bluuebunny/crossref_metadata_2025 huggingface dataset:
A Cellular Model of Lung Elasticity
Authors: Kimmel E. , Kamm R. D. , Shapiro A. H.
Published: June 2009

The mechanics of the lung parenchyma is studied using models comprised of line members interconnected to form 3-D cellular structures. The mechanical properties are represented as elastic constants of a continuum. These are determined by perturbing each individual cell from a reference state by an increment in stress which is superimposed upon the uniform stretching forces initially present in the members due to the transpulmonary pressure. A force balance on the distorted structure, together with a force-deformation law for the members, leads to a calculation of the strain increments of the members. Predictions based on the analysis of the 3-D isotropic dodecahedron are in good agreement with experimental values for the Young’s, shear, and bulk moduli reported in the literature. The model provides an explanation for the dependence of the elastic moduli on transpulmonary pressure, the geometrical details of the structure, and the stress-strain law of the tissue.
An Experimental Study of Newtonian and Non-Newtonian Flow Dynamics in a Ventricular Assist Device
Authors: Mann K. A. , Deutsch S. , Tarbell J. M. , Geselowitz D. B. , Rosenberg G. , Pierce W. S.
Published: June 2009

The fluid dynamic behavior of a Newtonian water/glycerol solution, a non-Newtonian polymer (separan) solution, and bovine blood were compared in the Penn State Electrical Ventricular Assist Device (EVAD). Pulsed doppler ultrasound velocimetry was used to measure velocities in the near wall region (0.95–2.7 mm) along the perimeter of the pump. Mean velocity, turbulence intensity, local and convective acceleration, and shear rate were calculated from the PDU velocity measurements. Flow visualization provided qualitative information about the general flow patterns in the EVAD. Results indicate that water/glycerol does not accurately model the flow characteristics of bovine blood in the EVAD. The non-Newtonian separan solution produced results closer to those of the bovine blood than did the water/glycerol solution. Near wall velocity magnitudes for the separan were similar to those of the bovine blood, but the profile shapes differed for portions of the pump cycle. All three fluids exhibited periods of stagnation. Bovine blood results indicated the presence of a desired rotational washout pattern at mid-systole, while results with the other fluids did not show this feature.
A Study on a Vibratory Model of a Human Body
Authors: Nigam S. P. , Malik M.
Published: June 2009

This paper is concerned with the modeling of the human body as a spring mass system. Based on certain assumptions, an analysis for evaluating the mass and stiffness values of the model is developed. As an illustration of the modeling procedure, a 15-degree-of-freedom model of a male body is considered. The computed natural frequencies of the model are found to be within the range of available experimental values.
Lungs Under Cyclic Compression and Expansion
Authors: Tao Z. L. , Fung Y. C.
Published: June 2009

The pressure-volume relationship of lungs subjected to repeated compression and expansion is studied in detail. The investigation was motivated by an attempt to understand why lungs are frequently injured by compression waves; hence the lung was compressed to a degree greater than normally encountered in physiological conditions. Attention was focused on the collapse of the lung at a critical strain and the reopening of the trap at a critical stress. We found that when a rabbit lung is compressed, about one-half to one-quarter of its gas may be trapped in the alveoli because of the closure of airways. Reopening of the trap occurs at a pressure higher than the critical pressure for collapsing. The difference of the critical pressures of collapsing and reopening is influenced by the rate of strain and the strain history, especially by the maximum compressive stress imposed on the lung. The stress-strain relationship of the lung tissue, which resembles the PV curves, depends strongly on the strain history.
Numerical Advances in Gross-Motion Simulations of Head/Neck Dynamics
Authors: Tien C. S. , Huston R. L.
Published: June 2009

An efficient method for gross-motion simulation of head/neck dynamics in accidents and high acceleration environments is presented. The method uses finite-segment modelling to develop a 3-body model of the head/neck system. The model is shown to compare favorably with an analogous 9-body model and with experimental data. The model is expected to be useful for: (1) efficient analysis of gross-motion head/neck dynamics during accidents; (2) for developing increased intuitive understanding of head/neck behavior; and (3) for use with gross-motion, whole-body, crash-victim simulators.
Direct Comparison of Muscle Force Predictions Using Linear and Nonlinear Programming
Authors: Pedersen D. R. , Brand R. A. , Cheng C. , Arora J. S.
Published: June 2009

Estimating forces in muscles and joints during locomotion requires formulations consistent with available methods of solving the indeterminate problem. Direct comparisons of results between differing optimization methods proposed in the literature have been difficult owing to widely varying model formulations, algorithms, input data, and other factors. We present an application of a new optimization program which includes linear and nonlinear techniques allowing a variety of cost functions and greater flexibility in problem formulation. Unified solution methods such as the one demonstrated here, offer direct evaluations of such factors as optimization criteria and constraints. This unified method demonstrates that nonlinear formulations (of the sort reported) allow more synergistic activity and in contrast to linear formulations, allow antagonistic activity. Concurrence of EMG activity and predicted forces is better with nonlinear predictions than linear predictions. The prediction of synergistic and antagonistic activity expectedly leads to higher joint force predictions. Relaxation of the requirement that muscles resolve the entire intersegmental moment maintains muscle synergism in the nonlinear formulation while relieving muscle antagonism and reducing the predicted joint contact force. Such unified methods allow more possibilities for exploring new optimization formulations, and in comparing the solutions to previously reported formulations.
A Comparative Analysis of Thermal Blood Perfusion Measurement Techniques
Authors: Kress R. , Roemer R.
Published: June 2009

The object of this study was to devise a unified method for comparing different thermal techniques for the estimation of blood perfusion rates and to perform a comparison for several common techniques. The approach used was to develop analytical models for the temperature response for all combinations of five power deposition geometries (spherical, one- and two-dimensional cylindrical, and one- and two-dimensional Gaussian) and three transient heating techniques (temperature pulse-decay, temperature step function, and constant-power heat-up) plus one steady-state heating technique. The transient models were used to determine the range of times (the time window) when a significant portion of the transient temperature response was due to blood perfusion. This time window was defined to begin when the difference between the conduction-only and the conduction-plus-blood flow transient temperature (or power) responses exceeded a specified value, and to end when the conduction-plus-blood flow transient temperature (or power) reached a specified fraction of its steady-state value. The results are summarized in dimensionless plots showing the size of the time windows for each of the transient perfusion estimation techniques. Several conclusions were drawn, in particular: (a) low perfusions are difficult to estimate because of the dominance of conduction, (b) large heated regions are better suited for estimation of low perfusions, (c) noninvasive heating techniques are superior because they have the potential to minimize conduction effects, and (d) none of the transient techniques appears to be clearly superior to the others.
Least-Squares Matrix Correlations Between Stump Stresses and Prosthesis Loads for Below-Knee Amputees
Authors: Winarski D. J. , Pearson J. R.
Published: June 2009

Stump stresses were correlated to prosthesis loads for two unilateral, below-knee amputees over a range of flexion-extension angular adjustments. Normal stresses on the patellar tendon and gastrocnemius were related to the axial force and flexion-extension moment of the prosthesis via a matrix equation. Elements of this matrix, influence factors calculated by least-squares algorithms, identified the contributions of each time-dependent load component acting to produce the time-dependent normal stresses. The flexion-extension angular sensitivity of the way these sagittal plane loads combined to produce normal stresses was included in the matrix equation via a first-order Maclaurin series. Highly favorable correlation coefficients between empirically measured and theoretically predicted stump stresses were calculated. This demonstrated that, in future studies, using an influence-factor matrix holds promise for quantifying sensitivities of normal stresses of the stump to multiple adjustments in prostheses.
Strain Energy Descriptions of Biological Swelling I: Single Fluid Compartment Models
Authors: Bogen D. K.
Published: June 2009

Strain energy functions are derived from biphasic soft tissue models in order to describe large-deformation, large-swelling, elastic behavior of nonlinear materials. The resulting analysis leads to calculations of stress-extension relations and tissue fluid pressure. Also explored are the elastic stability of the biphasic tissue models and the manner in which tissue pressure is altered by material deformation.
Orthogonal Bone Cutting: Saw Design and Operating Characteristics
Authors: Krause W. R.
Published: June 2009

The cutting process of orthopaedic bone saws was considered as orthogonal (two-dimensional) cutting for determination of the horizontal and vertical force components of single edge cutting tools with rake angles of 0 to −30 degrees. The Merchant analysis for orthogonal cutting was used to determine the resultant force and other force and work relationships. The effect of an imposed lateral vibration on the cutting tool was also investigated. The results of the tests indicated a strong interaction between the measured and derived forces with the rake angle and feed velocity. It was concluded that to reduce the cutting forces and work expenditure, a negative rake angle between 0 and −10 degrees, high feed velocity, and an imposed lateral vibration provided the greatest reduction in force and energy expenditure.
A Compact Centrifugal Blood Pump for Extracorporeal Circulation: Design and Performance
Authors: Tanaka Shinobu , Yamamoto Shuzo , Yamakoshi Ken-ichi , Kamiya Akira
Published: June 2009

A new compact centrifugal blood pump driven by a miniature DC servomotor has been designed for use for short-term extra corporeal and cardiac-assisted circulation. The impeller of the pump was connected directly to the motor by using a simple-gear coupling. The shaft for the impeller was sealed from blood by both a V-ring and a seal bearing. Either pulsatile or nonpusatile flow was produced by controlling the current supply to the motor. The pump characteristics and the degree of hemolysis were evaluated with regard to the configuration of the impeller with a 38-mm outer diameter in vitro tests; the impeller having the blade angles at the inlet of 20 deg and at the outlet of 50 deg was the most appropriate as a blood pump. The performance in an operation, hemolysis and thrombus formation in the pump were assessed by a left ventricular bypass experiment in dogs. It was suggested by this study that this prototype pump appears promising for use not only in animal experiments but also in clinical application.
On Constitutive Relations and Finite Deformations of Passive Cardiac Tissue: I. A Pseudostrain-Energy Function
Authors: Humphrey J. D. , Yin F. C. P.
Published: June 2009

A three-dimensional constitutive relation for passive cardiac tissue is formulated in terms of a structurally motivated pseudostrain-energy function, W, while the mathematical simplicity of phenomenological approaches is preserved. A specific functional form of W is proposed on the basis of limited structural information and multiaxial experimental data. The material parameters are determined in a least-squared sense from both uniaxial and biaxial data. Our results suggest that (1) multiaxially-loaded cardiac tissue is nearly transversely-isotropic with respect to local muscle fiber directions, at least for a limited range of strain histories, (2) material parameters determined from uniaxial papillary muscle data result in gross underestimates of the stresses in multiaxially-loaded specimens, and (3) material parameters determined from equibiaxial tests predict the behavior of the tissue under various nonequibiaxial stretching protocols reasonably well.
A Theoretical Model for Water Flux Through the Artery Wall
Authors: Jain R. , Jayaraman G.
Published: June 2009

A two layer model for water flux through the artery is studied using a matematical model based on the theory for the consolidation of water saturated soils. The matrix is considered to be constituted by two layers with different permeabilities and different elastic constants and the two systems of equations are coupled with the condition of continuity of pressure, total stress, solid displacement and fluid seepage velocity at the interface. The luminal pressure is considered to be harmonic in time. Exact solutions are obtained for displacements and pressures in both the layers. For large consolidation times, large pressure gradients are found to exist near the boundaries and at the interface. The heterogeneous model may not only be useful to understand the mechanics of transport in the physiological system but it will also help the bioengineers to choose proper implant materials to design artificial vascular organs for the purpose of prosthesis.
Kinematic and Passive Resistive Properties of Human Elbow Complex
Authors: Engin Ali Erkan , Chen Shuenn-Muh
Published: June 2009

In recent years, owing to their versatility and reduced cost of operation, multisegmented mathematical models of the total human body have gained increased attention in gross biodynamic motion studies. This, in turn, has stimulated the need for a proper biomechanical data base for the major human articulating joints. The lack of such a database for the humero-elbow complex is the impetus for this study. The total angular range of motion permitted by the complex and the passive resistive properties beyond the full elbow extension were studied. Results obtained on ten normal male subjects were utilized to establish a statistical data base for the humero-elbow complex. Results are also expressed in functional expansion form suitable for incorporation into the existing multisegmented models.
Developing Oscillatory Flow in a Circular Pipe: A New Solution
Authors: Cen Ren-Jing , Liu Bao-Sen , Hwang Ned H. C.
Published: June 2009

The problem of oscillatory flow in a circular pipe was analyzed by Atabek and associates more than two decades ago. Their formulas for velocity and pressure distributions in developing pipe flows under oscillatory conditions have been often cited. However, the application of these formulas for flow field computations requires a rather complex procedure involving plotting of a set of curves and predetermination of the phase angles. This paper presents a method using the imaginary argument of the Bessel function to solve the Navier-Stokes equations. A different set of solution formulas are obtained. A comparison of the formulas obtained in this paper with those of Atabek shows that the former is considerably simpler and more convenient to use in flow computations. Numerical results computed using this paper’s formulas are consistent with Atabek’s and with the experimental measurements.
Theory on Thermal Probe Arrays for the Distinction Between the Convective and the Perfusive Modalities of Heat Transfer in Living Tissues
Authors: Arkin H. , Holmes K. R. , Chen M. M.
Published: June 2009

Recent suggestions for an improved model of heat transfer in living tissues emphasize the existence of a convective mode due to flowing blood in addition to, or even instead of, the perfusive mode, as proposed in Pennes’ “classic” bioheat equation. In view of these suggestions, it might be beneficial to develop a technique that will enable one to distinguish between these two modes of bioheat transfer. To this end, a concept that utilizes a multiprobe array of thermistors in conjunction with a revised bioheat transfer equation has been derived to distinguish between, and to quantify the perfusive and convective contribution of blood to heat transfer in living tissues. The array consists of two or more temperature sensors one of which also serves to locally insert a short pulse of heat into the tissue prior to the temperature measurements. A theoretical analysis shows that such a concept is feasible. The construction of the system involves the selection of several important design parameters, i.e., the distance between the probes, the heating power, and the pulse duration. The choice of these parameters is based on computer simulations of the actual experiment.
Biomechanics
Authors: Fung Y. C.
Published: June 2009

Mechanics is as relevant to living organisms as to conventional engineering, and engineers are making contributions to the understanding of physiology, pathology, cell biology, as well as to the establishment of medical, rehabilitation, and genetic engineering industries. Living organisms do have unique features not found in conventional engineering. These features include the ability to grow, change, and reproduce, the process of aging and dying, and the existence of a most intricate system of feedback and control. Mechanics plays a role in all of these topics. Many things are still unknown or not fully understood, or not controllable, and therein lies the attraction of the field.
Polymers and Viscoelasticity
Authors: Christensen R. M.
Published: June 2009

The mechanics of polymers offers a variety of emerging technical problems ranging from basic properties characterization to simulation of complex manufacturing operations. Of particular importance are the means of expressing nonlinear constitutive equations for solids with evolving states of damage. Corresponding forms for polymeric fluids will enable the solution of many important problems of non-Newtonian rheology.
Fiber Reinforced Composite Materials
Authors: Christensen R. M.
Published: June 2009

Fiber-reinforced composite materials offer considerable performance advantages over conventional materials. New fiber developments place a premium upon understanding the mechanical interactions between phases in order to optimize the composition. Of particular importance are the means of quantifying damage states and predicting nonlinear behavior. Special attention is given to such areas as damage/failure/life prediction, environmental effects, nondestructive evaluation, interface conditions, and data base generation.
Fracture Mechanics
Authors: Rice J. R.
Published: June 2009

Fracture mechanics is an active research field that is currently advancing on many fronts. This appraisal of research trends and opportunities notes the promising developments of nonlinear fracture mechanics in recent years and cites some of the challenges in dealing with topics such as ductile-brittle transitions, failure under substantial plasticity or creep, crack tip processes under fatigue loading, and the need for new methodologies for effective fracture analysis of composite materials. Continued focus on microscale fracture processes by work at the interface of solid mechanics and materials science holds promise for understanding the atomistics of brittle vs ductile response and the mechanisms of microvoid nucleation and growth in various materials. Critical experiments to characterize crack tip processes and separation mechanisms are a pervasive need. Fracture phenomena in the contexts of geotechnology and earthquake fault dynamics also provide important research challenges.
Experimental Mechanics
Authors: Clifton R. J. , Chiang F. P.
Published: June 2009

Mechanical failure of machine parts, structures, and microelectronic components has a strong negative impact on the safety, security, and productivity of our people. Prevention of these failures is a principal focus of solid mechanics, which uses analysis, experiment, and computation to provide the understanding necessary for failure reduction through improved design, fabrication, and inspection. Experimental mechanics plays a critical role in this effort since it provides the data base for the calculations and the means for testing the validity of proposed theoretical models of failure. Current trends in experimental mechanics show increased use of optical methods for monitoring the displacements, velocities, and strains of surfaces. This trend has gained impetus from the attractiveness of noncontact methods for hostile environments and dynamically loaded bodies. Advances in laser technology have enhanced the instrumentation associated with these methods. Another trend is the investigation of material behavior under more complex loading conditions, made possible by the availability of servo-controlled testing machines with computer interfaces. Still another trend is the increased attention given to defects, such as inclusions, cracks, and holes, because of their importance in failure mechanisms. Opportunities for future contributions from experimental mechanics appear to be great and to occur across a broad range of technological problems. A central theme of future research appears to be increased emphasis on measurements at the micron and submicron scale in order to advance the understanding of material response and failure at the micromechanical level. Increased attention will also be given to internal measurements of defects, deformations and residual stresses because of their importance in developing a fundamental understanding of failure. Automated data reduction and control of experiments will greatly increase the information obtained from experiments and its usefulness for the development of mathematical models. Other important research directions include improved methods for measurements of in situ stresses in rocks, improved measurements of displacements and physiological parameters in biological systems, capability for long-term monitoring of the integrity of structures, and improved sensors for feedback control of mechanical systems.
Structural Dynamics
Authors: Moon F. C. , Dowell E. H.
Published: June 2009

While much of the linear theory of structural dynamics has been codified in numerous computer software, important problems remain such as inverse methods (modal synthesis or system identification) and optimization problems. Nonlinear problems, however, are a fertile ground for new research, especially those involving large deformations (e.g., crash simulation) and material nonlinearities. Structure interaction problems will continue to be a fruitful area of research including fluid-structure dynamics and interaction with acoustic noise, thermal fields, soils, and electromagnetic forces. For example, new knowledge about unsteady flows around bluff bodies is needed to make significant progress with dynamic interaction problems with bridge and building structures in unsteady winds. A new field which shows great promise for application is the theory of feedback control of flexible structures. Advances in this area could pay off in near-space engineering and robotics. The training of new researchers with backgrounds in both structural dynamics and control theory and experience is a high priority for the control-structure field, however.
Structural Systems for Elevated Temperatures and Hostile Environments
Authors: Leckie F. A.
Published: June 2009

The demand on load-carrying structural systems for increased operating temperatures in hostile environments has led to the development of new metallic alloys and non-metallic materials. Because of the intensity of operating conditions the materials are frequently subjected to severe loading and corrosive environments, and it is then only possible to design structural systems for finite life. To complete effective designs, it is necessary to understand the physical and mechanical properties of materials and how these properties are related to the performance of the system. The range of associated problems is discussed as well as some of the fundamental and computational questions which must be addressed in searching for improved and more economic performance.
Mechanics of Electronic and Electromechanical Devices
Authors: Moon F. C.
Published: June 2009

Problems involving the interaction of electromagnetic material effects and forces with stresses, deformations, and dynamics span a wide spectrum from thermal strain problems in microelectronic chips to stresses in large superconducting magnets for fusion reactors, NMR scanners, and levitated trains. An important class of problems that merits increased research effort are the mechanics problems associated with transducers or sensors based on ferroelectric, ferromagnetic, semiconductor, or microelectronic materials. Another area which may have technological payoff is that of electromechanical actuators. Further work is also required on numerical methods for calculating electromagnetic fields, forces, torques, and currents in order to allow engineers to better design and optimize electromagnetic devices. Interaction of laser radiation and high energy particles with solids is another area for new research. Progress in this field has not been steady. The interdisciplinary nature of these problems has meant that the field has no natural home for funding. This will present a problem for future progress in this field.
Processing and Manufacturing
Authors: Leckie F. A. , McMeeking R. M.
Published: June 2009

The general problems associated with the mechanics of forming processes are discussed. Particular topics include: (i) processing of electronic devices; (ii) flexible robotic systems; (iii) manufacturing methods for modern materials; (iv) process control for optimal properties.
Foundations of Solid Mechanics
Authors: Carroll M. M.
Published: June 2009

Solid mechanics is a basic discipline which supports much of the practice of mechanical and civil engineering, and contributes significantly to other engineering and scientific disciplines. Research in solid mechanics, at the foundational level, emphasizes comprehensive understanding and well-formulated analyses of mechanical phenomena occurring in engineering systems. The increasing availability of large computers has had a tremendous impact on the field. The traditional emphasis on analysis has shifted toward development of more realistic and detailed descriptions of material response, more efficient computational methodologies, and accurate numerical solution of initial and boundary value problems. Despite (or perhaps because of) this trend, theory and analysis must continue to play a vital role in modern solid mechanics. Solid mechanics is enriched by the increasing level of activity in interdisciplinary research. Within the field, there is a need for better communication and interaction between computation, experiment, and theory.
Flow Separation, an Important Mechanism in the Formation of Mean Pulmonary Pressure During High-Frequency Oscillation
Authors: Bush E. H. , Spahn D. R. , Niederer P. F. , Schmid E. R.
Published: June 2009

Mean pressures within the lungs and lung volume, respectively, are clinically important parameters. During ventilation by way of high-frequency oscillation (HFO), these parameters have been shown to be strongly frequency dependent. To identify mechanisms leading to mean pressure formation during HFO, findings of the theory of stationary flow were extended to oscillatory flow by a quasi-stationary approach. To confirm the theoretical findings, in-vitro experiments on HFO-models were performed. Flow separation was found to be an important mechanism in the formation of mean pressure. Flow separation causes a significant flow resistance, which may be distinctly different for in- and outflow. During oscillatory flow, a mean pressure difference thus results. This mechanism is of particular importance in bifurcations, which are present in the HFO-circuit as well as in the airways. With the direction-dependent flow separation, a general mechanism was found, which accounts for differing mean pressure values within the lungs with different HFO-circuits. This mechanism also contributes to interregionally different mean pressure values within the lungs.
On the Flow of a Non-Newtonian Liquid Induced by Intestine-Like Contractions
Authors: Phan-Thien N. , Low H. T.
Published: June 2009

This paper considers the flow of an inelastic liquid which is generated by contractions like those of the intestine. Unlike regular peristaltic motion, these contractions occur locally over a finite length and have a finite amplitude. We adopt a contraction model due to Macagno and Christensen and repeat their analysis for an inelastic liquid. Our analysis, which is based on a Boundary Element Method, indicates that the net flow rate depends very weakly on the power-law index. The pumping action is therefore similar to that of a positive displacement pump.
A Model of Oxygen Exchange Between an Arteriole or Venule and the Surrounding Tissue
Authors: Weerappuli D. P. V. , Popel A. S.
Published: June 2009

A mathematical model is developed to study the effect of capillary convection on oxygen transport around segments of arterioles and venules that are surrounded by capillaries. These capillaries carry unidirectional flow perpendicular to the vessel. The discrete capillary structure is distributed in a manner determined by the capillary blood flow and capillary density. A nonlinear oxyhemoglobin dissociation curve described by the Hill equation is used in the analysis. Oxygen flux from the vessel is expressed as a relationship between Sherwood and Peclet numbers, as well as other dimensionless combinations involving parameters of the capillary bed. A numerical solution is obtained with a finite difference method. The numerical results obtained within the physiological range of parameters allow the prediction of longitudinal gradients of hemoglobin-oxygen saturation along the arterioles and venules.
The Fahraeus Effect in Sheet Flows With a Gap Thickness of 4 to 36 μm
Authors: Deng L. H. , Wu Y. P. , Wang G. R. , Yang R. F. , Lee J. S.
Published: June 2009

We measured the Fahraeus effect of blood flowing in a sheet flow model formed with two glass slides. The number of red blood cells in the sheet flow was counted to determine a sheet hematocrit Hs and the discharge hemotocrit Hd was measured from blood collection. For a Hd in the range of 3 to 30 percent, we find that Hs/Hd is about .83 for a gap of 4.1 μm. When the discharge hematocrit is 30 percent, the ratio decreases to .66 as the gap approaches 7 μm and then increases as the gap becomes thicker. The results indicate that the hematocrit ratio for a gap thicker than 4.1 μm is an increasing function of the discharge hematocrit. The value of Hs/Hd found for the sheet flow models and its dependence on Hd are comparable to those of circular tubes when their diameter equals the gap thickness.
On the Discrimination Between Band-Limited Coherent and Random Apparent Stresses in Transitional Pulsatile Flow
Authors: Lieber B. B. , Giddens D. P. , Kitney R. I. , Talhami H.
Published: June 2009

A frequency domain approach that incorporates a matched filter was examined for discriminating between ordered velocity fluctuations with band-limited frequency content and random velocity variations in pulsatile disturbed flows. Fluctuations at pseudo-discrete frequencies may yield a significant contribution to the apparent stress tensor computed from the unsteady Navier Stokes equations, and an estimate of the stresses arising from these ordered structures can be obtained once the velocity variations have been decomposed. This type of decomposition permits the estimation of the apparent stresses in turbulent flows, consisting of coherent and random parts, in blood flow applications such as diseased constricted arteries or downstream of artificial heart valves.
A Spherical Source Model for the Thermal Pulse Decay Method of Measuring Blood Perfusion: A Sensitivity Analysis
Authors: Diederich C. J. , Clegg S. , Roemer R. B.
Published: June 2009

The thermal pulse-decay method, as developed and analyzed by Chen et al. [1–6], is a thermal clearance technique that uses a small thermistor probe for determining the blood perfusion and thermal conductivity of the tissue immediately surrounding the probe. They described the energy transfer of the probe/tissue system mathematically with a simple analytical model, the point source model, which assumes that the heating source is infinitely small. This paper introduces a new, more accurate analytical description that assumes the heating source is spherically symmetric with a finite radius. A numerical study of these two alternative mathematical models is presented in which the solutions of each model are compared to transient temperature decay data generated from a detailed finite difference simulation of the probe/tissue system. The accuracy and sensitivity of the predictions of each of these models to variations in tissue thermal conductivity and perfusion, probe characteristics, and heating time are presented. In all cases, the accuracy of the spherical source model was better than the point source model. It is also shown that the spherical source model can accurately predict low rates of perfusion (on the order of 1 kg/m3s) unlike the point source model. The spherical source model also allows for the possibility of the measurement probes to be calibrated for an “effective bead radius” which accounts for the nonideal characteristics of the probe, thereby giving even more accurate determinations of perfusion.
One-Dimensional Steady Continuum Model of Retraction of Pseudopod in Leukocytes
Authors: Zhu Cheng , Skalak Richard , Schmid-Scho¨nbein Geert W.
Published: June 2009

A one-dimensional steady state continuum mechanics model of retraction of pseudopod in leukocytes is developed. The retracting pseudopod is assumed to move bodily toward the main cell body, the bulk motion of which can be represented by cytoplasmic flow within a typical stream tube through the leukocyte. The stream tube is approximated by a frictionless tube with prescribed geometry. The passive rheological properties of cytoplasm in the main cell body and in the pseudopod are modeled, respectively, by Maxwell fluid and Hookean solid. The two regions are assumed to be separated by a sharp interface at which actin gel solates and thereby changes its rheological properties as it flows from the pseudopod to the main cell body. The driving mechanism responsible for the active retraction motion is hypothesized to be a spontaneous deformation of the actin gel, analogous but not necessarily equal to the well known actin-myosin interaction. This results in an active contractile stress being developed in the pseudopod as well as in the cell cortex. The transverse traction pulls against the inclined wall of the stream tube and is transduced into an axial stress gradient, which in turn drives the flow. The tension on the tube wall is picked up by the prestressed cortical shell. Governing equations and boundary conditions are derived. A solution is obtained. Sample data are computed. Comparison of the theory with experiments shows that the model is compatible to the observations.
What Nei Jing and Mai Jing Say About Arterial Pulse Waves and Our Attempt to Illustrate Some of Their Statements
Authors: Xue H. , Fung Y. C.
Published: June 2009

A rich group of fluid mechanical problems are suggested in the classical Chinese books Nei Jing and Mai Jing. In this article the methods of pulse wave palpation described in these books are briefly explained, and an attempt to understand some of their statements is presented.
A Numerical Model of Expired Flow in a Monoalveolar Lung Model Subjected to Pressure Ramps
Authors: Thiriet M. , Bonis M. , Adedjouma A. S. , Yvon J. P.
Published: June 2009

A numerical investigation of pulmonary flow properties was carried out in a monoalveolar model composed of a balloon and a compliant tube in series, subjected to pressure ramps. The flow is shown to become quickly limited by a wave-speed mechanism, occurring at the peak flow. The critical point then travels upstream, while the main part of the exit flow rate is provided by the tube collapse. After the critical flow period, the flow becomes subcritical and viscous effects are predominant in the deeply collapsed tube.
Three-Dimensional Kinematic Modelling of the Human Shoulder Complex—Part I: Physical Model and Determination of Joint Sinus Cones
Authors: Engin A. E. , Tu¨mer S. T.
Published: June 2009

Modelling of the human shoulder complex is essential for the multi-segmented mathematical models as well as design of the shoulder mechanism of anthropometric dummies. In Part I of this paper a three-dimensional kinematic model is proposed by utilizing the concepts of kinematic links, joints, and joint sinuses. By assigning appropriate coordinate systems, parameters required for complete quantitative description of the proposed model are identified. The statistical in-vivo data base established by Engin and Chen (1986) is cast in a form compatible with the model by obtaining a set of unit vectors describing circumductory motion of the upper arm in a torso-fixed coordinate system. This set of unit vectors is then employed in determining the parameters of a composite shoulder complex sinus of a simplified version of the proposed model. Two methods, namely the flexible tolerance and the direct methods, are formulated and tested for the determination of an elliptical cone surface for a given set of generating unit vectors. Numerical results are presented for the apex angles and orientation of the composite joint sinus cone with respect to the anatomical directions.
The Second Stiffest Axis of a Beam-Column: Implications for Cervical Spine Trauma
Authors: Liu Y. King , Dai Q. Guo
Published: June 2009

Based on an idealized model of a homogeneous, isotropic beam-column, the second stiffest axis under static loading was derived. The maximum allowable force for the second stiffest axis was then examined. The ratio of the maximum allowable forces of the second stiffest axis to the stiffest axis was established. The stiffness ratio of the second stiffest axis to the stiffest axis was also found. Taking buckling into consideration, the safe load region for all possible acting directions was derived. The implications of the idealized model for cervical spine trauma are discussed.
Analytical Studies of Injury Criteria for the Thorax
Authors: Wang J. T.
Published: June 2009

The viscous criterion is a recently developed criterion to assess injury severity of the human thorax. In the viscous criterion, the peak viscous response, which is defined as the maximum product of deformation velocity and compression of an object, is proposed as a predictor of injury risk. However, the physical meaning of the criterion is not very clear. In this paper, the mathematical properties of the viscous criterion are analyzed. A mechanical thorax model is then used to relate the criterion to the physical quantities of the model using energy concepts. It is found that the so-called peak viscous response is strongly related to the peak energy storing rate of the thorax which is not related to the viscosity of the thorax. It is also shown that the viscous response of the thorax is given by the integral of the velocity squared with respect to time. The analysis is further expanded to a more general case to result in four criteria based upon the energy concepts. A hypothesis for injury assessment is proposed by using the four criteria.
The Effects of Orientation and Location on the Strength of Dorsal Rat Skin in High and Low Speed Tensile Failure Experiments
Authors: Haut R. C.
Published: June 2009

The tensile strength of skin is associated, in part, with its potential for laceration from impact. The quasi-static tensile strength of skin depends on orientation. The objective of this study was to determine whether the strength of skin in high speed tensile failure experiments exhibits a similar dependence on orientation. Tensile experiments were conducted at 6000 percent/s and 30 percent/s on dorsal skin of rats aged 1–6 months. Experiments were performed on specimens cut perpendicularly and longitudinally to the spine at cranial and caudal locations. The tensile failure properties depended on location, orientation, age and strain rate. The strength was dependent on orientation to the same degree in high and low speed tests. This helps explain why accident statistics show that skin lacerates preferentially on the body.
A Theoretical Description of Blood Flow Through the Mitral Orifice
Authors: Bakalyar D. M. , Hauser A. M. , Timmis G. C.
Published: June 2009

A nonlinear differential equation describing the Doppler velocity profile for blood flow through the mitral valve has been derived. This equation is based on fluid dynamics and a simple, but comprehensive model of atrial and ventricular mechanics. A numerical solution to the equation is described and provides excellent agreement with Doppler velocity curves obtained clinically. One important result of the theory is that in patients with mitral stenosis, the slope of the clinically observed straight-line descent of the velocity profile is proportional to the mitral orifice area and inversely proportional to the atrioventricular compliance.
Motion of Nonaxisymmetric Red Blood Cells in Cylindrical Capillaries
Authors: Hsu R. , Secomb T. W.
Published: June 2009

We analyze theoretically the single-file flow of asymmetric red blood cells along cylindrical capillaries. Red cells in narrow capillaries are typically nonaxisymmetric, with the cell membrane moving continuously around the cell. In our analysis, cell shape and streamlines of membrane motion are prescribed. Lubrication theory is used to compute velocities and pressures in the fluid surrounding the cell. Conditions of zero lift, zero torque, zero drag, and energy conservation in the cell are imposed. Predicted tank-treading frequency, cell inclination and transverse displacement are small. Cell asymmetry and tank-treading are found to have little effect on the apparent viscosity of blood in capillaries with diameters up to 7 μm.
Enhancement of Heat Transfer in Red Cell Suspensions In Vitro Experiments
Authors: Carr R. T. , Tiruvaloor N. R.
Published: June 2009

New data on laminar heat convection with red cell suspensions have been gathered for both heating and cooling. When compared to data for the suspending medium alone, it is apparent that the red cells enhance laminar heat transfer when Pe > 4. This is probably due to particle movements. These new data disagree with earlier studies which indicated no enhancement of heat transfer for blood cell suspensions. The data do agree with previous correlations for enhanced thermal transport in sheared suspensions.
Kinetics of Xanthan Production When NH3-N Limits Biomass Synthesis and Glucose Limits Polysaccharide Synthesis
Authors: Schweickart R. W. , Quinlan A. V.
Published: June 2009

The bacterium Xanthomonas campestris, which synthesizes the commercially important polysaccharide xanthan, was grown aseptically in 1.2 L fermenters using semicontinuous cell culture technique (d′ = 0.0035 h−1). The effects of carbon-substrate concentration on xanthan production were investigated at three initial glucose concentrations (G0 = 15, 20, 25 g/L). Cell biomass synthesis was nitrogen-limited by use of a chemically defined medium that contained NH3-N as the sole nitrogen source at a concentration where it was exhausted before glucose. A linear relationship between biomass synthesis and NH3-N depletion was observed. This relationship remained valid only until NH3-N exhaustion, after which biomass concentration slowly rose another 20 percent before declining. Another linear relationship was found between xanthan synthesis and glucose uptake. This relationship was unaffected by the disappearance of NH3-N and held through glucose exhaustion. The quasi-stoichiometric yield coefficients obtained for each linear relationship were not affected by G0. Biomass synthesis kinetics showed no variation with G0 before NH3-N exhaustion; afterwards, cell biomass decline was delayed by increasing G0. Xanthan synthesis kinetics displayed no detectable response to depletion of NH3-N and plateauing of biomass concentration; however, there was a marked slow down in the net rate of xanthan synthesis and a drop in xanthan yield after cell biomass decline became noticeable.
Flow in a Two-Dimensional Collapsible Channel With Rigid Inlet and Outlet
Authors: Matsuzaki Y. , Matsumoto T.
Published: June 2009

This paper examines mainly oscillatory behavior of a fluid-conveying collapsible tube using a two-dimensional flexible channel made of a pair of membranes. The equation of equilibrium of the membrane in a large deflection theory is coupled with the equations of continuity and momentum of an incompressible flow in a one-dimensional flow theory accounting for flow separation. An explicit finite difference method was used to solve the governing equations numerically. According to numerical results, the fluids in the inlet and outlet rigid channels have strong effects on the oscillation of the system. Depending on initial values for the numerical integration, there may exist both a stable static equilibrium and an oscillatory solution for the same parameter values, but only if the external pressure is sufficiently large.
Oscillations in a Collapsed-Tube Analog of the Brachial Artery Under a Sphygmomanometer Cuff
Authors: Bertram C. D. , Raymond C. J. , Butcher K. S. A.
Published: June 2009

To determine whether self-excited oscillations in a Starling resistor are relevant to physiological situations, a collapsible tube conveying an aqueous flow was externally pressurized along only a central segment of its unsupported length. This was achieved by passing the tube through a shorter and wider collapsible sleeve which was mounted in Starling resistor fashion in a pressure chamber. The tube size and material, and all other experimental parameters, were as used in our previous Starling resistor studies. Both low- and high-frequency self-excited oscillations were observed, but the low-frequency oscillations were sensitive to the sleeve type and length relative to unsupported distance. Pressure-flow characteristics showed multiple oscillatory modes, which differed quantitatively from those observed in comparable Starling resistors. Slow variation of driving pressure gave differing behavior according to whether the pressure was rising or falling, in accord with the hysteresis noted on the characteristics and in the tube law. The results are discussed in terms of the various possible mechanisms of collapsible tube instability, and reasons are presented for the absence of the low-frequency mode under most physiological circumstances.
Parametric Evaluation of Forced Expiration Using a Numerical Model
Authors: Elad D. , Kamm R. D.
Published: June 2009

Numerical calculations were performed to study the influence of several physiologic parameters on a forced expiration. It was found that the axial distribution of airway compliance produced profound changes in the detailed flow pattern, as characterized by the axial distributions of speed index and area ratio, but had little effect on the flow-volume curve. Similar results were obtained when the expression for frictional losses was changed to reflect new experimental results. In contrast, changes in airway size and geometry altered both the detailed flow pattern and the mean expiratory flow rate. The shape of the flow-volume curve remained unchanged.