bluuebunny/crossref_metadata_2025 huggingface dataset:
Buckling of Shear Deformable Antisymmetric Angle-Ply Laminated Cylindrical Panels Under Axial Compression (Design Paper)
Authors: Soldatos K. P.
Published: June 2008

This paper deals with the buckling problem of antisymmetric angle-ply laminated circular cylindrical panels subjected to a uniform axial compression. Since a flat plate configuration occurs as a particular case of the cylindrical panel geometry (zero shallow angle parameter), the corresponding flat plate problem is studied as a particular case of the problem considered. The theoretical analysis is based on a nonlinear theory developed in a previous paper (Soldatos, 1992), which accounts for parabolically distributed transverse shear strains through the shell thickness. The linearized differential equations, governing the buckling behavior of a simply supported panel, are solved on the basis of Galerkin’s method. Comparisons of corresponding numerical results, based on both the refined shell theory employed and a classical Love-type shell theory, show the influence of transverse shear deformation on the buckling loads of such laminated composite panels.
Galerkin Finite Element Displacement Formulation of Coupled Thermoelasticity Spherical Problems
Authors: Eslami M. , Vahedi H.
Published: June 2008

When the time rate of change of the thermomechanical forces in a continuum is high enough to produce stress wave, the solution must be sought through the simultaneous consideration of the first law of thermodynamics and the equations of thermoelasticity. The general finite element formulation of coupled thermoelasticity along with a general discussion for inclusion of mechanical and thermal boundary conditions is presented. The case is then considered for a spherical symmetry and the governing coupled thermoelastic equations are reduced for a thick sphere. Based on the Galerkin method, a Kantrovich approximation is applied to the displacement and temperature field and the finite element formulation of the problem is obtained.
Elastic-Plastic Fracture of Circumferential Through-Wall Cracked Pipe Welds Subject to Bending
Authors: Rahman S. , Brust F.
Published: June 2008

A methodology is proposed to carry out elastic-plastic fracture analysis of through-wall cracked ductile pipe weldments subjected to pure bending loads. It is based on deformation theory of plasticity, constitutive law characterized by Ramberg-Osgood model, and an equivalence criteria incorporating reduced thickness analogy for simulating system compliance due to the presence of a crack in weld metal. Closed-form solutions are obtained in terms of elementary functions for approximate evaluation of energy release rate and center crack opening displacement. The method utilizes material properties of both base and weld metals which are not considered in the current estimation methods. It is general and can be applied in the complete range between elastic and fully plastic conditions. Numerical examples are presented to illustrate the proposed technique. Comparisons of results with reference solutions from finite element method indicate satisfactory prediction of foregoing fracture parameters.
Finite Element Simulation of Tightening Process of Bolted Joint With a Tensioner
Authors: Fukuoka T.
Published: June 2008

In tightening structural members with bolts or studs, hydraulic bolt tensioners are frequently used in the case where the clamping force must be controlled with high accuracy. The most important factor in the operation is the ratio of desired clamping force to initial tension applied by a hydraulic tensioner, which is termed “effective tensile coefficient” here. In this paper, a numerical approach of the tightening process is proposed using the finite element method, which can deal with axisymmetric elastic contact problems. The amounts of the coefficient are estimated for various design factors such as grip length, nominal diameter of screw thread, and coefficients of friction on contact surfaces.
Leakage Flow-Induced Vibrations of Heat Exchanger Fins
Authors: Weaver D. S. , Huang X. Y.
Published: June 2008

The failure of a number of fins of a large two-stage reciprocating compressor intercooler was studied. It appeared that leakage flow across the ends of the fins excited the vibrations and eventually led to fatigue failure. A series of simple laboratory tests were conducted to confirm this excitation mechanism. It is seen that the fins may be excited to resonance by coupling with the shear layer oscillations in several ways. The heat exchanger problem was cured by using sealing strips to prevent the leakage flow.
Multiaxial Relaxation and Creep Damage Assessments—A Comparison of ASME N-47 and GLOSS Time-Scaling Methods
Authors: Seshadri R.
Published: June 2008

Two simplified methods for determining multiaxial relaxation and creep damage, the GLOSS time-scaling and the ASME Code Case N-47 method, are described in this paper. The theoretical basis and applicability of the methods to various pressure component configurations are discussed in detail. The G-factor in the ASME formula in effect speeds up or slows down the uniaxial relaxation process, similar to the GLOSS time-scaling method. The two methods are compared, and the differences are attributed to local follow-up not being accounted for in the ASME formula.
Hot Clamp Design for LMFBR Piping Systems
Authors: Kobayashi T. , Tateishi M.
Published: June 2008

Thin-wall, large-diameter piping for liquid metal fast breeder reactor (LMFBR) plants can be subjected to significant thermal transients during reactor scrams. To reduce local thermal stresses, an insulated “cold” clamp was designed for the fast flux test facility and was also applied to some prototype reactors thereafter. However, the cost minimization of LMFBR requires much simpler designs. This paper presents a “hot” clamp design concept, which uses standard clamp halves directly attached to the pipe surface leaving an initial gap. Combinations of flexible pipe and rigid clamp achieved a self-control effect on clamp-induced pipe stresses due to the initial gap. A 3-D contact and inelastic history analysis were performed to verify the hot clamp concept. Considerations to reduce the initial stress at installation, to mitigate the clamp restraint on the pipe expansion during thermal shocks, and to maintain the pipe-clamp stiffness desired during a seismic event were discussed.
Chaotic Vibrations of Nonlinearly Supported Tubes in Crossflow
Authors: Cai Y. , Chen S. S.
Published: June 2008

Chaotic vibrations associated with the fluidelastic instability of nonlinearly supported tubes in a crossflow is studied theoretically on the basis of the unsteady-flow theory and a bilinear mathematical model. Effective tools, including phase portraits, power spectral density, Poincare maps, Lyapunov exponent, fractal dimension, and bifurcation diagrams, are utilized to distinguish periodic and chaotic motions when the tubes vibrate in the instability region. The results show periodic and chaotic motions in the region corresponding to fluid-damping-controlled instability. Nonlinear supports, with symmetric or asymmetric gaps, significantly affect the distribution of periodic, quasi-periodic, and chaotic motions of a tube exposed to various flow velocities in the instability region of the tube-support-plate-inactive mode.
Design Procedure for Stress Intensification Factors of 90-Deg Curved Pipe Having Various Tangent Lengths (Design Paper)
Authors: Nordham D. J. , Kaldor L. M.
Published: June 2008

A simple design procedure, based on 114 finite element analyses, was derived to predict the stress intensification factor for 90-deg curved pipe with end constraints composed of tangents of any length terminated by rigid flanges and no internal pressure loads. The results of this design procedure were then compared to stress intensification factors obtained from additional finite element analyses and experimental work. Stress intensification factors calculated using the design equations in the Power Piping Code (ANSI/ASME B31.1-1986) were also compared to all the finite element and experimental work. It was found that this design procedure more accurately predicts the stress intensification factors than the Power Piping Code.
Design Procedure for Flexibility Factors of 90-Deg Curved Pipe Having Various Tangent Lengths (Design Paper)
Authors: Nordham D. J. , Kaldor L. M.
Published: June 2008

A simple design procedure, based on 175 finite element analyses, was derived to predict the flexibility factor due to an in-plane or out-of-plane moment for a 90-deg curved pipe with end constraints composed of tangents of any length terminated by rigid flanges and no internal pressure loads. The results of this design procedure were then compared to flexibility factors obtained from additional finite element analyses and experimental work. Flexibility factors calculated using the design equations in the Power Piping Code (ANSI/ASME B31.1-1986) were also compared to all finite element and experimental work. It was found that this design procedure more accurately predicts the flexibility factors than the Power Piping Code.
New Higher Order Engineering Beam Theory
Authors: Widera G. E. O. , Zheng W. C.
Published: June 2008

A refined engineering theory for beams is presented. It contains higher order effects not present in such refined theories as the one by Timoshenko. A comparison with the latter theory is carried out.
A Strain Gage Analysis of Fracture in Wide Plate Tests of Reactor Grade Steel
Authors: Berger J. R. , Dally J. W. , deWit R. , Fields R. J.
Published: June 2008

A new method of fracture analysis is described. Strains recorded by gages in the immediate vicinity of a propagating crack are analyzed. From the analysis, crack tip position, propagation toughness, and crack velocity are determined. The analysis procedure Is demonstrated using data from the dynamic fracturing of a large-scale, wide plate test. The results are then used to describe the propagation toughness-crack velocity-temperature relation for the 2.25 Cr-1 Mo steel used in the test.
Extending the Theory of Creep to Viscoplasticity
Authors: Freed A. D. , Walker K. P. , Verrilli M. J.
Published: June 2008

A viscoplastic theory is developed that reduces to creep theory analytically under steady-state conditions. A fairly simple model is constructed from this theoretical framework by defining material functions that have close ties to the physics of inelasticity; consequently, the model is characterized easily. The computational characteristics of the model are enhanced, in general, by converting the kinetics equation from a hyperbolic relationship to a power-law relationship. The resulting model is applied to copper and to the copper alloy, NARloy Z.
The Effect of Multiaxiality on the Evaluation of Weldment Strength Reduction Factors in High-Temperature Creep
Authors: Sandstro¨m R. , Tu S.-T.
Published: June 2008

The conventional way to define the weldment creep strength reduction factor is usually based on uniaxial creep data of weld metals and parent metals. In order to take the multiaxial effect into consideration, this paper has defined a structural transfer function which can be evaluated from general creep stress analysis. An analytical model is then proposed in the light of the function. Two numerical examples of typical weld properties show that the transfer function has a load-independent feature, which allows one to obtain multiaxial stress components in a weldment through minimal computation effort. Fairly good estimation of the stress level in the weld metal is achieved. On the basis of the present semi-analytical procedure, the weldment creep strength reduction factors are evaluated. For a 0.5Cr0.5Mo0.25V butt-welded tube under internal pressure, which has a higher weld metal creep-rupture strength, and lower weld metal creep strain rate, the reduction factors range from 0.9 to 0.95. For the AISI 316 butt-welded tube of cold-worked parent metal and creep soft weld metal, lower strength reduction factors are found, but they may still be nonconservative due to stress enhancement in the heat-affected zone.
The Effect of Crack Depth (a) and Crack Depth to Width Ratio (a/W) on the Fracture Toughness of A533-B Steel
Authors: Smith J. A. , Rolfe S. T.
Published: June 2008

Constraint, as related to specimen crack depth (a) or crack depth to specimen width ratio (a/W), can have a significant effect on fracture toughness. In laboratory specimens, both crack depth and the a/W ratio can be varied. However, it is not always possible to model the constraint of a structurally relevant geometry in the laboratory. Nonetheless, an understanding of the role of both crack depth and a/W ratio on the toughness behavior of laboratory specimens will help clarify the role of constraint on fracture toughness and better enable engineers to model the effect of constraint on a flaw in an actual structure. An experimental study of the effect of crack depth and a/W ratio on the fracture toughness of an A533-B steel was conducted and results were compared with large-scale specimens tested at Oak Ridge National Labs (ORNL). Smaller size specimens tested at the University of Kansas (KU) were taken from the actual ends of the specimens tested at ORNL. The specimens tested at both KU and ORNL were square single-edge-notched bend (SENB) specimens with widths ranging from 20.3 to 100.0 mm (0.8 to 4.0 in.), crack depths ranging from 2.0 to 50.0 mm (0.08 to 2.0 in.), and a/W ratios ranging from 0.1 to 0.5. The geometries of the specimens tested at KU were chosen such that comparisons of the toughness of specimens with constant crack depth and varying a/W ratio, as well as comparisons of the toughness of specimens with constant a/W ratio and varying crack depths, could be made. A forthcoming paper, containing finite element analysis results, will compare the analytical basis for the behavior of these various size specimens. The results indicate that both crack depth and a/W ratio affect the fracture toughness of the steel. For deep crack geometries (a/W = 0.5), crack depth has limited effect on the fracture toughness. However, for shallow crack geometries (a/W = 0.1), crack depth has a significant effect on the fracture toughness. For constant crack depth, varying the a/W ratio does affect the fracture toughness. Thus, crack depth and a/W ratio are interdependent with respect to fracture toughness. The findings of this study are significant in helping to understand the role of both crack depth and a/W ratio on fracture toughness and serve as a basis for understanding the effect of constraint on the behavior of actual structures with cracks.
Probabilistic Analysis of Fatigue Crack Propagation Under Random Loading
Authors: Wu W.-F. , Shin C. S. , Shen J.-J.
Published: June 2008

In order to predict the fatigue crack growth curve under random loading, an analytical model is proposed in this paper. In addition to the mean crack growth curve, the model also considers the statistical variation of the crack growth curves under the same nature of random loading, as well as the material reliability after certain loading cycles are applied. To check the applicability of the prediction model, several fatigue experiments are performed. After comparing the analytical result with the experimental result, the following conclusions are drawn. (i) Under the same mean value and standard deviation for the stress amplitudes, the fatigue crack growth curves are influenced by the probability density function of the stresses. (ii) An “equivalent constant loading” and a crack closure model lead to better prediction than any other model. (iii) The variation of the crack growth curves can be predicted accurately for shorter crack lengths and conservatively for longer crack lengths. (iv) The prediction of the statistical variation can be improved by modifying the definition of the equivalent constant loading. (v) Fatigue reliability can be reasonably estimated. The foregoing conclusions can be taken into consideration in the design of pressure vessels which are frequently subjected to transients of random nature.
Two-Phase Flow-Induced Vibration: An Overview (Survey
Paper)
Authors: Pettigrew M. J. , Taylor C. E.
Published: June 2008

Two-phase flow exists in many industrial components. To avoid costly vibration problems, sound technology in the area of two-phase flow-induced vibration is required. This paper is an overview of the principal mechanisms governing vibration in two-phase flow. Dynamic parameters such as hydrodynamic mass and damping are discussed. Vibration excitation mechanisms in axial flow are outlined. These include fluidelastic instability, phase-change noise, and random excitation. Vibration excitation mechanisms in cross-flow, such as fluidelastic instability, periodic wake shedding, and random excitation, are reviewed.
Verification of Warm Prestressing Effect Under a Pressurized Thermal
Shock (PTS) Event
Authors: Okamura H. , Yagawa G. , Hidaka T. , Urabe Y. , Satoh M. , Tomimatsu M. , Iida M.
Published: June 2008

Fracture tests for the verification of WPS (warm prestressing) effect were carried out by using large flat specimens and big compact specimens with low toughness. In the case of monotonical KI increasing during cooling, the specimen broke within the scatter band of KIC. On the other hand, when KI was decreasing during cooling, the specimens did not break even if KI values were beyond the scatter band of KIC. That is, WPS effect was confirmed even for the low toughness steel like reactor pressure vessel wall under neutron irradiation. Also, KI values at fracture can be predicted by Chell’s theory. By applying WPS effect and the predictive equations for irradiation embrittlement for Japanese PWR reactor steels to the PTS integrity analysis, much more temperature margin can be expected.
Monitoring of Transient Temperature Distribution in Piping
Authors: Baba K. , Ochi M.
Published: June 2008

A numerical method for monitoring temperature distribution in which boundary flux and initial state are unknown is presented. Regularizations based on Tikhonov and Beck’s method are employed. Then, regularization parameters are evaluated by the L-curve. The method is applied to an actual piping problem in a steam power plant and compared with measured data, and it is also applied to a two-dimensional thermal shock problem.
Fluid Pressures in Partially Liquid-Filled Horizontal Cylindrical Vessels Undergoing Impact Acceleration
Authors: Ye Z. , Birk A. M.
Published: June 2008

An experimental investigation has been carried out to study the fluid pressures in partially liquid-filled vessels when they are suddenly accelerated by impact along the longitudinal axis. The experiments were conducted with three horizontal cylindrical tanks of different length-to-diameter ratios of L/D = 6.0, 3.5, 2.0. The tanks were filled with water at ambient pressure and temperature and were accelerated using a large steel impact hammer. Internal tank wall pressures caused by the acceleration were measured with transient pressure transducers. Six types of pressure-time histories have been observed and results indicated that the pressure profile changes with fill level and transducer location. The peak pressures on the end of the tank are strongly affected by the fill level and the tank length-to-diameter ratio L/D. A modal change in the behavior of liquid movement has been found around fill level h/D = 0.95. For fill levels h/D above 0.95, the pressure in the tanks acted like either a water hammer or an accelerated fluid column, depending on the duration of the impact relative to the pressure wave transit time. For the fill levels with h/D below 0.95, liquid sloshing activity was involved and the pressure at the end of the tank was a function of the liquid dynamic pressure. This modal change also caused the location of maximum peak pressure to move from the impact end of the tank to the tank top. In some cases the pressure on the tank top was two times larger than that at the tank impact end. The maximum pressure observed from the tests was on the top of the tank. This modal change may have some significance in some transportation applications.
Torsional Impact Response of a Thick-Walled Cylinder With a Circumferential Edge Crack
Authors: Shindo Y. , Li W.
Published: June 2008

This paper considers the torsional impact response of a long thick-walled cylinder containing an internal or external circumferential edge crack. Laplace and Hankel transforms are used to reduce the elastodynamic problem to a pair of dual integral equations. The dual integral equations are solved by using the standard transform technique, and the result is expressed in terms of an integral equation which has a generalized Cauchy kernel as the dominant part. The kernel of the integral equation is improved in order that the calculation may be made easy. A numerical Laplace inversion technique is used to recover the time dependence of the solution. The dynamic singular stress field is determined, and the numerical results on the dynamic stress intensity factor are obtained to show the influence of inertia, geometry, and their interactions.
Thermal Protection of Pressure Vessels by Internal Wall Cooling During Pressure Relief
Authors: Birk A. M.
Published: June 2008

When pressure vessels are exposed to external fire impingement, high wall temperatures can result and these can lead to material degradation and the ultimate failure of the vessel. To protect against this possibility, vessels can be protected by means of pressure relief devices, external thermal barriers or external water spray cooling. This paper deals with a device that cools the walls of fire-impinged vessels carrying pressurized liquids by directing 2-phase fluid along the upper internal surface of the vessel when the vessel pressure relief valve is in action. The device consists of a concentric secondary internal shell that partitions the interior into a core region and an annulus. The bottom of the internal shell is open to allow communication between the two regions. When vapor is vented from the annulus, it results in significant fluid swelling in the annular space. This swelling results in large areas of the wall being wetted and cooled by liquid. Experimental results are presented for the case of a short electrically heated cylindrical vessel with and without the cooling device installed. From the limited tests conducted, it was shown that the device cools areas of the vessel wall that would normally have experienced high wall temperatures and possible material degradation.
Dynamics of a Radially Rotating Beam With Impact, Part 2: Experimental and Simulation Results
Authors: Yigit A. S. , Ulsoy A. G. , Scott R. A.
Published: June 2008

A theoretical and computational model to study the dynamics of a radially rotating beam with impact were presented in Part 1. In this paper the experimental results are presented and they are compared with simulations using the momentum balance model described in Part 1. Excellent agreement was found between the experiments and simulation. Sensitivity studies were employed to show that the model is applicable for a fairly wide range of parameter values. Thus, the momentum balance method has been demonstrated to be capable of accurately predicting the dynamics of systems which consist of rigid and elastic links undergoing impact.
The Sufficient and Necessary Conditions for Decomposability of Mechanical Systems
Authors: Wang Zeng-Gang
Published: June 2008

Many mechanical systems have the mathematical model as Mx¨ + Dx˙ + Kx=0. For this mathematical model of systems T. K. Caughey, M. E. J. Kelly, and D. W. Nicholson studied its uncoupling properties and gave out the sufficient and necessary conditions for the complete decomposition of the system. In this paper the author made an effort to develop the results obtained before. The concept of decomposition degree of mechanical system is given and the sufficient and necessary conditions for determining a system to be locally decomposable are obtained. In the last section a system is given which is not completely decomposable but locally decomposable.
Frequency Response of Nonproportionally Damped, Lumped Parameter, Linear Dynamic Systems
Authors: Bellos J. , Inman D. J.
Published: June 2008

The frequency response of nonproportionally (or nonclassically or non-Raleigh) damped linear lumped mass systems is discussed here. The exact method, via Laplace transforms, is presented and the practical difficulties revealing the necessity of approximate methods are emphasized. Modal analysis is used to transform the governing equations of motion to the respective modal coupled equations of motion. The Laplace transform is performed to transfer to the frequency domain. The modal coupling is then analyzed through coupling terms. A criterion in the form of nonproportionality indices is developed, in order to measure the extent of the modal coupling and to predict the error introduced by neglecting this coupling either partially or completely. An attempt to interpret the frequency spectrum of the modal coupling is also made. A specific application to a six degree of freedom system, with two sets of closely spaced undamped natural frequencies and moderate damping is given as an illustrative example. Useful information about the accuracy, the applicability, and the advantages of the proposed method over the exact method, as well as over the common procedure of ignoring the modal coupling, are derived.
Active Control of Sound Radiation Pressure
Authors: Meirovitch L. , Thangjitham S.
Published: June 2008

This paper is concerned with the problem of suppressing the acoustic radiation pressure generated by a structure vibrating in air. The approach is to control the vibration of the modes of the structure most responsible for the radiation pressure. This control is carried out by active means, i. e., by feedback control. As a numerical example, the problem of active control of the far-field radiation pressure generated by the vibration of a simply-supported rectangular elastic plate is considered. The influence on the control effectiveness of various design parameters, such as the number of controlled modes, the choice of controlled modes, the number of actuators and the location of the actuators, is investigated. The conclusion is that, depending on the magnitude of the excitation frequency, satisfactory control can be achieved by using a sufficient number of actuators and by controlling a relatively large number of modes.
Iterative Solution of Boundary Element Equations for the Exterior Helmholtz Problem
Authors: Amini S. , Ke Chen , Harris P. J.
Published: June 2008

In this paper we study an efficient boundary element method for the determination of the acoustic field around arbitrary-shaped finite structures immersed in an infinite homogeneous acoustic medium. The direct boundary integral equation due to Burton and Miller is employed to overcome the nonuniqueness of solution associated with the classical boundary integral formulations of the exterior Helmholtz equation. The choice of the coupling parameter in the Burton and Miller formulation is discussed in order to minimize the condition number of the boundary integral equation. Numerical results are presented for the problem of acoustic radiation from several structures of practical interest.
Vibration and Stress Analysis for Condition Monitoring of Symon Cone Crushers
Authors: Szczepanik Andre , Roy Ian , Kuhnell B. T.
Published: June 2008

Condition-Monitoring of the crusher frames, using stress and vibration analysis, is described. It is shown that the meshing clearances between the countershaft pinion and the eccentric ring gear are critical to safe operation. It also is shown that shock stresses occur for very small close-side settings and these stresses are caused by lateral vibration of the relief springs.
Prediction of Periodic Response of Flexible Mechanical Systems With Nonlinear Characteristics
Authors: Shiau Ting-Nung , Jean An-Nan
Published: June 2008

A numerical-analytical method for the prediction of steady state periodic response of large order nonlinear rotordynamic systems is addressed. Using this method, the set of nonlinear differential equations governing the motion of the rotor systems is transformed to a set of nonlinear algebraic equations. A condensation technique is proposed to reduce the nonlinear algebraic equations to those only related to the physical coordinates associated with nonlinear components. The method allows for the inclusion of searching for sub, super, ultra-sub and ultra-super harmonic components of the system response. Furthermore it can be used to locate limit cycles of an autonomous system. Three examples are employed to demonstrate the accuracy and the efficiency of the present method.
Modeling the Wavevector-Frequency Spectrum of Boundary-Layer Wall Pressure During Transition on a Flat Plate
Authors: Josserand M. A. , Lauchle G. C.
Published: June 2008

A spectral model for the wall-pressure fluctuations induced on a zero pressure gradient, flat, rigid surface by a transitioning boundary layer at low Mach number is developed in this paper. The central assumption used in this modeling is that the space-time statistics associated with the formation, convection, and interaction of turbulent spots in a naturally occurring boundary-layer transition are independent of the space-time statistics of the wall-pressure fluctuations that are induced by the turbulence in the individual spots. Space-time correlations for the spots were determined experimentally and semi-empirical formulae are developed to predict these correlations. Previously published statistical descriptions of turbulence-induced wall-pressure fluctuations are coupled with the spot statistics to arrive at the model for the wavevector-frequency spectrum of the transition region. The basic result suggests that the wall-pressure wavevector-frequency spectrum of a transitioning boundary layer is approximately that produced by a fully-turbulent layer weighted by the intermittency factor.
Power Flow and Mechanical Intensity Calculations in Structural Finite Element Analysis
Authors: Hambric S. A.
Published: June 2008

The identification of power flow paths in dynamically loaded structures is an important, but currently unavailable, capability for the finite element analyst. For this reason, methods for calculating power flows and mechanical intensities in finite element models are developed here. Formulations for calculating input and output powers, power flows, and mechanical intensities for beam and plate/shell element types are derived. NASTRAN is used to calculate the required velocity, force, and stress results of an analysis, which a post-processor then uses to calculate power flow quantities. Test models include a simple truss and a beam-stiffened cantilever plate. Both test cases showed reasonable power flow fields over low to medium frequencies.
Accurate Backbone Curves for a Modified-Duffing Equation for Vibrations of Imperfect Structures With Viscous Damping
Authors: Hui D.
Published: June 2008

This paper deals with the Runge-Kutta numerical solution of the modified-Duffing ordinary differential equation with viscous damping. Accurate backbone curves for the finite-amplitude vibrations of geometrically imperfect rectangular plates and shallow spherical shells are presented. For a structure with a sufficiently large initial imperfection, the well-known soft-spring nature of the backbone curve is confirmed for small vibration amplitude. However, for large vibration amplitude, the backbone curves tend to exhibit the usual hard-spring behavior. The predominantly “inward” deflection response (as viewed from the center of curvature) of an imperfect system is found for undamped systems, but this is not necessarily true for a viscously damped structure. Both the initial-deflection and initial-velocity problems are examined.
A Fast Rational Model Approach to Parametric Spectral Estimation—Part II: Properties and Performance Evaluation
Authors: Fassois S. D.
Published: June 2008

In the first part of this paper (Fassois, 1990), the basic form of a novel, fast rational model approach to parametric spectral estimation was introduced. In this second part the consistency property of the approach is proven, and two modified versions, characterized by mathematically guaranteed stability, developed. Unlike most alternative techniques, the proposed approach is then capable of effectively estimating all types of spectra, including those characterized by sharp valleys. Its performance is finally evaluated via numerical simulations and comparisons with the Blackman-Tukey and the AR spectral analysis methods.
Planar Vibration of an Elastica Arch: Theory and Experiment
Authors: Perkins N. C.
Published: June 2008

This investigation examines the planar, linear vibration of a deep arch that is described by a simply supported elastica. The arch is formed from an elastic rod that buckles nonlinearly under the action of a large, steady end-load. A theoretical model is proposed that governs the planar response of the rod about a generally curved, pre-stressed equilibrium. The model utilizes a geometrically nonlinear rod theory to describe the planar bending and extension of the rod centerline. The equations of motion are linearized about an elastica equilibrium and numerical solutions for free vibration are determined using a variational formulation of the associated eigenvalue problem. Natural frequencies and mode shapes are computed over a large range of centrally and eccentrically applied end-loads. Results from an experimental modal test provide support for the model.
A Method for Calculating Labyrinth Seal Inlet Swirl Velocity
Authors: Kirk R. Gordon
Published: June 2008

The results of numerous investigators have shown the importance of inlet swirl on the calculated dynamic stiffness and stability of labyrinth seals. These results have not included any calculation of inlet leakage of swirl as a function of complex disk geometry including the sealing conditions of the given seal. This paper outlines a method of calculating the inlet swirl at the entrance of the labyrinth seal by introducing a radial chamber which when added to the axial flow solution allows the prediction of the gas swirl as it flows radially from the stage tip along the disk face inward to the seal location. This solution is consistent with the leakage model for the seal and allows rapid evaluation of seal designs. For a centrifugal compressor, this added feature permits the designer to include the flow path from the impeller discharge, down the back of the disk or front of the cover, then into the shaft seal or eye packing, respectively. The solution includes the friction factors of both the disk and stationary wall with account for mass flow rate and calculation of radial pressure gradients by a free vortex solution. The results of various configurations are discussed and comparisons made to other published results of disk circumferential velocity swirl.
The Formation Conditions of Chondrules and Chondrites
Authors: Alexander C. M. O'D. , Grossman J. N. , Ebel D. S. , Ciesla F. J.
Published: June 2008

Chondrules, which are roughly millimeter-sized silicate-rich spherules, dominate the most primitive meteorites, the chondrites. They formed as molten droplets and, judging from their abundances in chondrites, are the products of one of the most energetic processes that operated in the early inner solar system. The conditions and mechanism of chondrule formation remain poorly understood. Here we show that the abundance of the volatile element sodium remained relatively constant during chondrule formation. Prevention of the evaporation of sodium requires that chondrules formed in regions with much higher solid densities than predicted by known nebular concentration mechanisms. These regions would probably have been self-gravitating. Our model explains many other chemical characteristics of chondrules and also implies that chondrule and planetesimal formation were linked.
Bora and the Kinase Aurora A Cooperatively Activate the Kinase Plk1 and Control Mitotic Entry
Authors: Seki Akiko , Coppinger Judith A. , Jang Chang-Young , Yates John R. , Fang Guowei
Published: June 2008

A central question in the study of cell proliferation is, what controls cell-cycle transitions? Although the accumulation of mitotic cyclins drives the transition from the G
2
phase to the M phase in embryonic cells, the trigger for mitotic entry in somatic cells remains unknown. We report that the synergistic action of Bora and the kinase Aurora A (Aur-A) controls the G
2
-M transition. Bora accumulates in the G
2
phase and promotes Aur-A–mediated activation of Polo-like kinase 1 (Plk1), leading to the activation of cyclin-dependent kinase 1 and mitotic entry. Mechanistically, Bora interacts with Plk1 and controls the accessibility of its activation loop for phosphorylation and activation by Aur-A. Thus, Bora and Aur-A control mitotic entry, which provides a mechanism for one of the most important yet ill-defined events in the cell cycle.
A Molecular Clutch Disables Flagella in the
Bacillus subtilis
Biofilm
Authors: Blair Kris M. , Turner Linda , Winkelman Jared T. , Berg Howard C. , Kearns Daniel B.
Published: June 2008

Biofilms are multicellular aggregates of sessile bacteria encased by an extracellular matrix and are important medically as a source of drug-resistant microbes. In
Bacillus subtilis
, we found that an operon required for biofilm matrix biosynthesis also encoded an inhibitor of motility, EpsE. EpsE arrested flagellar rotation in a manner similar to that of a clutch, by disengaging motor force-generating elements in cells embedded in the biofilm matrix. The clutch is a simple, rapid, and potentially reversible form of motility control.
Slaying Monsters for Science
Authors: Bohannon John
Published: June 2008

The first scientific conference held in Azeroth, the online universe of the role-playing game World of Warcraft, went off virtually without a hitch. Although the participants all died during the final day's social event — a massive raid on an enemy fort — they agree that this event is a glimpse at the future of scientific exchange.
Elimination of Interfering Activity in Serum Samples in the Chinese Hamster Ovary Pertussis Serology Assay
Authors: Østergaard Erik , Sørensen Charlotte , Nielsen Lene , Stawski Gitte
Published: June 2008

An interfering substance in various frozen serum samples was observed to inhibit the adhesion of Chinese hamster ovary (CHO) cells to microplate surfaces during a CHO pertussis neutralization test, resulting in wells that lacked cells or wells with dead cells after 2 days of incubation. The interfering activity in the serum could be eliminated by (i) transferring cells to other wells after their initial incubation, (ii) adding fetal calf serum (FCS) to the sample dilution buffer, (iii) precoating microplates with FCS, or (iv) preincubating the samples at 4°C for 5 days. Preincubating the samples at 4°C for 5 days reduced the interfering activity in only some of the samples. Adding serum to the sample dilution buffer or precoating the microplates with serum did not influence the antibody titers in the serum samples. The method described may be used for routine applications.
Kinetics of the Immune Response Associated with Tularemia: Comparison of an Enzyme-Linked Immunosorbent Assay, a Tube Agglutination Test, and a Novel Whole-Blood Lymphocyte Stimulation Test
Authors: Eliasson Henrik , Olcén Per , Sjöstedt Anders , Jurstrand Margareta , Bäck Erik , Andersson Sören
Published: June 2008

We have developed and evaluated a novel and simplified whole-blood lymphocyte stimulation assay that focuses on the measurement of gamma interferon after 24 h of stimulation with whole-cell tularemia antigen and a tularemia enzyme-linked immunosorbent assay (ELISA) based on highly purified lipopolysaccharide antigen. Comparison of the kinetics of the two assays and those of the traditional tube agglutination test shows that the cellular immune response can be detected earlier by the lymphocyte stimulation assay. This test already shows a high proportion of positive results during the first week after the onset of the disease, may be applicable in everyday laboratory practice, and has the potential of changing routine diagnostics for tularemia. The new ELISA has a high sensitivity and becomes positive to a high degree during the second week of disease.
Pediatric Norovirus Diarrhea in Nicaragua
Authors: Bucardo Filemon , Nordgren Johan , Carlsson Beatrice , Paniagua Margarita , Lindgren Per-Eric , Espinoza Felix , Svensson Lennart
Published: June 2008

Information about norovirus (NoV) infections in Central America is limited. Through a passive community and hospital pediatric diarrhea surveillance program, a total of 542 stool samples were collected between March 2005 and February 2006 in León, Nicaragua. NoV was detected in 12% (65/542) of the children; of these, 11% (45/409) were in the community and 15% (20/133) were in the hospital, with most strains (88%) belonging to genogroup II. NoV infections were age and gender associated, with children of <2 years of age (P< 0.05) and girls (P< 0.05) being most affected. Breast-feeding did not reduce the number of NoV infections. An important proportion (57%) of NoV-infected children were coinfected with diarrheagenicEscherichia coli. A significant proportion (18/31) of NoV-positive children with dehydration required intravenous rehydration. Nucleotide sequence analysis (38/65) of the N-terminal and shell region in the capsid gene revealed that at least six genotypes (GI.4, GII.2, GII.4, GII.7, GII.17, and a potentially novel cluster termed “GII.18-Nica”) circulated during the study period, with GII.4 virus being predominant (26/38). The majority (20/26) of those GII.4 strains shared high nucleotide homology (99%) with the globally emerging Hunter strain. The mean viral load was approximately 15-fold higher in children infected with GII.4 virus than in those infected with other G.II viruses, with the highest viral load observed for the group of children infected with GII.4 and requiring intravenous rehydration. This study, the first of its type from a Central American country, suggests that NoV is an important etiological agent of acute diarrhea among children of <2 years of age in Nicaragua.
Use of Fluorescence In Situ Hybridization for Rapid Identification of Staphylococci in Blood Culture Samples Collected in a Portuguese Hospital
Authors: Tavares Ana , Inácio João , Melo-Cristino José , Couto Isabel
Published: June 2008

Fluorescence in situ hybridization was used for the direct identification of staphylococci in blood cultures collected at a Portuguese hospital where staphylococci account for up to 35% of clinically relevant blood cultures. The assay was able to detect the presence/absence of staphylococci and distinguish
Staphylococcus aureus
from coagulase-negative staphylococci in 4.5 h.
High Rate of Intestinal Colonization with Extended-Spectrum-β-Lactamase-Producing Organisms in Household Contacts of Infected Community Patients
Authors: Valverde Aránzazu , Grill Fabio , Coque Teresa M. , Pintado Vicente , Baquero Fernando , Cantón Rafael , Cobo Javier
Published: June 2008

Fecal carriage of extended-spectrum-β-lactamase (ESBL)-producing organisms was detected in 70% of index cases of patients (
n
= 40) with community-acquired infections due to ESBL producers and reached 16.7% in household contacts (
n
= 54). A total of 66% of ESBL-producing organisms from index cases were indistinguishable from isolates from household contacts by pulsed-field gel electrophoresis. Patients with community infections and members of their households represent a reservoir for ESBL producers, increasing dispersal of resistance in healthy people.
Measles Virus Circumvents the Host Interferon Response by Different Actions of the C and V Proteins
Authors: Nakatsu Yuichiro , Takeda Makoto , Ohno Shinji , Shirogane Yuta , Iwasaki Masaharu , Yanagi Yusuke
Published: June 2008

Measles is an acute febrile infectious disease with high morbidity and mortality. The genome of measles virus (MV), the causative agent, encodes two accessory products, V and C proteins, that play important roles in MV virulence. The V but not the C protein of the IC-B strain (a well-characterized virulent strain of MV) has been shown to block the Jak/Stat signaling pathway and counteract the cellular interferon (IFN) response. We have recently shown that a recombinant IC-B strain that lacks C protein expression replicates poorly in certain cell lines, and its growth defect is related to translational inhibition and strong IFN induction. Here, we show that the V protein of the MV IC-B strain also blocks the IFN induction pathway mediated by the melanoma differentiation-associated gene 5 product, thus actively interfering with the host IFN response at two different steps. On the other hand, the C protein per se possesses no activity to block the IFN induction pathway. Our data indicate that the C protein acts as a regulator of viral RNA synthesis, thereby acting indirectly to suppress IFN induction. Since recombinant MVs with C protein defective in modulating viral RNA synthesis or lacking C protein expression strongly stimulate IFN production, in spite of V protein production, both the C and V proteins must be required for MV to fully circumvent the host IFN response.
Cathepsin L Functionally Cleaves the Severe Acute Respiratory Syndrome Coronavirus Class I Fusion Protein Upstream of Rather than Adjacent to the Fusion Peptide
Authors: Bosch Berend Jan , Bartelink Willem , Rottier Peter J. M.
Published: June 2008

Unlike other class I viral fusion proteins, spike proteins on severe acute respiratory sydrome coronavirus virions are uncleaved. As we and others have demonstrated, infection by this virus depends on cathepsin proteases present in endosomal compartments of the target cell, suggesting that the spike protein acquires its fusion competence by cleavage during cell entry rather than during virion biogenesis. Here we demonstrate that cathepsin L indeed activates the membrane fusion function of the spike protein. Moreover, cleavage was mapped to the same region where, in coronaviruses carrying furin-activated spikes, the receptor binding subunit of the protein is separated from the membrane-anchored fusion subunit.
Changing the Protease Specificity for Activation of a Flavivirus, Tick-Borne Encephalitis Virus
Authors: Fischl Wolfgang , Elshuber Sigrid , Schrauf Sabrina , Mandl Christian W.
Published: June 2008

The infectivity of flavivirus particles depends on a maturation process that is triggered by the proteolytic cleavage of the precursor of the M protein (prM). This activation cleavage is naturally performed by ubiquitous cellular proteases of the furin family, which typically recognize the multibasic sequence motif R-X-R/K-R. Previously, we demonstrated that a tick-borne encephalitis virus (TBEV) mutant with an altered cleavage motif, R-X-R, produced immature, noninfectious particles that could be activated by exogenous trypsin, which cleaves after single basic residues. Here, we report the adaptation of this mutant to chymotrypsin, a protease specific for large, hydrophobic amino acid residues. Using selection pressure in cell culture, two different mutations conferring a chymotrypsin-dependent phenotype were identified. Surprisingly, one of these mutations (Ser85Phe) occurred three positions upstream of the natural cleavage site. The other mutation (Arg89His) arose at the natural cleavage position but involved a His residue, which is not a typical chymotrypsin cleavage site. Efficient cleavage of protein prM and activation by the heterologous protease were confirmed using various recombinant TBEV mutants. Mutants with only the originally selected mutations exhibited unimpaired export kinetics and were genotypically stable during at least six cell culture passages. However, in contrast to the wild-type virus or trypsin-dependent mutants, chymotrypsin-dependent mutants were not neurovirulent in suckling mice. Our results demonstrate that flaviviruses with altered protease specificities can be generated and suggest that this approach can be used for the construction of viral mutants or vectors that can be activated on demand and have restricted tissue tropism and virulence.