Active Self-Assembly of Algorithmic Shapes and Patterns in Polylogarithmic Time

We describe a computational model for studying the complexity of self-assembled structures with active molecular components. Our model captures notions of growth and movement ubiquitous in biological systems. The model is inspired by biology's fantastic ability to assemble biomolecules that form systems with complicated structure and dynamics, from molecular motors that walk on rigid tracks and proteins that dynamically alter the structure of the cell during mitosis, to embryonic development where large-scale complicated organisms efficiently grow from a single cell. Using this active self-assembly model, we show how to efficiently self-assemble shapes and patterns from simple monomers. For example, we show how to grow a line of monomers in time and number of monomer states that is merely logarithmic in the length of the line. Our main results show how to grow arbitrary connected two-dimensional geometric shapes and patterns in expected time that is polylogarithmic in the size of the shape, plus roughly the time required to run a Turing machine deciding whether or not a given pixel is in the shape. We do this while keeping the number of monomer types logarithmic in shape size, plus those monomers required by the Kolmogorov complexity of the shape or pattern. This work thus highlights the efficiency advantages of active self-assembly over passive self-assembly and motivates experimental effort to construct general-purpose active molecular self-assembly systems

Improved single-ended traveling-wave fault- location algorithm based on experience with conventional substation transducers

Single-ended unsynchronized traveling-wave fault-location algorithms have been around for several years. They avoid the costs and complexities associated with remote-end synchronization. Nevertheless, there is a corresponding increase in required signal processing as each reflection must be identified and then related in time to the signal wavefront. The current signal processing techniques include a combination of modal and wavelet analysis, where the resulting vectors are often squared. However, the performance of this process degrades dramatically with the filtering associated with the substation transducers and secondary circuits. Furthermore, the variation in observed reflection patterns demonstrates that these methods cannot adequately distinguish between faults on the near, or far half of the transmission line. This paper considers the traveling-wave data observed on a 330-kV transmission system and presents a new signal processing methodology to cater for the observations. This is based on the continuous wavelet transform that is calculated at a suitably large scale. The polarities of the resulting coefficients are used to confirm the nature of the fault and to infer the true fault location. © 2006 IEEE

A fast hybrid time-synchronous/event appraach to parallel discrete event simulation of queuing networks

The trend in computing architectures has been toward multicore central processing units (CPUs) and graphics processing units (GPUs). An affordable and highly parallelizable GPU is practical example of Single Instruction, Multiple Data (SIMD) architectures oriented toward stream processing. While the GPU architectures and languages are fairly easily employed for inherently time-synchronous based simulation models, it is less clear if or how one might employ them for queuing model simulation, which has an asynchronous behavior. We have derived a two-step process that allows SIMD-style simulation on queuing networks, by initially performing SIMD computation over a cluster and following this research with a GPU experiment. The two-step process simulates approximate time events synchronously and then reduces the error in output statistics by compensating for it based on error analysis trends. We present our findings to show that, while the outputs are approximate, one may obtain reasonably accurate summary statistics quickly.

A parallel algorithm for switch-level timing simulation on a hypercube multiprocessor

The parallel approach to speeding up simulation is studied, specifically the simulation of digital LSI MOS circuitry on the Intel iPSC/2 hypercube. The simulation algorithm is based on RSIM, an event driven switch-level simulator that incorporates a linear transistor model for simulating digital MOS circuits. Parallel processing techniques based on the concepts of Virtual Time and rollback are utilized so that portions of the circuit may be simulated on separate processors, in parallel for as large an increase in speed as possible. A partitioning algorithm is also developed in order to subdivide the circuit for parallel processing

An Accurate Offline Phasor Estimation Technique For Fault Location In Series Compensated Lines

In series compensated transmission lines, current and voltage signals measured by the line protection system include considerable sub-synchronous frequency components (SSFCs) which are not sufficiently damped within a typical fault clearing time of line protection system. This does not allow accurate phasor estimation and thereby phasor-based fault location. This paper presents an accurate algorithm which effectively filters out the unwanted frequency components and noise to perform accurate phasor estimation for fault location in series compensated transmission lines. Phasor estimation of a theoretical signal is first evaluated using the proposed method, Direct-Prony analysis and 4-cycle discrete Fourier transform algorithm. Then, various fault locations of a 500 kV series compensated transmission line simulated in PSCAD/EMTDC are used to comprehensively evaluate the performance of the proposed technique. It is shown that the proposed method can effectively attenuate SSFCs and other unwanted frequency components in current and voltage signals allowing accurate phasor estimation

Wide-Area Backup Protection Against Asymmetrical Faults Using Available Phasor Measurements

This paper proposes a robust and computationally efficient wide-area backup protection (WABP) scheme against asymmetrical faults on transmission systems using available synchronized/unsynchronized phasor measurements. Based on the substitution theorem, the proposed scheme replaces the faulted line with two suitable current sources. This results in a linear system of equations for WABP, with no need of full system observability by measurement devices. The identification of the faulted line is attributed to the sum of squared residuals (SoSR) of the developed system of equations. To preserve accuracy, the scheme limits the calculations to the assessment of the negative-sequence circuit of the gird. Relevant practical aspects that have not been properly addressed in the literature, namely the non-simultaneous opening of circuit breakers (CBs) and their single-pole tripping for single-phase to ground faults are investigated. The linearity of the formulations derived removes concerns over convergence speed and potential time-synchronization challenges. The proposed scheme is able to identify the faulted line and retain this capability for hundreds of milliseconds following the fault inception. More than 20 000 simulations conducted on the IEEE 39-bus test system verify the effectiveness of the proposed WABP scheme

High performance photonic reservoir computer based on a coherently driven passive cavity

Reservoir computing is a recent bio-inspired approach for processing time-dependent signals. It has enabled a breakthrough in analog information processing, with several experiments, both electronic and optical, demonstrating state-of-the-art performances for hard tasks such as speech recognition, time series prediction and nonlinear channel equalization. A proof-of-principle experiment using a linear optical circuit on a photonic chip to process digital signals was recently reported. Here we present a photonic implementation of a reservoir computer based on a coherently driven passive fiber cavity processing analog signals. Our experiment has error rate as low or lower than previous experiments on a wide variety of tasks, and also has lower power consumption. Furthermore, the analytical model describing our experiment is also of interest, as it constitutes a very simple high performance reservoir computer algorithm. The present experiment, given its good performances, low energy consumption and conceptual simplicity, confirms the great potential of photonic reservoir computing for information processing applications ranging from artificial intelligence to telecommunicationsComment: non

Synchronization and application of delay-coupled semiconductor lasers

The work in this thesis is focused on the complex dynamics of semiconductor laser (SL) devices which receive time-delayed feedback from an external cavity or are delay-coupled with a second semiconductor laser. We investigate fundamental properties of the dynamics and study the utilization of transient complex dynamics of a single SL arising from delayed feedback and external signal injection for a neuro-inspired photonic data processing scheme. Based on experiments and numerical modelling, we investigate systems of two coupled SLs, gaining insights into the role of laser and coupling parameters for the synchronization characteristics of these systems. We link certain features of the synchronization dynamics, like intermittent desynchronization events, to the underlying nonlinear dynamics in the coupled laser system. Our research thus combines both fundamental insights into delay-coupled lasers as well as novel application perspectives