<p> This thesis is a study of numerically controlled machine tools (NCMT), and is divided into four sections. </p> <p> Section A is a literature survey of current concepts, criteria and techniques in design of MCMT structures and drives. Several of the authors own ideas are also included. </p> <p> Section B deals with NCMT manual and computer aided programming techniques. The structure and function of post processors is also covered. </p> <p> Section C is a practical combination of computer design optimization and numerical control manufacture. In an example the geometrical dimensions of a hydrostatic thrust bearing are optimized and used as an input to a generalized APT programme, written to produce a numerical control tape for manufacture of this bearing type. </p> <p> Section D is the discussion and conclusion. </p> / Thesis / Master of Engineering (MEngr)

<p> The effects of hydrostatic pressure on the superconducting transition temperatures of the simple metals aluminum, lead, mercury, tin and indium are investigated within the strong-coupling theory of superconductivity. The experimental variation of the transition temperature with volume change can be understood within a simple scaling model. Strong-coupling effects in the pressure dependence of superconductivity in lead and mercury are investigated.</p> <p> A formalism which includes effects of force constant disorder on superconductivity in a binary alloy of simple metals is established within pseudopotential theory.</p> / Thesis / Doctor of Philosophy (PhD)

This study was motivated by a theoretical formulation on mechanobiology of soft and hard skeletal tissue differentiation. To prove this formulation experimentally, I hypothesized that cartilaginous phenotype can be induced in vitro in a seemingly non-cartilaginous cell source from fibrous tissue. In testing this hypothesis, I have focused on cartilage as a target and fibrous tissue as an origin or the source of cell. Four different trials were pursued with one supposition in common, i.e. hydrostatic pressure is one of the main driving forces for chondroinduction in vitro. The first and second trials pertained to the influence of a relatively short and long duration cyclic hydrostatic compression on rat Achilles tendon fibroblasts. The third trial was to examine the effect of two different drugs on cytoskeletal elements of mesenchymal stem cells or mouse embryonic fibroblast lines in pellet cultures combined with the similar duration and/or frequency of cyclic hydrostatic pressure adopted in the aforesaid trials with no pharmacological agents added. Last, attempts were made to implement an advanced technique in molecular biology called 'PCR array' to further quantify expression levels of eighty four pathway-specific genes in mouse TGFbeta/BMP signaling traffic under the same physiological regimen of hydrostatic compression. Results demonstrated that transdifferentation in phenotype from tendon to fibrocartilage may have occurred in vitro in tendon fibroblasts in pellet cultures exposed to hydrostatic pressure. Experiments on the role of the cytoskeleton in mechanotransduction of the applied level of hydrostatic pressure demonstrated that disruption of microfilaments in the presence of cytochalasin-D did not significantly interfere with the anabolic effect of cyclic pressure. However, disruption of microtubule assembly by nocodazole abolished the pressure-induced stimulation in cartilage marker genes. These findings suggest that microtubules, but not microfilaments, are involved in mechanotransduction of hydrostatic pressure by mesenchymal stem cells.

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Hyporheic exchange is an ecologically and biogeochemically essential function of rivers and streams. One important driver of hydrostatic (hyporheic) exchange is gra- dients in the hydrostatic hydraulic head at the streambed. This thesis investigates the impact of discharge on hydrostatic exchange in two stream reaches in Uppland, Sweden, with different geomorphological characteristics. By comparing 1D approx- imations of hydrostatic head variations along different longitudinal profiles across the streams, the use of a 2D hydraulic model for defining such variations is evaluated. Channel topography and discharge data have been obtained through field surveys in the two streams and form the basis for the setup of two HEC-RAS 2D models. The models have been calibrated against stream-depth measurements, validated against stream depth and stream velocity, and used for simulation of a range of discharges in both reaches. Water surface elevations, obtained for the different discharges in three profiles along each reach, have been used as input in a spectral model evaluating flow across streambed area; average hyporheic exchange velocity W. The results show that W , and thereby the hydrostatic exchange, decreases with increasing dis- charge and varies between different longitudinal profiles in the reach with the most complex geomorphology. For the reach with simpler geomorphology, the effects of discharge, as well as variations across the streams, are negligible. This implies that a 1D approximation of the hydrostatic head variations at the streambed can be sat- isfactory for a stream with simple geomorphology, whereas a 2D evaluation is more accurate for a stream with a complex geomorphology. / Denna uppsats handlar om hur ett vattendrags geomorfologi (form och geologi) och vattenföring påverkar hyporheiskt utbyte. Hyporheiskt utbyte är en process där ytvat- ten tränger igenom vattendragets botten, flödar i den så kallade hyporheiska zonen och blandas med grundvatten för att sedan återvända till vattendraget. Det är en vik- tig funktion på grund av dess påverkan på ekologi och biogeokemiska reaktioner, exempelvis genom syresättning av botten. Hyporheiskt utbyte påverkas bland annat av variationer i vattnets energinivå (hydrau- lisk tryckhöjd) vid bottnen. Den hydrauliska tryckhöjden varierar med vattenytans höjd, som är summan av bottnens topografi och vattnets djup. Målet med studien var att undersöka vattenföringens påverkan på hydrostatiskt, hyporheiskt utbyte i två vattendrag med olika geomorfologiska egenskaper. Endimensionella (1D) approx- imationer av hydraulisk tryckhöjd används ibland vid modellering av hyporheiskt utbyte. Därför var ytterligare ett mål att utvärdera flera endimensionella (1D) ap- proximationer av hydraulisk tryckhöjd vid botten, för att på så sätt undersöka om tvådimensionell (2D) modellering tillför mer information. För att uppnå målen genomfördes fältstudier vid två vattendrag i Uppland, vid vilka topografimätningar och spårämnesförsök gjordes. Dessa lade grunden för uppbygg- nad av 2D-modeller över vattendragen i modelleringsverktyget HEC-RAS. Model- lerna kalibrerades mot uppmätta djupdata och användes sedan för simulering av ett antal olika vattenföringar. Longitudinella profiler placerades i mitten samt till vänster respektive höger om mitten i vattendragen. Längs dessa profiler, för de olika vatten- föringarna, erhölls vattenytans höjd, som blev indata till en spektral modell. Utifrån topografi och vattenytans höjd längs en profil beskriver den spektrala modellen hur den hydrauliska trycknivån varierar med hjälp av en Fourier-serie. Den spektrala modellen beräknar det hyporheiska utbytets medelhastighet W , vil- ken är ett mått på hur stor volym vatten som genomtränger bottenarea per tid. Re- sultaten visar att för vattendraget med mest komplex geomorfologi minskar W med ökande vattenföring, och W varierar också mellan de olika longitudinella profilerna. För det andra vattendraget, som har en enklare geomorfologi, syns inga betydande skillnader, varken mellan olika vattenföringar eller profiler. Därutöver är W mind- re för vattendraget med enklare geomorfologi jämfört med vattendraget med kom- plex geomorfologi. Resultaten antyder därmed att 1D-approximationer av hydraulisk tryckhöjd vid bottnen är tillräckliga för vattendrag med enkel geomorfologi, medan 2D-modellering tillför information för ett vattendrag med komplex geomorfologi.

Foodborne disease outbreaks associated with the protozoan parasite Cryptosporidium spp. are an emerging public health concern. Shellfish, including Eastern oysters (Crassostrea virginica) in Chesapeake Bay and other Atlantic coastal waters, have been identified as a potential source of Cryptosporidium parvum infection for humans. The inactivation of C. parvum and other pathogens in raw molluscan shellfish would provide increased food safety for normal and at-risk consumers. The objectives of this study were to evaluate the efficacy of three alternative food-processing treatments (e-beam irradiation, microwave energy, and high hydrostatic pressure processing) on the viability of C. parvum oocysts in Eastern oysters. Oysters were artificially infected with the Beltsville strain of C. parvum and subjected to the three treatments in separate experiments. The effects of the treatments were evaluated by inoculation of the processed oyster tissues using the neonatal mouse bioassay. E-beam radiation of in-shell and shucked oysters treated with doses of 1.0, 1.5 or 2.0 kGy produced significant reductions (P < 0.05) in C. parvum mouse infectivity. A dose of 2.0 kGy completely terminated the infectivity of C. parvum and did not adversely affect the visual appearance of the oysters. Microwave treatments of shucked oysters at time (temperature) exposures of 1 sec (43.2°C), 2 sec (54.0°C), and 3 sec (62.5°C) produced a reduction in C. parvum mouse infectivity of 26.7%, 33.3%, and 46.7%, respectively. Microwave treatments at 2 sec (54.0°C) and 3 sec (62.5°C) showed extensive changes in oyster meat texture and color. Thus due to lack of efficacy and unacceptable tissue changes, microwave treatment of oysters is not considered a viable food processing method. High pressure processing of shucked oysters at all pressures tested (305 MPa, 370 MPa, 400 MPa, 480 MPa, 550 MPa) significantly (P < 0.05) reduced infectivity of C. parvum oocysts as measured by the neonatal mouse bioassay. A treatment of 550 MPa at 180 sec produced the maximum decrease of C. parvum infectivity (93.3%). The results indicate that HPP (high pressure processing) can produce significant (P < 0.05) reductions in infectivity of C. parvum oocysts. Measurement of tristimulus color values of pressurized raw oysters at extended processing times from 120 sec to 360 sec at 550 MPa showed an increase (P < 0.05) in whiteness. One (e-beam irradiation) of the three food-processing treatments shows promise for commercial applications to reduce public health risks from cryptosporidiosis in Eastern oysters. / Ph. D.

The Food and Drug Administration has recently expressed concern for the safety of seafood and seafood products. One of the concerns is the presence of Bacillus cereus in fresh blue crab meat. Bacillus cereus is a spore-forming pathogen whose spores survive the customary thermal treatments applied during cooking and pasteurization; therefore it could potentially present a health concern to consumers as the microorganism could increase to pathogenic levels. The objectives of this study were to evaluate the effects of a post-processing method i.e. high hydrostatic pressure treatment on the quality of fresh crab meat and to evaluate the effectiveness of high pressures on the inactivation of B. cereus spores. Fresh blue crab meat was pressurized at 300 and 550 MPa at 25° C for 5 min and stored at 4° C for 31 days to determine the pressurization effects on the microbiological, physical, and sensory quality of the meat. A pressure of 300 MPa caused a 1 log reduction in total aerobic plate count and a 3 day lag period, whereas 550 MPa inactivated 2 logs in total aerobic plate count with no evident lag phase. Physical and sensory qualities of pressurized crab meat were not statistically different from the untreated crab meat (P>0.05). A pressure of 300 MPa extended the shelf-life from 17 to over 24 days with the prevalence of Carnobacterium piscicola at the time of spoilage. Crab meat treated with 550 MPa was not rejected by sensory panels at day 31 and Enterococcus spp. was identified as the predominant microorganism. High hydrostatic pressure (550 MPa at 40° C for 15 min) inactivated less than 1 log (0.66 log) of B. cereus spores inoculated in fresh crab meat. The meat essentially had a protective effect on pressure inactivation of the spores. During storage (31 days), surviving B. cereus was suppressed and outgrown by the other pressure resistant microflora at a storage temperature of 12° C. At 4° C, B. cereus could compete with the other pressure-resistant microflora and was isolated even at the end of the storage period (day 31); however, diarrheal toxin was not detected in any stored samples. / Ph. D.