University of Lisbon

About: University of Lisbon is a education organization based out in Lisbon, Lisboa, Portugal. It is known for research contribution in the topics: Population & European union. The organization has 19122 authors who have published 48503 publications receiving 1102623 citations. The organization is also known as: Universidade de Lisboa & Lisbon University.

Diversity in bacterial lysis systems: bacteriophages show the way

Abstract: Bacteriophages have developed multiple host cell lysis strategies to promote release of descendant virions from infected bacteria. This review is focused on the lysis mechanisms employed by tailed double-stranded DNA bacteriophages, where new developments have recently emerged. These phages seem to use a least common denominator to induce lysis, the so-called holin-endolysin dyad. Endolysins are cell wall-degrading enzymes whereas holins form ‘holes’ in the cytoplasmic membrane at a precise scheduled time. The latter function was long viewed as essential to provide a pathway for endolysin escape to the cell wall. However, recent studies have shown that phages can also exploit the host cell secretion machinery to deliver endolysins to their target and subvert the bacterial autolytic arsenal to effectively accomplish lysis. In these systems the membrane-depolarizing holin function still seems to be essential to activate secreted endolysins. New lysis players have also been uncovered that promote degradation of particular bacterial cell envelopes, such as that of mycobacteria.

Linearized stability analysis of thin-shell wormholes with a cosmological constant

Abstract: Spherically symmetric thin-shell wormholes in the presence of a cosmological constant are constructed applying the cut-and-paste technique implemented by Visser. Using the Darmois–Israel formalism the surface stresses, which are concentrated at the wormhole throat, are determined. This construction allows us to apply a dynamical analysis to the throat, considering linearized radial perturbations around static solutions. For a large positive cosmological constant, i.e., for the Schwarzschild–de Sitter solution, the region of stability is significantly increased, relatively to the null cosmological constant case, analysed by Poisson and Visser. With a negative cosmological constant, i.e., the Schwarzschild–anti de Sitter solution, the region of stability is decreased. In particular, considering static solutions with a generic cosmological constant, the weak and dominant energy conditions are violated, while for a0 ≤ 3M the null and strong energy conditions are satisfied. The surface pressure of the static solution is strictly positive for the Schwarzschild and Schwarzschild–anti de Sitter spacetimes, but takes negative values, assuming a surface tension in the Schwarzschild–de Sitter solution, for high values of the cosmological constant and the wormhole throat radius.

A review of the distribution of hydrothermal vent communities along the northern Mid-Atlantic Ridge: dispersal vs. environmental controls

Abstract: Until 1985, seven vent fields were described from the Mid-Atlantic Ridge (MAR). An eighth field, Mount Saldanha (36° N), discovered in 1998, showed unusual geological and biological settings. Vent sites on the MAR exhibit varied environmental conditions, resulting from depth variation of the axis and associated physical parameters, and different source rocks. These could be considered as first order (i.e. most dominant) factors affecting the composition of vent communities on the MAR, in contrast to the East Pacific Rise (EPR) where geographical isolation appears to be a major determinant of faunal differences. In this paper, the geological setting and vent fluid composition of the fields are considered together with their community composition to tentatively ascertain the order of a hierarchy between dispersal and environmental control. The deepest fields (>3000 m) are rather stable systems. The shallower fields, especially Rainbow and Menez Gwen, present some evidence of instability in time and space. The variability in fluid composition is related to phase separation processes (boiling/distillation of subsurface vent fluids) and to the nature of the basement rocks. Depending on depth, phase separation produces gas-enriched and metal-depleted fluids (Menez Gwen, Lucky Strike) or metal-enriched brines (Rainbow, TAG). In addition, high methane content characterises the fluids formed in ultramafic rocks (Rainbow, Logatchev) compared to basaltic rocks. The discrepancy in mineral particulate fluxes at Lucky Strike and Menez Gwen, on one hand, and TAG and Rainbow, on the other, is correlated to the predominance of the vapour or brine phase. The semi-quantitative description of the faunal composition of the different vent fields displays a continuum from Rimicaris-dominated to Bathymodiolus-dominated assemblages. Rather than geographic or bathymetric zonation, this gradation appears to be related to the metal content of the fluids. In addition, the penetration of non vent species into the vent environment increases with decreasing hydrostatic pressure and/or metal content in the fluids. Similarity analysis between vent communities shows that similarity is strongest between Menez Gwen and Lucky Strike (the shallowest fields), less significant between these sites and Rainbow, and weakest for Snake Pit. The inverse relationship between filter feeding organisms and metal concentration in vent fluids could result from a hindrance of mussel bed development by particulate or toxic metal fluxes, and has to be further investigated. Conversely, high metal and particulate content would less affect the more mobile Rimicaris populations. Considering specific similarities of endemic fauna between the four best known hydrothermal vents, the distance between vent fields appears to be a first order parameter. Nevertheless, within the proximity of the Azores Triple Junction area, and in the absence of geographical discontinuity, the similarity between fields stays rather low suggesting faunal islands that have distinct composition and habitat requirements.

An initial assessment of the bioclimatic comfort in an outdoor public space in Lisbon

Abstract: This paper describes the application of a methodology designed to analyse the relationship between climatic conditions and the perception of bioclimatic comfort. The experiment consisted of conducting simultaneous questionnaire surveys and weather measurements during 2 sunny spring days in an open urban area in Lisbon. The results showed that under outdoor conditions, thermal comfort can be maintained with temperatures well above the standard values defined for indoor conditions. There seems to be a spontaneous adaptation in terms of clothing whenever the physiological equivalent temperature threshold of 31°C is surpassed. The perception of air temperature is difficult to separate from the perception of the thermal environment and is modified by other parameters, particularly wind. The perception of solar radiation is related to the intensity of fluxes from various directions (i.e. falling upon both vertical and horizontal surfaces), weighted by the coefficients of incidence upon the human body. Wind was found to be the most intensely perceived variable, usually negatively. Wind perception depends largely on the extreme values of wind speed and wind variability. Women showed a stronger negative reaction to high wind speed than men. The experiment proved that this methodology is well-suited to achieving the proposed objectives and that it may be applied in other areas and in other seasons.