Towards complexity metrics for Ada tasking

Using Ada as a representative distributed programming language, the author discusses some ideas on complexity metrics that focus on Ada tasking and rendezvous. Concurrently active rendezvous are claimed to be an important aspect of communication complexity. A Petri net graph model of Ada rendezvous is used to introduce a rendezvous graph, an abstraction that can be useful in viewing and computing effective communication complexity     

Activity-dependent cortical target selection by thalamic axons

Connections in the developing nervous system are thought to be formed initially by an activity-independent process of axon pathfinding and target selection and subsequently refined by neural activity. Blockade of sodium action potentials by intracranial infusion of tetrodotoxin in cats during the early period when axons from the lateral geniculate nucleus (LGN) were in the process of selecting visual cortex as their target altered the pattern and precision of this thalamocortical projection. The majority of LGN neurons, rather than projecting to visual cortex, elaborated a significant projection within the subplate of cortical areas normally bypassed. Those axons that did project to their correct target were topographically disorganized. Thus, neural activity is required for initial targeting decisions made by thalamic axons as they traverse the subplate.     

Tool integration for flexible simulation of distributed algorithms

Over the last two decades, considerable research has been done in distributed operating systems, which can be attributed to faster processors and better communication technologies. A distributed operating system requires distributed algorithms to provide basic operating system functionality like mutual exclusion, deadlock detection, etc. A number of such algorithms have been proposed in the literature. Traditionally, these distributed algorithms have been presented in a theoretical way, with limited attempts to simulate actual working models. This paper discusses our experience in simulating distributed algorithms with the aid of some existing tools, including OPNET and Xplot. We discuss our efforts to define a basic model‐based framework for rapid simulation and visualization, and illustrate how we used this framework to evaluate some classic algorithms. We have also shown how the performance of different algorithms can be compared based on some collected statistics. To keep the focus of this paper on the approach itself, and our experience with tool integration, we only discuss some relatively simple models. Yet, the approach can be applied to more complex algorithm specifications. Copyright © 2001 John Wiley & Sons, Ltd.     

A framework for model-based design of agent-oriented software

Agents are becoming one of the most important topics in distributed and autonomous decentralized systems, and there are increasing attempts to use agent technologies to develop large-scale commercial and industrial software systems. The complexity of such systems suggests a pressing need for system modeling techniques to support reliable, maintainable, and extensible design. G-nets are a type of Petri net defined to support system modeling in terms of a set of independent and loosely-coupled modules. In this paper, we customize the basic G-net model to define a so-called "agent-based G-net" that can serve as a generic model for agent design. Then, to progress from an agent-based design model to an agent-oriented model, new mechanisms to support inheritance modeling are introduced. To illustrate our formal modeling technique for multiagent systems, an example of an agent family in electronic commerce is provided. Finally, we demonstrate how we can use model checking to verify some key behavioral properties of our agent model. This is facilitated by the use of an existing Petri net tool.     

An improved snare system for the nonsurgical retrieval of intravascular foreign bodies

We have modified a snare technique originally described for transcolonoscopic removal of colonic polyps for the retrieval of intravascular foreign bodies. The key difference from other snare techniques is the employment of a wire snare with a crimp in its midportion that enables the formation of a loop in a plane perpendicular to the axial direction of the guiding catheter. With this technique we have quickly removed a variety of objects from the right heart and pulmonary arteries in four patients.     

Models and algorithms for reliability-oriented task-allocation inredundant distributed-computer systems

Reliability-oriented task-allocation for heterogeneous distributed-computer systems with hardware redundancy is discussed. Redundancy of both processors and communication links is considered. A quantitative allocation model is derived and used to present and discuss models and algorithms for systems with level-two or level-three redundancy. The results contribute to the body of knowledge on task allocation and provide an alternative to performance-oriented methods     

Activity-dependent regulation of NMDAR1 immunoreactivity in the developing visual cortex

NMDA receptors have been implicated in activity-dependent synaptic plasticity in the developing visual cortex. We examined the distribution of immunocytochemically detectable NMDAR1 in visual cortex of cats and ferrets from late embryonic ages to adulthood. Cortical neurons are initially highly immunostained. This level declines gradually over development, with the notable exception of cortical layers 2/3, where levels of NMDAR1 immunostaining remain high into adulthood. Within layer 4, the decline in NMDAR1 immunostaining to adult levels coincides with the completion of ocular dominance column formation and the end of the critical period for layer 4. To determine whether NMDAR1 immunoreactivity is regulated by retinal activity, animals were dark-reared or retinal activity was completely blocked in one eye with tetrodotoxin (TTX). Dark-rearing does not cause detectable changes in NMDAR1 immunoreactivity. However, 2 weeks of monocular TTX administration decreases NMDAR1 immunoreactivity in layer 4 of the columns of the blocked eye. Thus, high levels of NMDAR1 immunostaining within the visual cortex are temporally correlated with ocular dominance column formation and developmental plasticity; the persistence of staining in layers 2/3 also correlates with the physiological plasticity present in these layers in the adult. In addition, visual experience is not required for the developmental changes in the laminar pattern of NMDAR1 levels, but the presence of high levels of NMDAR1 in layer 4 during the critical period does require retinal activity. These observations are consistent with a central role for NMDA receptors in promoting and ultimately limiting synaptic rearrangements in the developing neocortex.     

Effects of language and task on children's patterns of sentence verification and denial.

Japanese-speaking and English-speaking children differ in performance on sentence-verification and denial tasks (M. M. Akiyama, see PA, Vol 71:14618 and PA, Vol 72:16907). Although the Japanese and Korean languages are similar, Korean-speaking children performed like English speakers on such tasks. In Experiment 1, 32 monolingual Korean and 24 English speakers with a mean age of 4 years, 5 months were asked to respond "right" or "wrong" on a sentence–picture or a sentence–knowledge verification task. Both language groups found true negatives the hardest sentences to verify in both tasks. In Experiment 2, 16 Korean speakers aged 4–7 years were asked to deny statements. Like English speakers, they produced more affirmative denials than negative ones. The common performances of Korean-speaking and English speaking children were accounted for by considering differences in pragmatics and the types of negative constructions found in the 3 languages. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Neurobehavioral and life-quality changes after cerebral revascularization.

[Correction Notice: An erratum for this article was reported in Vol 56(4) of Journal of Consulting and Clinical Psychology (see record 2008-10691-001). The authors' names were incorrectly ordered. The correct order is as follows: Anne Dull Baird, Kenneth M. Adams, Mark W. Shatz, James I. Ausman, Fernando G. Diaz, and Manuel Dujovny.] Neuropsychological and life-quality changes were studied 6 months after carotid endarterectomy, superficial temporal artery to middle cerebral artery bypass, multiple revascularization, and vertebrobasilar revascularization procedures. These changes were compared with those in patients with recent severe spinal complaints and in patients for whom revascularization was considered but not elected. Subjects were enrolled prospectively. We did not see statistically significant differences in neurobehavioral gains in patients undergoing cerebral revascularization versus those considered but not selected for surgery and versus patients with spinal complaints. Small sample size, marked intragroup variability, and lack of randomized subject assignments may have obscured modest-to-moderate treatment effects in some individuals. (PsycINFO Database Record (c) 2010 APA, all rights reserved)