The immersive impact of meta-media in a virtual world

With the increasing importance of virtual settings, we observe a complexification of the media used by members of the virtual communities. Using as the model the Star Wars Role-Play community of the virtual environment of Second Life, and a related news-styled blog, the “Galactic News Network”, we analysed here the impact of this media complexification on immersion process. Specifically, we analysed how meta-media can act on virtual community behavior, and on the immersive potential of the virtual world. We combined “out-of-world” analysis of the blog, and “in-world” qualitative and quantitative evaluation of meta-media-related social activities. Our results demonstrate that meta-media strongly contribute to reinforce the immersive potential of the virtual setting via several mechanisms: by increasing three parameters of the virtual world (cohesion, coherence, and commitment), by increasing the social density of the virtual community, and by acting on the perceived time factor. The combined “in-world” and “out-of-world” action of the meta-media increases the possibilities of inter-individual connections. The combination of 2D asynchronous media and 3D instantaneous virtual settings in a homogeneous and coherent immersive environment reinforces the immersive potential of the virtual world. Thus, meta-media seem to be a factor of long-term stabilization of social structures in virtual environments.     

Synchrotron UV-Visible Multispectral Luminescence Microimaging of Historical Samples

UV-visible luminescence techniques are fre-quently used for the study of cultural heritage materials, despite their limitations for identification and discrimination in the case of complex heterogeneous materials. In contrast to tabletop setups, two methods based on the vacuum ultraviolet (VUV)-UV-visible emission generated at a bending magnet of a synchrotron source are described. The main advantages of the source are the extended wavelength range attained, the continuous tunability of the source, and its brightness, leading to a submicrometer lateral resolution. Raster-scanning microspectroscopy and full-field microimaging were implemented and tested at the DISCO beamline (synchrotron SOLEIL, France). Investigative measurements were performed on a sample from a varnished musical instrument and a paint sample containing the pigment zinc white (ZnO) in order to illustrate some of the challenges analyzing heterogeneous cultural heritage cross-section samples with the novel imaging approach. The data sets obtained proved useful for mapping organic materials at the submicrometer scale and visualizing heterogeneities of the semiconductor pigment material. We propose and discuss the combined use of raster-scanning microspectroscopy and full-field microimaging in an integrated analytical methodology. Synchrotron UV luminescence appears as a novel tool for identification of craftsmen's and artists' materials and techniques and to assess the condition of artifacts, from the precise identification and localization of luminescent materials.     

Further insights into the photodegradation of poly(3-hexylthiophene) by means of X-ray photoelectron spectroscopy

X-ray photoelectron spectroscopy (XPS) was used to monitor the chemical changes resulting from irradiation (> 295 nm) in air of poly(3-hexylthiophene) (P3HT), polymer which is a good candidate for photovoltaic applications. The formation of carbonyl moieties and the stepwise oxidation of sulphur atoms were characterised. The oxidation and the cleavage of the hexyl side-chain was monitored. It is also shown that sulfur was first converted into sulfoxides, then into sulfones and finally into sulfinate esters. The formation of these ultimate degradation products provoked a disruption of π-conjugation in P3HT, leading to diminished visible absorbance. Based on these results, a mechanism of P3HT photooxidation is proposed. Comparison of XPS data with previously reported infrared and UV-visible spectral analysis showed that the information provided by these techniques is completely consistent.     

Stability of Parallel Queueing Systems with Coupled Service Rates

This paper considers a parallel system of queues fed by independent arrival streams, where the service rate of each queue depends on the number of customers in all of the queues. Necessary and sufficient conditions for the stability of the system are derived, based on stochastic monotonicity and marginal drift properties of multiclass birth and death processes. These conditions yield a sharp characterization of stability for systems where the service rate of each queue is decreasing in the number of customers in other queues, and has uniform limits as the queue lengths tend to infinity. The results are illustrated with applications where the stability region may be nonconvex.     

Feature-based approach to semi-supervised similarity learning

For the management of digital document collections, automatic database analysis still has difficulties to deal with semantic queries and abstract concepts that users are looking for. Whenever interactive learning strategies may improve the results of the search, system performances still depend on the representation of the document collection. We introduce in this paper a weakly supervised optimization of a feature vector set. According to an incomplete set of partial labels, the method improves the representation of the collection, even if the size, the number, and the structure of the concepts are unknown. Experiments have been carried out on synthetic and real data in order to validate our approach.     

Individual cyclists' probability distributions of severe/fatal crashes in large French urban areas

The present article deals with individual cyclists’ probabilities of severe injury or death from a bicycle accident. We use an empirical Bayesian method to conduct an analysis of the fatal/severe probability distribution of a bicycle accident, at the level of individuals, in dense French urban areas. Among intuitive results, it is found that wearing a helmet lowers the average probability of such a crash; it is also shown that young bicyclists are, on average, more exposed to severe and/or fatal crashes. Finally, the results highlight a decrease of attention paid by all types of road users following road infrastructure improvements in favor of cyclists.     

Mercury content in commercial pelagic fish and its risk assessment in the Western Indian Ocean

As top predators of pelagic food webs, large fish naturally bioaccumulate mercury (Hg). Determining Hg burdens in commercialized fish is essential considering the concern about effects of contaminants on human health and the legal thresholds that are therefore set for local consumption and/or exportation. Total Hg levels were measured in the muscular tissue of 183 fish of five commercially important species from the tropical zone of the Western Indian Ocean. All individuals were measured and sexed in order to study the impregnation of Hg with size and sex within each species. Values of Hg found in this part of the Indian Ocean were comparable to Hg in muscular tissue of the same species studied in other areas. The highest Hg levels were noted in Swordfish (Xiphias gladius) caught in waters surrounding Reunion Island (3.97+/-2.67 microg g(-1) dry weight). Following the Swordfish, in decreasing order of Hg content, were the Yellowfin Tuna (Thunnus albacares) and the Skipjack (Katsuwonus pelamis), then the Common Dolphinfish (Coryphaena hippurus) and the Wahoo (Acanthocybium solandri). In the North of the Mozambique Channel, Swordfish had higher Hg levels than Yellowfin Tunas, and Dolphinfish exhibited intermediate Hg levels. The size of a fish was a determining factor of its Hg burden, as was the species. Differences in size-normalized Hg levels were observed between the two study zones for Swordfish and Common Dolphinfish. Sex, in contrast, did not influence Hg levels suggesting that females and males have similar feeding habits. The muscular Hg levels presented here suggest that consumers of fish originating from the Western Indian Ocean should limit themselves to one Swordfish based meal per week, or one fish meal a day if they choose to eat tuna or Common Dolphinfish.     

In situ tracking of enzymatic breakdown of starch granules by synchrotron UV fluorescence microscopy

Synchrotron UV fluorescence microscopy was used for the first time to visualize the adsorption and diffusion of an enzyme while degrading a solid substrate. The degradation pathway of single starch granules by two amylases, optimized for biofuel production and industrial starch hydrolysis, was followed by tryptophan fluorescence (excitation at 280 nm, emission filter at 300-400 nm) and visible light imaging. Thus, both the adsorption of enzyme onto starch granules at 283 nm resolution and the resulting morphological changes were recorded at different stages of hydrolysis. It is the first time that amylases were localized on starch without staining or adding a fluorescent probe at such high resolution. This technique presents a very high potential for imaging proteins in complex systems. Its sensitivity was demonstrated by the detection of GBSS (the granular bound starch synthase) at high recording times, GBSS being present at very low levels in maize starch granules.     

Growth of germanium nanowires on silicon(111) substrates by molecular beam epitaxy

Heteroepitaxial growth of Ge nanowires was carried out on Si(111) substrates by MBE. Au seeds were used as precursor for the VLS growth of the nanowires. Even if the Au droplets do not act as catalyst for the dissociation of gas, they are local preferential areas where the energetic barrier of Ge nucleation is lowered compare to the remaining non activated surface. Two sets of Au seeds were used as precursors for the VLS process. The first set have an average diameter of 125 nm and the second of 25 nm. In-situ RHEED monitoring showed a Au wetting layer between these seeds before the nanowires growth as well as at the end of the Ge nanowires growth. It means that the wetting layer acted as a surfactant from the Si(111) surface to the Ge grown layer between the nanowires. Analysis of SEM images brought the fact that the diffusion of gold from the droplets on the surface and the sidewalls of the nanowires via the Ostwald ripening is a key parameter of the growth of the nanowires.