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The Design and Implementation of an Effective Vision-Based Leader-Follower Tracking Algorithm Using PI Camera
No full textThe thesis implements a vision-based leader-follower tracking algorithm on a ground robot system. One camera is the only sensor installed the leader-follower system and is mounted on the follower. One sphere is the only feature installed on the leader. The camera identifies the sphere in the openCV Library and calculates the relative position between the follower and leader using the area and position of the sphere in the camera frame. A P controller for the follower and a P controller for the camera heading are built. The vision-based leader-follower tracking algorithm is verified according to the simulation and implementation
Hansen solubility parameters as a quantifiable tool to study 12HSA self-assembly
No full textOrganogels are thermal reversible semisolid materials that show great potential for use in foods to replace saturated fats and trans fats in processed foods. They are comprised of an organic liquid and low concentration (~ 2 wt%) of low molecular-mass organogelators (LMOGs) that spontaneously undergo formation of three-dimensional (3-D) self-assembled fibrillar networks (SAFiNs) capable of entrapping the solvent among the entangled nanofibers. SAFiNs formation requires the meticulous balance between contrasting solvent-gelator interactions. To elucidate the role of solvent properties on molecular gels formation, Hansen solubility parameters (HSPs) are used to correlate the nature of solvents to the gelation behavior of 12-hydroxystearic acid (12HSA). The hydrogen-bonding HSP (h) is found to be particularly useful in studying and predicting the solvent effect on 12HSA self-assembly and ultimately on gelation ability. Transparent 12HSA organogels only form in the solvents studied with hydrogen-bonding HSP less than 4.7 MPa1/2 while solution remains when h > 5.1MPa1/2. A strong linear correlation has also been established between h and critical gelator concentration (CGC). The macroscopic properties, microstructure and nanostructure of 12HSA molecular gels illustrate the importance of the nature of solvents that greatly affect SAFiN properties including: crystallinity, thermal properties, polymorphic forms, carboxylic dimer structure, domain size, fiber morphology and microstructure. Each of the aforementioned properties is influenced by h and to a lesser extent the polar component of the HSPs (p). 12HSA in solvents with a h < 4.4 MPa1/2 form transparent organogels that contain fibrillar crystal aggregates with the hexagonal polymorpic form. As the h of the solvent increases, the polymorph of 12HSA organogels undergoes transition from the hexagonal form to triclinic parallel form, which corresponds to the transitions observed in dimer structure, crystal morphology and the decrease in crystallinity.M.S.Includes bibliographical referencesby Songwei W
Hierarchical Model Predictive Control for on-Line High-Speed Railway Delay Management and Train Control in a Dynamic Operations Environment
No full textIn practice, the operation of high-speed trains is often affected by adverse weather conditions or equipment failures, which result in delays and even cancellations of train services. In this article, a novel two-layer hierarchical model predictive control (MPC) model is proposed for on-line high-speed railway delay management and train control for minimizing train delays and cancellations. The upper layer manages the global objectives of the train operation, that is, minimizing the total train delays and providing guidance for the speed control in the lower layer. The objectives of the lower layer are to satisfy the running time requirements given by the upper layer and to save energy at the same time. The optimization problems in both levels of the hierarchical MPC framework are formulated as small-scale mixed integer linear programming problems, which can be solved efficiently by existing solvers. Particularly, the train control problem is solved in a distributed way for each train. Simulation analysis based on the real-life data of the Beijing-Shanghai high-speed railway shows that the proposed hierarchical MPC framework can meet the real-time requirements and reduce train delays effectively when compared with widely accepted strategies, for example, first-scheduled-first-serve and first-come-first-serve. Moreover, the proposed hierarchical MPC framework also provides good robustness performance for different disturbance scenarios.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Team Bart De Schutte
LONG-DISTANCE AND BROAD-BAND AERIAL COMMUNICATION USING DIRECTIONAL ANTENNAS: THEORY, IMPLEMENTATION, AND APPLICATIONS
No full textUnmanned aerial vehicles (UAV) have found broad civilian applications. However, existing commercial usages are limited to single UAVs. To facilitate commercial multi-UAV applications, robust UAV-to-UAV communication with long-distance and broad-band capabilities is critical. Such a communication architecture should not rely on ground infrastructure support, and hence can be applied whenever needed in scenarios where infrastructures are not available. It is foreseen to have extensive usages in a wide spectrum of commercial UAV applications such as emergency response, remote sensing, and nondestructive health monitoring. A promising solution for such a communication architecture is aerial communication using directional antennas (ACDA). We developed several preliminary ACDA solutions. This dissertation presents improvements to the ACDA system, in terms of theory, implementation, and applications. With respect to theory, a critical component of the ACDA system is the automatic alignment of directional antennas to maximize communication performance. To account for an unstable global position system GPS environment, we develop a novel stochastic optimal control solution that integrates reinforcement learning (RL), an effective uncertainty evaluation method called multivariate probabilistic collocation method (MPCM), and an unscented Kalman filter (UKF) for the nonlinear random switching dynamics. Part of this theoretical solution is implemented. With respect to implementation, we redesign the hardware and software to improve robustness, throughput and endurance. Two versions of the ACDA system are implemented. The first version includes a complete new design of platform, communication, computing, control, middleware, and interface components. It features a communication and control co-design to achieve robust performance in a GPS-denied environment. The second version is upgraded with a UAV platform, computing component, battery solution, and rotation structure to reduce interference and improve endurance. Beyond the visual line of sight UAV control using the ACDA system delay is also implemented. With respect to applications, built upon the ACDA system, we first develop a UAV-carried vision-based monitoring system that allows a UAV to continuously track and monitor a mobile infrastructure and transmit back the monitoring information in real-time from a remote location. We then develop a leader-follower tracking system using the ACDA system, that enables cooperative UAV control over a long distance, which can be used in broad multi-UAV remote sensing, monitoring, and emergency response applications
Neutron Star Low-Mass X-Ray Binaries In And Out Of Focus: Nustar Stray Light
No full textNeutron star low-mass X-ray binaries (NS LMXBs) provide crucial insights into the physics of accretion under extreme gravity. In this dissertation, we explore the capabilities of NuSTAR’s stray light (SL) observations to supplement, and in some cases, surpass focused data in spectral studies of bright LMXBs. Utilizing the use of SL datasets, we perform detailed spectral analyses of two Z sources: GX 340+0 and Sco X-1.
For GX 340+0, we compare 7 focused and 25 SL observations across multiple spectral states, demonstrating that SL data significantly expand temporal coverage and allow for the detection of long-term spectral evolution not evident in focused observations alone. Continuum modeling with double thermal components, along with relativistic reflection modeling using the {\sc relxillNS} framework, enables constraints on NS surface and disk temperatures, disk inclination and ionization.
For Sco X-1, we present the first spectral analysis using an intentional SL observation. The dataset captures the source in the flaring branch (FB) and it is modeled with thermal Comptonization. Reflection analysis shows a disk inclination consistent with previous X-ray and radio studies. This work validates the high precision spectra of intentional SL data and underscores its potential in extending exposure time for extremely bright sources limited by telemetry constraints in focused observations.
Together, these studies demonstrate that properly reduced NuSTAR SL observations offer a powerful tool for high-energy astrophysics. This dissertation establishes a framework for SL data analysis and highlights its value for future missions aiming to maximize science return without additional observing time
Coordination chemistry of sterically bulky N-donor ligands with early transition metals, and supramolecular assembly of silver(I) thiolate nano-sized molecular clusters
No full textPh.D.This thesis is composed of two sections. Part I reports on synthetic, structural and reactivity studies of early transition metal complexes derived from a sterically bulky triazenide and amidinate system, respectively. Part II focuses on a synthetic and structural study of new multinuclear silver(I) thiolate clusters.Part I deals with the coordination chemistry of sterically bulky triazenide ligand [(DippN)N(NDipp)]⁻ (L¹) and formamidinate ligand [(DippN)C(H)(NDipp)]⁻(L²), where Dipp = 2,6-ⁱPr₂C₆H₃, with early transition metals (Sc, Y, Ti, V). Mono(triazenide) complexes of Sc(III) and Y(III) were obtained as [Sc(L¹)Cl₂(THF)₂] (3) and [Y(L¹)(THF)(μ-Cl)₂(μ₃-Cl)Li(OEt₂)]₂ (5) via the salt metathesis reactions between [Li(L¹)(THF)₂] (1) and the corresponding metal chlorides. The dimeric scandium(III) mono(formamidinate) complex [Sc(L²)Cl(μ-Cl)(THF)]₂ (9) was isolated using one equiv. of [Li(L²)(THF)₂] (7) from the reaction with ScCl₃(THF)₃. The yttrium(III) bis(formamidinate) complex [Y(L²)₂Cl(THF)] (11) was prepared from the reactions of YCl₃(THF)₃.₅ and one or two equiv. of complex 7. Four isostructural heterobimetallic bis(ligand) complexes with the general formula [M(L)₂(μ Cl)₂Li(TMEDA)] [M, L = Sc, L¹ (4); Y, L¹ (6); Sc, L² (10); Y, L² (12)] were successfully synthesized using two equiv. of [Li(L¹)(TMEDA)] (2) and [Li(L²)(TMEDA)] (8) as ligand transfer reagents respectively.Mononuclear vanadium(III) mono(triazenide) complexes [V(L¹)Cl₂(THF)₂] (13) and [V(L¹)Cl₂(TMEDA)] (14) were obtained through reactions of VCl₃(THF)₃ with one molar equiv. of 1 and 2, respectively. Treatment of VCl₃(THF)₃ with two molar equiv. of 2 led to the corresponding bis(triazenide) complex {[Li(TMEDA)₂][V(L¹)₂Cl₂]} (15). Alternatively, complex 15 could be prepared by treatment of mono(triazenide) complex 14 with one molar equiv. of 2. Attempts to synthesize analogous titanium(III) derivatives have not been successful. However, a titanium(IV) imido complex, [Ti(=NDipp)Cl₂(TMEDA)] (16), was isolated by reacting TiCl₃(THF)₃ with one molar equiv. of 2. The formamidinate analogues, [V(L²)Cl₂(THF)₂] (17) and [V(L²)Cl₂(TMEDA)] (18) were generated by the reactions of VCl₃(THF)₃ with one molar equiv. of lithium formamidinate complexes 7 and 8, respectively. Treatment of MCl₃(THF)₃ (M = V, Ti) with two molar equiv. of 8 led to the corresponding bis(formamidinate) complexes [M(L²)₂Cl] (M = V, 19; Ti, 20)The reaction chemistry of the present vanadium(III) triazenide and formamidinate complexes have also been examined. Complex 14 underwent facile ligand substitution reactions with two molar equiv. of an appropriate lithium acetylide, yielding the corresponding triazenide acetylide complexes [V(L¹)(C≡CR)₂(TMEDA)] (R = phenyl, 21; isopropyl, 22; tert butyl, 23). Addition of KBEt3H to complexes 13 and 14 led to isolation of dinuclear vanadium(II) complexes [V(L¹)(μ-Cl)(THF)₂]₂ (24) and [V(L¹)(μ-Cl)(TMEDA)]₂ (25), respectively. Treatment of complex 14 with zinc metal afforded a triangulo trivanadium(II) cluster [V₃(L¹)(μ- Cl)₃(μ₃-Cl)₂(TMEDA)₂] (26) and a zinc mono(triazenide) complex [Zn(L¹)Cl(TMEDA)] (27). Vanadium(IV) imido complex [V(=NDipp)Cl₂(TMEDA)] (28) was generated by the reactions of 14 with elemental sulphur or selenium. Vanadium(III) formamidinate complex 18 showed similar reactivity as that of complex 14. Dinuclear vanadium(II) complex [V(²)(μ-Cl)(TMEDA)]₂ (29) was isolated by the reaction of 18 with one molar equiv. of KBEt3H. An analogous triangulo trivanadium(II) cluster [V₃(L²)(μ- Cl)₃(μ₃-Cl)₂(TMEDA)₂] (30) was generated by the reduction of 18 with zinc metal. The solid state structures of complexes 1-30 are determined by single crystal X ray diffraction analysis. Complexes 13-15 and 21-26 are first examples of vanadium triazenide complexes being structurally characterized.Part II reports on the synthesis and structures of seven new complexes including silver thiolate molecular clusters, which were prepared from a silver(I) ethynide precursor Ag₂C₂ using a C₂²⁻ pre templated approach. Two prototype clusters Ag₁₄(SR)₆ and CO₃@Agₘ(SR)₁₀ (R = isopropyl, cyclohexyl or tert butyl; m = 18 or 20) were employed to construct cluster based metal organic frameworks of different dimensions. Two new ellipsoidal tetradecanuclear cluster complexes, namely [Ag₁₄(SⁱPr)₆(CF3CO2)₈(DMSO)₆] (consisting of two polymorphic forms 31 and 32) and {[Ag₁₄(SCy)₆(CF₃CO₂)₈(DMSO)₄]·3DMSO} (33), and a three dimensional framework {Ag₃[Ag₁₄(SⁱPr)₆(CF₃CO₂)₁₁(H₂O)₃CH₃OH]·(H₂O)₂.₅}ₙ (34) were synthesized and structurally characterized by single crystal X ray diffraction analysis. A carboxylate templated chain like complex {[HN(CH₃)₂CO][CO₃@Ag₁₈(SᵗBu)₁₀(NO₃)₇(DMF)₄]·DMF}ₙ (35), two layer type complexes {Ag[CO₃@Ag₂₀(SⁱPr)₁₀(CF₃CO₂)9(CF₃CO₂H)(CH₃OH₂)]}ₙ (36) and {Ag₂[CO₃@Ag₂₀(SCy)₁₀(CF₃CO₂)₁₀(CF₃CO₂H)₂(H₂O)₂]·(H₂O)₃·(CH₃OH)₃}ₙ (37) were prepared by raising the acidity of the reaction mixture. An infinite coordination chain of silver(I) ethynediide complex [Ag₂₃(C≡C)₄(CF₃CO₂)₁₅(DMSO)₁₁]ₙ (38) was isolated when the precursor [Ag₂C₂]ₙ was saturated in the reaction condition. Our work has demonstrated that a C≡C²⁻ pre template plays an important role in the construction of complexes 31-37 by aggregating Ag⁺ ions to form the C₂@Agₙ moiety.本論文分別兩個部份。第一部份主要針對叠氮基配體[(DippN)N(NDipp)]⁻ (Dipp = 2,6-ⁱPr₂C₆H₃; L¹) 及脒基配體[(DippN)C(H)(NDipp)]⁻ (L²) 衍生出來的前期過渡金屬的配位化學研究，當中包括其絡合物的合成、結構分析及化學反應研究。第二部份為高核巰基銀簇的合成及結構分析。第一部份描述了叠氮基配體L¹ 及脒基配體L2 所衍生的鈧、釔、鈦及釩絡合物的合成及結構。透過相應的無水金屬鹵化物與一倍摩爾當量的叠氮基鋰[Li(L¹)(THF)₂] (1) 反應，成功合成單叠氮基三價鈧及釔絡合物 [Sc(L¹)Cl₂(THF)₂](3) 及 [Y(L¹)(THF)(μ-Cl)₂(μ₃-Cl)Li(OEt₂)]₂ (5)。二聚體單脒基三價鈧絡合物 [Sc(L²)Cl(μ-Cl)(THF)]₂ (9) 則由一倍摩爾當量的脒基鋰 [Li(L²)(THF)₂] (7) 與ScCl₃(THF)₃ 的反應取得。一倍或兩倍摩爾當量 [Li(L²)(THF)₂] (7) 與YCl₃(THF)₃.₅ 生成雙脒基三價釔絡合物 [Y(L²)₂Cl(THF)] (11)。四個同構雙配體異雙金屬絡合物[M(L)₂(μ Cl)₂Li(TMEDA)] [M, L = Sc, L¹ (4); Y, L¹ (6); Sc, L² (10); Y, L² (12)] 成功由相應金屬鹵化物與兩倍摩爾當量的叠氮基鋰[Li(L¹)(TMEDA)] (2) 及脒基鋰 [Li(L²)(TMEDA)] (8) 分別反應後獲得。我們從VCl₃(THF)₃ 分別與一倍摩爾當量叠氮基鋰 (1) 和 (2) 的反應中得到單叠氮基三價釩絡合物 [V(L¹)Cl₂(THF)₂] (13) 及 [V(L¹)Cl₂(TMEDA)](14) 。兩倍摩爾當量 (2) 與VCl₃(THF)₃ 取得雙叠氮基三價釩絡合物{[Li(TMEDA)₂][V(L¹)₂Cl₂]} (15) 。而一倍摩爾當量 (2) 亦可與[V(L¹)Cl₂(TMEDA)] (14) 合成 (15)。TiCl₃(THF)₃ 與一倍摩爾當量 (2) 未能成功製備叠氮基絡合物，但是得出亞胺基四價鈦酰絡合物 [Ti(=NDipp)Cl₂(TMEDA)](16)。脒基三價釩絡合物 [V(L²)Cl₂(THF)₂]] (17) 及[V(L²)Cl₂(TMEDA)] (18) 則由VCl₃(THF)₃ 與一倍摩爾當量相應脒基鋰 (7) 及 (8) 反應中合成。而MCl₃(THF)₃ (M = V, Ti) 與兩倍摩爾當量 (8) 反應後生成同構雙脒基絡合物[M(L²)₂Cl] (M = V, 19; Ti, 20)。叠氮基及脒基三價釩絡合物的化學反應亦在此報告中闡述。叠氮基絡合物 [V(L¹)Cl₂(TMEDA)] (14) 與相應乙炔基鋰反應後得出[V(L¹)(C≡CR)₂(TMEDA)] (R = Ph, 21; ⁱPr, 22; ᵗBu, 23)。絡合物 (13) 及 (14) 分別與KBEt₃H 反應得出雙核二價釩絡合物 [V(L¹)(μ–Cl)(THF)2]2 (24) 及[V(L¹)(μ-Cl)(TMEDA)]₂ (25)。三核二價釩簇 [V₃(L¹)(μ- Cl)₃(μ₃-Cl)₂(TMEDA)₂] (26) 及單叠氮基鋅絡合物 [Zn(L¹)Cl(TMEDA)] (27) 可由 (14) 與鋅金屬的反應中取得。而 (14) 跟硫和硒元素反應可生成亞胺基四價釩絡合物 [V(=NDipp)Cl₂(TMEDA)] (28)。脒基三價釩絡合物 [V(L²)Cl₂(TMEDA)] (18) 與叠氮基絡合物 (14) 持有相似的化學反應。絡合物 (18) 與一倍摩爾當量KBEt₃H 反應得出雙核二價釩絡合物 [V(²)(μ-Cl)(TMEDA)]₂ (29)。類似的三核二價釩簇 [V₃(L²)(μ- Cl)₃(μ₃-Cl)₂(TMEDA)₂] (30) 能夠從 (18) 與鋅金屬的反應中取得。絡合物 1–30 的份子結構均以X 射線衍射晶體學表徵，而絡合物13–15 及 21–26 是首個結構表徵的叠氮基釩絡合物例子。第二部份的研究主要為通過使用碳化銀前驅體 (Ag₂C₂) 主導的預範本方法，合成一系列份子型的巰基銀簇及其共價超分子骨架。兩個原型簇Ag₁₄(SR)₆和CO₃@Agₘ(SR)₁₀ (R = ⁱPr、Cy 或ᵗBu，m = 18 或 20) 被用來構建不同維度的基於簇的金屬有機框架。我們成功合成並結構表徵兩個新的份子型十四核橢圓體簇絡合物 [Ag₁₄(SⁱPr)₆(CF3CO2)₈(DMSO)₆] ( 多形的31 及 32) 和 {[Ag₁₄(SCy)₆(CF₃CO₂)₈(DMSO)₄]·3DMSO} (33) ， 以及三維網狀結構的{Ag₃[Ag₁₄(SⁱPr)₆(CF₃CO₂)₁₁(H₂O)₃CH₃OH]·(H₂O)₂.₅}ₙ (34)。羧酸鹽模板簇能組裝成鏈狀化合物 {[HN(CH₃)₂CO][CO₃@Ag₁₈(SᵗBu)₁₀(NO₃)₇(DMF)₄]·DMF}ₙ (35)，以及兩個層狀結構化合物 {Ag[CO₃@Ag₂₀(SⁱPr)₁₀(CF₃CO₂)9(CF₃CO₂H)(CH₃OH₂)]}ₙ (36) 及 {Ag₂[CO₃@Ag₂₀(SCy)₁₀(CF₃CO₂)₁₀(CF₃CO₂H)₂(H₂O)₂]·(H₂O)₃·(CH₃OH)₃}ₙ (37)。當[Ag₂C₂]ₙ在飽和狀態下，則產生炔銀配位鏈 [Ag₂₃(C≡C)₄(CF₃CO₂)₁₅(DMSO)₁₁]ₙ (38)。我們證明了 C≡C²⁻ 作為前模板將多個銀離子拉近到一起形成C₂@Agₙ 實體，在這些化合物的合成中起著不可或缺的作用。Tam, Yiu Sun."November 2019."Thesis Ph.D. Chinese University of Hong Kong 2020.Includes bibliographical references.Abstracts also in Chinese.Title from PDF title page (viewed on 1, April 2021)
Efficient Variational Bayes Learning of Graphical Models with Smooth Structural Changes
No full textEstimating a sequence of dynamic undirected graphical models, in which adjacent graphs share similar structures, is of paramount importance in various social, financial, biological, and engineering systems, since the evolution of such networks can be utilized for example to spot trends, detect anomalies, predict vulnerability, and evaluate the impact of interventions. Existing methods for learning dynamic graphical models require the tuning parameters that control the graph sparsity and the temporal smoothness to be selected via brute-force grid search. Furthermore, these methods are computationally burdensome with time complexity O(NP3)O(NP3) for PP variables and NN time points. As a remedy, we propose a low-complexity tuning-free Bayesian approach, named BASS. Specifically, we impose temporally dependent spike and slab priors on the graphs such that they are sparse and varying smoothly across time. An efficient variational inference algorithm based on natural gradients is then derived to learn the graph structures from the data in an automatic manner. Owing to the pseudo-likelihood and the mean-field approximation, the time complexity of BASS is only O(NP2)O(NP2). To cope with the local maxima problem of variational inference, we resort to simulated annealing and propose a method based on bootstrapping of the observations to generate the annealing noise. We provide numerical evidence that BASS outperforms existing methods on synthetic data in terms of structure estimation, while being more efficient especially when the dimension PP becomes high. We further apply the approach to the stock return data of 78 banks from 2005 to 2013 and find that the number of edges in the financial network as a function of time contains three peaks, in coincidence with the 2008 global financial crisis and the two subsequent European debt crisis. On the other hand, by identifying the frequency-domain resemblance to the time-varying graphical models, we show that BASS can be extended to learning frequency-varying inverse spectral density matrices, and further yields graphical models for multivariate stationary time series. As an illustration, we analyze scalp EEG signals of patients at the early stages of Alzheimer's disease (AD) and show that the brain networks extracted by BASS can better distinguish between the patients and the healthy controls.</p
MEAM interatomic potential for thermodynamic and mechanical properties of lithium allotropes
No full textLi has relatively simple electronic structure but exhibits complex allotropic phase transitions. Atomistic modeling is important to reveal thermodynamic and mechanical properties at grain and interface scales in multi-phase Li. However, extant interatomic potentials have limited accuracy in reproducing properties in the FCC, BCC and HCP phases of Li. Here, we develop a new interatomic potential for multi-phase Li using the classical MEAM approach. The new potential is fit to key properties of all three phases based on both extant and new DFT calculations. An extensive range of simulations are performed to validate the new potential. Good accuracy and transferability are demonstrated in all three phases and over a wide range of temperatures. The current potential is thus suitable for modeling both thermodynamic and mechanical behavior of Li and can be applied generally in a wide range of applications.link_to_subscribed_fulltex
Hybrid cooperative spectrum sharing for cognitive radio networks: A contract-based approach
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