Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Physics, 1982. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Includes bibliographical references. / by Daryush Ila. / M.S.

Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Physics, 1982. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE / Includes bibliographical references. / by Igor Klebanov. / B.S.

Standard local control theory, which describes Ca²⁺ release during excitation-contraction coupling (ECC), assumes that all Ryanodine Receptor (RyR) complexes are equivalent. Recent data from our laboratory has called this assumption into question. Specifically, we have shown that RyR complexes in ventricular myocytes differ depending on their location within the cell. This, and other data, has led us to hypothesize that similar differences occur within the rat atrial cell. To test this hypothesis, we have triple-labeled enzymatically-isolated, fixed myocytes to examine the distribution and colocalization of RyR, calsequestrin (CSQ), voltage-gated Ca²⁺ channels (Cav1.2), sodium-calcium exchangers (NCX), and caveolin-3 (cav-3). All images were acquired on a wide-field microscope, deconvolved, and subject to extensive analysis, including a novel method of measuring statistical significance of the recorded colocalization values. Overall, eight surface RyR populations were identified, depending on its binding partners. One of these groups, in which RyR, Cav1.2, and NCX colocalize, may provide the structural basis for ‘eager’ sites of Ca²⁺ release in atria, while other groups were defined based on their association with cav-3, and are therefore highly likely to be under the influence of other signaling molecules located within caveolae. Importantly, although a small portion of the surface RyR in atria do colocalize with NCX alone, the majority are tightly linked to Cav1.2 alone or Cav1.2 and NCX together. Therefore, it appears likely that Cav1.2-mediated calcium-induced calcium release (CICR) is the primary method of initiating Ca²⁺ release from the SR during EC coupling.

Oil-free microturbomachinery (MTM) are inevitably subjected to base or foundation excitations: multiple periodic load excitations from internal combustion (IC) engines in turbochargers, for example. Too large base excitations can produce severe damage, even failure, due to hard collision or rubbing contact between a rotor and its bearings. Therefore, it is paramount to evaluate the reliability of rotor-air bearing systems to withstanding base load excitations. In 2008, intermittent shock excitations, up to 30 g (pk-pk), were introduced to a test rig consisting of a rotor (0.825 kg) supported on two hybrid flexure pivot tilting pad gas bearings (FPTPBs). The experiments demonstrated the reliability of the gas bearings to withstanding external transient load excitations. Presently, a shaker delivers periodic load excitations to the base plate supporting the test rig. The whole system, weighing 48 kg, is supported on two soft coil springs and its lowest natural frequency is ~5 Hz. The rod connecting the shaker to the base plate is not affixed rigidly to the test rig base. The rod merely pushes on the base plate and hence the induced based motions are intermittent with multiple impacts and frequencies. As with most practical conditions, the base motion frequencies (5-12 Hz) are low respective to the operating speed of the rotor-bearing system. Rotor speed coast down tests evidence the rotor-bearing system natural frequency when the gas bearings are supplied with feed pressures increasing from 2.36 to 5.08 bar (ab). Shaker excitation induced rotor response, relative to the bearing housings, contains the main input frequency (5-12 Hz) and its super harmonics; and because of the intermittency of the base motions, it also excites the rotor-bearing system natural frequency, with smaller motion amplitudes than synchronous motion components. The excitation of the system natural frequency does not mean rotordynamic instability. With base induced motions, the rotor motion amplitude at the system natural frequency increases as the gas bearing feed pressure decreases, as the rotor speed increases, and as the shaker input excitation frequency increases (5-12 Hz). Hence, the test rotor-air bearing system is highly sensitive to base motions, intermittent in character, in particular when the gas bearings are supplied with a low feed pressure. Predicted rotor motion responses obtained from XLTRC2 and an analytical rigid rotor model, both including the (measured) periodic base motions, show good correlation with the measurements. The research results demonstrate further the applicability of gas bearings into oil-free high speed MTM.

Thesis (M. Sc.)--York University, 2002. Graduate Programme in Kinesiology and Health Science. / Typescript. Includes bibliographical references. Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://wwwlib.umi.com/cr/yorku/fullcit?pMQ71630.

No description available.

The use of physiological concepts in psychological theory has led to attempts by psychologists and physiologists to establish neurophysiological correlates of behaviour (Hebb, 1955; John & Killam, 1959). While studies of the effects of lesions and electrical or chemical stimulation of cerebral tissue have provided useful insights into the physiological basis of behaviour, attempts to observe the ongoing activity of the central nervous system in an awake, behaving organism have encountered serious problems. [...]

Standard local control theory, which describes Ca²⁺ release during excitation-contraction coupling (ECC), assumes that all Ryanodine Receptor (RyR) complexes are equivalent. Recent data from our laboratory has called this assumption into question. Specifically, we have shown that RyR complexes in ventricular myocytes differ depending on their location within the cell. This, and other data, has led us to hypothesize that similar differences occur within the rat atrial cell. To test this hypothesis, we have triple-labeled enzymatically-isolated, fixed myocytes to examine the distribution and colocalization of RyR, calsequestrin (CSQ), voltage-gated Ca²⁺ channels (Cav1.2), sodium-calcium exchangers (NCX), and caveolin-3 (cav-3). All images were acquired on a wide-field microscope, deconvolved, and subject to extensive analysis, including a novel method of measuring statistical significance of the recorded colocalization values. Overall, eight surface RyR populations were identified, depending on its binding partners. One of these groups, in which RyR, Cav1.2, and NCX colocalize, may provide the structural basis for ‘eager’ sites of Ca²⁺ release in atria, while other groups were defined based on their association with cav-3, and are therefore highly likely to be under the influence of other signaling molecules located within caveolae. Importantly, although a small portion of the surface RyR in atria do colocalize with NCX alone, the majority are tightly linked to Cav1.2 alone or Cav1.2 and NCX together. Therefore, it appears likely that Cav1.2-mediated calcium-induced calcium release (CICR) is the primary method of initiating Ca²⁺ release from the SR during EC coupling.

DNA photocleaving reagents are a unique class of molecules that display the ability to cleave DNA, causing strand breaks, upon exposure to an irradiation source. In terms of biological applications, achieving excitation through a two-photon absorption event provides for unique benefits that can be useful in such applications as photodynamic therapy and cell viability studies. Thus, this thesis pertains to the study of a class of photocleaving reagents that have been shown to become excited through a twophoton process during irradiation with a pulsed femtosecond laser at 775 nm. N-(Alkoxy)pyridinethiones were selected as possible oxygen-based radical generators upon irradiation at two-photon wavelengths. Experiments were carried out with pBR 322 plasmid DNA to determine if these N-(alkoxy)pyridinethiones could cause strand cleavage and if so how efficient they are in doing so. Several compounds were found to be effective DNA strand cleavers when irradiated at two-photon wavelengths, displaying the utility of two-photon excitation in biological studies. Rationale is suggested for the observed variation in cleaving efficiency based on inherent properties of the generated radicals. A second study was done to measure the two-photon cross section of the compound N-(anthracenoyloxy)pyridinethione. The two-photon cross section was found by measuring the fraction of substrate remaining after specific periods of femtosecond laser irradiation at 775 nm, and the two-photon cross section was found to be 0.051 GM.

An Optima 3000 ICP-AES instrument was modified and the equipment necessary to carry out axial excitation atomic fluorescence was designed and constructed. Using this calibrated system, preliminary fluorescence experiments were not successful. As fluorescence is proportional to source intensity, it was considered that the excitation source, a hollow cathode lamp, may not have been sufficiently intense to produce fluorescence. A novel excitation source-driver system was designed and built in-house to operate HCLs, BDHCLs and LEDs with variable modulation frequencies and duty cycle capabilities. Studies investigating lamp response to changes in modulation frequency and duty cycle indicated that a lamp operated with a lower modulation frequency range (167 - 542 Hz) and higher duty cycles (30 - 50 %) should provide the preferred intense excitation conditions for the production of fluorescence in the ICP, When a Thermo Elemental PQ2 instrument was used, fluorescence was obtained immediately. Um'variate searches were used to optimise several plasma parameters, i.e. forward power; viewing height ALC; plasma, nebuliser and auxiliary gas flow rates. Once the optimum conditions had been determined, calibration curves were plotted for each of the elements studied (Ba, Li, Mg and Na). The calibration showed excellent linearity over five orders of magnitude (R? values ranged from 0.99995 to 1.0000) and the precision on each data point was better than 5 % RSD. Limits of detection were determined to be 27.6, 0.51, 0.43 and 0.20 ug 1* for Ba, L i , Mg and Na, respectively, which approached those reported in the literature for a commercial system. Vertical profiles of the plasma, using radial excitation, were obtained for Ba, Li , Mg and Na. Using the optimum conditions for Li and Na, vertical profiles of the plasma, using axial excitation with the more intense LEDs, were obtained. Both profiles showed that there was a relatively sharp optimum, with respect to fluorescence signal, as a function of viewing height ALC. The optimum viewing heights ALC obtained, for both radial and axial excitation fluorescence, were identical, suggesting that, irrespective of the excitation arrangement employed, only particular conditions produced in the plasma give the optimum conditions for fluorescence and that these are spatially dependent. Plasma diagnostics were performed in an attempt to explain why fluorescence was observed using the plasma produced by the Thermo Elemental but not by the Optima 3000 generator. At a viewing height of 50 mm ALC, Texc and Trot were 3080 and 2500 K for plasmas produced using the Thermo Elemental generator and 3600 and 2830 K for the Optima 3000 generator, respectively. Temperatures were calculated using the mean emission intensity at particular wavelengths. The intensities of the emitting species from the Thermo Elemental ICP were lower than those obtained from the Optima 3000 ICP for supposedly 'identical' conditions. If the number of excited species gives rise to lower emission intensities, then there must be more atoms in the lower/ground state from the plasma produced using the Thermo Elemental generator. This is of vital importance because for fluorescence to occur the fluorescence emission intensity will be dependent on the number available in the ground state for excitation {i.e. a relatively 'cool' plasma is required for fluorescence to occur). As very similar plasma operating conditions and the same concentration solutions were used in the fluorescence experiments performed using both the Optima 3000 and the Thermo Elemental ICPs, the differences observed in plasma performance may be attributed to efficiency of coupling of the generators used.