bluuebunny/crossref_metadata_2025 huggingface dataset:
Environmental features are important in determining protein secondary structure
Authors: Macdonald J. Randy , Johnson W. Curtis
Published: July 2002

We have investigated amino acid features that determine secondary structure: (1) the solvent accessibility of each side chain, and (2) the interaction of each side chain with others one to four residues apart. Solvent accessibility is a simple model that distinguishes residue environment. The pairwise interactions represent a simple model of local side chain to side chain interactions. To test the importance of these features we developed an algorithm to separate α‐helices, β‐strands, and “other” structure. Single residue and pairwise probabilities were determined for 25,141 samples from proteins with <30% homology. Combining the features of solvent accessibility with pairwise probabilities allows us to distinguish the three structures after cross validation at the 82.0% level. We gain 1.4% to 2.0% accuracy by optimizing the propensities, demonstrating that probabilities do not necessarily reflect propensities. Optimization of residue exposures, weights of all probabilities, and propensities increased accuracy to 84.0%.
Crystal structure of a deletion mutant of human thymidylate synthase Δ (7–29) and its ternary complex with Tomudex and dUMP
Authors: Almog Rami , Waddling Christopher A. , Maley Frank , Maley Gladys F. , Van Roey Patrick
Published: July 2002

The crystal structures of a deletion mutant of human thymidylate synthase (TS) and its ternary complex with dUMP and Tomudex have been determined at 2.0 Å and 2.5 Å resolution, respectively. The mutant TS, which lacks 23 residues near the amino terminus, is as active as the wild‐type enzyme. The ternary complex is observed in the open conformation, similar to that of the free enzyme and to that of the ternary complex of rat TS with the same ligands. This is in contrast to Escherichia coli TS, where the ternary complex with Tomudex and dUMP is observed in the closed conformation. While the ligands interact with each other in identical fashion regardless of the enzyme conformation, they are displaced by about 1.0 Å away from the catalytic cysteine in the open conformation. As a result, the covalent bond between the catalytic cysteine sulfhydryl and the base of dUMP, which is the first step in the reaction mechanism of TS and is observed in all ternary complexes of the E. coli enzyme, is not formed. This displacement results from differences in the interactions between Tomudex and the protein that are caused by differences in the environment of the glutamyl tail of the Tomudex molecule. Despite the absence of the closed conformation, Tomudex inhibits human TS ten‐fold more strongly than E. coli TS. These results suggest that formation of a covalent bond between the catalytic cysteine and the substrate dUMP is not required for effective inhibition of human TS by cofactor analogs and could have implications for drug design by eliminating this as a condition for lead compounds.
Convective Heat Transfer past Small Cylindrical Bodies
Authors: Titcombe Michèle S. , Ward Michael J.
Published: July 2002

Convective heat transfer from an array of small, cylindrical bodies of arbitrary shape in an unbounded, two‐dimensional domain is a singular perturbation problem involving an infinite logarithmic expansion in the small parameter ε, representing the order of magnitude of the size of the bodies. Using the method of matched asymptotic expansions, we formulate a hybrid asymptotic‐numerical method to solve for the dimensionless, steady‐state temperature. We assume that the velocity field of the fluid surrounding the bodies is arbitrary but known. From our asymptotic solution for an arbitrary velocity field, we present the results for two special cases: a uniform flow field and a simple shear flow field. We demonstrate the asymptotic results of the hybrid method through a number of examples and, in a particular case, we compare these results to an exact analytical solution.
Approximate Conditional Unit Root Inference
Authors: HANSEN HENRIK , RAHBEK ANDERS
Published: July 2002

Based on Cox and Reid (1987) adjustments of likelihood ratio (LR) tests for unit roots in higher‐order autoregressive models are proposed. While unit root inference does not fit directly into the framework of Cox and Reid, the ideas are applied in models with multi‐dimensional parameters of interest and only asymptotic orthogonality of parameters. The adjustments are very simple to apply in that they are of the degrees of freedom type. Detailed Monte Carlo experiments reveal that, for a wide range of admissible parameter values, adjusted LR statistics approximate the asymptotic percentiles of the unit root distributions at a much faster rate than unadjusted ones. In addition, the proposed adjustments are compared with simulated Bartlett type corrected LR tests. They behave equally well in a reasonable parameter region, while both fail on the boundary of the parameter region where an additional unit root is introduced.
Pricing American Stock Options by Linear Programming
Authors: Dempster M. A. H. , Hutton J. P.
Published: July 2002

We investigate numerical solution of finite difference approximations to American option pricing problems, using a new direct numerical method: simplex solution of a linear programming formulation. This approach is based on an extension to the parabolic case of the equivalence between linear order complementarity problems and abstract linear programs known for certain elliptic operators. We test this method empirically, comparing simplex and interior point algorithms with the projected successive overrelaxation (PSOR) algorithm applied to the American vanilla and lookback puts. We conclude that simplex is roughly comparable with projected SOR on average (faster for fine discretizations, slower for coarse), but is more desirable for robustness of solution time under changes in parameters. Furthermore, significant speedups over the results given here have been achieved and will be published elsewhere.
TEA‐ and apamin‐resistant KCa channels in guinea‐pig myenteric neurons: slow AHP channels
Authors: Vogalis Fivos , Harvey John R. , Furness John B.
Published: July 2002

The patch‐clamp technique was used to record from intact ganglia of the guinea‐pig duodenum in order to characterize the K+ channels that underlie the slow afterhyperpolarization (slow AHP) of myenteric neurons. Cell‐attached patch recordings from slow AHP‐generating (AH) neurons revealed an increased open probability (Po) of TEA‐resistant K+ channels following action potentials. The Po increased from < 0.06 before action potentials to 0.33 in the 2 s following action potential firing. The ensemble averaged current had a similar time course to the current underlying the slow AHP. TEA‐ and apamin‐resistant Ca2+‐activated K+ (KCa) channels were present in inside‐out patches excised from AH neurons. The Po of these channels increased from < 0.03 to approximately 0.5 upon increasing cytoplasmic [Ca2+] from < 10 nm to either 500 nm or 10 μm. Po was insensitive to changes in transpatch potential. The unitary conductance of these TEA‐ and apamin‐resistant KCa channels measured approximately 60 pS under symmetric K+ concentrations between −60 mV and +60 mV, but decreased outside this range. Under asymmetrical [K+], the open channel current showed outward rectification and had a limiting slope conductance of about 40 pS. Activation of the TEA‐ and apamin‐resistant KCa channels by internal Ca2+ in excised patches was not reversed by washing out the Ca2+‐containing solution and replacing it with nominally Ca2+‐free physiological solution. Kinetic analysis of the single channel recordings of the TEA‐ and apamin‐resistant KCa channels was consistent with their having a single open state of about 2 ms (open dwell time distribution was fitted with a single exponential) and at least two closed states (two exponential functions were required to adequately fit the closed dwell time distribution). The Ca2+ dependence of the activation of TEA‐ and apamin‐resistant KCa channels resides in the long‐lived closed state which decreased from > 100 ms in the absence of Ca2+ to about 7 ms in the presence of submicromolar cytoplasmic Ca2+. The Ca2+‐insensitive closed dwell time had a time constant of about 1 ms. We propose that these small‐to‐intermediate conductance TEA‐ and apamin‐resistant Ca2+‐activated K+ channels are the channels that are primarily responsible for the slow AHP in myenteric AH neurons.
Postextrasystolic regulation patterns of blood pressure and heart rate in patients with idiopathic dilated cardiomyopathy
Authors: Voss Andreas , Baier Vico , Schumann Agnes , Hasart Annette , Reinsperger Franziska , Schirdewan Alexander , Osterziel Karl‐Josef , Leder Uwe
Published: July 2002

Assessment of fluctuations in heart rate (HR) following a premature ventricular complex (PVC) is valuable for identifying patients at high risk of sudden cardiac death. We hypothesised that postextrasystolic potentiation is the main determinant of the regulation patterns of blood pressure (BP) and HR following a PVC. Twelve patients with idiopathic dilated cardiomyopathy (IDC) and 13 control subjects with single PVCs (comparable coupling intervals) were investigated. Non‐invasive finger arterial BP and ECGs were analysed. Regulation patterns following a single PVC were quantified using the indices postextrasystolic amplitude potentiation (PEAP) and maximum turbulence slope of five consecutive mean BP values (MBP‐TS), and compared with the HR turbulence parameters turbulence slope (HR‐TS) and turbulence onset (HR‐TO). PEAP was significantly higher in IDC patients compared to controls (48.7 ± 32.6 vs. 9.8 ± 5.4 %, P < 0.01), whereas MBP‐TS was lower (0.97 ± 0.60 vs. 2.07 ± 1.04 mmHg BBI−1 (BBI, beat‐to‐beat interval), P < 0.05), as was HR‐TS (8.46 ± 7.90 vs. 30.73 ± 22.90 ms BBI−1, P < 0.01). HR‐TO was significantly higher in IDC patients (−0.56 ± 2.19 vs.−5.52 ± 4.13 %, P < 0.01). In addition, the regulation patterns of BP and HR following a single PVC differed significantly between IDC patients and controls. Specifically, we observed pronounced PEAPs in IDC patients. The baroreflex response initiated by the low pressure amplitude of the PVC was suppressed in IDC patients due to the augmented potentiation of the first postextrasystolic blood pressure. Furthermore, IDC patients displayed impressive postextrasystolic pulsus alternans phenomena, whereas healthy subjects exhibited a typical baroreflex pattern. The pulsus alternans phenomenon seems to be triggered by a PVC.
Propionate‐induced relaxation in rat mesenteric arteries: a role for endothelium‐derived hyperpolarising factor
Authors: Knock G. , Psaroudakis D. , Abbot S. , Aaronson P. I.
Published: July 2002

Short chain fatty acids, including propionate, are generated in the caecum and large intestine, and when absorbed may elicit localised increases in intestinal blood flow. We sought to assess the mechanism by which propionate caused vasorelaxation. Propionate‐mediated relaxation of noradrenaline‐preconstricted rat mesenteric small arteries (RMSAs, i.d. 200–300 μm) was studied using small vessel myography. Propionate (1–30 mm) produced a concentration‐dependent relaxation. Relaxation induced by 10 mm propionate (the approximate EC50) was almost abolished by endothelial denudation, although a marked relaxation to a very high concentration of propionate (50 mm) persisted in the absence of the endothelium. In endothelium‐intact RMSAs, relaxation to 10 mm propionate was almost abolished by elevating [K+]o to 25 mm, but was unaffected by 100 μmNω‐nitro‐l‐arginine methyl ester (l‐NAME) (68 ± 4 vs. 66 ± 3 % in controls, n= 35), or by 1 μm indomethacin (60 ± 4 vs. 61 ± 7 % in controls, n= 15). In the presence of l‐NAME, relaxation to 10 mm propionate was significantly and markedly (i.e. > 50 %) inhibited by 50 μm Ba2+ and by the combination of 100 nm charybdotoxin and 100 nm apamin. A similar effect on propionate‐mediated relaxation was also exerted by 100 μm ouabain, and by the combination of 50 μm barium with ouabain. Relaxation was also significantly and markedly inhibited by pre‐treatment of RMSAs with 100 nm thapsigargin or 10 μm cyclopiazonic acid (CPA). The results demonstrate that 10 mm propionate relaxes RMSAs via endothelium‐derived hyperpolarising factor (EDHF). The observation that relaxation by propionate is inhibited by thapsigargin and CPA suggests that this action of propionate involves the release of endothelial cell Ca2+ stores.
Coupling between the ribs and the lung in dogs
Authors: Troyer André De , Wilson Theodore A.
Published: July 2002

In contrast to the conventional theory, the external and internal intercostal muscles show marked rostrocaudal gradients in their actions on the lung. We hypothesized that these gradients are the result of a non‐uniform coupling between the ribs and the lung. Rib displacements (Xr) and the changes in airway opening pressure (Pa,o) were thus measured in anaesthetized, pancuronium‐treated, supine dogs while loads were applied in the cranial direction to individual pairs of odd‐numbered ribs and in the caudal direction to individual pairs of even‐numbered ribs. During cranial loading, Xr induced by a given load increased gradually with increasing rib number. The decrease in Pa,o also increased from the third to the fifth rib pair but then decreased markedly to the eleventh pair. A similar pattern was observed during caudal loading, although Xr and ΔPa,o were smaller. These results were then combined to calculate the net Xr and the net ΔPa,o that a hypothetical intercostal muscle lying parallel to the longitudinal body axis would produce in different interspaces. The net Xr was cranial in all interspaces. However, whereas the net ΔPa,o was negative in the cranial interspaces, it was positive in the caudal interspaces. These observations confirm that the coupling between the ribs and the lung varies from the top to the base of the ribcage. This coupling confers to both the external and the internal intercostal muscles an inspiratory action on the lung in the cranial interspaces and an expiratory action in the caudal interspaces.
Mechanisms and physiological role of enhancement of mGlu5 receptor function by group II mGlu receptor activation in rat perirhinal cortex
Authors: Cho K. , Brown M. W. , Bashir Z. I.
Published: July 2002

In this study we have investigated mechanisms underlying enhancement by group II metabotropic glutamate (mGlu) receptors of group I mGlu receptor‐induced calcium mobilization. Inhibition of protein kinase A (PKA) caused an enhancement of mGlu5 receptor‐mediated calcium mobilization and occluded the enhancement by group II mGlu receptors. A peptide (Ht31) that prevents interaction between A‐kinase anchoring protein (AKAP) and PKA also enhanced mGlu5‐mediated calcium mobilization. Enhancement of mGlu5 function, by inhibition of PKA or by activation of group II mGlu receptors, was prevented by the protein phosphatase 2B (PP2B) inhibitor cyclosporin A. Furthermore, the enhancement by activation of group II mGlu receptors was prevented by raising intracellular cAMP. These results suggest that the regulation by PKA and PP2B of phosphorylation of a substrate on mGlu5 and/or on group II mGlu receptors is intimately involved in the mechanisms underlying interaction between group II mGlu and mGlu5 receptors. Long‐term depression (LTD) in perirhinal cortex requires group I, group II and NMDA receptor activation at resting membrane potentials but does not require group II mGlu receptor activation at depolarized potentials. We previously suggested that interaction between group I and group II mGlu receptors is required for induction of LTD at resting potentials. In support of this, we demonstrate in perirhinal cortex slices that blocking mechanisms underlying mGlu receptor synergy (by raising intracellular cAMP or by inhibition of PP2B) selectively prevented LTD at resting membrane potentials. This study thus provides a potential explanation for the co‐requirement in LTD of group I and group II mGlu receptor activation. Similar mechanisms of synergistic interaction may also be important in other physiological processes dependent on mGlu receptors.
An M‐like outward current regulates the excitability of spinal motoneurones in the adult turtle
Authors: Alaburda Aidas , Perrier Jean‐François , Hounsgaard Jørn
Published: July 2002

The excitatory action of muscarine on spinal motoneurones was investigated with intracellular recordings in a slice preparation from adult turtles. In these cells muscarine is known to facilitate a persistent inward current mediated by L‐type Ca2+ channels. When this effect was blocked by nifedipine, muscarine still increased the excitability. In voltage clamp, a slowly activating outward current, generated during depolarizing voltage commands and deactivating as a tail current on return to the holding voltage, was reduced by muscarine. This outward current was activated when the voltage was stepped to potentials positive to −60 mV, was voltage sensitive and had a deactivation time constant of ≈80 ms. These findings are compatible with an M‐current. This possibility was also supported by the finding that the current was reduced by XE‐991 ‐ a selective blocker of the KCNQ potassium channels underlying M‐currents in other cell types. Our findings suggest that an M‐like current, mediated by a KCNQ channel, contributes to the intrinsic response properties of motoneurones in the adult spinal cord by increasing adaptation of repetitive firing and decreasing the slope of the frequency‐current relation.
A Statistical Analysis of Expulsion Limits in Resistance Spot Welding
Authors: Zhang Hongyan , Hu S. Jack , Senkara Jacek , Cheng Shaowei
Published: July 2002

Expulsion is an important phenomenon in resistance spot welding. It involves loss of metal from the liquid nugget, which often results in the reduction of weld strength. Various models have been proposed to understand expulsion mechanisms. In these models the occurrence of expulsion is often treated as a deterministic event, and depicted by a line (boundary) in conventional lobe diagrams. In this study, statistical analysis is employed to explore expulsion with consideration of the influence of random factors. Models are built based on experimental data, and one steel and two aluminum alloys are used as examples. Expulsion probabilities are presented as a function of electrode force, welding current, and time. Analytical models and their graphical form of expression (contours and surfaces) are created to present expulsion limits under various combinations of welding parameters. This study provides not only quantitative model predictions on expulsion limits for the materials studied, but also a generic statistical methodology that can be used for analyzing expulsion in various material systems. [S1087-1357(00)00602-X]
Optimal Tolerance Allocation With Loss Functions
Authors: Choi Hoo-Gon R. , Park Man-Hee , Salisbury Erik
Published: July 2002

The tolerance allocation problem is formulated as a nonlinear integer model under the constraints of process capability. The problem is to minimize the sum of machining cost and quality loss. When the statistical tolerance limits are used and Taguchi’s quadratic loss function is defined, the total cost function becomes a convex function for a given feature and process. A complex search method is used to solve the model and ensure the optimal tolerance allocation. Numerical examples are presented demonstrating successful model implementation for both linear and nonlinear design functions. [S1087-1357(00)02602-2]
Fatigue Life Analysis of Solder Joints in Flip Chip Bonding
Authors: Tsukada Yutaka , Nishimura Hideo , Sakane Masao , Ohnami Masateru
Published: July 2002

This paper describes the life assessment of flip chip joints. Flip chip joints of 63Sn-37Pb and 5Sn-95Pb solders on a printed circuit board were stressed thermally for fatigue. Fatigue lives of the joints were determined by an electrical potential drop method and the effect of encapsulation on fatigue life was discussed. The encapsulation had a significant effect of prolonging the fatigue life of the joints. Thermo-mechanical finite element analyses proved that the encapsulation lowered the strain amplitude of the joints by distributing the strain over a whole package and bending effect. Cracking location was also discussed in relation with the strain concentration in the joints. Fatigue lives of the flip chip joints were compared with those of bulk round bar specimens and the difference in fatigue life between two types of specimens was discussed from the specimen dimensions and ratchet effect. [S1043-7398(00)00203-6]
The Effect of Seat Geometry on Gate Valve Noise
Authors: Smith Bruce A. W. , Luloff Brian V.
Published: July 2002

Gate valves often act as a source of tonal noise in piping systems. Occasionally, this can lead to excessive environmental noise levels. This paper presents the results of a model testing program that was conducted to determine the most cost-effective way to eliminate the noise source in one such valve. Over 300 tests were conducted on 25 different valve configurations. Testing of the original valve configuration indicated that the noise was caused by vortex shedding over the valve seat cavity coupled with an acoustic resonance across the throat of the valve. Numerous modifications to the valve seats, seat cavity, and disk were tested to determine how the vortex shedding could best be controlled. The effect of these modifications on the unsteady pressures in the valve and adjacent piping are presented and discussed. For the valve under consideration, it was concluded that the noise could best be eliminated by chamfering the upstream and downstream valve seats. Recommendations for avoiding noise problems in other valve installations are presented. [S0094-9930(00)00503-5]
Modeling and Calibration of Grid Structured Light Based 3-D Vision Inspection
Authors: Zhang Guangjun , Ma Liqun
Published: July 2002

The principle of structured light 3-D vision is introduced, and using projective and perspective transformations, the mathematical model of grid structured light based 3-D vision inspection is established in homogeneous coordinate system in this paper. Based on the image feature analysis of grid structured light, a calibration method of grid structured light based 3-D vision inspection is proposed, and experimental results are also presented. This method is easy, efficient and fast to carry out. It simplifies the calibration process while guaranteeing its accuracy. [S1087-1357(00)00703-6]
Evaluation and Improvement of Productivity in High-Speed NC Machining
Authors: Yan X. , Shirase K. , Hirao M. , Yasui T.
Published: July 2002

The productivity of machining centers is influenced inherently by the quality of NC programs. To evaluate productivity, first an effective feedrate factor and a productivity evaluation factor are proposed. It has been found that in high-speed machining, these two factors depend on a kinematic factor which is a function of (1) command feedrate, (2) average per-block travel of the tool, (3) moving vectorial variation of the tool, and (4) ac/deceleration or time constants. Then an NC program simulator has been developed to evaluate productivity. With the simulator, the machining time can be calculated accurately and the cutting conditions can be extracted. Finally, three NC programs were implemented on high-speed machining centers and analyzed by the simulator. It was found that in mold and die machining, the productivity can be improved by increasing the acceleration and average travel and reducing the vectorial variation of the tool rather than the command feedrate. [S1087-1357(00)01303-4]
Tension and Speed Regulation for Axially Moving Materials
Authors: Nagarkatti Siddharth P. , Zhang Fumin , Rahn Christopher D. , Dawson Darren M.
Published: July 2002

During continuous manufacture of axially moving materials such as fiber, paper, foil, and film, accurate speed and tension control are essential. In this paper, control torques applied to rollers at the boundaries of an axially moving system regulate the material speed and tension using speed and tension sensors for each roller. Given a distributed parameter model, Lyapunov techniques are used to develop a model-based boundary control system that exponentially stabilizes the material tension and speed at desired setpoints and stabilizes longitudinal vibration. Experimental results compare the tension and speed setpoint regulation provided by the proposed control strategy with proportional plus integral speed control and proportional tension feedback. [S0022-0434(00)00203-3]
A High Performance Pneumatic Force Actuator System: Part I—Nonlinear Mathematical Model
Authors: Richer Edmond , Hurmuzlu Yildirim
Published: July 2002

In this paper, we developed a detailed mathematical model of dual action pneumatic actuators controlled with proportional spool valves. Effects of nonlinear flow through the valve, air compressibility in cylinder chambers, leakage between chambers, end of stroke inactive volume, and time delay and attenuation in the pneumatic lines were carefully considered. We performed system identification, numerical simulation, and model validation experiments for two types of air cylinders and different connecting tubes length. The mathematical model of the present article is used in a sequel article to develop high performance nonlinear pneumatic force controllers. [S0022-0434(00)00503-7]
Initial Crack Depth and POD Values Inferred From In-Service Observations of Cracks in North Sea Jackets
Authors: Moan Torgeir , Va˚rdal Ole T. , Hellevig Nils-C. , Skjoldli Knut
Published: July 2002

Observations made during more than 4000 in-service nondestructive examinations of tubular joints in North Sea jackets are utilized to determine the initial crack depth and probability of detecting (POD) cracks in magnet particle and eddy current inspections. Based on exponential distributions of the initial crack size and POD, it was found that the mean initial crack size and detectable crack depth was 0.94 and 1.95 mm, respectively. This initial crack size is referred to one crack occurrence per three joints and corresponds to a mean crack depth of 0.38 mm with a frequency of one crack per hot-spot area. The predicted number and size of undetected cracks are found to correspond well with actually reported “second inspection” cracks. The estimated depth of undetected cracks is used to estimate how deep the post-inspection grinding should be, to establish a certain residual fatigue life. [S0892-7219(00)00503-3]
Markov Data-Based LQG Control1
Authors: Shi Guojun , Skelton Robert E.
Published: July 2002

In this paper the Markov data-based LQG control problem is considered. The Markov data-based LQG control problem is to find the optimal control sequence which minimizes a quadratic cost function over some finite interval [0, N]. To solve this problem, we show that a complete input-output description of the system is not necessary. Obviously, a complete state space model is not necessary for this problem either. The main contributions of this paper include: (i) develop a new data-based LQG controller in a recursive form and a batch-form, (ii) derive a closed-form expression for the system’s optimal performance in terms of the Markov parameters, (iii) develop an algorithm for choosing the output weighting matrix, and (iv) demonstrate that the amount of information about the system required by the data-based controller design is less than the amount required to construct the full state space model. A numerical example is given to show the effectiveness of the data-based design method. [S0022-0434(00)02503-X]
On the Stability of Parallel Bubbly Cavitating Flows
Authors: d’Agostino Luca , Burzagli Fabio
Published: July 2002

This paper illustrates the effects of the dynamics of bubbles with arbitrary vapor-gas contents on the inviscid and viscous stability of two-dimensional parallel bubbly flows of low void fraction. The linear perturbation equations derived for the stability analysis include the effects of bubble compressibility, inertia, and energy dissipation due to the viscosity of the liquid and the transfer of heat and mass as a consequence of compression/expansion of the noncondensable gas and evaporation/condensation of the vapor contained in the bubbles. Numerical solution of the spatial stability problem for two-dimensional inviscid shear layers and Blasius boundary layers confirms that the presence of the dispersed phase is generally in favor of stability. Significant deviations from the classical results for compressible and incompressible single phase fluids are observed, especially when the occurrence of large compliant and/or resonant oscillations of the bubbles greatly enhances their dynamic coupling with the perturbation field. More importantly, the present analysis points out some major differences in the stability of parallel flows with noncondensable gas bubbles with respect to cavitating flows containing bubbles with a dominant content of vapor. Unconditional stability is predicted in the travelling bubble cavitation limit for low pressures and high vapor mass fraction of the bubble contents. Results are shown to illustrate these effects for some representative flow configurations and conditions. [S0098-2202(00)00603-9]
Experimental and Numerical Studies of Two-Stage Ethane-Air Flames
Authors: Waly M. M. Y. , Li S. C. , Williams F. A.
Published: July 2002

This paper reports results of experimental and numerical investigations on ethane-air two-stage combustion in a counterflow burner where the fuel stream, which is partially premixed with air for equivalence ratios from 1.6 to 3.0, flows against a pure air stream. Similar to methane, the two-stage ethane combustion exhibits a green fuel-rich premixed flame and a blue diffusion flame. Flame structures, including concentration profiles of stable intermediate species such as C2H4,C2H2 and CH4, are measured by a gas chromatography and are calculated by numerical integrations of the conservation equations employing an updated elementary chemical-kinetic data base. The implications of the results from these experimental measurements and numerical predictions are summarized, the flame chemistry of ethane two-stage combustion at different degrees of premixing (or equivalence ratio) is discussed, and the relationship between NOx formation and the degree of premixing is established. The present work helps to increase understanding of flame chemistry of hydrocarbon fuels, identify important reactions for pollutant formation and suggest means to reduce emissions. [S0742-4795(00)01303-X]
A Comparison of Ship-Mounted and Cage-Mounted Passive Heave Compensation Systems
Authors: Driscoll Frederick R. , Nahon Meyer , Lueck Rolf G.
Published: July 2002

Tethered marine systems experience large tensile loads in their tether when operating in rough seas. Heave compensation systems can be used to reduce these loads and increase the safe operating sea states. In this work, a discrete representation of a passive heave compensator is developed and added to a finite-element model of a deep-sea ROV system to investigate the performance of ship-mounted and cage-mounted compensation systems. Numerical simulations are performed for operating depths ranging from 3280–16,400 ft (1000–5000 m) and a range of compensator stiffnesses. Both ship and cage-mounted systems reduced the natural frequencies, rms cage motion and rms tension, and extended the operating sea state of the ROV. During extreme seas, the cage-mounted compensator effectively eliminated all snap loads. However, the compensator’s characteristics must be carefully chosen because a poorly designed compensator can exacerbate operational problems. [S0892-7219(00)00903-1]
Flow Characteristics of Transitional Boundary Layers on an Airfoil in Wakes
Authors: Lee H. , Kang S.-H.
Published: July 2002

Transition characteristics of a boundary layer on a NACA0012 airfoil are investigated by measuring unsteady velocity using hot wire anemometry. The airfoil is installed in the incoming wake generated by an airfoil aligned in tandem with zero angle of attack. Reynolds number based on the airfoil chord varies from 2.0×105 to 6.0×105; distance between two airfoils varies from 0.25 to 1.0 of the chord length. To measure skin friction coefficient identifying the transition onset and completion, an extended wall law is devised to accommodate transitional flows with pressure gradient and nonuniform inflows. Variations of the skin friction are quite similar to that of the flat plate boundary layer in the uniform turbulent inflow of high intensity. Measured velocity profiles are coincident with families generated by the modified wall law in the range up to y+=40. Turbulence intensity of the incoming wake shifts the onset location of transition upstream. The transitional region becomes longer as the airfoils approach one another and the Reynolds number increases. The mean velocity profile gradually varies from a laminar to logarithmic one during the transition. The maximum values of rms velocity fluctuations are located near y+=15-20. A strong positive skewness of velocity fluctuation is observed at the onset of transition and the overall rms level of velocity fluctuation reaches 3.0–3.5 in wall units. The database obtained will be useful in developing and evaluating turbulence models and computational schemes for transitional boundary layer. [S0098-2202(00)01603-5]
Thermal Characterization of Electronic Packages Using a Three-Dimensional Fourier Series Solution
Authors: Culham J. R. , Yovanovich M. M. , Lemczyk T. F.
Published: July 2002

The need to accurately predict component junction temperatures on fully operational printed circuit boards can lead to complex and time consuming simulations if component details are to be adequately resolved. An analytical approach for characterizing electronic packages is presented, based on the steady-state solution of the Laplace equation for general rectangular geometries, where boundary conditions are uniformly specified over specific regions of the package. The basis of the solution is a general three-dimensional Fourier series solution which satisfies the conduction equation within each layer of the package. The application of boundary conditions at the fluid-solid, package-board and layer-layer interfaces provides a means for obtaining a unique analytical solution for complex IC packages. Comparisons are made with published experimental data for both a plastic quad flat package and a multichip module to demonstrate that an analytical approach can offer an accurate and efficient solution procedure for the thermal characterization of electronic packages. [S1043-7398(00)01403-1]
Identification of Material Constants of Composite Laminates Using Measured Strains
Authors: Kam T. Y. , Lin C. H. , Wang W. T.
Published: July 2002

A method for nondestructive evaluation of material constants of composite laminates is presented. An error function is established to measure the differences between the theoretically and experimentally predicted strains. The identification of the material constants is formulated as a constrained minimization problem in which the material constants are determined to make the error function a global minimum. A global minimization method, together with an appropriate bounding technique for constraining the variations of the material constants, are used to solve the above minimization problem. The applications of the proposed method are demonstrated by means of several examples on the material constants identification of laminated composite cylindrical pressure vessels. [S0094-4289(00)02704-3]
Approximating Spatial Locations With Spherical Orientations for Spherical Mechanism Design
Authors: Tse David M. , Larochelle Pierre M.
Published: July 2002

In this paper we present a novel method for approximating a finite set of n spatial locations with n spherical orientations. This is accomplished by determining a design sphere and the associated orientations on this design sphere which are nearest the n spatial locations. The design sphere and the orientations on it are optimized such that the sum of the distances between each spatial location and its approximating spherical orientation is minimized. The result is a design sphere and n spherical orientations which best approximate a set of n spatial locations. In addition, we include a modification to the method which enables the designer to require that one of the n desired spatial locations be exactly preserved. This method for approximating spatial locations with spherical orientations is directly applicable to the synthesis of spherical mechanisms for motion generation. Here we demonstrate the utility of the method for motion generation task specification in spherical mechanism design. [S1050-0472(00)00204-X]
Parametric Study of Motor/Shroud Heat Transfer Performance in an Electrical Submersible Pump (ESP)
Authors: Rodriguez Jesus R. , Finaish Fathi , Dunn-Norman Shari
Published: July 2002

A shroud is commonly used around the motor of an electrical submersible pump (ESP) to accelerate reservoir fluids past the motor for cooling. Standard practice has been to design the shroud/motor configuration relative to the casing using a minimum fluid velocity of 0.3048 m/s (1 ft/s) rule of thumb as a production strategy. The increase in the use of ESPs to exploit heavy oil reservoirs has brought up the necessity of revising this rule in order to prevent motor burnouts. A parametric study has been conducted using the computational fluid dynamics software CFX4.2 to examine the heat transfer behavior of the shroud motor configuration as a function of motor/shroud standoff. The objective of this effort is to examine the validity of the historical rule of thumb for heavy oils. Results for a case study on an oil with a viscosity of 78 cp @ 320 K are presented. Further, to explore the possibility of enhancing the heat transfer characteristics, the flow configuration was modified by incorporating several openings on the shroud. Based on the obtained results, it can be concluded that fluid velocity should be kept around 0.85 m/s (2.8 ft/s) as opposed to 1 ft/s to assure proper cooling of the motor. Also, flow redistribution by proper placement of the slots on the shroud may produce better heat transfer between the oil and the motor wall. [S0195-0738(00)00703-2]
Stability of Elliptical Cylinders in Two-Dimensional Channel Flow
Authors: Zhao Yu , Sharp M. Keith
Published: July 2002

The flow around rigid cylinders of elliptical cross section placed transverse to Poiseuille flow between parallel plates was simulated to investigate issues related to the tumbling of red blood cells and other particles of moderate aspect ratio in the similar flow in a Field Flow Fractionation (FFF) channel. The torque and transverse force on the cylinder were calculated with the cylinder freely translating, but prevented from rotating, in the flow. The aspect ratios (long axis to short axis) of the elliptical cylinders were 2, 3, 4, and 5. The cylinder was placed transversely at locations of y0/H=0.1, 0.2, 0.3, and 0.4, where y0 is the distance from the bottom of the channel and H is the height of the channel, and the orientation of the cylinder was varied from 0 to 10 deg with respect to the axis of the channel for a channel Reynolds number of 20. The results showed that equilibrium orientations (indicated by a zero net torque on the cylinder) were possible for high-aspect-ratio cylinders at transverse locations y0/H<0.2. Otherwise, the net torque on the cylinder was positive, indicating that the cylinder would rotate. For cylinders with a stable orientation, however, a transverse lift force existed up to about y0/H=0.25. Thus, a cylinder of neutral or low buoyancy might be lifted with a stable orientation from an initial position near the wall until it reached y0/H<0.2, whereupon it would begin to tumble or oscillate. The dependence of lift and torque on cylinder orientation suggested that neutral or low-buoyancy cylinders may oscillate in both transverse location and angular velocity. Cylinders more dense than the carrier fluid could be in equilibrium both in terms of orientation and transverse location if their sedimentation force matched their lift force for a location y0/H<0.2.[S0148-0731(00)00505-7]
Thermodynamic Model for Cold Water Survival
Authors: Van Dorn W. G.
Published: July 2002

A thermodynamic heat flow model for the human body gives survival time as a function of water temperature, assuming constant specific heat and thermal conductance. [S0148-0731(00)01305-4]
Micro-Mechanical Deformation Analysis of Surface Laminar Circuit in Organic Flip-Chip Package: An Experimental Study
Authors: Han B. , Kunthong P.
Published: July 2002

Thermo-mechanical deformations of microstructures in a surface laminar circuit (SLC) substrate are quantified by microscopic moire´ interferometry. Two specimens are analyzed; a bare SLC substrate and a flip chip package assembly. The specimens are subjected to a uniform thermal loading of ΔT=−70°C and the microscopic displacement fields are documented at the identical region of interest. The nano-scale displacement sensitivity and the microscopic spatial resolution obtained from the experiments provide a faithful account of the complex deformation of the surface laminar layer and the embedded microstructures. The displacement fields are analyzed to produce the deformed configuration of the surface laminar layer and the strain distributions in the microstructures. The high modulus of underfill produces a strong coupling between the chip and the surface laminar layer, which produces a DNP-dependent shear deformation of the layer. The effect of the underfill on the deformation of the microstructures is investigated and its implications on the package reliability are discussed. [S1043-7398(00)01304-9]
On the Development and Application of the Fast-Response Aerodynamic Probe System in Turbomachines—Part 3: Comparison of Averaging Methods Applied to Centrifugal Compressor Measurements
Authors: Ko¨ppel Pascal , Roduner Christian , Kupferschmied Peter , Gyarmathy Georg
Published: July 2002

Typically several hundred million data points arise from a comprehensive measurement campaign carried out in a centrifugal compressor test rig with the fast-response aerodynamic probe system (see Part 1). In order to obtain a maximum of information about the unsteady flow at any position in this turbomachine, the time-resolved data processing method has to be optimized. In contrast to the standard time-averaged flow measurements with pneumatic probes, the objective of fast-response aerodynamic probe measurements and of data processing is to extract novel information about crucial unsteady phenomena like turbulence, row-to-row interaction, modal or rotating stall, leakage flow effects, etc. In such cases, the simultaneous measurement of static and total pressures and flow vectors is of particular interest. Novel information means the analysis of averaged and time-resolved (wavelet) spectra, autocorrelations or time averages properly conserving physical fluxes, etc. Different averaging methods are applied to compress the time-dependent data measured by a one-sensor-probe (see Part 2) in a centrifugal compressor. Such results could be used for comparison with pneumatic sensor measurements and CFD calculations. The comparison of averaging methods includes the averaging theories by Traupel and by Dzung, which are compared to simple arithmetic time averaging. From there the specific stage work is calculated. In analyzing the time dependency, several ensemble-averaging procedures for flow pressure and velocity are utilized for separating deterministic from stochastic fluctuations, extracting blade row finger prints or investigating low-frequency surge type fluctuations. With respect to the selection and overall optimization of data processing methods, an overview of generic tools is given and the modularity of the processing procedures is discussed. [S0889-504X(00)01203-4]
Explicit Modal Analysis of an Axially Loaded Timoshenko Beam With Bending-Torsion Coupling
Authors: Banerjee J. R.
Published: July 2002

Exact analytical expressions for the natural frequencies and mode shapes of a uniform bending-torsion coupled Timoshenko beam are presented. The beam is taken to be axially loaded, and for which cantilever end conditions apply. A symbolic computing package (REDUCE) has been used, which simplifies the analysis greatly. Results are presented for an illustrative example, which confirms the accuracy of the method, and provides a convenient benchmark for the validation of the finite element or other alternative approximate methods. The approach offers the prospect of aeroelastic development, and is computationally efficient, thus holding out the promise of eventual optimization. [S0021-8936(00)01002-3]
Direct Method for Optimization of a Centrifugal Compressor Vaneless Diffuser
Authors: Lee Yu-Tai , Luo Lin , Bein Thomas W.
Published: July 2002

A Direct Method for Optimization (DMO) is developed for investigating pressure rise and energy loss in a vaneless diffuser of a generic compressor used in shipboard air-conditioning systems. The scheme uses Reynolds-Averaged Navier–Stokes (RANS) results and evaluates gradients of a predetermined objective function. The current Direct Method for Optimization differs from the popular Inverse Design Method in the process of obtaining final configurations and in the final configurations obtained. The Direct Method for Optimization achieves a final shape from maximizing/minimizing a nonlinear function, i.e., the objective function. Both gradient and nongradient Direct Methods for Optimization are compared with respect to accuracy and efficiency. The coupled DMO/RANS optimization code is benchmarked using a plane turbulent diffuser also investigated by Zhang et al. using an adjoint method. The benchmark indicates that if a global optimum exists, the result should be independent of the methodologies or design parameters used. The DMO/RANS method is applied to redesign a three-dimensional centrifugal vaneless diffuser used in a modern generic compressor. The objective function is a composite function of the diffuser’s pressure rise and total energy loss. The new optimum diffuser has a minimum width at a location far beyond the conventional diffuser pinch point. The new diffuser also provides an efficient section for pressure recovery, which takes place after the minimum width location. Test data for the new diffuser validate the current approach at the design condition. Furthermore, improved performance is also recorded experimentally at off-design conditions for the optimized diffuser.
Sliding Mode Friction Compensation for a 20 DOF Sensor Glove
Authors: Korondi Pe´ter , Szemes Pe´ter T. , Hasimoto Hideki
Published: July 2002

A high-performance human interface device needs accurate force feedback from the manipulated environment to the operator to improve the operation. The mechanism applied in the human interface device usually has a reasonable imminent friction. This friction must be compensated in a way that the operator cannot feel this friction force but only the force from the manipulated environment. The main contribution of this paper is a practical application of direct model based chattering free sliding mode friction estimator and compensator for a human interface device, which is used for virtual telemanipulation. Experimental results are presented for a sensor glove type haptic device with 20 degrees of freedom. [S0022-0434(00)01104-7]