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  • 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.
61

Efficient Procedure for Valuing American Lookback Put Options

Wang, Xuyan January 2007 (has links)
Lookback option is a well-known path-dependent option where its payoff depends on the historical extremum prices. The thesis focuses on the binomial pricing of the American floating strike lookback put options with payoff at time $t$ (if exercise) characterized by \[ \max_{k=0, \ldots, t} S_k - S_t, \] where $S_t$ denotes the price of the underlying stock at time $t$. Build upon the idea of \hyperlink{RBCV}{Reiner Babbs Cheuk and Vorst} (RBCV, 1992) who proposed a transformed binomial lattice model for efficient pricing of this class of option, this thesis extends and enhances their binomial recursive algorithm by exploiting the additional combinatorial properties of the lattice structure. The proposed algorithm is not only computational efficient but it also significantly reduces the memory constraint. As a result, the proposed algorithm is more than 1000 times faster than the original RBCV algorithm and it can compute a binomial lattice with one million time steps in less than two seconds. This algorithm enables us to extrapolate the limiting (American) option value up to 4 or 5 decimal accuracy in real time.
62

Inherent insensitivity to RF inhomogeneity in FLASH imaging

Wang, Danli 12 December 2003 (has links)
MRI as a non-invasive method for studying the internal structure and function of the human body was developed over the past three decades. In MRI, radiofrequency (RF) field inhomogeneity is an unavoidable problem in practice and becomes severe at high magnetic fields due to the dependence of B1 on the sample. It leads to nonuniformities in image intensity and contrast, causing difficulties in quantitative interpretation and image segmentation. In this thesis, we report an interesting observation that the fast low-angle shot (FLASH) sequence, which is often used for anatomic imaging and morphometric studies, can be insensitive to RF inhomogeneity when the same coil is used for both transmission and reception and a proper nominal flip angle is employed. Recommendations also are given for optimum processing procedures for FLASH imaging. This observation can be useful in understanding the signal behavior of FLASH in the presence of RF inhomogeneity and provides a guide for selecting parameters in FLASH imaging.
63

Mechanism of Foaming on Polymer-Paperboard Composites

Annapragada, Sriram Kiran 08 November 2007 (has links)
This thesis addresses a new technique of foaming on polymer-paperboard composites which combines the advantages of traditional polymeric foam with the environmental benefits of paperboard. Paperboard is sandwiched between two extruded polymeric layers of different densities. On application of heat, one face is foamed by the evaporating moisture in the board; the other face serves as a barrier. This work is directed at gaining a better understanding of the fundamental processes in foaming polymers on paperboard. The ultimate goal is to be able to produce uniform bubbles of a predetermined size on the surface so as to give optimum heat insulation and good tactile properties. Bubble growth was studied as a function of paperboard properties, polymer melt index, extrusion speed, polymer thickness, temperature and moisture content. The foam quality (thickness) is also related to the cell size distribution and various factors affecting it are identified. A combination of experimental techniques such as high speed imaging, infrared thermography and scanning electron microscopy is used for this purpose. Foaming on paper-polymer composites is caused by water vapor escaping through the pores present in the paperboard substrate and then foaming the polymer. The vapor driving force which dominates foaming and overcomes the less significant viscoelastic and surface tension opposition forces depends on the paperboard properties as well as on the ability of the polymer to bond with the paperboard. It was found that the bubble size distribution directly relates to the pore size distribution on the paperboard. The bubble size was also controlled by the thickness of the polymer layer and its ability to bond with the paperboard. Coalescence subsequently led to thicker foams due to the formation of larger sized bubbles.
64

Effect of Bolts Assembly on the Deformation and Pressure Distribution of Flow-Channel Plates in Micro-PEMFC

Chen, Li-chong 03 August 2010 (has links)
In general, a PEMFC was assembled by using a number of locked bolts. But this assembly will cause concentrated loads existed on the upper and lower portions of the end plates, so that the pressure distributed non-uniformly at the internal structures in the PEMFC and thus causing uneven distributed deformations of flow-channel plates. This phenomenon may lead to the leak of reaction gas, and causing not only the decrease of the efficiency of PEMFC, but also the increase of the dangerous. If the fuel cell size getting smaller, the influence may be more severely. The main aim of this study is to simulate the response of a micro-PEMFC numerically by utilizing a 3-D FEM model while the micro-PEMFC was assembled by three pairs of bolts along the upper and lower portions, respectively, of the end plates. The effects of different bolts locking sequences on the deformation and pressure distributions at flow-channel plates and on the porosity of gas diffusion layers in the micro-PEMFC were investigated. The simulated results showed that if one locked the middle bolt either on the upper or lower portion first, then the obtained uniformities of warpage, deformation, von Mises stress and porosity were superior than the corresponding obtained results if one locked either one of the four corner bolts first. Also, among the three pairs of bolts used for assembling the cell, the first locking bolt of the first pair of locking bolts and the first locking bolt of the rest of two pairs of locking bolts were suggested on the reverse portions of the end plates.
65

A trend study on the uniformity of ASEAN members regarding the South China Sea

Lin, Ken-Li 18 July 2012 (has links)
The issue of South China Sea is one of the hottest international disputes in South East Asia due its location amid the connection between Southeast Asia to Northeast Asia and the rich resources. The undecided maritime delimitation makes the situation more complicated. Because each one of the ASEAN Claims has her own consideration of the interest, their claims and policies confront from each other's, and no consensus has been reached. However, encountering the fact that China proclaimed the entire region of South China Sea, ASEAN Claims attempt to unit themselves to deal with the threat, to negotiate the issue of South China Sea with China as a whole, and attempt to internationalize the issue. Thus, this paper is aimed to realize under what circumstance, ASEAN Claims will tend to unite in the issue of South China Sea, or vise versa, in what circumstance makes ASEAN Claims tend to collapse. According to the "Balance of Threat," China's threat to South China Sea affairs leads the changing of the unity of ASEAN Claims directly, and influences the consistency of South China Sea's policy. Besides the United States, the other side of the balance of the two counter powers, the treat brought by China in South China Sea affairs is the key to influence the South China Sea policy consistency of ASEAN Claims. "South China Sea Core interest" is one of match instance.
66

The Fabrication and Uniformity Analysis of Low Temperature Ce3+¡GYAG Doped Glass

Chen, Ji-Hung 15 August 2012 (has links)
Using low-temperature (650¢J) Ce3+:YAG doped glass (LTCeYDG) phosphor layer instead of conventional Ce:YAG doped silicone phosphor layer applied to high-power phosphor-converted white-light-emitting diodes (PC-WLEDs) is demonstrated.The glass transition temperature (Tg) of silicone is 150¢J but glass is 750¢J,it shows the glass were employed in high power LED than silicon. The uniformity of phosphor powder doped glass is an important item to discriminates between good and bad. Quantize the uniformity of glass phosphor by image processing software and Distribution Uniformity (Du). Calculate the uniformity of phosphor powder mix with glass powder which has different particle size and measurement optical properties of glass phosphor which has different uniformity. The Du of glass phosphor are 64.46%, 84.65%, 85.24% , 91.85% and the quantum efficiency are 18.49%, 28.31%, 29.73%, 28.56% ,respectively. By using Ceramic tube and low temperature glass powder sintering glass phosphor is a new fabrication. Compare with last fabrication, new fabrication reduce 100¢Jfabrication temperature from 750¢J to 650¢J, 70% material savings and high luminous efficiency. The quantum efficiency and lumen per watt were improved about 7 percentage point from 22.3% to 29.1% and 4.2 lm/W from 36.4 lm/W to 40.68 lm/W. We used the XRD to analyze the glass phosphor of last fabrication and new fabrication and the results show that the higher thermal stress destroys the structure of YAG, lower fabrication temperature used to get higher luminous efficiency.
67

Compaction Effects on Uniformity, Moisture Diffusion, and Mechanical Properties of Asphalt Pavements

Kassem, Emad Abdel-Rahman Ahmed 2008 December 1900 (has links)
Field compaction of asphalt mixtures is an important process that influences performance of asphalt pavements; however there is very little effort devoted to evaluate the influence of compaction on the uniformity and properties of asphalt mixtures. The first part of this study evaluated relationships between different field compaction patterns and the uniformity of air void distribution in asphalt pavements. A number of projects with different asphalt mixture types were compacted, and cores were taken at different locations from these projects. The X-ray Computed Tomography (X-ray CT) system was used to capture the air void distributions in these cores. The analysis results have revealed that the uniformity of air void distribution is highly related to the compaction pattern and the sequence of different compaction equipment. More importantly, the efficiency of compaction (reducing air voids) at a point was found to be a function of the location of this point with respect to the compaction roller width. The results in this study supported the development of the "Compaction Index (CI)," which quantifies the degree of field compaction. The CI is a function of the number of passes at a point and the position of the point with respect to the compaction roller width. This index was found to correlate reasonably well with percent air voids in the pavement. The CI calculated from field compaction was also related to the slope of the compaction curve obtained from the Superpave gyratory compactor. This relationship offers the opportunity to predict field compactability based on laboratory measurements. The compaction of longitudinal joints was investigated, and recommendations were put forward to improve joint compaction. The air void distributions in gyratory specimens were related to the mixture mechanical properties measured using the Overlay and Hamburg tests. The second part of this study focused on studying the relationship between air void distribution and moisture diffusion. A laboratory test protocol was developed to measure the diffusion coefficient of asphalt mixtures. This important property has not measured before. The results revealed that the air void phase within the asphalt mixtures controls the rate of moisture diffusion. The measured diffusion coefficients correlated well with the percent and size of connected air voids. The measured diffusion coefficient is a necessary parameter in modeling moisture transport and predicting moisture damage in asphalt mixtures. The last part of this study investigated the resistance of asphalt mixtures with different percent air voids to moisture damage by using experimental methods and a fracture mechanics approach that accounts for fundamental material properties.
68

Entwicklung einer Niederenergie-Implantationskammer mit einem neuartigen Bremslinsensystem

Borany, Johannes von, Teichert, Jochen 31 March 2010 (has links) (PDF)
In diesem Report wird eine Niederenergie-Implantationskammer (NEI-Kammer) beschrieben, die im Forschungszentrum Rossendorf entwickelt und aufgebaut wurde. Die Kammer ermöglicht es, die Implantation von Ionen bei niedrigen Energien (< 30 keV) mit einer Implantationsanlage für mittlere Energien durchzuführen. In der Kammer werden der Ionenstrahl, den der Implanter liefert, auf die erwünschte niedrige Energie abgebremst. Dazu wird ein elektrostatisches Bremslinsensystem eingesetzt, das auf einem neuartigen Prinzip basiert. Das System besteht aus einer Sammellinse und einer Zerstreuungslinse, wobei die Öffnungsfehler beider Linsen entgegengesetzte Vorzeichen besitzen und sich gegenseitig kompensieren. Dadurch ist es möglich, Wafer gebräuchlicher Größe bei geringer Energie mit hoher Dosishomogenität zu implantieren. Die NEI-Kammer ist insbesondere für Forschungseinrichtungen eine vorteilhafte Lösung, da sie eine wesentlich kostengünstigere und flexiblere Alternative zur Anschaffung einer Niederenergie-Implantationsanlage darstellt.
69

Evaluation of the application uniformity of subsurface drip distribution systems

Weynand, Vance Leo 30 September 2004 (has links)
The goal of this research was to evaluate the application uniformity of subsurface drip distribution systems and the recovery of emitter flow rates. Emission volume in the field, and laboratory measured flow rates were determined for emitters from three locations. Additionally, the effects of lateral orientation with respect to slope on emitter plugging was evaluated. Two different emitters were tested to evaluate slope effects on emitter plugging (type Y and Z). The emitters were alternately spliced together and installed in an up and down orientation on slopes of 0, 1, 2 and 4% and along the contour on slopes of 1 and 2%. The emitters were covered with soil and underwent a simulated year of dosing cycles, and then flushed with a flushing velocity of 0.6 m/s. Initial flow rates for the two emitter types were 2.38 L/hr with a C.V. of 0.07. There was no significant difference in flow rates among slopes for type Y emitters, but there was a significant difference between the 1% and 2 % contour slopes for type Z emitters. Application uniformity of three different laterals at each site was evaluated. Sections of the lateral from the beginning, middle and end were excavated and emission volumes were recorded for each emitter. Application uniformity of laterals ranged from 48.69 to 9.49%, 83.55 to 72.60%, and 44.41 to 0% for sites A, B, and C, respectively. Mean emitter flow rate was 2.21, 2.24, and 2.56 L/hr for sites A, B, and C, respectively under laboratory conditions. Application uniformity under laboratory conditions ranged from 70.97 to 14.91%, 86.67 to 79.99%, and 85.04 to 0.00% for sites A, B, and C, respectively. A flushing velocity of 0.15 m/s with no chlorination, shock chlorination of 3400 mg/L and flushing velocity of 0.15 m/s, and shock chlorination of 3400 mg/L and flushing velocity of 0.6 m/s treatment regiments were applied to all laterals collected to assess emitter flow rate recovery to the nominal flow rate published by the manufacturer. All laterals showed an increase in the number of emitters within 10% of the published nominal flow rate.
70

Multi-Objective Design Optimization of Electric Vehicle Battery Cooling Plates Considering Thermal and Pressure Objective Functions

Jarrett, Anthony 07 September 2011 (has links)
The current stimuli of climate change and rising oil prices have spurred the development of hybrid electric (HEV), and battery electric vehicles (BEV): collectively termed EVs. However, the battery technology needs much development: at the time of writing, the range of a BEV is too low to be practical in many situations. A critical limitation is the sensitivity of batteries to temperature: the heat generated during operation affects their performance and reduces the lifetime. This study investigates battery cooling using cooling plates: thin rectangular fabrications inserted between battery cells. A coolant pumped through internal channels absorbs heat and transports it away from the battery. Previous studies of liquid heat exchangers have indicated that the geometry of the channels plays a significant role in the performance; however, there is a lack of rigorous numerical optimization applied to EV cooling plates. By developing a numerical optimization framework utilizing parametric geometry generation and computational fluid dynamics, this research has investigated the characteristics of optimum cooling plate geometry with respect to three objectives: average temperature, temperature uniformity, and coolant pressure drop. By applying each objective separately, improvements of up to 70% have been made compared to a reference design. The influence of boundary conditions on performance and optimum design has been assessed, and multi-objective optimization has investigated the trade-off between competing objective functions. Although care should be taken when extrapolating the results beyond the geometry and conditions in the study, some general design principles can be proposed. Objectives of average temperature and pressure drop can both be satisfied by a common design with wide cooling channels, but different characteristics are needed for temperature uniformity. Additional assessments have revealed that optimizations of temperature uniformity are especially sensitive to the boundary conditions, whereas the other objective functions are largely insensitive. The optimization process developed in this work can be applied to any potential cooling plate design and will lead to gains in the targeted performance measure. In doing so, the performance of the EV will be incrementally improved, thereby advancing the day when an EV is not only an environmental choice, but also a practical choice. / Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2011-09-07 16:24:14.6

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