Self-organized aggregation without computation

This paper presents a solution to the problem of self-organized aggregation of embodied robots that requires no arithmetic computation. The robots have no memory and are equipped with one binary sensor, which informs them whether or not there is another robot in their line of sight. It is proven that the sensor needs to have a sufficiently long range; otherwise aggregation cannot be guaranteed, irrespective of the controller used. The optimal controller is found by performing a grid search over the space of all possible controllers. With this controller, robots rotate on the spot when they perceive another robot, and move backwards along a circular trajectory otherwise. This controller is proven to always aggregate two simultaneously moving robots in finite time, an upper bound for which is provided. Simulations show that the controller also aggregates at least 1000 robots into a single cluster consistently. Moreover, in 30 experiments with 40 physical e-puck robots, 98.6% of the robots aggregated into one cluster. The results obtained have profound implications for the implementation of multi-robot systems at scales where conventional approaches to sensing and information processing are no longer applicable

Power-efficient modulation formats in coherent transmission systems

Coherent optical transmission systems have a four-dimensional (4-D) signal space (two quadratures in two polarizations). These four dimensions can be used to create modulation formats that have a better power efficiency (higher sensitivity) than the conventional binary phase shift keying/quadrature phase shift keying (BPSK/QPSK) signals. Several examples are given, with some emphasis on a 24-level format and an 8-level format, including descriptions of how they can be realized and expressions for their symbol and bit error probabilities. These formats are, respectively, an extension and a subset of the commonly used 16-level dual-polarization QPSK format. Sphere packing simulations in 2, 3, and 4 dimensions, up to 32 levels, are used to verify their optimality. The numerical results, as the number of levels increases, are shown to agree with lattice-theoretical results. Finally, we point out that the use of these constellations will lead to improved fundamental sensitivity limits for optical communication systems, and they may also be relevant as a way of reducing power demands and/or nonlinear influence. \ua9 2009, IEEE. All rights reserved

Multidimensional Optimized Optical Modulation Formats

This chapter overviews the relatively large body of work (experimental and theoretical) on modulation formats for optical coherent links. It first gives basic definitions and performance metrics for modulation formats that are common in the literature. Then, the chapter discusses optimization of modulation formats in coded systems. It distinguishes between three cases, depending on the type of decoder employed, which pose quite different requirements on the choice of modulation format. The three cases are soft-decision decoding, hard-decision decoding, and iterative decoding, which loosely correspond to weak, medium, and strong coding, respectively. The chapter also discusses the realizations of the transmitter and transmission link properties and the receiver algorithms, including DSP and decoding. It further explains how to simply determine the transmitted symbol from the received 4D vector, without resorting to a full search of the Euclidean distances to all points in the whole constellation

Combinatorics, Probability and Computing

The main theme of this workshop was the use of probabilistic methods in combinatorics and theoretical computer science. Although these methods have been around for decades, they are being refined all the time: they are getting more and more sophisticated and powerful. Another theme was the study of random combinatorial structures, either for their own sake, or to tackle extremal questions. The workshop also emphasized connections between probabilistic combinatorics and discrete probability

Scale Invariant Dynamics of Interfaces and Sheared Solids

In this thesis we study three types of non-equilibrium processes: the depinning of elastic interfaces, the yielding of sheared disordered solids, and the fracture and granular flow of brittle solids. All three display scale-invariant behavior. The first two systems evolve in discrete bursts of motion or avalanches whose magnitudes follow a power law distribution, while breakup of brittle solids produces a power law distribution of grain sizes. The motion of elastic interfaces is studied using simulations of the random field Ising model. The interface is driven by gradually increasing an external magnetic field, leading to a series of avalanches whose maximum size diverges at a critical field. Growth is anisotropic, with the height of an avalanche growing as its width to a power $\chi = 0.85 \pm 0.01$. Scaling relations and finite-size scaling techniques are used to relate $\chi$ to other critical exponents. The roughness exponent of the growing interface is predicted to equal $\chi$ but is substantially smaller at accessible system sizes. Molecular dynamics simulations are used to study critical behavior in slowly sheared disordered solids. The average flow stress rises as a power $\beta$ of the strain rate. Finite-size scaling is used to determine $\beta$ and the exponent describing the divergence of the correlation length with distance to the critical point. The temporal correlations in the average kinetic energy of the system are used to measure the dynamical exponent relating the duration of an avalanche to its spatial size. Lastly, a discrete element model of brittle systems is developed. The model parameters can be calibrated to match specific material properties including elastic constants and fracture toughness. The model is used to study the impact of defect density and strain rate on the fracture of sheared brittle solids. A measure of damage is related to the initial yield and fragmentation. Subsequent granular flow produces a power-law distribution of grain sizes that suggests critical behavior at quasistatic strain rates and large strains. The maximum grain size decreases with increasing strain rate

Swarm Robotic Systems with Minimal Information Processing

This thesis is concerned with the design and analysis of behaviors in swarm robotic systems using minimal information acquisition and processing. The motivation for this work is to contribute in paving the way for the implementation of swarm robotic systems at physically small scales, which will open up new application domains for their operation. At these scales, the space and energy available for the integration of sensors and computational hardware within the individual robots is at a premium. As a result, trade-offs in performance can be justified if a task can be achieved in a more parsimonious way. A framework is developed whereby meaningful collective behaviors in swarms of robots can be shown to emerge without the robots, in principle, possessing any run-time memory or performing any arithmetic computations. This is achieved by the robots having only discrete-valued sensors, and purely reactive controllers. Black-box search methods are used to automatically synthesize these controllers for desired collective behaviors. This framework is successfully applied to two canonical tasks in swarm robotics: self-organized aggregation of robots, and self-organized clustering of objects by robots. In the case of aggregation, the robots are equipped with one binary sensor, which informs them whether or not there is another robot in their line of sight. This makes the structure of the robots’ controller simple enough that its entire space can be systematically searched to locate the optimal controller (within a finite resolution). In the case of object clustering, the robots’ sensor is extended to have three states, distinguishing between robots, objects, and the background. This still requires no run-time memory or arithmetic computations on the part of the robots. It is statistically shown that the extension of the sensor to have three states leads to a better performance as compared to the cases where the sensor is binary, and cannot distinguish between robots and objects, or robots and the background

In His Wake: Applying Life\u27s Truths in Fiction

The culmination of the creative work and its introduction attempt to delve into the psyche of what it means to lose someone you love. The screenplay explores the grieving process and the coping mechanisms that accompanies it, with an examination on how far some people are willing to go for closure. To reach my conclusions, I draw from my own life experience, the experiences of others, and a fine amount of research. It also means to shed light on the impermanent mental strain that chaperon’s grief