bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of a Dilatometer for Measurement of the PVT Properties of a Polymer/CO2 Solution Using a Foaming Extruder and a Gear Pump
Authors: Park Simon S. , Park Chul B. , Ladin Dmitry , Naguib Hani E. , Tzoganakis Costas
Published: July 2002

This paper presents an innovative dilatometer that can measure the pressure-volume-temperature (PVT) properties of polymer/CO2 solutions in a molten state. The basic rationale of the design is to determine the density (or equivalently, the specific volume) of a polymer/CO2 solution by separately measuring the mass and volume flow rates of the solution flowing in an extruder at each temperature and pressure. A positive-displacement gear pump mounted on an extruder is used to measure the volume flow rate of the solution. A single-phase polymer/CO2 solution is formed by injecting a metered amount of CO2 into a polymer melt and completely dissolving it in the melt using a foam extrusion line. The temperature of solution was precisely controlled and homogenized by using the second extruder in a tandem system and a heat exchanger with a static mixer. The pressure was controlled by the rotational speed of the screw in the second extruder. In order to reduce leakage across the gear pump, the difference between the upstream and downstream pressures was minimized using a variable resistance valve attached downstream of the gear pump. The mass flow rate was measured by directly collecting the extruded polymer melt for a fixed time after degassing CO2. A critical set of experiments was carried out to verify the functions of the system using pure polymer melts with known PVT data. Finally, the system was used to measure the specific volume of PS/CO2 solutions as a function of CO2 concentration, temperature, and pressure.
Variable Resistance Type Energy Regenerative Damper Using Pulse Width Modulated Step-up Chopper
Authors: Kim Sang-Soo , Okada Yohji
Published: July 2002

This paper describes a new technique for improving the damping property and efficiency of an energy regenerative damper. It is intended for a linear DC motor type vibration damper to regenerate vibration energy efficiently. Normally a regenerative damper can regenerate vibration energy only at high speed motion. For low speed motion, the damper has nonlinear characteristics with dead zone and cannot regenerate energy. In order to overcome this problem, a step-up chopper is introduced between the actuator and the charging circuit. The energy is regenerated from low speed and low voltage actuator to high voltage charging circuit. This paper also proposes a new control technique to the step-up chopper by using pulse width modulated signals. The damper can change its damping coefficient and the energy can be regenerated more efficiently. The proposed damper is applied to an active mass damper system. A simple experimental setup is used to validate the proposed technique. The results show an increase in performance and energy regeneration as compared to the previously proposed regenerative damper.
Self-Preserving Properties of Unsteady Round Nonbuoyant Turbulent
Starting Jets and Puffs in Still Fluids
Authors: Sangras R. , Kwon O. C. , Faeth G. M.
Published: July 2002

The self-preserving properties of round nonbuoyant turbulent starting jets, puffs, and interrupted jets were investigated both experimentally and theoretically for flows in still and unstratified environments. The experiments involved dye-containing fresh water sources injected into still fresh water within a large windowed tank. Time-resolved video images of the flows were obtained using a CCD camera. Experimental conditions were as follows: jet exit diameters of 3.2 and 6.4 mm, jet exit Reynolds numbers of 3000–12,000, jet passage lengths in excess of 50 injector passage diameters, volume of injected fluid for puffs and interrupted jets up to 191 source diameters, and streamwise penetration lengths up to 140 source diameters. Near-source behavior varied significantly with source properties but the flows generally became turbulent within 5 source diameters from the source and self-preserving behavior was generally observed at distances greater than 20–30 source diameters from the source. Within the self-preserving region, both the normalized streamwise penetration distance and the normalized maximum flow radius varied as functions of time in agreement with estimates for self-preserving turbulent flows to the following powers: 1/2 for starting nonbuoyant jets and 1/4 for nonbuoyant puffs and interrupted jets. Effects of injected fluid quantity for self-preserving puffs and interrupted jets could be handled by correlating the location of the virtual origin as a function of the volume of the injected fluid represented by the number of passage lengths of injected fluid. In particular, the virtual origin for puffs was independent of injected fluid volume for injected passage lengths less than 120 but became proportional to the injected fluid volume thereafter, defining a boundary between puff and interrupted-jet behavior.
Measurements of Heat Transfer Coefficients From Supercritical Carbon
Dioxide Flowing in Horizontal Mini/Micro Channels
Authors: Liao S. M. , Zhao T. S.
Published: July 2002

Heat transfer from supercritical carbon dioxide flowing in horizontal mini/micro circular tubes cooled at a constant temperature has been investigated experimentally. Six stainless steel circular tubes having inside-diameters of 0.50 mm, 0.70 mm, 1.10 mm, 1.40 mm, 1.55 mm, and 2.16 mm were tested. Measurements were carried out for the pressures ranging from 74 to 120 bar, the temperatures ranging from 20 to 110°C, and the mass flow rates ranging from 0.02 to 0.2 kg/min. It is found that the buoyancy effect was still significant, although supercritical CO2 was in forced motion through the horizontal tubes at Reynolds numbers up to 105. The experimental results also indicate that the existing correlations developed in the previous studies for large tubes deviate significantly from the experimental data for the present mini/micro tubes. Based on the experimental data, a correlation was developed for the axially averaged Nusselt number in terms of appropriate dimensionless parameters for forced convection of supercritical carbon dioxide in horizontal mini/micro tubes cooled at a constant temperature.
A Comprehensive Model to Predict Three-Way Catalytic Converter Performance
Authors: Shamim T. , Shen H. , Sengupta S. , Son S. , Adamczyk A. A.
Published: July 2002

This paper describes the development of a comprehensive mathematical and numerical model for simulating the performance of automotive three-way catalytic converters, which are employed to reduce engine exhaust emissions. The model simulates the emission system behavior by using an exhaust system heat conservation and catalyst chemical kinetic submodel. The resulting governing equations are solved numerically. Good agreements were found between the numerical predictions and experimental measurements under both steady-state and transient conditions. The developed model will be used to facilitate the converter design improvement efforts, which are necessary in order to meet the increasingly stricter emission requirements.
Allocating the Causes of Performance Deterioration in Combined Cycle Gas Turbine Plants
Authors: Mathioudakis K. , Stamatis A. , Bonataki E.
Published: July 2002

A method for defining which parts of a combined cycle gas turbine (CCGT) power plant are responsible for performance deviations is presented. When the overall performances deviate from their baseline values, application of the method allows the determination of the component(s) of the plant, responsible for this deviation. It is shown that simple differentiation approaches may lead to erroneous conclusions, because they do not reveal the nature of deviations for individual components. Contributions of individual components are then assessed by separating deviations due to permanent changes and deviations due to change of operating conditions. A generalized formulation is presented together with the way of implementing it. Test cases are given, to make clearer the ideas put forward in the proposed method.
Relative Contribution of Wall Shear Stress and Injury in Experimental Intimal Thickening at PTFE End-to-Side Arterial Anastomoses
Authors: Loth Francis , Jones Steven A. , Zarins Christopher K. , Giddens Don P. , Nassar Raja F. , Glagov Seymour , Bassiouny Hisham S.
Published: July 2002

Background : Intimal hyperplastic thickening (IHT) is a frequent cause of prosthetic bypass graft failure. Induction and progression of IHT is thought to involve a number of mechanisms related to variation in the flow field, injury and the prosthetic nature of the conduit. This study was designed to examine the relative contribution of wall shear stress and injury to the induction of IHT at defined regions of experimental end-to-side prosthetic anastomoses. Methods and Results: The distribution of IHT was determined at the distal end-to-side anastomosis of seven canine Iliofemoral PTFE grafts after 12 weeks of implantation. An upscaled transparent model was constructed using the in vivo anastomotic geometry, and wall shear stress was determined at 24 axial locations from laser Doppler anemometry measurements of the near wall velocity under conditions of pulsatile flow similar to that present in vivo. The distribution of IHT at the end-to-side PTFE graft was determined using computer assisted morphometry. IHT involving the native artery ranged from 0.0±0.1 mm to 0.05±0.03 mm. A greater amount of IHT was found on the graft hood (PTFE) and ranged from 0.09±0.06 to 0.24±0.06 mm. Nonlinear multivariable logistic analysis was used to model IHT as a function of the reciprocal of wall shear stress, distance from the suture line, and vascular conduit type (i.e. PTFE versus host artery). Vascular conduit type and distance from the suture line independently contributed to IHT. An inverse correlation between wall shear stress and IHT was found only for those regions located on the juxta-anastomotic PTFE graft. Conclusions: The data are consistent with a model of intimal thickening in which the intimal hyperplastic pannus migrating from the suture line was enhanced by reduced levels of wall shear stress at the PTFE graft/host artery interface. Such hemodynamic modulation of injury induced IHT was absent at the neighboring artery wall.
Optimal Sizing Procedure for Stand-Alone Photovoltaic Systems by Fuzzy Logic
Authors: Conti S. , Tina G. , Ragusa C.
Published: July 2002

In this paper, an automatic procedure to perform the optimal sizing of a stand-alone solar electrical system with battery storage is developed by a fuzzy logic based multi-objective optimization approach. The procedure aims at finding the configuration that yields the best compromise for the two considered objectives: the long-term average performance and the overall cost of the generating system. In particular, the objectives of the optimization problem are: the maximization of the Supplied Load Fraction, that is the fraction of the actual electrical load that can be supplied by the system, and the minimization of the Relative Unit Electricity Cost, that is the net cost of generating each kWh during the lifetime of the stand-alone solar electrical system referred to the UEC calculated in case of loads supplied by the grid. The control variables are the solar cell array surface, the tilt angle of the modules, and the storage system capacity. The fuzzy multi-objective optimization procedure is described and the application results are presented considering different configurations characterized by some parameters, such as the electrical load, the yearly power demand, the distance from the utility grid, and the solar cells unit cost.
Maximally Robust Input Preconditioning for Residual Vibration Suppression Using Low-Pass FIR Digital Filters
Authors: Economou D. , Mavroidis C. , Antoniadis I. , Lee C.
Published: July 2002

A method for suppressing residual vibrations in flexible systems is presented and experimentally demonstrated. The proposed method is based on the preconditioning of the inputs to the system using low-pass Finite Impulse Response (FIR) digital filters. Provided that the cutoff frequency of FIR filters is selected lower than the lowest expected natural frequency of the system and their stop-band is maximized, we show that these filters can be designed to exhibit maximally robust behavior with respect to changes of the system natural frequencies. To perform the proper design of FIR filters for robust vibration suppression, this paper introduces a series of dimensionless performance indexes and the Delay-Error-Order (DEO) curves that represent graphically the delay time introduced by the filter as a function of the remaining residual vibrations, and the filter order. Several classes of FIR filters such as: a) Parks-McClellan; b) Window-based methods (using Chebyshev window); and c) Constrained Least Squares method, are shown to present maximally robust behavior, almost identical to the theoretically predicted. Parallel, they demonstrate excellent vibration suppression while they introduce the minimum possible delay. Further advantages offered by the proposed method, is that no modeling of the flexible system is required, the method can be used in a variety of systems exhibiting vibrations, it is independent of the guidance function and it is simple to implement in practical applications. The results are experimentally verified on a flexible aluminum beam with a significantly varying mass, attached to the end-effector of a robot manipulator. The beam is rotated, using one joint of the manipulator, from an initial to a final position. It is shown that the preconditioned inputs to the flexible system induce very little amount of residual vibrations compared to the inputs with no preconditioning.
Design of Continuous Backbone, Cable-Driven Robots
Authors: Li Changquing , Rahn Christopher D.
Published: July 2002

Continuous backbone robots driven by cables have many potential applications in dexterous manipulation for manufacturing and space environments. Design of these robots requires specification of a stiff yet bendable backbone, selection of cable support heights and spacings, and development of a cable drive system. The robot arm divides into sections that are subdivided into segments bounded by cable supports. Cable pairs attach to the end of each section and provide two axis bending. Thus, with many sections, the arm can be bent into complex shapes to allow redundant positioning of the end effector payload. The kinematics of the entire arm are determined from the segment kinematics. This paper derives and numerically solves the nonlinear kinematics for a single segment of a continuous backbone robot. Optimal spacing of the cable supports maximizes displacement, load capacity, and simplicity of the robot kinematics. An experimental system verifies the theoretically predicted performance.
Constant-Wall-Temperature Nusselt Number in Micro and Nano-Channels1
Authors: Hadjiconstantinou Nicolas G. , Simek Olga
Published: July 2002

We investigate the constant-wall-temperature convective heat-transfer characteristics of a model gaseous flow in two-dimensional micro and nano-channels under hydrodynamically and thermally fully developed conditions. Our investigation covers both the slip-flow regime 0⩽Kn⩽0.1, and most of the transition regime 0.1<Kn⩽10, where Kn, the Knudsen number, is defined as the ratio between the molecular mean free path and the channel height. We use slip-flow theory in the presence of axial heat conduction to calculate the Nusselt number in the range 0⩽Kn⩽0.2, and a stochastic molecular simulation technique known as the direct simulation Monte Carlo (DSMC) to calculate the Nusselt number in the range 0.02<Kn<2. Inclusion of the effects of axial heat conduction in the continuum model is necessary since small-scale internal flows are typically characterized by finite Peclet numbers. Our results show that the slip-flow prediction is in good agreement with the DSMC results for Kn⩽0.1, but also remains a good approximation beyond its expected range of applicability. We also show that the Nusselt number decreases monotonically with increasing Knudsen number in the fully accommodating case, both in the slip-flow and transition regimes. In the slip-flow regime, axial heat conduction is found to increase the Nusselt number; this effect is largest at Kn=0 and is of the order of 10 percent. Qualitatively similar results are obtained for slip-flow heat transfer in circular tubes.
Stick-slip Whirl Interaction in Drillstring Dynamics
Authors: Leine R. I. , van Campen D. H. , Keultjes W. J. G.
Published: July 2002

This paper attempts to explain the complicated behavior of oilwell drillstring motion when both torsional stick-slip and lateral whirl vibration are involved. It is demonstrated that the observed phenomena in experimental drillstring data could be due to the fluid forces of the drilling mud. A Stick-slip Whirl Model is presented which consists of a submodel for the whirling motion and a submodel for the stick-slip motion, both as simple as possible. The Stick-slip Whirl Model is a simplification of a drillstring confined in a borehole wall with drilling mud. The model is as simple as possible to expose only the basic phenomena but is discontinuous. Bifurcation diagrams of this discontinuous model for varying rotation speeds reveal discontinuous bifurcations. The disappearance of stick-slip vibration when whirl vibration appears is explained by bifurcation theory. The numerical results are compared with the experimental data from a full-scale drilling rig.
Optimal Trajectory Planning For Material Handling of Compliant Sheet Metal Parts
Authors: Li Huifang , Ceglarek Dariusz
Published: July 2002

One of the most critical issues in the material handling of compliant objects is excessive part deformation. The deformation of compliant sheet metal parts during the handling process can significantly impact both part dimensional quality and production rate. Increasing production rate while maintaining part quality requires an optimal design of the part transfer trajectory. This paper describes a new methodology of time-optimal trajectory planning for compliant parts by discretizing the part transfer path into N segments that have equal horizontal distance and by approximating the trajectory as having piecewise constant acceleration that can only change its value at the end of each segment. The contribution of the methodology is that part deformation determined by transfer velocity and acceleration is considered as a nonlinear constraint, which is obtained from FEA simulation and model fitting. Part permanent deformation, trajectory smoothness, and static obstacle avoidance are also considered. The methodology is validated by simulations at different motion conditions and obstacle configurations. This paper addresses the lack of current design guidelines for material handing development and simultaneously provides a mathematical tool to significantly enhance the production efficiency in manufacturing of compliant sheet metal parts.
Reduced Order Nonlinear Navier-Stokes Models for Synthetic Jets
Authors: Rediniotis Othon K. , Ko Jeonghwan , Kurdila Andrew J.
Published: July 2002

While the potential for the use of synthetic jet actuators to achieve flow control has been noted for some time, most of such flow control studies have been empirical or experimental in nature. Several technical issues must be resolved to achieve rigorous, model-based, closed-loop control methodologies for this class of actuators. The goal of this paper is consequently two-fold. First, we seek to derive and evaluate model order reduction methods based on proper orthogonal decomposition that are suitable for synthetic jet actuators. Second, we seek to derive rigorously stable feedback control laws for the derived reduced order models. The realizability of the control strategies is discussed, and a numerical study of the effectiveness of the reduced order models for two-dimensional flow near the jet exit is summarized.
Quantifying Skeletal Muscle Properties in Cadaveric Test Specimens: Effects of Mechanical Loading, Postmortem Time, and Freezer Storage
Authors: Van Ee C. A. , Chasse A. L. , Myers B. S.
Published: July 2002

Investigators currently lack the data necessary to define the state of skeletal muscle properties within cadaveric specimens. The purpose of this study is to define the temporal changes in the postmortem properties of skeletal muscle as a function of mechanical loading and freezer storage. The tibialis anterior of the New Zealand white rabbit was chosen for study. Modulus and no-load strain were found to vary significantly from live after eight hours postmortem. Following the changes that occur during rigor mortis, a stable region of postmortem, post-rigor properties occurred between 36 to 72 hours postmortem. A freeze–thaw process was not found to have a significant effect on the post-rigor response. The first loading cycle response of post-rigor muscle was unrepeatable but stiffer than live passive muscle. After preconditioning, the post-rigor muscle response was repeatable. The preconditioned post-rigor response was less stiff than the live passive response due to a significant increase in no-load strain. Failure properties of postmortem muscle were found to be significantly different from live passive muscle with a significant decrease in failure stress (61 percent) and energy (81 percent), while failure strain was unchanged. These results suggest that the post-rigor response of cadaveric muscle is unaffected by freezing but sensitive to even a few cycles of mechanical loading. [S0148-0731(00)00301-0]
Viscoelastic Dissipation in Compact Bone: Implications for Stress-Induced Fluid Flow in Bone
Authors: Garner Elijah , Lakes Roderic , Lee Taeyong , Swan Colby , Brand Richard
Published: July 2002

Viscoelastic properties of wet and dry human compact bone were studied in torsion and in bending for both the longitudinal and transverse directions at frequencies from 5 mHz to 5 kHz in bending to more than 50 kHz in torsion. Two series of tests were done for different longitudinal and transverse specimens from a human tibia. Wet bone exhibited a larger viscoelastic damping tan δ (phase between stress and strain sinusoids) than dry bone over a broad range of frequency. All the results had in common a relative minimum in tan δ over a frequency range, 1 to 100 Hz, which is predominantly contained in normal activities. This behavior is inconsistent with an optimal “design” for bone as a shock absorber. There was no definitive damping peak in the range of frequencies explored, which could be attributed to fluid flow in the porosity of bone. [S0148-0731(00)00102-3]
Modeling and Identification of Lubricated Polymer Friction Dynamics
Authors: Hsu Geesern , Yagle Andrew E. , Ludema Kenneth C. , Levitt Joel A.
Published: July 2002

A systematic approach is proposed to model the dynamics of lubricated polymer friction. It starts with the development of a physical model to describe the fundamental mechanisms of the friction. The physical model then serves as the basic structure for the development of a complex model able to capture a wider spectrum of the deterministic and stochastic dynamics of friction. To assess the accuracy of the complex model, two estimation algorithms are formulated to estimate the unknown parameters in the model and to test the model against experimental data. One algorithm is based on the maximum likelihood principle to estimate the constant parameters for stationary friction dynamics, and the other based on the extended Kalman filter to estimate the time-varying parameters for nonstationary friction dynamics. The model and the algorithms are all validated through experiments. [S0022-0434(00)00601-8]
A Linearized Electrohydraulic Servovalve Model for Valve Dynamics Sensitivity Analysis and Control System Design
Authors: Kim Dean H. , Tsao Tsu-Chin
Published: July 2002

This paper presents the derivation of a linearized model for flapper-nozzle type two-stage electrohydraulic servovalves from the nonlinear state equations. The coefficients of the linearized model are derived in terms of the valve physical parameters and fluid properties explicitly, and are useful for valve design and sensitivity analysis. When using this model structure to fit experimental frequency response data, the results render closer agreement than when using existing low order linear models. This model also suggests important servovalve dynamic properties such as the nonminimum phase zero and the transfer function relative degree, and how they relate to the valve component arrangement. Because of the small modeling errors over a wide frequency range, a high bandwidth control system can be designed. A robust performance controller is designed and implemented to demonstrate the utility of the model. [S0022-0434(00)03401-8]
Globally Feedback Linearizable Time-Invariant Systems: Optimal Solution for Mayer’s Problem
Authors: Schlemmer M. , Agrawal S. K.
Published: July 2002

This paper discusses the optimal solution of Mayer’s problem for globally feedback linearizable time-invariant systems subject to general nonlinear path and actuator constraints. This class of problems includes the minimum time problem, important for engineering applications. Globally feedback linearizable nonlinear systems are diffeomorphic to linear systems that consist of blocks of integrators. Using this alternate form, it is proved that the optimal solution always lies on a constraint arc. As a result of this optimal structure of the solution, efficient numerical procedures can be developed. For a single input system, this result allows to characterize and build the optimal solution. The associated multi-point boundary value problem is then solved using direct solution techniques. [S0022-0434(00)02002-5]
The Use of Refractory Metals as High Temperature Structural Materials
Authors: Briant C. L.
Published: July 2002

The use of refractory metals as high temperature structural materials has been limited in the past because of the rapid oxidation and low creep strength of the metals. Recently, a number of advances have been made in which alloying additions have improved these properties. This paper reviews these advances in the Cr-Ta and Nb-Si systems. Further needs for improvement are also described. [S0094-4289(00)01603-0]
On the Mechanical Reliability of Photo-BCB-Based Thin Film Dielectric Polymer for Electronic Packaging Applications
Authors: Im Jang-hi , Shaffer Edward O. , Stokich, Theodore , Strandjord Andrew , Hetzner Jack , Curphy James , Karas Cheryl , Meyers Greg , Hawn David , Chakrabarti Ashok , Froelicher Steve
Published: July 2002

This work examines the mechanical performance of thin film coatings from Photosensitive-benzocyclobutene (Photo-BCB) formulations (Cyclotene2 4024, 4026 and 7200), on various substrate surfaces such as Al, Cu, Si, and SiN. The adhesion promoter used was designated AP-3000 and was based on vinyltriacetoxysilane (VTAS), which had been properly hydrolyzed and advanced. Measurement of the interfacial adhesion was performed primarily using the modified Edge Liftoff Test m-ELT. It was found that, by applying the newly developed adhesion promoter, AP-3000, the interfacial energy of Photo-BCB to Al, Cu, Si, and SiN was significantly improved, often approaching the toughness of Photo-BCB, ca. 45 J/m2. The x-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) analyses of the delaminated surfaces of the Photo-BCB/Al structure revealed distinct differences in surface roughness and the chemical composition depending on whether or not adhesion promoter was used. Other parameters important for long term stability (e.g., moisture uptake and thermal stability) of Photo-BCB were also measured. The equilibrium moisture content at 84 percent RH in ambient temperature was low, 0.14 wt percent and the thermally induced weight loss at 330°C in helium atmosphere was less than 1 percent/h. The low moisture absorption and good thermal stability, together with the given mechanical toughness and adhesion, allow the Photo-BCB to be widely usable for various microelectronic packaging applications, for up to 40 μm thick build in the case of silicon substrate. [S1043-7398(00)00701-5]
A Study on Warpage of Flexible SS Substrates for Large Area MCM-D Packaging
Authors: Dang Anh X. H. , Ume I. Charles , Bhattacharya Swapan K.
Published: July 2002

This paper presents potential application of stainless steel (SS) as a base substrate material for large area multi-chip module-deposited (MCM-D) packaging. Preliminary results on via formation on SS substrates by laser drilling, dielectric coating on SS surface and on via sidewall, via filling for front-to-back interconnects, and subsequent curing of via filling material are reported in this paper. The objective of this DARPA funded MCM-D Consortium is to investigate the feasibility of application of stainless steel materials for large area MCM-D packaging through laboratory prototypes and simulated thin film process. This paper particularly addresses the warpage issues related to via formation, dielectric coating on the substrates, and via filling process after substrates were exposed to temperatures above 130 °C for two hours. The change in process induced warpage was quantified by the simple non-destructive Shadow Moire´ technique. The end objective of this work is to be able to fabricate large area 24 in.×24 in.SS substrates with minimum warpage. The study shows that SS can be a candidate substrate for large area MCM-D packaging. [S1043-7398(00)00702-7]
Cyclic Oxidation Behavior of Aluminide, Platinum Modified Aluminide, and MCrAlY Coatings on GTD-111
Authors: Cheruvu N. S. , Chan K. S. , Leverant G. R.
Published: July 2002

Cyclic oxidation behavior of aluminide, platinum modified aluminide, and MCrAlY coatings has been investigated at three temperatures. Aluminide and platinum modified coatings were deposited on GTD 111 material using an outward diffusion process. CoCrAlY coating was applied on GTD-111 by Electron Beam Physical Vapor Deposition (EB-PVD). The oxidation behavior of these coatings is characterized by weight change measurements and by the variation of β phase present in the coating. The platinum modified aluminide coating exhibited the highest resistance to oxide scale spallation (weight loss) during cyclic oxidation testing. Metallographic techniques were used to determine the amount of β phase and the aluminum content in a coating as a function of cycles. Cyclic oxidation life of these coatings is discussed in terms of the residual β and aluminum content present in the coating after exposure. These results have been used to calibrate and validate a coating life model (COATLIFE) developed at the Material Center for Combustion Turbines (MCCT). [S0742-4795(00)00801-2]
Isothermal Fatigue Behavior and Damage Modeling of a High Temperature Woven PMC
Authors: Gyekenyesi A. L.
Published: July 2002

This study focuses on the fully reversed fatigue behavior exhibited by a carbon fiber/polyimide resin woven laminate at room and elevated temperatures. Nondestructive video edge view microscopy and destructive sectioning techniques were used to study the microscopic damage mechanisms that evolved. The elastic stiffness was monitored and recorded throughout the fatigue life of the coupon. In addition, residual compressive strength tests were conducted on fatigue coupons with various degrees of damage as quantified by stiffness reduction. Experimental results indicated that the monotonic tensile properties were only minimally influenced by temperature, while the monotonic compressive and fully reversed fatigue properties displayed greater reductions due to the elevated temperature. The stiffness degradation, as a function of cycles, consisted of three stages; a short-lived high degradation period, a constant degradation rate segment covering the majority of the life, and a final stage demonstrating an increasing rate of degradation up to failure. Concerning the residual compressive strength tests at room and elevated temperatures, the elevated temperature coupons appeared much more sensitive to damage. At elevated temperatures, coupons experienced a much larger loss in compressive strength when compared to room temperature coupons with equivalent damage. The fatigue damage accumulation law proposed for the model incorporates a scalar representation for damage, but admits a multiaxial, anisotropic evolutionary law. The model predicts the current damage (as quantified by residual stiffness) and remnant life of a composite that has undergone a known load at temperature. The damage/life model is dependent on the applied multiaxial stress state as well as temperature. Comparisons between the model and data showed good predictive capabilities concerning stiffness degradation and cycles to failure. [S0742-4795(00)01001-2]
Effect of Planform Aspect Ratio on Flow Oscillations in Rectangular Cavities
Authors: Disimile Peter J. , Toy Norman , Savory Eric
Published: July 2002

An experimental investigation was undertaken to examine the effect of cavity lateral width on the flow oscillations that occur in an open cavity placed within a turbulent subsonic boundary layer. A rectangular cavity with a length to depth ratio L/D=1 and planform aspect ratio L/W=0.115 was placed within a thick turbulent boundary layer with a corresponding Reθ=10.5×103. Pressure time histories were acquired at six separate cavity widths (or L/W values) using microphone-type pressure transducers. The spectral character of these signals was analyzed and the pressure levels and dominant frequencies determined. This study indicates that large changes in the pressure level occur as L/W varies from 0.115 to 0.682. A state of fluid dynamic resonance was observed at L/W=0.137 and fluid–acoustic resonance at L/W=0.682, the smallest cavity width. Relative sound pressure level calculations indicate that the energy within the cavity compared with that of the boundary layer, was observed to increase by approximately 40 percent at L/W=0.137. [S0098-2202(00)00601-5]
Determination of Entrained Fraction in Vertical Annular Gas/Liquid Flow
Authors: Azzopardi Barry J. , Zaidi Sohail H.
Published: July 2002

A new technique for the measurement of drop concentration in annular gas/liquid flow is presented. This is based on scattering of light by the drops. From the measured concentration, entrained liquid flow rate and thence the entrained fraction can be determined. The technique has been employed to obtain new data for vertical upward annular flow in a 0.038 m diameter pipe. The results have been compared with data from different pipe diameters and with the predictions of an annular flow model. [S0098-2202(00)02201-X]
Efficient Geometric Disassembly of Multiple Components from an Assembly Using Wave Propagation
Authors: Srinivasan Hari , Gadh Rajit
Published: July 2002

This paper analyzes the problem of disassembling multiple selected components from an assembly, defined as selective disassembly, and presents algorithms for efficient disassembly analysis of geometric models. Applications for selective disassembly include assembling, maintenance and recycling. A new approach called ‘Disassembly Wave Propagation’ is proposed to determine a selective disassembly sequence with minimal component removals from an assembly. This approach defines: (i) disassembly waves to topologically arrange the components denoting the disassembly order and (ii) intersection events between the waves to determine the selective disassembly sequences. In order to evaluate a minimal removal sequence in a feasible computation time, algorithms are proposed that prioritize and process the intersection events based on the order in which they occurred. The proposed algorithms analyze selective disassembly from the geometric perspective and are applicable for both two-dimensional and three-dimensional product assemblies. [S1050-0472(00)01402-1]
Wear Testing of UHMWPE Tibial Components: Influence of Oxidation
Authors: Young Sarah K. , Keller Tony S. , Greer Keith W. , Gorhan Michael C.
Published: July 2002

An AMTI knee simulator was used to evaluate the wear of UHMWPE tibial inserts which were gamma sterilized in air and displayed a high or low level of oxidation. After 5 million cycles, four out of five samples from the high oxidation group displayed subsurface cracking and/or delamination. The five specimens in the low oxidation group experienced burnishing only. These results indicate that gamma irradiation in air together with high oxidation due to shelf aging can increase susceptibility to wear. The appearance of the wear scars indicates that knee simulator testing is a valid method of producing burnishing, cracking, and delamination similar to that seen in-vivo. [S0742-4787(00)04301-0]
Effects of increasing nitrogen concentration on the structure of carbon nitride films deposited by ion beam assisted deposition
Authors: Hammer P. , Victoria N. M. , Alvarez F.
Published: July 2002

Amorphous carbon nitride films containing increasing concentrations of nitrogen were deposited by ion beam assisted deposition at a substrate temperature of 150 °C. The relationship between the deposition conditions and the chemical bonding structure was investigated by x-ray photoelectron, ultraviolet photoelectron, infrared, and Raman spectroscopies. Film properties were examined by ultraviolet–vis spectroscopy, conductivity, hardness, density, and internal stress measurements. The experimental results confirm a pronounced change of the structure and properties at a nitrogen concentration of about 20 at. %. After reaching a maximum at this concentration, properties like hardness, conductivity, and density show a strong decrease up to a nitrogen content of 35 at. %. In order to identify the formed microstructure and better understand the cause of the structural transformation a statistical model is introduced and the results are compared with the intensities of the deconvoluted spectral features obtained by photoelectron spectroscopy. On the basis of the obtained correlation between independent experiments it is demonstrated that below 20 at. % N an increasing number of nonaromatic CN bonds is formed inducing a localization of nitrogen lone pair electrons and thus stressing the former planar aromatic structures. The addition of more N causes a further reduction of aromatic configurations and a relaxation of the strained network due to the formation of isocyanide structures (C≡N–), aliphatic CN bonds, and terminating nitrile groups (–C≡N). The nitrogen induced rearrangement of the bonding structure accounts for the lower intrinsic stress values and higher optical gap of these films. Structural information from both Raman and infrared spectra support these findings.
Effects of surface oxides on field emission from silicon
Authors: Shaw Jonathan
Published: July 2002

This report documents energy distribution measurements of field emission from single-tip Si field emitter arrays. The emission energy distributions are much broader than clean metal distributions, extending several volts below the Fermi level and often including multiple peak structure. The peak positions typically move to lower energy as the gate voltage is increased, however, the emission history as well as the emission current and/or gate voltage can change the energy as well as intensity of the energy distributions. Changes in the distribution including shifts to higher energy occur suddenly and spontaneously as well as slowly during emission. These results show that the emission comes from oxide and interface states, which refill at a finite rate, limiting the emission current. Changes in the local electric potential due to single charges becoming trapped in the oxide account for large and discrete changes in the emission distribution.
Ion channeling effects on the focused ion beam milling of Cu
Authors: Kempshall B. W. , Schwarz S. M. , Prenitzer B. I. , Giannuzzi L. A. , Irwin R. B. , Stevie F. A.
Published: July 2002

The use of focused ion beam (FIB) instruments for device modification and specimen preparation has become a mainstay in the microelectronics industry and in thin film characterization. The role of the FIB as a tool to rapidly prepare high quality transmission electron microscopy specimens is particularly significant. Special attention has been given to FIB milling of Cu and Si in the microelectronics arena. Although FIB applications involving Si have been extremely successful, it has been noted that Cu tends to present significant challenges to FIB milling because of effects such as the development of milling induced topographical features. We show evidence that links the occurrence of milling induced topography to the severity of redeposition. Specifically, Cu, which sputters ∼2.5 times faster than Si, exhibits an increased susceptibility to redeposition related artifacts. In addition, the effects and the mechanism of Ga+ channeling in Cu is used to illustrate that Ga+ channeling reduces the sputtering yield, improves the quality of FIB mill cuts, and improves the surface characteristics of FIB milled Cu. Finally, a technique for improving FIB milling across grain boundaries or interfaces using ion channeling contrast is suggested.
Scanning spreading resistance microscopy and spectroscopy for routine and quantitative two-dimensional carrier profiling
Authors: Eyben P. , Xu M. , Duhayon N. , Clarysse T. , Callewaert S. , Vandervorst W.
Published: July 2002

As emphasized in the International Technological Roadmap for Semiconductors (ITRS), two-dimensional carrier profiling is one of the key elements in support of technology development. Scanning spreading resistance microscopy (SSRM) has been demonstrated to have attractive concentration sensitivity, an easy quantification, and is applicable to complementary metal–oxide–semiconductor Si and InP structures. Its commercial implementation and availability together with an ample supply of appropriate (diamond based) tips has enabled its more widespread use during recent years. In this article we propose a number of measurement procedures and software tools for its more reliable and fast routine application. First we present a program for the automatic generation of calibration curves and the fast quantification of one-dimensional and two-dimensional resistivity (and carrier) profiles. In view of the large tip consumption, a fast evaluation and calibration of newly mounted conductive tips is a major issue. Furthermore, the fast extraction of the underlying carrier distributions leads to an easier data interpretation. We also propose an overview of the implementation and of the applications of the scanning spreading resistance spectroscopy (SSRS), where a full I–V curve is collected at each measurement point. SSRS proves to be particularly interesting to study the point-contact characteristics (in scanning mode) and simplifies significantly the junction delineation. SSRS can also be used for the selection of the optimal bias settings for the quantification procedure.
Influence of the surface on photoluminescence from indium phosphide crystals
Authors: Street R. A. , Williams R. H. , Bauer R. S.
Published: July 2002

The photoluminescence of indium phosphide has been measured on crystals in ultrahigh vacuum and subsequently oxidized in a controlled manner. The luminescence intensity can vary by more than an order of magnitude and shows a close correspondence to the known shift of the Fermi level at the surface under oxidation. We conclude that the oxidation-induced surface space charge layer is nonradiative due to the presence of the electric field. The band bending and surface charge variation can be estimated quantitatively from the data. The influence of surface contamination on Schottky barrier formation is also reported.
Effects of H2S adsorption on surface properties of GaAs {100} grown i
n s
i
t
u by MBE
Authors: Massies J. , Dézaly F. , Linh N. T.
Published: July 2002

We report here results dealing with the effects of H2S adsorption on crystallographic and electronic surface properties of GaAs {100} layers grown in situ by molecular beam epitaxy (MBE). The adsorption was studied by AES, LEED and ELS. At room temperature, the adsorption is found to be very dependent on the electron irradiation, whereas this effect vanishes at 700 K. This behavior indicates that the mechanism of adsorption is temperature dependent: H2S is adsorbed mainly in molecular form at low temperature (300 K) and in dissociated form at higher temperature (700 K). Adsorption of the molecular form leads to a disordered layer, whereas the dissociative adsorption process induces a (2×1) reconstruction of the GaAs surface near the saturation coverage. This structural reordering is also associated with changes observed in the loss spectra. Moreover, Auger measurements indicate that it is characterized by significant changes in arsenic and gallium lines: it is most likely that the (2×1) structure corresponds to an important modification of the sulfur bonding at the surface. To tentatively investigate the influence of the nature of the semiconductor surface in the determination of the metal/GaAs interface properties, electrical characteristics of in situ Al contacts on H2S saturated surfaces were investigated and compared to those obtained on virgin surfaces. Contacts on clean MBE layers exhibit nearly ideal Schottky behavior (barrier height 0.76 eV, ideality factor 1.01) both as deposited (300 K) and after annealing up to 800 K. On the contrary, room temperature contacts on H2S saturated surfaces were found to be degenerate.
Trends in surface atomic geometries of compound semiconductors
Authors: Duke C. B. , Meyer R. J. , Mark P.
Published: July 2002

A brief synopsis is presented of low-energy electron diffraction structure analyses reported for the cleavage faces of zincblende and wurtzite compound semiconductor surfaces, specifically GaAs(110), InSb(110), ZnTe(110), InP(110), and ZnO(101̄0). In all of these cases the surface atomic geometry is distorted from that of a truncated bulk solid, although the space group symmetries at the surface are indistinguishable from those of the corresponding bulk materials. The surface reconstructions involve large (Δd∠0.5 Å) displacements of the species in the uppermost atomic layer and often smaller displacements (Δd∠0.1 Å) in the layer beneath. The character of these reconstructions depends, however, on the nature of the chemical bonding in the bulk materials. For the most covalent materials, i.e., GaAs and InSb, the anion rotates outward and the cation inward in a fashion such that bond lengths remain unaltered to within 1% except for a 5% contraction of the bond between the uppermost anion and the cation in the layer beneath. Morever, these ’’covalent’’ reconstructions penetrate at least two atomic layers into the surface with the displacements in the second layer being in the opposite sense to those in the first. The surface reconstructions of the more ionic materials, i.e., ZnTe and ZnO, are characterized by generally smaller displacements of the anion species and the absence of definitve evidence for distortions of the second and deeper layers from the bulk geometry. Therefore available structural data suggest a systematic change in the nature of the surface reconstructions of the cleavage faces of tetrahedrally coordinated compound semiconductors with increasing ionicity. The change is most pronounced for materials with ionicities in the vicinity of those of ZnTe and InP, and seems to be associated with the transition from III–V materials (which exhibit ionicities Fi?0.5) to II–VI materials (which exhibit ionicities fi?0.5).
Origins of (111) surface reconstructions of Si and Ge
Authors: Chadi D. J.
Published: July 2002

Several possible mechanisms leading to surface reconstruction are discussed and applied to a description of the 2×1 and 7×7 reconstructions of Si (111) and the 2×1 and 2×8 reconstructions of Ge (111) surfaces. Other types of (111) surface reconstructions such as, for example, those with (n√3)×(n√3) and (6n)×(6n) unit cells, which have been observed experimentally on impurity stabilized surfaces, are also predicted.