• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 39
  • 8
  • 8
  • 7
  • 7
  • 2
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • Tagged with
  • 84
  • 14
  • 14
  • 11
  • 9
  • 8
  • 8
  • 7
  • 7
  • 7
  • 7
  • 7
  • 7
  • 7
  • 6
  • 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.
1

Exponentially Accurate Error Estimates of Quasiclassical Eigenvalues

Toloza, Julio Hugo 16 December 2002 (has links)
We study the behavior of truncated Rayleigh-Schröodinger series for the low-lying eigenvalues of the time-independent Schröodinger equation, when the Planck's constant is considered in the semiclassical limit. Under certain hypotheses on the potential energy, we prove that, for any given small value of the Planck's constant, there is an optimal truncation of the series for the approximate eigenvalues, such that the difference between an approximate and actual eigenvalue is smaller than an exponentially small function of the Planck's constant. We also prove the analogous results concerning the eigenfunctions. / Ph. D.
2

Stochastic generation of biologically accurate brain networks

Aluri, Aravind 12 April 2006 (has links)
Basic circuits, which form the building blocks of the brain, have been identiffied in recent literature. We propose to treat these basic circuits as "stochastic generators" whose instances serve to wire a portion of the mouse brain. Very much in the same manner as genes generate proteins by providing templates for their construction, we view the catalog of basic circuits as providing templates for wiring up the neurons of the brain. This thesis work involves a) deffining a framework for the stochastic generation of brain networks, b) generation of sample networks from the basic circuits, and c) visualization of the generated networks.
3

Advanced Technologies for Fabrication and Testing of Large Flat Mirrors

Yellowhair, Julius Eldon January 2007 (has links)
Classical fabrication methods alone do not enable manufacturing of large flat mirrors that are much larger than 1 meter. This dissertation presents the development of enabling technologies for manufacturing large high performance flat mirrors and lays the foundation for manufacturing very large flat mirrors. The enabling fabrication and testing methods were developed during the manufacture of a 1.6 meter flat. The key advantage over classical methods is that our method is scalable to larger flat mirrors up to 8 m in diameter.Large tools were used during surface grinding and coarse polishing of the 1.6 m flat. During this stage, electronic levels provided efficient measurements on global surface changes in the mirror. The electronic levels measure surface inclination or slope very accurately. They measured slope changes across the mirror surface. From the slope information, we can obtain surface information. Over 2 m, the electronic levels can measure to 50 nm rms of low order aberrations that include power and astigmatism. The use of electronic levels for flatness measurements is analyzed in detail.Surface figuring was performed with smaller tools (size ranging from 15 cm to 40 cm in diameter). A radial stroker was developed and used to drive the smaller tools; the radial stroker provided variable tool stroke and rotation (up to 8 revolutions per minute). Polishing software, initially developed for stressed laps, enabled computer controlled polishing and was used to generate simulated removal profiles by optimizing tool stroke and dwell to reduce the high zones on the mirror surface. The resulting simulations from the polishing software were then applied to the real mirror. The scanning pentaprism and the 1 meter vibration insensitive Fizeau interferometer provided accurate and efficient surface testing to guide the remaining fabrication. The scanning pentaprism, another slope test, measured power to 9 nm rms over 2 meters. The Fizeau interferometer measured 1 meter subapertures and measured the 1.6 meter flat to 3 nm rms; the 1 meter reference flat was also calibrated to 3 nm rms. Both test systems are analyzed in detail. During surface figuring, the fabrication and testing were operated in a closed loop. The closed loop operation resulted in a rapid convergence of the mirror surface (11 nm rms power, and 6 nm rms surface irregularity). At present, the surface figure for the finished 1.6 m flat is state of the art for 2 meter class flat mirrors.
4

Nonlinear Dynamics and Vibration of Gear and Bearing Systems using A Finite Element/Contact Mechanics Model and A Hybrid Analytical-Computational Model

Dai, Xiang 11 September 2017 (has links)
This work investigates the dynamics and vibration in gear systems, including spur and helical gear pairs, idler gear trains, and planetary gears. The spur gear pairs are analyzed using a finite element/contact mechanics (FE/CM) model. A hybrid analytical-computational (HAC) model is proposed for nonlinear gear dynamics. The HAC predictions are compared with FE/CM results and available experimental data for validation. Chapter 2 investigates the static and dynamic tooth root strains in spur gear pairs using a finite element/contact mechanics approach. Extensive comparisons with experiments, including those from the literature and new ones, confirm that the finite element/contact mechanics formulation accurately predicts the tooth root strains. The model is then used to investigate the features of the tooth root strain curves as the gears rotate kinematically and the tooth contact conditions change. Tooth profile modifications are shown to strongly affect the shape of the strain curve. The effects of strain gage location on the shape of the static strain curves are investigated. At non-resonant speeds the dynamic tooth root strain curves have similar shapes as the static strain curves. At resonant speeds, however, the dynamic tooth root strain curves are drastically different because large amplitude vibration causes tooth contact loss. There are three types of contact loss nonlinearities: incomplete tooth contact, total contact loss, and tooth skipping, and each of these has a unique strain curve. Results show that different operating speeds with the same dynamic transmission error can have much different dynamic tooth strain. Chapters 3, 4, and 5 develops a hybrid-analytical-computational (HAC) method for nonlinear dynamic response in gear systems. Chapter 3 describes the basic assumptions and procedures of the method, and implemented the method on two-dimensional vibrations in spur gear pairs. Chapters 4 and 5 extends the method to two-dimensional multi-mesh systems and three-dimensional single-mesh systems. Chapter 3 develops a hybrid analytical-computational (HAC) model for nonlinear dynamic response in spur gear pairs. The HAC model is based on an underlying finite element code. The gear translational and rotational vibrations are calculated analytically using a lumped parameter model, while the crucial dynamic mesh force is calculated using a force-deflection function that is generated from a series of static finite element analyses before the dynamic calculations. Incomplete tooth contact and partial contact loss are captured by the static finite element analyses, and included in the force-deflection function. Elastic deformations of the gear teeth, including the tooth root strains and contact stresses, are calculated. Extensive comparisons with finite element calculations and available experiments validate the HAC model in predicting the dynamic response of spur gear pairs, including near resonant gear speeds when high amplitude vibrations are excited and contact loss occurs. The HAC model is five orders of magnitude faster than the underlying finite element code with almost no loss of accuracy. Chapter 4 investigates the in-plane motions in multi-mesh systems, including the idler chain systems and planetary gear systems, using the HAC method that introduced in Chap. 3. The details of how to implement the HAC method into those systems are explained. The force-deflection function for each mesh is generated individually from a series of static finite element analyses before the dynamic calculations. These functions are used to calculated the dynamic mesh force in the analytical dynamic analyses. The good agreement between the FE/CM and HAC results for both the idler chain and planetary gear systems confirms the capability of the HAC model in predicting the in-plane dynamic response for multi-mesh systems. Conventional softening type contact loss nonlinearities are accurately predicted by HAC method for these multi-mesh systems. Chapter 5 investigates the three-dimensional nonlinear dynamic response in helical gear pairs. The gear translational and rotational vibrations in the three-dimensional space are calculated using an analytical model, while the force due to contact is calculated using the force-deflection. The force-deflection is generated individually from a series of static finite element analyses before the dynamic calculations. The effect of twist angle on the gear tooth contact condition and dynamic response are included. The elastic deformations of the gear teeth along the face-width direction are calculated, and validated by comparing with the FE/CM results. / Ph. D.
5

The person from the inside and outside

Vazire, Simine 30 April 2014 (has links)
How do we discover a person’s true personality? How does personality appear from the inside (i.e., to the self)? How does that differ from how personality appears from the outside (i.e., to the observer)? Given that people often see themselves differently than they are seen by others, what are the conditions under which each perspective is accurate? These questions are central to understanding who a person really is and, in turn, how much people are aware of their own and others’ personalities. The goal of this dissertation is to examine these questions. I begin by providing a descriptive account of the differences between self- and other-perceptions in terms of positivity and accuracy. Specifically, in the first two studies, I compare how people see themselves to how they are seen by their friends, romantic partners, parents, and siblings (Chapter 2). Then, in the next two studies, I test the accuracy of self- and other-predictions of behavior by comparing them to actual naturalistic behavior recorded from people’s everyday lives (Chapter 3). Finally, in the fourth study, I examine the accuracy of self, friend, and stranger ratings of personality by comparing personality judgments to laboratory-based behavioral tests of personality (Chapter 4). The results show that self-perceptions are more negative than others’ perceptions of them, people are more aware of their own negative traits than their positive traits, and they fail to notice a substantial number of their own characteristics. Observers agree substantially about what a person is like, and their knowledge of a target’s observable personality is quite good. By comparing perceptions of the person from the inside and outside with objective behavioral criteria, we can come to understand the strengths and limitations of each perspective. In fact, the two perspectives often complement each other – one filling in the gaps left by the other. Furthermore, even when both perspectives are accurate, they are often accurate in different ways. Thus, although neither perspective alone can explain the whole puzzle of who a person really is, they both provide different pieces of the puzzle and together deepen our understanding of the person. / text
6

A Novel Boost Converter Based LED Driver Chip Targeting Mobile Applications

January 2016 (has links)
abstract: A novel integrated constant current LED driver design on a single chip is developed in this dissertation. The entire design consists of two sections. The first section is a DC-DC switching regulator (boost regulator) as the frontend power supply; the second section is the constant current LED driver system. In the first section, a pulse width modulated (PWM) peak current mode boost regulator is utilized. The overall boost regulator system and its related sub-cells are explained. Among them, an original error amplifier design, a current sensing circuit and slope compensation circuit are presented. In the second section – the focus of this dissertation – a highly accurate constant current LED driver system design is unveiled. The detailed description of this highly accurate LED driver system and its related sub-cells are presented. A hybrid PWM and linear current modulation scheme to adjust the LED driver output currents is explained. The novel design ideas to improve the LED current accuracy and channel-to-channel output current mismatch are also explained in detail. These ideas include a novel LED driver system architecture utilizing 1) a dynamic current mirror structure and 2) a closed loop structure to keep the feedback loop of the LED driver active all the time during both PWM on-duty and PWM off-duty periods. Inside the LED driver structure, the driving amplifier with a novel slew rate enhancement circuit to dramatically accelerate its response time is also presented. / Dissertation/Thesis / Doctoral Dissertation Electrical Engineering 2016
7

The Effects of Training in Interaction Analysis on Teachers' Interpersonal Behavior

Buckner, John Wordy 08 1900 (has links)
The specific purposes investigated were to ascertain the effect of training in interaction analysis upon the levels of 1. accurate empathy in teachers, 2. nonpossissive warmth in teachers, 3. genuineness in teachers, and 4. an analysis of the relationship between interaction analysis and the interpersonal behavior of the classroom teacher in view of its implications in teacher education.
8

Role trenéra v přípravě mládeže / The role of the coach in preparation of youth players

Ostaš, Radek January 2016 (has links)
Title: The role of the coach in preparation of youth players Objective: The aim of my work was to observe 3 coaches of football players in age 11-13, their usage of teaching styles used during training units and success of coaches idea's communication towards to their youth players. Hypothesis: Hypothesis 1: I suppose , that coaches will mostly use the direct teaching style Hypothesis 2: I suppose, that most of the ideas will not be told so precisely towards to the players to be able understand them immediately Methods: In my work I used direct and indirect method, structured and opened observation of every single coach and player's reaction to the coaches instruction Results: The aim of my work was reached, I successfully collected and evaluated all needed data Hypothesis 2 => confirmed Hypothesis 2 => unconfirmed Keywords: Coach, teaching style, accurate idea, inaccurate idea
9

Avaliação de protocolos para estimativa do consumo voluntário por caprinos em pasto nativo

ARCANJO, Helton Grégory Santos 26 February 2014 (has links)
Submitted by Mario BC (mario@bc.ufrpe.br) on 2017-02-20T13:27:48Z No. of bitstreams: 1 Helton Gregory Santos Arcanjo.pdf: 4191162 bytes, checksum: 452240cd8f0bf89315fa2e6185a06c0d (MD5) / Made available in DSpace on 2017-02-20T13:27:48Z (GMT). No. of bitstreams: 1 Helton Gregory Santos Arcanjo.pdf: 4191162 bytes, checksum: 452240cd8f0bf89315fa2e6185a06c0d (MD5) Previous issue date: 2014-02-26 / Considering all the knowledge about the variation of native grasses quality and quantity is dependent on the time of year, plus the unknowing and inability in determine the dry matter intake of goats, it sought with this research estimate the pasture intake by these animals. The experiment was conducted to evaluate the external markers chromium oxide (Cr2O3), titanium dioxide (TiO2) and insoluble lignin purified and enriched (LIPE®), such as internal markers: indigestible dry matter (MSi), neutral detergent fiber indigestible (NDFi) and acid detergent fiber indigestible (ADFi) to estimate the dry matter apparent digestibility, fecal dry matter production and estimated dry matter intake by goats kept on native pasture in the semiarid region. It worked with 20 castred males without defined breed, with average body weight of 26 ± 8.4 kg, when five of all were rumen fistulated and 15 did not. The field activity lasted 30 days, 15 days to adapt the animals and the other 15 to providing indicators and colect samples (feces and extrusa). The statistic experimental design was completely randomized (CRD), and the results submitted to the Tukey test at 5% for comparison of means. The internal markers were submitted to descriptive analysis with in vitro digestibility of dry matter (DM) through regression analysis. And then, the results presented that estimates of dry matter intake considering IVDMD, through internal markers were more precise and accurate when used MSi and NDFi, and the opposite being observed for ADFi and the equation. Although about the internal markers, IVDMD and equations were used to estimate the dry matter intake, but significant differences (P<0.05) were observed for the equations while the estimates fecal output through external markers differed significantly (P>0.05) from the result of the total collection. TiO2, Cr2O3 and LIPE ® markers presented statistically different estimate (P>0.05) from total collection, as well as the TiO2 from others markers. LIPE® and Cr2O3 underestimated the fecal output. Regarding the time and method of collection no statistical differences (P>0.05), for any marker and/or method. Therefore, even on native grazing, internal markers proved to be a relevant tool in obtaining data on digestibility and dry matter intake. Can thus supply management supplementation for goats when grazing in rangeland. / Com o conhecimento da oscilação da qualidade e quantidade do pasto nativo em função da época do ano, aliado ao desconhecimento e impossibilidade de determinar o consumo de matéria seca de caprinos, buscou-se com esse experimento estimar o consumo a pasto por esses animais. O experimento foi conduzido com o objetivo de avaliar os indicadores externos óxido de cromo (Cr2O3), dióxido de titânio (TiO2) e Lignina insolúvel purificada e enriquecida (LIPE®), como os internos matéria seca indigestível (MSi), fibra em detergente neutro indigestível (FDNi) e fibra em detergente ácido indigestível (FDAi) para estimativa da digestibilidade aparente da matéria seca, produção de matéria seca fecal e estimativa do consumo de matéria seca por caprinos mantidos em pasto nativo no semiárido. Foram utilizados 20 animais, machos, sem padrão racial definido, castrados, com peso corporal médio de 26±8,4 kg, sendo cinco animais fistulados no rúmen e 15 não fistulados. O experimento teve duração de 30 dias, 15 destinados à adaptação e 15 ao fornecimento dos indicadores e das coletas (fezes e extrusa). O delineamento utilizado foi o inteiramente casualizado (DIC), e os resultados submetidos ao teste de Tukey a 5% para comparação de médias. Os indicadores internos foram submetidos à análise descritiva com a digestibilidade in vitro da matéria seca (DIVMS) por meio da análise de regressão. De posse dos resultados, as estimativas do consumo de matéria seca considerando a DIVMS, por meio dos indicadores internos foram mais acuradas e precisas quando se fez uso da MSi e FDNi, não sendo observado o mesmo para a FDAi e pela equação. Ainda os indicadores internos, a DIVMS e as equações foram utilizados para a estimativa do consumo de matéria seca, porém diferenças significativas (P<0,05) foram observadas para as equações Já as estimativas da produção fecal por meio dos indicadores externos diferiram significativamente (P>0,05) do resultado da coleta total. Os indicadores TiO2, Cr2O3 e LIPE® apresentaram estimativa diferente estatisticamente (P>0,05) da coleta total, assim como o TiO2 dos outros indicadores. O LIPE® e o Cr2O3 subestimaram a produção fecal. Em relação aos horários e métodos de coleta, não foram observadas diferenças estatísticas (P>0,05), para nenhum indicador e/ou método utilizado. Portanto, mesmo em condições de pastejo nativo os indicadores internos mostraram ser uma ferramenta relevante na obtenção de dados sobre digestibilidade e consumo de matéria seca. Podendo assim, estabelecer planos de suplementação para caprinos quando em pastejo em pasto nativo.
10

Étude de deux solutions pour le support matériel de la programmation parallèle dans les multiprocesseurs intégrés : vol de travail et mémoires transactionnelles

Meunier, Quentin 29 October 2010 (has links) (PDF)
L'avènement des puces multicoeurs repose certaines questions quant aux moyens d'écrire les programmes, qui doivent alors intégrer un degré élevé de parallélisme. Nous abordons cette question par l'intermédiaire de deux points de vue orthogonaux. Premièrement via le paradigme du vol de travail, pour lequel nous effectuons une étude visant d'une part à rechercher quelles sont les caractéristiques architecturales simples donnant les meilleures performances pour une implémentation de ce paradigme ; et d'autre part à montrer que le surcout par rapport à une parallélisation statique est faible tout en permettant des gains en performances grâce à l'équilibrage dynamique des charges. Cette question est néanmoins surtout abordée via le paradigme de programmation à base de transactions -- ensemble d'instructions s'exécutant de manière atomique du point de vue des autres coeurs. Supporter cette abstraction nécessite l'implantation d'un système dit TM, souvent complexe, pouvant être logiciel ou matériel. L'étude porte premièrement sur la comparaison de systèmes TM matériels basés sur des choix architecturaux différents (protocole de cohérence de cache), puis sur l'impact d'un point de vue performances de plusieurs politiques de résolution des conflits, autrement dit des actions à prendre quand deux transactions essaient d'accéder simultanément les mêmes données.

Page generated in 0.0588 seconds