Stop Failure Research Articles

Visual-tactile saccadic inhibition

In an eye movement countermanding paradigm it is demonstrated for the first time that a tactile stimulus can be an effective stop signal when human participants are to inhibit saccades to a visual target. Estimated stop signal processing times were 90-140 ms, comparable to results with auditory stop signals, but shorter than those commonly found for manual responses. Two of the three participants significantly slowed their reactions in expectation of the stop signal as revealed by a control experiment without stop signals. All participants produced slower responses in the shortest stop signal delay condition than predicted by the race model (Logan and Cowan 1984) along with hypometric saccades on stop failure trials, suggesting that the race model may need to be elaborated to include some component of interaction of stop and go signal processing.

Automated application-level checkpointing of MPI programs

The running times of many computational science applications, such as protein-folding using ab initio methods, are much longer than the mean-time-to-failure of high-performance computing platforms. To run to completion, therefore, these applications must tolerate hardware failures.In this paper, we focus on the stopping failure model in which a faulty process hangs and stops responding to the rest of the system. We argue that tolerating such faults is best done by an approach called application-level coordinated non-blocking checkpointing, and that existing fault-tolerance protocols in the literature are not suitable for implementing this approach.We then present a suitable protocol, which is implemented by a co-ordination layer that sits between the application program and the MPI library. We show how this protocol can be used with a precompiler that instruments C/MPI programs to save application and MPI library state. An advantage of our approach is that it is independent of the MPI implementation. We present experimental results that argue that the overhead of using our system can be small.

Countermanding saccades: evidence against independent processing of go and stop signals.

In a stop signal paradigm, subjects were instructed to make a saccade to a visual target appearing left or right of the fixation point. In 25% of the trials, an auditory stop signal was presented after a variable delay that required the subject to inhibit the saccade. Observed saccadic response times in stop failure trials were longer than predicted by Logan and Cowan's (1984) race model. Saccadic response time and amplitude decreased with the time between stop signal presentation and saccade execution, suggesting an inhibitory effect between the stop signal and the go signal processes that is not compatible with an independent race assumption. Moreover, countermanding a saccade was more difficult when stop and go signals appeared at the same location.

The BG distributed simulation algorithm

We present a shared memory algorithm that allows a set of f+1 processes to wait-free “simulate” a larger system of n processes, that may also exhibit up to f stopping failures.

A Fault-Tolerant Directory Service for Mobile Agents based on Forwarding Pointers

A reliable communication layer is an essential component of a mobile agent system. We present a new fault-tolerant directory service for mobile agents, which can be used to route messages reliably to them, even in the presence of failures of intermediary nodes between senders and receivers. The directory service, based on a technique of forwarding pointers, introduces some redundancy in order to ensure resilience to stopping failures of nodes containing forwarding pointers; in addition, it avoids cyclic routing of messages, and it supports a technique to collapse chains of pointers that allows direct communication between agents. We have formalised the algorithm and derived a fully mechanical proof of its correctness using the proof assistant Coq; we report on our experience of designing the algorithm and deriving its proof of correctness. The complete source code of the proof is made available from the WWW.

Neuroelectric mapping reveals precursor of stop failures in children with attention deficits

Children with attention deficit disorders (ADD) may have specific problems with response inhibition in the STOP task. This task requires that subjects stop responses to a primary task if a second signal follows. However, it is unclear whether these problems reflect an impairment of the stopping process per se, whether they are related to reduced frontal lobe activation and whether they are confined to severe and pervasive forms of ADD. In 11 ADD and nine control children, 32 channel event-related EEG potentials (ERPs) were recorded in a STOP and a delayed GO task. Mapping revealed that both tasks evoked a similar sequence of neuroelectric microstates, i.e. of time segments with stable map topography. Adaptive segmentation identified the transition between these microstates. Reliable group differences were found in several microstates and in both tasks despite matched performance. In the GO task, ADD children had topographically altered P2/N2 microstates and attenuated P300-type microstates. In the STOP task, a topographically altered N1 microstate which coincided with the onset of the stop signal preceded the stop failures of ADD children. The timing of this microstate is too early to reflect deficits in actual stop signal processing and instead suggests altered initial orienting of attention to the primary signal in ADD children. Imaging with low resolution tomography (LORETA) during this microstate to stop failures indicated mainly posterior activation for both groups and increased rather than reduced frontal activation in ADD children. For a later microstate (P550), LORETA indicated strong frontal activation after successful stopping, but no group differences. The results suggest that information processing of ADD children deviates during activation of posterior mechanisms which may be related to the orienting of attention and which precedes and partly determines inhibitory control problems in ADD.

Parallel Algorithms with Processor Failures and Delays

We study efficient deterministic parallel algorithms on two models: restartable fail-stop CRCW PRAMs and asynchronous PRAMs. In the first model, synchronous processes are subject to arbitrary stop failures and restarts determined by an on-line adversary and involving loss of private but not shared memory; the complexity measures arecompleted work(where processors are charged for completed fixed-size update cycles) andoverhead ratio(completed work amortized over necessary work and failures). In the second model, the result of the computation is a serialization of the actions of the processors determined by an on-line adversary; the complexity measure istotal work(number of steps taken by all processors). Despite their differences, the two models share key algorithmic techniques. We present new algorithms for theWrite-Allproblem (in whichPprocessors write ones into an array of sizeN) for the two models. These algorithms can be used to implement a simulation strategy for anyNprocessor PRAM on a restartable fail-stopPprocessor CRCW PRAM such that it guarantees a terminating execution of each simulatedNprocessor step, withO(log2N) overhead ratio, andO(min{N+Plog2N+MlogN,N·P0.59}) (subquadratic) completed work (whereMis the number of failures during this step's simulation). This strategy has a range of optimality. We also show that theWrite-AllrequiresN+Ω(PlogP) completed/total work on these models forP≤N.

Beam stop failure — A potential hazard in tritium gas targets

Blistering of gold and platinum beam stops used in cells to contain tritium gas for neutron production targets has been observed. Such blistering becomes apparent after heavy bombardment by proton or deuteron beams of 2–10 MeV. Left unchecked, the blisters grow and eventually rupture, weakening the beam stop and possibly allowing leakage of tritium.

The Hybrid Boost Bearing—A Method of Obtaining Long Life in Rolling Contact Bearing Applications

Abstract A new bearing concept is described which offers the almost unlimited life of the fluid film bearing combined with the free starting, stopping, and oil system failure characteristics of the rolling element bearing. This new bearing type is termed the Hybrid Boost Bearing. It is envisioned as having application in jet engines to extend bearing life, and in land turbine equipment as a means of providing high overload capacity.