154 research outputs found
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
Generalized Sturmian Functions in prolate spheroidal coordinates
With the aim of describing bound and continuum states for diatomic molecules,
we develop and implement a spectral method that makes use of Generalized
Sturmian Functions (GSF) in prolate spheroidal coordinates. In order to master
all computational issues, we apply here the method to one--electron molecular
ions and compare it with benchmark data for both ground and excited states. We
actually propose two different computational schemes to solve the two coupled
differential equations.
The first one is an iterative 1d procedure in which one solves alternately
the angular and the radial equations, the latter yielding the state energy. The
second, named direct method, consists in representing the Hamiltonian
matrix in a two--dimensional GSF basis set, and its further diagonalization.
Both spectral schemes are timewise computationally efficient since the basis
elements are such that no derivatives have to be calculated numerically.
Moreover, very accurate results are obtained with minimal basis sets. This is
related on one side to the use of the natural coordinate system and, on the
other, to the intrinsic good property of all GSF basis elements that are
constructed as to obey appropriate physical boundary conditions. The present
implementation for bound states paves the way for the study of continuum states
involved in ionization of one or two--electron diatomic targets
A Rapid Road to Employment?: The Impacts of a Bus Rapid Transit System in Lima
Despite the growing interest in and proliferation of Bus Rapid Transit (BRT) systems around the world, their causal impacts on labor market outcomes remain unexplored. Reduced travel times for those who live near BRT stations or near feeder lines, may increase access to a wider array of job opportunities, potentially leading to increased rates of employment, access to higher quality (or formal) jobs, and increased labor hours and earnings. This paper assesses the effects of the Metropolitano, a BRT system in Lima (Peru), on individual-level job market outcomes. We rely on a difference-in-differences empirical strategy, based on comparing individuals who live close to the BRT system with a comparison group that lives farther from the system, before and after the system started to operate. We find large impacts on employment, hours worked and labor earnings for those individuals close to the BRT stations, but not for those who live close to the feeder lines. Despite the potential to connect poor populations, we find no evidence of impacts for populations living in lower income areas
Generalized Sturmian Functions applied to double continuum problems
The Generalized Sturmian Functions method aims to deal with atomic physics
problems. It has seen application to two and three?body problems, and its flexibility enables one to work with bound systems as well as with particles in the continuum. In the present contribution we analyze how the method expands the atomic double continuum in collision problems, using the double ionization of Helium by fast electrons as a showcase. We first test the robustness of the method in a particularly challenging situation, the zero energy case. We then present fully differential cross sections for a scattering problem which after 15 years of continued efforts has not been satisfactorily solved: the double ionization of Helium by electron impact in the fast projectile regime, as measured by the Orsay group.Fil: Ambrosio, Marcelo José. Consejo Nacional de Investigaciónes CientÃficas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de AstronomÃa y FÃsica del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de AstronomÃa y FÃsica del Espacio; ArgentinaFil: Colavecchia, Flavio Dario. Comisión Nacional de EnergÃa Atómica. Centro Atómico Bariloche; ArgentinaFil: Mitnik, Dario Marcelo. Consejo Nacional de Investigaciónes CientÃficas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de AstronomÃa y FÃsica del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de AstronomÃa y FÃsica del Espacio; ArgentinaFil: Gasaneo, Gustavo. Universidad Nacional del Sur; ArgentinaFil: Ancarani, L. U.. Université de Lorraine; Franci
Double ionization of helium by proton impact: A generalized-Sturmian approach
We present ab initio calculations for the double ionization of helium by fast proton impact, using the generalized-Sturmian-functions methodology and within a perturbative treatment of the projectile-target interaction. The cross-section information is extracted from the asymptotic behavior of the numerical three-body function that describes the emission process. Our goal is to provide benchmark first-order Born fully differential cross sections with which one may investigate the suitability of transition matrices calculated using approximate analytic-type solutions for the double continuum (the choice of effective charges or effective momenta to partially account for the internal target interactions being, to some extent, arbitrary). We also provide fully differential cross sections for the low-ejection-energy regime, which is beyond the suitable range of such perturbative methods. We find, however, that the effective momentum approach allows one to get at least a rough characterization of the most dominant physical process involved. We also compare our calculations with the only available relative experimental set, showing an agreement in shape that can be well understood within the given momentum transfer regime.Fil: Ambrosio, Marcelo José. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de AstronomÃa y FÃsica del Espacio(i); ArgentinaFil: Mitnik, Dario Marcelo. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de AstronomÃa y FÃsica del Espacio(i); ArgentinaFil: Ancarani, L. U.. Université de Lorraine; Francia. Centre National de la Recherche Scientifique; FranciaFil: Gasaneo, Gustavo. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - BahÃa Blanca. Instituto de FÃsica del Sur. Universidad Nacional del Sur. Departamento de FÃsica. Instituto de FÃsica del Sur; ArgentinaFil: Gaggioli, Enzo Leopoldo. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - BahÃa Blanca. Instituto de FÃsica del Sur. Universidad Nacional del Sur. Departamento de FÃsica. Instituto de FÃsica del Sur; Argentin
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Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/67109/2/10.1177_000992286900800511.pd
Interference effects in the photorecombination of argonlike Sc3+ ions: Storage-ring experiment and theory
Absolute total electron-ion recombination rate coefficients of argonlike
Sc3+(3s2 3p6) ions have been measured for relative energies between electrons
and ions ranging from 0 to 45 eV. This energy range comprises all dielectronic
recombination resonances attached to 3p -> 3d and 3p -> 4s excitations. A broad
resonance with an experimental width of 0.89 +- 0.07 eV due to the 3p5 3d2 2F
intermediate state is found at 12.31 +- 0.03 eV with a small experimental
evidence for an asymmetric line shape. From R-Matrix and perturbative
calculations we infer that the asymmetric line shape may not only be due to
quantum mechanical interference between direct and resonant recombination
channels as predicted by Gorczyca et al. [Phys. Rev. A 56, 4742 (1997)], but
may partly also be due to the interaction with an adjacent overlapping DR
resonance of the same symmetry. The overall agreement between theory and
experiment is poor. Differences between our experimental and our theoretical
resonance positions are as large as 1.4 eV. This illustrates the difficulty to
accurately describe the structure of an atomic system with an open 3d-shell
with state-of-the-art theoretical methods. Furthermore, we find that a
relativistic theoretical treatment of the system under study is mandatory since
the existence of experimentally observed strong 3p5 3d2 2D and 3p5 3d 4s 2D
resonances can only be explained when calculations beyond LS-coupling are
carried out.Comment: 11 pages, 7 figures, 3 tables, Phys. Rev. A (in print), see also:
http://www.strz.uni-giessen.de/~k
Radiative recombination of bare Bi83+: Experiment versus theory
Electron-ion recombination of completely stripped Bi83+ was investigated at
the Experimental Storage Ring (ESR) of the GSI in Darmstadt. It was the first
experiment of this kind with a bare ion heavier than argon. Absolute
recombination rate coefficients have been measured for relative energies
between ions and electrons from 0 up to about 125 eV. In the energy range from
15 meV to 125 eV a very good agreement is found between the experimental result
and theory for radiative recombination (RR). However, below 15 meV the
experimental rate increasingly exceeds the RR calculation and at Erel = 0 eV it
is a factor of 5.2 above the expected value. For further investigation of this
enhancement phenomenon the electron density in the interaction region was set
to 1.6E6/cm3, 3.2E6/cm3 and 4.7E6/cm3. This variation had no significant
influence on the recombination rate. An additional variation of the magnetic
guiding field of the electrons from 70 mT to 150 mT in steps of 1 mT resulted
in periodic oscillations of the rate which are accompanied by considerable
changes of the transverse electron temperature.Comment: 12 pages, 14 figures, to be published in Phys. Rev. A, see also
http://www.gsi.de/ap/ and http://www.strz.uni-giessen.de/~k
Sturmian bases for two-electron systems in hyperspherical coordinates
We give a detailed account of an spectral approach
for the calculation of energy spectra of two active electron atoms in a system
of hyperspherical coordinates. In this system of coordinates, the Hamiltonian
has the same structure as the one of atomic hydrogen with the Coulomb potential
expressed in terms of a hyperradius and the nuclear charge replaced by an angle
dependent effective charge. The simplest spectral approach consists in
expanding the hyperangular wave function in a basis of hyperspherical
harmonics. This expansion however, is known to be very slowly converging.
Instead, we introduce new hyperangular sturmian functions. These functions do
not have an analytical expression but they treat the first term of the
multipole expansion of the electron-electron interaction potential, namely the
radial electron correlation, exactly. The properties of these new functions are
discussed in detail. For the basis functions of the hyperradius, several
choices are possible. In the present case, we use Coulomb sturmian functions of
half integer angular momentum. We show that, in the case of H, the accuracy
of the energy and the width of the resonance states obtained through a single
diagonalization of the Hamiltonian, is comparable to the values given by
state-of-the-art methods while using a much smaller basis set. In addition, we
show that precise values of the electric-dipole oscillator strengths for
transitions in helium are obtained thereby confirming the
accuracy of the bound state wave functions generated with the present method.Comment: 28 pages, 4 figure
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