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arXiv 2018年

作者： Rezazadeh, Siavash Quintero, David Divekar, Nikhil Reznick, Emma Gray, Leslie Gregg, Robert D. Department of Bioengineering University of Texas at Dallas RichardsonTX75080 United States School of Engineering San Francisco State University San FranciscoCA94132 United States Department of Health Care Sciences University of Texas Southwestern Medical Center DallasTX75390 United States Department of Electrical Engineering and Computer Science Robotics Institute University of Michigan Ann ArborMI48109 United States

Although there has been recent progress in control of multi-joint prosthetic legs for rhythmic tasks such as walking, control of these systems for non-rhythmic motions and general real-world maneuvers is still an open problem. In this article, we develop a new controller that is capable of both rhythmic (constant-speed) walking, transitions between speeds and/or tasks, and some common volitional leg motions. We introduce a new piecewise holonomic phase variable, which, through a finite state machine, forms the basis of our controller. The phase variable is constructed by measuring the thigh angle, and the transitions in the finite state machine are formulated through sensing foot contact along with attributes of a nominal reference gait trajectory. The controller was implemented on a powered knee-ankle prosthesis and tested with a transfemoral amputee subject, who successfully performed a wide range of rhythmic and non-rhythmic tasks, including slow and fast walking, quick start and stop, backward walking, walking over obstacles, and kicking a soccer ball. Use of the powered leg resulted in clinically significant reductions in amputee compensations for rhythmic tasks (including vaulting and hip circumduction) when compared to use of the take-home passive leg. In addition, considerable improvements were also observed in the performance for nonrhythmic tasks. The proposed approach is expected to provide a better understanding of rhythmic and non-rhythmic motions in a unified framework, which in turn can lead to more reliable control of multi-joint prostheses for a wider range of real-world tasks. Copyright © 2018, The Authors. All rights reserved.

关键词： Artificial limbs

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NANOROBOTS: Intracellular manipulation and measurement with multipole magnetic tweezers

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science robotics 2019年第28期4卷

作者： Wang, X. Ho, C. Tsatskis, Y. Law, J. Zhang, Z. Zhu, M. Dai, C. Wang, F. Tan, M. Hopyan, S. McNeill, H. Sun, Y. Department of Mechanical and Industrial Engineering University of Toronto TorontoONM5S 3G8 Canada Institute of Biomaterials and Biomedical Engineering TorontoONM5S 3G9 Canada Lunenfeld-Tanenbaum Research Institute Mt. Sinai Hospital TorontoONM5G 1X5 Canada Program in Developmental and Stem Cell Biology Hospital for Sick Children TorontoONM5G 1X8 Canada HRG Central Institute of Robotics HIT Robot Group Harbin Heilongjiang150001 China Institute of Automation Chinese Academy of Sciences Beijing100190 China Division of Orthopaedic Surgery Hospital for Sick Children and University of Toronto TorontoONM5G 1X8 Canada Department of Developmental Biology Washington University School of Medicine St. LouisMO63108 United States Department of Electrical and Computer Engineering University of Toronto TorontoONM5S 3G4 Canada

The capability to directly interrogate intracellular structures inside a single cell for measurement and manipulation is important for understanding subcellular and suborganelle activities, diagnosing diseases, and developing new therapeutic approaches. Compared with measurements of single cells, physical measurement and manipulation of subcellular structures and organelles remain underexplored. To improve intracellular physical measurement and manipulation,we have developed amultipole magnetic tweezers system for micromanipulation involving submicrometer position control and piconewton force control of a submicrometermagnetic bead inside a single cell for measurement in different locations (spatial) and different time points (temporal). The beadwas three-dimensionally positioned in the cell using a generalized predictive controller that addresses the control challenge caused by the low bandwidth of visual feedback from high-resolution confocal imaging. The average positioning error was quantified to be 0.4 mm, slightly larger than the Brownianmotion-imposed constraint (0.31 mm). The system is also capable of applying a force up to 60 pN with a resolution of 4 pN for a period of time longer than 30 min. The measurement results revealed that significantly higher stiffness exists in the nucleus' major axis than in the minor axis. This stiffness polarity is likely attributed to the aligned actin filament. We also showed that the nucleus stiffens upon the application of an intracellularly applied force, which can be attributed to the response of structural protein lamin A/C and the intracellular stress fiber actin filaments. © 2019 The Authors.

关键词： Cells

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Recurrent predictive state policy networks

arXiv

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arXiv 2018年

作者： Hefny, Ahmed Marinho, Zita Sun, Wen Srinivasa, Siddhartha Gordon, Geoffrey Machine Learning Department Carnegie Mellon University Pittsburgh United States Robotics Institute Carnegie Mellon University Pittsburgh United States ISR/IT Instituto Superior Técnico Lisbon Portugal Paul G. Allen School of Computer Science & Engineering University of Washington Seattle United States

We introduce Recurrent Predictive State Policy (RPSP) networks, a recurrent architecture that brings insights from predictive state representations to reinforcement learning in partially observable environments. Predictive state policy networks consist of a recursive filter, which keeps track of a belief about the state of the environment, and a reactive policy that directly maps beliefs to actions, to maximize the cumulative reward. The recursive filter leverages predictive state representations (PSRs) (Rosencrantz & Gordon, 2004;Sun et al., 2016) by modeling predictive state —a prediction of the distribution of future observations conditioned on history and future actions. This representation gives rise to a rich class of statistically consistent algorithms (Hefny et al., 2018) to initialize the recursive filter. Predictive state serves as an equivalent representation of a belief state. Therefore, the policy component of the RPSP-network can be purely reactive, simplifying training while still allowing optimal behaviour. Moreover, we use the PSR interpretation during training as well, by incorporating prediction error in the loss function. The entire network (recursive filter and reactive policy) is still differentiable and can be trained using gradient based methods. We optimize our policy using a combination of policy gradient based on rewards (Williams, 1992) and gradient descent based on prediction error. We show the efficacy of RPSP-networks under partial observability on a set of robotic control tasks from OpenAI Gym. We empirically show that RPSP-networks perform well compared with memory-preserving networks such as GRUs, as well as finite memory models, being the overall Copyright © 2018, The Authors. All rights reserved.

关键词： Gradient methods

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Dynamic path planning and replanning for mobile robots using RRT

arXiv

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arXiv 2017年

作者： Connell, Devin La, Hung Manh Advanced Robotics and Automation Lab Department of Computer Science and Engineering University of Nevada Reno NV89519

It is necessary for a mobile robot to be able to efficiently plan a path from its starting, or current, location to a desired goal location. This is a trivial task when the environment is static. However, the operational environment of the robot is rarely static, and it often has many moving obstacles. The robot may encounter one, or many, of these unknown and unpredictable moving obstacles. The robot will need to decide how to proceed when one of these obstacles is obstructing it's path. A method of dynamic replanning using RRT* is presented. The robot will modify it's current plan when an unknown random moving obstacle obstructs the path. Various experimental results show the effectiveness of the proposed method. Copyright © 2017, The Authors. All rights reserved.

关键词： Mobile robots

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The Design of Automatic Bird Data Capture Systems

The Design of Automatic Bird Data Capture Systems

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IEEE International Conference on Consumer Electronics-Taiwan (ICCE-TW)

作者： Chia-Yuan Lin Yi-Chun Lin Che-Jui Chang Chi-Feng Chen Ming-Fong Tsai Department of Information Engineering and Computer Science Feng Chia University Taiwan Information and Communications Research Laboratories Industrial Technology Research Institute Taiwan Industrial Ph.D. Program of Internet of Things Feng Chia University Taiwan Departrnent of Electronic Engineering National United University Taiwan

This paper implements an automatic bird data capture system which uploads data captured from social network websites to the server and stores them in the database. When using the Facebook API to capture data of interest, the system needs to filter the captured data to avoid false data storage. This paper takes building an automatic system that includes reinforcing the training database of the bird community as a top priority.

关键词： Birds Databases Facebook Machine learning Servers System implementation

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Maximum Willis Coupling in Acoustic Scatterers

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Physical Review Letters 2018年第25期120卷 254301-254301页

作者： Li Quan Younes Ra’di Dimitrios L. Sounas Andrea Alù Department of Electrical and Computer Engineering The University of Texas at Austin Austin Texas 78712 USA Photonics Initiative Advanced Science Research Center City University of New York New York New York 10031 USA Physics Program Graduate Center City University of New York New York New York 10026 USA Department of Electrical Engineering City College of New York New York New York 10031 USA

Willis coupling in acoustic materials defines the cross-coupling between strain and velocity, analogous to bianisotropic phenomena in electromagnetics. While these phenomena have been garnering significant attention in recent years, to date their effects have been considered mostly perturbative. Here, we derive general bounds on the Willis response of acoustic scatterers, show that these bounds can be reached in suitably designed scatterers, and outline a systematic venue for the realistic implementation of maximally bianisotropic acoustic inclusions. We then employ these inclusions to realize acoustic metasurfaces for bending and steering of sound with unitary efficiency.

关键词： Acoustic metamaterials Acoustic wave phenomena Acoustics Mechanical & acoustical properties

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Laser micro-ablated multi-point side-firing optical fiber for deep-tissue light delivery 30

Laser micro-ablated multi-point side-firing optical fiber fo...

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30th Annual Conference of the IEEE Photonics Society, IPC 2017

作者： Nguyen, Hoang ParvezArnob, Masud Shih, Wei-Chuan Program of Materials Science and Engineering University of Houston TX77204 United States Department of Electrical and Computer Engineering University of Houston TX77204 United States Department of Biomedical Engineering University of Houston TX77204 United States Department of Chemistry University of Houston TX77204 United States

ISBN: (纸本)9781509065783

A compact light delivery device capable of delivering light to multiple desired locations is essential for many biomedical applications. Here, we demonstrate the use of laser micro-ablation to create controllable conicalshaped cavities on optical fiber to enable a multi-point side-firing configuration using a single fiber. © 2017 IEEE.

关键词： Tissue

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Active Microwave Cloaking Using Parity-Time-Symmetric Satellites

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Physical Review Applied 2018年第5期10卷 054040-054040页

作者： Ahmed Kord Dimitrios L. Sounas Andrea Alù Department of Electrical and Computer Engineering the University of Texas at Austin Austin Texas 78712 USA Photonics Initiative Advanced Science Research Center City University of New York New York New York 10031 USA Physics Program Graduate Center City University of New York New York New York 10026 USA Department of Electrical Engineering City College of New York New York New York 10031 USA

In this paper, we present and study the dynamics of an active microwave cloaking technique that alleviates the trade-offs between loss, bandwidth, and size inherent in passive approaches. The presented cloak consists of a finite number of satellite antennas loaded with parity-time-symmetric lumped admittances, which, without external control, can track in real time the amplitude, frequency, and phase variations of the impinging signals and generate the required current distributions at the antennas to totally suppress the scattered waves, including reflections and shadows. We analytically derive the optimal density and frequency dispersion of the antenna satellites surrounding the object in order to achieve substantial reduction in the scattering crosssection over a wide bandwidth. We also investigate the conditions necessary to maintain the cloak stability and study its transient response for excitation with pulsed signals.

关键词： Cloaking Metamaterials Optical cloaking PT-symmetry Microwave techniques

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Manifold learning for organizing unstructured sets of process observations

arXiv

引用

arXiv 2018年

作者： Dietrich, Felix Kooshkbaghi, Mahdi Bollt, Erik M. Kevrekidis, Ioannis G. Department of Chemical and Biomolecular Engineering Department of Applied Mathematics and Statistics Johns Hopkins University BaltimoreMD21218 United States Program in Applied and Computational Mathematics Princeton University PrincetonNJ08544 United States Department of Mathematics Department of Electrical and Computer Engineering Clarkson Center for Complex Systems Science Clarkson University PotsdamNY13699-5815 United States

Data mining is routinely used to organize ensembles of short temporal observations so as to reconstruct useful, low-dimensional realizations of an underlying dynamical system. In this paper, we use manifold learning to organize unstructured ensembles of observations ("trials") of a system's response surface. We have no control over where every trial starts;and during each trial operating conditions are varied by turning "agnostic" knobs, which change system parameters in a systematic but unknown way. As one (or more) knobs "turn" we record (possibly partial) observations of the system response. We demonstrate how such partial and disorganized observation ensembles can be integrated into coherent response surfaces whose dimension and parametrization can be systematically recovered in a data-driven fashion. The approach can be justified through the Whitney and Takens embedding theorems, allowing reconstruction of manifolds/attractors through different types of observations. We demonstrate our approach by organizing unstructured observations of response surfaces, including the reconstruction of a cusp bifurcation surface for Hydrogen combustion in a Continuous Stirred Tank Reactor. Finally, we demonstrate how this observation-based reconstruction naturally leads to informative transport maps between input parameter space and output/state variable *** codes 37M20 Copyright © 2018, The Authors. All rights reserved.

关键词： Dynamical systems

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Quantifying Gerrymandering in North Carolina

arXiv

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arXiv 2018年

作者： Herschlag, Gregory Kang, Han Sung Luo, Justin Graves, Christy Vaughn Bangia, Sachet Ravier, Robert Mattingly, Jonathan C. Department of Mathematics Duke University DurhamNC27708 United States Department of Biomedical Engineering Duke University DurhamNC27708 United States Department of Computer Science Duke University DurhamNC27708 United States Department of Electrical and Computer Engineering Duke University DurhamNC27708 United States Department of Economics Duke University DurhamNC27708 United States Program in Applied and Computational Mathematics Princeton University PrincetonNJ United States Department of Statistical Science Duke University DurhamNC27708 United States

Using an ensemble of redistricting plans, we evaluate whether a given political districting faithfully represents the geo-political landscape. Redistricting plans are sampled by a Monte Carlo algorithm from a probability distribution that adheres to realistic and non-partisan criteria. Using the sampled redistricting plans and historical voting data, we produce an ensemble of elections that reveal geo-political structure within the state. We showcase our methods on the two most recent districtings of NC for the U.S. House of Representatives, as well as a plan drawn by a bipartisan redistricting panel. We find the two state enacted plans are highly atypical outliers whereas the bipartisan plan accurately represents the ensemble both in partisan outcome and in the fine scale structure of district-level results. Copyright © 2018, The Authors. All rights reserved.

关键词： Probability distributions

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