bluuebunny/crossref_metadata_2025 huggingface dataset:
An Evaluation of Analysis Methodologies for Predicting Cleavage Arrest of a Deep Crack in an RPV Subjected to PTS Loading Conditions
Authors: Keeney J. A. , Bass B. R.
Published: June 2008

Several calculational procedures are compared for predicting cleavage arrest of a deep crack in the wall of a prototypical reactor pressure vessel (RPV) subjected to pressurized-thermal-shock (PTS) types of loading conditions. Three procedures examined in this study utilized the following models: 1) a static finite-element model (full bending); 2) a radially constrained static model; and 3) a thermo-elastic dynamic finite-element model. A PTS transient loading condition was selected that produced a deep arrest of an axially oriented initially shallow crack according to calculational results obtained from the static (full-bending) model. Results from the static models were compared with those generated from detailed thermoelastic dynamic finite-element analysis. The dynamic analyses modeled cleavage-crack propagation using a node-release technique and an application-mode methodology based on dynamic fracture toughness curves generated from measured data. Comparisons presented here indicate that the degree to which the dynamic solutions can be approximated by the static models is highly dependent on several factors, including the material dynamic fracture curves and the propensity for cleavage reinitiation of the arrested crack under PTS loading conditions. Additional work is required to develop and validate a satisfactory dynamic fracture toughness model applicable to post cleavage arrest conditions in an RPV.
Unusual Acoustic Vibration of a Shell and Tube Process Heat Exchanger
Authors: Eisinger F. L.
Published: June 2008

Acoustic vibration was experienced in a shell and tube process heat exchanger over a large range of operating conditions. Test and analysis results confirmed that the vibration was of an unusual type, characterized by a predominantly longitudinal acoustic wave rather than the usual diametral one. The typical approach of adding acoustic baffles or changing the baffle arrangement leads to relatively small frequency shifts which do not assure elimination of the problem. It is proposed to solve this problem by introducing sufficient acoustic damping to prevent the establishment of the longitudinal acoustic wave.
Stress Limits for Pressurized Piping Branch Junctions Under In-Plane Run Pipe Simulated Seismic Loadings
Authors: Yahiaoui K. , Moffat D. G. , Moreton D. N.
Published: June 2008

This paper summarizes results from 420 tests on 23 fabricated or machined, pressurized piping branch junctions subjected to simulated seismic loadings that induce resonant in-plane run pipe bending. The general background to this research contribution is outlined and some justifications for the chosen material, type of loading and geometries are given, with simple indications to situate this testing program in the general overall picture of simulated seismic testing of piping components and systems. Brief descriptions of the experimental program are also included. The various parameters of ASME III Eq. (9), which forms the basis of the current Code rules for nuclear power plant, are discussed next and the test load levels are assessed with reference to the current allowables of the aforementioned equation and those being proposed in the current debate for future Code revisions. The results presented here indicate strong support for these proposed Code revisions. A summary of strain data is also included and it is concluded that the proposed design philosophy to limit the total accumulated effective strain, averaged through the thickness, to 5 percent in 10 cycles may still be conservative.
Contact Analysis for Collinear Multiple Cracks in Residual Stress Field
Authors: Nishimura T.
Published: June 2008

A method is proposed for analyzing stress intensity factors and crack profiles for collinear multiple cracks perpendicular to welded joints in an infinite plate. Using the basic solution of a single crack and taking unknown density of fictitious tractions, Fredholm integral equations and algebraic equations are formulated based upon traction-free conditions and crack face displacements, respectively. These equations are solved simultaneously, considering the contact effect of crack surfaces. Using the derived density of fictitious tractions, the stress intensity factors and displacements of multiple cracks are determined. Some numerical examples are analyzed.
Method and Mechanism of Beneficial Residual Stresses in Tubes
Authors: Leˆ N. V.
Published: June 2008

It is shown in this paper that residual stresses in a tube could be created in such a way that they are in tension in the middle region of the wall and in compression throughout the entire inside and outside surfaces of the tube. The method of treatment consists of applying an internal pressure and some appropriate alternating hot and cold thermal shocks to the tube. The mechanism of stress evolution in tube wall is demonstrated using elastic-perfectly plastic analysis of a generalized plane strain ID model subjected to a primary tension load σm, and an alternating linear temperature difference ΔT across the thickness. Theoretical combinations of loads (σm, ΔT) which give such residual stress configurations and formulas for predicted residual stresses are developed. A possible application of this treatment is for prolonging the life of U-bend region of heat exchanger tubes against stress corrosion cracking.
Effect of Material Properties on the Strain to Failure of Thick-Walled Cylinders Subjected to Internal Pressure
Authors: Roach D. P. , Priddy T. G.
Published: June 2008

The determination of the fully plastic response and pressure limit of a pressure vessel is of considerable importance in design, especially in autofrettage considerations. This paper presents the results of an experimental study which measured the maximum internal pressure which can be applied to thick-walled cylindrical vessels. Both aluminum and steel, with material properties ranging from ductile to brittle, were tested at stress levels through plastic and strain hardening ranges to fracture. From these tests, the pressure-expansion and through-thickness yielding characteristics were determined for these specimens. It is shown that a strain-to-failure criterion, based on the triaxiality of stress in the critical region, can be used to predict the complete pressure versus strain relations and maximum pressure for these cylinders. A simple tension-true stress-strain relation of the material is employed to analytically predict the response of the cylinder into the plastic regime. Finally, simplified theoretical and empirical formulas for bursting pressures are checked against the experimental results.
Risk-Based Considerations in Developing Strategies to Ensure Pipeline
Integrity—Part I: Theory
Authors: Leis B. N. , Rahman S.
Published: June 2008

As pipelines age, a flaw population that varies initially along the pipeline can advance in size and number. Analysis of the serviceability of pipelines based on either inline inspection or hydrotesting can lead to overly conservative decisions or an excessive risk of failure when the random nature of this population and the pipeline’s properties are represented by a “typical” flaw and “average” properties. It follows that decisions on serviceability should reflect the random nature of the variables involved or be justified by demonstrating that the uncertainty in these parameters does not adversely affect cost and safety. This is the first in series of two papers generated from a recent study on risk-based analysis for developing strategies to ensure pipeline integrity. In this paper (Part I—Theory), a new probabilistic methodology is developed to conduct fracture evaluations of pipelines subjected to ductile flaw growth in service. The study is made under the assumption that continuing serviceability is based on the use of hydrotesting. The analysis involves time-dependent elastic-plastic fracture mechanics for the underlying deterministic model, and Monte Carlo simulation for structural reliability analysis. Using these models, pipe fracture evaluations will be conducted in the light of a hydrotest-based approach to ensure pipeline integrity. They will be discussed in the companion paper, Part II—Applications (Rahman and Leis, 1994).
Residual Stress Estimation and Shakedown Evaluation Using GLOSS
Analysis
Authors: Seshadri R.
Published: June 2008

A simple method for estimating residual stresses using the GLOSS analysis is presented, and a shakedown assessment method is proposed. Practical pressure components exhibit some local elastic follow-up, and thereby induce smaller residual stresses than implied by uniaxial models. In this context, the effectiveness of “autofrettaging” is examined by studying a thick-walled cylinder subjected to an internal pressure. Modifications to the P + Q stress-intensity limit are suggested, and compared with Roche’s criterion. The method presented here is useful for configurations experiencing small to medium amounts of follow-up, which covers many practical situations.
Dynamic Behavior of Elastic-Plastic Simply Supported
Pipes
Authors: Gau J. S. , Scavuzzo R. J. , Lam P. C.
Published: June 2008

Nonlinear responses of the dynamic behavior of simply supported pipes were analyzed using a nonlinear finite element program. In the first model, a 1 1/2-in. schedule 40 stainless steel pipe 48 in. long was studied. An elastic-plastic material was specified. The dynamic response of the pipe to a sinusoidal force input was calculated. There was no internal pressure and the magnitude of the force input was held constant as the frequency was varied. A total of 26 cases were studied starting with low frequencies that exhibited static behavior to twice the natural frequency. In addition, a 1-in. straight piping system studied experimentally by Beaney (1985a, b) was modeled analytically. Calculations are compared to experiment. The response of the piping at input frequencies of one-quarter and one-half of the natural frequency exhibited resonance behavior. At one forced frequency, an almost chaotic behavior of the dynamic pipe response was observed. However, at all other specified excitation frequencies, the system reaches a steady-state response. Output in the form of strain and displacement time histories and force displacement plots is developed. In addition, both work and equivalent viscous damping are calculated and presented.
Turbulence-Induced Vibration of Tube Arrays in Two-Phase
Flow
Authors: Papp L. , Chen S. S.
Published: June 2008

Two-phase flow exists in many engineering systems and is a dominant type of flow in heat exchangers, steam generators, and condensers. A flowing two-phase fluid is a source of energy that can cause vibration of tube bundles of these systems. A simple correlation is presented to predict the response of tube bundles in two-phase flow. The model correlates with experimental data reasonably well and is a useful tool in the prediction of tube response.
Background of the Half-Pipe Jacket Rules in Section VIII, Division
1
Authors: Jawad M. H.
Published: June 2008

New rules for the design of half-pipe jackets were developed by the ASME Subgroup on Design of Section VIII. This article gives the background information for the derivation and various assumptions made in developing the rules.
An Axisymmetric Stress Release Method for Measuring the Autofrettage Level in Thick-Walled Cylinders—Part II: Experimental Validation
Authors: Perl M. , Arone´ R.
Published: June 2008

The basic concept of a new experimental method for measuring the level of autofrettage in thick-walled cylinders as well as a comprehensive numerical simulation were presented in Part I of this paper. A pilot test is conducted herein on a 105-mm autofrettage gun barrel to validate the proposed procedure. First, a preliminary test is performed to determine the minimum thickness required for a ring, cut from the barrel, in order to be a representative, valid, and free of edge-effect specimen. Then, the main experiment is conducted consisting of the gradual release of the residual stress field due to autofrettage prevailing in the ring specimen. An array of seven equally spaced, identical, radial notches is progressively cut at the inner surface of the ring, while the released hoop stress is continuously measured by a strain gage-based computerized data acquisition system. The process is accomplished by a detailed numerical simulation enabling a qualitative and quantitative monitoring of the procedure. The proposed experimental procedure is found to be feasible, reliable, and cost-effective, and to yield accurate results.
A Kt-Based Method for Calculating LCF Life of Notched Specimens
Authors: Merah N. , Bui-Quoc T. , Bernard M.
Published: June 2008

Under cyclic loading, the effect of stress raisers on the fatigue life depends upon several parameters, the most important being the stress concentration factor, the stress level, and the material notch sensitivity. In particular, in the low-cycle fatigue region, a number of procedures are currently used, but additional developments are required for improvement of the life prediction capabilities. In this paper, a method is proposed for calculating notched specimen low-cycle fatigue life from unnotched specimen data using as the main parameter the stress concentration factor combined with the applied stress level and the cyclic-hardening properties of the material. The proposed method is then applied to several materials with a variety of notch geometries to obtain the predicted lives. The correlation between the calculated lives and the experimental data is discussed in connection with the predictions obtained from Neuber’s and Zwicky’s relations.
Analysis of the Tightening Process of Bolted Joint With a Tensioner Using Spring Elements
Authors: Fukuoka T.
Published: June 2008

Hydraulic bolt tensioners are frequently used to tighten critical structural members with accurately controlled clamping force. The ratio of desired clamping force to initial tension is the most important factor to be predicted in advance for given joint configurations, which is termed “effective tensile coefficient” here. In this paper, an elementary and extensive approach to estimate the coefficient is proposed using spring elements, and a simple and practical equation is presented to evaluate the magnitude of “effective tensile coefficient” in terms of five spring rates of each part consisting of the joint. The relationship between “effective tensile coefficient” and grip length is investigated, including the influences of Young’s modulus of fastened plate. The validity of the elementary method proposed here is ascertained by comparing the results to those by experiment and FEM.
Fatigue Curve Needs for Higher Strength 2-1/4Cr-1Mo Steel for Petroleum Process Vessels (Survey Paper)
Authors: Jaske C. E.
Published: June 2008

This paper reviews the data needed to develop fatigue design rules for pressure vessels fabricated from heat-treated 2-1/4Cr-1Mo steel (SA-387, Grade 22, Class 2 plates and SA-336, Grade F22 forgings) that are operated or designed to operate at temperatures greater than 371 C (700 F). The available data were reviewed, and the results of that review were used to develop recommendations for needed analytical and experimental work. Extension of the fatigue-curve approach currently used for temperatures up to 371 C (700 F) and development of a fracture-mechanics-based, crack-growth approach were addressed. Both of these two approaches must include means for assessing the time-dependent effects of oxidation and/or creep when fatigue cycling occurs at low strain rates or includes hold times. The recommendations of this study provide a plan for the development of fatigue design rules for the use of heat-treated 2-1/4Cr-1Mo steel at temperatures in the range of 371 to 482 C (700 to 900 F).
Assessment of the Engineering Approach for the Evaluation of C-Shaped Specimens
Authors: Goan J. M. , Sutton M. A. , Chao Y. J.
Published: June 2008

A baseline study has been carried out to assess the accuracy of the engineering approach for J-integral determination when applied to various standard specimens. Detailed finite element calculations were used to assess the accuracy of this approach. Although certain discrepancies were found when comparing the approximated functions obtained in this work to those in previous work, the error trends are similar and consistent throughout the analysis. Then, the engineering approach outlined in the baseline study is applied to the 2-D plane stress problem of a C-shaped specimen subjected to tension. Derivation of limit-load, fully plastic solutions and elastic-plastic estimation formulas are given in detail. Detailed comparisons between results from estimation solutions and finite element calculations are presented.
SIF Calculation for Two Cracks Emanating From the Internal Boundary of a Tube
Authors: Wang Y. H. , Li C. Z.
Published: June 2008

The stress intensity factor (SIF) corresponding to two collinear cracks emanating from the internal boundary of a tube is calculated by boundary collocation method (BCM). Uniform internal pressure acts in the cylinder and on the crack surfaces or a uniform external tension on the outer boundary. For different ratios of the internal to the external radius, Ri/Re, and different ratios of the crack length to the cylinder thickness, 1/(Re−Ri), SIF values have been obtained. At the same time, the calculation shows that the convergence of the method is satisfactory.
Vibration of Fluid-Filled Pipeline Buried in Soil
Authors: Fu-Iu M. , Xiaoming Y.
Published: June 2008

Liquid-filled pipelines buried in soils are commonly used structural components in lifeline engineering. The aim of this paper is to analyze the vibration of such a component under axial excitation with due consideration of soil-pipe-liquid interaction. Besides the formal solution of the system some numerical results are obtained for certain values of material and structural parameters, which shed, to some extent, light on the effect of the contained and the surrounding soil on the pipe response. Meanwhile, the frequency of free vibration, the dynamic amplification factor versus frequency of excitation, and the displacement response time history due to the excitation of 1971 San Fernando earthquake wave form are given.
Stress Singularity in Transient Thermoelastic Field of a Fiber-Reinforced Composite Tube
Authors: Noda N. , Ashida F.
Published: June 2008

The present paper discusses a transient thermoelastic contact problem in a fiber-reinforced composite tube. The tube is inserted into a supporting body such as a ring, and subjected to heating and hydrostatic pressure in it. The fiber-reinforced composite possesses strong thermal and mechanical anisotropies, so the thermoelastic analysis of anisotropic material is very important. The stress produced in the tube has singularity at the end of contacted surface of the tube. The stress singularity may lead to a crack on the surface so that the tube may fracture. If we consider the safety of the tube in service, it is very important to evaluate the stress singularity. For that, the transient thermoelastic contact problem of the tube is analyzed, and the stress distribution and the strength of the stress singularity become clear.
Local Flexibilities in Cylindrical Shells Due to External Loadings (Design Paper)
Authors: Reed J. N.
Published: June 2008

A shortcoming in Welding Research Council Bulletin 107, “Local Stresses in Spherical and Cylindrical Shells Due to External Loadings,” Wichman et al. (1965, 1979), has been the absence of a method for determining the flexibilities of vessels under local loads. Bulletin 107 is based in part on the work of Bijlaard (1954, 1955, 1959). These works of Bijlaard contain sufficient data such that flexibilities can be determined graphically for cylindrical shells under local (nozzle) loads. A relatively simple graphic method is presented for determining the radial, circumferential rotational and longitudinal rotational flexibilities at nozzle connections in cylindrical vessels where radial and bending loads are introduced through the nozzle.
A Direct Two Response Approach for Updating Analytical Dynamic Models of Structures With Emphasis on Uniqueness
Authors: Ibrahim S. R. , Stavrinidis C. , Fissette E. , Brunner O.
Published: June 2008

An approach, based on utilizing only two sets of structural responses and the enforcement of the conditions for a unique solution, is presented for the updating of Finite Element Models. The responses required can be any two identified normal modes, any two identified complex modes, or two forced harmonic response vectors in the neighborhood of any two natural frequencies of the structure under test. The mass, stiffness, and damping matrices are interactively and simultaneously corrected in a direct noniterative procedure. A uniqueness factor is automatically computed in the procedure to indicate the correctability of the Finite Element Model under consideration. The number of measurement locations is assumed to be less than the number of degrees of freedom of the analytical model. Provisions for completing and smoothing the measured or identified responses are included to reduce the effects of measurement noise and identification error. Preliminary results on simple models are presented in support of the proposed technique.
Experimental and Numerical Analysis of Read/Write Head Suspension Dynamics for High-Performance Floppy Drive Systems
Authors: Frees G. M. , Miu D. K.
Published: June 2008

Read/write head suspensions are critical components of high-performance floppy disk drives. Their dynamics affect head/media compliance, wear, and tracking performance. Vibration measurements are necessary in order to verify and adjust finite element models, to observe the influence of actual loading and operating conditions, and to study the effects of unmodeled components such as electrical wires and adhesives. A nonintrusive measurement technique using a Laser Doppler Vibrometer is utilized to measure the submicron vibrations. Excitation of the suspension is provided by a specially designed miniature air hammer and a piezoelectric transducer. Natural frequencies and mode shapes are extracted from the measurements and compared with numerical data from the finite element model. Research shows that boundary conditions are the most important parameters in the modeling of the suspension. A new design is proposed, using the verified model, to increase the tracking performance of the suspension. Synergy between experimentation and numerical analysis is emphasized.
An Experiment to Identify the Structural Dynamics of a Portal Frame
Authors: Mottershead J. E. , Tee T. K. , Foster C. D. , Stanway R.
Published: June 2008

This paper describes the application of sequential frequency domain techniques to the estimation of mass, stiffness, and damping parameters using measured frequency response functions from a portal frame rig. The theory of the method has been described in the authors’ previous publications. A portal frame is representative of many engineering structures. It is lightly damped and may be thought of as an element of several larger structures such as bridges, transmission towers, and the steel foundations of modern power generating plant. The results offered in this paper are thus of interest to a broad range of engineering problems where it is required to obtain mathematical models in terms of physical parameters.
Vibration-Isolation Characteristics of an Active Electromagnetic Force Generator and the Influence of Generator Dynamics
Authors: Su Hong , Rakheja S. , Sankar T. S.
Published: June 2008

Vibration-isolation characteristics of an active vibration control system incorporating an electromagnetic force generator (actuator) are investigated. The electromagnetic force generator is modeled as a first-order dynamical system and the influence of dynamics of the force generator on the vibration-isolation performance of the active isolator is investigated via computer simulation. It is concluded that the dynamics of the force generator affect the vibration-isolation performance significantly. An active control scheme, based upon absolute position, velocity, and relative position response variables, is proposed and investigated. In view of the adverse effects of generator dynamics, the proposed control scheme yields superior vibration isolation performance. Stability analysis of the active vibration control system is carried out to determine the limiting values of various feedback control gains.
An Integrated Approach for Friction Damper Design
Authors: Cameron T. M. , Griffin J. H. , Kielb R. E. , Hoosac T. M.
Published: June 2008

A procedure is outlined for determining the optimal design of friction dampers for high-speed turbomachinery blading. The procedure includes: An integration of bench test results with finite-element analysis and a single-mode blade model to ensure accuracy of the analytical model and improve reliability of the friction damper design; an extension of the single-mode blade model to predict the engine behavior of friction dampers; and a new way of viewing analytical and experimental results in terms of a damper performance curve to determine optimal design parameters, when the levels of excitation and damping in the system are unknown. Unique experiments are performed on a test disk in order to demonstrate and verify the accuracy of the design procedure.
The Effect of Transverse Shear Deformation on the Natural Frequencies of Layered Composite Paraboloidal Shells
Authors: Kayran A. , Vinson J. R.
Published: June 2008

An analysis is presented for the study of the effect of transverse shear deformation on the natural frequencies of layered composite paraboloidal shells. The applicability of linear shell theory due to Reissner is assumed and governing equations are solved for the natural frequencies using the transfer matrix approach. The results of the present analysis are compared with the results for paraboloidal shells reported in the literature and good agreement is found. Transverse shear deformation effects are carried out separately for axisymmetric torsional vibration modes, axisymmetric bending-extensional vibration modes and nonsymmetric vibration modes. The variation of the effect of transverse shear deformation with respect to different rim boundary conditions, geometry of the paraboloid, material type (isotropic-orthotropic), lamination arrangement and particular meridional and circumferential vibration modes is investigated.
Acoustic Characteristics of an Expansion Chamber With Constant Mass Flow and Steady Temperature Gradient (Theory and Numerical Simulation)
Authors: Kim Yang-Hann , Choi Jae Woong , Lim Byung Duk
Published: June 2008

The governing equation of acoustic wave propagation in a circular expansion chamber with mean flow and temperature gradient is solved. The circular chamber is divided into N segments and the flow speed and temperature are assumed to be constant in each segment. The solution is obtained in recursive form by applying the matching condition on the boundary of adjacent elements. The solution is verified by comparing it with the experimental results. The results demonstrate that the present theory can well predict the transmission loss of an expansion chamber which has offset, a twisting angle, mean flow, and temperature gradient.
Extensions of the Modal Assurance Criterion
Authors: Heylen W. , Janter T.
Published: June 2008

The modal assurance criterion (MAC) in general measures the degree of proportion between two (modal) vectors, in the form of a correlation coefficient of a least squares ratio estimate. The MAC principle can be extended in several ways, thus increasing its field of applications. The partial MAC (PMAC) correlates parts of (modal) vectors. The spatial MAC (SMAC) allows to compare different vector spaces. Furthermore this paper suggests a way of calculating the MAC sensitivities to model changes. All those extensions are illustrated by their possible uses in correlating measured dynamic data with (finite element) matrix models and in the area of model updating. Those applications might be helpful tools to indicate regions of poor measurement-model correlation, to complete measured vectors, to judge approximate eigenvalue solvers, or to improve model updating procedures.
Vibration Characteristics of a Beam With Support Accompanying Clearance
Authors: Murakami K. , Sato H.
Published: June 2008

Experimental and analytical investigations were conducted to identify the frequency response characteristics of a beam system with a minute clearance at the support. A beam in the shape of the letter L was adopted as the system, which made it possible to compare the results of the two investigations easily by restricting the direction of vibration at the clearance. The frequency response characteristics of the systems were evaluated in terms of the equivalent linearization method using the describing function approach. The jump phenomena around the natural frequency and the suppression of the compliance around the natural frequency could be evaluated by the analytical method; the results agreed well with those obtained by experiment. The computation time needed for the proposed method was significantly shorter than that needed by a numerical integration approach, the approach most commonly used in conventional design practice. The method also made it possible to evaluate the response characteristics in detail in terms of compliance.
An Innovative Method of Investigating the Role of Turbulence in the Velocity Coupling Phenomenon
Authors: Ma Y. , Van Moorhem W. K. , Shorthill R. W.
Published: June 2008

An investigation has been conducted of the velocity coupling phenomenon reported in acoustically unstable solid propellant rocket motors. An innovative simulation facility has been built using solid carbon dioxide as the simulated propellant. The use of dry ice allows us to focus directly on the fluid mechanical aspect of the problem. Dry ice is contained in a two-meter long chamber. The acoustic disturbance in the chamber is introduced by means of a mechanically driven piston. Mass flow rate and acoustic pressure measurements indicate the existence of a coupling mechanism, other than pressure coupling, between the acoustic disturbance and dry ice sublimation process. Flow visualization using a high speed camera shows a high degree of mixing, near resonance, within the flow above the dry ice surface. The flow over the dry ice is very chaotic, probably turbulent. Hot film anemometry measurements show a broad-band spectrum at low frequencies with strong peaks at the driving frequency and its harmonics near resonance. A broad band spectrum is generally taken as an indication of turbulent flow. Acoustically induced turbulent forced convection is believed to be responsible for the increase in the sublimation rate of the dry ice (simulated burning of the propellant). We believe that turbulence is one of the principal mechanisms in the velocity coupling phenomenon.
Boundary Element Methods in Probabilistic Acoustic Radiation Problems
Authors: Daddazio R. P. , Ettouney M. M.
Published: June 2008

Boundary Element Methods (BEM) are suited to a wide range of engineering problems, especially those of a semi-infinite nature. Examples of such problems can be found in the fluid-structure interactions of acoustic radiation and scattering problems and in the soil-structure interactions of earthquake and machine foundation problems. The required input parameters, dynamic loads, and system properties for such problems are not in general well-defined and can be considered random variables. Probabilistic structural analysis through the use of the BEM has been introduced by Ettouney et al. (1989a, 1989b) for the solution of plane elastic systems with uncertain material properties. The method was applied to solution of problems in the fields of structural and geotechnical engineering. In this work, we extend the use of this probabilistic approach to area of fluid-structure interaction by applying this technique to the problem of acoustic radiation from structures. The advantages of the probabilistic viewpoint are discussed with regard to current engineering practices. The importance of confidence estimates for criteria of nonexceedance response is emphasized.
Design Optimization of Response Amplitudes in Viscously Damped Structures
Authors: Watts D. , Starkey J.
Published: June 2008

An optimization technique is presented which reduces the response of damped linear systems without neglecting the cost of the required design changes. A two-part function represents the design objective as a weighted sum of a function of the response levels at important locations on the structure in critical frequency ranges, and a function of the cost of potential design changes. Numerical examples are included, and experimental verification of the technique’s ability to reduce response at a specified location on a beam is also included. The technique is shown by these examples to be an effective design tool.
Time Domain Method for Parameter System Identification
Authors: Hac A. , Spanos P. D.
Published: June 2008

In this paper a method of parameter identification for a multi-degree-of-freedom structural system in a noisy environment is presented. The method involves an iterative procedure in which initial parameter estimates are obtained by relying on a least squares kind of approximation. This estimate is used in an adaptive Kalman filter to obtain an improved estimate of the system state. The improved estimate is then utilized in the least squares approximation to produce refined estimates of the system parameters. The iteration is repeated until it converges within an acceptable margin. The parameter errors are compensated during filtering by adding pseudonoise to the system equation; the noise itensity is updated in each iteration. Results of a simulation study conducted for a two-degree-of-freedom system indicate that the method can yield, for a relatively low computational cost, reliable estimates of system parameters, even when the data record is short.
A New Method for the Optimization of a Vibration Isolation System
Authors: Lin Y. , Luo W. , Zhang Y. M.
Published: June 2008

Formerly the optimization of the passive vibration isolator is mainly founded on the nonlinear programming algorithms. The methods are iterative in nature and time-consuming. In this paper a frequency domain suboptimal method is developed for the optimization of the passive vibration isolators. The method is based on the linear optimal control results and has advantages of high efficiency in computation and high reliability of results. It is especially applicable to the microcomputer environment.
Comment on "Athabasca Valles, Mars: A Lava-Draped Channel System"
Authors: Page David P.
Published: June 2008

Jaeger
et al
. (Reports, 21 September 2007, p. 1709) presented images of the Athabasca Valles channel system on Mars and asserted that the observed deposits are composed of thin, fluid lavas. However, all the features they described are secondary and postdate the surface by many millions of years, as documented by structural relationships with small, young impact craters.
Response to Comment on "Athabasca Valles, Mars: A Lava-Draped Channel System"
Authors: Jaeger W. L. , Keszthelyi L. P. , McEwen A. S. , Titus T. N. , Dundas C. M. , Russell P. S.
Published: June 2008

The recent geologic history of Athabasca Valles, Mars, is controversial. Some studies report ice-rich sediment in its channels, whereas others find only lava. Data from the High-Resolution Imaging Science Experiment camera now confirm that, although certain features exhibit a superficial similarity to ice-related landforms, solidified lava coats the entire channel system.
Tuned Responses of Astrocytes and Their Influence on Hemodynamic Signals in the Visual Cortex
Authors: Schummers James , Yu Hongbo , Sur Mriganka
Published: June 2008

Astrocytes have long been thought to act as a support network for neurons, with little role in information representation or processing. We used two-photon imaging of calcium signals in the ferret visual cortex in vivo to discover that astrocytes, like neurons, respond to visual stimuli, with distinct spatial receptive fields and sharp tuning to visual stimulus features including orientation and spatial frequency. The stimulus-feature preferences of astrocytes were exquisitely mapped across the cortical surface, in close register with neuronal maps. The spatially restricted stimulus-specific component of the intrinsic hemodynamic mapping signal was highly sensitive to astrocyte activation, indicating that astrocytes have a key role in coupling neuronal organization to mapping signals critical for noninvasive brain imaging. Furthermore, blocking astrocyte glutamate transporters influenced the magnitude and duration of adjacent visually driven neuronal responses.
Iron Isotope Fractionation During Magmatic Differentiation in Kilauea Iki Lava Lake
Authors: Teng Fang-Zhen , Dauphas Nicolas , Helz Rosalind T.
Published: June 2008

Magmatic differentiation helps produce the chemical and petrographic diversity of terrestrial rocks. The extent to which magmatic differentiation fractionates nonradiogenic isotopes is uncertain for some elements. We report analyses of iron isotopes in basalts from Kilauea Iki lava lake, Hawaii. The iron isotopic compositions (
56
Fe/
54
Fe) of late-stagemeltveins are 0.2 permil (‰) greater than values for olivine cumulates. Olivine phenocrysts are up to 1.2‰ lighter than those of whole rocks. These results demonstrate that iron isotopes fractionate during magmatic differentiation at both whole-rock and crystal scales. This characteristic of iron relative to the characteristics of magnesium and lithium, for which no fractionation has been found, may be related to its complex redox chemistry in magmatic systems and makes iron a potential tool for studying planetary differentiation.
Phylogeny-Aware Gap Placement Prevents Errors in Sequence Alignment and Evolutionary Analysis
Authors: Löytynoja Ari , Goldman Nick
Published: June 2008

Genetic sequence alignment is the basis of many evolutionary and comparative studies, and errors in alignments lead to errors in the interpretation of evolutionary information in genomes. Traditional multiple sequence alignment methods disregard the phylogenetic implications of gap patterns that they create and infer systematically biased alignments with excess deletions and substitutions, too few insertions, and implausible insertion-deletion–event histories. We present a method that prevents these systematic errors by recognizing insertions and deletions as distinct evolutionary events. We show theoretically and practically that this improves the quality of sequence alignments and downstream analyses over a wide range of realistic alignment problems. These results suggest that insertions and sequence turnover are more common than is currently thought and challenge the conventional picture of sequence evolution and mechanisms of functional and structural changes.
Reverse Enzyme-Linked Immunosorbent Assay Using Monoclonal Antibodies against SAG1-Related Sequence, SAG2A, and p97 Antigens fromToxoplasma gondiiTo Detect Specific Immunoglobulin G (IgG), IgM, and IgA Antibodies in Human Sera
Authors: Carvalho Fernando R. , Silva Deise A. O. , Cunha-Júnior Jair P. , Souza Maria A. , Oliveira Taísa C. , Béla Samantha R. , Faria Gabriele G. , Lopes Carolina S. , Mineo José R.
Published: June 2008

The present study aimed to evaluate the performance of three monoclonal antibodies (MAbs) in reverse enzyme-linked immunosorbent assays (ELISAs) for detecting immunoglobulin G (IgG), IgM, and IgA antibodies againstToxoplasma gondiiin 175 serum samples from patients at different stages ofT. gondiiinfection, as defined by both serological and clinical criteria, as follows: recent (n= 45), transient (n= 40), and chronic (n= 55) infection as well as seronegative subjects (n= 35). The results were compared with those obtained by indirect ELISA using solubleToxoplasmatotal antigen (STAg). Our data demonstrated that MAb A3A4 recognizes a conformational epitope in SAG1-related-sequence (SRS) antigens, while A4D12 and 1B8 recognize linear epitopes defined as SAG2A surface antigen and p97 cytoplasmatic antigen, respectively. Reverse ELISA for IgG with A3A4 or A4D12 MAbs was highly correlated with indirect ELISA for anti-STAg IgG, whereas only A4D12 reverse ELISA showed high correlation with indirect ELISA for IgM and IgA isotypes. To our knowledge, this is the first report analyzing the performance of a reverse ELISA for simultaneous detection of IgG, IgM, and IgA isotypes active toward native SAG2A, SRS, and p97 molecules from STAg, using a panel of human sera from patients with recent and chronic toxoplasmosis. Thus, reverse ELISA based on the capture of native SAG2A and SRS antigens of STAg by MAbs could be an additional approach for strengthening the helpfulness of serological tests assessing the stage of infection, particularly in combination with highly sensitive and specific assays that are frequently used nowadays for diagnosis of toxoplasmosis during pregnancy or congenital infection in newborns.
Influenza Virus Vaccination Induces Interleukin-12/23 Receptor β1 (IL-12/23Rβ1)-Independent Production of Gamma Interferon (IFN-γ) and Humoral Immunity in Patients with Genetic Deficiencies in IL-12/23Rβ1 or IFN-γ Receptor I
Authors: de Boer Tjitske , van Dissel Jaap T. , Kuijpers Taco W. J. , Rimmelzwaan Guus F. , Kroon Frank P. , Ottenhoff Tom H. M.
Published: June 2008

To investigate whether protective immune responses can be induced in the absence of normal interleukin-12/23/gamma interferon (IL-12/23/IFN-γ) axis signaling, we vaccinated with the seasonal influenza virus subunit vaccine two patients with complete IL-12/23 receptor β1 (IL-12/23Rβ1) deficiencies, two patients with partial IFN-γ receptor I (pIFN-γRI) deficiencies, and five healthy controls. Blood samples were analyzed before, 7 days after, and 28 days after vaccination. In most cases, antibody titers reached protective levels. Moreover, although T-cell responses in patients were lower than those observed in controls, significant influenza virus-specific T-cell proliferation, IFN-γ production, and numbers of IFN-γ-producing cells were found in all patients 7 days after the vaccination. Interestingly, influenza virus-specific IFN-γ responses were IL-12/23 independent, in striking contrast to mycobacterium-induced IFN-γ production. In conclusion, influenza virus vaccination induces IL-12/23-independent IFN-γ production by T cells and can result in sufficient humoral protection in both IL-12/23Rβ1- and pIFN-γRI-deficient individuals.
Development of a More Efficient Algorithm for Identifying False-Positive Reactivity Results in a Dengue Virus Immunoglobulin M Screening Assay
Authors: Prince Harry E. , Yeh Cindy , Lapé-Nixon Mary
Published: June 2008

Of 2,692 sera screened for dengue virus immunoglobulin M by using a μ-capture enzyme-linked immunosorbent assay (ELISA), 954 had equivocal (index from 0.90 to 1.10) or positive (index of >1.10) results and were retested using a background subtraction (BS) ELISA that identifies screen false positives. No false positives were found among 427 sera with screen ELISA indices of >6.00; thus, retesting this specimen subset by BS ELISA is unnecessary.
Marked Variability of BK Virus Load Measurement Using Quantitative Real-Time PCR among Commonly Used Assays
Authors: Hoffman Noah G. , Cook Linda , Atienza Ederlyn E. , Limaye Ajit P. , Jerome Keith R.
Published: June 2008

BK virus (BKV) is the infectious cause of polyomavirus-associated nephropathy. Screening guidelines for renal-transplant recipients define levels of viremia and viruria that are actionable for additional testing or intervention. However, standardized real-time PCR primers, probes, and standards are unavailable, and the extent of agreement among published assays is unknown. We compared seven TaqMan real-time PCR primer/probe sets (three designed at this institution, three described in the literature, and one purchased) in conjunction with two different standards to prospectively measure BKV titers in 251 urine specimens submitted to our clinical laboratory. We observed substantial disagreement among assays attributable both to features of primer and probe design and to choice of reference material. The most significant source of error among individual specimens was primer or probe mismatch due to subtype-associated polymorphisms, primarily among subtype III and IV isolates. In contrast, measurement of the most abundant subtypes (Ia, V, and VI) were typically uniform among all seven assays. Finally, we describe and validate a new clinical assay designed to reliably measure all subtypes encountered in our study population (Ia, Ic, III, IV, and VI). Consideration of available BKV sequence information in conjunction with details of subtype distribution allowed us to develop a redesigned assay with markedly improved performance. These results suggest that both accurate BKV measurement and the uniform application of BKV screening guidelines could be significantly improved by the use of standardized reference materials and PCR primers and probes.
Development and Validation of a Negative-Strand-Specific Reverse Transcription-PCR Assay for Detection of a Chicken Strain of Hepatitis E Virus: Identification of Nonliver Replication Sites
Authors: Billam P. , Pierson F. W. , Li W. , LeRoith T. , Duncan R. B. , Meng X. J.
Published: June 2008

As a positive-strand RNA virus, hepatitis E virus (HEV) produces an intermediate negative-strand RNA when it replicates. Thus, the detection of negative-strand viral RNA is indicative of HEV replication. The objective of this study was to develop a negative-strand-specific reverse transcription-PCR (RT-PCR) assay for the identification of extrahepatic sites of HEV replication. Briefly, a 494-bp fragment within the
orf1
gene of a chicken strain of HEV (designated avian HEV) was amplified and cloned into a pSK plasmid. A synthetic negative-strand viral RNA was generated from the plasmid by in vitro transcription and was used to standardize the assay. A nested set of primers was designed to amplify a 232-bp fragment of the negative-strand viral RNA. The assay was found to detect up to 10 pg and 10
−5
pg of negative-strand HEV RNA in first- and second-round PCRs, respectively. The standardized negative-strand-specific RT-PCR assay was subsequently used to test 13 conveniently obtained tissue specimens collected sequentially on different days postinoculation from chickens experimentally infected with avian HEV. In addition to the liver, the negative-strand-specific RT-PCR assay identified replicative viral RNA in gastrointestinal tissues, including the colorectal, cecal, jejunal, ileal, duodenal, and cecal tonsil tissues. The detection of replicative viral RNA in these tissues indicates that after oral ingestion of the virus, HEV replicates in the gastrointestinal tract before it reaches the liver. This is the first report on the identification of extrahepatic sites of HEV replication in animals after experimental infection via the natural route. The assay should be of value for studying HEV replication and pathogenesis.