Evaluation of a method for treatment of iron gall ink corrosion on paper

Iron gall ink was the most widely used writing ink for paper from the Middle Ages to the twentieth century. Unfortunately, the ink ingredients contain corrosive transition metal ions and acids that cause severe damage to the paper carrier. New or improved paper conservation methods for iron gall ink stabilization are constantly sought. The aim of the study was evaluation of a recently proposed stabilization treatment, adapted to lower relative humidity, applied to various model and historical paper samples containing iron gall ink. The effect of stabilization treatment on paper samples during artificial thermal aging was followed by the determination of the molecular weight distribution by size exclusion chromatography and colorimetry. Migration of iron and copper compounds from the ink lines was monitored by laser ablation inductively coupled plasma mass spectrometry. The results demonstrate that effective stabilization of iron gall ink-containing paper can be successfully achieved by interleaving with papers impregnated with the antioxidant tetrabutylammonium bromide and alkaline buffer under experimental conditions. Negative side effects of the stabilization treatment, such as migration of iron or copper ions from the ink lines and changes of color after the treatment and after accelerated thermal degradation, were limited, proving that the proposed stabilization treatment can be considered for future use by conservators.     

Radio emission from stellar active regions

Several types of stars present a variable radio emission. In this paper we present a time-dependent model aimed to reproduce the RS CVn emission, which however can be easily extended to other types of stars. The time evolution of a population of electrons following an initial power-law distribution is studied. It is shown that the spectrum of the emitted radiation evolves, in a time scale of a few days, from the typical spectrum of the flaring emission to the flat one observed in quiescent periods. It is also shown that the intensity distribution reproduces the core-halo structure observed using VLBI for a period of about one day after the flare.Department of Astronomy and Space Science, University of Florence, Italy. Published in Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 37, No. 5, pp. 634–643, May, 1994.     

Colloidal interactions between monoclonal antibodies in aqueous solutions

Colloidal interactions between proteins determine the behavior and stability of globular proteins such as monoclonal antibodies (mAbs) against their propensity to cluster formation in solution. We study interactions between these proteins through their dilute solution behavior. Experiments to quantify intermolecular interactions were done using Dynamic and Static Light Scattering (DLS and SLS) in a high-throughput manner in parallel with zeta potential measurements with Laser Doppler Electrophoresis method (M3-PALS). This approach offers a rapid indirect determination of colloidal interactions through their measured second virial coefficient. Electrostatic part of the DLVO interaction was conveniently parameterized via the corresponding surface charge and/or surface potential, while the van der Waals interactions were parameterized via their Hamaker coefficient, both as functions of ionic strength and pH of the bathing solution. This parametrization of protein-protein interactions improves our understanding of mAb assembly and provides a means for its control by solution parameter variation. Additionally, our results also provide a consistency check and validation of applicability of the DLVO theory in mAbs solution assembly processes.     

Hilbert's Theorem 90 for Hopf Galois Extensions

For a faithfully flat extension A/B and a right A-module M, we give a new characterization of the set of descent data on M. Assuming that B is a simple Artinian ring and A/B is H-Galois, for a certain finite dimensional Hopf algebra H, we prove that Sweedler's noncommutative cohomology H ¹(H?, A) is trivial as a pointed set.     

Deposition of titanium nitride and hydroxyapatite-based biocompatible composite by reactive plasma spraying

Titanium nitride is a bioceramic material successfully used for covering medical implants due to the high hardness meaning good wear resistance. Hydroxyapatite is a bioactive ceramic that contributes to the restoration of bone tissue, which together with titanium nitride may contribute to obtaining a superior composite in terms of mechanical and bone tissue interaction matters.The paper presents the experimental results in obtaining composite layers of titanium nitride and hydroxyapatite by reactive plasma spraying in ambient atmosphere. X-ray diffraction analysis shows that in both cases of powders mixtures used (10% HA + 90% Ti; 25% HA + 75% Ti), hydroxyapatite decomposition occurred; in variant 1 the decomposition is higher compared with the second variant. Microstructure of the deposited layers was investigated using scanning electron microscope, the surfaces presenting a lamellar morphology without defects such as cracks or microcracks. Surface roughness values obtained vary as function of the spraying distance, presenting higher values at lower thermal spraying distances.     

Incompressible Flow Around a Small Obstacle and the Vanishing Viscosity Limit

In this article we consider viscous flow in the exterior of an obstacle satisfying the standard no-slip boundary condition at the surface of the obstacle. We seek conditions under which solutions of the Navier-Stokes system in the exterior domain converge to solutions of the Euler system in the full space when both viscosity and the size of the obstacle vanish. We prove that this convergence is true assuming two hypotheses: first, that the initial exterior domain velocity converges strongly in L ² to the full-space initial velocity and second, that the diameter of the obstacle is smaller than a suitable constant times viscosity, or, in other words, that the obstacle is sufficiently small. The convergence holds as long as the solution to the limit problem is known to exist and stays sufficiently smooth. This work complements the study of incompressible flow around small obstacles, which has been carried out in [4–6].