Viral Induced Protein Aggregation: A Mechanism of Immune Evasion

Various intrinsic and extrinsic factors can interfere with the process of protein folding, resulting in protein aggregates. Usually, cells prevent the formation of aggregates or degrade them to prevent the cytotoxic effects they may cause. However, during viral infection, the formation of aggregates may serve as a cellular defense mechanism. On the other hand, some viruses are able to exploit the process of aggregate formation and removal to promote their replication or evade the immune response. This review article summarizes the process of cellular protein aggregation and gives examples of how different viruses exploit it. Particular emphasis is placed on the ribonucleotide reductases of herpesviruses and how their additional non-canonical functions in viral immune evasion are closely linked to protein aggregation.     

Optimal reconstruction for closed-loop ground-layer adaptive optics with elongated spots

The design of the laser-guide-star-based adaptive optics (AO) systems for the Extremely Large Telescopes requires careful study of the issue of elongated spots produced on Shack-Hartmann wavefront sensors. The importance of a correct modeling of the nonuniformity and correlations of the noise induced by this elongation has already been demonstrated for wavefront reconstruction. We report here on the first (to our knowledge) end-to-end simulations of closed-loop ground-layer AO with laser guide stars with such an improved noise model. The results are compared with the level of performance predicted by a classical noise model for the reconstruction. The performance is studied in terms of ensquared energy and confirms that, thanks to the improved noise model, central or side launching of the lasers does not affect the performance with respect to the laser guide stars' flux. These two launching schemes also perform similarly whatever the atmospheric turbulence strength.     

Effects of mismatch strain and alloy composition on the formation of InAs islands on InAlAs templates

InAs islands self-assembled on InAlAs layers lattice mismatched on GaAs substrates have been grown by molecular beam epitaxy. Both pseudomorphic and metamorphic InAlAs buffer layers were used as a template to investigate the effects of strain relaxation on the formation of the islands. The effect of alloy composition in the metamorphic templates is shown on the density and the shape of the islands. The present observations confirms the reduction of surface mass transport due to aluminum in the buffer layers.     

Plasticity in pentacene thin films

We have investigated the structure, defects and plasticity of thermally evaporated thin films of the organic molecular semiconductor pentacene using X-ray Diffraction (XRD), Optical microscopy (OM), Transmission Electron Microscopy (TEM), Electron Diffraction (ED), and High Resolution Electron Microscopy (HREM). Using XRD the degree of (001) texturing present in the as-grown films was characterized. The nature of pentacene plasticity and deformation-induced molecular alignment was investigated using rubbing and scratching techniques, as well as nanoindentation. Rubbing of the bulk powder produced thin oriented films, and a deformation length scale dependence was seen. Under stress pentacene crystals initially fail by cracking, until they reach a critical size of about one micron, when they tend to plastically deform into thin sheets. Alignment of thermally evaporated films was achieved under a controlled load scratch, and the degree of molecular orientation inside the scratched region was directly imaged using HREM. Finally, using nanoindentation we measured pentacene's plastic hardness to be 0.25 GPa at a loading rate 0.05 mN/s. A loading rate dependence of the hardness and stiffness was measured, with thin films behaving harder and stiffer at faster indentation rates.     

Microstructural and photocatalytic properties distribution of TiO2 coatings reactively sputtered as a function of the substrate position relatively to the Ti target

Amorphous and porous TiO₂ coatings were deposited by reactive magnetron sputtering at high pressure (3.4 Pa) on cold soda-lime glass placed at different positions relatively to the magnetron target, which corresponds to different impingement angles and target-to-substrate distances. The as-deposited coatings were heated at 450 °C under ambient air to crystallise into the photoactive anatase phase. The structural analyses combined with AFM experiments have shown a reduction of the crystallites and the lateral grain size with the removal of the substrate from the target axis inducing a specific area rise. Moreover, the stress state is all the less as compressive as the substrates are far away from the target. As a result, the photocatalytic properties are improved with the decrease of the incidence angle and with the target-to-substrate distance rise.     

Adaptive optics with four laser guide stars: correction of the cone effect in large telescopes

We study the performance of an adaptive optics (AO) system with four laser guide stars (LGSs) and a natural guide star (NGS). The residual cone effect with four LGSs is obtained by a numerical simulation. This method allows the adaptive optics system to be extended toward the visible part of the spectrum without tomographic reconstruction of three-dimensional atmospheric perturbations, resolving the cone effect in the visible. Diffraction-limited images are obtained with 17-arc ms precision in median atmospheric conditions at wavelengths longer than 600 nm. The gain achievable with such a system operated on an existing AO system is studied. For comparison, performance in terms of achievable Strehl ratio is also computed for a reasonable system composed of a 40 x 40 Shack-Hartmann wave-front sensor optimized for the I band. Typical errors of a NGS wave front are computed by use of analytical formulas. With the NGS errors and the cone effect, the Strehl ratio can reach 0.45 at 1.25 microm under good-seeing conditions with the Nasmyth Adaptive Optics System (NAOS; a 14 x 14 subpupil wave-front sensor) at the Very Large Telescope and 0.8 with a 40 x 40 Shack-Hartmann wave-front sensor.     

Better use of European (regional) resources

In case of an accidental release of radioactivity and subsequent contamination of the food chain, many samples need to be collected and analysed, and this is far from being a simple issue. The determination of contamination levels requires accredited laboratories, approved and certified procedures and methods, transparency and above all prompt results, as stakeholders in general cannot afford waiting. Adequate decisions require fixed norms, stable in time, and accepted internationally. Moreover, an effective policy relies on traceability of products as well. There are huge requirements of harmonisation of procedures, traceability of data, database management, priority settings etc. Accredited laboratories tend to make use of reliable techniques but these have been optimised for low radiation levels and high accuracy for routine analyses, often in the framework of radiological surveillance of the territory, drinking waters or the food chain. It is obvious that such procedures, although very accurate and sensitive, are not suited for urgent decisions in crisis situations. Similarly, accredited analysis methodologies may start from large quantities of product in order to decrease limits of detection; however, this involves sometimes long times for drying or chemical treatment, introducing important delays. Furthermore, large quantities of samples would simply result in the saturation of the analytical capabilities of one country. Adequate actions and informed decisions during a nuclear accident will require an analytical infrastructure that individual countries do not have; hence there is a clear need to establish regional collaboration and co-operation. This paper includes an example of such collaborative work and mutual assistance, and also touches on how sharing tools for decision making, analytical resources, sample collection procedures and analysis would promote trust, reliablity in the results, a common approach toward minimizing the effects of a radiological disaster and above all unity. Last but not least, this paper also poses a challenge: Nuclear accident management implies that all responsible parties have to guarantee that decision support systems have access to data and information in the best available and consistent manner. This will not be achieved in an independent and isolated manner.     

Laser guide star wavefront sensing for ground-layer adaptive optics on extremely large telescopes

We propose ground-layer adaptive optics (GLAO) to improve the seeing on the 42?m European Extremely Large Telescope. Shack-Hartmann wavefront sensors (WFSs) with laser guide stars (LGSs) will experience significant spot elongation due to off-axis observation. This spot elongation influences the design of the laser launch location, laser power, WFS detector, and centroiding algorithm for LGS GLAO on an extremely large telescope. We show, using end-to-end numerical simulations, that with a noise-weighted matrix-vector-multiply reconstructor, the performance in terms of 50% ensquared energy (EE) of the side and central launch of the lasers is equivalent, the matched filter and weighted center of gravity centroiding algorithms are the most promising, and approximately 10×10 undersampled pixels are optimal. Significant improvement in the 50% EE can be observed with a few tens of photons/subaperture/frame, and no significant gain is seen by adding more than 200 photons/subaperture/frame. The LGS GLAO is not particularly sensitive to the sodium profile present in the mesosphere nor to a short-timescale (less than 100?s) evolution of the sodium profile. The performance of LGS GLAO is, however, sensitive to the atmospheric turbulence profile.     

Optical properties of a silicon-nanocrystal-based-microcavity prepared by evaporation

A silicon-based microcavity constituted by a SiO/SiO₂ multilayer and Si/SiO₂ Bragg mirrors was prepared by the evaporation technique. We give details about the microcavity realization process. The optical properties of the Si nanocrystals, obtained by the thermal dissociation of the SiO layers, were analyzed by continuous-wave and angle-resolved photoluminescence (PL) experiments. The results show a strong anisotropy of the light emitted by the silicon nanocrystals for a cavity constituted by mirrors with only two distributed Bragg reflectors (DBR).