5,165 research outputs found
Measurement of glass transition in native wheat flour by dynamic mechanical thermal analysis (DMTA)
This work describes a method to study glass transition on native starch powders, based
on dynamical mechanical thermal analysis using compression tests, and was applied to
wheat flour (13.5% water content). This method will allow the determination of Tg in
native (unprocessed) starchy materials, with minimal disturbance of the natural structures.
The influence of the test conditions (heating rate, frequency and strain) on the glass
transition measurements was determined using factorial designs. The values of Tg determined
as the maxima of the energy dissipation (peaks in E ) of native flour and of freezedried
pre-gelatinized flour were not statistically different (around 64 C). The heating rate
did not affect the measurements in the range tested (0.25 to 1 C min 1). An interactive
effect of the strain amplitude and the frequency was detected. The significance of this
interaction can be caused by differences in mechanical energy dissipation, which would
indicate that not only temperature but also the total energy input may affect this transition.
Slight effects of phase separation between gluten and starch were found on native
flour
Exchange market pressure and the credibility of Macau's currency Board
In this study, we assess the credibility of the currency board arrangement (CBA) of the Macau Special Administrative Region by studying the relationship between exchange market pressure (EMP) and the anchors of a rule-based CBA, namely, interest rate arbitrage, exchange rate arbitrage and economic discipline. A pure CBA signals its credibility by allowing the first two anchors to function automatically and by pursuing sound fiscal policies. The analysisâ results suggest that Macauâs CBA has been characterised by a state of low volatility since late 1992, with the brief exception of the East Asian financial crisis period. The paperâs main finding is that fiscal fundamentals seem to have a more pronounced role in reducing EMPâs variability during periods of low volatility whilst interest rate arbitrage is more important in periods of high volatility. We conclude that Macauâs CBA is credible at present as reflected in the low frequency of observed EMP, in the narrowing of Macauâs interest rate differential vis-Ă -vis U.S. interest rates and in Macauâs substantial fiscal reserves.
Um novo mĂ©todo de dimensionamento de reforços de pavimentos flexĂveis considerando a reflexĂŁo de fendas
No presente trabalho Ă© proposto um mĂ©todo de dimensionamento de reforços de pavimentos flexĂveis, considerando como critĂ©rios de ruĂna o aparecimento de fendas Ă superfĂcie da camada de desgaste, resultantes da reflexĂŁo do fendilhamento existente nas camadas betuminosas do pavimento existente, bem como o fendilhamento por fadiga.
O método proposto baseia-se no dimensionamento estrutural corrente, acrescido duma verificação do critério de reflexão de fendas, tendo como base resultados laboratoriais de avaliação da reflexão de fendas em misturas betuminosas, realizados em deslocamento controlado e associados ao conceito de actividade das fendas após reforço
The improvement of pavement performance using asphalt rubber hot mixes
The need of a better pavement performance has led researchers to develop new road
materials, mainly for the asphalt layers, where the modification of the asphalt is the
main example. This modification usually forces the use of polymers and fibers and,
more recently, the use of crumb rubber from ground tires, where the modified asphalt is
known as asphalt rubber. This asphalt rubber used in asphalt mixtures produces a
superior performance if compared to the asphalt mixtures with conventional asphalt.
The crumb rubber modification of the asphalts also presents a higher resistance to
climatic effects, compared to the other binders. Based on these assumptions, this paper
presents the results of the evaluation of mechanical properties, related to the pavement
performance, of asphalt rubber mixtures when compared to conventional mixtures. Two
types of aggregate were used (pebble and diorites) and two binders utilized (asphalt
rubber and conventional asphalt). The aging effect due to the asphalt mixture
production and compaction was taken into account. The materials performance was
evaluated through stiffness, fatigue and permanent deformation tests. Reflective
cracking performance was also predicted using a mechanistic-empirical method
Reabilitação de pavimentos utilizando misturas betuminosas com betumes modificados
Na reabilitação estrutural do pavimento do lanço CRIL-Loures da A8, a Auto-Estradas
do Atlùntico utilizou duas soluçÔes distintas de reforço recorrendo a misturas betuminosas
com betumes modificados. No sentido Norte-Sul foi utilizada uma mistura betuminosa com
betume modificado com borracha reciclada de pneus usados (BMB) e no sentido Sul-Norte
foi utilizada uma mistura betuminosa com um betume modificado com polĂmeros (SBS).
O betume com polĂmeros foi utilizado num betĂŁo betuminoso aplicado com 5 cm de
espessura e o betume modificado com borracha foi utilizado numa mistura betuminosa aberta
aplicada com uma espessura de 2 cm.
Após quatro anos em serviço foi realizado um estudo para determinar as
caracterĂsticas mecĂąnicas das misturas betuminosas aplicadas de modo a avaliar a sua
qualidade e obter indicaçÔes relativamente ao seu desempenho futuro.
Para a realização deste trabalho foram retiradas lajes dos trechos experimentais que
permitiram a avaliação laboratorial do mĂłdulo de deformabilidade, da resistĂȘncia Ă fadiga e
da resistĂȘncia Ă deformação permanente.
Este trabalho permitiu concluir que, em termos de comportamento mecĂąnico, a mistura
BMB, com apenas 2 cm de espessura apresenta uma resistĂȘncia Ă fadiga e Ă deformação
permanente superior Ă mistura SBS aplicada com 5 cm de espessura
O tipo de modelação dos pneus dos veĂculos pesados na avaliação do desempenho dos pavimentos
Os veĂculos pesados sĂŁo os principais responsĂĄveis pela degradação dos pavimentos rodoviĂĄrios provocando
principalmente fendilhamento por fadiga e deformaçÔes permanentes. Os pavimentos rodoviårios são dimensionados para
suportar o trĂĄfego de projecto, o qual Ă© composto por diferentes tipos de veĂculos com diferentes tipos de eixos e rodas,
sendo a carga total do veĂculo função de vĂĄrios factores. Alguns destes veĂculos pesados causam maiores degradaçÔes nos
pavimentos devido ao tipo de suspensão, tipo de pneu, localização dos eixos ou pressão de enchimento dos pneus. No
entanto, em termos de dimensionamento, esta diversidade de veĂculos Ă© considerada de modo semelhante pela atribuição de
uma ĂĄrea onde Ă© aplicada a carga dos veĂculos, verificando-se que a configuração desta ĂĄrea nĂŁo representa correctamente o
contacto dos pneus com o pavimento.
Deste modo, este trabalho pretende estudar a acção dos veĂculos pesados na avaliação do comportamento do pavimento
considerando a carga dos veĂculos pesados modelada de forma mais aproximada da real, nomeadamente, considerando os
sulcos dos pneus e a variação não uniforme da pressão de contacto pneu-pavimento. Assim, neste trabalho é modelado um
pavimento representativo da rede rodoviåria no qual são aplicadas diferentes configuraçÔes de carga sendo obtido o estado
de tensão/deformação instalado no pavimento. A modelação numérica do pavimento foi realizada utilizando um modelo
elĂĄstico linear de elementos finitos em trĂȘs dimensĂ”es desenvolvido para analisar a influĂȘncia de um veĂculo pesado
possuindo uma configuração de pneus duplos com 245mm de largura. Neste estudo foram consideradas duas configuraçÔes
de distribuição de pressÔes de contacto, em que foram considerados as seguintes pressÔes totais: 700, 800, 900, 1200 e
1500 kPa. Com base nos resultados obtidos Ă© possĂvel observar as diferenças significativas no estado de tensĂŁo/deformação
do pavimento, principalmente Ă superfĂcie a qual poderĂĄ ser responsĂĄvel pelo fendilhamento com origem Ă superfĂcie.Road pavements have been designed to support the design traffic which is composed by different type of vehicles with
different axle configurations, load magnitudes, wheel types and tire inflation pressures. Traffic loads are the major source
of pavement damage by causing fatigue, which leads to cracking and permanent deformation. Heavy vehicles do not cause
equal damage because the differences in wheel loads, number and location of axles, types of suspensions and tires.
Furthermore, the damage is specific to the pavement properties, operating conditions and environmental factors. This
research proposes a model for predicting the mechanical behaviour of flexible pavement subjected to heavy load vehicle
with dual-tire configuration using a numerical simulation. An elastic finite element model in three dimensions (3D) was
developed to analyze the influence of a heavy vehicle with dual-tire configuration featuring 245 mm wide on each tire. This
research studied three configurations of contact pressure considering the following pressures: 700, 800, 900, 1200 and 1500
kPa. The results show that it is possible to observe significant differences in the state of stress/strain on the pavement,
especially on the surface which is responsible for cracking originating at the surface. The simulation model present here
will be useful for future pavement design and material selection
Transversely projective foliations on surfaces: existence of normal forms and prescription of the monodromy
We introduce a notion of normal form for transversely projective structures
of singular foliations on complex manifolds. Our first main result says that
this normal form exists and is unique when ambient space is two-dimensional.
From this result one obtains a natural way to produce invariants for
transversely projective foliations on surfaces. Our second main result says
that on projective surfaces one can construct singular transversely projective
foliations with prescribed monodromy
Genetic diversity of two Portuguese populations of the pullet carpet shell Venerupis senegalensis, based on RAPD markers: contribution to a sustainable restocking program
The pullet carpet shell Venerupis senegalensis
(=V. pullastra) is a commercially important species in
Portugal, Spain, France, and Italy. In Portugal, this species
was once abundant in the Ria Formosa (southern Portugal
Recycling of porous bituminous mixtures
Once flexible pavements reach minimal bearing capacity, their structural rehabilitation is
normally undertaken us ing bituminous mixture overlay. The number of layers and the
thickness depend of the existing quality of the pavement and of the required quality
determined by the rehabilitation program for a next life period.
The rehabilitation of a pavement with a porous bituminous mixture wearing course is usually
undertaken without any treatment to increase its bearing capacity.
The bearing capacity of this type of mixture can be increased by the use of a grout to fill its
voids, increasing its resistance. The new material is produced by spreading a grout over the
pavement surface, with the help of rubber scrapers, penetrating the voids of the mixture until
it reaches the bottom of the layer. The properties of this material are dependent on void
connectivity, in order to allow the grout to flow through them. An adequate viscosity of the
grout is essential so as to fill the voids completely.
The objective of this paper is to analyse the recycling of porous bituminous mixtures,
studying the grout and evaluating new mixture properties in terms of stiffness, fatigue life and
permanent deformation
A model for pavement temperature prediction
A finite element model has been developed to calculate the temperature of a pavement located in the Northeast
of Portugal. The goal of the case study presented in this paper is the validation of this model. Input data to the
model are the hourly values for solar radiation and temperature, and mean daily values of wind speed obtained
from a meteorological station. The thermal response of a multilayered pavement structure is modeled using a
transient thermal analysis for four months time-period (December 2003 - April 2004) and the analysis was
initiated with the full depth constant initial temperature obtained from field measurements. During these four
months, pavement temperature was measured at a new pavement section, located at IP4 main road, near
Bragança, in the north of Portugal. At that location, seven thermocouples were installed in the AC layers, at
seven different depths. These pavement data was used to validate this simulation model, by comparing model
calculated data with measured pavement temperatures.
As conclusion, the 3-D finite-element analysis proved to be an interesting tool to simulate the transient behavior
of asphalt concrete pavements. The suggested simulation model can predict the pavement temperature at
different levels of bituminous layers with a good accuracy.Instituto de Estradas de Portugal, Direcção de Bragança
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