The performance of an ultra-short baseline (USBL) positioning system is limited by noises and errors from physical environment and other sources. One of the major errors in USBL positioning is to neglect the sensor misalignment which produces static yaw, pitch, and roll offsets. In this study, a circular survey observation scheme is first proposed to study the positioning errors of a USBL system with a fixed seabed transponder. The center of the circular survey scheme is assumed to be located over the top of the transponder. Mathematical equations of the transponder positioning with yaw, pitch, and roll offsets are derived, respectively. According to characteristics of positioning errors arose from yaw, pitch, and roll offsets, an iterative procedure of first getting roll offset, next computing yaw offset, and then obtaining pitch offset for sensor misalignment correction is established. Simulation results indicate that the iterative procedure can effectively obtain all offsets with high determination accuracy and the computation can rapidly converge to desired error tolerance in a few iterations. However, the center of circular vessel survey scheme is almost impossible to be exactly located over the top of the transponder. In such a case, the horizontal positioning error resulting from pitch offset or roll offset is no more a circle function. As a result, it will fail to evaluate the angle offsets through above iterative procedure unless the deviation from real and estimate horizontal transponder position is extremely small comparing to the transponder depth. Therefore, in addition to circular survey scheme, this study proposed a straight survey scheme to study the patterns of positioning error resulting from yaw, pitch, and roll offsets. Similar to the philosophy of establishing the iterative procedure described above, the iterative procedure of first getting pitch offset, next computing roll offset, and then obtaining yaw offset for sensor misalignment correction is established. Again, simulation results show that the iterative procedure can find all offsets with high determination accuracy and has the advantage of quick converging. Besides, the iterative procedure can still obtain correct angle offsets even though there is a constant heading deviation from the direction of the straight vessel track during vessel survey.

Thesis (M.Sc. (Physics & Electronics)) - Rhodes University, 2008.

During the last decade, many baseline estimation methods have been proposed, but many of these approaches are either only useful for specific kinds of analytical signals or require the adjustment of many parameters. This complicates the selection of an appropriate approach for each kind of chemical signal and the optimization of multiple parameters itself is not an easy task. In this work, an asymmetric least squares (ALS) approach is used with truncated and augmented Fourier basis functions to provide a universal basis space for baseline approximation for diverse analytical signals. The proposed method does not require extensive parameter adjustment or prior baseline information. The basis set used to model the baselines includes a Fourier series truncated to low frequency sines and cosines (consistent with the number of channels) which is then augmented with lower frequencies. The number of basis functions employed depends mainly on the frequency characteristics of the baseline, which is the only parameter adjustment required for baseline estimation. The weighting factor for the asymmetric least squares in this case is dependent mainly on the level of the noise. The adjustment of these two parameters can be easily performed by visual inspection of results. To estimate and eliminate the baseline from the analytical signals, a novel algorithm, called Truncated Fourier Asymmetric Least Squares (TFALS) was successfully developed and optimized. It does not require baseline representative signals or extensive parameter adjustments. The method is described only with parameters optimization using simulated signals. The results with simulated and experimental data sets having different baseline artefacts show that TFALS is a versatile, effective and easy-to-use baseline removal method.

No description available.

Αντικείμενο της εργασίας είναι η δημιουργία ενός ολοκληρωμένου συστήματος με DSP για λήψη, κωδικοποίηση σύμφωνα με το πρότυπο JPEG και αποστολή εικόνας με τη βοήθεια του πρωτοκόλλου TCP/IP. Η ανάπτυξη της εφαρμογής έγινε σε γλώσσα προγραμματισμού c, ενώ ο έλεγχος του συστήματος γίνεται μέσω ενός γραφικού περιβάλλοντος αλληλεπίδρασης με το χρήστη. Στο πρώτο κεφάλαιο περιγράφεται η αναπτυξιακή πλατφόρμα DSK C6416T. Γίνεται αναφορά στην αρχιτεκτονική του επεξεργαστή ψηφιακού σήματος TMSC3206416T της εταιρείας Texas Instruments καθώς και στις υπόλοιπες περιφερειακές συσκευές. Στο δεύτερο κεφάλαιο περιγράφεται η αρχιτεκτονική της θυγατρικής κάρτας DSKeye Gigabit της εταιρείας Bitec, που συνδέεται στο DSK. Η κάρτα αυτή διαχειρίζεται τα δεδομένα για την αποστολή τους μέσω TCP/IP, καθώς και την έγχρωμη κάμερα OV5610 της εταιρείας Omnivision, η οποία είναι απαραίτητη για τη λήψη των εικόνων. Περιγράφεται επίσης ο τρόπος διασύνδεσης όλων των συσκευών από άποψη υλικού, ενώ στη συνέχεια περιγράφεται και η διασύνδεση λογισμικού. Στο τρίτο κεφάλαιο γίνεται αναλυτική περιγραφή του προτύπου JPEG, ιδιαίτερα του τμήματος που αναφέρεται στο Baseline DCT. Ακολουθεί παράδειγμα με το οποίο γίνεται κατανοητή η διαδικασία κωδικοποίησης σύμφωνα με το JPEG πρότυπο. Στο τέταρτο κεφάλαιο περιγράφεται η υλοποίηση του συστήματος, το διάγραμμα ροής του βασικού προγράμματος ενώ παρουσιάζονται τα αποτελέσματα με τη βοήθεια του γραφικού περιβάλλοντος. Τέλος στο παράρτημα αναφέρονται τα είδη EDMA μεταφορών και τρόποι προγραμματισμού. / This master thesis main purpose is to create a complete system using a DSP, for capturing images, encoding them according to the ISO/IEC 10918-1 specification widely known as JPEG and sending them to a remote client using the TCP/IP protocol. The source code was developed using the c programming language and a GUI was built in order to act as the remote client and also to control the capturing procedure. In the first chapter we review the C6416T DSP starter kit module, which incorporates the Texas Instruments 1GHz TMS320C6416T processor. In the next chapter we analyse the DSKeye gigabit daughtercard made by Bitec. This board features a 5.2 Megapixel colour camera used for capturing the desired images in Bayern format and also a gigabit Ethernet interface, allowing us to establish the TCP/IP communication. The following chapter explains the theoretical aspects of a baseline DCT JPEG encoder, laying emphasis on the details of the encoding procedure. Finally we present the flow charts and we summarise our results. The current project is a follow up to Bitec’s “webview” example, which uses the above hardware in order to capture and send a true colour bitmap image to a web browser. We used the DSKeye API with slight modifications in order to overcome memory restrictions imposed by image resolution and overall code size. The TCP stack was accessed using the BSD socket API. The encoder was ported to the DSP from the free JPEG c code available from the Independent JPEG Group. It was developed and tested using Microsoft’s Visual Studio 2005 Express Edition as well as TI’s Code Composer Studio v3.1. Finally the GUI was created using Labview 8.0.

This thesis reports the calibration, imaging and analysis of one epoch of VLBA observations of the 1612 MHz OH maser emission from the protoplanetary nebula OH 0.9+1.3. These are the first polarisation VLBI observations of this source and the spatial morphology of the OH emission is resolved on this scale. Proto-planetary nebulae represent the transition phase in the evolution of stars between the asymptotic giant branch (AGB) phase and their emergence as planetary nebulae. A long-standing astronomical question is how the predominantly spherical circumstellar envelopes of AGB stars evolve into the bipolar and axisymmetric structures that are commonly observed in planetary nebula. Proto-planetary nebulae offer a unique opportunity to study this transformation process. The high-resolution VLBI maps produced in this thesis were used to investigate the morphology and kinematics of OH 0.9+1.3 with a view to gaining insight into the development of asymmetries in the circumstellar material. The OH maser emission of OH 0.9+1.3 has a double-peaked profile with one peak blue-shifted and the other red-shifted with respect to the stellar velocity. The total intensity maser maps demonstrate a considerable degree of asymmetry with the blue- and red-shifted emission located in spatially distinct regions of the envelope. The blue-shifted emission is distributed preferentially along an axis at a projected position angle of » 135± ( North through East). The morphology of this source is not consistent with the standard symmetric thin-shell model and an attempt to fit the traditional OH/IR kinematic model of a simple expanding shell to the maser components was found to be unsatisfactory. No definitive evidence of a bipolar outflow was observed either. The high degree of asymmetry observed in the source is consistent with its status as a proto-planetary nebula. The source was imaged in all four Stokes parameters and the fractional linear and circular polarisations of the maser components were derived from the Stokes parameter maps. In all except one of the components the total fractional polarisation was found to be low ( < 15%). The mean fractional linear and circular polarisation were calculated to be 5.54% and 7.11% respectively. The absence of an identifiable Zeeman pair in the Stokes V map prohibited the estimation of the magnetic field in the circumstellar envelope of this source.

This thesis reports the results of an investigation into techniques for the calibration and imaging of spectral line polarization observations in Very Long Baseline Interferometry (VLBI). A review is given of the instrumental and propagation effects which need to be removed in the course of calibrating such obervations, with particular reference to their polarization dependence. The removal of amplitude and phase errors and the determination of the instrumental feed response is described. The polarization imaging of such data is discussed with particular reference to the case of poorly sampled cross-polarization data. The software implementation of the algorithms within the Astronomical Image Processing System (AlPS) is discussed and the specific case of spectral line polarization reduction for data observed using the MK3 VLBI system is considered in detail. VLBI observations at two separate epochs of the 1612 MHz OH masers towards the source IRC+ 10420 are reduced as part of this work. Spectral line polarization maps of the source structure are presented, including a discussion of source morphology and variability. The source is sigmficantly circularly polarized at VLBI resolution, but does not display appreciable linear polarization. A proper motion study of the circumstellar envelope is presented, which supports an ellipsoidal kinematic model with anisotropic radial outflow. Kinematic modelling of the measured proper motions suggests a distance to the source of ~ 3 kpc. The cirumstellar magnetic field strength in the masing regions is determined as 1-3 mG, assuming Zeeman splitting as the polarization mechanism.

The aim of this thesis is to perform observational tests of SiO maser polarisation and excitation models, using component-level comparisons of multiple SiO maser transitions in the 43 GHz and 86 GHz bands at milliarcsecond resolution. These observations reqwre very long baseline interferometric imaging with very accurate polarimetric calibration. The supergiant star VY CMa was chosen as the object of this study due to its high SiO maser luminosity, many detected SiO maser lines, and intrinsic scientific interest. Two epochs of full-polarisation VLBA observations of VY CMa were performed. The Epoch 2 observations were reduced using several new data reduction methods developed as part of this work, and designed specifically to improve the accuracy of circular polarisation calibration of spectral-line VLBI observations at millimetre wavelengths. The accuracy is estimated to be better than 1% using these methods. The Epoch 2 images show a concentration of v= l and v=2 J= 1-0 SiO masers to the east and northeast of the assumed stellar position. The v=l J=2-1 masers were more evenly distributed around the star, with a notable lack of emission in the northeast. There is appreciable spatial overlap between these three lines. The nature of the overlap is generally consistent with the predictions of hydrodynamical circumstellar SiO maser simulations. Where the v=l J = 1-0 and J =2-1 features overlap, the v=l J = 2-1 emission is usually considerably weaker. This is not predicted by current hydrodynamical models, but can be explained in the context of collisional pumping in a low density environment. Six observational tests of weak-splitting maser polarisation models were performed, including intercomparisons of linear polarisation in the v=l J=1-0 and J=2-1lines, linear polarisation versus saturation level, linear polarisation versus distance from the star, circular polarisation in the v= l J = 1-0 and J=2-1 lines, circular versus linear polarisation and modeling of ~ 900 electric-vector position angle rotations. The polarisation model tests generally do not support non-Zeeman circular polarisation mechanisms. For the linear polarisation tests, the results are more consistent with models that predict similar linear polarisation across transitions. The scientific importance of these tests is described in detail and avenues for future work are described.

Magister Scientiae (Biodiversity and Conservation Biology) - MSc (Biodiv and Cons Biol) / The geometric tortoise is one of the world‟s rarest terrestrial tortoises and is endemic to the Southwestern Cape, South Africa. There has been cause for conservation concern for Psammobates geometricus, yet as is common for many species, quantitative physiological research has been lacking. Considering the important role of red blood cells in oxygen circulation, and the role of white blood cells in immune resistance, blood profiles have been used across taxa as a reliable indicator of health status and physiological processes. Forming part of a larger chelonian conservation programme in South Africa, I studied the haematological changes in P. geometricus, to better understand their physiological responses to changes in climatic conditions. Sampled peripheral blood from males, females and juveniles of the largest known wild geometric tortoise population over four seasons (spring, summer, autumn and winter) from August 2000 to June 2001. Blood samples were used to make smears and determine red cell count (RCC), packed cell volume (PCV), haemoglobi concentration (Hb), red cell indices and differential white cell counts. Digital imaging analysis was used for the histological evaluation of stained blood smears, including descriptions of red and white blood cell morphologies, as well as erythrocyte developmental stages. In the cooler periods, geometric tortoises showed low Hb and mean cell haemoglobin concentration values. Erythrocytes were larger and rounder in winter and spring, which were likely due to hydration states. In addition, increased numbers of immature erythrocytes in circulation suggested an erythropoietic response in winter and spring. This regenerative response is common in reptiles emerging from periods of limited activity and is associated with increasing primary production following rainfall events. In the following summer and autumn, increased mean cell haemoglobin concentrations suggested elevated metabolic rates influenced by rising temperatures. This would seem pertinent to meet the extra physical demands associated with foraging effort in the season characterised with limited water and food supply, and mating behaviour, which occurs in the summer. Low body conditions across all cohorts provided evidence for nutrition stress, while erythrocyte size, shape and degenerative responses indicated dehydration stress. Physiological responses to seasonal influences are specific to growth or reproductive demands and differed for each cohort. Males experienced increased Hb, PCV, RCC, and erythrocyte sizes in summer and autumn, which relate to the erythropoieticstimulating effects of androgens. Female erythropoietic cycles in spring accommodate the increased metabolic demands of increased foraging needed for a larger body size and egg production, and again in autumn again for vitellogenesis. Juvenile tortoises showed minimal differences, and could indicate species-specific responses to environmental changes. A spring-related erythropoiesis was observed in juveniles while during summer and autumn, juveniles showed less evidence for dehydration stress than in adults. No haemoparasites were observed in peripheral blood. Seven leukocyte types were identified and included heterophils, eosinophils, basophils, lymphocytes, plasma cells, monocytes and azurophils, in addition to thrombocytes. Heterophils were the most abundant leukocyte, followed by lymphocytes and eosinophils while monocytes and basophils were equally low; plasma cells and azurophils were rare. Heterophil counts were higher in spring than in summer and autumn, and in summer, were more abundant in females than in juveniles. Eosinophil counts were low in spring for all cohorts, and additionally, female and juvenile counts were low in summer. Eosinophils in juveniles were significantly lower than in adults in winter and spring. Lymphocyte numbers increased in autumn for all cohorts, while summer counts were higher in juveniles than in adults. Basophils and monocytes showed minimal seasonal changes, although basophil counts in females in winter tended to be high. Thrombocytes were lowest in spring for all cohorts. Understanding the physiological responses associated with seasonal changes and for each cohort is critical for effective chelonian conservation management. Results obtained from this study indicate a clinically healthy population of Psammobates geometricus and represented the first of this kind to establish baseline haematological reference data for this Critically Endangered tortoise species.

The study attempted to analyse the impacts of the ‘fast track’ land reform on maize production in Zimbabwe. This purpose was tackled by constructing a partial equilibrium model that depicted what could have happened if no further policy shifts had taken place after 2001. Setting up a partial equilibrium model required a sound understanding of the functioning of the Zimbabwe’s maize market. The institutional structure of the Zimbabwean maize market was explored to inform the model development process that would allow for the development of the baseline model. Developing the model started off with the estimation of single equations which were collapsed into a simultaneous system of equations through the use of a combination of ordinary least squares and generalised least squares techniques. The development of the simulation model required that assumptions be made for exogenous variables, and crafted assumptions were based on the 2000 macro-economic and institutional environment as well as agricultural policies. The re-simulated baseline model that was constructed in this study was used to make projections based on the various trends of exogenous variables in 2000. This means that the model generated an artificial data set based on what the maize market would have looked like under a set of the pre-2000 existent policy conditions. As such, all the shifts in the political and economic environment that took place after 2000 were not introduced in the model. The ‘fast track’ land reform policy was thus assessed based on the performance of the baseline model using a range of “what if” assumptions. Therefore, the re-simulated baseline solutions discussed result not only from policy shifts that occurred before 2000, but also from the convergence of hypothetical political and economic stability within the period in question. The results of the re-simulated baseline indicated that the commercial area harvested was negatively affected by the expropriation of commercial farms. The arguments in literature that the ‘fast track’ land reform policy shift contributed the loss in area planted owing to the stalling of farming operations due to political unrest, economic instability and input shortages were supported by the model results which showed that total area harvested would have been higher under pre-2000 conditions. From the re-simulated baseline results, the difference between actual and would be outcomes revealed that the total maize production was 13.27% less than what could have been produced in 2001, the year that the ‘fast track’ land reform policy was formally implemented. In view of the 2002/03 drought, output was 57.44% less and 33.53% less than what could have actually been produced for the 2002 and 2003 seasons respectively. In the 2005 drought season, the total maize production was 41.8% less than what could have been produced without the ‘fast track’ land reform. This may imply that droughts would have been less severe if the ‘fast track’ land reform was not implemented. In 2007, the baseline showed that the nation could have produced almost 48.03% more than what was actually produced. Therefore, according to the model results, the assertion that the ‘fast track’ land reform contributed, to a fair extent, to the underperformance of the maize sector still holds. The model developed in this dissertation contributes to an understanding of not only the general structure of the maize market, but also of the impact of the ‘fast track’ land reform policy on the Zimbabwean maize market based on how the market itself could have performed under the absence of these land reforms. The baseline model revealed that the maize sector performed below potential within the period of the ‘fast track’ land reform. The maize market model could thus be used as a tool that may assist policymakers to design future strategies that will help enhance maize sector performance. / Dissertation (MSc(Agric))--University of Pretoria, 2010. / Agricultural Economics, Extension and Rural Development / unrestricted