Linearly Implicit Time Integration Methods for Real-Time Dynamic Substructure Testing

The simulation in real time of heterogeneous systems has to guarantee that the time integration of the equations of motion is always successfully completed within an a priori fixed sampling time interval. Therefore, numerical and/or physical substructures as well as numerical solution methods have to be adapted to the needs of real-time simulations. Monolithic stable numerical methods are implicit and cannot be easily used in real-time applications because of their iterative strategies necessary to solve the nonlinear corrector equations. As an alternative, in the present paper, we consider linearly implicit Rosenbrock-based L-stable real-time (LSRT) compatible algorithms with both two-stage and three-stage. Moreover, other linearly implicit structural integrators used nowadays to perform coupled simulations in real time are introduced too. Successively, typical properties of monolithic algorithms are shown when large time steps are employed. The loss of stability and the reduction of accuracy of these algorithms, when applied to coupled systems caused by kinematically closed loops, are analyzed in-depth through a split-inertia substructured system. In this respect, the benefits of the L-stability property are shown. Finally, the performance of the algorithms under investigation appears in a number of more realistic tests considering both nonstiff and stiff substructures.     

Efficient Parallel Implementation of Hybrid Optimization Approaches for Solving Groundwater Inverse Problems

Inverse problems that are constrained by large-scale partial differential equation (PDE) systems demand very large computational resources. Solutions to these problems generally require the solution of a large number of complex PDE systems. Three-dimensional groundwater inverse problems fall under this category. In this paper, we describe the implementation of a parallel simulation-optimization framework for solving PDE-based inverse problems and demonstrate it for the solution of groundwater contaminant source release history reconstruction problems that are of practical importance. The optimization component employs several optimization algorithms, including genetic algorithms (GAs) and several local search (LS) approaches that can be used in a hybrid mode. This hybrid GA-LS optimizer is used to drive a parallel finite-element (FEM) groundwater forward transport simulator. Parallelism is exploited within the transport simulator (fine grained parallelism) as well as the optimizer (coarse grained parallelism) through the exclusive use of the Message Passing Interface (MPI) communication library. Algorithmic and parallel performance results are presented for an IBM SP3 supercomputer. Simulation and performance results presented in this paper illustrate that an effective combination of efficient optimization algorithms and parallel computing can enable solution to three-dimensional groundwater inverse problems of a size and complexity not attempted before.     

Viscoelastic Dampers at Expansion Joints for Seismic Protection of Bridges

This paper presents the result of a study on the use of viscoelastic dampers at expansion joints of highway bridges for preventing superstructure decks from falling off the seats and∕or from colliding with each other in the event of a severe earthquake. The Kelvin and Maxell models, consisting of an elastic spring and a linear viscous damper combined in parallel and in series, respectively, are considered for analysis. A 2D finite-element analysis using bilinear hysteretic models for bridge substructures joints was performed on example bridges constructed with one or two expansion joints. It was demonstrated that the damper is effective in suppressing the relative displacements at the expansion joints without introducing a significant increase in ductility demands for the substructures. The result also showed that the spring component of the Kelvin and Maxwell models has little effect on the performance of the damper component. This study clearly indicated that the use of linear viscous dampers offers a practical solution to the seismic problem that often arises from bridges with expansion joints.     

Bond strengths of resin-to-metal bonding systems

STATEMENT OF PROBLEM: Resinous materials for the veneers of fixed prostheses commonly require mechanical retention on metal substructures because there is no chemical adhesion. However, mechanical retention does not restrict creation of a marginal gap at the resin-metal interface, which can cause discoloration or detachment of resinous material. The development of a chemical resin-to-metal bonding could resolve this problem and also reduce the need for mechanical retention (pearls, wires) on metal frameworks. PURPOSE: This study evaluated six current methods with the use of various storage conditions to predict clinical efficacy. MATERIAL AND METHODS: Six resin-to-metal bonding systems were tested: Silicoater, Silicoater MD, Rocatec, OVS, Sebond, and Spectra-Link. All specimens were examined in bending tests after 24 hours of dry storage (category A), after 24 hours of water storage and thermocycling (category B), and after 2 months of water storage and thermocycling (category C). Tensional tests were completed for all bonding systems after dry storage, and microscopic examination (optical and SEM) was performed for all specimens. RESULTS AND CONCLUSIONS: This study indicated that certain systems can provide stable bonding of resin to metal substructures despite prolonged wet storage and intensive thermocycling. These systems can also be used clinically without retentive configurations on metal frameworks, resulting in better esthetics. Some bonding systems revealed progressive weakening of bond strengths, so research is needed to verify their clinical efficacy.     

Analytical Solution for Plane Trusses with Equidistant Supports

The type of plane truss considered in this paper is the continuous Warren truss resting on equidistant roller supports, subjected to transverse nodal loads. In order to uncouple the governing equation, we need to replace the original structure, which does not possess cyclic periodicity, by an equivalent system that is cyclic biperiodic. By applying the U-transformation twice, the governing equation for the equivalent system can be uncoupled and become a set of single degree of freedom equations, which leads to the explicit form solution for the supporting reaction and nodal displacement. The expressions of the solution include two numbers of substructures and supports. As an example, a Warren truss with six substructures and four supports subjected to a concentrated load acting at its center node in the symmetric line of the original structure is worked out by means of the formulas obtained in the present study. It is shown that the result is exact.     

Parallel Computing Framework for Optimizing Construction Planning in Large-Scale Projects

Available construction optimization models can be used to generate optimal tradeoffs between construction time and cost, however their application in optimizing large-scale projects is limited due to their extensive and impractical computational time requirements. This paper presents the development of a parallel computing framework in order to circumvent this limitation. The framework incorporates a multi-objective genetic algorithm module that identifies optimal trade-offs between construction time and cost; and a parallel computing module that distributes genetic algorithm computations over a network of processors. The performance of the framework is evaluated using 150 experiments that represent various combinations of project sizes and numbers of processors. The results of this analysis illustrate the robust capabilities of the developed parallel computing framework in terms of its efficiency in reducing the computational time requirements for large-scale construction optimization problems, and its effectiveness in obtaining high quality solutions identical to those generated by a single processor.     

Axisymmetric Deformation of a Pressurized Thin Elastic Membrane with Nonuniform Thickness

Many circular elastic membranes used in practice involve nonuniform thickness, which is a main source of error that affects the functionality of the membrane. An analytical framework is developed in this paper to solve the deflection profile of a pressurized circular membrane with nonuniform thickness. The nonlinear solution is established within the deformed configuration. The results are compared with finite-element simulation with good agreement.     

Aberrant temporal patterning of slow-wave sleep in siblings of SIDS victims

Most economic studies of picture archiving and communication systems (PACS) to date, including our own, have focused on the perspectives of the radiology department and its direct costs. However, many researchers have suggested additional cost savings that may accrue to the medical center as a whole through increased operational capacity, fewer lost images, rapid simultaneous access to images, and other decreases in resource utilization. We describe here an economic analysis framework we have developed to estimate these potential additional savings. Our framework is comprised of two parallel measurement methods. The first method estimates the cost of care actually delivered through online capture of charge entries from the hospital's billing computer and from the clinical practices' billing database. Multiple regression analyses will be used to model cost of care, length of stay, and other estimates of resource utilization. The second method is the observational measurement of actual resource utilization, such as technologist time, frequency and duration of film searches, and equipment utilization rates. The costs associated with changes in resource use will be estimated using wage rates and other standard economic methods. Our working hypothesis is that after controlling for the underlying clinical and demographic differences among patients, patients imaged using a PACS will have shorter lengths of stay, shorter exam performance times, and decreased costs of care. We expect the results of our analysis to explain and resolve some of the conflicting views of the cost-effectiveness of PACS.     

Buckling and Vibration Analysis of Laminated Panels Using VICONOPT

The analysis aspects of the 23,000‐line FORTRAN program VICONOPT are described. Overall stiffness matrices assembled from the earlier exact VIPASA flat plate stiffnesses are optionally coupled by Lagrangian multipliers to find critical buckling loads, or natural frequencies of undamped vibration, of prismatic assemblies of anisotropic flat plates with arbitrarily located point supports or simple transverse supporting frames. The longitudinal continuity of typical wing and fuselage panels is closely approximated because the solutions are for the infinitely long structure obtained by repeating a bay and its supports longitudinally. Any longitudinally invariant in‐plane plate stresses are permitted, and very rapid solutions are guaranteed by numerous refinements, including multilevel substructuring and a method for repetitive cross sections that is exact for regular polygons used to represent cylinders. Modal displacements and stresses in or between plies of laminated plates are calculated and plotted, with values being recovered at all nodes of substructures. Comparison with usual approximate finite‐element methods confirms that, for comparably converged solutions, VICONOPT is typically between 100 and 104 times faster.     

Effect of dislocation trapping on deuterium diffusion in deformed, single-crystal Pd

Small-angle neutron scattering (SANS) has been used to characterize deuterium trapping at dislocations in deformed, single-crystal Pd during in situ gas evolution experiments. Two methods of deformation were employed—cold rolling and hydride cycling—which create different dislocation arrangements or substructures in Pd. The reduction of the trapped deuterium concentration at dislocations during evolution was directly monitored with SANS. Exponential decay rates of the trapped concentration were observed for both sample types, as is expected in a bulk diffusion process modified by the dislocation trapping interaction. The deuterium concentration reduction proceeded 1.2 to 1.4 times faster in the cold-rolled sample material than in the cycled material. This is attributed to the presence of a smaller number of dislocation trapping sites in the cold-rolled material. The binding energy of deuterium at dislocations was determined by applying a diffusion-based model. A binding energy of 0.20 eV was found to characterize the trapping interaction in both cold-rolled and hydride-cycled Pd.     

Ag-Au-Pd合金键合引线中银的测定

Ag-Au-Pd合金键合引线主要用于功率芯片和组件的键合连接线。应用最多的是LED发光组件的连接。银是Ag-Au-Pd合金键合引线中的主要元素。根据实际使用要求,银含量直接影响质量、成品率和生产成本。目前国内外尚无简便准确的Ag-Au-Pd合金键合引线中银的测定方法。本文研究了用电位滴定法测定键合合金引线中质量分数为10%~90%的银。采用氯化银沉淀分离,在硫酸及硫酸铵介质中,以氯化钠标准滴定溶液,选用银复合电极,在电位滴定仪上滴定至电位突跃最大的滴定终点,经计算得到Ag-Au-Pd合金键合引线中银的准确含量。采用本方法对Ag-Au-Pd合金键合引线中的银进行8次平行的测定,相对标准偏差(RSD)在0.14%、加标回收率在95%~100.01%之间。此方法精密度好、准确度高,解决了以往直接滴定法、指示剂滴定法、火试金法及仪器测定法中诸多干扰因素的影响。为Ag-Au-Pd合金键合引线中银的含量测定提供简便精准的测量方法。     

Effect of two obturation techniques on the filling of lateral canals and the main canal

The three-dimensional obturation of the root canal system is widely accepted as a key factor for successful endodontic therapy. The purpose of this study was to evaluate the obturation of lateral canals and the main canal using cold lateral condensation versus the gutta-percha coated rigid carrier. Thirty epoxy blocks with five lateral canals placed at varying angles from the main canal were used. Each experimental group was obturated by a board certified endodontist with clinical experience in the respective obturation technique. The length of gutta-percha and sealer in the lateral canals was measured under a microscope (x30, Unitron) to the nearest 0.5 mm. The blocks were sectioned with an Isomet Plus precision saw (Buehler, Lake Bluff, IL) and copious water irrigation perpendicular to the main canal at the apex, the height of contour, and at 0.8, 1.6 and 2.4 mm from the canal apex. A microscope (x100, Leitz, Switzerland) was used to determine voids. There was significantly (p < .001) more gutta-percha in the lateral canals with the gutta-percha coated rigid carrier technique. In contrast, the cold lateral condensation technique had significantly (p < .001) more sealer in the lateral canals. However, there was no significant (p < .05) difference, in gutta-percha-plus-sealer filling of the lateral canals, between the two techniques. In the apical 1 mm of the main canal there were significantly (p < .011) fewer voids with the gutta-percha coated rigid carrier technique compared to the cold lateral condensation. In the model chosen, the gutta-percha coated rigid carrier technique and the cold lateral condensation technique were equally effective in filling lateral canals. In filling the main canal, however, the coated rigid carrier technique was more effective.     

Calculation of weld metal composition change in high-power conduction mode carbon dioxide laser-welded stainless steels

The use of high-power density laser beam for welding of many important alloys often leads to appreciable changes in the composition and properties of the weld metal. The main difficulties in the estimation of laser-induced vaporization rates and the resulting composition changes are the determination of the vapor condensation rates and the incorporation of the effect of the welding plasma in suppressing vaporization rates. In this article, a model is presented to predict the weld metal composition change during laser welding. The velocity and temperature fields in the weld pool are simulated through numerical solution of the Navier-Stokes equation and the equation of conservation of energy. The computed temperature fields are coupled with ve-locity distribution functions of the vapor molecules and the equations of conservation of mass, momentum, and the translational kinetic energy in the gas phase for the calculation of the evap-oration and the condensation rates. Results of carefully controlled physical modeling experi-ments are utilized to include the effect of plasma on the metal vaporization rate. The predicted area of cross section and the rates of vaporization are then used to compute the resulting com-position change. The calculated vaporization rates and the weld metal composition change for the welding of high-manganese 201 stainless steels are found to be in fair agreement with the corresponding experimental results.     

Substructural Identification Method without Interface Measurement

Substructural identification provides a novel means by which to reduce a large problem to smaller problems of manageable size, thereby improving numerical convergence and accuracy. Various methods proposed by several researchers thus far require interface response measurements, which are then treated as input to the substructures of concern. In practice, however, it is not always possible to obtain interface measurements, particularly if rotational response is required for beam/frame structures. In this paper, a method for parameter identification of substructures without the need of interface measurements is proposed. On the basis of receptance theory, an inverse problem is formulated in the frequency domain. Interface forces are eliminated by using different sets of measurements in the substructure concerned under the same dynamic excitation. The genetic algorithms approach is employed to determine the unknown parameters, and the fitness function is defined to minimize the difference between the estimates of interface forces obtained using different sets of response measurements. Three numerical examples are presented to illustrate the proposed method, and account for effects of measurement noise.     

Electroconvulsive therapy: a guide for family physicians

Electroconvulsive therapy, which works by creating a generalized seizure, is used most frequently to treat medication-resistant depression. Other indications for electroconvulsive therapy includes severe depression with suicidal ideation, acute mania and severe psychiatric illness with food and fluid refusal. Electroconvulsive therapy may be administered as an inpatient or outpatient procedure. Treatments are usually administered three times a week for six to 12 treatments. Before this therapy is used, a thorough medical and anesthetic history should be obtained, and a complete physical examination, an electrocardiogram and appropriate laboratory studies should be performed to rule out anemia, electrolyte imbalances, and cardiopulmonary and neurologic risk factors. Heart rate and rhythm, oxygenation, blood pressure and, often, the electroencephalogram are monitored continuously while the patient is anesthetized with a short-acting hypnotic agent and a muscle depolarizing agent. After electroconvulsive therapy, antidepressant or lithium therapy significantly reduces the symptom relapse rate.     

Local Time Stepping for Modeling Open Channel Flows

This paper presents two time accurate local time stepping (LTS) algorithms developed within aeronautics and develops the techniques for application to the Saint-Venant equations of open channel flow. The LTS strategies are implemented within an explicit finite volume framework based on using the Roe Riemann solver together with an upwind treatment for the source terms. The benefits of using an LTS approach over more traditional global time stepping methods are illustrated through a series of test cases, and a comparison is made between the two LTS algorithms. The results demonstrate how local time stepping can reduce computer run times, increase the reliability of the error control, and also increase the accuracy of the solution in certain regions.     

Parallel Genetic Algorithms for Optimizing Resource Utilization in Large-Scale Construction Projects

This paper presents the development of a parallel multiobjective genetic algorithm framework to enable an efficient and effective optimization of resource utilization in large-scale construction projects. The framework incorporates a multiobjective optimization module, a global parallel genetic algorithm module, a coarse-grained parallel genetic algorithm module, and a performance evaluation module. The framework is implemented on a cluster of 50 parallel processors and its performance was evaluated using 183 experiments that tested various combinations of construction project sizes, numbers of parallel processors and genetic algorithm setups. The results of these experiments illustrate the new and unique capabilities of the developed parallel genetic algorithm framework in: (1) Enabling an efficient and effective optimization of large-scale construction projects; (2) achieving significant computational time savings by distributing the genetic algorithm computations over a cluster of parallel processors; and (3) requiring a limited and feasible number of parallel processors/computers that can be readily available in construction engineering and management offices.     

Electrostatically balanced subnanometer imaging of biological specimens by atomic force microscope

To achieve high-resolution topographs of native biological macromolecules in aqueous solution with the atomic force microscope (AFM) interactions between AFM tip and sample need to be considered. Short-range forces produce the submolecular information of high-resolution topographs. In contrast, no significant high-resolution information is provided by the long-range electrostatic double-layer force. However, this force can be adjusted by pH and electrolytes to distribute the force applied to the AFM tip over a large sample area. As demonstrated on fragile biological samples, adjustment of the electrolyte solution results in a local reduction of both vertical and lateral forces between the AFM tip and proteinous substructures. Under such electrostatically balanced conditions, the deformation of the native protein is minimized and the sample surface can be reproducibly contoured at a lateral resolution of 0.6 nm.     

High-Performance Computing for Large-Scale Analysis, Optimization, and Control

Research papers published on parallel processing, supercomputing, and distributed computing since 1994 are reviewed in this article. The focus is on review of the archival journal articles published in three areas: analysis, optimization, and control. The review is divided into three main sections: (1) parallel processing on dedicated shared memory and distributed memory parallel machines; (2) distributed computing on a cluster of networked workstations; and (3) parallel computing and object-oriented programming. The great majority of the journal articles published since 1987 deal with fundamental issues and academic problems. The trend in the future, at least in part, should be more toward solution of large-scale and complicated real-life engineering problems, the kind of problems that cannot be solved readily by conventional uniprocessor computers.     

Stochastic Analysis of Internal Erosion in Soil Structures—Implications for Risk Assessments

A new modeling framework for internal erosion in heterogeneous stratified soils is developed by combining existing methods used to study sediment transport in canals, filtration phenomena, and stochastic processes. The framework is used to study the erosion process in sediments caused by a flow of water through a covering filter layer that deviates from geometrical filter rules. By the use of spectral analysis and Laplace transforms, mean value solutions to the transport rate and the variance about the mean are derived for a transport constraint at the upstream boundary and a constant initial transport. Increasing the heterogeneity of a defective filter layer in a canal retards the propagation of the expected bed degradation. An implication is that the heterogeneity of the riprap in this respect prolongs the expected degradation process and the expected lifespan of the structure. The increased variance and decreased correlation length of the riprap reduces the confidence of the mean value solution. The stochastic analysis is therefore suitable as part of risk analyses of extreme events such as failure of embankment dams, for which empirical observations are rare.