The plasmas produced in electromagnetic shock tubes have previously been studied in this laboratory and elsewhere. In general the temperatures and electron densities deduced from time-resolved spectra emitted by the plasma do not agree with the values calculated from shock theory. Photographs taken with a Kerr cell shutter revealed that luminous discharge gases with a very irregular front were driven down the tube and that no separate shock front could be seen ahead. The plasma behind the luminous front consisted of a mixture of rest gas and a considerable amount (~50%) of impurity from the driving discharge. In the work reported here, further attempts were made to produce shock heated plasmas. Various electrode configurations were tried but no improvement was observed. Some measure of success was attained with an electrodeless driver on the shock tube. Kerr cell photographs showed that with argon in the tube a shock wave appeared to be formed ahead of the discharge plasma. The shock speed was much slower than the speed of the advancing luminous front in the tubes with electrodes. However, no shock wave could be observed with helium. With argon in the electrodeless tube radiation could be observed from the gas ahead of the shock wave. Time resolved spectroscopic measurements on this radiation allowed rough determination of electron density and of the population of excited states of argon atoms and ions ahead of the shock front. This "preheating" of the gas is presumably due to ultraviolet light emitted from the discharge and the shock plasma. The values of electron density and temperature expected behind the shock front were calculated from shock theory, taking into account the preheating of the gas. The expected values agreed well with the electron density and temperature determined from spectroscopic measurements on the shock plasma. The study of the precursor radiation was continued in a shock tube with electrodes. In this tube the driving discharge was more luminous and the excitation and ionization of helium and argon ahead of the luminous front could be more readily observed than with the electrodeless tube. The number densities of helium atoms in various excited states were determined from the time resolved line intensities before and after the passage of the luminous front. The ratios of atoms in different levels differ from the expected ratios for thermal equilibrium conditions, both ahead of the luminous front and behind it. An estimate was made of the time required for the attainment of equilibrium by electron impact. The calculation indicates that ahead of the luminous front there is not sufficient time to attain equilibrium. On the other hand, for the high electron density found behind the luminous front, the equilibrium distribution is expected to be reached in times shorter than the observation times, in disagreement with the behaviour observed. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Treatments such as electroconvulsive shock (ECS) impair later performance of learned responses if presented shortly after learning, but not if delayed for a sufficient time. These gradients are frequently termed retrograde amnesia and interpreted as reflecting a memory consolidation process. The present investigation was concerned with the relationship of the length of the gradient produced by a single ECS to the duration of the memory consolidation process. In the first experiment, rats were trained on a one-trial passive avoidance task and then presented with one of three ECS treatments. The treatments were five ECSs of 0.5 seconds duration spaced either 1 minute apart, 5 seconds apart, or in one continuous 2.5 second duration burst. The five ECSs spaced 1 minute apart were found to impair performance when presented immediately, 1 hour, 24 hours, and 48 hours but not 9 days after passive avoidance training. Five ECSs spaced 5 seconds apart impaired performance when presented immediately or 1 hour but not 24 hours after training. In contrast, the single 2.5 second duration ECS impaired performance when presented immediately but not 1 hour or longer after training. The impairments produced by the five ECSs spaced 1 minute apart at 1 hour and 24 hours were found to be permanent over 11 days. The second experiment examined whether the long gradient produced by five ECSs spaced 1 minute apart was qualitatively different from single ECS gradients. Five ECSs spaced 1 minute apart were presented following passive avoidance training to rats anesthetized with ether or sodium pentobarbital. In both cases, the series of ECSs still impaired performance when presented 1 or 24 hours but not 9 days following passive avoidance training. This finding does not provide support for a distinction between the gradients produced by a single ECS and a series of ECSs. These results were therefore interpreted as showing that the length of the gradient produced by a single ECS in a passive avoidance task is not a good estimate of the duration of time required for memory consolidation. In this passive avoidance task, consolidation appears to continue for a period of at least several days, while the gradient produced by a single ECS was less than 1 hour. In the third experiment, rats were trained on a one - trial appetitive taste and then presented with either five ECSs spaced 1 minute apart, or a single ECS of 0.5 seconds or 2.5 seconds duration. In contrast to the results in the passive avoidance task, the five ECSs paced 1 minute apart did not produce a longer gradient than a single ECS of either 0.5 or 2.5 seconds duration. All three treatments impaired performance when presented 15 seconds but not 1 hour after training. Several possible explanations for the different effects of the series of ECSs in the two tasks are considered, and it is concluded that this difference probably reflects differences between the memory consolidation processes in the two tasks. / Arts, Faculty of / Psychology, Department of / Graduate

Recent experimental evidence indicates that the effectiveness of posttraining electroconvulsive shock in disturbing retention is not constant but highly variable. One factor which appears to contribute to this variation is the strength of the electroshock current. Currents of higher intensity or of longer duration have generally been found to be more effective in disturbing retention. Indirectly, this evidence suggests that an electroshock treatment does not invariably stop memory consolidation. It appears that following a weak electroshock treatment, the interference with consolidation is not complete and that consolidation may continue afterwards. This possibility was directly examined in the present experiment with a one-trial passive avoidance task. The results showed that rats given one electroconvulsive shock 5 min after the passive avoidance training suffered only a slight loss of retention. However, when a second electroconvulsive shock was given at 1 hr after training, there was a significantly greater retention loss than that following one electroconvulsive shock at 5 min or at 1 hr. Additional results indicate that the disruptiveness of the second electroconvulsive shock is time-dependent and that the retention deficit does not appear to be due to punishing or disinhibitory effects of the electroconvulsive shocks. These findings are interpreted as indicating that memory consolidation can continue after electroconvulsive shock. / Arts, Faculty of / Psychology, Department of / Graduate

Unsteady shock waves are formed by the coalescence of pressure waves. The attenuationof pressure and shock waves in general is of great importance in a wide varietyof application such as vehicle performance, health and safety. Previous researcheshave been carried out on a variety of geometries to understand the physics. Theaim of this project is to advance the previous-state-of-the-art and to shed furtherlight into the fundamental physics associated with the shock wave interactions andphenomena. Shock wave attenuation was studied by using rough walls in a three-pipe system. The roughness at the walls is added by placing grooves on the upper and lower wallsof the junctions. The angles of the branch pipe were varied from 30 to 150 degrees. Shock wave interactions with a co-flow jet were also examined. All the experimentswere performed for driver gas (air) pressures of 4, 8, and 12 bar and atmosphericpressure within the driven section, giving theoretical Mach number of 1.34, 1.54, and1.66, respectively. Three different velocities, 114, 138, and 178 m/s, were used forthe co-flow jet. High-speed schlieren photography, particle image velocimetry (PIV),and pressure measurements techniques were employed to visualise and quantify theflow field. Expansion and compression waves produced by the grooves led to a highly unsteadyflow field, an increase to the pressure upstream, and the formation of asecondary shock wave. The pressure of the incident shock front was reduced by anestimated 20%. A maximum of 10% reduction of velocity of the shock front at theexit was achieved. The shock vortex/ structure led to multiple reflections, distortionof the vortical field, a lambda-shock configuration and pressure fluctuations. Theinfluence of the co-flow jet dissipated the shock/vortex structure, and attenuatedthe pressure peaks caused by multiple reflections. Complementing this investigation the testing of pressure sensitive paints (PSP)for the use of unsteady and high speed flows was carried out. The results showedthat the use of luminophores with high intensity output, and pressure sensitivityapplied on a porous material were the most suitable PSPs for these applications.

The formation of a laser-driven shock in fused silica was observed experimentally. Fused silica slabs were irradiated with 0.53 /µm laser light in a pulse of 2 ns FWHM at intensities ranging from 10¹² W/cm² to 5 x 10¹³ W/cm², producing a pressure pulse ranging from < 30 GPa to 500 GPa. Shock trajectories were observed using streaked shadowgram and schlieren methods. The experiment was modelled with a one-dimensional Lagrangean laser-plasma hydrocode. Comparison of the simulation results with the experimental observations indicate that the high pressure shock develops anomalously slowly at intensities > 1 x 10¹³ W/cm². Furthermore the shock displayed non-steady propagation for a transient period following its formation. The non-steady propagation is interpreted to be due to a relaxation process in the phase transformation of the fused silica to the high pressure stishovite phase which occurs in the shock front. The slow formation of the shock at high intensities is consistent with a significant volume collapse (phase transition) possibly induced by isentropic compression; however, this interpretation is uncertain due to the complications introduced by non-equilibrium thermodynamics and the possibility of two-dimensional motion. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

With recent improvement in wood manufacturing technologies, taller and larger wooden structures are being constructed, thereby increasing the risk for potential damage due to a blast threat against such structures. Recent studies on the effects of high strain rate in wood have been undertaken, however the vast majority of these studies have focussed on structural elements with idealized boundary conditions. Some studies included realistic connections as the boundary conditions, but little progress has been made to date in order to quantify the behaviour of connections in isolation. The current study aims to investigate the response of steel-wood-steel bolted connections when subjected to blast loads. This includes determining the dynamic increase in resistance and stiffness for stocky and slender bolts in both the parallel and perpendicular to grain directions. The study also explores analytical solutions to predict the joint behaviour and discusses the validity of current blast design provisions. Bolted wood connections were investigated under both static and simulated blast loading using the University of Ottawa’s shock tube. The study found a dynamic increase in resistance and stiffness when the failure mode was dominated by wood crushing in both the parallel and perpendicular to grain directions. No increase in resistance or stiffness was observed when bolt yielding dominated the failure. A loss of ductility was observed under dynamic loading for the parallel to the grain connections designed to fail in wood crushing. It was found that the use of self-tapping screw reinforcement was an effective method of preventing premature splitting failures and enhancing the performance of a connection. The results showed that connections which engaged the fastener in bending exhibited more favourable behaviour than connections which engaged only in wood crushing. A two degree-of-freedom model was capable of modelling the connections even when the support frame system had some flexibility. The validated model was used to investigate cases where the connection could contribute to the energy dissipation. It was found that the performance of the assembly improved when the connections were considered. Recommended future work includes an investigation of brittle failure modes in bolted connections, exploring connections with more deformation capacities, and expanding the experimental component of the study to include full-scale structural assemblies with wood elements and boundary connections. Limited design recommendations have been proposed in the current study, however testing at the assembly level could shed more light on such an important topic.

Shock wave lithotripsy is the preferred treatment modality for kidney stones in the United States. Despite clinical use for over twenty-five years, the mechanisms of stone fragmentation are still under debate. A piezoelectric array was employed to examine the effect of waveform shape and pressure distribution on stone fragmentation in lithotripsy. The array consisted of 170 elements placed on the inner surface of a 15 cm-radius spherical cap. Each element was driven independently using a 170 individual pulsers, each capable of generating 1.2 kV. The acoustic field was characterized using a fiber optic probe hydrophone with a bandwidth of 30 MHz and a spatial resolution of 100 μm. When all elements were driven simultaneously, the focal waveform was a shock wave with peak pressures p+ =65±3MPa and p−=−16±2MPa and the −6 dB focal region was 13 mm long and 2 mm wide. The delay for each element was the only control parameter for customizing the acoustic field and waveform shape, which was done with the aim of investigating the hypothesized mechanisms of stone fragmentation such as spallation, shear, squeezing, and cavitation. The acoustic field customization was achieved by employing the angular spectrum approach for modeling the forward wave propagation and regression of least square errors to determine the optimal set of delays. Results from the acoustic field customization routine and its implications on stone fragmentation will be discussed. / National Institutes of Health DK043881

The present study involved two types of analyses as a part of the investigation leading to the design of a shock absorber providing optimal vibration control and minimum transmissibility. Those two types of analyses were the following.

The literature indicates a continuous cycle of difficulties for transfer students, leading to a failure to acclimate, persist, and obtain a degree. The purpose of this study was to examine the effect the Promise Student Support Program (PSSP) had on community college transfer students. More specifically, the study examined the effect of the PSSP on transfer shock, retention, and graduation rates. Two groups were compared: (a) community college transfer students entering the 4-year university as part of the PSSP between 2006 and 2011, and (b) community college transfer students entering the 4-year university between 2006 and 2011 who met the criteria for the PSSP but did not participate. A comparison was made between the 2 groups to determine if significant differences exist between students benefiting from the programming and support of the PSSP and those students without it. The study utilized the quantitative, quasi-experimental study research design. The research was conducted using descriptive statistics to analyze data related to GPA, retention, and graduation rates. Then, an independent sample t-test was administered to assess if statistical differences existed for GPA from transfer GPA to the 1st semester GPA at the 4-year institution between participants and non-participants in the PSSP. Finally, chi-square test of independence was used to determine if there were differences in retention and graduation rates. The findings, as determined by this study, concluded that participants of the PSSP experienced less transfer shock and had higher rates of retention. However, the PSSP showed no effect on graduation rates. This study is expected to provide 4-year institutions clear evidence of the importance of bridging the gap for transfer students, in general, with transitional programs of support.

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