Skin conductance responses were used to assess the effects of THC on conditioned fear response amplitude and extinction using a fear conditioning and extinction paradigm that paired an aversive unconditioned stimulus (shock) with a conditioned stimulus (angry face). Participants (N = 10 males) exhibited conditioning to the CS+, as indicated by a larger CR to the CS+ than to the CS-. THC did not have a significant effect on extinction of the CR across trials, but there was a significant interaction of social anxiety with drug that suggests that THC may facilitate extinction of CR to fear-conditioned stimuli in more socially anxious individuals. These results provide support for the hypothesis that THC may act as an anxiolytic in fear-eliciting situations. The current study was limited by a small sample size and a potential confound that may have influenced the SCL during conditioned responding.

Climate warming during the latest Permian is associated with the most severe mass extinction event of the Phanerozoic, and the expansion of hypoxic and anoxic conditions into shallow shelf settings. Our understanding of the magnitude, pattern and duration of the extinction event and subsequent recovery remains equivocal. Evidence suggests that the action of waves provided an oxygenated refuge, i.e. ‘habitable zone’, above wave base that may be limited to high latitudes, in association with a faster pace of recovery. In addition, advanced recovery faunas have been documented from the Induan and there is evidence from the pelagic realm that further biotic crises may have delayed the recovery of benthic organisms coinciding with large carbon isotope perturbations at the Lower Triassic sub-stage boundaries. To test these hypotheses, novel palaeoecological data was collected from localities in Hungary, northern Italy, and Svalbard. To understand better the ecological impact of the extinction, a database of all known benthic marine invertebrates from the Permian and Triassic periods was created, with each taxon assigned to a functional group based on their inferred lifestyle. This study found that the skeletal and ichnofaunal assemblages consistent with advanced ecological recovery are limited to settings aerated by wave activity, which supports the habitable zone hypothesis. In the western Palaeotethyan sections it was found that the proximal end of the ‘habitable zone’ was limited by persistent environmental stress attributed to increased runoff that resulted in large salinity fluctuations, increased sedimentation rates and eutrophication creating an environment only favourable for opportunistic taxa. In the Tirolites carniolicus Zone, however, the ‘habitable zone’ expands into more proximal and offshore settings. This is associated with climate cooling in the late Spathian. The data also demonstrate that despite the taxonomic severity of the extinction, only one mode of life went extinct and only one subsequently evolved in the aftermath. Functional diversity was, however, reduced in particular regions and environmental settings, and recovery varied spatially and temporally. In western Palaeotethys, benthic communities record evidence for biotic crises, such as reduced tiering in the Smithian, associated with Early Triassic carbon isotope excursions, but, until the Spathian there was no significant change in the composition of the benthic faunas.

The successful reduction of fear is the aim of clinicians treating people with anxiety disorders such as post-traumatic stress disorder or phobias. Existing treatments for these conditions, however, require many treatment sessions and are prone to relapse. A new technique, first demonstrated in rats by Monfils, Cowansage, Klann, & LeDoux (2009) and later shown to be effective in humans (Schiller et al., 2010), provides a method of efficiently reducing fear in a manner which is resistant to various known triggers of relapse. This procedure involves a single presentation of the fear-inducing stimulus one hour prior to extinction training. This procedure produces extinction learning that is resistant to the return of fear resulting from a change of context, the passage of time, exposure to the unconditioned stimulus, and even further conditioning of the stimulus with an aversive stimulus. This dissertation focuses on one particular property of this procedure: that a stimulus extinguished using this procedure is resistant to subsequent retraining of the fear association. The first four experiments presented here are aimed at replicating this phenomenon and determining whether prediction error at retrieval is necessary for the effect to occur. Following on from these studies, the next chapter presents three experiments which investigate whether trial spacing effects could explain the enhanced extinction and highlights conditions under which the effect is weakened, or possibly reversed. The next three experiments compare the properties of a stimulus extinguished under these conditions with a stimulus extinguished under normal conditions. These studies focus on explanations involving inhibition, inattention and the disruption of stimulus representations. In the final three experiments, the possibility of reversing the effect is investigated. These studies look at the effect of memory retrieval prior to retraining of the stimulus to determine the conditions under which the stimulus can again come to elicit a fear response.

Sutherland, Mackintosh, and Wolfe (1965) demonstrated that continuous reinforcement given subsequent to partial reinforcement resulted in superior resistance to extinction than did continuous reinforcement administered prior to partial reinforcement. Because the experimenters did not make compensations for different acquisition asymptotes in their analysis of the extinction data, the interpretation of their results is questionable. Thelos and McGinnis (1967) obtained results contrary to those obtained by the latter experimenters. This study was run in order to obtain additional information pertaining to the effects of shifts of reinforcement schedules on resistance to extinction. Extended acquisition trials were used with the expectation of bringing the six experimental groups up to the same terminal asymptotic levels. When Ss were approximately 45 days old, Ss were randomly assigned to one of six acquisition conditions. These conditions were: 96 partial reinforcement trials, 192 partial reinforcement trials, 96 partial reinforcement trials followed by 96 continuous reinforcement trials, 96 continuous reinforcement trials followed by 96 partial reinforcement trials, 192 continuous reinforcement trials, and 96 continuous reinforcement trials. Following training in a straight runway, all Ss received 60 nonreward trials given in blocks of 6 trials a day. Time measures were taken of runway performance on acquisition and extinction trials. The results supported the hypothesis that extended training would produce equivalent terminal asymptotic running speeds in acquisition. None of the hypotheses made by Sutherland, Mackintosh, and Wolfe (1965) or by Thelos and McGinnis (1967) were supported by the results of the experiment; no significant partial reinforcement effect was obtained. / Arts, Faculty of / Psychology, Department of / Graduate

In recent years, forestry programmes in British Columbia have increasingly used helicopters to expedite operations, particularly in the areas of fire suppression and prescribed burning. Between 1970 and 1977 the population of Canadian helicopters doubled, reflecting the increased usage resulting from new, more efficient designs. The number of accidents per year decreased in the 8 years, but the percentage of fatal accidents increased In British Columbia, the accident rate per 10,000 hours in the years 1975 and 1976, was 3.6, the third highest in Canada. After an extensive period of field work in this province, by the author, it is clear that the people working in and around helicopters do not generally receive enough training in the safety precautions necessary. This lack of training was evident at both the worker level and the supervisory level. In fire suppression operations, the inadequate training is aggravated by haste, which greatly increases the chances of unnecessary accidents. This report identifies areas of training that need greater-attention, and it offers some guidelines for future training programmes. The report discusses the fundamentals of helicopter flight, in order that the layman may gain some appreciation of what problems the pilot has to tolerate. Several types of operations are then detailed with safety prescriptions for each one. Some causative factors in each operation are also discussed. The report then analyses the use of helicopters in aerial ignition systems. Of the several systems currently in use, it is clear that the helicopter drip torch is potentially the most hazardous, but to date there have been no serious helicopter drip torch accidents. Finally the report looks at crew deployment techniques, in particular, helicopter rappelling and helitack. The level of training and hazard awareness in these two operations is higher than was generally seen elsewhere, and provides a good example of how helicopters can be used safely and efficiently. Throughout the report, reference is made to past accidents. These accidents show a fundamental lack of safe practice; a situation that would be improved with better training programmes. They also illustrate some of the diverse and disastrous results of poor training. The report recommends that the Workers' Compensation Board of British Columbia should seriously consider setting up a series of training films, which, along with posters and leaflets, could be distributed to the various companies and organisations who use helicopters in the course of their operations. Transport Canada is now preparing a series of general training aids, and these will be made available to interested parties. / Forestry, Faculty of / Graduate

In arid lands, a major contribution to water loss is by soil water evaporation. Desert sand dunes in arid regions are devoid of runoff and have high rates of infiltration. Rainwater is commonly stored within them because of the low permeability soils in the underlying desert pavement. In such cases, moisture is confined in the sand dune below a depth, termed as the “extinction depth”, where it is protected from evaporation during long dry periods. Moreover, desert sand dunes have sparse vegetation, which results in low transpiration losses from the stored water. The water accumulated below the extinction depth of the sand dunes can be utilized for various purposes such as in irrigation to support desert agriculture. In this study, field experiments were conducted in Western Saudi Arabia to monitor the soil moisture gradients and determine the diffusive extinction depth of dune sand. The dune sand was saturated with water and was exposed to natural conditions (evaporation and precipitation). The decline of the water level in the sand column was continuously recorded using transducers and sensors installed at different depths monitored the temporal variation of temperature and moisture content within the sand. The hydrological simulator HYDRUS-1D was used to construct the vertical profiles of soil water content and temperature and the results obtained from HYDRUS-1D were compared to the gradients monitored by the sensors.

No description available.

Adaptive radiations, or evolutionary diversifications, are the evolutionary divergence of a single lineage into many different adaptive forms. They play a critical role in the history of life as groups of organisms speciate and fill new ecological roles over geologically rapid time intervals. There is currently no agreed upon operational unit, timeframe, or amount of divergence for organisms to be considered to have undergone an adaptive radiation. Additionally, the paucity of both comparative and fossil studies has limited the utility of the adaptive radiation in framing macroevolutionary questions, such as, is ecological and morphological diversification simultaneous? An ideal fossil clade to test this question is the Archosauriformes (crocodylians, birds, and their closest relatives). Archosauriforms radiated following the end-Permian mass extinction and their lineage diversification through the Early to Late Triassic is well documented in the literature. Prior to the end-Permian mass extinction, these reptiles were both species poor and ecologically limited, but by the Late Triassic they dominated terrestrial ecosystems in both species abundance and ecological breadth. However, continued environmental instability following the end-Permian extinction has led to the hypothesis that ecological expansion of archosauriforms lagged behind the diversification of lineages. The first chapter of my dissertation uses a Middle Triassic archosauriform tooth assemblage from Tanzania to reconstruct dietary specialization, estimated by morphological disparity of teeth. In addition to comparing tooth disparity of isolated and in situ teeth, this also provides a lens for comparing the timing of dietary specialization and species diversification. I found the archosauriforms to be faunivorous with little morphological disparity amongst the teeth. The second chapter uses an Early Triassic reptile tooth assemblage from South Africa to reconstruct the dietary specialization of archosauriforms early in their radiation to compare the amount of morphological disparity and lineage diversity. I use methods from Chapter 1 and integrate 3D morphometrics to better capture shape. I described several tooth morphotypes including six new to the locality. The morphological and dietary differences were minimal, indicating a greater species diversity than ecological diversity. The third chapter is a description of a new pseudosuchian archosaur taxon from the Middle Triassic of Tanzania. As species descriptions form the basic data unit of macroevolutionary analyses, this assists future studies of the archosauriform radiation. I recover this new taxon as the oldest known aetosaur. This species provides insights into the evolution of an armored carapace in crocodylian-line archosaurs and shows morphology related to armor evolved prior to the evolution of an herbivorous diet. / Doctor of Philosophy / There is an incredible diversity of life on Earth, but this is a small fraction of the life that once existed on our planet. The fossil record provides us a window into the past to reconstruct the history of life on our planet. Two of the patterns we see in the fossil record are rapid drops in biodiversity called mass extinctions, and rapid increases in biodiversity called biological radiations. Both of these events are often related and mass extinctions are followed by biological radiations throughout earth history. A particularly interesting case is the end-Permian mass extinction, not only because it is the largest extinction event, but also because the subsequent radiation was delayed by continuing environmental instability. An ideal group of animals to study in this time period are the archosaurs, the group of reptiles including crocodylians, birds, and their extinct relatives. Archosaur reptiles went from very few species before the extinction, to dominate ecosystems for the next 200 million years. However, we do not know if the radiation of many archosaur species occurred at the same time as they filled new roles in their communities. The first two chapters of my dissertation focus on using fossil teeth to reconstruct the diets of archosaurs at a single location. My first chapter describes teeth from the Middle Triassic (247-237 million years ago) of Tanzania. I measured the shapes of these teeth and used that to help assign them to diets. Doing this I found there were more species than types of diets indicating the radiation of species may have occurred before specialization of life habits. In the second chapter where I describe a reptile tooth assemblage from the Early Triassic (252-247 million years ago) of South Africa. I added additional methods for measuring tooth shape, found several different types of teeth (likely different species) but mostly similar diets, indicating again a delay in life habit specialization. In my third chapter I name a new species of archosaur reptile from the Middle Triassic of Tanzania. This new species helps us to understand how heavily armored plant eaters evolved in early crocodylian relatives during the archosaur radiation.

<p> Two experiments, involving 140 subjects, were performed to study the effects of two partial reinforcement variables on measures of stimulus control in extinction. Pigeons were required to make a fixed number of responses ranging from 1 to 64) to terminate discrete trial presentations and were rewarded on a predetermined percentage (ranging from 100% to 25%) of those completed trials. Generalization tests involved repeated nonreinforced presentations of the training stimulus and a new stimulus until animals ceased responding. Stimulus control measured by differences or ratios of responding to the two stimuli increased as response requirement increased. The percent of trials reinforced had no significant effect on either measure of control. Within-trial analyses showed that maximum stimulus control is exerted over the first response, some control continues to be exerted over successive responses, and there is a tendency for control to increase near the end of the requirement. Implications of the research were discussed.</p> / Thesis / Doctor of Philosophy (PhD)

No description available.