Time filter

Source Type

Nascimento S.R.V.,Federal University of Pernambuco | Lira C.A.B.O.,Federal University of Pernambuco | Lapa C.M.F.,Brazilian National Nuclear Energy Commission | Lima F.R.A.,Brazilian Northeast Regional Center of Nuclear Science (CRCN-NE) | And 4 more authors.
Annals of Nuclear Energy | Year: 2017

Small Modular Reactors, SMRs, are variants of compact modular reactors of generation III+ that present attractive features such as simplicity, enhanced safety and are economically competitive. In an iPWR (integral pressurized water reactor), the pressurizer is located at the top of the reactor vessel; this configuration requires the investigation of the mechanisms adopted for the homogenization of boron. The present work shows the contributions to the design of an experimental installation proposed to provide relevant data to study the boron homogenization phenomena in a pressurizer of an SMR. For this, an experimental installation was built with a test section made of stainless steel with a volumetric scale equal to 1:200, representing one-fourth of the pressurizer of an iPWR. The experimental installation has a test section, a heat exchanger, two pumps, five flow meters and three stainless steel tanks with capacities of 0.143, 0.069 and 0.216 m3. The test facility layout was mounted so that the test section was fed with water or saline solutions with different concentrations, representing scenarios of boration or deboration. To determine the concentration at the inlet and outlet of the test section, samples have been collected every 10 min during the experiments representing some scenarios (boration/deboration). The electrical conductivity of these samples was determined by a conductivity meter and converted to the concentration of the tracer element (NaCl) used. Three representative experiments were conducted and it was possible to prove the viability of using the experimental setup in a reliable form, for the range of values occurring in the boron homogenization phenomenon in a pressurizer of a compact modular reactor. © 2017 Elsevier Ltd


Penate-Rodriguez H.C.,Instituto Superior Of Tecnologia Y Ciencias Aplicadas | Penate-Rodriguez H.C.,Institute Fisica Fundamental CSIC | Dorta-Urra A.,CSIC Institute Fisica Fundamental CSIC | Bargueno P.,Complutense University of Madrid | And 3 more authors.
Chirality | Year: 2013

A canonical framework for chiral two-level systems coupled to a bath of harmonic oscillators is developed to extract, from a stochastic dynamics, the thermodynamic equilibrium values of both the population difference and coherences. The incoherent and coherent tunneling regimes are analyzed for an Ohmic environment in terms of a critical temperature defined by the maximum of the heat capacity. The corresponding numerical results issued from solving a non-linear coupled system of equations are fitted to approximate path-integral analytical expressions beyond the so-called non-interacting blip approximation in order to determine the different time scales governing both regimes. © 2013 Wiley Periodicals, Inc. © 2013 Wiley Periodicals, Inc.


Penate-Rodriguez H.C.,Instituto Superior Of Tecnologia Y Ciencias Aplicadas | Penate-Rodriguez H.C.,Institute Fisica Fundamental CSIC | Bargueno P.,Complutense University of Madrid | Miret-Artes S.,Institute Fisica Fundamental CSIC
Chemical Physics Letters | Year: 2012

Geometric phases within a canonical formulation of chiral molecules are analyzed paying special attention to the fundamental role played by the parity violating energy difference. We study the Hamiltonian dynamics in terms of canonically conjugate variables, showing how parity-violating energy difference could be locked (PVED-locking) by means of a circularly polarized electric field. Signatures of this locking are predicted to occur both in the geometric phase and in the interference between chiral states. © 2011 Elsevier B.V. All rights reserved.


Dorta-Urra A.,Institute Fisica Fundamental | Peate-Rodriguez H.C.,Instituto Superior Of Tecnologia Y Ciencias Aplicadas | Peate-Rodriguez H.C.,Institute Fisica Fundamental | Bargueo P.,Complutense University of Madrid | And 3 more authors.
Journal of Chemical Physics | Year: 2012

Within a generalized Langevin framework for open quantum systems, the cyclic evolution of a two-level system is analyzed in terms of the geometric phase extended to dissipative systems for Ohmic friction. This proposal is applied to the dynamics of chiral molecules where the tunneling and parity violating effects are competing. The effect of different system-bath coupling functions in the dissipated energy is shown to be crucial to understand the behavior of the geometric phase as well as the decoherence displayed by the corresponding interference patterns. © 2012 American Institute of Physics.


Hernandez-Valdes D.,Instituto Superior Of Tecnologia Y Ciencias Aplicadas | Rodriguez-Riera Z.,Instituto Superior Of Tecnologia Y Ciencias Aplicadas | Diaz-Garcia A.,University of Habana | Benoist E.,Toulouse 1 University Capitole | Jauregui-Haza U.,Instituto Superior Of Tecnologia Y Ciencias Aplicadas
Journal of Molecular Modeling | Year: 2016

The development of novel radiopharmaceuticals for nuclear medicine based on M(CO)3 (M = Tc, Re) complexes has attracted great attention. The versatility of this core and the easy production of the fac-[M(CO)3(H2O)3]+ precursor could explain this interest. The main characteristics of these tricarbonyl complexes are the high substitution stability of the three CO ligands and the corresponding lability of the coordinated water molecules, yielding, via easy exchange of a variety of bi- and tridentate ligands, complexes xof very high kinetic stability. Here, a computational study of different tricarbonyl complexes of Re(I) and Tc(I) was performed using density functional theory. The solvent effect was simulated using the polarizable continuum model. These structures were used as a starting point to investigate the relative stabilities of tricarbonyl complexes with various tridentate ligands. These complexes included an iminodiacetic acid unit for tridentate coordination to the fac-[M(CO)3]+ moiety (M = Re, Tc), an aromatic ring system bearing a functional group (−NO2, −NH2, and –Cl) as a linking site model, and a tethering moiety (a methylene, ethylene, propylene butylene, or pentylene bridge) between the linking and coordinating sites. The optimized complexes showed geometries comparable to those inferred from X-ray data. In general, the Re complexes were more stable than the corresponding Tc complexes. Furthermore, using NH2 as the functional group, a medium length carbon chain, and ortho substitution increased complex stability. All of the bonds involving the metal center presented a closed shell interaction with dative or covalent character, and the strength of these bonds decreased in the sequence Tc-CO > Tc-O > Tc-N. © 2016, Springer-Verlag Berlin Heidelberg.


Enriquez-Victorero C.,Instituto Superior Of Tecnologia Y Ciencias Aplicadas | Hernandez-Valdes D.,Instituto Superior Of Tecnologia Y Ciencias Aplicadas | Montero-Alejo A.L.,University of Habana | Durimel A.,University of the French West Indies and Guiana | And 2 more authors.
Journal of Molecular Graphics and Modelling | Year: 2014

Activated carbon (AC) is employed in drinking water purification without almost any knowledge about the adsorption mechanism of persistent organic pollutants (POPs) onto it. Hexachlorocyclohexane (HCH) is an organochlorinated contaminant present in water and soils of banana crops production zones of the Caribbean. The most relevant isomers of HCH are γ-HCH and β-HCH, both with great environmental persistence. A theoretical study of the influence of AC surface groups (SGs) on HCH adsorption is done in order to help to understand the process and may lead to improve the AC selection process. A simplified AC model consisting of naphthalene with a functional group was used to assess the influence of SGs over the adsorption process. The Multiple Minima Hypersurface (MMH) methodology was employed to study γ-HCH and β-HCH interactions with different AC SGs (hydroxyl and carboxyl) under different hydration and pH conditions. The results obtained showed that association of HCH with SGs preferentially occurs between the axial protons of HCH and SG's oxygen atom, and the most favorable interactions occurring with charged SGs. An increase in carboxylic SGs content is proposed to enhance HCH adsorption onto AC under neutral pH conditions. Finally, this work presents an inexpensive computer aided methodology for preselecting activated carbon SGs content for the removal of a given compound. © 2014 Elsevier Inc.


Cata G.F.,National Autonomous University of Mexico | Cata G.F.,Instituto Superior Of Tecnologia Y Ciencias Aplicadas | Rojas H.C.,National Autonomous University of Mexico | Rojas H.C.,Instituto Superior Of Tecnologia Y Ciencias Aplicadas | And 4 more authors.
Soft Matter | Year: 2011

A series of molecular dynamics simulations were performed in order to explore the initial (10.5 ns) structure of CTAB micelles formed in aqueous solutions. The determination of the aggregation number of CTAB is a long-standing and fundamental problem. Therefore we simulated eight model systems of micelles in aqueous solution. Some micellar structural characteristics, local solvation environments, and counter ion distributions are described. Topological and geometrical concepts are used to characterize the resulting micelle structures. Our findings indicate that for certain aggregation numbers micelles are formed by layered spherical structures. © 2011 The Royal Society of Chemistry.


PubMed | Toulouse 1 University Capitole, University of Habana and Instituto Superior Of Tecnologia Y Ciencias Aplicadas
Type: Journal Article | Journal: Journal of molecular modeling | Year: 2016

The development of novel radiopharmaceuticals for nuclear medicine based on M(CO)3 (M=Tc, Re) complexes has attracted great attention. The versatility of this core and the easy production of the fac-[M(CO)3(H2O)3](+) precursor could explain this interest. The main characteristics of these tricarbonyl complexes are the high substitution stability of the three CO ligands and the corresponding lability of the coordinated water molecules, yielding, via easy exchange of a variety of bi- and tridentate ligands, complexes xof very high kinetic stability. Here, a computational study of different tricarbonyl complexes of Re(I) and Tc(I) was performed using density functional theory. The solvent effect was simulated using the polarizable continuum model. These structures were used as a starting point to investigate the relative stabilities of tricarbonyl complexes with various tridentate ligands. These complexes included an iminodiacetic acid unit for tridentate coordination to the fac-[M(CO)3](+) moiety (M=Re, Tc), an aromatic ring system bearing a functional group (-NO2, -NH2, and -Cl) as a linking site model, and a tethering moiety (a methylene, ethylene, propylene butylene, or pentylene bridge) between the linking and coordinating sites. The optimized complexes showed geometries comparable to those inferred from X-ray data. In general, the Re complexes were more stable than the corresponding Tc complexes. Furthermore, using NH2 as the functional group, a medium length carbon chain, and ortho substitution increased complex stability. All of the bonds involving the metal center presented a closed shell interaction with dative or covalent character, and the strength of these bonds decreased in the sequence Tc-CO>Tc-O>Tc-N.


PubMed | Instituto Superior Of Tecnologia Y Ciencias Aplicadas
Type: Journal Article | Journal: Chirality | Year: 2013

A canonical framework for chiral two-level systems coupled to a bath of harmonic oscillators is developed to extract, from a stochastic dynamics, the thermodynamic equilibrium values of both the population difference and coherences. The incoherent and coherent tunneling regimes are analyzed for an Ohmic environment in terms of a critical temperature defined by the maximum of the heat capacity. The corresponding numerical results issued from solving a non-linear coupled system of equations are fitted to approximate path-integral analytical expressions beyond the so-called non-interacting blip approximation in order to determine the different time scales governing both regimes.


PubMed | Instituto Superior Of Tecnologia Y Ciencias Aplicadas
Type: Journal Article | Journal: Archives of environmental contamination and toxicology | Year: 2015

In this work, 14 polycyclic aromatic hydrocarbons (PAHs) included in the United States Environmental Protection Agency pollutant priority list were analyzed in the surface water of the upper urbanized part of Almendares River, the most important water course in Havana, Cuba. Surface water from five sampling sites was collected at the end of dry season and analyzed by high-performance liquid chromatography-fluorescence detection method after solid phase extraction procedure. Total PAHs concentrations varied from 836 to 15 811ngL(-1) with a geometric mean value of 2512ngL(-1). PAH typology was dominated by low molecular-weight PAHs (2- to 3-ring components). Pollutant source appraisal was determined by diagnostic ratios method in five sampling sites. Factor analysis of normalized samples was used to concentration identified two factors as the main significant pollutant sources and to cluster similar sampling sites corresponding to petrogenic and combustion inputs, respectively. Ecological risks were considered. For animal aquatic life, acute toxicity values exceed the permissible values in the more-polluted sampling sites.

Loading Instituto Superior Of Tecnologia Y Ciencias Aplicadas collaborators
Loading Instituto Superior Of Tecnologia Y Ciencias Aplicadas collaborators