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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
131

Photopolymerized materials and patterning for improved performance of neural prosthetics

Tuft, Bradley William 01 July 2014 (has links)
Neural prosthetics are used to replace or substantially augment remaining motor and sensory functions of neural pathways that were lost or damaged due to physical trauma, disease, or genetics. However, due to poor spatial signal resolution, neural prostheses fail to recapitulate the intimate, precise interactions inherent to neural networks. Designing materials and interfaces that direct de novo nerve growth to spatially specific stimulating elements is, therefore, a promising method to enhance signal specificity and performance of prostheses such as the successful cochlear implant (CI) and the developing retinal implant. In this work, the spatial and temporal reaction control inherent to photopolymerization was used to develop methods to generate micro and nanopatterned materials that direct neurite growth from prosthesis relevant neurons. In particular, neurite growth and directionality has been investigated in response to physical, mechanical, and chemical cues on photopolymerized surfaces. Spiral ganglion neurons (SGNs) serve as the primary neuronal model as they are the principal target for CI stimulation. The objective of the research is to rationally design materials that spatially direct neurite growth and to translate fundamental understanding of nerve cell-material interactions into methods of nerve regeneration that improve neural prosthetic performance. A rapid, single-step photopolymerization method was developed to fabricate micro and nanopatterned physical cues on methacrylate surfaces by selectively blocking light with photomasks. Feature height is readily tuned by modulating parameters of the photopolymerizaiton including initiator concentration and species, light intensity, separation distance from the photomask, and radiation exposure time. Alignment of neural elements increases significantly with increasing feature amplitude and constant periodicity, as well as with decreasing periodicity and constant amplitude. SGN neurite alignment strongly correlates with the maximum feature slope. Neurite alignment is compared on unpatterned, unidirectional, and multidirectional photopolymerized micropatterns. The effect of substrate rigidity on neurite alignment to physical cues was determined by maintaining equivalent pattern microfeatures, afforded by the reaction control of photopolymerization, while concomitantly altering the composition of several copolymer platforms to tune matrix stiffness. For each platform, neurite alignment to unidirectional patterns increases with increasing substrate rigidity. Interestingly, SGN neurites respond to material stiffness cues that are orders of magnitude higher (GPa) than what is typically ascribed to neural environments (kPa). Finally, neurite behavior at bioactive borders of various adhesion modulating molecules was evaluated on micropatterned materials to determine which cues took precedence in establishing neurite directionality. At low microfeatures aspect ratios, neurites align to the pattern direction but are then caused to turn and repel from or turn and align to bioactive borders. Conversely, physical cues dominate neurite path-finding as pattern feature slope increases, i.e. aspect ratio of sloping photopolymerized features increases, causing neurites to readily cross bioactive borders. The photopolymerization method developed in this work to generate micro and nanopatterned materials serves as an additional surface engineering tool that enables investigation of cell-material interactions including directed de novo neurite growth. The results of this interdisciplinary effort contribute substantially to polymer neural regeneration technology and will lead to development of advanced biomaterials that improve neural prosthetic tissue integration and performance by spatially directing nerve growth.
132

Morphological studies of model and native environmental surface films

Grant, Jacob Scott 01 May 2019 (has links)
The body of work in this dissertation focuses on the properties of an environmental thin film system, including the roughness and composition of the surface. The deposition of particles, such as airborne soil and plant pollen, from the atmosphere creates a thin film known as “environmental film” or “urban film” that covers virtually all of Earth’s solid surfaces. Environmental films have been shown to accumulate a variety of chemicals, including toxic pollutants. To investigate the means by which environmental films uptake chemicals, model films are made in the lab and real films are collected outside. Model films serve to mimic the properties of native films and allow for a simple analysis of a complex system. Native films serve to provide real field samples to analyze. The properties of model and native films are characterized using reflected light to determine what the film is made of and microscopes capable of imaging small particles. The results of the model film study indicate a model capable of reproducing the surface roughness and other properties of native films. This study serves as a platform with the goal of making model films that better mimic native films. The results of the native film study indicate successful imaging using microscopes capable of revealing the structure and chemical composition of the films. This imaging adds an important contribution to the field that has not previously been performed.
133

A Cultural Topography of the Sovereign Citizens Movement: Are They a Terrorist Threat?

Biery, Piper Blotter 01 May 2014 (has links)
This thesis analyzes the Sovereign Citizens Movement—considered a domestic terrorist organization by the FBI— to determine if the label “terrorist organization” is appropriately applied, and then to assess the effectiveness of government protocols. The Sovereign Citizens Movement is a loose organization of individuals who adhere to an anti-government ideology. In most cases their actions are limited to fraudulent activity; however there have been individuals who resorted to violence in their engagements with government officials. This thesis concludes that the label “terrorist organization” does not describe the movement well, but that it is more likely that some individuals extrapolate the ideology and choose violence on their own, making them lone-wolf terrorists. Another conclusion of this thesis is that there needs to be a regular set of protocols established for all government agencies for interacting with Sovereigns. The method created by Rob Finch and Kory Flowers, which incorporates both law enforcement officials and legal professionals, provides the most effective way to interact with Sovereigns.
134

Home Range and Habitat Use of Santa Rosa Island Foxes (Urocyon littoralis santarosae)

Drake, Elizabeth Marie 01 March 2013 (has links)
Island foxes (Urocyon littoralis) are currently listed as federally endangered on four of the six Channel Islands to which they are endemic. The Santa Rosa Island (SRI) population declined by 99% during the 1990’s due to non-native golden eagle (Aguila chrysaetos) predation and is currently the lowest fox population (~280) and density (0.86 foxes/km2) of any of the Channel Islands. The goals of this study were to assess new miniaturized GPS technology and to quantify home range and habitat use of the SRI population. This is only the second use of Global Positioning System (GPS) collars on Channel Island foxes and provides essential baseline data for the recovering population. These results can be used to guide management decisions and future habitat restoration efforts after the recent removal of non-native ungulates. In fall 2009, 14 GPS collars were deployed on male foxes on the east side of SRI. Nine collars and three remote download datasets were recovered in 2010. The collars’ battery life was 40% lower than expected at an average (±SE) of 16.5 ± 1.7 weeks but had high performance in precision and fix rate. Collars yielded an average of 347 ± 33 locations with a fix rate of 82.3% ± 2.1% and 88% of locations categorized as high precision. From these data, 95% minimum convex polygon (MCP) home ranges and 95% kernel density isopleth (KDI) home ranges were created. The average 95% MCP home range size was 3.39 ± 0.59km2 and the area of overlap with adjacent home ranges had a median of 5.3%. The average 95% KDI home range size was 3.82 ± 0.68km2 with a median overlap of 6.0%. These home range sizes are almost triple the size reported in other island fox studies, likely due to the low fox densities in the recovering SRI population. Habitat analysis was performed using KDI home ranges and a Euclidian distance analysis (EDA) method to assess habitat selection within the study area, the home range and the core area. Results showed selection for lupine within the study area, which no previous studies have documented. There was no significant habitat selection within the home ranges or core areas. Foxes selected for valley bottom topography and for bare and grassland habitat at night. One shortcoming of EDA is that its reliance on random points for determining second order selection can lead to unused areas being identified as selected habitat. The lack of significant selection within home ranges and core areas may be attributed to small sample sizes, use of male foxes only and the timing of the study in relation to fox reproductive biology. I recommend further investigation in the use of lupine habitat and associated resources through prey inventory studies to further assess these findings. When densities reach historic levels of 4 foxes/km2, follow up studies should be conducted to reassess home range size, overlap and habitat use to determine if home range sizes have decreased and overlap has increased. Future studies should incorporate spring and summer seasons and females to determine if foxes select a particular habitat within the core area during denning and pupping periods.
135

Topographical Enhancement of Cell Adhesion on Poorly Adhesive Materials

Muniz Maisonet, Maritza 16 September 2015 (has links)
The overall thrust of this dissertation is to gain a fundamental understanding of the synergistic effects between surface topography and chemical functionality of poorly adhesive materials on enhancing the adhesion of mouse embryonic fibroblasts. Cellular response to surface topography and chemical functionality have been extensively studied on their own providing valuable information that helps in the design of new and improved biomaterials for tissue engineering applications. However, there is a lack of understanding of the synergistic effect of microscale and nanoscale topography with chemical functionality and the relative impact and contribution of each in modulating cellular behavior. By understanding the relationship between these cues, in particular using materials that are poorly adhesive, this study will provide new clues as to how cells adapt to their environment and also suggest new dimensions of biomaterial design for fine-tuning cellular control. A microstructure that combined non adhesive materials with defined surface topography and surface chemistry is presented, to assess and correlate the enhancement of mouse embryonic fibroblasts cell adhesion and spreading. Poly (N-isopropylacrylamide) or PNIPAAm electrospun fibers were overlaid on PNIPAAm thin films (100 nm) at various time points to investigate the role of topography on such coatings by keeping the chemical functionality the same. After doing this, several topographical patterns were developed, spanning from sparse to dense fiber mats, and cell adhesion strongly depended on the relative available areas for attachment on either the fibers or the supporting surface. To gain a better understanding of this finding, two surface chemistries, non-adhesive (self-assembled monolayer of polyethylene glycol (PEGSAM) alkanethiol on gold) or an adhesive coating (3-aminopropyltriethoxysilane (APTES) on glass) with well characterized adhesive properties were included in this study to assess the effect of topographical cues provided by the PNIPAAm electrospun fibers on cellular responses. With the deposition of the PNIPAAm fibers onto a PEGSAM surface, cell adhesion increased to almost 100%, and unlike the PNIPAAm surface, cell spreading was significantly enhanced. With the deposition of PNIPAAm fibers onto APTES, both cell adhesion and spreading were unaffected up to 60% fiber coverage. For both surfaces, PNIPAAm fiber densities above 60% coverage lead to adhesion and spreading independent of the underlying surface. These findings indicate the presence of a sparse topographical feature can stimulate cell adhesion on a typically non-adhesive material, and that a chemical dissimilarity between the topographic features and the background enhances this effect through greater cell-surface interaction. In addition to the aforementioned studies, cell response was also assessed on PNIPAAm thin films coatings with thicknesses ranging from 100 nm to 7 nm. Cell adhesion and spreading was enhanced as the thickness of the thin film decreased. This change was more noticeable below 30 nm, wherein 7 nm shows the highest cell adhesion and spreading enhancement. The results reported are preliminary results and further experiments will be conducted, to support the data. It is believed that cellular response was enhanced due to a change in surface topography at the nanoscale level.
136

Explicit use of road topography for model predictive cruise control in heavy trucks / Explicit användning av vägtopografi för modellprediktiv farthållningsfunktion i tunga fordon

Hellström, Erik January 2005 (has links)
<p>New and exciting possibilities in vehicle control are revealed by the consideration of topography through the combination GPS and three dimensional road maps. This thesis explores how information about future road slopes can be utilized in a heavy truck with the aim at reducing the fuel consumption over a route without increasing the total travel time. </p><p>A model predictive control (MPC) scheme is used to control the longitudinal behavior of the vehicle, which entails determining accelerator and brake levels and also which gear to engage. The optimization is accomplished through discrete dynamic programming. A cost function is used to define the optimization criterion. Through the function parameters the user is enabled to decide how fuel use, negative deviations from the reference velocity, velocity changes, gear shifts and brake use are weighed. </p><p>Computer simulations with a load of 40 metric tons shows that the fuel consumption can be reduced with 2.5% with a negligible change in travel time, going from Link¨oping to J¨onk¨oping and back. The road slopes are calculated by differentiation of authentic altitude measurements along this route. The complexity of the algorithm when achieving these results allows the simulations to run two to four times faster than real time on a standard PC, depending on the desired update frequency of the control signals.</p>
137

Driver training with look ahead

Stribeck, Robert January 2010 (has links)
<p>The ambition to lower fuel consumption has been a goal for the vehicle industrysince many years.  During the first oil crisis in the seventies this first came intolight and it has become more relevant during the last years climate change debate.Fuel costs are also an issue.  Reducing lifetime costs, in which fuel is 30 %, givesa competitive advantage to the vehicle producer.  Over the years the drive trainhas been made efficient to the point where a reduction in fuel consumption due toimprovements in the drive train is highly expensive to develop.  The fact that thedriver behavior is a big factor in the vehicle’s fuel consumption has recently comeinto attention.  This master thesis has been performed at Scania in Södertälje andpresents a way to give the driver advice in advance of difficult road segments.  Theadvice will help the driver drive in a fuel efficient manner. Focus is put on a specificcase where the vehicle approaches a downhill and advice is given for the driver tolet the vehicle coast up to the start of the downhill so that the vehicle can regainits speed in the downhill.  The detection of the downhill is made with look-aheadtechnology where a GPS and a digital 3D road map makes the topography of theroad segment ahead available.</p>
138

A finite element approach to the 3D CSEM modeling problem and applications to the study of the effect of target interaction andtopography

Stalnaker, Jack Lee 01 November 2005 (has links)
The solution of the secondary coupled-vector potential formulation of Maxwell??s equations governing the controlled-source electromagnetic (CSEM) response of an arbitrary, threedimensionalconductivitymodelmust be calculatednumerically.The finite elementmethod is attractive, because it allows the model to be discretized into an unstructured mesh, permitting the specification of realistic irregular conductor geometries, and permitting the mesh to be refined locally, where finer resolution is needed. The calculated results for a series ofsimple test problems, ranging from one-dimensionalscalar differentialequations to three-dimensional coupled vector equations match the known analytic solutions well, with error values several orders of magnitude smaller than the calculated values. The electromagnetic fields of a fully three-dimensional CSEM model, recovered from the potentials using the moving least squares interpolation numerical differentiation algorithm, compares well with published numerical modeling results, particularly when local refinement is applied. Multiple buried conductors in a conductive host interact via mutual induction and current flow through the host due to the dissipation of charge accumulated on the conductor boundary. The effect of this interaction varies with host conductivity, transmitter frequency, and conductor geometry, orientation, and conductivity. For three test models containingtwo highly conductive plate-like targets, oriented in various geometries (parallel, perpendicular, and horizontal), mutual coupling ranges as high as twenty times the total magnetic field. The effect of varying host conductivity is significant, especially at high frequencies. Numerical modeling also shows that the vorticity of the currents density induced in a vertically oriented plate-like conductor rotates from vertical at high frequencies, to horizontal at low frequencies, a phenomenon confirmed by comparison with time domain field data collected in Brazos County, Texas. Furthermore, the effect of the presence of a simple horst on the CSEM response of a homogeneous conductive earth is significant, even when the height of the horst is only a fraction of the skin depth of the model. When the transmitter is placedon topofthe horst, the currents inducedtherein account for nearly all of the total magnetic field of the model, indicating that topography, like mutual coupling must be accounted for when interpreting CSEM data.
139

The effects of meso-scale topography on the performance of engineered soil covers

Kelln, Christopher James 12 September 2008
Understanding the hydrological controls on subsurface flow and transport is of considerable importance in the study of reclaimed landscapes in the oil sands region of Canada. A significant portion of the reclaimed landscape will be comprised of a thin veneer (~ 1 m) of clay-rich reclamation soil overlying saline-sodic shale overburden, which is a waste by-product from the mining process. The global objective of this study was to investigate the first-order controls on soil moisture and salt transport dynamics within clay-rich reclamation covers overlying low permeability waste substrates. The study site is located in a cold, semi-arid climate in the oil sands region of northern Alberta. Preferential flow was the dominant mechanism responsible for the development of perched water table conditions on the cover-waste interface during the spring snow melt. Hydrological and geochemical data indicated that snowmelt infiltration occurs via the macroporosity while the ground is still frozen. An isotope hydrograph separation conducted on water collected in a weeping tile confirmed the presence of fresh snowmelt water at the onset of subsurface flow. This water transitions to a chemical signature that is comprised of approximately 80% connate pore water as a result of chemical equilibration between pore water in the soil matrix and fresh water in the macropores.<p>Detailed mapping of the spatial distribution of soil moisture and salts within a reclamation cover indicated the lower-slope positions are wetter due to the accumulation surface run-off and frozen ground infiltration in spring. Increased soil moisture conditions in lower-slope positions accelerate salt ingress, while drier conditions in middle and upper-slope positions attenuate salt ingress. The data indicated that fresh snowmelt water is bypassing the soil matrix higher in the cover profile. Subsurface flow and deep percolation are key mechanisms mitigating vertical salt ingress in lower and upper slope positions. The mesotopography of the cover-waste interface imposes a direct control on the depth of perched water and the downslope routing of water. Undulations in the cover-waste interface cause the depth of perched water to vary considerably (± 20 60 cm) over short distances (< 5 m), while saturated subsurface flow is routed through the lowest elevations in the cover profile. A numerical analysis of subsurface flow was able to simulate both the discharge rate and cumulative volume of flow to a weeping tile. Composite hydraulic functions were used in the simulations to account for the increased hydraulic conductivity and drainable porosity created by the macroporosity at near-saturated conditions. The transient Na+ concentration of discharge water was modelled using the concept of an equivalent porous medium. The good match between measured and modelled data verified the conceptual model, which contends that saturated subsurface flow is dominated by the fracture network and that the concentration of discharge water is function of the depth of perched water. Finally, the results from this study suggest the mesotopography of the cover-waste interface could be used to manage excess water and salts within the landscape.
140

Definition of topographic organization of skull profile In normal population and its implication on the role of sutures in skull morphology

Pirouzmand, Farhad 02 January 2007
Objectives<p>The geometric configuration of skull is complex and unique to each individual. The main objectives of this study are two fold: 1) to provide a new technique to define the outline of skull profile and 2) to find the common factors defining the ultimate skull configuration in adult population. The secondary objective was to explore the effect of age and sex on skull shape formation.<p>Materials & Methods <p>Ninety-three lateral skull x-ray from the CT scan films were selected and digitized. The lateral skull surface was divided into 3 regions based on the presumed location of coronal and lambdoid sutures. A software program (Canvas 7) was used to match the outer surface of lateral skull with circular curves. Three main curvatures (frontal, parietal, occipital) were consistently identified to overlap the skull periphery. The radius, cord length and inclination of each curvature were measured.. Factor analysis technique was also used to reduce the number of variables explaining the overall shape of skull. Student t-test and regression analysis was also used to explore the effect of sex and age on skull shape. <p>Results <p>There were total of 93 patients in this study (54% male). The average values for three defined curvatures of the skull profile were recorded. Factor analysis produced 3 factors. The first factor explained 32% of total variance and was related to the overall size of the head as represented by total length and the radius of the curvature in vertex and back of the head. The second factor covered 26% of the variance representing the inverse correlation between the angle of the frontal and parietal curves. The third factor revealed the direct correlation of occipital and parietal angle. In all of these factors, the frontal zone variation was independent or opposite of the parieto-occipital zone. A strong direct association between the total length of skull, occipital curve radius and length with the sex was shown. No age related variable was identified.<p>Conclusions <p>There is a large variation in the values of different part of the skull. The skull profile topography can be defined mathematically by two distinct territories: frontal and parieto-occipital zones. These territories hinge on the coronal suture. Therefore, coronal suture may play a dominant role in final skull configuration.

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