2884857
A genetic approach to planning in heterogeneous computing environments
Planning is an artificial intelligence problem with a wide range of real-world applications. Genetic algorithms, neural networks, and simulated annealing are heuristic search methods often used to solve complex optimization problems. In this paper, we propose a genetic approach to planning in the context of workflow management and process coordination on a heterogenous grid. We report results for two planning problems, the Towers of Hanoi and the Sliding-tile puzzle.
16013631
Populating Genomes in a Dynamic Grid
We study the behavior of a spatially distributed GA (Collins and Jefferson 1991) that has several unique features. First, individuals are allowed to move within a two dimensional grid over time. Such movement results in a continual change in the local environment in which each individual interacts. Second, selection is directly based on an individual’s energy value and indirectly based on fitness. The fitness of an individual determines its initial energy level, but an individual’s energy level at any point during a run reflects a combination of its fitness and its interactions in the environment. Third, the population size can change dynamically throughout a run.
15665141
An incremental genetic algorithm approach to multiprocessor scheduling
We have developed a genetic algorithm (GA) approach to the problem of task scheduling for multiprocessor systems. Our approach requires minimal problem specific information and no problem specific operators or repair mechanisms. Key features of our system include a flexible, adaptive problem representation and an incremental fitness function. Comparison with traditional scheduling methods indicates that the GA is competitive in terms of solution quality if it has sufficient resources to perform its search. Studies in a nonstationary environment show the GA is able to automatically adapt to changing targets.
11499161
Minimal replication cost for availability
Today, the utility of many replicated Internet services is limited by availability rather than raw performance. To better understand the effects of replica placement on availability, we propose the problem of minimal replication cost for availability. Let replication cost be the cost associated with replica deployment, dynamic replica creation and teardown at n candidate locations. Given client access patterns, replica failure patterns, network partition patterns, a required consistency level and a target level of availability, the minimal replication cost is the lower bound on a system's replication cost. Solving this problem also answers the dual question of optimal availability given a constraint on replication cost.We design the first algorithm we are aware of to solve the problem, through reduction to integer linear programming and enumeration of pruned serialization orders. Using practical faultloads and workloads, we demonstrate that the exponential complexity of our algorithm is tractable for practical problems with hundreds of candidate locations. The lower bound computed by our algorithm is tight, but the tightness can be sacrificed by a proposed optimization for large problems. We also show that with low replica creation and teardown costs, the bound is close to tight in practical problems even with the optimization.
8892885
The costs and limits of availability for replicated services
As raw system and network performance continues to improve at exponential rates, the utility of many services is increasingly limited by availability rather than performance. A key approach to improving availability involves replicating the service across multiple, wide-area sites. However, replication introduces well-known tradeoffs between service consistency and availability. Thus, this paper explores the benefits of dynamically trading consistency for availability using a continuous consistency model. In this model, applications specify a maximum deviation from strong consistency on a per-replica basis. In this paper, we: i) evaluate availability of a prototype replication system running across the Internet as a function of consistency level, consistency protocol, and failure characteristics, ii) demonstrate that simple optimizations to existing consistency protocols result in significant availability improvements (more than an order of magnitude in some scenarios), iii) use our experience with these optimizations to prove tight upper bounds on the availability of services, and iv) show that maximizing availability typically entails remaining as close to strong consistency as possible during times of good connectivity, resulting in a communication versus availability trade-off.
6880755
Implicit Trajectory Modeling through Gaussian Transition Models for Speech Recognition
It is well known that frame independence assumption is a fundamental limitation of current HMM based speech recognition systems. By treating each speech frame independently, HMMs fail to capture trajectory information in the acoustic signal. This paper introduces Gaussian Transition Models (GTM) to model trajectories implicitly. Comparing to alternative approaches, such as segment modeling and parallel path HMM, GTM has the advantage that it integrates seamlessly with the HMM frame-work; it can model a large number of trajectories and there is no need to define a topology a priori. Preliminary experiments on Switchboard, a large vocabulary conversational speech recognition task, have shown promising results.
14802960
Combining generality and practicality in a conit-based continuous consistency model for wide-area replication
Replication is a key approach to scaling wide-area applications. However, the overhead associated with large-scale replication quickly becomes prohibitive across wide-area networks. One effective approach to addressing this limitation is to allow applications to dynamically trade reduced consistency for increased performance and availability. Although extensive study has been performed on relaxed consistency models in traditional replicated databases, none of the models can simultaneously achieve the following two typically conflicting requirements imposed by wide-area applications: generality (capturing application-specific consistency semantics) and practicality (enabling efficient application-independent consistency protocols to be designed and providing natural ways to express application semantics). We propose a conit-based continuous consistency model designed to simultaneously achieve generality and practicality. Our conit theory provides generality, where application-specific consistency requirements are exported as conits. Practicality is achieved by using a simple, spanning set of metrics for conit consistency and by using a per-write weight specification. We demonstrate the generality of our model through representative wide-area applications and by showing that a number of existing models can be expressed as instances of our model. Our efficient, application-independent consistency protocols and prototype implementation verify its practicality.
28648006
Molecular dynamics simulations of liquid methanol and methanol-water mixtures with polarizable models
A polarizable model for simulation of liquid methanol, compatible with the COS/G2 water model, has been developed using the Charge-on-Spring (COS) technique. The model consists of three point charges, with one polarizable center on the oxygen atom. The Lennard-Jones parameters on the oxygen atom together with the molecular polarizability were varied to reproduce the experimental heat of vaporization and density of liquid methanol at ambient conditions. We examined the energies of various methanol dimers in the gas phase and compared them with values obtained from ab initio calculations. The model was then used to study the thermodynamic, dynamic, structural, and dielectric properties of liquid methanol as well as of a methanol-water mixture. A microscopic picture of the structure of pure liquid methanol and of the methanol-water mixture is provided. Good agreement was found between the results from our model simulations and available experimental and ab initio calculation data. In particular, the experimental dielectric permittivity of 32 could be reproduced, which had been shown to be difficult when using nonpolarizable models.