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- Li, Bo, 1982-
(författare)
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Interest Curves : Concept, Evaluation, Implementation and Applications
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Image features play important roles in a wide range of computer vision applications, such as image registration, 3D reconstruction, object detection and video understanding. These image features include edges, contours, corners, regions, lines, curves, interest points, etc. However, the research is fragmented in these areas, especially when it comes to line and curve detection. In this thesis, we aim to discover, integrate, evaluate and summarize past research as well as our contributions in the area of image features. This thesis provides a comprehensive framework of concept, evaluation, implementation, and applications for image features.Firstly, this thesis proposes a novel concept of interest curves. Interest curves is a concept derived and extended from interest points. Interest curves are significant lines and arcs in an image that are repeatable under various image transformations. Interest curves bring clear guidelines and structures for future curve and line detection algorithms and related applications.Secondly, this thesis presents an evaluation framework for detecting and describing interest curves. The evaluation framework provides a new paradigm for comparing the performance of state-of-the-art line and curve detectors under image perturbations and transformations.Thirdly, this thesis proposes an interest curve detector (Distinctive Curves, DICU), which unifies the detection of edges, corners, lines and curves. DICU represents our state-of-the-art contribution in the areas concerning the detection of edges, corners, curves and lines. Our research efforts cover the most important attributes required by these features with respect to robustness and efficiency.Interest curves preserve richer geometric information than interest points. This advantage gives new ways of solving computer vision problems. We propose a simple description method for curve matching applications. We have found that our proposed interest curve descriptor outperforms all state-of-the-art interest point descriptors (SIFT, SURF, BRISK, ORB, FREAK). Furthermore, in our research we design a novel object detection algorithm that only utilizes DICU geometries without using local feature appearance. We organize image objects as curve chains and to detect an object, we search this curve chain in the target image using dynamic programming. The curve chain matching is scale and rotation-invariant as well as robust to image deformations. These properties have given us the possibility of resolving the rotation-variance problem in object detection applications. In our face detection experiments, the curve chain matching method proves to be scale and rotation-invariant and very computational efficient.
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| 2. |
- Li, Bo
(författare)
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Development and Application of Laser-Induced Emission Techniques for Combustion Diagnostics -High-Resolution Visualization of Turbulent Reacting Flows
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Nowadays, more than 90% of our energy comes from combustion processes. Hence, it is very important to perform combustion research to reduce emissions, improve efficiency, find clean and renewable fuels, strengthen safety, etc. The complexity of combustion processes asks for advanced diagnostic tools, among which the laser spectroscopy has been proved to be a powerful one. This thesis is about the application and development of laser-induced emission techniques for combustion diagnostics. Different laser techniques have been adopted, i.e., laser-induced fluorescence (LIF), laser Rayleigh scattering, and laser-induced phosphorescence (LIP). Brief descriptions of these techniques and the main equipment used are given in the thesis. The first part of the thesis deals with application of laser techniques in turbulent combustion. The high spatial resolution of planar LIF (PLIF) and Rayleigh thermometry were performed in premixed and partially premixed laboratory flames. Visualization of flame fronts by CH2O, CH, and OH PLIF as well as temperature fields were achieved to study the interaction between turbulence and chemistry. Simulated results were used to explain the combustion phenomena, and the experimental results were analyzed for model validation The second part focuses on the development of the combustion apparatus and diagnostic techniques. A novel burner, featuring a multi-jet structure, was developed as a temperature calibration source. We can easily achieve a wide range of temperatures from ~1000 K up to ~2000 K in the burned gas region of the burner, which were measured by Rayleigh scattering. Another development is on the Heat Flux burner. By application of LIP technique instead of thermocouples (TC), the temperature distribution along the radius of the burner perforated plate was measured more precisely, which reduces the uncertainty of measured flame burning velocity, e.g., from ±1.5 cm/s (TC-introduced uncertainty) to ±0.25 cm/s (LIP-introduced uncertainty) in a Φ=0.7 methane/air flame. Development was also achieved by extending the technique of photofragmentation LIF (PF-LIF) of H2O2 in an HCCI engine. Quantitative concentration as well as single-shot imaging of H2O2 were acquired. A similar technique like PF-LIF was also carried out for C2H2 measurements under atmospheric pressure.
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| 3. |
- Li, Hongjie, 1988-
(författare)
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Collective Excitations in Transitional Nuclei Studied by Means of gamma-ray Spectroscopy and Lifetime Measurements
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Despite that it is more than 100 years since the atomic nucleus was first dis- covered by Ernest Rutherford and coworkers, many of its features still elude our understanding. The fact that the fundamental interactions between the nuclear constituents; nucleons, and ultimately quarks, are not yet known in detail, and the complexity of the nuclear many-body system compound the great challenges facing theoretical interpretations of experimental data. It is therefore important to focus on distinct phenomena where experimental mea- surements can be compared with theoretical predictions, providing stringent tests of theory. One such area is the nuclear phenomenology of collective excitations related to rotations and vibrations of the nucleus as a whole, and how such modes of excitation may develop from the interactions between a few nucleons occupying single-particle orbits outside closed shells.This thesis is devoted to experimental studies of excited states in the 99Tc, 162W, and 166Re nuclei. These nuclei lie in “transitional” regions of the Segrè chart, where collective excitation mechanisms start becoming important when adding valence nucleons outside closed neutron and proton shells. Such nuclei are important for testing state-of-the-art theoretical models. The excited states of the nuclei studied in the present work were populated using heavy-ion fusion-evaporation reactions. Prior to the present work, high-spin data were still lacking in 99Tc since in the previous works [1–5] excited states were only populated up to around 3 MeV. Two collective bands have been extended to intermediate angular momentum states in the present work. The experimental results were compared with the systematics of other technetium isotopes, evaluating electromagnetic characteristics based on semiclassical calculations and the particle-rotor model. The 162W and 166Re nuclei are situated in the very neutron-deficient 160-170 mass region, requiring special techniques for identifying their excited-state structures. The level scheme of 162W was first reported by Dracoulis et al. in 1993 [6], where the first excited 2+ state was assigned to be 450 keV above the ground state. However, the lack of selectivity made the γ-ray identification for higher energy levels of 162W uncertain. In this work, the highly selective recoil-decay tagging technique was used to uniquely identify γ-ray transitions from excited states in 162W and to construct its level scheme. In addition, the experimental setup enabled a precise determination of the half-life of the α-decaying ground state of 162W. The α-formation probability for 162W was extracted from the measurement of the half-life and systematical comparisons with the neighboring nuclei were performed. Two rotational-like bands were identified in 166Re for the first time and the lifetimes of the lowest three excited states in band (1) were measured using the recoil distance Doppler shift method. The results were compared with theoretical calculations based on a semiclassical approach, the particle-rotor model, and the tilted axis cranking model in a relativistic mean field approach. The microscopic mechanisms (configuration and alignment, etc) of the rotational bands were interpreted under the framework of total Routhian surface predictions and cranked shell model calculations.
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| 4. |
- Li, Wenjuan, 1963-
(författare)
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Firms and people in place : driving forces for regional growth
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aim of the thesis is to quantitatively study the driving forces and mechanisms for regional growth from an endogenous and exogenous perspective and reveal the most important factors contributing to regional growth, by focusing on three aspects: local labour market, the supply side and the demand side of the labour market. The thesis is designed to use Swedish micro register data to develop spatial models with higher spatial resolution. It was found that endogenous factors are important and probably explain about at least one third of total regional economic growth. Among the endogenous factors, localised demographic composition, labour force and labour market, firms, and business environment have the strongest influence on regional economic growth. The findings from the Swedish context were briefly compared to China’s economic growth in the last fifty years. The thesis consists of three related papers. The first paper studied the endogenous and exogenous factors in 108 Swedish LA regions during the 1990s. By using the SNI92 code, individual longitudinal data and an improved shift-share analysis method, it was found that the endogenous factor is important for regional economic growth because it is able to accelerate, decelerate or reverse the impact from exogenous factors during the period studied. The second paper studied regional growth from the supply side of the labour market by focusing on population redistribution and place attractiveness. A ‘floating grid’ approach was developed to understand the factors shaping place attractiveness. The approach disregards administration zones by focusing on a small spatial unit—vicinity which is one kilometre square. Each unit has a unique set of surrounding zones that are local area and hinterland. By constructing spatial models, the total explained variance in place attractiveness was decomposed into partial explanatory effects that are assigned for physical attraction, demographic, service and labour market factors over the spatial scales. The finding is that the spatial scale of vicinity and demographic factors contribute most to place attractiveness. The third paper studied regional growth from the demand side of the labour market by focusing on workplace and its economic performance. The ‘floating grid’ approach was once more applied while the basic analysis unit is a constructed workplace that holds working-square, local area and hinterland as surrounding zones. The economic performance of the workplace was attributed to external demand, local demand, business environment and labour force factors over different spatial scales. A method was developed to quantitatively identify intervals of partial explanatory effects that are components of the total explained variance. It was found that working-square and labour force factors contribute most to workplace economic performance.
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