bluuebunny/crossref_metadata_2025 huggingface dataset:
Progress of Research on Impact Biomechanics
Authors: King Albert I.
Published: March 2008

Impact biomechanics is an area of research primarily associated with the protection of vehicular occupants. It is also concerned with the prevention of sports-related injuries and with injuries due to falls. It deals mainly with loads that have high rates of onset and with durations that are considerably less than one second. The objectives of impact biomechanics are to understand how a body region is injured in an impact and to seek means to minimize injury through environmental modifications. A secondary objective is to ensure that such environmental modifications do not become a secondary source of injury. Impact biomechanics can be broadly categorized into four areas. They are Mechanisms of Injury, Human Response to Impact, Human Tolerance to Impact, and Development of Human Surrogates for Impact Simulation. Each area plays a role in the design of automotive restraint systems and interior structures and in the understanding of how injury is caused so that effective countermeasures can be taken to minimize the injury. This paper describes advances made in all four areas of impact biomechanics over the last two decades. Areas of current research interest are also discussed. They point to the need for new data and further research work in impact biomechanics.
Thermal (Heat) Shock Biothermomechanical Viewpoint
Authors: Yang Wen-Hei
Published: March 2008

Thermal (or heat) shock phenomena have been observed in all organisms at the cellular level. They cause an acceleration in the rate of expression of specific genes (heat shock genes), resulting in an increase and accumulation of heat shock proteins in cells. The purpose of this study is to investigate the mechanisms of thermal shock from two different viewpoints: biothermal and biothermomechanical aspects. The former predicts more severe consequences on cells that the latter, whose thermal wave fronts are smoothed due to the coupling effects of thermoelasticity. In conclusion, it is the thermal wave propagation (the so-called “second sound” effect) which triggers a perturbation of normal gene expression. Thermotolerance is found to be inherited in the heat flux equation of the thermal wave model. The information obtained from this study can also be useful to therapeutical hyperthermia, preservation of organs and tissues, and laser and cryogenic surgery.
Cartilage Stresses in the Human Hip Joint
Authors: Macirowski Thomas , Tepic Slobodan , Mann Robert W.
Published: March 2008

The total surface stress measured in vitro on acetabular cartilage when step-loaded by an instrumented hemiprosthesis are partitioned into fluid and cartilage network stresses using a finite element model of the cartilage layer and measurements of the layer consolidation. The finite element model is based on in situ measurements of cartilage geometry and constitutive properties. Unique instrumentation was employed to collect the geometry and constitutive properties and pressure and consolidation data. When loaded, cartilage consolidates and exudes its interstitial fluid through and from its solid network into the interarticular gap. The finite element solutions include the spatial distributions of fluid and network stresses, the normal flow velocities into the gap, and the contact network stresses at the cartilage surface, all versus time. Even after long-duration application of physiological-level force, fluid pressure supports 90 percent of the load with the cartilage network stresses remaining well below the drained modulus of cartilage. The results support the “weeping” mechanism of joint lubrication proposed by McCutchen.
Pulsatile Flow Through a Bifurcation With a Cerebrovascular Aneurysm
Authors: Liou Tong-Miin , Chang Tzung-Wu , Chang Wen-Chin
Published: March 2008

Laser-Doppler velocimetry measurements and flow visualization were complementarily made in pulsatile and steady flow in a cerebrovascular aneurysm model with bifurcation angles of 60, 90, and 140 deg, and volume-flow rate ratios between the branches of 1 to 1 and 3 to 1. The mean, peak, and minimal Reynolds numbers based on the bulk average velocity and diameter of the parent vessel were 600, 800, and 280, respectively. For uneven branch flow, it is found that the flow activity inside the aneurysm and the stresses acting on the aneurysmal wall increase with increasing bifurcation angle. More importantly, the present angle suggests the presence of a critical bifurcation angle below which the aneurysm is prone to thrombosis, whereas above which the aneurysm is susceptible to progression or rupture. For evenly distributed branch flow, the intra-aneurysmal flow is sluggish and therefore prone to thrombosis for all studied bifurcation angles.
Three-Dimensional Analysis of Left Ventricular Ejection Using Computational Fluid Dynamics
Authors: Taylor Tad W. , Okino Haruka , Yamaguchi Takami
Published: March 2008

We present in this study a method for constructing computational fluid mechanical models in order to study the effects of time-varying left ventricular ejection. A spherical left ventricular model was implemented in which three dimensional flow fields were obtained. The time course of the ventricular wall changes were assumed to have a trigonometrically varying nature. The wall grid was reformed 25 times during the calculation since the left ventricular wall motion was assumed to follow the blood flow, and the ventricle wall radius was reduced by 60 percent in 0.25 seconds. Centerline and cross-sectional velocity vectors greatly increased in magnitude at the aortic outlet, and pressure dropped from 1.17 × 104 dynes/cm2 (8.8 mmHg) to zero in the top 10 percent of the heart. The modeling framework will be used with left ventricular cast data coordinates in future studies. There is presently a lack of three-dimensional data based on a realistic model, and the computational method should make it possible to compare simulation results with important measurement techniques such as echocardiography and magnetic resonance imaging.
A Dynamic Material Parameter Estimation Procedure for Soft Tissue Using a Poroelastic Finite Element Model
Authors: Laible J. P. , Pflaster D. , Simon B. R. , Krag M. H. , Pope M. , Haugh L. D.
Published: March 2008

A three-dimensional finite element model for a poroelastic medium has been coupled with a least squares parameter estimation method for the purpose of assessing material properties based on intradiscal displacement and reactive forces. Parameter optimization may be based on either load or displacement control experiments. In this paper we present the basis of the finite element model and the parameter estimation process. The method is then applied to a test problem and the computational behavior is discussed. Sequential optimization on different parameter groups was found to have superior convergence properties. Some guidelines for choosing the starting parameter values for optimization were deduced by considering the form of the objective function. For load control experiments, in which displacement data is used for the optimization, the starting values for the elastic modulus should be lower in magnitude than an “anticipated” modulus. The permeability starting values should be higher than an anticipated permeability. For displacement control experiments, the reverse is true. The optimization scheme was also tested on data with random variations.
On the Measurement of Dynamic Stability of Human Locomotion
Authors: Hurmuzlu Yildirim , Basdogan Cagatay
Published: March 2008

The main focus of the present investigation is the development of quantitative measures to assess the dynamic stability of human locomotion. The analytical methodology is based on Floquet theory, which was developed to investigate the stability of nonlinear oscillators. Here the basic approach is modified such that it accommodates the study of the complex dynamics of human locomotion and differences among various individuals. A quantitative stability index has been developed to characterize the ability of humans to maintain steady gait patterns. Floquet multipliers of twenty normal subjects were computed from the kinematic data at Poincare´ sections taken at four instants of the gait cycle, namely heel strike, foot flat, heel off, and toe off. Then, an averaged stability index was computed for each subject. Statistical analysis was performed to demonstrate the utility of the stability indices as quantitative measures of dynamic stability of gait for the subject population tested during the present study.
An Extracorporeal Microscopy Perfusion Chamber for On-Line Studies of Environmental Effects on Cultured Hepatocytes
Authors: Borel Rinkes Inne H. M. , Toner Mehmet , Tompkins Ronald G. , Yarmush Martin L.
Published: March 2008

The development of bioartificial-hybrid organ support systems is hampered by the lack of knowledge on the effects of different (in vivo) environments on cells during extracorporeal perfusion. In the present study, a perfusion chamber was designed for continuous monitoring of cultured cells during perfusion with media, as well as during plasma perfusion in an extracorporeal circuit. Chamber characterization showed satisfactory thermal and perfusion profiles and no major pH fluctuations. Further testing was performed with hepatocytes that were cultured in between two collagen layers, a configuration which was previously shown to preserve hepatocyte morphology and function for over six weeks of culture. Perfusion of the hepatocytes with culture media did not adversely affect cell morphology and function, provided the perfusion time was ≤ 48 hours. Perfusion of the cultures during connection of the chamber to an extracorporeal circuit involving normal rats for six hours resulted in reversible cytoplasmic changes, unaltered cell shapes indices, and a 40 percent increase in albumin secretion rate during the first post-perfusion day, followed by a return to stable control levels. We expect that this chamber will be a valuable tool for on-line studies of cells under (extracorporeal) perfusion conditions and could be used for a large variety of studies on regeneration, reperfusion damage, and detoxification.
An Analysis of Coupled Multicomponent Diffusion in Interstitial Tissue
Authors: Schreuders P. D. , Diller K. R. , Beaman J. J. , Paynter H. M.
Published: March 2008

A one-dimensional multicomponent kinetic model was developed to simulate the interstitial diffusion of macromolecules in a three component system, consisting of water, the macromolecule and the interstitial matrix. Movement of the individual components was modeled as occurring in finite jumps between discrete low energy wells along paths defined in terms of species occupation. The flow rate was expressed as a function of the local species concentration, the jump distance, and a kinetic frequency parameter. The model, implemented in pseudo-bond graph form, was examined by fitting it to data obtained for the transport of fluorescein tagged dextran to determine the kinetic constants for that specific system.
Numerical Simulation of the Flow of Highly Viscous Drops Down a Tapered Tube
Authors: Tran-Son-Tay R. , Kirk T. F. , Zhelev D. V. , Hochmuth R. M.
Published: March 2008

The flow of a highly viscous drop surrounded by an inviscid fluid inside a tapered tube is analyzed according to a Newtonian, liquid-drop model in which a variational method is used to simultaneously solve the hydrodynamic equations for low Reynolds-number flow and the equations for membrane equilibrium with a constant membrane tension. It is found that the flow in the end caps is plug and radial in the conical section of the drop. The results are compared to a simplified analytical theory that makes these assumptions. Very good agreement is found between the two approaches. Both approaches are used to analyze existing experimental results of passive neutrophils flowing down a tapered tube. The theoretical models give a good fit to published experimental data by Bagge et al. (1977) at driving pressures of 20 and 40 mm H2O for a membrane cortical tension of 0.024 dyn/cm and an apparent cytoplasmic viscosity of about 2400 and 1400 poise, respectively.
A Numerical Analysis of a Focused Ultrasound Technique to Measure Perfusion
Authors: Anderson Gary T. , Ye Xiu
Published: March 2008

A noninvasive technique to measure perfusion using a focused ultrasound heating source and a thermistor placed on the surface of a tissue is proposed. The method is numerically examined in a model of the canine kidney. The perfusion measurement is shown to depend on several transducer and tissue thermal properties. A two level fractional factorial design simulation is used to map out a parameter value combination that maximizes the sensitivity of the measurement. A technique to numerically assess the uncertainty in the measurement due to uncertainties in the tissue and transducer parameter values is also described. The effects of the medulla and a subcapsular surface layer in the kidney are examined. It is determined that the maximum error in the measured perfusion rate due to all the factors considered is 17 percent for a kidney with a nominal perfusion rate of 300 mL/100g-min and a surface layer of 0.04 cm thickness.
LDA Measurements of Mean Velocity and Reynolds Stress Fields Within an Artificial Heart Ventricle
Authors: Baldwin J. T. , Deutsch S. , Geselowitz D. B. , Tarbell J. M.
Published: March 2008

Laser Doppler Anemometry measurements of mean (ensemble average) velocities and turbulent (Reynolds) stresses at 140 locations within the left ventricle of the Penn State 70 cc electric artificial heart/ventricular assist device are reported at 8 times during the cardiac cycle. Mean velocity patterns indicate that the surfaces of the blood sac and valve tracts are exposed to significant levels of wall shear stress (good wall washing) during some portion of the flow cycle, and there is no location where the flow is stagnant over the entire flow cycle. This implies that thrombus deposition within the artificial heart should be suppressed. Turbulent stresses in the main pumping chamber and the outflow tracts of the tilting disk valves do not exceed 2000 dynes/cm2. The highest turbulent stresses (20,000 dynes/cm2) and smallest turbulent microscales (6 μm) are found in the regurgitant jets on the minor orifice side of the aortic valve during diastole and the mitral valve during systole. Taken together, the data suggest that improvements in artificial heart fluid mechanics will come through valve design and pump operating conditions, not pumping chamber design.
A Nonliner Poroelastic Model for the Trabecular Embryonic Heart
Authors: Yang Ming , Taber Larry A. , Clark Edward B.
Published: March 2008

A theoretical model is presented for the primitive right ventricle of the stage 21 chick embryo. At this stage of development, the wall of the heart is trabecular with direct intramyocardial blood flow. The model is a pressurized fluid-filled cylinder composed of a porous inner layer of isotropic myocardium and a relatively thin compact outer layer of transversely isotropic myocardium. The analysis is based on nonlinear poroelasticity theory, modified to include residual strain and muscle activation. Correlating theoretical and experimental pressure-volume loops and epicardial strains gives first-approximation constitutive relations for stage 21 embryonic myocardium. The results from the model suggest three primary conclusions: (1) Some muscle fibers likely are aligned in the compact layer, with a fiber angle approximately +10 deg from the circumferential direction. (2) Blood is drawn into the wall of the ventricle during diastolic filling and isovolumic contraction and is squeezed out of the wall during systolic ejection, giving a primitive intramyocardial circulation before the coronary arteries form. As the heart rate increases, the transmural bloodflow velocity increases, but the volume of blood exchanged with the lumen per beat decreases. (3) Residual strain affects transmural stress distributions, producing nearly uniform stresses in the porous layer, where the peak end-systolic stress occurs. These results improve our understanding of the relation between form and function in the developing heart and provide directions for biological experiments to study cardiac morphogenesis.
A Finite Element Model of Skin Subjected to a Flash Fire
Authors: Torvi D. A. , Dale J. D.
Published: March 2008

A variable property, multiple layer finite element model was developed to predict skin temperatures and times to second and third degree burns under simulated flash fire conditions. A sensitivity study of burn predictions to variations in thermal physical properties of skin was undertaken using this model. It was found that variations in these properties over the ranges used in multiple layer skin models had minimal effects on second degree burn predictions, but large effects on third degree burn predictions. It was also found that the blood perfusion source term in Pennes’ bioheat transfer equation could be neglected in predicting second and third degree burns due to flash fires. The predictions from this model were also compared with those from the closed form solution of this equation, which has been used in the literature for making burn predictions from accidents similar to flash fires.
The Simulation of Discrete Vessel Effects in Experimental Hyperthermia
Authors: Rawnsley R. J. , Roemer R. B. , Dutton A. W.
Published: March 2008

The ability of two simple thermal models to predict experimentally measured in vivo temperature profiles was compared. These comparisons were done both with and without the inclusion of separate, discrete blood vessels. The two tissue models were: 1) Pennes’ Bio-Heat Transfer equation (BHTE), and 2) an effective thermal conductivity equation (ETCE). The experimental temperature data were measured (Moros, 1990; Moros et al., 1993) in the thighs of anesthetized greyhound dogs under hyperthermic conditions generated by scanned focused ultrasound. Blood vessels were added to the thermal models in counter-current pairs transiting the model domain. The blood vessels in both models were assumed to have a constant heat transfer coefficient, and an axially varying mixed mean temperature. The vessel locations were determined a posteriori, via inspection of the experimental temperature data. Least square error fits of the predicted model temperatures to the experimental temperature data were obtained by adjusting both (a) the mass flow rate within and (b) the position of each blood vessel, and (c) the value of either the perfusion parameter (W) in the BHTE or the effective thermal conductivity parameter (Keff) in the ETCE. When small numbers (3-4) of blood vessel pairs were included, both of the models showed significant improvement in their ability to predict the experimental temperatures. Although both models performed well in terms of predicting temperatures near large vessels, the BHTE had a statistically significant better ability to predict the complete set of measured temperatures at all locations.
Aortic Walls in Atherosclerotic Rabbits—Mechanical Study
Authors: Hayashi Kozaburo , Ide Kazuhiro , Matsumoto Takeo
Published: March 2008

Mechanical properties of the descending thoracic aortae harvested from endothelial cell-denuded and/or cholesterol diet-fed rabbits were studied primarily with their pressure-diameter relationships. Male Japanese white rabbits having 3.1 to 3.5 kg initial body weight were divided into 4 groups. The rabbits in Groups A and C were fed a regular chow, while those in Groups B and D were given 1 percent cholesterol diet; the luminal surfaces of the descending thoracic aortae in the rabbits of Groups C and D were injured by drawing catheter-tip balloons. These animals were sacrificed after keeping for 4, 8, 16 or 32 weeks and, then, their descending thoracic aortae were excised for the studies of pressure-diameter relationships. Stiffness parameter (β′) and incremental elastic modulus (Hθθ were used to quantitatively represent the structural stiffness of the aortic wall and the elastic modulus of the wall material, respectively. Denudation of endothelial cells thickened the aortic walls in Group C, but induced no significant changes in β′ and Hθθ. Shape of the pressure-diameter curve changed gradually with time in Group D, and β′, Hθθ, and thickness to wall radius ratio increased significantly, while those in Group B showed no significant changes with a few exceptions. Averaged percent fraction of the luminal surface area stained with Sudan IV (As) was around 50 percent in Group B and 100 percent in Group D at 32 weeks. Even if As is over 80 percent in Group D, 50 percent (7/14) of the walls gave significantly higher β′- and Hθθ-values at 100 mm Hg than the others. Significantly increased calcification and intimal hyperplasia were observed in the walls with high β′- and Hθθ-values.
Influence of Abdominal Aortic Curvature and Resting Versus Exercise Conditions on Velocity Fields in the Normal Abdominal Aortic Bifurcation
Authors: Pedersen Erik Morre , Sung Hsing-Wen , Yoganathan Ajit P.
Published: March 2008

Local hemodynamics are considered an important atherogenetic factor in the abdominal aortic bifurcation. This study addresses the quantitative flow fields in a pulsatile flow model of a normal abdominal aortic bifurcation when encountering realistic upstream anatomy, realistic inlet flow conditions and different physiologic flow conditions (rest vs. exercise). Two-dimensional laser Doppler anemometry measurements gave axial as well as radial velocities. The localization and magnitude of peak velocities, retrograde flow and secondary velocity patterns were found to be determined to a great extent by the curvature of the abdominal aorta, the triphasic flow wave form and the inlet velocity profile. Significant changes were also seen when simulating different physiologic flow conditions. Thus retrograde velocities were present at both the flow divider and the lateral vessel wall for the rest condition but not for the exercise flow conditions, and the location of low and retrograde velocities during diastole were as much determined by abdominal aortic curvature as by the bifurcation for nearly all flow conditions and locations. In conclusion, the anatomy and hemodynamics in the abdominal aorta cannot be neglected when studying the hemodynamics in the abdominal aortic bifurcation.
Nondestructive Detection of Cartilage Degeneration Using Electromechanical Surface Spectroscopy
Authors: Berkenblit Scott I. , Frank Eliot H. , Salant Evan P. , Grodzinsky Alan J.
Published: March 2008

We have constructed an electrokinetic surface probe capable of applying small sinusoidal currents to the surface of articular cartilage and measuring the resulting current-generated stress with a piezoelectric sensor. Using the probe, we have characterized the electromechanical response of excised discs of normal and chemically modified adult bovine femoropatellar groove cartilage. The measured stress amplitude was proportional to the applied current density and inversely proportional to the excitation frequency, consistent with a poroelastic model. As a function of bath pH, the stress amplitude exhibited a minimum in the range pH 2.4–2.8 and the phase underwent an abrupt 180° transition in the same range, consistent with an electrokinetic mechanism as the origin of the current-generated mechanical stress. Digestion of the tissue with trypsin resulted in a progressive loss of highly charged proteoglycan molecules from the tissue, with a concomitant decrease in the measured stress amplitude. These results support the feasibility of surface measurements as a means of assessing electromechanical transduction in cartilage and of detecting subtle molecular-level degradative changes in the extracellular matrix. This technique of surface spectroscopy provides a new means of nondestructively measuring the material properties of cartilage on intact joints and detecting degradative changes such as those seen in the earliest stages of osteoarthritis.
A Fiber Matrix Model for the Growth of Macromolecular Leakage Spots in the Arterial Intima
Authors: Huang Y. , Rumschitzki D. , Chien S. , Weinbaum S.
Published: March 2008

A new model is presented for the growth of cellular level macromolecular leakage spots in the arterial intima. The theoretical approach differs from the recent study by Yuan et al. [19] in that it directly models and calculates the intimal transport parameters based on Frank and Fogelman’s [22] ultrastructural observations of the extracellular subendothelial proteoglycan matrix that their rapid freeze etching technique preserves (see Addendum). Using a heterogeneous fiber matrix theory, which includes proteoglycan and collagen components, the model predicts that the Darcy permeability Kp and macromolecular diffusivity D of the subendothelial intima is two orders of magnitude larger than the corresponding values measured in the media, and supports the observations in Lark et al. [24] that the proteoglycan structure of the intima differs greatly from that of the media. Numerical results show that convection parallel to the endothelium is a very significant transport mechanism for macromolecules in the intima in a large region of roughly 200 μm diameter surrounding the leaky cleft. The predictions of the new model for the early-time spread of the advancing convective-diffusive front from the leakage spots in the intima are in close agreement with our experimental measurements for the growth of HRP spots in [20]. The regions of high concentration surrounding the leaky cell, however, are much more limited and cover an area that is typically equivalent to 20 cells. This prediction is consistent with the recent measurements of Truskey et al. for LDL spot size in rabbit aorta [21] and the hypothesis advanced in [19] that there is a colocalization of subendothelial liposome growth and cellular level leakage. Finally, comparison of predicted and experimentally-measured average LDL concentration in leakage spots strongly suggests that there is significant local molecular sieving at the interface between the fenestral openings in the internal elastic lamina and the media.
A Method for Real-Time In Vitro Observation of Cavitation on Prosthetic Heart Valves
Authors: Zapanta Conrad M. , Liszka Edward G. , Lamson Theodore C. , Stinebring David R. , Deutsch Steve , Geselowitz David B. , Tarbell John M.
Published: March 2008

A method for real-time in vitro observation of cavitation on a prosthetic heart valve has been developed. Cavitation of four blood analog fluids (distilled water, aqueous glycerin, aqueous polyacrylamide, and aqueous xanthan gum) has been documented for a Medtronic/Hall™ prosthetic heart valve. This method employed a Penn State Electrical Ventricular Assist Device in a mock circulatory loop that was operated in a partial filling mode associated with reduced atrial filling pressure. The observations were made on a valve that was located in the mitral position, with the cavitation occurring on the inlet side after valve closure on every cycle. Stroboscopic videography was used to document the cavity life cycle. Bubble cavitation was observed on the valve occluder face. Vortex cavitation was observed at two locations in the vicinity of the valve occluder and housing. For each fluid, cavity growth and collapse occurred in less than one millisecond, which provides strong evidence that the cavitation is vaporous rather than gaseous. The cavity duration time was found to decrease with increasing atrial pressure at constant aortic pressure and beat rate. The area of cavitation was found to decrease with increasing delay time at a constant aortic pressure, atrial pressure, and beat rate. Cavitation was found to occur in each of the fluids, with the most cavitation seen in the Newtonian fluids (distilled water and aqueous glycerin).
Transition to Turbulence in Pulsatile Flow Through Heart Valves—A Modified Stability Approach
Authors: Bluestein D. , Einav S.
Published: March 2008

The presence of turbulence in the cardiovascular system is generally an indication of some type of abnormality. Most cardiologists agree that turbulence near a valve indicates either valvular stenosis or regurgitation, depending on the phase of its occurrence during the cardiac cycle. As no satisfying analytical solutions of the stability of turbulent pulsatile flow exist, accurate, unbiased flow stability criteria are needed for the identification of turbulence initiation. The traditional approach uses a stability diagram based upon the stability of a plane Stokes layer where a (the Womersley parameter) is defined by the fundamental heart rate. We suggest a modified approach that involves the decomposition of α into its frequency components, where α is derived from the preferred modes induced on the flow by interaction between flow pulsation and the valve. Transition to turbulence in pulsatile flow through heart values was investigated in a pulse duplicator system using three polymer aortic valve models representing a normal aortic valve, a 65 percent stenosed valve and a 90 percent severely stenosed valve, and two mitral valve models representing a normal mitral valve and a 65 percent stenosed valve. Valve characteristics were closely simulated as to mimic the conditions that alter flow stability and initiate turbulent flow conditions. Valvular velocity waveforms were measured by laser Doppler anemometry (LDA). Spectral analysis was performed on velocity signals at selected spatial and temporal points to produce the power density spectra, in which the preferred frequency modes were identified. The spectra obtained during the rapid closure stage of the valves were found to be governed by the stenosis geometry. A shift toward higher dominant frequencies was correlated with the severity of the stenosis. According to the modified approach, stability of the flow is represented by a cluster of points, each corresponding to a specific dominant mode apparent in the flow. In order to compare our results with those obtained by the traditional approach, the cluster of points was averaged to collapse into a single point that represents the flow stability. The comparison demonstrates the bias of the traditional stability diagram that leads to unreliable stability criteria. Our approach derives the stability information from measured flow phenomena known to initiate flow instabilities. It differentiates between stabilizing and destabilizing modes and depicts an unbiased and explicit stability diagram of the flow, thus offering a more reliable stability criteria.
Formulation of a Statistical Model of Heat Transfer in Perfused Tissue
Authors: Baish J. W.
Published: March 2008

A new model of steady-state heat transport in perfused tissue is presented. The key elements of the model are as follows: (1) a physiologically-based algorithm for simulating the geometry of a realistic vascular tree containing all thermally significant vessels in a tissue; (2) a means of solving the conjugate heat transfer problem of convection by the blood coupled to three-dimensional conduction in the extravascular tissue, and (3) a statistical interpretation of the calculated temperature field. This formulation is radically different from the widely used Pennes and Weinbaum-Jiji bio-heat transfer equations that predict a loosely defined local average tissue temperature from a local perfusion rate and a minimal representation of the vascular geometry. Instead, a probability density function for the tissue temperature is predicted, which carries information on the most probable temperature at a point and uncertainty in that temperature due to the proximity of thermally significant blood vessels. A sample implementation illustrates the dependence of the temperature distribution on the flow rate of the blood and the vascular geometry. The results show that the Pennes formulation of the bio-heat transfer equation accurately predicts the mean tissue temperature except when the arteries and veins are in closely spaced pairs. The model is useful for fundamental studies of tissue heat transport, and should extend readily to other forms of tissue transport including oxygen, nutrient, and drug transport.
Complete Accessibility of Oscillations in Robotic Systems by Orthogonal Projections
Authors: Tosunoglu Sabri , Lin Shyng-Her , Tesar Delbert
Published: March 2008

The current practice of controller development for flexible robotic systems generally focuses on one-link robotic arms and is valid for small oscillations. This work addresses the control of n-link, serial, spatial robotic systems modeled with m1 joint and m2 link flexibilities such that n≥m1+m2. System compliance is modeled by local springs and nonactuated prismatic and revolute type pseudo joints. The coupled, nonlinear, error-driven system equations are derived for the complete model without linearization or neglecting certain terms. For this system, the complete accessibility of vibrations is studied by orthogonal projections. It is shown that under some configurations of a robotic system, the induced oscillations may not be accessible to the controller. Given accessibility, the controller developed in this work assures the global asymptotic stability of the system. Example numerical simulations are presented based on the model of a six-degree-of-freedom Cincinnati Milacron T3-776 industrial robot. One example models the system compliance in four joints, while another case study simulates four lateral link oscillations. These examples show that this controller, even under inaccurate payload description, eliminates the oscillations while tracking desired trajectories.
Constant Turning Force Adaptive Control Via Sliding Mode Control Design
Authors: Hwang Chih-Lyang , Chen Bor-Sen
Published: March 2008

In the constant turning force adaptive control (CTFAC) system, the open-loop gain will vary and the stability cannot be assured when a cutting tool cuts a workpiece at various cutting depths or spindle operates in different speeds. In this paper, the spirit of sliding mode control is extended into discrete-time form to combine with parameter estimation having variable forgetting factor to stabilize the turning system against the variable gain and unmodeled dynamics, such as nonlinear perturbations, inaccurate measurements etc.
H
∞ Observations Weighted Control Law
Authors: Grimble M. J.
Published: March 2008

A H∞ optimal control problem is considered which leads to a particularly simple controller structure. The expression for the optimal controller only requires the solution of one diophantine equation which makes it very appropriate for self-tuning control applications. The controller developed is related to the Observations Weighted control law which involves the minimization of tracking error and control signal variances. The H∞ criterion minimized may be expressed in a signal spectrum minimization form or in a sensitivity minimization form. The system can be guaranteed to be stable under low control weighting (high gain) conditions even for non-minimum phase open-loop unstable plants. The design of the controller depends upon the specification of the cost weighting transfer-functions and this is illustrated in a design example.
Track-Following Controller Design for a Compound Disk Drive Actuator
Authors: Yen Jia-Yush , Hallamasek Kurt , Horowitz Roberto
Published: March 2008

The use of compound actuators in both magnetic and optical disk files has become a means of achieving increased servo actuator bandwidths. A compound actuator, comprised of a fine actuator mounted “piggyback” on a coarse actuator, positions the read/write transducers above a radial track. This paper describes a design methodology for a discrete-time feedback control system for a compound actuator in which the dynamic interaction between the actuator stages is directly considered. The performance of the servosystem, including the range and bandwith limitations of each actuator, is specified in terms of the desired frequency response of the closed-loop transfer functions from the reference track position to the tracking error and to the relative position between the coarse and the fine actuator. Parameter uncertainties and structural resonances are quantified using singular value techniques to form a robustness criterion which sets limits on the attainable tracking performance. Compensator design techniques using linear-quadratic Gaussian optimal control combined with loop transfer recovery are described. The state feedback portion of the compensator is calculated using an automatic procedure, while the state estimator is calculated by solving an associated Kalman filtering problem with colored fictitious noise. The noise is colored to shape the frequency spectrum of the input energy to each actuator, the relative motion between the stages, and the position of the transducer.
Observations on Control of Automated Guided Vehicles
Authors: Thomas P. D. , Forsythe W.
Published: March 2008

After reviewing briefly the characteristics of guided transport systems under the general headings of system requirements and system constraints, the effect on throughput of velocity profiling is examined. Quality of service in any transport system is related to frequency and journey time; it is shown that the effect of shaping velocity profiles can provide a marked improvement to both. The brake limited profile discussed is simple to implement, and effective, but should not be considered optimal.
Measurement of Oscillations in Partially Penetrated Weld Pools Through Spectral Analysis
Authors: Sorensen C. D. , Eagar T. W.
Published: March 2008

Sensors of the weld in progress are necessary to provide feedback control of the arc welding process. Signal processing of the arc voltage and current is proposed as a dynamic sensor of the welding process. Optimization of sampling parameters and excitation waveform were performed. The sensitivity of this technique to arc length and weld pool oscillation amplitude was determined. Weld pool oscillation frequencies were measured in stationary welds and correlated with weld pool size. Signal processing was shown to serve as a weld pool oscillation monitor for stationary welds on steel with helium shielding gas at arc lengths of up to 13 mm.
Design of Stability Augmentation Systems for Automotive Vehicles
Authors: Lee A. Y.
Published: March 2008

The high-speed cruising stability of passenger vehicles may be enhanced with stability augmentation systems. These systems would modify the driver’s steering command to the vehicle’s front wheels, and steer the rear wheels according to measured vehicle conditions such as its yaw-rate. In this simulation study, an explicit driver model is used in the design of these stability augmentation systems. For ease of implementation, only low-order controllers are synthesized using parameter optimization. The high-speed, straight-line stability of a passenger vehicle in a cross-wind is simulated to evaluate steering performance with these controllers. Our results show that stability augmented steering has the potential to improve the directional stability of passenger vehicles.
Dynamics of Flexible Bodies Using Generalized Newton-Euler Equations
Authors: Shabana A. A.
Published: March 2008

A force acting on a rigid body produces a linear acceleration for the whole body together with an angular acceleration about its center of mass. This result is in fact Newton-Euler equations which are used as basis for developing many recursive formulations for open loop multibody systems consisting of interconnected rigid bodies. In this paper, generalized Newton-Euler equations are developed for deformable bodies that undergo large translational and rotational displacements. The configuration of the deformable body is identified using coupled sets of reference and elastic variables. The nonlinear generalized Newton-Euler equations are formulated in terms of a set of time invariant scalars and matrices that depend on the spatial coordinates as well as the assumed displacement field. A set of intermediate reference frames having no mass or inertia are introduced for the convenience of defining various joints between interconnected deformable bodies. The use of the obtained generalized Newton-Euler equations for developing recursive dynamic formulation for open loop deformable multibody systems containing revolute, prismatic and cylindrical joints is also discussed. The development presented in this paper demonstrates the complexities of the formulation and the difficulties encountered when the equations of motion are defined in the joint coordinate systems.
A Simulation Analysis of Pose Measurement Error in Robot Calibration
Authors: Hutton D. V. , Riley D. L.
Published: March 2008

Calibration of a robotic manipulator and subsequent application of accuracy improvement techniques require precise measurement of manipulator position and orientation. This paper presents a comparison of two methods for computing position and orientation based on six or nine linear displacements measured in a test fixture.
Computational Alternative to a Gain Setting Procedure of Brown and Campbell
Authors: Kitis L.
Published: March 2008

A numerical method for setting the gain of a linear control system to obtain a specified peak closed-loop frequency response amplitude is presented. The essential computational step in the algorithm is the calculation of all positive roots of a polynomial. This step provides the set of all possible resonant frequencies. A gain constant for each of these frequencies is then found by a simple function evaluation. The possibility of multiple solutions is demonstrated by an example.
Design of PPD Controllers for Position Servos
Authors: de Silva C. W.
Published: March 2008

In this paper the classical time domain design problem of position servoactuators having proportional plus derivative (PPD) error controllers is reconsidered. Control system stability is represented by percentage overshoot and the speed of response by peak time. The associated design equations are strongly coupled and nonlinear. Design curves are presented to facilitate the realization of fast yet accurate designs. A design algorithm that generates exact values for the controller parameters is given. A numerical example is included to illustrate the design procedure.
The Use of Monte Carlo Simulations for the Interpretation of Light Scattering and Fluorescence Data on Self-Assembling Polymer Systems in Solutions
Authors: Matějíček Pavel , Uhlík Filip , Limpouchová Zuzana , Procházka Karel
Published: March 2008

In this feature article, we demonstrate the usefulness of tailor-made computer simulations for the interpretation of experimental data. Two examples of studies on self-assembling copolymer systems (by light scattering and fluorescence spectroscopy) performed some time ago are reviewed. It is shown how some unexpected and confusing results could have been interpreted using of Monte Carlo simulations. In both cases, a short outline of the experimental study including the motivation and the most important results is given first. Then the results of simulations are described and discussed with respect to the questions generated by experimental work. In this paper, we included both unpublished and already published data. Thus, the interpretation of the behavior and general conclusions are formulated in a retrospective way. The paper shows that simulations based on a considerably simplified model can complete the mosaic of evidences necessary for a reasonable interpretation of experimental results and can help to understand basic principles of their behavior. The necessary condition is that the model, even though strongly simplified, has to show all essential qualitative features of the behavior.
Independence of phytochrome destruction and physiological response in Avena and Pisum segment elongation
Authors: Hopkins W. G.
Published: March 2008

Control over elongation in Avena coleoptile and Pisum epicotyl segments by cyclic far-red light treatment is dependent on the timing of successive irradiations and independent of total energy. The effect of each far-red irradiation in a cycle is cumulative. Maximum efficiency of far-red light in a cycle is obtained when the light treatments follow within 2 to 3 h of each other. Additional increments of elongation may also be obtained by successive red light treatment only when presented at least 8 to 9 h apart. The effect of a single far-red treatment is to establish a maximum rate of elongation which is maintained for no more than 3 h. The results offer support for the hypothesis that low-energy phytochrome mediated responses result from maintenance of low but maximally effective levels of Pfr and that Pfr destruction is essentially independent of physiological action.
Taxonomic notes on pollen genera Callistopollenites, Tricolporites, and Carpinipites
Authors: Srivastava Satish K.
Published: March 2008

The date of publication of the genus Callistopollenites precedes that of the genus Pseudoexpressipollis by about 3 months. Thus Callistopollenites S. K. Srivastava has priority over Pseudoexpressipollis Krutzsch.The genus Tricolporites Cookson has been considered here as a valid monotypic genus because it meets the requirements stipulated by the International Code of Botanical Nomenclature.The acceptable spelling and taxonomic position of the genus Carpinipites S. K. Srivastava have been discussed.
Tilletiaria: a new genus in the Ustilaginales
Authors: Bandoni R. J. , Johri B. N.
Published: March 2008

Tilletiaria anomala gen. et sp. nov. is described. The species is characterized by aculeate teliospores similar to those of some Ustilaginales. The transversely septate metabasidia, sterigmata, and basidiospores are as in the Auriculariaceae. The hyphal cells are monokaryotic and haploid; fertile branches are subtended by a fusion bridge through which dikaryotization occurs.
Studies on the rosette plant Hieracium floribundum.: I. Observations related to flowering and axillary bud development
Authors: Yeung Edward C. , Peterson R. L.
Published: March 2008

Hieracium floribundum is a rosette species requiring a number of long days for flower induction. Histological studies of vegetative, transition, and floral apices showed the structural changes associated with flower induction in this species. One striking histochemical change observed was the absence of starch in vegetative apices and the accumulation and retention of quantities of starch in prefloral and floral apices. A study of initiation and development of axillary buds at the time of flowering revealed that there was a gradient in the potential to flower shown by these buds along the developing flower stalk to the base of the plant. The buds in the axils of upper peduncle bracts always develop as capitula while the apices of the buds in the axils of the next few bracts assume the shape of floral buds but fail to develop unless the upper developing inflorescences are removed. Buds in the axils of the lowest bracts and upper (youngest) leaves have the potential to form rosettes, stolons, or inflorescences depending on the environmental conditions in which the plants are grown. Buds formed in the lower (oldest) leaf axils normally fail to grow out until after seed set when a few may develop as rosettes. Possible explanations for these results are discussed, and some experimental approaches being used to elucidate the physiological basis for bud expression are indicated.
Apollo 12 lunar material: effects on plant pigments
Authors: Weete John D. , Walkinshaw Charles H.
Published: March 2008

Tissue cultures of tobacco grown for 12 weeks in contact with lunar material returned by Apollo 12 contained 21 to 35% more total pigment than control tissues. This difference is due primarily to increased chlorophyll a concentrations per gram fresh weight of tissue in experimental cultures. No differences were noted in the fresh or dry weight of the experimental and control cultures.