bluuebunny/crossref_metadata_2025 huggingface dataset:
Oxidation induces a Cl−‐dependent cation conductance in human red blood cells
Authors: Duranton Christophe , Huber Stephan M. , Lang Florian
Published: July 2002

Oxidative stress induces complex alterations of membrane proteins in red blood cells (RBCs) eventually leading to haemolysis. To study changes of membrane ion permeability induced by oxidative stress, whole‐cell patch‐clamp recordings and haemolysis experiments were performed in control and oxidised human RBCs. Control RBCs exhibited a small cation‐selective whole‐cell conductance (236 ± 38 pS; n= 8) which was highly sensitive to the external Cl− concentration: replacement of NaCl in the bath by sodium gluconate induced an increase of this cation conductance by about 85 %. Exposing RBCs to t‐butylhydroxyperoxide (1 mm for 10 min) induced a twofold increase in this cation conductance which was further stimulated after replacement of extracellular Cl− by gluconate, Br−, I− or SCN−. In addition, lowering the ionic strength of the bath solution by isosmotic substitution of NaCl by sorbitol activated the cation conductance. The Cl−‐sensitive and oxidation‐induced cation conductance was Ca2+ permeable, exhibited a permselectivity of Cs+ > K+ > Na+= Li+ >> NMDG+, and was partially inhibited by amiloride (1 mm) and almost completely inhibited by GdCl3 (150 μm), but was insensitive to TEA, BaCl2, NPPB, flufenamic acid or quinidine. DIDS (100 μm) reversibly inhibited the activation of the cation conductance by removal of external Cl−. Oxidation induced haemolysis in NaCl‐bathed human RBCs. This haemolysis was attenuated by amiloride (1 mm) and inhibited by replacement of bath Na+ by the impermeant cation NMDG+. The Na+‐ and Ca2+‐permeable conductance might be involved in haemolytic diseases induced by elevated oxidative stress, such as glucose‐6‐phosphate dehydrogenase deficiency.
NC Verification of Up to 5 Axis Machining Processes Using Manifold Stratification
Authors: Abdel-Malek Karim , Seaman Walter , Yeh Harn-Jou
Published: July 2002

A numerically controlled machining verification method is developed based on a formulation for delineating the volume generated by the motion of a cutting tool on the workpiece (stock). Varieties and subvarieties that are subsets of some Eucledian space defined by the zeros of a finite number of analytic functions are computed and are characterized as closed form equations of surface patches of this volume. The motion of a cutter tool is modeled as a surface undergoing a sweep operation along another geometric entity. A topological space describing the swept volume will be built as a stratified space with corners. Singularities of the variety are loci of points where the Jacobian of the manifold has lower rank than maximal. It is shown that varieties appearing inside the manifold representing the removed material are due to a lower degree strata of the Jacobian. Some of the varieties are complicated and will be shown to be reducible because of their parametrization and are addressed. Benefits of this method are evident in its ability to depict the manifold and to compute a value for the volume.
Biaxial Mechanical Properties of the Native and Glutaraldehyde-Treated Aortic Valve Cusp: Part II—A Structural Constitutive Model
Authors: Billiar Kristen L. , Sacks Michael S.
Published: July 2002

We have formulated the first constitutive model to describe the complete measured planar biaxial stress–strain relationship of the native and glutaraldehyde-treated aortic valve cusp using a structurally guided approach. When applied to native, zero-pressure fixed, and low-pressure fixed cusps, only three parameters were needed to simulate fully the highly anisotropic, and nonlinear in-plane biaxial mechanical behavior. Differences in the behavior of the native and zero- and low-pressure fixed cusps were found to be primarily due to changes in the effective fiber stress–strain behavior. Further, the model was able to account for the effects of small <10deg misalignments in the cuspal specimens with respect to the biaxial test axes that increased the accuracy of the model material parameters. Although based upon a simplified cuspal structure, the model underscored the role of the angular orientation of the fibers that completely accounted for extreme mechanical anisotropy and pronounced axial coupling. Knowledge of the mechanics of the aortic cusp derived from this model may aid in the understanding of fatigue damage in bioprosthetic heart valves and, potentially, lay the groundwork for the design of tissue-engineered scaffolds for replacement heart valves. [S0148-0731(00)00504-5]
Mixed Exact-Approximate Position Synthesis of Planar Mechanisms
Authors: Holte Jennifer E. , Chase Thomas R. , Erdman Arthur G.
Published: July 2002

A new approach to the synthesis of planar linkage mechanisms with fuzzy constraints is proposed. Design methods for two exact positions and an unlimited number of approximate positions are presented. The use of approximate specifications allows the designer to represent design objectives more realistically. A precision position synthesis approach is used to generate a three-dimensional solution space of dyads satisfying all exact and approximate constraints. The three-dimensional solution space is reduced to a two-dimensional ground-pivot map. Computer implementation of the proposed methodologies would allow designers with little or no knowledge of the synthesis techniques to interactively explore maps of solutions for four-bar motion generation. [S1050-0472(00)00803-5]
Pool Boiling Heat Transfer From Plain and Microporous, Square Pin-Finned Surfaces in Saturated FC-72
Authors: Rainey K. N. , You S. M.
Published: July 2002

The present research is an experimental study of “double enhancement” behavior in pool boiling from heater surfaces simulating microelectronic devices immersed in saturated FC-72 at atmospheric pressure. The term “double enhancement” refers to the combination of two different enhancement techniques: a large-scale area enhancement (square pin fin array) and a small-scale surface enhancement (microporous coating). Fin lengths were varied from 0 (flat surface) to 8 mm. Effects of this double enhancement technique on critical heat flux (CHF) and nucleate boiling heat transfer in the horizontal orientation (fins are vertical) are investigated. Results showed significant increases in nucleate boiling heat transfer coefficients with the application of the microporous coating to the heater surfaces. CHF was found to be relatively insensitive to surface microstructure for the finned surfaces except in the case of the surface with 8-mm-long fins. The nucleate boiling and CHF behavior has been found to be the result of multiple, counteracting mechanisms: surface area enhancement, fin efficiency, surface microstructure (active nucleation site density), vapor bubble departure resistance, and re-wetting liquid flow resistance. [S0022-1481(00)02603-7]
Structure, Mechanics and Failure of Stochastic Fibrous Networks: Part II—Network Simulations and Application
Authors: Wang C. W. , Sastry A. M.
Published: July 2002

Applications for porous fibrous materials range from electrochemical substrates to web reinforcement in polymeric composite materials. The details of local load transfer are studied in a class of cost-effective, stochastic fibrous networks used in battery applications. The connectivity of these materials is quantitatively related to modulus and strength, and detailed results of different simulations approaches in approximating material construction are discussed. In Part II, we focus on the consequences of various microscale assumptions concerning bonding, beam type, failure mode and simulation scale on effective moduli and peak loads. We show that the effects of scale are important even in a tight range of window sizes (one-tenth to ten times the staple length), especially as compared to the relative insensitivity of conductivity to scale, when only bulk conduction is considered. We also discuss issues of connectivity at the scale of the porous material rather than element-by-element. This work points toward use of simple constructions to model complex behavior, and may ultimately provide insight into modeling of a large class of porous materials. [S0094-4289(00)01604-2]
Transition of Refrigeration Thermodynamic Analysis From Component to a Radar Power System
Authors: Ramalingam Mysore , Donovan Brian , Beam Jerry E.
Published: July 2002

Preliminary feasibility studies based on breakeven refrigeration thermodynamics, have been conducted for candidate power conditioning components in a transportable radar power system (Donovan, B.D. et al., 1995 “Effects of Refrigeration in a Transportable Cryogenic Aerospace Application,” Proc. 30th IECEC, Vol. 1, pp. 473–478; Ramalingam, M. et al., 1996 “Systems Analysis for a Cryogenic Aerospace Terrestrial Radar Power System,” Proc. 31st IECEC, Vol. 1). The analysis based on breakeven refrigeration thermodynamics revealed that in the case of a general switching device such as a power MOSFET, it would be more beneficial to operate it at 150 to 220 K, using a Stirling cycle-based cryocooler. The overall system efficiency was jeopardized by way of large input power requirements to cool small heat loads at lower temperatures, while the performance of the device itself suffered at higher temperatures. The break-even refrigeration thermodynamic analysis was also applied to multilayer ceramic capacitors at cryogenic temperatures. It was found that in order to avoid a power penalty for cooling the capacitor to 77 K, the cryocooled equivalent series resistance (ESR) value would have to be a factor of 40 lower than that of a conventional capacitor ESR value if using a Gifford-McMahon (GM) cooling cycle. A factor of 12 better improvement in ESR is required for a yet-to-be-developed more efficient Stirling cycle. In this paper, this break-even thermodynamic analytical concept was then partially extended from the component level to the radar power system level. The entire power system was sized based on several combinations of cryocooled generators, power conditioning, and antenna equipment. The analysis revealed that even though the radar output could potentially be increased two-to threefold by the introduction of cryocooled technologies, the sizes of the coolers begin to negate these advantages. Several power systems were evaluated with reference to a common figure-of-merit to arrive at an optimum configuration. [S0195-0738(00)00803-7]
Effect of Shaft Flexibility on Control System Parameters
Authors: Diken H.
Published: July 2002

A dynamic system consisting of a servomotor, elastic shaft and inertial load, which may represent a disk or a robot arm, is chosen as an elastic control system. Equations of the torsional vibratory system are coupled with the servomotor control system equations and the transfer function of the elastic control system relating output angle to the desired input angle is obtained including not only control parameters but also the structural natural frequency and the structural damping of the torsional vibratory system. The ratio of the structural natural frequency to the substructural natural frequency and the ratio of substructural natural frequency to the control system frequency are defined as nondimensional parameters. System behavior is analyzed with respect to these parameters. The fourth order elastic control system transfer function is also reduced to the second order one and formulas for elastic control system frequency and damping are developed with respect to these parameters. [S0739-3717(00)70104-8]
Pool Boiling Heat Transfer in Aqueous Solutions of an Anionic Surfactant
Authors: Wasekar V. M. , Manglik R. M.
Published: July 2002

Saturated nucleate pool boiling of aqueous surfactant solutions on a horizontal cylindrical heater has been experimentally investigated. Sodium dodecyl or lauryl sulfate (SDS or SLS), an anionic surfactant, is employed. Boiling performance, relative to that for pure water, is found to be enhanced significantly by the presence of SDS, with an early onset of nucleate boiling. An optimum level of enhancement is observed in solutions at or near critical micelle concentration of the surfactant; the enhancement, however, decreases considerably in higher concentration solutions. The dynamic surface tension measurements indicate a substantial influence of temperature on the overall adsorption isotherm. The diffusion kinetics of surfactant molecules and micelles is, therefore, expected to be quite different at boiling temperature than at room temperature. This greatly modifies the boiling mechanism that is generally characterized by the formation of smaller-size bubbles with increased departure frequencies, and a decreased tendency to coalesce which causes considerable foaming. [S0022-1481(00)00704-0]
Robust Discrete-Time Variable Structure Control Methods
Authors: Kim Jung-ho , Oh Seung-Hyun , Cho Dong-il “Dan” , Hedrick J. Karl
Published: July 2002

The invariance and robustness properties of variable structure control are lost in digital implementation. This paper presents three discrete-time variable structure control (DVSC) methods that can recover those properties for linear uncertain systems. The first method uses a disturbance compensator formulated in the variable structure framework and a decoupling law to separate the disturbance estimation dynamics from the closed loop dynamics. In the second approach, a recursive switching function is developed, which allows recovering the lost invariance and robustness properties, without using the disturbance compensator. The first method can result in slow transient dynamics, and the second can result in a large overshoot. In the third method, a new recursive switching function is developed and combined with the decoupled disturbance compensator method to recover the lost invariance and robustness properties. The three DVSC methods are applied to control the motion of an xy-stage of a CNC milling machine. In this experiment, the third method provided the best result. [S0022-0434(00)02204-8]
Eliminating the Reaching Phase From Variable Structure Control
Authors: Yilmaz Cuneyt , Hurmuzlu Yildirim
Published: July 2002

In this paper, we present a variable structure control method that eliminates the reaching phase. The approach is based on modifying the sliding domain equations through the use of exponential functions. In addition, the proposed method insures optimal convergence parameters with respect to the tracking errors and control effort. [S0022-0434(00)02504-1]
Sub-Continuum Simulations of Heat Conduction in Silicon-on-Insulator Transistors
Authors: Sverdrup Per G. , Sungtaek Ju Y. , Goodson Kenneth E.
Published: July 2002

The temperature rise in sub-micrometer silicon devices is predicted at present by solving the heat diffusion equation based on the Fourier law. The accuracy of this approach needs to be carefully examined for semiconductor devices in which the channel length is comparable with or smaller than the phonon mean free path. The phonon mean free path in silicon at room temperature is near 300 nm and exceeds the channel length of contemporary transistors. This work numerically integrates the two-dimensional phonon Boltzmann transport equation (BTE) within the silicon region of a silicon-on-insulator (SOI) transistor. The BTE is solved together with the classical heat diffusion equation in the silicon dioxide layer beneath the transistor. The predicted peak temperature rise is nearly 160 percent larger than a prediction using the heat diffusion equation for the entire domain. The disparity results both from phonon-boundary scattering and from the small dimensions of the region of strongest electron-phonon energy transfer. This work clearly shows the importance of sub-continuum heat conduction in modern transistors and will facilitate the development of simpler calculation strategies, which are appropriate for commercial device simulators.
Evaluation Procedures for Irradiation Effects and Sodium Environmental Effects for the Structural Design of Japanese Fast Breeder Reactors
Authors: Asayama Tai , Abe Yasuhiro , Miyaji Noriko , Koi Mamoru , Furukawa Tomohiro , Yoshida Eiichi
Published: July 2002

In the structural design of fast breeder reactors, irradiation effects and sodium environmental effects on structural materials have to be taken into account. In this paper, firstly, an evaluation procedure for irradiation effects on the mechanical properties of 316FR (FBR Grade 316 stainless steel), which is a newly developed stainless steel for the Japanese demonstration fast breeder reactor, is proposed. The procedure gives a limit of accumulated fast neutron fluence E>0.1 MeV as a function of temperature, so that the minimum tensile fracture elongation of 10 percent, which is the threshold for material to stay ductile, is maintained. Furthermore, the procedure determined a creep life reduction factor and a creep rate increase factor as a function of accumulated thermal neutron fluence E<0.4 eV, within the limitation of the accumulated fast neutron fluence, to account for the creep life reduction and the increase of creep rate due to irradiation. Secondly, an evaluation procedure for sodium environmental effects on the integrity of 316FR and modified 9Cr-1Mo steel was proposed. It gave a corrosion allowance as a function of temperature, oxygen content, and service time, based on corrosion tests. It determined that no correction factors that correspond to sodium environment on design allowable stresses, etc., are needed, because no adverse effects of sodium on the mechanical properties of 316FR and modified 9Cr-1Mo steel were to be expected in the service conditions of FBRs. Both the procedures have been incorporated into the Japanese Elevated Temperature Structural Design Guide for Demonstration Fast Breeder Reactor.
Forced Convection Board Level Thermal Design Methodology for Electronic Systems
Authors: Cole Reena , Dalton Tara , Punch Jeff , Davies Mark R. , Grimes Ronan
Published: July 2002

The case is made for the continued use of single valued thermal resistances for the prediction of component junction temperature, and, hence, reliability. These values are adjusted using empirically determined influence factors to account for thermal and aerodynamic interactions at board level. The paper presents measured values of influence factors for arrays of Plastic Quad Flat Packs (PQFPs) over a range of Reynolds numbers and with a series of board level obstacles modeling upstream passive components. The results are formulated into a novel set of design rules.
Nonlinear State Estimation by Adaptive Embedded RBF Modules
Authors: Gan Chengyu , Danai Kourosh
Published: July 2002

A modeling compensation method is introduced to enhance the performance of the extended Kalman filter (EKF) in coping with the uncertainty of estimation model. In this method, single-input single-output radial basis function (RBF) modules are embedded within the nonlinear estimation model to provide additional degrees of freedom for model adaptation. The weights of the embedded RBF modules are adapted by the EKF, concurrent with state estimation. This compensation method is tested in application to a benchmark problem. Simulation results indicate that the RBF modules provide the means to model the uncertain components of the estimation model within their range of variation.
A Discourse on Geometric Feature Recognition From CAD Models
Authors: Shah Jami J. , Anderson David , Kim Yong Se , Joshi Sanjay
Published: July 2002

This paper discusses the past 25 years of research in feature recognition. Although a great variety of feature recognition techniques have been developed, the discussion here focuses on the more successful ones. These include graph based and “hint” based methods, convex hull decomposition, and volume decomposition-recomposition techniques. Recent advances in recognizing features with free form features are also presented. In order to benchmark these methods, a frame of reference is created based on topological generality, feature interactions handled, surface geometry supported, pattern matching criteria used, and computational complexity. This framework is used to compare each of the recognition techniques. Problems related to domain dependence and multiple interpretations are also addressed. Finally, some current research challenges are discussed.
Fatigue Lifetimes of PBGA Solder Joints Reflowed at Different Conveyor Speeds
Authors: Fan S. H. , Chan Y. C. , Lai J. K. L.
Published: July 2002

The shear cycle fatigue lifetimes of plastic ball grid array (PBGA) solder joints formed using different reflow profiles are studied in this paper. The profiles were devised to have the same “heating factor” but to have different conveyor speeds. The test results show that, by increasing the conveyor speed during reflow, the shear fatigue lifetime of solder joints can be improved substantially. On the other hand, the fatigue lifetime of the test specimens decreased with increasing the cycle displacement amplitude. Heat transmission analysis shows that increasing conveyor speed increases the cooling rate during solder solidification. SEM micrographs reveal that cracks initiated at the acute point near the PCB solder pad, then propagate along the interface of the bulk solder/IMC layer. The test results are ascribed to roughing interface of the bulk solder/IMC of the solder joints that results on increasing the cooling rate. The frictional sliding mechanism is used to explain the test results.
Interfacial Delamination Near Solder Bumps and UBM in Flip-Chip Packages
Authors: Gu Yu , Nakamura Toshio , Chen William T. , Cotterell Brian
Published: July 2002

Using detailed finite element models, a fracture analysis of solder bumps and under bump metallurgy (UBM) in flip-chip packages is carried out. Our objective is to identify likely fracture modes and potential delamination sites at or near these microstructural components. In order to study flip-chips, whose dimension spans from sub-micron thickness UBM layers to several millimeters wide package, we have applied a multi-scale finite element analysis (MS-FEA) procedure. In this procedure, initially, deformation of whole thermally loaded package is analyzed. Then, the results are prescribed as the boundary conditions in a very detailed cell model, containing a single solder bump, to investigate micro-deformation surrounding UBM. Using the models with two different scales, accurate stress fields as well as fracture parameters of various interface cracks can be determined. The MS-FEA is ideally suited for the flip-chip packages since they contain many identical solder bumps. A cell model can be repeatedly used to probe stress and fracture behaviors at different locations. The computed results show high stress concentrations near the corners of solder bumps and UBM layers. Based on the energy release rate calculations, solder bumps located near the edge of chip are more likely to fail. However, our results also suggest possible delamination growth at solder bumps near the center of chip. In addition, we have observed increasing energy release rates for longer cracks, which implies a possibility of unstable crack growth.
Feedback Stability Limits for Active Isolation Systems with Reactive and Inertial Actuators
Authors: Elliott S. J. , Serrand M. , Gardonio P.
Published: July 2002

Some of the compromises inherent in using a passive system to isolate delicate equipment from base vibration can be avoided using fully active skyhook damping. Ideally, a secondary force, which is made proportional to the absolute equipment velocity by a feedback controller, acts only on the equipment and so the response of the system under control, between the secondary force input and the collocated velocity output, i.e., the plant response, is proportional to the driving point mobility of the mounted equipment. The frequency response of the plant is guaranteed to have a positive real part under these ideal conditions, and so the feedback system is unconditionally stable for any positive real feedback gain. In practice, the actuator generating the secondary force must either react off the base structure or an inertial mass. In both of these cases the plant response is no longer guaranteed to be positive real and so the control system may become unstable at high gains. Expressions for the overall plant responses are derived for both of these arrangements, in terms of the dynamic response of the individual parts of the isolation system. When using a soft mount, the stability of the reactive system is found to be surprisingly tolerant of the additional contributions to the plant response from the reactive force. In order for the inertial system to be stable with a high feedback gain, however, the natural frequency of the actuator must be well below the natural frequency of the equipment on the mounts. Experimentally measured plant responses are compared with those predicted from theory for both types of actuator and the performance of practically implemented feedback controllers is discussed.
On the Application of Kinematic Units to the Topological Analysis of Geared Mechanisms
Authors: Liu Chia-Pin , Chen Dar-Zen
Published: July 2002

Based on the concept of kinematic fractionation, a systematic method for the topological analysis of geared mechanisms is presented in this paper. It is shown that a geared kinematic chain (GKC) can be regarded as a combination of kinematic unit(s). By identifying the embedded kinematic units, kinematic insight in the GKC can be exposed. The disclosed information leads to straightforward and promising rules to prevent redundant links. These rules form the basis of a by-inspection procedure to determine admissible assignments of the ground, input and output links in a GKC. Admissible assignments of the ground, input and output links of one degree-of-freedom 5 link GKCs are determined as an illustrative example.
Fatigue Crack Growth Curve for Austenitic Stainless Steels in BWR Environment
Authors: Itatani M. , Asano M. , Kikuchi M. , Suzuki S. , Iida, K.
Published: July 2002

Fatigue crack growth data obtained in the simulated BWR water environment were analyzed to establish a formula for reference fatigue crack growth rate (FCGR) of austenitic stainless steels in BWR water. The effects of material, mechanical and environmental factors were taken into the reference curve, which was expressed as: da/dN=8.17×10−12s˙Tr0.5s˙ΔK3.0/1−R2.121≦ΔK≦50 MPam where da/dN is fatigue crack growth rate in m/cycle, Tr is load rising time in seconds, ΔK is range (double amplitude) of K–value in MPam, and R is stress ratio. Tr=1 s if Tr<1 s, and Tr=1000 s if Tr cannot be defined. ΔK=Kmax−Kmin if R≧0.ΔK=Kmax if R<0.R=Kmin/Kmax. The proposed formula provides conservative FCGR at low stress ratio. Although only a few data show higher FCGR than that by proposed formula at high R, these data are located in a wide scatter range of FCGR and are regarded to be invalid. The proposed formula is going to be introduced in the Japanese Plant Operation and Maintenance Standard.
Development of Methanol Steam Reformer for Chemical Recuperation
Authors: Nakagaki T. , Ogawa T. , Murata K. , Nakata Y.
Published: July 2002

The purpose of the present work is to establish the design method of methanol steam-reformer for application to chemical recuperation in a gas turbine system. The reaction rate of the methanol steam-reforming was measured with a small amount of catalyst using the gaseous mixture of methanol, water, hydrogen, and carbon dioxide as a simulated product gas. The reaction rate equation could be expressed by power law of methanol mole fraction and total pressure. The reaction and heat transfer in the catalyst-packed bed was analyzed numerically using the reaction rate equation. The analytical results of temperature distribution and conversion were compared with the experimental results using a reforming tube. These results agreed well except for the region of high methanol conversion.
Improving the Stability of Labyrinth Gas Seals
Authors: Kwanka K.
Published: July 2002

The flow through labyrinth seals of turbomachinery generates forces which can cause self-excited vibrations of the rotor above the stability limit. The stability limit is reached at a specific rotating speed or power. The continuous growth of power density and rotating speed necessitates an exact prediction of the stability limit of turbomachinery. Usually the seal forces are described with dynamic coefficients. A new, easy-to-handle identification procedure uses the stability behavior of a flexible rotor to determine the dynamic coefficients. Systematic measurements with a great number of labyrinth seal geometries lead to reasonable results and demonstrate the accuracy and sensitivity of the procedure. A comparison of the various methods used to minimize the excitation indicates which seal is more stable and will thus improve the dynamic behavior of the rotor.
Effect of Leg Inertia on Dynamics of Sliding-Leg Hexapods
Authors: Xi Fengfeng , Sinatra Rosario , Han Wanzhi
Published: July 2002

In this paper the effect of leg inertia on hexapod dynamics is investigated. Hexapods under investigation are a new type that is made of sliding legs with constant lengths. A complete dynamic model of sliding-leg hexapods is developed including leg inertia. Based on this dynamic model, the effect of leg inertia on hexapod dynamics is investigated in terms of two parameters. The first parameter is the ratio of the total leg mass to the mass of the moving platform, and the second parameter is the acceleration of the moving platform. Numerical studies reveal that the effect of leg inertia may be negligible at low speeds, but becomes significant at high speeds. Hence, leg inertia must be included for modeling hexapod dynamics for high-speed applications.
Determination of Friction Coefficient by Employing the Ring Compression Test
Authors: Sofuoglu Hasan , Gedikli Hasan , Rasty Jahan
Published: July 2002

The main objective of this research was to investigate the effect of material properties, strain-rate sensitivity, and barreling on the behavior of friction calibration curves. The compression tests were conducted to obtain the necessary material properties for the finite element analysis. A series of ring compression tests were then conducted in order to determine the magnitude of the friction coefficient, μ. The experiments were first conducted for the modeling materials, namely, white and black plasticine and later on, for aluminum, copper, bronze, and brass. The experiments were then simulated via an elastic-plastic finite element code (ABAQUS). Contrary to the results available in the literature, where the same friction calibration curves are recommended for all types of materials and test conditions, the results of this investigation showed that friction calibration curves are indeed affected by the material properties and test conditions.
Heat Transfer in Direct Contact Condensation of Steam to Subcooled Water Spray
Authors: Takahashi Minoru , Nayak Arun Kumar , Kitagawa Shin-ichi , Murakoso Hiroyuki
Published: July 2002

The condensation heat transfer of saturated steam to a hollow-cone spray of subcooled water was investigated experimentally and analytically. The spray water temperature rose more steeply in flow direction than those in the previous studies, because of the use of smaller thermocouple which was capable of measuring the temperature in a thin water sheet and water droplets more accurately. The result of the condensation heat transfer coefficient suggested the breakup of the water sheet into droplets. A pure conduction model underpredicted the heat transfer in the sheet region significantly, which was better predicted by considering turbulence in the sheet. The heat transfer in the droplet region was well estimated by considering internal circulation and mixing inside the droplets.
Molecular Dynamics Simulation of Nanodroplet Evaporation
Authors: Walther J. H. , Koumoutsakos P.
Published: July 2002

Molecular dynamics simulations are used to study the sub-critical evaporation of a nanometer-size droplet at 300 K and 3 MPa. Classical molecular dynamics techniques are combined with an adaptive tree data structure for the construction of the neighbor lists, allowing efficient simulations using hundreds of thousands of molecules. We present a systematic convergence study of the method demonstrating its convergence for heat conduction problems in submicron scales. These high resolution simulations compute values of the evaporation coefficient that are in excellent agreement with theoretical predictions.
An Integral Formulation of Transient Radiative Transfer
Authors: Tan Z.-M. , Hsu P.-F.
Published: July 2002

A time-dependent integral formulation is developed for modeling transient radiative transfer. The development is based on a rigorous analysis of the wave propagation process inside the participating media. The physical significance of the present integral formulation is the consideration of the time-dependent domain of computation, which is different from the domain disturbed by radiation (i.e., the wave front envelope). Numerical computations are performed for the medium that is an absorbing and isotropically scattering one-dimensional plane slab geometry. The spatial and temporal incident radiation and radiative flux distributions are presented for different boundary conditions and for uniform and nonuniform property distribution. The transient results at large time step are compared with steady-state solutions by the finite volume and quadrature methods and show excellent agreement. The solutions of reflecting boundary condition exhibit distinctive behavior from that of the non-reflecting boundary.
Noninvasive Fluid Dynamic Power Loss Assessments for Total Cavopulmonary Connections Using the Viscous Dissipation Function: A Feasibility Study
Authors: Healy Timothy M. , Lucas Carol , Yoganathan Ajit P.
Published: July 2002

The total cavopulmonary connection (TCPC) has shown great promise as an effective palliation for single-ventricle congenital heart defects. However, because the procedure results in complete bypass of the right-heart, fluid dynamic power losses may play a vital role in postoperative patient success. Past research has focused on determining power losses using control volume methods. Such methods are not directly applicable clinically without highly invasive pressure measurements. This work proposes the use of the viscous dissipation function as a tool for velocity gradient based estimation of fluid dynamic power loss. To validate this technique, numerical simulations were conducted in a model of the TCPC incorporating a 13.34 mm (one caval diameter) caval offset and a steady cardiac output of 2 Ls˙min−1. Inlet flow through the superior vena cava was 40 percent of the cardiac output, while outflow through the right pulmonary artery (RPA) was varied between 30 and 70 percent, simulating different blood flow distributions to the lungs. Power losses were determined using control volume and dissipation function techniques applied to the numerical data. Differences between losses computed using these techniques ranged between 3.2 and 9.9 percent over the range of RPA outflows studied. These losses were also compared with experimental measurements from a previous study. Computed power losses slightly exceeded experimental results due to different inlet flow conditions. Although additional experimental study is necessary to establish the clinical applicability of the dissipation function, it is believed that this method, in conjunction with velocity gradient information derived from imaging modalities such as magnetic resonance imaging, can provide a noninvasive means of assessing power losses within the TCPC in vivo.
Building Integrated Photovoltaic Test Facility*
Authors: Fanney A. Hunter , Dougherty Brian P.
Published: July 2002

The widespread use of building integrated photovoltaics appears likely as a result of the continuing decline in photovoltaic manufacturing costs, the relative ease in which photovoltaics can be incorporated within the building envelope, and the fact that buildings account for over 40% of the U.S. energy consumption. However, designers, architects, installers, and consumers need more information and analysis tools in order to judge the merits of building-integrated solar photovoltaic products. In an effort to add to the knowledge base, the National Institute of Standards and Technology (NIST) has undertaken a multiple-year project to collect high quality experimental performance data. The data will be used to validate computer models for building integrated photovoltaics and, where necessary, to develop algorithms that may be incorporated within these models. This paper describes the facilities that have been constructed to assist in this effort. The facilities include a mobile tracking photovoltaic test facility, a building integrated photovoltaic test bed, an outdoor aging rack, and a meteorological station.
A New Methodology for Use in Engine Diagnostics and Control, Utilizing “Synthetic” Engine Variables: Theoretical and Experimental Results
Authors: Moskwa John J. , Wang Wenbo , Bucheger Duane J.
Published: July 2002

This paper describes new methodologies and algorithms for use in engine diagnostics that simplify and improve combustion quality monitoring and closed-loop engine control in order to meet stringent emission standards. The “synthetic” variables these algorithms produce can be used to indicate the work produced by each cylinder combustion event at all engine speeds, and can be effectively used for on-board combustion quality measurements, engine diagnostics, and closed-loop control. The algorithms are very simple in form, run in real time, and the methodologies can be applied to compression ignition or spark ignition, 2-stroke or 4-stroke gasoline or diesel engines. Both simulation and experimental results are given for a two-stroke, two-cylinder in-line engine. The rotational dynamics and firing sequence of this configuration of engine is very similar to a four-stroke, four cylinder in-line engine, and nearly identical results will be seen with these two designs. Even more dramatic improvements can be seen with engines of fewer cylinders because of greater variations in their inertial forces. The algorithms can be successfully applied to many other engine configurations as well. Therefore, benefits can be derived from the application of these algorithms and their “synthetic” variables to control strategies for almost all modern small and medium size automotive and marine engines, as well as utility engines used for lawn care, snow removal, and other similar applications.
A Haptic Assembly and Disassembly Simulation Environment and Associated Computational Load Optimization Techniques
Authors: Coutee Adam S. , McDermott Scott D. , Bras Bert
Published: July 2002

There exist a large body of work in the field of assembly, sometimes involving the use of a virtual environment to assist the user in assembly analysis. Typically, these environments limit the user’s interaction with the environment to one sense, sight, and two dimensions, the table upon which the mouse rests. The introduction of a haptic interface into the computer-aided design environment allows users to incorporate both a third dimension and a second sense, that of touch, into their work. In this paper, the development of an application called HIDRA (Haptic Integrated Dis/Re-assembly Analysis) is discussed, which integrates haptic feedback into an assembly/disassembly simulation environment. In particular, the focus is on the computer architecture developed to support such haptic simulations and the methods that have been created to meet some of the application time constraints unique to haptic simulation. Although focused on assembly and disassembly simulations, these issues and developments are relevant for the broader development of haptically enabled simulations in general.
Quadratic Optimality of the Zero-Phase Repetitive Control
Authors: Ko¨rog˘lu Hakan , Morgu¨l O¨mer
Published: July 2002

We consider the quadratically optimal repetitive control problem in discrete-time and show that the existing zero-phase repetitive controller is quadratically optimal for stable plants.
Process Modeling and Thermal/Mechanical Behavior of ACA/ACF Type Flip-Chip Packages
Authors: Chiang K. N. , Chang C. W. , Lin C. T.
Published: July 2002

Development of flip-chip-on-glass (FCOG) assembly technology using anisotropic conductive adhesive/film (ACA/ACF) is currently underway to achieve fine pitch interconnections between driver IC and flat panel display. Conductive adhesives are characterized by fine-pitch capability and more environment compatibility. Anisotropic conductive adhesive/film (ACA/ACF) is composed of an adhesive resin and conductive particles, such as metallic or metal-coated polymer particles. In contrast to a solder type flip chip interconnection, the electric current passing through conductive particles becomes the dominant conduction paths. The interconnection between the particles and the conductive surfaces is constructed by the elastic/plastic deformation of conductive particles with contact pressure, which is maintained by tensile stress in the adhesive. Although loss of electric contact can occur when the adhesive expands or swells in the Z- axis direction, delamination and cracking can occur in the adhesive layer while the tensile stress is excessive. In addition to performing processing simulations as well as reliability modeling, this research investigates the contact force that is developed and relaxed within the interconnection during the process sequence by using nonlinear finite element simulations. Environmental effects, such as high temperature and thermal loading, are also discussed. Moreover, a parametric study is performed for process design. To improve performance and reliability, variables such as ACF materials, proper processing conditions are discussed as well. Furthermore, this study presents a novel method called equivalent spring method, capable of significantly reducing the analysis CPU time and make process modeling and contact analysis of the 3D ACA/ACF process possible.
Experimental Evaluation of Air-Cooling Electronics at High Altitudes
Authors: Wong Henry , Peck Robert E.
Published: July 2002

The effect of altitude on electronic cooling is evaluated experimentally. Material properties of air vary as a function of altitude due to changes in atmospheric pressure and temperature. These changes have a negative impact on the heat transfer effectiveness and result in higher component temperature when compared to sea level conditions. Experiments are carried out in a hypobaric chamber using electronic printed circuit boards populated with heated rectangular blocks placed in a small wind tunnel. The altitude is varied between 0 and 5000 m above sea level and the air speed is varied between 1 and 5 m/s. The results show the local adiabatic heat transfer coefficient and thermal wake function diminish with altitude. This information is useful for design and analysis of electronic equipment for operation over a range of altitudes and air speeds typically encountered in forced air convection cooling applications.
Robust Adaptive Neural Estimation of Restoring Forces in Nonlinear Structures
Authors: Kosmatopoulos E. B. , Smyth A. W. , Masri S. F. , Chassiakos A. G.
Published: July 2002

The availability of methods for on-line estimation and identification of structures is crucial for the monitoring and active control of time-varying nonlinear structural systems. Adaptive estimation approaches that have recently appeared in the literature for on-line estimation and identification of hysteretic systems under arbitrary dynamic environments are in general model based. In these approaches, it is assumed that the unknown restoring forces are modeled by nonlinear differential equations (which can represent general nonlinear characteristics, including hysteretic phenomena). The adaptive methods estimate the parameters of the nonlinear differential equations on line. Adaptation of the parameters is done by comparing the prediction of the assumed model to the response measurement, and using the prediction error to change the system parameters. In this paper, a new methodology is presented which is not model based. The new approach solves the problem of estimating/identifying the restoring forces without assuming any model of the restoring forces dynamics, and without postulating any structure on the form of the underlying nonlinear dynamics. The new approach uses the Volterra/Wiener neural networks (VWNN) which are capable of learning input/output nonlinear dynamics, in combination with adaptive filtering and estimation techniques. Simulations and experimental results from a steel structure and from a reinforced-concrete structure illustrate the power and efficiency of the proposed method.
A Theoretical Model to Predict Pool Boiling CHF Incorporating Effects of Contact Angle and Orientation
Authors: Kandlikar Satish G.
Published: July 2002

A theoretical model is developed to describe the hydrodynamic behavior of the vapor-liquid interface of a bubble at the heater surface leading to the initiation of critical heat flux (CHF) condition. The momentum flux resulting from evaporation at the bubble base is identified to be an important parameter. A model based on theoretical considerations is developed for upward-facing surfaces with orientations of 0 deg (horizontal) to 90 deg (vertical). It includes the surface-liquid interaction effects through the dynamic receding contact angle. The CHF in pool boiling for water, refrigerants and cryogenic liquids is correctly predicted by the model, and the parametric trends of CHF with dynamic receding contact angle and subcooling are also well represented.
Nonintrinsicity of References in Rigid-Body Motions
Authors: Stramigioli S.
Published: July 2002

This paper shows that in the use of Lie groups for the study of the relative motion of rigid bodies some assumptions are not explicitly stated. A commutation diagram is shown which points out the “reference problem” and its simplification to the usual Lie group approach under certain conditions which are made explicit.
Theoretical Stress Concentration Factors for Short Rectangular Plates With Centered Circular Holes
Authors: Troyani N. , Gomes C. , Sterlacci G.
Published: July 2002

This work shows that the theoretical stress concentration factor depends on the length of the member in addition to the established other standard geometric parameters. In particular, the in-plane theoretical stress concentration factors for short rectangular plates with centered circular holes subjected to uniform tension are determined using the finite element method. It is shown that these factors can reach significantly larger values than the corresponding existing ones for long plates. The value of the transition length between long and short plates is computed and reported as well. Two new concepts are defined, short members and transition length.
Recent Mathematical Models for Turbulent Flow in Saturated Rigid Porous Media
Authors: de Lemos Marcelo J. S. , Pedras Marcos H. J.
Published: July 2002

Turbulence models proposed for flow through permeable structures depend on the order of application of time and volume average operators. Two developed methodologies, following the two orders of integration, lead to different governing equations for the statistical quantities. The flow turbulence kinetic energy resulting in each case is different. This paper reviews recently published mathematical models developed for such flows. The concept of double decomposition is discussed and models are classified in terms of the order of application of time and volume averaging operators, among other peculiarities. A total of four major classes of models are identified and a general discussion on their main characteristics is carried out. Proposed equations for turbulence kinetic energy following time-space and space-time integration sequences are derived and similar terms are compared. Treatment of the drag coefficient and closure of the interfacial surface integrals are discussed.