Teaching an automated agent to monitor the electrical power system of an orbital satellite

This paper illustrates an application of the Disciple knowledge acquisition methodology to build an intelligent adaptive agent for monitoring the electrical power system of an orbital satellite. This methodology is used by an expert to build and train an agent in much the same way that the expert would teach a human apprentice—by giving the agent specific examples of problems and solutions, explanations of these solutions, and supervising the agent as it solves new problems. During these interactions, the agent acquires general rules and concepts, continuously extending and improving its knowledge base. The agent learns by synergistically integrating the basic learning strategies: explanation-based learning, learning by analogy, and empirical inductive learning from examples. An important feature of Disciple-based agents is their ability to reason with incomplete and even partially incorrect information. The agent distinguishes between routine problems (problems it knows that it can solve correctly), innovative problems (problems to which it can recommend solutions, but for which it is not certain of the result), and creative problems (problems it is not able to solve). This allows the agent to solve a problem independently (for a routine problem), to ask confirmation of its solution (for an innovative problem), or simply to ask the expert to solve the problem (for a creative problem).     

Defeating Colluding Nodes in Desktop Grid Computing Platforms

Desktop Grid systems reached a preeminent place among the most powerful computing platforms in the planet. Unfortunately, they are extremely vulnerable to mischief, because computing projects exert no administrative or technical control on volunteers. These can very easily output bad results, due to software or hardware glitches (resulting from over-clocking for instance), to get unfair computational credit, or simply to ruin the project. To mitigate this problem, Desktop Grid servers replicate work units and apply majority voting, typically on 2 or 3 results. In this paper, we observe that simple majority voting is powerless against malicious volunteers that collude to attack the project. We argue that to identify this type of attack and to spot colluding nodes, each work unit needs at least 3 voters. In addition, we propose to post-process the voting pools in two steps. i) In the first step, we use a statistical approach to identify nodes that were not colluding, but submitted bad results; ii) then, we use a rather simple principle to go after malicious nodes which acted together: they might have won conflicting voting pools against nodes that were not identified in step i. We use simulation to show that our heuristic can be quite effective against colluding nodes, in scenarios where honest nodes form a majority.     

Wideband and dynamic characterization of the 60GHZ indoor radio propagation — future homeWLAN architectures

This paper presents some results of a study concerning the radio propagation at 60GHZ in residential environments performed by theIETR (Electronic and Telecommunication Institute of Rennes, France). This study is part of aRNTR project named “COMMINDOR”. This exploratory project concerns the very high data rate (155 Mbit/s) and small range (about 10 m) radio communication systems for future home networks, which will permit multimedia equipment interconnection and control. The study is based on several measurement campaigns realized with a channel sounder based on the sliding correlation technique. This channel sounder has a 500MhZ bandwidth and a 2.3 ns effective time resolution. The measurements have been performed in residential furnished environments. The study of the angles-of-arrival (AOA) emphases the importance of openings (such as doors, staircase, etc.) for the radio propagation between adjacent rooms. A particular attention is paid to the influence of human activity on radio propagation. It is shown that people movements can make the propagation channel unavailable during about one second. From the characterization study of the indoor radio propagation, several recommendations concerning the deployment of the very high data rate 60GHZ wireless networks are derived.     

Array-rewriting P systems

We consider array languages (sets of picturesconsisting of symbols placed in the lattice points of the 2D grid) and thepossibility to handle them with P systems. After proving binary normal formsfor array matrix grammars (which, even in the case when no appearance checking isused, are known to generate the array languages of arbitrary array grammars), weprove that the P systems with context-free rules (with three membranes and no control on the communication or the use of rules) are computationally universal, able togenerate all computable array languages. Some open problems are also formulated.     

Spatial domain wavelet design for feature preservation in computational data sets

High-fidelity wavelet transforms can facilitate visualization and analysis of large scientific data sets. However, it is important that salient characteristics of the original features be preserved under the transformation. We present a set of filter design axioms in the spatial domain which ensure that certain feature characteristics are preserved from scale to scale and that the resulting filters correspond to wavelet transforms admitting in-place implementation. We demonstrate how the axioms can be used to design linear feature-preserving filters that are optimal in the sense that they are closest in L2 to the ideal low pass filter. We are particularly interested in linear wavelet transforms for large data sets generated by computational fluid dynamics simulations. Our effort is different from classical filter design approaches which focus solely on performance in the frequency domain. Results are included that demonstrate the feature-preservation characteristics of our filters.     

Design and optimisation of a combination solar collector–thermal engine operating on Mars

A “dynamic” solar power plant (which consists of a solar collector–thermal engine combination) is proposed as an alternative for the more usual photovoltaic cells. A model for heat losses in a selective flat-plate solar collector operating on Mars is developed. An endoreversible Carnot cycle is used to describe heat engine operation. This provides upper limits for real performances. The output power is maximized. Meteorological and actinometric data provided by Viking Landers are used as inputs. Two strategies of collecting solar energy were considered: (i) horizontal collector; (ii) collector tilt and orientation are continuously adjusted to keep the receiving surface perpendicular on the Sun’s rays. The influences of climate and of various design parameters on solar collector heat losses, on engine output power and on the optimum sun-to-user efficiency are discussed.     

Synthesis of amorphous niobium-nickel alloys by vapor quenching

Thin film samples (10–15 μm thick) of niobium-nickel alloys in the composition range Nb-5 to 95 at. % Ni were vapor quenched bu r.f. sputtering onto fused quartz substrates held at a temperature of 180°C. It was found that fully glassy alloys were synthesized in the composition range Nb-30 to 85 at. % Ni, which is 2.5 times larger than that reported for splat-quenched alloys. Crystallization temperatures exhibited a maximum near the deepest eutectic in this alloys system and are comparable with those of splat-quenched materials. Nearest neighbor distances are in agreement with results for splat-quenched materials while “effective particle sizes” are consistently smaller. These results are discussed relative to the mechanism by which glassy alloys are synthesized during vapor quenching and the structure of the glassy state.     

EPR studies of the free radical kinetics in ��-rays irradiated Pleurotus ostreatus oyster mushrooms

The results concerning the free radicals kinetics of ⁶⁰Co gamma-ray irradiated Pleurotus ostreatus (Jacq. ex Fr.) dehydrated mushroom as observed by EPR are presented and discussed. Throughout irradiation, the amplitude of the free radicals EPR spectra gradually increases with the absorbed dose by following a saturated exponential dependence. During a 100 °C isothermal annealing, the EPR signal showed a sharp decrease within the first 3 min followed by an almost constant growth for the next 2 h. An Arrhenius plot of the EPR amplitude of the same samples illustrates three different regimes, corresponding to three different kinetic patterns of recombination and creation of the free radicals, each regime being characterized by its own activation energy whose value was calculated and discussed.