Physical forces in the cellular microenvironment play an important role in governing cell function. Forces transmitted through the cell cause distinct deformation of the nucleus, and possibly play a role in force-mediated gene expression. The work presented in this thesis drew upon innovative strategies employing simultaneous atomic force and laser-scanning confocal microscopy, as well as parallel optical stretching experiments, to gain unique insights into the response of eukaryotic cell nuclei to external force. Non-destructive approaches confirmed the existence of a clear anisotropy in nuclear mechanical properties, and showed that the nucleus' mechanical response to extracellular forces is differentially governed by both nuclear and cytoskeletal prestress: nuclear prestress regulates shape and anisotropic deformation, whereas cytoskeletal prestress modulates the magnitude and degree of deformation. Importantly, the anisotropic mechanical response was conserved among diverse differentiated cell types from multiple species, suggesting that nuclear mechanical anisotropy plays an important role in cell function.

The ubiquitin proteasome system targets proteins to the proteasome where they are degraded. Substrate recognition and processing prior to degradation take place at the 19S regulatory particle of the proteasome. A polyubiquitin chain, linked through isopeptide bonds formed between the C-terminal G76 and K48, is the signal responsible for delivery to the proteasome. Because chains linked via any of the seven lysine residues of ubiquitin exist in vivo and encode signals unrelated to protein degradation it is crucial for cells to avoid crosstalk between these different pathways. Several ubiquitin receptors related to proteasomal degradation have been identified but the selectivity between the different ubiquitin chains has not been assessed quantitatively while avoiding artefacts attributed to GST-dimerisation. By employing isothermal titration calorimetry, analytical ultracentrifugation and nuclear magnetic resonance, discrimination between K48- and K63-linked diubiquitin was established for the S. pombe proteasomal receptor Rpn10 and the shuttle protein Rhp23. The same methods allowed us to propose a discriminatory model for Rpn10. The crystal structures of the 19S regulatory particle subunits Rpn101-193 and Rpn121-224 have been determined and possible protein-protein interaction sites were identified by surface conservation and electrostatics analysis. Rpn12 surface residues were identified that had a negative effect on Rpn10-binding. This interaction was studied by surface plasmon resonance, fluorescence anisotropy and nuclear magnetic resonance. These experiments revealed a binding site on Rpn10 that is exclusively occupied by either ubiquitin or Rpn12 and for the first time demonstrated the interaction of a ubiquitin interacting motif with a protein other than ubiquitin.

Velocity distributions are a key to understanding the interplay between particles and waves in a plasma. Any deviation from a Maxwellian distribution may be unstable and result in wave generation. Using data from the ion mass spectrometer IMA (Ion Mass Analyzer) and the magnetometer MAG on-board Venus Express,  ion distributions in the plasma environment of Venus are studied. The focus lies on temperature anisotropy, that is, the difference between the ion temperature parallel and perpendicular to the background magnetic field. This study presents spatial maps of the average ratio between the perpendicular temperature <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?T_%5Cperp" /> and parallel temperature <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?T_%5Cparallel" />, both for proton and heavy ions (atomic oxygen, molecularoxygen and carbon dioxide). Furthermore average values of <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?T_%5Cperp" /> and <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?T_%5Cparallel" /> are calculated for different spatial areas around Venus. The results show that proton <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?T_%5Cperp" /> and <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?T_%5Cparallel" /> are nearly equal in the solar wind. At the bow shock and in the magnetosheath, the ratio <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?T_%5Cperp/T_%5Cparallel" /> increases to provide conditions favoring mirror mode wave generation. An even higher anisotropy is found in the magnetotail with <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?T_%5Cperp/T_%5Cparallel%5Capprox%202" /> for both protons and heavy ions.

Comportement différé, anisotrope à la descenderie de Saint-Martin-la-Porte / Time-dependent, anisotropic behavior of Saint-Martin-la-Porte gallery

Thermoplastische Kunststoffe werden zur Steigerung der mechanischen Eigenschaften häufig mit Kurzfasern verstärkt, wodurch sich jedoch eine anisotrope Eigenschaftscharakteristik einstellt. Dies führt oftmals zu ungewohntem Werkstoff- und Bauteilverhalten. Die Fertigungsparameter und -randbedingungen im Spritzgießprozess besitzen einen großen Einfluss auf lokale Faserorientierungen, wovon auch die globalen Bauteileigenschaften abhängen. Für eine werkstoffgerechte Auslegung von derartigen Bauteilen sind tiefgreifende Verständnisse über die mechanischen, thermischen und rheologischen Eigenschaften sowie die Kopplung von Spritzgieß- und Bauteilsimulation unerlässlich. Diese sogenannte integrative Simulation wird am Beispiel eines Strukturbauteiles aufgezeigt.

In this thesis, resonance enhanced multiphoton ionisation (REMPI) in combination with time-of-flight mass spectrometry (TOF-MS) has been used to detect nascent photofragments resulting from the UV dissociation of a variety of small molecules. The translational anisotropy and angular momentum polarisation of these photofragments has been measured and used to elucidate the underlying photodissociation dynamics. Firstly, the photodissociation of NO₂ at 320nm has been investigated and the vector correlations of the nascent NO photofragments have been measured in terms of a set of semi-classical bipolar moments. The measured angular momentum alignment is found to be consistent with an impulsive model for the dissociation, with <b>&mu;</b> and <b>&nu;</b> in the same molecular plane and both preferentially perpendicular to <b>J</b>, whilst angular momentum orientation measurements provide evidence for an additional torque due to the O-N-O bond opening during dissociation. These measurements were taken using a rotationally cooled, skimmed molecular beam and significant deviations were found between the bipolar moments measured using this source and previous measurements using a rotationally hotter source. The effect of parent molecular rotations on the measured bipolar moments has been quantified and successfully used to explain these deviations. The photodissociation of Cl₂ has been studied in the wavelength region (320-350)nm. UV absorption in this wavelength region may result in two dissociation channels, (Cl+Cl) and (Cl+Cl*), and the angular momentum polarisation of both the Cl(²P_3/2) and Cl*(²P_1/2) photofragments has been measured. This angular momentum polarisation has been reported in terms of a polarisation parameter formalism which, together with the measured translational anisotropies, has been used to determine the different potential energy surfaces contributing to the dissociation process. Translational anisotropy measurements of the Cl(²P_3/2) fragments have shown that, for the ground-state channel, dissociation results from a pure perpendicular transition to the C state, whilst alignment measurements show that non-adiabatic transitions to the A state are significant at large internuclear separations. The measured alignment parameters are found to be relatively constant for all dissociation wavelengths and are consistent with theoretical predictions. Translational anisotropy measurements of the Cl(2P_1/2) photofragments show that, for the excited-state channel, dissociation occurs following a mixed parallel and perpendicular excitation to the B and C states respectively and the interference between these two dissociation pathways has been shown to result in angular momentum orientation. The predissociation dynamics of the C ³&Pi;_g (&nu;=0) and (&nu;=1) Rydberg states of O₂ has been extensively studied. The translational anisotropy and angular momentum alignment of the O(³P) and O(¹D) photofragments resulting from this predissociation has been measured in terms of a polarisation parameter formalism, which has been extended for a two-photon dissociation process. Measurements have been taken at various fixed wavelengths within the two bands in order to investigate the differences in the predissociation dynamics of intermediate levels with different values of |&Omega;|(=0,1,2 in this case). The translational anisotropy is found to be dependent on the dissociation wavelength with the variations found to be consistent with rotational depolarisation due to the long lifetime of the excited C state. All photofragments have been found to be aligned, with the relationship between the measured O(³P) and O(¹D) alignment being found to be consistent with a diabatic model of the dissociation. In addition, all photofragments are found to display coherent orientation resulting from interference between two possible two-photon absorption pathways. The measured orientation is affected by rotational depolarisation due to the long lifetime of the excited C state; once this effect is accounted for the orientation is found to be nearly constant over all dissociation wavelengths. The origin of the coherent orientation is attributed to two-photon absorption to different spin-orbit components of the C state.

No description available.

Materials in nuclear reactors and satellites experience continually damaging radiation which leads to their degradation over time. Currently, a materials safe working lifetime within these environments is estimated with a large, costly, safety margin. The work of this thesis aims to improve the usefulness of an optical technique known as reflection anisotropy spectroscopy (RAS), which once fully characterised could allow materials to be actively monitored in such environments. The intrinsic optical anisotropy of the Cu(110) surface has been exploited to study nanoscale kinetics of ion bombarded surfaces. Within the Cu(110) RA spectrum the 2.1eV peak is particularly sensitive to surface defects and largely unaffected by the bulk of the substrate. Using the Poelsema-Comsa model (which assumes defects scatter surface electronic states within a patch centred on the defect) it can be demonstrated that at finite temperatures the decay of the 2.1eV peak contains information relating to the diffusion of surface defects. A kinetic Monte Carlo simulation has been created to model the destruction of this peak and allows further understanding of the diffusion processes involved. The decay of the 2.1eV peak with ion bombardment has been successfully modelled for a range of temperatures using experimental RAS data for comparison. Through a novel way of analysing RAS data, it has been shown that the total scattering cross section per ion impact decreases with bombardment time, which it is believed to be due to surface diffusion. This could give a novel way of measuring surface diffusion directly from RAS measurements. Clustering of ion induced surface defects has been analysed and the results found are consistent with STM images of the same surface obtained 30 minutes after bombardment. While molecular dynamics calculations have previously attempted to predict the surface topology and defect clustering nanoseconds after impact, using a kinetic Monte Carlo simulation improves on this, demonstrating that diffusion on long time scales (currently inaccessible using molecular dynamics calculations) play an important role in predicting nano-surface topology. 2.1eV peak recovery after surface damage by ion bombardment was also investigated. The peak was found to recover at finite temperatures, which is also seen in experimental data. It was concluded that the surface diffusivity values in the literature are too high and a new value for diffusivity has been calculated by comparing simulation and experimental data.

Le champ magnétique terrestre présente une vaste gamme de variations temporelles, de l'année à plusieurs millions d'années. J'ai étudié au cours de ma thèse divers aspects de ces fluctuations, des variations séculaires récentes aux renversements.La première partie de ma thèse porte sur l'archéomagnétisme, discipline qui permet de retracer l'évolution temporelle du champ magnétique terrestre au cours des derniers millénaires, principalement à partir des matériaux archéologiques. J'ai étudié deux jeux d'échantillons provenant pour l'un de la Grèce (période néolithique, 6800-3200 avant J.C.) et pour l'autre du Mexique (Palenque, période Maya Classique 320-840 après J.C.), dans le but d'acquérir de nouvelles données d'archéointensité et de mieux contraindre la variation séculaire du champ magnétique terrestre. La comparaison de mes données avec celles disponibles dans la bibliographie et avec les différents modèles globaux et régionaux a mis en évidence que les variations séculaires au Néolithique en Grèce et au cours du premier millénaire en Amérique Centrale sont très mal définies. Mes données suggèrent que des composantes locales, non prisent en compte dans les modèles globaux peuvent exister au niveau ces régions. Elles renforcent l'intérêt de développer des modèles régionaux précis, qui nécessitent un développement en harmoniques sphériques à un degré plus élevé. Pour ce faire, l'acquisition de nouvelles données de haute qualité est un élément majeur.La deuxième partie traite de la description d'un renversement du champ magnétique terrestre. Cette étude a été basée sur deux points précis: étudier les directions transitionnelles afin d'apporter de nouvelles contraintes sur le possible confinement longitudinal des pôles géomagnétiques virtuels (PGV) d'une part, et d'autre part vérifier des paléointensités transitionnelles obtenues sur la séquence volcanique d'Akaroa (Nouvelle Zélande), dont l'intensité est significativement supérieure à celles des intensités avant et après le renversement. Nous avons ré-échantillonné cette séquence, et l'évolution directionnelle obtenue pour ce renversement est une succession complexe de polarités N-T-R-T-N-T-R. Les PGV obtenus semblent se regrouper sous deux bandes longitudinales sous l'Australie et l'Amérique, ce qui renforce l'hypothèse d'une interaction entre le manteau et le noyau sur plusieurs millions d'années. Suite à une étude de minéralogie magnétique, j'ai sélectionné les échantillons susceptibles de fournir une valeur de paléointensité par les méthodes de Thellier et du multispecimen. Les paléointensités obtenues sont relativement faibles (environ 20 microT) au cours du changement de polarité et forte à la fin de la séquence. Mon interprétation, basée à la fois sur les valeurs de l'intensité du champ et sur les données radiochronologiques montrant que la séquence s'est mise en place très rapidement, est de considérer que seul le renversement C4Ar.1n-C4Ar.1r a été enregistré dans cette séquence. Dans cette hypothèse, le renversement montre un cheminement complexe comparable à d'autres renversements enregistrés dans l'hémisphère nord (Steens Mountain par exemple), incluant un phénomène de rebond avant de se stabiliser. La troisième partie de ma thèse est consacrée au développement d'une nouvelle méthodologie et d'un nouvel appareillage pour déterminer des paléointensités. Le faible taux de réussite des expériences de paléointensité de l'étude précédente m'a poussé à m'intéresser au protocole multispecimen, qui peut s'appliquer aux échantillons possédant un comportement polydomaine. L'inconvénient technique majeur de cette méthode réside dans l'application du champ le long de l'aimantation naturelle, difficile à réaliser avec précision dans les fours standards. Pour ce faire, nous avons décidé de développer des porte-échantillons permettant d'orienter les échantillons dans l'espace pour le four standard et un prototype de four à chauffage ultra-rapide particulièrement bie / The Earth's magnetic field shows a large range of temporal variations from the year to several million years. I studied during my PhD thesis several aspects of these fluctuations, from recent secular variations to reversals.The first part of my manuscript deals with archeomagnetism, a discipline that allows to track the temporal variations of the Earth's magnetic field through millennia, mainly from archeological materials. I studied two sets of samples, one from Greece (Neolithic period 6800-3200 B.C.) and the other from Mexico (Palenque, Maya Classic period 320-840 A.D.), to acquire new archeointensity data in order to better constrain the secular variation of the geomagnetic field. By comparing my data with those available in the literature and with the various global and regional models, I showed that the secular variations during the Neolithic in Greece and during the first millennium in Central America are poorly defined. My data suggest that local components, not described by global models, may exist in these regions. They reinforce the importance of developing specific regional models, which require development in higher spherical harmonic degree. As a consequence, the acquisition of new high quality data is of main importance. The second part presents the description of a geomagnetic field reversal. This work was based on two points: first by studying transitional directions to provide new constraints on the possible preferred longitudinal paths of virtual geomagnetic poles (VGPs) and second by checking transitional paleointensities obtained on a volcanic sequence in Akaroa volcano (New Zealand). Indeed the transitional field intensity is significantly higher than the field intensity before and after the reversal. We re-sampled this sequence, and the directional results show a complex sequence of N-T-R-T-N-T-R polarity. The transitional VGPs obtained are clustered in two longitudinal bands through Australia and America. This observation seems to reinforce the assumption of a core-mantle interaction over several million years. Following a rock magnetic study, I selected samples that could provide a value for the Thellier and multispecimen paleointensity methods. The obtained paleointensity are relatively low (about 20 microT) during the polarity change and strong at the end of the sequence.Based both on the field strength values and on the radiochronological ages, showing that the sequence was erupted in a very short time, I suggest that only the C4Ar.1n-C4Ar.1r reversal was recorded in this sequence. In this assumption, the reversal shows a complex path comparable to other reversals recorded in the northern hemisphere (for example the Steens Mountain), including a rebound before stabilizing.Finally the last part is devoted to the development of a new methodology and a new apparatus to determine absolute paleointensity. Following the low success rate of paleointensity experiments from the previous study, I decided to test the multispecimen protocol, which can be applied to samples yielding a predominant multidomaine behavior. The main technical drawback of this method lies in the application of the laboratory field along the natural remanent magnetization, a difficult task to perform accurately in standard paleointensity ovens. Thus, we decided to adapt sample holders from our standard oven in order to allow the sample orientation in space and to develop an ultra-fast heating oven prototype particularly well-suited for this method, allowing to apply the laboratory field in the 3 dimensions. I checked the different multispecimen protocols on historical lavas from Reunion and Etna volcano, yielding very different magnetic mineralogies. For all flows, I obtained paleointensities very close from the expected values, regardless from the magnetic mineralogy, revealing the feasibility of our apparatus and the promising interest of the method. The application of various corrections on the statistical estimation o

Call number: LD2668 .T4 1986 R57 / Master of Science / Mechanical and Nuclear Engineering