593 research outputs found
Rheological description at the minimum gelling conditions of kappa-carrageenan/locust bean gum systems
Poster presentation at ‘Gums and Stabilisers for the Food Industry-7’, July, 1993Kappa-carrageenan/locust bean gum interactions at the minimum gelling concentration have been studied by dynamic and viscosity measurements at 15°C. Both rheological methods used have been shown to be complementary. The existence of a weak network structure exhibiting thixotropic behaviour has been observed. The formation of the weak network is discussed
influence of the mechanics of escape on the instability of von mises truss and its control
Abstract The elastic von Mises truss model is a prototype for bi-stable structures. It allows a deep understanding of the static and dynamic buckling of several planar and spatial truss systems and shallow lattice shell structures, including the geodesic dome, and has a theoretical and practical interest. This structure has a highly nonlinear response in the presence of static and dynamic loads. The geometric nonlinearity is particularly significant even at low load levels when this structure is shallow. This paper presents an exact nonlinear formulation, which is used to investigate the mechanics of erosion and escape from the safe pre-buckling well. As the static pre-load increases, the probability of escape increases in a nonlinear manner. Permanent and transient escapes, as well as the influence of random noise, on the dynamic buckling load are investigated. To increase the load carrying capacity, a method for controlling the global nonlinear dynamics for the elastic von Mises truss is employed. The control method consists of the (optimal) elimination of homoclinic intersection by properly adding superharmonic terms to a given harmonic excitation. Permanent and transient basins of attraction are obtained. The results highlight the complex nonlinear dynamics of this class of structures and the effectiveness of the control method in increasing the integrity of the basins of attraction of the system and its practical safety
Tungsten oxide nanoparticles prepared with soft templating methods
Fundação para a Ciência e a Tecnologia (FCT
Elastoplastic analysis of plane steel frames under dynamic loading
Knowledge of structural behavior is essential for designing lighter constructions without affecting their safety and quality standards. Lack of levels and characteristics of dynamic response, for example, can lead to system failure during repetitive loading application, due to the accumulation of structural damage. Thus, it becomes necessary to use more complex theories, such as nonlinear formulations, avoiding simplifications in the process of analysis/design.
Plastic analysis of steel structures enhances several benefits compared to the elastic’s, because one of the most important characteristics of this material, the ductility - ability to withstand large deformations before breaking - is fully considered. This allows for force redistribution after the yielding limit of some structural member’s cross section has been achieved. This property also promotes the absorption of energy, which becomes extremely important in structures subjected to seismic excitation
Implications of flexible spacer rotational processes on the liquid crystal behavior of 4,5-dihydroisoxazole benzoate dimers
The synthesis of some novel non-symmetric liquid crystal dimers, {3-[4-(octyloxyphenyl)]-4,5-dihydroisoxazol-5-yl}alkyl 4-(decyloxy)benzoates (5a–d) and 4-{3-[4-(octyloxyphenyl)]-4,5-dihydroisoxazol-5-yl}alkyl 4-{[6-(octyloxy)naphthalen-2-yl]ethynyl}benzoate (9a–d), are reported. The liquid-crystalline properties, theoretical calculations based on the conformational aspects of the flexible alkyl spacer and X-ray experiments are discussed. The syntheses of the key intermediates, 2-{3-[4-(octyloxy)phenyl]-4,5-dihydroisoxazol-5-yl}alkanol (3a–d), presenting the flexible alkyl spacer were achieved through [3+2] cycloaddition reactions between nitrile oxides, which were generated in situ by oxidation of the respective aromatic oximes, and dipolarophile alkenols (CH2[double bond, length as m-dash]CH(CH2)nOH, n = 1, 2, 3, and 4). The benzoates 5a–d were synthesized through esterification of 3a–d and p-n-decyloxybenzoic acid (4). The esters 9a–d were synthesized through derivatization of isoxazolines 3a–d into 4-{3-[4-(octyloxyphenyl)]-4,5-dihydroisoxazol-5-yl}alkyl 4-bromobenzoate (7a–d) followed by a Sonogashira reaction with 2-ethynyl-6-octyloxynaphthalene (8). 5a and 5b showed a monotropic smectic C phase. 9a/c displayed a enantiotropic nematic (N) mesophase, whereas 9b/d showed a monotropic nematic mesophase. No mesophase was observed for 7a–d. An odd–even effect was observed for 5a–d and 9a–d associated with the crystal to isotropic phase transition and crystal to nematic phase, respectively, as the length of the spacer was increased from 1 to 4 carbon atoms. The transitional properties were higher for odd-numbered members (n = 1 and 3) for all of the series studied. The X-ray data of compounds 5a and 5b are in agreement with polarizing optical microscopy observations with the assignment of an SmC mesophase. Density functional theory calculations using the B3LYP hybrid functional with the level 6-311G(d,p) basis set were performed for molecules 5a–d to correlate the conformation of the flexible spacer and the transitional properties. The conformational analysis showed that the most stable conformation for 5a–d is one where all of the carbon atoms of the flexible spacer are orientated at 180° (antiperiplanar orientation) except for 5a because the spacer is too short. The odd-numbered members have a more bent shape and are less elongated molecules than the even-numbered members. Thus, mesomorphic behavior is dictated by the conformational constraint imposed by the flexible spacer on the mesogenic groups
Synthesis and photophysical properties of side-chain chlorinated 5,9-diaminobenzo[a]phenoxazinium salts
Fundação para a Ciência e Tecnologia (Portugal). National Program for Scientific Re-equipment, contract REDE/1517/RMN/2005 with funds from POCI 2010 (FEDER) and FCT
DNA fluorescence probes based on side-chain chlorinated benzo[a]phenoxazinium chlorides
Several side chain chlorinated benzo[a]phenoxazinium chlorides functionalized with various types of terminals at the 5- and 9-amino positions of the heteroaromatic ring were used in photophysical studies with DNA. It was found that the functionalised terminal has a dramatic influence on the type of interaction with the amino group at the 9-amino position greatly promoting intercalation.Thanks are due to Fundação para a Ciência e Tecnologia (Portugal) for its financial support of a BPD to B. R. Raju (SFRH/BPD/62881/2009), CQUM and CFUM
Scattering of graphene plasmons at abrupt interfaces: an analytic and numeric study
We discuss the scattering of graphene surface plasmon-polaritons (SPPs) at an
interface between two semi-infinite graphene sheets with different doping
levels and/or different underlying dielectric substrates. We take into account
retardation effects and the emission of free radiation in the scattering
process. We derive approximate analytic expressions for the reflection and the
transmission coefficients of the SPPs as well as the same quantities for the
emitted free radiation. We show that the scattering problem can be recast as a
Fredholm equation of the second kind. Such equation can then be solved by a
series expansion, with the first term of the series correspond to our
approximated analytical solution for the reflection and transmission
amplitudes. We have found that almost no free radiation is emitted in the
scattering process and that under typical experimental conditions the
back-scattered SPP transports very little energy. This work provides a
theoretical description of graphene plasmon scattering at an interface between
distinct Fermi levels which could be relevant for the realization of plasmonic
circuitry elements such as plasmonic lenses or reflectors, and for controlling
plasmon propagation by modulating the potential landscape of graphene.A.J.C. acknowledges the scholarship from the Brazilian agency CNPq (Conselho Nacional de Desenvolvimento Cientifico e Tecnologico). B.A., Y.V.B., and N.M.R.P. acknowledge support from the European Commission through the project "Graphene-Driven Revolutions in ICT and Beyond" (Ref. No. 696656). P.A.D.G. acknowledges financial support from the VILLUM Fonden (Grant No. 16498), and from the Center for Nanostructured Graphene sponsored by the Danish National Research Foundation (project DNRF103). N.M.R.P. also acknowledges the hospitality of the MackGraphe Center, at Mackenzie Presbyterian University, where this work has started, the projects Fapesp 2012/50259-8 and 2016/11814-7, and the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Financing UID/FIS/04650/2013.info:eu-repo/semantics/submittedVersio
Avaliação em laboratório do comportamento térmico de soluções construtivas em madeira
O presente trabalho apresenta a avaliação do comportamento térmico de quatro soluções
construtivas integralmente em madeira, recorrendo à previsão e análise experimental do seu
desempenho térmico. Foram avaliadas quatro soluções construtivas representativas do mercado, três
delas tendo por base troncos de madeira e uma outra do tipo entramado de madeira.
As principais tipologias de habitações que se encontram no mercado são, essencialmente casas em
painel e em troncos de madeira tratada. As casas de troncos possuem um aspeto mais rústico sendo
usualmente utilizadas em ambientes de montanha, estas recorrem a ligações metálicas entre troncos
e entre paredes, podendo ou não utilizar isolamento térmico colocado no interior da parede. As casas
em painel são, geralmente, do tipo modular, o que permite uma rápida execução e posterior
expansão. Aliadas a uma arquitetura moderna e cuidada, são difÃceis de distinguir das casas em
alvenaria.
O objetivo central do trabalho foi o de aumentar o conhecimento cientÃfico e técnico relativo ao
comportamento térmico das soluções construtivas em madeira, colmatando a ausência de valores
relativos ao coeficiente de transmissão térmica à disposição de técnicos e investigadores. Foi
analisado o desempenho térmico destas soluções construtivas segundo a regulamentação térmica
atual (RCCTE) [1], posteriormente estes resultados foram comparados com as soluções de
construções mais comuns em Portugal.
A análise dos resultados experimentais obtidos permitiu verificar que os coeficientes de transmissão
térmica destas soluções cumprem os requisitos mÃnimos. Sendo a solução com estrutura leve de
madeira revestida com aglomerados e preenchida com lã-de-rocha a que apresenta melhor
desempenho. Comparativamente com os sistemas construtivos mais comuns de paredes de alvenaria
as soluções construtivas com estrutura de madeira apresentam um comportamento térmico superiorRusticas
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