Development of an adequate model for verification of design safety-margins of the HTTR nuclear test facility

This work is based on the prototype High Engineering Test Reactor (HTTR) of the Japan Agency of Energy Atomic (JAEA). Its objective is to describe an adequate deterministic model to be used in the assessment of its design safety margins via damage domains. The concept of damage domain is defined and it is shown its relevance in the ongoing effort to apply dynamic risk assessment methods and tools based on the Theory of Stimulated Dynamics (TSD). To illustrate, we present results of an abnormal control rod (CR) withdrawal during subcritical condition and its comparison with results obtained by JAEA. No attempt is made yet to actually assess the detailed scenarios, rather to show how the approach may handle events of its kin

Dark Matter Subhalos in the Ursa Minor Dwarf Galaxy

Through numerical simulations, we study the dissolution timescale of the Ursa Minor cold stellar clump, due to the combination of phase-mixing and gravitational encounters with compact dark substructures in the halo of Ursa Minor. We compare two scenarios; one where the dark halo is made up by a smooth mass distribution of light particles and one where the halo contains 10% of its mass in the form of substructures (subhalos). In a smooth halo, the stellar clump survives for a Hubble time provided that the dark matter halo has a big core. In contrast, when the point-mass dark substructures are added, the clump survives barely for \sim 1.5 Gyr. These results suggest a strong test to the \Lambda-cold dark matter scenario at dwarf galaxy scale.Comment: accepted for publication in Ap

Dripping Faucet Dynamics Clarified by an Improved Mass-Spring Model

An improved mass-spring model for a dripping faucet is presented. The model is constructed based on the numerical results which we recently obtained from fluid dynamical calculations. Both the fluid dynamical calculations and the present mass-spring model exhibit a variety of complex behavior including transition to chaos in good agreement with experiments. Further, the mass-spring model reveals fundamental dynamics inherent in the dripping faucet system.Comment: 17 pages, 17 figure

Self-sufficient asymmetric reduction of β-ketoesters catalysed by a novel and robust thermophilic alcohol dehydrogenase co-immobilised with NADH

β-Hydroxyesters are essential building blocks utilised by the pharmaceutical and food industries in the synthesis of functional products. Beyond the conventional production methods based on chemical catalysis or whole-cell synthesis, the asymmetric reduction of β-ketoesters with cell-free enzymes is gaining relevance. To this end, a novel thermophilic (S)-3-hydroxybutyryl-CoA dehydrogenase from Thermus thermophilus HB27 (Tt27-HBDH) has been expressed, purified and biochemically characterised, determining its substrate specificity towards β-ketoesters and its dependence on NADH as a cofactor. The immobilization of Tt27-HBDH on agarose macroporous beads and its subsequent coating with polyethyleneimine has been found the best strategy to increase the stability and workability of the heterogeneous biocatalyst. Furthermore, we have embedded NADH in the cationic layer attached to the porous surface of the carrier. Since Tt27-HBDH catalyses cofactor recycling through 2-propanol oxidation, we achieve a self-sufficient heterogeneous biocatalyst where NADH is available for the immobilised enzymes but its lixiviation to the reaction bulk is avoided. Taking advantage of the autofluorescence of NADH, we demonstrate the activity of the enzyme towards the immobilised cofactor through single-particle analysis. Finally, we tested the operational stability in the asymmetric reduction of β-ketoesters in batch, succeeding in the reuse of both the enzyme and the co-immobilised cofactor up to 10 reaction cycles

Resonant Lifetime of Core-Excited Organic Adsorbates from First Principles

We investigate by first-principles simulations the resonant electron-transfer lifetime from the excited state of an organic adsorbate to a semiconductor surface, namely isonicotinic acid on rutile TiO$_2$(110). The molecule-substrate interaction is described using density functional theory, while the effect of a truly semi-infinite substrate is taken into account by Green's function techniques. Excitonic effects due to the presence of core-excited atoms in the molecule are shown to be instrumental to understand the electron-transfer times measured using the so-called core-hole-clock technique. In particular, for the isonicotinic acid on TiO$_2$(110), we find that the charge injection from the LUMO is quenched since this state lies within the substrate band gap. We compute the resonant charge-transfer times from LUMO+1 and LUMO+2, and systematically investigate the dependence of the elastic lifetimes of these states on the alignment among adsorbate and substrate states.Comment: 24 pages, 6 figures, to appear in Journal of Physical Chemistry

In vitro dissolution characteristics of patent, generic and similar brands of naproxen in various dissolution media

Purpose: To investigate the dissolution properties of various brands of naproxen in four dissolution media in order to forecast their biological availability. Methods: Dissolution tests were carried out in a dissolution tester with 48 tablets of different naproxen brands in 900 mL of 0.1 M phosphate buffer, pH 7.4. Subsequently, the medium was modified with 600 mL of buffer plus 300 mL of cola drink, grapefruit or milk. Each sample was taken and brought to a concentration approximating that of a reference solution. Absorbance at 332 nm was determined and the dissolution, Q, was calculated (Q values ≥ 80.0 ± 5 % were acceptable). Results: Dissolution in buffer was > 85 %. In cola drink, it was < 80 %, while in grapefruit juice, it was in the range of 7 - 68 %. Using 2-way ANOVA, these media and the three naproxen brands showed significant differences (F = 68.90, p = 0.0000; F = 23.18, p = 0.0000). With Fisher's LSD test, two of these media contributed consistently to dissolution, and the three drug brands showed statistically different dissolution profiles (p ≤ 0.05). Conclusion: Caution must be exercised cola drink, grapefruit juice and milk are used to administered naproxen as the biological availability of the drug may be altered

Gas Accretion and Star Formation Rates

Cosmological numerical simulations of galaxy evolution show that accretion of metal-poor gas from the cosmic web drives the star formation in galaxy disks. Unfortunately, the observational support for this theoretical prediction is still indirect, and modeling and analysis are required to identify hints as actual signs of star-formation feeding from metal-poor gas accretion. Thus, a meticulous interpretation of the observations is crucial, and this observational review begins with a simple theoretical description of the physical process and the key ingredients it involves, including the properties of the accreted gas and of the star-formation that it induces. A number of observations pointing out the connection between metal-poor gas accretion and star-formation are analyzed, specifically, the short gas consumption time-scale compared to the age of the stellar populations, the fundamental metallicity relationship, the relationship between disk morphology and gas metallicity, the existence of metallicity drops in starbursts of star-forming galaxies, the so-called G dwarf problem, the existence of a minimum metallicity for the star-forming gas in the local universe, the origin of the alpha-enhanced gas forming stars in the local universe, the metallicity of the quiescent BCDs, and the direct measurements of gas accretion onto galaxies. A final section discusses intrinsic difficulties to obtain direct observational evidence, and points out alternative observational pathways to further consolidate the current ideas.Comment: Invited review to appear in Gas Accretion onto Galaxies, Astrophysics and Space Science Library, eds. A. J. Fox & R. Dav\'e, to be published by Springe

Steel cathodic protection afforded by zinc, aluminium and zinc/aluminium alloy coatings in the atmosphere

Zinc has traditionally been the metallic material most widely used to protect steel against atmospheric corrosion due to its ability to afford cathodic protection to steel in all types of natural atmospheres. In recent decades, aluminium and zinc/aluminium alloy coatings have been used instead of zinc in certain atmospheric applications. Although these coatings present some advantages over zinc, they are not able to cathodically protect steel substrates in all types of natural atmospheres. The present paper assesses the cathodic protection afforded by Al (flame spraying), Al/13 Si (hot dipping), 55Al/Zn (hot dipping), Zn/15Al (flame spraying), Zn/5Al (hot dipping), Zn (hot dipping), Zn (discontinuous hot dipping) and Zn (electroplating). Aluminium and aluminium-rich alloy coatings (55%Al/Zn) provide cathodic protection to the steel substrate only in atmospheres that are highly contaminated with chloride ions (>100 mg Cl- m-2 day-1) where these coatings become active. © 2004 Elsevier B.V. All rights reserved.Peer Reviewe