bluuebunny/crossref_metadata_2025 huggingface dataset:
Strain Energy Descriptions of Biological Swelling II: Multiple Fluid Compartment Models
Authors: Bogen D. K.
Published: June 2009

A series of multicompartmental, biphasic elastic tissue models is developed. In its most general form, the models consist of multiple tubular networks, each with an internal spring network. In addition, another spring network occupies the extratubular compartment. Strain energy functions are derived for the models, as well as expressions for the fluid pressures in each compartment arising from volume expansion or swelling. Calculations also show that the distribution of fluid among compartments is a significant determinant of tissue elasticity.
The Response of the Seated Human to Sinusoidal Vibration and Impact
Authors: Pope M. H. , Wilder D. G. , Jorneus L. , Broman H. , Svensson M. , Andersson G.
Published: June 2009

Low back pain has been shown to occur more frequently among vehicle drivers than in representative control groups. Thus the response of the human to vibration and impact is of interest. This study investigated the response of the spine to both impact and sinusoidal excitation in either a relaxed or erect seated posture. The sinusoidal testing apparatus used was a resonating system consisting of two parallel wooden beams, simply supported, and the impact testing apparatus a bearing-guided, spring-suspended platform, struck from below. Ten subjects (5 males, 5 females) were evaluated using both methods. Transfer functions were compared at 2–4 Hz, 4–8 Hz and 8–16 Hz intervals using a sign test. Although in 24 comparisons of either test method (vibration or impact) or posture (erect or relaxed) where eleven showed differences significant at the p < .05 level, only 2 out of 24 comparisons were the differences distinct enough to be significant (at the p < .01 level). Both of these latter differences were due to test method while the subjects were sitting erect. In those instances where there were no significant differences due to test method, the impact method may be a viable replacement for the vibration test method. Where the levels of significance are higher (p < .01 or p < .05), further study of the magnitude of the differences is indicated and may reveal further insight into the seated individual as a system.
Upper Limb Loadings of Gait With Crutches
Authors: Opila K. A. , Nicol A. C. , Paul J. P.
Published: June 2009

Long-term crutch users and patients with arthritis are particularly susceptible to upper limb joint degeneration during aided gait. The function of the walking aid for stability, support, and restraint/propulsion must be optimized with the upper limb loadings caused by the aids. Post-operative total hip replacement (THR) patients, tibial fracture, and paraplegic subjects using sticks and elbow crutches were analyzed in this study. Elbow and shoulder joint centers and aid orientations were monitored simultaneously in three dimensions and combined with aid forces to determine upper limb moment loadings. Three loading effects were observed: tendency for the aids to cause 1) the elbow to flex and shoulder to extend, 2) the elbow and shoulder to extend, and 3) the shoulder to abduct. Moment values of up to 0.10 Nm per body weight (BW) causing the shoulder to extend were measured, i.e., of similar magnitude to the moments at the hip in unaided gait. A modification of the elbow crutch, designed to improve medial-lateral stability, was unsuccessful in use due to wrist instability. This reinforced the requirement that crutch designs integrate the aid’s function in gait with the ability of the upper limb joints to balance the applied loads.
Load Sharing Among Spinal Elements of a Motion Segment in Extension and Lateral Bending
Authors: Goel V. K. , Winterbottom J. M. , Weinstein J. N. , Kim Y. E.
Published: June 2009

A linear optimization model was formulated using a semi-experimental protocol to estimate the forces in the spinal elements of a lumbar motion segment subjected to an extension or lateral bending moment with and without a 120 N compressive preload. A morphometer was used to acquire the three-dimensional locations of the disk center, facet centers and ligament origin and insertion sites with the specimen in a “neutral” position. The relative motion of the superior vertebra, under the loading conditions tested, was monitored using a Selspot II® system. These data allowed the formulation of the static equilibrium equations for the superior vertebra at each of the loading conditions mentioned above. A linear optimization technique was used, along with a suitable cost function, to find an optimum solution for the set of equations and imposed constraints. Results showed that for 6.9 Nm of extension moment, each facet carried a load of 52 N, with the disk carrying an axial tensile load of 104 N. At the 6.9 Nm extension moment coupled with 120 N preload, each facet carried a load of 77.2 N and the disk an axial tensile load of 37 N. In right lateral bending, with and without preload, the load was distributed among the right facet, the disk, the left ligamentum flavum and the left capsular ligament. At the 6.9 Nm load step without preload the right facet carried an axial load of 127.01 N with the disk carrying an axial compressive load of 7.8 N. Ligament forces for this step for the left ligamentum flavum and capsular ligament, respectively, were 61.03 N and 65.14 N. The addition of 120 N of preload reduced the load on the right facet to 83.5 N. The compressive load in the disk increased to 107.5 N. The corresponding ligament forces were 43.2 N (left ligamentum flavum) and 50.7 N (left capsular ligament).
A Structural Model for Molded Thermoplastic Ankle-Foot Orthoses
Authors: Leone D. J.
Published: June 2009

The structural response of a posterior leaf spring, ankle-foot orthosis (AFO) was studied both experimentally and with a simple theoretical model. The theoretical model, which was compared with other analytical solutions and experimental data, predicted the bending and twisting of the AFO due to unit loads. The simple theoretical model utilized beam equations and small deflection theory. Excellent agreement between test and predicted values was achieved, indicating that the simple theoretical model, which was relatively easy to implement computationally, could serve as the major component of a computer-aided design program.
The Effects of RPM and Recycle on Separation Efficiency in a Clinical Blood Cell Centrifuge
Authors: Drumheller P. D. , Van Wie B. J. , Petersen J. N. , Oxford R. J. , Schneider G. W.
Published: June 2009

A COBE blood cell centrifuge, model 2997 with a single stage channel, was modified to allow computer controlled sampling, and to allow recycle of red blood cells (RBCs) and plasma streams using bovine whole blood. The effects of recycle of the packed RBC and plasma product streams, and of the centrifuge RPM on platelet and white blood cell (WBC) separation efficiencies were quantified using a central composite factorial experimental design. These data were then fit using second order models. Both the model for the WBC separation efficiency and the model for the platelet separation efficiency predict that RPM has the greatest effect on separation efficiency and that RBC and plasma recycle have detrimental effects at moderate to low RPM, but have negligible impact on separation efficiency at high RPM.
A Self-Heated Thermistor Technique to Measure Effective Thermal Properties From the Tissue Surface
Authors: Patel P. A. , Valvano J. W. , Pearce J. A. , Prahl S. A. , Denham C. R.
Published: June 2009

A microcomputer based instrument to measure effective thermal conductivity and diffusivity at the surface of a tissue has been developed. Self-heated spherical thermistors, partially embedded in an insulator, are used to simultaneously heat tissue and measure the resulting temperature rise. The temperature increase of the thermistor for a given applied power is a function of the combined thermal properties of the insulator, the thermistor, and the tissue. Once the probe is calibrated, the instrument accurately measures the thermal properties of tissue. Conductivity measurements are accurate to 2 percent and diffusivity measurements are accurate to 4 percent. A simplified bioheat equation is used which assumes the effective tissue thermal conductivity is a linear function of perfusion. Since tissue blood flow strongly affects heat transfer, the surface thermistor probe is quite sensitive to perfusion.
The Physical Dimensions of the Human Neonatal Cardiovascular System
Authors: Lofthus R. M. , Srebnik H. H.
Published: June 2009

To establish a data base for studies which seek to model and simulate the human perinatal cardiovascular system, we dissected three stillborn, full-term infants and measured the length, internal diameter, and wall thickness of over 1000 blood vessel segments. Cumulatively, these segments represent the major and minor vessels of the systemic and pulmonary circulation at birth. Statistical analysis showed that the methods used to obtain these physical dimensions were highly consistent and that storage of tissue samples in 10 percent formaldehyde solution caused a linear shrinkage of approximately 6.3 percent. A topological code was developed to illustrate the network relationships of blood vessel segments. An example of data utilization based on the topological code is presented and discussed.
Mechanics of Geological Materials
Authors: Carroll M. M.
Published: June 2009

Needed advances in various areas of energy resource recovery, underground construction, earthquake hazard reduction, and conventional and nuclear defense depend critically on the development of improved theories for mechanical and thermal behavior of geological materials. The areas include oil and gas (including off-shore and Arctic production), mining and in situ recovery, geothermal production, nuclear waste isolation, under-ocean tunneling, underground storage, nuclear test containment, and effects of surface explosions. The needed developments, some of which are detailed in earlier National Academy of Science reports, include constitutive theories for inelastic deformation, failure, and post-failure behavior, influence of microstructure and macrostructure, rock fracture (direct breakage, hydraulic fracture explosive fracture), frictional sliding, soil liquefaction, mechanics of ice, determination of in situ conditions, flow through porous media, and thermal effects. Advances in mechanics of geological materials will require adaptation of some established techniques in rheology, metal plasticity, composite materials, mixtures, etc., and also the development of some entirely new ideas and methods. The complicated nature of rocks and soils, the wide ranges of stress, temperature, strain rate, etc., the interactions encountered in geotechnical processes, and the vastly different dimensions and time scales involved, lead to a host of challenging problems in solid mechanics.
Metal Plasticity
Authors: Clifton R. J.
Published: June 2009

Advances in metal forming, lifetime of turbine blades, load carrying capacity of metal structures, armor penetration, and fracture resistance of structural metals all rely on improved understanding of the plasticity of metals. Because of the inherent complexity of the plastic response of metals, development of the required understanding requires a major sustained research effort. Advances in theory, experiment, and numerical methods are required. Classical plasticity theory, although of great value in routine applications involving nearly proportional loading of metal structures, is unsatisfactory for numerous important applications involving, for example, large deformations, cyclic loading, high temperatures, localized shearing, or high strain rates. A more physically based plasticity theory is needed to address the wide class of problems faced in modern technology. Development of such a theory requires critical experiments that show the relationship between microscopic mechanisms and macroscopic plastic response as well as provide a basis for determining the validity of proposed theories. Inclusion of rate dependence, large deformations, nonproportional loading, temperature sensitivity, and the effects of grain boundaries is important in the development of a more comprehensive theory. Remarkable increases in the size and speed of computers are removing computational obstacles to the use of more realistic plasticity theories. Relaxation of computing constraints provides an exceptional opportunity for major advances on technological problems involving plasticity. Accurate, efficient computer codes are required that are suitable even for cases involving softening due to such effects as grain rotations and the expansion of voids. Capability for predicting failure due to the formation of shear bands and the coalescence of voids is a major need. Physical principles governing damage accumulation during general loading histories need to be determined and represented in computer codes.
Stress Wave Propagation, Dynamic Material Response, and Quantitative Non-Destructive Evaluation
Authors: Clifton R. J.
Published: June 2009

Stress wave propagation is of fundamental importance in modern technology because it provides the primary means for the nondestructive examination of defects and in-homogeneities in opaque materials and the only means for studying the response of materials under the dynamic loading conditions associated with impact and explosions. Advances in such diverse technologies as nuclear reactor safety, integrated circuit inspection, and armor penetration depend strongly on advances in the modeling of the propagation of stress waves and in the improved characterization of the dynamic response of materials. Stress waves play a central role in a wide range of geotechnical and geophysical applications including reservoir exploration, earthquake monitoring, and the prediction of ground motion due to earthquakes and blast loading. Because of the inherent complexity of stress waves in solids (i.e., three wave speeds, anisotropy, and inhomogeneity), as well as the importance of nonlinearity in applications involving intense loading, progress in the modeling of stress wave phenomena depends critically on large scale computations. Increased availability of supercomputers provides an excellent opportunity for advances in the modeling of three dimensional phenomena, including such complicating features as anisotropy, inhomogeneity, defects, nonlinearity, and sliding interfaces. Research is needed on accurate and efficient algorithms for these calculations and for acoustic imaging which requires algorithms for inverse problems in which the size and shape of defects, as well as variations in density and in elastic moduli, are to be obtained by probing the region of interest with ultrasonic waves. Improved characterization of the sources and receivers of ultrasound is essential for reliable determination of the required geometrical features and material properties. Improved understanding of the dynamic inelastic response of materials is crucial to realizing the full benefits of the emerging computational power. Strain rate sensitivity, shear strain localization, crack propagation, twinning, and phase transformations are all aspects of mechanical response that need to be modeled in many dynamic loading applications. Basic experiments on these aspects of material behavior combined with computer simulation of the experiments should lead to significant progress in understanding the underlying mechanisms and, thereby, to improved models for use in computations.
Computational Mechanics
Authors: Needleman A.
Published: June 2009

Computational methods play a key role in solid mechanics, as a way of modelling fundamental aspects of mechanical behavior, as a vehicle for transferring this improved modelling capability into new engineering tools, and as a means of utilizing these tools in engineering practice. Modern computational methods enable realistic models of mechanical systems to be formulated without regard as to whether or not analytical solutions are feasible. Increased computational capability is also an incentive for developing more accurate theories, since it becomes possible to use such theories to solve complex engineering problems.
Nonlinear Dynamical Systems
Authors: Moon F. C.
Published: June 2009

New discoveries have been made recently about the nature of complex motions in nonlinear dynamics. These new concepts are changing many of the ideas about dynamical systems in physics and in particular fluid and solid mechanics. One new phenomenon is the apparently random or chaotic output of deterministic systems with no random inputs. Another is the sensitivity of the long time dynamic history of many systems to initial starting conditions even when the motion is not chaotic. New mathematical ideas to describe this phenomenon are entering the field of nonlinear vibrations and include ideas from topology and analysis such as Poincare´ maps, fractal dimensions, Cantor sets and strange attractors. These new ideas are already making their way into the engineering vibrations laboratory. Further research in this field is needed to extend these new ideas to multi-degree of freedom and continuum vibration problems. Also the loss of predictability in certain nonlinear problems should be studied for its impact on the field of numerical simulation in mechanics of nonlinear materials and structures.
Reflections on the Theory of Elastic Plates
Authors: Reissner Eric
Published: June 2009

We depart from a three-dimensional statement of the problem of small bending of elastic plates, for a survey of approximate two-dimensional theories, beginning with Kirchhoff’s fourth-order formulation. After discussing various variational statements of the three-dimensional problem, we describe the development of two-dimensional sixth-order theories by Bolle´, Hencky, Mindlin, and Reissner which take account of the effect of transverse shear deformation. Additionally, we report on an early analysis by Le´vy, on a direct two-dimensional formulation of sixth-order theory, on constitutive coupling of bending and stretching of laminated plates, on higher than sixth-order theories, and on an asymptotic analysis of sixth-order theory which leads to a fourth-order interior solution contribution with first-order transverse shear deformation effects included, as well as to a sequentially determined second-order edge zone solution contribution.
Persistence of Asymmetry in Nonaxisymmetric Entry Flow in a Circular Cylindrical Tube and Its Relevance to Arterial Pulse Wave Diagnosis
Authors: Xue H. , Fung Y. C.
Published: June 2009

In an experiment motivated by the study of arterial blood flow along the lines suggested by the traditional Chinese medicine, the flow in a pipe whose lumen was blocked by a semi-circular plug two tube-diameters long was visualized by suspended particles, recorded by cinematography, and analyzed digitally. The Reynolds number was in the range of 100 to 450 based on the pipe diameter, similar to that of blood flow in the radial artery in the arms of man. The blockage was found to have a profound effect on the velocity profile of the flow in the wake, but it had little influence on the symmetry of the velocity profile upstream of the block, except in its immediate neighborhood. When the end conditions far away from the block were steady, the flow in the wake was steady. The asymmetry of the flow in the wake can be judged by the deviation of the location of the maximum axial velocity from the center line of the pipe as seen in the plane of symmetry of the blockage. Our results show that the deviation can be described as the sum of two components. The first is a strong one which decays exponentially in an entry length which is about twice as long as the classical Boussinesq entry length of axisymmetric flow. The second is a weaker component which is wavy spatially and persists far downstream (many times the entry length). The separated flow and vortex system behind the blockage are sensitive to the flow rate. The relevance of these findings to the arterial pulse wave diagnosis methods used in the traditional Chinese medicine is discussed. We show that the human arteries are shorter than the entry length, hence nonaxisymmetric disturbances can be propagated throughout the circulation system. We propose that the propagation of the persistent, small, wavy asymmetric wave is relevant to the “localization” of the spheres of influence of internal and external organs in a two-inch region of the radial artery. We propose further that the method of pressing hard on the artery to “feel” the pulse is to amplify the signal by creating a wake that is very sensitive to velocity of flow.
Distribution of Mass Transfer Rate and Wall Shear Stress Behind Simple Rectangular Stenosis in Pulsating Flow
Authors: Yamaguchi R.
Published: June 2009

The distributions of mass transfer rate and wall shear stress in sinusoidal laminar pulsating flow through a two-dimensional asymmetric stenosed channel have been studied experimentally and numerically. The distributions are measured by the electrochemical method. The measurement is conducted at a Reynolds number of about 150, a Schmidt number of about 1000, a nondimensional pulsating frequency of 3.40, and a nondimensional flow amplitude of 0.3. It is suggested that the deterioration of an arterial wall distal to stenosis may be greatly enhanced by fluid dynamic effects.
Heat Generation in Laser Irradiated Tissue
Authors: Welch A. J. , Pearce J. A. , Diller K. R. , Yoon G. , Cheong W. F.
Published: June 2009

Many medical applications involving lasers rely upon the generation of heat within the tissue for the desired therapeutic effect. Determination of the absorbed light energy in tissue is difficult in many cases. Although UV wavelengths of the excimer laser and 10.6 μm wavelength of the CO2 laser are absorbed within the first 20 μm of soft tissue, visible and near infrared wavelengths are scattered as well as absorbed. Typically, multiple scattering is a significant factor in the distribution of light in tissue and the resulting heat source term. An improved model is presented for estimating heat generation due to the absorption of a collimated (axisymmetric) laser beam and scattered light at each point r and z in tissue. Heat generated within tissue is a function of the laser power, the shape and size of the incident beam and the optical properties of the tissue at the irradiation wavelength. Key to the calculation of heat source strength is accurate estimation of the light distribution. Methods for experimentally determining the optical parameters of tissue are discussed in the context of the improved model.
Boundary Conditions at the Cartilage-Synovial Fluid Interface for Joint Lubrication and Theoretical Verifications
Authors: Hou J. S. , Holmes M. H. , Lai W. M. , Mow V. C.
Published: June 2009

The objective of this study is to establish and verify the set of boundary conditions at the interface between a biphasic mixture (articular cartilage) and a Newtonian or non-Newtonian fluid (synovial fluid) such that a set of well-posed mathematical problems may be formulated to investigate joint lubrication problems. A “pseudo-no-slip” kinematic boundary condition is proposed based upon the principle that the conditions at the interface between mixtures or mixtures and fluids must reduce to those boundary conditions in single phase continuum mechanics. From this proposed kinematic boundary condition, and balances of mass, momentum and energy, the boundary conditions at the interface between a biphasic mixture and a Newtonian or non-Newtonian fluid are mathematically derived. Based upon these general results, the appropriate boundary conditions needed in modeling the cartilage-synovial fluid-cartilage lubrication problem are deduced. For two simple cases where a Newtonian viscous fluid is forced to flow (with imposed Couette or Poiseuille flow conditions) over a porous-permeable biphasic material of relatively low permeability, the well known empirical Taylor slip condition may be derived using matched asymptotic analysis of the boundary layer at the interface.
Peristaltic Transport of a Particle-Fluid Suspension
Authors: Srivastava L. M. , Srivastava V. P.
Published: June 2009

Peristaltic pumping by a sinusoidal traveling wave in the walls of a two-dimensional channel filled with a viscous incompressible fluid in which are distributed identical rigid spherical particles, is investigated theoretically. A perturbation solution is obtained which satisfies the momentum equations for the case in which amplitude ratio (wave amplitude/channel half width) is small. The results show that the fluid phase mean axial velocity decreases with increase in the particle concentration. The phenomenon of reflux (the mean flow reversal) is discussed. A reversal of velocity in the neighborhood of the centerline occurs when the pressure gradient is greater than that of the critical reflux condition. It is found that the critical reflux pressure is lower for the particle-fluid suspension than for the particle-free fluid. It is further observed that the mean flow reversal is strongly dependent on the particle concentration and the presence of particles in the fluid favors the reversal flow. A motivation of the present analysis has been the hope that such a theory of two-phase flow process is very useful in understanding the role of peristaltic muscular contraction in transporting bio-fluid behaving like a particle-fluid mixture. Also the theory is important to the engineering applications of pumping solid-fluid mixtures by peristalsis.
Knee Joint Motion and Ligament Forces Before and After ACL Reconstruction
Authors: Lewis J. L. , Lew W. D. , Hill J. A. , Hanley P. , Ohland K. , Kirstukas S. , Hunter R. E.
Published: June 2009

The goal of this in vitro study was to investigate the initial postoperative mechanical state of the knee with various types of anterior cruciate ligament (ACL) reconstructions. An experimental knee testing system was developed for the in vitro measurement of ligament forces and three-dimensional joint motion as external loads were applied to fresh knee specimens. Two groups of knee specimens were tested. In test series #1, two intraarticular reconstructions were performed in each of five specimens using semifree and free patellar tendon grafts with bone blocks. In test series #2, a more carefully controlled intraarticular reconstruction was performed in five specimens using a semifree composite graft consisting of the semitendinosus and gracilis tendons augmented with the Ligament Augmentation Device. Ligament force and joint motion data were collected as anteriorly directed tibial loads were applied to the normal joint, the joint with a cut ACL and the reconstructed joint. These knee joint states were compared on the basis of ACL or graft forces, joint motion and load sharing by the collateral ligaments. The dominate result of the study was that the forces and motions defining the mechanical state of the knee after the ACL reconstructions in both test series were highly variable and abnormal when compared to the normal knee state. The higher level of surgical control series #2 did not decrease this variability. There was a poor correlation between motion of the reconstructed knee relative to normal, and the ACL graft force. There was little consistent difference in force and motion results between the surgical procedures tested.
Flow of Urine Through the Ureter: A Collapsible, Muscular Tube Undergoing Peristalsis
Authors: Griffiths D. J.
Published: June 2009

In steady flow through nonuniform collapsible tubes a key concept is the compressive zone, at which flow limitation can occur at both high and low Reynolds numbers. Ureteral peristalsis can be considered as a series of compressive zones, corresponding to waves of active muscular contraction, that move at near-constant speed along the ureter towards the bladder. One-dimensional, lubrication-theory analysis shows that peristalsis can pump urine from kidney into the bladder only at relatively low mean rates of urine flow. Under these circumstances isolated boluses of urine are propelled steadily through the ureter (assumed uniform) by the contraction waves. At higher mean rates of flow the behavior depends on whether the frequency of peristalsis is higher or lower than a critical value. For frequencies above the critical value steady propagation of boluses that are in contact with contraction waves at both ends is possible. As the flow rate rises the urine begins to leak through the contraction waves and steady peristaltic flow breaks down. There is an upper limit to the mean flow rate that can be carried by steady peristalsis, which depends on the mechanical properties of the ureter. At high flow rates the peristaltic contractions do not pump but hinder the flow of urine through the ureter.
Flow Visualization Studies in a Mold of the Normal Human Aorta and Renal Arteries
Authors: Liepsch D. , Poll A. , Strigberger J. , Sabbah H. N. , Stein P. D.
Published: June 2009

To study the flow behavior in regions where hemodynamic effects have been suggested to participate in atherogenesis, we evaluated flow in a mold of the aorta and renal arteries of a previously healthy 27-year-old woman who died of trauma. A birefringent solution (vanadium-pentoxide) was used. When diluted, this material behaves like a Newtonian fluid. This method gives a complete picture of the entire flow field. Zones of flow separation and disturbed flow can be seen and the location and size of disturbed areas observed. Unseparated flow regions downstream from disturbed zones can be properly visualized and the method can be used for pulsatile flow as well as steady flow. During steady flow (only at branch to-trunk flow ratios > 0.20), zones of flow separation were observed in the aorta distal to the renal arteries. During pulsatile flow, disturbances were found at nearly all branch-to-trunk flow ratios.
A Preliminary Theoretical Study of Arterial Pressure Perturbations Under Shock Acceleration
Authors: Belardinelli E. , Ursino M. , Iemmi E.
Published: June 2009

The artero-venous system is often stressed by accelerative perturbation, not only during exceptional performances, but also in normal life. For example, when the body is subject to fast pressure changes, accelerative perturbations combined with a change in hydrostatic pressure could have severe effects on the circulation. In such cases a preliminary mathematical inquiry, whose results allow qualitative evaluation of the perturbation produced is useful. Pressure variations are studied in this work when the body is subjected both to rectilinear and rotational movements as well as posture change. The dominant modes of the hemodynamic oscillations are emphasized and the numerical simulation results presented. The artery model used for simulation is obviously simplified with respect to the anatomical structure of an artery. Nevertheless, behavior of the main arteries (like the common carotid and aorta) can be approximately described, choosing suitable model parameters. The frequency of blood oscillations strictly depends on the Young modulus of the arterial wall. This connection could be employed for new clinical tests on the state of the arteries.
An Analytical Model of Traumatic Diffuse Brain Injury
Authors: Margulies S. S. , Thibault L. E.
Published: June 2009

Diffuse axonal injury (DAI) with prolonged coma has been produced in the primate using an impulsive, rotational acceleration of the head without impact. This pathophysiological entity has been studied subsequently from a biomechanics perspective using physical models of the skull-brain structure. Subjected to identical loading conditions as the primate, these physical models permit one to measure the deformation within the surrogate brain tissue as a function of the forces applied to the head. An analytical model designed to approximate these experiments has been developed in order to facilitate an analysis of the parameters influencing brain deformation. These three models together are directed toward the development of injury tolerance criteria based upon the shear strain magnitude experienced by the deep white matter of the brain. The analytical model geometry consists of a rigid, right-circular cylindrical shell filled with a Kelvin-Voigt viscoelastic material. Allowing no slip on the boundary, the shell is subjected to a sudden, distributed, axisymmetric, rotational load. A Fourier series representation of the load allows unrestricted load-time histories. The exact solution for the relative angular displacement (V) and the infinitesimal shear strain (ε) at any radial location in the viscoelastic material with respect to the shell was determined. The strain response for brain tissue (μ = 345 Poise, G = 1.38 × 104 Pa) was examined at the non-dimensional radial location R = 0.3. The size (1.8<R0<6.8 cm) and constitutive properties of the brain, and the magnitude, duration (2<TD<100 msec) and waveform (sine, square, triangle) of the applied load were varied independently; each contributed to the response of the tissue. Strain increased linearly with increasing magnitude of the applied load and exponentially with increasing brain size (where the exponent n was frequency-dependent). Peak angular acceleration (Θ¨p) and peak angular velocity (ΔΘ˙p) were defined as appropriate load descriptors. As ΔΘ˙p increased, strain rose rapidly and was independent of Θ¨p, then levelled off and was highly sensitive to Θ¨p.
Bioheat Transfer in a Branching Countercurrent Network During Hyperthermia
Authors: Charny C. K. , Levin R. L.
Published: June 2009

A bioheat transfer model which computes the spatial variations in the arteriole, venule, and muscle temperatures in a human extremity under both resting and hyperthermic conditions is presented. This model uses the two-parameter model first proposed by Baish et al. [2] to account for the heat exchange between tissue and the paired arterioles and venules that comprise the microcirculation. Thermoregulation of the muscle blood flow during hyperthermia is also incorporated into the model. Results show that even when the paired arteriole and venule are assumed to have equal radii, the mean temperature under both steady and transient conditions is not equal to the mean of the arteriole and venule blood temperatures. Tissue temperature profiles during hyperthermia computed with the three-equation model presented in this study are similar in shape and magnitude to those predicted by the traditional one-equation Pennes bioheat transfer model [1]. This is due primarily to the influence of thermoregulatory mechanism in the heated muscle. The unexpected agreement is significant given the inherent relative simplicity of the traditional Pennes model. An “experimental” thermal conductivity is presented to relate the theoretical results to experimental procedures that are widely used to estimate the enhancement of conductivity by perfusion.
Attenuation of Flow Disturbances in Tapered Arterial Grafts
Authors: Black R. A. , How T. V.
Published: June 2009

Flow disturbances in tapered arterial grafts of angles of taper between 0.5 and 1.0 deg were measured in vitro using a pulsed ultrasound Doppler velocimeter. The increase in transition Reynolds numbers with angle of taper and axial distance was determined for steady flow. The instantaneous centerline velocities were measured distal to a 50 percent area stenosis (as a model of a proximal anastomosis), in steady and pulsatile flow, from which the disturbance intensities were calculated. A significant reduction in post-stenotic disturbance intensity was recorded in the tapered grafts, relative to a conventional cylindrical graft. In pulsatile flow with a large backflow component, however, there was an increase in disturbance intensity due to diverging flow during flow reversal. This was observed only in the 1.0 deg tapered graft. These findings indicate that taper is an important consideration in the design of vascular prostheses.
Analysis of Particle Trajectories in Aortic Artery Bifurcations With Stenosis
Authors: Nazemi M. , Kleinstreuer C.
Published: June 2009

The fluid-particle dynamics in a two-dimensonal symmetric branching channel with local occlusions representing a diseased segment of an aortic artery bifurcation has been analyzed. The validated finite element model simulates the trajectories and landing or impact sites of spherical particles for laminar flow in bifurcation channels with generalized wall conditions. Two hypotheses relating critical wall shear stress levels and plaque formation, previously postulated by Kleinstreuer et al. (1988) and Nazemi et al. (1989), have been confirmed. Low shear stress may contribute to the onset of atherosclerotic lesions and areas of critically low and high shear stresses are susceptible to accelerated growth of plaque.
Fluid Flow and Plaque Formation in an Aortic Bifurcation
Authors: Nazemi M. , Kleinstreuer C. , Archie J. P. , Sorrell F. Y.
Published: June 2009

Considering steady laminar flow in a two-dimensional symmetric branching channel with local occlusions, a finite element model has been developed to study velocity fields including reverse flow regions, pressure profiles and wall shear stress distributions for different Reynolds numbers, bifurcation angles and lumen reductions. The flow analysis has been extended to include a new submodel for the pseudo-transient formation of plaque at sites and deposition rates defined by the physical characteristics of the flow. Specifically, simulating the onset of atherosclerotic lesions, sinusoidal plaque layers have been placed in areas of critically low wall shear stresses, and simulating the growth of particle depositions, plaque layers have been added in a stepwise fashion in regions of critically high and low shear. Thus two somewhat conflicting hypothetical correlations between critical wall shear stress levels and atheroma have been tested and a solution has been postulated. The validated computer simulation model is a predictive tool for analyzing the effects of local changes in wall curvature due to surgical reconstruction and/or atherosclerotic lesions, and for investigating the design of aortic bifurcations which mitigate plaque formation.
Structural Finite Deformation Model of the Left Ventricle During Diastole and Systole
Authors: Nevo E. , Lanir Y.
Published: June 2009

A model of left ventricular function is developed based on morphological characteristics of the myocardial tissue. The passive response of the three-dimensional collagen network and the active contribution of the muscle fibers are integrated to yield the overall response of the left ventricle which is considered to be a thick wall cylinder. The deformation field and the distributions of stress and pressure are determined at each point in the cardiac cycle by numerically solving three equations of equilibrium. Simulated results in terms of the ventricular deformation during ejection and isovolumic cycles are shown to be in good qualitative agreement with experimental data. It is shown that the collagen network in the heart has considerable effect on the pressure-volume loops. The particular pattern of spatial orientation of the collagen determines the ventricular recoil properties in early diastole. The material properties (myocardial stiffness and contractility) are shown to affect both the pressure-volume loop and the deformation pattern of the ventricle. The results indicate that microstructural consideration offer a realistic representation of the left ventricle mechanics.
A New Device to Measure the Structural Properties of the Femur-Anterior Cruciate Ligament-Tibia Complex
Authors: Lyon R. M. , Woo Savio L-Y. , Hollis J. M. , Marcin J. P. , Lee E. B.
Published: June 2009

Previous studies of biomechanical properties of femur-anterior cruciate ligament-tibia complex (FATC) utilized a wide variety of testing methodologies, particularly with respect to ligament orientation relative to loading direction. A new device was designed and built to test the anterior-posterior displacement of the intact porcine knee at 30 and 90 deg of flexion, as well as the tensile properties of the FATC at any loading direction and flexion angle. Tensile tests were performed with the knees at 30 and 90 deg of flexion with the loading direction along either the axis of the tibia (tibial axis) or the axis of the anterior cruciate ligament (ligament axis). The results showed that the stiffness, ultimate load and energy absorbed were all significantly increased when the FATC was tested along the ligament axis. This study demonstrates the importance of alignment in the evaluation of the biomechanical characteristics of the femur-ACL-tibia complex.
The Effect of Stress Concentration on Bone Remodeling: Theoretical Predictions
Authors: Firoozbakhsh K. , Aleyaasin M.
Published: June 2009

Theoretical predictions of internal bone remodeling around an elliptical hole are studied. The internal remodeling theory due to Cowin and Hegedus is employed. The bone is modeled as an initially homogeneous adaptive elastic plate with an elliptical hole under a superposed steady compressive load. It is shown that there will exist a final inhomogeneous remodeling distribution around the hole that will disappear away from the hole. The remodeling is such that the compressive stress concentration causes the bone structure to evolve to one of greater density and stiffer elastic coefficients. The speed of remodeling around the hole and its variation with respect to distance is investigated and discussed. It is shown that the rate of bone reinforcement in the area of compressive stress concentration is much higher than the rate of bone resorption in the area of existing tensile stress. Special cases of a circular hole and vertical and horizontal slots are studied and discussed.
Method of Computation for Periodic Oscillations of a High Power Density Internal Combustion Engine Drive Train in the Presence of Backlash
Authors: Fridman Alexander , Privalova Olga , Piraner Ilya
Published: June 2009

It is well known that presence of backlash in the timing gear train of modern internal combustion engines leads to significant increase in dynamic loads and noise. Accounting for the backlash introduces non-linearity in the numerical model. Traditionally such a system is solved as an initial value problem using multi-cycle numerical integration of the equation of motion in time domain. Present work offers an efficient method for analysis of periodic oscillations of multi-mass system of complex structure by converting it into a chainlike system. At first, the method is applied to a linear system. It is also shown that this method is applicable to a nonlinear system offering significant improvement in the simulation time as compared to the traditional approach. The developed method is applied to studying dynamics of timing gear train of a high power density diesel engine.
Knock Prediction in Industrial Dual Fuel Engines Using a Two-Zone Combustion Model With Consideration of Chemical Kinetics
Authors: Al-Sened Ahmed , Safari Hesameddin , Keshavarz Mojtaba , Javadirad Ghasem
Published: June 2009

Knock is well recognized as a destructive phenomenon to be avoided when running dual fuel engines. Typically, it occurs at high loads and high ambient temperatures and its onset has always been difficult to predict, particularly where multiple fuels are present. In a dual fuel engine, knock can occur from either the diesel or the gaseous fuel and it is recognised that the ratio of diesel fuel mass to gaseous fuel mass is an important index in determining which type of knock is predominant. This paper describes the development of a two-zone predictive model for the onset of knock in a dual fuel engine. Prediction of spark knock onset is the main objective of present work. A 9-step short mechanism with 11 chemical species, developed specifically for modelling dual fuel operation, is used to determine the chemical reactivity of the end-gas zone. The contribution of pilot diesel fuel combustion is taken into account by a heat release model. Chemical equilibrium is assumed for the burned gas zone. Simulation results predict the point of knock-limited BMEP and its dependency on operating parameters such as air intake temperature, boost pressure, start of pilot fuel injection timing and compression ratio. The results were first validated against some published engine analysis data and also some in-house performance prediction data. Secondly, a known dual-fuel development engine was simulated. Finally, the performance of an engine which had been converted from diesel to dual fuel during its service life was modeled but commercial constraints prevent the identification of this engine within this paper. However, good agreement with existing performance data was demonstrated in all these cases.
The Effect of Using High FFA Rubber Seed Based Biodiesel With Cold and Hot EGR on Performance and Emissions of a CI Engine
Authors: Baiju B. , Das L. M. , Babu M. K. G.
Published: June 2009

This paper analyses the effect of exhaust gas recirculation (EGR) on the engine performance and emissions of a compression ignition (CI) engine operating on diesel-biodiesel (rubber seed oil methyl ester) blends. Biodiesel operated engines generally produce less unburned hydrocarbon, carbon monoxide and smoke compared to diesel fuel but more NOx emissions. NOx formation is a temperature dependent phenomenon and takes place when the combustion temperature is more than 2000K. EGR is an effective method for reducing NOx emissions in CI engines because it reduces the flame temperature and the oxygen concentration in the combustion chamber. In this study both hot EGR and cold EGR (5%, 10% and 15%) are used. It was found that NOx emission decreases substantially with both hot and cold EGR but smoke and carbon monoxide emissions are increasing with higher EGR rates. Brake thermal efficiency (BTE) increases with hot egr but cold EGR gives lower thermal efficiency than hot egr. Hot EGR emits less smoke and less NOx at higher loads compared to cold EGR. It was observed that exhaust gas between 10% and 15% can be recirculated for getting better results. The use of EGR is thus considered to be one of the most effective in reducing NOx emissions.