bluuebunny/crossref_metadata_2025 huggingface dataset:
Ulex europaeus agglutinin II (UEA‐II) is a novel, potent inhibitor of complement activation
Authors: Lekowski Robert , Collard Charles D. , Reenstra Wende R. , Stahl Gregory L.
Published: July 2002

Complement is an important mediator of vascular injury following oxidative stress. We recently demonstrated that complement activation following endothelial oxidative stress is mediated by mannose‐binding lectin (MBL) and activation of the lectin complement pathway. Here, we investigated whether nine plant lectins which have a binding profile similar to that of MBL competitively inhibit MBL deposition and subsequent complement activation following human umbilical vein endothelial cell (HUVEC) oxidative stress. HUVEC oxidative stress (1% O2, 24 hr) significantly increased Ulex europaeus agglutinin II (UEA‐II) binding by 72 ± 9% compared to normoxic cells. UEA‐II inhibited MBL binding to HUVEC in a concentration‐dependent manner following oxidative stress. Further, MBL inhibited UEA‐II binding to HUVEC in a concentration‐dependent manner following oxidative stress, suggesting a common ligand. UEA‐II (≤ 100 μmol/L) did not attenuate the hemolytic activity, nor did it inhibit C3a des Arg formation from alternative or classical complement pathway‐specific hemolytic assays. C3 deposition (measured by ELISA) following HUVEC oxidative stress was inhibited by UEA‐II in a concentration‐dependent manner (IC50 = 10 pmol/L). UEA‐II inhibited C3 and MBL co‐localization (confocal microscopy) in a concentration‐dependent manner on HUVEC following oxidative stress (IC50 ≈ 1 pmol/L). Finally, UEA‐II significantly inhibited complement‐dependent neutrophil chemotaxis, but failed to inhibit fMLP‐mediated chemotaxis, following endothelial oxidative stress. These data demonstrate that UEA‐II is a novel, potent inhibitor of human MBL deposition and complement activation following human endothelial oxidative stress.
Folding and stability of the b subunit of the F1F0 ATP synthase
Authors: Revington Matthew , Dunn Stanley D. , Shaw Gary S.
Published: July 2002

The F1F0 ATP synthase is a reversible molecular motor that employs a rotary catalytic cycle to couple a chemiosmotic membrane potential to the formation/hydrolysis of ATP. The multisubunit enzyme contains two copies of the b subunit that form a homodimer as part of a narrow, peripheral stalk structure that connects the membrane (F0) and soluble (F1) sectors. The three‐dimensional structure of the b subunit is unknown making the nature of any interactions or conformational changes within the F1F0 complex difficult to interpret. We have used circular dichroism and analytical ultracentrifugation analyses of a series of N‐ and C‐terminal truncated b proteins to investigate its stability and structure. Thermal denaturation of the b constructs exhibited distinct two‐state, cooperative unfolding with Tm values between 30 and 40°C. CD spectra for the region comprising residues 53–122 (b53–122) showed θ222/θ208 = 0.99, which reduced to 0.92 in the presence of the hydrophobic solvent trifluoroethanol. Thermodynamic parameters for b53–122 (ΔG, ΔH and ΔCp) were similar to those reported for several nonideal, coiled‐coil proteins. Together these results are most consistent with a noncanonical and unstable parallel coiled‐coil at the interface of the b dimer.
Strain‐specified relative conformational stability of the scrapie prion protein
Authors: Peretz David , Scott Michael R. , Groth Darlene , Williamson R. Anthony , Burton Dennis R. , Cohen Fred E. , Prusiner Stanley B.
Published: July 2002

Studies of prion biology and diseases have elucidated several new concepts, but none was more heretical than the proposal that the biological properties that distinguish different prion strains are enciphered in the disease‐causing prion protein (PrPSc). To explore this postulate, we examined the properties of PrPSc from eight prion isolates that propagate in Syrian hamster (SHa). Using resistance to protease digestion as a marker for the undenatured protein, we examined the conformational stabilities of these PrPSc molecules. All eight isolates showed sigmoidal patterns of transition from native to denatured PrPSc as a function of increasing guanidine hydrochloride (GdnHCl) concentration. Half‐maximal denaturation occurred at a mean value of 1.48 M GdnHCl for the Sc237, HY, SHa(Me7), and MT‐C5 isolates, all of which have ∼75‐d incubation periods; a concentration of 1.08 M was found for the DY strain with a ∼170‐d incubation period and ∼1.25 M for the SHa(RML) and 139H isolates with ∼180‐d incubation periods. A mean value of 1.39 M GdnHCl for the Me7‐H strain with a ∼320‐d incubation period was found. Based on these results, the eight prion strains segregated into four distinct groups. Our results support the unorthodox proposal that distinct PrPSc conformers encipher the biological properties of prion strains.
External anions and cations distinguish between AMPA and kainate receptor gating mechanisms
Authors: Bowie Derek
Published: July 2002

Experiments were designed to examine if ion‐flow through α‐amino‐3‐hydroxy‐5‐methyl‐isoxazolepropionic acid (AMPA) or kainate receptors interferes with protein structures associated with the gating machinery. Gating was studied using ultra‐fast drug perfusion of outside‐out patches containing rat GluR‐A or GluR6 subunits excised from transfected human embryonic kidney cells. Deactivation rates of GluR6 kainate receptors observed following brief l‐glutamate (10 mm Glu, 1 ms) applications differed by two to threefold in high (405 mm symmetrical Na+, τdecay= 2.7 ms at −100 mV) and low ionic strength (55 mm, τdecay= 1.1 ms) solutions. In comparison, GluR‐A AMPA receptors were much less sensitive. Ion effects on GluR6 receptors did not reflect surface potential screening or ion‐agonist competition at the agonist‐binding site since deactivation rates were slower in high ionic strength solutions. Moreover, the apparent agonist affinity did not decrease with increasing ionic strength (e.g. 55 mm, EC50= 110 μmvs. 405 mm, EC50= 61 μm). GluR6 responses were strongly dependent on ions present on the external, but not the internal, side of the plasma membrane. Decay kinetics was regulated by the type of ion present suggesting that the chemical nature of the solution, not its ionic strength, governed channel behaviour. Both external anions and cations modulated the amplitude and decay kinetics of GluR6 responses in a concomitant manner. AMPA receptor responses recorded in identical ionic conditions did not exhibit this behaviour. These results identify a novel mechanism that distinguishes AMPA and kainate receptors. External ions regulate the gating machinery of kainate receptors through an allosteric mechanism that involves both anions and cations.
A New Model and Analysis of Orthogonal Machining With an Edge-Radiused Tool
Authors: Manjunathaiah Jairam , Endres William J.
Published: July 2002

A new machining process model that explicitly includes the effects of the edge hone is presented. A force balance is conducted on the lower boundary of the deformation zone leading to a machining force model. The machining force components are an explicit function of the edge radius and shear angle. An increase in edge radius leads to not only increased ploughing forces but also an increase in the chip formation forces due to an average rake angle effect. Previous attempts at assessing the ploughing components as the force intercept at zero uncut chip thickness, which attribute to the ploughing mechanism all the changes in forces that occur with changes in edge radius, are seen to be erroneous in view of this model. Calculation of shear stress on the lower boundary of the deformation zone using the new machining force model indicates that the apparent size effect when cutting with edge radiused tools is due to deformation below the tool (ploughing) and a larger chip formation component due to a lower shear angle. Increases in specific energy and shear stress are also due to shear strain and strain rate increases. A consistent material behavior model that does not vary with process input conditions like uncut chip thickness, rake angle and edge radius can be developed based on the new model. [S1087-1357(00)01302-2]
The Green Function and Its Application to Heat Transfer in a Low Permeability Porous Channel
Authors: Cui C. , Huang X. Y. , Liu C. Y.
Published: July 2002

This paper describes an analytical technique for heat transfer in a low permeability porous channel with initially a point heat source and then multiple discrete sources. The solution of the temperature field for the point source is derived as a Green function, from which the temperature field for other geometrical heat sources can be obtained by using the Green integral. An application of the Green function and Green integral to the porous channel with discrete heat sources is presented. The results are compared with the existing numerical results and good agreements are achieved. [S1043-7398(00)01503-6]
An Alternate Method to API RP 14E for Predicting Solids Erosion in Multiphase Flow
Authors: McLaury Brenton S. , Shirazi Siamack A.
Published: July 2002

One commonly used method for determining oil and gas production velocities is to limit production rates based on the American Petroleum Institute Recommended Practice 14E (API RP 14E). This guideline contains an equation to calculate an “erosional” or a threshold velocity, presumably a flow velocity that is safe to operate. The equation only considers one factor, the density of the medium, and does not consider many other factors that can contribute to erosion in multiphase flow pipelines. Thus, factors such as fluid properties, flow geometry, type of metal, sand production rate and size distribution, and flow composition are not accounted for. In the present paper, a method is presented that has been developed with the goal of improving the procedure by accounting for many of the physical variables including fluid properties, sand production rate and size, and flowstream composition that affect sand erosion. The results from the model are compared with several experimental results provided in the literature. Additionally, the method is applied to calculate threshold flowstream velocities for sand erosion and the results are compared with API RP 14E. The results indicate that the form of the equation that is provided by the API RP 14E is not suitable for predicting a production flowstream velocity when sand is present. [S0195-0738(00)00203-X]
Nonlinear Vibrations and Multiple Resonances of Fluid-Filled, Circular Shells, Part 1: Equations of Motion and Numerical Results
Authors: Amabili M. , Pellicano F. , Vakakis A. F.
Published: July 2002

The response-frequency relationship in the vicinity of a resonant frequency, the occurrence of travelling wave response and the presence of internal resonances are investigated for simply supported, circular cylindrical shells. Donnell’s nonlinear shallow-shell theory is used. The boundary conditions on radial displacement and the continuity of circumferential displacement are exactly satisfied. The problem is reduced to a system of four ordinary differential equations by means of the Galerkin method. The radial deflection of the shell is expanded by using a basis of four linear modes. The effect of internal fluid is also investigated. The equations of motion are studied by using a code based on the Collocation Method. The present model is validated by comparison of some results with others available. A water-filled shell presenting the phenomenon of 1:1:1:2 internal resonances is investigated for the first time; it shows intricate and interesting dynamics. [S0739-3717(00)01204-6]
Advanced Geothermal Wellbore Hydraulics Model
Authors: Tian Shifeng , Finger John T.
Published: July 2002

A model has been developed to simulate multiphase flow in the wellbore and heat transfer processes between the well and formations. The model is capable of handling dynamic well depth during drilling, varying flow regimes in multiphase flow, phase change between liquid and gas, and kicks or lost circulation depending on the pressure difference between the wellbore annulus and formation. The model requires simple data input and is able to handle complicated drilling cases such as casing installation, changing drilling fluids, and drillpipe/coiled tubing connections during drilling operations. [S0195-0738(00)00303-4]
A Time-Linearized Navier–Stokes Analysis of Stall Flutter
Authors: Clark William S. , Hall Kenneth C.
Published: July 2002

A computational method for predicting unsteady viscous flow through two-dimensional cascades accurately and efficiently is presented. The method is intended to predict the onset of the aeroelastic phenomenon of stall flutter. In stall flutter, viscous effects significantly impact the aeroelastic stability of a cascade. In the present effort, the unsteady flow is modeled using a time-linearized Navier–Stokes analysis. Thus, the unsteady flow field is decomposed into a nonlinear spatially varying mean flow plus a small-perturbation harmonically varying unsteady flow. The resulting equations that govern the perturbation flow are linear, variable coefficient partial differential equations. These equations are discretized on a deforming, multiblock, computational mesh and solved using a finite-volume Lax–Wendroff integration scheme. Numerical modeling issues relevant to the development of the unsteady aerodynamic analysis, including turbulence modeling, are discussed. Results from the present method are compared to experimental stall flutter data, and to a nonlinear time-domain Navier–Stokes analysis. The results presented demonstrate the ability of the present time-linearized analysis to model accurately the unsteady aerodynamics associated with turbomachinery stall flutter. [S0889-504X(00)00203-8]
On the Thermal Behavior of Giant Magnetoresistance Heads
Authors: Gupta B. K. , Young Kenneth , Chilamakuri Sameera K. , Menon Aric K.
Published: July 2002

The magnetic/mechanical spacing between the transducer and the disk significantly decreases due to thermal expansion of pole tips at stressed high temperature and high humidity tests. The protruded pole tips and alumina overcoat can cause head/disk contacts, resulting in thermal asperities and pole tip damage. The damage at the head–disk interface due to protruded pole tips and alumina overcoat may degrade the drive mechanical performance when flying height is below 10 nm. In this study the change in pole tin recession (PTR) with temperature and current in the writer coil, are measured using an optical profiler and an atomic force microscope for heads having a stack design with single and dual layers of writer coils. The pole tips protrude above the ABS surface by 3–4 nm when the temperature of the head is raised by 50°C. Heads with a single layer of writer coils exhibit significantly lower thermal PTR than those with dual layers of coils. The ABS profiles at elevated temperature generated using the finite element modeling of the differential thermal expansion of various layers in the head stack are in close agreement with the measured profiles. The thermal PTR and alumina overcoat protrusion can be reduced by optimizing the thermal expansion coefficient of the alumina basecoat and overcoat, the height of the head stack, and by replacing alumina by SiO2 and SiC.
A Device for Evaluating the Multiaxial Finite Strain Thermomechanical Behavior of Elastomers and Soft Tissues
Authors: Ortt E. M. , Doss D. J. , Legall E. , Wright N. T. , Humphrey J. D.
Published: July 2002

Described here is the design and development of a computer-controlled device capable of measuring the finite strain thermomechanical behavior of a general class of polymeric materials including elastomers and biological soft tissues. The utility of this device for thermoelastic and thermophysical investigations is demonstrated by the measurement of the in-plane stress-stretch response and in-plane and out-of-plane components of thermal diffusivity of neoprene rubber undergoing finite deformations.[S0021-8936(00)01603-2]
A Conductance Based Solids Concentration Sensor for Large Diameter Slurry Pipelines
Authors: Klausner James F. , Fu Feng , Mei Renwei
Published: July 2002

An instrument has been developed that measures the solids concentration in slurry pipelines ranging in diameter from 5–150 cm. The operating principle is based on conductance, and in contrast to the gamma densitometer, the instrument does not require a nuclear radiation source. The instrument operates on-line, is nonintrusive, and provides real-time output. The instrument measures local concentration around the pipe periphery, and the local values are integrated to obtain the area-average concentration. A graphical display shows the variation of concentration from the top of the pipe to the bottom as well as the area-average concentration history. The instrument has been extensively tested in an experimental slurry transport facility as well as on-line at the Swift Creek phosphate mine in the state of Florida. When compared with a quick-closing valve measuring technique, the mean deviation of solids concentration measured with the conductance based instrument is 0.81 percent based on mass. [S0098-2202(00)00704-5]
Modeling an Integral Dual Solar/Gas-Fired Generator for a Water-Lithium Bromide Absorption Chiller
Authors: Cao J. , Christensen R. N.
Published: July 2002

This paper presents a design procedure for a dual solar/gas-fired generator of an absorption chiller. The solar energy is the primary driving source for the generator, while the natural gas serves as the backup heat when the solar energy is unavailable or insufficient. Saturated forced convective boiling for binary mixtures has been considered to account for the reduction in the heat transfer coefficient observed for most mixtures. The simultaneous solar and gas-fired desorption process was investigated. The generator constructed based on modeling results yielded good performance in the experiment. [S0195-0738(00)00704-4]
Thermoeconomic Analysis on the Performance Characteristics of a Multi-Stage Irreversible Combined Heat Pump System
Authors: Chen Jincan , Wu Chih
Published: July 2002

A cycle model of a multi-stage combined heat pump system, which includes the irreversibility of finite rate heat transfer across finite temperature differences and the irreversibilities inside the working fluid, is established and used to investigate the influence of these irreversibilities on the performance of the system. The profit of operating the heat pump system is taken as an objective function for optimization. The maximum profit is calculated for a given total heat transfer area or total thermal conductance of heat exchangers. The coefficient of performance, heating load, and power input at the maximum profit are determined. The distribution of the heat transfer areas or the thermal conductances of heat exchangers and the temperature ratios of the working fluids of two adjacent cycles in heat exchange processes are optimized. The results obtained here are generally significant. They are suitable for an arbitrary-stage irreversible and endo- reversible combined heat pump system. [S0195-0738(00)01104-3]
Numerical Simulation of Streaming Potentials Due to Deformation-Induced Hierarchical Flows in Cortical Bone
Authors: Mak A. F. T. , Zhang J. D.
Published: July 2002

Bone is a very dynamic tissue capable of modifying its composition, microstructure, and overall geometry in response to the changing biomechanical needs. Streaming potential has been hypothesized as a mechanotransduction mechanism that may allow osteocytes to sense their biomechanical environment. A correct understanding of the mechanism for streaming potential will illuminate our understanding of bone remodeling, such as the remodeling associated with exercise hypertrophy, disuse atrophy, and the bone remodeling around implants. In the current research, a numerical model based on the finite element discretization is proposed to simulate the fluid flows through the complicated hierarchical flow system and to calculate the concomitant stress generated potential (SGP) as a result of applied mechanical loading. The lacunae–canaliculi and the matrix microporosity are modeled together as discrete one-dimensional flow channels superposed in a biphasic poroelastic matrix. The cusplike electric potential distribution surrounding the Haversian canal that was experimentally observed and reported in the literature earlier was successfully reproduced by the current numerical calculation.
Thermodynamic Optimization of the HAT Cycle Plant Structure—Part I: Optimization of the “Basic Plant Configuration”
Authors: Lazzaretto A. , Segato F.
Published: July 2002

A method for the thermodynamic optimization of the humid air turbine cycle plant structure is presented here. The method is based on the optimization of a “basic configuration of the plant” including “basic components” (compressor, turbine, combustion chamber, regenerator, and saturator), always present and connected in the same way in the plant structure and a heat exchange section which is viewed as a “black-box” where the heat transfer between hot and cold thermal flows occurs regardless of how many heat exchangers there are and of how they are interconnected. The optimal boundary conditions between the basic components and black-box are determined by calculating the conditions of maximum heat transfer in the black-box independently of the structure of the heat exchanger network. This is done by defining optimal composite curves in a Fortran routine at each step in the main optimization procedure. Once the structure of the heat exchanger networks that fulfill the optimal boundary conditions have been found, the optimal structure of the whole plant is obtained (see Section 2). The method is useful in a general sense as it can be applied to highly integrated energy systems in which it is difficult to define the optimal structure of the heat exchanger network in advance.
Life Cycle Assessment Estimation for Eco-Management of Co-Generation Systems
Authors: Kato Seizo , Maruyama Naoki , Nikai Yasuki , Takai Hidekazu , Widiyanto Anugerah
Published: July 2002

A LCA (life cycle assessment) scheme for any industrial activity system is introduced to estimate the quantitative load on the environment with the aid of the NETS (numerical environment total standard) method proposed by the authors as a numerical measure. Two kinds of environmental loads respecting fossil fuel depletion as input resources to the system and global warming due to CO2 emission as output are taken into account in the present eco-criterion, in which the total eco-load (EcL) value is calculated from the summation of respective environmental load factors on the whole process in a life cycle of the system. This NETS method is applied to eco-management co-generation systems, in which a computer-aided output navigator proceeds the LCA estimation with ICON and Q&A communication. An operation scheme most friendly to the environment with a minimum EcL value, i.e., an eco-operation scheme, is derived from the optimization theory.
Determination of Poisson’s Ratio by Spherical Indentation Using Neural Networks—Part II: Identification Method
Authors: Huber N. , Tsakmakis Ch.
Published: July 2002

In a previous paper it has been shown that the load and the unloading stiffness are, among others, explicit functions of the Poisson’s ratio, if a spherical indenter is pressed into a metal material. These functions can be inverted by using neural networks in order to determine the Poisson’s ratio as a function of the load and the unloading stiffness measured at different depths. Also, the inverse function possesses as an argument the ratio of the penetration depth and that depth, at which plastic yield occurs for the first time. The latter quantity cannot be measured easily. In the present paper some neural networks are developed in order to identify the value of Poisson’s ratio. After preparing the input data appropriately, two neural networks are trained, the first one being related to Set 2 of the previous paper. In order to avoid an explicit measurement of the yield depth, the second neural network has to be trained in such a way, that its solution intersects with that of Set 2 at the correct value of Poisson’s ratio. This allows to identify Poisson’s ratio with high accuracy within the domain of finite element data.
Kinematic Synthesis of Spatial R-R Dyads for Path Following With Applications to Coupled Serial Chain Mechanisms
Authors: Krovi Venkat , Ananthasuresh G. K. , Kumar Vijay
Published: July 2002

The dimensional synthesis of a spatial two revolute jointed dyad for path following tasks with applications to coupled serial chain mechanisms is presented. The precision point synthesis equations obtained using the rotation matrix approach form a rank-deficient linear system in the link-vector components. The nullspace of this rank-deficient linear system is derived analytically and interpreted geometrically. The nullspace vectors lead to the specification of additional constraints via the so-called auxiliary equations and to the solution of the linear system of equations. The geometry also allows the derivation of a closed form solution for the three design position problem. Finally, optimal path following by coupled R-R dyads is achieved by optimization over the free choice variables.
Flow Past Rotating Cylinders: Effect of Eccentricity
Authors: Mittal S.
Published: July 2002

Computational results are presented for flows past a translating and rotating circular cylinder. A stabilized finite element method is utilized to solve the incompressible Navier-Stokes equations in the primitive variables formulation. To validate the formulation and its implementation certain cases, for which the flow visualization and computational results have been reported by other researchers, are computed. Results are presented for Re=5, 200 and 3800 and rotation rate, (ratio of surface speed of cylinder to the freestream speed of flow), of 5. For all these cases the flow reaches a steady state. The values of lift coefficient observed for these flows exceed the limit on the maximum value of lift coefficient suggested by Goldstein based on intuitive arguments by Prandtl. These observations are in line with measurements reported, earlier, by other researchers via laboratory experiments. To investigate the stability of the computed steady-state solution, receptivity studies involving an eccentrically rotating cylinder are carried out. Computations are presented for flow past a rotating cylinder with wobble; the center of rotation of the cylinder does not match its geometric center. These computations are also important from the point of view that in a real situation it is almost certain that the rotating cylinder will be associated with a certain degree of wobble. In such cases the flow is unsteady and reaches a temporally periodic state. However, the mean values of the aerodynamic coefficients and the basic flow structure are still quite comparable to the case without any wobble. In this sense, it is found that the two-dimensional solution is stable to purely two-dimensional disturbances.
Inverse Boundary Design Combining Radiation and Convection Heat Transfer
Authors: Franc¸a Francis H. R. , Ezekoye Ofodike A. , Howell John R.
Published: July 2002

This work investigates inverse boundary design for radiation, convection and conduction combined-mode heat transfer. The problem consists of finding the heat flux distribution on a heater that satisfies both the temperature and the heat flux prescribed on a design surface of an enclosure formed by two finite parallel plates. A gray participating medium flows in laminar regime between the walls, which are gray, diffuse emitters and absorbers. All the thermal properties are uniform. This problem is described by an ill-conditioned system of non-linear equations. The solution is obtained by regularizing the system of equations by means of truncated singular value decomposition (TSVD).
Constructal Placement of High-Conductivity Inserts in a Slab: Optimal Design of “Roughness”
Authors: Neagu and M. , Bejan A.
Published: July 2002

This paper addresses the fundamental problem of how to facilitate the flow of heat across a conducting slab heated from one side. Available for distribution through the system is a small amount of high-conductivity material. The constructal method consists of optimizing geometrically the distribution of the high-conductivity material through the material of lower conductivity. Two-dimensional distributions (plate inserts) and three-dimensional distributions (pin inserts) are optimized based on the numerical simulation of heat conduction in a large number of possible configurations. Results are presented for the external and internal features of the optimized architectures: spacings between inserts, penetration distances, tapered inserts and constant-thickness inserts. The use of optimized pin inserts leads consistently to lower global thermal resistances than the use of plate inserts. The side of the slab that is connected to the high-conductivity intrusions is in effect a “rough” surface. This paper shows that the architecture of a rough surface can be optimized for minimum global contact resistance. Roughness can be designed.
Transcritical Patterns of Cavitating Flow and Trends of Acoustic Level
Authors: Gu Wei , He Yousheng , Hu Tianqun
Published: July 2002

Hydroacoustics of the transcritical cavitating flows on a NACA16012 hydrofoil at a 2/5/8-degree angle of attack and axisymmetric bodies with hemispherical and 45-degree conical headforms were studied, and the process of cloud cavitation shedding was observed by means of high-speed cinegraphy. By expressing the cavitation noise with partial acoustic level, it is found that the development of cavitation noise varies correspondingly with cavitation patterns. The instability of cavitation is a result of cavity-flow interaction, and is mainly affected by the liquid flow rather than by the cavitation bubbles. A periodic flow structure with a large cavitation vortex is observed and found to be responsible for inducing the reentrant-jet and consequent cavitation shedding, and explains the mechanism of periodic cavitation shedding from a new viewpoint. New terms for the three stages, growing, hatching and breaking, are used to describe the process of cavity shedding.
Three-Dimensional Swirl Flow Velocity-Field Reconstruction Using a Neural Network With Radial Basis Functions
Authors: Pruvost J. , Legrand J. , Legentilhomme P.
Published: July 2002

For many studies, knowledge of continuous evolution of hydrodynamic characteristics is useful but generally measurement techniques provide only discrete information. In the case of complex flows, usual numerical interpolating methods appear to be not adapted, as for the free decaying swirling flow presented in this study. The three-dimensional motion involved induces a spatial dependent velocity-field. Thus, the interpolating method has to be three-dimensional and to take into account possible flow nonlinearity, making common methods unsuitable. A different interpolation method is thus proposed, based on a neural network algorithm with Radial Basis Functions.
The Fluid Dynamics of LPT Blade Separation Control Using Pulsed Jets
Authors: Bons Jeffrey P. , Sondergaard Rolf , Rivir Richard B.
Published: July 2002

The effects of pulsed vortex generator jets on a naturally separating low-pressure turbine boundary layer have been investigated experimentally. Blade Reynolds numbers in the linear turbine cascade match those for high-altitude aircraft engines and industrial turbine engines with elevated turbine inlet temperatures. The vortex generator jets (30 deg pitch and 90 deg skew angle) are pulsed over a wide range of frequency at constant amplitude and selected duty cycles. The resulting wake loss coefficient versus pulsing frequency data add to previously presented work by the authors documenting the loss dependency on amplitude and duty cycle. As in the previous studies, vortex generator jets are shown to be highly effective in controlling laminar boundary layer separation. This is found to be true at dimensionless forcing frequencies F+ well below unity and with low (10 percent) duty cycles. This unexpected low-frequency effectiveness is due to the relatively long relaxation time of the boundary layer as it resumes its separated state. Extensive phase-locked velocity measurements taken in the blade wake at an F+ of 0.01 with 50 percent duty cycle (a condition at which the flow is essentially quasi-steady) document the ejection of bound vorticity associated with a low-momentum fluid packet at the beginning of each jet pulse. Once this initial fluid event has swept down the suction surface of the blade, a reduced wake signature indicates the presence of an attached boundary layer until just after the jet termination. The boundary layer subsequently relaxes back to its naturally separated state. This relaxation occurs on a timescale which is five to six times longer than the original attachment due to the starting vortex. Phase-locked boundary layer measurements taken at various stations along the blade chord illustrate this slow relaxation phenomenon. This behavior suggests that some economy of jet flow may be possible by optimizing the pulse duty cycle and frequency for a particular application. At higher pulsing frequencies, for which the flow is fully dynamic, the boundary layer is dominated by periodic shedding and separation bubble migration, never recovering its fully separated (uncontrolled) state.
Experimental Optimization of Pivot Point Height for Swing-Arm Type Rear Suspensions in Off-Road Bicycles
Authors: Karchin Ari , Hull M. L.
Published: July 2002

Towards the ultimate goal of designing dual suspension off-road bicycles which decouple the suspension motion from the pedaling action, this study focused on determining experimentally the optimum pivot point height for a swing-arm type rear suspension such that the suspension motion was minimized. Specific objectives were (1) to determine the effect of interaction between the front and rear suspensions on the optimal pivot point height, (2) to investigate the sensitivity of the optimal height to the pedaling mechanics of the rider in both the seated and standing postures, (3) to determine the dependence of the optimal height on the rider posture. Eleven experienced subjects rode a custom-built adjustable dual suspension off-road bicycle, [Needle, S., and Hull, M. L., 1997, “An Off-Road Bicycle With Adjustable Suspension Kinematics,” Journal of Mechanical Design 119, pp. 370–375], on an inclined treadmill. The treadmill was set to a constant 6 percent grade at a constant velocity of 24.8 km/hr. With the bicycle in a fixed gear combination of 38×14, the corresponding cadence was 84 rpm. For each subject, the pivot point height was varied randomly while the motions across both the front and rear suspension elements were measured. Subjects rode in both the seated and standing postures and with the front suspension active and inactive. It was found that the power loss from the rear suspension at the optimal pivot point height was not significantly dependent on the interaction between the front and rear suspensions. In the seated posture, the optimal pivot point height was 9.8 cm on average and had a range of 8.0–12.3 cm. The average optimal pivot point height for the seated posture corresponded to an average power loss for the rear suspension that was within 10 percent of the minimum power loss for each subject for 8 of the 11 subjects. In the standing posture, the average height was 5.9 cm and ranged from 5.1–7.2 cm. The average height for the standing posture was within 10 percent of the minimum power loss for each subject for 9 of the 11 subjects. While the optimum height was relatively insensitive to pedaling mechanics in both the seated and standing postures, the choice of the optimal pivot point height in production bicycles necessitates some compromise in performance given the disparity in the averages between the seated and standing postures.
Non-Gaussian Narrow-Band Random Fatigue
Authors: Blevins R. D.
Published: July 2002

Fatigue is produced by the sum of randomly phased sine waves. Fatigue damage during this non-Gaussian, finite random process is a function of the noise bandwidth, the fatigue slope, mean stress, and the rms stress. Methods are developed for predicting the cycles to failure. Comparison is made with data.
Synchronous Sensor Runout and Unbalance Compensation in Active Magnetic Bearings Using Bias Current Excitation
Authors: Setiawan Joga D. , Mukherjee Ranjan , Maslen Eric H.
Published: July 2002

Sensor runout and unbalance are the dominant sources of periodic disturbances in magnetic bearings. Many algorithms have been investigated for individual runout and unbalance compensation but the problem of simultaneous compensation of the two disturbances remains essentially unsolved. The problem stems fundamentally from a lack of observability of disturbances with the same frequency content and is critical for applications where the rotor needs to be stabilized about its geometric center. A credible way to distinguish between the synchronous disturbances is to vary rotor speed but speed variation is not acceptable for many applications. We present in this paper a new method for simultaneous identification and compensation of synchronous runout and unbalance at constant rotor speed. Based on traditional adaptive control design, our method guarantees geometric center stabilization of the rotor through persistency of excitation generated by bearing stiffness variation. The variation in magnetic stiffness is achieved through perturbation of the bias currents in opposing electromagnetic coils in a manner that does not alter the equilibrium condition of the rotor. Our theoretical results are first validated through numerical simulations and then experiments on a laboratory test-rig. The experimental results adequately demonstrate efficacy of our approach and provide clues for future research directions.
A Polynomial Equation for a Coupler Curve of the Double Butterfly Linkage
Authors: Pennock Gordon R. , Hasan Atif
Published: July 2002

This paper presents a closed-form polynomial equation for the path of a point fixed in the coupler links of the single degree-of-freedom eight-bar linkage commonly referred to as the double butterfly linkage. The revolute joint that connects the two coupler links of this planar linkage is a special point on the two links and is chosen to be the coupler point. A systematic approach is presented to obtain the coupler curve equation, which expresses the Cartesian coordinates of the coupler point as a function of the link dimensions only; i.e., the equation is independent of the angular joint displacements of the linkage. From this systematic approach, the polynomial equation describing the coupler curve is shown to be, at most, forty-eighth order. This equation is believed to be an original contribution to the literature on coupler curves of a planar eight-bar linkage. The authors hope that this work will result in the eight-bar linkage playing a more prominent role in modern machinery.
Stochastic Modeling of Flow-Structure Interactions Using Generalized Polynomial Chaos
Authors: Xiu Dongbin , Lucor Didier , Su C.-H. , Karniadakis George Em
Published: July 2002

We present a generalized polynomial chaos algorithm to model the input uncertainty and its propagation in flow-structure interactions. The stochastic input is represented spectrally by employing orthogonal polynomial functionals from the Askey scheme as the trial basis in the random space. A standard Galerkin projection is applied in the random dimension to obtain the equations in the weak form. The resulting system of deterministic equations is then solved with standard methods to obtain the solution for each random mode. This approach is a generalization of the original polynomial chaos expansion, which was first introduced by N. Wiener (1938) and employs the Hermite polynomials (a subset of the Askey scheme) as the basis in random space. The algorithm is first applied to second-order oscillators to demonstrate convergence, and subsequently is coupled to incompressible Navier-Stokes equations. Error bars are obtained, similar to laboratory experiments, for the pressure distribution on the surface of a cylinder subject to vortex-induced vibrations.
Performance Evaluation of a Window Room Air Conditioner With
Microchannel Condensers
Authors: Kim Man-Hoe , Bullard Clark W.
Published: July 2002

A performance evaluation for a residential window air conditioning system with microchannel condensers has been performed. First, a series of wind-tunnel calorimeter tests were conducted for two different prototype microchannel heat exchangers. The measured heat transfer and pressure drop characteristics for the heat exchangers were then compared to calculated value for four conventional finned round-tube designs, which were obtained using a validated simulation model for identical air and refrigerant inlet conditions. Finally, two prototype microchannel condensers are installed in the system and system performance tests were conducted. System characteristics such as capacity, energy efficiency ratio, and suction and discharge pressures and temperatures are presented, and compared with those for the conventional system. Refrigerant charge requirements for a window air conditioner with a microchannel condenser can be decreased by 35 percent compared to the conventional baseline system. The condenser core volume and weight can be reduced by 55 and 35 percent, respectively.
Oscillatory Flow in a Physical Model of a Thin Slab Casting Mould With a Bifurcated Submerged Entry Nozzle
Authors: Lawson Nicholas J. , Davidson Malcolm R.
Published: July 2002

Laser Doppler anemometry (LDA) measurements are presented of the oscillatory flow in a 33% scale water model of thin slab casting mould when the flow enters as two lateral jets through a bifurcated nozzle. The submerged entry nozzle (SEN) and the mould were geometrically scaled to be representative of industrial thin slab casters. Mean and RMS LDA velocity measurements were taken at three selected points in the region surrounding the SEN, at 500 points in the central plane parallel to the broad face of the mould, and at points in selected transverse sections, for casting rates up to 1.53 m/min. Flow visualization was also taken at two selected planes in the mould. The LDA results showed each jet to form an upper and lower recirculation zone with the lower zones adjacent to one another bounded by the jets and the mould walls and the upper zones bounded by the jet, the SEN, the mould walls and the free surface. Both jets were found to have most oscillatory energy at frequencies below 5 Hz with high energy low frequency modes occurring at frequencies below 0.2 Hz. However, no single dominant frequency occurred in the spectrum and flow visualization revealed an apparently chaotic flow pattern in the oscillation. Midpoint jet deflection was restricted to 6–8 mm RMS, and no coherence was observed between jet (and free surface) movements on either side of the mould. The time averaged flow pattern was found to be almost symmetric across the wide face of the mould. It is concluded that both shear layer instability in the impinging jets, and deflection of the jets due to cross-flow at the SEN-mould wall, contribute to the flow oscillation.
Burnett equations for simulation of transitional flows
Authors: Agarwal Ramesh K , Yun Keon-Young
Published: July 2002

Hypersonic flows about space vehicles in low earth orbits and flows in microchannels of microelectromechanical devices produce local Knudsen numbers which lie in the continuum-transition regime. The Navier-Stokes equations cannot model these flows adequately since they are based on the assumption of small deviation from local thermodynamic equilibrium. A number of extended hydrodynamics (E-H) or generalized hydrodynamics (G-H) models as well as the Direct Simulation Monte Carlo (DSMC) approach have been proposed to model the flows in the continuum-transition regime over the past 50 years. One of these models is the Burnett equations which are obtained from the Chapman-Enskog expansion of the Boltzmann equation (with Knudsen number (Kn) as a small parameter) to OKn2. With the currently available computing power, it has been possible in recent years to numerically solve the Burnett equations. However, attempts at solving the Burnett equations have uncovered many physical and numerical difficulties with this model. Several improvements to the conventional Burnett equations have been proposed in recent years to address both the physical and numerical issues; two of the most well known are the Augmented Burnett Equations and the BGK-Burnett Equations. This review article traces the history of the Burnett model and describes some of the recent developments. The relationship between the Burnett equations and Grad’s 13 moment equations as shown by Struchtrup by employing the Maxwell-Truesdell-Green iteration is also presented. Also, the recent work of Jin and Slemrod on regularization of the Burnett equations via viscoelastic relaxation that ensures positive entropy production and eliminates the instability paradox is discussed. Numerical solutions in 1D, 2D, and 3D are provided to assess the accuracy and applicability of Burnett equations for modeling flows in the continuum-transition regime. The important issue of surface boundary conditions is addressed. Computations are compared with the available experimental data, Navier-Stokes calculations, Burnett solutions of other investigators, and DSMC solutions wherever possible. This review article cites 56 references.
An Anti-Windup Design for Linear System With Asymptotic Tracking Subjected to Actuator Saturation
Authors: Niu Weiguang , Tomizuka Masayoshi
Published: July 2002

This paper deals with asymptotic tracking for linear systems with actuator saturation in the presence of disturbances. Both reference inputs and disturbances are assumed to belong to a class which may be regarded as the zero-input responses of linear systems. The controller includes an anti-windup term which reduces the degradation in the system performance due to saturation. The stability of the overall system is established based on the Lyapunov stability theory. Both state and output feedback solutions are given. The proposed scheme is evaluated for a two axis motion control system by simulation. [S0022-0434(00)01002-9]
Modeling the Effects of Damage and Microstructural Evolution on the Creep Behavior of Engineering Alloys
Authors: McLean M. , Dyson B. F.
Published: July 2002

A quantitative representation of the creep behavior of materials is required to determine the operating lives of high temperature plant. Although the creep performance of such materials is normally governed by the development of microstructural features that can either be associated with the normal aging phenomena or by the development of damage in the material, most previous analyses of creep data have been empirical. It has been implicitly assumed that similar forms of creep curves can be adequately represented by a single generic equation. However, it is clear that different materials are subject to different combinations of structural change during their creep lives (e.g., cavitation/cracking, particle coarsening, phase changes, dislocation accumulation) all of which can influence the creep performance. An empirical representation can always be made to fit an available database, but effective extrapolation to longer lives and more complex loading conditions requires that the differing mechanisms be integrated in the creep equations. This paper will explore the implications of the evolution of microstructure and damage on the creep performance of a range of materials and will consider the potential of a microstructure-based state-variable (or damage-mechanics) approach for improved design life prediction of new plant and remaining life assessment of geriatric plant. [S0094-4289(00)00603-4]