Departmental Papers (ESE) Copyright (c) 2013 University of Pennsylvania All rights reserved. http://repository.upenn.edu/ese_papers Recent documents in Departmental Papers (ESE) en-us Wed, 05 Jun 2013 01:50:39 PDT 3600 A Bioinspired Dynamical Vertical Climbing Robot http://repository.upenn.edu/ese_papers/634 http://repository.upenn.edu/ese_papers/634 Mon, 03 Jun 2013 12:33:22 PDT This paper describes the inspiration, design, analysis, implementation of and experimentation with the first dynamical vertical climbing robot. Biologists have proposed a pendulous climbing model that abstracts remarkable similarities in dynamic wall scaling behavior exhibited by radically different animal species. We study numerically a version of that pendulous climbing template dynamically re-scaled for applicability to utilitarian payloads with conventional electronics and actuation. This simulation study reveals that the incorporation of passive compliance can compensate for an artifact’s poorer power density and scale disadvantages relative to biology. However the introduction of additional dynamical elements raises new concerns about stability regarding both the power stroke and limb coordination that we allay via mathematical analysis of further simplified models. Combining these numerical and analytical insights into a series of design prototypes, we document the correspondence of the various models to the variously scaled platforms and report that our approximately two kilogram platform climbs dynamically at vertical speeds up to 1.5 bodylengths per second. In particular, the final 2.6 kg final prototype climbs at an average steady state speed of 0.66 m/s against gravity on a carpeted vertical wall, in rough agreement with our various models’ predictions.

]]> Goran A. Lynch et al. Analytical study of subwavelength imaging by uniaxial epsilon-near-zero metamaterial slabs http://repository.upenn.edu/ese_papers/633 http://repository.upenn.edu/ese_papers/633 Thu, 09 May 2013 15:32:45 PDT We discuss the imaging properties of uniaxial epsilon-near-zero metamaterial slabs with possibly tilted optical axis, analyzing their subwavelength focusing properties as a function of the design parameters. We derive in closed analytical form the associated two-dimensional Green's function in terms of special cylindrical functions. For the near-field parameter ranges of interest, we are also able to derive a small-argument approximation in terms of simpler analytical functions. Our results, validated and calibrated against a full-wave reference solution, expand the analytical tools available for computationally efficient and physically incisive modeling and design of metamaterial-based subwavelength imaging systems.

]]> Giuseppe Castaldi et al. Lensing system and Fourier transformation using epsilon-near-zero metamaterials http://repository.upenn.edu/ese_papers/632 http://repository.upenn.edu/ese_papers/632 Thu, 09 May 2013 15:32:42 PDT Metamaterials and metastructures with effective relative permittivity near zero exhibit unusual wave properties such as uniform phase distributions across such domains. Here we discuss the possibility of using ε-near-zero (ENZ) metamaterials for lensing and Fourier transforming. Owing to the possibility of having ENZ metamaterials in different wavelength regimes, the concepts shown here can be utilized at any frequency bands in which such materials can be constructed.

]]> M. Navarro-Cía et al. Experimental Verification of <em>n</em> = 0 Structures for Visible Light http://repository.upenn.edu/ese_papers/631 http://repository.upenn.edu/ese_papers/631 Thu, 09 May 2013 15:32:39 PDT We fabricate and characterize a metal-dielectric nanostructure with an effective refractive index n=0 in the visible spectral range. Light is excited in the material at deep subwavelength resolution by a 30-keV electron beam. From the measured spatially and angle-resolved emission patterns, a vanishing phase advance, corresponding to an effective ϵ=0 and n=0, is directly observed at the cutoff frequency. The wavelength at which this condition is observed can be tuned over the entire visible or near-infrared spectral range by varying the waveguide width. This n=0 plasmonic nanostructure may serve as a new building block in nanoscale optical integrated circuits and to control spontaneous emission as experimentally demonstrated by the strongly enhanced radiative optical density of states over the entire n=0 structure.

]]> Ernst Jan R. Vesseur et al. <em>PTM</em> Metamaterials via Complex-Coordinate Transformation Optics http://repository.upenn.edu/ese_papers/630 http://repository.upenn.edu/ese_papers/630 Thu, 09 May 2013 15:32:35 PDT We extend the transformation-optics paradigm to a complex spatial coordinate domain, in order to deal with electromagnetic metamaterials characterized by balanced loss and gain, giving special emphasis to parity-time (PT) symmetric metamaterials. We apply this general theory to complex-source-point radiation and anisotropic transmission resonances, illustrating the capability and potentials of our approach in terms of systematic design, analytical modeling, and physical insights into complex-coordinate wave objects and resonant states.

]]> Giuseppe Castaldi et al. Affordance http://repository.upenn.edu/ese_papers/629 http://repository.upenn.edu/ese_papers/629 Fri, 03 May 2013 09:53:29 PDT 1. (n.) An affordance is an action possibility formed by the relationship between an agent and its environment (J. Gibson 1977; J. Gibson 1979). For any combination of agent or environment, any given affordance either exists or does not exist. There is no middle ground. The most inclusive definition of affordances considers only the physical possibility of an action occurring. An agent does not need to be aware of the afforded action, such as the affordance of opening a secret door. This definition is rooted in perceptual psychology and its primary source is The Ecological Approach to Visual Perception by James J. Gibson (1979).

2. (n.) An affordance may refer to a perceived affordance. Perceived affordances are a subset of affordances. A perceived affordance uses a more restrictive definition that requires an agent to be aware of the affordance, either through direct perception or experience. A perceived affordance is a possible action to an agent (Norman 1988). Unlike the traditional definition, a perceived affordance is primarily a relationship between an agent’s cognition and the environment. This definition is commonly used within the humancomputer interaction (HCI) community.

3. (n.) Affordance may refer to how appealing an action possibility is to an agent, as in “this switch has affordance.” While the other definitions are dichotomous, this definition implies a magnitude (continuum) of affordance. This usage combines the ease of perceiving and/or perceived ease of performing a possible action. Since this usage refers to one or both of these qualities, this form is unclear from a theoretical standpoint.

]]> Benjamin D. Nye et al. Affordances in AI http://repository.upenn.edu/ese_papers/628 http://repository.upenn.edu/ese_papers/628 Fri, 03 May 2013 09:53:28 PDT Affordances in AI refer to a design methodology for creating artificial intelligence systems that are designed to perceive their environment in terms of its affordances (Sahin et al. 2007). Affordances in AI are adapted from affordances introduced in The Ecological Approach to Visual Perception by James J. Gibson (1979). Design methodologies in the applied sciences use affordances to represent potential actions that exist as a relationship between an agent and its environment. This approach to artificial intelligence is designed for autonomous agents, making it suitable for robotics and simulation.

]]> Benjamin D. Nye et al. Lyapunov Analysis of Robot Motion http://repository.upenn.edu/ese_papers/627 http://repository.upenn.edu/ese_papers/627 Fri, 03 May 2013 09:53:27 PDT The practice of automatic control has its origins in antiquity. It is only recently - within the middle decades of this century - that a body of scientific theory has been developed inform and improve that practice. Control theorists tend to divide their history into two periods. A "classical" period, prior to the sixties witnessed the systematization of feedback techniques based upon frequency domain analysis dominated by applications to electronics and telephony. A "modern" period in the sixties and seventies was characterized by a growing concern with formal analytical techniques pursued within the time domain motivated by the more stringent constraints posed by space applications and the enhanced processing capability of digital technology. The hallmark of control theory has been, by and large, a systematic exploitation of the properties of linear dynamical systems whether in the frequency or time domain. The dynamical behavior of mechanical systems appears to depart dynamically from the familiar linear case. The intent of this article is to show that a systematic application of Lyapunov Theory affords qualitative understanding of certain aspects of the input/output properties of a broad class of nonlinear systems (which includes all robots) analogous to that available for linear time invariant systems. For concreteness, this discussion is limited to robot arms - open kinematic chains with rigid links.

]]> Daniel E. Koditschek Robotics in an Intermittent Dynamical Environment: A Prelude to Juggling http://repository.upenn.edu/ese_papers/626 http://repository.upenn.edu/ese_papers/626 Fri, 03 May 2013 09:53:26 PDT We explore a very simple representative of a class of of robotic tasks which require "dynamic dexterity", among them the task of "juggling". In this initial paper we propose a formal definition of a "vertical one juggle", report a few preliminary analytical results, and offer illustrative simulations. This analysis is being currently applied to the design of and experimentation with "juggling algorithms" for a one-degree of freedom "robot" operative in the gravitational field.

]]> Martin Buehler et al. High Gain Feedback and Telerobotic Tracking http://repository.upenn.edu/ese_papers/625 http://repository.upenn.edu/ese_papers/625 Tue, 16 Apr 2013 09:18:17 PDT Asymptotically stable linear time invariant systems are capable of tracking arbitrary reference signals with a bounded error proportional to the magnitude of the reference signal (and its derivatives). It is shown that a similar property holds for a general class of nonlinear dynamical systems which includes all robots. As in the linear case, the error bound may be made "arbitrarily" small by increasing the magnitude of the feedback gains which stabilize the system.

]]> Daniel E. Koditschek Optical Frequency Mixing Through Nanoantenna Enhanced Difference Frequency Generation: Metatronic Mixer http://repository.upenn.edu/ese_papers/624 http://repository.upenn.edu/ese_papers/624 Thu, 28 Feb 2013 10:35:54 PST A design for a subwavelength all-optical frequency mixer is proposed. The method relies on enhanced difference-frequency generation, which is achieved in two steps with the help of plasmonic nanoantennas. The interaction of the two input signals with the nonlinear material is increased through the use of input nanoantennas, which focus the incident energy of two different frequencies onto the nanoparticle formed by a nonlinear material. Next, the difference-frequency emission is enhanced through the Purcell effect by the use of a separate output nanoantenna that is resonant at the difference frequency. The application of this twofold approach allows for a significant enhancement in the difference-frequency generation efficiency. Simulation results are presented highlighting the features of the method. This multi-element nanostructure is indeed an optical mixer circuit element in the metatronic paradigm.

]]> Uday K. Chettiar et al. Transformation Electronics: Tailoring the Effective Mass of Electrons http://repository.upenn.edu/ese_papers/623 http://repository.upenn.edu/ese_papers/623 Thu, 28 Feb 2013 10:35:51 PST The speed of integrated circuits is ultimately limited by the mobility of electrons or holes, which depend on the effective mass in a semiconductor. Here, building on an analogy with electromagnetic metamaterials and transformation optics, we describe a transport regime in a semiconductor superlattice characterized by extreme anisotropy of the effective mass and a low intrinsic resistance to movement—with zero effective mass—along some preferred direction of electron motion. We theoretically demonstrate that such a regime may permit an ultrafast, extremely strong electron response, and significantly high conductivity, which, notably, may be weakly dependent on the temperature at low temperatures. These ideas may pave the way for faster electronic devices and detectors and functional materials with a strong electrical response in the infrared regime.

]]> Mário G. Silveirinha et al. Metamaterial-Inspired Model for Electron Waves in Bulk Semiconductors http://repository.upenn.edu/ese_papers/622 http://repository.upenn.edu/ese_papers/622 Thu, 28 Feb 2013 10:35:49 PST Based on an analogy with electromagnetic metamaterials, we develop an effective medium description for the propagation of electron matter waves in bulk semiconductors with a zinc-blende structure. It is formally demonstrated that even though departing from a different starting point, our theory gives results for the energy stationary states consistent with Bastard’s envelope-function approximation in the long-wavelength limit. Using the proposed approach, we discuss the time evolution of a wave packet in a bulk semiconductor with a zero-gap and linear energy–momentum dispersion.

]]> Mário G. Silveirinha et al. Multistable Phase Regulation for Robust Steady and Transitional Legged Gaits http://repository.upenn.edu/ese_papers/621 http://repository.upenn.edu/ese_papers/621 Thu, 14 Feb 2013 08:27:01 PST We develop robust methods that allow specification, control, and transition of a multi-legged robot’s stepping pattern—its gait—during active locomotion over natural terrain. Resulting gaits emerge through the introduction of controllers that impose appropriately-placed repellors within the space of gaits, the torus of relative leg phases, thereby mitigating against dangerous patterns of leg timing. Moreover, these repellors are organized with respect to a natural cellular decomposition of gait space and result in limit cycles with associated basins that are well characterized by these cells, thus conferring a symbolic character upon the overall behavioral repertoire. These ideas are particularly applicable to four- and six-legged robots, for which a large variety of interesting and useful (and, in many cases, familiar) gaits exist, and whose tradeoffs between speed and reliability motivate the desire for transitioning between them during active locomotion. We provide an empirical instance of this gait regulation scheme by application to a climbing hexapod, whose “physical layer” sensor-feedback control requires adequate grasp of a climbing surface but whose closed loop control perturbs the robot from its desired gait. We document how the regulation scheme secures the desired gait and permits operator selection of different gaits as required during active climbing on challenging surfaces.

]]> G. C. Haynes et al. Time-triggered Implementations of Dynamic Controllers http://repository.upenn.edu/ese_papers/620 http://repository.upenn.edu/ese_papers/620 Thu, 14 Feb 2013 08:26:58 PST Bridging the gap between model-based design and platform-based implementation is one of the critical challenges for embedded software systems. In the context of embedded control systems that interact with an environment, a variety of errors due to quantization, delays, and scheduling policies may generate executable code that does not faithfully implement the model-based design. In this paper, we show that the performance gap between the model-level semantics of linear dynamic controllers, e.g. the proportional- integral-derivative (PID) controllers, and their implementation-level semantics can be rigorously quantified if the controller implementation is executed on a predictable time-triggered architecture. Our technical approach uses lifting techniques for periodic, time-varying linear systems in order to compute the exact error between the model semantics and the execution semantics. Explicitly computing the impact of the implementation on overall system performance allows us to compare and partially order different implementations with various scheduling or timing characteristics.

]]> Truong X. Nghiem et al. Duopoly Pricing Game in Networks With Local Coordination Effects http://repository.upenn.edu/ese_papers/619 http://repository.upenn.edu/ese_papers/619 Wed, 23 Jan 2013 10:21:04 PST In this paper, we study a duopoly pricing problem in which two firms compete for selling two products in a network. Our proposed model consists of two stages. In the first stage, firms set the price they charge agents for their product and the quality of the product they offer. For agents, the quality of the product can be interpreted as the payoff of a local coordination game played among them in the network. In the second stage, agents in the network decide what fraction of these two products to purchase. We first characterize the Nash equilibrium of the game played among agents in the network. We show that agents’ actions in the Nash equilibrium consist of two terms, one of which is proportional to the agents’ centrality in the network. Conditioned on agents playing the equilibrium policy, we find the Nash equilibrium of the pricing game played between firms. We show that even when firms are similar and offer a uniform price for agents, their Nash equilibrium price depends on the network structure.We then analyze sensitivity of the agents’ consumption with respect to the price and quality of the product. We finally show that depending on a firm’s opponent’s price and quality, the optimal price of a firm can be higher, equal or less than the monopoly optimal price.

]]> Arastoo Fazeli et al. Game Theoretic Analysis of a Strategic Model of Competitive Contagion and Product Adoption in Social Networks http://repository.upenn.edu/ese_papers/618 http://repository.upenn.edu/ese_papers/618 Wed, 23 Jan 2013 10:21:03 PST In this paper we propose and study a strategic model of marketing and product adoption in social networks. Two firms compete for the spread of their products in a social network. Considering their fixed budgets, they initially determine the payoff of their products and the number of their initial seeds in a network. Afterwards, neighboring agents play a local coordination game over a fixed network which determines the dynamics of the spreading. Assuming myopic best response dynamics, agents choose a product based on the payoff received by actions of their neighbors. This local update dynamics results in a game-theoretic diffusion process in the network. Utilizing earlier results in the literature, we find a lower and an upper bound on the proportion of product adoptions. We derive an explicit characterization of these bounds based on the payoff of products offered by firms, the initial number of adoptions and the underlying structure of the network. We then consider a case in which after switching to the new product, agents might later switch back to the old product with some fixed rate. We show that depending on the rate of switching back to the old product, the new product might always die out in the network eventually. Finally, we consider a game between two firms aiming to optimize their products adoptions while considering their fixed budgets. We describe the Nash equilibrium of this game and show how the optimal payoffs offered by firms and the initial number of seeds depend on the relative budgets of firms.

]]> Arastoo Fazeli et al. Targeted Marketing and Seeding Products with Positive Externality http://repository.upenn.edu/ese_papers/617 http://repository.upenn.edu/ese_papers/617 Wed, 23 Jan 2013 10:21:01 PST We study a strategic model of marketing in social networks in which two firms compete for the spread of their products. Firms initially determine the production cost of their product, which results in the payoff of the product for consumers, and the number and the location of the consumers in a network who receive the product as a free offer. Consumers play a local coordination game over a fixed network which determines the dynamics of the spreading of products. Assuming myopic best response dynamics, consumers choose a product based on the payoff received by actions of their neighbors. This local update dynamics results in a game-theoretic diffusion process in the network. Utilizing earlier results in the literature, we derive a lower and an upper bound on the proportion of product adoptions which not only depend on the number of initial seeds but also incorporate their locations as well. Using these bounds, we then study which consumers should be chosen initially in a network in order to maximize product adoptions for firms. We show consumers should be seeded based on their eigenvector centrality in the network. We then consider a game between two firms aiming to optimize their products adoptions while considering their fixed budgets. We describe the Nash equilibrium of the game between firms in star and k-regular networks and compare the equilibrium with our previous results.

]]> Arastoo Fazeli et al. Multi-agent Flocking With Random Communication Radius http://repository.upenn.edu/ese_papers/616 http://repository.upenn.edu/ese_papers/616 Wed, 23 Jan 2013 10:21:00 PST In this paper, we consider a multi-agent system consisting of mobile agents with second-order dynamics. The communication network is determined by a metric rule based on a random interaction range. The goal of this paper is to determine a bound on the probability that the agents asymptotically agree on a common velocity (i.e. a flocking behavior is achieved). This bound should depend on practical conditions (on the initial positions and velocities of agents) only. For this purpose, we exhibit an i.i.d. process bounding the original system’s dynamics. We build upon previous work on multi-agent systems with switching communication networks. Though conservative, our approach provide conditions that can be verified a priori.

]]> Samuel Martin et al. Consensus Over Martingale Graph Processes http://repository.upenn.edu/ese_papers/615 http://repository.upenn.edu/ese_papers/615 Wed, 23 Jan 2013 10:20:58 PST In this paper, we consider a consensus seeking process based on repeated averaging in a randomly changing network. The underlying graph of such a network at each time is generated by a martingale random process. We prove that consensus is reached almost surely if and only if the expected graph of the network contains a directed spanning tree. We then provide an example of a consensus seeking process based on local averaging of opinions in a dynamic model of social network formation which is a martingale. At each time step, individual agents randomly choose some other agents to interact with according to some arbitrary probabilities. The interaction is one-sided and results in the agent averaging her opinion with those of her randomly chosen neighbors based on the weights she assigns to them. Once an agent chooses a neighbor, the weights are updated in such a way that the expected values of the weights are preserved. We show that agents reach consensus in this random dynamical network almost surely. Finally, we demonstrate that a Polya Urn process is a martingale process, and our prior results in [1] is a special case of the model proposed in this paper.

]]> Arastoo Fazeli et al.