Nuclear data sensitivity/uncertainty analysis for XT-ADS

The XT-ADS, an accelerator-driven system for an experimental demonstration, has been investigated in the framework of IP EUROTRANS FP6 project. In this study, the sensitivity and uncertainty analyses were performed to comprehend the reliability of the XT-ADS neutronic design.     

Investigating the Role of Conformational Effects on Laccase Stability and Hyperactivation under Stress Conditions

Fungal laccase from Steccherinum ochraceum 1833 displays remarkable stability under different harsh conditions: organic/buffer mixtures, thermal treatment, and microwave radiation. The behavior is particularly significant in the light of the sharp inactivation observed for two different fungal laccases. Laccase from S. ochraceum 1833 also displays hyperactivation under mild thermal treatment (60 °C). Molecular dynamics simulations at 80 °C explained how this laccase retains the geometry of the electron transfer pathway, thereby assuring electron transfer through the copper ions and thus maintaining its catalytic activity at high temperature. Spectroscopic studies revealed that the thermal activation corresponds to specific conformational changes in the protein. The results indicate that this laccase is potentially applicable under denaturing conditions that might be beneficial for the biotransformation of recalcitrant substrates.     

Modulation of Aβ42 Aggregation Kinetics and Pathway by Low-Molecular-Weight Inhibitors

The aggregation of amyloid-β 42 (Aβ42) is directly related to the pathogenesis of Alzheimer's disease. Here, we have investigated the early stages of the aggregation process, during which most of the cytotoxic species are formed. Aβ42 aggregation kinetics, characterized by the quantification of Aβ42 monomer consumption, were tracked by real-time solution NMR spectroscopy (RT-NMR) allowing the impact that low-molecular-weight (LMW) inhibitors and modulators exert on the aggregation process to be analysed. Distinct differences in the Aβ42 kinetic profiles were apparent and were further investigated kinetically and structurally by using thioflavin T (ThT) and transmission electron microscopy (TEM), respectively. LMW inhibitors were shown to have a differential impact on early-state aggregation. Insight provided here could direct future therapeutic design based on kinetic profiling of the process of fibril formation.     

The effect of red pigment on the amyloidization of yeast proteins

The intensity of amyloid-bound thioflavine T fluorescence was studied in crude lysates of yeast strains carrying mutations in the ADE1 or ADE2 genes and accumulating the red pigment (a result of polymerization of aminoimidazoleribotide), and in white isogenic strains--either adenine prototrophs or carrying mutations at the first stages of purine biosynthesis. We found that the red pigment leads to a drop of amyloid content. This result, along with the data on separation of protein polymers of white and red strains in PAGE, suggests that the red pigment inhibits amyloid fibril formation. The differences in transmission of the thioflavine T fluorescence pattern by cytoduction and in blot-hybridization of pellet proteins of red and white [PSI(+) ] strains with Sup35p antibodies confirmed this conclusion. Purified red pigment treatment also led to a decrease of fluorescence intensity of thioflavine T bound to insulin fibrils and to yeast pellet protein aggregates from [PSI(+) ] strains. This suggests red pigment interaction with amyloid fibrils. Comparison of pellet proteins from red and white isogenic strains separated by 2D-electrophoresis followed by MALDI analysis has allowed us to identify 48 pigment-dependent proteins. These proteins mostly belong to functional classes of chaperones and proteins involved in glucose metabolism, closely corresponding to prion-dependent proteins that we characterized previously. Also present were some proteins involved in stress response and proteolysis. We suppose that the red pigment acts by blocking certain sites on amyloid fibrils that, in some cases, can lead in vivo to interfere with their contacts with chaperones and the generation of prion seeds.     

Range-only measurements based target following for wheeled mobile robots

We consider the problem of navigation and guidance of a wheeled mobile robot towards a maneuvering target based on the measurements concerning only the distance from the robot to the target. We propose a sliding mode controller that drives the robot to the predefined distance from the target and makes the robot follow the target at this distance. Mathematically rigorous proof of convergence and stability of the proposed guidance law is presented. Simulation results confirm the applicability and performance of the proposed guidance approach.     

Geometry of the Structure of Amorphous Metal Evaporated Under Microgravity Condition

In Ref. 1 the principle of the adequacy between the stability of the structure of amorphous metals and the completeness of the set of configuration vacancies has been introduced. The principle of adequacy is valid for all the methods of amorphous solid metals production described in Ref. 2. This principle is the basis of the proposed novel technology of production of stable amorphous films sputtered on the cold substrate. The technology proposed takes into account the geometry of microgravity in the film structure and thus excludes the effect of the film burst crystallization.     

Thermally Stable, Latent Olefin Metathesis Catalysts

Highly thermally stable N-aryl,N-alkyl N-heterocyclic carbene (NHC) ruthenium catalysts were designed and synthesized for latent olefin metathesis. These catalysts showed excellent latent behavior toward metathesis reactions, whereby the complexes were inactive at ambient temperature and initiated at elevated temperatures, a challenging property to achieve with second generation catalysts. A sterically hindered N-tert-butyl substituent on the NHC ligand of the ruthenium complex was found to induce latent behavior toward cross-metathesis reactions, and exchange of the chloride ligands for iodide ligands was necessary to attain latent behavior during ring-opening metathesis polymerization (ROMP). Iodide-based catalysts showed no reactivity toward ROMP of norbornene-derived monomers at 25 °C, and upon heating to 85 °C gave complete conversion of monomer to polymer in less than 2 hours. All of the complexes were very stable to air, moisture, and elevated temperatures up to at least 90 °C, and exhibited a long catalyst lifetime in solution at elevated temperatures.     

Possibilities of production of nanopowders with high power ELV electron accelerator

Electron-beam evaporation of various natural and industrial materials in the atmosphere of different gases at atmospheric pressure can be used for the synthesis of nanosize powders. These powders are characterized by high purity and may exhibit unusual properties. In particular, nanopowders of silicon dioxide and oxide (SiO₂, SiO), magnesia (MgO), alumina (Al₂O₃), titania (TiO₂), gadolinium oxide (Gd₂O₃), various metals (tantalum, molybdenum, nickel, aluminium, copper, silver), semiconductor (Si), nitrides (AlN, TiN), and some other substances had been produced. The process of nanopowder synthesis is highly effective; in particular, the yield of oxides can exceed ten kilograms per hour.     

Vapor-Liquid Steady Meniscus at a Superheated Wall: Asymptotics in an Intermediate Zone Near the Contact Line

The study concerns steady configurations of a perfectly wetting liquid in contact with its pure vapor and a superheated substrate/wall maintained at a constant temperature. Despite the perfect wetting, the system is characterized by a finite apparent contact angle formed at a microscale, within a steady microstructure of the contact line, the finiteness owing itself to an actually dynamic situation caused by the evaporation process. The angle is assumed to be small here, which is the case for sufficiently small superheats. When macroscopically treating a steady meniscus, one typically implies that the wall is met at the contact angle given by the microstructure. This remains somewhat an intuitive, heuristic approach unless a more rigorous asymptotic matching is carried out between the meniscus and the microstructure, which is accomplished in the present paper by studying an intermediate zone connecting these two regions. The analysis, based upon a standard one-sided planar model of an evaporating liquid layer in the lubrication approximation, confirms the validity of the mentioned approach. A possible uncertainty in the definition of the contact angle is shown to be small given that the macroscopic curvature (i.e. that of the meniscus and of the wall) is small on the scale of the contact line microstructure.     

Nanocrystalline Powders Based on ZrO2 for Biomedical Applications and Power Engineering

An 80 mass% ZrO₂ ― 20 mass% Al₂O₃ powder was produced using a complex method which integrates sol-gel technology and hydrothermal synthesis. The specific surface areas of the powder varied from 39 to 5.3 m²/g depending on the thermal treatment conditions. Metastable F-ZrO₂ formed after powder annealing at 400°C. The phase transformation F-ZrO₂ → T-ZrO₂ (traces of M-ZrO₂) occurred under powder thermal treatment from 700 to 1000°C. Only Θ-Al₂O₃ was detected under experimental conditions. The powder was characterized by sintering activity. Operating the processes under powder thermal treatment in the ZrO₂ ― Y₂O₃ ― CeO₂ ― Al₂O₃ system will allow one to produce a variety of ceramic microstructures from fine-grained to “self-reinforced.” These powders can be used in manufacturing surgical cutting tools as well as in ceramic passive bioimplants and solid electrolytes for fuel elements.