bluuebunny/crossref_metadata_2025 huggingface dataset:
Excision of a proposed electron transfer pathway in cytochrome c peroxidase and its replacement by a ligand‐binding channel
Authors: Rosenfeld Robin J. , Hays Anna‐Maria A. , Musah Rabi A. , Goodin David B.
Published: July 2002

A previously proposed electron transfer (ET) pathway in the heme enzyme cytochrome c peroxidase has been excised from the structure, leaving an open ligand‐binding channel in its place. Earlier studies on cavity mutants of this enzyme have revealed structural plasticity in this region of the molecule. Analysis of these structures has allowed the design of a variant in which the specific section of protein backbone representing a previously proposed ET pathway is accurately extracted from the protein. A crystal structure verified the creation of an open channel that overlays the removed segment, extending from the surface of the protein to the heme at the core of the protein. A number of heterocyclic cations were found to bind to the proximal‐channel mutant with affinities that can be rationalized based on the structures. It is proposed that small ligands bind more weakly to the proximal‐channel mutant than to the W191G cavity due to an increased off rate of the open channel, whereas larger ligands are able to bind to the channel mutant without inducing large conformational changes. The structure of benzimidazole bound to the proximal‐channel mutant shows that the ligand accurately overlays the position of the tryptophan radical center that was removed from the wild‐type enzyme and displaces four of the eight ordered solvent molecules seen in the empty cavity. Ligand binding also caused a small rearrangement of the redesigned protein loop, perhaps as a result of improved electrostatic interactions with the ligand. The engineered channel offers the potential for introducing synthetic replacements for the removed structure, such as sensitizer‐linked substrates. These installed “molecular wires” could be used to rapidly initiate reactions, trap reactive intermediates, or answer unresolved questions about ET pathways.
Diagnostic Checks for Discrete Data Regression Models Using Posterior Predictive Simulations
Authors: Gelman Andrew , Goegebeur Yuri , Tuerlinckx Francis , Van Mechelen Iven van
Published: July 2002

Model checking with discrete data regressions can be difficult because the usual methods such as residual plots have complicated reference distributions that depend on the parameters in the model. Posterior predictive checks have been proposed as a Bayesian way to average the results of goodness-of-fit tests in the presence of uncertainty in estimation of the parameters. We try this approach using a variety of discrepancy variables for generalized linear models fitted to a historical data set on behavioural learning. We then discuss the general applicability of our findings in the context of a recent applied example on which we have worked. We find that the following discrepancy variables work well, in the sense of being easy to interpret and sensitive to important model failures: structured displays of the entire data set, general discrepancy variables based on plots of binned or smoothed residuals versus predictors and specific discrepancy variables created on the basis of the particular concerns arising in an application. Plots of binned residuals are especially easy to use because their predictive distributions under the model are sufficiently simple that model checks can often be made implicitly. The following discrepancy variables did not work well: scatterplots of latent residuals defined from an underlying continuous model and quantile–quantile plots of these residuals.
Effect of eccentric muscle contractions on Golgi tendon organ responses to passive and active tension in the cat
Authors: Gregory J. E. , Brockett C. L. , Morgan D. L. , Whitehead N. P. , Proske U.
Published: July 2002

To investigate the possibility of a peripheral contribution to the perturbations of force sensation reported to occur after eccentric exercise, responses to passive and active tension were recorded from Golgi tendon organs in the medial gastrocnemius muscle of the anaesthetised cat, before and after a series of eccentric contractions. After the eccentric contractions, nearly all tendon organs commenced firing at a shorter muscle length during slow passive stretch than before, probably because of a rise in whole muscle passive tension. There was a small drop in the sensitivity to incremental tension, but no mean change in tension threshold. Following the eccentric contractions, there was a small, but not significant, increase in tendon organ sensitivity to active tension, which was graded using a method of optimised, distributed stimulation of divided ventral roots. Sensitivity was estimated as the mean response over a range of tensions and as the change in discharge rate in response to incremental tension. The experiments provided the opportunity of comparing tendon organ sensitivities to graded passive and active whole muscle tension. In agreement with previous work in which whole muscle nerve stimulation was employed, little difference was found. It was concluded that the peripheral contribution to perturbations of force perception after eccentric exercise is likely to be small and that the centrally derived sense of effort plays the dominant role. Tendon organs appear to be remarkably reliable in signalling whole muscle tension, whether passive or active, and even after the muscle's force production has been disturbed by fatigue or eccentric exercise.
Mutation of Walker‐A lysine 464 in cystic fibrosis transmembrane conductance regulator reveals functional interaction between its nucleotide‐binding domains
Authors: Powe Allan C. , Al‐Nakkash Layla , Li Min , Hwang Tzyh‐Chang
Published: July 2002

The cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel bears two nucleotide‐binding domains (NBD1 and NBD2) that control its ATP‐dependent gating. Exactly how these NBDs control gating is controversial. To address this issue, we examined channels with a Walker‐A lysine mutation in NBD1 (K464A) using the patch clamp technique. K464A mutants have an ATP dependence (EC50≈ 60 μm) and opening rate at 2.75 mm ATP (∼ 2.1 s−1) similar to wild type (EC50≈ 97 μm; ∼ 2.0 s−1). However, K464A's closing rate at 2.75 mm ATP (∼ 3.6 s−1) is faster than that of wild type (∼ 2.1 s−1), suggesting involvement of NBD1 in nucleotide‐dependent closing. Delay of closing in wild type by adenylyl imidodiphosphate (AMP‐PNP), a non‐hydrolysable ATP analogue, is markedly diminished in K464A mutants due to reduction in AMP‐PNP's apparent on‐rate and acceleration of its apparent off‐rate (∼ 2‐ and ∼ 10‐fold, respectively). Since the delay of closing by AMP‐PNP is thought to occur via NBD2, K464A's effect on the NBD2 mutant K1250A was examined. In sharp contrast to K464A, K1250A single mutants exhibit reduced opening (∼ 0.055 s−1) and closing (∼ 0.006 s−1) rates at millimolar [ATP], suggesting a role for K1250 in both opening and closing. At millimolar [ATP], K464A‐K1250A double mutants close ∼ 5‐fold faster (∼ 0.029 s−1) than K1250A but open with a similar rate (∼ 0.059 s−1), indicating an effect of K464A on NBD2 function. In summary, our results reveal that both of CFTR's functionally asymmetric NBDs participate in nucleotide‐dependent closing, which provides important constraints for NBD‐mediated gating models.
Multiple inhibitory effects of Au(CN)2− ions on cystic fibrosis transmembrane conductance regulator Cl− channel currents
Authors: Linsdell Paul , Gong Xiandi
Published: July 2002

Lyotropic pseudohalide anions are potentially useful as high affinity probes of Cl− channel pores. However, the interaction between these pseudohalides and the cystic fibrosis transmembrane conductance regulator (CFTR) Cl− channel have not been described in detail. Here we show that Au(CN)2− ions applied to the intracellular face of membrane patches from stably transfected baby hamster kidney cells inhibit CFTR channel currents by at least two mechanisms, which can be distinguished at the single channel level or by inhibiting channel closure using 2 mm pyrophosphate. Low concentrations (< 10 μm) of Au(CN)2− significantly reduced CFTR channel open probability. This effect was apparently voltage insensitive, independent of extracellular Cl− concentration, and lost following exposure to pyrophosphate. Higher concentrations of intracellular Au(CN)2− caused an apparent reduction in unitary current amplitude, presumably due to a kinetically fast blocking reaction. This effect, isolated following exposure to pyrophosphate, was strongly voltage dependent (apparent Kd 61.6 μm at −100 mV and 913 μm at +60 mV). Both the affinity and voltage dependence of block were highly sensitive to extracellular Cl− concentration. We propose that Au(CN)2− has at least two inhibitory effects on CFTR currents: a high affinity effect on channel gating due to action on a cytoplasmically accessible aspect of the channel and a lower affinity block within the open channel pore. These results offer important caveats for the use of lyotropic pseudohalide anions such as Au(CN)2− as specific high affinity probes of Cl− channel pores.
Dominance of pressure natriuresis in acute depressor responses to increased renal artery pressure in rabbits and rats
Authors: Correia Anabela G. , Bergström Göran , Jia Jing , Anderson Warwick P. , Evans Roger G.
Published: July 2002

Increasing renal artery pressure (RAP) activates pressure diuresis/natriuresis and inhibits renal renin release. There is also evidence that increasing RAP stimulates release of a putative depressor hormone from the renal medulla, although this hypothesis remains controversial. We examined the relative roles of these antihypertensive mechanisms in the acute depressor responses to increased RAP in anaesthetized rabbits and rats. In rabbits, an extracorporeal circuit was established which allows RAP to be set and controlled without direct effects on systemic haemodynamics. When RAP was maintained at ∼65 mmHg, cardiac output (CO) and mean arterial pressure (MAP) did not change significantly. In contrast, when RAP was increased to ∼160 mmHg, CO and MAP fell 20 ± 5 % and 36 ± 5 %, respectively, over 30 min. Urine flow also increased more than 28‐fold when RAP was increased. When compound sodium lactate was infused intravenously at a rate equal to urine flow, neither CO nor MAP fell significantly in response to increased RAP. In 1 kidney‐1 clip hypertensive rats, MAP fell by 54 ± 10 mmHg over a 2 h period after unclipping. In rats in which isotonic NaCl was administered intravenously at a rate equal to urine flow, MAP did not change significantly after unclipping (−14 ± 9 mmHg). Our results suggest that the depressor responses to increasing RAP in these experimental models are chiefly attributable to hypovolaemia secondary to pressure diuresis/natruresis. These models therefore appear not to be bioassays for release of a putative renal medullary depressor hormone.
Development of T‐tubular vacuoles in eccentrically damaged mouse muscle fibres
Authors: Yeung Ella W. , Balnave Christopher D. , Ballard Heather J. , Bourreau J.‐P. , Allen David G.
Published: July 2002

Single fibres were dissected from mouse flexor digitorum brevis muscles and subjected to a protocol of eccentric stretches consisting of ten tetani each with a 40 % stretch. Ten minutes later the fibres showed a reduced force, a shift in the peak of the force‐length relation and a steepening of the force‐frequency relation. Addition of the fluorescent dye sulforhodamine B to the extracellular space enabled the T‐tubular system to be visualized. In unstimulated fibres and fibres subjected to 10 isometric tetani, the T‐tubules were clearly delineated. Sulforhodamine B diffused out of the T‐tubules with a half‐time of 18 ± 1 s. Following the eccentric protocol, vacuoles connected to the T‐tubules were detected in six out of seven fibres. Sulforhodamine B diffused out of the vacuoles of eccentrically damaged fibres extremely slowly with a half‐time of 6.3 ± 2.4 min and diffused out of the T‐tubules with a half‐time of 39 ± 4 s. Vacuole production was eliminated by application of 1 mm ouabain to the muscle during the eccentric protocol. On removal of the ouabain, vacuoles appeared over a period of 1 h and were more numerous and more widely distributed than in the absence of ouabain. We propose that T‐tubules are liable to rupture during eccentric contraction probably because of the relative movement associated with the inhomogeneity of sarcomere lengths. Such rupture raises intracellular sodium and when the sodium is pumped from the cell by the sodium pump, the volume load of Na+ and water exceeds the capacity of the T‐tubules and causes vacuole production. The damage to the T‐tubules may underlie a number of the functional changes that occur in eccentrically damaged muscle fibres.
A Ca2+‐inhibited non‐selective cation conductance contributes to pacemaker currents in mouse interstitial cell of Cajal
Authors: Koh Sang Don , Jun Jae Yeoul , Kim Tae Wan , Sanders Kenton M.
Published: July 2002

Interstitial cells of Cajal (ICC) provide pacemaker activity in some smooth muscles. The nature of the pacemaker conductance is unclear, but studies suggest that pacemaker activity is due to a voltage‐independent, Ca2+‐regulated, non‐selective cation conductance. We investigated Ca2+‐regulated conductances in murine intestinal ICC and found that reducing cytoplasmic Ca2+ activates whole‐cell inward currents and single‐channel currents. Both the whole‐cell currents and single‐channel currents reversed at 0 mV when the equilibrium potentials of all ions present were far from 0 mV. Recordings from on‐cell patches revealed oscillations in unitary currents at the frequency of pacemaker currents in ICC. Voltage‐clamping cells to −60 mV did not change the oscillatory activity of channels in on‐cell patches. Depolarizing cells with high external K+ caused loss of resolvable single‐channel currents, but the oscillatory single‐channel currents were restored when the patches were stepped to negative potentials. Unitary currents were also resolved in excised patches. The single‐channel conductance was 13 pS, and currents reversed at 0 mV. The channels responsible were strongly activated by 10−7m Ca2+, and 10−6m Ca2+ reduced activity. The 13 pS channels were strongly activated by the calmodulin inhibitors calmidazolium and W‐7 in on‐cell and excised patches. Calmidazolium and W‐7 also activated a persistent inward current under whole‐cell conditions. Murine ICC express Ca2+‐inhibited, non‐selective cation channels that are periodically activated at the same frequency as pacemaker currents. This conductance may contribute to the pacemaker current and generation of electrical slow waves in GI muscles.
Thermal Aspects of Grinding: The Case of Upgrinding
Authors: Demetriou Marios D. , Lavine Adrienne S.
Published: July 2002

Conventional grinding is usually carried out in upgrinding mode, with the wheel moving in the opposite direction from the workpiece. In this paper, a thermal model is developed for upgrinding. This model is similar to our previous models of downgrinding in that the behavior of the workpiece, grains, fluid, and chips are all coupled. The model is used to compare the workpiece temperature rises in upgrinding and downgrinding, and to explore the effect of the location of heat generation. The model results are also compared with experimental data and are seen to yield reasonable agreement. Finally, the sensitivity of the results to some parameters which are not well known is explored. [S1087-1357(00)01002-9]
Finite Element Analysis of the Crimping Process of the Piston-slipper Component in Hydraulic Pumps
Authors: Yao Y. , Qamhiyah A. Z. , Fang X. D.
Published: July 2002

Hydraulic pumps and motors are widely used in mobile equipment for construction, mining and agriculture. The piston-slipper component is one of the critical parts of a hydraulic pump. A crimping process is used for connecting the piston to the slipper component. Like most of the manufacturing processes that involve large deformations, high stresses are created in the slipper and piston during the crimping process. This paper presents a finite element method for the analysis of the stresses, strains, and forces associated with the crimping process. This method can be used in the optimization of the piston, slipper and die designs. The commercial finite element package ANSYS was used to simulate the crimping process. The simulation procedure is used to obtain a better understanding of the effect of the die geometry on the crimping process. [S1050-0472(00)00303-2]
Dynamic Response of a Planetary Gear System Using a Finite Element/Contact Mechanics Model
Authors: Parker Robert G. , Agashe Vinayak , Vijayakar Sandeep M.
Published: July 2002

The dynamic response of a helicopter planetary gear system is examined over a wide range of operating speeds and torques. The analysis tool is a unique, semianalytical finite element formulation that admits precise representation of the tooth geometry and contact forces that are crucial in gear dynamics. Importantly, no a priori specification of static transmission error excitation or mesh frequency variation is required; the dynamic contact forces are evaluated internally at each time step. The calculated response shows classical resonances when a harmonic of mesh frequency coincides with a natural frequency. However, peculiar behavior occurs where resonances expected to be excited at a given speed are absent. This absence of particular modes is explained by analytical relationships that depend on the planetary configuration and mesh frequency harmonic. The torque sensitivity of the dynamic response is examined and compared to static analyses. Rotational mode response is shown to be more sensitive to input torque than translational mode response. [S1050-0472(00)00403-7]
Parallel Optimal Kalman Filtering for Stochastic Systems in Multimodeling Form
Authors: Coumarbatch Cyril , Gajic Zoran
Published: July 2002

In this paper we show how to completely and exactly decompose the optimal Kalman filter of stochastic systems in multimodeling form in terms of one pure-slow and two pure-fast, reduced-order, independent, Kalman filters. The reduced-order Kalman filters are all driven by the system measurements. This leads to a parallel Kalman filtering scheme and removes ill-conditioning of the original full-order singularly perturbed Kalman filter. The results obtained are valid for steady state. In that direction, the corresponding algebraic filter Riccati equation is completely decoupled and solved in terms of one pure-slow and two pure fast, reduced-order, independent, algebraic Riccati equations. A nonsingular state transformation that exactly relates the state variables in the original and new coordinates (in which the required decomposition is achieved) is also established. The eighth order model of a passenger car under road disturbances is used to demonstrate efficiency of the proposed filtering technique. [S0022-0434(00)01703-2]
Studies on the Three-Dimensional Temperature Transients in the Canine Prostate During Transurethral Microwave Thermal Therapy
Authors: Liu Jing , Zhu Liang , Xu Lisa X.
Published: July 2002

Thermal therapy of benign prostatic hyperplasia requires accurate prediction of the temperature distribution induced by the heating within the prostatic tissue. In this study, the Pennes bioheat transfer equation was used to model the transient heat transfer inside the canine prostate during transurethral microwave thermal therapy. Incorporating the specific absorption rate of microwave energy in tissue, a closed-form analytical solution was obtained. Good agreement was found between the theoretical predictions and in-vivo experimental results. Effects of blood perfusion and the cooling at the urethral wall on the temperature rise were investigated within the prostate during heating. The peak intraprostatic temperatures attained by application of 5, 10, or 15 W microwave power were predicted to be 38°C,41°C, and 44°C. Results from this study will help optimize the thermal dose that can be applied to target tissue during the therapy. [S0148-0731(00)01004-9]
On the Development and Application of the Fast-Response Aerodynamic Probe System in Turbomachines—Part 1: The Measurement System
Authors: Kupferschmied Peter , Ko¨ppel Pascal , Roduner Christian , Gyarmathy Georg
Published: July 2002

This contribution gives an overview of the current state, performance, and limitations of the fast-response aerodynamic probe measurement system developed at the Turbomachinery Lab of the ETH Zurich. In particular, the following topics are addressed:

 • Probe technology: Miniature probes with tip diameter ranging from 0.84 to 1.80 mm (one-sensor and three-sensor probes, respectively) have been developed. New technologies derived from microelectronics and micromechanics have been used to achieve an adequate packaging of the microsensor chips used. Both the sensor packaging and the sensor calibration (time-independent and time-dependent) are crucial issues for the DC accuracy of any measurement.

 • Aerodynamic probe calibration: The methods used for the sensor calibration and the aerodynamic probe calibration, the pertinent automated test facilities, and the processing of the output data are briefly presented. Since these miniature probes are also capable of measuring the mean flow temperature, aspects related to the effective recovery factor and the self-heating of the probe tip are treated and some recommendations related to sensor selection are given.

 • Measurement system and data evaluation: The early measurement chain described in Gossweiler et al. (1995) has evolved into the fast-response aerodynamic probe system. This automatic system incorporates dedicated measurement concepts for a higher accuracy and a more efficient operation in terms of time and failures. An overview of the data evaluation process is given.

The fast-response aerodynamic probe system has been tested in real-sized turbomachines under industrial conditions within the temperature limits of 140°C imposed by the sensor technology (axial-flow turbofan compressor, axial-flow turbine, centrifugal compressor). These applications confirmed the potential of the system and encouraged its further development. Now, the system is routinely used in the facilities of the Turbomachinery Lab and in occasional measurement campaigns in other laboratories.

Part 2 of this contribution (Roduner et al.) will focus on the application of the fast-response aerodynamic probe system in a transonic centrifugal compressor of the ETH Turbomachinery Laboratory, while Part 3 (Ko¨ppel et al.) treats more sophisticated data analysis methods. [S0889-504X(00)01003-5]
The Compressible Calibration of Miniature Multi-Hole Probes
Authors: Johansen Espen S. , Rediniotis Othon K. , Jones Greg
Published: July 2002

This work presents the development of a data reduction algorithm for non-nulling, multihole pressure probes in compressible, subsonic flowfields. The algorithm is able to reduce data from any 5- or 7-hole probe and generate very accurate predictions of the velocity magnitude and direction, total and static pressures, Mach and Reynolds number and fluid properties like the density and viscosity. The algorithm utilizes a database of calibration data and a local least-squares interpolation technique. It has been tested on four novel miniature 7-hole probes that have been calibrated at NASA Langley Flow Modeling and Control Branch for the entire subsonic regime. Each of the probes had a conical tip with diameter of 1.65 mm. Excellent prediction capabilities are demonstrated with maximum errors in angle prediction less than 0.6 degrees and maximum errors in velocity prediction less than 1 percent, both with 99 percent confidence.
Dynamic Behavior of Complex Fluid-Filled Tubing Systems—Part 2: System Analysis
Authors: Tentarelli Stephen C. , Brown Forbes T.
Published: July 2002

The pipe segments modeled in Part 1 are incorporated into a larger scheme permitting branching, fittings, valves, added masses, rigid, flexible and dissipative mechanical constraints, accumulators and various boundary conditions. The concept of the global matrix also is extended to systems with junctions and closed loops, permitting practical solution for frequency responses without round-off error problems. The procedure can be generalized to handle a broad class of systems comprising a combination of lumped elements and quasi one-dimensional distributed-parameter elements. A complex example with experimental corroboration is given.
Precision Sensing of Arc Length in GTAW Based on Arc Light Spectrum
Authors: Li P. J. , Zhang Y. M.
Published: July 2002

This work aims to improve the measurement accuracy of arc length using the arc light at a particular wavelength during gas tungsten arc welding (GTAW) with argon shield. To this end, the effects of welding parameters on spectral distributions were studied. To verify the effects of base metal and arc length, the arc column was also sampled horizontally as layers for spectral analysis. Results showed that intensity of argon atom lines is determined by arc length and is independent of variation of welding conditions. Based on these findings, a compact arc light sensor has been developed to measure the arc length with a narrow-band filter (wavelength: 696.5 nm; half-width: 15 nm). Control experiments showed that the arc length was controlled with an accuracy of ±0.2 mm for the arc length in the range from 0.5 mm to 5 mm.
Nucleate Pool Boiling From Coated and Spirally Wrapped Tubes in Saturated R-134a and R-600a at Low and Moderate Heat Flux
Authors: Hsieh Shou-Shing , Yang Tsung-Ying
Published: July 2002

Pool nucleate boiling heat transfer experiments from coated surfaces with porous copper (Cu) and molybdenum (Mo) and spirally wrapped with helical wire on copper surfaces with micro-roughness immersed in saturated R-134a and R-600a were conducted. The influence of coating thickness, porosity, wrapped helical angle, and wire pitch on heat transfer and boiling characteristics including bubble parameters were studied. The enhanced surface heat transfer coefficients with R-600a as refrigerant found are 2.4 times higher than those of the smooth surfaces. Photographs indicate that the average number of bubbles and bubble departure diameters has been found to increase linearly with heat flux, while the bubble diameters exhibit opposite trend in both refrigerants. Furthermore, the heat transfer of the boiling process for the present enhanced geometry (coated and wrapped) was modeled and analyzed. The experimental data for plasma coating and spirally wrapped surfaces were correlated in terms of relevant parameters, respectively to provide a thermal design basis for engineering applications.
An Analytic Algorithm of Stresses for Any Double Hole Problem in Plane Elastostatics
Authors: Zhang Lu-qing , Lu Ai-zhong
Published: July 2002

This paper gives an analytic algorithm to plane elastostatic problem of an infinite medium containing two holes of arbitrary shapes and arrangement, using Schwarz’s alternating method, and finds that the method has a very quick convergence speed even for solving a complex double hole problem.
The Elastic Stability of Twisted Plates
Authors: Mockensturm E. M.
Published: July 2002

Since Coulomb’s and Saint-Venant’s fundamental work, many researches have studied the effect of twisting on elastic bodies. The work presented here investigates instabilities that can occur when thin bodies are subject to large twists and extends work by A. E. Green published in 1937. Because large twists are considered, a fully nonlinear plate theory is used. This theory predicts compressive lateral membrane stresses not predicted by Green’s weakly nonlinear theory. These stresses can significantly alter the twist angle at which buckling occurs. Two conditions for the opposing twisted end supports are considered. In one case the supports are held a fixed distance apart and in the other case the force applied to the supports is held fixed during twist. The buckling modes and critical twist angles vary significantly depending on the support condition used.
Formaldehyde Characterization Utilizing In-Cylinder Sampling in a Large Bore Natural Gas Engine
Authors: Olsen D. B. , Holden J. C. , Hutcherson G. C. , Willson B. D.
Published: July 2002

This research addresses the growing need to better understand the mechanisms through which engine-out formaldehyde is formed in two-stroke cycle large bore natural gas engines. The investigation is performed using a number of different in-cylinder sampling techniques implemented on a Cooper-Bessemer GMV-4TF four-cylinder two-stroke cycle large bore natural gas engine with a 36-cm (14-in.) bore and a 36-cm (14-in.) stroke. The development and application of various in-cylinder sampling techniques is described. Three different types of valves are utilized, (1) a large sample valve for extracting a significant fraction of the cylinder mass, (2) a fast sample valve for crank angle resolution, and (3) check valves. Formaldehyde in-cylinder sampling data are presented that show formaldehyde mole fractions at different times during the engine cycle and at different locations in the engine cylinder. The test results indicate that the latter part of the expansion process is a critical time for engine-out formaldehyde formation. The data show that significant levels of formaldehyde form during piston and end-gas compression. Additionally, formaldehyde is measured during the combustion process at mole fractions five to ten times higher than engine-out formaldehyde mole fractions. Formaldehyde is nearly completely destroyed during the final part of the combustion process. The test results provide insights that advance the current understanding and help direct future work on formaldehyde formation.
Investigation of Paraffin Deposition During Multiphase Flow in Pipelines and Wellbores—Part 2: Modeling
Authors: Apte Mandar S. , Matzain Ahmadbazlee , Zhang Hong-Quan , Volk Michael , Brill James P. , Creek Jeff L.
Published: July 2002

A Joint Industry Project to investigate paraffin deposition in multiphase flowlines and wellbores was initiated at The University of Tulsa in May 1995. As part of this JIP, a computer program, based on the molecular diffusion theory, was developed for prediction of wax deposition during multiphase flow in pipelines and wellbores. The program is modular in structure and assumes a steady-state, one-dimensional flow, energy conservation principle. This paper will describe the simulator developed for predicting paraffin deposition during multiphase flow that includes coupling of multiphase fluid flow, solid-liquid-vapor thermodynamics, multiphase heat transfer, and flow pattern-dependent paraffin deposition. Predictions of the simulator are compared and tuned to the experimental data by adjusting the film heat transfer and diffusion coefficients and the thermal conductivity of the wax deposit.
An Improved Design and Rating Analyses of Counter Flow Wet Cooling Towers
Authors: Khan Jameel-ur-Rehman , Zubair Syed M.
Published: July 2002

Cooling towers are one of the largest heat and mass transfer devices that are in common use. In this paper, we present a detail model of counter flow wet cooling towers. The authenticity of the model is checked by experimental data reported in the literature. The values of number of transfer units (NTU) and tower effectiveness (ε) obtained from the model were compared with the commonly described models. Appreciable difference in NTU and ε values is found if the resistance to heat transfer in the water film and non-unity of Lewis number is considered in the calculations. The results demonstrate that the errors in calculating the tower effectiveness could be as much as 15 percent when considering the effect of air-water interface temperature. A procedure for the use of the model in designing and rating analyses of cooling towers is demonstrated through example problems. The limiting performance of the cooling towers; that is effectiveness equal to one, is explained in terms of air-approach temperature. The model is also used for obtaining the maximum possible mass-flow rate ratio of water-to-air, for different operating conditions.
Modeling of Vertical Core-Annular Flows and Application to Heavy Oil Production
Authors: Prada Jose´ W. Vanegas , Bannwart Antonio C.
Published: July 2002

The use of core-annular flow pattern may be attractive as an artificial lift method in heavy oil wells. This flow pattern can be induced by the lateral injection of relatively small quantities of water, in order to get a lubricated oil core along the pipe. Frictional pressure drop measurements for upward vertical core flow in a 1-in. pipe, using a 17.6-Pa.s, 963-kg/m3 oil and water at room temperature reported a decrease by over 1000-fold with respect to single-phase oil flow, being comparable to the flow of water alone in the pipe at mixture flow rate. The total pressure drop was reduced by over 45-fold. The frictional pressure drop model proposed includes both irreversible and buoyancy terms. The model was adjusted to fit our data and shows excellent agreement with laboratory data available.
Heat/Mass Transfer Measurement Within a Film Cooling Hole of Square and Rectangular Cross Section
Authors: Cho Hyung Hee , Kang Seung Goo , Rhee Dong Ho
Published: July 2002

An experimental study has been conducted to investigate the heat/mass transfer characteristics within film cooling holes of square and rectangular cross section. The experiments for this study have been performed using a naphthalene sublimation method, and the flow field has been analyzed by numerical calculation using a commercial code (FLUENT). The rectangular cross section has the aspect ratio of 2 and the same hydraulic diameter as the square cross section. A duct flow enters into a film cooling hole in a cross direction. For the film cooling hole with square cross section, it is observed that the reattachment of separated flow and the vortices within the hole enhance considerably the heat/mass transfer around the hole entrance region. The heat/mass transfer on the leading edge side of hole exit region increases as the blowing rates decrease because the mainflow induces a secondary vortex. Heat/mass transfer patterns within the film cooling hole are changed slightly with the various Reynolds numbers. For the film cooling hole with rectangular cross section, overall heat/mass transfer characteristics are similar with those for the square cross section. However, heat/mass transfer on the leading edge side of hole entrance region has two peak regions due to split flow reattachment, and heat/mass transfer on the leading edge side of hole exit region is less sensitive to the blowing ratios than the square cross-sectional case.
The Significance of Oil Thermal Properties on the Performance of a Tilting-Pad Thrust Bearing
Authors: Glavatskih Sergei B. , Fillon Michel , Larsson Roland
Published: July 2002

This paper is a report into an experimental and theoretical investigation of the effect of oil thermal properties on the performance of a tilting-pad thrust bearing. Three oils, namely poly-α-olefin, ester and mineral base, were chosen for this study. These oils all have same viscosity grade (ISO VG46) but differ in their rates of viscosity variation with temperature and in their heat capacity and thermal conductivity values. Mineral base oil of a higher viscosity grade (ISO VG68) was also analyzed for comparison. Experimental data were obtained from an equalizing tilting-pad thrust bearing with an outer diameter of 228.6 mm operating in a flooded lubrication mode. Simultaneous measurements of pad and collar temperatures, friction torque, pressures and oil film thickness were taken. In the tests, oil supply temperature and flow rate were held constant for all load-speed combinations. The theoretical analysis of oil performance was based on a three-dimensional TEHD model. In the analysis, thermal effects were locally taken into account and heat transfer into the pads was considered. The displacements of the active surface of the pads, due to pressure and temperature fields, were determined. The effect of initial pad crowning on the oil film thickness is discussed. Experimental and theoretical results are compared and analyzed in terms of the inlet and outlet oil film thickness, bearing operating temperature and power loss.
The Effect of Platen Fins on the Flow-Induced Vibrations of an In-Line Tube Array
Authors: Weaver D. S. , Ziada S. , Sun Z. , Feenstra P.
Published: July 2002

This paper presents the results of an experimental study of the effect of streamwise “platen” fins on the fluidelastic instability of an in-line tube array. The fins are fixed parallel to the axis of the tubes in the streamwise direction and effectively prevent any transverse flow between streamwise tube rows. A geometrically identical, dynamically scaled bundle of finless tubes were used as a datum case for comparison. The results showed that, while the fins eliminate vortex shedding, they enhance the fluidelastic coupling between adjacent tubes and substantially reduce the stability threshold.
Predicting Design Wind Turbine Loads from Limited Data: Comparing Random Process and Random Peak Models
Authors: Fitzwater LeRoy M. , Winterstein Steven R.
Published: July 2002

This paper considers two distinct topics that arise in reliability-based wind turbine design. First, it illustrates how general probability models can be used to predict long-term design loads from a set of limited-duration, short-term load histories. Second, it considers in detail the precise choice of probability model to be adopted, for both flap and edge bending loads in both parked and operating turbine conditions. In particular, a 3-moment random peak model and a 3- or 4-moment random process model are applied and compared. For a parked turbine, all models are found to be virtually unbiased and to notably reduce uncertainty in estimating extreme loads (e.g., by roughly 50%). For an operating turbine, however, only the random peak model is found to retain these beneficial features. This suggests the advantage of the random peak model, which appears to capture the rotating blade behavior sufficiently well to accurately predict extremes.
Analysis of Vortical Flow Field in a Propeller Fan by LDV Measurements and LES—Part II: Unsteady Nature of Vortical Flow Structures Due to Tip Vortex Breakdown
Authors: Jang Choon-Man , Furukawa Masato , Inoue Masahiro
Published: July 2002

The unsteady nature of vortex structures has been investigated by a large eddy simulation (LES) in a propeller fan with a shroud covering only the rear region of its rotor tip. The simulation shows that the tip vortex plays a major role in the structure and unsteady behavior of the vortical flow in the propeller fan. The spiral-type breakdown of the tip vortex occurs near the midpitch, leading to significant changes in the nature of the tip vortex. The breakdown gives rise to large and cyclic movements of the tip vortex, so that the vortex impinges cyclically on the pressure surface of the adjacent blade. The movements of the tip vortex cause the leading edge separation vortex to oscillate in a cycle, but on a small scale. The movements of the vortex structures induce high-pressure fluctuations on the rotor blade and in the blade passage.
Thermoelastic Stress Analysis: An NDE Tool for Residual Stress
Assessment of Metallic Alloys
Authors: Gyekenyesi A. L.
Published: July 2002

The primary objective of this report involves studying and developing various experimental techniques for accurate measurement of the mean stress effect in thermoelastic stress analysis (TSA, also recognized as SPATE: stress pattern analysis by thermal emission). The analysis of cyclic mean stresses at the coupon level directly relates to the measurement of residual stresses in structures. In a previous study by the authors, it was shown that cyclic mean stresses significantly influenced the TSA results for titanium and nickel-based alloys, although, difficulties were encountered concerning the quantification of the mean stress effect because of large test-to-test variations. This study continues the effort of accurate direct measurements of the mean stress effect by implementing various experimental modifications. In addition, a more in-depth analysis is included which involves analyzing the second harmonic of the temperature response. By obtaining the amplitudes of the first and second harmonics, the stress amplitude and the mean stress at a given point on a structure subjected to a cyclic load can be simultaneously obtained. The rather complex analysis of the temperature response involves obtaining the first and second harmonic amplitudes for 16384 infrared detectors (128×128 focal plane array). Upon establishing a protocol for mean stress measurements in the laboratory using the TSA technique, the next step is to utilize the method to assess residual stress states in complex structures during manufacturing and life.
Total Unsteadiness Downstream of an Axial Flow Fan With Variable Pitch Blades
Authors: Velarde-Sua´rez Sandra , Ballesteros-Tajadura Rafael , Santolaria-Morros Carlos , Blanco-Marigorta Eduardo
Published: July 2002

Variable pitch axial flow fans are widely used in industrial applications to satisfy variable operating conditions. The change of the blade pitch leads to a different rotor geometry and has a major influence on the unsteady operation of the machine. In this work, an experimental research on an axial flow fan with variable pitch blades has been carried out. First of all, the fan performance curves has been obtained. Then the flow field has been measured at ten radial locations both at the inlet and exit rotor plane using hot wire anemometry. Velocity components and total unsteadiness were determined and analyzed in order to characterize the influence of pitch blade and operating conditions on the flow structure.
Boundary Element Grid Optimization for Stokes Flow With Corner Singularities
Authors: Pozrikidis C.
Published: July 2002

The accuracy of boundary-element methods for computing Stokes flow past boundaries with sharp corners where singularities occur is discussed. To resolve the singular behavior, a graded mesh of boundary elements whose length increases in a geometrical fashion with respect to distance from the corners according to a prescribed stretch ratio is used. Numerical results for two-dimensional Stokes flow past bodies with polygonal shapes reveal the existence of an optimal value of the stretch ratio for best accuracy in the computation of the force and torque. When the optimal value is used, fast convergence is achieved with respect to the number of boundary elements.
Comparison of the Numerical and Experimental Flowfield Downstream of a Plate Array
Authors: Guillaume D. W. , LaRue J. C.
Published: July 2002

The findings of a numerical solution of the flowfield downstream of a six-plate array are compared to a previous experimental study. In both studies, the chord-to-thickness ratio, c/t, is 6.67, the Reynolds number, Re, is 500, and the spacing-to-thickness ratio, H/t, is 3.67. Consistent with experimental results, the numerical simulation shows that the recirculation zones formed at the trailing edges of the surfaces that form channels in the plate array are in-phase. Also consistent, they are nearly 180 deg out-of-phase with the recirculation zones formed at the trailing edges of the surfaces of adjacent channels. Comparison of the locations of recirculation zones and peaks in the downstream variation in axial velocity confirms that “vortex pumping” is described by 1) the axial velocity increase on the midplane of the channel in the region where the separation between pairs of recirculation zones is a minimum and 2) the axial velocity decrease in the region where the separation between pairs of recirculation zones is a maximum.
Twin Web Disk: A Step Beyond Convention
Authors: Cairo R. R. , Sargent K. A.
Published: July 2002

This paper will discuss a study of an innovative design for an advanced turbine rotor that could have a great impact on future engines. The design challenge is to provide a minimum weight turbine rotor system that can withstand beyond state-of-the-art levels of AN2 (turbine annulus area multiplied by speed squared). An AN2 limit has been reached for high-pressure turbine (HPT) disks configured in conventional (single web) geometry with state-of-the-art nickel alloys. The problem has reached the point where increased AN2 has been declared a “break-through” technology. The twin-web disk has the potential to provide this break through. This paper will present the history of this turbine rotor design, analytical results, material/component processing, and concept validation results. All work was performed under an Air Force sponsored program entitled “Composite Ring Reinforced Turbine” (CRRT).
Finite Element Simulation of Segmented Chip Formation of Ti6Al4V
Authors: Ba¨ker Martin , Ro¨sler Joachim , Siemers Carsten
Published: July 2002

The mechanism behind chip segmentation of titanium alloys is still unclear. Experimentally, different kinds of deformation patterns are observed. In this paper we perform a finite element analysis where chip segmentation is done by introducing cracks from the chip surface into the material. A fine mesh is used within the segments, allowing a high resolution of the occurring strain gradients. Because of stress concentration at the crack tip, adiabatic shear bands can form and lead to a strongly segmented chip with pronounced deformation in the crack region. Depending on the cracking parameters, different deformation patterns at the crack flanks are observed.
A New Creep Constitutive Model for Eutectic Solder Alloy
Authors: Shi X. Q. , Wang Z. P. , Zhou W. , Pang H. L. J. , Yang Q. J.
Published: July 2002

In this study, a large number of creep tests were carried out to study the effect of stress level and testing temperature on the creep behavior of 63 Sn/37Pb solder in a systematic manner. Based on the dislocation controlled creep mechanism and Gibbs’ free-energy theory, a new creep constitutive model was proposed. The model was found to describe accurately the creep flow of the solder and to be capable of explaining the issues of stress and temperature dependent stress exponent and activation energy in the Arrhenius power-law creep model. Furthermore, the model was employed to predict accurately the long-term reliability of solder joints in a PBGA assembly.
An Update on Solar Central Receiver Systems, Projects, and Technologies
Authors: Romero Manuel , Buck Reiner , Pacheco James E.
Published: July 2002

Central Receiver Systems that use large heliostat fields and solar receivers located on top of a tower are now in the position to deploy the first generation of grid-connected commercial plants. The technical feasibility of the CRS power plants technology can be valued as sufficiently mature after the pioneering experience at the early 1980s of several pilot plants in the 0.5–10 MW power range and the subsequent improvement of key components like heliostats and solar receiver in many projects merging international collaboration during the past 15 years. Solar-only plants like Solar Tres and PS10 or hybrid schemes like SOLGAS, CONSOLAR, or SOLGATE are being developed and supply a portfolio of alternatives leading to the first scaling-up plants during the period 2000–2010. Those projects with still non-optimized small sizes of 10–15 MW are already revealing a dramatic reduction of costs versus previous feasibility studies and give the path for the formulation of a realistic milestone of achieving a LEC of $0.08/kWh by the year 2010 and penetrating initial competitive markets by 2015 with LECs between $0.04/kWh–$0.06/kWh.