bluuebunny/crossref_metadata_2025 huggingface dataset:
A Computational Issue and Modified Formulas for Nonlinear Dissipative Controllers
Authors: Hu Shr-Shiung , Yang Pao-Hwa , Chang B. C.
Published: September 2003

Ball, Helton, and Walker (BHW) derived the nonlinear dissipative controller formulas with the assumption implying that no stable mode uncontrollable from the exogenous input. The assumption is more restrictive than that considered in DGKF. In this paper, we address the numerical difficulty encountered by BHW’s controller formulas when the assumption is not satisfied. Next, we propose a modified nonlinear dissipative controller and successfully remove the numerical difficulty. We also show that the linear version of the proposed controller formulas is identical to the DGKF H∞ controller. An example is given to demonstrate constructing the proposed controller and simulating the closed-loop pulse responses.
Filtering of Linear Systems With Unknown Inputs
Authors: Emara-Shabaik Hosam E.
Published: September 2003

State estimation of linear systems under the influence of both unknown deterministic inputs as well as Gaussian noise is considered. A Kalman like filter is developed which does not require the estimation of the unknown inputs as is customarily practiced. Therefore, the developed filter has reduced computational requirements. Comparative simulation results, under the influence of various types of unknown disturbance inputs, show the merits of the developed filter with respect to a conventional Kalman filter using disturbance estimation. It is found that the developed filter enjoys several practical advantages in terms of accuracy and fast tracking of the system states.
Output Feedback Linear Parameter Varying (LPV) L2-gain Control
Authors: Hong Boe-S. , Ray Asok , Yang Vigor
Published: September 2003

This brief paper synthesizes an output feedback L2-gain Control law for linear parameter varying (LPV) systems. The control law is embedded with an observer that does not require on-line measurements of the scheduling parameter variation rate. Results of simulation experiments are presented to evaluate the control law on a simulation experiments on a two-degree-of-freedom mass-spring-damper system.
Receding Horizon Stabilization of a Rigid Spacecraft With Two Actuators
Authors: Marchand Nicolas , Alamir Mazen
Published: September 2003

In this paper, a receding-horizon control, using systematic projection on a Chebyshev’s polynomial basis, is proposed for the stabilization of a rigid spacecraft operating with only two actuators. The proposed scheme privileges the speed of the algorithm. Simulations on SPOT4 spacecraft with a robustness test are provided.
Adaptive Parameter Identification of an Accurate Nonlinear Dynamical Model for Marine Thrusters
Authors: Bachmayer Ralf , Whitcomb Louis L.
Published: September 2003

Recently reported finite-dimensional nonlinear thruster models employing empirically determined lift–drag curves have been shown to accurately model both the transient and steady state response of marine thrusters. These reports have employed the standard off-line paradigm for model parameter identification: First, real-time sensor data (force, torque, fluid velocity) is logged in laboratory experiments. Second, the experimental data is analyzed with a least-square regression technique to complete a best fit for the model parameters. This paper reports an on-line technique for adaptive identification of model parameters for marine thrusters. The stability of the proposed technique is shown analytically. The performance of the on-line adaptive identification technique, evaluated with respect to an experimentally validated plant model, is shown to compare favorably to its off-line counterpart, but does not require the thrust and torque instrumentation required by conventional off-line least-squares parameter identification techniques.
On Frequency-Domain and Time-Domain Input Shaping for Multi-Mode Flexible Structures
Authors: Pao Lucy Y. , Cutforth Craig F.
Published: September 2003

The technique of input shaping has been successfully applied to the problem of maneuvering flexible structures without excessive residual vibration. Because a shaper is designed such that vibration is eliminated at the end of the shaped input, a short shaper length means that vibration is eliminated sooner. As different shaper design methods yield different shapers, it is advantageous to know how the shaper lengths of these different methods compare. In this paper we draw comparisons between time-domain input shaping methods and frequency-domain input shaping methods after outlining conditions when non-negative amplitude shapers exist when using frequency-domain methods.
Instability Due to Interacting Hydraulic and Mechanical Dynamics in Backhoes
Authors: Margolis Donald , Shim Taehyun
Published: September 2003

A backhoe is a tractor-like vehicle that has a hydraulically actuated bucket loader at the front and a hydraulically actuated backhoe shovel at the rear. The operator sits inside a canopy or cab that is mounted to the tractor chassis, and operates the hydraulic controls. The cab is typically isolated somewhat from the chassis using cab mounts. There are instances when the bucket is raised or lowered or wrapped that an instability of the entire machine is excited. In this mode, a frequency oscillation of the vehicle occurs and the operator is unable to keep his hands on the controls. This instability is investigated here and demonstrated through simulation. The instability described here is due to an interaction between the mechanical dynamics and hydraulic dynamics of the machine. All instabilities require an energy source, and, in this case, the energy comes from the fuel. It turns out that the hydro-mechanical interaction has positive feedback components and produces an instability. In order to expose the fundamental cause of the instability, a model is needed that allows the interaction of mechanical and hydraulic components. Bond graphs are a logical choice for development of the model. Bond graphs are a concise pictorial representation of the interactive dynamics of all types of energetic systems. They allow the model to be developed in pieces and then put together into an overall computational model. This procedure is demonstrated for the system here. The end result is a reasonably low order model that exposes the fundamental cause of the instability in backhoes. It also allows assessment of cures for the problem, some requiring redesign of components, and some requiring an automatic stabilization control system.
Fault Tolerant Control and Classification for Longitudinal Vehicle Control
Authors: Song Bongsob , Hedrick J. Karl , Howell Adam
Published: September 2003

In this paper, a new method of analyzing for the performance loss caused by faults in the systems is presented, and applied to the design of a fault tolerant longitudinal controller for a transit bus. Based on the amount of performance loss measured by a quadratic function, fault impact assessment is developed for both single and multiple faults. More specifically, ellipsoidal approximation of the tracking error bounds via dynamic surface control (DSC) is obtained via convex optimization technique for the nonlinear closed-loop system. Relying on the fault impact to the closed loop system and its isolatability on a fault detection and diagnosis system, the fault classification is proposed to provide a switching logic in the framework of a switched hierarchical structure. Finally, simulation results of the fault tolerant controller and corresponding fault classification are shown for multiple multiplicative faults.
Improved Vibration Isolating Seat Suspension Designs Based on Position-Dependent Nonlinear Stiffness and Damping Characteristics
Authors: Wan Yi , Schimmels Joseph M.
Published: September 2003

The design of seat suspensions having linear stiffness and damping characteristics involves a tradeoff between three performance measures. These measures are: (1) suspension range of motion, (2) improved average vibration isolation (weighted average across a wide exposure spectrum), and (3) improved isolation at the frequency of peak transmissibility. To overcome the limitations associated with this tradeoff, nonlinear mechanical properties are used here in the design of a seat suspension. From the infinite number of possible nonlinear mechanical characteristics, several possibilities that showed promise in previous studies were selected. The selected nonlinear force-deflection relationship (stiffness) of the seat is described by a combination of cubic and linear terms. The selected damping behavior of the seat is described by a combination of a linear term and a position-dependent term. A lumped parameter model (linear-human/nonlinear-seat) of the human/seat-suspension coupled system and a robust direct search routine are used to obtain pseudo-optimal values of the seat design parameters (mass, stiffness, and damping) via simulation in the time domain. Results indicate that the optimal nonlinear seat suspension is significantly better than the optimal linear seat suspension in overall vibration isolation characteristics.
Carrier Phase GPS-Aided INS-Based Vehicle Lateral Control
Authors: Farrell Jay A. , Tan Han-Shue , Yang Yunchun
Published: September 2003

This paper describes the design, analysis, and implementation of a vehicle control system using control state information obtained from a carrier phase (CP) differential global positioning system (DGPS) aided inertial navigation system (INS). Experimental data from CP DGPS/INS control experiments onboard a PATH1 vehicle is included. This testing was completed with a magnetometer sensing system onboard and running to provide a ground truth reference for comparison with the CP DGPS/INS. Navigation accuracy has previously been demonstrated at the cm level with the full navigation state updated at 150 Hz. In this article, lateral position control performance is demonstrated during challenging high-speed maneuvers with trajectory tracking accuracy at the decimeter level. During these initial experiments, the control state updated at 30 Hz. Increased trajectory following accuracy is possible, but there is an inherent tradeoff between the tracking accuracy and the ride comfort. This level of performance demonstrates that CP DGPS/INS technology has the potential to serve as one component of the reliable multisensor centimeter-level position reference system that is necessary for vehicle position control applications, including automated highway systems (AHS).
Practical Strategies for Controlling Railway Wheelsets Independently Rotating Wheels
Authors: Mei T. X. , Goodall R. M.
Published: September 2003

This paper presents the development of an active control strategy for railway vehicles with independently rotating wheels. The proposed control scheme is intuitively formulated with a simple control structure and adaptive to vehicle speed. It does not require basic guidance measurements (e.g., wheel-rail deflection and angle of attack) that are expensive and impractical to implement. Speed sensors are used to measure the relative rotational speed of the two wheels on a same axle and sensors are also used to measure the relative yaw velocity of the wheelset and the body it is connected. Both curving performance and passenger ride comfort of the actively controlled vehicle are compared with that of a typical passive vehicle and an optimal control scheme.
An Improved Acoustic Model for Active Noise Control in a Duct
Authors: Zimmer Benjamin J. , Lipshitz Stanley P. , Morris Kirsten A. , Vanderkooy John , Obasi Edmund E.
Published: September 2003

This paper presents a model of sound propagation in a duct, for the purpose of active noise control. A physical model generally different from those explored in much of the literature is derived, with non-constant acoustic load impedance at the one end, and a coupled disturbance loudspeaker model at the other end. Experimental results are presented which validate the derived transfer function.
Robust Position Control of an Electrohydraulic Actuator With a Faulty Actuator Piston Seal
Authors: Karpenko M. , Sepehri N.
Published: September 2003

The development of a fault tolerant control (FTC) strategy to compensate for the degrading effects of fluid leakage across a faulty actuator piston seal in an electrohydraulic positioning system is presented. Due to relatively large variations in the dynamics of the plant, accomplishing the FTC task with a single controller requires a compensator of relatively high gain. Hence, the problem is first reformulated by discretizing the desired range of fault tolerance into a number of distinct levels. Next, a set of low gain local controllers is synthesized via quantitative feedback theory, such that the resulting closed-loop systems all conform to a priori defined performance specifications. Each controller is designed to compensate for a specific level of leakage. A simple switching algorithm is then employed to determine the appropriate control action by scaling each controller’s output based upon an estimate of the leakage level. Experimental results illustrate the ability of the designed FTC scheme to compensate for the degrading effect of the leakage fault.
Analysis of Electromagnetic Nonlinearities in Stage Control of a Stepper Motor and Spool Valve
Authors: Burton Rich , Ruan Jian , Ukrainetz Paul
Published: September 2003

In digital valves, stepper motors are often used as the electro-to-mechanical interface. To sustain both high speed of response and good quantitative accuracy, a special algorithm has been designed to control the stepper motor to produce a continuous rotary displacement. Since in this algorithm the current to each coil is cyclic as the rotor tooth advances, several cycles can be used to achieve the desired angular displacement of the motor. This process can result in a reduction or “scaling down” of magnetic nonlinearities such as hysteresis and saturation. This cyclic algorithm has been defined as “stage control” because the algorithm need only be developed for one stage and then repeated when applied to subsequent stages. Critical to the development and understanding of the algorithm is an accurate model of the electromagnetic saturation and hysteresis which exist between the input current and output torque. In this paper, a special mathematical formulation is developed to simulate magnetic saturation and hysteresis which can be applied to a more generic situation. The mathematical formulation derived is one in which hysteresis and saturation parameters are established; an error rate of both saturation and hysteresis is defined from this. Since the error rates are easily determined experimentally or through manufacturers’ specifications, the parameters can be found from these mathematical formulations. The parameters can then be used to predict the hysteresis and saturation characteristics. Special experiments are designed to obtain the input-output characteristics of a stepper motor/valve system under single and multistage control. The model follows the experimental results reasonably well and can be used with confidence to model any system with hysteresis and saturation. The model also predicts very well the effects of using stage control in reducing hysteresis and saturation in a practical valve.
Practical Considerations for Setting Up A Virtual Reality System for Virtual Prototyping
Authors: De Kroon Joseph P. , Bras Bert
Published: September 2003

As smaller companies in a wider range of industries seek to implement virtual reality (VR) in their product development cycles, they are presented with a wide range of choices for commercial off-the-shelf hardware and software components that make up a virtual reality system. In this article, results and learning from efforts in an industry project (as well as from our continued work in this field of research) are shared, which are expected to be of practical use for the engineer in industry or researcher in academia who wishes to use VR for virtual prototyping. Some findings are presented about what VR is and is not, and advice is provided about selecting a candidate application and selecting VR system components, suggesting a list of criteria by which VR system components may be compared and selected.
Local Heat Transfer Characteristics in Simulated Electronic Modules
Authors: Yoo Seong-Yeon , Park Jong-Hark , Chung Min-Ho
Published: September 2003

When heat is released by forced convection from electronic modules in a narrow printed circuit board channel, complex flow phenomena—such as stagnation and acceleration on the front surface, separation and reattachment on the top surface, wake or cavity flow near the rear surface—affect the heat transfer characteristics. The purpose of this study is to investigate how these flow conditions influence the local heat transfer from electronic modules. Experiments are performed on a three-dimensional array of hexahedral elements as well as on a two-dimensional array of rectangular elements. Naphthalene sublimation technique is employed to measure three-dimensional local mass transfer, and the mass transfer data are converted to their counterparts of the heat transfer process using the analogy equation between heat and mass transfer. Module location and streamwise module spacing are varied, and the effect of vortex generators on heat transfer enhancement is also examined. Dramatic change of local heat transfer coefficients is found on each surface of the module, and three-dimensional modules have a little higher heat transfer value than two-dimensional modules because of bypass flow. Longitudinal vortices formed by vortex generator enhance the mixing of fluids and thereby heat transfer, and the rectangular wing type vortex generator is found to be more effective than the delta wing type vortex generator.
A Simplified Conduction Based Modeling Scheme for Design Sensitivity Study of Thermal Solution Utilizing Heat Pipe and Vapor Chamber Technology
Authors: Prasher Ravi S.
Published: September 2003

This paper introduces a simplified modeling scheme for the prediction of heat transport capability of heat pipes and vapor chambers. The modeling scheme introduced in this paper enables thermal designers to model heat pipes and vapor chambers in commercially available conduction modeling tools such as Ansys™ and IcePak™. This modeling scheme allows thermal designers to perform design sensitivity studies in terms of power dissipation of heat pipes and vapor chambers for different scenarios such as configurations, heat sink resistance for a given temperature drop between the heating source and the ambient. This paper also discusses how thermal designers can specify requirements to heat pipe/vapor chamber suppliers for their thermal design, without delving into the complete thermo-fluidic modeling of this technology.
Interfacial Stress Analysis and Fracture of a Bi-Material Strip With a Heterogeneous Underfill
Authors: Park Ji Eun , Jasiuk Iwona , Zubelewicz Aleksander
Published: September 2003

Flip chip assemblies used in electronic packaging consist of three main components (layers): chip, underfill, and substrate. In this paper, the flip chip assembly is represented as a bi-material strip consisting of the chip and underfill. Our analysis is focused on delamination along the chip-underfill interface due to thermal loading. The underfill is modeled as a composite material made of a polymer matrix and silica particles. Interfacial stresses are studied for several particle configurations: cases of one, two, or three particles near the interface and 30 different random particle arrangements. Interfacial fracture is investigated by evaluating the J integral and stress intensity factors. Statistics of random particle arrangements in the underfill are also discussed. The interfacial stress and fracture analyses give the same trends.
Parametric Modeling of Part Family Machining Process Plans From Independently Generated Product Data Sets
Authors: Huang Zhengdong , Yip-Hoi Derek
Published: September 2003

Parametric modeling has become a widely accepted mechanism for generating data set variants for product families. These data sets include geometric models and feature-based process plans. They are created by specifying values for parameters within feasible ranges that are specified as constraints in their definition. These ranges denote the extent or envelope of the product family. Increasingly, with globalization the inverse problem is becoming important: Given independently generated product data sets that on observation belong to the same product family, create a parametric model for that family. This problem is also of relevance to large companies where independent design teams may work on product variants without much collaboration only to later attempt consolidation to optimize the design of manufacturing processes and systems. In this paper we present a methodology for generating a parametric representation of the machining process plan for a part family through merging product data sets generated independently from members of the family. We assume that these data sets are feature-based machining process plans with relationships such as precedences between the machining steps for each feature captured using graphs. Since there are numerous ways in which these data sets can be merged, we formulate this as an optimization problem and solve using the A* algorithm. The parameter ranges generated by this approach will be used in the design of tools, fixtures, material handling automation and machine tools for machining the given part family.
Dependence of Thermal Conductivity and Mechanical Rigidity of Particle-Laden Polymeric Thermal Interface Material on Particle Volume Fraction
Authors: Prasher Ravi S. , Koning Paul , Shipley James , Devpura Amit
Published: September 2003

This paper reports the measurement of the thermal conductivity of particle-laden polymeric thermal interface materials for three different particle volume fractions. The experimental data are further compared with the percolation model and effective medium theory. We then introduce a method of obtaining the contact resistance between the particles and the polymeric matrix by a combination of percolation modeling and experimental data. We also discuss the dependence of the mechanical response of these particle-laden polymers for different filler or particle loading. A novel mechanical length scale is defined to understand the mechanical response of these materials, and is correlated to the viscosity of these materials.
Failure Analysis of Full Delamination on the Stacked Die Leaded Packages
Authors: Lin T. Y. , Xiong Z. P. , Yao Y. F. , Tok Lane , Yu Z. Y. , Njoman Budi , Chua K. H. , Ma Y. Y.
Published: September 2003

There has been significant demand for stacked die technology during the past few years. The stacked die devices are mainly used in portable consumer products. This kind of silicon integration technology provides flexibility in space reduction, weight savings, and excellent electrical functionality. In this article, the stacked die construction was built into the leaded package. It was found that the test vehicles had full delamination at the lead-frame paddle/mold compound interface after 100 temperature cycles (−65°C to 150°C) with moisture preconditioning at level 3 (60°C at 60% relative humidity for 40 h) although the electrical test passed 1000 temperature cycles. The fishbone diagram was used to identify the possible failure root causes. The material, process, and design factors were extensively evaluated by the experiments and finite element analysis. The evaluation results showed that die attach paste voids were major factors affecting the package integrity and could produce the delamination initiation at the edge of the die attach paste and propagate down to the lead-frame paddle/mold compound interface due to high stress concentration and weak adhesion strength. The finite element analyses were implemented to address the stress distribution in the stacked die package and verified by the scanning acoustic microscope. It demonstrated that excellent package integrity could be obtained by applying the void-free die attach paste and improving the adhesion strength at the lead-frame paddle level.
Delamination and Encapsulant Resin Cracking in LSI Plastic Packages Subjected to Temperature Cyclic Loading
Authors: Saitoh Takehiro , Matsuyama Hidehito , Toya Masayuki
Published: September 2003

Using Kr85 radioactive tracer techniques, initial sites of edge delaminations occurring during temperature cyclic tests in large-scale integrated circuit (LSI) plastic packages with either Cu alloy or alloy 42 leadframes are experimentally identified. Based on the experimental results, the processes of delamination growth and subsequent resin cracking are clarified. The effect of the length of the delaminations on the resin cracking is numerically analyzed on the basis of the linear fracture mechanics approach combined with finite element calculations. The directions of resin cracking predicted from the analysis are found to agree well with those of actual packages.
Coarsening in BGA Solder Balls: Modeling and Experimental Evaluation
Authors: Basaran Cemal , Wen Yujun
Published: September 2003

The reliability of solder joints in electronic packaging is becoming more important as the ball grid array (BGA) develops rapidly into the most popular packaging technology. Thermal fatigue of solder joints has been a reliability concern in the electronic packaging industry since the introduction of surface mount technology (SMT). Microstructural coarsening (phase growth) is considered to be closely related to thermomechanical fatigue failure. Many researchers proposed coarsening models for bulk scale metals. But these models have never been verified for micron-scale actual BGA solder balls. In the present study, three different phase growth models are investigated experimentally on BGA solder balls in a real-life electronic package. Model simulations obtained from three models were compared against test data. The best performing model was chosen for finite element fatigue reliability studies based on continuum damage mechanics.
Pumpless Loop for Narrow Channel and Micro-Channel Boiling
Authors: Mukherjee Swaraj , Mudawar Issam
Published: September 2003

A compact cooling system is examined which capitalizes upon fluid density differences between two vertical, parallel, interconnected tubes to achieve a pumpless cooling loop. A heat-dissipating device is incorporated into a boiler at the bottom of the hot tube. The large density differences between the two tubes produces a substantial nonequilibrium in hydrostatic pressure, drawing liquid downwards through the cold tube as a two-phase mixture is released upwards in the hot tube. Cooling with this pumpless loop is fundamentally different from, and far superior to, pool boiling thermosyphons because of the former’s ability to separate the path of replenishment liquid from that of the released vapor. Experiments were performed to explore the effects of boiler gap (separation distance between the boiling surface and opposite insulating wall) on cooling performance and critical heat flux (CHF) for water and FC-72. The gap, which is the primary measure of boiler miniaturization, was varied from 0.051 to 21.46 mm. For large gaps, CHF showed insignificant dependence on the gap for both fluids. However, small gaps produced CHF variations that were both drastic and which followed opposite trends for the two fluids. Decreasing the gap below 3.56 mm produced a substantial rise in CHF for FC-72. For water, CHF was fairly insensitive down to 0.51 mm, below which it began to decrease sharply. These trends are shown to be closely related to the small surface tension and contact angle of FC-72 producing very small bubbles which can easily pass through narrow gaps in FC-72, while much larger bubbles in water obstruct liquid replenishment in narrow gaps. A numerical model is constructed to determine how the gap influences the various components of pressure drop, velocities, coolant flow rate, and hence system response to heat input.
Comparison Between the Standard and Staggered Layout for Cooling Fins in Forced Convection Cooling
Authors: Leon Octavio , De Mey Gilbert , Dick Erik , Vierendeels Jan
Published: September 2003

The performance of an array of staggered and nonstaggered cooling fins is compared, looking not only into the traditional objective of maximum heat transfer flux, but also to obtain it with the minimum flow resistance. Three different models were studied to obtain the ratio between the heat removed and the energy spent for the coolant flow going through the cooling fins. The study is done numerically using the computational fluid dynamic software FLUENT. The results show the advantages of the staggered model compared to the standard model since for a given incoming velocity, the use of a staggered heat sink always leads to a maximization of the heat transfer flux. The significant positive difference in the thermal performance of the staggered model permits the reduction of the incoming velocity with the consequent reduction in the pressure drop, and power consumption. The authors consider this research as a quite interesting approach as compared to other research where the flow resistance has not been taken into account.
A Reverse Glue Approach to Automated Construction of Multi-Piece Molds
Authors: Chen Yong , Rosen David W.
Published: September 2003

Mold design can be a difficult, time-consuming process. Determining how to split a mold cavity into multiple mold pieces (e.g., core, cavity) manually can be a tedious process. This paper focuses on the mold construction step of the automated mold design process. By investigating glue operations and its relations with parting faces, an approach based on a new reverse glue operation is presented. The key to the reverse glue operation is to generate parting faces. A problem definition of parting face generation for a region is provided. Correspondingly, three face generating criteria are identified. Based on the parting lines of a region, our algorithms to generate the parting faces are presented. Our mold construction algorithms for two-piece molds and multi-piece molds are also presented with brief discussions. Some industrial examples are provided which illustrate the efficiency and effectiveness of our approach. We tested our mold designs by fabricating stereolithography mold inserts (a rapid tooling method) and molding parts.
Thin-Wall Calculation for Layered Manufacturing
Authors: McMains Sara , Smith Jordan , Se´quin Carlo
Published: September 2003

We describe a new algorithm for making partially hollow layered parts with thin, dense walls of approximately uniform thickness, for faster build times and reduced material usage. We have implemented our algorithm and tested its output on a fused deposition modeling (FDM) machine, using separate build volumes for a loosely filled interior and a thin, solid, exterior wall. The build volumes are derived as Boolean combinations of slice contours and their offsets. The Booleans are efficiently calculated via OpenGL winding number rules and the offset contours are generated from robustly generated Voronoi diagrams of the slices. Our algorithm guarantees that the exterior surface of the final part will be of high quality with no gaps while still allowing an efficient build.
Feature-Based Optimization of Beam Structures Represented by Polygonal Meshes
Authors: Shen Jie
Published: September 2003

In this paper, a new shape optimization approach, feature-based optimization of beam structures, is proposed to provide an efficient optimization solution of beam components in complex mechanical structures represented by polygonal meshes. Our approach consists of two main steps: 1) feature recognition of beam components: 2) gradient-based shape optimization of these components by reducing a weighted compliance among all load cases. The main contribution is to propose a new scheme to automate time-consuming shape optimization processes on polygonal meshes with beam components. Numerical experiments have been conducted and the results indicate the effectiveness of the approach.
Algorithms for Computing Global Accessibility Cones
Authors: Dhaliwal Savinder , Gupta Satyandra K. , Huang Jun , Priyadarshi Alok
Published: September 2003

This paper describes algorithms for computing global accessibility cones for each face (i.e., the set of directions from which faces are accessible) on a polyhedral object. We describe exact mathematical conditions and the associated algorithm for determining the set of directions from which a planar face with triangular boundary is inaccessible due to another face on the object. By utilizing the algorithm to compute the exact inaccessibility region for a face, we present algorithms for computing global accessibility cones for each face on the object. These global accessibility cones are represented as a matrix structure and can be used to support a wide variety of accessibility queries for the object.
Geometric and Kinetic Model Based Computer-Aided Fixture Design Verification
Authors: Kang Y. , Rong Y. , Yang J. A.
Published: September 2003

Computer-aided fixture design (CAFD) techniques have advanced to the point that fixture configurations can be generated automatically, for both modular fixtures and dedicated fixtures. Computer-aided fixture design verification (CAFDV) is a technique for verifying and improving existing fixture designs. This paper introduces a first comprehensive CAFDV framework which uses both geometric and kinetic models to verify locating completeness, locating accuracy, and fixturing stability. The models can be also used for locating tolerance assignment and the determination of minimum clamping force required in machining operations. The system is integrated with commercial CAD package and applied in industrial real-cases.
Shape Analysis and Parameterized Modeling of Hip Joint
Authors: Xi Juntong , Hu Xin , Jin Ye
Published: September 2003

This paper presented a new method of shape analysis of hip joint. The bony surfaces of 12 male hipbone specimens and 26 female hipbone specimens were scanned using a 3D laser scanner. After performing local and global morphology analyses on the acetabulum surface, a rotation ellipsoid CAD model was applied to fit the acetabulum surface, and then an optimization technique was used to find the geometric parameters of the model. This study compared the fitting error between the sphere and rotation ellipsoid. The result is that the fitting error of rotation ellipsoid is smaller than the sphere, and the rotation ellipsoid can describe the shape of the acetabulum better. This shape likely decreases the cases of hip joint subluxation compared to a ball and socket joint.
Fractals in the Classroom
Authors: Knutson Paul , Dahlberg E. Dan
Published: September 2003

In examples of fractals such as moon craters,1 rivers,2 cauliflower,3 and bread,4 the actual growth process of the fractal object is missed. In the simple experiment described here, one can observe and record the growth of calcium carbonate crystals — a ubiquitous material found in marble and seashells — in real time. The video frames can be digitized and analyzed to determine the fractal dimension.
Rectangles in Physics
Authors: Spartalian Kevork
Published: September 2003

In a recent article,1 Greenslade presents a nomograph from an old textbook describing a geometrical construction for the equivalent resistance of two resistors in parallel. Greenslade's final remark is that the motivation for this construction “is obscure.” When I saw the article, I realized I could make an educated guess for the motivation. In this paper I will use the nomograph discovered by Greenslade as a springboard and present some of my thoughts on the geometrical presentation of physics in hopes to amuse the experts.
Teaching Measurement in the Introductory Physics Laboratory
Authors: Allie Saalih , Buffler Andy , Campbell Bob , Lubben Fred , Evangelinos Dimitris , Psillos Dimitris , Valassiades Odysseas
Published: September 2003

Traditionally physics laboratory courses at the freshman level have aimed to demonstrate various principles of physics introduced in lectures. Experiments tend to be quantitative in nature with experimental and data analysis techniques interwoven as distinct strands of the laboratory course.1 It is often assumed that, in this way, students will end up with an understanding of the nature of measurement and experimentation. Recent research studies have, however, questioned this assumption.2,3 They have pointed to the fact that freshmen who have completed physics laboratory courses are often able to demonstrate mastery of the mechanistic techniques (e.g., calculating means and standard deviations, fitting straight lines, etc.) but lack an appreciation of the nature of scientific evidence, in particular the central role of uncertainty in experimental measurement. We believe that the probabilistic approach to data analysis, as advocated by the International Organization for Standardization (ISO), will result in a more coherent framework for teaching measurement and measurement uncertainty in the introductory physics laboratory course.
System Schemas
Authors: Turner Lou
Published: September 2003

In studying Newton's laws, most teachers expect their students to be able to construct a free-body diagram that shows each of the forces that act on an object whose motion they want students to analyze. However, many students frequently cannot identify the correct number of forces that act on the object, or, having decided that a particular force should be added to the diagram, they cannot accurately identify what object exerts that force. In addition, many students have difficulty implementing Newton's third law and correctly identifying action-reaction pairs of forces as well as internal and external forces. In general students do not have an organized process for creating an abstract free-body diagram given a concrete physical situation. They make educated guesses without any way of knowing if what they have done is correct. The purpose of this article is to describe a tool that has been found to be valuable in helping students address each of these problems.
Gravitational Force Due to a Sphere: A Noncalculus Calculation
Authors: Ruby Lawrence
Published: September 2003

In teaching noncalculus physics, an instructor is tempted to introduce an occasional formula with the explanation, “This formula is easily proved through the use of calculus.” This rabbit-from-the-hat approach is regrettable from the standpoint that physics should be presented as a logical development of experiment and theory. Yet, from the experience of this author, it is very rare that a student will object to the explanation quoted above. Nevertheless, an instructor should be prepared with a noncalculus justification if so challenged, and in most instances such is available. For example, the areas, volumes, and moments of inertia of simple geometric figures can be calculated by means of The Method of Exhaustion developed by Archimedes.1 The purpose of this paper is to treat two theorems that are important in introductory physics, and that cannot be established by such a method. Instead, we shall provide an alternative justification. However, we anticipate that students will be satisfied to hear only a description of the methods used in the calculations and of the final results.
Physics Was Once First and Was Once for All
Authors: Sheppard Keith , Robbins Dennis M.
Published: September 2003

The analysis of historical trends in science education can provide valuable insights for future reforms. Yet, despite their potential, such studies are rare.2 An increasingly significant reform effort in physics education is the push to reverse the sequence in which the sciences are taught in high school — the Physics First movement. This reform effort gained considerable momentum recently when the AAPT issued a statement promoting Physics for All.3 Is there anything we can learn from the past that might inform the Physics First/Physics for All debate? A recent article in this journal4 outlined the historical development of the Biology-Chemistry-Physics (B-C-P) science sequence and its impact on enrollment, time allocation, methodology, and status of physics in the high school curriculum. Further analysis of the history of the B-C-P sequence shows that surprisingly physics was once first and was once for all in U.S. high schools. So what happened? How and why did the sequence change? This article describes how science course offerings and enrollment at different grade levels have evolved from 1890 to the present day. The factors behind these changes are analyzed, and the implications for physics education are discussed with the intent of using the past to inform the future.
A Demonstration Seasonal “Thermocline”
Authors: Heavers Richard M. , Bayly Tara E.
Published: September 2003

The variation of water temperature in the top-most 100 meters of the deep ocean depends on the annual cycle of heating and cooling of the surface water and on mixing by the wind. Here we describe a laboratory model that uses salt instead of heat to produce density differences and that helps us to understand how the ocean's temperature structure changes with the seasons.
Projectile Motion Model
Authors: Cordry Sean
Published: September 2003

Textbooks almost always have a stroboscopic photograph of a ball falling alongside of one with an initial horizontal speed. These photos are great for showing how the two objects experience the same vertical acceleration; however, the photos don't usually illustrate what happens if a projectile is launched at some angle. There are a number of ways to illustrate the effects of the launch angle: shooting a ball or stream of water through hoops, for example.1 Those demonstrations, though, do not allow for side-by-side comparison of the effects of various launch angles. Thus, a few years ago I constructed this three-dimensional projectile model to do just that. The model is composed of two three-dimensional “stroboscopic sculptures” representing the trajectory of two projectiles.
Hidden Amplifier for a Galvanometer
Authors: Weichman Frank
Published: September 2003

We often do demonstrations at local schools that require the use of a sensitive galvanometer. For example, we show that a thermocouple responds to warm fingers and will respond with opposite polarity to cool water. In years past we brought along a Pye galvanometer, which had adequate sensitivity for the purpose but which suffered from drift due to ambient temperature changes (cold car to warm classroom) and slow response time. There are of course many digital instruments available with adequate sensitivity, but for a classroom setting with 20 to 30 itchy children, an analogue device is preferable to a fluctuating digital output.
When Is a Good Day Teaching a Bad Thing?
Authors: Slater Timothy F.
Published: September 2003

Tim Slater is an associate professor of astronomy and the director of the Science and Mathematics Education Center at the University of Arizona, where his scholarship is focused on the teaching and learning of astronomy and preservice science teacher education.
Bidirectional Transmembrane Signaling by Cytoplasmic Domain Separation in Integrins
Authors: Kim Minsoo , Carman Christopher V. , Springer Timothy A.
Published: September 2003

Although critical for development, immunity, wound healing, and metastasis, integrins represent one of the few classes of plasma membrane receptors for which the basic signaling mechanism remains a mystery. We investigated cytoplasmic conformational changes in the integrin LFA-1 (α
L
β
2
) in living cells by measuring fluorescence resonance energy transfer between cyan fluorescent protein–fused and yellow fluorescent protein–fused α
L
and β
2
cytoplasmic domains. In the resting state these domains were close to each other, but underwent significant spatial separation upon either intracellular activation of integrin adhesiveness (inside-out signaling) or ligand binding (outside-in signaling). Thus, bidirectional integrin signaling is accomplished by coupling extracellular conformational changes to an unclasping and separation of the α and β cytoplasmic domains, a distinctive mechanism for transmitting information across the plasma membrane.
A Zinc Clasp Structure Tethers Lck to T Cell Coreceptors CD4 and CD8
Authors: Kim Peter W. , Sun Zhen-Yu J. , Blacklow Stephen C. , Wagner Gerhard , Eck Michael J.
Published: September 2003

The T cell coreceptors CD4 and CD8 both associate via their cytoplasmic tails with the N-terminus of the Src-family tyrosine kinase Lck. These interactions require zinc and are critical for T cell development and activation. We examined the folding and solution structures of ternary CD4-Lck-Zn
2
+
and CD8α-Lck-Zn
2
+
complexes. The coreceptor tails and the Lck N-terminus are unstructured in isolation but assemble in the presence of zinc to form compactly folded heterodimeric domains. The cofolded complexes have similar “zinc clasp” cores that are augmented by distinct structural elements. A dileucine motif required for clathrin-mediated endocytosis of CD4 is masked by Lck.
Demography of Dietary Restriction and Death in
Drosophila
Authors: Mair William , Goymer Patrick , Pletcher Scott D. , Partridge Linda
Published: September 2003

Dietary restriction (DR) increases life-span in organisms from yeast to mammals, presumably by slowing the accumulation of aging-related damage. Here we show that in
Drosophila
, DR extends life-span entirely by reducing the short-term risk of death. Two days after the application of DR at any age for the first time, previously fully fed flies are no more likely to die than flies of the same age that have been subjected to long-term DR. DR of mammals may also reduce short-term risk of death, and hence DR instigated at any age could generate a full reversal of mortality.
Amazonia 1492: Pristine Forest or Cultural Parkland?
Authors: Heckenberger Michael J. , Kuikuro Afukaka , Kuikuro Urissapá Tabata , Russell J. Christian , Schmidt Morgan , Fausto Carlos , Franchetto Bruna
Published: September 2003

Archaeology and indigenous history of Native Amazonian peoples in the Upper Xingu region of Brazil reveal unexpectedly complex regional settlement patterns and large-scale transformations of local landscapes over the past millennium. Mapping and excavation of archaeological structures document pronounced human-induced alteration of the forest cover, particularly in relation to large, dense late-prehistoric settlements (circa 1200 to 1600 A.D.). The findings contribute to debates on human carrying capacity, population size and settlement patterns, anthropogenic impacts on the environment, and the importance of indigenous knowledge, as well as contributing to the pride of place of the native peoples in this part of the Amazon.
Resurrecting the Ancestral Steroid Receptor: Ancient Origin of Estrogen Signaling
Authors: Thornton Joseph W. , Need Eleanor , Crews David
Published: September 2003

Receptors for sex and adrenal steroid hormones are absent from fully sequenced invertebrate genomes and have not been recovered from other invertebrates. Here we report the isolation of an estrogen receptor ortholog from the mollusk
Aplysia californica
and the reconstruction, synthesis, and experimental characterization of functional domains of the ancestral protein from which all extant steroid receptors (SRs) evolved. Our findings indicate that SRs are extremely ancient and widespread, having diversified from a primordial gene before the origin of bilaterally symmetric animals, and that this ancient receptor had estrogen receptor–like functionality. This gene was lost in the lineage leading to arthropods and nematodes and became independent of hormone regulation in the
Aplysia
lineage.