bluuebunny/crossref_metadata_2025 huggingface dataset:
The CaV2.3 Ca2+ channel subunit contributes to R‐Type Ca2+ currents in murine hippocampal and neocortical neurones
Authors: Sochivko Dmitry , Pereverzev Alexey , Smyth Neil , Gissel Cornelia , Schneider Toni , Beck Heinz
Published: October 2002

Different subtypes of voltage‐dependent Ca2+ currents in native neurones are essential in coupling action potential firing to Ca2+ influx. For most of these currents, the underlying Ca2+ channel subunits have been identified on the basis of pharmacological and biophysical similarities. In contrast, the molecular basis of R‐type Ca2+ currents remains controversial. We have therefore examined the contribution of the CaV2.3 (α1E) subunits to R‐type currents in different types of central neurones using wild‐type mice and mice in which the CaV2.3 subunit gene was deleted. In hippocampal CA1 pyramidal cells and dentate granule neurones, as well as neocortical neurones of wild‐type mice, Ca2+ current components resistant to the combined application of ω‐conotoxin GVIA and MVIIC, ω‐agatoxin IVa and nifedipine (ICa,R) were detected that were composed of a large R‐type and a smaller T‐type component. In CaV2.3‐deficient mice, ICa,R was considerably reduced in CA1 neurones (79 %) and cortical neurones (87 %), with less reduction occurring in dentate granule neurones (47 %). Analysis of tail currents revealed that the reduction of ICa,R is due to a selective reduction of the rapidly deactivating R‐type current component in CA1 and cortical neurones. In all cell types, ICa,R was highly sensitive to Ni2+ (100 μM: 71–86 % block). A selective antagonist of cloned CaV2.3 channels, the spider toxin SNX‐482, partially inhibited ICa,R at concentrations up to 300 nm in dentate granule cells and cortical neurones (50 and 57 % block, EC50 30 and 47 nm, respectively). ICa,R in CA1 neurones was significantly less sensitive to SNX‐482 (27 % block, 300 nm SNX‐482). Taken together, our results show clearly that CaV2.3 subunits underlie a significant fraction of ICa,R in different types of central neurones. They also indicate that CaV2.3 subunits may give rise to Ca2+ currents with differing pharmacological properties in native neurones.
The effect of testosterone on regional blood flow in prepubertal anaesthetized pigs
Authors: Molinari C. , Battaglia A. , Grossini E. , Mary D. A. S. G. , Vassanelli C. , Vacca G.
Published: October 2002

This work was undertaken to study the effects of testosterone on the coronary, mesenteric, renal and iliac circulations and to determine the mechanisms of action involved. In prepubertal pigs of both sexes anaesthetized with sodium pentobarbitone, changes in left circumflex or anterior descending coronary, superior mesenteric, left renal and left external iliac blood flow caused by intra‐arterial infusion of testosterone were assessed using electromagnetic flowmeters. Changes in heart rate and arterial blood pressure were prevented by atrial pacing and by connecting the arterial system to a pressurized reservoir containing Ringer solution. In 12 pigs, intra‐arterial infusion of testosterone for 5 min to achieve a stable intra‐arterial concentration of 1 μg l−1 increased coronary, mesenteric, renal and iliac blood flow without affecting the maximum rate of change of left ventricular systolic pressure (left ventricular dP/dtmax) and filling pressures of the heart. In a further five pigs, a concentration‐response curve was obtained by graded increases in the intra‐arterial concentration of the hormone between 0.125 and 8 μg l−1. The mechanisms of these responses were studied in the 12 pigs by repeating the experiment after haemodynamic variables had returned to the control values before infusions. In six pigs, blockade of muscarinic cholinoceptors and adrenoceptors with atropine, propranolol and phentolamine did not affect the responses caused by intra‐arterial infusion of testosterone performed to achieve a stable intra‐arterial concentration of 1 μg l−1. In the same pigs and in the remaining six pigs, the increases in coronary, mesenteric, renal and iliac blood flow caused by intra‐arterial infusion of testosterone performed to achieve a stable intra‐arterial concentration of 1 μg l−1 were prevented by intra‐arterial injection of Nω‐nitro‐L‐arginine methyl ester. The present study shows that intra‐arterial infusion of testosterone dilated coronary, mesenteric, renal and iliac circulations. The mechanism of this response involved the release of nitric oxide.
Distribution of the forces produced by motor unit activity in the human flexor digitorum profundus
Authors: Kilbreath S. L. , Gorman R. B. , Raymond J. , Gandevia S. C.
Published: October 2002

In humans, the flexor digitorum profundus (FDP), which is a multi‐tendoned muscle, produces forces that flex the four distal interphalangeal joints of the fingers. We determined whether the force associated with activity in a single motor unit in the FDP was confined to a single finger or distributed to more than one finger during a natural grasp. The discharge of single low‐threshold motor units (n= 69) was recorded at sites across the muscle during weak voluntary grasping involving all fingers and spike‐triggered averaging of the forces under each of the finger pads was used to assess the distribution pattern. Spike‐triggered averaging revealed that time‐locked changes in force occurred under the ‘test’ finger (that finger on which the unit principally acted) as well as under the ‘non‐test’ fingers. However, for the index‐, middle‐ and ring‐finger units, the changes in force under non‐test fingers were typically small (< 20 % of those under the test finger). For little‐finger units, the mean changes in force under the adjacent ring finger were large (>50 % of those under the test finger). The distribution of forces by little‐finger units differed significantly from that for each of the other three fingers. Apart from increases in force under non‐test fingers, there was occasional unloading of adjacent fingers (22/267 combinations), usually affecting the index finger. The increases in force under the test finger correlated significantly with the background force for units acting on the middle, ring and little fingers. During a functional grasp, the activity of single units in the FDP allows for a relatively selective control of forces at the tips of the index, middle and ring fingers, but this is limited for little‐finger units.
Disinhibition in the human motor cortex is enhanced by synchronous upper limb movements
Authors: Stinear James W. , Byblow Winston D.
Published: October 2002

The phasic modulation of wrist flexor corticomotor disinhibition has previously been demonstrated during the flexion phase of rhythmical passive flexion‐extension of the human wrist. Here we ask if rhythmical bimanual flexion‐extension movements of the wrists of neurologically intact subjects, modulate inhibitory activity in the motor cortex. In the first experiment intracortical inhibition was assessed when one wrist was passively flexed and extended on its own, with the addition of the opposite limb voluntarily moving synchronously in a mirror symmetric pattern, and also in a near‐symmetric asynchronous pattern. Two subsequent experiments investigated firstly the modulation of spinal reflex pathway activity during the same three movement conditions, and secondly the effect of contralateral wrist movement alone on the excitability of corticomotoneuronal pathways to a static test limb. When the wrist flexors of both upper limbs were shortening simultaneously (i.e. synchronously), intracortical inhibition associated with flexor representations was suppressed to a greater extent than when the two muscles were shortening asynchronously. The results of the three experiments indicate that modulation of inhibitory activity was taking place at the cortical level. These findings may have further application in the study of rehabilitation procedures where the effects of simultaneous activation of affected and unaffected upper limbs in hemiparetic patients are to be investigated.
Effect of Simulation Methodology on Solder Joint Crack Growth Correlation and Fatigue Life Prediction
Authors: Darveaux Robert
Published: October 2002

A generalized solder joint fatigue life model for surface mount packages was previously published in [1,2]. The model is based on correlation to measured crack growth data on BGA joints during thermal cycling. It was subsequently discovered by Anderson et al. that the ANSYS™1 5.2 finite element code used in the model had an error in its method for calculating plastic work [3]. It was shown that significant error in life prediction could result by using a recent version of the code where the bug has been fixed. The error comes about since the original crack growth constants were derived based on plastic work calculations that had the bug. In this paper, crack initiation and growth constants are recalculated using ANSYS™ 5.6. In addition, several other model related issues are explored with respect to the crack growth correlations. For example, 3D slice models were compared to quarter symmetry models. Anand’s constitutive model was compared with Darveaux’s constitutive model. It was shown that the crack growth rate dependence on strain energy density always had an exponent of 1.10+/−0.15. This is in the range of the original correlation. The model was applied to several data sets of tape-based and laminate-based BGAs. The accuracy of absolute predictions is mostly within +/−2X. The accuracy of relative predictions is within +/−25%. However, the accuracy of absolute predictions could be off by a factor of 7 in the worst case, if the analyst uses a modeling procedure that is not consistent with that used for the crack growth correlation. The key to good accuracy is to maintain consistency in the modeling procedure.
Shape Optimal Design of Contact Springs of Electronic Connectors
Authors: Hsu Yeh-Liang , Hsu Yuan-Chan , Hsu Ming-Sho
Published: October 2002

An electronic connector provides a separable interface between two subsystems of an electronic system. The contact spring is probably the most critical component in an electronic connector. Mechanically, the contact spring provides the contact normal force, which establishes the contact interface as the connector is mated. However, connector manufacturers have a basic struggle between the need for high normal contact forces and low insertion forces. Designing connectors with large numbers of pins that are used with today’s integrated circuits and printed circuit boards often results in an associated rise in connector insertion force. It is possible to lower the insertion force of a connector by redesigning the geometry of the contact spring, but this also means a decrease in contact normal force. In this paper, structural shape optimization techniques are used to find the optimal shape of the contact springs of an electronic connector. The process of the insertion of a PCB into the contact springs of a connector is modeled by finite element analysis. The maximum insertion force and the contact normal force are calculated. The effects of several design parameters are discussed. The geometry of the contact springs is then parameterized and optimized. The required insertion force is minimized while the normal contact force and the resulting stress are maintained within specified values. In our example, the insertion force of the final contact spring design is reduced to 68.3% of that of the original design, while the contact force and the maximum stress are maintained within specified values.
Application of Fractional Calculus to Fluid Mechanics
Authors: Kulish Vladimir V. , Lage Jose´ L.
Published: October 2002

In this note we present the application of fractional calculus, or the calculus of arbitrary (noninteger) differentiation, to the solution of time-dependent, viscous-diffusion fluid mechanics problems. Together with the Laplace transform method, the application of fractional calculus to the classical transient viscous-diffusion equation in a semi-infinite space is shown to yield explicit analytical (fractional) solutions for the shear-stress and fluid speed anywhere in the domain. Comparing the fractional results for boundary shear-stress and fluid speed to the existing analytical results for the first and second Stokes problems, the fractional methodology is validated and shown to be much simpler and more powerful than existing techniques.
The Application of Advanced Methods in Analyzing the Performance of the Air Curtain in a Refrigerated Display Case
Authors: Navaz Homayun K. , Faramarzi Ramin , Gharib Morteza , Dabiri Dana , Modarress Darius
Published: October 2002

Computational Fluid Dynamics (CFD) modeling is effectively coupled with the experimental technique of Digital Particle Image Velocimetry (DPIV), to study the flowfield characteristics and performance of the air curtain of a medium-temperature open vertical refrigerated display case used in supermarkets. A global comparison of the flowfield and quantification of the entrained air into the case indicate that there is a considerable amount of cold air spillage from a typical display case that is replaced by the ambient warm entrained air across the air curtain, lowering the energy efficiency of the case. The computational model that is developed from the marriage of CFD and DPIV techniques provides a reliable simulation tool that can be used for the design optimization of air curtains. A correct estimate of the infiltration rate by changing different parameters in a validated computational simulation model will provide a feasible tool for minimizing the spillage of the cold air, and thereby designing more energy efficient open display cases.
Evaluation and Comparison of Alternative Compliant Overrunning Clutch Designs
Authors: Roach Gregory M. , Howell Larry L.
Published: October 2002

Compliance criteria are used to evaluate the general class of over-running clutches to determine which type is best suited to benefit from compliance. The criteria used in the evaluation include the presence and angle of rotation of revolute joints, the possibility for part count reduction, the presence of springs, possible reduction in weight, and the method of clutch engagement. Sprag, spring, roller or ball, and ratchet and pawl clutch types were evaluated, and the ratchet and pawl type of over-running clutch was demonstrated to be the most promising. Within this type of over-running clutch, different designs incorporating bending, tension, and compression loading of the pawls were explored to determine the best method for loading the pawls. The clutches were compared using the maximum output torque. It was determined that the clutch incorporating rigid pawls loaded in compression produced the largest output torque. The maximum output torque for this clutch was measured at 65.6 N-m.
Elasticity Solution for a Laminated Orthotropic Cylindrical Shell Subjected to a Localized Longitudinal Shear Force
Authors: Bhaskar K. , Ganapathysaran N.
Published: October 2002

A three-dimensional elasticity solution is presented for the title problem. The solution is in terms of a double Fourier series in the surface-parallel directions and a power series in the thickness direction. On the basis of this solution, it is shown that the classical lamination theory is inadequate for this problem because the steep displacement and stress gradients near the load cannot be captured by it correctly even if the shell is thin.
Spatial Mechanism Design in Virtual Reality With Networking
Authors: Kihonge John N. , Vance Judy M. , Larochelle Pierre M.
Published: October 2002

Mechanisms are used in many devices to move a rigid body through a finite sequence of prescribed locations. The most commonly used mechanisms are four-bar planar mechanisms that move an object in one plane in space. Spatial mechanisms allow motion in three-dimensions (3D), however, to date they are rarely implemented in industry in great part due to the inherent visualization and design challenges involved. Nevertheless, they do provide promise as a practical solution to spatial motion generation and therefore remain an active area of research. Spatial 4C mechanisms are two degree-of-freedom kinematic closed-chains consisting of four rigid links simply connected in series by cylindrical (C) joints. A cylindrical joint is a two degree-of-freedom joint, which allows translation and rotation about a line in space. This paper describes a synthesis process for the design of 4C spatial mechanisms in a virtual environment. Virtual reality allows the user to view and interact with digital models in a more intuitive way than using the traditional human-computer interface (HCI). The software developed as part of this research also allows multiple users to network and share the designed mechanism. Networking tools have the potential to greatly enhance communication between members of the design team at different industrial sites and therefore reduce design costs. This software presents the first effort to provide a three-dimensional digital design environment for the design of spatial 4C mechanisms.
Constitutive Model of a Transversely Isotropic Bingham Fluid
Authors: Robinson D. N. , Kim K. J. , White J. L.
Published: October 2002

A constitutive theory is presented for a transversely isotropic, viscoplastic (Bingham) fluid. The theory accounts for threshold (yield) and viscous flow characteristics through inclusion of a potential function serving the dual role of a threshold function and a viscous flow potential. The arguments and form of the potential function derive from the theory of tensorial invariants. The model reduces to a transversely isotropic model of perfect plasticity in the limit of vanishing viscosity. In the limit of isotropy, it reduces to the Hohenemser-Prager generalization of Bingham’s model. A characterization procedure is prescribed based on correlation with experiments conducted under simple states of stress. Application is made to polymer melts filled with talc particles.
Design of H∞ Position Tracking Controllers for Current-Fed Induction Motors Used in Articulated Mechanical Loads
Authors: Chiaverini Stefano , Fusco Giuseppe
Published: October 2002

This paper describes a systematic procedure to design H∞ position and flux-norm tracking controllers for current-fed induction motors. The designed controllers achieve convergence to zero of both position and flux-norm tracking errors while ensuring robustness with respect to unknown load torque disturbances. The proposed procedure offers the possibility of a simple development of the controllers’ design; in particular, it does not require a numerical solution of the Riccati matrix equation. A case study has been set up which considers the application of the proposed control scheme to a two-link robot manipulator system actuated by two induction motors. Numerical simulation results confirm the validity of the proposed design methodology, even in the presence of rotor resistance uncertainty.
Stability Analysis for a Class of Uncertain Discrete Singularly Perturbed Systems With Multiple Time Delays
Authors: Chen Ching-Fa , Pan Shing-Tai , Hsieh Jer-Guang
Published: October 2002

In this paper, the robust stability problem for a class of nominally stable uncertain discrete singularly perturbed linear systems with multiple time delays is considered. A stability criterion for the slow and fast subsystems is first derived. A delay-dependent criterion is then proposed to guarantee the robust stability of the system subject to norm-bounded perturbations. A numerical example is provided to illustrate our main results.
A New Approach to Evaluate Temperature Effects on Rheological Behavior of Formate-Based Fluids
Authors: Lomba Rosana F. T. , de Sa´ Carlos H. M. , Branda˜o Edimir M.
Published: October 2002

Organic salt brines represent a good alternative to drill through deep productive zones. The literature presents these salts as thermal stabilizers of polymers used in the formulation of drill-in fluids. An extensive study was carried out to evaluate the rheological behavior of formate-based fluids as a function of temperature and density. An analytical expression was developed to correlate shear stresses with temperature for general drilling fluids and a special case of this expression results in a greatly simplified expression that is valid for a number of drilling and completion fluids produced using different alkali-metal salts of formic acid. The advantage of this new approach is the lack of dependence between the proposed correlation and the choice of a rheological model. Unlike many expressions presented in the literature, the expression proposed and methodology that follows allows the choice of a best-fit model to predict the fluid’s rheological behavior as a function of temperature. Experimental results show that formates do improve the thermal stability of polymers. The proposed correlations will soon be incorporated in a wellbore cleaning numerical simulator to compensate for thermal effects.
Design Evaluation of Multi-station Assembly Processes by Using State Space Approach
Authors: Ding Yu , Ceglarek Dariusz , Shi Jianjun
Published: October 2002

This paper considers the problem of evaluating and benchmarking process design configuration in a multi-station assembly process. We focus on the unique challenges brought by the multi-station system, namely, (1) a system level model to characterize the variation propagation in the entire process, and (2) the necessity to describe the system response to variation inputs at both global (system level) and local (station level and single fixture level) scales. State space representation is employed to recursively describe the propagation of variation in such a multi-station process, incorporating process design information such as fixture locating layout at individual stations and station-to-station locating layout change. Following the sensitivity analysis in control theory, a group of hierarchical sensitivity indices is defined and expressed in terms of the system matrices in the state space model, which are determined by the given process design configuration. Implication of these indices with respect to variation control is discussed and a three-step procedure of applying the sensitivity indices for selecting a better design and prioritizing the critical station/fixture is presented. We illustrate the proposed method using the group of sensitivity indices in design evaluation of the assembly process of an SUV (Sport Utility Vehicle) side panel.
An Adaptive State Filtering Algorithm for Systems With Partially Known Dynamics
Authors: Parlos Alexander G. , Menon Sunil K. , Atiya Amir F.
Published: October 2002

On-line filtering of stochastic variables that are difficult or expensive to directly measure has been widely studied. In this paper a practical algorithm is presented for adaptive state filtering when the underlying nonlinear state equations are partially known. The unknown dynamics are constructively approximated using neural networks. The proposed algorithm is based on the two-step prediction-update approach of the Kalman Filter. The algorithm accounts for the unmodeled nonlinear dynamics and makes no assumptions regarding the system noise statistics. The proposed filter is implemented using static and dynamic feedforward neural networks. Both off-line and on-line learning algorithms are presented for training the filter networks. Two case studies are considered and comparisons with Extended Kalman Filters (EKFs) performed. For one of the case studies, the EKF converges but it results in higher state estimation errors than the equivalent neural filter with on-line learning. For another, more complex case study, the developed EKF does not converge. For both case studies, the off-line trained neural state filters converge quite rapidly and exhibit acceptable performance. On-line training further enhances filter performance, decoupling the eventual filter accuracy from the accuracy of the assumed system model.
Inverse-Dynamics Based State and Disturbance Observers for Linear Time-Invariant Systems
Authors: Liu Chia-Shang , Peng Huei
Published: October 2002

An output-feedback observer is proposed in this paper to simultaneously estimate unknown states and disturbances of linear time invariant systems. The states are estimated using a Luenberger-like observer while the disturbance signals are estimated based on an inverse-dynamics motivated algorithm. The proposed schemes can be applied to a wide variety of disturbances since no disturbance model is required in the estimation. Depending on the input/output rank conditions of the plant, two different designs are proposed. The observer gains are selected based on sufficient conditions for exponentially converging estimation. The design procedure is illustrated step-by-step by using two examples: a hypothetical problem and the ground vehicle lateral speed estimation problem. A standard H∞-filter is used as the benchmark to illustrate the performance of the proposed method.
A Microstructurally Based Orthotropic Hyperelastic Constitutive Law
Authors: Bischoff J. E. , Arruda E. A. , Grosh K.
Published: October 2002

A constitutive model is developed to characterize a general class of polymer and polymer-like materials that displays hyperelastic orthotropic mechanical behavior. The strain energy function is derived from the entropy change associated with the deformation of constituent macromolecules and the strain energy change associated with the deformation of a representative orthotropic unit cell. The ability of this model to predict nonlinear, orthotropic elastic behavior is examined by comparing the theory to experimental results in the literature. Simulations of more complicated boundary value problems are performed using the finite element method.
Field Verification of Model-Derived Natural Frequencies of a Drill String
Authors: Jogi Pushkar N. , Macpherson John D. , Neubert Michael
Published: October 2002

Vibrations generated in a drill string while drilling generally lead to a reduction in drilling efficiency and often cause premature failure of drill string components and bit damage. It is also known that lateral vibrations, in particular, are responsible for most measurement-while-drilling (MWD) tool failures while drilling. One way to increase drilling efficiency and avoid tool damage is to monitor and analyze drilling vibrations so that drilling parameters can be adjusted while drilling to reduce such vibrations. An alternative method is to analyze and determine the natural frequencies of the bottom-hole assembly (BHA) so that resonant conditions caused by various excitation mechanisms in the drill string can be avoided. Even though models have been developed in the past in the drilling industry to determine the natural frequencies of a BHA, few attempts have been made to demonstrate that such models do actually help reduce vibrations or failures. This paper deals with the process of field validation of model-derived frequencies for axial, torsional and lateral vibrations. The results presented in this paper are based on the analysis of drilling data from a field test using downhole vibration measurement sensors. The downhole measurements included X and Y bending moments, axial acceleration, dynamic weight-on-bit, dynamic torque, and X and Y-axis magnetometers mounted in an MWD sub. The data analysis demonstrates that the natural frequencies predicted by the models match well with actual field (measured) values at the locations of interest, particularly for lateral vibrations. This analysis therefore shows that model derived results can be used with a degree of confidence to help avoid resonant conditions in a BHA while drilling and to help reduce failures.
PIV Measurements in the Impeller and the Vaneless Diffuser of a Radial Flow Pump in Design and Off-Design Operating Conditions
Authors: Wuibaut G. , Bois G. , Dupont P. , Caignaert G. , Stanislas M.
Published: October 2002

This paper presents and discusses the results of an experimental program that has been made on an air test rig of a radial flow pump. The tested impeller is the so-called SHF impeller. Many experimental data have already been produced (tests in air and in water) on that geometry and these results are still used as databases for the validation of CFD codes. For the present study, an air test rig has been chosen for optical access facilities and measurements were realized with a vaneless diffuser. The 2D Particle Image Velocimetry technique has been used and measurements of flow velocities have been made simultaneously in the outer part of the impeller and in the vaneless diffuser. Measurements have been realized in five planes, in the hub to shroud direction, for various relative flow rates (design and off-design operating conditions). First, the paper focus on the evolutions of the phase averaged velocity charts in the impeller and the diffuser. Limitations of the phase averaging technique clearly appear in the very low partial flow rates and this will be related to previous pressure measurements analysis establishing the occurrence of rotating stall within the impeller for such operating conditions. The paper also proposes an analysis of the rates of fluctuations of the velocity charts and the evolutions in the various measuring planes as the relative flow rate becomes lower.
Impact of Perforating on Well Performance and Cumulative Production
Authors: Yildiz Turhan
Published: October 2002

This study presents a simplified method to predict inflow performance of and cumulative production from selectively perforated wells in bounded reservoirs. The model first calculates the pseudo-skin for a fully perforated well penetrating a formation with only unit thickness. Then, perforation pseudo-skin is superimposed on a two-dimensional selectively open completed well model. Using the new model, a sensitivity study is carried out to identify the parameters controlling the well flow rate and total recovery. The sensitivity study includes the impact of shot density, perforation size and length, phasing angle, perforated length/formation thickness ratio, and the degree of formation damage around the wellbore and perforations.
A New Method for Predicting the Opening Angle for Soft Tissues
Authors: Van Dyke Timothy J. , Hoger Anne
Published: October 2002

The purpose of this paper is to present a simple new method for calculating the opening angle produced by a given residual stress field in a soft biological tissue. The method uses minimization of potential energy, and is therefore named the MPE method. The accuracy of the MPE method is evaluated by comparing the opening angle it predicts to results from a finite element model of the opening angle experiment. We show that the MPE method provides good predictions of the opening angle, and that it is significantly more accurate than two other methods previously used in the literature.
New Approach for Analyzing Solar Collectors Subjected to Unequal Front/Rear Ambient Temperatures: The Equivalent Ambient Temperature Concept, Part 1: Modeling
Authors: Ho Kam T. K. , Loveday Dennis L.
Published: October 2002

Standard analyses of solar collector thermal performance are based upon an energy balance in which the environments adjoining the front and rear of the collector are assumed to be at the same temperature. This assumption is inappropriate for some collector designs, particularly building-integrated collectors. An approach for analyzing such situations is presented based upon a new conceptual temperature termed the “equivalent ambient temperature.” The concept is explained, the new temperature is defined, and the approach is applied to a typical collector geometry. The approach retains the convenience of the standard analysis while accounting for the unequal front/rear ambient temperatures and permits collector characterization in terms of the conventional parameters: plate efficiency factor, F′; heat removal factor, FR; overall heat loss coefficient, UL, and effective transmittance–absorptance product, ταe.
New Approach for Analyzing Solar Collectors Subjected to Unequal Front/Rear Ambient Temperatures: The Equivalent Ambient Temperature Concept, Part 2: Validation and Implications for Design
Authors: Ho Kam T. K. , Loveday Dennis L.
Published: October 2002

An approach based on a new conceptual temperature termed the “equivalent ambient temperature” has been introduced for analyzing solar collector thermal performances when the environments to the front and rear of a collector are at different temperatures. Using a specially-designed solar simulator, experimental work is presented which validates the new approach as applied to a wall-integrated covered profiled metal solar air collector. Using both the new and traditional approaches, collector thermal performances are predicted to reveal the practical conditions for which use of the new approach is warranted. The latter findings will be of importance to designers. Performance characteristics for this collector geometry are also presented for use by designers.
Radiation Loading of a Cylindrical Source in a Fluid-Filled Cylindrical Cavity Embedded Within a Fluid-Saturated Poroelastic Medium
Authors: Hasheminejad S. M. , Hosseini H.
Published: October 2002

Radiation loading on a vibrating structure is best described through its radiation impedance. In the present work the modal acoustic radiation impedance load on an infinitely long cylindrical source harmonically excited in circumferentially periodic (axially independent) spatial pattern, while positioned concentrically within a fluid cylinder, which is embedded in a fluid-saturated unbounded elastic porous medium, is computed. This configuration, which is a realistic idealization of an acoustic logging tool suspended in a fluid-filled borehole within a permeable surrounding formation (White, J. E., 1983, Underground Sound Application of Seismic Waves, Elsevier, Amsterdam, Fig. 5.29, p. 183), is of practical importance with a multitude of possible applications in seismo-acoustics and noise control engineering. The formulation utilizes the Biot phenomenological model to represent the behavior of the sound in the porous, fluid-saturated, macroscopically homogeneous and isotropic surrounding medium. Employing the appropriate wave-harmonic field expansions and the pertinent boundary conditions for the given boundary configuration, a closed-form solution in the form of an infinite series is developed and the resistive and reactive components of modal radiation impedances are determined. A numerical example for a cylindrical surface excited in vibrational modes of various order, immersed in a water-filled cavity which is embedded within a water-saturated Ridgefield sandstone environment, is presented and several limiting cases are examined. Effects of porosity, frame stiffness, source size, and the interface permeability condition on the impedance values are presented and discussed.
Optical In-Situ Assessment of a Nonimaging Secondary Concentrator in a Solar Tower
Authors: Kribus Abraham , Timinger Andreas
Published: October 2002

A method for remote optical measurement of the geometry of nonimaging concentrators is presented. A concentrator installed in a solar tower was measured by observation of transmission patterns from the heliostat field, and comparison of the measured patterns to a ray tracing simulation. The actual geometry of the concentrator was derived from optimization of the match between real and simulated patterns. The measurement was sensitive and accurate enough to detect small errors in the concentrator geometry, such as 1 millimeter in linear dimension and 0.1° in concentrator tilt angle. The measurement procedure is simple and can be easily adapted to a wide range of nonimaging optical systems.
On an Elastic Circular Inhomogeneity With Imperfect Interface in Antiplane Shear
Authors: Schiavone P.
Published: October 2002

We develop a rigorous solution to the antiplane problem of a circular inhomogeneity embedded within an infinite isotropic elastic medium (matrix) under the assumption of nonuniform remote loading. The bonding at the inhomogeneity/matrix interface is assumed to be homogeneously imperfect. We examine both the case of a single circular inhomogeneity and the more general case of a three-phase circular inhomogeneity. General expressions for the corresponding complex potentials are derived explicitly in both the inhomogeneity and in the surrounding matrix. The analysis is based on complex variable methods. The solutions obtained demonstrate the effect of the prescribed nonuniform remote loading on the stress field within the inhomogeneity. Specific solutions are derived in closed form which are verified by comparison with existing solutions.
Analysis of a Three-Dimensional Crack Terminating at an Interface Using a Hypersingular Integral Equation Method
Authors: Qin T. Y. , Noda N. A.
Published: October 2002

Using a body force method and the finite-part integral concepts, a set of hypersingular integral equations for a vertical crack terminating at an interface in a three-dimensional infinite bimaterial subjected to arbitrary loads are derived. The stress singularity orders and singular stress fields around the crack front terminating at the interface are obtained by the main-part analytical method of hypersingular integral equations. Then, a numerical method for the solution of the hypersingular integral equations in case of a rectangular crack is proposed, in which the crack displacement discontinuities are approximated by the product of basic density functions and polynomials. Numerical solutions for the stress intensity factors of some examples are given.
Elastic-Plastic Contact Analysis of a Sphere and a Rigid Flat
Authors: Kogut L. , Etsion I.
Published: October 2002

An elastic-plastic finite element model for the frictionless contact of a deformable sphere pressed by a rigid flat is presented. The evolution of the elastic-plastic contact with increasing interference is analyzed revealing three distinct stages that range from fully elastic through elastic-plastic to fully plastic contact interface. The model provides dimensionless expressions for the contact load, contact area, and mean contact pressure, covering a large range of interference values from yielding inception to fully plastic regime of the spherical contact zone. Comparison with previous elastic-plastic models that were based on some arbitrary assumptions is made showing large differences.
Inception of Turbulence in the Stokes Boundary Layer Over a Transpiring Wall
Authors: Majdalani Joseph , Barron James , Van Moorhem William K.
Published: October 2002

In this work, the onset of turbulence inside a rectangular chamber is investigated, with and without side-wall injection, in the presence of an oscillatory pressure gradient. Two techniques are used to define the transition from laminar to turbulent regimes: statistical analysis and flow visualization. Calibrated hot film anemometry and a computer data acquisition system are used to record and analyze acoustical flow data. Four classifications of flow regimes are reported: (a) laminar, (b) distorted laminar, (c) weakly turbulent, and (d) conditionally turbulent. Despite numerous attempts to promote turbulence, a fully turbulent flow does not develop at any of the driving frequencies tested. Statistical measurements reveal that a periodic drop in standard deviation of axial velocity fluctuations always occurs, indicating relaminarization within each cycle. Transition between flow regimes is assessed from the standard deviation of velocity data correlated as a function of the acoustic Reynolds number ReA. Under predominantly laminar conditions, the standard deviation is found to vary approximately with the square of the acoustic Reynolds number. Under turbulent conditions, the standard deviation becomes almost directly proportional to the acoustic Reynolds number. Inception of turbulence in the oscillatory flow with side-wall injection is found to be reproducible at the same critical value of ReA≅200.
Residual and Applied Stress Estimation From Directional Magnetic Permeability Measurements With MWM Sensors
Authors: Zilberstein Vladimir , Fisher Mike , Grundy David , Schlicker Darrell , Tsukernik Vladimir , Vengrinovich Valeriy , Goldfine Neil , Yentzer Thomas
Published: October 2002

Conformable eddy current sensors with grid methods can provide an effective means for applied stress measurements and for characterization of residual stresses in steel components. This paper describes conformable MWM® (meandering winding magnetometer) sensors and high-resolution scanning MWM-Arrays for directional magnetic permeability measurements over a wide range of frequencies with grid methods. MWMs and MWM-Arrays are used for fatigue monitoring, crack detection, characterization of process-affected layers, including coatings, detection of surface-connected and hidden degradation, and damage characterization, e.g., detection and imaging of grinding burns. Tests have shown that these sensors can also provide the capability for residual/applied stress measurements in ferromagnetic materials, e.g., in steels. Specific examples described here illustrate this capability to estimate stresses in steels and other ferromagnetic materials from MWM measured permeability. Results of directional MWM permeability measurements, including permeability mapping, are presented here for (a) a 4340 steel specimen subjected to a series of tensile load tests with an incrementally increasing maximum load, (b) a broken 4340 tensile test specimen, (c) a shot-peened 300M steel specimen subjected to bending load tests, and (d) a shot-peened and subsequently ground high-strength steel component. Quick and inexpensive stress measurements at a point or, in a scanning mode, over a selected area are now becoming possible without permanently mounting sensors, albeit MWM sensors can be readily mounted, if needed, as well.
Coupling of Convective and Radiative Heat Transfer in PV Cooling Ducts
Authors: Brinkworth B. J.
Published: October 2002

In a PV cooling duct, heat transfer from the heated side to the cooling air flow takes place partly by convection at the walls and partly by radiation exchange between them. A method is developed for representing these effects in combination, avoiding the uncertainties and iterations involved in treating the two mechanisms as independent and parallel. Though the radiative element introduces two further parameters, the procedure has a straightforward closed form, convenient for routine engineering calculations. An approximation, that treats the radiation exchange as determined by the local wall temperatures, is validated by comparison with published results in which the diffusion due to the axial temperature distribution is fully represented. The method is applicable to both laminar and turbulent flows, employing coefficients already available in the literature. The incorporation of duct heat transfer within thermal models of the PV installation is discussed briefly, highlighting further areas which are being refined by on-going work.
New Model of a Basin-Type Solar Still
Authors: De Paul Irene
Published: October 2002

Thermal and productivity measurements and flow visualization experiences were performed on a real scale module of a basin type solar still, whose geometry and thermal conditions could be changed in a controlled way. The convective stage was studied with the aim of acquiring information about the nature of the medium inside it and the influence of different parameters over the productivity. Literature shows a great number of experimental and numerical works dealing with different aspects of the performance of solar stills: thermal losses, vapor losses, salt deposit on the tray, geometry, thermal inertia, etc. Few works are reported that take into account convective phenomena and the fluiddynamic characteristics of the medium inside the still. Most of these works are based on Dunkle’s and Copper’s models of the still that does not take into account the characteristics of the environment. A new physical model based on these experiments is presented.
Effect of H2 on the etch profile of InP/InGaAsP alloys in Cl2/Ar/H2 inductively coupled plasma reactive ion etching chemistries for photonic device fabrication
Authors: Rommel Sean L. , Jang Jae-Hyung , Lu Wu , Cueva Gabriel , Zhou Ling , Adesida Ilesanmi , Pajer Gary , Whaley Ralph , Lepore Allen , Schellanbarger Zane , Abeles Joseph H.
Published: October 2002

This study demonstrates etch profile engineering of InP, In1−xGaxAs1−yPy, and In0.53Ga0.47As heterostructures results from adding H2 to standard Cl2/Ar inductively coupled plasma-reactive ion etching chemistries. Etch rate curves of bulk InP, In1−xGaxAs1−yPy, and In0.53Ga0.47As show a general parabolic trend as a function of the H2 component of the Cl2/Ar/H2 ratio. Three distinct etching profiles of InP/InGaAsP layers were realized by varying the Cl2/Ar/H2 ratio. Highly anisotropic profiles result for Cl2/Ar/H2 ratios between 2/3/1 and 2/3/2. Waveguiding structures fabricated using this technology are presented with a loss as low as 2 dB/cm. An InP racetrack resonator with a quality factor (Q)>8000 is also presented.
Miniature fuel cells for portable power: Design considerations and challenges
Authors: Maynard Helen L. , Meyers Jeremy P.
Published: October 2002

We discuss key integration issues and engineering trade offs germane to all miniaturized fuel cell systems: thermal management, humidification control, water recirculation, air movement, fuel delivery, and power conditioning. We propose a design for a miniaturized protonexchange-membrane methanol-based fuel cell for powering 0.5–20 W portable telecommunication and computing devices. Our system is implemented on a silicon substrate to leverage advanced silicon processing and microelectromechanical systems technology enabling optimal fuel cell performance and minimizing production costs. We propose two alternative designs: a bipolar design using separate Si wafers for the anode and cathode and a monolithic design incorporating anode and cathode onto a single Si wafer.
Silicon dioxide film with lower deposition temperature in hot-wall, single-type chamber
Authors: Yoon Soosik , Park Haejin , Song Juho
Published: October 2002

A lower-temperature process for the deposition of silicon dioxide was developed in a hot-wall, single-type chamber, using a gaseous mixture of SiH4 and N2O. The deposition rate was measured as a function of deposition temperature, pressure, and SiH4/N2O flow-rate ratio. At fixed SiH4/N2O, two types of silicon dioxide, which had the same deposition rate, were deposited. One was deposited at low temperature (700 °C) and high pressure (20 Torr), and the other was deposited at high temperature (850 °C) and low pressure (2.5 Torr). The film characteristics of the two types of silicon dioxide were compared. The results revealed that the low-temperature film exhibited similar characteristics to those of the high-temperature film. Therefore, the current high-temperature process can be replaced by a low-temperature process to achieve low thermal budget in semiconductor device processing.