PREPARATION, IDENTIFICATION AND BIOLOGICAL PROPERTIES OF NEW FLUORIDE NANOCOMPOUNDS

Indexación: Web of Science; Scopus.Nanoparticles (NPs) of new fluoride (SrF2 and MgF2) nanocompounds were synthesized by the simple chemical method of precipitation in ethanol. Synthesis of the strontium fluoride (SrF2)-magnesium oxide (MgO) nanocomposite was achieved through the ultrasonic method. These prepared nanopowders were characterized through Fourier transform infrared (FT-IR) spectroscopy, ultraviolet-visible (UV-Vis) spectroscopy, Powder X-ray Diffraction (PXRD) and Scanning Electron Microscopy (SEM). FT-IR confirmed the purity of the synthesized fluoride NPs by evaluation of the vibrations, and UV-Visible showed the intense absorption peaks of NPs. PXRD analysis indicated the average of particle size, and SEM demonstrated a nearly spherical morphology of the NPs. The antibacterical properties of the nanopowders on Staphylococcus Aureus, Bacillus Subtilis and E. Aklay bacteria were studied, with the strongest effect by the magnesium fluoride (MgF2) NPs and the SrF2-MgO nanocomposite.http://ref.scielo.org/yfr3f

Similarities in the temporal properties of gamma-ray bursts and soft gamma-ray repeaters

Magnetars are modelled as sources that derive their output from magnetic energy that substantially exceeds their rotational energy. An implication of the recent polarization measurement of GRB 021206 is that the emission mechanism may be dominated by a magnetic field that originates in the central engine. Similarities in the temporal properties of SGRs and GRBs are considered in light of the fact that the central engine in GRBs may be magnetically dominated. The results show that 1) the time intervals between outbursts in SRG 1806-20 and pulses in GRBs are consistent with lognormal distributions and 2) the cumulative outputs of SGRs and GRBs increase linearly with time. This behaviour can be successfully modelled by a relaxation system that maintains a steady state situation.Comment: To appear in the proceedings of the 2003 GRB Conference, Santa Fe, 4 pages, 4 figure

Detailed analysis of the continuum limit of a supersymmetric lattice model in 1D

We present a full identification of lattice model properties with their field theoretical counter parts in the continuum limit for a supersymmetric model for itinerant spinless fermions on a one dimensional chain. The continuum limit of this model is described by an $\mathcal{N}=(2,2)$ superconformal field theory (SCFT) with central charge c=1. We identify states and operators in the lattice model with fields in the SCFT and we relate boundary conditions on the lattice to sectors in the field theory. We use the dictionary we develop in this paper, to give a pedagogical explanation of a powerful tool to study supersymmetric models based on spectral flow. Finally, we employ the developed machinery to explain numerically observed properties of the particle density on the open chain presented in Beccaria et al. PRL 94:100401 (2005).Comment: 28 pages, 7 figures, 3 tables, 1 appendix, this work is based on chapter 4 of the authors PhD Thesis: L. Huijse, A supersymmetric model for lattice fermions, University of Amsterdam (2010

Nonlinear electrophoresis in the presence of dielectric decrement

The nonlinear phenomena that occur in the electric double layer (EDL) that forms at charged surfaces strongly influence electrokinetic effects, including electro-osmosis and electrophoresis. In particular, saturation effects due to either dielectric decrement or ion crowding effects are of paramount importance. Dielectric decrement significantly influences the ionic concentration in the EDL at high ζ potential, leading to the formation of a condensed layer near the particle's surface. In this article, we present a model incorporating both steric effects due to the finite size of ions and dielectric decrement to describe the physics in the electric double layer. The model remains valid in both weakly and strongly nonlinear regimes, as long as the electric double layer remains in quasiequilibrium. We apply this model to the study of two archetypal problems in electrokinetics, namely the electrophoresis of particles with fixed surface charges and the electrophoresis of ideally polarizable particles

Dating Around: Investigating Gender Differences in First Date Behavior Using Self‐Report and Content Analyses from Netflix

In the current studies, we used qualitative, quantitative, and content analysis to understand which frst date behaviors individuals perceive as critical for landing second dates. In Study 1 (N=100), men and women reported tactics or behaviors that they believed someone of their gender would perform on a successful frst date. We observed that men and women perceive similar behaviors as important to engage in on successful frst dates. Study 2 (N=131) had men and women rate the perceived efectiveness of these tactics. When the behaviors are aggregated, men perceive women who engage in “Involvement” behaviors as better at obtaining sec- ond dates. In contrast, women perceive men who engage in “Etiquette” behaviors as more likely to land second dates. In Study 3, we coded the Netfix show, Dat- ing Around, using the tactics from Study 1 to examine if engaging in these tactics more frequently predicted having a successful date. Results revealed that receiving a second date was not related to an individual’s engagement in these tactics. This research is the frst to attempt to empirically delineate tactics that occur on frst dates and lead to second dates for men and women

In the Shadow of the Accretion Disk: Higher Resolution Imaging of the Central Parsec in NGC 4261

The physical conditions in the inner parsec of accretion disks believed to orbit the central black holes in active galactic nuclei can be probed by imaging the absorption (by ionized gas in the disk) of background emission from a radio counterjet. We report high angular resolution VLBI observations of the nearby (about 40 Mpc) radio galaxy NGC 4261 that confirm free-free absorption of radio emission from a counterjet by a geometrically thin, nearly edge-on disk at 1.6, 4.8, and 8.4 GHz. The angular width and depth of the absorption appears to increase with decreasing frequency, as expected. We derive an average electron density of ~10E4 per cc at a disk radius of about 0.2 pc, assuming that the inner disk inclination and opening angles are the same as at larger radii. Pressure balance between the thermal gas and the magnetic field in the disk implies an average field strength of 0.1 milligauss at a radius of 0.2 pc. These are the closest-in free-free absorption measurements to date of the conditions in an extragalactic accretion disk orbiting a black hole with a well-determined mass. If a standard advection-dominated accretion flow exists in the disk center, then the transition between thin and thick disk regions must occur at a radius less than 0.2 pc (4000 Schwarzschild radii).Comment: 20 pages including 12 figures. Accepted for publication in Ap

21cm Absorption by Compact Hydrogen Disks Around Black Holes in Radio-Loud Nuclei of Galaxies

The clumpy maser disks observed in some galactic nuclei mark the outskirts of the accretion disk that fuels the central black hole and provide a potential site of nuclear star formation. Unfortunately, most of the gas in maser disks is currently not being probed; large maser gains favor paths that are characterized by a small velocity gradient and require rare edge-on orientations of the disk. Here we propose a method for mapping the atomic hydrogen distribution in nuclear disks through its 21cm absorption against the radio continuum glow around the central black hole. In NGC 4258, the 21cm optical depth may approach unity for high angular-resolution (VLBI) imaging of coherent clumps which are dominated by thermal broadening and have the column density inferred from X-ray absorption data, ~10^{23}/cm^2. Spreading the 21cm absorption over the full rotation velocity width of the material in front of the narrow radio jets gives a mean optical depth of ~0.1. Spectroscopic searches for the 21cm absorption feature in other galaxies can be used to identify the large population of inclined gaseous disks which are not masing in our direction. Follow-up imaging of 21cm silhouettes of accelerating clumps within these disks can in turn be used to measure cosmological distances.Comment: 4 page

A commentary on the intellectual health of the nation

The record of high-quality research at South African universities is not as impressive as we may have thought, according to some international rankings. Whatever we might think of these assessments, we have to take them seriously. We suggest ways in which our universities and other institutions of higher learning might raise the level of their game