ISEL - Física - Comunicações
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- Experimental results on electrorheology of liquid crystalline polymer solutionsPublication . Neves, S.; Leal, Catarina R.; Cidade, M. T.The electrorheological (ER) effect is known as the enhancement of the apparent viscosity upon apphcation of an external electric field. Suspensions of polarizable particles in non-conducting solvents are the most studied electrorheological fluids, however, liquid crystalline materials may also present ER effect as long as their dielectric anisotropy is positive. In the liquid crystalline state of a positive dielectric anisotropy, the application of the electric field makes the director align perpendicular to the fiow direction, thus increasing the apparent viscosity. In this work results of two liquid crystalline polymer solutions, acetoxypropylcellulose (APC) in dimethylacetamide (DMAc) and poly-y-benzyl-L-glutamate (PBLG) in 1,4-dioxane, presenting opposite behavior upon application of the electric field, will be presented. APC/DMAc (negative dielectric anisotropy) presents a decrease of the apparent viscosity upon application of the electric field, as expected, while PBLG/l,4-dioxane (positive dielectric anisotropy) presents the opposite behavior. For this last solution we will present the shear fiow curves for different electric fields in function of polymer molecular weight and solution concentration.
- Following micelles with rheo-NMRPublication . Almeida, Pedro L.; Feio, G.; Pereira, M.; Scheven, U.; R. Leal, CatarinaThe rheological behaviour of the micellar system Cetyltrimethylammonium Bromide (CTAB)/Sodium Salicylate (NaSal) in water is highly dependent on the components concentration and temperature. The surfactant CTAB forms spherical micelles in water above a certain concentration (CD), which upon addition of a salt (NaSal) elongate to form entangled wormlike structures, also known as “living polymers”. The viscosity of wormlike micelles solutions increases dramatically with the increase of salt concentration (CS), changing from quasi-newtonian to a viscoelastic behaviour in the gel-like, highly entangled state. Such rich rheological behaviour has already been characterized by some of the authors and in the literature, e.g., [1-3]. The rheological behaviour of CTAB/NaSal aqueous solutions in the regime CD/Cs>1 are presented in this work. Furthermore, we followed the rheological behaviour of these solutions by a rheo-NMR technique, allowing for an insight of “what happens” inside the sample during the application of a shear flow. To achieve this goal we performed quantitative flow rate measurements using velocity NMR mapping in the rheo-NMR experiments, developed by Callaghan [4]. Attempts to characterize the velocity profile in this system has already been described [5] using an optical-shear flow experimental setup, although for solutions with CD/Cs<1, where the surfactant [CTAB] has always a smaller concentration than the salt [NaSal].
- Bacterial growth screened by rheologyPublication . Portela, Raquel; Pereira, M.; Sobral, Rita; Almeida, Pedro L.; R. Leal, CatarinaThe study of bacterial growth is a challenging field since it aims to describe the behaviour of microorganisms under different physical or chemical conditions. Bacterial growth as a biofilm is of particular interest as these gel-like structures are detrimental for all applications where “clean” surfaces are most important, and are related to failure of infection treatment, food spoilage and oil pipeline contamination, amongst others. In the literature one can find several works concerning the characterization of the mechanical behaviour of bacterial biofilms, although mostly are implemented over solid biofilms, as they appear in real situations [1-3], to study the adhesion properties in surfaces. In this work we applied a different technique to monitor the growth rate of a coccoid shaped bacterial species, the human pathogen Staphylococcus aureus.
- Deep structure of crust and mantle beneath Iberia and Western Mediterranean from P and S Receiver functions and SKS WaveformsPublication . Morais, I.; Vinnik, Lev; Silveira, Graça; Matias, L.; Kieselev, S.We have conducted a P and S receiver functions [PRFs and SRFs] analysis for 19 seismic stations on the Iberia and western Mediterranean. In the transition zone [TZ] the PRFs analysis reveals a band [from Gibraltar to Balearic] increased by 10-20 km relative to the standard 250 km. The TZ thickness variations are strongly correlated with the P660s times in PRFs. We interpret the variable depth of the 660-km discontinuity as an effect of subduction. Over the anomalous TZ we found a reduced velocity zone in the upper mantle. Joint inversion of PRFs and SRFs reveals a subcrustal high S velocity lid and an underlying LVZ. A reduction of the S velocity in the LVZ is less than 10%. The Gutenberg discontinuity is located at 65±5 km, but in several models sampling the Mediterranean, the lid is missing or its thickness is reduced to ~30 km. In the Gibraltar and North Africa this boundary is located at ~100 km. The lid Vp/Vs beneath Betics is reduced relative to the standard 1.8. Another evidence of the Vp/Vs anomaly is provided by S410p phase late arrivals in the SRFs. The azimuthal anisotropy analysis with a new technology was conducted at 5 stations and at 2 groups of stations. The fast direction in the uppermost mantle layer is ~90º in Iberian Massif. In Balearic is in the azimuth of ~120º. At a depth of ~60 km the direction becomes 90º. Anisotropy in the upper layer can be interpreted as frozen, whereas anisotropy in the lower layer is active, corresponding to the present-day or recent flow. The effect of the asthenosphere in the SKS splitting is much larger than the effect of the subcrustal lithosphere.
- C3G - A portuguese collaboration for geology, geodesy and geophysicsPublication . Caldeira, Bruno; Caldeira, R.; Carrilho, F.; Carvalho, J.; Custódio, S.; Dias, Nuno; Fernandes, R.; Moreira, M.; Seixas, T.; Silva, M.; Quental, L.; Silveira, GraçaPortugal joined the effort to create the EPOS infrastructure in 2008, and it became immediately apparent that a national network of Earth Sciences infrastructures was required to participate in the initiative. At that time, FCT was promoting the creation of a national infrastructure called RNG - Rede Nacional de Geofísica (National Geophysics Network). A memorandum of understanding had been agreed upon, and it seemed therefore straightforward to use RNG (enlarged to include relevant participants that were not RNG members) as the Portuguese partner to EPOS-PP. However, at the time of signature of the EPOS-PP contract with the European Commission (November 2010), RNG had not gained formal identity yet, and IST (one of the participants) signed the grant agreement on behalf of the Portuguese consortium. During 2011 no progress was made towards the formal creation of RNG, and the composition of the network – based on proposals submitted to a call issued in 2002 – had by then become obsolete. On February 2012, the EPOS national contact point was mandated by the representatives of the participating national infrastructures to request from FCT the recognition of a new consortium - C3G, Collaboratory for Geology, Geodesy and Geophysics - as the Portuguese partner to EPOS-PP. This request was supported by formal letters from the following institutions: ‐ LNEG. Laboratório Nacional de Energia e Geologia (National Geological Survey); ‐ IGP ‐ Instituto Geográfico Português (National Geographic Institute); ‐ IDL, Instituto Dom Luiz – Laboratório Associado ‐ CGE, Centro de Geofísica de Évora; ‐ FCTUC, Faculdade de Ciências e Tecnologia da Universidade de Coimbra; ‐ Instituto Superior de Engenharia de Lisboa; ‐ Instituto Superior Técnico; ‐ Universidade da Beira Interior. While Instituto de Meteorologia (Meteorological Institute, in charge of the national seismographic network) actively supports the national participation in EPOS, a letter of support was not feasible in view of the organic changes underway at the time. C3G aims at the integration and coordination, at national level, of existing Earth Sciences infrastructures, namely: ‐ seismic and geodetic networks (IM, IST, IDL, CGE); ‐ rock physics laboratories (ISEL); ‐ geophysical laboratories dedicated to natural resources and environmental studies; ‐ geological and geophysical data repositories; ‐ facilities for data storage and computing resources. The C3G - Collaboratory for Geology, Geodesy and Geophysics will be coordinated by Universidade da Beira Interior, whose Department of Informatics will host the C3G infrastructure.
- Ultrafast laser texturing of Ti-6Al-4V surfaces for biomedical applicationsPublication . Cunha, Alexandre; Oliveira, Vitor; Serro, Ana Paula; Zouani, Omar El-Farouk; Almeida, Amélia; Durrieu, Marie-Christine; Vilar, RuiBy controlling processing parameters such as the average fluence, number of laser pulses and beam polarization direction, different types of multiscale surface textures were produced on Ti-6Al-4V surfaces by ultrafast laser processing. The samples were textured in ambient atmosphere using an Yb:KYW chirped-pulse-regenerative amplification laser with a wavelength of 1030 nm and pulse duration of 500 fs. The wetting of simulated biological fluids as well as the human mesenchymal stem cells (hMSCs) behavior were assessed. Three types of textured surfaces were tested, consisting of: (1) Laser-Induced Periodic Surface Structures-LIPSS; (2) nanopillars-like structures; and (3) LIPSS overlapped to microcolumns. The laser textured surfaces present hydrophilic behavior and high affinity for HBSS (Hank's balanced salt solution). Cell spreading and adhesion strength is reduced by the laser nanotextures as compared to a polished control surface. Cytoskeleton stretching and stress fibers were clearly observed on LIPSS while significant filopodia formation was verified on nanopillars. There was no cell proliferation on the laser nanotextured surfaces. Ultrafast laser texturing of Ti-6Al-4V surfaces is an efficient technique for increasing surface wettability, and is potentially useful as a technique to control the behavior of hMSCs by changing the cytoskeleton shape, FAPs distribution and area, and proliferation.
- Structural, electrical and magnetic studies of Co:SnO2 and (Co,Mo):SnO2 films prepared by pulsed laser depositionPublication . Dalui, S.; Rout, S.; Silvestre, António Jorge; Lavareda, G.; Pereira, L. C. J.; Brogueira, P.; Conde, O.Here we report on the structural, optical, electrical and magnetic properties of Co-doped and (Co,Mo)-codoped SnO2 thin films deposited on r-cut sapphire substrates by pulsed laser deposition. Substrate temperature during deposition was kept at 500 degrees C. X-ray diffraction analysis showed that the undoped and doped films are crystalline with predominant orientation along the [1 0 1] direction regardless of the doping concentration and doping element. Optical studies revealed that the presence of Mo reverts the blue shift trend observed for the Co-doped films. For the Co and Mo doping concentrations studied, the incorporation of Mo did not contribute to increase the conductivity of the films or to enhance the ferromagnetic order of the Co-doped films. (C) 2012 Elsevier B.V. All rights reserved.
- Staphylococcus aureus strains rheology during growthPublication . Portela, Raquel; Almeida, Pedro L.; Patricio, Pedro; M.T., Cidade; Sobral, Rita; R. Leal, CatarinaThe study of the mechanical properties of living bacteria in a liquid rich medium, environment commonly used in laboratorial settings, opens a new perspective on the bacterial physiology and behaviour during population growth. In this work, the human pathogen Staphylococcus aureus was used as a study model due to its coccoid shape and regular morphology: MRSA strain COL [1] and its mutant strain RUSAL9 [2], which presents a deficient daughter-cell separation mechanism. Cultures were grown under a mechanical stress solicitation in parallel with optical density monitorization. Complex viscoelastic behaviour was revealed by these bacterial systems [3]. In particular the shear viscosity measurement during growth time, for a constant shear rate, showed an unexpected behaviour that cannot be observed by common optical experimental techniques.
- Cell necklaces behave as a soft glassy materialPublication . Franco, Jose M.; Patricio, Pedro; Almeida, Pedro L.; Portela, Raquel; Sobral, Rita; R. Leal, CatarinaPreviously we have reported a complex and rich viscoelastic behavior observed during the Planktonic growth of S. aureus strain COL1. In particular, in stationary shear flow, the viscosity Keeps increasing during the exponential phase and returns close to its initial value for the late phase of growth, where the bactéria population stabilizes. In oscillatory flow, the elastic and viscous moduli exhibit power--‐law behaviors whose exponentes are dependente on the bacteria growth stage. These power--‐law dependencies of G’ and G’’ match a Soft Glassy Material behavior. To describe this observed behavior, we have hypothesized a microscopic model considering the formation of a dynamic web--‐like structure, where percolation phenomena can occur, depending on growth stage and cell density. In this communication we describe the formation of these web--‐like structures, resembling cell necklaces at a specific time interval during bacterial growth. These findings were obtained by combining the previous data with new measurements performed in a rheometer with real--‐time image acquisition.
- Living S. aureus bacteria rheologyPublication . Portela, R.; Franco, J. M.; Patricio, Pedro; Almeida, Pedro L.; Sobral, R. G.; Leal, Catarina R.The rheological characterization of Staphylococcus aureus cultures has shown a complex and rich viscoelastic behavior, during the bacteria population growth, when subject to a shear flow [1,2]. In particular, in stationary shear flow, the viscosity keeps increasing during the exponential phase reaching a maximum value (∼30x the initial value) after which it drops and returns close to its initial value in the stationary phase of growth, where the cell number of the bacterial population stabilizes. These behaviors can be associated with cell density and aggregation patterns that are developed during culture growth, showing a collective behavior. This behavior has no counterpart in the bacterial growth curve obtained by optical density monitorization (OD620nm and cfus/ml measurements). In oscillatory flow, the elastic and viscous moduli exhibit power-law behaviors whose exponents are dependent on the bacteria growth stage. These power-law dependencies of G’ and G’’ are in accordance with the Soft Glassy Material model [3], given by: G’~ ωx and G’’~ ωx To describe the observed behavior, a microscopic model considering the formation of a dynamic web-like structure was hypothesized [1], where percolation phenomena can occur, depending on the growth stage and on cell density. Recently, using real-time image rheology was possible to visualize the aggregation process associated with these dramatic changes in the viscoelastic behavior. In particular, the formation of web-like structures, at a specific time interval during the exponential phase of the bacteria growth and the cell sedimentation and subsequent enlargement of bacterial aggregates in the passage to the stationary phase of growth. These findings were essential to corroborate the microscopic model previously proposed and the main results of this study are compiled and presented in this work, see Fig.1.