bluuebunny/crossref_metadata_2025 huggingface dataset:
Relationships Between Alveolar Size and Fibre Distribution in a Mammalian Lung Alveolar Duct Model
Authors: Denny E. , Schroter R. C.
Published: February 2008

A finite element model, comprising an assemblage of tetrakaidecahedra or truncated octahedra, is used to represent an alveolar duct unit. The dimensions of the elastin and collagen fibre bundles, and the surface tension properties of the air-liquid interfaces, are based on available published data. Changes to the computed static pressure-volume behavior with variation in alveolar dimensions and fibre volume densities are characterized using distensibility indices (K). The air-filled lung distensibility (Ka) decreased with a reduction in the alveolar airspace length dimensions and increased with a reduction of total fibre volume density. The saline-filled lung distensibility (Ks) remained constant with alveolar dimensions and increased with decreasing total fibre volume density. The degree of geometric anisotropy between the duct lumen and alveoli was computed over pressure-volume cycles. To preserve broadly isotropic behavior, parenchyma with smaller alveolar airspace length dimensions required higher concentrations of fibres located in the duct and less in the septa in comparison with parenchyma of larger airspace dimensions.
Gas Dispersion in a Model Pulmonary Bifurcation During Oscillatory Flow
Authors: Nishida M. , Inaba Y. , Tanishita K.
Published: February 2008

In order to clarify the gas transport process in high-frequency oscillation, we measured the axial velocity profile and the axial effective diffusivity in a single asymmetric bifurcating tube, based on the Horsfield airway model, with sinusoidally oscillatory flow. The axial velocity profiles were measured using a laser-Doppler velocimeter, and the effective diffusivities were evaluated using a simple bolus injection method. The axial velocity profile was found to be nonuniform, promoting axial gas dispersion by the spread of the concentration profile and lateral mixing. The geometric asymmetry of the bifurcation was responsible for the difference in gas transport between the main bronchi. The axial gas transport in the left main bronchus was 2.3 times as large as that of the straight tube, whereas the gas transport in the right main bronchus was slightly larger than that of the straight tube. Thus localized variation in gas transport characterized the heterogeneous respiratory function of the lung.
Stress Wave Velocities in Bovine Patellar Tendon
Authors: Crisco J. J. , Dunn T. C. , McGovern R. D.
Published: February 2008

The velocity of longitudinal stress waves in an elastic body is given by the square root of the ratio of its elastic modulus to its density. In tendinous and ligamentous tissue, the elastic modulus increases with strain and with strain rate. Therefore, it was postulated that stress wave velocity would also increase with increasing strain and strain rate. The purpose of this study was to determine the velocity of stress waves in tendinous tissue as a function of strain and to compare these values to those predicted using the elastic modulus derived from quasi-static testing. Five bovine patellar tendons were harvested and potted as bone–tendon–bone specimens. Quasi-static mechanical properties were determined in tension at a deformation rate of 100 mm/s. Impact loading was employed to determine wave velocity at various strain levels, achieved by preloading the tendon. Following impact, there was a measurable delay in force transmission across the specimen and this delay decreased with increasing tendon strain. The wave velocities at tendon strains of 0.0075, 0.015, and 0.0225 were determined to be 260 ± 52 m/s, 360 ± 71 m/s, and 461 ± 94 m/s, respectively. These velocities were significantly (p < 0.01) faster than those predicted using elastic moduli derived from the quasi-static tests by 52, 45, and 41 percent, respectively. This study has documented that stress wave velocity in patellar tendon increases with increasing strain and is underestimated with a modulus estimated from quasi-static testing.
Investigation Into the Biphasic Properties of a Hydrogel for Use in a Cushion Form Replacement Joint
Authors: Goldsmith A. A. J. , Clift S. E.
Published: February 2008

A hydrogel with potential applications in the role of a cushion form replacement joint bearing surface material has been investigated. The material properties are required for further development and design studies and have not previously been quantified. Creep indentation experiments were therefore performed on samples of the hydrogel. The biphasic model developed by Mow and co-workers (Mak et al., 1987; Mow et al., 1989a) was used to curve-fit the experimental data to theoretical solutions in order to extract the three intrinsic biphasic material properties of the hydrogel (aggregate modulus, HA, Poisson’s ratio, νs, and permeability, k). Ranges of material properties were determined: aggregate modulus was calculated to be between 18.4 and 27.5 MPa, Poisson’s ratio 0.0–0.307, and permeability 0.012–7.27 × 10−17 m4/Ns. The hydrogel thus had a higher aggregate modulus than values published for natural normal articular cartilage, the Poisson’s ratios were similar to articular cartilage, and finally the hydrogel was found to be less permeable than articular cartilage. The determination of these values will facilitate further numerical analysis of the stress distribution in a cushion form replacement joint.
Simulation of a Cold-Stressed Finger Including the Effects of Wind, Gloves, and Cold-Induced Vasodilatation
Authors: Shitzer A. , Bellomo S. , Stroschein L. A. , Gonzalez R. R. , Pandolf K. B.
Published: February 2008

The thermal response of fingers exposed to cold weather conditions has been simulated. Energy balance equations were formulated, in a former study, for the tissue layers and the arterial, venous, and capillary blood vessels. The equations were solved by a finite difference scheme using the Thomas algorithm and the method of alternating directions. At this stage of development the model does not include any autonomic control functions. Model simulations assumed an electrical heating element to be embedded in the glove layers applied on the finger. A 1.3 W power input was calculated for maintaining finger temperatures at their pre-cold exposure level in a 0°C environment. Alternate assumptions of nutritional (low) and basal (high) blood flows in the finger demonstrated the dominance of this factor in maintaining finger temperatures at comfortable levels. Simulated exposures to still and windy air, at 4.17 m/s (15 km/h), indicated the profound chilling effects of wind on fingers in cold environments. Finally, the effects of variable blood flow in the finger, known as “cold-induced vasodilatation,” were also investigated. Blood flow variations were assumed to be represented by periodic, symmetric triangular waves allowing for gradual opening-closing cycles of blood supply to the tip of the finger. Results of this part of the simulation were compared with measured records of bare finger temperatures. Good conformity was obtained for a plausible pattern of change in blood flow, which was assumed to be provided in its entirety to the tip of the finger alone.
Factor Xa Generation at the Surface of Cultured Rat Vascular Smooth Muscle Cells in an in Vitro Flow System
Authors: Hall C. L. , Taubman M. B. , Nemerson Y. , Turitto V. T.
Published: February 2008

The purpose of the present investigation was to explore the effects of well-defined flow conditions on the activity of tissue factor (TF) expressed on the surface of cultured rat vascular smooth muscle cells. Cells were cultured to confluence on Permanox brand slides and stimulated to express TF by a 90 min incubation with fresh growth medium containing 10 percent calf serum. The stimulated cells were then placed in a parallel plate flow chamber and perfused with Hank’s Balanced Salt Solution containing factor VIIa, factor X (FX), and calcium. The chamber effluent was collected and assayed for factor Xa (FXa) and the steady-state flux of FXa was calculated. The flux values were 68.73, 94.81, 139.75, 138.19, 316.82, and 592.92 fmole/min/cm2 at wall shear rates of 10, 20, 40, 80, 320, and 1280 s−1 respectively. The FXa flux depended on the wall shear rate to a greater degree than predicted by classical mass transport theory. The flux at each shear rate was three to five times less than that calculated according to the Leveque solution. These features of the experimental data imply nonclassical behavior, which may partially result from a direct effect of flow on the cell layer.
A Hub Dynamometer for Measurement of Wheel Forces in Off-Road Bicycling
Authors: De Lorenzo D. S. , Hull M. L.
Published: February 2008

A dynamometric hubset that measures the two ground contact force components acting on a bicycle wheel in the plane of the bicycle during off-road riding while either coasting or braking was designed, constructed, and evaluated. To maintain compatibility with standard mountain bike construction, the hubs use commercially available shells with modified, strain gage-equipped axles. The axle strain gages are sensitive to forces acting in the radial and tangential directions, while minimizing sensitivity to transverse forces, steering moments, and variations in the lateral location of the center of pressure. Static calibration and a subsequent accuracy check that computed differences between applied and apparent loads developed during coasting revealed root mean squared errors of 1 percent full-scale or less (full-scale load = 4500 N). The natural frequency of the rear hub with the wheel attached exceeded 350 Hz. These performance capabilities make the dynamometer useful for its intended purpose during coasting. To demonstrate this usefulness, sample ground contact forces are presented for a subject who coasted downhill over rough terrain. The dynamometric hubset can also be used to determine ground contact forces during braking providing that the brake reaction force components are known. However, compliance of the fork can lead to high cross-sensitivity and corresponding large (>5 percent FS) measurement errors at the front wheel.
The Effects of the Surface Topography of Micromachined Titanium Substrata on Cell Behavior in Vitro and in Vivo
Authors: Brunette D. M. , Chehroudi B.
Published: February 2008

Surface properties, including topography and chemistry, are of prime importance in establishing the response of tissues to biomaterials. Microfabrication techniques have enabled the production of precisely controlled surface topographies that have been used as substrata for cells in culture and on devices implanted in vivo. This article reviews aspects of cell behavior involved in tissue response to implants with an emphasis on the effects of topography. Microfabricated grooved surfaces produce orientation and directed locomotion of epithelial cells in vitro and can inhibit epithelial downgrowth on implants. The effects depend on the groove dimensions and they are modified by epithelial cell–cell interactions. Fibroblasts similarly exhibit contact guidance on grooved surfaces, but fibroblast shape in vitro differs markedly from that found in vivo. Surface topography is important in establishing tissue organization adjacent to implants, with smooth surfaces generally being associated with fibrous tissue encapsulation. Grooved topographies appear to have promise in reducing encapsulation in the short term, but additional studies employing three-dimensional reconstruction and diverse topographies are needed to understand better the process of connective-tissue organization adjacent to implants. Microfabricated surfaces can increase the frequency of mineralized bone-like tissue nodules adjacent to subcutaneously implanted surfaces in rats. Orientation of these nodules with grooves occurs both in culture and on implants. Detailed comparisons of cell behavior on micromachined substrata in vitro and in vivo are difficult because of the number and complexity of factors, such as population density and micromotion, that can differ between these conditions.
An In Vitro Osteotomy Method to Expose the Medial Compartment of the Human Knee
Authors: Martens T. A. , Hull M. L. , Howell S. M.
Published: February 2008

This study was conducted to validate a new in vitro method to expose the medial compartment of the knee to be used in subsequent studies aimed at examining the load bearing capabilities of medial meniscal allografts. The new method involves an osteotomy and reattachment of the medial femoral condyle. The primary hypothesis was that the new method does not alter tibio-femoral contact pressure and area. To validate this method, the baseline contact pressure of the intact medial compartment was measured using a new nondestructive procedure for inserting pressure measurement film into the intact medial hemijoint. A secondary and related hypothesis was that incising the coronary ligament, a destructive method used by previous investigators to position pressure measurement film, alters the normal tibio-femoral contact pressure. To test these hypotheses, Fuji Prescale pressure-sensitive film was used to measure both tibio-femoral contact pressure and area within the medial compartment of the (1) intact knee, (2) the knee after osteotomizing and reattaching the medial femoral condyle, and (3) the osteotomized knee with an incised coronary ligament, using seven cadaver specimens. Measurements were taken at a compressive load of approximately two times body weight with the knee in 0, 15, 30, 45 deg of flexion. No significant differences between the intact and osteotomized knee were detected. Likewise, no significant differences were observed between the osteotomized knee and the osteotomized knee with an incised coronary ligament. These results confirm the utility of the new method in exposing the medial compartment for manipulation and placement of medial meniscal allografts in future studies examining the load-bearing characteristics of meniscal allografts.
Intraoperative Measurement and Biomechanical Modeling of the Flexor Carpi Ulnaris-to-Extensor Carpi Radialis Longus Tendon Transfer
Authors: Lieber R. L. , Fride´n J.
Published: February 2008

Sarcomere length was measured intraoperatively in five patients undergoing tendon transfer of the flexor carpi ulnaris (FCU) to the extensor carpi radialis longus (ECRL) for radial nerve palsy. All measurements were made with the elbow in 20 deg of flexion. Prior to tendon transfer, FCU sarcomere length ranged from 2.84 ±. 12 μm (mean ± SEM) with the wrist flexed to 4.16 ± .15 μm with the wrist extended. After transfer into the ECRL tendon, sarcomere length ranged from 4.82 ± .11 μm with the wrist flexed (the new longest position of the FCU) to 3.20 ± .09 μm with the wrist extended, resulting in a shift in the sarcomere length operating range to significantly longer sarcomere lengths (p < 0.001). At these longer sarcomere lengths, the FCU muscle was predicted to develop high active tension only when the wrist was highly extended. A biomechanical model of this tendon transfer was generated using normative values obtained from previous studies of muscle architectural properties, tendon compliance, and joint moment arms. Predicted sarcomere lengths pre- and post-tendon transfer agreed well with intraoperative experimental measurements. The theoretical wrist extension moment-wrist joint angle relationship was also calculated for a variety of values of FCU muscle length. These different lengths represented the different conditions under which the FCU could be sutured into the ECRL tendon. Variation in FCU muscle length over the range 200 mm to 260 mm resulted in large changes in absolute peak moment produced as well as the angular dependence of peak moment. This was due to the change in the region of FCU operation on its sarcomere length-tension curve relative to the magnitude of the ECRL moment arm. These data demonstrate the sensitivity of a short-fibered muscle such as the FCU to affect the functional outcome of surgery. In addition, we demonstrated that intraoperative sarcomere length measurements, combined with biomechanical modeling provide the surgeon with a powerful method for predicting the functional effect of tendon transfer surgery.
Measurements of Airway Dimensions and Calculation of Mass Transfer Characteristics of the Human Oral Passage
Authors: Cheng K.-H. , Cheng Y.-S. , Yeh H.-C. , Swift D. L.
Published: February 2008

This paper presents measurements of the geometric shape, perimeter, and cross-sectional area of the human oral passage (from oral entrance to midtrachea) and relates them through dimensionless parameters to the depositional mass transfer of ultrafine particles. Studies were performed in two identical replicate oral passage models, one of which was cut orthogonal to the airflow direction into 3 mm elements for measurement, the other used intact for experimental measurements of ultrafine aerosol deposition. Dimensional data were combined with deposition measurements in two sections of the oral passage (the horizontal oral cavity and the vertical laryngeal–tracheal airway) to calculate the dimensionless mass transfer Sherwood number (Sh). Mass transfer theory suggests that Sh should be expressible as a function of the Reynolds numper (Re) and the Schmidt number (Sc). For inhalation and exhalation through the oral cavity (O-C), an empirical relationship was obtained for flow rates from 7.5–30.0 1 min−1: Sh=15.3Re0.812Sc−0.986 An empirical relationship was likewise obtained for the laryngeal–tracheal (L-T) region over the same range of flow rates: Sh=25.9Re0.861Sc−1.37 These relationships were compared to heat transfer in the human upper airways through the well-known analogy between heat and mass transfer. The Reynolds number dependence for both the O-C and L-T relationships was in good agreement with that for heat transfer. The mass transfer coefficients were compared to extrathoracic uptake of gases and vapors and showed similar flow rate dependence. For gases and vapors that conform to the zero concentration boundary condition, the empirical relationships are applicable when diffusion coefficients are taken into consideration.
The Accuracy of Digital Image-Based Finite Element Models
Authors: Guldberg R. E. , Hollister S. J. , Charras G. T.
Published: February 2008

Digital image-based finite element meshing is an alternative approach to time-consuming conventional meshing techniques for generating realistic three-dimensional (3D) models of complex structures. Although not limited to biological applications, digital image-based modeling has been used to generate structure-specific (i.e., nongeneric) models of whole bones and trabecular bone microstructures. However, questions remain regarding the solution accuracy provided by the digital meshing approach, particularly at model or material boundaries. The purpose of this study was to compare the accuracy of digital and conventional smooth boundary models based on theoretical solutions for a two-dimensional (2D) compression plate and a 3D circular cantilever beam. For both the plate and beam analyses, the predicted solution at digital model boundaries was characterized by local oscillations, which produced potentially high errors within individual boundary elements. Significantly, however, the digital model boundary solution oscillated approximately about the theoretical solution. A marked improvement in solution accuracy was therefore achieved by considering average results within a region composed of several elements. Absolute errors for Von Mises stress averaged over the beam cross section, for example, converged to less than 4 percent, and the predicted free-end displacement of the cantilever beam was within 1 percent of the theoretical solution. Analyses at several beam orientations and mesh resolutions suggested a minimum discretization of three to four digital finite elements through the beam cross section to avoid high numerical stiffening errors under bending.
Cervical Spine Vertebral and Facet Joint Kinematics Under Whiplash
Authors: Yoganandan N. , Pintar F. A. , Klienberger M.
Published: February 2008

Whiplash injuries sustained during a rear-end automobile collision have significant societal impact. The scientific literature on whiplash loading is both diverse and confusing. Definitive studies are lacking to describe the local mechanisms of injury that induce either acute or chronic pain symptoms. A methodology has been presented to quantify the kinematics of the cervical spine components by inducing controlled whiplash-type forces to intact human head-neck complexes. The localized facet joint kinematics and the overall segmental motions of the cervical spine are presented. It is anticipated that the use of this methodology will assist in a better delineation of the localized mechanisms of injury leading to whiplash pain.
A Numerical Study of Blood Flow Patterns in Anatomically Realistic and Simplified End-to-Side Anastomoses
Authors: Moore J. A. , Steinman D. A. , Prakash S. , Johnston K. W. , Ethier C. R.
Published: February 2008

Purpose: Recently, some numerical and experimental studies of blood flow in large arteries have attempted to accurately replicate in vivo arterial geometries, while others have utilized simplified models. The objective of this study was to determine how much an anatomically realistic geometry can be simplified without the loss of significant hemodynamic information. Method: A human femoral-popliteal bypass graft was used to reconstruct an anatomically faithful finite element model of an end-to-side anastomosis. Nonideal geometric features of the model were removed in sequential steps to produce a series of successively simplified models. Blood flow patterns were numerically computed for each geometry, and the flow and wall shear stress fields were analyzed to determine the significance of each level of geometric simplification. Results: The removal of small local surface features and out-of-plane curvature did not significantly change the flow and wall shear stress distributions in the end-to-side anastomosis. Local changes in arterial caliber played a more significant role, depending upon the location and extent of the change. The graft-to-host artery diameter ratio was found to be a strong determinant of wall shear stress patterns in regions that are typically associated with disease processes. Conclusions: For the specific case of an end-to-side anastomosis, simplified models provide sufficient information for comparing hemodynamics with qualitative or averaged disease locations, provided the “primary” geometric features are well replicated. The ratio of the graft-to-host artery diameter was shown to be the most important geometric feature. “Secondary” geometric features such as local arterial caliber changes, out-of-plane curvature, and small-scale surface topology are less important determinants of the wall shear stress patterns. However, if patient-specific disease information is available for the same arterial geometry, accurate replication of both primary and secondary geometric features is likely required.
An In Vitro Study of Implant-Tooth-Supported Connections Using a Robot Test System
Authors: Wang L. , Sadler J. P. , Breeding L. C. , Dixon D. L.
Published: February 2008

Many unsolved problems in dental implant research concern the interfacial stress distributions between the implant components, as well as between the implant surface and contacting bone. To obtain a mechanical understanding of how vertical and horizontal occlusal forces are distributed in this context, it is crucial to develop in vitro testing systems to measure the force transmission between dental implants and attached prostheses. A new approach to such testing, involving a robotic system, is described in this investigation. The system has been designed to produce simulated mandibular movements and occlusal contact forces so that various implant designs and procedures can be thoroughly tested and evaluated before animal testing or human clinical trials. Two commonly used fixed prosthesis designs used to connect an implant and a tooth, a rigid connection and a nonrigid connection, were fabricated and used for experimental verification. The displacement and force distributions generated during simulated chewing activities were measured in vitro. Force levels, potentially harmful to human bone surrounding the connected dental implant and tooth, were analyzed. These results are useful in the design of prostheses and connecting components that will reduce failures and limit stress transfer to the implant/bone interface.
A Fluid-Structure Interaction Finite Element Analysis of Pulsatile Blood Flow Through a Compliant Stenotic Artery
Authors: Bathe M. , Kamm R. D.
Published: February 2008

A new model is used to analyze the fully coupled problem of pulsatile blood flow through a compliant, axisymmetric stenotic artery using the finite element method. The model uses large displacement and large strain theory for the solid, and the full Navier-Stokes equations for the fluid. The effect of increasing area reduction on fluid dynamic and structural stresses is presented. Results show that pressure drop, peak wall shear stress, and maximum principal stress in the lesion all increase dramatically as the area reduction in the stenosis is increased from 51 to 89 percent. Further reductions in stenosis cross-sectional area, however, produce relatively little additional change in these parameters due to a concomitant reduction in flow rate caused by the losses in the constriction. Inner wall hoop stretch amplitude just distal to the stenosis also increases with increasing stenosis severity, as downstream pressures are reduced to a physiological minimum. The contraction of the artery distal to the stenosis generates a significant compressive stress on the downstream shoulder of the lesion. Dynamic narrowing of the stenosis is also seen, further augmenting area constriction at times of peak flow. Pressure drop results are found to compare well to an experimentally based theoretical curve, despite the assumption of laminar flow.
Velocity and Wall Shear Stress Patterns in the Human Right Coronary Artery
Authors: Kirpalani A. , Park H. , Butany J. , Johnston K. W. , Ojha M.
Published: February 2008

Blood flow dynamics in the human right coronary artery have not been adequately quantified despite the clinical significance of coronary atherosclerosis. In this study, a technique was developed to construct a rigid flow model from a cast of a human right coronary artery. A laser photochromic method was used to characterize the velocity and wall shear stress patterns. The flow conditions include steady flow at Reynolds numbers of 500 and 1000 as well as unsteady flow with Womersley parameter and peak Reynolds number of 1.82 and 750, respectively. Characterization of the three-dimensional geometry of the artery revealed that the largest spatial variation in curvature occurred within the almost branch-free proximal region, with the greatest curvature existing along the acute margin of the heart. In the proximal segment, high shear stresses were observed on the outer wall and lower, but not negative, stresses along the inner wall. Low shear stress on the inner wall may be related to the preferential localization of atherosclerosis in the proximal segment of the right coronary artery. However, it is possible that the large difference between the outer and inner wall shear stresses may also be involved.
The Effects of Cross-Fiber Deformation on Axial Fiber Stress in Myocardium
Authors: Zahalak G. I. , de Laborderie V. , Guccione J. M.
Published: February 2008

We incorporated a three-dimensional generalization of the Huxley cross-bridge theory in a finite element model of ventricular mechanics to examine the effect of nonaxial deformations on active stress in myocardium. According to this new theory, which assumes that macroscopic tissue deformations are transmitted to the myofilament lattice, lateral myofilament spacing affects the axial fiber stress. We calculated stresses and deformations at end-systole under the assumption of strictly isometric conditions. Our results suggest that at the end of ejection, nonaxial deformations may significantly reduce active axial fiber stress in the inner half of the wall of the normal left ventricle (18–35 percent at endocardium, depending on location with respect to apex and base). Moreover, this effect is greater in the case of a compliant ischemic region produced by occlusion of the left anterior descending or circumflex coronary artery (26–54 percent at endocardium). On the other hand, stiffening of the remote and ischemic regions (in the case of a two-week-old infarct) lessens the effect of nonaxial deformation on active stress at all locations (9–32 percent endocardial reductions). These calculated effects are sufficiently large to suggest that the influence of nonaxial deformation on active fiber stress may be important, and should be considered in future studies of cardiac mechanics.
On the Kinematic Modeling and the Parameter Estimation of the Human Knee Joint
Authors: Bao H. , Willems P. Y.
Published: February 2008

This paper presents some results on the modeling and the parameter estimation of the human knee joint. Based on the geometric characteristics of the femur condyle and the tibia plateau, a part of femoro-tibial joint model includes an involute-on-plane submodel. Data recorded by camera type device are used to analyze the kinematic characteristics of the knee joint and to estimate the corresponding submodel parameters. Experimental results are presented and the model is further validated.
A Whisker Probe System for Shape Perception of Solids
Authors: Wilson James F. , Chen Zhenhai
Published: February 2008

A computer-controlled whisker probe system was designed to measure contours of solid objects. The system’s mechanical components include the whisker: a cantilevered spring steel wire instrumented with strain gages; and the whisker’s base sweep mechanism: an assembly of tubes that bend when pressurized. The base mechanism is programmed to sweep the whisker over a solid object, during which measures of whisker strain and tube pressure are combined with closed-loop control to compute and display the object’s shape. Experiments demonstrate the system’s precision and accuracy in measuring object boundaries. Future applications include whisker cluster systems mounted on mobile robots and programmed for robot obstacle avoidance.
An Integrated Control Strategy for Multifingered Systems
Authors: Chung Wen-Yeuan , Waldron Kenneth J.
Published: February 2008

A method of force allocation by optimizing the friction angles at finger contacts was combined with the computed torque method to find the torques to be commanded at finger joints for multifingered systems. In this way, slip can be avoided when the object is grasped or manipulated. The proposed method can be used to efficiently find the input torques, and is applicable for real-time computation. A history-based method is also proposed to improve the smoothness of the input torque commands. Three-dimensional simulation results are given.
Adaptive Control of Robot Manipulators in Constrained Motion—Controller Design
Authors: Yao Bin , Tomizuka Masayoshi
Published: February 2008

Adaptive motion and force control of manipulators in constrained motion in the presence of parametric uncertainties both in the robot and contact surfaces are considered in this paper. A new constrained dynamic model is obtained to account for the effect of contact surface friction. An adaptive law is suggested with unknown parameters updated by both the motion and force tracking errors to guarantee asymptotic motion and force tracking without any persistent excitation conditions to be satisfied. The suggested controller has the expected PI type force feedback control structure with a low proportional (P) force feedback gain. Detailed simulation results are given to show the effectiveness of the proposed controller.
A Finite Element Formulation of a Flexible Slider Crank Mechanism Using Local Coordinates
Authors: Fallahi Behrooz , Lai S. , Venkat C.
Published: February 2008

The need for higher manufacturing throughput has lead to the design of machines operating at higher speeds. At higher speeds, the rigid body assumption is no longer valid and the links should be considered flexible. In this work, a method based on the Modified Lagrange Equation for modeling a flexible slider-crank mechanism is presented. This method possesses the characteristic of not requiring the transformation from the local coordinate system to the global coordinate system. An approach using the homogeneous coordinate for element matrices generation is also presented. This approach leads to a formalism in which the displacement vector is expressed as a product of two matrices and a vector. The first matrix is a function of rigid body motion. The second matrix is a function of rigid body configuration. The vector is a function of the elastic displacement. This formal separation helps to facilitate the generation of element matrices using symbolic manipulators.
Multivariable Transfer Functions for a Slewing Piezoelectric Laminate Beam
Authors: Pota H. R. , Alberts T. E.
Published: February 2008

In this paper a distributed parameter model of a slewing beam system with piezoelectric actuators and sensors is considered. The system has a torque motor at a pinned (proximal) end, an endpoint motion sensor at the distal end, and patches of thin piezoelectric laminates attached to its surface. The partial differential equation of motion for this system is transformed to Laplace domain transfer functions after application of the appropriate boundary conditions. Transfer functions relating the various actuator/sensor pairs are developed. The results are shown to reduce to previously known results which are special cases of the system under consideration. Examples and experimental results are presented using a beam experiment at the US Air Force, Frank J. Seller Research Laboratory.
An Evaluation of Several Controller Synthesis Methodologies Using a Rotating Flexible Beam as a Test Bed
Authors: Chang Pei-Ming , Jayasuriya Suhada
Published: February 2008

The objective of this study is to assess the effectiveness of a number of control system synthesis methodologies as practical design tools. The effectiveness is measured by the extent to which a controller obtained by a specific methodology has to be tuned for it to work in a real implementation. For this purpose we consider as a test bed a highly flexible beam attached to a d.c. motor driven rigid hub. Included in the study are five synthesis methodologies. They are (i) classical PD control, (ii) the LQR technique, (iii) robust servomechanism theory, (iv) the Lyapunov method, and (v) Quantitative Feedback Theory (QFT). Used are extensive computer simulations and actual experiments with each of the controllers synthesized using these methodologies. Each of the compensators performed satisfactorily in simulations. In actual implementation, however, some of the controllers did not work as predicted by simulations. The higher the d.c. gain and the bandwidth of the synthesized controller it is less likely to work in reality. This was clearly observed with the LQR controller, the servo controller and the Lyapunov based controllers. The QFT controller is the only one that accounted for the bandwidth limit at the synthesis stage. The other controllers require much fine tuning by trial and error for satisfying actual physical limits including the bandwidth. It is established that controllers designed using methodologies which incorporate real practical considerations such as modeling uncertainties, bandwidth limitations and input saturations need very little tuning whereas the others yield controllers which after tuning are quite different from the synthesized ones.
Stiffness Analysis and Control of Multi-Fingered Robot Hands
Authors: Choi H. R. , Chung W. K. , Youm Y.
Published: February 2008

In this paper, we describe the stiffness of a grasp as a function of grasp configuration, grasp forces and joint stiffness of the fingers. The effects caused by the change of joint configuration is included in the computation of the joint stiffness in terms of Stiffness Induced from Configuration Change and Force (SICC). Based on the analysis, the Decentralized Object Stiffness Control (DOSC) method is proposed so as to achieve the desired overall grasp stiffness. The effects of SICC at the joint stiffness and the performance of the proposed stiffness control.
Modeling Transition to Turbulence in Eccentric Stenotic Flows
Authors: Varghese Sonu S. , Frankel Steven H. , Fischer Paul F.
Published: February 2008

Mean flow predictions obtained from a host of turbulence models were found to be in poor agreement with recent direct numerical simulation results for turbulent flow distal to an idealized eccentric stenosis. Many of the widely used turbulence models, including a large eddy simulation model, were unable to accurately capture the poststenotic transition to turbulence. The results suggest that efforts toward developing more accurate turbulence models for low-Reynolds number, separated transitional flows are necessary before such models can be used confidently under hemodynamic conditions where turbulence may develop.
Evaluation of the Effectiveness of Transurethral Radio Frequency Hyperthermia in the Canine Prostate: Temperature Distribution Analysis
Authors: Zhu Liang , Xu Lisa X.
Published: February 2008

The heating pattern of a transurethral radio frequency (RF) applicator and its induced steady-state temperature field in the prostate during transurethral hyperthermia treatment were investigated in this study. The specific absorption rate (SAR) of the electromagnetic energy was first quantified in a tissue-equivalent gel phantom. It was used in conjunction with the Pennes bioheat transfer equation to model the steady-state temperature field in prostate during the treatment. Theoretical predictions were compared to in vivo temperature measurements in the canine prostate and good agreement was found to validate the model. The prostatic tissue temperature rise and its relation to the effect of blood perfusion were analyzed. Blood perfusion is found to be an important factor for removal of heat especially at the higher RF heating level. To achieve a temperature above 44°C within 10 percent of the prostatic tissue volume, the minimum RF power required ranges from 5.5 W to 36.4 W depending on the local blood perfusion rate (ω = 0.2−1.5 ml/gm/min). The corresponding histological results from the treatment suggest that to obtain better treatment results, either higher RF power level or longer treatment time (>180 minutes) is necessary. This is consistent with the predictions from the theoretical model developed in this study.
In Vivo Tracking of the Human Patella Using Cine Phase Contrast Magnetic Resonance Imaging
Authors: Sheehan F. T. , Zajac F. E. , Drace J. E.
Published: February 2008

Improper patellar tracking is often considered to be the cause of patellar-femoral pain. Unfortunately, our knowledge of patellar-femoral-tibial (knee) joint kinematics is severely limited due to a lack of three-dimensional, noninvasive, in vivo measurement techniques. This study presents the first large-scale, dynamic, three-dimensional, noninvasive, in vivo study of nonimpaired knee joint kinematics during volitional leg extensions. Cine-phase contrast magnetic resonance imaging was used to measure the velocity profiles of the patella, femur, and tibia in 18 unimpaired knees during leg extensions, resisted by a 34 N weight. Bone displacements were calculated through integration and then converted into three-dimensional orientation angles. We found that the patella displaced laterally, superiorly, and anteriorly as the knee extended. Further, patellar flexion lagged knee flexion, patellar tilt was variable, and patellar rotation was fairly constant throughout extension.
Airway Area by Acoustic Reflection: A Corrected Derivation for the Two-Microphone Method
Authors: Poort K. L. , Fredberg J. J.
Published: February 2008

A corrected derivation is provided for the relationship between the impulse response of a wave tube termination and pressure signals measured at two different locations within the tube. This derivation yields exactly the same final result as was reported previously by Louis et al. (1993), despite the omission of the active source term in that earlier derivation. This technique has become the basis of an important medical diagnostic technology. This report revises and corrects the earlier theory upon which that technology rests.
Block-Recursive Identification of Parameters and Delay in the Presence of Noise
Authors: Young G. E. , Rao K. S. Suresh , Chatufale Vijay R.
Published: February 2008

This paper presents a method for identification of parameters and delays of a linear system in the presence of noise. The estimation procedure is based on transforming the input-output data into the discrete Fourier domain. The transformed data is then solved block recursively to obtain both the system parameters and unknown delay. For systems with no delays or known delays, the equations are linear in the parameters and the standard estimation techniques can be applied. For systems with unknown delays, the resulting equations are nonlinear in the delay term. A recursive nonlinear estimation technique similar to the least-squares in the time domain has been developed. In the presence of Gaussian white noise, simulation studies indicate that the parameters converge to their true values in the mean.
Thermal Manufacturing Process Control by Lumped Mimo and Distributed-Parameter Methods
Authors: Doumanidis C. C.
Published: February 2008

A variety of geometric, material structure, and stress/distortion attributes are needed to characterize the quality of thermally manufactured products. Because of in-process sensing difficulties and transportation lags, these features must be regulated in real time through appropriate thermal outputs, measured by non-contact infrared pyrometry. In thermal processes with a localized, sequentially moving heat source, the necessary heat input distribution on the part surface is supplied by an innovative timeshared or scanned torch modulation, in a raster or vector pattern. A unified lumped multivariable and a distributed-parameter quasilinear modeling formulation provide a design methodology and real-time reference for the development of finite- or infinite-state adaptive thermal control systems. These controllers modulate the power and motion of a single torch, supplying distinct concentrated heat inputs or a continuous power distribution on the part surface, so as to obtain the specified thermal characteristics or the entire temperature field. These regulation strategies are computationally tested and implemented experimentally in arc welding, but their applicability can be extended to a variety of thermal manufacturing processes.
On Robust Stability and Performance With Time-Varying Control
Authors: Dahleh Mohammed
Published: February 2008

The analysis of time-varying control for robust stabilization and performance improvement is considered. This problem has been investigated in recent years from the point of view of assessing the capabilities of time-varying control to stabilize plants with structured norm bounded perturbations. In this paper, it is shown that time-varying compensation provides no improvement over time-invariant compensation for the stability and performance robustness of discrete-time systems with structured, causal, time-varying, and norm-bounded perturbations, where the norm on the perturbations is the l2-induced norm. The results of this paper help in completing the picture for the case of time-varying perturbations.
Real-Time Implementation of a Robust H∞ Controller for a 2-DOF Magnetic Micro-Levitation Positioner
Authors: Mohamed Abdelfatah M. , Vestgaard Bard , Busch-Vishniac Ilene
Published: February 2008

Robust H∞ optimal control theory has proven to be one of the best techniques in linear control system design. The achievable robust stability and performance are high, but the resulting controllers are very complex and difficult to implement. As a result, few practical implementations of H∞ control can be found in the literature. This paper presents a robust H∞ controller for a two-degree-of-freedom magnetic micro-levitation positioner and its real time experimental implementation. The experimental device used in this study is designed for use in semiconductor manufacturing and consists of two U-shaped electromagnets and a manipulator. First, we describe the system dynamics in state space form. Second, the system which is unstable in nature is stabilized using the H∞ synthesis. The H∞ control design problem is described and formulated in the standard form with emphasis on the selection of weighting transfer functions that reflect robustness and performance goals. The interactive computing environment MATLAB is used to calculate the controller. Third, the controller is implemented digitally using a digital signal processor with 16 bit A/D and 12 bit D/A converters. Finally, some simulation and experimental results are presented. The results obtained show that robust stability against model uncertainties is achieved and the performance goals are satisfied.
Theory and Implementation of a Repetitive Robot Controller With Cartesian Trajectory Description
Authors: Guglielmo Kennon , Sadegh Nader
Published: February 2008

This paper presents a new repetitive learning controller for motion control of mechanical manipulators undergoing periodic tasks defined in Cartesian space. The controller does not require knowledge of the manipulator dynamic parameters beyond a simple geometric description. The desired task will be defined in Cartesian coordinates, and no inverse kinematics or inverse Jacobian will be calculated. The asymptotic stability of this algorithm is proven using the Lyapunov approach, and the nonlinear characteristics of the manipulator are explicitly taken into account. The results of implementation of this new repetitive learning controller on an IBM 7545 robotic manipulator are presented. Cartesian feedback was obtained from optical joint position encoders using forward kinematics, and velocity was estimated by simple numerical differentiation of the Cartesian position signal in software. The performance of the algorithm was compared to that of a simple PD feedback system, and a modified “Computed Torque” controller using inverse kinematics on the Cartesian path. The learning algorithm outperformed both of these controllers by a significant margin, exhibited convergence within approximately three cycles, and did not require inverse kinematics to execute the Cartesian path.
Adaptive Output Regulation of a Flexible Arm
Authors: Lucibello P. , Bellezza F.
Published: February 2008

A self-tuned version of a controller for asymptotic trajectory tracking of the end point of a two-link flexible robot arm is presented. The bounded solution to the inverse system, which is used in the control law, is tuned by the estimates of the unknown robot parameters, generated by a least square identification scheme. Soundness of the state of the adaptive controller is achieved by a stabilizing linear feedback from the output error, with fixed gains and robust with respect to variations of the parameters. This guarantees the total stability of the system, which is the main ingredient used in the proof of the controller properties, through a Lyapunov-like approach. The controller performance is finally illustrated by numerically simulating the tracking of an end point ramp under payload mass variations.
Eulerian Bond Graphs for Fluid Continuum Dynamics Modeling
Authors: Fahrenthold E. P. , Venkataraman M.
Published: February 2008

The development of high resolution, general purpose models of viscous, compressible flows is extremely difficult with existing system dynamics modeling tools. Published work admits to significant limitations, with regards to the treatment of flow geometry, inertia effects, or mass and energy convection. Combining a finite element discretization scheme with a bond graph based model formulation procedure provides a very general purpose tool for continuum fluid system modeling.