bluuebunny/crossref_metadata_2025 huggingface dataset:
Oral health care for the patient with schizophrenia
Authors: Friedlander Arthur H. , Liberman Robert P.
Published: March 2008

Schizophrenia is a psychiatric disorder affecting 1%of the United States population. Conceptualizing the disorder as consisting of “positive” and “negative” symptoms has led to improved treatment modalities. Medications used in managing the “positive” symptoms have numerous systemic and orofacial adverse side effects that must be recognized by the dentist. Dental treatment strategies for the identification and management of these side effects art! described. “Negative” symptoms are responsible for chronicity of the disorder and frequently impede rehabilitation. These symptoms are potentially devastating to oral health as they impair a patient's desire and ability to invoke preventive oral hygiene. Treatment strategies to improve compliance with oral hygiene techniques are outlined. A medication specifically indicated for patients with treatment‐ resistent disease and marked “negative” symp toms has recently been approved for use in the United States. The systemic and orofacial adverse side effects of this medication and its influence on dental management are reviewed.
MRSA: an important consideration for geriatric dentistry practitioners
Authors: Staat Robert H. , Van Stewart Arthur , Stewart Jacqueline Fischer
Published: March 2008

Methicillin‐resistant Staphylococcus aureus (MRSA) can cause life‐threatening disease in older populations. MRSA is readily spread by patient to patient or by health care workers to patient contact. Implications for dental practitioners include the fact that they may be passive vectors for the disease and that dental treatment of patients with active MRSA infections must follow effective infection control practices.
An intraoral prosthesis to control drooling in a patient with amyotrophic lateral sclerosis
Authors: Moulding M.B. , Koroluk L.D.
Published: March 2008

Many alternatives exist for treating chronic drooling. The treatment of a patient with amyotrophic lateral sclerosis who complained of chronic drooling and lack of retention of fluids while drinking is presented. In this case, an alternative type of intraoral prosthesis, not previously reported in the dental literature, was used to treat chronic drooling. A lip plumper prosthesis was fabricated to approximate the partially incompetent lips and create an oral seal. The results of the prosthesis therapy for this patient are encouraging both physically and psychologically.
Relevance between lipid metabolism‐associated genes and rat liver regeneration
Authors: Xu Cunshuan , Lin Fang , Qin Shaowei
Published: March 2008

Aim:  Lipids are important in constituting cell structure and participating in many biological processes, particularly in energy supplementation to cells. The aim of the present study is to elucidate the action of lipid metabolism‐associated genes on rat liver regeneration (LR).

Methods:  Lipid metabolism‐associated genes were obtained by collecting website data and retrieving related articles, and their expression changes in the regenerating rat liver were checked by the Rat Genome 230 2.0 array.

Results:  In total, 280 genes involved in lipid metabolism were proven to be LR‐associated by comparing the gene expression discrepancy between the partial‐hepatectomy and sham‐operation groups. The initial and total expression numbers of these genes occurring in the initial phase, G0/G1 transition, cell proliferation, cell differentiation, and structure–functional rebuilding of LR were 128, 33, 135, 6, and 267, 147, 1026, 306, respectively, illustrating that these genes were initially expressed mainly in the initiation stage and functioned in different phases. Upregulation (850 times) and downregulation (749 times), as well as 25 types of expression patterns, showed that the physiological and biochemical activities were diverse and complicated in LR.

Conclusion:  According to the results of the chip detection, it was presumed that fatty acid synthesis at 24–66 h, leukotriene and androgen synthesis at 16–168 h, prostaglandin synthesis at 2–96 h, triglyceride synthesis at 18–24 h, glycosphingolipid synthesis at 0.5–66 h, metabolism of phosphatidyl inositol and sphingomyelin at 2–16 h, and cholesterol catabolism at 30–168 h were enhanced. Throughout almost the whole LR, the genes participating in estrogen, glucocorticoid, and progesterone synthesis, and triglyceride catabolism were upregulated, while phospholipid and glycosphingolipid catabolism were downregulated.
Geometric Waldspurger periods
Authors: Lysenko Sergey
Published: March 2008

Let X be a smooth projective curve. We consider the dual reductive pair $H=\mathrm {G\mathbb {O}}_{2m}$, $G=\mathrm {G\mathbb {S}p}_{2n}$ over X, where H splits on an étale two-sheeted covering $\pi :\tilde X\to X$. Let BunG (respectively, BunH) be the stack of G-torsors (respectively, H-torsors) on X. We study the functors FG and FH between the derived categories D(BunG) and D(BunH), which are analogs of the classical theta-lifting operators in the framework of the geometric Langlands program. Assume n=m=1 and H nonsplit, that is, $H=\pi _*{\mathbb {G}_m}$ with $\tilde X$ connected. We establish the geometric Langlands functoriality for this pair. Namely, we show that FG :D(BunH)→D(BunG) commutes with Hecke operators with respect to the corresponding map of Langlands L-groups LH→LG. As an application, we calculate Waldspurger periods of cuspidal automorphic sheaves on BunGL2 and Bessel periods of theta-lifts from $\mathrm {Bun}_{\mathrm {G\mathbb {O}}_4}$ to $\mathrm {Bun}_{\mathrm {G\mathbb {S}p}_4}$. Based on these calculations, we give three conjectural constructions of certain automorphic sheaves on $\mathrm {Bun}_{\mathrm {G\mathbb {S}p}_4}$ (one of them makes sense for ${\mathcal D}$-modules only).
The zeros of random polynomials cluster uniformly near the unit circle
Authors: Hughes C. P. , Nikeghbali A.
Published: March 2008

In this paper we deduce a universal result about the asymptotic distribution of roots of random polynomials, which can be seen as a complement to an old and famous result of Erdős and Turan. More precisely, given a sequence of random polynomials, we show that, under some very general conditions, the roots tend to cluster near the unit circle, and their angles are uniformly distributed. The method we use is deterministic: in particular, we do not assume independence or equidistribution of the coefficients of the polynomial.
The arithmetic of Prym varieties in genus 3
Authors: Bruin Nils
Published: March 2008

Given a curve of genus 3 with an unramified double cover, we give an explicit description of the associated Prym variety. We also describe how an unramified double cover of a non-hyperelliptic genus 3 curve can be mapped into the Jacobian of a curve of genus 2 over its field of definition and how this can be used to perform Chabauty- and Brauer–Manin-type calculations for curves of genus 5 with an fixed-point-free involution. As an application, we determine the rational points on a smooth plane quartic and give examples of curves of genus 3 and 5 violating the Hasse principle. The methods are, in principle, applicable to any genus 3 curve with a double cover. We also show how these constructions can be used to design smooth plane quartics with specific arithmetic properties. As an example, we give a smooth plane quartic with all 28 bitangents defined over $\mathbb {Q}(t)$. By specialization, this also gives examples over $\mathbb {Q}$.
The contribution of intrapulmonary shunts to the alveolar‐to‐arterial oxygen difference during exercise is very small
Authors: Vogiatzis Ioannis , Zakynthinos Spyros , Boushel Robert , Athanasopoulos Dimitris , Guenette Jordan A. , Wagner Harrieth , Roussos Charis , Wagner Peter D.
Published: March 2008

Exercise is well known to cause arterial to fall and the alveolar–arterial difference (Aa ) to increase. Until recently, the physiological basis for this was considered to be mostly ventilation/perfusion / inequality and alveolar–capillary diffusion limitation. Recently, arterio‐venous shunting through dilated pulmonary blood vessels has been proposed to explain a significant part of the Aa during exercise. To test this hypothesis we determined venous admixture during 5 min of near‐maximal, constant‐load, exercise in hypoxia (in inspired O2 fraction, , 0.13), normoxia (, 0.21) and hyperoxia (, 1.0) undertaken in balanced order on the same day in seven fit cyclists (, 61.3 ± 2.4 ml kg−1 min−1; mean ±s.e.m.). Venous admixture reflects three causes of hypoxaemia combined: true shunt, diffusion limitation and / inequality. In hypoxia, venous admixture was 22.8 ± 2.5% of the cardiac output; in normoxia it was 3.5 ± 0.5%; in hyperoxia it was 0.5 ± 0.2%. Since only true shunt accounts for venous admixture while breathing 100% O2, the present study suggests that shunt accounts for only a very small portion of the observed venous admixture, Aa and hypoxaemia during heavy exercise.
Peri‐implantation and late gestation maternal undernutrition differentially affect fetal sheep skeletal muscle development
Authors: Costello Paula M. , Rowlerson Anthea , Astaman Nur Aida , Anthony Fred Erick W. , Sayer Avan Aihie , Cooper Cyrus , Hanson Mark A. , Green Lucy R.
Published: March 2008

Poor prenatal nutrition is associated with a greater risk of adult glucose intolerance and insulin insensitivity in the offspring. Skeletal muscle is the primary tissue for glucose utilization, and insulin resistance in muscle is the earliest identifiable abnormality in the pre‐diabetic patient. We investigated the effect of early and late gestation undernutrition on structure and markers of growth and glucose metabolism regulation in the fetal triceps brachii (TB, slow‐ and fast‐twitch myofibres) and soleus (slow‐twitch myofibres) muscles. Pregnant sheep were fed 100% nutrient requirements (C, n= 8) or a restricted diet peri‐implantation (PI, n= 9; 40%, 1–31 days gestation (dGA) (term ∼147)) or in late gestation (L, n= 6; 50%, 104–127 dGA). At 127 ± 1 dGA we measured myofibre and capillary density in the fetal TB and soleus muscles, and mRNA levels in the TB of insulin receptor (InsR), glucose transporter‐4 (GLUT‐4) and type 1 insulin‐like growth factor receptor (IGF‐1R). Total myofibre and capillary densities were lower in the TB, but not the soleus, of PI and L fetuses. The predominant effect in the L group was on slow‐twitch myofibres. In TB, InsR, GLUT‐4 and IGF‐1R mRNA levels were greater in L group fetuses. Our finding of reduced myofibre density is consistent with a redistribution of resources at the expense of specific peripheral tissues by early and late gestation undernutrition which may be mediated by a decrease in capillary density. The increase in key regulatory components of glucose uptake following late gestation undernutrition may constitute a short‐term compensation to maintain glucose homeostasis in the face of fewer type I (insulin‐sensitive) myofibres. However, together these adaptations may influence the risk of later metabolic disease and thus our findings have implications for future strategies aimed at improving maternal diet.
Heat Transport by Countercurrent Blood Vessels in the Presence of an Arbitrary Temperature Gradient
Authors: Baish J. W.
Published: March 2008

This paper presents a three-dimensional analysis of the temperature field around a pair of countercurrent arteries and veins embedded in an infinite tissue that has an arbitrary temperature gradient along the axes of the vessels. Asymptotic methods are used to show that such vessels are thermally similar to a highly conductive fiber in the same tissue. Expressions are developed for the effective radius and thermal conductivity of the fiber so that it conducts heat at the same rate that the artery and vein together convect heat and so that its local temperature equals the mean temperature of the vessels. This result allows vascular tissue to be viewed as a composite of conductive materials with highly conductive fibers replacing the convective effects of the vasculature. By characterizing the size and thermal conductivity of these fibers, well-established methods from the study of composites may be applied to determine when an effective conductive model is appropriate for the tissue and vasculature as a whole.
Evaluation of Magnetic Resonance Velocimetry for Steady Flow
Authors: Ku D. N. , Biancheri C. L. , Pettigrew R. I. , Peifer J. W. , Markou C. P. , Engels H.
Published: March 2008

Whole body magnetic resonance (MR) imaging has recently become an important diagnostic tool for cardiovascular diseases. The technique of magnetic resonance phase velocity encoding allows the quantitative measurement of velocity for an arbitrary component direction. A study was initiated to determine the ability and accuracy of MR velocimetry to measure a wide range of flow conditions including flow separation, three-dimensional secondary flow, high velocity gradients, and turbulence. A steady flow system pumped water doped with manganese chloride through a variety of test sections. Images were produced using gradient echo sequences on test sections including a straight tube, a curved tube, a smoothly converging-diverging nozzle, and an orifice. Magnetic resonance measurements of laminar and turbulent flows were depicted as cross-sectional velocity profiles. MR velocity measurements revealed such flow behavior as spatially varying velocity, recirculation and secondary flows over a wide range of conditions. Comparisons made with published experimental laser Doppler anemometry measurements and theoretical calculations for similar flow conditions revealed excellent accuracy and precision levels. The successful measurement of velocity profiles for a variety of flow conditions and geometries indicate that magnetic resonance imaging is an accurate, non-contacting velocimeter.
Analytical Model of Corneal Surgery
Authors: Rand R. H. , Lubkin S. R. , Howland H. C.
Published: March 2008

We present a model of the human cornea in order to study the changes in its shape resulting from surgical operations (e.g., radial keratotomy). A simple closed-form solution is given for a thin linearly elastic spherical shell model of the cornea. We assume axisymmetry and isotropy in the shell surface. The surgery is modeled by permitting Young’s modulus and shell thickness to depend on position. The analytical nature of the solution permits principal shell curvatures to be explicitly calculated. The model is used to in vestigate the effect of surgery on corneal flattening and the associated sensitivity to intraocular pressure changes.
Thermal Modeling of Polymerizing Polymethylmethacrylate, Considering Temperature-Dependent Heat Generation
Authors: Baliga B. R. , Rose P. L. , Ahmed A. M.
Published: March 2008

A methodology for the modeling of unsteady heat conduction in polymethylmethacrylate (PMMA) during its exothermic polymerization is presented. The emphasis is on the formulation of a model for the volumetric rate of heat generation, including its temperature-dependent characteristics. Three parameters appear in the proposed model. The empirical determination of these parameters using Differential Scanning Calorimetry is demonstrated. The incorporation of the proposed model into finite volume methods is also demonstrated, in the context of unsteady, onedimensional, radial heat conduction in cylindrical coordinates. In addition, the application of the proposed model to two test problems is presented and discussed. The results are encouraging, and the proposed methodology appears to be applicable to the thermal modeling of exothermic polymerization processes in general.
Running on an Incline
Authors: Iversen J. R. , McMahon T. A.
Published: March 2008

Seven male subjects ran at 3.0 m/s on a motorized treadmill including a force platform under the tread. The subjects ran at each of five treadmill inclinations: + 0.17, +0.077, 0, -0.077, and -0.17 radians. The position of the subjects’ legs were read from cine´ films (100 frames/s). Results of the film and force plate analysis generally corroborated the “hanging triangle” hypothesis, which postulates that the angle between the leg and the vertical upon foot strike does not change as the treadmill is tipped up or down. A mathematical model of running, in which the leg is represented as a nonlinear spring, made satisfactory predictions of the way many parameters of running change with the treadmill angle, including the length of the leg at touchdown and liftoff and the peak leg force in the middle of a step. The peak leg force reaches a maximum at a treadmill angle near −0.12 radians, close to the downhill angle where other authors have found a minimum in the rate of oxygen consumption.
The Effects of Large Blood Vessels on Temperature Distributions During Simulated Hyperthermia
Authors: Chen Zong-Ping , Roemer Robert B.
Published: March 2008

Several three-dimensional vascular models have been developed to study the effects of adding equations for large blood vessels to the traditional bioheat transfer equation of Pennes when simulating tissue temperature distributions. These vascular models include “transiting” vessels, “supplying” arteries, and “draining” veins, for all of which the mean temperature of the blood in the vessels is calculated along their lengths. For the supplying arteries this spatially variable temperature is then used as the arterial temperature in the bioheat transfer equation. The different vascular models produce significantly different locations for both the maximum tumor and the maximum normal tissue temperatures for a given power deposition pattern. However, all of the vascular models predict essentially the same cold regions in the same locations in tumors: one set at the tumors’ corners and another around the inlets of the large blood vessels to the tumor. Several different power deposition patterns have been simulated in an attempt to eliminate these cold regions; uniform power in the tumor, annular power in the tumor, preheating of the blood in the vessels while they are traversing the normal tissue, and an “optimal” power pattern which combines the best features of the above approaches. Although the calculations indicate that optimal power deposition patterns (which improve the temperature distributions) exist for all of the vascular models, none of the heating patterns studied eliminated all of the cold regions. Vasodilation in the normal tissue is also simulated to see its effects on the temperature fields. This technique can raise the temperatures around the inlet of the large blood vessles to the tumor (due to the higher power deposition rates possible), but on the other hand, normal tissue vasodilation makes the temperatures at the tumor corners slightly colder.
Flow Studies in Canine Artery Bifurcations Using a Numerical Simulation Method
Authors: Xu X. Y. , Collins M. W. , Jones C. J. H.
Published: March 2008

Three-dimensional flows through canine femoral bifurcation models were predicted under physiological flow conditions by solving numerically the time-dependent threedimensional Navier-stokes equations. In the calculations, two models were assumed for the blood, those of (a) a Newtonian fluid, and (b) a non-Newtonian fluid obeying the power law. The blood vessel wall was assumed to be rigid this being the only approximation to the prediction model. The numerical procedure utilized a finite volume approach on a finite element mesh to discretize the equations, and the code used (ASTEC) incorporated the SIMPLE velocity-pressure algorithm in performing the calculations. The predicted velocity profiles were in good qualitative agreement with the in vivo measurements recently obtained by Jones et al. [1]. The non-Newtonian effects on the bifurcation flow field were also investigated, and no great differences in velocity profiles were observed. This indicated that the non-Newtonian characteristics of the blood might not be an important factor in determining the general flow patterns for these bifurcations, but could have local significance. Current work involves modeling wall distensibility in an empirically valid manner. Predictions accommodating these will permit a true quantitative comparison with experiment.
Theoretical Analysis of the Large Blood Vessel Influence on the Local Tissue Temperature Decay After Pulse Heating
Authors: Xu L. X. , Chen M. M. , Holmes K. R. , Arkin H.
Published: March 2008

The influence of a large blood vessel (larger than 500 μm in diameter) on the local tissue temperature decay following a point source heating pulse was determined numerically using a sink/source method. It was assumed that the vessel was large enough so that the temperature of blood flowing within it remained essentially constant and was unaffected by any local tissue temperature transients. After the insertion of a point source heating pulse, the vessel influence on the local tissue transient temperature field was estimated by representing the vessel as a set of negative fictitious instantaneous heat sources with strength just sufficient to maintain the vessel at a constant temperature. In the surrounding tissue, the Pennes’ tissue heat transfer equation was used to describe the temperature field. Computations have been performed for a range of vessel sizes, probe-vessel spacings and local blood perfusion rates. It was found that the influence of a large vessel on the local tissue temperature decay is more sensitive to its size and location rather than to the local blood perfusion rate. For a heating pulse of 3s duration and 5 mW of power, there is a critical probe-vessel center distance 7R (R, vessel radius) beyond which the larger vessel influence on tissue temperature at the probe can be neglected.
Microscopic Instrumentation and Analysis of Laser-Tissue Interaction in a Skin Flap Model
Authors: Gourgouliatos Z. F. , Welch A. J. , Diller K. R.
Published: March 2008

A dorsal skin flap model for microcirculatory studies has been modified for “in vivo” studies of laser-tissue interaction with microcirculation. An experimental apparatus has been built implementing a laser delivery system, video microscopy during irradiation, and thermal recordings. This model has been used to study irradiation effects on microcirculation using the argon laser (488 and 514.5 nm) and the argon pumped dye laser at 577 nm. The results include: measurements of the optical properties of the model; dosimetry measurements for the production of embolized and stationary coaguli in arterioles and venules; and focal vessel disappearance of venules irradiated with the argon or the argon pumped dye laser at 577 nm; a method to determine light attenuation in the model; a unique method for measurements of blood flow velocity in arterioles and venules and measurements obtained with this method; measurements of transient and steady state temperatures during irradiation and a study of laser induced photorelaxation phenomena in venules.
Mechanically Induced Pendelluft Flow in a Model Airway Bifurcation During High Frequency Oscillation
Authors: High K. C. , Ultman J. S. , Karl S. R.
Published: March 2008

A single bifurcation with adjustable branch compliances, resistances and inertances was used to study the generation of pendelluft flows during ventilation at tidal volumes of 5–15 ml and frequencies of 6–26 Hz, corresponding to parent branch Reynolds numbers of 400–8000 and Womersley parameter values of 12–25. Pendelluft was quantified by the ratio of tidal volume sum in sibling branches to tidal volume in the parent branch. This tidal volume fraction being greater than one in all experiments where an asymmetry in branch mechanics was imposed, indicated that some degree of pendelluft was always present. Asymmetries in compliance and in inertance produced much greater pendelluft than an asymmetry in resistance. The largest tidal volume fraction, equal to 2.75, was recorded when inertance in both sibling branches was high, resistance was low, and compliances differed by a factor of five. Tidal volume fraction always peaked at an optimal frequency between 12–24 Hz, similar to the frequencies at which physiologic transport optima have previously been observed.
Differentiation of Human Motion Data Using Combined Spline and Least Squares Concepts
Authors: Simons W. , Yang K. H.
Published: March 2008

A differentiation method, which combines the concepts of least squares and splines, has been developed to analyze human motion data. This data smoothing technique is not dependent on a choice of a cut-off frequency and yet it closely reflects the nature of the phenomenon. Two sets of published benchmark data were used to evaluate the new algorithm.
A Composite Micromechanical Model for Connective Tissues: Part II—Application to Rat Tail Tendon and Joint Capsule
Authors: Ault H. K. , Hoffman A. H.
Published: March 2008

A micromechanical model of fibrous soft tissue has been developed which predicts upper and lower bounds on mechanical properties based on the structure and properties of tissue components by Ault and Hoffman [3, 4]. In this paper, two types of biological tissue are modeled and the results compared to experimental test data. The highly organized structure of rat tail tendon is modeled using the upper bound aggregation rule which predicts uniform strain behavior in the composite material. This model fits the experimental data and results in a correlation coefficient of 0.98. Applied to cat knee joint capsule, the lower bound aggregation rule of the model correlates with the data and predicts uniform stress within this more loosely organized tissue structure. These studies show that the nature of the interactions between the components in tissue differs depending upon its structure and that the biomechanical model is capable of analyzing such differences in structure.
Mechanical Performance of External Fixators With Wires for the Treatment of Bone Fractures—Part I: Load-Displacement Behavior
Authors: Delprete C. , Gola M. M.
Published: March 2008

Using matrix algebra, a mathematical model is formulated for a particular type of external fixator with wires (system developed by Ilizarov) for the treatment of bone fractures. The mathematical model is used to give a linear estimate of the stiffness under lateral and axial loads in a representative number of practical conditions. Relative displacements of the bone ends at the fracture site are calculated not only in the common case of a gap, but also for various angles of inclined sliding contact; in this case, a realistic load is applied and nonlinear stiffening of the wires under transversal loads is iteratively taken into account.
Comparison of the Adjoint and Influence Coefficient Methods for Solving the Inverse Hyperthermia Problem
Authors: Liauh C.-T. , Hills R. G. , Roemer R. B.
Published: March 2008

An adjoint formulation is derived and used to determine the elements in the Jacobian matrix associated with the inverse problem of estimating the blood perfusion and temperature fields during hyperthermia cancer treatments. This method and a previously developed influence coefficient method for obtaining that matrix are comparatively evaluated by solving a set of numerically simulated inverse hyperthermia problems. The adjoint method has the advantage of requiring fewer solutions of the bioheat transfer equation to estimate the Jacobian than does the influence coefficient method when the number of measurement sensors is significantly smaller than the number of unknown parameters. Thus, it could be a preferable method to use in hyperthermia applications where the number of sensors is strictly limited by patient considerations. However, the adjoint method requires that CPU time intensive convolutions be numerically evaluated. Comparisons of the performance of the adjoint formulation and the influence coefficient method show that, first, there is a critical ratio of the number of measurement sensors to the number of unknown parameters at which the CPU time per iteration required to calculate the Jacobian matrix is the same for both methods. The adjoint method is faster than the influence coefficient method only when the value of the ratio is less than that critical value. For the hyperthermia problems investigated in the present study, this only occurs for cases with a very small number of measurement sensors. This presents a potential problem for clinical applications because the fewer measurement sensors used, the less information that can be gathered to correctly solve the inverse problem. Thus, second, when both techniques were utilized to solve several inverse hyperthermia problems it was found that the total CPU time for the adjoint formulation was larger than that for the influence coefficient method for all of the cases which were solved successfully. That is, all inverse solutions which were successful had ratios greater than the critical value. Thus, for practical hyperthermia problems it appears that the influence coefficient method is preferable to the adjoint formulation.
In Vitro Evaluation of an Implantable Force Transducer (IFT) in a Patellar Tendon Model
Authors: Glos D. L. , Butler D. L. , Grood E. S. , Levy M. S.
Published: March 2008

A new implantable transducer has been developed for in situ evaluation of ligament and tendon forces. Unlike previous devices, this sensor is placed within the specimen, minimizing measurement errors due to impingement on surrounding soft tissues and bone. In this study, we present the sensor design details as well as test results from initial in vitro trials in the goat patellar tendon model. Device performance and influence of the device on the specimen were evaluated under several loading conditions. In all cases, device output had a strong correlation with induced tissue load. Significant variations in device performance were only noted at high tissue deformation rates. More extensive investigations will be conducted to assess how changes in transducer design might alter performance characteristics.
Reconstruction of Experimental Hyperthermia Temperature Distributions: Application of State and Parameter Estimation
Authors: Clegg S. T. , Roemer R. B.
Published: March 2008

Subsets of data from spatially sampled temperatures measured in each of nine experimental heatings of normal canine thighs were used to test the feasibility of using a state and parameter estimation (SPE) technique to predict the complete measured data set in each heating. Temperature measurements were made at between seventy-two and ninety-six stationary thermocouple locations within the thigh, and measurements from as few as thirteen of these locations were used as inputs to the estimation algorithm. The remaining (non “input”) measurements were compared to the predicted temperatures for the corresponding “unmeasured” locations to judge the ability of the estimation algorithm to accurately reconstruct the complete experimental data set. The results show that the predictions of the “unmeasured” steady-state temperatures are quite accurate in general (average errors usually < 0.5°C; and small variances about those averages) and that this reconstruction procedure can yield improved descriptors of the steady-state temperature distribution. The accuracy of the reconstructed temperature distribution was not strongly affected by either the number of perfusion zones or by the number of input sensors used by the algorithm. One situation extensively considered in this study modeled the thigh with twenty-seven independent regions of perfusion. For this situation, measurements from ninety-six to thirteen sensors were used as input to the estimation algorithm. The average error for all of these cases ranged from −0.55°C to +0.75°C, respectively, and was not strongly related to the number of sensors used as input to the estimation algorithm. For these same cases the maximum prediction error (the maximum absolute difference between the measured temperature and the predicted temperature determined by a search over all locations) ranged from 0.92°C to 5.08°C, respectively. To attempt to explain the magnitude of the maximum error, several possible sources of model mismatch and of experimental uncertainty were considered. For this study, a significant source of error appears to arise from differences between the true power deposition field, the power deposition model predictions, and the experimentally measured powers. In summary, while large errors can be present for a few isolated locations in the predicted temperature fields, the SPE algorithm can accurately predict the average characteristics of the temperature field. This predictive ability should be clinically useful.
Remodeling of the Constitutive Equation While a Blood Vessel Remodels Itself Under Stress
Authors: Fung Y. C. , Liu S. Q. , Zhou J. B.
Published: March 2008

Changes in the mechanical properties of a blood vessel when it remodels itself under stress are reviewed. One of the recent findings about blood vessels is the rapidity of tissue remodeling when the blood pressure is changed. When the tissue structure and material composition remodel, the zero-stress state of the vessel changes. The mechanical properties change also in the remodeling process. If the elastic behavior is expressed in terms of a pseudo-elastic strain-energy function, then the constants in the function will change in the course of the remodeling. With all these changes taking place, the scope of constitutive equations broadens: it should now include a mass-and-structure growth-stress relationship as well as a stress-strain-relationship. To obtain the mass-and-structure growth-stress relationship, one must be able to determine the mechanical properties of the different layers of the vessel wall, as well as the chemical composition and morphology. For the blood vessels, new methods of mechanical testing must be introduced. A key thought is to use bending of the blood vessel wall. By bending, different layers of the vessel wall are subjected to different stresses, leading to equations that can be used to solve the inverse problem of determining the stress-strain law from measured stress and strain. In vitro and in vivo experiments and theoretical prospectives are presented.
Bone Stress Adaptation Models
Authors: Cowin Stephen C.
Published: March 2008

The basic concepts employed in formulating models of the process of stress adaptation in living bone tissue are reviewed. A purpose of this review is to define and separate issues in the formulation of bone remodeling theories. After discussing the rationale and objective of these models, the concepts and techniques involved in the modeling process are reviewed one by one. It is concluded that some techniques will be more successful than others in achieving the goals of computational bone remodeling. In particular, rationale is given for the preference of surface bone remodeling approaches over internal bone remodeling approaches, and for interactive multi-scale level, rather than mono-scale level, computational strategies.
Arteriosclerosis Research Using Vascular Flow Models: From 2-D Branches to Compliant Replicas
Authors: Friedman Morton H.
Published: March 2008

A large body of evidence implicates fluid dynamic forces in the genesis and progression of atherosclerosis, the leading cause of death in the United States. To understand the mechanism by which hemodynamics influences the disease process, and to identify the specific flow variable(s) responsible for its localization, it is essential to know the distribution of hemodynamic variables in susceptible regions of the vasculature. Vascular flow models have been used more than any other means to gain insight into the details of arterial hemodynamics. The first flow models were not very realistic. Our first attempt, reported at an early Biomechanics Symposium, was probably the most unrealistic of all: a “2-D branch” that was constructed to validate a 2-D computed flow field. Most of the first models were made of cylindrical tubes, and their geometry too only approximated that of real arteries. Much was learned about the fluid dynamics in branches and bends using such models, but measurements in them could be related only generally to the fluid dynamics in living vessels. Accordingly, we began to make flow field measurements in replicas prepared from human arteries. Others challenged their glassblowers and shops to make models more representative of real vessels. These flow-through casts and fabricated models were initially rigid and perfused with Newtonian fluids. Using these more realistic systems, we and others were able to demonstrate relationships between specific hemodynamic variables and localized arterial pathology. The fidelity of flow simulations today exceeds that of only a few years ago. We now perfuse compliant replicas as small as coronary diagonal branches with fluids whose rheology mimics blood. This level of fidelity is harder to justify for the present application than the switch from tubes to flow-through casts. There is no evidence that the disease has kept secrets from the rigid casts that will be exposed in compliant ones. Nonetheless, there is comfort in simulating the real world as faithfully as possible, and one never knows until one tries whether the next increment of reality will yield unexpected new insights.
Pulsatile Velocity Measurements in a Model of the Human Abdominal Aorta Under Simulated Exercise and Postprandial Conditions
Authors: Moore J. E. , Ku D. N.
Published: March 2008

This study examines the hemodynamics of the abdominal aorta during physiological changes in flow rates and pulse rate that occur under exercise and postprandial conditions. Hemodynamic measurements were performed using an in vitro model which took into account seven major branches, the curvature, and the pulsatile nature of blood flow of the abdominal aorta. Magnetic Resonance Imaging velocimetry employing phase-velocity encoding was used to measure the pulsatile axial velocity profiles for the entire cross-section at three axial locations. Under simulated exercise conditions, the forward velocities were approximately double those seen during rest, and the flow reversal seen for resting conditions was greatly reduced. Near the posterior wall of the infrarenal aorta, the velocities were negative for only 21 percent of the cardiac cycle as compared with 82 percent for resting conditions. Postprandial conditions produced a 25 percent reduction in peak velocity and a 33 percent reduction in mean velocity near the left anterior wall of the aorta just distal to the superior mesenteric artery (in comparison with resting conditions). The changes that can occur in abdominal aorta hemodynamics under different physiologic conditions may affect the rate of progression of atherosclerosis at this site.
A MADYMO Model of Near-Side Human Occupants in Side Impacts
Authors: Huang Yue , King Albert I. , Cavanaugh John M.
Published: March 2008

The protection of automotive occupants against broadside collisions is of current interest due to the implementation of a new Federal standard on side impact. There is controversy as to the validity of the standard, the best criterion to assess injury to the thorax and the type and manner in which padding should be used. Although it has been shown in a series of 17 cadaveric tests that paper honeycomb can reduce thoracic injuries dramatically, there are still concerns regarding the loss of air space between the door and the occupant due to the presence of the padding and regarding the loss of protection for the thorax when there is no engagement of the shoulder with the intruding side structure of the car. This paper describes the development of a three-dimensional rigid body model to simulate cadaveric experiments carried out at Wayne State University. Model parameters were chosen to yield human-like responses at the level of the shoulder, thorax, abdomen and pelvis. The model was then used to study the effect of padding on injury parameters related to the nearside occupant when a relatively thick padding is used (up to 100 mm). It was also used to study the increase in force on the thorax when shoulder engagement is lost. Laboratory tests were conducted with full shoulder engagement but in the field most cars have a low beltline (window sill) which effectively eliminates shoulder contact if the arms are outstretched in a normal driving posture. If a sufficiently soft padding was used, the model did not predict an increase in thoracic force level or any of the injury parameters. This result contradicted those from previous models which either used a dummy as the near-side occupant or did not take into account the acceleration of the target vehicle. The model also predicted that the shoulder can provide substantial protection to the thorax and that without shoulder engagement, the force on the thorax can be approximately 45 percent higher. A door design which can lower its first velocity peak to match the second peak and which has 75 mm of soft padding is predicted by this model as being able to provide protection to the nearside occupant for moderate impacts. Additional cadaveric testing is needed to confirm these results.
Comparison of Arm Up and Down in Side Impacts With BioSID and Different Armrests
Authors: Viano David C.
Published: March 2008

BioSID dummy tests were run with the arm down at the side during loading of different armrests in simulated side impact crashes. The Hyge sled tests duplicated previous studies of BioSID with the arm up, SID, and animals. When the BioSID arm is against the side, the arm extends from the shoulder to the bottom of the third rib and has a steel shank covered by foam and vinyl. Loading through the arm transfers force to the three chest ribs and shoulder. In comparison, direct armrest loading of the chest or abdomen primarily involves a single rib and substantial rib deflection, when the armrest crush-force exceeds the strength of the rib. The Viscous response in BioSID showed the greatest difference of all criteria for the arm up or down. The response of the third rib correlated with injury risks determined from animal tests using the different armrest designs in a simulated high position. While injury data are not available for the arm at the side or for the armrest in the low position, the STIFF armrest may cause injury when the arm is not at the side and the armrest loads the liver and spleen. Rib deflection in BioSID showed the protrusion of the STIFF armrest into the abdominal region in both arm positions, because the loading was below the arm even in the down position. However, the arm extends laterally so it involves the upper ribs earlier than in the arm-up condition where more space is available. Torso deflection showed similar maxima with the arm down and a high armrest position, because the bridging action of the arm and shoulder increases the stiffness of the dummy. The armrest designs cover a range in crush characteristics for occupant protection systems based on experience with other interior safety features, knowledge of human tolerance, and results of injury in animal tests. The SOFT design was most appropriate for interior use. The STIFF design produced serious injury in companion tests with animals, and the BioSID correctly assessed injury risk by peak rib deflection or Viscous response when tested similarly. In contrast, SID and TTI(d) did not indicate injury risks or safety performance. The current study indicates that response differences can be expected with arm placement, and BioSID can assess safety implications of different armrest types and arm placement.
Derivation of Shear Rates From Near-Wall LDA Measurements Under Steady and Pulsatile Flow Conditions
Authors: Fatemi Ray S. , Rittgers Stanley E.
Published: March 2008

Atherosclerosis, thrombosis, and intimal hyperplasia are major forms of cardiovascular diseases in the United States. Previous studies indicate a significant correlation between hemodynamics, in particular, wall shear rate, and pathology of the arterial walls. While results of these studies implicate morphologic and functional changes related to wall shear rate magnitude, a standard technique for wall shear rate measurement has not been established. In this study, theoretical and in-vitro experimental fully developed steady and physiologic pulsatile flow waveforms have been used to obtain velocity profiles in the near-wall region. The estimated wall shear rates from these results are compared to the theoretical value to assess the accuracy of the approximating technique. Experimentally obtained results from LDA suggest that in order to minimize the error in velocity data, and subsequently, the wall shear rate, the first measured velocity has to be 500 μm away from the wall. While a linear approximation did not produce errors larger than 16.4 percent at peak systole, these errors substantially increased as the velocity magnitudes decreased during late systole and diastole. Overall, a third degree polynomial curve fit using four points produced the most accurate estimation of wall shear rate through out the cardiac cycle. Results of higher degree curve-fitting functions can be unpredictable due to potential oscillations of the function near the wall. Hence, based on the results of this study, use of a linear approximation is not recommended; a third degree curve-fitting polynomial, using four points provided the most accurate approximation for these flow waveforms.
Optimization of the Contact Damping and Stiffness Coefficients to Minimize Human Body Vibration
Authors: Amirouche F. M. L. , Xie M. , Patwardhan A.
Published: March 2008

In this paper, a lumped mass human model is used to minimize the energy absorption at the feet/hip level when the body is subjected to vertical vibration. The contact forces are assumed unknown. By coupling the dynamic response of the body with certain objective criteria, the optimum damping and stiffness coefficients of shoes/ chairs are sought. The optimization technique is based on the quasi-Newton and finite-difference gradient method and is used to seek optimum coefficients of the contact forces in the solution of the body’s response in the frequency domain. The criteria of acceleration, displacement and internal forces response area swept for a range of 0–15 Hz form the basis of our simulation study. In the seated/standing postures it is found that for each criteria the frequency response shifts the peak of resonance of each body segment response from 4.5/3.67 Hz to 2.5/2.255 Hz. In addition, the total energy reduces drastically when the contact conditions are optimum. The method presented in this paper is useful in modeling the medium of contacts and especially in controlling the effects of human body vibration.
Spatially Distributed Transducers: Part I—Coupled Two-Port Models
Authors: Busch-Vishniac Ilene J.
Published: March 2008

The process of modeling transducers generally involves the use of a finite number of discrete lumped elements connected using circuit-like conventions. However, such models are difficult to use for transducers which implicitly depend upon variation of a physical parameter with location since they view the transducer as existing only at points or discrete intervals in space. In this article a general modeling procedure is developed which views a transducer as a spatially distributed device. The model introduced here uses the theory of connected two-ports to determine the overall transfer matrix and scattering matrix representations. This directly yields the transducer sensitivities and efficiencies. The model is limited to transducers which may be thought of as being comprised of an infinite number of infinitesimal twoport elements, each of which is mechanically independent of the others. Coupling between the elements occurs through the input and output ports. The modeling procedure is demonstrated using an acoustic antenna, and shown to accurately predict the directional behavior.