2,691 research outputs found
Friedmann cosmology with decaying vacuum density
Among the several proposals to solve the incompatibility between the observed
small value of the cosmological constant and the huge value obtained by quantum
field theories, we can find the idea of a decaying vacuum energy density,
leading from high values at early times of universe evolution to the small
value observed nowadays. In this paper we consider a variation law for the
vacuum density recently proposed by Schutzhold on the basis of quantum field
estimations in the curved, expanding background, characterized by a vacuum
density proportional to the Hubble parameter. We show that, in the context of
an isotropic and homogeneous, spatially flat model, the corresponding solutions
retain the well established features of the standard cosmology, and, in
addition, are in accordance with the observed cosmological parameters. Our
scenario presents an initial phase dominated by radiation, followed by a dust
era long enough to permit structure formation, and by an epoch dominated by the
cosmological term, which tends asymptotically to a de Sitter universe. Taking
the matter density equals to half of the vacuum energy density, as suggested by
observation, we obtain a universe age given by Ht = 1.1, and a decelerating
parameter equals to -1/2.Comment: Accepted for publication in General Relativity and Gravitatio
On the performance of profile extrusion dies
This work presents a study performed with an in-house 3D numerical modelling code, used to evaluate the sensitivity of extrusion dies, optimized with alternative strategies, to process parameters, such as machining inaccuracies, melt rheology and processing conditions.FC
Numerical modelling code based on the finite volume method in unstructured grids
In this work, the implementation employed in the new modeling code is described. It is based on the FVM with on a SIMPLE type scheme suitable for unstructured meshes.Fundação para a Ciência e a Tecnologia (FCT
Design of complex profile extrusion dies through numerical modeling
The achievement of a balanced flow is one of the major tasks encompassed in the design of profile extrusion
dies [1]. For this purpose numerical modeling codes may be a very useful aid. The research team
involved in this work has been working during the last decade on the development of numerical tools
to aid the conception of extrusion dies [1,2]. The design code developed so far carries out the automatic
search of a final geometry via an optimization routine coupled with geometry and mesh generators and a
3D computational fluid dynamics (CFD) code based on the finite volume method (FVM). This CFD code is
able to model the flow of polymer melts in confined channels, but is inadequate to deal with complex
geometries, since it is limited to structured meshes. This work describes the recent efforts made to
enlarge the scope of the design procedures, that are currently focused on the development of a modeling
code able to deal with unstructured meshes. This code solves the continuity and linear momentum conservation
equations, with generalized Newtonian fluids, using a SIMPLE based approach. This paper
describes the developed numerical modelling code and its employment in a case study that involves
the design of a medical catheter extrusion die, focused on the search of a balanced flow distribution.
The results obtained show that the developed numerical code is able to deal with complex geometrical
problems, being thus a valuable tool to aid the design of extrusion dies to produce complex profiles.The authors gratefully acknowledge funding from Fundacao para a Ciencia e Tecnologia through the PhD Grant SFRH/BD43632/2008 and FCT (COMPETE Program) under the Projects FCOMP-01-0124 - FEDER-010190 (Ref. PTDC/EME - MFE/102729/2008) and FCOMP-01-0124-FEDER-015126 (Refa. FCT PTDC/EME-MFE/113988/2009), and FEDER, via FCT, under the PEst-C/CTM/LA0025/2011 (Strategic Project - LA 25 - 2011-2012)
Development of numerical tools to aid the design of complex geometry profile extrusion dies
The research team of this work is involved since the
mid-nineties on the development of computational tools
to aid the design of profile extrusion dies. Initially, the
numerical code employed was based on structured
meshes that limited its application to simple geometries.
The work planned in this PhD programme comprises the
development of a numerical modelling code able to deal
with unstructured meshes and its application on the
design of profile extrusion dies comprising complex
cross sections.
In its current state the numerical code under
development is able to model de flow of generalized
Newtonian fluids inside flow channels using
unstructured meshes.
This paper describes briefly the current state of the
developed code and illustrates its application in a case
study involving the design of a profile extrusion die
comprising a complex cross section
An effective interface tracking method for simulating the extrudate swell phenomenon
The extrudate swell, i.e., the geometrical modifications that take place when the flowing material leaves the confined flow inside a channel and moves freely without the restrictions that are promoted by the walls, is a relevant phenomenon in several polymer processing techniques. For instance, in profile extrusion, the extrudate cross-section is subjected to a number of distortions that are motivated by the swell, which are very difficult to anticipate, especially for complex geometries. As happens in many industrial processes, numerical modelling might provide useful information to support design tasks, i.e., to allow for identifying the best strategy to compensate the changes promoted by the extrudate swell. This study reports the development of an improved interface tracking algorithm that employs the least-squares volume-to-point interpolation method for the grid movement. The formulation is enriched further with the consistent second-order time-accurate non-iterative Pressure-Implicit with Splitting of Operators (PISO) algorithm, which allows for efficiently simulating free-surface flows. The accuracy and robustness of the proposed solver is illustrated through the simulation of the steady planar and asymmetric extrudate swell flows of Newtonian fluids. The role of inertia on the extrudate swell is studied, and the results that are obtained with the newly improved solver show good agreement with reference data that are found in the scientific literatureSearch-ON2
(NORTE-07-0162-FEDER-000086) the HPC infrastructure of UMinho under NSRF through ERDF;
and FCT I.P. through the Advanced Computing Project CPCA/A00/6057/2020 using the Minho
Advanced Computing Center (MACC
On the simulation of the Newtonian fluid Extrudate Swell using a moving mesh finite volume interface tracking method
The extrudate swell, the geometrical modifications that take place when the flowing
material leaves a confined flow inside a channel and moves freely without the restrictions
promoted by the walls, is a relevant phenomenon in several polymer processing
techniques. For instance, in profile extrusion, the extrudate cross-section is subjected to
a number of distortions motivated by the swell, which are very difficult to anticipate,
especially for complex geometries. As happens in many industrial processes, numerical
modelling might provide useful information to support design tasks, i.e., to allow
identifying the cross section geometry which produces the desired profile, after the
changes promoted by the extrudate swell.
In this work we study the capability of an open-source moving mesh finite volume
interface tracking solver, to simulate the extrudate swell process in profile extrusion. For
this purpose, the data provided by Mitsoulis et al. (E. Mitsoulis, G.C. Georgiou, and Z.
Kountouriotis. A study of various factors affecting Newtonian extrudate swell. Computers
& Fluids, 57:195{207, 2012) on the simulation of the extrudate swell flow of a Newtonian
fluid at different Reynolds number, is considered as the reference for validation. The
results obtained with the OpenFOAM solver show a very good agreement with the
reference data.NORTE-07-0162-FEDER-000086 and the Minho Advanced Computing
Center (MACC) for providing HPC. CPCA_A00_6057202
Validation of a moving mesh finite volume interface tracking method through the numerical simulation of the Newtonian extrudate swell
The geometrical modifications that take place when the flowing material leaves a
confined flow inside a channel and moves freely without the restrictions promoted by
the walls, commonly designated by extrudate swell, is a relevant phenomenon in
several polymer processing techniques. For instance, in profile extrusion, the
extrudate cross-section is subjected to a number of distortions motivated by the
swell, which are very difficult to anticipate, especially for complex geometries. To
circumvent those problems numerical modelling might provide useful information to
support design tasks, i.e., to allow identifying the cross section geometry which
produces the desired profile, after the changes promoted by the extrudate swell.
In this work we employed an open-source moving mesh finite volume interface
tracking solver to simulate the extrudate swell process in profile extrusion. The data
provided by Mitsoulis et al. (E. Mitsoulis, G.C. Georgiou, and Z. Kountouriotis. A study
of various factors affecting Newtonian extrudate swell. Computers & Fluids,
57:195{207, 2012) on the simulation of the extrudate swell flow of a Newtonian fluid
at different Reynolds number is considered as the reference for validation. The
results obtained with the OpenFOAM solver show a very good agreement with the
reference dataCPCA_A00_60572020. NORTE-07-0162-FEDER-000086 and the Minho Advanced
Computing Center (MACC) for providing HPC resources that contributed to the
research results reported within this abstrac
AVALIAÇÂO DE UMA NOVA TÉCNICA DE QUIMIOLUMINESCÊNCIA PARA DETERMINAÇÃO DE ANTICORPOS ANTI-DSDNA
Introdução
A determinação dos anticorpos anti-dsDNA é um teste de grande importância para o diagnóstico e monitorização de doentes com Lúpus Eritematoso Sistémico (LES), fazendo parte dos critérios de classificação de LES do ACR. (American College of Rheumathology). Existem actualmente vários métodos laboratoriais disponÃveis, que respondem de forma desigual na determinação destes anticorpos nos doentes, em diferentes fases de evolução da patologia.
Objectivo
Avaliar o desempenho do novo método automatizado de determinação dos anticorpos anti-dsDNA por técnica de quimioluminescência (CLIA), Zenit RA dsDNA (Menarini), comparando-o com os métodos de imunofluorescência indirecta (IFI) e fluoroimunoensaio (FEIA), utilizados na rotina assistencial no Serviço de Imunologia do CHP.
Material e Métodos
A população estudada incluiu 151 amostras seriadas de doentes com LES, 33 doentes com doença infecciosa, 28 doentes com outras patologias com envolvimento autoimune e 38 indivÃduos saudáveis. Realizou-se a determinação dos anticorpos anti-dsDNA por técnica CLIA no equipamento ZENIT RA (Menarini), por técnica FEIA no equipamento ImmunoCAP 250 (Phadia) e por IFI em lâminas de Crithidia luciliae (BioRad) processadas no aparelho PhD (BioRad).
Resultados
Todos os testes apresentaram uma baixa sensibilidade nos doentes com LES (33,1% a 44,4%), traduzindo o facto de um grande número de doentes se encontrar em tratamento e com fraca actividade da doença. O teste CLIA apresentou uma especificidade semelhante à da IFI (93,9% vs. 95,6%), superior à observada no FEIA (85,9%).
Conclusões
O teste dsDNA ZENIT RA revelou uma sensibilidade inferior ao FEIA mas uma melhor especificidade e valor preditivo positivo, semelhantes aos observados na técnica de IFI. Sendo um teste totalmente automatizado e sem a subjectividade da IFI, será agora importante a sua avaliação numa população com critérios de actividade bem definidos
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