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The Global ETD Search service is a free service for researchers
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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.
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Showing 101 to 104 of 104 (0.063 seconds)| 101 |
Robot navigation in sensor spaceKeeratipranon, Narongdech January 2009 (has links)
This thesis investigates the problem of robot navigation using only landmark bearings. The proposed system allows a robot to move to a ground target location specified by the sensor values observed at this ground target posi- tion. The control actions are computed based on the difference between the current landmark bearings and the target landmark bearings. No Cartesian coordinates with respect to the ground are computed by the control system. The robot navigates using solely information from the bearing sensor space. Most existing robot navigation systems require a ground frame (2D Cartesian coordinate system) in order to navigate from a ground point A to a ground point B. The commonly used sensors such as laser range scanner, sonar, infrared, and vision do not directly provide the 2D ground coordi- nates of the robot. The existing systems use the sensor measurements to localise the robot with respect to a map, a set of 2D coordinates of the objects of interest. It is more natural to navigate between the points in the sensor space corresponding to A and B without requiring the Cartesian map and the localisation process. Research on animals has revealed how insects are able to exploit very limited computational and memory resources to successfully navigate to a desired destination without computing Cartesian positions. For example, a honeybee balances the left and right optical flows to navigate in a nar- row corridor. Unlike many other ants, Cataglyphis bicolor does not secrete pheromone trails in order to find its way home but instead uses the sun as a compass to keep track of its home direction vector. The home vector can be inaccurate, so the ant also uses landmark recognition. More precisely, it takes snapshots and compass headings of some landmarks. To return home, the ant tries to line up the landmarks exactly as they were before it started wandering. This thesis introduces a navigation method based on reflex actions in sensor space. The sensor vector is made of the bearings of some landmarks, and the reflex action is a gradient descent with respect to the distance in sensor space between the current sensor vector and the target sensor vec- tor. Our theoretical analysis shows that except for some fully characterized pathological cases, any point is reachable from any other point by reflex action in the bearing sensor space provided the environment contains three landmarks and is free of obstacles. The trajectories of a robot using reflex navigation, like other image- based visual control strategies, do not correspond necessarily to the shortest paths on the ground, because the sensor error is minimized, not the moving distance on the ground. However, we show that the use of a sequence of waypoints in sensor space can address this problem. In order to identify relevant waypoints, we train a Self Organising Map (SOM) from a set of observations uniformly distributed with respect to the ground. This SOM provides a sense of location to the robot, and allows a form of path planning in sensor space. The navigation proposed system is analysed theoretically, and evaluated both in simulation and with experiments on a real robot.
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Defining the mechanism of prostaglandin E₂-enhanced hematopoietic stem and progenitor cell homingSpeth, Jennifer M. 02 April 2014 (has links)
Indiana University-Purdue University Indianapolis (IUPUI) / Hematopoietic stem cell (HSC) transplantation is a lifesaving therapy for a number of hematological disorders. However, to be effective, transplanted HSCs must efficiently “home” to supportive niches within the bone marrow. Limited HSC number and poor function are complications of transplant in some circumstances, and can lead to delayed engraftment and immune reconstitution, or in some cases, bone marrow failure. Enhancing HSC homing is a strategy to improve stem cell transplantation efficiency. We have previously shown that ex vivo treatment of mouse or human HSCs with 16-16 dimethyl PGE2 (dmPGE2) increases their bone marrow homing efficiency and engraftment, resulting in part from upregulation of surface CXCR4 expression. We now show that pulse-treatment of mouse or human HSPCs with dmPGE2 stabilizes HIF1α in HSPCs, and that similar treatment with the hypoxia mimetic DMOG produces analogous effects to dmPGE2 on HSPC CXCR4 expression and homing. This suggests that HIF1α is responsible for PGE2’s enhancing effects on HSPCs. Pharmacological inhibition of HIF1α stabilization in vitro with Sodium Nitroprusside (SNP), confirms the requirement of HIF1α for dmPGE2-enhanced migration and CXCR4 upregulation. Additionally, we confirm the requirement for HIF1α in dmPGE2-enhanced in vivo homing using a conditional knockout mouse model of HIF1α gene deletion. Finally, we validate that the hypoxia response element located 1.3kb from the transcriptional start site within the CXCR4 promoter is required for enhanced CXCR4 expression after PGE2 treatment. Interestingly, we also observe an increase in the small GTPase Rac1 after dmPGE2 treatment, as well as a defect in PGE2-enhanced migration and CXCR4 expression in Rac1 knockout HSPCs. Using state-of-the-art imaging technology we, confirm an increase in Rac1 and CXCR4 colocalization after dmPGE2 treatment that likely explains enhanced sensitivity of PGE2-treated HSPCs to SDF-1. Taken together, these results define a precise mechanism through which ex vivo pulse treatment of HSPC with dmPGE2 enhances HSPC function through alterations in cell motility and homing, and describe a role for hypoxia and HIF1α in enhancement of hematopoietic transplantation.
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Impact of ALCAM (CD166) on homing of hematopoietic stem and progenitor cellsAleksandrova, Mariya Aleksandrova 18 December 2012 (has links)
Indiana University-Purdue University Indianapolis (IUPUI) / The potential of hematopoietic stem cells (HSC) to home and to anchor within the bone marrow (BM) microenvironment controls the ability of transplanted HSCs to establish normal hematopoiesis. Activated Leukocyte Cell Adhesion Molecule (ALCAM; also identified as CD166), which participates in homophilic interactions, is expressed on a group of osteoblasts in the hematopoietic niche capable of sustaining functional HSC in vitro. Since we could also detect ALCAM expression on HSC, we suspect that ALCAM may play a role in anchoring primitive hematopoietic cells to ALCAM expressing components of the hematopoietic niche via dimerization. We investigated the role of ALCAM on the homing abilities of hematopoietic stem and progenitor cells (HSPC) by calculating recovery frequency of Sca-1+ALCAM+ cells in an in vivo murine bone marrow transplantation model. Our data supports the notion that ALCAM promotes improved homing potential of hematopoietic Sca-1+ cells. Recovery of BM-homed Sca-1+ cells from the endosteal region was 1.8-fold higher than that of total donor cells. However, a 3.0-fold higher number of Sca-1+ALCAM+ cells homed to the endosteal region compared to total donor cells. Similarly, homed Sca-1+ALCAM+ cells were recovered from the vascular region at 2.1-fold greater frequency than total homed donor cells from that region, compared to only a 1.3-fold increase in the recovery frequency of Sca-1+ cells. In vitro quantitation of clonogenic BM-homed hematopoietic progenitors corroborate the results from the homing assay. The frequency of in vitro clonogenic progenitors was significantly higher among endosteal-homed Sca-1+ALCAM+ cells compared to other fractions of donor cells. Collectively, these data demonstrate that engrafting HSC expressing ALCAM home more efficiently to the BM and within the BM microenvironment, these cells preferentially seed the endosteal niche.
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Exploratory study of market entry strategies for digital payment platformsMarcinkowska, Anna January 2018 (has links)
The digital payment industry has become one of the fastest evolving markets in the world, but in the wake of its rapid advancement, an ever increasing gap between academic theory and the actual reality of this market widens - and especially so when it comes to entry theory. It is widely acknowledged that the world is moving towards an ever more homogeneous economy, but despite the fact that payment preferences differ greatly from country to country - research on this subject continues to revolve mainly around localized efforts. But as historical inequalities between poor and rich societies continue to dissipate - learning from nations at the forefront of technological advancement increases the likelihood that the developed strategy becomes applicable to an increased number of countries. By selecting a nation most conducive to technological growth, the purpose of this report is to map the present dynamics in its digital payment industry using both recent and traditional market entry theory. However, studies geared towards globalized strategy formulation cannot be assumed as having guaranteed access to internal company-data at all times. So in order to facilitate such studies, the level of dependency on primary data required for conducting such research needs to be understood first, which is why the work in this report is constrained strictly to data of secondary nature. This, not only to further map the characteristics of this market, but also to see how open the market is to public inspection. Ultimately, the academic contribution becomes that of providing a road-map towards adapting currently available market entry theory to suit the rapidly evolving conditions of the digital payment industry from a global perspective and, when failing to do so, the aim is to also explore avenues for further research towards this end goal.
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