acase@tulane.edu

acase@tulane.edu

The mechanics of head injury has been of special interest in biomechanics research. Since experimentation is costly and often difficult to perform, mathematical and computer models which simulate head injury are primary research tools. Previous investigators have formulated finite element models of the human brain and of the human skull. A finite element model of the human head and neck, as a system, is presented which incorporates the brain and skull models of previous investigators and a model of the cervical spine into a single model. The 'exact' geometry of the cerebrospinal fluid (CSF) space is included, and morphological continuity of the CSF space and brain material in the region of the head/spine connection is maintained in order that the proper 'flow' of material between the head and spinal cavity may take place during a simulated head impact or whiplash. The 3-dimensional geometry of the brain, spinal cord, CSF space, cervical vertebrae, and the intervertebral disks is defined by means of eight-node, isoparametric brick elements. The jaw and the thick portion of the skull in the floor of the cranium are also described by brick elements, but the frontal and parietal bones of the skull and the superior portions of the occipital and temporal bones of the skull are represented by thin shell elements. The falx cerebri and the tentorium cerebelli are partitioned into plane stress membrane elements. Midsagittal symmetry was assumed in the construction of the model Accelerations usually exceed 100 g's during a head impact. Hence, inertial forces will cause large changes in the pressure and shear stress gradients within the central nervous system (CNS) during the contact phase of the impact. The model was therefore made inertially correct, at least to a reasonable approximation, by optimally locating point masses at the surface nodes of the skull in order that the total mass, center of mass, and mass and product moments of inertia of the head/neck system would agree with experimentally determined values in the literature. The point masses represent the additional mass of the system contributed by the hair, facial and neck muscles, and other soft tissue of the head and neck, and therefore care was taken so that the point mass distribution would be anatomically correct The material properties assigned to the brain and spinal cord elements of the model were the standard literature values of E = 66.7 kPa (9.68 psi) and a Poisson's ratio of (nu) = .499, which expresses the essential incompressibility of the brain material. The boundary conditions consist of fixing the spine at the T1 level in order to simulate the effect of the large torso mass on the head/neck system. A half-sine wave contact force of 4 ms duration with a peak load of 6000 N (1349 lb) was applied to the occiput of the skull over an area of 26.7 cm('2) (4.14 in('2)), and the model was exercised using the linear finite element program EASE2 with the split energy option The results gave peak pressures in the coup region of the brain of approximately 93.5 kPa (13.6 psi) at 1.6 ms; the peak negative pressure in the contre-coup region was -100.1 kPa (-14.5 psi) at 1.6 ms. These values agree with the experimental data reported in the literature if they are scaled relative to the magnitude of the contact force used in the experiment (impact study) / acase@tulane.edu

acase@tulane.edu

In this dissertation the results of two lateral load tests, performed at Chalmette, Louisiana for the Louisiana Power and Light Company, is presented. The two instrumented test piles were both forty feet long. However, the geometry of the two piles was different, resulting in piles having differing stiffness and resistability to lateral loads. One pile was fabricated without wings. The other, the rocket shaped pile, had wings attached to the upper twenty feet The soil at the test site generally consisted of fifteen feet of very soft organic clay and peat, overlying very soft to soft highly plastic clay. The water table was above the ground surface. The lateral load was applied to the foundation pile at fifty nine feet above ground line, simulating hurricane generated loads on tower structures. The loading procedure followed in the testing program included (1) short-term static loading, (2) cyclic loading, (3) unloading and reloading, and (4) load to failure The reaction of the test piles was predicted, utilizing an available finite difference computer program and procedures for constructing soil resistance and pile deflection (p-y) curves. In situ-p-y curves were developed from the field data and compared to those calculated from laboratory compression tests. Correlations between the in situ p-y curves and experimental curves were made and a new method for constructing p-y curves for very soft cohesive soil is presented. Other subjects addressed include (1) the relative insensitivity of highly plastic, very soft soils to cyclic loading, (2) the effect of unloading the test piles and subsequent reloading, (3) the effectiveness of the wings on the upper twenty foot length, and (4) design optimization / acase@tulane.edu

Experimental and theoretical research directed toward synthesis of triglycerides by lipase catalyzed interesterification and esterification are presented In the experimental portion of the work, considerations of enzyme stereospecificity and of the conditions in the microaqueous phase surrounding the enzyme are utilized in order to synthesize interesterification products in the systems triacetin-tributyrin; tripalmitin-tristearin; and olive oil-hydrogenated cottonseed oil. Minimal water and reversed micelle configurations are compared in the triacetin-tributyrin system and in a model esterification reaction between 1-butanol and palmitic acid. In the experiments with C50, C52, and C54 triglycerides, high temperature gas chromatography (HTGC) is employed to follow the course of the reaction In the theoretical portion of the work, a completely general expression is derived for the optimal flow rate path in a CSTR with deactivating, immobilized enzyme catalyst Potential applications and areas for further research are noted / acase@tulane.edu

acase@tulane.edu

Mathematical models of the transport of oxygen and the simultaneous transport of carbon dioxide, glucose and lactic acid within the microcirculation of the human brain have been developed. These were solved for both steady-state and dynamic cases which included normal and pathological conditions The models are distributed parameter, interactive systems of non-linear partial differential equations. These were reduced to finite difference equations and solved using various numerical techniques. All three models employ the Price-Varga-Warren finite difference approximations for the capillary equations. The steady-state constant tissue metabolism model (SSCM) requires an analytical steady-state radial mass flux from the capillary. The dynamic non-linear tissue metabolism model (DNLM) uses Crank-Nicolson analogs in solving the non-linear, radial diffusion tissue equations. The third model is similar to the DNLM model but also includes axial diffusion in the tissue. Both the Extrapolated Liebmann and the Alternating Direction Implicit methods were used to solve the tissue equations of this model. Steady-state overall mass balances for normal conditions revealed errors of 0.1, 2.0 and 12.0 percent, respectively, for each of the three models The models incorporate in the transport description, the processes associated with the interaction of components through the Bohr and Haldane effects and the non-linear metabolism. Also studied was the oxygen mass transfer coefficient of the red blood cell and its effect on tissue oxygen delivery. Other cases investigated include normal conditions, arterial and venous hypoxia, reduced flow and hematocrit, hypocapnia, reduced glucose and with the dynamic models transient arterial upsets Results indicate that local concentration deficits of oxygen and/or glucose and excesses of lactic acid can exist with the system described by the models and therefore possibly could exist in the tissues of the human brain under similar circumstances. The implications are that the local energy production may be impaired directly or indirectly by the lack of oxygen and/or glucose and the existence of a local acidic environment. It is also proposed that local variations of components can be masked in experimental studies of regions of multiple capillaries, since the total chemical content gives no indication of local deficits and/or excesses / acase@tulane.edu

The objectives of this investigation were to measure the effect of the various factors that contribute to differential-pressure pipe sticking and to utilize this information in the development of a procedure to select casing setting depths The investigation differs from other investigations in that it (1) evaluates several areas in the Gulf of Mexico, not just one specific area; (2) evaluates both deviated and straight holes; (3) analyzes both wells that experience and did not experience sticking problems; and (4) analyzes the factors that may contribute to differential-pressure pipe sticking The results of this investigation normalized all factors that contribute to differential-pressure pipe sticking except differential pressure. It was concluded that the average differential pressure for those wells that experienced sticking problems and those that did not were not similar. It was also concluded that, of the wells that experienced sticking problems, more than 99 percent of them were stuck at pressures greater than 1,298 pounds per square inch The major application of this investigation is a procedure to select casing setting depths based on the ability to withstand a design-size kick and the potential of pipe sticking off-bottom / acase@tulane.edu

acase@tulane.edu