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Computers RSS FeedsIntroduction to the Special Issue on Probability Models in Performance Analysis - This special issue includes research papers related to a workshop held at the Royal Society on 21st of September 2010, honouring Erol Gelenbe on his 65th birthday. The workshop brought together some 40 participants including some of Erol's former and current PhD students, colleagues and friends with whom he has interacted over the years, both in Europe and the USA. The papers focus on probability models in computer science, at the core of the field of computer performance engineering, which Erol pioneered. ...Feed Source: comjnl.oxfordjournals.org Neural Memories and Oscillatory Operation -
This paper develops two themes. The first is to show that the task of ‘recognition’ can be realized by an artificial neural net, and that the structures thus generated can be in close analogy to those observed in nature. The second is to note that absolute signal levels are almost meaningless in biological contexts; for these, the current state of a system is revealed by dynamic rather than static behaviour. This was Walter Freeman's observation, which led him to the oscillatory models which he has developed so notably; see the reference list. Coupling of the two sets of ideas leads to some striking conclusions, developed in Whittle (Neural Nets and Chaotic Carriers (1998) and Neural Nets and Chaotic Carriers, 2nd edn. (2010). Imperial College Press, London).
... Chaotic Evolution via Generalized Probabilistic Automata (Probabilistic Arrays) -
An n-state generalized probabilistic automaton/array maps a list of d states stochastically into a next state, resulting in a degree-d polynomially nonlinear transformation of the n-component state-probability vector, in contrast with the linear transformation given by the conventional Markovian model. This nonlinearity introduces the possibility of chaotic behaviour as time (iteration) progresses. It is shown that for two-state systems, the d = 2 case is nonchaotic, while chaotic behaviour is found for degree d as low as 5. Examples, and open issues for other values of n and/or d, are also noted.
... A Stochastic Geometry Model for Cognitive Radio Networks -
We propose a probabilistic model based on stochastic geometry to analyze cognitive radio in a large wireless network with randomly located users sharing the medium with carrier sensing multiple access. Analytical results are derived on the impact of the interaction between primary and secondary users, on their medium access probability, coverage probability and throughput. These results can be seen as the continuation of the theory of priorities in queueing theory to spatial processes. They give insight into the guarantees that can be offered to primary users and more generally on the possibilities offered by cognitive radio to improve the effectiveness of spectrum utilization in such networks.
... Scheduling Services in a Queuing System with Impatience and Setup Costs -
We consider a single-server queue in discrete time, in which customers must be served before some limit sojourn time of geometrical distribution. A customer who is not served before this limit leaves the system: it is impatient. The service of customers, the loss due to impatience and the holding of customers in the queue induce costs. The purpose is to decide when to serve the customers so as to minimize them. We use a Markov decision process with infinite horizon and discounted cost. We establish the structural properties of the stochastic dynamic programming operator and we deduce that the optimal policy is of threshold type. In addition, we are able to compute explicitly the optimal value of this threshold in terms of the parameters of problem.
... Bounding Aggregations for Transient and Stationary Performance Analysis of Subnetworks -
We consider large queueing networks for which transient and stationary probability distributions are very difficult or impossible to obtain due to the state space explosion problem. In performance analysis, we need in general to study only a part of the network (a node or a path). Thus, we propose to define bounding systems that lead to compute bounds on performance measures of the considered subsystem. The original large state space is mapped into a smaller space to overcome the state space explosion problem, and bounds both on stationary and on transient performance measures are computed from these reduced-size models. This approach provides an interesting solution for complex networks since we have a trade-off between the quality of the bounds and the state space size, thus the computational complexity. As an application, we study a general multi-server queueing network, with finite capacity queues. We define bounding systems to compute blocking probabilities. The influence of p... An Optimal Inherently Stabilizing 2-Neighborhood Crash Resilient Protocol for Secure and Reliable Routing in Hypercube Networks -
Many fundamental problems in the area of distributed systems such as security, reliable routing, network survivability and broadening available bandwidth can be addressed through the use of disjoint paths between communication endpoints. Therefore, distributed solutions to the disjoint paths problem are of crucial importance to these fundamental problems. Disjoint paths naturally exist in traditional networks; however, these networks provide no guarantees regarding the presence and the number of available disjoint paths. On the other hand, network topologies structured based on Caley graphs such as hypercube, star networks and their variations possess many desirable properties related to disjoint paths. Therefore, it is anticipated that backbones of future networks will be structured following some Caley graph topologies. In this paper, we present a simple novel stabilizing and inherently stabilizing algorithm to route messages over all node-disjoint paths of optimal length from on... Analyzer: A Complex System for Data Analysis -
Recently eXtensible Markup Language (XML) has achieved the leading role among languages for data representation and, thus, we can witness a massive boom of corresponding techniques for managing XML data. Most of the processing techniques, however, suffer from various bottlenecks worsening their time and/or space efficiency. We assume that the main reason is they consider XML collections too globally, involving all their possible features, although real-world data are often much simpler. Even though some techniques do restrict the input data, the restrictions are mostly unnatural. This paper aims to introduce Analyzer—a complex framework for performing statistical analyses of real-world documents. Exploitation of results of these analyses is a classical way how data processing can be optimized in many areas. Although this intent is legitimate, ad hoc and dedicated analyses soon become obsolete, they are usually built on insufficiently extensive collections and ar... Design Techniques Targeting Low-Area-Power-Delay Product in Hyperbolic CORDIC Algorithm -
The COordinate Rotation DIgital Computer (CORDIC) algorithm is a famous technique for realizing complex arithmetic functions using simple shift-add operations. This paper presents a novel completely scaling-free CORDIC algorithm in rotation mode for high performance hyperbolic computations. We target algorithm level improvements to achieve low area and power-delay product on FPGA. Instead of complex search algorithms, we use the most significant one bit detection technique for micro-rotation sequence identification, which helps in significantly reducing the number of pipelining stages. The proposed technique uses mathematical identities to extend the range of convergence. The eight-staged pipelined architecture implementation requires a ROM in the preprocessing unit for storing the initial coordinate values, while the ROM for storing the elementary angles is eliminated. The FPGA implementation of the proposed processor requires 46.35% less gates and has 31.81% less delay when compa... RNS-Based Elliptic Curve Point Multiplication for Massive Parallel Architectures -
Acceleration of cryptographic applications on massive parallel computing platforms, such as Graphic Processing Units (GPUs), becomes a real challenge concerning practical implementations. In this paper, we propose a parallel algorithm for Elliptic Curve (EC) point multiplication in order to compute EC cryptography on these platforms. The proposed approach relies on the usage of the Residue Number System (RNS) to extract parallelism on high-precision integer arithmetic. Results suggest a maximum throughput of 9827 EC multiplications per second and minimum latency of 29.2 ms for a 224-bit underlying field, in a commercial Nvidia 285 GTX GPU. Performances up to an order of magnitude better in latency and 122% in throughput are achieved regarding other approaches reported in the related art. An experimental analysis of the scalability, based on OpenCL descriptions of the proposed algorithms, suggest that further advantage can be obtained from the proposed RNS approach for GPUs and... DNA Profiles Link Dope to Its Source - 09 Jul 03
Forensic scientists in the U.S. are applying DNA fingerprinting methods to the cannabis plant. They say the technique, which is being used to create a database of DNA profiles of different marijuana plants, will help them to trace the source of any sample.
'It links everybody together: the user, the distributor, the grower,' says the database's creator, Heather Miller Coyle of the Connecticut State Forensic Science Laboratory in Meriden. 'That's the real intent of it, to show it's not just one guy with a little bag of marijuana, but it's a group of people.'
A method for spotting the tiniest traces of marijuana, based on detecting DNA unique to cannabis chloroplasts, has already been developed in the UK (New Scientist print edition, 07 Aug 1999). B... Mathematics: Does the Proof Stack Up? - by George Szpiro
03 Jul 03
Just under five years ago, Thomas Hales made a startling claim. In an e-mail he sent to dozens of mathematicians, Hales declared that he had used a series of computers to prove an idea that has evaded certain confirmation for 400 years. The subject of his message was Kepler's conjecture, proposed by the German astronomer Johannes Kepler, which states that the densest arrangement of spheres is one in which they are stacked in a pyramid - much the same way as grocers arrange oranges.
Soon after Hales made his announcement, reports of the breakthrough appeared on the front pages of newspapers around the world. But today, Hales's proof remains in limbo. It has been submitted to the prestigious Annals of Mathematics, but... Scientists Discover Planetary System Similar to Our Own -
The image shows an impression by David A. Hardy of a possible scene from a moon orbiting the extra-solar planet in orbit around the star HD70642. Photo Credit: David A. Hardy.
... Hacker How-To Good Summer Reading - by Michelle Delio
27 Jun 03
Stealing the Network: How to Own the Boxby Ryan RussellSyngress, 330 pp., $49.95
Stealing The Network: How to Own the Box, a compendium of tales written by well-known hackers, is a perfect summer read. The stories are fictional. The technology and techniques described are very real.
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