Intelligent virtual environments for virtual reality art

The development of virtual reality (VR) art installations is faced with considerable difficulties, especially when one wishes to explore complex notions related to user interaction. We describe the development of a VR platform, which supports the development of such installations, from an art+science perspective. The system is based on a CAVE™-like immersive display using a game engine to support visualisation and interaction, which has been adapted for stereoscopic visualisation and real-time tracking. In addition, some architectural elements of game engines, such as their reliance on event-based systems have been used to support the principled definition of alternative laws of Physics. We illustrate this research through the development of a fully implemented artistic brief that explores the notion of causality in a virtual environment. After describing the hardware architecture supporting immersive visualisation we show how causality can be redefined using artificial intelligence technologies inspired from action representation in planning and how this symbolic definition of behaviour can support new forms of user experience in VR.     

Linear scaling first-principles molecular dynamics with controlled accuracy

In our quest for accurate linear scaling first-principles molecular dynamics methods for pseudopotential DFT calculations, we investigate the accuracy of real-space grid approaches, with finite differences and spherical localization regions. We examine how the positions of the localization centers affect accuracy and the convergence rate in the optimization process. In particular we investigate the accuracy of the atomic forces computation compared to the standard O(N³) approach. We show the exponential decay of the error on the energy and forces with the size of the localization regions for a variety of realistic physical systems. We propose a new algorithm to automatically adapt the localization centers during the ground state computation which allows for molecular dynamics simulations with diffusion processes. The combination of algorithms proposed lead to a genuine linear scaling First-Principles Molecular Dynamics method with controlled accuracy. We illustrate our approach with examples of microcanonical molecular dynamics with localized orbitals.     

In vitro fermentation of beet fibre and barley bran,of their insoluble residues after digestion and of ileal effluents

The main objective of this study was to determine the form in which beet and barley bran fibres reach the colon, and to evaluate the influence of endogeneous compounds on their patterns of fermentation. Raw fibres (RF), corresponding ileal effluents (IE) from pigs, and insoluble fibre residues (IR) extracted from IE, were fermented with human faecal inoculum for 24 h in an in vitro batch system. For beet fibre, rate but not extent of cell wall sugars degradation was increased (+34% at 6 h, P<0·05) after oroileal transit, due to a more porous structure. For barley bran, oroileal conditions degraded endosperm compounds such as β-glucans, leading to a lower extent of cell wall glucose fermentation compared with RF (-22% at 24 h, P<0·05). In the presence of endogeneous substances, degradation of beet fibre polysaccharides was delayed (P<0·05) at each incubation time but that of barley bran fibre was unaltered. Compared to RF, IR and IE significantly exhibited lower acetate production for beet fibre, and higher propionate and lower butyrate production for barley bran after 24 h. It is concluded that in vivo digestion modified fermentation patterns of both fibres in a manner depending on botanical structure. ©1997 SCI     

Human Colonic Bacterial Degradability of Dietary Fibres from Sea-Lettuce (Ulva sp)

Sea-lettuce (Ulva sp) is one of the commonly consumed seaweeds which contains 16·5% of water-soluble and 13·3% insoluble dietary fibres. Since physiological effects of fibres are partly related to their colonic bacteria fermentability, Ulva sp and its constitutive soluble and insoluble fibres were incubated with faecal bacteria in an in vitro batch fermenter system. After 24 h of incubation, 32·0±0·4%, 25·9±0·4% and 50·9±7·4% of Ulva, soluble and insoluble fibres constitutive sugars, respectively, were degraded. Consequently, Ulva and its soluble fibre, ulvan, are poorly fermented by colonic bacteria. The constitutive sugars, rhamnose and glucuronate and the aldobiouronate β-D -glucuronosyluronate-(1,4)-L -rhamnose of the glucuronoxylorhamnan sulphate present in the soluble fibre are highly fermented. Chemical desulphation and/or carboxyl group reduction did not modify this fermentation behaviour. Thus, the particular chemical structure of ulvan is responsible for the resistance of this polysaccharide and of Ulva to colonic bacterial fermentation. As a physiological consequence of this particular behaviour, consumption of dietary fibres from sea-lettuce could be expected to act mainly as bulking agents with little effect on nutrient metabolism due to colonic bacterial fermentation products (short-chain fatty acids). © 1997 SCI.     

Normal and lateral modulation with a scanning force microscope,an analysis: implication in quantitative elastic and friction imaging

Results and an analysis are presented on elastic and friction imaging by indirect force modulation with a scanning force microscope. Two techniques are compared, normal modulation (Z-modulation, perpendicular to the surface of the sample) and lateral modulation of the contact (X-modulation in the plane of the sample, perpendicular to the axis of the cantilever). Theoretical and experimental results show that lateral modulation offers great advantages compared to normal modulation: the images are free of artifacts and can be easily quantified. This revised version was published online in August 2006 with corrections to the Cover Date.     

New approaches for studying the chemical diversity of natural resources and the bioactivity of their constituents

Natural products (NPs) have historically been an important source of lead molecules in drug discovery. However, the interest that the pharmaceutical industry has had in NPs has declined in part because of the lack of compatibility of traditional natural-product extract libraries with high-throughput screenings and the low hit rate. Furthermore, in contrast to the synthetic libraries, compounds from natural sources are likely to have complex structures which slow down the identification process and contribute to problems related to supply and manufacturing. In this paper, we summarise some of the strategies that are being developed in our research unit to address these issues. On one hand, differential screening strategies were established with the aim of identifying dynamically induced NPs from silent biosynthetic pathways in plants and fungi that had been exposed to different stress situations. On the other hand, high-resolution HPLC techniques were optimised for biological and chemical profiling of crude extracts. This led to an integrated platform for rapid and efficient identification of new drug-leads and biomarkers of interest that were based on miniaturised technological approaches and metabolomics.     

Photo- and thermal degradation of MDMO-PPV:PCBM blends

This paper is devoted to the study of the photo- and thermal-ageing of MDMO-poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylenevinylene (PPV) blended with methano-fullerene[6,6]-phenyl C₆₁-butyric acid methyl ester ([60] PCBM), a commonly used active layer of organic solar cells. Thin films of MDMO-PPV, PCBM and MDMO-PPV:PCBM were submitted to photo- and thermal ageing in presence or in absence of oxygen. The modifications of the chemical structure of the materials were analysed by UV-visible and IR spectroscopies. Studying the degradation of pristine materials (MDMO-PPV and PCBM) permit the identification of the markers for characterizing the degradation of each component of the active layer. The degradation of MDMO-PPV was shown to involve a radicalar oxidation implying at first the ethers functions and secondly the double bonds; the photo-oxidation of PCBM was shown to involve the oxidation of its C₆₀ moiety. Photo-oxidation of MDMO-PPV:PCBM blends involved the degradation of both components and the presence of PCBM was observed to largely reduce the rate of degradation of MDMO-PPV in comparison with pristine MDMO-PPV. On a kinetic point of view, the same conclusion was obtained for thermo-oxidation and photolysis (irradiation in absence of oxygen). Our experimental results suggest that the decrease of the rate of degradation of MDMO-PPV in blended films during the three kind of ageing (hυ, T, O₂) is mainly related to the radical scavenging properties of the PCBM.