Hot-pressing process modeling for medium density fiberboard (MDF)

In this paper we present a numerical solution for the mathematical modeling of the hot-pressing process applied to medium density fiberboard. The model is based in the work of Humphrey[82], Humphrey and Bolton[89] and Carvalho and Costa[98], with some modifications and extensions in order to take into account mainly the convective effects on the phase change term and also a conservative numerical treatment of the resulting system of partial differential equations.Comment: LaTeX, 11 figures. Added references. Fixed some errors. To appear in International Journal of Mathematics and Mathematical Sciences, http://jam.hindawi.co

Fostering a Culture of Innovation: A Case Study of Elementary School Principals in Costa Rica

To help promote a culture of innovation, the Ministry of Education andthe Ministry of Science, Technology, and Telecommunication of Costa Rica estab-lished a national executive decree requiring all public schools in the country partic-ipate in the National Program of Science and Technology Fairs (NPSTF). This casestudy examines the role of five elementary school principals in Costa Rica in implementing and preparing their schools for the NPSTF initiative. Principals played threesignificant roles: the motivator of teachers and students; acquirer of NPSTF resources;and the organizer of NPSTF committees and coalitions to help train and finance theinitiative. It is recommended the Ministry of Education establish a budget solely ded-icated to support infrastructure and professional development for NPSTF while aligning goals with all stakeholders

Numerical simulation of sloshing in liquid storing tanks by an arbitrary Lagrangian-Eulerian strategy

La agitación de fluidos contenidos en tanques de almacenamiento con superficie libre es numéricamente simulada mediante una formulación lagrangiana-euleriana arbitraria. El fluido es considerado viscoso y de comportamiento newtoniano, mientras que el flujo se asume laminar e incompresible. Se emplea un código computacional particionado y distribuido, que resuelve tres instancias en cada paso de tiempo: (i) la determinación del estado en el fluido, representado por las ecuaciones de Navier–Stokes; (ii) el desplazamiento de la superficie libre; y (iii) la actualización de la posición de los nodos interiores de la malla de elementos finitos, que es deformada como consecuencia del desplazamiento de la superficie libre. El propósito del trabajo es verificar la aplicabilidad del método en problemas de agitación de solución conocida, así como también resolver algunos ejemplos prácticos. Los ejemplos numéricos incluyen la validación con soluciones analíticas, en las cuales el período de la onda y la tasa de amortiguamiento viscoso son bien capturadas, comparaciones con soluciones de referencia tomadas de otros autores y un caso de agitación inducida por acción sísmica.Sloshing of fluids with a free surface contained in liquid storage tanks is numerically simulated by an arbitrary Lagrangian-Eulerian formulation. The fluid is considered viscous and Newtonian, while the flow is assumed laminar and incompressible. A partitioned and distributed computational code is employed, which solves three instances each time step: (i) the determination of the fluid state, given by the Navier–Stokes equations; (ii) the displacement of the free surface; and (iii) the update of the position of the internal nodes of the mesh, that is deformed as a consequence of the free surface displacement. The purpose of the work is verifying the applicability of the method to sloshing problems with known solutions, as well as the resolution of some practical examples. Numerical examples include validations against analytical solutions, where the wave period and damping rate are well captured, comparisons with reference results from other authors and a sample of sloshing induced by seismic actions.Peer Reviewe

Coplanar back contacts for thin silicon solar cells

The type of coplanar back contact solar cell described was constructed with interdigitated n(+) and p(+) type regions on the back of the cell, such that both contacts are made on the back with no metallization grid on the front. This cell construction has several potential advantages over conventional cells for space use namely, convenience of interconnects, lower operating temperatures and higher efficiency due to the elimination of grid shadowing. However, the processing is more complex, and the cell is inherently more radiation sensitive. The latter problem can be reduced substantially by making the cells very thin (approximately 50 micrometers). Two types of interdigitated back contact cells are possible, the types being dependent on the character of the front surface. The front surface field cell has a front surface region that is of the same conductivity type as the bulk but is more heavily doped. This creates an electric field at the surface which repels the minority carriers. The tandem junction cell has a front surface region of a conductivity type that is opposite to that of the bulk. The junction thus created floats to open circuit voltage on illumination and injects carriers into the bulk which then can be collected at the rear junction. For space use, the front surface field cell is potentially more radiation resistant than the tandem junction cell because the flow of minority carriers (electrons) into the bulk will be less sensitive to the production of recombination centers, particularly in the space charge region at the front surface

Clinical phenotypes of SARS-CoV-2 : implications for clinicians and researchers

Patients with COVID-19 present a broad spectrum of clinical presentation. Whereas hypoxaemia is the marker of severity, different strategies of management should be customised to five specific individual phenotypes. Many intubated patients present with phenotype 4, characterised by pulmonary hypoxic vasoconstriction, being associated with severe hypoxaemia with "normal" (>40 mL·cmH2O-1) lung compliance and likely representing pulmonary microvascular thrombosis. Phenotype 5 is often associated with high plasma procalcitonin and has low pulmonary compliance, Which is a result of co-infection or acute lung injury after noninvasive ventilation. Identifying these clinical phenotypes and applying a personalised approach would benefit the optimisation of therapies and improve outcomes

An Observation of Resistance Training History in Ultramarathon Runners and Implications on Performance

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Implementation and Assessment Methodologies of Teachers' Training Courses for STEM Activities

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A novel process for recovery and exploitation of polyesters and polyamides from waste polymeric artifacts

Plastic waste is one of the world's biggest sources of pollution. Despite the growing trend towards recycling, there are currently no effective technologies to offset the continuous increase in plastic production. Polyesters and polyamides are among the most widely produced single-use plastics, mainly used in the manufacture of textiles and soft drink bottles. Currently, only a small proportion of these polymers can be effectively recycled. The two primary methods employed for this purpose are mechanical and chemical recycling. Presently, mechanical recycling remains the more widely adopted process within the industrial sector. However, the treatment process is limited to a narrow range of waste materials as it is impossible to remove dyes and the mechanical properties deteriorate due to incompatibility between different plastic materials. Another critical limit of this recycling technology is the limited number of recycling loops that can be done due to the thermal degradation that occurs during the extrusion process. The alternative option is chemical recycling, which allows the depolymerization of the original product to recover the monomers directly. The main drawbacks are the long reaction times and the many solvents needed to achieve high-purity products. As a results, chemical recycling is only economically feasible for large companies that can produce the virgin polymer in situ. In this work, a new technology has been patented. This process consists of three main steps. The first one is the distillation-assisted cyclodepolymerization (DA-CDP), introduced as a modification of the CDP process. In this unit, cyclic oligomers together with high molecular weight compounds are produced. Then, after polymer purification, it is possible to achieve the same molecular weight as the initial polymer in less than 30 min, exploiting the ring-opening polymerization (ROP) of the next step