Forward with Active Clamp for space applications: clamp capacitor, dynamic specifications and EMI filter impact on the power stage design

The impact of the clamp capacitor design, the dynamic specifications and the EMI filter design on the power stage design of a 28V 50W Forward with Active Clamp converter for space applications is analyzed along this paper. Clamp capacitor is designed by considering the ECSS standards limitations for the semiconductors and saturation of the magnetic components, and considering the influence of the resonance between this capacitance and the magnetizing inductance on the input impedance of the converter. Dynamic specifications influence are analyzed. Additionally, the EMI filter design process is described. Singlestage and Multi-stage approaches are proposed. All these features make an increase of 2:4W losses and 1:6 higher area of the converter, compared with a preliminary design of the power stage, before considering these aspects

Transposable elements: Powerful contributors to angiosperm evolution and diversity

Transposable elements (TEs) are a dominant feature of most flowering plant genomes. Together with other accepted facilitators of evolution, accumulating data indicate that TEs can explain much about their rapid evolution and diversification. Genome size in angiosperms is highly correlated with TE content and the overwhelming bulk (>80%) of large genomes can be composed of TEs. Among retro-TEs, long terminal repeats (LTRs) are abundant, whereas DNA-TEs, which are often less abundant than retro-TEs, are more active. Much adaptive or evolutionary potential in angiosperms is due to the activity of TEs (active TE-Thrust), resulting in an extraordinary array of genetic changes, including gene modifications, duplications, altered expression patterns, and exaptation to create novel genes, with occasional gene disruption. TEs implicated in the earliest origins of the angiosperms include the exapted Mustang, Sleeper, and Fhy3/Far1 gene families. Passive TE-Thrust can create a high degree of adaptive or evolutionary potential by engendering ectopic recombination events resulting in deletions, duplications, and karyotypic changes. TE activity can also alter epigenetic patterning, including that governing endosperm development, thus promoting reproductive isolation. Continuing evolution of long-lived resprouter angiosperms, together with genetic variation in their multiple meristems, indicates that TEs can facilitate somatic evolution in addition to germ line evolution. Critical to their success, angiosperms have a high frequency of polyploidy and hybridization, with resultant increased TE activity and introgression, and beneficial gene duplication. Together with traditional explanations, the enhanced genomic plasticity facilitated by TE-Thrust, suggests a more complete and satisfactory explanation for Darwin’s “abominable mystery”: the spectacular success of the angiosperms

A comparative study on homogenization strategies for multi-scale analysis of materials

One of the most important engineering tasks over the years has been the design and manufacture of increasingly sophisticated structural materials as a result of the requirements related to the technological progress. In the last decades, the growing needs for improved properties of products have been partially solved through the development of composite materials. A key to the success of many modern structural components is the tailored behavior of the material to given applications. Therefore, research efforts in material science engineering have been focused in the design of new materials either through the creation of new structures at the scale of single atoms and molecules or through the development of structural materials by changing the composition, size, arrangement and topology of the constituents at larger scales: the microscopic/mesoscopic level. The development of new materials has been linked to the development of a new theoretical field within the mechanics of solids. This branch of the mechanical, known as Continuum Micromechanics, introduces a series of new concepts that are key to the definition of the macroscopic properties of composite materials on the basis of the definition of the characteristics of its components. Starting from the premise of separation of scales and the concept of Representative Volume Element, defined the so-called homogenization methods, whose number has been increasing as the Micromechanics is gone extend over the years. Such methods are many and varied, although especially there have been two that have been used and developed by the majority of authors: the so-called Mean-Homogenization techniques and the multi-scale based on Finite Element Approaches. Mean-fifieeld homogenization schemes are an efficient way to predict the behavior of heterogeneous materials. They range from the simplest hypotheses of the stress or strain sharing among the phases which do not require analytical solution on the associated boundary-value problem to more involved geometric models based on the solution of a boundary-value problem involving a single or composite inclusion embedded in an equivalent homogenized medium whose elastic module become part of the solution procedure. In general, they are based on analytical solutions of the boundary value problem defined in the microstructure level of the inhomogeneous material and provide good predictions for the mean values over the RVE. Although originally designed for elastic materials, some approaches to deal with elastoplastic materials and even with viscoplastic materials have been developed over the years and compared with the results obtained using Finite Element Approaches. The comparison between different methods of homogenization allows the definition of a range of validity between the different methods, which helps to discover the limitations of the various methods and aspects to take into account for future developments and research. The main goal of this work is, firstly, to present a general overview of the different techniques that have been developed in the last years in order to obtain a prediction of the behavior of elastoplastic composites by taking into account geometrical and mechanical aspects. Secondly, a comparison between the different approaches is carried out through a numerical implementation of such techniques. Both objectives will be carried out through eight different chapters. The first chapter serves as an introduction and historical review of the advances that have been made in the field of micromechanics. On the other hand, the second chapter deals with some important theoretical background that is important in the field of Continuum Micromechanics, as well as a short introduction of the different approaches that traditionally have been considered to solve the problem. One group of methods, based on analytical solutions { the so-called Mean Field Analysis { will be commented in chapter 3. Chapter 4 is devoted to the implementation and validation of a numerical tool that solves the mean-field homogenization using analytical schemes for elastoplastic materials. Subsequent chapters are devoted to the comparison of the results with the results given by the Finite Element Method. The general formulation of such method { applied to multi-scale problems { is presented in chapter 5 from a theoretical point of view, as well as the corresponding numerical examples. Finally, last chapter will be dedicated to enumerate some conclusions extracted from the present work, including some aspects that can be object of future works or improvements. The current work presents some important aspects about the theoretical concepts and the numerical implementation of some key approaches for solving the mechanical problem regarding composite materials. There exist a large number of possibilities to approximate the response of such complex materials, based in different assumptions. This document shows the general efficiency of the so-called mean-field homogenization schemes to capture correctly the macroscopic behavior of composites. Although these techniques show some limitations, like the incapability to provide results for the distribution of the different variables over the microgeometry or the low accuracy in the case of complex microgeometries (like porous materials), they represent an efficient way to predict the main general behavior of a composite material spending low computational effort. They are specially indicated to be used in the previous steps of an analysis or as a tool to validate the results with more involved approaches

High-performance model reduction procedures in multiscale simulations

Technological progress and discovery and mastery of increasingly sophisticated structural materials have been inexorably tied together since the dawn of history. In the present era — the so-called Space Age —-, the prevailing trend is to design and create new materials, or improved existing ones, by meticulously altering and controlling structural features that span across all types of length scales: the ultimate aim is to achieve macroscopic proper- ties (yield strength, ductility, toughness, fatigue limit . . . ) tailored to given practical applications. Research efforts in this aspect range in complexity from the creation of structures at the scale of single atoms and molecules — the realm of nanotechnology —, to the more mundane, to the average civil and mechanical engineers, development of structural materials by changing the composition, distribution, size and topology of their constituents at the microscopic/mesoscopic level (composite materials and porous metals, for instance)

On the modelling of granular flows in industrial applications via the Particle Finite Element Method

The aim of this work is to present a new procedure for modelling industrial processes that involve granular material flows, using a numerical model based on the Particle Finite Element Method (PFEM). The numerical results herein presented show the potential of this methodology when applied to different branches of industry. Due to the phenomenological richness exhibited by granular materials, the present work will exclusively focus on the modelling of cohesionless dense granular flows. The numerical model is based on a continuum approach in the framework of large-deformation plasticity theory. For the constitutive model, the yield function is defined in the stress space by a Drucker-Prager yield surface characterized by two constitutive parameters, the cohesion and the internal friction coefficient, and equipped with a non-associative deviatoric flow rule. This plastic flow condition is considered nearly incompressible, so the proposal is integrated in a u- p mixed formulation with a stabilization of the pressure term via the Polynomial Pressure Projection (PPP). In order to characterize the non-linear dependency on the shear rate when flowing a visco-plastic regularization is proposed. The numerical integration is developed within the Impl-Ex technique, which increases the robustness and reduces the iteration number, compared with a typical implicit integration scheme. The spatial discretization is addressed within the framework of the PFEM which allows treating the large deformations and motions associated to granular flows with minimal distortion of the involved finite element meshes. Since the Delaunay triangulation and the reconnection process minimize such distortion but do not ensure its elimination, a dynamic particle discretization of the domain is proposed, regularizing, in this manner, the smoothness and particle density of the mesh. Likewise, it is proposed a method that ensures conservation of material or Lagrangian surfaces by means of a boundary constraint, avoiding in this way, the geometric definition of the boundary through the classic -shape method. For modelling the interaction between the confinement boundaries and granular material, it is advocated for a method, based on the Contact Domain Method (CDM) that allows coupling of both domains in terms of an intermediate region connecting the potential contact surfaces by a domain of the same dimension than the contacting bodies. The constitutive model for the contact domain is posed similarly to that for the granular material, defining a correct representation of the wall friction angle. In order to validate the numerical model, a comparison between experimental results of the spreading of a granular mass on a horizontal plane tests, and finite element predictions, is carried out. These sets of examples allow us validating the model according to the prediction of the different kinematics conditions of granular materials while spreading – from a stagnant condition, while the material is at rest, to a transition to a granular flow, and back to a deposit profile. The potential of the numerical method for the solution and optimization of industrial granular flows problems is achieved by focusing on two specific industrial applications in mining industry and pellet manufacturing: the silo discharge and the calculation of the power draw in tumbling mills. Both examples are representative when dealing with granular flows due to the presence of variations on the granular material mechanical response

Sacrificial Materials for the Fabrication of Complex Geometries with LENS

Mechanical Engineerin

Spatio-temporal analysis of the degradation of salts-affected soils in the lacustre system of Texcoco Valley (Mexico)

El Valle de Texcoco, uno de los cinco lagos que conformaban el gran lago de Tenochticlan en el periodo colonial de la ciudad de México (año 1520), es hoy en día una de las regiones del planeta con mayor superficie de suelos afectados por salinidad extrema (>10 000 ha). La salinidad de los suelos es un grave problema en regiones áridas o semiáridas, ya que afecta a la productividad agrícola y la calidad de las aguas, con graves consecuencias socioeconómicas, como la desertificación y migración a las ciudades. Además, las sales se disuelven con facilidad en el suelo, por lo que se requieren herramientas de monitorización precisas que permitan evaluar la alta variabilidad espacio-temporal de los suelos afectados por sales. Este trabajo tiene como objetivo evaluar el estado de los suelos afectados por salinidad en el valle de Texcoco, así como los cambios de uso de suelo acontecidos en los últimos 30 años. Para ello se emplearán técnicas de GIS, imágenes de satélite Landsat desde la década de los 80 hasta la actualidad (1985-2015), y radiómetros de campo para identificar las firmas espectrales de los suelos en condiciones de laboratorio. Una vez procesadas las imágenes de satélite Landsat (corrección radiométrica y atmosférica, y aplicación de filtros), se identificaron diferentes cubiertas o usos de suelo: agua, vegetación semi-natural, tierras de cultivo, suelos sin vegetación y suelos salinos. Se calcularon diferentes índices radiométricos para distinguir la vegetación de las tierras de cultivo y de los suelos salinos. El sistema de clasificación no supervisada mostró cambios de uso de la tierra en el 80% de la superficie en 30 años. Disminuye el agua potable y las tierras agrícolas e incrementan en más de un 20% los suelos degradados por sales o de uso urbano. Se trata de una región con riesgo extremo por pérdida y degradación de las tierras de cultivo por efecto de la salinidadThe Valley of Texcoco, one of the five lakes that formed the great lake of Tenochticlan in the colonial period of Mexico City (year 1520), is today one of the regions with the largest surface area of soils affected by extreme salinity (>10 000 ha). The salinity of soil is a serious problem in arid or semi-arid regions. It affects to agricultural productivity and water quality, with serious socioeconomic consequences, such as desertification and migration of the rural populations to the cities. So, salts dissolve easily in the soil, so precise monitoring tools are necessary to evaluate the high spatiotemporal variability by salts-affected soils. The aim is to evaluate the state of salts-affected soils in the Texcoco Valley, as well as the land use changes in the last 30 years. GIS, Landsat satellite images from the 1980s to the present (1985-2015), and field radiometers will be used to identify the spectral signatures of salts-affected soils under laboratory conditions. Once processed the multispectral images (radiometric and atmospheric correction, and filters application), different land uses were identified: water, semi-natural vegetation, agricultural lands, soil without vegetation and saline soils. Different radiometric indices were used to differentiate vegetation from agricultural and saline soils. The unsupervised classification system showed changes at 80% of the surface in land use in 30 years. Clear water and agricultural land decreased and increased at 20% the soils degraded by salts or urban use. It is a region with extreme risk due to the salts-affected soil

Band 3 mutations, distal renal tubular acidosis, and Southeast Asian ovalocytosis

Band 3 mutations, distal renal tubular acidosis, and Southeast Asian ovalocytosis. Familial distal renal tubular acidosis (dRTA) and Southeast Asian ovalocytosis (SAO) may coexist in the same patient. Both can originate in mutations of the anion-exchanger 1 gene (AE1), which codes for band 3, the bicarbonate/chloride exchanger in both the red cell membrane and the basolateral membrane of the collecting tubule alpha-intercalated cell. Dominant dRTA is usually due to a mutation of the AE1 gene, which does not alter red cell morphology. SAO is caused by an AE1 mutation that leads to a nine amino acid deletion of red cell band 3, but by itself does not cause dRTA. Recent gene studies have shown that AE1 mutations are responsible for autosomal recessive dRTA in several countries in Southeast Asia; these patients may be homozygous for the mutation or be compound heterozygotes of two different AE1 mutations, one of which is usually the SAO mutation