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Generalized Fréchet bounds for cell entries in multidimensional contingency tables

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arXiv 2017年

作者： Uhler, Caroline Richards, Donald Laboratory for Information and Decision Systems Department of Electrical Engineering and Computer Science Institute for Data Systems and Society Massachusetts Institute of Technology CambridgeMA02139 United States Department of Statistics Pennsylvania State University University ParkPA16802 United States

We consider the lattice, L, of all subsets of a multidimensional contingency table and establish the properties of monotonicity and supermodularity for the marginalization function, n(·), on L. We derive from the supermodularity of n(·) some generalized Fréchet inequalities complementing and extending inequalities of Dobra and Fienberg. Further, we construct new monotonic and supermodular functions from n(·), and we remark on the connection between supermodularity and some correlation inequalities for probability distributions on lattices. We also apply an inequality of Ky Fan to derive a new approach to Fréchet inequalities for multidimensional contingency *** 2010 subject classifications: Primary 06D05, 62H17;Secondary 05A20, *** Codes 06D05, 62H17 (Primary), 05A20, 62J12 (Secondary) Copyright © 2017, The Authors. All rights reserved.

关键词： Probability distributions

Fast Deformable Model for Pedestrian Detection with Haar-like features

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Fast Deformable Model for Pedestrian Detection with Haar-lik...

IEEE Symposium Series on Computational Intelligence (SSCI)

作者： Kuang-Pen Chou Mukesh Prasad Deepak Puthal Ping-Hung Chen Dinesh Kumar Vishwakarma Suresh Sundarami Chin-Teng Lin Wen-Chieh Lin Institute of Computer Science and Engineering National Chiao-Tung University Hsinchu Taiwan Centre for Artificial Intelligence University of Technology Sydney Australia School of Electrical and Data Engineering University of Technology Sydney Australia Institute of Electrical and Control Engineering National Chiao-Tung University Hsinchu Taiwan Department of Electronics & Communication Engineering Delhi Technological University India Nanyang Technological University Singapore Singapore SG Department of Computer Science National Chiao-Tung University Hsinchu Taiwan

This paper proposes a novel Fast Deformable Model for Pedestrian Detection (FDMPD) to detect the pedestrians efficiently and accurately in the crowded environment. Despite of multiple detection methods available, detection becomes difficult due to variety of human postures and perspectives. The proposed study is divided into two parts. First part trains six Adaboost classifiers with Haar-like feature for different body parts (e.g., head, shoulders, and knees) to build the response feature maps. Second part uses these six response feature maps with full-body model to produce spatial deep features. The combined deep features are used as an input to SVM to judge the existence of pedestrian. As per the experiments conducted on the INRIA person dataset, the proposed FDMPD approach shows greater than 44.75 % improvement compared to other state-of-the-art methods in terms of efficiency and robustness.

关键词： Feature extraction Support vector machines Magnetic heads Computational modeling Knee Head Adaptation models

Graphene-Based Josephson-Junction Single-Photon Detector

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Physical Review Applied 2017年第2期8卷 024022-024022页

作者： Evan D. Walsh Dmitri K. Efetov Gil-Ho Lee Mikkel Heuck Jesse Crossno Thomas A. Ohki Philip Kim Dirk Englund Kin Chung Fong Department of Electrical Engineering and Computer Science Massachusetts Institute of Technology Cambridge Massachusetts 02139 USA School of Engineering and Applied Sciences Harvard University Cambridge Massachusetts 02138 USA ICFO-Institut de Ciències Fotòniques The Barcelona Institute of Science and Technology 08860 Castelldefels Barcelona Spain Department of Physics Harvard University Cambridge Massachusetts 02138 USA Department of Physics Pohang University of Science and Technology Pohang 790-784 Republic of Korea Raytheon BBN Technologies Quantum Information Processing Group Cambridge Massachusetts 02138 USA

We propose to use graphene-based Josephson junctions (GJJs) to detect single photons in a wide electromagnetic spectrum from visible to radio frequencies. Our approach takes advantage of the exceptionally low electronic heat capacity of monolayer graphene and its constricted thermal conductance to its phonon degrees of freedom. Such a system could provide high-sensitivity photon detection required for research areas including quantum information processing and radio astronomy. As an example, we present our device concepts for GJJ single-photon detectors in both the microwave and infrared regimes. The dark count rate and intrinsic quantum efficiency are computed based on parameters from a measured GJJ, demonstrating feasibility within existing technologies.

关键词： Electron thermal conductivity Hybrid quantum systems Photonics Quantum measurements Thermal conductivity Graphene Josephson junctions Photon counting

Unveiling the role of Co-O-Mg bond in magnetic anisotropy of Pt/Co/MgO using atomically controlled deposition and in situ electrical measurement

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Physical Review B 2017年第9期95卷 094417-094417页

作者： Yumeng Yang Jiaren Yuan Long Qi Ying Wang Yanjun Xu Xiaowei Wang Yuanping Feng Baoxi Xu Lei Shen Yihong Wu Department of Electrical and Computer Engineering National University of Singapore 4 Engineering Drive 3 Singapore 117583 Singapore College of Science Nanjing University of Aeronautics and Astronautics Nanjing 210016 People's Republic of China Department of Physics Centre for Advanced Two-dimensional Materials National University of Singapore Singapore 117542 Singapore Data Storage Institute Agency for Science Technology and Research (A*STAR) 2 Fusionopolis Way 08-01 Innovis Singapore 138634 Singapore Department of Mechanical Engineering Engineering Science Programme Faculty of Engineering National University of Singapore Singapore 117575 Singapore

Despite the crucial role of interfacial perpendicular magnetic anisotropy in a Co(Fe)/MgO-based magnetic tunnel junction, the underlying mechanism is still being debated. Here, we report an anatomical study of the oxygen and Mg effect on Pt/Co bilayers through repeated in situ anomalous Hall effect measurements, controlled oxygen exposure, and Mg deposition in an ultrahigh vacuum system. We found that chemisorbed oxygen not only quenches the effective magnetic moment of the Co surface layer, but also softens its magnetic anisotropy. However, a subsequent Mg dusting on the oxygen preexposed Pt/Co surface can recover the magnetic anisotropy. The ab initio calculations on the exchange splitting and orbital hybridization near the Fermi level give a clear physical explanation of the experimental observations. Our results suggest that the Co(Fe)-O-M bond plays a more important role than the widely perceived Co(Fe)-O bond does in realizing interfacial perpendicular magnetic anisotropy in Co(Fe)/MgO heterostructures.

关键词： Magnetic anisotropy Spintronics Ab initio calculations

Spectral Structure of Elastic Neumann–Poincaré Operators

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Journal of Physics: Conference Series 2018年第1期965卷

作者： Yoshihisa Miyanishi Kazunori Ando Hyeonbae Kang Center for Mathematical Modeling and Data Science Osaka University Osaka 560-8631 Japan Department of Electrical and Electronic Engineering and Computer Science Ehime University Ehime 790-8577 Japan Department of Mathematics and Institute of Applied Mathematics Inha University Incheon 22212 S. Korea

In [1, 2], it is proved that the elastic Neumann–Poincaré operator defined on the smooth boundary of a bounded domain, which is known to be non-compact, is in fact polynomially compact. As a consequence, it is shown that the spectrum of the elastic Neumann-Poincaré operator consists of non-empty sets of eigenvalues accumulating to certain numbers determined by Lamé parameters. The purpose of this paper is to review these results and their proofs, and to discuss about some questions related to these results.

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Mathematics of deep learning

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arXiv 2017年

作者： Vidal, René Bruna, Joan Giryes, Raja Soatto, Stefano Center for Imaging Science Biomedical Engineering Johns Hopkins University Baltimore United States Courant Institute of Mathematical Sciences Center for Data Science New York University United States School of Electrical Engineering Tel-Aviv University Tel Aviv Israel Department of Computer Science University of California Los Angeles United States

Recently there has been a dramatic increase in the performance of recognition systems due to the introduction of deep architectures for representation learning and classification. However, the mathematical reasons for this success remain elusive. This tutorial will review recent work that aims to provide a mathematical justification for several properties of deep networks, such as global optimality, geometric stability, and invariance of the learned representations. Copyright © 2017, The Authors. All rights reserved.

关键词： Deep learning

Self adaptation of chimera states

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arXiv 2018年

作者： Yao, Nan Huang, Zi-Gang Ren, Hai-Peng Grebogi, Celso Lai, Ying-Cheng Department of Applied Physics Xi’an University of Technology Xi’an710048 China School of Life Science and Technology Xi’an Jiao Tong University Xi’an710049 China Shaanxi Key Laboratory of Complex System Control and Intelligent Information Processing Xi’an University of Technology Xi’an710048 China Institute for Complex Systems and Mathematical Biology King’s College University of Aberdeen AberdeenAB24 3UE United Kingdom School of Electrical Computer and Energy Engineering Arizona State University TempeAZ85287 United States Department of Physics Arizona State University TempeAZ85287 United States

Chimera states in spatiotemporal dynamical systems have been investigated in physical, chemical, and biological systems, and have been shown to be robust against random perturbations. How do chimera states achieve their robustness? We uncover a self-adaptation behavior by which, upon a spatially localized perturbation, the coherent component of the chimera state spontaneously drifts to an optimal location as far away from the perturbation as possible, exposing only its incoherent component to the perturbation to minimize the disturbance. A systematic numerical analysis of the evolution of the spatiotemporal pattern of the chimera state towards the optimal stable state reveals an exponential relaxation process independent of the spatial location of the perturbation, implying that its effects can be modeled as restoring and damping forces in a mechanical system and enabling the articulation of a phenomenological model. Not only is the model able to reproduce the numerical results, it can also predict the trajectory of drifting. Our finding is striking as it reveals that, inherently, chimera states possess a kind of "intelligence" in achieving robustness through self adaptation. The behavior can be exploited for controlled generation of chimera states with their coherent component placed in any desired spatial region of the system. Copyright © 2018, The Authors. All rights reserved.

关键词： Dynamical systems

Zero-bias photocurrents in highly-disordered networks of Ge and Si nanowires

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arXiv 2017年

作者： Rabbani, M. Golam Patil, Sunil R. Verma, Amit Villarreal, Julian E. Korgel, Brian A. Nekovei, Reza Khader, Mahmoud M. Darling, R.B. Anantram, M.P. Department of Electrical Engineering University of Washington SeattleWA98195 United States Department of Physics College of Engineering PuneMS411005 India Department of Electrical Engineering and Computer Science Texas A&M University – Kingsville KingsvilleTX78363 United States McKetta Department of Chemical Engineering Texas Materials Institute Center for Nano- and Molecular Science and Technology University of Texas at Austin AustinTX78712 United States Gas Processing Center College of Engineering Qatar University DohaP.O2713 Qatar

Semiconducting nanowire (NW) devices have garnered attention in self-powered electronic and optoelectronic applications. This work explores and exhibits, for the first time for visible light, a clear evidence of the zero-biased optoelectronic switching in randomly dispersed Ge and Si NW networks. The test bench, on which the NWs were dispersed for optoelectronic characterization, was fabricated using standard CMOS fabrication process, and utilized metal contacts with dissimilar work functions - Al and Ni. The randomly dispersed NWs respond to light by exhibiting substantial photocurrents and, most remarkably, demonstrate zero-bias photo-switching. The magnitude of the photocurrent is dependent on the NW material, as well as the channel length. The photocurrent in randomly dispersed GeNWs was found to be higher by orders of magnitude compared to SiNWs. In both of these material systems, when the length of the NWs was comparable to the channel length, the currents in sparse NW networks were found to be higher than that in dense NW networks, which can be explained by considering various possible arrangements of NWs in these devices. Copyright © 2017, The Authors. All rights reserved.

关键词： Photocurrents

Consistency guarantees for greedy permutation-based causal inference algorithms

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arXiv 2017年

作者： Solus, Liam Wang, Yuhao Uhler, Caroline Institutionen för Matematik KTH StockholmSE-100 44 Sweden Institute for Interdisciplinary Information Sciences Tsinghua University Beijing China Shanghai Qi Zhi Institute Shanghai China Department of Electrical Engineering and Computer Science Institute for Data Systems and Society Massachusetts Institute of Technology CambridgeMA United States

Directed acyclic graphical models, or DAG models, are widely used to represent complex causal systems. Since the basic task of learning such a model from data is NP-hard, a standard approach is greedy search over the space of directed acyclic graphs or Markov equivalence classes of directed acyclic graphs. As the space of directed acyclic graphs on p nodes and the associated space of Markov equivalence classes are both much larger than the space of permutations, it is desirable to consider permutation-based greedy searches. Here, we provide the first consistency guarantees, both uniform and high-dimensional, of a greedy permutation-based search. This search corresponds to a simplex-like algorithm operating over the edge-graph of a sub-polytope of the permutohedron, called a DAG associahedron. Every vertex in this polytope is associated with a directed acyclic graph, and hence with a collection of permutations that are consistent with the directed acyclic graph ordering. A walk is performed on the edges of the polytope maximizing the sparsity of the associated directed acyclic graphs. We show via simulated and real data that this permutation search is competitive with current approaches. Copyright © 2017, The Authors. All rights reserved.

关键词： Bayesian networks