bluuebunny/crossref_metadata_2025 huggingface dataset:
Stretching-Induced Collagen Type I Synthesis in Human Tendon Fibroblasts Is Mediated by TGF-β1
Authors: Yang Guoguang , Crawford Richard C. , Wang James H.-C.
Published: May 2008

This study investigated the effect of cyclic mechanical stretching on the collagen gene expression and protein synthesis of human patellar tendon fibroblasts (HPTFs). We hypothesized that cyclic mechanical stretching of HPTFs would increase collagen synthesis via transforming growth factor-beta 1 (TGF-β1). To test the hypothesis, the tendon fibroblasts were cultured on microgrooved surfaces of silicone dishes under serum-free conditions. The cells were subjected to cyclic uniaxial stretching with a constant frequency and duration (0.5Hz, 4hr), and one of three stretching magnitudes (no stretch, 4%, and 8%) followed by 4 hours of rest. It was found that the gene and protein expression of both collagen type I and TGF-β1 were significantly increased in a stretching-magnitude dependent manner, whereas collagen type III gene and protein levels were not significantly changed. The exogenous addition of antibody to TGF-β1 eliminated the stretching-induced increase in collagen type I protein synthesis. The results therefore confirmed our working hypothesis and suggest that mechanical stretching of tendon fibroblasts can lead to matrix remodeling by modulating the collagen production of tendon fibroblasts, a process at least particially mediated by TGF-β1.
Image-Based Modeling of Arteriovenous Hemodialysis Access Graft Flow
Authors: Schmidt Brian R. , Kim Chang-Beom , Mohamed Feroze B. , Nunes Linda W. , Ahmed Ziauddin , Wootton David M.
Published: May 2008

Thrombosis in an arteriovenous hemodialysis access graft is a major cause of graft failure. Changes in flow features due to increasing resistance at the venous anastomosis may promote the development of thrombosis. A three-dimensional computational fluid dynamics model was developed to analyze flow at the arterial anastomosis of a PTFE brachial-brachial arteriovenous access graft. The geometry was obtained from contrast-enhanced magnetic resonance images. A surface mesh was extracted using Amira software, and the final volume mesh was generated by Tgrid (Fluent, Inc). The simulation was carried out for steady flow conditions using Fluent CFD software with low-Reynolds number k-ω turbulence model. Small areas of recirculation can be seen in the area of the bifurcation, and results show a pressure difference between the proximal artery and the graft that is consistent with reported values.
Computational Modeling of a Dynamic Knee Simulator for Reproduction of Joint Loading
Authors: Guess Trent M. , Maletsky Lorin P.
Published: May 2008

A three-dimensional dynamic computational model was developed for the dual purposes of predicting and replicating joint loading generated by a five-axis dynamic knee simulator. The model was verified through an analog knee that was constrained for accurate modeling and instrumented to directly measure joint forces. The verified model was then used to generate control profiles to the five axes of the simulator for replication of desired joint loading. Reproduction of a walking profile is demonstrated.
Roof Strength Survey of Production Passenger Cars, Light Trucks, and Vans
Authors: Sigel Jason J. , Bish Jack , Honikman Terence , Friedman Donald , Nash Carl E.
Published: May 2008

We have developed and used a repeatable roof strength survey tool to assess the force resistance characteristics of over 50 passenger car, SUV, pickup, and van roofs. In a rollover, the initial roof-to-ground contact typically fractures and/or separates the vehicle’s bonded windshield. Subsequent trailing-side roof-to-ground impacts apply lateral forces to the roof and its support pillars. In 1971 the National Highway Safety Bureau (NHSB) recognized this rollover sequence and proposed a Federal Motor Vehicle Safety Standard (FMVSS) that tested both sides of the roof in sequence. Our repeatable roof strength survey tool uses a hydraulic cylinder to pull the upper A-pillar, roof rail, windshield header intersection toward the rear of the opposite front door sill imitating the proposed 1971 test, but at a more realistic roll angle. It is used first on one side of the vehicle with the windshield intact before being repositioned on the other side after the fractured and separated windshield is removed and the test repeated. Tests on three vehicles of the same make, model, and model year have validated the repeatability of the test and protocol. Results from all the vehicles demonstrate that in the first side test, the strength of the roof is typically about half the strength recorded in a typical FMVSS 216 test, a further decrease in force resistance occurs after the windshield has failed, and similar elastic restoration of the deformed structure occurs on both sides.
Estimation of ACL Forces Utilizing a Novel Non-Invasive Methodology That Reproduces Knee Kinematics Between Sets of Knees
Authors: Darcy Shon P. , Kilger Robert H. P. , Woo Savio L.-Y. , Debski Richard E.
Published: May 2008

A non-invasive, non-contact methodology to estimate forces in the anterior cruciate ligament (ACL) in response to in vivo knee kinematics will allow surgical procedures and rehabilitation protocols for ACL injuries to be improved. During the last decade, intensive efforts have been made to quantify the forces in the ACL in vivo (Holden, 1994; Lundberg, 1997; Zacharias, 2001). With the use of these methods, valuable information on the forces experienced by the ACL has been obtained, however many of these methods were invasive, and involved direct contact with the ACL, which may affect the force measurements. It has been proposed at our research center that the forces in the ACL during activities of daily living and rehabilitation exercises can be estimated in a non-contact, non-invasive manner by reproducing in vivo kinematics in 6-degrees of freedom (DOF) on a cadaveric knee. Therefore, the specific aim of this study was to evaluate the feasibility of a non-invasive, non-contact methodology for estimating force in the ACL by reproducing average kinematics in 6-DOF degrees of freedom from one set of porcine knees (source) onto a separate set of porcine knees (target).
Experimental Verification of a Dynamic Finger Model Using Real-Time Data Acquisition
Authors: McNeal David , Amirouche Farid , Gonzalez Mark
Published: May 2008

The purpose of this experiment is to create a mathematical model for the function of the annular pulleys of the human finger in flexion. We have assumed that the flexion moment of the middle and proximal phalanges occurs at the proximal and distal ends of the A-2 and A-4 pulleys. The amount of force generated is dependent on the angle of flexion at the adjacent joint, the tension in the tendon and the stiffness constant of the pulley.
Inflation Testing as a Means of Measuring Failure Strength of Aortic Tissue
Authors: Kinkaid Jeffrey N. , Marra Steven P. , Kennedy Francis E. , Fillinger Mark F.
Published: May 2008

Abdominal Aortic Aneurysms (AAAs) are localized enlargements of the aorta. If untreated, AAAs will grow irreversibly until rupture occurs. Ruptured AAAs are usually fatal and are a leading cause of death in the United States, killing 15,000 per year (National Center for Health Statistics, 2001). Surgery to repair AAAs also carries mortality risks, so surgeons desire a reliable tool to evaluate the risk of rupture versus the risk of surgery.
Kinematic Synthesis of a Medical Bed for Decubitus Ulcer Patients
Authors: Shim Jae Kyung , Shim Chang Sup , Kwon Jin Wook
Published: May 2008

A decubitus ulcer or bedsore is a pressure-induced ulceration of the skin occurring in persons confined to bed for long periods of time. Reduction of pressure over bony prominences is of primary importance to prevent and cure bedsores. For this purpose, specially designed mattresses can be used and/or the patient should be turned frequently to avoid ischemia of soft tissue. In addition to pressure, other principal factors causing bedsore are friction and shear forces. In this paper, we designed a new 5 degree of freedom bed mechanism that can be used to change the posture of pressure ulcer patients, which generates 7 motions including backrest elevation, kneerest elevation, lounge position, left and right rotation, trendelenberg and reverse trendelenberg motion, and straight elevation. Particularly, we focused on the synthesis of a backrest and seatrest assembly that can reduce sliding between the bed and the patient.
The Effect of Random Skin Motion on Knee Kinematics Calculated With Surface Markers: A Comparison of Three Marker Sets
Authors: Fisk Jesse A. , Rollins Melissa L. , Van Scyoc Andrew H. , Woo Savio L.-Y.
Published: May 2008

The use of surface markers to calculate kinematics of diarthrodial joints is subject to error from relative motion between the markers on the skin and the underlying bones. It has been demonstrated that markers placed over the knee and hip joints could move 10–30 mm with respect to the skeleton which can have significant effects on the accuracy of calculated knee kinematics (Cappozzo et al., 1996, Manal et al., 2000). Several methods have been developed to calculate knee kinematics from marker locations and decrease error resulting from skin motion. The Helen Hayes method uses markers attached to the skin over anatomical landmarks and on wands to calculate the locations of the hip, knee, and ankle joints (Vaughan et al., 1999). The location and orientation of the thigh and shank segments can then be calculated based on anthropometric correlations. Other methods, such as that developed by the Cleveland Clinic, record the position of the femur and tibia using triads of markers attached to each segment (Manal et al., 2000). Additionally, a Point Cluster Technique was developed using clusters of markers attached to each segment to reduce error from skin motion (Andriacchi et al., 1998).
Occupant Extrication in Vehicular Crashes: NASS and CIREN Analyses
Authors: Pintar Frank A. , Yoganandan Narayan
Published: May 2008

Improvements in occupants extrication techniques are required due to enhanced safety features in modern vehicles. The research questions were focused on what force directions and what vehicle types, were most highly associated with an extricated occupant. Two national databases, FARS and CIREN were queried. Principal direction of force for the occupant vehicle and vehicle weight were used as delineating variables. From FARS data, the percentage of extricated occupants increased between 1993 and 2000. Left-sided crashes account for the highest percentage of occupants requiring extrication (18.8%) compared to occupants in rear crashes (lowest at 8.6%). Occupants in vehicles less than 2500 pounds were most often extricated (19.1%) compared to vehicles greater than 3500 pounds (lowest at 11.3%). From the CIREN database, for left-sided crashes, occupants required extrication 33.0% of the time when involved in truck-into-car crashes whereas car-into-car crash victims were extricated only 27.3%. These results imply an increased risk for extrication need for those occupants struck by a vehicle that is mismatched.
Nondimensional Damping Analysis of Flow-Mode Magnetorheological and Electrorheological Dampers
Authors: Hu Wei , Wereley Norman M.
Published: May 2008

In an effort to develop a Magnetorheological (MR) and Electrorheological (ER) damper initial design method, a quasi-steady relationship between force and velocity exhibited by a flow-mode MR/ER damper is developed based on a Bingham plastic model and a parallel plate assumption. A nondimensional damping coefficient is described as a nonlinear explicit function of an independent nondimensional Bingham number. Since the nondimensional damping coefficient is not a simple analytical function of the Bingham number, a uniform rational approximation approaches is used to determine the relationship between nondimensional damping coefficient and Bingham number. Approximate linear relationship is obtained in a certain Bingham number range. Thus, the quasi-steady flow mode damping approximately consists of a controllable damping and a linear viscous or post-yield damping, which is similar to the behavior of a shear mode damper. The effect on the nondimensional damping coefficient due to the magnetic circuit is also considered by introducing a ration of the length of active region to the total flow gap length.
Pressure-Flow Characteristics During Peristaltic Transport of Non-Newtonian Fluid in Distensible Tube With Different Wave Forms
Authors: Hariharan Prasanna , Banerjee Rupak K.
Published: May 2008

This study analyzes the pressure-flow characteristics during the peristaltic pumping of power law fluids in an axi-symmetric non-uniform distensible tube. The analyzed geometry is of a diverging shape that is common in several biological flow conduits, especially in mammals. Using the Fourier series, the dimensionless wall coordinates for sinusoidal, triangular, trapezoidal, and square wave forms are obtained to simulate wall movement. Equations expressing the pressure-flow rate relationship for different wall shapes are developed from the wave equation. Pressure-flow and velocity plots are obtained by solving the equations numerically. The results indicate that there is significant difference in pressure-flow relationship between Newtonian and non-Newtonian fluid. Also, the maximum flow rate can be achieved when the wall movement follows a square wave form.
The Use of Injury Biomechanics Principles and Tools in Transportation Accident Investigation
Authors: Poland Kristin M.
Published: May 2008

The National Transportation Safety Board is furthering its accident investigation capabilities by implementing biomechanical tools and principles in its accident investigative process. Vehicle dynamics simulation is a commonly used investigative tool implemented to develop a complete understanding of how the vehicle moved and accelerated during an accident. Now the Safety Board is looking at both the reactions and actions of the occupants within the vehicle in response to the vehicle dynamics. This paper highlights two cases in which the principles and tools of biomechanics are applied to aid in the investigative process.
Polymer-Filled Calcium Phosphate Cement: Mechanical Properties and Controlled Release of Growth Factor
Authors: Wang Francis W. , Khatri Chetan A. , Hsii Judy F.
Published: May 2008

Novel calcium phosphate cement (CPC) was developed by incorporating pore-forming particulates (porogens) to induce macropores and proteins to stimulate bone growth. A paste was made from CPC powder (0.15 g, equimolar mixture of tetracalcium phosphate and dicalcium phosphate), biodegradable polymer microspheres [0.1 g, volume fraction of 0.6, (0.17 to 0.36) mm in diameter], and 0.062 g of water. Disks for determining diametral tensile strength (DTS) and mass loss were prepared from the paste in a mold at 37 °C. Disks for the release of a protein were similarly prepared using a solution of the protein, and biodegradable polymer microspheres or water-soluble crystals (mannitol or salicylic acid) as porogens. The disks were immersed at 37 °C in an aqueous solution in order to quantify the effects of the solution on DTS and mass loss, as well as the release of the protein into the solution. The initial DTS value for the disks was (6.4 ± 0.9) MPa. The release of the protein from the CPC/porogen disks persisted for at least 300 h. The release rate of Protein A from the CPC/mannitol disks increased with the volume fraction of mannitol crystals. At a fixed volume fraction of porogens, the release rate of TGF-β1 from the CPC/porogen disks increased with the dissolution rate of the porogens. Thus, the release of a protein from composite grafts consisting of CPC and porogens can be modulated by the volume fraction and the dissolution rate of the porogens.
Acceleration Amplification in Safety Belt Buckle Systems
Authors: Herbst Brian , Meyer Steven E. , Forrest Stephen , Sances Anthony , Kumaresan Srirangam
Published: May 2008

Multi-planar rollover accidents report belt usage rates that are noted to be significantly lower than that of planar crash modes.1 One explanation for this dramatic difference in reported belt usage in rollovers as compared to planar crashes is that highway patrol officers often conclude that an ejection would not have occurred had the occupant been belted. Restrained occupants can be ejected from the vehicle if the seat belts fail to restrain occupants as a result of belt spool out or buckle unlatching.2,3 Previous studies have documented the susceptibility of certain safety belt buckles to inertially unlatch.4,5,6,7 Under sufficient vertical accelerations, top button safety belt buckles have inertially unlatched in testing which would obviously negate the safety belts ability to restrain the occupant. This study expands on the mechanisms that could lead to inertial release under vertical loading in safety belt buckle systems with stiff attachments to the vehicle floor. An audio transducer was attached to a vehicle floorpan to induce accelerations at variable frequency and amplitude. Accelerations were recorded at the floorpan and safety belt buckle body simultaneously. Accelerations measured at the buckle body were up to 13 times greater than the accelerations measured at the floor pan for frequencies up to 8.5 kHz. The present study provides a first step to better understand the injury biomechanics by quantifying the accelerations at the floor pan and safety belt buckle.
Towards the Development of Transient Compact Thermal Models of Electronic Packages That Are Consistent With Steady State Limits
Authors: Gabel Colleen M. , Ortega Alfonso
Published: May 2008

Recent progress is presented in the development of a class of transient compact thermal models (CTM’s) that may be used for predicting transient package junction temperatures independently of the boundary conditions imposed on the physical surfaces. The models are traditional RC networks in which the unknown capacitances are extracted by a non-linear optimization process. The resistors of the compact RC network model are values extracted in a traditional steady-state parameter extraction method. Validation results are presented for a canonical transient one-dimensional fin problem with a known analytical solution. Transient CTM’s were formulated for a three layer model exposed to three different BC sets. Using an optimization process based on error minimization of the transient junction temperature, the capacitances networks were extracted at early, middle, and late time intervals. The junction temperature predicted by the dynamic CTM was within 15% of a numerical model. As expected, for a fixed number of parameters, the optimal values of the capacitances are dependent on the time domain. Because the resistances are extracted from the steady state formulations, the dynamic CTM’s asymptote to steady state limits that are consistent with steady state CTM formulations. We hypothesize that the non-uniqueness of the parameter set for this type of reduced order thermal model leads to disparate sets of values that yield similar accuracy.
Application of a Computational Micro-Electro-Mechanical Model for the Prediction of Self-Heating of Ferroelectric Ceramic Materials
Authors: Weiland Lisa Mauck
Published: May 2008

Application of ferroelectric materials in devices subject to high fields and a range of drive frequencies is becoming increasingly common. As a result, self-heating of these devices is of concern. An energy based polycrystalline model including thermal and rate effects has been developed. The model has been developed from the thermodynamics of piezoelectrics, and includes elastic, dielectric, and piezoelectric anisotropy. It captures ferroelectric and ferroelastic switching under combined loading. In the current work the model is expanded to include self-heating effects. Model results are compared to experimental data. Results from the model give insight into material behavior.
AFM Studies of Tumor Cell Invasion
Authors: Chasiotis I. , Street D. C. , Fillmore H. L. , Gillies G. T.
Published: May 2008

Our recent investigations on human brain tumor (glioma) cell micro and nanodynamics via AFM methodologies have shown that brain tumor invadopodia (malignant cytostructural cell extensions with sensory, motility, and invasive characteristics extended by tumor cells into their environment) can assume specific geometries based on cell plating density and the location/distance of neighboring cells indicating strong cell sensing and signaling mechanisms between malignant cells and their surroundings. In certain occasions, cancer cell processes (extensions) have been found to be highly directional measuring more than 80 μm while invading neighboring cells by following a connecting straight path. Moreover, strong chemical gradients are suggested to influence the growth and motility of cell processes allowing for gradual adjustments of the direction of the invasive tumor extension. In response to external signals, tumor cell invadopodia develop micron-sized side-ligaments that follow the chemical gradients in their neighborhood and assist the reorientation of their main intrusive elements.
On the Strength of Kagome Structure for Multifunctional Materials
Authors: Hyun S.
Published: May 2008

From its intrinsic multiple phases, a composite with optimally designed microstructure is considered as one of ideal candidates for multifunctional materials. A structural optimization method (topology optimazation) was utilized to determine the optimal microstructure for multiple properties. From the optimization method which allows identifying the connectivity and shape of material phases in a composite, certain optimal structures have been found in the form of kagome lattice pattern. Numerical simulation and experimental test verified the kagome structures possess superior performance on transport properties and mechanical strength. I suggest their wide applications as a new class of multifunctional material in various length scales.
Phase Velocity Mapping Through a NiTi Stent With Different Levels of Stenosis
Authors: Holton Andrea D. , Venugopalan Ramakrishna , Walsh Edward G. , Brott Brigitta C. , Anayiotos Andreas S.
Published: May 2008

Magnetic Resonance Imaging has the potential to become the new gold standard in the management of cardiovascular disease, particularly in the assessment of arterial lesions and post-intervention restenosis. NiTi stents exhibit superior MRI compatibility and allow direct MR imaging through the stented area. In the present study, pulsatile in-vitro flow measuremnts were obtained by Magnetic Resonance Phase-Velocity mapping (MR-PVM) through a nickel-titanium alloy stent with different grades of stenosis: a) 75%, 90% (symmetric) and 50% (asymmetric). The results showed clear visibility of the lumen through the stenosis and good correlation of the phase velocity maps through the stent/stenosis when compared with independent calculations of flow. The detection and evaluation of instent restenosis using these techniques could provide a non-invasive means of screening for further management of patients.
Thermal Management of a Polyimide V-Groove Leg Actuator for a Walking Micro-Robot
Authors: Khire Ritesh A. , Kandlikar Satish G. , Walter Wayne W. , Raisanen Alan , Sahin Ferat
Published: May 2008

A model for a Polyimide V-groove leg actuator with a Polysilicon type heater was simulated using ANSYS 5.6. Potential areas for improvement were identified. These include the relative expansion of the Polyimide within the V-groove during the heating cycle, and the heat conduction path during the Cooling cycle. Various geometries were investigated, and results were compared with a Plane Wall V-groove design. Significant Net Gain was observed for the case of uniform diaphragm thickness at the V-groove bottom. Considering the simplicity of fabrication of this case, the uniform diaphragm V-groove geometry appears worthy of further investigation.
An Elastic/Viscoplastic Finite Element Model for Predicting Polymerization Stresses in Light-Activated Dental Composites
Authors: Laughlin Gayle A. , Williams John L. , Eick J. David
Published: May 2008

The purpose of this paper is to apply a finite deformation, elastic/viscoplastic approach to predict curing stresses in three light-cured dental composites, using Perzyna’s theory. Time-dependent constitutive parameters were obtained from mercury dilatometry, dynamic mechanical analysis and constrained shrinkage strerss testing. The numerical approach was verified by using the results of an experiment on a simple aluminum tooth model of a cavity preparation that was bulk-filled with light-cured dental composite restorative materials. The numerically predicted strain patterns were similar to those seen experimentally for the three different dental composites.
Elasto-Multibody Dynamic Simulation of Impact Induced High Frequency Vehicular Driveline Vibrations
Authors: Gnanakumarr M. , Theodossiades S. , Rahnejat H. , Menday M.
Published: May 2008

This paper investigates an NVH (Noise, Vibration and Harshness) phenomenon, which occurs as a load reversal in the presence of lashes in the driveline and is known in industry as clonk. A combined study of rigid multi-body dynamic analysis and flexible body oscillations, using super-element FEA techniques is being deployed. The results show high contribution in the driveline vibrational response of certain structural modes of the driveshaft pieces, induced by remote impacting of meshing transmission teeth trough backlash. The predicted spectrum of vibration shows good conformance with previously obtained experimental values, for both impact testing of the driveshaft pieces, as well as those obtained by vibration monitoring of experimental rigs (Vafaei et al, 2001).
Tibiofemoral Contact After Conventional and High-Flexion Posterior Cruciate-Retaining Total Knee Arthroplasty
Authors: Most Ephrat , Li Guoan , Rubash Harry E.
Published: May 2008

The human knee is capable of flexing up to 160°, yet most patients do not achieve more than 120° after total knee arthroplasty (TKA). The translation of the tibiofemoral contact points with flexion is important in the overall understanding of knee kinematics and knee stability, particularly in high flexion. In this study, cadaveric knees were used in conjunction with a robotic testing system and TekScan® film to quantify the tibiofemoral contact between 0°–150° for two TKA designs. We found that, for both TKAs, with increasing knee flexion, the peak contact point moved posteriorly and that the contact area decreased with increasing knee flexion.
Dynamics of Cerebrospinal Fluid in the Subrachnoid Space Within Spinal Cavity
Authors: Peng Jifeng , Zheng Lili , Egnor Michael , Wagshul Mark
Published: May 2008

In this paper, a computational study was carried out to investigate the CSF dynamics in the spinal cavity. A theoretical and computational model was developed to simulate the pulsatile CSF flow and the deformation of the spinal cavity that results from transmission of the CSF pulse wave from the cranial cavity. Under a pulsatile pressure gradient, the velocity profile of the flow is blunt for large Womersley numbers, while for small Womersley numbers the velocity profile is parabolic. The phase relationship between the pressure and the velocity is also related to Womersley number. This is the first step to understand the pulsatile dynamics of the CSF in the spinal cavity and will help explain the cause of related diseases and improve the clinical treatment.
Evaluation of a Pure Moment Exciter for Measurement of Rotational DOF Frequency Response Functions
Authors: Majewski Michael J. , Tretheway Martin W. , Sommer H. Joseph
Published: May 2008

Experimental data in the form of a mobility matrix is needed for a variety of purposes including substructure synthesis, Structural Dynamics Modification (SDM) and updating of Finite Element Models (FEM). A computational based mobility matrix contains responses from both translational and rotational components. Experimentally, the rotational components are usually ignored because of the inherent difficulty in their measurement. A review of previous direct and indirect efforts to estimate rotationally excited frequency response functions is presented. Next a novel direct experimental method to measure translation and rotation responses from a pure moment excitation is discussed. The method uses a set of geared eccentric masses to create a pure moment. The theory of operation is discussed first. A set of laboratory tests was performed to evaluate the performance of a prototype device. Analytical predictions were nominally within 5% of the experimental values for the desired moment excitation. However, unwanted forces and cross axis moment excitations were also measured. Simulations indicate that nonideal performance results from maufacturing and assembly variations. The investigation concludes with an assessment of the method’s potential for direct experimental measurement of rotational components in the mobility matrix.
Combined Edge and Anisotropy Effects on Fickian Mass Diffusion in Polymer Composites
Authors: Aktas Levent , Hamidi Youssef K. , Altan M. Cengiz
Published: May 2008

The common methods used to determine the diffusion coefficients of polymer composites are based on the solution of Fickian diffusion equation in one-dimensional rectangular domain. However, these diffusivities usually involve errors primarily due to finite sample dimensions and anisotropy introduced by fiber reinforcements. In this study, the solution of transient, three-dimensional anisotropic Fickian diffusion equation is non-dimensionalized using six parameters. The solution is then used to analyze the combined contribution of finite sample dimensions and anisotropy to the errors involved in diffusion constants calculated by one-dimensional methods. The small time solution of the Fickian diffusion equation in three-dimensional domain is used to analyze the slope used in diffusivity calculations. It is shown that the diffusion coefficient calculated by one-dimensional approach is exact only if the correct slope of percent mass gain versus root square time curve at t=0 is used. However, it has also been shown that depending on the part geometry and degree of anisotropy, there might be considerable differences between the measured slope from the experimental data and the actual slope at t=0. The mismatch between the slopes results in as much as 50% errors in estimates of diffusion coefficients. Using the three-dimensional solution in non-dimensional form, the magnitudes of these errors are studied. A least square curve fit method, which yields accurate anisotropic diffusion coefficients, is proposed. The method is demonstrated on artificially generated experimental data for a polymer composite containing 50% unidirectional reinforcement. The anisotropic diffusion coefficients used to generate the data are recovered with less than 1% error.
High Frequency Vibration Analysis of Automotive Bodies With Panels That Have Attached Viscoelastic Layers
Authors: Kurosawa Yoshio , Enomoto Hideki , Matsumura Shuji , Yamaguchi Takao
Published: May 2008

A technique has been developed for estimating vibrations of an automotive body structures with viscoelastic damping materials using large-scale finite element (FE) model, which will enable us to grasp and to reduce high-frequency road noise (200∼500Hz). In the new technique, first order solutions for modal loss factors are derived applying asymptotic method. This method saves calculation time to estimate modal damping as a practical tool in the design stages of the body structures. Frequency responses were calculated using this technique and the results almost agreed with the test results. This technique can show the effect of the viscoelastic damping materials on the automotive body panels, and it enables the more efficient layout of the viscoelastic damping materials. Further, we clarified damping properties of the automotive body structures under coupled vibration between frames and panels with the viscoelastic damping materials.
Non-Linear Intracranial Dynamics of Shunt Siphoning
Authors: Capanzano Vanessa A. , Peng Jifeng , Zheng Lili , Egnor Michael , Washgul Mark
Published: May 2008

Siphoning is commonly associated with shunts, a treatment used in patients suffering from Hydrocephalus. Siphoning is known to have a negative effect on intracranial dynamics. In this paper, a model will be developed for the intracranial dynamics in the presence of siphoning based on the assumption of pulsatile intracranial dynamics as a forced non-linear van der Pol oscillator. This non-linear model is used to simulate how various degrees of siphoning can effect intracranial dynamics and create an understanding of painful side effects, such as vascular headaches. The model suggests that vascular headaches are due to an increase in the amplitude of arterial pulsations caused by the force exerted on the cranium by siphoning rather than due to volume shifts of cerebrospinal fluid (CSF).
Experiments for Online Estimation of Heavy Vehicle’s Mass and Time-Varying Road Grade
Authors: Vahidi Ardala , Stefanopoulou Anna , Peng Huei
Published: May 2008

In this paper application of recursive least squares with multiple forgetting factors is explained for online estimation of Heavy Duty Vehicle mass and road grade. The test data is obtained from highway experiments with a Freightliner truck. The experimental setup is explained in detail. This data is used to validate the longitudinal dynamics model of the truck. Then two distinct driving cycles are used to investigate the performance of the mass and grade estimation scheme. In he first scheme no gear shift occurs and the only concern is persistence of excitations. It is shown that if the excitations are persistent, mass and time-varying grade are estimated with good accuracy. In the second cycle gearshifts occur and the challenge is the unmodelled dynamics during gearshifts which cause large overshoots in the estimates. A method is proposed to circumvent this problem and good estimation results are shown with this provision.
Thermal Modeling of a Reversing Valve in a Refrigeration System
Authors: Raichintala Shirish , Kulkarni Manohar
Published: May 2008

A mathematical model of a reversing valve was developed in order to evaluate the losses and for determining the effects of a reversing valve, on the performance of a heat pump. This mathematical model of the reversing valve was tested using the experimental data of Fang and Nutter (1999). The theoretical predictions made by this model agreed with that of the experimental data. Further, the mathematical model isolated the pressure losses due to friction; pipe-fittings, mass-leakage and heat transfer from the total losses. The evaluation of constituent losses assisted in detecting a faculty reversing valve, and also determining the effect of mass leakage and heat leakage on the compressor work input and COP of the heat pump.
Suppression of Persistent Rotor Vibrations Using Adaptive Techniques
Authors: Matras Alex L. , Flowers George T. , Fuentes Robert , Balas Mark , Fausz Jerry
Published: May 2008

Recent work in the area of adaptive control has seen the development of techniques for the adaptive rejection of persistent disturbances for structural systems. They have been implemented and tested for large-scale structural systems, with promising results, but have not been widely applied to smallerscale systems and devices. Rotor systems are subject to a variety of persistent disturbances (for example, due to mass imbalance, blade-pass effects) that occur at the rotor running speed or multiples of the running speed. The frequencies of such disturbance forces are generally known, but their magnitudes tend to vary over time. Adaptive techniques to counter the effects of such disturbances would appear to be a promising strategy in this regard. In order to assess the effectiveness of adaptive disturbances rejection for rotor applications and identify issues associated with implementation, and adaptive disturbance rejection control is developed, implemented, and tested for a magnetic-bearing-supported rotor system. Some conclusions and insights concerning the application of this method to rotor system vibration suppression are presented and discussed.
Particle Separation Using Dielectrophoresis
Authors: Kadaksham J. , Singh P. , Aubry N.
Published: May 2008

A numerical scheme based on the distributed Lagrange multiplier (DLM) method is used to simulate the process of separation of particles with different dielectric properties suspended in an electrorheological (ER) fluid and subjected to a nonuniform electric field. The dielectrophoresis induced separation of particles is possible only when the sign of Clausius-Mossoti factor for the particles is different, as in this case the dielectrophoretic force moves them to different regions of the device. The time required for separation of particle in simulations is larger than that given by an order or magnitude analysis because of the formation of particle chains which arise due to the dipole-dipole interactions among the particles and move much more slowly than isolated particles.
Virtual DesignWorks: Designing 3D CAD Models Via Touch Interaction
Authors: Liu X. , Dodds G. , Hinds B. K. , McCartney J.
Published: May 2008

Virtual reality (VR) devices, such as haptic (force feedback) devices, provide users with virtual environments where they can interact with digital models in 3D. Haptic devices show great promise for use in design. However, current haptic systems are used primarily to verify rather than to interact with CAD systems to modify a design. In order to use haptic devices in the design of CAD models, we use component technology (COM+) to develop a novel haptic model system—which we have termed super-object modeling. The novel haptic model solves several crucial problems for seamlessly integrating CAD models with haptic models, such as the efficient exchange of complex models in real-time, real-time model updating, and the issue related to CPU power etc. Based on this super-object modeling, we have developed a virtual reality system, called Virtual DesignWorks. The system provides a new approach to 3D design—Designing CAD models via touch interaction. Engineers or designers can, in virtual space, directly touch native B-rep CAD models, feel and deform the CAD models rather than just verify a design. Super-object modeling represents the first development of haptic geometric models based on component technology. It demonstrates significant advantages compared to the traditional haptic models. With this technology, touch interaction has the potential to become a critical interface of design, and force feedback gives designers the greatest flexibility for 3D design.
High Authority Piezoelectric Actuation System Synthesis Through Mechanical Resonance and Electrical Tailoring
Authors: Kim Jun-Sik , Wang K. W. , Smith Edward C.
Published: May 2008

In this research, a new approach is proposed to enhance the effectiveness of piezoelectric actuators without the trade off between force and stroke. Through mechanical tailoring, the resonant frequencies of the actuation system (includes the piezoelectric actuator and the related mechanical and the electrical elements for actuation) can be tuned to the required actuation frequencies. This obvious will increase the authority (both stroke and force) of the actuation system. However, resonant actuation system could be hard to control and non-robust, due to its narrow operating bandwidth. This issue can be resolved through electric circuit tailoring. With the aid of a network of inductance, resistance, and negative capacitance, the actuation resonant peak can be significantly broadened and flattened. In this case, one can achieve a high authority actuation system without the negative effects of resonant problems. The electrical networks can also a achieve a fail-safe system due to its passive shunting characteristic. The proposed concept is evaluated using a PZT tube actuator for trailing edge flap control of rotocraft blades. Promising results are demonstrated, showing that the treatment can indeed create a high authority and robust actuation system that satisfies the performance requirements of the example application. Also, the proposed concept is verified by experiments using an equivalent circuit model with synthetic inductor and negative impedance converter of capacitance.
Electrokinetic Microflow Instability With Conductivity Gradients
Authors: Chen Chuan-Hua , Lin Hao , Lele Sanjiva K. , Santiago Juan G.
Published: May 2008

We have experimentally identified and quantified an electrokinetic flow instability that occurs in DC-electric-field driven microfluidic channels with significant conductivity gradients. We have, for the first time, developed a physical model for this instability which captures the interactions between bulk charge accumulation, electromigration, convection, and diffusion. A linear stability analysis based on this model captures key physics of this convective instability with a threshold electric field. The model and experiments show conductivity gradients and their associated bulk charge accumulation are crucial for such instabilities.
Enhanced Diffusion Due to Swimming Bacteria
Authors: Kim Min Jun , Breuer Kenneth S.
Published: May 2008

The effect of bacterial motion of the diffusion of a high molecular weight molecule is studied by observing the mixing of two streams of fluid in a micro-fabricated flow cell. The presence of Escherichia coli (E.coli) in one of the streams results in an increase in the effective diffusion coefficient of Dextran, which rises linearly with the concentration of bacteria from a baseline value of 2 × 10−7 cm2/s to 8 × 10−7 cm2/s at a concentration of 2.1 × 109 /ml (approximately 0.5 % by volume). The diffusion process is also observed to undergo a change from standard “Fickian” diffusion to a superdiffusive behavior in which the diffusion exponent rises from 0.5 to 0.55 as the concentration of bacteria rises from 0 to 2.1 × 109/ml.
Near-Surface Velocimetry Using Evanescent Wave Illumination
Authors: Jin Songwan , Huang Peter , Park Jinil , Yoo Jung Yul , Breuer Kenneth S.
Published: May 2008

Total internal reflection fluorescent microscopy (TIRFM) is used to measure particle motion in the near wall region of a microfluidic system. TIRFM images have minimum background noise and contain only particles that are very close to channel surface, where slip velocities may be present. Submicron sized fluorescent particles suspended in water are used as seed particles and images are analyzed with a PTV algorithm to extract information about apparent slip velocity. At relatively low shear rates (less than 2500 sec−1), an apparent slip velocity, proportional to the shear rate was observed. However, numerical simulations show that this observation is a direct consequence of the small, but finite thickness of the illuminated region, and most likely not due to physical slip at the surface. The statistical difference in apparent slip velocities measured over hydrophilic and hydrophobic surfaces is found to be minimal. Issues associated with the experimental technique and the interpretation of the experimental results are also discussed.
Transit Characteristics of a Deformed Neutrophil Through a Moderate Constriction
Authors: Shirai Atsushi , Fujita Ryo , Hayase Toshiyuki
Published: May 2008

This paper deals with the transit of a neutrophil through narrow capillary segments. In the segments are modeled by arc-shaped constrictions arranged in a straight pipeline. Initially the spherical cell deforms in transit through the first constriction. We focus on the transit time to the deformed cell through the second constriction. We investigate the effects of segment geometry on the transit time. Finally, it is shown that the transit time is independent of the shape of the first segment so long as it is organized by the entrance cell radius.
Bifurcation Control of Ro¨ssler System
Authors: Wu Z. Q. , Yu P.
Published: May 2008

In this paper, a new method is proposed for controlling bifurcations of nonlinear dynamical systems. This approach employs the idea used in deriving the transition variety sets of bifurcations with constraints to find the stability region of equilibrium points in parameter space. With this method, one can design, via a feedback control, appropriate parameter values to delay either static, or dynamic or both bifurcations as one wishes. The approach is applied to consider controlling bifurcations of the Ro¨ssler system. The uncontrolled Ro¨ssler has two equilibrium solutions, one of which exhibits static bifurcation while the other has Hopf bifurcation. When a feedback control based on the new method is applied, one can delay the bifurcations and even change the type of bifurcations. An optimal control law is obtained to stabilize the Ro¨ssler system using all feasible system parameter values. Numerical simulations are used to verify the analytical results.
A Computational Study of Interfacial Stress Distribution in Unidirectional Composites and Its Use in Prediction of Brittle Failure
Authors: Chen Xiaoming , Papathanasiou Thanasis D.
Published: May 2008

A computational investigation has been conducted to examine the effect of key microstructural and material parameters, namely the minimum inter-fiber spacing (δ) and the fiber/matrix stiffness ratio (Ef/Em), on the interfacial stress distributions in unidirectional composites subjected to transverse uniaxial tensile load. Representative Volume Elements (RVE’s) containing 144 fibers are constructed using a Monte-Carlo (MC) algorithm, imitating random composite structures. The boundary element method is then used to solve the multi-region elasticity problem on these microstructures. We pay particular attention to the statistics of the distribution of the maximum interfacial stresses computed on each fiber; these are found to follow a Weibull distribution, whose specific shape depends on both microstructural and material parameters. Following the weakest-link theory of Batdorf and Crose [1], we derive a statistical formula for the prediction of brittle failure of composite structures caused by interfacial failure. The limitations and possible extensions to the proposed approach are discussed as well.
Position/Rate Haptic Control of a Hydraulic Forklift
Authors: Konz Matthew E. , Book Wayne J.
Published: May 2008

This paper discusses a haptic control strategy that can switch between position and rate control on the fly. When manipulating a remote device through teleoperation it is often desirable to complete tasks in position mode. This is because the slave is mimicking the motion of the master device (i.e. the human operator). Pure position control breaks down if the slave is a non holonomic device such as a forklift truck, earth moving vehicle or a skid-steer loader and the master has a holonomic robot with a finite workspace. In order to drive around, the forward motion must be controlled in rate mode when the device is move over long distances. Horizontal motion of the vehicle is also used to manipulate the end effector. Since tasks done by end effector are often done in a small region it is desirable to be able to switch into position mode in order to complete tasks with the end effector. Experimental results are presented using a PHANTOM as the haptic display and a Hydraulically Actuate Lifter (HAL) as a remote manipulator. These results show how a position/rate controller would behave in unconstrained motion, in the presence of virtual constraints and while picking up a load with the end effector.