Distributed diagnosis in dynamic fault environments

The problem of distributed diagnosis in the presence of dynamic failures and repairs is considered. To address this problem, the notion of bounded correctness is defined. Bounded correctness is made up of three properties: bounded diagnostic latency, which ensures that information about state changes of nodes in the system reaches working nodes with a bounded delay, bounded start-up time, which guarantees that working nodes determine valid states for every other node in the system within bounded time after their recovery, and accuracy, which ensures that no spurious events are recorded by working nodes. It is shown that, in order to achieve bounded correctness, the rate at which nodes fail and are repaired must be limited. This requirement is quantified by defining a minimum state holding time in the system. Algorithm heartbeatcomplete is presented and it is proven that this algorithm achieves bounded correctness in fully-connected systems while simultaneously minimizing diagnostic latency, start-up time, and state holding time. A diagnosis algorithm for arbitrary topologies, known as algorithm forwardheartbeat, is also presented. Forwardheartbeat is shown to produce significantly shorter latency and state holding time than prior algorithms, which focused primarily on minimizing the number of tests at the expense of latency.     

Integrating cache coherence protocols for heterogeneous multiprocessor system. Part 2

In this second part of this two-part article, we present two examples of integrating heterogeneous processors and show the limitation of integrating processors without native support for cache coherence. Finally, we discuss the Verilog simulation results of applying our techniques to actual heterogeneous multiprocessor platforms. Experiments with actual heterogeneous multiprocessor platforms on a shared-bus measure the effectiveness of two cache coherence techniques. This integration approach, snoop-hit buffer, and the accompanying region-based cache coherence approach yield significant speedups compared to a pure software solution.     

Transport of single cells using an actin bundle-myosin bionanomotor transport system

The potential of using actin bundles for the transport of liposomes and single cells across myosin-coated surfaces is investigated. Compared to that observed with filamentous actin, the liposome transport using actin bundles was more linear in nature and able to occur over longer distances. Bundles, but not filamentous actin, were capable of moving single cells. Cargo unloading from bundles was achieved by incubation with Triton X-100. These data suggest that actin bundling may improve the ability of the myosin motor system for nanotransport applications.     

Context reinforcement degrades discriminative control: A memory approach.

This study measured effects of context reinforcement on a visual discrimination. Five pigeons responded to 1 key in the presence of 6 shorter wavelengths and to another key for 6 longer wavelengths. Psychometric functions provided measures of discriminative sensitivity (d') and overall stimulus control. Sensitivity and control were slightly but significantly better when 20% of correct choices yielded reinforcement than when 5% did. Reinforcement of pecks to the sample stimulus reduced control substantially and sensitivity slightly; noncontingent reinforcement during intertrial intervals also reduced control, whether such reinforcement was signaled or not. Accuracy was excellent during an extinction session, but it fell substantially when reinforcement for sample pecks was added during choice extinction. Simulations based on a memory model of the discrimination process reproduced most of the experimental findings. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Attentional priming and visual search in pigeons.

Advance information about a target's identity improved visual search efficiency in pigeons. Experiments 1 and 2 compared information supplied by visual cues with information supplied by trial sequences. Reaction times (RTs) were lower when visual cues signaled a single target rather than two. RTs were lower (Experiment 1) or accuracy improved (Experiment 2) when a sequence of trials presented a single target rather than a mixture of 2. Experiments 3, 4, and 5 considered the selectivity of visual priming by introducing probe trials that reversed the usual cue–target relationship. RT was higher following such miscues than following the usual 1- or 2-target cuing relationships (Experiment 3); the miscuing effect persisted over variations in the target's concealment (Experiments 4 and 5), but did not occur when the target was presented alone (Experiment 4). Findings indicate that priming modifies an attentional mechanism and suggest that this effect accounts for search images. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Utilization of Myosin and Actin Bundles for the Transport of Molecular Cargo

The utilization of motor proteins for the movement and assembly of synthetic components is currently a goal of nanoengineering research. Application of the myosin actin motor system for nanotechnological uses has been hampered due to the low flexural rigidity of individual F‐actin filaments. Here it is demonstrated how actin bundling can be used to affect the translational behavior of myosin‐propelled filaments, transport molecules across a motor‐patterned surface, and that the movement of bundled actin can be regulated photonically. These data suggest that actin bundling may significantly improve the applicability of the myosin motor for future nanotechnological applications.     

Mechanisms of the aqueous photodegradation of polycyclic aromatic hydrocarbons

The role of O2 and photoionization as well as the involvement of polycyclic aromatic hydrocarbon (PAH) cation radicals (P+) in the photodegradation of nine PAHs was examined. Photodegradation quantum yields for all PAHs increased with increasing O2 concentration, illustrating the key role of O2 in the photodegradation mechanism. In the presence of a series of electron donors (to P+), the photodegradation rate constants of most PAHs were largely unaffected at low O2 concentrations (< or = 250 microM), indicating that P+ is not extensively produced. However, at higher O2 concentrations (up to 1.2 mM), the presence of the donors substantially lowered photodegradation rates for most PAHs, indicating that P+ is produced and is arising from O2 reaction with the excited singlet state. Because little P+ was detected at low O2 concentrations and, further, because degradation rates were not enhanced in the presence of N2O, we conclude that photoionization is unimportant. With some exceptions, photodegradation can proceed through reaction of O2 with both excited singlet and triplet states of the PAHs. Our results indicate that photodegradation via the excited singlet state occurs primarily through electron transfer to O2, whereas degradation via the triplet occurs predominately through a direct reaction of O2 with the PAH within the collision complex.     

A random-walk model of accuracy and reaction time applied to three experiments on pigeon visual discrimination.

A random-walk model of visual discrimination is described and applied to reaction time (RT) distributions from three discrete-trial experiments with pigeons. Experiment 1 was a two-choice hue discrimination task with multiple hues. Choice percentages changed with hue discriminability; RTs were shortest for the least and most discriminable stimuli. Experiments 2 and 3 used go/no-go hue discriminations. Blocks of sessions differed in reward probability associated with a variable red stimulus in Experiment 2 and with a constant green stimulus in Experiment 3. Changes in hue had a large effect on response percentage and a small effect on RT; changes in reward shifted RT distributions on the time axis. The “random-walk, pigeon” model applied to these data is closely related to Ratcliff's diffusion model (Ratcliff, 1978; Ratcliff & Rouder, 1998). Simulations showed that stimulus discriminability affected the speed with which evidence accumulated toward a response threshold, in line with comparable effects in human subjects. Reward probability affected bias, modeled as the amount of evidence needed to reach one threshold rather than the other. The effects of reward probability are novel, and their isolation from stimulus effects within the decision process can guide development of a broader model of discrimination. (PsycINFO Database Record (c) 2011 APA, all rights reserved)