Acquisition and extinction of runway performance under escape,avoidance, and partial-avoidance procedures

The acquisition and extinction of locomotor responses of rats in a straight alley were examined for groups trained under escape, partial-avoidance, and avoidance procedures. During acquisition, one group (escape) received a 0-sec delay between being dropped into the alley and the onset of shock; two groups (partial avoidance) had 0.5- and 1-sec delays; and two groups (avoidance) had delays of 2 and 4 sec. On the final day of acquisition, the partial-avoidance rats displayed higher running speeds than either the escape- or avoidance-trained animals. The 4-sec avoidance group was consistently slower than all other groups. Speeds for all groups decreased during extinction, with rate of decline showing some relation to terminal acquisition level. Relative group performance levels proved to be consistent with a simple arithmetic model based on the assumption that changes in running speeds affect the aversiveness of the situation by altering US duration, CS duration, and effective US length.     

Trade-offs between knowledge exploitation and exploration activities

This paper explores trade-offs between knowledge exploitation and exploration activities. The study of exploitation and exploration activities is not new; however, rarely has past research perceived exploitation and exploration activities as two edges of one continuum. Furthermore, little evidence has been reported as to the actual trade-offs that firms face when launching either exploration or exploitation activities. This paper sets about filling this gap by addressing the following question: To what extent does an investment in one exploitation activity hinder the development of an exploration activity within the firm? A new process innovation targeting the exploitation of the firm's internal capabilities through an extensive component reuse and reconfiguration program is studied and the implications for inter-related exploration activities, such as the development of engineers' expertise is examined. To reveal the trade-offs between exploration and exploitation activities, both changes within and between these exploitation and exploration activities, over time, are studied. Based on data drawn from an in-depth study of several product development project teams in one high-tech company, we conclude that by investing in exploitation activities, a firm may limit some specific exploration activities.     

How cells communicate: the system used by slime moulds

The way in which cells in multicellular organisms communicate and inform each other of their presence and relative position is an intriguing but mysterious problem. The form of communication used during the phase of aggregation in the cellular slime moulds represents a particularly amenable system for study. When these organisms run short of nutrients, some of the cells of the amoebal population emit rhythmic pulses of cyclic adenosine monophosphate. These chemical signals are slowly relayed to all the other amoebae within range and bring about an ordered migration of them towards the pulsating centre and the triggering of cellular development.     

On modeling and analyzing multi-agent systems using n-calculus

Dynamic architecture of multi-agent systems （MAS） is important for critical systems. As the existing formal specifications of MAS cannot describe its dynamic architecture, a formal approach using n-calculus is presented, which is suited for the describing and analyzing of concurrent MAS with dynamic topology, n-calculus describes the belief-desireintention （BDI） model that represents agent＇s mental states and provides many useful facilities to analyze MAS model such as deadlock, behavior equivalence, and model checking. To illustrate the favorable representation capability of n-calculus, an example of dynamic multi-agent systems in e-commerce is provided. Finally, by using an existing n-calculus supporting tool, MAS model and some key behaviors properties are analyzed and verified.     

Parent and Child References to Letters During Alphabet Book Reading: Relations to Child Age and Letter Name Knowledge

Research Findings: The purpose of this study was to examine the frequency of extratextual references to letters made by parents and preschoolers during shared reading of an alphabet book. The frequency of letter references was also examined in relation to child age and knowledge of letter names. Participants consisted of 44 preschoolers and their primary caregivers. Videotaped book-reading data were transcribed verbatim and coded for their inclusion of 14 types of letter references (e.g., naming requests, labels, repetitions). Significant findings included the following: Parent labels were significantly correlated with child age; and child knowledge of letter names was significantly correlated with parent naming requests, corrections, and repetitions, and child answers and initiations. Practice or Policy: Findings are discussed in reference to the literature regarding parental sensitivity to child age and knowledge in educational interactions with their child.