Species survival and scaling laws in hostile and disordered environments

In this work we study the likelihood of survival of single-species in the context of hostile and disordered environments. Population dynamics in this environment, as modeled by the Fisher equation, is characterized by negative average growth rate, except in some random spatially distributed patches that may support life. In particular, we are interested in the phase diagram of the survival probability and in the critical size problem, i.e., the minimum patch size required for surviving in the long time dynamics. We propose a measure for the critical patch size as being proportional to the participation ratio (PR) of the eigenvector corresponding to the largest eigenvalue of the linearized Fisher dynamics. We obtain the (extinction-survival) phase diagram and the probability distribution function (PDF) of the critical patch sizes for two topologies, namely, the one-dimensional system and the fractal Peano basin. We show that both topologies share the same qualitative features, but the fractal topology requires higher spatial fluctuations to guarantee species survival. We perform a finite-size scaling and we obtain the associated scaling exponents. In addition, we show that the PDF of the critical patch sizes has an universal shape for the 1D case in terms of the model parameters (diffusion, growth rate, etc.). In contrast, the diffusion coefficient has a drastic effect on the PDF of the critical patch sizes of the fractal Peano basin, and it does not obey the same scaling law of the 1D case.Comment: 20 pages, 5 Figure

Synge's dynamic problem for two isolated point charges. A new method to find global solutions for Functional Differential Equations System

Synge's problem consists in to determine the dynamics of two point electrical charges interacting through their electromagnetic fields, without to take into account the radiation terms due to the self-forces in each charge. We discuss how this problem is related to the question on to establish initial conditions for the electromagnetic fields that are compatible with the two point charges system isolation, that is, the charges are free from the action of external forces. This problem stems from the existence of inter-temporal constraints for the charges trajectories, which implies that the relativistic Newton equations for the charges is not a system of ODEs, but rather a system of Functional Differential Equations (FDEs). We developed a new method to obtain global solutions that satisfies this system of FDEs and a given initial condition for the charges positions and velocities. This method allows the construction of a recursive numerical algorithm that only use integration methods for ODEs systems. Finally, we apply this algorithm to obtain numerical approximations for the quasi-circular solutions that are predicted in Synge's problem.Comment: 32 pages, 10 Figures, 2 Tables, Preprint Article. J. Phys. A: Math. Theor (2023

Flow and hemocompatibility study of straight-bladed impeller VADs

Ventricular Assist Devices are continuous flow pumps that act as cardiac orthoses. The evaluation of the compatibility of such devices with blood involves, among other aspects, the study of thrombogenicity, hemolysis, and platelet activation. Computational Fluid Dynamics simulation is one of the tools used in this kind of evaluation. Thus, this work used Computational Fluid Dynamics simulations in the analysis of three Ventricular Assist Devices models under development, generating their velocity and pressure contours, their characteristic curves, and the distribution of shear stresses in their walls. A blood model has also been developed in order to estimate the damage inflicted on the blood by the devices. Steady-state simulations were performed, applying the Multiple Reference Frame method. The numerical blood modeling used the Lagrangean approach, with a discrete phase. The estimation of the damage on the blood was based on the relationship between the residence time of the discrete phase and the scalar shear stress. The prototype of one of the models was bench tested to validate the simulations. The simulation results relate the geometry of the models to the characteristics and magnitudes of the recirculation and stagnation regions and to the distribution of shear stresses. The energy performance of each pump and the blood damage index were used as comparison metrics between the devices

EUCALYPTUS SPP. GLUED LAMINATED TIMBER WITH REINFORCED FIBER FINGER-JOINTS

Reinforcement for flexion in structural elements with finger-joints using fibers has emerged as a particularly suitable technique for timber. Thus, the objective of this study was to evaluate the performance of Glued Laminated Timber (GLULAM) produced with Eucalyptus spp. wood and three reinforcement compositions, “Glass”, “Glass2” and “Carbon” regarding parallel-to-grain tensile strength, normal tensile strength, shear strength and the three-point bending test. All the tests were performed according to the NBR 7190/1997 using the Tukey test for statistical analyzes and a 95% confidence interval. The performance of the Eucalyptus spp. GLULAM did not present significant differences in evaluation of the bonding lines. However, the “Glass 2” and “Carbon” treatments were significantly superior to the GLULAM samples without reinforcement in bending strength, reaching increments of 37.8% and 40.5%, respectively. The modulus of elasticity did not differ significantly between them. A tensile rupture was observed in the region of the finger-joints in all the evaluated samples; however, the flexural tensions were superior to the parallel-to-grain tensile strengths, indicating an influence of the timber thickness and reinforcement thickness on the performance of the reinforced joints. Thus, it is possible to conclude that applying concentrated reinforcement in the region of the finger-joints significantly improves the performance of Eucalyptus spp. GLULAM samples

Donor liver optimisation and real-time pre-implant assessment

Ph. D. ThesisThe number of livers offered for cadaveric donation currently exceeds demand in the United Kingdom. However, the quality of these organs means that nearly a third are rejected for transplantation. In particular utilisation of fatty (steatotic) and organs from donors after circulatory death (DCD) are poor. The aims of this project were to develop novel cost effective ex-situ perfusion viability and reconditioning techniques and explore accurate methods of steatosis quantification. Ex situ perfusion was introduced using our previous experience in kidney perfusion, taking advantage of the inherent safety benefits of hypothermic perfusion before progressing to normothermic perfusion. A novel perfusion setup was utilised for Hypothermic Oxygenated Perfusion of livers (HOPE), with a custom-designed circuit and adapting existing experience of ex-vivo kidney perfusion using Medtronic perfusion equipment. A total of 10 livers were transplanted following HOPE, all with significant donor and recipient risk factors, with very promising results. All recipients are alive with a minimum of 20-months follow-up and none have developed clinically-significant ischaemic cholangiopathy. This compares favourably with a historical local cohort that would have met current inclusion criteria for perfusion. Only 1 recipient has had a retransplant, due to rejection. A number of modalities for assessing livers during perfusion have been explored. We have demonstrated that lactate clearance in normothermic machine perfusion (NMP) cannot be safely relied upon, as livers that had sustained damage well beyond the scope of transplantation still cleared lactate. Bile production has proved to be of some importance in our series, but not all published evidence supports this. Extensive analysis of perfusate biomarkers has identified a potential scoring system that could differentiate between transplantable and untransplantable livers in our series, but needs further validation. We have described an objective method of analysing liver microcirculation, and have demonstrated that NMP improved the arterial microcirculation, but that with extended ischaemia the benefit of NMP is lost. We have demonstrated in rodent cell lines that steatosis adversely affects viability in hypoxia. In addition we have developed a preliminary point-of-care steatosis assessment method, which could prove beneficial with further calibration and validation. Utilising ex-situ perfusion to modulate and treat organs is an exciting potential to further improve marginal organs. We selected Pregnane-X Receptor (PXR) activation as our treatment target for this based on rodent experiments demonstrating its benefit in reducing ischaemia-reperfusion injury. These experiments demonstrate upregulation of the end-targets of PXR during human NMP, proving its potential as a platform for drug delivery. We were unable to demonstrate significant benefits to the livers within the limited timeframe of perfusion, as it is likely that any potential advantages of PXR activation would only become apparent in a much longer time period.NHSBT Blood and Transplant Research Unit, Royal College of Surgeons, LiverNorth, Live Life Give Lif

Debt mutualisation in the eurozone

Mestrado em Economia Internacional e Estudos EuropeusO objectivo desta Dissertação prende-se com o estudo da mutualização da dívida na Zona Euro para resolução dos elevados níveis de endividamento, com os quais muitos Estados Membros se confrontam. Para a resolução da Grande Recessão, as instituições europeias criaram mecanismos de assistência financeira, os quais constituíram meramente uma resposta de curto prazo para a crise das dívidas soberanas. No entanto, a resolução de tal problema requer uma solução de longo prazo, que permita a gestão eficiente da dívida pública. Tendo em conta propostas apresentadas por outros autores, esta Dissertação propõe uma alternativa que permite aos governos lidarem com a disciplina orçamental, sem comprometer o crescimento económico.The objective of this Dissertation is to study debt mutualisation in the Eurozone as a means of dealing with the high levels of indebtedness that many Member States face. For the resolution of the Great Recession, the EU institutions created financial assistance mechanisms, which were merely a short-term answer to the sovereign debt crisis. However, the resolution of such problem requires a long-term solution that allows for the proper management of public debt. Bearing in mind proposals presented by other authors, this Dissertation provides an alternative way in which governments can deal with fiscal discipline without compromising economic growth