bluuebunny/crossref_metadata_2025 huggingface dataset:
Quality control, assurance and assessment – the link to
continuous improvement
Authors: Colling Clive , Harvey Lee
Published: July 2002

Discusses the different forms of external enquiry into the
operations of HEIs that constitute existing quality control, assurance
and assessment processes and procedures. Proposes that external scrutiny
of operations should adopt an approach that ensures accountability,
enhances quality, is practical, efficient, effective and offers a degree
of autonomy. Asserts that putting continuous quality improvement into
practice in higher education requires the implementation of key
principles of procedure and practical team approaches which are
currently far from endemic across institutions. Describes and explains
how the identification of specific roles and responsibilities within
academic teams can provide one way of successfully establishing the link
between quality control, assurance and assessment and the process of
continuous quality improvement in the provision of higher education.
A model for monitoring Web site effectiveness
Authors: Day Abby
Published: July 2002

Presents a model which organizations can use to monitor Web site effectiveness. Argues that anecdotal evidence can be colorful but is not useful in structuring and managing an effective site. Suggests that traditional disciplines of composition and communication ‐ explicit purpose, coherent structure, relevant conclusion ‐ should be applied to Web site design. Concludes that customer feedback must be managed in a disciplined way, by ensuring that feedback is representative of the customer population as a whole, not just of those with a propensity to comment; and that the purpose and aims of a Web site must be thought through with the utmost care and attention to give a higher likelihood of creating an effective site.
The calculation of investment worth – Issues of market efficiency, variable estimation and risk analysis
Authors: Hutchison Norman , Nanthakumaran Nanda
Published: July 2002

The Mallinson Report, published in 1994, emphasised the need for valuers to develop expertise for the purpose of estimating the worth of property investments. Implicit in attempts to estimate worth is the assumption that the property market displays some level of inefficiency and that, in such a market, price and worth may diverge. It is believed that astute investors can exploit such inefficiencies in the market to add value to their portfolios. This paper reviews the main issues relating to the calculation of worth. Specifically it examines market efficiency, individual and market worth, and the use of risk analysis in the calculation. Finally, it recommends a shorter analysis period in view of the uncertainty in the estimation of the variables.
Catalytic center of an archaeal type 2 ribonuclease H as revealed by X‐ray crystallographic and mutational analyses
Authors: Muroya Ayumu , Tsuchiya Daisuke , Ishikawa Momoyo , Haruki Mitsuru , Morikawa Masaaki , Kanaya Shigenori , Morikawa Kosuke
Published: July 2002

The catalytic center of an archaeal Type 2 RNase H has been identified by a combination of X‐ray crystallographic and mutational analyses. The crystal structure of the Type 2 RNase H from Thermococcus kodakaraensis KOD1 has revealed that the N‐terminal major domain adopts the RNase H fold, despite the poor sequence similarity to the Type 1 RNase H. Mutational analyses showed that the catalytic reaction requires four acidic residues, which are well conserved in the Type 1 RNase H and the members of the polynucleotidyl transferase family. Thus, the Type 1 and Type 2 RNases H seem to share a common catalytic mechanism, except for the requirement of histidine as a general base in the former enzyme. Combined with the results from deletion mutant analyses, the structure suggests that the C‐terminal domain of the Type 2 RNase H is involved in the interaction with the DNA/RNA hybrid.
Monotonicities in a Markov Chain Model for Valuing Corporate Bonds Subject to Credit Risk
Authors: Kijima Masaaki
Published: July 2002

In recent years, it has become common to use a Markov chain model to describe the dynamics of a firm's credit rating as an indicator of the likelihood of default. Such a model can be used not only for describing the dynamics but also for valuing risky discount bonds. The aim of this paper is to explain how the Markov chain model leads to the known empirical findings such that prior rating changes carry predictive power for the direction of future rating changes and a firm with low (high, respectively) credit rating is more likely to be upgraded (downgraded) conditional on survival as the time horizon lengthens. The model will also explain practically plausible statements such as that bond prices as well as credit risk spreads would be ordered according to their credit qualities. Stochastic monotonicities of absorbing Markov chains play a prominent role in these issues.
Temperature effect on isometric tension is mediated by regulatory proteins tropomyosin and troponin in bovine myocardium
Authors: Fujita Hideaki , Kawai Masataka
Published: July 2002

The effect of temperature on isometric tension with and without the regulatory proteins tropomyosin and troponin was studied in bovine myocardium using a thin filament removal and reconstitution protocol. In control bovine myocardium, isometric tension increased linearly with temperature in the range 5–40 °C: isometric tension at 10 and 30 °C was 0.65 and 1.28 times that at 20 °C, respectively, with a Q10 of about 1.4. In actin filament‐reconstituted myocardium without regulatory proteins, the temperature effect on isometric tension was less: isometric tension at 10 and 30 °C was 0.96 and 1.17 times that at 20 °C, respectively, with a Q10 of about 1.1. The temperature dependence of the apparent rate constants was studied using sinusoidal analysis. The temperature dependence of 2πb (rate constant of delayed tension phase) did not vary significantly with the regulatory proteins under the standard activating condition (5 mm MgATP, 8 mm Pi, 200 mm ionic strength, pCa 4.66, pH 7.00). Q10 for 2πb in control and actin filament‐reconstituted myocardium was 3.8 and 4.0, respectively. There were two phases to the temperature dependence of 2πc (rate constant of quick recovery). In control and thin filament‐reconstituted myocardium, Q10 for 2πc was approximately 5.5 in the low temperature range (≤ 25 °C) and 2.7 in the high temperature range (≥ 30 °C). In actin filament‐reconstituted myocardium, Q10 for 2πc was 8.5 in the low temperature range and 3.6 in the high temperature range. The above results demonstrate that regulatory proteins augment the temperature dependence of isometric tension, indicating that the regulatory proteins may modify the actomyosin interaction.
Excitation and desensitization of mouse rod photoreceptors in vivo following bright adapting light
Authors: Derwent Jennifer J. Kang , Qtaishat Nasser M. , Pepperberg David R.
Published: July 2002

Electroretinographic (ERG) methods were used to determine response properties of mouse rod photoreceptors in vivo following adapting illumination that produced a significant extent of rhodopsin bleaching. Bleaching levels prevailing at ∼10 min and ∼20 min after the adapting exposure were on average 14% and 9%, respectively, based on the analysis of visual cycle retinoids in the eye tissues. Recovery of the rod response to the adapting light was monitored by analysing the ERG a‐wave response to a bright probe flash presented at varying times during dark adaptation. A paired‐flash procedure, in which the probe flash was presented at defined times after a weak test flash of fixed strength, was used to determine sensitivity of the rod response to the test flash. Recovery of the response to the adapting light was 80% complete at 13.5 ± 3.0 min (mean ±s.d.; n= 7) after adapting light offset. The adapting light caused prolonged desensitization of the weak‐flash response derived from paired‐flash data. By comparison with results obtained in the absence of the adapting exposure, desensitization determined with a test‐probe interval of 80 ms was ∼fourfold after 5 min of dark adaptation and ∼twofold after 20 min. The results indicate, for mouse rods in vivo, that the time scale for recovery of weak‐flash sensitivity substantially exceeds that for the recovery of circulating current following significant rhodopsin bleaching. The lingering desensitization may reflect a reduced efficiency of signal transmission in the phototransduction cascade distinct from that due to residual excitation.
Group II metabotropic glutamate receptor activation is required for normal hippocampal mossy fibre development in the rat
Authors: Koyama Ryuta , Yamada Maki Kobayashi , Nishiyama Nobuyoshi , Matsuki Norio , Ikegaya Yuji
Published: July 2002

Glutamate is the main neurotransmitter at hippocampal mossy fibre (MF) terminals. Because neurotransmitters have been proposed as regulating factors of neural network formation and neurite morphogenesis in the developing CNS, we examined the possible contribution of glutamate to MF pathfinding. Entorhino‐hippocampal slices prepared from early postnatal rats were cultivated in the presence of glutamate receptor antagonists. Timm histochemical staining revealed that pharmacological blockade of metabotropic glutamate receptors (mGluR), but not of ionotropic glutamate receptors, induced abnormal outgrowth of the MFs. When slices were cultured in the presence of mGluR antagonists, DiI‐labelled MF axons displayed a great degree of defasciculation, and MF‐mediated EPSPs in the CA3 pyramidal cells were altered. Similar results were obtained for a selective antagonist of group II mGluR, but not of group I or III mGluR. Glutamate is, therefore, likely to regulate MF outgrowth via activation of group II mGluR. The present study may provide a novel role of glutamate in hippocampal development.
Dynamic Response of Risers Conveying Fluid
Authors: Bar-Avi Patrick
Published: July 2002

Riser conveying fluid is one category in a wide research area known as moving continua dynamic that was the subject to many research studies in the past 50 yr. The structure investigated in this paper is assumed to be a flexible pipe having a geometry of a simple catenary with a buoyancy force at the top. The riser is modeled as a beamlike continuous system subjected to wave, current, and wind forces. The derivation of the partial differential equation of motion included the following aspects: nonlinearities due to geometry, i.e., large displacements as well as wave drag force, fluid internal and external pressure, and internal fluid velocity and acceleration. The wave forces are approximated via Morison’s equation, where the drag force is proportional to the square of the relative velocity between the riser and the waves. All forces are calculated at the instantaneous position of the riser, causing the equation to be highly nonlinear. The nonlinear partial differential equation of motion is then solved numerically. Finite difference approximation code that was imbedded in ACSL software is used. The equation of motion is solved to evaluate the riser’s response to different environmental conditions and other physical parameters such as internal pressure and fluid velocity and acceleration. [S0892-7219(00)00203-X]
A Geometric Path Planner for Car-like Robots
Authors: Chen Shiang-Fong , Deng Jiansong
Published: July 2002

This technical brief presents a refined slabbing method, originally used for free-flying robots, for finding efficient paths for nonholonomic robots. Our method takes kinematic constraints and reversal maneuvers into account. We create orientation levels for each orientation configuration of the robot. The slopes of slabbing lines in each orientation level match the orientation of a robot in that level. The resulting slabbing lines act as “rails” to guide the robot. Thus, a robot, if it keeps moving in a given orientation level, can only translate straight forward or straight backward along a given slabbing line. Limiting robot movement to straight forward or straight backward along a slabbing line prevents the robot from violating kinematic constraints, by moving sideways to another slabbing line. [S1050-0472(00)01403-3]
Statistical Considerations in the Analysis of Data From Fatigue Tests on Delaminated Cross-Ply Graphite/Epoxy Composites
Authors: La Saponara Valeria , Kardomateas George A.
Published: July 2002

The objective of this paper is to analyze the results of compressive fatigue experiments performed on a set of delaminated Graphite/Epoxy cross-ply composites. Crack branching, the failure mode we are interested in, occurred during the tests. Due to scatter, it is somewhat difficult to draw conclusions on the values of the branching angles, the key parameter of the problem, unless the tools of statistical and exploratory data analysis (EDA) are used. Here, a brief discussion on some of these techniques is presented, and their application to the set of obtained test data is carried out. The results seem to indicate that the crack grows faster when it is not self-similar, with a higher rate of growth for cracks that branch with a greater angle out of the interface. [S0094-4289(00)03204-7]
New Racing Equation for Championship Performance
Authors: Van Dorn W. G.
Published: July 2002

A separate investigation of swimming endurance has led to a family of expressions relating maximal human locomotor activity to time and/or distance having such wide application to medicine, physiology, and sports as to merit independent publication. Specifically, variations of a single racing equation with one variable parameter suffice to predict record times, speeds, energy, power, and endurance accurately for cycling, running, and swimming, provided only that performance be categorized as steady-state, aerobic effort. [S0148-0731(00)01405-9]
Intake Flow Structure and Swirl Generation in a Four-Valve Heavy-Duty Diesel Engine
Authors: Kang Kern Y. , Reitz Rolf D.
Published: July 2002

Intake flow structure was studied using various port geometries in a four-valve heavy-duty diesel engine. Swirl ratio, LDV measurements of bulk flow and turbulence, and flow visualization experiments were conducted on a steady-state bench rig. In addition to the standard production port, archetypal intake port flows (swirl, anti-swirl and tumble) were created using intake valve shrouds. These flow types are not usually found in heavy-duty engines, which typically employ quiescent combustion chamber designs. However, recent CFD analyses have indicated that intake flow structures can significantly influence engine pollutant emissions (Fuchs and Rutland, 1998). Thus, it was of interest to characterize these flows in a heavy-duty engine. The measured swirl and axial velocity components were analyzed to reveal the swirl and tumble generation mechanisms, and the LDV data compared favorably with the swirl meter results. The flow visualization confirmed the existence of flow recirculation regions under the intake valves also seen in the LDV data. These flow structures help to explain the origins of the overall swirl and tumble flow fields. The results were also compared with available CFD predictions made using the same port configurations. The measured swirl levels were found to agree with the CFD trends. However, in some cases quantitative differences were found, presumably due to the effect of piston motion in the actual engine. These differences need to be accounted for when evaluating port designs from steady-flow measurements, especially in cases with high tumble flow components. [S0742-4795(00)00804-8]
Spectral Measurements in Transitional Boundary Layers on a Concave Wall Under High and Low Free-Stream Turbulence Conditions
Authors: Volino Ralph J. , Simon Terrence W.
Published: July 2002

The relationship between free-stream turbulence and boundary layer behavior has been investigated using spectral measurements. The power spectral densities of turbulence quantities in transitional and fully turbulent boundary layers were computed and compared to the power spectra of the same quantities measured in the free stream. Comparisons were made using the “transfer function.” The transfer function is the ratio of two spectra at each frequency in the spectra. Comparisons were done in flows with low (0.6 percent) and high (8 percent) free-stream turbulence intensities. Evidence was gathered that suggests that relatively low-frequency, large-scale eddies in the free stream buffet the boundary layer, causing boundary layer unsteadiness at the same low frequencies. These fluctuations are present in both transitional and fully turbulent boundary layers. They are seen under both high and low free-stream turbulence conditions, although they are stronger in the high-turbulence case. Examination of the turbulent shear stress suggests that the low-frequency fluctuations enhance transport in the boundary layer but they are not so effective in promoting eddy transport as are turbulent eddies produced and residing within the boundary layer. In the fully-turbulent boundary layer, higher-frequency fluctuations are added to the low-frequency unsteadiness. These higher-frequency fluctuations, not seen in the transitional boundary layer, are associated with turbulence production in the boundary layer and appear not to be directly related to free-stream unsteadiness. [S0889-504X(00)00403-7]
Pressure Gradient and Choking Velocity for Adiabatic Pipe Flow of a Homogeneous Steam-Water-Solids Mixture
Authors: Fluerenbrock F.
Published: July 2002

Mixtures containing steam, water, and solids develop when processing ore slurries at elevated temperature and pressure. Based on homogeneous one-dimensional three-phase flow theory equations are derived for pressure gradient, choking velocity, and sonic velocity of a steam-water-solids mixture flowing in a pipe. It is concluded that a quasi-choking condition may occur when the flow changes from subcooled to flashing conditions. [S0098-2202(00)00104-8]
Analysis of EHL Circular Contact Start Up: Part II—Surface Temperature Rise Model and Results
Authors: Zhao Jiaxin , Sadeghi Farshid , Hoeprich Michael H.
Published: July 2002

A numerical model of surface temperature rise in elastohydrodynamic lubrication start up process is presented. The frictional heat flux is modeled as the product of lubricated contact pressure or solid contact pressure with its respective coefficient of friction. The temperature rise is calculated by numerically integrating the solution of point heat source moving over a half space. The constant speed restriction is removed to allow calculation of temperature rise on a surface with a variable speed. The FFT method is incorporated to speed up the temperature rise calculation. Surface temperature rise in elastohydrodynamic lubrication start up condition is calculated, for the case when speed increase from zero to desired speed occurs in one step and the case when speed is linearly increased to desired speed.
Experimental Heat Transfer and Bulk Air Temperature Measurements for a Multipass Internal Cooling Model With Ribs and Bleed
Authors: Thurman Douglas , Poinsatte Philip
Published: July 2002

An experimental study was made to obtain heat transfer and air temperature data for a simple three-leg serpentine test section that simulates a turbine blade internal cooling passage with trip strips and bleed holes. The objectives were to investigate the interaction of ribs and various bleed conditions on internal cooling and to gain a better understanding of bulk air temperature in an internal passage. Steady-state heat transfer measurements were obtained using a transient technique with thermochromic liquid crystals. Trip strips were attached to one wall of the test section and were located either between or near the bleed holes. The bleed holes, used for film cooling, were metered to simulate the effect of external pressure on the turbine blade. Heat transfer enhancement was found to be greater for ribs near bleed holes compared to ribs between holes, and both configurations were affected slightly by bleed rates upstream. Air temperature measurements were taken at discrete locations along one leg of the model. Average bulk air temperatures were found to remain fairly constant along one leg of the model.
Gasification Kinetics of Coal Chars Carbonized Under Rapid and Slow Heating Conditions at Elevated Temperatures
Authors: Luo Chunhua , Watanabe Tomokazu , Nakamura Makoto , Uemiya Shigeyuki , Kojima Toshinori
Published: July 2002

Measurements of CO2 gasification kinetics of coal chars at temperatures of 1273–1873 K were conducted by using a bench-scale fluidized bed reactor (FBR) made of alumina. The gasification rates of chars carbonized under both rapid heating and slow heating conditions were measured using a high-volatile bituminous coal and a medium-volatile bituminous coal. The significant difference in reactivity between rapid heating chars and slow heating chars, and the decrease of char reactivity at high temperature were discussed.
Heat Transfer in Rotating Narrow Rectangular Ducts With Heated Sides Oriented at 60° to the r-z Plane
Authors: Willett Fred T. , Bergles Arthur E.
Published: July 2002

Gas turbine blade life is often limited by the effectiveness of the cooling in the trailing edge convective cavity, which generally has a narrow cross-section. Previous research on rotational effects considered cavity shapes quite different from those of typical trailing edge cavities. In this research, experiments were conducted to determine the effect of rotation on heat transfer in ducts of narrow cross-section (height-to-width ratio of 1:10), oriented with the heated sides at 60° to the r-z plane. In the experiment, a high-molecular-weight gas (Refrigerant-134A) at ambient pressure and temperature conditions was used to match the dimensionless parameters at engine conditions. Thin foil heaters were used to produce a constant heat flux at the long sides of the duct; the narrow sides were unheated. Duct Reynolds numbers were varied up to 20,000; rotation numbers were varied up to 0.25. The test results show the effect of rotation and aspect ratio on duct leading and trailing side heat transfer. In addition, the results show the variation in heat transfer coefficient with transverse location in the duct, demonstrating the effect of rotation not only on lead and trail side heat transfer, but also on forward and aft end heat transfer.
Flow Interaction From the Exit Cavity of an Axial Turbine Blade Row Labyrinth Seal
Authors: Pfau A. , Treiber M. , Sell M. , Gyarmathy G.
Published: July 2002

The structure of labyrinth cavity flow has been experimentally investigated in a three fin axial turbine labyrinth seal (four cavities). The geometry corresponds to a generic steam turbine rotor shroud. The relative wall motion has not been modeled. The measurements were made with specially developed low-blockage pneumatic probes and extensive wall pressure mapping. Instead of the classical picture of a circumferentially uniform leakage sheet exiting from the last labyrinth clearance, entering the channel, and uniformly spreading over the downstream channel wall, the results reveal uneven flow and the existence of high circumferential velocity within the entire exit cavity. The circumferential momentum is brought into the cavity by swirling fluid from the main channel. This fluid penetrates the cavity and breaks up the leakage sheet into individual jets spaced according to the blade passages. This gives rise to strong local cross flows that may also considerably disturb the performance of a downstream blade row.
Thermohydraulic Study of Laminar Swirl Flow Through a Circular Tube Fitted With Twisted Tapes
Authors: Saha S. K. , Dutta A.
Published: July 2002

Heat transfer and pressure drop characteristics in a circular tube fitted with twisted tapes have been investigated experimentally. Laminar swirl flow of a large Prandtl number 205<Pr<518 viscous fluid was considered. The swirl was generated by short-length twisted-tape inserts; regularly spaced twisted-tape elements with multiple twists in the tape module and connected by thin circular rods; and smoothly varying (gradually decreasing) pitch twisted-tapes. The heat transfer test section was heated electrically imposing axially and circumferentially constant wall heat flux (UHF) boundary condition. Reynolds number, Prandtl number, twist ratio, space ratio, number of tuns in the tape module, length of the twisted-tape and smoothness of the swirling pitch govern the characteristics. Friction factor and Nusselt number are lower for short-length twisted-tape than those for full-length twisted-tape. On the basis of constant pumping power and constant heat duty, however, short-length twisted-tapes are found to perform better than full-length twisted-tapes for tighter twists. Thermohydraulic performance shows that twisted-tapes with multiple twists in the tape module is not much different from that with single twist in the tape module. Friction factor and Nusselt number are approximately 15 percent lower for twisted-tapes with smooth swirl having the average pitch same as that of the uniform pitch (throughout) twisted-tape and the twisted-tapes with gradually decreasing pitch perform worse than their uniform-pitch counterparts.
Design and Analysis of Robust Total Joint Replacements: Finite Element Model Experiments With Environmental Variables
Authors: Chang Paul B. , Williams Brian J. , Bhalla Kanwaljeet Singh Bawa , Belknap Thomas W. , Santner Thomas J. , Notz William I. , Bartel Donald L.
Published: July 2002

Computer simulations of orthopaedic devices can be prohibitively time consuming, particularly when assessing multiple design and environmental factors. Chang et al. (1999) address these computational challenges using an efficient statistical predictor to optimize a flexible hip implant, defined by a midstem reduction, subjected to multiple environmental conditions. Here, we extend this methodology by: (1) explicitly considering constraint equations in the optimization formulation, (2) showing that the optimal design for one environmental distribution is robust to alternate distributions, and (3) illustrating a sensitivity analysis technique to determine influential design and environmental factors. A thin midstem diameter with a short stabilizing distal tip minimized the bone remodeling signal while maintaining satisfactory stability. Hip joint force orientation was more influential than the effect of the controllable design variables on bone remodeling and the cancellous bone elastic modulus had the most influence on relative motion, both results indicating the importance of including uncontrollable environmental factors. The optimal search indicated that only 16 to 22 computer simulations were necessary to predict the optimal design, a significant savings over traditional search techniques.
Developing Film Flow on an Inclined Plane With a Critical Point
Authors: Ruschak Kenneth J. , Weinstein Steven J. , Ng Kam
Published: July 2002

Viscous, laminar, gravitationally-driven flow of a thin film on an inclined plane is analyzed for moderate Reynolds number under critical conditions. A previous analysis of film flow utilized a momentum integral approach with a semiparabolic velocity profile to obtain an ordinary differential equation for the film thickness for flow over a round-crested weir, and the singularity associated with the critical point for a subcritical-to-supercritical transition was removable. For developing flow on a plane with a supercritical-to-subcritical transition, however, the same approach leads to a nonremovable singularity. To eliminate the singularity, the film equations are modified for a velocity profile of changing shape. The resulting predictions compare favorably with those from the two-dimensional boundary-layer equation obtained by finite differences and with those from the Navier-Stokes equation obtained by finite elements.
Thermal-Fluid Phenomena Induced by Nanosecond-Pulse Heating of Materials in Water
Authors: Ueno I. , Shoji M.
Published: July 2002

Thermal-hydraulic phenomena adjacent to the liquid metal-water and solid material-water interfaces induced by nanosecond pulsed Nd:YAG laser (wavelength: 532 nm, FWHM: ∼13 ns) heating with the fluence F of 5.0×101∼1.0×103 mJ/cm2 were experimentally investigated. By applying the high-speed photography with a frame speed up to 2.0×107 fps, the aspects of the bubble formation, shock wave generation and propagation were observed. The bubble formation on the heated material’s surface of about 80 nm in diameter was detected in Si-water system from the time-resolved reflection (TRR) signal by applying the pump and probe method.
Diffusion-Controlled Dopant Transport During Magnetically-Stabilized Liquid-Encapsulated Czochralski Growth of Compound Semiconductor Crystals
Authors: Morton Joseph L. , Ma Nancy , Bliss David F. , Bryant George G.
Published: July 2002

During the magnetically-stabilized liquid-encapsulated Czochralski (MLEC) process, a single compound semiconductor crystal is grown by the solidification of an initially molten semiconductor (melt) contained in a crucible. The melt is doped with an element in order to vary the electrical and/or optical properties of the crystal. During growth, the so-called melt-depletion flow caused by the opposing relative velocities of the encapsulant-melt interface and the crystal-melt interface can be controlled with an externally applied magnetic field. The convective dopant transport during growth driven by this melt motion produces nonuniformities of the dopant concentration in both the melt and the crystal. This paper presents a model for the unsteady transport of a dopant during the MLEC process with an axial magnetic field. Dopant distributions in the crystal and in the melt at several different stages during growth are presented.
Three-Dimensional Simulations of Enhanced Heat Transfer in a Flat Passage Downstream From a Grooved Channel
Authors: Greiner M. , Fischer P. F. , Tufo H. M. , Wirtz R. A.
Published: July 2002

Spectral element simulations of three-dimensional flow and augmented convection in a flat passage downstream from a fully developed channel with symmetric, transverse grooves on opposite walls were performed for 405⩽Re⩽764. Unsteady flow that develops in the grooved region persists several groove-lengths into the flat passage, increasing both local heat transfer and pressure gradient relative to that in a steady flat passage. Moreover, the heat transfer for a given pumping power in the first three groove-lengths of the flat passage was greater than the levels observed in a fully developed grooved passage.
Unsteady Effects on the Flow Across Tilting Disk Valves
Authors: Rosenfeld Moshe , Avrahami Idit , Einav Shmuel
Published: July 2002

The present study simulates numerically the flow across two-dimensional tilting disk models of mechanical heart valves. The time-dependent Navier-Stokes equations are solved to assess the importance of unsteady effects in the fully open position of the valve. Flow cases with steady or physiological inflow conditions and with fixed or moving valves are solved. The simulations lead into mixed conclusions. It is obvious that steady inflow cases that account for vortex shedding only cannot model realistic physiological cases. In cases with imposed physiological inflow, the details of the flow field for fixed and moving valves might differ in the fully open position as well, although the gross features are quite similar. The fixed valve case consistently results in safe estimations of several critical quantities such as the axial force, the maximal shear stress on the valve, or the transvalvular pressure drop. Thus, fixed valve simulations can provide useful information for the design of prosthetic heart valves, as long as the properties in the fully open position only are sought.
Modeling a Pneumatic Turbine Speed Control System
Authors: Upchurch Eric R. , Vu Hung V.
Published: July 2002

[S0022-0434(00)01001-7]
Optimization of Well Placement
Authors: Guyaguler Baris , Horne Roland
Published: July 2002

Optimal placement of oil, gas or water wells is a complex problem that depends on reservoir and fluid properties, well and surface equipment specifications, as well as economic parameters. An optimization approach that enables the evaluation of all these information is presented. A hybrid of the genetic algorithm (GA) forms the basis of the optimization technique. GA operators such as uniform, single-point, two-point crossover, uniform mutation, elitism, tournament and fitness scaling were used. An additional operator that employs kriging is proposed. The GA was hybridized with the polytope algorithm, which makes use of the trends in the search space. The hybrid algorithm was tested on a set of mathematical functions with different characteristics in order to determine the performance sensitivity to GA operators and hybridization. Simple test cases of oil production optimization on 16×16 simulation grids with known optimum well locations were carried out to verify the hybrid GA results. Next, runs were carried out for a 32×32 problem. The locations of a production and injection well were optimized in the case of three existing producers. Exhaustive runs were carried out for these cases to determine the effects of the operators, hybridization and the population size on the performance of the algorithm for well placement problems. Subsequently, the optimum configuration of two injection wells were determined with two existing producers in the field. It was observed that the hybrid algorithm is able to reduce the required number of simulations substantially over simple GA. [S0195-0738(00)00502-1]
Experimental Analysis of the Heat Transfer Induced by Thermocapillary
Convection Around a Bubble
Authors: Arlabosse P. , Tadrist L. , Tadrist H. , Pantaloni J.
Published: July 2002

The surface tension driven flow in the liquid vicinity of gas bubbles on a heated wall and its contribution to the heat transfer are investigated experimentally in a configuration where surface tension force and buoyancy forces oppose one another. This liquid flow caused by the temperature gradient along the interface is called thermocapillary or thermal Marangoni convection. The studies were made with silicone oils of different viscosities so that a wide range of dimensionless numbers were encountered. The velocity fields are determined from the motion of carbon particles in the meridian plane of the bubble. The influence of the temperature gradient, the oil viscosity, and the bubble shape on the profiles along the interface and in the direction normal to the interface is analyzed. The temperature field is determined by holographic interferometry. For the axisymmetric problem, the interferograms are evaluated by solving the Abel-integral equation. From the isotherms, the temperature distribution along the bubble surface and in the liquid beneath the bubble is measured. To quantify the contribution of thermocapillarity to the heat transfer, the heat flux transferred by thermocapillarity is measured. A heat exchange law giving the increase in heat flux due to Marangoni convection in comparison to the conductive regime is proposed. [S0022-1481(00)70501-9]
A Finite Element Analysis of Surface Pocket Effects in Hertzian Line Contact
Authors: Zhao Jiaxin , Sadeghi Farshid , Nixon Harvey M.
Published: July 2002

During start up and shut down of heavily loaded rolling/sliding contacts, the lubricant film separating the surfaces is extremely thin and not fully developed. The load is supported by both the solid and the lubricant. Under extreme conditions, there is no lubricant film and the load is solely supported by the solid contact. However, when surface pockets are engineered on the surface of rolling/sliding elements, lubricant can be trapped in the pockets and deform with the pockets. Finite element analysis [FEA] of the deformation of a single empty pocket indicates that the volume of the pocket significantly decreases under an applied load. Therefore, when the pocket is filled with a lubricant, the lubricant will undergo significant compression. This compression enables lubricant to support part of the load and provide beneficial effects, such as reducing friction and expelling the lubricant during start up and shut down. This research presents an FEA model of a rigid cylinder in contact with an elastic and/or elastic-linear-kinematic-hardening-plastic half space with lubricant filled surface pocket(s). Results of lubricant filled pockets are compared with those of empty pockets. The results demonstrate the beneficial effects of load sharing mechanism by the lubricant. [S0742-4787(00)00801-8]
Interfacial Fluid Mechanics and Pressure Prediction in Chemical Mechanical Polishing
Authors: Shan Lei , Levert Joseph , Meade Lorne , Tichy John , Danyluk Steven
Published: July 2002

This paper reports on the measurement of fluid (water) pressure distribution at a soft (polyurethane) pad/steel interface. The distribution of the interfacial fluid pressure has been measured with a specially-designed fixture over the typical range of normal loads and velocities used in the chemical mechanical polishing/planarization of silicon wafers. The results show that, for most cases, the leading two-thirds of the fixture exhibits a subambient pressure, and the trailing third a positive pressure. The average pressure is sub-ambient and may be of the order of 50∼100% of the normal load applied. An analytical model has been developed to predict the magnitude and distribution of the interfacial fluid pressure. The predictions of this model fit the experimental results reasonably well, especially for low sliding velocities. [S0742-4787(00)00902-4]
Weld Repair of 1-1/4Cr-1/2Mo Steel Piping Girth Welds
Authors: Viswanathan R. , Gandy D. , Findlan S.
Published: July 2002

Weld repairs have been performed to 1-1/4Cr-1/2Mo steel girth weldments from a hot reheat pipe returned from service at 1000°F538°C for 244,000h. Shielded metal arc weld (SMAW) repairs were performed to excavated portions of the ex-service welds with post weld heat treatment (PWHT) and using a temperbead technique. The welds were evaluated prior to and after repair to study the effects of degradation on repairability, the effectiveness of temperbead repairs and the remaining life achievable by weld repair. Temperbead repairs result in higher peak hardness compared to the PWHT repairs (320 Hv versus 230 Hv). Both PWHT and temperbead repairs resulted in increased yield strength compared to the ex-service base metal and weld at both room temperature and at 1050°F565°C, the maximum benefits being realized for the temperbead repairs. Effects on tensile strength were more marginal. Both PWHT and temperbead repairs resulted in improved toughness at room temperature as measured by Charpy impact energy. The temperbead repair produced a greater enhancement of toughness compared to the PWHT repair in composite weldment specimens. Larson-Miller parameter extrapolations of stress rupture data indicate a remaining life of about 46 yr for temperbead repairs and 28 yr for PWHT repairs under design conditions of 1000°F538°C and 6.6 ksi 46MPa. Other isostress extrapolation procedures yield lower lives, but the temperbead repairs are consistently superior regardless of the extrapolation procedure used. [S0094-9930(00)01502-X]
The role of feedgas chemistry, mask material, and processing parameters in profile evolution during plasma etching of Si(100)
Authors: Lane J. M. , Bogart K. H. A. , Klemens F. P. , Lee J. T. C.
Published: July 2002

Profile evolution of trenches and lines, both nested and isolated, during etching with Cl2, HBr, and HCl plasmas in a high density, commercial etch tool was investigated. Features patterned with and without an insulating SiO2 mask layer produced similar profiles with Cl2 and HCl plasma etching, but markedly different profiles with HBr plasma etching. The contribution of the SiO2 mask material to sidewall passivation is discussed. Under certain plasma conditions without a SiO2 mask, severe facets on the silicon lines were observed. The importance and relevance of this facet formation to the profile evolution process is reviewed. Profile evolution with increasing reactor pressure was identical during etching with HBr and Cl2 plasma etching, although the profiles etched in either gas at the same pressure were markedly different. These experimental results are compared to plasma etching models and molecular beam experiments reported in the literature, and the contribution of these data to feature profile evolution simulators is presented.
In-plane optical anisotropy of quantum well structures: From fundamental considerations to interface characterization and optoelectronic engineering
Authors: Cortez S. , Krebs O. , Voisin P.
Published: July 2002

The recently discovered in-plane optical anisotropy of (001)-grown quantum wells offers a new theoretical and experimental insight into the electronic properties of semiconductor interfaces. We first discuss the coupling of X and Y valence bands due to the breakdown of rotoinversion symmetry at a semiconductor heterointerface, with special attention to its dependence on effective parameters such as the valence band offset. The intracell localization of Bloch functions is explained from simple theoretical arguments and evaluated numerically from a pseudopotential microscopic model. The role of envelope functions is then considered, and we discuss the specific case of no-common atom interfaces. Experimental results and applications to interface characterization are presented, and the potential of the “quantum confined Pockels effect” for device applications is finally discussed.
Polarized laser light scattering applied to surface morphology characterization of epitaxial III–V semiconductor layers
Authors: González M. U. , Sánchez-Gil J. A. , González Y. , González L. , Méndez E. R.
Published: July 2002

In this paper, we analyze typical morphologies of epitaxial III–V semiconductor layers by using a polarized laser light scattering technique. Crosshatched topographies, which are developed during heteroepitaxial growth, are studied. A sample with an intentionally high density of oval defects is also explored to establish how the laser light scattering pattern is affected by the presence of these defects, which are unavoidable in the epitaxial layers grown by molecular beam epitaxy. The former topographies produce a scattered light pattern that is highly anisotropic, with the intensity concentrated along two preferential directions; the latter defects give rise to a fairly isotropic pattern. Employing a perturbation-theoretical model, whose applicability and consistency are explicitly demonstrated by our results, the surface power spectral density is retrieved from the angle-resolved light scattering experimental data. For the samples exhibiting crosshatched topography, the scattering measurements provide information that allows us to model the roughness of the surface in terms of two quasi-one-dimensional, anisotropic components, and one two-dimensional, isotropic, long-range background. The root mean square heights and the typical lateral distances between ridges are obtained in quantitative agreement with the values extracted from the atomic force microscopy measurements. For the sample presenting oval defects, we consider their contribution to the surface power spectral density by means of a simple model of randomly distributed particles on a surface, and we compare the resulting power spectral density with typical behavior found in the literature for good-morphology GaAs layers. With the help of the ex situ information thus obtained, we also discuss the implementation of the light scattering technique for in situ monitoring during epitaxial growth.
Structure and property relationships for bulk electrodeposits
Authors: Safranek W. H.
Published: July 2002

The properties of bulk electrodeposits depend on structure. Fine-grained deposits exhibit greater strength than coarse, columnar structures. For example, the tensile strengths of fine-grained copper and nickel reach values as high as 90 000 and 150 000 psi, respectively, in comparison with only 25 000 and 50 000 psi for the coarser-grained deposits. Analogously, the tensile strengths of fine-grained cobalt, gold, iron, and silver can be two to five times the strength of the coarse-grained counterpart. Nickel containing 0.02% sulfur (as nickel sulfide) exhibits a tensile strength as high as 235 000 psi. Some metals deposited at a high rate (> 0.001 in./min) are finer grained and stronger than their counterparts deposited conventionally at a rate < 0.00005 in./min. The physical properties of the fine-grained structures are dependent on the conditions adopted for refining grain size. High density, low electrical resistivity, and good thermal stability can be obtained with conditions that avoid undesirable inclusions.
Condensation of Gases during Cryopumping—The Effect of Surface Temperature on the Critical Energy for Trapping
Authors: Eisenstadt Melvin M.
Published: July 2002

The critical energy for trapping was defined and was then calculated for five gases (N2, Ar, CO, CO2, and N2O). The gas and the solid on which it is trapped were of the same chemical species. The calculations were made using measured values of the capture coefficient which came from cryopumping data [J. P. Dawson and J. D. Haygood, Cryogenics 5, 57 (1965)]. The calculated values were obtained from an interpretation of experimental results; they were not derived from calculation of the energy and momentum exchange between a gas particle and a perfect lattice. Capture coefficients were available for a range of both surface and gas temperatures. Two cases were treated; in the first the capture coefficient was independent of surface temperature while the second case considered the surface temperature dependent values of the capture coefficients. For the first case, it was found that Ec/D was of the order of 1, where Ec is the critical energy for trapping and D is the depth of the surface potential well. For the second case, the relationship Ec=Aexp(B/Tsurface) fitted the data for all five gases.
Low-Temperature Migration of Silicon in Metal Films on Silicon Substrates Studied by Backscattering Techniques
Authors: Hiraki Akio , Lugujjo Eriabu
Published: July 2002

The backscattering method using 2-MeV4He+ ions is employed to obtain microscopic information about solid-solid reaction of Si with thin layers (200∼4000 Å) of Au, Ag, and Al which are vacuum evaporated onto Si crystal substrates. The interesting observation is the migration of Si atoms into these metal films at temperatures (for example, 150°C in Au, 400°C in Ag) well below their eutectic points (375°C for Au and 850°C for Ag). This phenomenon also indicates that at these low temperatures the dislodgment of Si atoms from tightly bound Si crystal does occur. Our experiments clarify that the origin of this effect is the interaction of Si with metals at the interface.
The Electronic Structure of Solid Surfaces: Core Level Excitation Techniques
Authors: Park Robert L. , Houston J. E.
Published: July 2002

The local density of states of atoms at solid surfaces can only be examined indirectly by techniques which use the core levels of the atoms as windows. The core levels themselves are measurably shifted by changes in the distribution of valence electrons. These “chemical” shifts are frequently measured by x-ray photoelectron spectroscopy (XPS), but more specific information on the local density of states is provided by techniques based on excitation by electron bombardment. Ionization spectroscopy (IS) extracts excitation edges from the total secondary emission spectrum. The threshold core level excitation probabilities can be obtained by soft x-ray characteristic isochromat spectroscopy (CIS), or more simply by soft x-ray appearance potential spectroscopy (SXAPS). Auger electron appearance potential spectroscopy (AEAPS) provides similar information. In each of these techniques the shape of the excitation edges is related to the density of conduction band states, but may be modified by final state interactions and core hole lifetime broadening. The lifetimes can be determined independently by XPS.