bluuebunny/crossref_metadata_2025 huggingface dataset:
Modelling and Control of a Manipulator With Hydraulic Actuators
Authors: Liu Y. , Handroos H.
Published: May 2008

Modelling and control for a large-scale manipulator, the structure of which is a three-link manipulator with hydraulic actuators is studied in the presented paper. Firstly, a numerically efficient simulation model is set up for the purpose of real time and control application. Secondly, a control using sliding mode is developed to exploit the full potential of the hydraulic manipulator. In order to design sliding mode control to track a trajectory of the end effector in task space directly, it is necessary to build a mapping between the joint space coordinate to the task space. To demonstrate the control performance, Proportional control is used for simulation to compare with SMC, and the experimental results are also given.
Design and Fabrication of a High Efficiency Piezoelectric Vibration-Induced Micro Power Generator
Authors: Wang Gou-Jen , Lin Ying-Hsu , Yang His-Harng , Pan Cheng-Tang
Published: May 2008

To fulfill the increasing self-power demanding of the embedded and remote microsystems, theoretical and experimental study of a piezoelectric vibration-induced micro power generator that can convert mechanical vibration energy into electrical energy is presented. A complete energy conversion model regarding the piezoelectric transducer is discussed first. To verify the theoretical analysis, two clusters of transducer structures are fabricated. The piezoelectric lead zirconate titanate (PZT) material that has better energy conversion efficiency among the piezoelectric materials is chosen to make of the energy conversion transducer. The desired shape of the piezoelectric generator with its resonance frequency in accordance with the ambient vibration source is designed by finite element analysis (FEA) approach. Conducting wires and load resistor are soldered on the electrodes to output and measure the vibration induced electrical power. Experimental results shows that the maximum output voltages are generated at the first mode resonance frequencies of the structure. It is also found from the experimental results that the induced voltage is irrelevant to the width of the structure but is inverse proportion to the length of the structure. It takes 7 minutes to charge a 10,000 μF capacitors array to a 7 V level. The total amount of electricity and energy stored in the capacitors are 0.7 Coulomb and 0.245 J, respectively. The experimental results are coincidence with the theoretical analysis.
Modeling Gait Transitions Between Two Periodic Gaits for Quadrupeds and Hexapods
Authors: Lin Jian-Nan , Song Shin-Min
Published: May 2008

Gait study is important to the development of a practical legged robot. While many works of gait study have been presented in the past, gait transition between two gaits has not been fully studied. In this paper, an approach to formulate gait transition between two periodic gaits and between a wave gait and a continuous follow-the-leader (FTL) gait is developed for quadrupeds and hexapods. Special foot placement conditions such as the FTL feature during the transition cycle can be included in the formulation process. This approach can be extended to formulate gait transition between other gaits.
Risk-Based Analysis and Decision Making in Multi-Disciplinary Environments
Authors: Feather Martin S. , Cornford Steven L. , Moran Kelly
Published: May 2008

A risk-based decision-making process conceived of and developed at JPL and NASA, has been used to help plan and guide novel technology applications for use on spacecraft. These applications exemplify key challenges inherent in multidisciplinary design of novel technologies deployed in mission-critical settings: 1) Cross-disciplinary concerns are numerous (e.g., spacecraft involve navigation, propulsion, telecommunications). These concerns are cross-coupled and interact in multiple ways (e.g., electromagnetic interference, heat transfer). 2) Time and budget pressures constrain development, operational resources constrain the resulting system (e.g., mass, volume, power). 3) Spacecraft are critical systems that must operate correctly the first time in only partially understood environments, with no chance for repair. 4) Past experience provides only a partial guide: New mission concepts are enhanced and enabled by new technologies, for which past experience is lacking. The decision-making process rests on quantitative assessments of the relationships between three classes of information-objectives (the things the system is to accomplish and constraints on its operation and development), risks (whose occurrence detracts from objectives), and mitigations (options for reducing the likelihood and/or severity of risks). The process successfully guides experts to pool their knowledge, using custom-built software to support information gathering and decision-making.
Unsteady RANS Simulation of Turbulent Flow and Heat Transfer in a Channel With Periodic Array of Cubic Pin-Fins
Authors: Saha A. K. , Acharya Sumanta
Published: May 2008

An unsteady three-dimensional numerical study is performed to explore flow and heat transfer in a periodic array of cubic pin-fins housed inside a narrow channel. Short cubic pin-fins are arranged in an inline pattern with both streamwise and transverse periodicity set to 2.5 times the pin-fin dimension. Calculations are done in the turbulent flow regime for Reynolds numbers in the range of 7090–13280. The unsteady Reynolds-Averaged Navier Stokes (RANS) and energy equations are solved using higher order temporal and spatial discretization schemes. An unsteady k-ε turbulence model is employed to model the unresolved turbulence fluctuations. The unsteady RANS results are able to resolve discrete large scale spatial and temporal fluctuations in the flow. These fluctuations appear to mostly influence the flow in the region between the cubic fins, but are linked to low amplitude oscillations in the outer flow. Three thermal boundary conditions are studied: (1) only channel wall heated (2) only pin-fins heated and (3) both channel wall and pin-fins heated. The overall heat transfer enhancement is about 1.8–2.0 times the heat transfer from a smooth duct flow. The heat transfer from pin-fins is found to be 5–9% higher than that from the top wall at low Reynolds number (7090 and 8900), while it is of comparable magnitude at higher Reynolds number (=13280).
Common Components of Human Error in Design, Maintenance, or Operations
Authors: Balkey Joseph P.
Published: May 2008

Often, public reports of accidents only identify the last, obvious failure or immediate cause of the accident. If human error is the immediate cause or final failure, further assessment of accident contributors may stop, and an enhanced training program is often determined to be the primary solution for preventing further accidents of this type. However, in many cases, the accident is the final result of many inputs, decisions, actions and inactions. To demonstrate this characteristic of accidents, the 20 stories in a publication titled “Set Phasers on Stun” have been categorized into action errors and planning errors that involve designers, mechanics, or operators. For each story, the hazard and the number of simultaneous failures are listed. Then two of the 20 stories are assessed in detail; one story involves an action error and the other one involves a planning error. In each of these two stories, the system is first described as it should operate and then its risk is quantitatively assessed to identify findings, lessons learned, recommendations, analogies to the other 18 stories, and applications. This paper has three immediate goals. One, to recognize the difference between an action error and a planning error. Two, to recognize that most accidents involve 2 to 4 simultaneous failures. Three, to appreciate that quantifying the failure frequency serves two benefits. Because it is usually difficult to find out exactly what happened after an accident, the calculated frequency can help confirm what actually happened. When various alternatives are recommended, it can also help to select the most economic ones. This paper has two long term goals. One, consider assessing the failure rates of near misses. By reducing near misses, larger accidents will be reduced. Two, consider assessing the failure rates of personal near misses because you know what actually happened.
Design and Control of a 6-DOF Positioner With High Precision
Authors: Kim Wong-Jong , Hu Tiejun , Bhat Nikhil
Published: May 2008

This paper presents the design and construction of a 6-degree-of-freedom (6-DOF) multi-dimensional positioner. This positioner is based on a novel concentrated-field magnet matrix, and its electromagnetic operational principle is presented. This high-precision positioning system consists of a magnet-matrix base and a triangular single-moving platen that carries three 3-phase permanent-magnet linear levitation motor stators. With a combination of six independent force components, the moving platen can generate any 6-DOF motion. Three aerostatic bearings are used to provide the suspension force against gravity for the system. We designed and implemented digital lead-lag controllers running on a digital signal processor (DSP). Currently, the positioner has a position resolution of 20 nm and position noise of 10 nm rms. The planar traveling range is 160 mm × 160 mm and the maximum velocity achieved so far is 0.5 m/s with 5-m/s2 acceleration in the y-direction, which is highly suitable for semiconductor manufacturing applications. Several 2-dimensional motion profiles are presented to demonstrate the stage’s capability of accurately tracking any extended planar paths.
Effects of the Managerial Factors on CAD/CAM Adoption in U.S. Textile and Apparel Industries
Authors: Yan He , Fiorito Susan
Published: May 2008

The study examines the managerial determinants of the adoption of computer-aided design (CAD) and computer-aided manufacturing (CAM) in the U.S. textile and apparel industries. A variety of sources were used to develop the survey which was mailed to a national random sample of 500 textile and apparel manufacturers. The responses of 103 manufacturers from 30 different states were analyzed. Factor analysis was used to identify the dimensions of different kinds of information technology (IT) based knowledge. Hypotheses were tested with multiple regression analysis procedures. The product related IT knowledge of the CEOs/CIOs had a positive effect on CAD/CAM adoption. Generally CAD/CAM users had higher levels of IT vision than non-users.
Peculiarities of the Power Hydrocannon Operation
Authors: Atanov G. A. , Semco A. N. , Petrenko O. P. , Geskin E. S. , Samardzic V. , Goldenberg B.
Published: May 2008

The paper is concerned with improvement of the devices for formation of super high-speed fluid jets termed hydro cannon. Two modes of the energy injection into the fluid (the piston impact and the powder explosion) are considered and advantages of the use of the gunpowder are determined. A numerical technique for prediction of the jet formation, developed previously by one of the authors is applied for description of the velocity and pressure fields within the hydro cannon. Effect of the design parameters on the fluid acceleration is explored and suggestions for improvement of the hydro cannon design are made.
A Sensor-Driven Approach to Distributed Shop Floor Planning and Control
Authors: Wang Lihui , Shen Weiming , Li Xiaoqian , Lang Sherman
Published: May 2008

The objective of this research is to develop methodology and framework for distributed shop floor planning, real-time monitoring, and remote device control supported by intelligent sensors. An intelligent sensor serves runtime data from bottom up to facilitate high-level decision-making. It assures that correct decisions are made in a timely manner, if compared with the best estimations of engineers. Being an adaptive system, a so-designed framework will improve the flexibility and dynamism of shop floor operations, and provide a seamless integration among process planning, resource scheduling, job execution, process monitoring, and device control. This paper presents principles of the methodology, details in architecture design, module interactions, information flow, and a proof-of-concept prototype implementation.
Experimental Investigation of the Effects of Catalyst Layer Composition on the Performance of Proton Exchange Membrane Fuel Cells
Authors: Russell Jason , Ellis Michael W.
Published: May 2008

The catalyst layer of a proton exchange membrane (PEM) fuel cell is a porous mixture of polymer, carbon, and platinum. The characteristics of the catalyst layer play a critical role in determining the performance of the PEM fuel cell. In this research, sample membrane electrode assemblies (MEAs) are prepared using various combinations of polymer and carbon loadings while the platinum catalyst surface area is held constant. For each MEA, polarization curves are determined at common operating conditions. The polarization curves are compared to assess the effects of the catalyst layer composition. The results show that both Nafion and carbon content significantly affect MEA performance. The physical characteristics of the catalyst layer including porosity, thickness, and apparent Nafion film thickness are investigated to explain the variation in performance. The results show that for the range of compositions considered in this work, the porosity and thickness have little effect on performance but the apparent Nafion film thickness is significant.
Fuzzy Logic Real-Time Digital Control of a Hardware in the Loop Maglev Device Using MATLAB and xPC Target
Authors: Taghavi O. , Shiakolas P. S. , Kuljaca O.
Published: May 2008

This work will discuss the use of a single environment for real-time digital control with a hardware-in-the-loop (HIL) magnetic levitation (maglev) device for modeling and controls education, with emphasis on fuzzy logic (FL) feedforward control. This environment utilizes two computers (host and target), an off-the-shelf data acquisition card, and the HIL device (a nonlinear, open-loop, unstable, and time varying, custom-built maglev). The software includes tools from MathWorks Inc., and a C++ compiler. The values of any parameter (control law, reference trajectory) in the Smulink model can be changed dynamically on the host computer and their effects observed in real-time on the HIL system. Real-time data was collected from the HIL device and used in designing, tuning and implementing a feedforward FL controller all using MathWorks tools that controlled the HIL device in real-time. It was observed that the tracking error was substantially improved when the FL augmented the control effort of a classical lead compensator. The procedure for the FL development, tuning and hardware implementation along with examples will be presented. This system has been recently completed and was successfully used in an educational setting for one graduate and undergraduate Mechanical Engineering course.
Computation and Visualizaion of 3-D Marangoni and Magnetically-Driven Flows in Droplets
Authors: Huo Y. , Ai X. , Li B. Q.
Published: May 2008

This paper presents a computational and visualization tool kit for the numerical modeling of 3-D Marangoni and/or magnetically-driven turbulent flows in droplets under normal and/or microgravity conditions. The computational part involves the finite element solution of steady-state and transient 3-D Marangoni flows in electrically levitated droplets and the higher order finite difference method for the direction numerical simulation of tubulences in electromagnetically levitated droplets. Both the electrically and magnetically droplets have been used for study of fundamentals governing solidification processing in normal and mcrio gravity. The visualization part is developed based on the UNIX/X-motif platform and on the advanced algorithms for multi-dimensional computer graphics. The visualization tool kit employs the algorithms for data retrieving, partitoning, sorting and searching algorithms, and 3-D/2-D object clipping. An efficient algorithm used for plane and body cutting and particle tracing is presented. The mathematical formulation used in developing the above computational tool kit, including computational and differential geometry, is also discussed. Examples are given to illustrate the effectiveness and efficiency of the tool kit as applied to the numerical simulation and computer visualization of complex steady state and transient three-dimensional Marangoni and turbulent magnetically driven flows in free droplets.
A Packaging Solution for Pressure Sensor MEMS
Authors: Wei J. , Qi G. J. , Wang Z. F. , Jin Y. F. , Lim P. C. , Wong C. K.
Published: May 2008

In this paper, a wafer-level packaging solution for pressure sensor microelectromechanical system (MEMS) is reported. Sensor and glass cap wafers are anodically bonded at a bonding temperature less than 400°C. Bubble free interfaces are obtained and the bond strength is higher than 20 MPa. Sensor and bottom silicon cap wafers are bonded at a temperature of 400–450°C with the assistance of a gold intermediate layer. The bond strenght is higher than 5 MPa. The via holes, used for feedthroughs leading out the circuit, on bottom silicon cap wafer are anisotropically formed in KOH etching solution. Aluminum layer is sputtered on the bottom silicon wafer for electrical connection, re-routing circuit and the seed layer of under bump metallization (UBM). During sputtering process, the sidewalls of via holes are also sputtered with aluminum film. At the same time, the metal pads on sensor wafer are also built up to connect with metallized via holes. It is found that the cavities are vacuum sealed. Sputtered Cr/Ni/Au layers are used for UBM layers. Finally, solder bumps can printed or plated on the UBM. The whole process leads to promising performance of the devices.
Computation of Turbulent Flows in Complex and Moving Geometries Using Immersed Boundary Method
Authors: Tyagi Mayank , Acharya Sumanta
Published: May 2008

A solution methodology for complex turbulent flows of industrial interests is developed using Immersed Boundary Method (IBM). IBM combines the efficiency inherent in using a fixed Cartesian grid to compute the fluid motion, along with the ease of tracking the immersed boundary at a set of moving Lagrangian points. IBM relies upon the body force terms added in the momentum equations to represents the complex geometry on a fixed Cartesian mesh. Resolution issues for turbulent flows can be addressed by Large Eddy Simulation (LES) technique provided an accurate and robust Subgrid Stress (SGS) model is available. Higher order of numerical accuracy schemes for turbulent flows can be maintained as well as the geometrical complexities can be rendered physically by combining LES with IBM. The proposed methodology is simple and ideally suited for the moving geometries involving no-slip walls with prescribed trajectories and locations. IBM is validated for the laminar flow past a heated cylinder in a channel and LES is validated for the turbulent lid-driven cavity flow. LES-IBM is then is used to render complex geometry of trapped vortex combustor to study fluid mixing inside trapped vortex cavity. To demonstrate the full potential of LES-IBM, a complex moving geometry problem of stator-rotor interaction is solved.
Analysis of Volumetric Residence Time of Blood Elements in Stenosed Arteries
Authors: Kim M. C. , Lee C. S. , Kim C. J.
Published: May 2008

Blood flow in arteries is known to be closely related to atherosclerosis. Presence of recirculation zones, and low, high, and oscillatory wall shear stresses have been suggested to be important fluid dynamic factors causing development and progress of atherosclerosis. Our study was motivated to develop fluid mechanical indices between residence time of blood particles in arteries and atherosclerosis. In rigid models of stenosed arteries with 75% area reduction, trajectories of blood particles were numerically computed and used to determine local volumetric residence time (VRT) of platelets. The motion of particles in the model artery was computed by considering viscous drag forces between blood particles and presolved transient flow field from computational fluid dynamics (CFD). Many cardiac cycles were considered in the computation to reflect temporally accumulative characteristics of VRT in the recirculation zones. Our results showed that VRT in the recirculation zone was relatively low in the first cardiac cycle. However it increased in the subsequent cycles as more particles were trapped in the same zone. The results suggested that VRT contour calculated in the present study would be an effective indicator of the presence of atherosclerosis.
Simulation of the Discharging Process Throughout a Porous Medium Initially Saturated With Fluid
Authors: Carbajal G. J. , Gonza´lez J. E. , Diaz R.
Published: May 2008

This paper presents the development of a theoretical model and simulation analysis for the discharging process that takes place in a porous medium initially saturated with ink. During the discharging process the porous material provides enough surface area to hold the fluid by capillarity effects. It was found by the numerical solution that the velocity profile through the porous region was uniform and the backpressure had a linear behavior as function of time. A parametric study also revealed that the permeability, void volume and surface tension have a significant effect on the pressure drop. The numerical formulation was validated with experimental data and good agreements were found between both data sets.
Stability Analysis of a Class of Nonlinear Controllers
Authors: Ravichandran T. , Heppler G. R. , Wang D. W. L.
Published: May 2008

The stability analysis of a class of nonlinear PD-plus-feedforward controllers is presented for the tracking control of rigid robot manipulators. The controller structure is composed of a nonlinear gain PD feedback controller and a manipulator dynamics feedforward term. The class of representations used for the nonlinear gain PD feedback controller is extended and global exponential stability is proved. Simulation results are included to illustrate the performance of this class of nonlinear controllers.
Segmented Wing Aircraft Lateral Directional Flight Control Design With Minimum Drag Constraints
Authors: Chavez Frank R. , Vogel Jerry
Published: May 2008

Following the current trend for developing biologically inspired flight configurations, flight control system for a transport type aircraft with no vertical tail and segmented main wing is to be developed. The transport configuration is inspired by the fact that birds do not have vertical tails and their wings have various trailing edge feathers that serve to form independent wing segments for roll and yaw control. An aerodynamic model for a generic transport aircraft, modeled after the Boeing 747, is obtained using NASA’s PMARC software. The aircraft is modeled with no vertical tail and the main wing has several independently controlled trailing edge segments. A flight control design will be carried out to satisfy roll and yaw moment commands. These moment commands might come from desired roll or yaw rate commands from the pilot. In addition, for increased performance, it is desirable to maintain a minimum drag configuration. This will result in a reduction in fuel usage for maximum range, endurance, or maximum flight speed. The final controller will provide main wing segment deflection commands designed to meet desired roll and yaw moment commands while attaining a minimum drag configuration.
Monte Carlo Analysis of Safe Following Distances Under Different Road Conditions
Authors: Kimbrough Scott
Published: May 2008

In order to avoid accidents drivers must maintain an adequate amount of separating distance between themselves and vehicles in front of them. If the driver of the lead vehicle suddenly applies his brakes, the driver of the following vehicle needs sufficient time and space to react and apply his brakes to come to a stop. If all vehicles and drivers had the same brake performance, then the required separating distance would simply be the distance traveled while reacting; basically the product of the speed being traveled times the reaction time of the driver. This simple rule would guarantee that a following driver would be able to apply his brakes before arriving at the place on the road where the lead driver applied his brakes. In real life though, all vehicle and drivers do not have the same stopping performance. There are variations due to the different tires on the vehicles, the brake balance of the vehicles, the reaction rates of the drivers, the skills of the drivers, and the traction afforded by the particular wheel paths followed by the vehicles. One way to deal with these variations is to use probability theory [2–6]. In this paper probability theory is used to determine how following distance should vary as a function of speed, average road friction, and variation of the road friction, so that the probability of a collision remains below a desired threshold.
Analysis of the Deformation of the Nucleus as a Result of Alterations of the Cell Adhesion Area
Authors: Jean Ronald P. , Chen Christopher S. , Spector Alexander A.
Published: May 2008

The area of cell spreading has been proven to be critical to a cell’s fate, and direct physical connections between integrins, cytoskeleton, and the nucleus have been found [1]. We investigate the cell adhesion-cytoskeleton-nucleus mechanical pathway using experimental and theoretical tools. We measured changes in adhesion area and corresponding elliptical projected nuclear stretches caused by disruption of cell adhesions with trypsin. For our analysis, we treated the nucleus as an incompressible, neo-Hookean material. Using our measurements of the two-dimensional nuclear stretches, we calculated the stretch in the normal direction. We then estimated the strains of the nuclear deformation, and used these to estimate the cytosolic/cytoskeletal pressure and tangential forces that act upon the nucleus. Comparing our estimates of the internal forces acting on the nucleus to measurements of cell surface traction force in the literature, both are on the same order of magnitude.
Modal Response of Polymers With SMA Ribbon Reinforcements
Authors: Pai Mizar Shivananda , Weir William C. S. , Klempner Adam R. , Hefti Peter , Pryputniewicz Ryszard J.
Published: May 2008

Shape Memory Alloy (SMA) based composites are unique because their static and dynamic characteristics can be controlled. Active modal modification and active strain energy tuning are two common techniques used to control the dynamics of SMA based composite materials. Using Active Modal Modification Technique (AMMT), the stiffness of the SMA composite can be modified by changing the temperature of the SMA. The stiffness change is a result of a reversible phase transformation, which is tempeature activated. The Active Strain Energy Tuning Method (ASETM) takes advantage of the SMA’s ability to impart forces to the structure thereby changing the stored strain energy within the composite. The result is a change in the modal characteristics of the composite material. This paper will present the results of the application of an AMMT used to modify the dynamic characteristics of an SMA composite. A rectangular example of quasi-isotropic SMA composite was used in this study. As a result of a temperature change, the stiffness of the composite changed. This change is stiffness altered the dynamic responses such as the resonant frequency of the composite. Time Average Opto-Electronic Holography (TAOEH) [6] was used to monitor the dynamic behavior of the structure. Analytical modeling was used along with the experimental results to obtain the temperature history of the composite as a result of the activation of the SMA.
Brain Tissue Properties at Moderate Strain Rates
Authors: Bilston Lynne E.
Published: May 2008

Bovine brain tissue has been tested in shear under oscillatory, relaxation and constant strain rate test protocols. Compression data has been obtained in confined compression. The data from these tests suggests that brain tissue is a highly nonlinear viscoelastic material, with a linear viscoelastic limit of approximately 0.1% strain. The storage and loss modulus are strain dependent above this loading level, requiring careful interpretation of oscillatory data. Brain tissue is also highly strain rate dependent, not strain-time separable, and exhibits a low long term elastic modulus. Modelling the complex behaviour is a challenge.
Molecular Beacons for Sensitive Gene Detection in Living Cells
Authors: Tsurkas Andrew , Bao Gang
Published: May 2008

Real-time imaging of gene expression in living cells has the potential to significantly impact clinical and laboratory studies of cancer, including cancer diagnosis and analysis. Molecular beacons (MBs) provide a simple and promising tool for the detection of target mRNA as tumor markers due to their high signal-to-background ratio, and their improved specificity in detecting point mutations. However, the harsh intracellular environment does limit the sensitivity of MB-based gene detection. Specifically, MBs bound to target mRNAs cannot be distinguished from those degraded by nucleases, or opened due to non-specific interactions. To overcome this difficulty, we have developed a novel dual FRET molecular beacons approach in which a pair of molecular beacons, one with a donor fluorophore and a second with an acceptor fluorophore, hybridize to adjacent regions on the same target resulting in fluorescence resonance energy transfer (FRET). The detection of a FRET signal leads to a substantially increased signal-to-background ratio compared with that in single molecular beacon assays and enables discrimination between fluorescence due to specific probe/target hybridization and a variety of false-positive events. We have performed systematic in-solution and cellular studies of dual FRET molecular beacon and demonstrated that this new approach allows for real-time imaging of gene expression in living cells.
Arachnoid Trabeculae and CSF Roles in Blunt Head Impacts
Authors: Zoghi-Moghadam M. , Sadegh Ali , Watkins Charles
Published: May 2008

The blunt head impacts due to vehicular collisions, contact sports or falls cause relative motion between the brain and skull and an increase in contact and shear stresses in meningeal region. Several models have been developed to better understand brain injuries. In this study the mechanical role of the fibrous trabeculae and the Cerebrospinal Fluid (CSF) in Subarachnoid space (SAS) is investigated. Two-dimensional solid and fluid global models of the head and a local model of the SAS trabeculae were developed. The CSF pressure distribution and the trabeculae deformations were determined. It is concluded that the arachnoid trabeculae reduce the pressure in the CSF and both play a major role in damping the blunt head impact.
Improving Fracture Toughness of Brittle Matrix Composites Using End-Shaped Ductile Fibers: The Effects of Adhesion and Matrix Shrinkage
Authors: Wetherhold Robert C. , Bagwell Renee M.
Published: May 2008

Ductile fibers are added to brittle matrix composites to increase the fracture toughness. To further improve fracture toughness, end shaped ductile fibers are added to act as anchors to utilize more of the fibers’ plasticity. Previous research focused on optimizing the volume of the shaped end for a given end shape family. Results indicate that for a given end shape family there is an optimum volume; above or below this volume results in a lower fracture toughness contribution. This research investigates two additional factors, adhesion of the matrix to the fiber and matrix shrinkage, and determines their effects on the fracture toughening of brittle matrix composites. The fiber was an annealed copper and the matrices used were a low shrinkage epoxy, a high shrinkage epoxy, and polyester. Results indicate that controlling the surface chemistry of the fiber can give an additional degree of freedom to the utilization of the fiber plasticity, although the importance of this control depends on the particular system. The fiber surface chemistry affects the bond strength and the adhesion; if the fiber cannot debond from the matrix, then shaping the end does not permit use of the plastic potential. Depending on the system, the adhesion and bond strength of the matrix to the fiber significantly affects the amount of fiber plasticity utilized. To determine the effects of friction and matrix shrinkage on the utilization of the fiber plasticity, release agent was applied to the end shaped fibers to reduce the adhesion, bond strength, and friction during pull out. Results indicate that frictional work and adhesion has a large impact on the utilization of the fiber plasticity; with release agent, the end shaped fiber utilizes little of the fiber plasticity. Furthermore, this indicates that for the matrices investigated, matrix shrinkage has a minor influence on the utilization of the fiber plasticity.
Microfluidic Logic: Addressing Complexity at the Microscale
Authors: Thorsen Todd A.
Published: May 2008

Elastomer-based microfluidic devices, created by soft lithography methods, are emerging as valuable tools in a constantly expanding research field. As their complexity inevitably increases, robust design and fabrication methods become critical to ensure that all of the components are well-integrated and functional. Microfluidics offers the possibility of solving system integration issues for biochemistry, while minimizing the necessity for external control hardware. Many applications, such as enzymatic library screening in bacteria, are currently carried out as a series of multiple, labor-intensive steps. While the industrial approach to complexity has been to develop elaborate mechanical workstations, this technology comes at a price, requiring considerable expense, space and labor. For small laboratories or research institutions, this technology is simply out of reach. Devices consisting of addressable elastomeric microfluidic networks can dramatically simplify the screening process, providing an environment where reagents can be injected and compartmentalized into sub-nanoliter aliquots to create a platform for high-throughput, sensitive analysis of biological material.
Stochastic Multi-Objective Optimisation of a Gearbox Synchroniser and Selector Mechanism
Authors: Gobbi Massimiliano , Mastinu Giampiero , Caudano Massimo
Published: May 2008

In the paper a new approach is presented for the design of the synchroniser and selector mechanism of a road vehicle gearbox. The main aim is to improve shiftability and driver comfort. The new approach is based not only on the theory of multi-objective optimisation but also on robust design. A multi-body physical system model of the synchroniser and selector mechanism has been developed and vaildated experimentally. The physical model is stochastic being many of the system parameters defined by stochastic processes. The fifty-eight parameters of the system model have been tuned in order to achieve the desired dynamic behaviour of the synchroniser and selector mechanism during a reference shift action, defined by nine performance indices. The new approach is characterised both by the optimisation of the objective functions (corresponding to system performance indices) and by the reduction (or minimisation) of the sensitivity (variance) of the performance indices to stochastic perturbations. Such variances are computed (very quickly) by means of an original procedure based on the global approximation of the objective functions. Additionally, with respect to the mentioned features, the new approach is based on both a special study to explore all of the feasible design solutions, and on a global sensitivity procedure to analyse (in a stochastic context) the influence of each design variable on each objective function. Pareto-optimal design solutions for different levels of “robustness” have been computed in a very short time. The optimisation method has been applied with successful results. A number of optimised synchronisers and selector mechanisms have been defined, all of them featuring relevant improvements in terms of performance and robustness with respect to the reference system, already effective and under production.
The Response of Mechanoreceptors in Rat Skin to Biaxial Loading: A Preliminary Study
Authors: Robichaud Daniel R. , Grigg Peter , Hoffman Allen H.
Published: May 2008

Mechanoreceptor neurons were studied in an isolated rat skin preparation subjected to dynamic biaxial stretch. The strength of the relationship between neuronal responses and mechanical variables was determined using multiple logistic regression. The experimental protocol allowed the normal stresses as well as the maximum shear stress to be manipulated. In n=4 neurons, response was associated with the time rate of change of normal stress and this response was affected by the direction of loading. There was no relationship between response and the value of maximum shear stress. There was a strong association with the rate of change of maximum shear stress.
Improved Prosthetic Bone Implants
Authors: Mehta Bhavin V. , Setlock Robert J.
Published: May 2008

An improved method for manufacturing prosthetic bones is examined. We are developing a new improved method for designing and manufacturing prosthetic bones that have a porous interior core covered by a solid outer shell, more closely matching the morphology of natural bone. The new method is compatible with a wide variety of materials, including polymers, metals, composites, and biodegradable scaffold materials. Use of biodegradable scaffold material holds the potential for eventual bone regeneration within and throughout the prosthesis. Regardless of the material selection, this improved type of prosthesis is expected to more closely mimic the overall material and structural properties of natural bone, including shape, strength, weight, and weight distribution. By fabricating prosthetic bones that duplicate the material and structural properties of natural bone, implants could be made to operate as precision replacements, feeling and functioning exactly like natural bone. In addition to improving patient comfort, these new prostheses are expected to reduce the occurrence of unnatural secondary wear patterns caused by current style prosthetic bones that function in unnatural fashions due to their non-matching material and structural properties.
Architectures for Integration of Cellular Microscale Actuator Arrays
Authors: Garcia Ephrahim , Nam Yoonsu , Lobontiu Nicolae
Published: May 2008

The paper proposes the design of several amplification microelectromechanical devices formed of many identical micro-units that are connected in a serial-parallel configuration, each being individually actuated and amplifying its own input motion. The micro-devices realize the border-crossing from the micro- to the meso-scale displacement domain as they combine the micron-level individual inputs into millimeter-range output levels. The base structural unit is a flexure-based compliant device that is capable of transforming the input from a thermoactuator into an amplified displacement, about a direction perpendicular to the input one. The base unit is designed based on performance criteria such as displacement amplification, input stiffness and output stiffness by utilizing finite element simulation and an algorithm based on closed-form compliance equations of the incorporated flexure hinges. The microelectromechanical amplification device is monitored by means of embedded capacitive displacement sensors, for both the input and output ports. This preliminary analysis will be further utilized to produce and analyze several micro-scale amplification devices.
Abnormal Internal/External and Varus/Valgus Rotations in ACL-Reconstructed Knees During Running: Analysis by High Frame-Rate Stereo-Radiography
Authors: Tashman Scott , Anderst William
Published: May 2008

The effectiveness of ACL reconstruction for restoring normal joint mechanics is poorly understood, especially during physically demanding tasks. For this study, 3D kinematics of ACL-reconstructed and contralateral (uninjured) knees were assessed during down-hill running, using a unique high frame rate stereo-radiography system. Though anterior/posterior tibial translation was restored to normal levels, significant rotational abnormalities were identified in the ACL-reconstructed knees in both the coronal and transverse planes.
Analysis of Solute Transport in Cartilaginous Tissue Under Dynamic Unconfined Compression
Authors: Yao Hai , Gu Wei Yong
Published: May 2008

Transport of fluid and solutes through the extracellular matrix plays a key role in the nutrition and growth of cartilaginous tissues that lack blood supply. It has been found that the mechanical loading can alter the transport rates of solutes within cartilage [Bonassar, 2000; O’Hara, 1990; Quinn, 2002]. Dynamic compression may enhance the transport of large solutes (e.g., growth factors) within the tissue. Many theoretical analyses have been reported in literature on the transport of fluid and solutes, as well as physical signals (stress, strain, pressure, concentrations, and electrical potential) in cartilage under unconfined compression [Armstrong, 1984; Levenston, 1999; Mow, 2002]. However, little is known as to how the tissue fixed charge density (FCD) affects the transport of fluid and neutral solutes (e.g., glucose and IGF-1) in cartilage sample in dynamic compression. In this study, we numerically analyzed the transport of fluid and solutes, as well as the mechano-electrochemical signals within the cartilage sample in dynamic unconfined compression, using the finite element method (FEM). The objective of this study was to investigate the effects of FCD, loading frequency, and loading platens (permeable vs. impermeable) on the transport of fluid, ions, and neutral solutes within cartilage. This study is essential for the understanding of tissue nutrition and signal transduction mechanisms in cartilage subjected to mechanical forces.
Design and Test of Hydrostatic Gas Bearings for a Hybrid Cryogenic Refrigerator
Authors: Evans Jonathan C. , Nellis Gregory F.
Published: May 2008

A hybrid pulse-tube/reverse-Brayton cryocooler is being developed that integrates a regenerative, pulse-tube upper stage with a recuperative, reverse-Brayton lower stage using a flow rectification system consisting of check-valves and buffer volumes. This system shows the potential for high performance with high reliability and low mass, and simple electrical, mechanical, and thermal integration. The turbine in the reverse-Brayton stage will be supported on hydrostatic gas bearings. The performance of the hybrid cryocooler system is strongly dependent upon the performance of these bearings; in particular their stiffness and mass flow consumption. This is a unique application of hydrostatic bearings; the miniature bearings are operating at cryogenic temperatures using high pressure helium. This paper describes the theoretical model that was developed to predict journal bearing performance as geometry and operating conditions change. The model is verified against experimental measurements of stiffness and mass flow consumption for a prototypical set of journal bearings. The model is subsequently used to optimize a set of journal bearings for the cryogenic turbine and parametrically investigate the effect of journal bearing clearance on system performance.
A Numerical Method for Estimating Tendon Slack Length
Authors: Manal Kurt , Buchanan Thomas S.
Published: May 2008

Forces generated by muscle are transferred to bone via tendon. Since muscle force cannot be measured directly, computer modeling is a useful tool to enhance our understanding of normal and pathological movement. Hill-type muscle models have been used to estimate force based on information about a muscle’s architecture, activation and kinematics (Delp et al., 1995; Manal et al., 2002). Architectural parameters include optimal fiber length (lom), tendon slack length (lst), pennation angle (α), and maximum isometric force (Fmax). In addition, musculotendon length (lmt) and activation (a) are required inputs when estimating isometric muscle force (Equation I). Fm=f(lmt,lom,lst,Fmax,α,a)(1) Musculotendon length can be determined from MR images (Arnold et al., 2000), and activation recorded from EMGs (Manal, et al., 2002). Optimal fiber length and pennation angle can be measured experimentally (Murray, 2002), while Fmax can be estimated from the muscle’s physiologic cross-sectional area. Tendon slack length however cannot be measured readily, and therefore few estimates of lst can be found in the literature. In this paper we present a numerical method for estimating tendon slack from subject specific muscle parameters and musculotendon lengths. An advantage of this method is that it yields subject specific estimates of tendon slack length.
Sample Dispersion Due to Buffer Disturbances and Zeta Potential Variability in Electroosmotic Microchannel Flows
Authors: Debusschere Bert J. , Najm Habib N. , Matta Alain , Knio Omar M. , Ghanem Roger R. , Le Maiˆtre Olivier P.
Published: May 2008

This paper presents detailed simulations to study analyte dispersion in electroosmotic microchannel flow. We focus on electrokinetic and hydrodynamic dispersion caused by buffer disturbances and random zeta potential variability. A two-dimensional microchannel model is used that considers the coupled momentum, species transport, and electrostatic field equations, including a model for the dependence of the zeta potential on pH and buffer molarity. The chemistry model accounts for pH-dependent protein labeling reactions as well as detailed buffer electrochemistry in a mixed finite-rate/equilibrium formulation. The model also has the unique capability to account for uncertainty in input parameters, such as species mobilities, as well as for stochastic processes, such as random zeta potential variability. These uncertainties and variabilities are handled using polynomial chaos representations for model inputs and field quantities. The results show a strong increase of analyte dispersion for increasing species charge number and for increasing zeta potential variability.
Modeling of a Flexible Link in Contact: Strain vs. Force Output
Authors: Ziaei K. , Wang D. W. L. , Heppler G. R.
Published: May 2008

Many control design techniques for force control of flexible link manipulators, require an adequate transfer function model of the manipulator in contact. In this paper we derive a simple transfer function model for a single flexible link in contact with stiff environment. While the transfer function from input torque to contact force is nonminimum phase, we show that the transfer function from input torque to strain results in a minimum phase transfer function and thus, it provides an attractive, alternative output for force control of flexible link manipulators. Experimental results verify the validity of the presented models.
Exercise Can Reverse the Phenotype of Biglycan Deficient Mice
Authors: Wallace Joseph M. , Rajachar Rupak M. , Chen Xiao-Dong , Shi Songtao , Allen Matthew R. , Bloomfield Susan A. , Robey Pamela G. , Young Marian F. , Kohn David H.
Published: May 2008

Biglycan (Bgn) is a small leucine-rich proteoglycan (SLRP) that is enriched in bone and other skeletal connective tissues and is responsible, in part, for the regulation of postnatal skeletal growth (Bianco, 1990). Mice lacking Bgn display reduced skeletal development and a lower peak bone mass that leads to age-dependent osteopenia (Xu, 1998). We hypothesized that mechanical loading could reverse the skeletal phenotype of Bgn knockout mice. To test this hypothesis, we determined the effects of treadmill running on the geometric, mechanical and mineral properties of Bgn deficient mice bones. After sacrifice, femora and tibiae were tested in 4 point bending and cross-sectional geometric properties and bone mineral parameters were measured. Exercise was able to partially reverse the skeletal phenotype of the Bgn knockouts by increasing both the geometric and mechanical properties of the tibiae to values equal to or greater than those of wild type control mice.