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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.
431

Fast interactive 2D and 3D segmentation tools.

January 1998 (has links)
by Kevin Chun-Ho Wong. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1998. / Includes bibliographical references (leaves 74-79). / Abstract also in Chinese. / Chinese Abstract --- p.v / Abstract --- p.vi / Acknowledgements --- p.vii / Chapter 1 --- Introduction --- p.1 / Chapter 2 --- Prior Work : Image Segmentation Techniques --- p.3 / Chapter 2.1 --- Introduction to Image Segmentation --- p.4 / Chapter 2.2 --- Region Based Segmentation --- p.5 / Chapter 2.2.1 --- Boundary Based vs Region Based --- p.5 / Chapter 2.2.2 --- Region growing --- p.5 / Chapter 2.2.3 --- Integrating Region Based and Edge Detection --- p.6 / Chapter 2.2.4 --- Watershed Based Methods --- p.8 / Chapter 2.3 --- Fuzzy Set Theory in Segmentation --- p.8 / Chapter 2.3.1 --- Fuzzy Geometry Concept --- p.8 / Chapter 2.3.2 --- Fuzzy C-Means (FCM) Clustering --- p.9 / Chapter 2.4 --- Canny edge filter with contour following --- p.11 / Chapter 2.5 --- Pyramid based Fast Curve Extraction --- p.12 / Chapter 2.6 --- Curve Extraction with Multi-Resolution Fourier transformation --- p.13 / Chapter 2.7 --- User interfaces for Image Segmentation --- p.13 / Chapter 2.7.1 --- Intelligent Scissors --- p.14 / Chapter 2.7.2 --- Magic Wands --- p.16 / Chapter 3 --- Prior Work : Active Contours Model (Snakes) --- p.17 / Chapter 3.1 --- Introduction to Active Contour Model --- p.18 / Chapter 3.2 --- Variants and Extensions of Snakes --- p.19 / Chapter 3.2.1 --- Balloons --- p.20 / Chapter 3.2.2 --- Robust Dual Active Contour --- p.21 / Chapter 3.2.3 --- Gradient Vector Flow Snakes --- p.22 / Chapter 3.2.4 --- Energy Minimization using Dynamic Programming with pres- ence of hard constraints --- p.23 / Chapter 3.3 --- Conclusions --- p.25 / Chapter 4 --- Slimmed Graph --- p.26 / Chapter 4.1 --- BSP-based image analysis --- p.27 / Chapter 4.2 --- Split Line Selection --- p.29 / Chapter 4.3 --- Split Line Selection with Summed Area Table --- p.29 / Chapter 4.4 --- Neighbor blocks --- p.31 / Chapter 4.5 --- Slimmed Graph Generation --- p.32 / Chapter 4.6 --- Time Complexity --- p.35 / Chapter 4.7 --- Results and Conclusions --- p.36 / Chapter 5 --- Fast Intelligent Scissor --- p.38 / Chapter 5.1 --- Background --- p.39 / Chapter 5.2 --- Motivation of Fast Intelligent Scissors --- p.39 / Chapter 5.3 --- Main idea of Fast Intelligent Scissors --- p.40 / Chapter 5.3.1 --- Node position and Cost function --- p.41 / Chapter 5.4 --- Implementation and Results --- p.42 / Chapter 5.5 --- Conclusions --- p.43 / Chapter 6 --- 3D Contour Detection: Volume Cutting --- p.50 / Chapter 6.1 --- Interactive Volume Cutting with the intelligent scissors --- p.51 / Chapter 6.2 --- Contour Selection --- p.52 / Chapter 6.2.1 --- 3D Intelligent Scissors --- p.53 / Chapter 6.2.2 --- Dijkstra's algorithm --- p.54 / Chapter 6.3 --- 3D Volume Cutting --- p.54 / Chapter 6.3.1 --- Cost function for the cutting surface --- p.55 / Chapter 6.3.2 --- "Continuity function (x,y, z) " --- p.59 / Chapter 6.3.3 --- Finding the cutting surface --- p.61 / Chapter 6.3.4 --- Topological problems for the volume cutting --- p.61 / Chapter 6.3.5 --- Assumptions for the well-conditional contour used in our algo- rithm --- p.62 / Chapter 6.4 --- Implementation and Results --- p.64 / Chapter 6.5 --- Conclusions --- p.64 / Chapter 7 --- Conclusions --- p.71 / Chapter 7.1 --- Contributions --- p.71 / Chapter 7.2 --- Future Work --- p.72 / Chapter 7.2.1 --- Real-time interactive tools with Slimmed Graph --- p.72 / Chapter 7.2.2 --- 3D slimmed graph --- p.72 / Chapter 7.2.3 --- Cartoon Film Generation System --- p.72
432

Binocular tone mapping. / 雙目色調映射 / CUHK electronic theses & dissertations collection / Shuang mu se diao ying she

January 2012 (has links)
隨著3D電影和遊戲的蓬勃發展,雙目(立體)顯示設備日益流行,也變得更為廉價。 立體顯示設備 引入了一個額外的圖像空間,使得用於顯示的圖像域翻倍(一個圖像域對應左眼,另一個對應右眼)。 目前的雙目(立體)顯示設備主要把這個額外的圖像空間用於顯示三維立體信息。 / 人們的雙目視覺系統不僅可以把雙眼看到的具有深度差異信息的兩個圖像融合起來,而且可以把兩個在亮度,色彩, 對比度,甚至是內容細節上有一定程度不同的圖像融合到一起,形成一個單一的視界。 這個現象叫做雙眼單視界(Binocular Single Vision)。通過一些列複雜的神經生理融合過成,人們可以通過雙眼單視界比只用任意一隻單眼 觀察到更多視覺內容和信息,其獲得的信息量也多於兩個視野的線性組合。 / 在本畢業論文中,雙眼單視界首次被應用到了計算機圖形學領域,基於這一現象,提出了一個新穎的雙目色調映射框架(Binocular Tone Mapping Framework)。對於輸入的高動態範圍(High-Dynamic Range, HDR)圖像,我們的雙目色調映射 構架將生成一組用於雙目觀看的低動態範圍(Low-Dynamic Range, LDR)圖像對,用以從原HDR圖像中保留 更多的人們可感知到的視覺內容和信息。 給定任意一個指定的色調映射方法,我們的雙目計算框架首先通過使用其默認或者 人工選擇的參數生成一張LDR圖像(不失一般性,我們指定為左視野圖),隨後,圖像對中的另一張LDR圖像 將由系統從同一HDR圖像源使用最優化算法生成。 結果的兩張LDR圖像是不相同的,它們分別保留了不同的視覺信息。通過使用雙目顯示設備,它們可以合計表現出比任一單張LDR圖像更豐富的圖像內容。 / 人們的兩個視野對圖像差異不是無限的,也存在一個容忍度。一旦超過了某個限制閾值,視覺上的不適感覺就會出現。 了避免不適 的產生,我們設計了一個全新的雙目視覺舒適預測預器(Binocular Viewing Comfort predictor)用以預測 雙目視覺的不舒適閾值。 在我們的雙目色調映射構架中,BVCP用於指導LDR圖像對的生成,同時避免觸發 任何視覺不適。 通過一些列的實驗和用戶調查,我們提出的工作框架的有效性以及BVCP預測不適閾值的準確程度都得到了驗證。 / With the booming of 3D movies and video games, binocular (stereo) display devices become more and more popular and affordable. By introducing one additional image space, stereo displays double the image domains for visualization, one for the left eye and the other for the right eye. Existing binocular display systems only utilize this dual image domain for stereopsis. / Our human binocular vision is not only able to fuse two images with disparity, but also two images with difference in luminance, contrast and even detail, into a single percept, up to a certain limit. This phenomenon is known as binocular single vision. By a complicated neurophysiologic fusion process, humans can perceive more visual content via binocular single vision than one arbitrary single view or the linear blending of two views. / In this thesis, for the first time, binocular single vision has been utilized into computer graphics. Based on this phenomenon, a novel binocular tone mapping framework is proposed. From the source high-dynamic range (HDR) image, the proposed framework generates a binoc- ular low-dynamic range (LDR) image pair that preserves more human- perceivable visual content than a single LDR image using the additional image domain. Given a tone mapping method, our framework firstly generates one tone-mapped LDR image (left, without loss of generality) by the default or user selected parameters. Then its counterpart image (right) of the LDR pair is optimally synthesized from the same source HDR image. The two LDR images are not identical, and contain different visual information. Via binocular displays, they can aggregately present more human-perceivable visual richness than a single arbitrary LDR image. / Human binocular vision has a tolerance on the difference between two views. When such limit is exceeded, binocular viewing discomfort appears. To prevent such visual discomfort, a novel binocular view- ing comfort predictor (BVCP) is also proposed to predict the comfort threshold of binocular vision. In our framework, BVCP is used to guide the generation of LDR image pair without triggering visual discomfort. Through several user studies, the effectiveness of the proposed framework in increasing human-perceivable visual richness and the pre- dictability of the proposed BVCP in predicting the binocular discomfort threshold have been demonstrated and validated. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Yang, Xuan. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2012. / Includes bibliographical references (leaves 108-115). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese. / Abstract --- p.i / Acknowledgement --- p.ix / Chapter 1 --- Introduction --- p.1 / Chapter 2 --- Background Study --- p.5 / Chapter 2.1 --- Stereo Display --- p.5 / Chapter 2.2 --- HDR Tone Mapping --- p.9 / Chapter 2.2.1 --- HDR lmage --- p.9 / Chapter 2.2.2 --- Tone Mapping --- p.11 / Chapter 3 --- Binocular Vision --- p.16 / Chapter 3.1 --- Binocular Single Vision --- p.16 / Chapter 3.1.1 --- Binocular Single Vision --- p.16 / Chapter 3.1.2 --- Motor Fusion and Sensory Fusion --- p.19 / Chapter 3.1.3 --- Fusion, Suppression and Rivalry --- p.21 / Chapter 3.1.4 --- Rivalry --- p.23 / Chapter 3.1.5 --- Fusional Theory --- p.24 / Chapter 3.1.6 --- Fusion with Stereopsis --- p.27 / Chapter 3.2 --- Binocular discomfort --- p.29 / Chapter 3.2.1 --- Fusional area --- p.31 / Chapter 3.2.2 --- Contour difference --- p.32 / Chapter 3.2.3 --- Failure of rivalry --- p.33 / Chapter 3.2.4 --- Contour and regional contrast --- p.34 / Chapter 4 --- Binocular Visual Comfort Predictor (BVCP) --- p.37 / Chapter 4.1 --- Introduction --- p.37 / Chapter 4.2 --- Design of BVCP --- p.40 / Chapter 4.2.1 --- Fusional Area --- p.40 / Chapter 4.2.2 --- Contour Fusion --- p.42 / Chapter 4.2.3 --- Failure of Rivalry --- p.48 / Chapter 4.2.4 --- Contour and Regional Contrast --- p.53 / Chapter 4.2.5 --- The Overall Fusion Predictor --- p.54 / Chapter 4.3 --- Experiments and User Study --- p.56 / Chapter 4.4 --- Discussion --- p.60 / Chapter 5 --- Binocular Tone Mapping --- p.62 / Chapter 5.1 --- Introduction --- p.62 / Chapter 5.2 --- Binocular Tone Mapping Framework --- p.66 / Chapter 5.2.1 --- System Overview --- p.66 / Chapter 5.2.2 --- Optimization --- p.68 / Chapter 5.3 --- Experiments and Results --- p.71 / Chapter 5.4 --- Userstudy --- p.77 / Chapter 5.4.1 --- Visual Richness --- p.77 / Chapter 5.4.2 --- Binocular Symmetry --- p.81 / Chapter 5.5 --- Discussion --- p.82 / Chapter 5.5.1 --- Incorporating Stereopsis --- p.82 / Chapter 5.5.2 --- Limitation --- p.84 / Chapter 5.5.3 --- Extension --- p.85 / Chapter 6 --- Conclusion --- p.91 / Chapter 6.1 --- Contribution --- p.91 / Chapter 6.2 --- Future Work --- p.92 / Chapter A --- More Results of Binocular Tone Mapping --- p.94 / Chapter B --- Test Sequence for BVCP --- p.103 / Bibliography --- p.108
433

Numerical solution of linear and nonlinear eigenvalue problems

Akinola, Richard O. January 2010 (has links)
Given a real parameter-dependent matrix, we obtain an algorithm for computing the value of the parameter and corresponding eigenvalue for which two eigenvalues of the matrix coalesce to form a 2-dimensional Jordan block. Our algorithms are based on extended versions of the implicit determinant method of Spence and Poulton [55]. We consider when the eigenvalue is both real and complex, which results in solving systems of nonlinear equations by Newton’s or the Gauss-Newton method. Our algorithms rely on good initial guesses, but if these are available, we obtain quadratic convergence. Next, we describe two quadratically convergent algorithms for computing a nearby defective matrix which are cheaper than already known ones. The first approach extends the implicit determinant method in [55] to find parameter values for which a certain Hermitian matrix is singular subject to a constraint. This results in using Newton’s method to solve a real system of three nonlinear equations. The second approach involves simply writing down all the nonlinear equations and solving a real over-determined system using the Gauss-Newton method. We only consider the case where the nearest defective matrix is real. Finally, we consider the computation of an algebraically simple complex eigenpair of a nonsymmetric matrix where the eigenvector is normalised using the natural 2-norm, which produces only a single real normalising equation. We obtain an under-determined system of nonlinear equations which is solved by the Gauss-Newton method. We show how to obtain an equivalent square linear system of equations for the computation of the desired eigenpairs. This square system is exactly what would have been obtained if we had ignored the non uniqueness and nondifferentiability of the normalisation.
434

An Inertial-Optical Tracking System for Quantitative, Freehand, 3D Ultrasound

Goldsmith, Abraham Myron 16 January 2009 (has links)
Three dimensional (3D) ultrasound has become an increasingly popular medical imaging tool over the last decade. It offers significant advantages over Two Dimensional (2D) ultrasound, such as improved accuracy, the ability to display image planes that are physically impossible with 2D ultrasound, and reduced dependence on the skill of the sonographer. Among 3D medical imaging techniques, ultrasound is the only one portable enough to be used by first responders, on the battlefield, and in rural areas. There are three basic methods of acquiring 3D ultrasound images. In the first method, a 2D array transducer is used to capture a 3D volume directly, using electronic beam steering. This method is mainly used for echocardiography. In the second method, a linear array transducer is mechanically actuated, giving a slower and less expensive alternative to the 2D array. The third method uses a linear array transducer that is moved by hand. This method is known as freehand 3D ultrasound. Whether using a 2D array or a mechanically actuated linear array transducer, the position and orientation of each image is known ahead of time. This is not the case for freehand scanning. To reconstruct a 3D volume from a series of 2D ultrasound images, assumptions must be made about the position and orientation of each image, or a mechanism for detecting the position and orientation of each image must be employed. The most widely used method for freehand 3D imaging relies on the assumption that the probe moves along a straight path with constant orientation and speed. This method requires considerable skill on the part of the sonographer. Another technique uses features within the images themselves to form an estimate of each image's relative location. However, these techniques are not well accepted for diagnostic use because they are not always reliable. The final method for acquiring position and orientation information is to use a six Degree-of-Freedom (6 DoF) tracking system. Commercially available 6 DoF tracking systems use magnetic fields, ultrasonic ranging, or optical tracking to measure the position and orientation of a target. Although accurate, all of these systems have fundamental limitations in that they are relatively expensive and they all require sensors or transmitters to be placed in fixed locations to provide a fixed frame of reference. The goal of the work presented here is to create a probe tracking system for freehand 3D ultrasound that does not rely on any fixed frame of reference. This system tracks the ultrasound probe using only sensors integrated into the probe itself. The advantages of such a system are that it requires no setup before it can be used, it is more portable because no extra equipment is required, it is immune from environmental interference, and it is less expensive than external tracking systems. An ideal tracking system for freehand 3D ultrasound would track in all 6 DoF. However, current sensor technology limits this system to five. Linear transducer motion along the skin surface is tracked optically and transducer orientation is tracked using MEMS gyroscopes. An optical tracking system was developed around an optical mouse sensor to provide linear position information by tracking the skin surface. Two versions were evaluated. One included an optical fiber bundle and the other did not. The purpose of the optical fiber is to allow the system to integrate more easily into existing probes by allowing the sensor and electronics to be mounted away from the scanning end of the probe. Each version was optimized to track features on the skin surface while providing adequate Depth Of Field (DOF) to accept variation in the height of the skin surface. Orientation information is acquired using a 3 axis MEMS gyroscope. The sensor was thoroughly characterized to quantify performance in terms of accuracy and drift. This data provided a basis for estimating the achievable 3D reconstruction accuracy of the complete system. Electrical and mechanical components were designed to attach the sensor to the ultrasound probe in such a way as to simulate its being embedded in the probe itself. An embedded system was developed to perform the processing necessary to translate the sensor data into probe position and orientation estimates in real time. The system utilizes a Microblaze soft core microprocessor and a set of peripheral devices implemented in a Xilinx Spartan 3E field programmable gate array. The Xilinx Microkernel real time operating system performs essential system management tasks and provides a stable software platform for implementation of the inertial tracking algorithm. Stradwin 3D ultrasound software was used to provide a user interface and perform the actual 3D volume reconstruction. Stradwin retrieves 2D ultrasound images from the Terason t3000 portable ultrasound system and communicates with the tracking system to gather position and orientation data. The 3D reconstruction is generated and displayed on the screen of the PC in real time. Stradwin also provides essential system features such as storage and retrieval of data, 3D data interaction, reslicing, manual 3D segmentation, and volume calculation for segmented regions. The 3D reconstruction performance of the system was evaluated by freehand scanning a cylindrical inclusion in a CIRS model 044 ultrasound phantom. Five different motion profiles were used and each profile was repeated 10 times. This entire test regimen was performed twice, once with the optical tracking system using the optical fiber bundle, and once with the optical tracking system without the optical fiber bundle. 3D reconstructions were performed with and without the position and orientation data to provide a basis for comparison. Volume error and surface error were used as the performance metrics. Volume error ranged from 1.3% to 5.3% with tracking information versus 15.6% to 21.9% without for the version of the system without the optical fiber bundle. Volume error ranged from 3.7% to 7.6% with tracking information versus 8.7% to 13.7% without for the version of the system with the optical fiber bundle. Surface error ranged from 0.319 mm RMS to 0.462 mm RMS with tracking information versus 0.678 mm RMS to 1.261 mm RMS without for the version of the system without the optical fiber bundle. Surface error ranged from 0.326 mm RMS to 0.774 mm RMS with tracking information versus 0.538 mm RMS to 1.657 mm RMS without for the version of the system with the optical fiber bundle. The prototype tracking system successfully demonstrated that accurate 3D ultrasound volumes can be generated from 2D freehand data using only sensors integrated into the ultrasound probe. One serious shortcoming of this system is that it only tracks 5 of the 6 degrees of freedom required to perform complete 3D reconstructions. The optical system provides information about linear movement but because it tracks a surface, it cannot measure vertical displacement. Overcoming this limitation is the most obvious candidate for future research using this system. The overall tracking platform, meaning the embedded tracking computer and the PC software, developed and integrated in this work, is ready to take advantage of vertical displacement data, should a method be developed for sensing it.
435

Lagrangian study of the Southern Ocean circulation

McAufield, Ewa Katarzyna January 2019 (has links)
The Southern Ocean is an important region for the sequestration of heat, carbon dioxide and other tracers. The Southern Ocean circulation is typically described in a circumpolarly averaged sense as a Meridional Overturning Circulation (MOC), but the detailed 3-D pathways that make up this circulation remain poorly understood. We use Lagrangian particle trajectories, obtained from eddy permitting numerical models, to map out and quantify different aspects of the 3-D circulation. We first introduce various definitions used to quantify efficient export from the Antarctic Circumpolar Current (ACC) to the subtropical gyres. Using these definitions, we show that the permanent northward export varies by water mass and occurs in localised regions; with 11 key pathways identified. We then examine the dynamics setting the location and efficiency of the identified pathways, which includes the investigation of the role of diapycnal mixing and the impact of short and long time variability in the flow. Although we show that the flow of particles in the 3-D model is predominantly isopycnal, we find that particles that are forced to remain on isopycnals lead to approx. 60% lower export (mainly via three pathways) than identical releases where the diapycnal component of advection is included. Enhanced upward mixing near rough topography, and downward mixing in the southeast Pacific, were shown to be mostly responsible for the export. In addition, we show that most of the export pathways are mainly influenced by timescales from 90 days to 20 years, which suggests that mesoscale eddies are not the leading-order importance in the northward export from the ACC to the subtropical gyres. However, we also find that mesoscale eddies and the mean-ACC flow play a significant role in setting the export from the ACC in some pathways. These results highlight the role of temporal variability and vertical transport in enhancing the northward flow from the ACC by allowing transport across barotropic streamlines and onto more efficiently exporting isopycnals. In addition, the asymmetrical response of the studied quantities emphasises the importance of the three dimensions in understanding the dynamics driving the overturning circulation. We also demonstrated that the annually repeating velocity fields, which are commonly used for trajectory calculations, increase the diapycnal transport of particles and as a consequence, increase the overall 20-year northward export from the ACC by approx. 10%. In the study of the meridional overturning circulation, we diagnose the geographical distribution of the streamwise averaged diffusivity calculated from meridional displacements of the Lagrangian particles. We examine streamwise averaging using both latitude and equivalent latitude and argue that the latter gives a more useful measure. Reconciling tracer and particle horizontal diffusivities, we show that in the ACC, the average diffusivity peaks between 1500m and 2500m with an average value of 1500 m$^{2}$/s and that it is highest near the topographic features. We compare the exact diffusivity and its approximation to show that an assumption of time homogeneity does not hold and therefore that standard expressions for diffusivity that assume time homogeneity are of limited usefulness. Finally, we use the calculated trajectories to provide a streamwise averaged 2-D advection-diffusion model of the Southern Ocean MOC and then examine the extent to which this 2-D model can capture the overall effect of the actual 3-D transport.
436

Penalised regression for high-dimensional data : an empirical investigation and improvements via ensemble learning

Wang, Fan January 2019 (has links)
In a wide range of applications, datasets are generated for which the number of variables p exceeds the sample size n. Penalised likelihood methods are widely used to tackle regression problems in these high-dimensional settings. In this thesis, we carry out an extensive empirical comparison of the performance of popular penalised regression methods in high-dimensional settings and propose new methodology that uses ensemble learning to enhance the performance of these methods. The relative efficacy of different penalised regression methods in finite-sample settings remains incompletely understood. Through a large-scale simulation study, consisting of more than 1,800 data-generating scenarios, we systematically consider the influence of various factors (for example, sample size and sparsity) on method performance. We focus on three related goals --- prediction, variable selection and variable ranking --- and consider six widely used methods. The results are supported by a semi-synthetic data example. Our empirical results complement existing theory and provide a resource to compare performance across a range of settings and metrics. We then propose a new ensemble learning approach for improving the performance of penalised regression methods, called STructural RANDomised Selection (STRANDS). The approach, that builds and improves upon the Random Lasso method, consists of two steps. In both steps, we reduce dimensionality by repeated subsampling of variables. We apply a penalised regression method to each subsampled dataset and average the results. In the first step, subsampling is informed by variable correlation structure, and in the second step, by variable importance measures from the first step. STRANDS can be used with any sparse penalised regression approach as the ``base learner''. In simulations, we show that STRANDS typically improves upon its base learner, and demonstrate that taking account of the correlation structure in the first step can help to improve the efficiency with which the model space may be explored. We propose another ensemble learning method to improve the prediction performance of Ridge Regression in sparse settings. Specifically, we combine Bayesian Ridge Regression with a probabilistic forward selection procedure, where inclusion of a variable at each stage is probabilistically determined by a Bayes factor. We compare the prediction performance of the proposed method to penalised regression methods using simulated data.
437

Asymptotics and scaling analysis of 2-dimensional lattice models of vesicles and polymers

Haug, Nils Adrian January 2017 (has links)
The subject of this thesis is the asymptotic behaviour of generating functions of different combinatorial models of two-dimensional lattice walks and polygons, enumerated with respect to different parameters, such as perimeter, number of steps and area. These models occur in various applications in physics, computer science and biology. In particular, they can be seen as simple models of biological vesicles or polymers. Of particular interest is the singular behaviour of the generating functions around special, so-called multicritical points in their parameter space, which correspond physically to phase transitions. The singular behaviour around the multicritical point is described by a scaling function, alongside a small set of critical exponents. Apart from some non-rigorous heuristics, our asymptotic analysis mainly consists in applying the method of steepest descents to a suitable integral expression for the exact solution for the generating function of a given model. The similar mathematical structure of the exact solutions of the different models allows for a unified treatment. In the saddle point analysis, the multicritical points correspond to points in the parameter space at which several saddle points of the integral kernels coalesce. Generically, two saddle points coalesce, in which case the scaling function is expressible in terms of the Airy function. As we will see, this is the case for Dyck and Schröder paths, directed column-convex polygons and partially directed self-avoiding walks. The result for Dyck paths also allows for the scaling analysis of Bernoulli meanders (also known as ballot paths). We then construct the model of deformed Dyck paths, where three saddle points coalesce in the corresponding integral kernel, thereby leading to an asymptotic expression in terms of a bivariate, generalised Airy integral.
438

Personalized perspectives in 3-D assembly.

Stead, Lawrence Scarritt January 1978 (has links)
Thesis. 1978. M.S.--Massachusetts Institute of Technology. Dept. of Architecture. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ROTCH. / Bibliography: leaf 35. / M.S.
439

Solutions to multiple criteria and multiple dimensional problems in marketing. / 解決多重標準和多重空間的市場問題 / CUHK electronic theses & dissertations collection / Digital dissertation consortium / ProQuest dissertations and theses / Jie jue duo zhong biao zhun he duo zhong kong jian de shi chang wen ti

January 2000 (has links)
The second marketing model addresses interpretation issues of traditional multiple dimensional scaling (MDS) model, and has three key features. First, it can provide an explicit meaning to each dimension. Second, it can directly provide a link between brand positions and brand attributes, so that marketing mix can be designed to optimize share or profit. Third, for a case of n brands and m product attributes, we only need to estimate m nonzero parameters to represent all brand positions in the reduced space of d dimensions where d < m. The model is applied to a real data set of thirty four cars and nine attributes. Empirical findings suggest that the proposed model is a viable alternative to existing methods. / This thesis proposes two marketing models. The first model is a multiple criteria ranking (MCR) model. It proposes a consensus approach to solve multiple criteria ranking problems. Marketing decisions frequently involve ranking various subjects using multiple criteria. However, it is difficult to have acceptance from all subjects. The proposed multiple criteria ranking model allows each subject to have a "say" in the evaluation process. All subjects together resolve their conflicts through voting so that consensus ranking can be derived under the majority rule principle. The new ranking procedure can be formulated as a series of mathematical programming models, and illustrated with two cases. First, ranking the research performance of thirty one marketing scholars according to their publications in four leading marketing journals. Second, ranking the performance of one hundred information technology companies. / Lam Pong Yuen. / "June 2000." / Added t.p. in Chinese. / Director: Lau Kin Nam. / Source: Dissertation Abstracts International, Volume: 61-08, Section: A, page: 3259. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2000. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. Ann Arbor, MI : ProQuest dissertations and theses, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. Ann Arbor, MI : ProQuest Information and Learning Company, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese. / School code: 1307.
440

Three-dimensional medical ultrasound image reconstruction using noise reduction and data compression. / CUHK electronic theses & dissertations collection

January 1998 (has links)
by Xiang Shao hua. / Thesis (Ph.D.)--Chinese University of Hong Kong, 1998. / Includes bibliographical references (p. 233-[248]). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

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