Tribological evaluation of unlubricated and marginally lubricated bearing materials

This thesis presents friction and wear rate measurements of the copper based bearing materials used in thrust bearing of aircraft fuel pumps. Highly detailed friction and wear data was collected from 20% and 30% lead in bronze (leaded bronze) substrates and 10% indium in lead (lead/indium) coated leaded bronze substrates in unlubricated and marginally lubricated conditions. Measurements were made under a wide range of load and speed using a thrust washer test apparatus and pin on disc test equipment

Modeling of Fiber Reinforced Polymer confined concrete cylinders

Fiber Reinforced Polymer (FRP) confined concrete columns have been developed for new construction and rebuilding of concrete piers/piles in engineering structures. Design of these FRP confined concrete columns requires an accurate estimate of the performance enhancement due to the confinement mechanism. Therefore, the key is to develop a confinement model, a model that relates the confined concrete strength with the unconfined concrete strength and the confining pressure provided by the FRP. Due to its closed-form expression and ease of application, design-oriented confinement models predominate in designing FRP confined concrete columns. Design oriented models are directly based on the interpretation of experimental results. Each existing design oriented model is based on a certain range of test database and is accurate in predicting the results within its respective considered range. All the models are based on limited database. In the present research, an attempt was made to expand the test database with larger range. A 3-D finite element model of FRP confined concrete column was developed using ANSYS and was validated by published experimental results available in the literature. Based on the FEA results, a test data base was developed taking into account all the possible ranges of the design parameters which affect the confined concrete strength. Analyses of the test database revealed that the confinement effectiveness depends on thickness, hoop tensile strength, modulus of elasticity of the FRP and unconfined concrete strength and behaves nonlinearly with each of them. Therefore, in the present study the main emphasis was to explore a possible approach for a design oriented confinement model which considers this nonlinear relation between the confinement effectiveness and the design parameters

A study of the histozoic oyster parasite, Perkinsus marinus: I. Disease processes in American oysters (Crassostrea virginica). II. Biochemistry of Perkinsus marinus

Numerous studies have investigated the disease processes of Perkinsus marinus in the oyster, Crassostrea virginica. However, the transmission dynamics and factors affecting P. marinus infection are still unclear. The objectives of this study were to investigate: (1) the principal and most effective lifestage of P. marinus, (2) the synergistic effects of temperature, salinity and P. marinus dose on disease prevalence, (3) suppression of host reactive oxygen intermediates by P. marinus, (4) the localization of acid phosphatase in the parasite, (5) the effects of temperature and salinity on acid phosphatase secretion, and (6) the P. marinus lipid and fatty acid composition. Meronts were more infective than prezoosporangia, and infectivity was dose dependent (100 cells minimum). High temperatures, salinities and P. marinus doses increased infection prevalence and intensity. Temperature was the most important factor influencing disease susceptibility, followed by cell dosage and salinity. Both temperature and salinity significantly affected the host cellular and humoral factors in oysters. P. marinus suppression of hemocyte reactive oxygen intermediates production, as assessed by chemiluminescence was dose dependent. Zymosan stimulated hemocyte chemiluminescence was reduced, suggesting that live P. marinus cells or their extra-cellular products suppress host reactive oxygen intermediates production. Acid phosphatase activity in P. marinus cells increased with increasing temperature. Meronts had higher acid phosphatase activity than prezoosporangia. Extracellular acid phosphatase secretion by P. marinus was dose dependent, increasing with temperature and osmolality. Electron microscopy revealed that acid phosphatase activity was localized primarily in the nucleus, but was also present in the cell membrane. Lipid classes of meronts resembled those found in their media. Phospholipids were the major lipid class in meronts, while triacylglycerols were dominant in prezoosporangia isolated from infected oyster tissue. Results indicated that meronts may be capable of interconversion of lipid classes. Both meronts and prezoosporangia had much higher levels of arachidonic acid than the host

Disease processes of the parasite Perkinsus marinus in eastern oyster Crassostrea virginica: Minimum dose for infection initiation, and interaction of temperature, salinity and infective cell dose

Experiments were conducted to: (1) test the response of oysters to different doses of the oyster parasite Perkinsus marinus and to 2 stages, meronts or prezoosporangia; and (2) investigate the synergistic effects of temperature, salinity and infective cell concentration on P. marinus infection in oysters. A dose-dependent response of P. marinus infection was found in oysters inoculated with 0, 10, 10(2), 10(4), and 10(5) meronts or prezoosporangia per oyster and maintained at 22 to 25 degrees C and 14 to 21 ppt for 8 to 12 wk. The minimum dose required to infect oysters was 10(2) meronts or prezoosporangia per oyster through shell cavity inoculation. Interactive effects between temperature, salinity, and infective cell dose on P. marinus prevalence was insignificant in the experiment, in which oysters were challenged by 0, 2.5 x 10(3) or 2.5 x 10(4) meronts per oyster and held at 9 temperature-salinity regimes (10, 15 and 25 degrees C at 3, 10 and 20 ppt). However, there was a significant positive interaction relevant to infection intensity between temperature and salinity, and between temperature and meront dose. Temperature was the most important factor followed, respectively, by the infective cell dose and salinity in determining the susceptibility to P. marinus in oysters. Reduced condition index was observed in moderately to heavily infected oysters and in oysters at 25 degrees C

Aspects of the pathophysiology of blue crabs, Callinectes sapidus, infected with the parasitic dinoflagellate Hematodinium perezi

Blue crabs, Callinectes sapidus, infected with Hematodinium perezi frequently show signs of weakness and lethargy and die when stressed by handling or capture. Radical changes to the hemolymph of heavily infected crabs are obvious by reduced clotting ability, discoloration. and a 50% to 70% decline in total hemocyte density. Few other signs of infection are associated with infections and the resulting mortalities of blue crabs. To assay physiological changes in infected crabs, we measured serum proteins, hemocyanin, serum acid phosphatase, various hemolymph enzymes, hernagglutination activity, and tissue glycogen levels in relation to intensity of infection with H. perezi. Serum proteins and hemocyanin levels were lower in infected versus uninfected males, but not in infected versus uninfected females. Acid phosphatase activity was directly related to infection by the parasite. Acid phosphatase activity in the hemolymph was below the detection limit in uninfected crabs, but was detectably high in lightly, moderately and heavily infected crabs. Hemagglutination, possible indicator of innate Immoral defense activity, was not affected by infection. Glycogen levels in the hepatopancreas of infected crabs decreased by 50% in females and 70% in males compared to controls. Infection by H. perezi caused significant alterations to the hemolymph chemistry and metabolism of the crab. Changes in serum proteins, hemocyanin, and glycogen levels in heavy infections indicate that crabs probably die from metabolic exhaustion

Comparison Of Infectivity And Pathogenicity Of Meront (Trophozoite) And Prezoosporangiae Stages Of The Oyster Pathogen Perkinsus-Marinus In Eastern Oysters, Crassostrea-Virginica (Gmelin, 1791)

Two experiments were conducted to compare the infectivity and pathogenicity of two life stages of the parasite Perkinsus marinus, meronts (trophozoites) and prezoosporangia (hypnospores), in eastern oysters, Crassostrea virginica. Oysters were inoculated with 5 X 10(4) meronts or prezoosporangia per oyster by injection into the shell cavity. Prevalence and intensity of P. marinus infections, condition index, serum protein concentrations, and lysozyme activities were measured in oysters after 15, 25, 40, and 65 days in experiment 1 and after 20, 40, 50, 65, and 75 days postchallenge by P. marinus cells in experiment 2. Controls were injected with filtered York River water. In the first experiment, P. marinus infections were initially detected in oysters exposed to prezoosporangia after 15 days postchallenge. In the second experiment, infection was not detected in oysters until 40 days postchallenge with either meronts or prezoosporangia. Intensity and prevalence of P. marinus infection were significantly higher (p \u3c 0.002) in oysters challenged by meronts compared with prezoosporangia-challenged oysters at the end of both experiments. In experiment 1, a significant decrease (p \u3c 0.05) was observed in serum protein in infected oysters challenged by prezoosporangia compared with uninfected oysters. Condition index was higher in uninfected oysters compared with infected oysters challenged by prezoosporangia. The differences in condition index and protein were insignificant between oysters infected by meronts or prezoosporangia. Lysozyme activities were significantly lower (p \u3c 0.05) in infected oysters than in uninfected oysters challenged with meronts. No significant differences were observed in condition index, protein concentrations, and lysozyme activities between oysters challenged by meronts and prezoosporangia in experiment 2. Lower condition index and protein concentrations in the groups of oysters infected with prezoosporangia compared with the groups infected by meronts and nonchallenged at the end of experiment 1 suggest a higher energetic demand on these oysters

Tribological evaluation of unlubricated and marginally lubricated bearing materials

This thesis presents friction and wear rate measurements of the copper based bearing materials used in thrust bearing of aircraft fuel pumps. Highly detailed friction and wear data was collected from 20% and 30% lead in bronze (leaded bronze) substrates and 10% indium in lead (lead/indium) coated leaded bronze substrates in unlubricated and marginally lubricated conditions. Measurements were made under a wide range of load and speed using a thrust washer test apparatus and pin on disc test equipment.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

A Comparison Of Crassostrea gigas And Crassostrea virginica: Effects Of Temperature And Salinity On Susceptibility To The Protozoan Parasite, Perkinsus marinus

The susceptibility of diploid and triploid (2N and 3N) Crassostrea gigas to Perkinsus marinus was compared, in the laboratory, with that of Crassostrea virginica al three test temperatures (10, 15, and 25 degrees C) at 20-22 ppt and at three test salinities (3, 10, and 20 ppt) at a temperature of 19-22 degrees C. Experimental oysters were challenged twice with freshly isolated P, marinus meronts, after acclimation to test temperatures and salinities. Although infection prevalence and intensity increased with temperature (p = 0.0001) and salinity in P. marinus-challenged oysters of both oyster species: they were highest in C. virginica groups. Infection intensity was significantly (p = 0.001) higher in P. marinus-challenged C. virginica than C. gigas (2N and 3N) at all temperatures; however, infection prevalence was not statistically different at any temperature treatment. In all salinity treatments, prevalence and infection intensity were significantly higher (p = 0.0001) in P. marinus-challenged C. virginica than 2N and 3N C. gigas. Because high infection prevalence and intensity were found in non-challenged C. virginica, part of the recorded prevalence and intensity in challenged C. virginica was probably attributed to latent infection carried over from the field. High mortality occurred in both 2N and 3N C. gigas during temperature and salinity adjustment, particularly at 25 degrees C and 3 psu

Heat-Shock Proteins Of The Oyster Parasite Perkinsus-marinus

The susceptibility of the eastern oyster Crassostrea virginica to infection by the protozoan parasite Perkinsus marinus is influenced by temperature. Because of the crucial roles of heat shock proteins in cellular thermal tolerance and in host-parasite adaptations in other species, we compared the in vitro heat shock responses of cultured P. marin us and of oyster hemocytes. The parasite and host heat shock proteins were different in size and in immunochemical specificity. In addition, the thermal threshold for inducing the response was higher for P. marinus acclimated to the same temperature as the oysters. The results suggest that EI marinus is likely to employ heat shock proteins as part of its adaptive survival repertoire and that it may be able to function normally under conditions of hyperthermia that evoke an emergency physiological response from the oyster defense cells. Furthermore, they indicate that it is feasible to investigate the host\u27s and parasite\u27s adaptive responses to each other, since their individual responses are readily distinguishable