Fases de Ruddlesden-Popper de cobalto y materiales relacionados : síntesis, caracterización y propiedades de magneto-transporte

[Resumen] En la bibliografía existen numerosos trabajos sobre las propiedades magnéticas, y de transporte magnetorresistivas de las perovskitas de cobalto Ln1-xAxCoO3 en los que el cobalto presenta valencia +3 y +4. Sin embargo, existe muy poca información sobre dichas propiedades en compuestos equivalentes de cobalto con estructuras de menor dimensionalidad. Por ello, este trabajo pretende explorar un campo muy poco conocido: la influencia de la dimensionalidad de la estructura sobre las propiedades de mangnetotransporte de óxidos mixtos de cobalto en alto estado de oxidación (>+3) con estructuras relacionadas con la perovskita. Así, como materiales para la realización de este estudio se han utilizado compuestos de la familia de Ruddlesden-Popper (RP): compuestos bidimensionales con n=1 Ln1-xSr1+xCoO4 GLn=La,Nd y Gd) y compuestos cuasi-bidimensionales con n=2 Ln2-xSr1+xCo2O7 (Ln=Gd y Sm). La realización del este trabajo ha implicado a abordar los siguientes aspectos: 1,- Búsqueda de métodos de síntesis adecuados para la preparación de los diferentes miembros de las series de RP como fases puras. Para ello se han utilizado métodos de química suave y, en los casos que pareció conveniente, técnicas de síntesis a alta presión. 2,- Caracterización de los compuestos obtenidos: conocimiento de sus características estructurales, microestructurales, morfológicas, térmicas y su estequiometría en oxígeno. 3,- Estudio de sus propiedades magnéticas, de transporte y de magnetorresistencia. Por otra parte, teniendo en cuenta que en perovskitas de otros elementos de transición el valor de la magnetorresistencia se ve incrementada por dopajes con cobalto y que, por otro lado, una disminución de la dimensionalidad también la favorece, hemos tratado de combinar sinégicamente ambos efectos preparando fases de Ruddlesden-Popper, con n=2, de manganeso La1.2Sr1.8Mn2-xCoxO7 y hierro Sr3Fe1.5Co0.5O6.6.7 dopadas con esté ión

A methodology for sizing backup fuel-cell/battery hybrid power systems

Hybridization of fuel cells and batteries combines the advantages of both power sources. This paper proposes the use of fuel-cell/battery hybrid power systems as backup power systems and develops a methodology for sizing both fuel cell and battery bank, according to a minimum lifecycle cost criterion, from any defined hourly load profile and any defined backup time. For this purpose, an existing power-system-sizing computer tool has been used, but its initial capabilities have been extended. The developed methodology allows decisions to be taken before any investment is made. As a practical application, the methodology is used for the sizing of a backup power system for a telecommunication system

The Remote Access to Laboratories: a Fully Open Integrated System

An existing lab experience can be made remotely accessible in a relatively easy way. The problem is with the design of a tool which allows any kind of experience to be made remotely accessible. The complexity of this tool is out of discussion. Several universities have been working on it for years. In fact, the Huelva University presented the work “A Complete Solution for Developing Remote Labs†in the 10th IFAC Symposium on Advances in Control Education (2013). Such complete solution was the result of those universities working together. Since then, the joint-work has continued and improvements have also been achieved. Hereafter, a fully open integrated system is presented whose scope is greater than that of 2013. It offers a way to easily implement cloud services for managing the configuration and access to all type of sensors, actuators and controllers (the devices base of the any remote lab). The access proposed is secure, controlled, organized and collaborativ

Testing Bench for Remote Practical Training in Electric Machines

Remote labs are emerging as a necessary tool to support practical classes in engineering studies. It is due to the increasing number of students who combine their studies with work. In fact, there are numerous developments in areas such as electronics and automatic. However, there are only a few of them in the area of electrical machines. This paper presents a testing bench for remote practical training in electric machines. The security challenges presented by these experiments are overcome by software within the remote lab. In addition, a friendly interface has been designed including augmented reality to identify the different elements and to provide information on these items if the student requires it. The testing bench has been developed to be used in different kinds of electrical machines test

A Fully Integrated Open Solution for the Remote Operation of Pilot Plants

Nowadays remote access to systems in the instrumentation and measurement fields is both a reality and a challenge. There is a growing interest in replacing manual actions performed on site by remote actions carried out from anywhere around the world. To do that, besides the availability of suitable communication networks, it is necessary for the elements involved in the network to recognize each other, this latter task perhaps being the most complex one of the two. Integrating different hardware/software from different manufacturers into a single system with controlled remote access is not a trivial task. This paper presents a fully integrated open solution for the operation of pilot plants (scaled down, laboratory level industrial plants operated in university and other environments) using open access hardware/software on public networks. The proposed solution is independent of the nature of the pilot plant and its elements and can therefore be considered standard. In order to illustrate the capabilities of the proposed solution, two different types of pilot plant are presented

A Complete Solution for Developing Remote Labs

The use of remote laboratories for education is increasing because it is a method that allows a better use of resources (laboratories operate 24 hours a day) and students interact with real equipment from different locations. However, we can say that there are as many particular solutions as remote labs can be found today. In this paper, we present a design framework for remote laboratories, covering the various aspects involved and completely based on free software. Within this approach, professors have all the tools required to convert a laboratory experiment in a remote experiment. Moreover, they can also design an user interface that includes augmented reality techniques to enrich the user experience

Controlled and Secure Access to Promote the Industrial Internet of Things

Internet of Things (IoT) aims at facilitating access to all devices that are connected to the internet, both wired and wireless. This scenario can initially seem interesting. Nevertheless, it has a lack of privacy and danger of malicious interaction with the devices. Therefore, IoT, as it stands, is not suitable for companies to make their data and devices accessible through the internet, since they could find an untidy cloud, made up of devices without the necessary control of use. This paper proposes the use of the cloud computing advantages to develop a secure access global system based on a cloud. The company will decide the controlled access to the chosen devices and data, both by employees and external people. The developed system can be used from different scenarios such as: a public cloud; an Infrastructure as a Service (IaaS); and a private cloud. To illustrate the operation of the developed system, a representative network of heterogeneous multiprotocol devices has been designed

Comparing Remote Laboratories from the Student Perspective

The objective of this paper is the identification of the variables which affect the acceptation by the students of two kinds of remote laboratories (photovoltaic panels and electric machines) in Higher Education. To achieve it, the Technology Acceptation Model is used and usability and usefulness are the considered factors. Two pilot experiences are carried out over a sample of 86 students which are studying the Energy Engineering Degree. 45 of them (52.3%) carry out the electric machines lab class and 41 (47.7%) the photovoltaic one. After a descriptive analysis, an exploratory and multivariate analysis is carried out. It allows the identification of relations between several variables which affect to the acceptation of both remote labs

Charge ordering and dielectric properties in the near half-doped Pr0.79Na0.21MnO3 perovskite

[Abstract] The Pr0.79Na0.21MnO3 perovskite has been prepared in polycrystalline form by a ceramic method. We have carried out its structural characterization by synchrotron X-ray powder diffraction (SXRPD) at room temperature and at 150 K (T<TCO). In the charge ordering (CO) state, the SXRPD data can be refined both on the basis of the site-centred model and the bond-centred model proposed for half-doped manganites, without a clear advantage of one model over the other. From the dielectric point of view, at the CO temperature this manganite shows a maximum in the dielectric constant whose origin is intrinsic, and cannot be attributed to the presence of extrinsic factors. We relate this dielectric behaviour to the formation of polar entities at the temperature of charge condensation, due to an asymmetric charge distribution intermediate between site-centred and bond-centred type.Xunta de Galicia; PGIDIT06PXB103298PRMinisterio de Educación y Ciencia; Project FEDER MAT 2004-0513

Studies on the power factor of (Ba,Sr)Co2+xRu4−xO11 compounds

[Abstract] We have prepared polycrystalline single-phase ACo2+xRu4−xO11 (A = Sr, Ba; 0 ≤ x ≤ 0.5) using the ceramic method and we have studied their structure, electrical resistivity and Seebeck coefficient, in order to estimate their power factor (P.F.). These layered compounds show values of electrical resistivity of the order of 10−5 Ωm and their Seebeck coefficients are positive and range from 1 μV K−1 (T = 100 K) to 20 μV K−1 (T = 450 K). The maximum power factor at room temperature is displayed by BaCo2Ru4O11 (P.F.: 0.20 μW K−2 cm−1), value that is comparable to that shown by compounds such as SrRuO3 and Sr6Co5O15.Ministerio de Ciencia e Innovación; Project FEDER MAT 2007-6669