Detecting Blackholes and Volcanoes in Directed Networks

In this paper, we formulate a novel problem for finding blackhole and volcano patterns in a large directed graph. Specifically, a blackhole pattern is a group which is made of a set of nodes in a way such that there are only inlinks to this group from the rest nodes in the graph. In contrast, a volcano pattern is a group which only has outlinks to the rest nodes in the graph. Both patterns can be observed in real world. For instance, in a trading network, a blackhole pattern may represent a group of traders who are manipulating the market. In the paper, we first prove that the blackhole mining problem is a dual problem of finding volcanoes. Therefore, we focus on finding the blackhole patterns. Along this line, we design two pruning schemes to guide the blackhole finding process. In the first pruning scheme, we strategically prune the search space based on a set of pattern-size-independent pruning rules and develop an iBlackhole algorithm. The second pruning scheme follows a divide-and-conquer strategy to further exploit the pruning results from the first pruning scheme. Indeed, a target directed graphs can be divided into several disconnected subgraphs by the first pruning scheme, and thus the blackhole finding can be conducted in each disconnected subgraph rather than in a large graph. Based on these two pruning schemes, we also develop an iBlackhole-DC algorithm. Finally, experimental results on real-world data show that the iBlackhole-DC algorithm can be several orders of magnitude faster than the iBlackhole algorithm, which has a huge computational advantage over a brute-force method.Comment: 18 page

Gate-tunable negative differential conductance in hybrid semiconductor-superconductor devices

Negative differential conductance (NDC) manifests as a significant characteristic of various underlying physics and transport processes in hybrid superconducting devices. In this work, we report the observation of gate-tunable NDC outside the superconducting energy gap on two types of hybrid semiconductor-superconductor devices, i.e., normal metal-superconducting nanowire-normal metal and normal metal-superconducting nanowire-superconductor devices. Specifically, we study the dependence of the NDCs on back-gate voltage and magnetic field. When the back-gate voltage decreases, these NDCs weaken and evolve into positive differential conductance dips; and meanwhile they move away from the superconducting gap towards high bias voltage, and disappear eventually. In addition, with the increase of magnetic field, the NDCs/dips follow the evolution of the superconducting gap, and disappear when the gap closes. We interpret these observations and reach a good agreement by combining the Blonder-Tinkham-Klapwijk (BTK) model and the critical supercurrent effect in the nanowire, which we call the BTK-supercurrent model. Our results provide an in-depth understanding of the tunneling transport in hybrid semiconductor-superconductor devices.Comment: 15+6 pages, 4+6 figure

Développements théoriques et évaluation expérimentale d'un nouveau système collaboratif multidrones de saisie et de manipulation de grands objets

This thesis proposes a new concept of aerial manipulation robot named Flying Gripper that is intended to perform grasping, manipulating, and transporting of large objects autonomously. The Flying Gripper robot is composed of four quadrotors, four self-adaptive fingers and a body structure. The main contributions of these works are: (1) an original mechanical concept using multiple quadrotors to obtain full manipulability in SE(3) and taking advantage of their yaw rotations to actuate a self-adaptive and intrinsically safe grasping mechanism; (2) a wrench capability analysis method taking into account the equality and inequality constraints imposed by actuation limits, mechanical stops and equilibrium relations; (3) a model predictive controller to deal with unknown mass, inertia and center of mass due to the grasped object; (4) a Dynamic Control Allocation algorithm to distribute the control output in a way that guarantees the continuity of actuator's velocity, improves the energy efficiency and satisfies the robot mechanical limits.Numerical simulations and experimental tests have been carried out to validate the controller performances.Cette thèse propose un nouveau concept de robot de manipulation aérienne appelé Flying Gripper. Ce robot est un manipulateur aérien, destiné à la saisie, la manipulation et le transport de grands objets de manière autonome. Le robot Flying Gripper est composé de quatre quadrotors, de quatre doigts auto-adaptatifs et d'un châssis. Les principaux apports de ces travaux sont: (1) un concept mécanique original reposant sur l'utilisation de plusieurs quadrotors et tirant parti de la rotation en lacet des quadrotors pour actionner un mécanisme de préhension auto-adaptatif et intrinsèquement sûr (2) une méthode pour analyser des torseurs disponibles en tenant compte des contraintes d'égalité et d'inégalité imposées par les limites d'actionnement, les butées mécaniques et les relations d'équilibre; (3) une commande prédictive permettant de manipuler l'objet saisie avec une masse, des inerties et un centre de masse inconnus; (4) un algorithme d'allocation de contrôle dynamique pour la distribution de l'effort de contrôle, de manière à optimiser l'efficacité énergétique et à assurer la continuité de la commande, en considérant les limites mécaniques du robot.Des simulations numériques et des tests expérimentaux ont été effectués pour valider les performances du contrôleur

Heegaard diagrams and applications

The main objective of this thesis is to study Heegaard diagrams and their applications. First, we investigate Heegaard diagrams of closed 3-manifolds and introduce the circle and chord presentation for a connected, closed 3-manifold. The equivalence problem for Heegaard diagrams after connected sum moves and Dehn twists will be investigated. Presentations will be used to detect reducible Heegaard diagrams and homeomorphic 3-manifolds. We also investigate Heegaard diagrams of the 3-sphere. The main result of this part is that if two Heegaard diagrams of the 3-sphere have the same genus, then there is a sequence of connected sum moves and Dehn twists to pass from one to the other. If we use connected sum moves only, Heegaard curves can be changed to primitive curves and if we use Dehn twists only Heegaard curves can be brought into a simple position. Finally, we construct an immersion of a compact, orientable, connected 3-manifold with non-empty boundary into R³ with at most double and triple points as singularities. Further, we prove that if the boundary of the 3-manifold consists of 2-spheres and the 3-manifold can immerse into R³ with only double points as singularities, then the 3- manifold must be a punctured 3-sphere or a punctured (S¹ x S²)# • • • #(S¹ x S²).Science, Faculty ofMathematics, Department ofGraduat

WHICH 3-MANIFOLDS EMBED IN TRIOD ð I ð I?

ABSTRACT. We classify the compact 3-manifolds whose boundary is a union of 2-spheres, and which embed in T ð I ð I,whereTis a triod and I the unit interval. This class is described explicitly as the set of punctured handlebodies. We also show that any 3-manifold in T ð I ð I embeds in a punctured handlebody. 1. Introduction and statement of results. Working in the PL category, we let I denote the interval [0Ò 1], and T the triod consisting of three intervals joined together at a common endpoint, that is, the cone on three points. One of the authors [4] showed that the contractible 3-complex T ð T ð I is universal for 3-manifolds, meaning that every compact 3-manifold, which does not have a closed component, can be embedde

Wrench Capability Analysis and Control Allocation of a Collaborative Multi-Drone Grasping Robot

This paper presents the wrench capability analysis, the controller design, and experimental results of an aerial robot flying gripper. This robot uses four quadrotors to actuate four fingers such as to grasp and manipulate large size objects. The yaw motion of each quadrotor is used to open/close one of the four fingers. A method is proposed to analyze its manipulability considering inequality constraints such as the propellers’ capabilities and equality constraints such as the yaw torque applied by each quadrotor to open or close a finger and the equilibrium conditions of passive joints. This allows concluding on the full manipulability of the robot and evaluating its force and torque capabilities. A dynamic control allocation algorithm is implemented to distribute the control effort among all quadrotors while guaranteeing an achievable solution satisfying the aforementioned constraints. A proof of concept is realized and allows presenting preliminary experimental results of the flying gripper

Dynamic Modeling and Controller Design of a novel aerial grasping robot

International audienceThis paper presents dynamic modelling, controller design and simulation results of a novel aerial robot dedicated to manipula- tion and grasping of large-size objects. This robot can be described as a flying hand composed of four fingers, four quadrotors and a body struc- ture. The four quadrotors are arranged so as to allow the full actuation of the body structure in SE(3). This permits the system to maintain its position and attitude while closing the fingers despite external distur- bances. The opening/closing motion of each finger is actuated by the yaw rotation of one quadrotor and transmitted through a non-backdrivable worm-gear mechanism so that the hand can produce secured grasps. We design a model predictive controller to deal with unknown mass, inertia and center of mass. The effectiveness of the controller and its robustness against external disturbances and noise are validated through several simulations using ADAMS-SIMULINK co-simulation

EMB-YOLO: Dataset, method and benchmark for electric meter box defect detection

The electric meter box is a terminal device with a large number in the power grid. It may cause electrical hazards and property loss if damaged. Inspection of electricity meter boxes still relies on manual inspection with low efficiency and low automation. But image-based automated inspection is also limited by equipment battery and insufficient computing power, which makes the inspection system in urgent need of efficient model. However, lightweight model may reduce model robustness and be susceptible to interference from complex backgrounds due to insufficient feature extraction. Meanwhile, there are no publicly available datasets for electric meter boxes at present. To address the above issues, we firstly constructed a dataset, named EMB-11. After that, we improved the YOLOv7-tiny to design a novel model for electric meter box defect detection, named EMB-YOLO. In EMB-YOLO, we proposed the Big Kernel ShuffleBlock which can increase the effective receptive field and reduce the model parameters. Additionally, we proposed ELAN-CBAM to enhance the robustness of the model and reduce the interference of background noise. Finally, we constructed RepBSB based on the idea of structural reparameterization to reduce the size of the trained model. Compared to YOLOv7-tiny, the size of EMB-YOLO is only 4.82 Mb, which is reduced by 20.3 %. The detection speed is 343 frames/s, which is increased by 14.3 %. Most importantly, mAP can reach 82.8 %, which is increased by 3.5 %, reaching the SOTA level

Development of a novel prediction model based on protein structure for identifying RPE65-associated inherited retinal disease (IRDs) of missense variants

Purpose This study aimed to develop a prediction model to classify RPE65-mediated inherited retinal disease (IRDs) based on protein secondary structure and to analyze phenotype-protein structure correlations of RPE65 missense variants in a Chinese cohort. Methods Pathogenic or likely pathogenic missense variants of RPE65 were obtained from UniProt, ClinVar, and HGMD databases. The three-dimensional structure of RPE65 was retrieved from the Protein Data Bank (PDB) and modified with Pymol software. A novel prediction model was developed using LASSO regression and multivariate logistic regression to identify RPE65-associated IRDs. A total of 21 Chinese probands with RPE65 variants were collected to analyze phenotype-protein structure correlations of RPE65 missense variants. Results The study found that both pathogenic and population missense variants were associated with structural features of RPE65. Pathogenic variants were linked to sheet, β-sheet, strands, β-hairpins, Fe2+ (iron center), and active site cavity, while population variants were related to helix, loop, helices, and helix–helix interactions. The novel prediction model showed accuracy and confidence in predicting the disease type of RPE65 variants (AUC = 0.7531). The study identified 25 missense variants in Chinese patients, accounting for 72.4% of total mutations. A significant correlation was observed between clinical characteristics of RPE65-associated IRDs and changes in amino acid type, specifically for missense variants of F8 (H68Y, P419S). Conclusion The study developed a novel prediction model based on the protein structure of RPE65 and investigated phenotype-protein structure correlations of RPE65 missense variants in a Chinese cohort. The findings provide insights into the precise diagnosis of RPE65-mutated IRDs