Since the 1970's, NASA has relied on the use of rigid aeroshells and supersonic parachutes to enable robotic mission to Mars. These technologies are constrained by size and deployment condition limitations that limit the payload they can deliver to the surface of Mars. One candidate technology envisioned to replace the supersonic parachute is the supersonic inflatable aerodynamic decelerator (IAD). This dissertation presents an overview of work performed in maturing a particular type of IAD, the tension cone. The tension cone concept consists of a flexible shell of revolution that is shaped so as to remain under tension and resist deformation. Systems analyses that evaluated trajectory impacts of a supersonic IAD demonstrated several key advantages including increases in delivered payload capability of over 40%, significant gains in landing site surface elevation, and the ability to accommodate growth in the entry mass of a spacecraft. A series of supersonic wind tunnel tests conducted at the NASA Glenn and Langley Research Centers tested both rigid and flexible tension cone models. Testing of rigid force and moment models and pressure models demonstrated the new design to have favorable performance including drag coefficients between 1.4 and 1.5 and static stability at angles of attack from 0º to 20º. A separate round of tests conducted on flexible tension cone models showed the system to be free of aeroelastic instability. Deployment tests conducted on an inflatable model demonstrated rapid, stable inflation in a supersonic environment. Structural modifications incorporated on the models were seen to reduce inflation pressure requirements by a factor of nearly two. Through this test program, this new tension cone IAD design was shown to be a credible option for a future flight system. Validation of CFD analyses for predicting aerodynamic IAD performance was also completed and the results are presented. Inviscid CFD analyses are seen to provide drag predictions accurate to within 6%. Viscous analyses performed show excellent agreement with measured pressure distributions and flow field characteristics. Comparisons between laminar and turbulent solutions indicate the likelihood of a turbulent boundary layer at high supersonic Mach numbers and large angles of attack.

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<p>The theme of this thesis is the reaction to fire performanceof wood and other building products, andparticularly thematerial fire properties time to ignition, rate of heat releaseand smoke production. These properties have been measured by asmall-scale fire test method, the Cone Calorimeter, andpresented for different types of building products.</p><p>Uncertainty analysis, included instrument and assumptionuncertainty, has been performed for the case that both O2 andCO2 are measured for calculation of the rate of heat release inthe Cone Calorimeter. The partial derivatives for theuncertainty analysis are given. The relative uncertainty forthe rate of heat release measurements in the Cone Calorimeteris between ±5% to ±10% for rate of heat releasevalues larger than about 50 kW/m2.</p><p>The time to ignition in the Cone Calorimeter is compatiblewith the time to ignition in the ISO Ignitability test, whichis the main test method for measuring time to ignition. Thetime to ignition is an increasing linear function of density.The rate of heat release in the Cone Calorimeter is dependentof material thickness and of use of retainer frame. Thematerial thickness gives the heat release curve duration andshape. Thin materials have short burning time and two maximumvalues. Thick materials have long burning time and when thematerial is thicker than about 35 mm no second maximum appears.When the retainer frame is used the actual exposed surface isreduced from 0.01 m2 to 0.0088 m2, the rate of heat release isreduced and the burning time is increased. A comparison ofresults with and without use of the retainer frame gives thenequal results when the exposed area is set to 0.0088 m2 in thecase of using the retainer frame.</p><p>The time to flashover in the full-scale room corner test waspredicted on the basis of Cone Calorimeter data at 50 kW/m2 bya power law of ignition time, the total heat release calculatedover 300 s after ignition and the density of the product. Therelation gives a simple relation to evaluate if a productreaches flashover in the room corner test.</p><p>The smoke production has also been measured in the ConeCalorimeter. The white light and the laser smoke measurementsystems have shown similar results. There is a correlationbetween Cone Calorimeter and room corner test smoke productionwhen the products are divided into groups: those that reachflashover in the room corner test in less than 10 min and thosethat have more than 10 min to flashover. Temperature profilesin wood have been measured in the Cone Calorimeter by a simpletechnique. The effect of fire protective gypsum plasterboardson the charring of wood frame members has been determined andcompared with fullscale furnace wall tests. The protectiveeffects of twenty different boards have been presented. ConeCalorimeter and furnace tests show similar charring of wooduntil the boards fall down in furnace tests. After that, thecharring of wood is higher in the furnace, because the wood isexposed directly to the fire.</p><p><b>Keywords:</b>building products, charring of wood, ConeCalorimeter, fire retardant treated wood, fire tests,ignitability, mass loss, rate of heat release, reaction tofire, smoke production, wood products</p>

As a consequence of the 2010 – 2011 Canterbury earthquake sequence, Christchurch experienced widespread liquefaction, vertical settlement and lateral spreading. These geological processes caused extensive damage to both housing and infrastructure, and increased the need for geotechnical investigation substantially. Cone Penetration Testing (CPT) has become the most common method for liquefaction assessment in Christchurch, and issues have been identified with the soil behaviour type, liquefaction potential and vertical settlement estimates, particularly in the north-western suburbs of Christchurch where soils consist mostly of silts, clayey silts and silty clays. The CPT soil behaviour type often appears to over-estimate the fines content within a soil, while the liquefaction potential and vertical settlement are often calculated higher than those measured after the Canterbury earthquake sequence. To investigate these issues, laboratory work was carried out on three adjacent CPT/borehole pairs from the Groynes Park subdivision in northern Christchurch. Boreholes were logged according to NZGS standards, separated into stratigraphic layers, and laboratory tests were conducted on representative samples. Comparison of these results with the CPT soil behaviour types provided valuable information, where 62% of soils on average were specified by the CPT at the Groynes Park subdivision as finer than what was actually present, 20% of soils on average were specified as coarser than what was actually present, and only 18% of soils on average were correctly classified by the CPT. Hence the CPT soil behaviour type is not accurately describing the stratigraphic profile at the Groynes Park subdivision, and it is understood that this is also the case in much of northwest Christchurch where similar soils are found. The computer software CLiq, by GeoLogismiki, uses assessment parameter constants which are able to be adjusted with each CPT file, in an attempt to make each more accurate. These parameter changes can in some cases substantially alter the results for liquefaction analysis. The sensitivity of the overall assessment method, raising and lowering the water table, lowering the soil behaviour type index, Ic, liquefaction cutoff value, the layer detection option, and the weighting factor option, were analysed by comparison with a set of ‘base settings’. The investigation confirmed that liquefaction analysis results can be very sensitive to the parameters selected, and demonstrated the dependency of the soil behaviour type on the soil behaviour type index, as the tested assessment parameters made very little to no changes to the soil behaviour type plots. The soil behaviour type index, Ic, developed by Robertson and Wride (1998) has been used to define a soil’s behaviour type, which is defined according to a set of numerical boundaries. In addition to this, the liquefaction cutoff point is defined as Ic > 2.6, whereby it is assumed that any soils with an Ic value above this will not liquefy due to clay-like tendencies (Robertson and Wride, 1998). The method has been identified in this thesis as being potentially unsuitable for some areas of Christchurch as it was developed for mostly sandy soils. An alternative methodology involving adjustment of the Robertson and Wride (1998) soil behaviour type boundaries is proposed as follows:  Ic < 1.31 – Gravelly sand to dense sand  1.31 < Ic < 1.90 – Sands: clean sand to silty sand  1.90 < Ic < 2.50 – Sand mixtures: silty sand to sandy silt  2.50 < Ic < 3.20 – Silt mixtures: clayey silt to silty clay  3.20 < Ic < 3.60 – Clays: silty clay to clay  Ic > 3.60 – Organics soils: peats. When the soil behaviour type boundary changes were applied to 15 test sites throughout Christchurch, 67% showed an improved change of soil behaviour type, while the remaining 33% remained unchanged, because they consisted almost entirely of sand. Within these boundary changes, the liquefaction cutoff point was moved from Ic > 2.6 to Ic > 2.5 and altered the liquefaction potential and vertical settlement to more realistic ii values. This confirmed that the overall soil behaviour type boundary changes appear to solve both the soil behaviour type issues and reduce the overestimation of liquefaction potential and vertical settlement. This thesis acts as a starting point towards researching the issues discussed. In particular, future work which would be useful includes investigation of the CLiq assessment parameter adjustments, and those which would be most suitable for use in clay-rich soils such as those in Christchurch. In particular consideration of how the water table can be better assessed when perched layers of water exist, with the limitation that only one elevation can be entered into CLiq. Additionally, a useful investigation would be a comparison of the known liquefaction and settlements from the Canterbury earthquake sequence with the liquefaction and settlement potentials calculated in CLiq for equivalent shaking conditions. This would enable the difference between the two to be accurately defined, and a suitable adjustment applied. Finally, inconsistencies between the Laser-Sizer and Hydrometer should be investigated, as the Laser-Sizer under-estimated the fines content by up to one third of the Hydrometer values.

Entangled polymeric fluids subjected to shear display a stress plateau through a range of shear rates. The formation of this plateau is often attributed to an entanglement-disentanglement transition in scientific literature. However, to our best knowledge in situ studies recovering the intermediate scattering function of polymer dynamics under shear have until now never been performed. This thesis documents the successful development of a high viscosity shear device whose interaction with polarized neutrons is small enough to allow use for Neutron Spin Echo spectroscopy. Further, first measurements towards the direct observation of the variation of the degree of entanglement throughout increasing shear are documented, albeit yet for too short Fourier times to measure beyond Rouse dynamics.

<p>A bench-top dual cone-beam computed tomography (CBCT) system was developed consisting of two orthogonally placed 40x30 cm<super>2</super> flat-panel detectors and two conventional X-ray tubes with two individual high-voltage generators sharing the same rotational axis. The X-ray source to detector distance is 150 cm and X-ray source to rotational axis distance is 100 cm for both subsystems. The objects are scanned through 200° of rotation. The dual CBCT (DCBCT) system utilized 110° of projection data from one detector and 90° from the other while the two individual single CBCTs utilized 200° data from each detector. The system performance was characterized in terms of uniformity, contrast, spatial resolution, noise power spectrum and CT number linearity. The uniformity, within the axial slice and along the longitudinal direction, and noise power spectrum were assessed by scanning a water bucket; the contrast and CT number linearity were measured using the Catphan phantom; and the spatial resolution was evaluated using a tungsten wire phantom. A skull phantom and a ham were also scanned to provide qualitative evaluation of high- and low-contrast resolution. Each measurement was compared between dual and single CBCT systems.</p><p>Compared with single CBCT, the DCBCT presented: 1) a decrease in uniformity by 1.9% in axial view and 1.1% in the longitudinal view, as averaged for four energies (80, 100, 125 and 150 kVp); 2) comparable or slightly better contrast to noise ratio (CNR) for low-contrast objects and comparable contrast for high-contrast objects; 3) comparable spatial resolution; 4) comparable CT number linearity with R<super>2</super> &#8805; 0.99 for all four tested energies; 5) lower noise power spectrum in magnitude. DCBCT images of the skull phantom and the ham demonstrated both high-contrast resolution and good soft-tissue contrast.</p><p>One of the major challenges for clinical implementation of four-dimensional (4D) CBCT is the long scan time. To investigate the 4D imaging capabilities of the DCBCT system, motion phantom studies were conducted to validate the efficiency by comparing 4D images generated from 4D-DCBCT and 4D-CBCT. First, a simple sinusoidal profile was used to confirm the scan time reduction. Next, both irregular sinusoidal and patient-derived profiles were used to investigate the advantage of temporally correlated orthogonal projections due to a reduced scan time. Normalized mutual information (NMI) between 4D-DCBCT and 4D-CBCT was used for quantitative evaluation.</p><p>For the simple sinusoidal profile, the average NMI for ten phases between two single 4D-CBCTs was 0.336, indicating the maximum NMI that can be achieved for this study. The average NMIs between 4D-DCBCT and each single 4D-CBCT were 0.331 and 0.320. For both irregular sinusoidal and patient-derived profiles, 4D-DCBCT generated phase images with less motion blurring when compared with single 4D-CBCT.</p><p>For dual kV energy imaging, we acquired 80kVp projections and 150 kVp projections, with an additional 0.8 mm tin filtration. The virtual monochromatic (VM) technique was implemented, by first decomposing these projections into acrylic and aluminum basis material projections to synthesize VM projections, which were then used to reconstruct VM CBCTs. The effect of the VM CBCT on metal artifact reduction was evaluated with an in-house titanium-BB phantom. The optimal VM energy to maximize CNR for iodine contrast and minimize beam hardening in VM CBCT was determined using a water phantom containing two iodine concentrations. The linearly-mixed (LM) technique was implemented by linearly combining the low- (80kVp) and high-energy (150kVp) CBCTs. The dose partitioning between low- and high-energy CBCTs was varied (20%, 40%, 60% and 80% for low-energy) while keeping total dose approximately equal to single-energy CBCTs, measured using an ion chamber. Noise levels and CNRs for four tissue types were investigated for dual-energy LM CBCTs in comparison with single-energy CBCTs at 80, 100, 125 and 150kVp.</p><p>The VM technique showed a substantial reduction of metal artifacts at 100 keV with a 40% reduction in the background standard deviation compared with a 125 kVp single-energy scan of equal dose. The VM energy to maximize CNR for both iodine concentrations and minimize beam hardening in the metal-free object was 50 keV and 60 keV, respectively. The difference in average noise levels measured in the phantom background was 1.2% for dual-energy LM CBCTs and equivalent-dose single-energy CBCTs. CNR values in the LM CBCTs of any dose partitioning were better than those of 150 kVp single-energy CBCTs. The average CNRs for four tissue types with 80% dose fraction at low-energy showed 9.0% and 4.1% improvement relative to 100 kVp and 125 kVp single-energy CBCTs, respectively. CNRs for low contrast objects improved as dose partitioning was more heavily weighted towards low-energy (80kVp) for LM CBCTs.</p><p>For application of the dual-energy technique in the kilovoltage (kV) and megavoltage (MV) range, we acquired both MV projections (from gantry angle of 0° to 100°) and kV projections (90° to 200°) with the current orthogonal kV/MV imaging hardware equipped in modern linear accelerators, as gantry rotated a total of 110°. A selected range of overlap projections between 90° to 100° were then decomposed into two material projections using experimentally determined parameters from orthogonally stacked aluminum and acrylic step-wedges. Given attenuation coefficients of aluminum and acrylic at a predetermined energy, one set of VM projections could be synthesized from two corresponding sets of decomposed projections. Two linear functions were generated using projection information at overlap angles to convert kV and MV projections at non-overlap angles to approximate VM projections for CBCT reconstruction. The CNRs were calculated for different inserts in VM CBCTs of a CatPhan phantom with various selected energies and compared with those in kV and MV CBCTs. The effect of overlap projection number on CNR was evaluated. Additionally, the effect of beam orientation was studied by scanning the CatPhan sandwiched with two 5 cm solid-water phantoms on both lateral sides and an electronic density phantom with two metal bolt inserts.</p><p>Proper selection of VM energy (30keV and 40keV for low-density polyethylene (LDPE), polymethylpentene (PMP), 2MeV for Delrin) provided comparable or even better CNR results as compared with kV or MV CBCT. An increased number of overlap between kV and MV projections demonstrated only marginal improvements of CNR for different inserts (with the exception of LDPE) and therefore one projection overlap was found to be sufficient for the CatPhan study. It was also evident that the optimal CBCT image quality was achieved when MV beams penetrated through the heavy attenuation direction of the object. </p><p>In conclusion, the performance of a bench-top DCBCT imaging system has been characterized and is comparable to that of a single CBCT. The 4D-DCBCT provides an efficient 4D imaging technique for motion management. The scan time is reduced by approximately a factor of two. The temporally correlated orthogonal projections improved the image blur across 4D phase images. Dual-energy CBCT imaging techniques were implemented to synthesize VM CBCT and LM CBCTs. VM CBCT was effective at achieving metal artifact reduction. Depending on the dose-partitioning scheme, LM CBCT demonstrated the potential to improve CNR for low contrast objects compared with single-energy CBCT acquired with equivalent dose. A novel technique was developed to generate VM CBCTs from kV/MV projections. This technique has the potential to improve CNR at selected VM energies and to suppress artifacts at appropriate beam orientations.</p> / Dissertation

Acquiring knowledge of the morphological, molecular, and functional changes that occur to neurons following axotomy is a key step for a comprehensive understanding of the nervous system and how it reacts to injury. Propriospinal commissural interneurons (PCIs or CINs) are a class of neuron with axons that project through the ventral commissure to the contralateral spinal cord. My goal was to examine the morphological, molecular, and functional changes that occur to adult feline PCIs following a proximal axotomy. We first determined whether proximally axotomized PCIs develop de novo axons from their dendrites. C3 PCIs were proximally axotomized and several weeks later we stained PCIs and prepared the tissue for histological evaluation. Two primary classes of axotomized PCI were identified: those with a very short axon (called permanently axotomized) and those with an axon that projected across the injury site. Permanently axotomized PCIs had processes with morphological features typical of axons that emerged from their distal dendrites. These axonal processes of the distal dendrites also had GAP-43 (an axonal marker) and lacked MAP2a/b (a dendritic marker). We concluded that permanently axotomized PCIs develop de novo axons from distal dendrites. We then determined whether the axons that crossed the lesion site were representative of spontaneous functional regeneration. First, we showed that PCI axons regenerate through an environment that is typically highly inhibitory to regenerating axons. Second, we established that the regenerated axons conduct action potentials. Finally, we found that regenerated PCI axons form functional synaptic connections with neurons in the contralateral spinal cord. Collectively, these data indicated that spinal interneurons are capable of spontaneous functional regeneration through an injured spinal cord. PCI growth cones are complex and unlike growth cones previously described in the literature. The final study of the thesis examines the morphologies of PCI growth cones within spinal cord injury sites. We found that PCI growth cones have a wide range of morphologies that is independent of their location within the lesion site. Taken together, these data indicate that PCIs have a remarkable capacity for axonal elongation and contribute to remodelling of spinal circuitry following spinal injury. / Thesis (Ph.D, Physiology) -- Queen's University, 2009-12-07 11:21:47.036

The overall objective of this thesis was to understand better the mechanisms that shape the diversity in colour vision of fish, and to explore the adaptive significance of this divergence. Among the vertebrates, teleost fish show the greatest diversity in colour vision systems. The cichlid model system illustrates that the visual system of fish may differ among species, sexes, individuals, and life stages of individuals. The large number of available cone opsin genes, which have resulted from multiple opsin gene duplications, facilitates this high degree of variation in the mechanisms of colour vision. In general, cichlids possessed complements of four to five cone pigments, and these complements varied across species, sexes, and individuals. Additionally, lens transmission, cone pigment expression, post-receptoral sensitivity, and retinal circuitry differed across life stages of individuals. My results suggest that the diversification of colour vision across species and across life stages of individuals contributes to sensory adaptations that enhance both the contrast of zooplanktonic prey, and the detection of optical signals from conspecifics. Therefore, both natural and sexual selection may have worked in concert to shape colour vision in fish. Since light is more complex under water than on land, fish required four to six cone classes to reconstruct the colour signals reflected from aquatic objects. This suggests that the large number of cone pigments in fish have likely evolved to enhance the reconstruction of the complex colour-signals in aquatic environments. Taken together, these findings improve our understanding of the variable nature of fish colour vision, and, more generally, help unravel the evolution of photoreceptors and colour vision. / Thesis (Ph.D, Biology) -- Queen's University, 2012-05-14 13:16:50.276

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal

X-ray scatter in cone-beam computed tomography (CBCT) is known to reduce image quality by introducing image artifacts, reducing contrast, and limiting computed tomography (CT) number accuracy. The extent of the effect of x-ray scatter on CBCT image quality is determined by the shape and magnitude of the scatter distribution in the projections. A method to allay the effects of scatter is imperative to enable application of CBCT to solve a wider domain of clinical problems. The work contained herein proposes such a method. A characterization of the scatter distribution through the use of a validated Monte Carlo (MC) model is carried out. The effects of imaging parameters and compensators on the scatter distribution are investigated. The spectral frequency components of the scatter distribution in CBCT projection sets are analyzed using Fourier analysis and found to reside predominately in the low frequency domain. The exact frequency extents of the scatter distribution are explored for different imaging configurations and patient geometries. Based on the Fourier analysis it is hypothesized the scatter distribution can be represented by a finite sum of sine and cosine functions. The fitting of MC scatter distribution estimates enables the reduction of the MC computation time by diminishing the number of photon tracks required by over three orders of magnitude. The fitting method is incorporated into a novel scatter correction method using an algorithm that simultaneously combines multiple MC scatter simulations. Running concurrent MC simulations while simultaneously fitting the results allows for the physical accuracy and flexibility of MC methods to be maintained while enhancing the overall efficiency. CBCT projection set scatter estimates, using the algorithm, are computed on the order of 1-2 minutes instead of hours or days. Resulting scatter corrected reconstructions show a reduction in artifacts and improvement in tissue contrast and voxel value accuracy.