Estudamos as propriedades eletrônicas, estruturais e hiperfinas, nos sítios de nitrogênio, para o composto imidazol nas fases gasosa e sólida. Utilizamos o método PAW que é um método ab initio all-electron, dentro da Teoria do Funcional da Densidade, através do código computacional CP-PAW. Nossos valores, tanto para a fase gasosa quanto para a fase cristalina do gradiente de campo elétrico no núcleo, de freqüência de acoplamento quadrupolar (ν) e parâmetro de assimetria (η) estão em ótima concordância com os resultados experimentais da literatura e são os primeiros resultados obtidos, por método ab initio no espaço recíproco, para os átomos de nitrogênio no imidazol cristalino. Utilizamos resultados da literatura e também aqui calculados para estudar a tendência de comportamento tanto de ν quanto de η para diferentes meros (um, dois, três, cadeia infinita) e cristal investigando, assim, a estreita influência das ligações de hidrogênio sobre os valores do Gradiente de Campo Elétrico nos núcleos de nitrogênio. / Here we study structural, electronic and hyperfine properties at the Nitrogen sites in imidazole in the gas and the crystal phases. We use the PAW method which is an ab initio all electron method in the framework of the Density Functional Theory, as embodied in the computer code CP-PAW. The results for quadrupole coupling (ν) and asymmetry parameter (η) at the gas and at the crystal phases are in excellent agreement with the experimental values in the literature. This is the first time that such calculations are performed for the crystalline imidazole through a reciprocal space approach. We also study the behavior of both ν and η trends studing diferent meres (one, two, three and infinite chain) and cristal to investigate the influence of hydrogen bonding on the Electric Field Gradient at the nucleus.

Tsang Hing Wa = 梯度粒子系統的扭轉運動 / 曾慶華. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2006. / Includes bibliographical references (leaves 66-68). / Text in English; abstracts in English and Chinese. / Tsang Hing Wa = Ti du li zi xi tong de niu zhuan yun dong / Zeng Qinghua. / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Localization --- p.1 / Chapter 1.1.1 --- Localization by Potential Confinement --- p.1 / Chapter 1.1.2 --- Localization by Interference --- p.2 / Chapter 1.2 --- Graded Materials --- p.2 / Chapter 1.3 --- Rotational Motion --- p.3 / Chapter 2 --- Torsional Motion of Rotating Particles with Graded Couplings / Chapter 2.1 --- Linear Couplings --- p.5 / Chapter 2.1.1 --- Model and Formalism --- p.5 / Chapter 2.1.2 --- Gradient in Coupling Constant --- p.7 / Chapter 2.1.3 --- Gradient in Moment of Inertia --- p.8 / Chapter 2.1.4 --- Numerical Results --- p.9 / Chapter 2.1.5 --- Discussion and Conclusion --- p.14 / Chapter 2.2 --- Non-Linear Couplings --- p.14 / Chapter 2.2.1 --- Model and Formalism --- p.14 / Chapter 2.2.2 --- Gradient in Coupling Constant --- p.16 / Chapter 2.2.3 --- Gradient in Moment of Inertia --- p.16 / Chapter 2.2.4 --- Numerical Results --- p.17 / Chapter 2.2.5 --- Discussion and Conclusion --- p.29 / Chapter 3 --- Torsional Motion of Rotating Particles with graded potential --- p.30 / Chapter 3.1 --- Linear Interaction --- p.30 / Chapter 3.1.1 --- Model and Formalism --- p.30 / Chapter 3.1.2 --- Gradient in On-site Torsional Potential --- p.32 / Chapter 3.1.3 --- Numerical Results --- p.33 / Chapter 3.1.4 --- Discussion and Conclusion --- p.43 / Chapter 3.2 --- Non-linear Interaction --- p.43 / Chapter 3.2.1 --- Model and Formalism --- p.43 / Chapter 3.2.2 --- Numerical Results --- p.45 / Chapter 3.2.3 --- Chaotic Effect --- p.62 / Chapter 3.2.4 --- Discussion and Conclusion --- p.64 / Chapter 4 --- Conclusion --- p.65 / Bibliography --- p.66

"This research concentrates on two major engineering areas associated with biomedical instrumentation that have recently gained significant academic and industrial interest: the gradient coil design for Magnetic Resonance Imaging (MRI) and the high frequency full-wave field simulations with the Method of Moments (MoM). A new computational approach to the design of gradient coils for magnetic resonance imaging is introduced. The theoretical formulation involves a constrained cost function between the desired field in a particular region of interest in space and the current-carrying coil plane. Based on Biot-Savart’s integral equation, an appropriate weight function is introduced in conjunction with linear approximation functions. This permits the transformation of the problem formulation into a linear matrix equation whose solution yields discrete current elements in terms of magnitude and direction within a specified coil plane. These current elements can be synthesized into practical wire configuration by suitably combining the individual wire loops. Numerical predictions and measurements underscore the success of this approach in terms of achieving a highly linear field while maintaining low parasitic fields, low inductance and a sufficient degree of shielding. Experimental results confirm the field predictions of the computational approach. Extending the numerical modeling efforts to dynamic phenomena, a novel MoM formulation permits the computation of electromagnetic fields in conductive surfaces and in three-dimensional biological bodies. The excitation can be provided with current loops, voltage sources, or an incident electromagnetic wave. This method enables us to solve a broad spectrum of problems arising in MRI: full-wave RF coil simulations, eddy currents predictions in the magnet bore, and induced currents in the biological body. Surfaces are represented as triangles and the three-dimensional bodies are subdivided into tetrahedra. This numerical discretization methodology makes the approach very flexible to handle a wide range of practical coil geometries. Specifically, in this thesis the MoM is employed to study the effect of switching gradient coils in the presence of a biological load. "

In multi-agent Markov Decision Processes, a controllable agent must perform optimal planning in a dynamic and uncertain environment that includes another unknown and uncontrollable agent. Given a task specification for the controllable agent, its ability to complete the task can be impeded by an inaccurate model of the intent and behaviors of other agents. In this work, we introduce an active policy inference algorithm that allows a controllable agent to infer a policy of the environmental agent through interaction. Active policy inference is data-efficient and is particularly useful when data are time-consuming or costly to obtain. The controllable agent synthesizes an exploration-exploitation policy that incorporates the knowledge learned about the environment's behavior. Whenever possible, the agent also tries to elicit behavior from the other agent to improve the accuracy of the environmental model. This is done by mapping the uncertainty in the environmental model to a bonus reward, which helps elicit the most informative exploration, and allows the controllable agent to return to its main task as fast as possible. Experiments demonstrate the improved sample efficiency of active learning and the convergence of the policy for the controllable agents.

Controlling fields and properties has attracted ever increasing interest over past decades due to the rapid advancement of nanofabrication techniques. In the field of nano-optics, to overcome the limit of signal processing speed and device scale of traditional electronic devices, optical devices using photon as the signal carriers have been chosen as the potential candidates. However, the diffraction limit of light has limited the integration of the micro-meter photonic components into electronic chips. Plasmonics offer the possibility to control electromagnetic fields at the subwavelength scale. Moreover , this controlling become tunable by introducing gradient into the material and/or structure, i.e., taking the concept of functionally graded materials (FGM) to design materials. / Gradon confinements in graded materials and/or systems open a door for tunable fields-controlling, which have potential applications in a variety of fields. Our research methods and results provide an effective way to understand field localization in a variety of systems, and they can be applied to design and manufacture thermal devices and even on-chip plasmonic-optical devices. / Gradon confinements, or referred as frequency-controlled localization of fields are investigated in various graded plasmonic lattices. The correspondences between gradon confinements and Bloch oscillations as well as nonBloch oscillations are explored. By taking into account retardation and loss effects, the asymmetric localization behavior and broadband localizat ion due to graded host permittivity are studied. / This thesis will concentrate on gradon confinements, which make controlling fields and properties tunable in graded materials and/or systems. We start with investigating gradon modes and their properties in graded elastic lattices. Using the quantum-classical analogue method, the analytic envelope function is obtained and can be used to analyze the system-size dependence of inverse participation ratio of gradon modes. In damping graded elastic lattices , the frequency-dependent behavior of relaxation rate are studied analytically and numerically. / We continue to study the three-dimensional graded plasmonic lattices with fully retarded electromagnetic interactions. A generalized Ewald-Kornfeld summation formula is developed to deal with the long-range interaction. In the quasistatic limit, various plasmonic gradon modes are investigated. Taking retardation and loss into account, field localization and enhancement are calculated in three-dimensional graded plasmonic lattices with graded size, spacing, and/or host permittivity in one direction. / Zheng, Mingjie = 弹性和等离子体梯度子禁闭研究 / 郑明杰. / Adviser: Kin Wah Yu. / Source: Dissertation Abstracts International, Volume: 72-11, Section: B, page: . / Thesis (Ph.D.)--Chinese University of Hong Kong, 2009. / Includes bibliographical references (leaves 117-124) and index. / 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 Information and Learning, [201-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese. / Zheng, Mingjie = Tan xing he deng li zi ti ti du zi jin bi yan jiu / Zheng Mingjie.

In this thesis, we will discuss the possibility of wave manipulation by graded materials and/or systems. In contrast to the traditional inhomogeneous media, i.e. periodically modulated system and randomly disordered system, graded system demonstrates a unique way to control wave, resulting in a new type of localization-delocalization transition, which can confine the primary excitations (e.g., photons, phonons, and surface plasmons) and redistribute them spatially. This is not only of fundamental significance, but will also pave new avenue for various applications, for example, in surface elastic waves, nanooptics, and plasmonics. It also has implications with practical problems in industry such as oil probing and earthquake study. / Manipulating waves (e.g., elastic or electromagnetic) inside nanostructures has attracted ever increasing interest over the past decades due to the rapid advancement of nanofabrication techniques. Particularly, interactions of light with structures modulated at the wavelength or subwavelength scale offer an opportunity to achieve novel properties and designated functionalities in nanophotonics. Notable examples include photonic crystals, various metamaterials, and plasmonic devices. / Moreover, we consider to combine the novel properties of gradons and surface plasmons (SPs), in an attempt to explore new mechanisms to manipulate SP. Firstly, we study an incrementally-spaced nanoparticle chain waveguide, in which coupled plasmon waves show a localization-delocalization transition, in analogy to the elastic gradons. Secondly, we propose waveguides using periodic plasmonic chains immersed in a graded host which can sustain "light", "heavy", and "light-heavy" plasmonic gradons. Existence of tunable passband is demonstrated in these systems. / Thus, in view of the success, we discuss many potential applications in plasmonics, such as junctions, transistors, and even on-chip integrated plasmonic-dielectric devices. In this regard, we further study the most commonly used coplanar photonic elements, i.e., ring resonators and their integrated devices. To explore the interactions between various gradons and typical excitations would be very interesting and rewarding. Our findings have important ramifications for understanding excitations with transition spectra in many condensed matter systems, ranging from ultrasonic waves, seismic waves to light waves, microwaves, as well as quantum waves. / We started with one-dimensional graded networks of coupled harmonic oscillators. By examining the vibrational mode characteristics, we have identified a new kind of vibrational excitations, which are named "gradons". The features of elastic gradon are elab orated. Gradon localization is also different from well-known mechanisms of localization transition, such as defect(s) and Anderson-type localization. Gradons in higher dimensional graded elastic networks show more intriguing behaviors; we proved the existence of "soft", "hard", and "soft-hard" gradons in two dimensional cases. / Xiao Junjun = 新型调波功能材料 : 梯度子及其在纳米光学中的应用 / 肖君军. / "May 2006." / Adviser: Kin Wah Yu. / Source: Dissertation Abstracts International, Volume: 68-03, Section: B, page: 1694. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2006. / Includes bibliographical references (p. 108-118). / 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 Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese. / School code: 1307. / Xiao Junjun = Xin xing diao bo gong neng cai liao : ti du zi ji qi zai na mi guang xue zhong de ying yong / Xiao Junjun.

We study optimization algorithms for the finite sum problems frequently arising in machine learning applications. First, we propose novel variants of stochastic gradient descent with a variance reduction property that enables linear convergence for strongly convex objectives. Second, we study distributed setting, in which the data describing the optimization problem does not fit into a single computing node. In this case, traditional methods are inefficient, as the communication costs inherent in distributed optimization become the bottleneck. We propose a communication-efficient framework which iteratively forms local subproblems that can be solved with arbitrary local optimization algorithms. Finally, we introduce the concept of Federated Optimization/Learning, where we try to solve the machine learning problems without having data stored in any centralized manner. The main motivation comes from industry when handling user-generated data. The current prevalent practice is that companies collect vast amounts of user data and store them in datacenters. An alternative we propose is not to collect the data in first place, and instead occasionally use the computational power of users' devices to solve the very same optimization problems, while alleviating privacy concerns at the same time. In such setting, minimization of communication rounds is the primary goal, and we demonstrate that solving the optimization problems in such circumstances is conceptually tractable.

by Tat-Ming Tso. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1997. / Includes bibliographical references (p. 43-45). / Chapter Chapter 1 --- INTRODUCTION --- p.1 / Chapter §1.1 --- Introduction --- p.1 / Chapter §1.2 --- Preconditioned Conjugate Gradient Method --- p.3 / Chapter §1.3 --- Outline of Thesis --- p.3 / Chapter Chapter 2 --- CIRCULANT AND NON-CIRCULANT PRECONDITIONERS --- p.5 / Chapter §2.1 --- Circulant Matrix --- p.5 / Chapter §2.2 --- Circulant Preconditioners --- p.6 / Chapter §2.3 --- Circulant Preconditioners from Kernel Function --- p.8 / Chapter §2.4 --- Non-circulant Band-Toeplitz Preconditioners --- p.9 / Chapter Chapter 3 --- B-SPLINES --- p.11 / Chapter §3.1 --- Introduction --- p.11 / Chapter §3.2 --- New Version of B-splines --- p.15 / Chapter Chapter 4 --- CIRCULANT PRECONDITIONERS CONSTRUCTED FROM B-SPLINES --- p.24 / Chapter Chapter 5 --- NUMERICAL RESULTS AND CONCLUDING REMARKS --- p.28 / Chapter Chapter 6 --- APPLICATIONS TO SIGNAL PROCESSING --- p.37 / Chapter §6.1 --- Introduction --- p.37 / Chapter §6.2 --- Preconditioned regularized least squares --- p.39 / Chapter §6.3 --- Numerical Example --- p.40 / REFERENCES --- p.43

Electroanalytical techniques are used to investigate mass transport through density gradient films; lanthanide triflate reduction and oxidation in a Nafion/acetonitrile matrix; and magnetic field effects on hydrogen evolution reaction (HER), oxygen reduction reaction (ORR), and lanthanide electrochemistry. Graded density films are more dense at the electrode surface and become less dense out into solution due to a brush polymer structure. Fick's second law expands to account for a diffusion coefficient that varies with distance x normal to the electrode surface. Confocal microscopy, cyclic voltammetry, and computer simulations are used to investigate density graded Ficoll® films. Mass transport approaches steady state (scan rate independence) at slow scan rates where the diffusion length samples the entire film. The use of Ficoll to template an ion exchange polymer is explored by casting Nafion® Ficoll composites. Lanthanide electrochemistry is enabled in acetonitrile at a Nafion modified platinum electrode in the presence of triflate ligands. Formal potentials are shifted into the voltage window of acetonitrile accessible due to triflate complexation. The Nafion further solubilizes the compounds. The mechanism (ECEC) is studied with cyclic voltammetry and x-ray photoelectron spectroscopy. Magnetic field effects on electrochemical systems have been of interest to researchers for the past 65 years. Mass transport effects, such as magnetohydrodynamics and magnetic field gradient effects have been reported, but the Leddy group focuses on electron transfer effects. Electrode surfaces are modified with composite films of magnetic microparticles suspended in ion exchange polymer Nafion. Effects are verified to be electron transfer related and due to the magnetization of chemically inert microparticles. The magnets catalyze the rates of important electron transfer reactions such as hydrogen evolution and oxygen reduction. Magnetic field effects on HER at various noncatalytic metal electrodes are explored with linear scan voltammetry. There is a correlation between the magnetic susceptibility of the electrode metals and the HER exchange currents (reaction rates). Exchange currents are 103× larger for a paramagnetic metal electrode than a diamagnetic one with the same work function. The overpotential at diamagnetic electrodes is decreased by modification with a Nafion + magnetic microparticle composite film. A decrease in overpotential of ∼70 % for all electrodes except platinum is observed. The overpotential decrease correlates with the magnetic susceptibility of the particles. Magnets can enhance differences between lanthanide cyclic voltammograms by shifting current densities at a given potential and enhancing current based on the number of 4f electrons and magnetic moment of each lanthanide ion. Magnetic field effects on ORR in acetonitrile are investigated with cyclic voltammetry. In aprotic solvents, ORR proceeds by a one electron transfer reaction to paramagnetic O2.–. Enhanced reversibility and electron transfer kinetics are observed as well as a decrease in overpotential of ∼100 mV. Magnetic field effects on ORR in a lanthanide triflate solution are also examined. Electron transfer kinetics and reversibility are further enhanced in the presence of lanthanide triflate.

Changes in land use such as mountaintop removal mining with valley fills (MTR/VF) affect chemical, physical, and hydrological properties of headwater streams. Although numerous stream taxa have experienced significant declines from MTR/VF, stream salamanders appear to be particularly sensitive. Yet, the specific mechanism(s) responsible for the population declines has eluded researchers. We sampled salamander assemblages across a continuous specific conductivity (SC) gradient in southeastern Kentucky and estimated occupancy rates and abundance estimates along this gradient. We also examined the diet of larval and adult salamanders to determine if autochthony (A/T prey), total prey volume, and body condition is influenced by SC. As SC increased, occupancy and abundance declined consistently among all salamander species and life stages. Diet composition explained the declines; for example, larval salamanders experienced a 12−fold decline in autochthony, a 4.2−fold decline in total prey volume, and a rapid decline in body condition as SC increased. Our results indicate that SC indirectly affects stream salamander populations by eliminating an adequate availability of aquatic prey for salamanders, which in turn lead may lead to reduced population persistence in streams with elevated SC.