316 research outputs found
Angular Inflation from Supergravity
We study supergravity inflationary models where inflation is produced along
the angular direction. For this we express the scalar component of a chiral
superfield in terms of the radial and the angular components. We then express
the supergravity potential in a form particularly simple for calculations
involving polynomial expressions for the superpotential and Kahler potential.
We show for a simple Polonyi model the angular direction may give rise to a
stage of inflation when the radial field is fixed to its minimum. We obtain
analytical expressions for all the relevant inflationary quantities and discuss
the possibility of supersymmetry breaking in the radial direction while
inflating by the angular component.Comment: 7 pages, one figure. Final version. Title changed, two figures
droppe
Metodología para Optimización Topológica y de Forma de Elementos Estructurales
The Hybrid Cellular Automaton (HCA) algorithm is a methodology developed to simulate the process of functional adaptation in bones. The HCA algorithm combines elements of the cellular automaton (CA) paradigm with finite element analysis. This methodology has proved to be computationally efficient to solve topology optimization problems. In this paper, the HCA algorithm is integrated with a shape optimization algorithm that uses sequential quadratic programming. The geometry of the topologically optimized structure is converted into a two-dimensional solid model using an edge detection algorithm and parametric B-splines. An example problem of a Michell structure is presented. Also shown is the application of the shape optimization algorithm in the redesign of the lightening holes in the transverse floors of a riverine patrol vessel designed by COTECMAR. In both cases an appreciable weight reduction was obtained.El método de los Autómatas Celulares Híbridos (HCA) para optimización topológica simula el proceso de adaptación funcional en estructuras óseas. El método HCA combina la técnica de los elementos finitos para análisis estructural con el paradigma de los Autómatas celulares (CA) para el diseño y ha demostrado ser una técnica efectiva para optimización topológica en estructuras continuas. En este trabajo se integra el método HCA con un algoritmo de optimización de forma que utiliza programación cuadrática secuencial. La geometría optimizada topológicamente es utilizada para construir un modelo bidimensional sólido aplicando un algoritmo de detección de bordes en imágenes y esplines paramétricos. Un ejemplo de una estructura Michell es presentado. También es presentada la aplicación de un algoritmo de optimización de forma en el diseño de unos aligeramientos en las varengas de un buque patrullero fluvial diseñado por COTECMAR. En ambos casos una apreciable reducción del peso fue obtenida
Banks’ Net Interest Margin in the 2000s: A Macro-Accounting International Perspective
This paper re-examines the determinants of Net Interest Margin (NIM) in the banking industries
of 15 developed and emerging economies. It presents three main contributions
with respect to previous studies: first, we analyze the determinants of NIM in the years
leading to the 2008 financial crisis; second, we account for the role of different accounting
standards across countries; third, we use multi-way cluster estimation methodologies
which control for cross-sectional and time-series dependence in macroeconomic and
banking variables. We find that the introduction of International Financial Reporting
Standards (IFRSs) contributed to lower NIM variations unexplained by standard accounting
variables. Interest rate volatility is found to be positively and strongly related to
NIM dynamics, whereas inflation risk is often found to be a relevant driver of NIM crosscountry
differences
Using coarse-grained molecular dynamics to rationalize biomolecule solubilization mechanisms in ionic liquid-based colloidal systems
Solubilizing agents are widely used to extract poorly soluble compounds from biological matrices.
Aqueous solutions of surfactants and hydrotropes are commonly used as solubilizers, however, the
underlying mechanism that determines their action is still roughly understood. Among these, ionic
liquids (IL) are often used not only for solubilization of a target compound but in liquid–liquid extraction
processes. Molecular dynamics simulations can shed light into this issue by providing a microscopic
insight of the interactions between solute and solubilising agents. In this work, a new coarse-grained
(CG) model was developed under the MARTINI framework for gallic acid (GA) while the CG models of
three quaternary ammonium ionic liquids and salts (QAILS) were obtained from literature. Three QAILS
were selected bearing in mind their potential solubilising mechanisms: trimethyl-tetradecylammonium
chloride ([N1,1,1,14]Cl) as a surfactant, tetrabutylammonium chloride ([N4,4,4,4]Cl) as a hydrotrope, and
tributyl-tetradecylammonium chloride ([N4,4,4,14]Cl) as a system combining the characteristics of the
other compounds. Throughout this hydrotrope-to-surfactant spectrum and considering the most
prevalent GA species across the pH range, the solvation of GA at two concentration levels in aqueous
QAILS solutions were studied and discussed. The results of this study indicate that dispersive interactions
between the QAILS and GA are generally the driving force in the GA solubilization. However,
electrostatic interactions play an increasingly significant role as the GA becomes deprotonated, affecting
their placement within the micelle and ultimately the solvation mechanism. The hydrotropic mechanism
seen in [N4,4,4,4]Cl corroborates recent models based on the formation of a hydrotrope-solute
aggregates driven by dispersive forces. This work contributes to the application of a transferable
approach to partition and solubilization studies using molecular dynamics, which could complement
experimental assays and quickly screen molecular candidates for these processes.publishe
Structural and magnetic properties study of nd16fe76-xnixb8 alloys with low ni contents
In this work we report a magnetic and structural study of Nd16Fe76-xNixB8 (x = 0, 2.5, 5, 7.5 and 10) alloys. This system was investigated by means of x-ray diffraction, Mössbauer spectrometry, and magnetization. The samples were melted in an arc furnace and then annealed during three days at 1000 oC. The results show the majority formation of the hard Nd2Fe14B tetragonal phase with lattice parameters a = 8.810 Å and c = 12.210 Å; these parameters do not vary substantially with the addition of Ni. Mössbauer results show a ferromagnetic contribution with six sites of iron associated to the Nd2Fe14B phase and a paramagnetic contribution as a doublet attributed to the Nd1,1Fe4B4 phase. The hysteresis cycles show that all the samples present a hard magnetic behavior, and the addition of Ni decreases this property.En este trabajo reportamos las propiedades magnéticas y estructurales de las aleaciones Nd16Fe76-xNixB8 (x=0, 2.5, 5, 7.5 y 10). Este sistema fue investigado por medio de difracción de rayos-x, espectrometría Mössbauer y magnetización. Las muestras fueron fundidas en un horno a arco y luego recocidas a 1000 oC durante tres días. Los resultados muestran la formación mayoritaria de la fase tetragonal dura Nd2Fe14B con parámetros de red a=8.810 Å y c=12.210 Å; estos parámetros no varían sustancialmente al agregar Ni. Los resultados Mössbauer muestran una contribución ferromagnética constituida por seis sitios de hierro asociados a la fase Nd2Fe14B y una contribución paramagnética en forma de doblete atribuida a la fase Nd1,1Fe4B4. Los ciclos de histéresis muestran que todas las muestras presentan un comportamiento magnético duro, y al agregar Ni esta propiedad disminuye
Theory of quantum fluctuations of optical dissipative structures and its application to the squeezing properties of bright cavity solitons
We present a method for the study of quantum fluctuations of dissipative
structures forming in nonlinear optical cavities, which we illustrate in the
case of a degenerate, type I optical parametric oscillator. The method consists
in (i) taking into account explicitly, through a collective variable
description, the drift of the dissipative structure caused by the quantum
noise, and (ii) expanding the remaining -internal- fluctuations in the
biorthonormal basis associated to the linear operator governing the evolution
of fluctuations in the linearized Langevin equations. We obtain general
expressions for the squeezing and intensity fluctuations spectra. Then we
theoretically study the squeezing properties of a special dissipative
structure, namely, the bright cavity soliton. After reviewing our previous
result that in the linear approximation there is a perfectly squeezed mode
irrespectively of the values of the system parameters, we consider squeezing at
the bifurcation points, and the squeezing detection with a plane--wave local
oscillator field, taking also into account the effect of the detector size on
the level of detectable squeezing.Comment: 10 figure
Quadrature and polarization squeezing in a dispersive optical bistability model
We theoretically study quadrature and polarization squeezing in dispersive
optical bistability through a vectorial Kerr cavity model describing a
nonlinear cavity filled with an isotropic chi(3) medium in which self-phase and
cross-phase modulation, as well as four--wave mixing, occur. We derive
expressions for the quantum fluctuations of the output field quadratures as a
function of which we express the spectrum of fluctuations of the output field
Stokes parameters. We pay particular attention to study how the bifurcations
affecting the non-null linearly polarized output mode squeezes the orthogonally
polarized vacuum mode, and show how this produces polarization squeezing.Comment: 10 text pages + 12 figure
Spanish Research Report for 1991
10 páginas, 14 tablasPeer reviewe
Using coarse-grained molecular dynamics to understand the effect of ionic liquids on the aggregation of Pluronic copolymer solutions
This study is aimed to enhance the understanding of the interaction between ionic liquids (ILs) and non-ionic Pluronic triblock copolymers in aqueous two-phase micellar systems (ATPMS) used for the selective separation/purification of hydrophobic biomolecules. The ILs allow a precise control of the cloud point phase separation temperature (CPT), particularly important when the stability of the molecule is highly dependent on temperature. The effect of choline-based ILs, with two different counter-anions, chloride and hexanoate, was evaluated using molecular dynamics simulations (MD) for F-68 and L-35 Pluronic aqueous solutions. The simulations revealed the role played by the anions during the Pluronic self-assembly, with choline chloride hindering Pluronic aggregation and the choline hexanoate favouring micelle formation and coalescence, in agreement with the experimental data. A detailed study of the accessible surface area of Pluronic showed a progressive dehydration of the Pluronic hydrophilic micelle corona in choline hexanoate mixtures promoting inter-micelle interactions and, consequently, micelle coalescence. With the addition of choline hexanoate, it was observed that the hydrophilic segments, which form the micelle corona, twisted towards the Pluronic micelle core. The electrostatic interaction is also shown to play a key role in this IL–Pluronic aqueous solution, as the hexanoate anions are accommodated in the Pluronic micelle core, while the choline cations are hosted by the Pluronic micelle corona, with the ions interacting with each other during the self-assembly process. In addition, a comparison study of F-68 and L-35 aqueous solutions shows that the IL impact depends on the length of the Pluronic hydrophilic segment. This work provides a realistic microscopic scenario of the complex interactions between Pluronic copolymers and ILs.This work was developed within the scope of the project
CICECO-Aveiro Institute of Materials, UIDB/50011/2020 &
UIDP/50011/2020, financed by national funds through the
FCT/MEC and when appropriate co-financed by FEDER under
the PT2020 Partnership Agreement. The authors acknowledge
the research contract under the project CENTRO-01-0145-
FEDER-000005: SusPhotoSolutions: Soluções Fotovoltaicas
Sustentáveis. G. Pérez-Sánchez and N. Schaeffer acknowledge
the national funds (OE), through FCT – Fundação para a
Ciência e a Tecnologia, I. P., in the scope of the framework
contract foreseen in the numbers 4, 5 and 6 of the article 23, of
the Decree-Law 57/2016, of August 29th, changed by Law
57/2017, of July 19th. A. M. Lopes acknowledges the support
from the State of São Paulo Research Foundation (FAPESP/Brazil,
processes #2017/10789-1 and #2018/10799-0). J. F. B. Pereira also
acknowledges FAPESP through the project 2014/16424-7.publishe
- …