The adsorption of fibrinogen from human plasma onto various surfaces was investigated under differing conditions of plasma composition. Previous studies by Vroman have indicated that fibrinogen is only transiently adsorbed from normal human blood plasma, possibly due to displacement by high molecular weight kininogen (HMWK). It is possible that this "Vroman Effect" is a manifestation of the activation of the intrinsic clotting pathway responsible, in part, for thrombus formation on artificial surfaces. The effect was studied using dilutions of human plasma from 0.01% to 20.0% of normal concentration trace-labelled with a small amount of ¹²⁵I labelled fibrinogen. Adsorption of fibrinogen to various materials, including glass and several potentially useful biomaterials was measured. Fibrinogen is initially adsorbed apparently under diffusion limitation and later displaced at a rate which depends on the type of material being tested. There does not appear to be a direct relationship between material properties (contact angle, biocompatibility) and the "Vroman Effect". Studies comparing the effect for a series of clotting factor deficient plasmas seem to indicate that plasminogen and HWNK are the main displacing agents on glass. Factors XI and XII, prekallikrein and other components do not appear to be involved. An attempt to mathematically model the effect was hampered by the lack of adequate models to describe even one-component protein adsorption. An isotherm equation was developed based on a theoretical model of protein exchange and spreading on the surface. The resulting parameter estimates based on data for different surfaces were well conditioned and may provide a good in vitro basis for comparing materials. It is hoped that the theoretical model will also be compatible with dynamic adsorption and ultimately a multicomponent system such as plasma (and the Vroman Effect). This work may lead to a better understanding of blood-material interactions and may provide the basis for a simple in vitro test for the characterization of potential biomaterials. / Thesis / Master of Engineering (ME)

No description available.

Thesis (M. S.)--Aerospace Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Panagiotis Tsiotras; Committee Member: Eric Feron; Committee Member: Joseph Saleh; Committee Member: Ryan Russell; Committee Member: William Cook

Thesis (LL. M.)--McGill University, 2000. / Includes bibliographical references (leaves 119-127).

No description available.

El presente estudio se realizó con el objetivo de evaluar y comparar la eficacia de dos tratamientos hormonales para la sincronización del celo e inseminación artificial a tiempo fijo en vacas cebuinas criadas al pastoreo en condiciones de trópico. Se seleccionaron 164 vacas de 2 a 4 partos, en condiciones ginecológicas óptimas, con parto normal y aparente actividad ovárica. Los animales fueron asignados al azar a uno de los 3 tratamientos en estudio: G1 (n= 34): aplicación de un análogo de progesterona, en forma de implante subcutáneo de silicona, que contiene 17ª –acetoxi-11b-metil-19 norpreg-4-en-3,20-diona por 10 días y simultáneamente una solución im de 5 mg de valerato de estradiol y 3 mg de norgestomet y al retirar el implante se aplicó 500 UI de gonadotropina sérica de yegua preñada intramuscular, para realizar la IA a las 56 horas después de retirado el implante; G 2 (n= 32): Aplicación de .0105 mg de acetato de bucerelina, un análogo de GnRH (d 0) y 0.5 mg de cloprostenol (d 7) y una nueva dosis de del análogo de GnRH (d 9), para realizar la IA después de 16 horas; G3 (n= 98), considerado como grupo control y sometidas a observación diaria de celo, por un periodo de 30 días. Los datos fueron evaluados por CHI cuadrado. Los resultados obtenidos indican un porcentaje de preñez del 47.06, 40.63 y 10.2% para los tratamientos 1, 2 y 3 respectivamente, con diferencias entre los tratamientos 1 y 2 respecto del 3. la tasa de presentación de conducta de celo fue del 58.82%, 68.75% y 18.37% para los tratamientos 1, 2 y 3 respectivamente. La tasa global de preñez fue del 23.78%. Los resultados sugieren que no existe diferencia estadística significativa entre los grupos tratados, pero si respecto al grupo control (P menor 0.01). / --- Two hormonal protocols for synchronization of ovulation and timed artificial insemination (TAI) was evaluated in lactating beef cows, (n = 164), under grazing in Peruvian tropic. Group 1 (n = 34) received a progestin implant and a injection 5mg of oestradiol + 3 mg of norgestomet (d-0), implant was removal and 500UI of eCG injection (d-9) followed by fixed timed AI 52 a 54 h latter. Cows in the second group (32) received 0.0105 mg of bucerelina acetate (d 0), 0.5 mg de cloprostenol (d 7), and bucerelina acetate (d 9) followed by fixed timed AI 16 a 18 h. latter of the last GnRH injection. Cows in the control group, didn’t have received treatment, but they were observed to heat twice a day and inseminated 12 h after estrus behavior presentation. Pregnancy rates after only one AI 60 days after of breeding were similar between treatment, the proportion cows that pregnant in progesterone group was 47.06%, GnRH group was 40.63% and control group was 10.2%. Non statistical significance between treatments was determined.

Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1978. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Includes bibliographical references. / B.S.

Conditional preference networks (CP-nets) model user preferences over objects described in terms of values assigned to discrete features, where the preference for one feature may depend on the values of other features. Most existing algorithms for learning CP-nets from the user's choices assume that the user chooses between pairs of objects. However, many real-world applications involve the the user choosing from all combinatorial possibilities or a very large subset. We introduce a CP-net learning algorithm for the latter type of choice, and study its properties formally and empirically.

The Spiral Vortex (SV) ventricular assist device (VAD) was investigated by 2-component laser Doppler anemometry (LDA) while pumping a refractive index-matched blood analogue fluid. The VAD was operated under physiological conditions corresponding to 75% assist (4 litres/minute) or weaning from assist (2 litres/minute). Data were sampled on a 5-mm grid throughout most of the interior of the blood chamber, using two orthogonal LDA configurations from which 3D velocity data were synthesised. Data were subjected to statistical analysis of quasistatic time intervals and approximation by Fourier series. The velocity vector fields were explored statically (via 2D plots) and dynamically (using 3D animations of the reduced data). Reynolds stresses were computed and visualised in 2D. Fluid pathlines were simulated and plotted in 3D. The flow was found to be dominated by an irrotational vortex that accelerated and precessed in phase with the pumping diaphragm. Two unexpected flow structures, a rising, swirling near-wall layer in diastole and a reflection of the outflow vortex upon valve closure, enhanced washing of the walls. The thickness of the boundary layer was estimated to be 2 mm. Fluid velocities were generally lower than those reported in steady-flow studies on the SV VAD, although turbulence was comparable. Under the weaning mode, the coherence of the main vortex was degraded and flow recirculation was observed distal to the inflow port; this operating mode must be regarded as an indication for anticoagulation. In both pumping modes, turbulence was elevated in association with asymmetric buckling of the pneumatically driven diaphragm. Suboptimal orientation of the tilting-disc inlet valve gave rise to augmented turbulence production and skewing of the main vortex; similar results were obtained for an axisymmetric polymer (Jellyfish) valve, despite its advantageous haemodynamics. Flow stagnation was apparent where the inflow stream impinged on the wall, opposite the inflow port. The overall design of the SV VAD appears to almost ideal, in the context of current technology. However, elimination of recirculation/stagnation zones, especially in the weaning mode, remains a priority for the ultimate optimisation of haemocompatibility. Pulsatile VADs will probably never be entirely free of flow recirculation or stagnation, and published claims to the contrary probably reflect study limitations.

Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.