet state of the basal tin(IV) porphyrin can, in principle, explain the fluorescence quenching observed in these donor-acceptor systems. The spectroscopic and redox features of these tin(IV) porphyrins are compared with those of the analogous phosphorus(V) porphyrins reported by us earlier.
Manganese and iron tetraphenylporphyrin-catalyzed oxidation of a cardanol derivative (hydrogenated tert-butylcardanol)
Authors: Tagliatesta Pietro , Crestini Claudia , Saladino Raffaele , Neri Veronica , Filippone Paolino , Fiorucci Chiara , Attanasi Orazio A.
Published: July 2009

Manganese and iron 2,6-disubstituted meso-tetraphenylporphyrins, bearing halogen atoms on the β-positions, have been used as catalysts for the oxidation of a cardanol derivative (hydrogenated tert-butylcardanol), using iodosilbenzene or hydrogen peroxide as oxygen atom donors. The reaction products can be correlated to the catalyst structure and to the nature of the oxidants.
Photoinduced hydrogen evolution with lysine-linked viologen and hydrogenase
Authors: Asakura Noriyuki , Miyaji Akimitsu , Kamachi Toshiaki , Okura Ichiro
Published: July 2009

Lysine-linked viologen was prepared as a substrate for the hydrogenase. By using reduced lysine-linked viologen ( LysV +•), the hydrogenase- LysV +• complex was formed efficiently, leading to effective hydrogen evolution compared with methyl viologen. Lysine-linked viologen as an electron carrier was applied for the photoinduced hydrogen evolution system containing hydrogenase, Tetrakis(4-carboxyphenyl)porphyrin ( TCPP ) as a photosensitizer, and a sacrificial electron donor for TCPP . In this system, effective photoinduced hydrogen evolution was observed.
Synthesis, electrochemistry, spectroscopy and photophysical properties of a series of meso-phenylpyridylporphyrins with one to four pyridyl rings coordinated to [Ru(bipy)2Cl]+ groups
Authors: Engelmann Fábio M. , Losco Pellegrino , Winnischofer Herbert , Araki Koiti , Toma Henrique E.
Published: July 2009

A series of meso-phenylpyridylporphyrins and their respective supermolecular species obtained by the coordination of [ Ru ( bipy )2 Cl ]+ groups to the pyridyl substituents was synthesized and characterized. Their spectroscopic and electrochemical behavior were similar to that observed for the meso-tetra(4-pyridyl)porphyrin derivative, but the redox potential of the Ru (III/II) redox pair was about 70 mV more negative. The porphyrin centered fluorescence quantum yield exhibited a linear decrease as a function of the number of pyridyl substituents on the porphyrin ring. Efficient intramolecular energy transfer processes from the 3 MLCT state of the ruthenium complexes to the porphyrin center were observed at 77K in ethanol glass.
Perhalogenated 2-pyridylporphyrin complexes: synthesis, self-coordinating aggregation properties, and catalytic studies
Authors: Rebouças Júlio S. , de Carvalho Maria Eliza M. D. , Idemori Ynara M.
Published: July 2009

The synthesis of 2, 3, 7, 8, 12, 13, 17, 18-octabromo-meso-tetrakis(2-pyridyl)porphyrin, H 2 Br 8 T 2 PyP , is described, including the comparison of four attempted methods for the demetallation of ZnBr 8 T 2 PyP . One of the methods represents a strategy of demetallation based on the acid-base properties of the macrocycle, the solvent-dependent kinetics of metal insertion into porphyrins and the pH -dependent solubility of the 2-pyridylporphyrin derivatives in water. Self-coordinating aggregation of ZnBr 8 T 2 PyP in non-coordinating solvents was verified by 1 H NMR spectroscopy. The Mn(III)/Mn(II) redox potential for MnBr 8 T 2 PyPCl is 0.38 V higher than the reduction potential measured for its first-generation analogue, MnT 2 PyPCl . Cyclohexane hydroxylation by iodosylbenzene was performed in CH3 CN catalyzed by MnBr 8 T 2 PyPCl and MnT 2 PyPCl . MnBr 8 T 2 PyPCl was highly active, even at low concentration (5 × 10−5 M ), but perhalogenation did not account for oxidative robustness. At such a low catalyst concentration, MnT 2 PyPCl exhibited no activity as inferred by comparison to blank experiments.