bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling, Realization, and Simulation of Thermo-Fluid Systems Using Singularly Perturbed Sliding Manifolds
Authors: Gordon Brandon W. , Asada Harry
Published: July 2002

A new approach based on sliding control is presented for modeling and simulation of thermo-fluid systems described by differential-algebraic equations (DAEs). The dynamics of thermo-fluid systems are often complicated by momentum interactions that occur on a time scale that is orders of magnitude faster than the time scale of interest. To address this problem the momentum equation is often modeled using algebraic steady state approximations. This will, in general, result in a model described by nonlinear DAEs for which few control methods are currently applicable. In this paper, the modeling problem is addressed using an approach that systematically constructs an explicit state space approximation of the DAEs. The state space model can in turn be used with existing control methods. This procedure, known as realization, is achieved by solving an associated nonlinear control problem by combining boundary layer sliding control with the singular perturbation method. The necessary criteria for key properties such as convergence, stability, and controllability are established. Further, the new approach is illustrated using a vapor compression cycle example. This demonstrates significant advantages over directly modeling momentum interactions. [S0022-0434(00)00904-7]
On the Seven Position Synthesis of a 5-SS Platform Linkage
Authors: Liao Qizheng , McCarthy J. Michael
Published: July 2002

This paper builds on Innocenti’s polynomial solution for the 5-SS platform that generates a one-degree of freedom movement through seven specified spatial positions of a rigid body. We show that his 60×60 resultant can be reduced to one that is 10×10. We then actuate the linkage using a prismatic joint on the sixth leg and determine the trajectory of the reference point through the specified positions. The singularity submanifold of this associated 6-SS platform provides information about the movement characteristics of the 5-SS linkage.
A Model for Squeeze Film Dampers Operating With Air Entrainment and Validation With Experiments
Authors: Diaz Sergio , San Andre´s Luis
Published: July 2002

Squeeze film dampers (SFDs) reduce vibrations and aid in suppressing instabilities in high performance rotor-bearing systems. However, air ingestion and entrapment, pervasive in open-ended dampers with low supply pressures, leads to a bubbly lubricant that severely reduces the dynamic film forces and the overall damping capability. Analyses based on conventional film rupture models, vapor or gaseous lubricant cavitation, fail to predict the actual performance of SFDs, and thus lack credibility in engineering practice. A modified Reynolds equation for prediction of the pressure in a homogeneous bubbly mixture flow is advanced along with an empirical formula for estimation of the amount of air entrained in an open-ended damper. Careful experimentation in a test SFD operating with controlled bubbly mixtures and freely entrained air evidenced similar physical behavior, guided the analytical developments, and provided the basis for validation of the model forwarded. Comparisons of predictions and test results show a fair correlation. A simple equation to predict the amount of air ingestion is also advanced in terms of the damper geometry, supplied flow and operating conditions. The criterion may lack practical implementation since the persistence of air entrainment increases with the frequency and amplitude of journal motions, unless enough lubricant is supplied at all operating conditions.
Repetitive Gait of Passive Bipedal Mechanisms in a Three-Dimensional Environment
Authors: Dankowicz Harry , Adolfsson Jesper , Nordmark Arne B.
Published: July 2002

The inherent dynamics of bipedal, kneed mechanisms are studied with emphasis on the existence and stability of repetitive gait in a three-dimensional environment, in the absence of external, active control. The investigation is motivated by observations that sustained anthropomorphic locomotion is largely a consequence of geometric and inertial properties of the mechanism. While the modeling excludes active control, the energy dissipated in ground and knee collisions is continuously re-injected by considering gait down slight inclines. The paper describes the dependence of the resulting passive gait in vertically constrained and unconstrained mechanisms on model parameters, such as ground compliance and ground slope. We also show the possibility of achieving statically unstable gait with appropriate parameter choices.
Design and Performance Verification of a 62-MWt CFB Boiler
Authors: Cen K. , Basu P. , Cheng L. , Fang M.-X. , Luo Z.-Y.
Published: July 2002

The present paper discusses the goals and methods of design of a circulating fluidized bed (CFB) boiler: A 62-MWt (75-T/h) CFB boiler was designed manually using experience and available published data. The design was regenerated by an Expert System for evaluation and confirmation of the manual design. Design choices and resulting surface areas from these two approaches were compared and validated. Final confirmation of the design can be obtained only from operation of the boiler. The boiler was built and commissioned in the Jiangshu Province, China, firing the design coal. A comprehensive test program was undertaken to monitor the performance of the boiler. Predicted performance from both the manual design and the Expert System is compared with those measured in the boiler. A reasonable agreement between the predicted performance and measured values was obtained, which confirmed both experience-based design decision and that from the Expert System.
Rotating Probe Measurements of the Pump Passage Flow Field in an Automotive Torque Converter
Authors: Dong Y. , Lakshminarayana B.
Published: July 2002

The relative flow in an automotive torque converter pump passage was measured at three locations inside the passage (mid-chord, 3/4-chord, and 4/4-chord) using a miniature high-frequency response five-hole probe in the pump rotating frame. A custom-designed brush-type slip-ring unit is used in the rotating probe system to transmit the amplified signal from the probe in the rotating frame to the stationary frame. At speed ratio of 0.6, a weak “jet-wake” flow pattern is observed at the pump mid-chord. High flow loss is observed in the core-suction corner due to the “wake” flow caused by the flow separation. A strong clockwise secondary flow is found to dominate the flow structure at the pump mid-chord. The Coriolis force and the through flow velocity deficit near the core at the pump inlet are the main reasons for this secondary flow. The jet-wake flow pattern at the 3/4-chord is enhanced by the upstream secondary flow. A jet-wake flow pattern is also observed at the pump 4/4-chord, with concentration of the flow near the passage pressure side. The secondary flow changes its direction of rotation from the 3/4-chord to 4/4-chord. This is mostly caused by the passage meridional curvature and the flow concentration. High loss is found in the core-suction corner wake flow due to a low kinetic energy flow accumulation and the flow separation. Finally, the pump flow field is assessed through the mass-averaged total pressure and relative pressure loss parameter. The data are also analyzed to assess the effect of the speed ratio on the flow field.
Geometry Modeling and Control by Infrared and Laser Sensing in Thermal Manufacturing with Material Deposition
Authors: Doumanidis Charalabos , Kwak Yong-Min
Published: July 2002

A lumped-parameter, analytical model of material and thermal transfer is established in this paper for metal deposition by a moving, concentrated source. This is a dynamic description of the distinct width, height, length, and temperature of the ellipsoidal molten puddle, expressed with respect to the torch power, material feed and angle, and the source motion. This is established through scalar mass, momentum and energy balances of the puddle control volume, and thermal conduction in the substrate. The model is validated by GMA welding experiments, through measurements by an infrared camera and a laser profilometry scanner. These sensors are next employed for real-time identification of the model efficiency parameters, and for output feedback in a closed-loop geometry control system. Because of sensor delays, the model is run in-process to provide substitute estimates to the controller in a Smith predictor scheme. Closed-loop testing was conducted for control of the bead cross section profile through the torch velocity, and the applicability of such geometry regulation to solid freeform fabrication is discussed.
A Method for Correlating the Influence of External Crossflow on the Discharge Coefficients of Film Cooling Holes
Authors: Rowbury D. A. , Oldfield M. L. G. , Lock G. D.
Published: July 2002

An empirical means of predicting the discharge coefficients of film cooling holes in an operating engine has been developed. The method quantifies the influence of the major dimensionless parameters, namely hole geometry, pressure ratio across the hole, coolant Reynolds number, and the freestream Mach number. The method utilizes discharge coefficient data measured on both a first-stage high-pressure nozzle guide vane from a modern aero-engine and a scale (1.4 times) replica of the vane. The vane has over 300 film cooling holes, arranged in 14 rows. Data was collected for both vanes in the absence of external flow. These noncrossflow experiments were conducted in a pressurized vessel in order to cover the wide range of pressure ratios and coolant Reynolds numbers found in the engine. Regrettably, the proprietary nature of the data collected on the engine vane prevents its publication, although its input to the derived correlation is discussed. Experiments were also conducted using the replica vanes in an annular blowdown cascade which models the external flow patterns found in the engine. The coolant system used a heavy foreign gas (SF6 /Ar mixture) at ambient temperatures which allowed the coolant-to-mainstream density ratio and blowing parameters to be matched to engine values. These experiments matched the mainstream Reynolds and Mach numbers and the coolant Mach number to engine values, but the coolant Reynolds number was not engine representative (Rowbury, D. A., Oldfield, M. L. G., and Lock, G. D., 1997, “Engine-Representative Discharge Coefficients Measured in an Annular Nozzle Guide Vane Cascade,” ASME Paper No. 97-GT-99, International Gas Turbine and Aero-Engine Congress & Exhibition, Orlando, Florida, June 1997; Rowbury, D. A., Oldfield, M. L. G., Lock, G. D., and Dancer, S. N., 1998, “Scaling of Film Cooling Discharge Coefficient Measurements to Engine Conditions,” ASME Paper No. 98-GT-79, International Gas Turbine and Aero-Engine Congress & Exhibition, Stockholm, Sweden, June 1998). A correlation for discharge coefficients in the absence of external crossflow has been derived from this data and other published data. An additive loss coefficient method is subsequently applied to the cascade data in order to assess the effect of the external crossflow. The correlation is used successfully to reconstruct the experimental data. It is further validated by successfully predicting data published by other researchers. The work presented is of considerable value to gas turbine design engineers as it provides an improved means of predicting the discharge coefficients of engine film cooling holes.
Thermal Damage in Particulate-Reinforced Metal Matrix Composites
Authors: Zhou Y. C. , Long S. G. , Duan Z. P. , Hashida T.
Published: July 2002

Thermal damage of SiC particulate-reinforced aluminum composites (MMCs) caused by laser thermal shock was investigated. The damage was induced by a combination of laser beam thermal shock and mechanical loads. The MMCs have two kinds of particle distributions, one is uniform and another is heterogeneous. The damage initiation, crack propagation, as well as the failure evolution, were observed. A damage parameter was defined and it was tested. One found that the damage mechanism was very different for crack initiation and crack propagation and for MMCs with different spatial particle distributions. The mechanism of MMCs failure is discussed by the ideas of shear stress transfer between matrix and reinforcement. The discussion can explain the distinct mechanism of damage and failure in SiC particulate-reinforced aluminum composites.
Numerical and Experimental Studies on Nonlinear Dynamic Behaviors of a Rotor-Fluid Film Bearing System With Squeeze Film Dampers
Authors: Hua Jun , Wan Fangyi , Xu Qingyu
Published: July 2002

In this paper, the nonlinear oil film forces of bearings and dampers with free boundary conditions are determined by the finite element method (FEM) and the complementary solution for variational inequalities. The mode synthesis technique is used to reduce the linear degrees of the high order finite element model. The periodic solution of the system and its stability are determined by the Poincare´ mapping method and the Floquet theory, respectively. The results of experiment show that squeeze film dampers (SFDs) can effectively prevent subsynchronous and nonsynchronous vibrations and some structural parameters have significant effects on the dynamic behaviors of the system. Comparing the numerical results with those of experiment, it is shown that the above theories and schemes are feasible and efficient in analyzing nonlinear behaviors of the high-order dynamic system with local nonlinearities.
Simultaneous Heat and Mass Transfer in Film Absorption With the Presence of Non-Absorbable Gases
Authors: Habib Hamza M. , Wood Byard D.
Published: July 2002

Numerical solutions are presented for the effect of a non-absorbable gas on the heat and mass transfer rates during the absorption of water vapor by a falling laminar smooth film of an aqueous lithium bromide or aqueous lithium chloride solution (absorbent). The geometry consists of a vertical channel with two walls, one of which is isothermal and the other adiabatic. The liquid film of an absorbent flows down over the isothermal wall, while a mixture of water vapor and air flows between the liquid free-surface and the adiabatic wall. The whole system is kept under vacuum pressure. Water vapor is absorbed by the film and air is the non-absorbable gas. The momentum, energy, and concentration equations are written with a set of interfacial and boundary conditions and solved numerically for the two phases. Variable property effects are included, as well as the interfacial shear. Heat and mass transfer results are presented over a wide range of inlet air concentrations. The average mass fluxes showed a continuous reduction with an increase in the amount of air for a concentration of air as high as 40 percent by weight. But the local mass fluxes showed a different behavior from the absorption of a pure vapor case. The decrease was much higher at the entrance than in a pure vapor case. The numerical results are in good agreement with the experimental data available for lithium chloride. The model has promise as means of predicting the heat and mass transfer characteristics of falling film absorber.
Viscoplastic Deformation of 40 Pb/60Sn Solder Alloys—Experiments and Constitutive Modeling
Authors: Sasaki Katsuhiko , Ohguchi Ken-ichi , Ishikawa Hiromasa
Published: July 2002

This study first proposes a simple constitutive model for viscoplasticity, which includes the elastic, plastic, and creep strains independently. The plastic strain is evaluated by the flow rule employing back stresses evolved with a Ziegler type of hardening rule. The creep strain is evaluated by the modified Norton’s law. The applicability of this constitutive model is evaluated with pure tensile tests, creep tests and cyclic tension-compression loading tests, to demonstrate the progress of viscoplastic deformation of 40Pb/60Sn solder alloys. The tests were conducted over both several temperature ranges and strain rates. As a result, it was found that the material constants used in the constitutive model could be determined by simple tests such as pure tensile and cyclic tension-compression loading tests. The simulation by the constitutive model explains accurately the viscoplastic deformation of the 40Pb/60Sn solder alloys.
Numerical Simulation of Unsteady Turbulent Flow in Axisymmetric Sudden Expansions
Authors: Guo Baoyu , Langrish Tim A. G. , Fletcher David F.
Published: July 2002

This paper is concerned with the numerical simulation of unsteady turbulent flows behind sudden expansions without inlet swirl. Time dependent simulations have been carried out using the VLES approach with the standard k-ε model. The expansion ratio investigated is in the range from 1.96–6.0. The simulations show that the flows in axisymmetric sudden expansions are inherently unstable when the expansion ratio is above a critical value. The precessing phenomenon, which features self-sustained precession of the global flowfield around the expansion centerline, is predicted successfully using CFD, with simulated oscillation frequencies that are in general agreement with reported data. For the case of expansion ratios from 3.5–6.0, a combination of a precession motion and a flapping motion in a rotating frame of reference is predicted in terms of the jet movement. Large-scale structures are identified in the downstream flowfield. Other important phenomena, such as the transition of the oscillation patterns, have also been predicted.
Multi-Direction Slicing for Layered Manufacturing
Authors: Singh Prabhjot , Dutta Debasish
Published: July 2002

Parts made by Layered Manufacturing (LM) have a limited surface accuracy and their build time is often long due to the deposition of sacrificial support structure. However, LM machines with an ability to deposit along multiple directions can improve upon the surface quality and reduce the support volume. In this paper we analyze the problem of multi-direction slicing. This analysis addresses the questions: How much of a part should be made along a particular direction and why. The strategy used in multi-direction slicing is to progressively decompose the part into sub-volumes, each of which can be completely built along a certain direction. Key issues are identified and a task framework for multidirection slicing is proposed. Algorithms and implemented examples are presented.
F110-GE-132: Enhanced Power Through Low-Risk Derivative Technology
Authors: Wadia A. R. , James F. D.
Published: July 2002

The F110-GE-132, originally referred to as the F110-GE-129 EFE (Enhanced Fighter Engine), presently undergoing qualification testing, is being offered at two different thrust/inspection levels with a maximum augmented thrust of 34,000 pounds. The EFE has been developed using low-risk derivative engine technology. It features a new increased airflow, high efficiency, three-stage long chord blisk fan, and an advanced radial augmentor that reduces complexity, improves maintainability, and provides increased parts life. The paper first provides a historical background of the F110 engines to relate the heritage of the F110-GE-132. The F110 engine model development roadmap is shown to illustrate the incremental low-risk approach used to provide thrust growth with improved product reliability. A detailed description of the unique power management features of the EFE engine to meet individual customer thrust and life requirements is outlined. The long chord blisk fan design, development, and test results are presented, followed by a description of the radial augmentor and the exhaust nozzle. The EFE engine has successfully completed sea level static and altitude development testing and fan aero mechanical qualification at the AEDC in Tullahoma, Tennessee.
Analysis and Test of a Robust Sector Thrust Bearing for a Cryogenic Turboalternator
Authors: Nellis G. F. , Zagarola M. V. , Sixsmith H.
Published: July 2002

The miniature turboalternator associated with a reverse-Brayton cryocooler requires geometrically simple, self-acting thrust bearings capable of reliable operation over a large temperature range and insensitive to secondary leakage flows. In order to meet this need, a robust sector thrust bearing has been developed. This thrust bearing is different from a classic stepped sector thrust bearing in that the restoring force at cryogenic temperatures originates primarily from inertial effects while at higher temperatures its restoring force is related primarily to viscous effects. This paper describes the analysis and initial test results for a prototypical robust sector thrust bearing.
Application of an Optimal Control Synthesis Strategy to an Electro-Hydraulic Positioning System
Authors: Abbott Richard D. , McLain Timothy W. , Beard Randal W.
Published: July 2002

Successive Galerkin Approximation (SGA) provides a means for approximating solutions to the Hamilton-Jacobi-Bellman (HJB) equation. The SGA strategy is applied to the development of optimal control laws for an electro-hydraulic positioning system (EHPS) having nonlinear dynamics. The theory underlying the SGA strategy is developed. Equations of motion for an EHPS are presented and simulation results are compared with those obtained experimentally. Results demonstrating the experimental application of the SGA synthesis strategy to an EHPS under a variety of operating conditions are presented. These results are compared to those obtained from a linear quadratic regulator developed from linearized model equations.
Prediction of Liquid Formation for Solder and Non-Solder Mask Defined Array Packages
Authors: Chen Wen-Hwa , Chiang Kuo-Ning , Lin Shu-Ru
Published: July 2002

This study presents an efficient method to accurately predict solder joint geometry after a reflow process. The proposed method can be utilized for Solder Mask Defined (SMD), Non-Solder Mask Defined (NSMD), or C4 type solder joints. The reflow process involves several design factors capable of influencing the final shape of the molten solder joint, such as solder joint volume, restoring force, surface tension, contact angle, pad thickness, and pad size. These factors are all considered in the calculations. The computed results are compared with those using the Surface Evolver program and also with available numerical/experimental results. Their excellent agreement shows that the method developed herein can be practically applied to predict the reflow shape of SMD/NSMD solder joints. The difference between SMD and NSMD is also examined in detail. Results in this study provide designers with a fundamental guideline for accurately predicting the liquid formation of solder joints during the reflow process.
Site-Specific Design Optimization of 1.5–2.0 MW Wind Turbines
Authors: Fuglsang Peter , Thomsen Kenneth
Published: July 2002

A method is presented for site-specific design of wind turbines where cost of energy is minimized. A numerical optimization algorithm was used together with an aeroelastic load prediction code and a cost model. The wind climate was modeled in detail including simulated turbulence. Response time series were calculated for relevant load cases, and lifetime equivalent fatigue loads were derived. For the fatigue loads, an intelligent sensitivity analysis was used to reduce computational costs. Extreme loads were derived from statistical response calculations of the Davenport type. A comparison of a 1.5 MW stall regulated wind turbine in normal onshore flat terrain and in an offshore wind farm showed a potential increase in energy production of 28% for the offshore wind farm, but also significant increases in most fatigue loads and in cost of energy. Overall design variables were optimized for both sites. Compared to an onshore optimization, the offshore optimization increased swept area and rated power whereas hub height was reduced. Cost of energy from manufacture and installation for the offshore site was reduced by 10.6% to 4.6¢. This reduction makes offshore wind power competitive compared with today’s onshore wind turbines. The presented study was made for one wind turbine concept only, and many of the involved sub models were based on simplified assumptions. Thus there is a need for further studies of these models.
Effect of Moisture on the Interfacial Adhesion of the Underfill/Solder Mask Interface
Authors: Ferguson Timothy , Qu Jianmin
Published: July 2002

Moisture poses a significant threat to the reliability of microelectronic assemblies and can be attributed as being the principal cause of many premature package failures. Of particular concern is characterizing the role of moisture with respect to the acceleration of the onset of package delamination. In this paper the effect of moisture on the interfacial fracture toughness of two no-flow underfill materials with a commercially available solder mask coated FR-4 board is experimentally determined. Bilayer specimens with prefabricated interface cracks are used in a four-point bend test to quantify the interfacial fracture toughness. Two groups of test specimens of varying underfill thickness were constructed. The first group was fully dried while the other was moisture preconditioned at 85°C/85%RH for 725 hours. The results of this study show that the interfacial toughness is significantly affected by the presence of moisture.
Control of the Shape of a Thrombus-Neointima-Like Structure by Blood Shear Stress
Authors: Liu S. Q. , Zhong L. , Goldman J.
Published: July 2002

Fluid mechanical factors are thought to influence vascular morphogenesis. Here we show how blood shear stress regulates the shape of a thrombus-neointima-like tissue on a polymer micro-cylinder implanted in the center of the rat vena cava with the micro-cylinder perpendicular to blood flow. In this model, the micro-cylinder is exposed to a laminar flow with a known shear stress field in the leading region and a vortex flow in the trailing region. At 1, 5, 10, 20, and 30 days after implantation, it was found that the micro-cylinder was encapsulated by a thrombus-neointima-like tissue with a streamlined body profile. The highest growth rate of the thrombus-neointima-like tissue was found along the trailing and leading stagnation edges of the micro-cylinder. Blood shear stress in the laminar flow region was inversely correlated with the rate of thrombus formation and cell proliferation, and the percentage of smooth muscle α actin-positive cells. These biological changes were also found in the trailing vortex flow region, which was associated with lowered shear stress. These results suggest that blood shear stress regulates the rate of thrombus and neointimal formation and, thus, influences the shape of the thrombus-neointima-like structure in the present model.
Modification of Near-Wall Structure in a Shear-Driven 3-D Turbulent Boundary Layer
Authors: Kiesow Robert O. , Plesniak Michael W.
Published: July 2002

The near-wall physics of a planar, shear-driven, 3-D turbulent boundary layer with varying strengths of crossflow are examined. Flow visualization data reveals a reduction of mean streak length by as much as 50% with increasing spanwise shear. Power spectra of velocity confirm this shift towards higher temporal frequencies, corresponding to decreased streamwise length scales. PIV measurements indicate a significant modification of the inner region of the boundary layer with increasing spanwise shear. Streamwise velocity profiles exhibit an increasing velocity deficit with increased crossflow. Increased levels of the normal Reynolds stresses u′2¯ and v′2¯ and an increase in the −u′v′¯ Reynolds shear stress are also observed. Modifications in the spanwise and transverse vorticity were also observed at higher shear rates.
Hydraulic Servo System With Mechanically Adjustable Compliance
Authors: Hayase Toshiyuki , Ishizawa Kazuhiro , Hayashi Satoru , Iimura Ikuro
Published: July 2002

This paper deals with a hydraulic servo system with compliance control for the operation in an environment with frequent machine-human interaction. The compliance is mechanically adjusted in the present hydraulic system by changing the neutral position of the bridge valves between the full opening and the full closing states. The mathematical model of the system is first derived, and the static and the dynamic behavior of the system are investigated through numerical simulation. Since the present system exhibits a strong nonlinear characteristic in the operating condition of large compliance, a nonlinear controller is designed with the feedback linearization technique. In the operating condition of small compliance, on the other hand, a conventional linear control is applicable as usual hydraulic control systems. The performance of the present control system is investigated through both numerical simulation and experiment, justifying that the present hydraulic servo system continuously adapts its performance between a rigid positioning against disturbances and a compliant positioning to prevent damage to obstacles on the path.
Computations of the Flow and Heat Transfer in Microdevices Using DSMC With Implicit Boundary Conditions
Authors: Fang Yichuan , Liou William W.
Published: July 2002

The heat transfer and the fluid dynamics characteristics of subsonic gas flows through microchannels are examined using the direct simulation Monte Carlo (DSMC) method. A simple implicit treatment for the low-speed inflow and outflow boundaries for the DSMC of the flows in microelectromechanical systems (MEMS) is used. Micro-Couette flows and micro-Poiseuille flows are simulated with the value of the Knudsen numbers ranging between 0.06 and 0.72. Where appropriate, the calculated velocity slip and temperature distribution are compared with analytical solutions derived from the Navier-Stokes equations with slip-boundary conditions. A patterned microstructure with nonuniform surface temperature is also simulated. The computational results show that the Knudsen number and the geometric complexity have significant effects on the heat transfer as well as the fluid dynamics properties of the microfluid flows studied.
Shock Wave Propagation Into a Dust-Gas Suspension Inside a Double-Bend Conduit
Authors: Igra O. , Wu X. , Hu G. Q. , Falcovitz J.
Published: July 2002

Using conduits in which a transmitted shock wave experiences abrupt changes in its direction of propagation is an effective means for shock wave attenuation. An additional attenuation of the transmitted shock wave is obtained when the medium contained inside the conduit (through which the shock wave is transmitted) is a suspension rather than a pure gas. The present numerical study shows that adding small solid particles (dust) into the gaseous phase results in sharp attenuation of all shock waves passing through the conduit. It is shown that the smaller the dust particles diameter is, the higher the shock attenuation becomes. Increasing the dust mass loading in the suspension also causes a quick attenuation. By proper choice of dust mass loading in the suspension, or the particles diameter, it is possible to ensure that the emerging wave from the conduit exit channel is a (smooth) compression wave, rather than a shock wave.
Effects of Cyclic Pressure on Bone Marrow Cell Cultures
Authors: Nagatomi Jiro , Arulanandam Bernard P. , Metzger Dennis W. , Meunier Alain , Bizios Rena
Published: July 2002

The present in-vitro study used bone marrow cell cultures and investigated the effects of cyclic pressure on osteoclastic bone resorption. Compared to control (cells maintained under static conditions), the number of tartrate resistant acid phosphatase (TRAP)-positive, osteoclastic cells was significantly p<0.05 lower when, immediately upon harvesting, bone marrow cells were exposed to cyclic pressure (10–40 kPa at 1.0 Hz). In contrast, once precursors in bone marrow cells differentiated into osteoclastic cells under static culture conditions for 7 days, subsequent exposure to the cyclic pressure of interest to the present study did not affect the number of osteoclastic cells. Most important, exposure of bone marrow cells to cyclic pressure for 1 h daily for 7 consecutive days resulted in significantly p<0.05 lower osteoclastic bone resorption and in lowered mRNA expression for interleukin-1 (IL-1) and tumor necrosis factor-α (TNF-α), cytokines that are known activators of osteoclast function. In addition to unique contributions to osteoclast physiology, the present study provided new evidence of a correlation between mechanical loading and bone homeostasis as well as insight into the molecular mechanisms of bone adaptation to mechanical loading, namely cytokine-mediated control of osteoclast functions.
Transient Improvement of Variable Structure Controlled Systems Via Multi-Model Switching Control
Authors: Corradini Maria Letizia , Orlando Giuseppe
Published: July 2002

A solution is presented in this note to the problem of improving the transient response of a MIMO nonlinear system driven by a VSC law, in the presence of large plant uncertainties. The proposed control scheme is given in terms of a supervisor and of a deterministic time-varying compensator, built using sliding-mode control and assuming a finite number of possible different configurations. The task of the supervisor is that of guiding the scanning among the elements of the family, according to a suitably defined experimental test. The proposed approach noticeably improves the performances of sliding-mode control in the presence of large plant uncertainties, and has the substantial advantage of a great simplicity of design and implementation. Moreover, even in case of a large number of configurations constituting the stabilizing family, it has been shown to be able to attain the stabilizing controller in an arbitrarily small time interval. Another appealing feature of the paper consists in the inclusion of an intelligent adaptation scheme in the control algorithm.
Robust Nonfragile Decentralized Controller Design for Uncertain Large-Scale Interconnected Systems With Time-Delays
Authors: Park Ju H.
Published: July 2002

This paper describes the synthesis of robust nonfragile decentralized controllers for uncertain large-scale systems with time-delays in the subsystem interconnections and controller gain variations. Based on the Lyapunov method, a sufficient condition for robust stability is derived in terms of a linear matrix inequality (LMI), and the measure of nonfragility in controller is presented.
Buckling of a Short Cylindrical Shell Surrounded by an Elastic Medium
Authors: Naili S. , Oddou C.
Published: July 2002

The lateral surface of a cylindrical structure, which is composed of a thin tube embedded in a large outer medium, is submitted to a uniform external pressure. The buckling pressure of such a structure, corresponding to a low flexural state of the inner tube wall, is theoretically analyzed on the basis of the asymptotic method. The theoretical results are compared with experimental ones obtained from a compression test realized on an elastic tube inserted in a foam. It is found that the Euler pressure and the associated buckling mode index strongly depend upon the rheological and geometrical parameters of both the tube and the surrounding medium. [S0021-8936(00)00201-4]
Pulsed Laser-Induced Thermal Damage in Whole Blood
Authors: Pfefer T. Joshua , Choi Bernard , Vargas Gracie , McNally Karen M. , Welch A. J.
Published: July 2002

An investigation of the effects of laser irradiation with a wavelength of 532 nm and pulse duration of 10 ms on whole blood was performed in vitro. Threshold radiant exposures for coagulation were quantified and transient radiometric temperatures were measured. The progression of effects with increasing radiant exposure—from evaporation to coagulation-induced light scattering to aggregated coagulum formation to ablation—is described. Results indicate that coagulation and ablation occur at temperatures significantly in excess of those assumed in previous theoretical studies. An Arrhenius rate process analysis based on hemoglobin data indicates good agreement with experimental results. [S0148-0731(00)00902-X]
On the Limit of Surface Integrity of Alumina by Ductile-Mode Grinding
Authors: Zarudi I. , Zhang L. C.
Published: July 2002

This paper investigates both experimentally and theoretically the subsurface damage in alumina by ductile-mode griding. It found that the distribution of the fractured area on a ground mirror surface, with the Rms roughness in the range from 30 nm to 90 nm, depends on not only the grinding conditions but also the pores in the bulk material. Surface pit formation is the result of interaction of abrasive grains of the grinding wheel with pores. Thus the surface quality achievable by ductile-mode grinding is limited by the initial microstructure of a material. The investigation shows that median and radial cracks do not appear and hence are not the cause of fracture as usually thought. [S0094-4289(00)02001-6]
Design by Composition for Layered Manufacturing*
Authors: Binnard Mike , Cutkosky Mark R.
Published: July 2002

Three dimensional rapid prototyping processes, also called layered manufacturing or solid freeform fabrication (SFF), promise designers the ability to automatically fabricate complex shapes. SFF processes were invented with the assumption that designers would submit complete part models for automated planning and manufacturing. This planning process is normally based on some form of “decomposition,” for example, slicing into layers. Especially for newer, more complex SFF processes, there are several disadvantages to this approach, primarily that decomposition is difficult and does not reliably produce good process plans. Furthermore, it is hard for the designer to get feedback on the manufacturability of his design, and today’s decomposition systems are not fully automated. This paper presents an alternative approach, “design by composition,” where users build designs from “primitives” that include high-level manufacturing plans. When the user combines two primitives with a Boolean operation, software will automatically generate a manufacturing plan for the new design from the plans for the source primitives. In contrast to the decomposition method, design by composition offers several benefits to designers, primarily access to manufacturability feedback during design-time, a greater degree of automation, the ability to create designs with embedded components (such as sensors, electronic circuits, bearings, and shafts), and enhanced control over manufacturing plans. These advantages make design by composition a more attractive approach to SFF processing, especially for designers who are new to these processes. [S1050-0472(00)01701-3]
Flow-Induced Vibrations in Power and Process Plant Components—Progress and Prospects
Authors: Weaver D. S. , Ziada S. , Au-Yang M. K. , Chen S. S. , Paı¨doussis M. P. , Pettigrew M. J.
Published: July 2002

This paper provides a brief overview of progress in our understanding of flow-induced vibration in power and process plant components. The flow excitation mechanisms considered are turbulence, vorticity shedding, fluidelastic instability, axial flows, and two-phase flows. Numerous references are provided along with suggestions for future research on unresolved issues. [S0094-9930(00)01203-8]
Characterization of Electrochemically Prepared γ-NiOOH by XPS
Authors: Mansour A. N. , Melendres C. A.
Published: July 2002

We report x-ray photoemission spectra (XPS) of electrochemically prepared γ-NiOOH. XPS spectra were measured with the Physical Electronics Model 5400 x-ray photoelectron spectrometer using unmonochromatized Mg Kα x rays at two pass energy settings corresponding to analyzer energy resolutions of 1.34 and 0.54 eV. We present the survey spectrum (binding energy range of 0–1100 eV) measured at an analyzer energy resolution of 1.34 eV. Multiplexes of the C, O, K, and Ni photoemission lines, valence band region, as well as Ni LMM Auger line were measured at an analyzer energy resolution of 0.54 eV. The γ–NiOOH sample was prepared by the anodic oxidation of anodically formed α-Ni(OH)2.
Etching of Si through a thick condensed XeF2 layer
Authors: Sebel P. G. M. , Hermans L. J. F. , Beijerinck H. C. W.
Published: July 2002

Etching of silicon by XeF2 is studied in a multiple-beam setup. Below 150 K XeF2 condenses and forms a layer on the silicon, which blocks the etching. Upon ion bombardment, this layer is removed and etching will resume. As a function of the layer thickness, the various removal mechanisms of the layer are studied. For a thick condensed layer it is found that 1 keV Ar+ ions sputter the condensed layer with a yield of 160 XeF2 molecules per ion for 1 keV Ar+ ions and 280 for 2 keV ions. For thinner layers (below 9 nm for 1 keV ions), this sputter rate by ions decreases significantly. Here, the removal is mainly due to consumption of XeF2 by etching at the bottom of the layer. This consumption rate reaches a maximum for a layer thickness of about 5 nm. In the steady-state situation, the layer thickness is further decreased, resulting in a smaller consumption and etch rate. Here, sputtering is the most important removal mechanism for the deposited XeF2 layer. From this, it is concluded that a pulsed ion beam should be used in cryogenic etching to obtain the highest etch rate.
Ionization of sputtered material in a planar magnetron discharge
Authors: Christou C. , Barber Z. H.
Published: July 2002

Emission spectra in the visible and near ultraviolet have been recorded for the magnetron sputtering of titanium by argon at pressures between 0.5 and 100 Pa. Intense emission lines from both atomic and ionic material were detected, and comparison of line intensities yielded an ionization fraction of over 10% and an electron temperature of the order of 1 eV for the sputtered material. The ionization fraction decreased with increasing magnetron power, and an optimal operating pressure was found for maximum ion content of the sputtered flux. Scaling laws of emission line intensity with magnetron power indicated the incomplete thermalization of sputtered metal with the sputtering plasma, and spatially resolved measurements of ionization profiles were used to investigate the transport and collisional ionization of sputtered material. Penning ionization of sputtered titanium by metastable argon was found to be the dominant ionization process, and the effect of diffusion of metastable argon was noted. Control of ion content in sputtered fluxes is of interest for the deposition of thin films and for metallization of semiconductors.
Deposition of High-Purity Nb Films by Tetrode Sputtering
Authors: Ogawa S. , Takiguchi K. , Hasegawa T.
Published: July 2002

Niobium thin films with extremly low resistivity (14.7 μΩ cm) have been deposited by tetrode sputtering in Ar gas purified by the getter action of titanium sublimation pump. The effect of gaseous impurities on the resistivity, superconducting transition temperature, and crystal structure were investigated. The superconducting transition temperature of such films was enhanced to 9.8±0.1 K and the temperature coefficient of resistance was increased to +3.0×103 ppm/deg.
Angular Distributions of Secondary Electrons Originating from Thin Films of Different Metals in Re-emission and Transmission
Authors: Jahrreiss H. , Oppel W.
Published: July 2002

Continuing preceding research on this field, angular distributions of η and δ electrons from thin films of Al and Au have been investigated by means of a considerably improved apparatus. Measurements have been made in forward and backward directions with primary energies in the interval 1 to 20 keV with normal as well as oblique incidence of the primaries. In addition, the angular distributions in reemission of bulk probes of Al and Au as well as other metals (Ag, Cu, In, Ni, Ta, W) have been investigated. There are several characteristic differences between the measured curves and the cosine distribution which are discussed in respect to the generating processes within these metals.

Im Anschluss an frühere Arbeiten wurden Winkelverteilungen von η- und δ-Elektronen aus dünnen Al- und Au-Schichten mittels einer wesentlich verbesserten Apparatur untersucht. Die Messungen wurden in Vorwärts- und Rückwärtsrichtung mit Primäirelektronenenergien zwischen 1 und 20 keV bei senkrechtem und schrägem Einfall der Primärelektronen ausgeführt. Zusätzlich wurden die Winkelverteilungen in Rückwärtsrichtung aus massiven Proben von Al und Au wie auch von weiteren Metallen (Ag, Cu, In, Ni, Ta, W) untersucht. Man beobachtet einige charakteristische Unterschiede zwischen den gemessenen Kurven und der Kosinus-Verteilung, die im Hinblick auf die zugrunde liegenden Prozesse innerhalb dieser Metalle diskutiert werden.
Sorption Effects on Epitaxic PbSe Films
Authors: Cepeda A. , McLane G. , Zemel J. N.
Published: July 2002

Recent studies of epitaxic films of PbSe have shown that atomic hydrogen, H, and oxygen, O2, produce changes in their electrical properties. To clarify the sorption phenomena, a study of the kinetics at room temperature was undertaken on as-grown films of different thicknesses. Analysis of the results has shown that O2 has a marked surface effect and also slowly diffuses into PbSe films; H diffuses substantial distances up to 2; approximately 1018 Pb and Se vacancies/cm3 exist in the as-grown PbSe films. Temperature measurements confirm that the activation energy for the H diffusion is close to 0.3 eV. The agreement between various measurements supports recent conjectures by Pratt and Parada on the nature of vacancies in the lead salts as well as Holloway and Logothetis on compensation in these materials.
Recent Advances in the Chemical Vapor Growth of Electronic Materials
Authors: Chu T. L. , Smeltzer R. K.
Published: July 2002

The chemical vapor growth technique has been used extensively for the preparation and crystal growth of electronic materials either in the bulk form or as thin layers on substrate surfaces. Using the chemical transport technique or the reaction of gaseous compounds containing the constituents of the desired material, electronic materials with thicknesses in a wide range can be prepared at temperatures considerably below their melting points or decomposition temperatures. Furthermore, the impurity concentration and distribution in the product can be controlled to an extent not obtainable by other techniques. The recent progress in the chemical vapor growth of semiconductors, insulators, conductors, magnetic materials, and superconductors is discussed with emphasis on the epitaxial growth of semiconductors.
Monte Carlo study of light transmission through a cylindrical tube
Authors: Blechschmidt D.
Published: July 2002

The transmission of light in vacuum through a cylindrical tube with specular walls has been evaluated using the Monte Carlo method. Uniform as well as cosine angular distributions have been assumed as the initial conditions at the entrance aperture; both cases were treated separately for a light cource of uniform density. From the results, which are given as a function of the tube's length-to-diameter ratio L / D and the reflectivity of the inner wall R (0 ≤ R ≤ 0.99), a simple expression has been derived that holds for long tubes L ≥ 4D/ln(1/R) and R ≤ 0.6. The relation T(L,D,R) also yields the molecular transmissivity if specular reflection applies with a sticking coefficient S = 1 − R.