Automatic Management of Sessions in Shared Spaces

In this paper we propose a session model suited for cooperative work in shared spaces such as virtual 3D spaces. Our session model aims at structuring interactions on shared objects, without requiring explicit session preparation. Sessions are rule driven: accessing objects triggers automatic session creation, deletion or merge. Automatic session management enhances the dynamics of cooperation: users are not constrained by predefined schemes and they can join and leave easily by accessing shared objects (e.g. editing documents, moving to locations in virtual spaces). Our session management model is well suited to coincidental encounters and cooperation in shared spaces. Moreover, sessions promote rules for shared access and help users to get a clear perception of the ongoing interactions. As cooperative applications are distributed by essence, maintaining data consistency is a difficult issue. Our session model helps to define groups of objects which can then be used by a distributed consistency management service. In this paper we detail our session model and its rules, together with an algorithm for automatic session management. We conclude with a scenario of an encounter in a virtual space.     

Will leaded young mallards take wing? Effects of a single lead shot ingestion on growth of juvenile game-farm Mallard ducks Anas platyrhynchos

This study aims to monitor retention of a single ingested lead shot in young mallards, and to evaluate effect on growth in relation to lead shot size class during late wing growth and the first wing molt period (8 to 12 weeks old). Toxicological tests, radiography and biometric measurements were conducted on 51 juvenile Mallard ducks. Forty one of them were given per os a single lead shot in three different commercially available sizes: No. 2 (LS2), No. 4 (LS4) and No. 6 (LS6). Less than 20% of total lead shots were found on X-rays at Day 21 (D) and none remained at D28, with mean retention time in gizzard calculated 12.85 ± 1.34 days for all treated groups. Young ducks developed high blood lead levels for each LS treatment at D15 in males and females, the maximal values being for LS2 (297.00 ± 78.64 μg/100 mL and 483.14 ± 83.70 μg/100 mL, respectively (p < 0.001)). Zinc protoporphyrin (ZPP) levels increased at D15 with LS2 and LS4 in males and only with LS6 in females. Treated ducks developed no symptoms of plumbism except light diarrhea, and at D40, all mallards had survived. We found that LS2 pellets released more lead in gizzards and produced the highest levels of blood lead, suggesting that LS2 pellets are more likely to intoxicate mallards than smaller sizes. The biometric measurements performed showed no statistical difference in weight or bill and wing length between control and treated groups, a finding suggesting that absorption of a single lead shot by young Mallard ducks does not affect their development during the first wing molt period, and appears not to compromise the flight capacity of young (post-juvenile) mallards. However, younger mallards and/or effects on growth of exposure to more than a single-shot dose still need to be investigated.     

Making components contract aware

Components have long promised to encapsulate data and programs into a box that operates predictably without requiring that users know the specifics of how it does so. Many advocates have predicted that components will bring about widespread software reuse, spawning a market for components usable with such mainstream software buses as the Common Object Request Broker Architecture (CORBA) and the Distributed Component Object Model (DCOM). In the Windows world, at least, this prediction is becoming a reality. Yet recent reports indicate mixed results when using and reusing components in mission-critical settings. Such results raise disturbing questions. How can you trust a component? What if the component behaves unexpectedly, either because it is faulty or simply because you misused it? Before we can trust a component in mission-critical applications, we must be able to determine, reliably and in advance, how it will behave. In this article the authors define a general model of sofware contracts and show how existing mechanisms could be used to turn traditional components into contract-aware ones