Дисертації з теми "Asymmetric profiles"

There is a growing recognition worldwide of the need for more powerful, smaller petrol engines, capable of delivering the higher picking power of larger engines, yet still being economical and environmentally friendly when used for day-to-day driving. An engineering solution for more efficient engines has been considered by research so far. It has been identified that superchargers can potentially improve the performance of automotive engines; therefore research has focused on developing superchargers and supercharger components with higher efficiency. Of particular interest to the research presented in this thesis has been the twin-screw supercharging compressor with design adapted for automotive use (the twin-screw supercharger). The performance of this supercharger type depends on the volume and total losses of the air flow through the supercharger rotors more than on any other aspects of its behaviour. To accurately predict the efficiency of the twin-screw su percharger for matching a particular engine system, accurate supercharger design is required. The main objective of this research was the investigation of the existing limitations of twin-screw superchargers, in particular leakage and reduced efficiency, leading to the development of optimal asymmetric rotor profiles. This research has been completed in four stages defining an innovative rotor design method. The parametric three-dimensional geometric model of twin-screw supercharger rotors of any aspect ratio was developed. For model validation through visualisation, CAD rotor models with scalable data were generated in commercial CAD software and calibrated experimentally by Laser Doppler Velocimetry (LDV) tests. Calibrated rotor profile data can be transferred into CAD-CFD interface for flow simulation and performance optimisation. Through the application of this new rotor design method, new opportunities are created for the twin-screw supercharger design practice, making it a part of the engineering solution for more efficient engines.

Recombination line profile shapes are derived for ionized spherical stellar winds at radio wavelengths. It is assumed that the wind is optically thick owing to free-free opacity. Emission lines of arbitrary optical depth are obtained assuming that the free-free photosphere forms in the outer, constant expansion portion of the wind. Previous works have derived analytic results for isothermal winds when the line and continuum source functions are equal. Here, semi-analytic results are derived for unequal source functions to reveal that line shapes can be asymmetric about line center. A parameter study is presented and applications discussed.

The technology of lubrication systems for aircrafts engines has seen significant development during the history of aeronautics and has progressed in parallel with the evolution of the engines themselves. Starting from the first, wetsump schemes derived from automotive applications, more complex systems and components have been introduced. The progressive increase of aeronautic engines’ power and speed, as well as that of the maximum operative altitude of the aircraft, have increased the lubricant flow rate required to avoid severe mechanical issues that can cause dangerous conditions for the vehicle and its users. Currently, the main focus on the development of novel lubrication pumps is aimed at reducing the pumps’ weight and envelope while maintaining, or possibly increasing, their reliability. The first two objective could be pursued by searching for novel pump types and/or increasing the pump speed in order to downsize its required capacity, but the low-pressure environment, typical of the lubrication circuits, over imposes a few, severe, limitations to avoid cavitation occurrence that decrease the effectiveness of this approach. The central aim of the presented research, performed within the program “Greening the Propulsion”, is to provide a theoretical framework to help in the development of a novel gerotor pump for the lubrication of aeronautic engines.The first step of the research involves the study of the state of the art of aeronautic engines’ lubrication systems, providing particular care to the effect that any design choice and possible operational condition may have on the lubrication pump design. Hence, the state of the art for gerotor pumps is investigated; results of this study are used, along with catalogue comparisons, to build simplified sizing tools to perform a benchmarking activity involving gerotors and other low pressure pumps type. This activity, performed to position gerotor pumps in the aeronautic engine lubrication market, is then used as a starting point to highlight the weak points of gerotors traditional design and to propose some possible solutions to enhance the pumps performances. To study the outcomes of these modifications, a rigorous theoretical framework is required; sizing and modeling criteria, based on the theory of gearing and compressible fluids, are hence detailed and used to build an Automatic Design and Simulation Framework, able to automatically design, validate and simulate a novel gerotor pump given a minimum number of geometrical and physical input parameters. This design and simulation tool is then used to evaluate the performance boost provided by the proposed variations and to optimize the gears profiles by pairing it with a multiobjective algorithm based on evolutionary strategies. Another critical component of any lubrication system is the pressure relief valve used to avoid the occurrence of dangerous conditions for the pipes integrity. A side activity involving the study of a preliminary sizing tool for pressure relief valve is hence performed. A preliminary design framework is presented and discussed, highlighting the importance of the valve discharge coefficient. To study its dependence on the valve’s geometry, a lengthy CFD simulation campaign is performed varying the poppet shape and the fluid Reynolds’ number. Results are hence discussed and used inside the design framework.

In this paper we analyze the small C1.5 class solar flare observed on June 30th 2013 by the Swedish Solar Telescope. The evolution of asym- metries in the Hα line profile of the solar flare was studied where it could be seen how the number of red asymmetric regions had a maximum value near the beginning of the flare and then decreases rapidly in the first 4 minutes of the observations. This could be interpreted as a correlation with the HXR and microwave emissions of the impulsive phase of the flare as these emissions also typically have a similar rapid increase and decrease of emission intensity.

Thesis (Ed.D.)--Teachers College, Columbia University, 1985.
Typescript; issued also on microfilm. Sponsor: J. R. Higgins. Dissertation Committee: A. M. Gentile. Includes bibliographical references: (leaves 48-52).

Clusters of galaxies are particularly interesting astrophysical systems, are the largest bound structures in the Universe, and contain fair sample of cosmic ingredients. Studies of cluster abundance as a function of mass and redshift were critical in establishing the standard model of cosmology. This dissertation presents results from X-ray imaging of massive distant (M > 10^14 M; 0:3 < z < 1.2) clusters, found via X-ray emission or Sunyaev-Zeldovich eff ect. This is the world's largest sample of massive galaxy clusters. We explore the radial and azimuthal profi les of the X-ray emitting gas and show that clusters are self-similar objects: their internal structure is largely independent of the cluster's mass or redshift, and the fractions of di fferent types of clusters does not change with redshift. We also present a new statistical technique for measuring a cluster's deviations from a perfect axisymmetric shape, which is especially useful in the case of low photon count observations of distant clusters.
Physics

The Global Value Chain Governance Framework is empirically tested in this thesis. The framework has become a highly influential in determining the governance structure of firms. Despite the framework being widely influential and used extensively across industry-specific case research and international development agencies, there has been limited empirical validation of the framework's predictions. Adopting a two-study quantitative methodology and configuration analysis, in this thesis an important foundational advancement is advanced in the application of configuration analysis to test the GVC governance framework. A foundational elaboration of theory is offered by, first, conceptualising the GVC core concepts and, second, executing empirical research as a basis for developing new theoretical insights.

This thesis proposes a method to reconstruct a frontal facial video basedon encoding done with the facial profile of another video sequence.The reconstructed facial video will have the similar facial expressionchanges as the changes in the profile video. First, the profiles for boththe reference video and for the test video are captured by edge detection.Then, asymmetrical principal component analysis is used to model thecorrespondence between the profile and the frontal face. This allows en-coding from a profile and decoding of the frontal face of another video.Another solution is to use dynamic time warping to match the profilesand select the best matching corresponding frontal face frame for re-construction. With this method, we can reconstructed the test frontalvideo to make it have the similar changing in facial expressions as thereference video. To improve the quality of the result video, Local Lin-ear Embedding is used to give the result video a smoother transitionbetween frames.

Une combinaison de moyens passifs et actifs de contrôle d'écoulement est utilisée pour réduire la traînée aérodynamique produite par le sillage turbulent d'une géométrie simplifiée de véhicule à culot droit. Ces sillages sont caractérisés par deux aspects principaux : une traînée de pression importante liée à la séparation massive de l'écoulement, et des asymétries à grande échelle. Ces dernières, se manifestant sous forme de dynamique bimodale ou de brisure de symétrie permanente, contribuent pour environ 10% de la traînée de pression. L'étude des basculements de sillage transitoires en dynamique bimodale s'opérant au travers d'états symétriques du sillage permet d'isoler le mécanisme responsable de l'augmentation de traînée des états à brisure de symétrie. Une interaction et un couplage entre l'écoulement de recirculation issu d'un côté et la couche cisaillée opposée propre aux états à brisure de symétrie déclenche et amplifie les instabilités de couche cisaillée, ce qui conduit à une augmentation de l'écoulement d'entraînement et de la traînée. Il est montré que ce mécanisme est caractéristique des sillages de corps à culot droit.Une stratégie de contrôle actif de l'écoulement combinant des jets pulsés émis tangentiellement aux bords de fuite et de surfaces courbées miniatures affleurantes est utilisée pour réduire la traînée de pression de la géométrie. Le recollement de l'écoulement sur les surfaces courbées résulte en un rétreint fluidique du sillage se traduisant par une réduction de trainée jusqu'à 12%, indépendamment de l'asymétrie initiale du sillage, et est notablement influencé par l'échelle de temps caractéristique de l'instationnarité du forçage. Une combinaison minutieuse entre l'échelle de temps du forçage et la taille caractéristique des surfaces courbées permet d'exploiter tout le potentiel de réduction de traînée de cet effet Coanda instationnaire comme le montre un modèle simple d'écoulement permettant la mise en évidence de lois d'échelles caractérisant le phénomène. De plus, un forçage localisé selon certaines arêtes seulement permet d'interagir avec les asymétries à grande échelle du sillage et impacte de manière très différente la traînée selon l'équilibre su sillage non-forcé. La symétrisation du sillage résultant d'un forçage asymétrique permet une réduction de traînée d'environ 7% à coup énergétique réduit. Des éléments clefs sont donnés concernant l'adaptation de la localisation du contrôle pour une réduction de traînée en présence de différentes asymétries du sillage. Comme le changement d'équilibre global du sillage résulte de changements géométriques et d'écoulement mineurs, des stratégies de contrôle adaptives et robustes sont essentielles pour les applications dans l'industrie automobile
Combination of passive and active flow control are used to experimentally reduce the aerodynamic drag produced by the turbulent wake past a simplified vehicle geometry with a blunt base. Such wakes are characterized by two main features: important pressure drag linked to the massive flow separation, and large-scale asymmetries. The latter,manifesting as bi-modal dynamics or permanent symmetry-breaking, are shown to contribute for around 10% of the pressure drag. The study of the transient wake reversais occurring in bi-modal dynamics though symmetric states enables to isolate the flow mechanism responsible for increased drag in symmetry-breaking states. An interaction and coupling between the recirculating flow from one side and the shear-layer from opposite side peculiar to symmetry-breaking states triggers shear-layer instabilities and their amplification leading to increased flow entrainment and drag.This mechanism is shown to be characteristic of the wakes of blunt bodies.An active flow control strategy combining tangential pulsed jets along the trailing-edges and small flush-mounted curved surfaces is used to reduce the pressure drag of the geometry. The flow reattachment and separation on thecurved surfaces results in a fluidic boat-tailing of the wake leading to drag reductions up to 12%, independently of the unforced large-scale asymmetry of the wake, and is noticeably influenced by the time-scale of unsteadiness of the forcing. Careful combination between forcing time-scale and size of the curved surfaces is needed to achieve ail thepotential of this unsteady Coanda effect in drag reduction as shown from a simple flow model providing scaling laws of the phenomenon. The model provided allows for an extension of the flow control mechanism to separated flows moregenerally. Furthermore, forcing along only selected edges enables to interact with the large-scale wake asymmetries and has very different impact on the drag depending on the unforced wake equilibrium. Symmetrisation of the wake through asymmetric forcing leads to 7% drag reduction at a reduced energetic cost. Key ingredients are provided to adapt forcing strategies for drag reduction in presence of various wake asymmetries. As global wake equilibrium changes result from minor geometric and flow conditions changes, adaptive and robust flow control strategies are essential for industrial automotive applications

碩士
國立彰化師範大學
電子工程學系
96
AlGaInAs material was used to design 1.31μm semiconductor laser diodes by applying asymmetric quantum wells. Commercial softwares APSYS and LASTIP was used to simulate the effect of quantum well thickness，composition，and arrangement on the gain profile of the laser. The effects of cavity length and mirror reflectance on the flatness of the gain profile were also studied. The simulation results indicated that the width of the gain profile can be manipulated by changing the width and number of the quantum wells while the flatness and intensity of the gain profile can be adjusted by changing the arrangement of quantum wells. Optical confinement factor played an important role by enhancing electrical and optical coupling. The gain corresponding to quantum wells with higher confinement factor will be enhanced. The threshold gain was increased when the cavity length was decreased. The threshold carrier density increased due to larger mirror loss. The gain profike corresponding to narrow quantum wells was enhanced due to higher injection and higher differential gain. Changing cavity length had similar effect.

碩士
明新科技大學
精密機電工程研究所
97
The worm gear set is one of the cross axes transmission mechanisms. Worm gear set can conquer the tooth undercutting problem, which occurs due to the small number of teeth of conventional gear sets with some special modules. Therefore, worm gear set can provide high gear ratios that spur and helical gear set could not offer. Besides, the worm gear set has a larger contact ratio which enables its loading capability. In this research, mathematical model of a worm gear set is developed based on the theory of gearing and the technique of computer aided design. The worm is generated by an asymmetrical grinding wheel. The mathematical model of the asymmetric ZK-type worm surfaces can be obtained by simulation of the generation mechanism of the grinding wheel and worm. With the design of an oversize worm type hob cutter, the mathematical model of the worm gear surfaces can be obtained according to the oversize hob cutter and worm gear hobbing mechanism. The equation of meshing between the oversize hob cutter and the produced worm gear surfaces is also studied. Based on the developed mathematical models of the worm and worm gear, the finite element stress analysis of the worm gear set is performed. Analysis results of the asymmetric ZK-type worm gear set are compared with those of conventional symmetric ZK-type worm gear set. The analysis results are most helpful to the designer and manufacturer of the worm gear set. Key words：Worm and worm gear set, ZK-type, Oversize hob cutter, Asymmetric tooth profile, Stress analysis.

碩士
國立屏東科技大學
機械工程系所
99
Gear pumps have been widely used in the fluid transmission systems nowadays. Generally, an external gear pump has a pair of gears, which are operated in an operation space in the housing. A sealed volume in the housing is reduced by the gears and accordingly fluid is compressed as the gears are engaged with each other and rotated. However, the outflow fluctuation may be induced by such a periodic variation of the sealed volume. The flow leakage may also occur because of the clearances between the gears and the housing. Moreover, since the gear design constraints, there will form trapped volumes between the gear surfaces and lead to gear pitting and low flow efficiency. This thesis aims to study the relationship between the asymmetric tooth profile parameters of the pump gears and the pump performance indices. The direct gear design (DGD) method is adopted to design the asymmetric gear tooth profile, wherein the tooth number, the circular pitch thickness, the pressure angle and the contact ratio are directly given and then the other geometric parameters used to depict a fully gear tooth profile can be derived. Compared with the traditional rack generating method, the DGD method can obtain the larger contact ratio and wider design range in gear tooth profile design under the same meshing pressure angle. Further, the contact positions in each engaged stage of a pair of pump gears are analyzed and calculated by transforming the contact length into the calculation of flow rate, outflow fluctuation amplitude and so on to estimate the flow characteristics of the gear pump under different gear tooth parameters. As shown in the numerical results, the coefficient of non-uniform flow rate can be reduced by increasing the tooth number and decreasing the contact ratio or the asymmetric coefficient of gears. Besides, the outflow fluctuation amplitude can be reduced by decreasing the tooth number, contact ratio or asymmetric coefficient of the pump gears. Further, as the tooth number, contact ratio or asymmetric coefficient of the pump gears increase, the average flow rate of the gear pump can be increased.

碩士
國立交通大學
資訊管理研究所
101
Since Fama defines the efficient market hypothesis, the researchers have published a study of empirical analysis of efficient markets, but because the different kinds of research methods, research data, and the research object, whether the market is efficient or not may also have different conclusions. Based on the theory of market profile, the study intends to analyze the eight-year Taiwan Stock Index Futures data using back-propagation neural network as an assessment tool for the future market direction. The study tries to find free exposure in the futures market, so as to achieve better profit point but low-risk trading position and discuss the relationship between risk and return in Taiwan futures market, then examine the Taiwan futures market meet the weak-form efficient market hypothesis. The research results show that indeed it finds out the relative low-risk trading price in the futures market. The experimental results not only verify the effectiveness of the market profile indicator, but also support the asymmetric relationships between risk and return exists in the Taiwan futures market, so that the Taiwan futures market does not meet the weak-form efficient market hypothesis.

The goal of the Q-weak experiment is to make a measurement of the proton's weak charge ($Q^p_W = 1-4\sin^2\theta_W$) to an accuracy of ~4%. This would represent a ~0.3% determination of the weak mixing angle ($\sin^2\theta_W$) at low energy. The measurement may be used for a precision test of the Standard Model (SM) prediction on the running of $\sin^2\theta_W$ with energy scale. The Q-weak experiment operates at Thomas Jefferson National Accelerator Facility (Jefferson Lab). The experiment determines the proton's weak charge by measuring the parity violating asymmetry in elastic electron-proton scattering at low momentum transfer $Q^2 = 0.026 (GeV/c)^2$ and forward angles (~8 degree). The anticipated size of the asymmetry, based on the SM, is about 230 parts per billion (ppb). With the proposed accuracy, the experiment may probe new physics beyond Standard Model at the TeV scale. This thesis focuses on my contributions to the experiment, including track reconstruction for momentum transfer determination of the scattering process, and the focal plane scanner, a detector I designed and built to measure the flux profile of scattered electrons on the focal plane of the Q-weak spectrometer to assist in the extrapolation of low beam current tracking results to high beam current. Preliminary results from the commissioning and the first run period of the Q-weak experiment are reported and discussed.

Introdução: A estética facial é um fator preponderante no diagnóstico ortodôntico. No entanto, é difícil definir o objetivo do tratamento com base apenas no perfil estético, visto que não existe apenas um perfil facial considerado por toda a população como esteticamente atrativo, pois cada indivíduo tem o seu próprio conceito de beleza, que se relaciona com diversos fatores. Este estudo tem como objetivo a obtenção de dados específicos e atualizados, referentes à atratividade facial de indivíduos caucasianos de nacionalidade portuguesa. Pretende-se avaliar o impacto da proeminência mandibular, da assimetria facial, do perfil labial e da altura facial inferior, determinar o limiar em que se tornam clinicamente significativos e esteticamente relevantes e o impacto destas características por género e histórico de tratamento ortodôntico. Metodologia: Procedeu-se à manipulação de fotografias de um indivíduo do género masculino e um do género feminino, considerados esteticamente normais segundo os padrões correntes, alterando as características em estudo, com o intuito de criar um álbum com as fotografias organizadas aleatoriamente, que foi distribuído a 30 médicos dentistas, 30 estudantes de Medicina Dentária da UCP e 30 leigos, que avaliaram cada fotografia numa VAS de 100 mm. Resultados: Verificámos que o perfil facial escolhido como o mais atrativo foi o perfil padrão para ambos os géneros, sendo que a protrusão mandibular severa, a retrusão labial severa, a altura facial inferior diminuída extrema e a assimetria facial severa foram considerados como menos atrativos para ambos os géneros. Verificou-se que os leigos são menos críticos que os estudantes e profissionais de medicina dentária. Também se verificou a inexistência de diferença significativa da influência do histórico de tratamento ortodôntico e do género. Conclusões: A estética facial é um fator que interfere com a autoestima do paciente, acarretando implicações a vários níveis, sendo de grande interesse para o médico dentista comparar os critérios de avaliação da atratividade facial, permitindo uma melhor satisfação por parte do paciente, no que toca aos ideais do tratamento ortodôntico
Introduction: Facial aesthetics is an important factor for orthodontic diagnosis. However, it is difficult to define the goal of treatment only based on aesthetic profile, since there is not one only facial profile credited for the entire world population as aesthetically attractive, because each individual has his own concept of beauty, which is related to several factors. This study aims at obtaining specific and updated data, regarding facial attractiveness of Portuguese caucasians individuals. It is intended to assess the impact of mandibular prominence, facial asymmetry, lip profile and lower facial height, determine the threshold where they become clinically significant and aesthetically relevant to different groups, and the impact of these characteristics by gender and history of orthodontic treatment. Methods: We manipulate the photographs of a male and a female, aesthetically considered normal according to current standards, increasing and decreasing the features under study, with the aim of creating an album with randomly organized photos, which was distributed to 30 dentists, 30 dental students of UCP and 30 laypeople. Each one assessed each photograph in a 100 mm visual analog scale. Results: We found that the facial profile by the sample chosen as the most attractive was the straight profile for both genders, with severe mandibular protrusion, severe lip retrusion, severe lower facial height decreased and severe facial asymmetry were considered less attractive to both genders. It was found that the laypeople are less critical that students and dental professionals. It was also found that there was no significant difference in the influence of the history of orthodontic treatment and gender. Conclusions: The facial aesthetics is a factor that interferes with the patient's self-esteem, with implications at various levels, being of great interest to the dentist compare the evaluation criteria of facial attractiveness, in terms the satisfaction of the ideals of orthodontic treatment