Made available in DSpace on 2014-10-09T12:49:54Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:02:15Z (GMT). No. of bitstreams: 1 10189.pdf: 7945514 bytes, checksum: fc959ff6c97125fc66c813f5c29a3647 (MD5) / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

No description available.

Controlled Source Audio Magnetotellurics (CSAMT) is a geophysical method for characterizing the resistivity of the subsurface with the help of electromagnetic waves. The method is used for various purposes, such as geothermal- and hydrocarbon exploration, mineral prospecting and for investigation of groundwater resources. Electromagnetic fields are created by running an alternating current in a grounded electric dipole and by varying the frequency, different depths can be targeted. Orthogonal components of the electromagnetic fields are measured at receiver stations a few kilometers away from the source. From these field components, so called magnetotellurics transfer functions are estimated, which can be used to invert for the resistivity of the subsurface. The data used in this project is from a survey conducted in 2014 and 2016 in Kiruna by Uppsala University and the mining company LKAB. Measurements were made at 31 stations along two orthogonal profiles. The data have been processed earlier, but due to noise, especially in the lower frequencies, a significant part of the data set could not be inverted. The aim of this project was to improve the results by analyzing the data and testing different methods to remove noise. First, robust regression was used to account for possible non-Gaussian noise in the estimation of the magnetotelluric transfer functions. Except for one station on profile 1, the robust method did not improve the results, which suggests that the noise is mostly Gaussian. Then modified versions of least squares, each affected by a different bias, were used to estimate the transfer functions. Where there is more noise, the estimates should differ more due to their different biases. The estimates differed most for low frequencies and especially on the part of profile 2 that was measured in 2014. It was investigated whether the railway network could explain part of the low frequency noise. Measures were taken to reduce spectral leakage from the railway signal at 16 ⅔ Hz to the closest transmitter frequencies 14 Hz and 20 Hz, but no clear improvement was seen and more detailed studies need to be conducted to determine this matter. Finally, a method based on comparing the ratio of short-term and long-term averages was tested to remove transients in the measured time series of the electromagnetic field components. This proved difficult to implement due to the variability of the time series’ behavior between different stations, frequencies and field components. However, the method showed some potential for stations 9 and 10 on profile 1, and could probably be developed further to remove transients more efficiently and thus improve the data. / Magnetotellurik med kontrollerad källa (förkortat CSAMT på engelska) är en metod där elektromagnetiska fält används för att undersöka markens resistivitet. Resisitivitet är ett mått på hur bra eller dåligt marken leder elektriska strömmar. Metoden används till exempel för att mäta djupet till berggrunden, som oftast har högre resistivitet (sämre ledningsförmåga) än marken ovanför. Man kan också hitta metaller, så som guld och koppar, vilka har väldigt låg resistivitet (bra ledningsförmåga). Elektromagnetiska vågor skapas genom att man låter en växelström gå igenom en lång ledning. Vågorna färdas först genom luften och sen ner i marken. Hur djupt ner de når beror på växelströmmens frekvens; med låga frekvenser når vågorna djupare ner i marken än med höga. Under markytan inducerar de elektromagnetiska vågorna elektriska strömmar, så kallade telluriska strömmar (dvs. jordströmmar). Strömmarna blir svagare ju längre de färdas och hur snabbt de avtar i styrka beror på jordens resistivitet. Strömmarna skapar också nya elektriska och magnetiska fält som färdas tillbaka mot ytan. Vid markytan mäter man fältens styrka för olika frekveser, vilket då ger information om resistiviteten på olika djup. Från mätningarna tar man ofta fram så kallade magnetotelluriska överföringsfunktioner. Dessa överföringsfunktioner gör det lättare att tolka datan och ta reda på resistiviteten hos marken. I detta projekt har CSAMT-data använts från en undersökning i Kiruna som genomfördes av Uppsala Universitet och gruvföretaget LKAB. Datan har bearbetats tidigare, men på grund av mycket brus i mätningarna blev inte resultatet så bra som väntat. Brus kan komma från allt som genererar elektromagnetiska fält, till exempel elledningar, tågledningar eller naturliga variationer i jordens egna magnetfält. Målet med projektet var att förbättra resultatet genom att analysera datan och testa olika metoder för att ta bort brus. Den vanligaste metoden för att beräkna överföringsfunktionerna antar att det magnetiska fältet är fritt från brus. Detta är inte nödvändigtvis sant och kan leda till bias, alltså ett snedvridet resultat. Andra sätt att beräkna överföringsfunktionerna på ger olika bias. Det här kan man utnyttja för att se hur mycket brus som finns i datan. Om det inte finns något brus alls så blir alla överföringsfunktioner lika, medan om det finns mycket brus så skiljer de sig mer åt. På detta sätt upptäcktes att det var mer brus för frekvenserna 14 och 20 Hz (där 1 Hz är 1 svängning per sekund). En förklaring till det kan vara att tågledningar, som genererar elektromagnetiska fält med 16.67 Hz, ligger nära i frekvens och stör dessa signaler. För att minska brusets påverkan testades så kallad robust processering. Det innebär att man lägger mindre vikt vid de mätningar som tycks vara mycket annorlunda (alltså innehåller mer brus) från andra mätningar. Tyvärr så hjälpte inte denna strategi nämnvärt för att förbättra resultatet. Till sist tog vi fram en metod för att ta bort transienter, vilket är kortvarigt brus med hög intensitet. Transienter kan till exempel komma från åskblixtar, som ju är kortvariga elektriska urladdningar. Det visade sig dock att detta inte var helt enkelt, då det var svårt att se vad som var brus och vad som bara var naturliga variationer hos de elektromagnetiska fälten. Men i några fall kunde bruset urskiljas och därför verkar det troligt att fortsatt arbete med denna metod skulle kunna ge ännu bättre resultat.

No description available.

At many American colleges and universities, efforts to enhance the retention of a diverse group of students have become a priority. This study represents part of this effort at the University of Central Florida, a large public suburban state university in the South. Specifically, this investigation evaluated Pegasus '95 and the Academic Mentoring Program offered in the Summer and Fall Semesters of 1995 to specially-admitted students who fell short of regular admissions requirements. During the summer, Pegasus '95 provided testing, orientation, guided course work, study skills workshops, and mentoring, both individually and in the context of cohesive socialization groups of approximately 15 students each. In the Fall 1995 Semester, students were highly encouraged to participate in one-on-one mentoring in the Academic Mentoring Program (AMP) available through the Student Academic Resource Center (SARC), a university-based office which provides a variety of academic assistance services. A multiple regression analysis was conducted using the following independent predictor variables: gender, SAT/ACT scores, Pegasus participation, use of the AMP in the Fall 1995 semester, four summary scores from the College Student Inventory (CSI), and eight scaled scores from the Noncognitive Questionnaire (NCQ). Dependent variables were individual student GPA in the Summer and Fall 1995 semesters, cumulative GPA after two semesters, and enrolled credit hours into the Spring 1996 academic term. Overall, it was expected that a combination of predictor variables, including both traditional cognitive factors (SAT/ACT scores and high school GPA) and noncognitive factors (NCQ scores and CSI scores, Pegasus participation, and mentoring by the SARC) would significantly predict GP A and retention. The study found that a regression equation including gender, high school GPA, overall SAT scores and the eight NCQ scale scores significantly predicted Fall 1995 and cumulative GPA after two semesters but not Summer 1995 GPA or credit hours enrolled in Spring 1996. Attendance at Pegasus meetings was also shown to be significantly and positively associated with Fall 1995 GPA and cumulative GPA after two semesters but not of Summer 1995 GPA or credit hours enrolled in Spring 1996. Gender, high school GP A, the ACT score and the CSI Dropout Proneness scale significantly predicted credit hours enrolled in Spring 1996, as did use of the AMP program provided by the SARC. Of particular interest was the finding that including noncognitive factors in significant equations led to a greater explanation of the variance than could be obtained with any of the traditional cognitive measurements alone, suggesting that with academically disadvantaged students noncognitive measures must be considered in predicting who can succeed and persist in college.

Locomotion is one of the most important behaviours and requires interaction between sensors at various levels of the nervous system and the limb muscles of an animal. The basic neural rhythm for locomotion in mammals has been shown to arise from local neural networks residing in the spinal cord and these networks are known as central pattern generators (CPGs). However, during the locomotion, these centres are constantly interacting with the sensory feedback signals coming from muscles, joints and peripheral skin receptors in order to adapt the stepping to varying environmental conditions. Conceptual models of mammalian locomotion have been constructed using mathematical models of locomotor subsystems based on the abundance of neurophysiological evidence obtained primarily in the cat. Several aspects of locomotor control using the cat as an animal model have been investigated employing computer simulations and here we use the same approach to address number of questions or/and hypotheses related to rhythmic locomotion in quadrupeds. Some of the involve questions are, role of mechanical linkage during deafferented walking, finding inherent stabilities/instabilities of muscle-joint interactions during normal walking, estimating phase dependent controlability of muscle action over joints. This thesis presents the basics of a biologically realistic model of mammalian locomotion and summarises methodological approaches in modelling quadruped locomotor subsystems such as CPGs, limb muscles and sensory pathways. In the first appended article, we extensively discuss the construction details of the three-dimensional computer simulator for the study of the hind leg neuro-musculo-skeletal-control system and its interactions during normal walking of the cat. The simulator with the walking model is programmed in Python scripting language with other supported open source libraries such as Open Dynamics Engine (ODE) for simulating body dynamics and OpenGL for three dimensional graphical representation. We have examined the functionality of the simulator and the walking model by simulating deafferented walking. It was possible to obtain a realistic stepping in the hind legs even without sensory feedback to the two controllers (CPGs) for each leg. We conclude that the mechanical linkages between the legs also play a major role in producing alternating gait. The use of simulations of walking in the cat for gaining insights into more complex interactions between the environment and the neuro-muscular-skeletal system is important especially for questions where a direct neurophysiological experiment can not be performed on a real walking animal. For instance, it is experimentally hard to isolate individual mechanisms without disrupting the natural walking pattern. In the second article, we introduce a different approach where we use the walking model to identify what control is necessary to maintain stability in the musculo-skeletal system. We show that the actions of most of the hindlimb muscles over the joints have an inherent stability during stepping, even without the involvement of proprioceptive feedback mechanisms. In addition, we observe that muscles generating movements in the ankle joint of the hind leg must be controlled by neural mechanisms, which may involve supraspinal structures, over the whole step cycle. / QC 20101111

The vocal tract shape is crucial to voice production. Its lower part seems particularly relevant for voice timbre. This study analyzes the detailed morphology of parts of the epilaryngeal tube and the hypopharynx for the sustained German vowels /a/, /e/, /i/, /o/, and /u/ by thirteen male singer subjects who were at the beginning of their academic singing studies. Analysis was based on two different phonatory conditions: a natural, speech-like phonation and a singing phonation, like in classical singing. 3D models of the vocal tract were derived from magnetic resonance imaging and compared with long-term average spectrum analysis of audio recordings from the same subjects. Comparison of singing to the speech-like phonation, which served as reference, showed significant adjustments of the lower vocal tract: an average lowering of the larynx by 8 mm and an increase of the hypopharyngeal cross-sectional area (+ 21.9%) and volume (+ 16.8%). Changes in the analyzed epilaryngeal portion of the vocal tract were not significant. Consequently, lower larynx-to-hypopharynx area and volume ratios were found in singing compared to the speech-like phonation. All evaluated measures of the lower vocal tract varied significantly with vowel quality. Acoustically, an increase of high frequency energy in singing correlated with a wider hypopharyngeal area. The findings offer an explanation how classical male singers might succeed in producing a voice timbre with increased high frequency energy, creating a singer‘s formant cluster.

Avec la réduction du bruit de jet et de soufflante dans les moteurs aéronautiques modernes, la contribution relative du bruit de combustion (BC) a augmenté de manière significative au cours des dernières décennies. Deux mécanismes ont été identifiés comme étant du BC dans les années 70 : le bruit de combustion direct (BCD) et le bruit de combustion indirect (BCI). Le coeurde la thèse est axé sur le BCI avec le développement d’un modèle semi-analytique 2D axisymétrique prenant en compte la distorsion des ondes entropiques afin de prédire le BCI dans des écoulements de tuyère. L’état de l’art réalisé dans le premier chapitre met en évidence la nécessité d’améliorer la prédiction du BCI des modèles 1D en introduisant la distorsion radiale des ondes entropiques dans la tuyère. Le second chapitre du manuscrit détaille les outils disponibles à l’ONERA pour l’étude du BCI. Le modèle 2D est développé dans le troisième chapitre où les équations d’Euler sont réécritesen 2D pour la partie entropique et en 1D pour les perturbations acoustiques. Le quatrième chapitre décrit les simulations numériques réalisées pendant la thèse sur la configuration retenue (la tuyère DISCERN) : un calcul RANS et deux simulations des grandes échelles (SGE) sont effectués respectivementpour l’utilisation et la validation du modèle 2D. Dans le dernier chapitre, l’application du nouveau modèle utilisant le champ moyen RANS est accompli, les résultats sont comparés au modèle 1D et validés par confrontation avec les prédictions SGE. / Due to the reduction of jet mixing noise and fan noise in modern aero engines, the relative contribution of combustion noise (CN) has significantly increased over the last few decades. Two mechanisms have been identified as CN in the 70’s: direct combustion noise (DCN) and indirect combustion noise (ICN). A focus is made on the ICN in this thesis with the development of a twodimensionalaxisymmetric semi-analytical model taking into account the distortion of the entropy waves in order to predict the ICN for nozzle flows. The state of the art performed in the first chapter highlights the necessity to improve the prediction of ICN of 1D models by introducing the radial distortion of the entropy waves inside the nozzle. The second chapter of the manuscript details the ONERA’s tools for studying ICN. The 2D model is developed in the third chapter where the Euler equations are rewritten in 2D formfor the entropic part while acoustic perturbations are considered to be 1D. The fourth chapter describes the numerical computations performed during the thesis onthe retained configuration (the DISCERN nozzle): a RANS and two large eddy simulations (LES) are carried out respectively for the use and the validation of the 2D model. In the last chapter, the application of the new model using the RANS meanfield is performed, the results are compared tothe 1D model and validated by confrontation with the LES predictions.

Title: Interactive Processing of Volumetric Data Author: Jan Kolomazník Department: Department of Software and Computer Science Education Supervisor: RNDr. Josef Pelikán, Department of Software and Computer Science Education Abstract: Interactive visualization and segmentation of volumetric data are quite lim- ited due to the increased complexity of the task and size of the input data in comparison to two-dimensional processing. A special interactive segmentation workflow is presented, based on minimal graph-cut search. The overall execution time was lowered by implementing all the computational steps on GPU, which required a design of massively parallel algorithms (using thousands of threads). To lower the computational burden even further the graph is constructed over the image subregions com- puted by parallel watershed transformation. As a suitable formalism for a range of massively parallel algorithms was chosen cellular automata. A set of cellular automata extensions was defined, which allows efficient mapping and computation on GPU. Several variants of parallel watershed transformation are then defined in the form of cellular automaton. A novel form of 2D transfer function was presented, to improve direct volume visualization of the input data, suited for discriminating image features by their shape and...

<p>The objective of the thesis was to explore the potential of diatoms (<i>Bacillariophyceae</i>) as indicators of Holocene climate and environmental change in northern Sweden (Abisko region, 68°21'N, 18°49'E). A modern surface-sediment calibration set including 100 lakes was developed and lake-water pH, sedimentary organic content (assessed by loss-on-ignition) and temperature were identified as most powerful environmental variables explaining the variance within the diatom assemblages. Transfer functions based on unimodal species response models (WA-PLS) were developed for lake-water pH and mean July air temperature (July T), yielding coefficients of determination of 0.77 and 0.70, and prediction errors based on leave-one-out cross-validation of 0.19 pH units and 0.96 °C for lake-water pH and July T, respectively. The transfer functions were validated with monitoring data covering two open-water seasons (lake-water pH) and meteorological records covering the 20th century (July T). The good agreement between diatom-based inferences and measured monitoring data confirmed the prediction ability of the developed transfer functions. </p><p>Analysing a Holocene sediment core from a lake nearby Abisko (Vuoskkujávri), diatoms infer a linearly decreasing July T trend (1.5 °C) since 6,000 cal. BP, which compares well with inferences based on chironomids and pollen from the same sediment core. The lake-water pH inference shows a pattern of moderate natural acidification (c. 0.5 pH units) since the early Holocene, reaching present-day pH values at c. 5,000 cal. BP. By fitting fossil diatom samples to the modern calibration set by means of residual distance assessment within canonical correspondence analysis (CCA), the early Holocene (between 10,600 and 6,000 cal. BP) was identified as a problematic time-period for diatom-based inferences and, consequently, reconstructions during this period are tentative. Pollen-based inferences also show 'poor' fit between 10,600 and 7,500 cal. BP and chironomids probably provide the most reliable July T reconstruction at Vuoskkujávri, with 'poor' fit only during the initial part of the Holocene (between 10,600 and 10,250 cal. BP). </p><p>Possible factors confounding diatom-based July T inferences were investigated. Using detrended CCA (DCCA), Holocene sediment sequences from five lakes indicate that during the early Holocene, mainly physical factors such as high minerogenic erosion rates, high temperature and low light availability may have regulated diatom assemblages, favouring <i>Fragilaria</i> species. In all five lakes, diatom assemblages developed in a directional manner, but timing and scale of development differed substantially between lakes. The differences are attributed primarily to the geological properties of the lake catchments (with strong effects on lake-water pH), but other factors such as climatic change, vegetation, hydrologic setting and in-lake processes appear to regulate diatom communities in each lake differently. The influence of long-term natural acidification on diatom assemblages progressively declined during the Holocene with corresponding increase of the influence of climatic factors.</p>