Romanian Academy

About: Romanian Academy is a archive organization based out in Bucharest, Romania. It is known for research contribution in the topics: Population & Nonlinear system. The organization has 3662 authors who have published 10491 publications receiving 146447 citations. The organization is also known as: Academia Română & Societatea Literară Română.

Surfactant double layer stabilized magnetic nanofluids for biomedical application

Abstract: Magnetite nanoparticles were coated with surfactant double layers in order to prepare water based magnetic fluids (MFs). The effects of head group (sulfonate, carboxylate) and alkyl chain length (11-17 C atoms) and the combination of surfactants were studied. Adsorption, dynamic light scattering (DLS) and electrophoretic mobility measurements were performed. The quantity of surfactant varied between 0.3 and 0.5 g, i.e. their specific amount ranges over 1.5-2 mmol g(-1) magnetite in MFs. The adsorption isotherm of Na oleate on magnetite proved the double layer formation with 2 mmol g(-1) saturation value in good harmony with the empirical doses. The effect of diluting MFs, pH and salt concentration was studied. The pH-dependent stability and the salt tolerance of MFs were different owing to the dissociation of the outermost hydrophilic groups and the hydrophobic interactions scaling with the alkyl chain length of surfactant. The hydrophobic interactions are favored only for oleic and myristic acid double layers. In these MFs, aggregation cannot be observed even in fairly dilute systems up to the physiological salt concentration around neutral pH 6-8 favored in biomedical application. The stable oleic and myristic acid double layers can hinder effectively the aggregation of magnetite particles due to the combined steric and electrostatic stabilization.

Local surface density of the galactic disk from a three-dimensional stellar velocity sample

Abstract: We have reestimated the surface density of the Galactic disk in the solar neighborhood within ±0.4 kpc of the Sun using the parallaxes and proper motions of a kinematically and spatially unbiased sample of 1476 old bright red giant stars from the Hipparcos catalog with measured radial velocities from Barbier-Brossat & Figon. We determine the vertical distribution of the red giants as well as the vertical velocity dispersion of the sample (14.4 ± 0.3 km s-1) and combine these to derive the surface density of the gravitating matter in the Galactic disk as a function of the Galactic coordinate z. The surface density of the disk increases from 10.5 ± 0.5 M⊙ pc-2 within ±50 pc to 42 ± 6 M⊙ pc-2 within ±350 pc. The estimated volume density of the Galactic disk within ±50 pc is about 0.1 M⊙ pc-3 which is close to the volume density estimates of the observed baryonic matter in the solar neighborhood.

Quasi-hopf algebra actions and smash products

Abstract: The construct,ion of quasi-Hopf algebras obtains its importance from its signficance in Physics, cf.[l], 151, 161. Since for usual quantum groups and Hopf algebras actions and coactions of Hopf algebras play an important r81e, it is natmal to try to define act,ions and coactions for quasi-Hopf algebras. Now, coactions of quasi-Hopf algebras have been introduced by I?. Hansser and F. Nil1 in [8], [9]. If H is a quasi-Hopf algebra and B is an (associative) algebra, then, roughly speaking, B is a right H-comodule algebra if there exists an algebra map p : B -+ B @ H which turns B into an \"almost\" H-comodule

On the Number of Non-terminal Symbols in Graph-Controlled, Programmed and Matrix Grammars

Abstract: We improve the results elaborated in [6] on the number of non-terminal symbols needed in matrix grammars, programmed grammars, and graph-controlled grammars with appearance checking for generating arbitrary recursively enumerable languages. Of special interest is the result that the number of non-terminal symbols used in the appearance checking mode can be restricted to two. In the case of graph controlled (and programmed grammars) with appearance checking also the number of non-terminal symbols can be reduced to three (and four, respectively); in the case of matrix grammars with appearance checking we either need four non-terminal symbols with three of them being used in the appearance checking mode or else again we only need two nonterminal symbols being used in the appearance checking mode, but in that case we cannot bound the total number of non-terminal symbols.