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Articles 1 - 13 of 13

Full-Text Articles in Mechanical Engineering

A Variational Shape Optimization Approach For Image Segmentation With A Mumford-Shah Functional, Günay Doğam, Pedro Morin, Ricardo H. Nochetto Oct 2008

A Variational Shape Optimization Approach For Image Segmentation With A Mumford-Shah Functional, Günay Doğam, Pedro Morin, Ricardo H. Nochetto

Departmental Papers (MEAM)

We introduce a novel computational method for a Mumford–Shah functional, which decomposes a given image into smooth regions separated by closed curves. Casting this as a shape optimization problem, we develop a gradient descent approach at the continuous level that yields nonlinear PDE flows. We propose time discretizations that linearize the problem and space discretization by continuous piecewise linear finite elements. The method incorporates topological changes, such as splitting and merging for detection of multiple objects, space–time adaptivity, and a coarse-to-fine approach to process large images efficiently. We present several simulations that illustrate the performance of the method ...


Effective-Medium Theory For Infinite-Contrast Two-Dimensionally Periodic Linear Composites With Strongly Anisotropic Matrix Behavior: Dilute Limit And Crossover Behavior, François Willot, Yves-Patrick Pellegrini, Martín I. Idiart, Pedro Ponte Castañeda Sep 2008

Effective-Medium Theory For Infinite-Contrast Two-Dimensionally Periodic Linear Composites With Strongly Anisotropic Matrix Behavior: Dilute Limit And Crossover Behavior, François Willot, Yves-Patrick Pellegrini, Martín I. Idiart, Pedro Ponte Castañeda

Departmental Papers (MEAM)

The overall behavior of a two-dimensional lattice of voids embedded in an anisotropic elastic matrix is investigated in the limit of vanishing porosity f. An effective-medium model (of the Clausius-Mossoti type), which accounts for elastic interactions between neighboring voids, is compared to fast Fourier transform numerical solutions and, in the limits of infinite anisotropy, to exact results. A crossover between regular and singular dilute regimes is found, driven by a characteristic length which depends on f and on the anisotropy strength. The singular regime, where the leading dilute correction to the elastic moduli is an O(f1/2), is ...


Origin Of Ultralow Friction And Wear In Ultrananocrystalline Diamond, Andrew R. Konicek, D. S. Grierson, P.U.P.A. Gilbert, W. G. Sawyer, A. V. Sumant, Robert W. Carpick Jun 2008

Origin Of Ultralow Friction And Wear In Ultrananocrystalline Diamond, Andrew R. Konicek, D. S. Grierson, P.U.P.A. Gilbert, W. G. Sawyer, A. V. Sumant, Robert W. Carpick

Departmental Papers (MEAM)

The impressively low friction and wear of diamond in humid environments is debated to originate from either the stability of the passivated diamond surface or sliding-induced graphitization/rehybridization of carbon. We find ultralow friction and wear for ultrananocrystalline diamond surfaces even in dry environments, and observe negligible rehybridization except for a modest, submonolayer amount under the most severe conditions (high load, low humidity). This supports the passivation hypothesis, and establishes a new regime of exceptionally low friction and wear for diamond.


Stretching Fields And Mixing Near The Transition To Nonperiodic Two-Dimensional Flow, M. J. Twardos, Paulo E. Arratia, M. K. Rivera, G. A. Voth, J. P. Gollub, R. E. Ecke May 2008

Stretching Fields And Mixing Near The Transition To Nonperiodic Two-Dimensional Flow, M. J. Twardos, Paulo E. Arratia, M. K. Rivera, G. A. Voth, J. P. Gollub, R. E. Ecke

Departmental Papers (MEAM)

Although time-periodic fluid flows sometimes produce mixing via Lagrangian chaos, the additional contribution to mixing caused by nonperiodicity has not been quantified experimentally. Here, we do so for a quasi-two-dimensional flow generated by electromagnetic forcing. Several distinct measures of mixing are found to vary continuously with the Reynolds number, with no evident change in magnitude or slope at the onset of nonperiodicity. Furthermore, the scaled probability distributions of the mean Lyapunov exponent have the same form in the periodic and nonperiodic flow states.


Decentralized Controllers For Shape Generation With Robotic Swarms, Mong-Ying Ani Hsieh, Vijay Kumar, Luiz Chaimowicz Apr 2008

Decentralized Controllers For Shape Generation With Robotic Swarms, Mong-Ying Ani Hsieh, Vijay Kumar, Luiz Chaimowicz

Departmental Papers (MEAM)

We address the synthesis of controllers for a swarm of robots to generate a desired two-dimensional geometric pattern specified by a simple closed planar curve with local interactions for avoiding collisions or maintaining specified relative distance constraints. The controllers are decentralized in the sense that the robots do not need to exchange or know each other’s state information. Instead, we assume that the robots have sensors allowing them to obtain information about relative positions of neighbors within a known range.We establish stability and convergence properties of the controllers for a certain class of simple closed curves.We illustrate ...


The Dynamics Of Two Spherical Particles In A Confined Rotating Flow: Pedalling Motion, Karthik Mukundakrishnan, Howard H. Hu, Portonovo S. Ayyaswamy Mar 2008

The Dynamics Of Two Spherical Particles In A Confined Rotating Flow: Pedalling Motion, Karthik Mukundakrishnan, Howard H. Hu, Portonovo S. Ayyaswamy

Departmental Papers (MEAM)

We have numerically investigated the interaction dynamics between two rigid spherical particles moving in a fluid-filled cylinder that is rotating at a constant speed. The cylinder rotation is about a horizontal axis. The particle densities are less than that of the fluid. The numerical procedure employed to solve the mathematical formulation is based on a three-dimensional arbitrary Larangian–Eulerian (ALE), moving mesh finite-element technique, described in a frame of reference rotating with the cylinder. Results are obtained in the ranges of particle Reynolds number, 1<Rep≤60, and shear Reynolds number, 1≤Res <10. Two identical particles, depending on initial conditions at release, approach each other (‘drafting’ and ‘kissing’), tumble in the axial direction, and axially migrate towards opposing transverse planes on which they ‘settle’ (settling planes). Under some other initial conditions, the particles migrate directly onto their settling planes. For two identical particles, the settling planes are equidistant from the mid-transverse plane of the cylinder and the locations of the planes are determined by particle–particle and particle–wall force balances. Furthermore, for identical particles and given values of Rep and Res ...


Automatic Configuration Recognition Methods In Modular Robots, Michael Park, Sachin Chitta, Alex Teichman, Mark Yim Mar 2008

Automatic Configuration Recognition Methods In Modular Robots, Michael Park, Sachin Chitta, Alex Teichman, Mark Yim

Departmental Papers (MEAM)

Recognizing useful modular robot configurations composed of hundreds of modules is a significant challenge. Matching a new modular robot configuration to a library of known configurations is essential in identifying and applying control schemes. We present three different algorithms to address the problem of (a) matching and (b) mapping new robot configurations onto a library of known configurations. The first method solves the problem using graph isomorphisms and can identify configurations that share the same underlying graph structure, but have different port connections amongst the modules. The second approach compares graph spectra of configuration matrices to find a permutation matrix ...


Effects Of Proprioceptive Motion Feedback On Sighted And Non-Sighted Control Of A Virtual Hand Prosthesis, Amy Blank, Allison M. Okamura, Katherine J. Kuchenbecker Mar 2008

Effects Of Proprioceptive Motion Feedback On Sighted And Non-Sighted Control Of A Virtual Hand Prosthesis, Amy Blank, Allison M. Okamura, Katherine J. Kuchenbecker

Departmental Papers (MEAM)

Current prosthetic devices lack the ability to provide proprioceptive feedback, requiring the user to visually track the device in order to accomplish the tasks of daily living. This work seeks to quantify the effect of proprioceptive feedback on the accuracy, speed, and ease of use of a one-degree-of-freedom virtual prosthetic finger in both sighted and unsighted conditions. An experimental apparatus was designed to allow a user to perform a virtual grasping task with and without visual and proprioceptive feedback. Preliminary results suggest that proprioception improves movement accuracy and ease of system use in the absence of vision.


Experimental Testbed For Large Multirobot Teams, Nathan Michael, Jonathan Fick, Vijay Kumar Mar 2008

Experimental Testbed For Large Multirobot Teams, Nathan Michael, Jonathan Fick, Vijay Kumar

Departmental Papers (MEAM)

Experimental validation is particularly important in multirobot systems research. The differences between models and real-world conditions that may not be apparent in single robot experiments are amplified because of the large number of robots, interactions between robots, and the effects of asynchronous and distributed control, sensing, and actuation. Over the last two years, we have developed an experimental testbed to support research in multirobot systems with the goal ofmaking it easy for users tomodel, design, benchmark, and validate algorithms. In this article, we describe our approach to the design of a large-scale multirobot system for the experimental verification and validation ...


A Coupled Electrochemical And Hydrodynamical Two-Phase Model For The Electrolytic Pickling Of Steel, Nulifer Ipek, Michael Vynnycky, A. Cornell Feb 2008

A Coupled Electrochemical And Hydrodynamical Two-Phase Model For The Electrolytic Pickling Of Steel, Nulifer Ipek, Michael Vynnycky, A. Cornell

Departmental Papers (MEAM)

In industrial electrolytic pickling, a steel strip with oxidized surfaces is passed through an aqueous electrolyte between a configuration of electrodes, across which a potential difference is applied. The strip is thereby indirectly polarized, and electrochemical reactions at the strip surface result in the dissolution of the oxide layer and the evolution of hydrogen and oxygen bubbles. In this paper, we extend an earlier mathematical model for the electrochemical aspects of the process, which took account only of the liquid phase, to include the effect of the gas phase. The model is two-dimensional, steady-state and isothermal, and comprises five ionic ...


Exploring The Detailed Location Patterns Of Uk Manufacturing Industries Using Microgeographic Data, Gilles Duranton, Henry G. Overman Feb 2008

Exploring The Detailed Location Patterns Of Uk Manufacturing Industries Using Microgeographic Data, Gilles Duranton, Henry G. Overman

Real Estate Papers

We use a point-pattern methodology to explore the detailed location patterns of U.K. manufacturing industries. In particular, we consider the location of entrants and exiters versus continuing establishments, domestic- versus foreign-owned, large versus small, and affiliated versus independent. We also examine colocalization between vertically-linked industries. Our analysis provides a set of new stylized facts and confirmation for others.


The Exergy Fields In Processes, Noam Lior Jan 2008

The Exergy Fields In Processes, Noam Lior

Departmental Papers (MEAM)

This paper is a very brief review of the method for analyzing the space and time dependent exergy and irreversibility fields in processes. It presents the basic equations, the method for their use, and three examples from the work of the author and his former graduate students: flow desiccation, combustion of oil droplets, and combustion of pulverized coal. Conclusions from this Second Law analysis are used to attempt process improvement suggestions.


Lab-On-A-Chip For Oral Cancer Screening And Diagnosis, Barry L. Ziober, Michael G. Mauk, Erica M. Falls, Zongyuan Chen, Amy F. Ziober, Haim H. Bau Jan 2008

Lab-On-A-Chip For Oral Cancer Screening And Diagnosis, Barry L. Ziober, Michael G. Mauk, Erica M. Falls, Zongyuan Chen, Amy F. Ziober, Haim H. Bau

Departmental Papers (MEAM)

Oral squamous cell carcinoma (OSCC) is a disfiguring and deadly cancer. Despite advances in therapy, many patients continue to face a poor prognosis. Early detection is an important factor in determining the survival of patients with OSCC. No accurate, cost-efficient, and reproducible method exists to screen patients for OSCC. As a result, many patients are diagnosed at advanced stages of the disease. Early detection would identify patients, facilitating timely treatment and close monitoring. Mass screening requires a rapid oral cancer diagnostic test that can be used in a clinical setting. Current diagnostic techniques for OSCC require modern laboratory facilities, sophisticated ...