• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 179
  • 46
  • 35
  • 20
  • 9
  • 9
  • 7
  • 6
  • 3
  • 2
  • 1
  • 1
  • 1
  • 1
  • 1
  • Tagged with
  • 416
  • 416
  • 86
  • 50
  • 47
  • 40
  • 37
  • 35
  • 30
  • 29
  • 27
  • 26
  • 25
  • 24
  • 23
  • 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.
231

THE SYNAPTIC CIRCUITS UNDERLYING OLFACTORY PROCESSING AND REPRESENTATIONS IN THE INSECT BRAIN: CHARACTERIZATION AND PLASTICITY OF THE MUSHROOM BODY CALYX

Butcher, Nancy J. 16 August 2010 (has links)
Sensory information is processed and encoded by neural networks. In order to understand how the nervous system is able to rapidly integrate and store sensory information, knowledge of the connections and properties of the neurons in these circuits is required. The fruit fly Drosophila melanogaster provides a particularly powerful species to investigate the neural circuits of the olfactory system because in addition to possessing a simple olfactory system amenable to circuit analysis, a host of genetic reagents are available, including the GAL4-UAS system for targeted gene expression. The mushroom bodies, paired structures historically implicated in olfactory learning and memory, receive olfactory information at the mushroom body calyx from second-order olfactory projection neurons (PNs). Within the calyx, individual PN axonal boutons are surrounded by dendritic arborizations from intrinsic Kenyon cells (KCs) and each tiny cluster constitutes a single microglomerulus. Cells that connect the calyx with other areas of the brain, extrinsic neurons (ENs), also contribute to microglomeruli. Most of these contain the neurotransmitter, GABA, and are presumed to be inhibitory. In this study, the synaptic characteristics, neural circuits, and plasticity of calycal cells have been investigated using a combination of serial section electron and confocal microscopy. The findings reveal several new features of the circuits in the calyx: 1) The calyx contains three ultrastructurally distinct types of PN boutons that are heterogeneous in shape and exhibit subtle differences in synaptic densities. 2) All PN boutons form both ribbon and non-ribbon synapses, and from their smaller size and fewer postsynaptic partners, non-ribbon synapses may possibly become converted to ribbon synapses after activity; the olfactory signal may then be transmitted more strongly and efficiently at ribbon synapses. 3) PN boutons with an electron-dense cytoplasm have the most ribbon synapses per unit area of membrane as well as the highest ratio of ribbon to non-ribbon synapses, and thus may be more active and efficient than other boutons. 4) KC neurites are not exclusively postsynaptic in the calyx and can form occasional ribbon synapses, the functional interpretation of which awaits identification of their postsynaptic partners and vesicle contents. 5) Each PN bouton may contribute input to a single dendritic KC claw at about three presynaptic sites. For the postsynaptic side, a single claw receives input from individual presynaptic sites that must be highly redundant. 6) There may be important processing of the olfactory signal by local circuits formed by ENs in the calyx; ENs form synaptic connections with PNs, KCs, and other ENs. 7) Extensive serial synapses link EN terminals into a network, presumed to be GABAergic and inhibitory, that extends between microglomeruli and may be autaptic. 8) The structure and synaptic connectivity of microglomeruli may undergo changes after adult emergence. 9) vGAT and GAD1-GAL4 lines drive ectopic expression of marker genes in KCs and are not reliable reporters of GABA-positive cells. 10) Previously identified calycal ENs (MB-C1, MB-C2/C3, MB-CP1) are not immunopositive for GAD1, a marker of GABA-containing cells. 11) A network of ENs expressing a GABA phenotype differently innervates anatomically and functionally discrete areas of the honeybee calyx, and in addition the density of innervation may change with alterations in age and/or experience.
232

THREE DIMENSIONAL FINITE ELEMENT MODELING OF PAVEMENT SUBSURFACE DRAINAGE SYSTEMS

Liu, Yinhui 01 January 2005 (has links)
Pavement subsurface drainage systems (PSDS) are designed to drain the entrapped water out of pavement. To investigate the effects of various factors on the performance of PSDS, three dimensional models were developed using the finite element method to simulate the unsaturated drainage process in pavement. The finite element models were calibrated using the field information on outflow, peak flow, layer saturations, and time to drain. Through a series of parametric analyses, the factors that significantly influence the performance of PSDS were screened out, and a set of recommendations were made to improve our current drainage practices.The effects of pavement geometry on drainage were studied in this research. The analysis results indicate that edgedrain system can significantly improve the drainage efficiency of a pavement. The drainage performance of a pavement is mainly affected by the geometric factors that related to the edgedrain itself and the geometric factors related to the driving lanes have very limited effects.To investigate the influences of the properties of various pavement materials, some physical-empirical equations were developed in this research. These equations were used to predict the material hydraulic properties from their grain-size distributions and aggregate/asphalt contents. The analysis results of the models with various material properties indicate that the use of permeable base is effective in improving the drainage ability of a pavement. The performance of PSDS is not only affected by material permeability but also by their waterretention ability. The pavement works as an integrated hydraulic system and the hydraulic compatibility of materials must be considered in the PSDS design.The effects of climatic factors on pavement drainage were also studied in this research. A method was developed in this research to numerically describe the rainfall events. The analysis results of the models under various rainfall events indicate that rainfall duration is a more important parameter than the rainfall quantity in influencing the pavement drainage. Based on the analysis results, regression equations were developed for the estimation of pavement drainage. Finally, for design application purpose, a series of tables were included in this report to help with proper selected of pavement drainage options.
233

Catalyse en synthèse organique : valorisation d'un biocatalyseur original et synthèse pallado-catalysée de nouveaux dérivés pyridopyrimidiniques

Riadi, Yassine 12 October 2013 (has links) (PDF)
La catalyse représente une thématique incontournable de la chimie moderne. Elle occupe une place stratégique dans la recherche de procédés de synthèse plus écologiques et plus économiques en atomes et en énergie. Notre travail réside, d'une part, dans la valorisation d'un biocatalyseur original et, d'autre part, dans la synthèse pallado-catalysée de nouveaux dérivés pyridopyrimidiniques. Dans la première partie, l'utilisation d'un nouveau support naturel préparé à base d'os animal (Animal Bone Meal : ABM) en catalyse hétérogène a été mise en oeuvre, ce qui représente une voie nouvelle et originale, permettant de remplacer les différents catalyseurs solides minéraux connus actuellement et ce, dans diverses réactions classiques de la synthèse organique. Outre les excellents rendements obtenus, les aspects positifs de l'ABM résident dans sa grande stabilité, sa facilité de manipulation et de régénération ainsi que dans l'absence de dangers sur l'environnement. Dans la deuxième partie, une nouvelle stratégie de synthèse simple et efficace de 2,4-di(hét)aryl-pyrido[2,3-d]pyrimidines via un couplage de Suzuki-Miyaura catalysée par le palladium a été développée. Nous avons ensuite étudié la réactivité de diverses 2,4,6-trihalogénopyrido[2,3-d]pyrimidines vis-à-vis des couplages de Suzuki. Cette étude a été étendue à la synthèse de nouvelles 2,4,6-tri(hét)arylpyrido[2,3-d]pyrimidines.
234

Etude de l'infuence de la séparation des degrés de liberté pour la manipulation 3-D à l'aide de surfaces tactiles multipoints

Martinet, Anthony 03 October 2011 (has links) (PDF)
Inventées au milieu des années 1980, nous assistons actuellement au développement à grande échelle des interfaces tactiles multipoints. Par comparaison avec la souris, les écrans multipoints nécessitent un nouveau processus d'étude afin de comprendre les changements apportés par cette technologie. Le travail déjà effectué avec d'autres périphériques d'entrée doit être repris à zéro afin de formuler de nouvelles théories pour la création d'interfaces tactiles multipoints. La manipulation à trois dimensions (3-D) d'un objet nécessite le contrôle de six degrés de liberté. Trois sont responsables de la position de l'objet et trois contrôlent son orientation. Dans ce mémoire, nous nous focalisons sur la manipulation 3-D d'un objet à l'aide de surfaces tactiles multipoints. Plus précisément, nous avons étudié le lien entre le périphérique d'entrée (ici la surface multipoint) et la tâche à effectuer (ici la manipulation 3-D). En premier lieu, nous avons introduit une taxonomie pour la représentation des techniques d'interaction 3-D spécifiques aux écrans multipoints. Cette taxonomie nous a permis de mettre en avant l'influence des stratégies de conception des techniques en termes d'intégration de degrés de liberté. Par la suite, nous avons mené une étude concernant les techniques d'interactions permettant le positionnement 3-D d'un objet. Nous avons présenté deux nouvelles techniques, tirant profit des capacités offertes par les écrans multipoints. L'évaluation de ces techniques nous révéla des conclusions quant à la coordination de l'utilisateur dans la réalisation de la tâche. Enfin, nous avons introduit une nouvelle technique d'interaction de manipulation 3-D. Cette technique a été évaluée plus rapide que les techniques existantes et nous avons pu déterminer les raisons expliquant cette performance accrue. Ces travaux, qui s'intéressent à la coordination de l'utilisateur lors de la réalisation de tâches 3-D à l'aide de surfaces multipoints, recommandent une approche favorisant la séparation des degrés de liberté, dans le but de pouvoir paralléliser les actions de l'utilisateur afin de tirer profit de la bande passante d'entrée plus importante offerte par les écrans multipoints.
235

A Study of the Herald-Phillipstown Fault in the Wabash Valley using Drillhole and 3-D Seismic Reflection Data

Kroenke, Samantha E. 01 August 2011 (has links)
In June 2009, a 2.2 square mile 3-D high resolution seismic reflection survey was shot in southeastern Illinois in the Phillipstown Consolidated oilfield. A well was drilled in the 3-D survey area to tie the seismic to the geological data with a synthetic seismogram from the sonic log. The objectives of the 3-D seismic survey were three-fold: 1.) To image and interpret faulting of the Herald-Phillipstown Fault using drillhole-based geological and seismic cross-sections and structural contour maps created from the drillhole data and seismic reflection data, 2.) To test the effectiveness of imaging the faults by selected seismic attributes, and 3.) To compare spectral decomposition amplitude maps with an isochron map and an isopach map of a selected geologic interval (VTG interval). Drillhole and seismic reflection data show that various formation offsets increase near the main Herald-Phillipstown fault, and that the fault and its large offset subsidiary faults penetrate the Precambrian crystalline basement. A broad, northeast-trending 10,000 feet wide graben is consistently observed in the drillhole data. Both shallow and deep formations in the geological cross-sections reveal small horst and graben features within the broad graben created possibly in response to fault reactivations. The HPF faults have been interpreted as originally Precambrian age high-angle, normal faults reactivated with various amounts and types of offset. Evidence for strike-slip movement is also clear on several faults. Changes in the seismic attribute values in the selected interval and along various time slices throughout the whole dataset correlate with the Herald-Phillipstown faults. Overall, seismic attributes could provide a means of mapping large offset faults in areas with limited or absent drillhole data. Results of the spectral decomposition suggest that if the interval velocity is known for a particular formation or interval, high-resolution 3-D seismic reflection surveys could utilize these amplitudes as an alternative seismic interpretation method for estimating formation thicknesses. A VTG isopach map was compared with an isochron map and a spectral decomposition amplitude map. The results reveal that the isochron map strongly correlates with the isopach map as well as the spectral decomposition map. It was also found that thicker areas in the isopach correlated with higher amplitude values in the spectral decomposition amplitude map. Offsets along the faults appear sharper in these amplitudes and isochron maps than in the isopach map, possibly as a result of increased spatial sampling.
236

In Support of High Quality 3-D Ultrasound Imaging for Hand-held Devices

January 2015 (has links)
abstract: Three dimensional (3-D) ultrasound is safe, inexpensive, and has been shown to drastically improve system ease-of-use, diagnostic efficiency, and patient throughput. However, its high computational complexity and resulting high power consumption has precluded its use in hand-held applications. In this dissertation, algorithm-architecture co-design techniques that aim to make hand-held 3-D ultrasound a reality are presented. First, image enhancement methods to improve signal-to-noise ratio (SNR) are proposed. These include virtual source firing techniques and a low overhead digital front-end architecture using orthogonal chirps and orthogonal Golay codes. Second, algorithm-architecture co-design techniques to reduce the power consumption of 3-D SAU imaging systems is presented. These include (i) a subaperture multiplexing strategy and the corresponding apodization method to alleviate the signal bandwidth bottleneck, and (ii) a highly efficient iterative delay calculation method to eliminate complex operations such as multiplications, divisions and square-root in delay calculation during beamforming. These techniques were used to define Sonic Millip3De, a 3-D die stacked architecture for digital beamforming in SAU systems. Sonic Millip3De produces 3-D high resolution images at 2 frames per second with system power consumption of 15W in 45nm technology. Third, a new beamforming method based on separable delay decomposition is proposed to reduce the computational complexity of the beamforming unit in an SAU system. The method is based on minimizing the root-mean-square error (RMSE) due to delay decomposition. It reduces the beamforming complexity of a SAU system by 19x while providing high image fidelity that is comparable to non-separable beamforming. The resulting modified Sonic Millip3De architecture supports a frame rate of 32 volumes per second while maintaining power consumption of 15W in 45nm technology. Next a 3-D plane-wave imaging system that utilizes both separable beamforming and coherent compounding is presented. The resulting system has computational complexity comparable to that of a non-separable non-compounding baseline system while significantly improving contrast-to-noise ratio and SNR. The modified Sonic Millip3De architecture is now capable of generating high resolution images at 1000 volumes per second with 9-fire-angle compounding. / Dissertation/Thesis / Doctoral Dissertation Electrical Engineering 2015
237

Avaliação de discos de corte de semeadora-adubadora em diferentes quantidades de cobertura vegetal

Santos, Alessandro José Marques [UNESP] 09 February 2008 (has links) (PDF)
Made available in DSpace on 2014-06-11T19:24:38Z (GMT). No. of bitstreams: 0 Previous issue date: 2008-02-09Bitstream added on 2014-06-13T19:52:11Z : No. of bitstreams: 1 santos_ajm_me_botfca.pdf: 1014705 bytes, checksum: a380df7d0c36dd92557eb57e9d7c7468 (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / A qualidade e eficiência no corte da palha realizado pelos mecanismos de corte das semeadoras-adubadoras são elementos determinantes no processo de semeadura, em função da ocorrência de “embuchamentos” e de paradas, no afastamento da palhada ou mesmo no conhecido efeito do “envelopamento” da semente que ocasiona a deposição sobre a palha enterrada pelo mecanismo. Dessa forma, o objetivo deste trabalho foi avaliar o desempenho de diferentes mecanismos de corte de palha de uma semeadora-adubadora de maneira individualizada em diferentes quantidades de cobertura vegetal adicionadas artificialmente em um solo de textura argilosa. Para a realização do trabalho foi utilizado um dinamômetro (anel ortogonal), projetado, construído e calibrado numa célula de carga padrão. O experimento foi conduzido na Fazenda Experimental Lageado, pertencente à Faculdade de Ciências Agronômicas – Unesp de Botucatu. O delineamento experimental utilizado foi em parcelas subdivididas com quatro repetições, sendo as parcelas principais constituídas de cinco quantidades de palhada de aveia preta, adicionadas artificialmente ao solo em área conduzida em plantio direto e as subparcelas de três mecanismos de abertura de sulco, sendo estes: disco liso (DL), disco corrugado (DC) e disco ondulado (DO). O disco ondulado proporcionou maior resistência ao rolamento, reduzindo a velocidade do conjunto (trator e equipamento). A mobilização do solo avaliada nos diferentes tratamentos principais (quantidade de palhada) e secundários (configuração de discos) apresentou diferenças de volume de solo mobilizado, as maiores quantidades de palhada proporcionaram maior taxa de cobertura do solo e consequentemente menor evaporação de água aumentando a área mobilizada. Os discos estriados e ondulados apresentam comportamento semelhante em relação às forças laterais, horizontal, momento... / The quality and efficiency in straw cutting are determinants in the sowing process, according to the occurrence of tamp and stops, the magnitude of the straw removal or even the known effects of the seed envelopment where the cutting mechanism can not cut the remaining straw. Thus, the objective of this study was to evaluate the performance of different mechanisms for straw cutting of a seeder individualized in different amounts of crop coverage artificially added in a clay soil. It was used a dynamometer (orthogonal ring), designed, built and calibrated in a standard load cell to carry out the work . The experiment was conducted at Unesp – Sao Paulo State University in the Experimental Farm Lageado, belonging to the College of Agricultural Sciences - Unesp, Botucatu. The experimental design was split plot with four replications, with main plots consisting of five quantities of black oat straw, artificially added to the soil in area with no-tillage system and subplots of three opening furrows mechanisms, which are: plane disk (PD), corrugated disk (CD) and wavy disk (WD). The wavy disk provided greater rolling resistance, reducing the speed of the set (tractor and equipment). The evaluation of the soil in the different main treatments (amount of straw) and secondary treatments (setting disks), showed differences in the volume. The largest quantities of straw provided higher rate of soil cover and consequently less water evaporation by increasing the mobilized area. The striated and wavy disks showed similar behavior with respect to lateral and, horizontal forces and longitudinal time and horizontal force in function of the mobilized area. In the settings of the studied disks, it was found that the plane disk needed less load to greater penetrate into the soil, due to the values found in the vertical force in the component of reaction, demonstrating higher efficiency... (Complete abstract click electronic access below)
238

Underwater 3-D imaging with laser triangulation

Norström, Christer January 2006 (has links)
The objective of this master thesis was to study the performance of an active triangulation system for 3-D imaging in underwater applications. Structured light from a 20 mW laser and a conventional video camera was used to collect data for generation of 3-D images. Different techniques to locate the laser line and transform it into spatial coordinates were developed and evaluated. A field- and a laboratory trial were performed. From the trials we can conclude that the distance resolution is much higher than the lateral- and longitudinal resolution. The lateral resolution can be improved either by using a high frame rate camera or simply by using a low scanning speed. It is possible to obtain a range resolution of less than a millimeter. The maximum range of vision was 5 meters under water measured on a white target and 3 meters for a black target in clear sea water. These results are however dependent on environmental and system parameters such as laser power, laser beam divergence and water turbidity. A higher laser power would for example increase the maximum range.
239

Mapeamento do embasamento da sub-bacia Olinda-PE e sub-bacia Alhandra-PB usando modelagem gravimétrica e magnetométrica 2-D e 3-D

Rodrigues Tavares Junior, João 31 January 2009 (has links)
Made available in DSpace on 2014-06-12T18:03:00Z (GMT). No. of bitstreams: 2 arquivo3916_1.pdf: 9426829 bytes, checksum: add6a4109c2db883333cd598661a8e0b (MD5) license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) Previous issue date: 2009 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Este trabalho apresenta os resultados da tese de doutorado sobre o mapeamento da geometria do embasamento da Sub-Bacia Olinda e Sub-Bacia Alhandra da Bacia Paraíba, utilizando o método gravimétrico e magnetométrico em uma área de 725 km2, nos municípios de Goiana PE, Pitimbú PB, Alhandra PB e Caaporã PB, NE do Brasil. Foram utilizadas 213 estações gravimétricas e 129 magnéticas, elaborados os respectivos mapas no software Oasis montaj, e a modelagem inversa 2-D gravimétrica e magnética, e 3-D gravimétrica, do embasamento em domínio continental. Os dados gravimétricos foram cedidos pelo Laboratório de Geofísica Aplicada da Universidade Federal de Pernambuco, e os mapas recalculados. Os dados magnéticos foram obtidos usando o magnetômetro de campo total de bombeamento ótico SM-5. De acordo com a denominação dada nesta tese, foram propostos o Horst de Cupissura, Graben de Goiana, Horst de Tejucupapo, Graben de Itapirema e Horst de Carrrapicho. O Graben de Goiana tem profundidade em torno de 380 m, e as isópacas entre 200 m e 400 m se estendem de norte a sul nas sub-bacias. A Sub-Bacia Olinda mostra profundidades médias de espessura sedimentar maiores do que a Sub-Bacia Alhandra. Este mapeamento indicou profundidades entre 30m e 440m, espessura sedimentar de até 420 m, espessura crustal de 25 km. A distribuição das estruturas é coerente com um modelo de cisalhamento rúptil dextral, onde a fratura de Ridel R é paralela às falhas NE-SW, e a R é paralela às falhas sinistrais NW-SE. Um banco de dados foi desenvolvido e usado no planejamento e execução do levantamento magnético, baseado na visualização de dados no ARCVIEW-GIS em carta-imagem e mapa-temático
240

Gram quantities of silver and alloy nanoparticles: synthesis through digestive ripening and the solvated metal atom dispersion (SMAD) method: antimicrobial properties, superlatteic[i.e. super lattice] selfassembly, and optical properties

Smetana, Alexander B. January 1900 (has links)
Doctor of Philosophy / Department of Chemistry / Kenneth J. Klabunde / This is an account of the synthesis of several drastically different forms of silver nanoparticles: Bare metal nanoparticles, dry nanoparticulate powders, aqueous soluble particles, and organic ligand coated monodisperse silver nanoparticles were all produced. The synthetic method was adapted from previous studies on gold nanoparticles and investigated to understand the optimal conditions for silver nanoparticle synthesis. Also the procedure for refinement of the nanoparticles was studied and applied to the formation of alloy nanoparticles. This extraordinary procedure produces beautifully colored colloids of spherical metal nanoparticles of the highest quality which under suitable conditions self-assemble into extensive three dimensional superlattice structures. The silver nanoparticle products were later tested against several biological pathogens to find dramatic increases in antimicrobial potency in comparison to commercially available silver preparations.

Page generated in 0.0379 seconds