The DSM-IV characterizes dissociation as “disruption in the usually integrated functions of consciousness, memory, identity, or perception of the environment” (American Psychiatric Association, 1994, p. 477) and it has been tenuously linked with trauma, but “lacks a single, coherent referent … that all investigators in the field embrace” (Cardena, 1994). It is known that dissociation is a spectrum (Bernstein and Putnam, 1986; Shor, Orne, and O’Connell, 1962; Spiegel, 1963; Tellegen and Atkinson, 1974), and low levels of dissociation can be a part of normal functioning, allowing us to do two things at once (Butler, Duran and Jasiukitis, 1996), but higher levels can interfere with daily functioning. The present study used survey techniques to investigate the link between dissociation and trauma. Survey results showed a significant correlation between trauma and dissociation. The current investigation also used the high temporal and spatial resolution of electroencephalographic techniques to identify the neurophysiological correlates of dissociation. Specifically, the current investigation recorded early and late event-related potentials in participants who rated high and low in dissociation while they viewed affective pictures in order to determine if there were electrophysiological differences in responses to emotional stimuli. Electroencephalographic results were nonsignificant, but trends indicated that high dissociators showed a heightened response to affective photos at P1 and the late positive potential compared with low dissociators. If the results are thought to be reliable, the trends may indicate that high dissociators were not actively dissociating during the task, and because high dissociators have usually experienced trauma, they are more sensitive to emotional stimuli. Further research is needed to support these theories.

Today we face the formidable challenge of meeting the fuel needs of a growing population while minimizing the adverse impacts on our environment. Thus, we search for technologies that can provide us with renewable fuels while mitigating the emission of global pollutants. To this end, use of non-thermal plasma processes can offer novel methods for efficiently and effectively converting carbon dioxide and water vapor into synthesis gas for the production of renewable fuels. Particularly, non-thermal plasma technologies offer distinct advantages over conventional methods including lower operating temperatures, reduced need for catalysts and potentially lower manufacturing and operation costs. The non-thermal plasma reactors have been studied for ozone generation, material synthesis, decontamination, thruster for microsatellites, and biomedical applications. This dissertation focuses on producing synthesis gas using a non-thermal, microhollow cathode discharge (MHCD) plasma reactor. The prototype MHCD reactor consisted of a mica plate as a dielectric layer that was in between two aluminum electrodes with a through hole. First, electrical characterization of the reactor was performed in the self-pulsing regime, and the reactor was modeled with an equivalent circuit which consisted of a constant capacitance and a variable, negative differential resistance. The values of the resistor and capacitors were recovered from experimental data, and the introduced circuit model was validated with independent experiments. Experimental data showed that increasing the applied voltage increased the current, self-pulsing frequency and average power consumption of the reactor, while it decreased the peak voltage. Subsequently, carbon dioxide and water vapor balanced with argon as the carrier gas were fed through the hole, and parametric experiments were conducted to investigate the effects of applied voltage (from 2.5 to 4.5 kV), flow rate (from 10 to 800 mL/min), CO₂ mole fraction in influent (from 9.95% to 99.5%), dielectric thickness (from 150 to 450 [mu]m) and discharge hole diameter (from 200 to 515 [mu]m) on the composition of the products, electrical-to-chemical energy conversion efficiency, and CO₂-to-CO conversion yield. Within the investigated parameter ranges, the maximum H2/CO ratio was about 0.14 when H2O and CO₂ were dissociated in different reactors. Additionally, at an applied voltage of 4.5 kV, the maximum yields were about 28.4% for H2 at a residence time of 128 [mu]s and 17.3% for CO at a residence time of 354 [mu]s. Increasing residence time increased the conversion yield, but decreased the energy conversion efficiency. The maximum energy conversion efficiency of about 18.5% was achieved for 99.5% pure CO₂ at a residence time of 6 [mu]s and an applied voltage of 4.5 kV. At the same applied voltage, the maximum efficiency was about 14.8% for saturated CO₂ at a residence time of 12.8 [mu]s. The future work should focus on optimizing the conversion yield and efficiency as well as analyzing the temporal and spatial changes in the gas composition in the plasma reactor. / text

Halo nuclei are among the strangest nuclear structures. They are viewed as a core containing most of the nucleons surrounded by one or two loosely bound nucleons. These have a high probability of presence at a large distance from the core. Therefore, they constitute a sort of halo surrounding the other nucleons. The core, remaining almost unperturbed by the presence of the halo is seen as a usual nucleus. <P> The Coulomb breakup reaction is one of the most useful tools to study these nuclei. It corresponds to the dissociation of the halo from the core during a collision with a heavy (high <I>Z</I>) target. In order to correctly extract information about the structure of these nuclei from experimental cross sections, an accurate theoretical description of this mechanism is necessary. <P> In this work, we present a theoretical method for studying the Coulomb breakup of one-nucleon halo nuclei. This method is based on a semiclassical approximation in which the projectile is assumed to follow a classical trajectory. In this approximation, the projectile is seen as evolving in a time-varying potential simulating its interaction with the target. This leads to the resolution of a time-dependent Schrödinger equation for the projectile wave function. <P> In our method, the halo nucleus is described with a two-body structure: a pointlike nucleon linked to a pointlike core. In the present state of our model, the interaction between the two clusters is modelled by a local potential. <P> The main idea of our method is to expand the projectile wave function on a three-dimensional spherical mesh. With this mesh, the representation of the time-dependent potential is fully diagonal. Furthermore, it leads to a simple representation of the Hamiltonian modelling the halo nucleus. This expansion is used to derive an accurate evolution algorithm. <P> With this method, we study the Coulomb breakup of three nuclei: ¹¹Be, ¹⁵C and ⁸B. ¹¹Be is the best known one-neutron halo nucleus. Its Coulomb breakup has been extensively studied both experimentally and theoretically. Nevertheless, some uncertainty remains about its structure. The good agreement between our calculations and recent experimental data suggests that it can be seen as a <I>s1/2</I> neutron loosely bound to a ¹⁰Be core in its 0⁺ ground state. However, the extraction of the corresponding spectroscopic factor have to wait for the publication of these data. <P> ¹⁵C is a candidate one-neutron halo nucleus whose Coulomb breakup has just been studied experimentally. The results of our model are in good agreement with the preliminary experimental data. It seems therefore that ¹⁵C can be seen as a ¹⁴C core in its 0⁺ ground state surrounded by a <I>s1/2</I> neutron. Our analysis suggests that the spectroscopic factor corresponding to this configuration should be slightly lower than unity. <P> We have also used our method to study the Coulomb breakup of the candidate one-proton halo nucleus ⁸B. Unfortunately, no quantitative agreement could be obtained between our results and the experimental data. This is mainly due to an inaccuracy in the treatment of the results of our calculations. Accordingly, no conclusion can be drawn about the pertinence of the two-body model of ⁸B before an accurate reanalysis of these results. <P> In the future, we plan to improve our method in two ways. The first concerns the modelling of the halo nuclei. It would be indeed of particular interest to test other models of halo nuclei than the simple two-body structure used up to now. The second is the extension of this semiclassical model to two-neutron halo nuclei. However, this cannot be achieved without improving significantly the time-evolution algorithm so as to reach affordable computational times.

Mining of datasets obtained from proteomics experiments was performed to investigate the dissociation pathways of protonated peptides activated in the gas phase under low energy collision-induced dissociation (CID). Intensity patterns in ion trap tandem mass spectra were exploited and different statistical approaches were employed to elucidate the dissociation mechanisms.Chapter 2 describes a study of 506 doubly-protonated tryptic peptides that shows the presence of an internal basic residue can increase the preferential fragmentation C-terminal to aspartic acid (Asp-Xxx) significantly. The degree of enhancement varies with the identity of the basic residues. The result corroborates a previously published mechanism based on studies from model peptides, and was incorporated into an existing peptide sequencing algorithm. A preliminary test on a separate dataset of 119 spectra shows that implementing rules to predict enhanced cleavages at Asp-Xxx improves the ability of the algorithm to identify the correct sequence from a list of candidates.Chapters 3-4 describe much more elaborate analyses on 28,330 peptides of different sequences and charge states. Extensive sorting based on prior knowledge was first performed to probe the correlation of fragmentation patterns with structural features. Pair-wise fragmentation maps reveal that the difference in basicity between Arg and Lys results in different dissociation patterns among singly-protonated tryptic peptides. While one dominant protonation form (proton localized) exists for Arg-ending peptides, a heterogeneous population of two or more protonated forms (proton partially-mobile) exist for Lys-ending peptides. Asp/Glu-Xxx dominates spectra from peptides that have a localized proton(s) and Xxx-Pro dominates those that have a mobile or partially mobile proton(s). When Pro is absent from peptides that have a mobile or partially mobile proton(s), cleavage at each peptide bond becomes more prominent. A fundamental dependence of gas phase peptide fragmentation on conformational constraints was found.A knowledge mining scheme was proposed in Chapter 5 to bypass the prior knowledge constraints and cluster the dissociation behaviors of 28,330 peptides into four distinct categories. The most influential factors in the fragmentation process are: the mobility of the proton(s), the presence and the location of Pro and Arg. Structural motifs responsible for each dissociation behavior are also elucidated.

This dissertation presents efforts to expand the role of mass spectrometry (MS) in structural biology. Determination of quaternary structure of a protein complex has been hindered by limited fragmentation from collision-induced dissociation (CID). As an alternative, surface-induced dissociation (SID) was implemented for a quadrupole - time-of-flight instrument in the Wysocki laboratory. This research tested the hypothesis that SID should produce fragmentation reflective of subunit organization. Furthermore, ion mobility (IM) was used to prove the direct relationship between precursor conformation and observed dissociation patterns, and the relationship between activation and product ion conformation. The structure and dynamics of a dimeric small heat shock protein (sHSP) with no solved structure was investigated. The importance of N- and C-terminal domains for dimerization was determined, and the dimers were shown to exchange subunits. From exchange kinetics it is proposed that subunit exchange is unrelated to heat shock activity. SID was used to elucidate the subunit architecture of heterogeneous protein assemblies, including one previously solved protein structure and two formerly uncharacterized proteins. The heterohexamer toyocamycin nitrile hydratase dissociated into trimers, revealing the hexamer to be a dimer of trimers. The bacterial ribonuclease toxin:antitoxin tetramer was shown to have an antitoxin dimer at its core, with flanking individual toxin subunits. The examples presented here are the first clear proof that SID results can clearly indicate the substructure of a protein assembly.IM was used to study the conformation of precursor and product ions. A greater understanding of the relationship between precursor conformation and observed dissociation patterns was developed. Different charge states of a dodecameric sHSP were found to have significantly different conformations, which were directly reflected in SID spectra. IM comparison of CID and SID product ions showed that the same charge state of a product ion from either method has the same CCS. This suggests the product ion conformation is dependent upon ion charge state, and independent of activation method and collision energy. The cause and effect relationship between precursor conformation and MS/MS patterns, and activation and product ion conformation were clearly illustrated. Together, this body of research expands the role of MS for structural biology.

No description available.

This thesis presents four studies that examine the potential role that intrusive thoughts, dissociation and mindfulness in self-harming behaviours in young people and adults. A large online study was conducted with students and staff at a UK university. This examined a range of risk factors for self-harm derived from the literature, including dissociation, family background/trauma history and intrusive thoughts. This study was followed up with a qualitative study investigating triggers of self-harm, and the role of intrusive thoughts. A third study then looked at these factors in young people who were inpatients in an American psychiatric hospital, and who had all expressed intent to self- harm or commit suicide. This study also introduced a measure of trait mindfulness in order to investigate this potential way of dealing with intrusive thoughts. Finally, the risk factors identified in these studies were further investigated with an online survey with undergraduate students at a second UK university, dissociation, mindfulness and thought suppression. Intrusive thoughts were found to differ in content, frequency and effect between people with experience of self-harm and those without. A subgroup of potentially maladaptive behaviours were found to be associated with high scores on the predictors of self-harm, and therefore potentially predictive of self-harm. In the young people in hospital, the extent to which they reacted to their intrusive thoughts was inversely associated with the extent to which they were naturally mindful. Trait mindfulness scores were lower for those individuals with a history of childhood trauma, and for those meeting diagnostic criteria for Borderline Personality Disorder, in which self-harm is a key feature. These findings together suggest that mindfulness skills may play an important role in both dealing with intrusive thoughts and for protecting against self-harm. Overall, intrusive thoughts and dissociation were associated with experience of self- harming behaviours, while mindfulness skills were negatively associated with self-harm. Some potentially maladaptive behaviours (including smoking and eating pathology) represent risk factors for self-harm, and therefore may provide professionals with a way of identifying people for early intervention, if further longitudinal research shows evidence of progression. Alternatively, the differences in mindfulness between this group and the self-harmers may indicate that mindfulness training could benefit people who self-harm.

No description available.

This study compares results of sighting, control, suppression and wink tests of visual dominance with a dissociation test administered to 240 high-achieving (ninetieth percentile and above academically) and low-achieving (twenty-fifth percentile and below academically) students at grades four, eight, and twelve. The study examines differences between visual dissociation and other visual-dominance tests. In so doing, the study tests the proportion of consistent dominance revealed by each test among underachievers with a high incidence of dominance variations, examines possible influences on choice of dominant eye, and compares distributions of dominance functions in high- and low-achieving populations.

Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal.