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Concentrated Solar Power (CSP) technologies offer significant potential as renewable energy sources, particularly when integrated with storage systems. To address the challenges of energy transport and re-radiation losses, beam-down configurations combined with paraboloid-type dish concentrators provide a compact and efficient solution. In this study, we perform an optical analysis of a Cassegrain concentrator using the open-source software OTSunWebApp, a ray-tracing program that allows for the spectral optical analysis of solar collectors. The analysis accounts for specular scattering of the reflectors, the spectral behavior of the materials, and the angular size of the sun. The geometric design is parametrized with six degrees of freedom, while some other parameters, such as the number of mirrors and the aperture area, have been previously chosen. The resulting aperture area is 67.52 m2. We optimize the optical efficiency for operation at 600C∘, identifying the key parameters that influence performance. The system achieves a power output greater than 45 kW under direct radiation of 900 W/m2. Additionally, maintaining optical efficiency above 74% requires a tracking error below 0.2∘, with peak radiation values at the receiver reaching 26 kW/m2. These results underscore the potential of Cassegrain concentrator designs to advance CSP technology, suggesting that they could significantly enhance this field.

In the field of solar energy, simulation tools based on ray tracing are crucial for the design and optimization of solar energy systems. However, the limitations of existing free ray tracing software, such as the inability to simulate both thermal and photovoltaic systems with any geometry while considering real optical phenomena, hinder their usefulness for researchers. In this paper, we present the webtool OTSunWebApp, built upon the python library OTSun, which allows the user to analyze solar harvesting devices regardless of its application (thermal/PV). It can be used either by installing the program locally, which is simplified thanks to the use of docker containers, or by using the server we provide, which means that the users does not have to install anything. The free software FreeCAD is used to draw the mechanical system to be simulated. Here we show the structure of the webtool, how to manage the FreeCAD file in order to simulate the system and which experiments can be performed. We finish giving two illustrative examples, one of a solar power tower plant, and one of a photovoltaic cell. Having already reported on the library OTSun in a previous publication, the present manuscript shows how the functionality of OTSunWebApp constitutes a very powerful scientific online tool for the design and improvement of solar harvesting systems.

The COVID-19 pandemic has infected more than 263 million people and claimed the lives of over 5 million people worldwide. Refugees living in camp settings are particularly vulnerable to infection because of the difficulty implementing preventive measures and lack of medical resources. However, very little is known about the factors that influence the behavioural response of refugees towards COVID-19. There is an urgent need for field evidence to inform the design and implementation of a robust social and behaviour change communication strategy to respond to the threat posed by COVID-19 in humanitarian settings. This study examines factors influencing COVID-19-related behavioural decisions in the Nguenyyiel refugee camp located in Gambella, Ethiopia using data collected from focus group discussions and key informant interviews in September 2020. The evidence suggests that while a number of factors have been facilitating the adoption of COVID-19 prevention measures, including good general knowledge about the virus and the necessary preventive strategies and the active engagement by community leaders and non-governmental organisations, important structural and cultural factors have hindered the uptake of COVID-19 prevention measures. These include: difficultly staying at home to minimise physical contact; overcrowding in the camp and within home dwellings; a lack of hand sanitizers and masks and of funds to purchase these; inconsistent use of facemasks when available; COVID-19 denial and misconceptions about the disease, and other cultural beliefs and habits. Overall, the study found that refugees perceived COVID-19 to pose a low threat (susceptibility and severity) and had mixed beliefs about the efficacy of preventive behaviours. This study identified gaps in the existing information education and communication strategy, including a lack of consistency, inadequate messaging, and a limited use of communication channels. While awareness of COVID-19 is a necessary first step, it is not sufficient to increase adoption of prevention measures in this setting. The current communication strategy should move beyond awareness raising and emphasise the threat posed by COVID-19 especially among the most vulnerable members of the camp population. This should be accompanied by increased community support and attention to other barriers and incentives to preventive behaviours.

Ray tracing software systems are commonly used to analyze the optics of solar energy devices, since they allow to predict the energy gains of devices in real conditions, and also to compare them with other systems constantly emerging in the market. However, the available open-source packages apply excessive simplifications to the model of light-matter interaction, making that the optical behaviour of the systems can not be properly characterized, which in turn implies disagreements between physical experiments and computer simulations. We present here the open source python package OTSun, which applies the Fresnel equations in their most general form, without further simplifications, and is suitable for the simulation of both solar-thermal and photovoltaic systems. The geometrical objects used in this package are created using the parametric 3D modeler FreeCAD, which is also a free and open source program and allows for the construction of arbitrary geometries that can be analyzed with OTSun. These, and other software capabilities, make OTSun extremely flexible and accurate for the optical analysis of solar devices with arbitrary geometry. Additionally, OTSun has a companion webtool, OTSunWebApp, that allows for the usage of certain features of the package without the need to install anything locally. We also show here two numerical experiments that we performed in order to validate the model and implementation: The analysis of the optical efficiency of a Linear Fresnel Reflector (with moving objects), and of a second surface mirror (with variable wavelengths). In each case, the numerical computations had deviations of less than 0.25% from reference models (either computed with another program or with exact formulas).

[This corrects the article DOI: 10.1371/journal.pcbi.1007347.].

Phylogenetic networks generalize phylogenetic trees by allowing the modelization of events of reticulate evolution. Among the different kinds of phylogenetic networks that have been proposed in the literature, the subclass of binary tree-child networks is one of the most studied ones. However, very little is known about the combinatorial structure of these networks. In this paper we address the problem of generating all possible binary tree-child (BTC) networks with a given number of leaves in an efficient way via reduction/augmentation operations that extend and generalize analogous operations for phylogenetic trees, and are biologically relevant. Since our solution is recursive, this also provides us with a recurrence relation giving an upper bound on the number of such networks. We also show how the operations introduced in this paper can be employed to extend the evolutive history of a set of sequences, represented by a BTC network, to include a new sequence. An implementation in python of the algorithms described in this paper, along with some computational experiments, can be downloaded from https://github.com/bielcardona/TCGenerators.

Several polynomial time computable metrics on the class of semibinary tree-sibling time consistent phylogenetic networks are available in the literature; in particular, the problem of deciding if two networks of this kind are isomorphic is in P. In this paper, we show that if we remove the semibinarity condition, then the problem becomes much harder. More precisely, we prove that the isomorphism problem for generic tree-sibling time consistent phylogenetic networks is polynomially equivalent to the graph isomorphism problem. Since the latter is believed not to belong to P, the chances are that it is impossible to define a metric on the class of all tree-sibling time consistent phylogenetic networks that can be computed in polynomial time.

Hasta marzo de 1937, cuando se inició la campaña de Mola en Vizcaya, los franquistas habían combatido siguiendo los cánones de las primitivas campañas de Marruecos. La única batalla planteada con criterios modernos había sido la ofensiva italiana en Guadalajara, que fracasó porque la mayor parte del CTV carecía de experiencia, se desencadenó un temporal de lluvias y faltó la cooperación de las tropas de Varela. En el Norte, las milicias vascas adoptaron una estrategia defensiva apoyadas en una difícil orografía. Era imposible tomar estas posiciones con la primitiva táctica de columnas utilizada hasta entonces y se pusieron en marcha operaciones combinadas con una buena masa de artillería y aviación. Los militares franquistas aprendieron técnicas modernas, con la ventaja de enfrentarse a un enemigo aislado geográficamente, con la costa bloqueada y sin suficiente artillería y aviación. Por su parte, la Luftwaffe, que había sido fundada dos años antes, desarrolló técnicas de ataque a tierra, hasta entonces desconocidas y que todas las fuerzas aéreas aplicarían intensamente durante la Segunda Guerra Mundial.