An overview of MAP/GLOBUS NO(x)

GLOBUS NO(x) is a combined observation of nitrogen compounds by more than 20 experiments, from satellites, remote and in situ instruments on board balloons and ground observatories, within a short time period. Held in September 1985 above Southern France, the field campaign has been a technical success. Most of the observations were achieved as anticipated. NO, NO2 and relevant species and physical parameters involved in their photochemistry, were measured between 5 and 40 km at several periods of the day. A first step of data interpretation which consists of instrumental intercomparisons, is now achieved. Several systematic biases between data of various origins which have appeared in the past, are now understood and reduced. A second step which deals with atmospheric photochemistry issues like diurnal cycles and budget, is now on its way. It will be the object of a close exchange between experimenters involved in the campaign and modelers

Assessing the Zone of Comfort in Stereoscopic Displays using EEG

The conflict between vergence (eye movement) and accommodation (crystalline lens deformation) occurs in every stereoscopic display. It could cause important stress outside the "zone of comfort", when stereoscopic effect is too strong. This conflict has already been studied using questionnaires, during viewing sessions of several minutes. The present pilot study describes an experimental protocol which compares two different comfort conditions using electroencephalography (EEG) over short viewing sequences. Analyses showed significant differences both in event-related potentials (ERP) and in frequency bands power. An uncomfortable stereoscopy correlates with a weaker negative component and a delayed positive component in ERP. It also induces a power decrease in the alpha band and increases in theta and beta bands. With fast responses to stimuli, EEG is likely to enable the conception of adaptive systems, which could tune the stereoscopic experience according to each viewer

Nets in Nets with SNAKES

International audienceThis paper presents the toolkit SNAKES, focusing on the ability to model Petri nets whose tokens are Petri nets (so called nets in nets). SNAKES is a general Petri net library that allows to model and execute Python-coloured Petri nets: tokens are Python objects and net inscriptions are Python expressions. Since SNAKES itself is programmed in Python, Petri net inscriptions can handle Petri net objects as data values, for instance as tokens

The Effects of Goal Setting on Student Work Completion in a Lower Elementary Montessori Classroom

This investigation explored if and how direct instruction on goal-setting and working toward a goal over a four-week period impacted the number of activities students independently completed in class. The amount of math and language work completed and the way the participants felt about their ability to manage their time and goals were measured and evaluated. The study took place at a diverse elementary school in the Midwest. The classroom involved is the only Montessori lower elementary classroom in the district. The 26 students were ages 6-9 at the time of the study. Students were taught how to set a goal and work toward that goal. They also planned for challenges and how to overcome those challenges. Students checked in with their teacher and peers daily to reflect and report how focused they were in regards to achieving the goal they set. Students were observed, data was collected about the type and amount of work completed, students were rated by a peer accountability partner daily, and students completed a pre and post-self-assessment about setting goals and how competent they felt in doing so. The results of the study showed that while the amount of work did not increase, students reported feeling more confident in their ability to set goals and use strategies to stay on task and on-task behavior increased. Direct instruction in goal setting enabled students to feel more confident in selecting a goal and working toward it. They gained tools for staying focused during work times. They were able to use these tools to be on task more frequently than before the intervention. Teachers may want to choose to include direct goal setting in their practice. Further studies may want to track data for a longer period of time to see if work output also would increase

Spectral analysis of extinguished sunlight

SAOZ (Systeme d'Analyse par Observation Zenitale) is a balloon born experiment which determines the column density of several molecular species from the visible spectrum of sunlight. We will use sequence of spectra collected during a sunset to discuss atmospheric extinction, and the nature of the radiation field in the atmosphere. The radiation field in the atmosphere is, from daylight to sunset, and with a clear sky, dominated by light coming from the direction of the sun. This light is composed of direct sunlight (extinguished by the gas), and of sunlight forward-scattered by aerosols. As the sun sets, aerosol scattering is first perceived towards the UV. It progressively replaces direct sunlight over all of the spectrum. Our analysis permits fixing the main parameters of each component of the radiation field at any time. The fits we find for the extinction of sunlight in the atmosphere must also apply to starlight. Thus, the present work can be used in astronomy to correct ground-based spectral observations for extinction in the atmosphere.Comment: 6 figure

Modelling, Verification, and Formal Analysis of Security Properties in a P2P System

International audienceWe present a security analysis of the SPREADS 1 system, a distributed storage service based on a centralized peer-to-peer architecture. We formally modelled the salient behavior of the actual system using ABCD, a high level specification language with a coloured Petri net semantics, which allowed the execution states of the system to be verified. We verified the behavior of the system in the presence of an external Dolev-Yao attacker, unearthing some replay attacks in the original system. Furthermore, since the implementation is also a formal model, we have been able to show that any execution of the model satisfies certain desirable security properties once these flaws are repaired

Proving a Petri net model-checker implementation

Petri nets are a widely used tool in verification through model-checking. In this approach, a Petri Net model of the system of interest is produced and its reachable states are computed, searching for erroneous executions. Compilation of such a Petri net model is one way to accelerate its verification. It consists in generating code to explore the reachable states of the considered Petri net, which avoids the use of a fixed exploration tool involving an "interpretation" of the Petri net structure. In this paper, we show how to compile Petri nets targeting the LLVM language (a high-level assembly language) and formally prove the correct-ness of the produced code. To this aim, we define a structural operational semantics for the fragment of LLVM we use. The acceleration obtained from the presented compilation techniques has been evaluated in [6]

Modular µ-calculus model-checking with formula-dependent hierarchical abstractions

International audienceThis paper defines a formal framework for the modular and hierarchical model-checking of µ-calculus against modular transitions systems. Given a formula ϕ, a module can be analysed alone, in such a way that the truth value of ϕ may be decided without the need to analyse other modules. If no conclusion can be drawn locally, the analysis provides information allowing to reduce the module to a smaller one that is equivalent with respect to the truth value of ϕ. This way, modules can be incrementally analysed, reduced and composed to other reduced modules until a conclusion is reached. On the one hand, modular analysis allows to avoid modules compositions and thus the corresponding combinatorial explosion; on the other hand, hierarchical analysis allows to reduce the modules that must be composed, which limits combinatorial explosion. Moreover, by proposing three complementary formula-dependent reductions, we expect better reductions than general approaches like bisimulation or τ * reductions. The current paper is focused on defining the theoretical tools for this approach; finding interesting strategies to apply them efficiently is left to future work

Faster simulation of (Coloured) Petri nets using parallel computing

International audienceFast simulation, i.e., automatic computation of sequential runs, is widely used to analyse Petri nets. In particular, it enables for quantitative statistical analysis by observing large sets of runs. Moreover, fast simulation may be used to actually run a Petri net model as a (prototype) implementation of a system, in which case such a net would embed fragments of the code of the system. In both these contexts, being able to perform faster simulation is highly desirable. In this paper, we propose a way to accelerate fast simulation by exploiting parallel computing, targeting both the multi-core cpus available nowadays in every laptop or workstation, and larger parallel computers including those with distributed memory (clusters). We design an algorithm to do so and assess in particular its correctness and completeness through its formal modelling as a Petri net whose state space is analysed. We also present a benchmark of a prototype implementation that clearly shows how our algorithm effectively accelerates fast simulation, in particular in the case of large concurrent coloured Petri nets, which is precisely the kind of nets that are usually slow to simulate

Proceedings of SUMo and CompoNet 2011

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