Engenharia Mecânica
BACTERIAL GROWTH SCREENED BY RHEOLOGY
Portela, R.a; Pereira, M.b; Sobral, R.G.a,c; Almeida, P.L.b,d; Leal, C.R.b,d
aLaboratory of Molecular Genetics, Instituto de Tecnologia Química e Biológica,
Universidade Nova de Lisboa, 2780 Oeiras, Portugal
bISEL, Inst Super Engn Lisboa, Secção Autónoma de Física, 1959-007 Lisbon, Portugal cCentro de Recursos Microbiológicos, DCV, Faculdade de Ciências e Tecnologia,
Universidade Nova de Lisboa, Quinta da Torre, 2829-516 Caparica, Portugal
dCENIMAT/I3N, Faculdade Ciências e Tecnologia, Universidade Nova de Lisboa, Campus
da Caparica, 2829-516 Caparica, Portugal
Fonte: Rheology Trends: from nano to macro systems, Pages 45-47, 2011
Conferência: IBERO2011 - Conferência Ibero-Americana de Reologia, Setembro 2011 Editor: M.T. Cidade, I.M.N. Sousa e J.M. Franco Eds
ISBN: 978-972-8669-50-8
Tipo de Documento: Proceeding Paper
Resumo: The 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. We chose as a study model a methicillin resistant S. aureus (MRSA) strain and followed its growth pattern in complex medium in the absence and in the presence of a sub-inhibitory concentration of oxacillin, a clinical relevant β-lactam antibiotic. Simple shear flow experiments were applied to aliquots of the bacterial cultures in the beginning of the growth procedure and at the same time points at which the optical density and cell viable counts were determined. The rheological measurements allowed to characterize the viscosity in function of the shear rate and to compare the viscosity for different growth time, at fixed shear rates.
CELLULOSE LIQUID CRYSTALLINE DEFECTS PROBED BY MRI Canejo, J.P.a; Feio, G.a; Almeida, P.L.a,b; Terentjev, E.M.c; Godinho, M.H.a
aDepartamento de Ciência dos Materiais and CENIMAT/I3N, Faculdade de Ciências e
Tecnologia, Universidade Nova de Lisboa, P-2829-516 Caparica, Portugal
bISEL, Inst Super Engn Lisboa, P-1959-007 Lisbon, Portugal
cCavendish Laboratory, University of Cambridge, J.J. Thomson Avenue, Cambridge CB3
OHE, U.K.
Fonte: Proceedings of ECLC 2011 - 11th European Conference on Liquid Crystals 2011 Conferência: ECLC 2011 - 11th European Conference on Liquid Crystals 2011, Maribor, Eslovénia, 2011
Tipo de Documento: Proceeding Paper
found in biological systems, such as plant tendrils, curled hair or snail shells [1]. Such conformational effects can also be observed in fibers obtained by electrospinning of cellulosic liquid crystalline solutions [2]. Liquid crystalline phases of cellulose derivatives can exhibit strongly colored circularly polarized reflections as a function of solvent concentration. These are associated with cholesteric ordering that arises because the cellulose molecules are chiral, that is, lack of inversion symmetry. However, previous studies indicate that fibers produced from right-handed cholesteric cellulosic solutions could wind with either left- or right-handed helicity, which rules out a direct relationship with the chirality of cellulose and the underlying cholesteric mesophase [2]. A qualitative explanation of creation of helices with opposite (or “wrong”) handedness can be understood if a filament has a given nonvanishing intrinsic curvature which is provided by an asymmetric deformation of some nature.
In order to investigate the origin of the intrinsic curvature found in the cellulosic fibers morphological and structural features are investigated in this work by means of magnetic resonance imaging (MRI). MRI analysis allowed imaging of characteristic structure at chosen filament cross-section along the capillary tube. Isotropic solutions confined in the capillary, which generate straight fibers on extrusion, showed a homogeneous symmetric cross-section structure (Figure 1 A and B), implying that the averaging of different structural features would maintain a straight fiber conformation. Confined solutions of cellulose in the cholesteric liquid- crystal phase, which generate curved fibers, showed a heterogeneous structure in cross-section with the hard “island” predominantly located closest to the tube walls and never in the middle of the tube. The off- axis position of the hard “islands” varies along the tube (Figure 1 C and D). MRI measurements indicate that from one layer to the following the hard objects rotate (in figure an anticlockwise rotation can be seen). The intrinsic curvature of the cellulosic electrospun fibers will be discussed in terms of defect disclinations lines which are present when the fibers were prepared from liquid crystalline solutions.
CYCLIC DEFORMATION OF BIDISPERSE TWO-DIMENSIONAL FOAMS Vaz, M.F.a; Cox, S. J.b; Teixeira, P.I.C.c,d
aUniv Tecn Lisboa, Inst Super Tecn, Inst Ciencia & Engn Mat Superficies, P-1049001
Lisbon, Portugal
bAberystwyth Univ, Inst Math & Phys, Aberystwyth SY23 3BZ, Dyfed, Wales cISEL, Inst Super Engn Lisboa, P-1959-007 Lisbon, Portugal
dUniv Lisbon, Ctr Fis Teor & Computac, 1649-003 Lisbon, Portugal
Fonte: Philosophical Magazine, Volume 91, Issue: 34, Pages 4345-4356, 2011 ISSN: 1478-6435
DOI: 10.1080/14786435.2011.620995 Editor: Taylor & Francis Ltd
Tipo de Documento: Article
Área Científica: Materials Science; Mechanics; Metallurgy & Metallurgical Engineering; Physics
Resumo: In-plane deformation of foams was studied experimentally by subjecting bidisperse foams to cycles of traction and compression at a prescribed rate. Each foam contained bubbles of two sizes with given area ratio and one of three initial arrangements: sorted perpendicular to the axis of deformation (iso-strain), sorted parallel to the axis of deformation (iso-stress), or randomly mixed. Image analysis was used to measure the characteristics of the foams,
including the number of edges separating small from large bubbles N-sl, the perimeter (surface energy), the distribution of the number of sides of the bubbles, and the topological disorder mu(2)(N).
Foams that were initially mixed were found to remain mixed after the deformation. The response of sorted foams, however, depended on the initial geometry, including the area fraction of small bubbles and the total number of bubbles. For a given experiment we found that (i) the perimeter of a sorted foam varied little; (ii) each foam tended towards a mixed state, measured through the saturation of N-sl; and (iii) the topological disorder mu(2)(N) increased up to an "equilibrium" value. The results of different experiments showed that (i) the change in disorder, Delta mu(2)(N), decreased with the area fraction of small bubbles under iso-strain, but was independent of it under iso-stress; and (ii) Delta mu(2)(N) increased with Delta N-sl under iso-strain, but was again independent of it under iso-stress. We offer explanations for these effects in terms of elementary topological processes induced by the deformations that occur at the bubble scale.
COMPACT STARS AND MAGNETIZED CFL MATTER Martinez, A.P.a; Felipe, R.G.b,c; Paret, D.M.
aInst Cibernet Matemat & Fis ICIMAF, Havana 10400, Cuba
bISEL, Inst Super Engn Lisboa, P-1959-007 Lisbon, Portugal
cUniv Tecn Lisboa, Inst Super Tecn, Ctr Fis Teor Particulas, P-1049-001 Lisbon, Portugal dUniv La Habana, Fac Fis, Havana 10400, Cuba
Fonte: International Journal of Modern Physics E-Nuclear Physics, Volume 20, Pages 84-92, Dec 2011
ISSN: 0218-3013
DOI: 10.1142/S0218301311040645
Editor: World Scientific Publ CO PTE LTD Tipo de Documento: Article
Área Científica: Physics
Resumo: The stability of the color flavor locked phase in the presence of a strong magnetic field is investigated within the phenomenological MIT bag model. It is found that the minimum value of the energy per baryon in a color flavor locked state at vanishing pressure is lower than the corresponding one for unpaired magnetized strange quark matter and, as the magnetic field increases, the energy per baryon decreases. This implies that magnetized color flavor locked matter is more stable and could become the ground state inside neutron stars. The anisotropy of the pressures is discussed. The mass-radius relation for such stars is also studied.