Dynamic Feature Integration for Simultaneous Detection of Salient Object, Edge and Skeleton

In this paper, we solve three low-level pixel-wise vision problems, including salient object segmentation, edge detection, and skeleton extraction, within a unified framework. We first show some similarities shared by these tasks and then demonstrate how they can be leveraged for developing a unified framework that can be trained end-to-end. In particular, we introduce a selective integration module that allows each task to dynamically choose features at different levels from the shared backbone based on its own characteristics. Furthermore, we design a task-adaptive attention module, aiming at intelligently allocating information for different tasks according to the image content priors. To evaluate the performance of our proposed network on these tasks, we conduct exhaustive experiments on multiple representative datasets. We will show that though these tasks are naturally quite different, our network can work well on all of them and even perform better than current single-purpose state-of-the-art methods. In addition, we also conduct adequate ablation analyses that provide a full understanding of the design principles of the proposed framework. To facilitate future research, source code will be released

Designing topological quantum matter in and out of equilibrium

Recent advances in experimental condensed matter physics suggest a powerful new paradigm for the realization of exotic phases of quantum matter in the laboratory. Rather than conducting an exhaustive search for materials that realize these phases at low temperatures, it may be possible to design quantum systems that exhibit the desired properties. With the numerous advances made recently in the fields of cold atomic gases, superconducting qubits, trapped ions, and nitrogen-vacancy centers in diamond, it appears that we will soon have a host of platforms that can be used to put exotic theoretical predictions to the test. In this dissertation, I will highlight two ways in which theorists can interact productively with this fast-emerging field. First, there is a growing interest in driving quantum systems out of equilibrium in order to induce novel topological phases where they would otherwise never appear. In particular, systems driven by time-periodic perturbations—known as “Floquet systems”—offer fertile ground for theoretical investigation. This approach to designer quantum matter brings its own unique set of challenges. In particular, Floquet systems explicitly violate conservation of energy, providing no notion of a ground state. In the first part of my dissertation, I will present research that addresses this problem in two ways. First, I will present studies of open Floquet systems, where coupling to an external reservoir drives the system into a steady state at long times. Second, I will discuss examples of isolated quantum systems that exhibit signatures of topological properties in their finite-time dynamics. The second part of this dissertation presents another way in which theorists can benefit from the designer approach to quantum matter; in particular, one can design analytically tractable theories of exotic phases. I will present an exemplar of this philosophy in the form of coupled-wire constructions. In this approach, one builds a topological state of matter from the ground up by coupling together an array of one-dimensional quantum wires with local interactions. I will demonstrate the power of this technique by showing how to build both Abelian and non-Abelian topological phases in three dimensions by coupling together an array of quantum wires

Physics at a 100 TeV pp collider: beyond the Standard Model phenomena

This report summarises the physics opportunities in the search and study of physics beyond the Standard Model at a 100 TeV pp collider.Comment: 196 pages, 114 figures. Chapter 3 of the "Physics at the FCC-hh" Repor

Statics and Dynamics of Skyrmions Interacting with Pinning: A Review

Magnetic skyrmions are topologically stable nanoscale particle-like objects that were discovered in 2009. Since that time, intense research interest has led to the identification of numerous compounds that support skyrmions over a range of conditions spanning cryogenic to room temperatures. Skyrmions can be set into motion under various types of driving, and the combination of their size, stability, and dynamics makes them ideal candidates for numerous applications. Skyrmions represent a new class of system in which the energy scales of the skyrmion-skyrmion interactions, sample disorder, temperature, and drive can compete. A growing body of work indicates that the static and dynamic states of skyrmions can be influenced strongly by pinning or disorder in the sample; thus, an understanding of such effects is essential for the eventual use of skyrmions in applications. In this article we review the current state of knowledge regarding individual skyrmions and skyrmion assemblies interacting with quenched disorder or pinning. We outline the microscopic mechanisms for skyrmion pinning, including the repulsive and attractive interactions that can arise from impurities, grain boundaries, or nanostructures. This is followed by descriptions of depinning phenomena, sliding states over disorder, the effect of pinning on the skyrmion Hall angle, the competition between thermal and pinning effects, the control of skyrmion motion using ordered potential landscapes such as one- or two-dimensional periodic asymmetric substrates, the creation of skyrmion diodes, and skyrmion ratchet effects. We highlight the distinctions arising from internal modes and the strong gyroscopic or Magnus forces that cause the dynamical states of skyrmions to differ from those of other systems with pinning. We also discuss future directions and open questions related to the pinning and dynamics in skyrmion systems.Comment: 66 pages, 71 figure

Document preprocessing and fuzzy unsupervised character classification

This dissertation presents document preprocessing and fuzzy unsupervised character classification for automatically reading daily-received office documents that have complex layout structures, such as multiple columns and mixed-mode contents of texts, graphics and half-tone pictures. First, the block segmentation algorithm is performed based on a simple two-step run-length smoothing to decompose a document into single-mode blocks. Next, the block classification is performed based on the clustering rules to classify each block into one of the types such as text, horizontal or vertical lines, graphics, and pictures. The mean white-to-black transition is shown as an invariance for textual blocks, and is useful for block discrimination. A fuzzy model for unsupervised character classification is designed to improve the robustness, correctness, and speed of the character recognition system. The classification procedures are divided into two stages. The first stage separates the characters into seven typographical categories based on word structures of a text line. The second stage uses pattern matching to classify the characters in each category into a set of fuzzy prototypes based on a nonlinear weighted similarity function. A fuzzy model of unsupervised character classification, which is more natural in the representation of prototypes for character matching, is defined and the weighted fuzzy similarity measure is explored. The characteristics of the fuzzy model are discussed and used in speeding up the classification process. After classification, the character recognition procedure is simply applied on the limited versions of the fuzzy prototypes. To avoid information loss and extra distortion, an topography-based approach is proposed to apply directly on the fuzzy prototypes to extract the skeletons. First, a convolution by a bell-shaped function is performed to obtain a smooth surface. Second, the ridge points are extracted by rule-based topographic analysis of the structure. Third, a membership function is assigned to ridge points with values indicating the degrees of membership with respect to the skeleton of an object. Finally, the significant ridge points are linked to form strokes of skeleton, and the clues of eigenvalue variation are used to deal with degradation and preserve connectivity. Experimental results show that our algorithm can reduce the deformation of junction points and correctly extract the whole skeleton although a character is broken into pieces. For some characters merged together, the breaking candidates can be easily located by searching for the saddle points. A pruning algorithm is then applied on each breaking position. At last, a multiple context confirmation can be applied to increase the reliability of breaking hypotheses

On effective field theory of dark matter

We investigate the feasibility of dark matter particles existing in the Universe as a spin-$\frac{1}{2}$ fermion using effective field theories to parametrise the higher order physics. Our goal is to determine the requirements for exclusion of such particles by direct and indirect detection. In part~\ref{part:1}, based on ref.~\cite{geytenbeek21}, we introduce a complete basis of operators up to dimension 5 for fermions that are part of singlet, doublet and triplet representation of the Standard Model $SU(2)$ electroweak symmetry group. Such particles correspond to the bino, higgsino and wino of supersymmetry models respectively. We determine the thermal relic density of particles interacting with each of our operators and show that viable thermal relics that evade experimental constraints can exist with masses as low as as 100\GeV and up to 10\TeV due to the mass splittings that arise at dimension 5. In part~\ref{part:2}, based on ref.~\cite{geytenbeek17} we further investigate the effect of fermionic dark matter that may interact through an electromagnetic dipole interaction at dimension 5 on energy transport in the Sun. In particular, we test whether the models can provide a solution to the solar abundance problem, a theoretical discrepancy between the observations of helioseismology and the theoretical Standard Solar Model. We introduce all of the necessary theoretical implementation and show that, although introducing dark matter may alleviate the tension of the solar abundance problem, the required interaction strengths are strongly ruled out by direct detection experiments.Gates Cambridg

DC microgrid protection

DC microgrids have gained increasing attention over the decades. Compared to AC micro grids, they have higher power delivery ability, higher efficiency, and fewer control levels. Although DC microgrid has better performance in many areas, they still face a significant challenge in protection. That is due to the feature of DC fault with no zero-crossing point, and there is no standard for protection. Thus, it is essential for DC microgrid to detect faults timely and have a comprehensive protection scheme to ensure the system work in a stable state. In this thesis, a comprehensive review of fault types and the protection scheme in the DC microgrid is presented. A hybrid protection method, including all-phase FFT and the window-by-window method, is proposed to detect the DC series arcing fault, which can detect the fault timely. Moreover, discrete wavelet transforms together with the derivative of teager energy method are provided to detect different fault types, such as line-to-line fault and DC series arcing fault. The extensive case studies including different series arc fault models and different disturbances have been conducted. Moreover, a novel differential evolution-based protection framework for DC microgrids is presented. Firstly, a simplified DC microgrid model is adopted to provide the analytical basis of the DE (differential evolution) algorithm. The simplified model does not sacrifice performance criteria in steady-state simulation, which is verified through extensive simulation studies. A DE-based novel overcurrent protection scheme is then proposed to protect DC microgrid. This DE method provides an innovative way to calculate the maximum line viii current, which can be used for the overcurrent protection threshold setting and the relay coordination time setting. The detailed load condition, battery discharging power, and solar irradiance can be obtained by the proposed DE-based method to work out each maximum line current. Finally, extensive case studies involving faults at different locations are performed to validate the proposed strategy’s effectiveness. The expandability of the proposed DE-based overcurrent protection framework has been confirmed by further case studies in seven bus mesh systems

Searches for an invisible Z' and for the dark Higgsstrahlung A'h' process in μ⁺μ⁻ plus missing energy final states at Belle II

The work presented in this thesis concerns two searches for dark sector mediators in e^+e^- annihilations at the center-of-mass energy of 10.58 GeV with the Belle II experiment. Two different processes have been investigated in the same final state, consisting of two muons plus missing energy, by using the first data collected by the experiment so far. The first search presented in this work investigates an invisibly decaying Z' boson (in the framework of a L_µ - L_τ symmetry) produced radiatively by muons in the process e^+e^- → μ^+μ^-Z'; Z'→ invisible. The only previous measurements in the same theoretical framework have been performed by the BaBar and CMS experiments for a Z' decaying to muons, while no results for an invisible decay have been reported before. For this measure, the data-set collected by Belle II during the so-called Phase 2 commissioning run in 2018 has been used, corresponding to an integrated luminosity of 276 pb^-1. No anomalies have been observed in data, and upper limits on the coupling constant g' in the range [5 × 10^2 − 1] have been placed for a Z' mass less than 6 GeV/c^2. As an extension of the above search, the existence of a LFV Z' boson has been investigated in the process e^+e^- → e^±μ^∓Z'; Z'→ invisible. Even in that case, no anomalies have been observed, and model independent upper limits on the cross section (times efficiency) have been computed. The search for a different process is also presented, consisting in the simultaneous production of a dark photon A' and a dark Higgs h' boson via the so-called dark Higgstrahlung process e^+e^- → A'h'; A'→ μ^+μ^-, h'→ invisible. The only similar measurement was performed by the KLOE experiment, for A' masses up to ~ 1 GeV/c^2. Therefore, Belle II would be able to produce a sizeable enlargement of the explored region. The analysis flow, optimized for the data collected by the experiment during 2019, corresponding to an integrated luminosity of ~ 9 fb^-1, is described and the expected upper limits on the cross section and in terms of the coupling constants product є × α_D are provided