bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of Ca2+ hotspots between Lymnaea neurons during synaptogenesis
Authors: Feng Zhong‐Ping , Grigoriev Nikita , Munno David , Lukowiak Ken , MacVicar Brian A. , Goldberg Jeffrey I , Syed Naweed I.
Published: July 2002

Calcium (Ca2+) channel clustering at specific presynaptic sites is a hallmark of mature synapses. However, the spatial distribution patterns of Ca2+ channels at newly formed synapses have not yet been demonstrated. Similarly, it is unclear whether Ca2+‘hotspots’ often observed at the presynaptic sites are indeed target cell contact specific and represent a specialized mechanism by which Ca2+ channels are targeted to select synaptic sites. Utilizing both soma–soma paired (synapsed) and single neurons from the mollusk Lymnaea, we have tested the hypothesis that differential gradients of voltage‐dependent Ca2+ signals develop in presynaptic neuron at its contact point with the postsynaptic neuron; and that these Ca2+ hotspots are target cell contact specific. Fura‐2 imaging, or two‐photon laser scanning microscopy of Calcium Green, was coupled with electrophysiological techniques to demonstrate that voltage‐induced Ca2+ gradients (hotspots) develop in the presynaptic cell at its contact point with the postsynaptic neuron, but not in unpaired single cells. The incidence of Ca2+ hotspots coincided with the appearance of synaptic transmission between the paired cells, and these gradients were target cell contact specific. In contrast, the voltage‐induced Ca2+ signal in unpaired neurons was uniformly distributed throughout the somata; a similar pattern of Ca2+ gradient was observed in the presynaptic neuron when it was soma–soma paired with a non‐synaptic partner cell. Moreover, voltage clamp recording techniques, in conjunction with a fast, optical differential perfusion system, were used to demonstrate that the total whole‐cell Ca2+ (or Ba2+) current density in single and paired cells was not significantly different. However, the amplitude of Ba2+ current was significantly higher in the presynaptic cell at its contact side with the postsynaptic neurons, compared with non‐contacted regions. In summary, this study demonstrates that voltage‐induced Ca2+ hotspots develop in the presynaptic cell, concomitant with the appearance of synaptic transmission between the soma–soma paired cells. The appearance of Ca2+ gradients in presynaptic neurons is target cell contact specific and is probably due to a spatial redistribution of existing channels during synaptogenesis.
Reduced glycogen availability is associated with an elevation in HSP72 in contracting human skeletal muscle
Authors: Febbraio Mark A. , Steensberg Adam , Walsh Rory , Koukoulas Irene , Hall Gerrit van , Saltin Bengt , Pedersen Bente Klarlund
Published: July 2002

To test the hypothesis that a decrease in intramuscular glycogen availability may stimulate heat shock protein expression, seven men depleted one leg of muscle glycogen the day before performing 4–5 h of exhaustive, two‐legged knee extensor exercise at 40 % of leg peak power output. Subjects then rested for a further 3 h. Muscle biopsies were obtained from the depleted and control leg before, immediately after and 3 h into recovery from exercise. These samples were analysed for muscle glycogen, and HSP72 gene and protein expression. In addition, catheters were placed in one femoral artery and both femoral veins and blood was sampled from these catheters prior to exercise and at 1 h intervals during exercise and into recovery for the measurement of arterial‐venous differences in serum HSP72. Plasma creatine kinase (CK) was also measured from arterial blood samples. Pre‐exercise muscle glycogen content was 40 % lower in the depleted compared with the control leg and this difference was maintained throughout the experiment (P < 0.05; main treatment effect). Neither HSP72 gene nor protein expression was different pre‐exercise. However, both HSP72 gene and protein increased (P < 0.05) post‐exercise in the depleted leg, but not in the control leg. Exercise did not increase plasma CK concentrations and we were unable to detect HSP72 in the serum of any samples. These results demonstrate that while acute, concentric exercise is capable of increasing HSP72 in human skeletal muscle, it does so only when glycogen is reduced to relatively low levels. Hence, our data suggest that HSP72 protein expression is related to glycogen availability. In addition, because CK did not increase and we found no evidence of HSP72 in the venous effluent, our data suggest that skeletal muscle is impermeable to HSP72.
Thin filament near‐neighbour regulatory unit interactions affect rabbit skeletal muscle steady‐state force‐Ca2+ relations
Authors: Regnier Michael , Rivera Anthony J. , Wang Chien‐Kao , Bates Mandy A. , Chase P. Bryant , Gordon Albert M.
Published: July 2002

The role of cooperative interactions between individual structural regulatory units (SUs) of thin filaments (7 actin monomers : 1 tropomyosin : 1 troponin complex) on steady‐state Ca2+‐activated force was studied. Native troponin C (TnC) was extracted from single, de‐membranated rabbit psoas fibres and replaced by mixtures of purified rabbit skeletal TnC (sTnC) and recombinant rabbit sTnC (D27A, D63A), which contains mutations that disrupt Ca2+ coordination at N‐terminal sites I and II (xxsTnC). Control experiments in fibres indicated that, in the absence of Ca2+, both sTnC and xxsTnC bind with similar apparent affinity to sTnC‐extracted thin filaments. Endogenous sTnC‐extracted fibres reconstituted with 100 % xxsTnC did not develop Ca2+‐activated force. In fibres reconstituted with mixtures of sTnC and xxsTnC, maximal Ca2+‐activated force increased in a greater than linear manner with the fraction of sTnC. This suggests that Ca2+ binding to functional Tn can spread activation beyond the seven actins of an SU into neighbouring units, and the data suggest that this functional unit (FU) size is up to 10–12 actins. As the number of FUs was decreased, Ca2+ sensitivity of force (pCa50) decreased proportionally. The slope of the force‐pCa relation (the Hill coefficient, nH) also decreased when the reconstitution mixture contained < 50 % sTnC. With 15 % sTnC in the reconstitution mixture, nH was reduced to 1.7 ± 0.2, compared with 3.8 ± 0.1 in fibres reconstituted with 100 % sTnC, indicating that most of the cooperative thin filament activation was eliminated. The results suggest that cooperative activation of skeletal muscle fibres occurs primarily through spread of activation to near‐neighbour FUs along the thin filament (via head‐to‐tail tropomyosin interactions).
In vivo muscle fibre behaviour during counter‐movement exercise in humans reveals a significant role for tendon elasticity
Authors: Kawakami Y. , Muraoka T. , Ito S. , Kanehisa H. , Fukunaga T.
Published: July 2002

Six men performed a single ankle plantar flexion exercise in the supine position with the maximal effort with counter movement (CM, plantar flexion preceded by dorsiflexion) and without counter movement (NoCM, plantar flexion only) produced by a sliding table that controlled applied load to the ankle (40 % of the maximal voluntary force). The reaction force at the foot and ankle joint angle were measured using a force plate and a goniometer, respectively. From real‐time ultrasonography of the gastrocnemius medialis muscle during the movement, the fascicle length was determined. The estimated peak force, average power, and work at the Achilles’ tendon during the plantar flexion phase in CM were significantly greater than those in NoCM. In CM, in the dorsiflexion phase, fascicle length initially increased with little electromyographic activity, then remained constant while the whole muscle‐tendon unit lengthened, before decreasing in the final plantar flexion phase. In NoCM, fascicle length decreased throughout the movement and the fascicle length at the onset of movement was longer than that of the corresponding phase in CM. It was concluded that during CM muscle fibres optimally work almost isometrically, by leaving the task of storing and releasing elastic energy for enhancing exercise performance to the tendon.
Inhibition of haem oxygenase activity increases leukocyte accumulation in the liver following limb ischaemia‐reperfusion in mice
Authors: Wunder Christian , Brock Robert W. , McCarter Sarah D. , Bihari Aurelia , Harris Kenneth , Eichelbrönner Otto , Potter Richard F.
Published: July 2002

The role of haem oxygenase (HO) in the hepatic accumulation of leukocytes in mice during the initiation of remote organ injury following normotensive limb ischaemia‐reperfusion (I‐R) was investigated. Remote organ injury was initiated by 1 h bilateral hindlimb ischaemia followed by either 1 or 1.5 h reperfusion (I‐R) in male C57BL/6 mice. Mice were randomly assigned to either sham (no I‐R, n= 4), I‐R (n= 4 for both time points), I‐R plus chromium mesoporphyrin (CrMP, n= 4) to inhibit HO or I‐R plus haemin (n= 4) to increase HO. Leukocyte accumulation and leukocyte‐endothelial interaction were directly measured using fluorescence intravital microscopy. Leukocytes were labelled via an injection of rhodamine 6G. In sinusoids the total number and the number of stationary leukocytes were assessed. In postsinusoidal venules the number of adherent and rolling leukocytes and the velocities of both red blood cells and leukocytes were measured. The total number of leukocytes increased in sinusoids of I‐R mice reaching a plateau within 1 h compared with sham animals, while the number of stationary leukocytes progressively increased over the entire study period. Stationary leukocytes in sinusoids increased after 1 and 1.5 h of I‐R following CrMP, while they were significantly reduced following haemin treatment compared to animals treated with I‐R only. In postsinusoidal venules a progressive increase in adherent leukocytes also occurred. As observed in sinusoids, CrMP significantly increased, while haemin significantly reduced leukocyte adhesion. The number of rolling leukocytes increased after CrMP in both I‐R groups (1 and 1.5 h). The velocities of rolling leukocytes declined following 1.5 h of I‐R compared with sham. Haemin treatment of 1.5 h I‐R animals restored the velocities back to sham levels. The calculated wall shear rates in postsinusoidal venules were significantly lower in all I‐R groups in comparison to sham animals. Combination of 1.5 h I‐R with CrMP resulted in the lowest shear rates of all I‐R groups. The number of stationary leukocytes within sinusoids and adherent leukocytes in postsinusoidal venules were correlated to the corresponding alanine aminotransferase (ALT) levels. In conclusion, endogenous HO reduces leukocyte‐endothelial interactions within the liver. Thus, endogenous HO activity provides an important mechanism controlling the hepatic inflammatory response during the initiation of remote organ injury following normotensive limb ischaemia‐reperfusion.
Evaluating Process Capability During the Design of Manufacturing Systems
Authors: Frey Daniel D. , Otto Kevin N. , Wysocki Joseph A.
Published: July 2002

This paper introduces the concept of a process capability matrix—an ordered set of dimensionless parameters that capture information on a manufacturing system’s response to disturbances. The matrix is similar to the process capability indices Cp and Cpk, but is extended to multiple acceptance criteria and multiple causes of variation. Equations are presented that use the matrix to estimate yield in manufacture of products with multiple acceptance criteria. The surface mount of large body electronic packages serves as an example of the effectiveness of the process capability matrix as a tool for design decision making. [S1087-1357(00)01601-4]
Improved Operating Efficiency Through the Use of Stabilized Thermocouples
Authors: Jablin Jeff , Storar Michael R. , Gray Phillip L.
Published: July 2002

The development of a “stabilized” temperature sensor has led to significant increases in turbine operating efficiency by maximizing output when compared with present sensor technology. These stabilized type K and E thermocouples are superior to existing standard non-stabilized thermocouples because they are not prone to the typical aging effects in the 400 to 600°C (752 to 1112°F) temperature range that can result in measurements errors. A complete set of 18 stabilized type K thermocouples were installed on the exhaust of several gas turbines used for power generation. These thermocouples were subjected to normal operating conditions for a period of one year. During that year, the increase in turbine output has ranged from 0.5 percent to almost 2.0 percent. This increase in output also translates into significant cost savings. In addition, the stabilized thermocouples have given the turbine maintenance technicians more confidence in the accuracy of their temperature measurements and resulted in improved troubleshooting and decision making. [S0742-4795(00)02502-3]
An Analytical Approach to the Prediction of Handling Qualities of Vehicles With Advanced Steering Control System Using Multi-Input Driver Model
Authors: Horiuchi Shinichiro , Yuhara Naohiro
Published: July 2002

This paper describes an analytical approach to predict the subjective rating on handling qualities of actively controlled vehicles. The approach was applied to the evaluation on handling qualities of 4 wheel steering vehicles. The validity of the approach is confirmed by comparison of the predicted results with test data. The essential feature of the approach is to use an objective function that takes into account three principal factors, i.e., the task performance, the driver’s mental workload, and his or her physical workload, to predict analytically the subjective ratings. The findings indicate that the predicted rating directly corresponds to the driver’s subjective ratings obtained through the proving ground test with a good correlation. [S0022-0434(00)00303-8]
Effect of Cutting-Edge Geometry and Workpiece Hardness on Surface Residual Stresses in Finish Hard Turning of AISI 52100 Steel
Authors: Thiele Jeffrey D. , Melkote Shreyes N. , Peascoe Roberta A. , Watkins Thomas R.
Published: July 2002

An experimental investigation was conducted to determine the effects of tool cutting-edge geometry (edge preparation) and workpiece hardness on surface residual stresses for finish hard turning of through-hardened AISI 52100 steel. Polycrystalline cubic boron nitride (PCBN) inserts with representative types of edge geometry including “up-sharp” edges, edge hones, and chamfers were used as the cutting tools in this study. This study shows that tool edge geometry is highly influential with respect to surface residual stresses, which were measured using x-ray diffraction. In general, compressive surface residual stresses in the axial and circumferential directions were generated by large edge hone tools in longitudinal turning operations. Residual stresses in the axial and circumferential directions generated by large edge hone tools are typically more compressive than stresses produced by small edge hone tools. Microstructural analysis shows that thermally-induced phase transformation effects are present at all feeds and workpiece hardness values with the large edge hone tools, and only at high feeds and hardness values with the small edge hone tools. In general, continuous white layers on the workpiece surface correlate with compressive residual stresses, while over-tempered regions correlate with tensile or compressive residual stresses depending on the workpiece hardness. [S1087-1357(00)00304-X]
Discussion: “Heat Transfer Measurement and Analysis for Sintered Porous Channels” (Hwang, G. J., and Chao, C. H., 1994, ASME J. Heat Transfer, 116, pp. 456–464)
Authors: Kim and S. J. , Kim D.
Published: July 2002

[S0022-1481(00)04103-7]
Simulation of a Single Cylinder Diesel Engine Under Cold Start Conditions Using Simulink
Authors: Liu H.-Q. , Chalhoub N. G. , Henein N.
Published: July 2002

A nonlinear dynamic model is developed in this study to simulate the overall performance of a naturally aspirated, single cylinder, four-stroke, direct injection diesel engine under cold start and fully warmed-up conditions. The model considers the filling and emptying processes of the cylinder, blowby, intake, and exhaust manifolds. A single zone combustion model is implemented and the heat transfer in the cylinder, intake, and exhaust manifolds are accounted for. Moreover, the derivations include the dynamics of the crank-slider mechanism and employ an empirical model to estimate the instantaneous frictional losses in different engine components. The formulation is coded in modular form whereby each module, which represents a single process in the engine, is introduced as a single block in an overall Simulink engine model. The numerical accuracy of the Simulink model is verified by comparing its results to those generated by integrating the engine formulation using IMSL stiff integration routines. The engine model is validated by the close match between the predicted and measured cylinder gas pressure and engine instantaneous speed under motoring, steady-state, and transient cold start operating conditions.
Study of Frictional Impact Using a Nonsmooth Equations Solver
Authors: Johansson L. , Klarbring A.
Published: July 2002

In this paper a mathematical formulation and a numerical algorithm for the analysis of impact of rigid bodies against rigid obstacles are developed. The paper concentrates on three-dimensional motion using a direct approach where the impenetrability condition and Coulomb’s law of friction are formulated as equations, which are not differentiable in the usual sense, and solved together with the equations of motion and necessary kinematical relations using Newton’s method. An experiment has also been performed and compared with predictions of the algorithm, with favorable results. [S0021-8936(00)01402-1]
Numerical Contact Analysis of Transversely Isotropic Coatings: A Cylinder Within a Circumferential Groove
Authors: Morrow, Clint , Lovell, Michael , Deng Zhi
Published: July 2002

The contact characteristics of transversely isotropic coatings are investigated for a cylinder within a circumferential groove using a two-dimensional finite element model. With the model, contact behavior is evaluated at more than 400 operating conditions by varying coating material, coating thickness, normal load, and cylinder/groove radii. Based on the finite element results, numerical expressions are derived for the maximum surface pressure, contact length, and approach distance as a function of a transversely isotropic coating parameter, ζ. The importance of these expressions, as related to design and the selection of materials for reducing wear in contacting surfaces, is subsequently discussed.
Groove Effects on Thrust Washer Lubrication
Authors: Yu To Him , Sadeghi Farshid
Published: July 2002

A numerical model was developed to investigate the effects of groove geometry on the hydrodynamic lubrication mechanism of thrust washers. In order to achieve the objectives the isothermal, time-dependent, polar-coordinate Reynolds equation, including the cavitation and centrifugal effects, was solved numerically to determine the pressure distribution for various groove geometries and operating conditions. The polar coordinate Reynolds equation was discretized using the control volume finite difference approach. The results indicate that thrust washers are capable of supporting a significant amount of load with proper groove geometries. Design curves were generated for load support and other operating parameters as a function of each of the groove geometrical parameters (i.e., depth, width, number of grooves, and shape) as well as the operating conditions so that thrust washers performance can be predicted and optimized.
Improvement of Operating Characteristics of High-Speed Hydrodynamic Journal Bearings by Optimum Design: Part I— Formulation of Methodology and Its Application to Elliptical Bearing Design
Authors: Hashimoto H. , Matsumoto K.
Published: July 2002

This paper describes the optimum design methodology for improving operating characteristics of hydrodynamic journal bearings and its application to elliptical journal bearing design used in high-speed rotating machinery. The hybrid optimization technique combining the direct search method and the successive quadratic programming is applied effectively to find the optimum solutions. In the optimum design of elliptical journal bearings, the design variables such as vertical and horizontal radial clearances, bearing length-to-diameter ratio and bearing orientation angle are determined to minimize the objective function defined by the weighted sum of maximum averaged oil film temperature rise, leakage flow rate, and the inversion of whirl onset speed of the journal under many constraints. The results obtained are shown in graphical form for a wide range of journal rotational speed. Comparing the optimized operating characteristics with the characteristics calculated from the random selected design variables, the effectiveness of optimum design is clarified.
Nonlinear Vibration of Rotating Thin Disks
Authors: Luo Albert C. J. , Mote, C. D.
Published: July 2002

The response and natural frequencies for the linear and nonlinear vibrations of rotating disks are given analytically through the new plate theory proposed by Luo in 1999. The results for the nonlinear vibration can reduce to the ones for the linear vibration when the nonlinear effects vanish and for the von Karman model when the nonlinear effects are modified. They are applicable to disks experiencing large-amplitude displacement or initial flatness and waviness. The natural frequencies for symmetric and asymmetric responses of a 3.5-inch diameter computer memory disk as an example are predicted through the linear theory, the von Karman theory and the new plate theory. The hardening of rotating disks occurs when nodal-diameter numbers are small and the softening of rotating disks occurs when nodal-diameter numbers become larger. The critical speeds of the softening disks decrease with increasing deflection amplitudes. [S0739-3717(00)02004-3]
Unstructured Adaptive Triangular Mesh Generation Techniques and Finite Volume Schemes for the Air Bearing Problem in Hard Disk Drives
Authors: Wu Lin , Bogy D. B.
Published: July 2002

Unstructured adaptive triangular mesh generation techniques and vertex based finite volume schemes that suit slider air bearing simulation of hard disk drives are constructed and implemented. Different refinement and adaptation techniques are used to generate several levels of good quality mesh over sliders with complex rail shapes. At each level, either one geometrical or one physical property of the problem is captured. A group of implicit vertex based finite volume schemes is first constructed. The resulting simultaneous linear algebraic equations are solved iteratively by the Gauss-Seidel method. Unconditional stability of the scheme is achieved. In addition, we present a non-nested full approximation storage (FAS) multi-grid algorithm that can significantly speed up the convergence rate of the implicit finite volume schemes. The steady state flying attitude is obtained by a quasi-Newton iteration method. [S0742-4787(00)01804-X]
Angular Velocity Stabilization of a Rigid Body Via VSS Control
Authors: Floquet T. , Perruquetti W. , Barbot J.-P.
Published: July 2002

This paper is devoted to the stabilization of the angular velocity of a rigid body via variable structure based controllers. The system is supposed to have only two control torques and to be subject to external disturbances. A finite time convergence is obtained by switching between a first-order and a second-order sliding mode controllers. [S0022-0434(00)00304-X]
Functional Tissue Engineering: The Role of Biomechanics
Authors: Butler David L. , Goldstein Steven A. , Guilak Farshid
Published: July 2002

“Tissue engineering” uses implanted cells, scaffolds, DNA, protein, and/or protein fragments to replace or repair injured or diseased tissues and organs. Despite its early success, tissue engineers have faced challenges in repairing or replacing tissues that serve a predominantly biomechanical function. An evolving discipline called “functional tissue engineering” (FTE) seeks to address these challenges. In this paper, the authors present principles of functional tissue engineering that should be addressed when engineering repairs and replacements for load-bearing structures. First, in vivo stress/strain histories need to be measured for a variety of activities. These in vivo data provide mechanical thresholds that tissue repairs/replacements will likely encounter after surgery. Second, the mechanical properties of the native tissues must be established for subfailure and failure conditions. These “baseline data” provide parameters within the expected thresholds for different in vivo activities and beyond these levels if safety factors are to be incorporated. Third, a subset of these mechanical properties must be selected and prioritized. This subset is important, given that the mechanical properties of the designs are not expected to completely duplicate the properties of the native tissues. Fourth, standards must be set when evaluating the repairs/replacements after surgery so as to determine, “how good is good enough?” Some aspects of the repair outcome may be inferior, but other mechanical characteristics of the repairs and replacements might be suitable. New and improved methods must also be developed for assessing the function of engineered tissues. Fifth, the effects of physical factors on cellular activity must be determined in engineered tissues. Knowing these signals may shorten the iterations required to replace a tissue successfully and direct cellular activity and phenotype toward a desired end goal. Finally, to effect a better repair outcome, cell-matrix implants may benefit from being mechanically stimulated using in vitro “bioreactors” prior to implantation. Increasing evidence suggests that mechanical stress, as well as other physical factors, may significantly increase the biosynthetic activity of cells in bioartificial matrices. Incorporating each of these principles of functional tissue engineering should result in safer and more efficacious repairs and replacements for the surgeon and patient. [S0148-0731(00)00206-5]
Position Analysis in Analytical Form of the 3-PSP Mechanism
Authors: Di Gregorio Raffaele , Parenti-Castelli Vincenzo
Published: July 2002

In this paper the direct and the inverse position analysis of a 3-dof fully-parallel mechanism, known as 3-PSP mechanism, is addressed and solved in analytical form. The 3-PSP mechanism consists of two rigid bodies, one movable (platform) and the other fixed (base), connected to each other by means of three equal serial kinematic chains (legs) of type PSP, P and S standing for prismatic and spherical pair respectively. Both the direct and the inverse position analysis of this mechanism lead to nonlinear equations that are difficult to solve. In particular, the inverse position analysis comprises different subproblems which need specific solution techniques. Finally a numerical example is reported.
Thermal and Dynamic Characterization of Wet Clutch Engagement With Provision for Drive Torque
Authors: Mansouri M. , Holgerson M. , Khonsari M. M. , Aung W.
Published: July 2002

Wet clutches that handle the gearshifts in automatic transmission undergo severe thermal stresses due to the occurrence of large temperature gradients during engagement. To accurately design wet clutches, better models to simulate the engagement process are needed. This work presents a finite element model for simulating wet clutch engagements. The total friction coefficient was used to describe the different lubrication regimes that a wet clutch engagement undergoes. The model also includes provision for drive torque that realistically simulates the engine torque of a car. The results of the simulations are successfully verified by comparison with laboratory experiments on a testrig specially designed to accommodate the drive torque, covering a wide range of typical engagements. Excellent agreement between experiment and simulations is reported in terms of both the dynamics of the engagement and the thermal characteristics. The results are indicative of the utility of the model as a useful engineering tool.
An Average Flow Model of Rough Surface Lubrication With Inter-Asperity Cavitation
Authors: Harp Susan R. , Salant Richard F.
Published: July 2002

An average Reynolds equation capable of predicting the effects of roughness induced inter-asperity cavitation is introduced. The average Reynolds equation is based on the JFO cavitation model and the Patir and Cheng flow factor method. The flow factors are calculated in numerical experiments as functions of the local surface separation, surface statistics, and cavitation number. The model is extended into a universal average Reynolds equation capable of predicting the combined effects of inter-asperity cavitation and macroscopic cavitation. Both the Patir and Cheng method and the present model are verified in numerical experiments.
Experimental Investigations of Radially Rotating Miniature High-Temperature Heat Pipes
Authors: Ling Jian , Cao Yiding , Lopez Alex P.
Published: July 2002

A radially rotating miniature high-temperature heat pipe employs centrifugal force to return the condensate in the condenser section to the evaporator section. The heat pipe has a simple structure, very high effective thermal conductance and heat transfer capacity, and can work in hostile high-temperature environments. In this research, a high-speed rotating test apparatus and data acquisition system for radially rotating miniature high-temperature heat pipes are established. Extensive experimental tests on two heat pipes with different dimensions are performed, and various effects of influential parameters on the performance characteristics of the heat pipes are investigated. The ranges of the important parameters covered in the current experiments are: 470⩽ω2Za¯/g⩽1881; 47 W⩽Q⩽325W; di=1.5 and 2 mm; and 1.05×10−3m3/s⩽W⩽13.4×10−3m3/s. The experimental data prove that the radially rotating miniature high-temperature heat pipe has a high effective thermal conductance, which is 60–100 times higher than the thermal conductivity of copper, and a large heat transfer capacity that is more than 300 W. Therefore, the heat pipe appears to be feasible for cooling high-temperature gas turbine components.
Pulsatile Flow in an End-to-Side Vascular Graft Model: Comparison of Computations With Experimental Data
Authors: Lei M. , Giddens D. P. , Jones S. A. , Loth F. , Bassiouny H.
Published: July 2002

Various hemodynamic factors have been implicated in vascular graft intimal hyperplasia, the major mechanism contributing to chronic failure of small-diameter grafts. However, a thorough knowledge of the graft flow field is needed in order to determine the role of hemodynamics and how these factors affect the underlying biological processes. Computational fluid dynamics offers much more versatility and resolution than in vitro or in vivo methods, yet computations must be validated by careful comparison with experimental data. Whereas numerous numerical and in vitro simulations of arterial geometries have been reported, direct point-by-point comparisons of the two techniques are rare in the literature. We have conducted finite element computational analyses for a model of an end-to-side vascular graft and compared the results with experimental data obtained using laser-Doppler velocimetry. Agreement for velocity profiles is found to be good, with some clear differences near the recirculation zones during the deceleration and reverse-flow segments of the flow waveform. Wall shear stresses are determined from velocity gradients, whether by computational or experimental methods, and hence the agreement for this quantity, while still good, is less consistent than for velocity itself. From the wall shear stress numerical results, we computed four variables that have been cited in the development of intimal hyperplasia—the time-averaged wall shear stress, an oscillating shear index, and spatial and temporal wall shear stress gradients—in order to illustrate the versatility of numerical methods. We conclude that the computational approach is a valid alternative to the experimental approach for quantitative hemodynamic studies. Where differences in velocity were found by the two methods, it was generally attributed to the inability of the numerical method to model the fluid dynamics when flow conditions are destabilizing. Differences in wall shear, in the absence of destabilizing phenomena, were more likely to be caused by difficulties in calculating wall shear from relatively low resolution in vitro data.
Film Cooling Downstream of a Row of Discrete Holes With Compound Angle
Authors: Goldstein R. J. , Jin P.
Published: July 2002

A special naphthalene sublimation technique is used to study the film cooling performance downstream of one row of holes of 35 deg inclination angle and 45 deg compound angle with 3d hole spacing and relatively small hole length to diameter ratio (6.3). Both film cooling effectiveness and mass/heat transfer coefficients are determined for blowing rates from 0.5 to 2.0 with density ratio of unity. The mass transfer coefficient is measured using pure air film injection, while the film cooling effectiveness is derived from comparison of mass transfer coefficients obtained following injection of naphthalene-vapor-saturated air with that of pure air injection. This technique enables one to obtain detailed local information on film cooling performance. General agreement is found in local film cooling effectiveness when compared with previous experiments. The laterally averaged effectiveness with compound angle injection is higher than that with inclined holes immediately downstream of injection at a blowing rate of 0.5 and is higher at all locations downstream of injection at larger blowing rates. A large variation of mass transfer coefficients in the lateral direction is observed in the present study. At low blowing rates of 0.5 and 1.0, the laterally averaged mass transfer coefficient is close to that of injection without compound angle. At the highest blowing rate used (2.0), the asymmetric vortex motion under the jets increases the mass transfer coefficient drastically ten diameters downstream of injection.
Cross-Sectional Mapping of Residual Stresses by Measuring the Surface Contour After a Cut
Authors: Prime M. B.
Published: July 2002

A powerful new method for residual stress measurement is presented. A part is cut in two, and the contour, or profile, of the resulting new surface is measured to determine the displacements caused by release of the residual stresses. Analytically, for example using a finite element model, the opposite of the measured contour is applied to the surface as a displacement boundary condition. By Bueckner’s superposition principle, this calculation gives the original residual stresses normal to the plane of the cut. This “contour method” is more powerful than other relaxation methods because it can determine an arbitrary cross-sectional area map of residual stress, yet more simple because the stresses can be determined directly from the data without a tedious inversion technique. The new method is verified with a numerical simulation, then experimentally validated on a steel beam with a known residual stress profile.
Free Abrasive Machining in Slicing Brittle Materials With Wiresaw
Authors: Yang Fuqian , Kao Imin
Published: July 2002

Wiresaw has emerged as a leading technology in wafer preparation for microelectronics fabrication, especially in slicing large silicon wafers (diameter⩾300 mm) for both microelectronic and photovoltaic applications. Wiresaw has also been employed to slice other brittle materials such as alumina, quartz, glass, and ceramics. The manufacturing process of wiresaw is a free abrasive machining (FAM) process. Specifically, the wiresaw cuts brittle materials through the “rolling-indenting” and “scratch-indenting” processes where the materials removal is resulting from mechanical interactions between the substrate of the workpiece and loss abrasives, which are trapped between workpiece and wire. Built upon results of previous investigation in modeling of wiresaw, a model of wiresaw slicing is developed based on indentation crack as well as the influence of wire carrying the abrasives. This model is used to predict the relationship between the rate of material removal and the mechanical properties of the workpiece together with the process parameters. The rolling, indenting, and scratching modes of materials removal are considered with a simple stochastic approach. The model provides us with the basis for improving the efficiency of the wiresaw manufacturing process based on the process parameters.
The Development of a Solar Chemical Reactor for the Direct Thermal Dissociation of Zinc Oxide
Authors: Mo¨ller S. , Palumbo R.
Published: July 2002

A solar chemical reactor was designed, constructed and tested for the direct thermal decomposition of zinc oxide at temperatures as high as 2250 K using concentrated sunlight. Along with the reactor, a 1-dimensional numerical model was developed to predict the reactor’s thermal performance under various solar flux levels and to identify the physio-chemical properties of ZnO that are critical for designing the reactor. An experimental study was also conducted to ascertain how best to employ a curtain of inert gas to keep the reactor’s window clean of Zn and ZnO. The reactor proved to be a reliable research tool for effecting the decomposition reaction and it possesses many features characteristic of a reactor scale-able to an industrial level: it is resilient to thermal shock; it has a low effective thermal inertia, and it can operate in a continuous mode when ZnO as a powder is fed to the reactor. Furthermore, experimental work led to insight on how best to keep the window clean in the course of an experiment. Also, comparisons between output from the numerical model and experimental results show that the solar flux and the ZnO’s thermal conductivity and emissivity are the most critical variables affecting the exergy efficiency of the reactor and the mass flux of product gases. The comparison further reveals the need to investigate whether or not the magnitude of the published pre-exponential term in the decomposition rate equation used in the numerical model should be reduced for improving agreement between the model and the experimental results.
Reduction of Secondary Flow Losses in Turbine Cascades by Leading Edge Modifications at the Endwall
Authors: Sauer H. , Mu¨ller R. , Vogeler K.
Published: July 2002

Experimental results are presented which show the influence on the secondary flow and its losses by a profile modification of the leading edge very close to the endwall. The investigation was carried out with a well-known turbine profile that originally was developed for highly loaded low pressure turbines. The tests were done in a low speed cascade wind tunnel. The geometrical modification was achieved by a local thickness increase; a leading edge endwall bulb. It was expected that this would intensify the suction side branch of the horse-shoe (hs-) vortex with a desirable weakening effect on the passage vortex. The investigated configuration shows a reduction of secondary losses by 2.1 percent points that represents approximately 50 percent of these losses compared to the reference profile. Detailed measurements of the total pressure field behind the cascade are presented for both the reference and the modified profile. The influence of the modified hs-vortex on the overall passage vortex can be clearly seen. The results of a numerical analysis are compared with the experimental findings. A numerical analysis shows that the important details of the experimental findings can be reproduced. Quantitative values are locally different. The theoretical approach taken cannot yet be used for an exact prediction of the loss reduction. However, the analysis of the interaction and the resulting tendencies are considered to be valid. Hence, theoretical investigations as a guideline for the design of a leading edge bulb at the endwall are a valuable tool.
Gas Turbine Compressor Washing State of the Art: Field Experiences1
Authors: Stalder J.-P.
Published: July 2002

Technology development in gas turbine compressor washing over the last 10 years and today’s state of the art technology is presented in this paper. Based on various long term field tests and observations, correlation between rate of power degradation and atmospheric conditions can be established. Questions about compressor on line washing with water alone against the use of detergents, as well as washing frequencies are also addressed in this paper. Performance degradation behavior between gas turbines of different sizes and models can be explained with an index of sensitivity to fouling. The implementation of an optimized regime of on line and off line washing in the preventive turbine maintenance program is important. It will improve the plant profitability by reducing the costs of energy production and contribute to a cleaner environment.
A Study on the Relationships Between Static/Dynamic Cutting Force Components and Tool Wear
Authors: Youn Jae-Woong , Yang Min-Yang
Published: July 2002

The development of flexible automation in the manufacturing industry is concerned with production activities performed by unmanned machining systems. A major topic relevant to metal-cutting operations is monitoring tool wear, which affects process efficiency and product quality, and implementing automatic tool replacements. In this paper, the measurement of the cutting force components has been found to provide a method for an in-process detection of tool wear. Cutting force components are divided into static and dynamic components in this paper. The static components of cutting force have been used to detect flank wear and the dynamic components of cutting force have been analyzed to detect crater wear. To eliminate the influence of variations in cutting conditions, tools, and workpiece materials, the relationships between normalized cutting forces and cutting conditions are established. According to the proposed method, the static and dynamic force components could provide the effective means to detect flank and crater wear for varying cutting conditions in turning operation.
On the Behavior of Folded Tape-Springs
Authors: Seffen K. A.
Published: July 2002

Tape-springs are thin-walled beams with a curved cross section that can be elastically deformed to yield a flexible region of high curvature known as a fold. This feature is exploited in the folding and self-deployment of a number of recently proposed deployable structures. This study characterizes the quasi-static response of a folded tape-spring under a prescribed rotation and separation between its support points. It is shown that the corresponding end loads and fold shape are accurately predicted by a variational technique, and are confirmed by a finite element analysis. This information may then be used in further design of tape-spring hinge systems.
The Thermoeconomic and Environomic Modeling and Optimization of the Synthesis, Design, and Operation of Combined Cycles With Advanced Options
Authors: Pelster S. , Favrat D. , von Spakovsky M. R.
Published: July 2002

Combined cycle power plants are currently one of the most important options for the construction of new generating capacity as well as for the replacement and repowering of existing units. Due to the complexity and the large number of options and parameters available to such plants, finding optimized solutions for system synthesis, design, and operation is very difficult if not impossible with these traditional methods such as case and parametric tradeoff studies. This is especially true when advanced options as well as thermodynamic, economic, and environmental criteria are considered. A thermoeconomic environomic methodology to deal with these difficulties is presented here. Results for the application of this methodology to a 50 MW cogeneration combined cycle power plant are presented and discussed.
Rotating Instabilities in an Axial Compressor Originating From the Fluctuating Blade Tip Vortex
Authors: Mailach R. , Lehmann I. , Vogeler K.
Published: July 2002

Rotating instabilities (RIs) have been observed in axial flow fans and centrifugal compressors as well as in low-speed and high-speed axial compressors. They are responsible for the excitation of high amplitude rotor blade vibrations and noise generation. This flow phenomenon moves relative to the rotor blades and causes periodic vortex separations at the blade tips and an axial reversed flow through the tip clearance of the rotor blades. The paper describes experimental investigations of RIs in the Dresden Low-Speed Research Compressor (LSRC). The objective is to show that the fluctuation of the blade tip vortex is responsible for the origination of this flow phenomenon. RIs have been found at operating points near the stability limit of the compressor with relatively large tip clearance of the rotor blades. The application of time-resolving sensors in both fixed and rotating frame of reference enables a detailed description of the circumferential structure and the spatial development of this unsteady flow phenomenon, which is limited to the blade tip region. Laser-Doppler-anemometry (LDA) within the rotor blade passages and within the tip clearance as well as unsteady pressure measurements on the rotor blades show the structure of the blade tip vortex. It will be shown that the periodical interaction of the blade tip vortex of one blade with the flow at the adjacent blade is responsible for the generation of a rotating structure with high mode orders, termed a rotating instability.
Research on a Methane-Fueled Low NOx Combustor for a Mach 3 Supersonic Transporter Turbojet Engine
Authors: Kinoshita Y. , Oda T. , Kitajima J.
Published: July 2002

Methane-fueled low NOx combustor research had been conducted under the Japanese supersonic/hypersonic propulsion research program. A unique form of premixture jet swirl combustor (PJSC) was proposed for the ultra low NOx combustor of a Mach 3 turbojet engine. Fuel-air mixing tests and fundamental combustion tests were conducted to obtain the design data and combustion characteristics in the first phase of the research. A single can-type combustor was fabricated and high-temperature and high-pressure combustion tests were carried out for the evaluation on NOx emission reduction capability of the PJSC concept in the second phase. In the final phase of research, a multisector combustor was fabricated and the performance demonstration test was conducted for the final evaluation of the pollutant exhaust emission goals and the combustor performance goals set in the HYPR project. The sequential three-phased program was completed successfully, and the project goals of NOx emission, combustion efficiency, pressure loss and exit gas temperature pattern factor at the Mach 3 cruise condition, together with the ICAO regulatory levels for supersonic aircraft at LTO conditions, were all achieved in the performance demonstration test.
The Effect of Tooth Wear on the Vibration Spectrum of a Spur Gear Pair
Authors: Kuang J. H. , Lin A. D.
Published: July 2002

In this paper, the effect of tooth wear on the vibration spectrum variation of a rotating spur gear pair is studied. In order to approximate the dynamic characteristics of an engaging spur gear pair, the load sharing alternation, position dependent mesh stiffness, damping factor and friction coefficient are considered in the mathematical model. The wear prediction model proposed by Flodin et al. is used to simulate the tooth profile wear process. The variation of the vibration spectra introduced from the interaction between the sliding wear and the dynamic load is simulated and analyzed. Numerical results indicate that the dynamic load histogram of an engaging spur gear pair may change greatly with the tooth wear. This finding implies that the variation of the gear vibration spectrum might be used to monitor the tooth wear of an engaging spur gear pair.