Fluctuations and Pattern Formation in Fluids with Competing Interactions

One of the most interesting phenomena in the soft-matter realm consists in the spontaneous formation of super-molecular structures (microphases) in condition of thermodynamic equilibrium. A simple mechanism responsible for this self-organization or pattern formation is based on the competition between attractive and repulsive forces with different length scales in the microscopic potential, typically, a short-range attraction against a longer-range repulsion. We analyse this problem by simulations in 2D fluids. We find that, as the temperature is lowered, liquid-vapor phase separation is inhibited by the competition between attraction and repulsion, and replaced by a transition to non-homogeneous phases. The structure of the fluid shows well defined signatures of the presence of both intra- and inter-cluster correlations. Even when the competition between attraction and repulsion is not so strong as to cause microphase formation, it still induces large density fluctuations in a wide region of the temperature-density plane. In this large-fluctuation regime, pattern formation can be triggered by a weak external modulating field.Comment: To appear in the proceedings of the "International workshop on collective phenomena in macroscopic systems", 2006 Villa Olmo (Como), Ital

Fluid-fluid demixing transitions in colloid--polyelectrolyte star mixtures

We derive effective interaction potentials between hard, spherical colloidal particles and star-branched polyelectrolytes of various functionalities and smaller size than the colloids. The effective interactions are based on a Derjaguin-like approximation, which is based on previously derived potentials acting between polyelectrolyte stars and planar walls. On the basis of these interactions we subsequently calculate the demixing binodals of the binary colloid--polyelectrolyte star mixture, employing standard tools from liquid-state theory. We find that the mixture is indeed unstable at moderately high overall concentrations. The system becomes more unstable with respect to demixing as the star functionality and the size ratio grow.Comment: 24 pages, 9 figures, submitted to Journal of Physics: Condensed Matte

Recent developments of the Hierarchical Reference Theory of Fluids and its relation to the Renormalization Group

The Hierarchical Reference Theory (HRT) of fluids is a general framework for the description of phase transitions in microscopic models of classical and quantum statistical physics. The foundations of HRT are briefly reviewed in a self-consistent formulation which includes both the original sharp cut-off procedure and the smooth cut-off implementation, which has been recently investigated. The critical properties of HRT are summarized, together with the behavior of the theory at first order phase transitions. However, the emphasis of this presentation is on the close relationship between HRT and non perturbative renormalization group methods, as well as on recent generalizations of HRT to microscopic models of interest in soft matter and quantum many body physics.Comment: 17 pages, 5 figures. Review paper to appear in Molecular Physic

Predictive Criteria to Study the Pathogenesis of Malaria-Associated ALI/ARDS in Mice

Malaria-associated acute lung injury/acute respiratory distress syndrome (ALI/ARDS) often results in morbidity and mortality. Murine models to study malaria-associated ALI/ARDS have been described; we still lack a method of distinguishing which mice will develop ALI/ARDS before death. This work aimed to characterize malaria-associated ALI/ARDS in a murine model and to demonstrate the first method to predict whether mice are suffering from ALI/ARDS before death. DBA/2 mice infected with Plasmodium berghei ANKA developing ALI/ARDS or hyperparasitemia (HP) were compared using histopathology, PaO2 measurement, pulmonary X-ray, breathing capacity, lung permeability, and serum vascular endothelial growth factor (VEGF) levels according to either the day of death or the suggested predictive criteria. We proposed a model to predict malaria-associated ALI/ARDS using breathing patterns (enhanced pause and frequency respiration) and parasitemia as predictive criteria from mice whose cause of death was known to retrospectively diagnose the sacrificed mice as likely to die of ALI/ARDS as early as 7 days after infection. Using this method, we showed increased VEGF levels and increased lung permeability in mice predicted to die of ALI/ARDS. This proposed method for accurately identifying mice suffering from ALI/ARDS before death will enable the use of this model to study the pathogenesis of this disease.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Univ São Paulo, Inst Ciencias Biomed, Dept Imunol, BR-05508900 São Paulo, BrazilUniversidade Federal de São Paulo, Dept Ciencias Biol, BR-09972270 Diadema, SP, BrazilUniv São Paulo, Inst Med Trop São Paulo, BR-05403000 São Paulo, BrazilUniversidade Federal de São Paulo, Dept Ciencias Exatas & Terra, BR-09972270 Diadema, SP, BrazilUniv São Paulo, Inst Ciencias Biomed, Dept Parasitol, BR-05508000 São Paulo, BrazilUniv São Paulo, Fac Med Vet & Zootecn, Dept Cirurgia, BR-05508270 São Paulo, BrazilUniv São Paulo, Fac Med Vet & Zootecn, Dept Med Vet Prevent & Saude Anim, BR-05508270 São Paulo, BrazilUniv São Paulo, Fac Ciencias Farmaceut, Dept Anal Clin & Toxicol, BR-05508000 São Paulo, BrazilUniversidade Federal de São Paulo, Dept Ciencias Biol, BR-09972270 Diadema, SP, BrazilUniversidade Federal de São Paulo, Dept Ciencias Exatas & Terra, BR-09972270 Diadema, SP, BrazilFAPESP: 2009/53256-7FAPESP: 2009/53889-0CNPq: 306668/2012-2CNPq: 470590/2009-2Web of Scienc

Relevance of the socio-cultural perspective in the discussion about critical thinking

This is the final version. Available on open access from the publisher via the DOI in this recordCritical thinking (CT) is considered a key skill for success in the 21st century. Worldwide educational policies advocate the promotion of CT, and scholars across different fields have been involved in a wide debate on its definition, without reaching an agreement. Currently, research has not adequately addressed CT assessment, nor the way in which it should be taught. In the present work, an overview of the topic is provided, as well as an evaluation of the practices, in order to provide researchers or practitioners (particularly those involved in primary school education) a reference for the development of further theories and methods about CT in edu-cation. CT is considered from the perspective of philosophy, cognitive psychology, and education sciences. In addition, we propose the inclusion of a fourth perspective, which could be referred as socio-cultural pedagogic perspective, due to its important implications in teaching and assessment practices

Microphase morphology in two dimensional fluids under lateral confinement

We study the effects of confinement between two parallel walls on a two dimensional fluid with competing interactions which lead to the formation of particle micro-domains at the thermodynamic equilibrium (microphases or microseparation). The possibility to induce structural changes of the morphology of the micro-domains is explored, under different confinement conditions and temperatures. In presence of neutral walls, a switch from stripes of particles to circular clusters (droplets) occurs as the temperature decreases, which does not happen in bulk. While the passage from droplets to stripes, as the density increases, is a well known phenomenon, the change of the stripes into droplets as an effect of temperature is rather unexpected. Depending on the wall separation and on the wall-fluid interaction parameters, the stripes can switch from parallel to perpendicular to the walls and also a mixed morphology can be stable.Comment: accepted by Physical Review E (rapid communications

Inter-individual differences in foraging tactics of a colonial raptor : consistency, weather effects, and fitness correlates

Background: Consistent inter-individual differences in behavioural phenotypes may entail differences in energy efficiency and expenditure, with different fitness payoffs. In colonial-breeding species, inter-individual differences in foraging behaviour may evolve to reduce resource use overlap among conspecifics exploiting shared foraging areas. Furthermore, individual differences in foraging behaviour may covary with individual characteristics, such as sex or physiological conditions. Methods: We investigated individual differences in foraging tactics of a colonial raptor, the lesser kestrel (Falco naumanni). We tracked foraging trips of breeding individuals using miniaturized biologgers. We classified behaviours from GPS data and identified tactics at the foraging trip level by cluster analysis. We then estimated energy expenditure associated to each tactic from tri-axial accelerometer data. Results: We obtained 489 foraging trips by 36 individuals. Two clusters of trips were identified, one (SF) characterized by more static foraging behaviour and the other (DF) by more dynamic foraging behaviour, with a higher proportion of flying activity and a higher energy expenditure compared to SF. Lesser kestrels showed consistent inter-individual differences in foraging tactics across weather condition gradients, favouring DF trips as solar radiation and crosswind intensity increased. DF trips were more frequent during the nestling-rearing than during the egg incubation stage. Nestlings whose tracked parent was more prone to perform DF trips experienced higher daily mass increase, irrespective of nestling feeding rates. Conclusions: Our study provided evidence that breeding lesser kestrels flexibly adopted different foraging tactics according to contingent weather landscapes, with birds showing consistent inter-individual differences in the tendency to adopt a given tactic. The positive correlation between the tendency to perform more energy-demanding DF trips and nestling growth suggests that individual differences in foraging behaviour may play a role in maintaining key life-history trade-offs between reproduction and self-maintenance

Tubulin-binding dibenz[c,e]oxepines: Part 2 Structural variation and biological evaluation as tumour vasculature disrupting agents

5,7-Dihydro-3,9,10,11-tetramethoxybenz[c,e]oxepin-4-ol 1, prepared from a dibenzyl ether precursor via Pd-catalysed intramolecular direct arylation, possesses broad-spectrum in vitro cytotoxicity towards various tumour cell lines, and induces vascular shutdown, necrosis and growth delay in tumour xenografts in mice at sub-toxic doses. The biological properties of 1 and related compounds can be attributed to their ability to inhibit microtubule assembly at the micromolar level, by binding reversibly to the same site of the tubulin αβ-heterodimer as colchicine 2 and the allocolchinol, N-acetylcolchinol 4