Un enfocament simple i analític per al sintonitzat robust de controladors PID

Un sistema de control realimentat negativament permet mantenir la sortida d'un procés a prop del valor desitjat encara que n'hi hagi pertorbacions. L'estratègia més comuna és obtenir primer un model matemàtic pel procés a controlar i, en base a aquest model, sintonitzar l'algorisme de control. En contraposició a molts mètodes de caire empíric, aquest article proposa una manera analítica de sintonitzar un controlador de tipus PID en base a un model de primer ordre més temps mort. L'objectiu és l'obtenció de respostes suaus.Un sistema de control realimentado negativamente permite mantener la salida de un proceso cerca del valor deseado aunque haya perturbaciones. La estrategia más común es obtener primero un modelo matemático para el proceso a controlar y, en base a este modelo, sintonizar el algoritmo de control. En contraposición a muchos métodos de tipo empírico, este artículo propone una manera analítica de sintonizar un controlador de tipo PID en base a un modelo de primer orden más tiempo muerto. El objetivo es la obtención de respuestas suaves.A simple negative feedback control loop makes the process variable close to the set-point even if there are disturbances. The common strategy is to develop a mathematical model of the process and, based on it, to select appropriate values for the control algorithm parameters. In contrast with many empirical methods, this communication proposes the analytical tuning of a commercial PID controller based on a FOPDT model. The objective is to obtain smooth responses

Fabricación de células solares sobre silicio multicristalino y silicio purificado por la vía metalúrgica

RESUMEN El objetivo de la presente Tesis Doctoral es la optimización de procesos de fabricación de células solares caracterizados por ser simples, repetitivos y con una baja carga térmica asociada, lo que los hará útiles para ser utilizados con cualquier tipo de substratos, tanto si son de calidad electrónica como si son de calidad solar. Como punto de partida se toma el proceso de P/Al desarrollado en el IES-UPM con el que se obtienen células solares de alta eficiencia con emisores relativamente profundos y moderadamente dopados, dando lugar a células con eficiencias en torno al 19% utilizando como substratos obleas de silicio monocristalino FZ de alta calidad. En nuestro caso, los substratos utilizados serán de silicio multicristalino caracterizados por poseer un menor tiempo de vida y por ser más sensibles a los pasos de horno. Por este motivo el proceso estándar de P/Al, debido a la alta carga térmica asociada al mismo, no resultó eficiente con muestras de bajo tiempo de vida. Se hace por lo tanto necesario realizar una adaptación del mismo para substratos de silicio multicristalinos (mc-Si), que serán utilizados en la mayoría de los casos a lo largo de esta Tesis. En el nuevo proceso propuesto se introduce como novedad un paso de extracción simultánea de impurezas por fósforo y por aluminio (co-gettering). Se van a plantear y estudiar en profundidad con el fin de optimizar la temperatura a la cual se produce una extracción más efectiva de las impurezas. Así, en primer lugar se estudia el efecto de la misma sobre el paso de extracción por fósforo. A continuación se procede de forma similar con el proceso de extracción por aluminio y, finalmente, con el proceso de extracción simultánea producida por ambos elementos. En el caso del fósforo, se encontró la temperatura para la cual se tiene la mejor relación entre la extracción de impurezas procedentes del substrato y la degradación del mismo debido a la carga térmica del paso de horno, la cual es responsable de la activación de otras impurezas así como de defectos cristalinos. En relación con el paso de extracción por aluminio, esta no resulta efectiva con nuestras muestras de mc-Si debido probablemente a que la mayoría de las impurezas presentes están atrapadas en defectos cristalinos (dislocaciones y fronteras de grano) o a que ocupan posiciones sustitucionales dentro de la red. En este sentido, si bien el paso de extracción simultánea consigue mejorar el tiempo de vida, el incremento introducido en el mismo es inferior al obtenido tras el paso de extracción por fósforo debido a que los autointersticiales inyectados durante la difusión de fósforo en condiciones de supersaturación son absorbidos por vacancias generadas por la capa de aluminio durante su difusión, retardando el efecto de extracción por fósforo. A continuación, tratando de disminuir la velocidad de recombinación en la cara frontal, se realiza un paso de pasivación de dicha superficie. Si bien la capa de óxido crecida consigue disminuir dicho valor, aparece una degradación en el tiempo de vida del volumen. Tratando de mejorar las limitaciones encontradas con el paso de extracción por aluminio para nuestro substrato de mc-Si, se planteó la posibilidad de realizar células solares evitando dicho paso de extracción y realizando el contacto posterior de forma puntual. El resto de la superficie se pasiva con una capa de óxido de silicio. Con ello también se pretende disminuir la velocidad de recombinación en dicha cara y disponer de un espejo posterior con el que aumentar la capacidad para absorber fotones de alta longitud de onda. Ambas propiedades son importantes si se tiene en cuenta que cada vez se utilizan substratos más delgados y con mayor tiempo de vida. Así, tomando como punto de partida el proceso PERC utilizado en el IES-UPM se ha desarrollado un nuevo proceso disminuyendo la carga térmica asociada, y utilizando capas pasivadoras de óxido seco y húmedo. Tanto las eficiencias obtenidas como la repetitividad en los resultados son mayores que en el caso anterior. Teniendo en cuenta que la demanda existente de silicio purificado está limitando el crecimiento del mercado fotovoltaico, la industria fotovoltaica está en la necesidad de encontrar una fuente de materia prima distinta de la utilizada para la industria de los semiconductores. En este sentido, y partiendo de obleas obtenidas a partir de lingotes purificados siguiendo la vía metalúrgica (mezclado o no con silicio reciclado de la industria fotovoltaica), se han realizado diversos experimentos de caracterización de las mismas así como tandas de células solares con el fin de analizar y ayudar en la optimización dichos lingotes. Se llevaron a cabo medidas de la variación de la resistividad, del tiempo de vida inicial y de la evolución del mismo a lo largo de las tandas realizadas con respecto a la cantidad de silicio reciclado procedente de la industria fotovoltaica presente en el lingote y al número de pasos de purificación realizados en el mismo. El proceso utilizado para realizar las células es el de P/Al optimizado para substratos de calidad solar, ya que este se puede utilizar como “evaluador” del mismo. A grandes rasgos, las conclusiones a las que se llegan en este caso son: Una mayor presencia en el lingote de silicio desechado por la industria fotovoltaica (y por lo tanto con un menor contenido de impurezas) da lugar a mayores resistividades, tiempos de vida y eficiencias. En el caso de lingotes realizados con la misma proporción de silicio solar, aquel que ha pasado un mayor número de pasos de purificación da lugar a células con mejores características. El nitruro de silicio se está introduciendo cada vez en mayor medida, tanto en laboratorios como a nivel industrial, para conseguir capas pasivadoras de la superficie y capas antirreflectantes. En relación con el hidrógeno presente en dicha capa, también puede actuar como pasivadora del volumen en el caso de ser depositadas sobre muestras de mc-Si. Sus procesos se caracterizan por realizarse a baja temperatura (< 450 ºC) y ser de corta duración (en general, menor a 3 minutos), siendo por lo tanto adecuados para ser utilizados con substratos de calidad solar. Se han optimizado los distintos parámetros de los que consta el proceso tratando de conseguir la mejor pasivación superficial posible: temperatura, flujo total de los gases constituyentes (silano y amoniaco), presión y potencias de las fuentes de excitación: radiofrecuencias y microondas. Las capas se han caracterizado realizando medidas de su índice de refracción, de su coeficiente de extinción y de su espesor. Finalmente, se ha tratado de integrar estas capas en el proceso de P/Al adaptado para substratos de calidad solar, a modo de capa antirreflectante y/o como capa máscara con la que definir el área activa de las células solares. En el primer caso, se ha optimizado el espesor de la misma teniendo en cuenta la duración del proceso es distinta según si se deposita la capa sobre una muestra pulida o texturada. Esto es debido a que para la muestra texturada, debido a las pirámides presentes en la superficie, el área a cubrir es mayor por lo que la duración del proceso también lo será. En el segundo caso se han realizado pruebas con capas de unos 300 nm de espesor para ver su comportamiento ante los ataques químicos para la apertura de las ventanas correspondientes al área activa de la célula solar, del texturado y como barrera ante el paso de difusión de fósforo. Se producen problemas a la hora de abrir las ventanas debido a que las capas de nitruro de silicio son muy resistentes a los ataques químicos. Por este motivo, se necesita de ataques en BHF cuya duración puede llegar a ser superior a una hora, apareciendo problemas con la resina protectora del resto de la superficie, la cual también aparece atacada en algunas ocasiones. También se produce un texturado poco eficiente debido probablemente a la presencia de restos de la mencionada capa de nitruro de silicio en el área activa. Por ello, la integración de estas capas debe ser aún optimizada. Por otro lado, debido a la baja carga térmica del proceso y a la hidrogenación producida en el volumen de las muestras de mc-Si tras un paso de recocido, se han obtenido los mayores tiempos de vida al finalizar la tanda, evitando la degradación sufrida en el mismo tras el paso de pasivación con óxido de silicio. ABSTRACT The aim of this Thesis has been the optimization of processes for manufacturing solar cells using silicon substrates of solar grade. Solar grade silicon wafers comprehends both wafers obtained with the method of crystallization by casting (multi-crystalline silicon) and substrates made from polysilicon purified by metallurgy. The starting point is the P/Al process, developed at the IES-UPM, which provides high efficiency solar cells with relatively deep, moderately doped emitters. The efficiency can be as high as 19% if high quality substrates (floating zone, mono-crystalline silicon) are used. For this Thesis the substrates were multi-crystalline ones, characterised for their lower carrier lifetimes and because they are more sensitive to furnace steps. Due to this sensitivity and the high temperature steps required by the P/Al process, the efficiency obtained with short lifetime substrates was very low. It was then necessary to adapt this process for multi-crystalline substrates (mc-Si), which were used in most of the experiments along this Thesis. In the new process proposed it has been introduced as an innovation the simultaneous impurity extraction by phosphorus and aluminum (co-gettering). Different processes have been carried out in order to determine at which temperature the extraction is more effective. At first, only the effect of temperature in extraction by phosphorus is studied. Later, the same procedure is repeated but with the aluminum extraction. Finally, the dependence with temperature of the simultaneous process, with both phosphorus and aluminium at the same time, is studied. In the case of phosphorus, it has been found the optimal temperature at which the balance between impurity gettering and degradation of the substrate due to high temperature occurs. This temperature is responsible for the activation of other impurities and crystalline defects. Regarding the extraction by aluminum, this process has no effect in mc-Si substrates, maybe due to the fact that most of the impurities are trapped on crystalline defects (stacking defaults and grain borders) or they occupy substitutional positions on the net. Both cases make gettering by aluminium very difficult. Whereas the simultaneous gettering process improves carrier lifetime, the increase obtained is lesser than that obtained after the gettering with phosphorus alone because the auto-insterstitials injected during phosphor diffusion, made in super-saturation conditions, are absorbed by the vacancies generated by the aluminum layer during diffusion, producing thus a delay in the gettering by phosphorus. Then, trying to decrease the front surface recombination velocity, a passivation step is done. Whilst it is true that the oxidation layer decreases that value, the process produce a degradation in the lifetime. As well, it has been explored the possibility to produce solar cells with local rear contacts, and doing a passivation of the rest of the surface with a silicon oxide layer. Furthermore we solve the failed phenomenon of the aluminum extraction, and we provide a mirror in that face which is responsible of an increase in the absorption of photons with large wavelength. Both properties are relevant if they are used wirh thinner substrates and/or with high lifetime values. Then, a new process has been developed decreasing the thermal load, and using dry and wet passivation layers. Both efficiencies and results achieved are higher than in the previous case. Taking in account that the actual demand of purified silicon is limiting the growth of the photovoltaic market, the industry has the need to find a different material source than the one used by the semiconductors industry. In this way, and using wafers grown using ingots purified following the metallurgical process (mixed or not with silicon recycled form the photovoltaic industry), different characterization experiments and batches have been carried out trying to analyze and optimise those ingots. An study of the dependence of the amount of recycled silicon from the photovoltaic industry present in the ingot based on the resistivity, on the initial lifetime and on the evolution of its value along the batch has been done. The process used to develop solar cells is the P/Al one optimised for solar grade substrates, because it can be used as “evaluator” of the substrates. Two important conclusions have been achieved: A greater presence in the ingot of silicon recycled from the photovoltaic industry (and thus a lower amount of impurities) gives higher resistivities, lifetimes and efficiencies. During the time that this project has been carried out, better polysilicon purification processes have been done, giving better efficiencies in spite of using ingots with the same proportion of solar grade silicon. Silicon nitride films are being introduced in laboratories as well as in the industry, giving passivation and antireflection coating layers. Related to the hydrogen presents at the film, it can passivate the bulk in the case of the use of mc-Si. Processes are characterised for their low temperature (< 450 ºC) and their short time (in general, less that 3 minutes), being suitable to be used with solar grade substrates. The deposition parameters have been optimised in order to achieve the best surface passivation: temperature, total gas flow (silane and ammonia), pressure and the power of the different excitation sources: radio frequencies and microwaves. Layers have been characterised by measuring the refractive index, extinction coefficient and thickness. Finally, we tried to incorporate those layers in the P/Al process adapted for solar grade substrates, like an antireflection coating and/or like a mask to define the active area window in the solar cells. On the first case, an optimisation of the layer’s thickness has been done taking in account that the process length is different depending on if the sample is polished or texturised. For the textured ones, due to the presence of pyramids on the surface the area to be covered is higher and, then, the length of the process does so. In the second case, different tests were done with 300 nm thick layers in order to study their behaviour versus different chemical baths used to open the active area window, to do the texturisation and as a phosphorus diffusion barrier. Different problems appears trying to open the active area window due to the high resistance to chemical baths of the silicon nitride layer. Because of that, the length of the BHF attack may last more than one hour, giving troubles with the resin used to protect the rest of the surface, which was attacked sometimes. Beside, a low efficient texturisation was achieved probably due to the presence of rests of the silicon nitride layer at the active area window. Because of that, the integration of those layers has to be further optimised. In other way, due to the low thermal load associated with the process and the bulk hydrogenation on mc-Si wafers after an annealing step, highest final lifetimes have been achieved at the end of the batches, avoiding the degradation produced after the passivation step with silicon oxide

Website design as moderating factor of online user behavior

It is widely assumed that online user behaviour is mainly utilitarian, although hedonic motivations such as enjoyment have also been found by recent research to have a marked influence on such behaviour. The present study explores the influence of website design (utilitarian motivation) on online user behaviour, in the context of a site promoting a tourist destination. The results underline the importance of utilitarian aspects for the effectiveness of online information-processing and the formation of perceived risk online. It is recommended that websites should reflect this type of motivation so as to make browsing useful for the online consumer.The authors appreciate the financial help provided via a research project of group ADEMAR (University of Granada) under the auspices of the Andalusian Program for R&D, number P06-SEJ02170, and Research Program from the Faculty of Education, Economy and Technology of Ceuta

The influence of website design, culture and language on perceived web usability, satisfaction and perceived risk online

The current markets globalization as a result of ICT development in general and the Internet in particular, have enhanced the importance of the websites design, which is a powerful communications medium for companies operating in international markets (Turban and Gehrek, 2000). The website of the company represents its image in the Internet as an intermediary with potential clients (Roy, Dewit and Aubert, 2001). Some researchers have found that much of the success of an e-service depends on website usability (Flavián, Guinalíu and Gurrea, 2006). Usability and appearance are two indicators that represent the utilitarian aspects of a website, together with its appeal. Those websites with a high level of usability in their design enable users to carry out their tasks coherently and achieve the results they expect (Palmer, 2000). In fact, this perception of control during the browsing process is positively related to the sensation of security and satisfaction (Diamantopoulos and Winklhofer, 2001; Casaló, Flavián and Guinalíu, 2008). In this international context, culture plays an increasingly relevant role in the use of information and communication technology. This is likely to affect how usability is understood, thus adding an additional factor to our understanding of culture´s effect on usability (Wallace, Reid, Clinciu and Kang, 2013). The importance of cultural factors in communications has been reinforced since the web can now link diverse regions and communities across the globe that were relatively isolated by time and space. The growth of global communications has increased and intensified the need for leaning to communicate successfully with a multitude of cultures. Regarding to these international situation, the crucial role of language in intercultural relations is widely acknowledged, with the words of a language being ‘symbols’ that acts as the vehicles for cultural transfer (Hofstede, 2001). The literature shows that the way in which a person processes information is conditioned by cultural values (Tavassoli, 2002). Furthermore, recent research has demonstrated that language is associated with cultural frameworks, such that communication in a given language can increase access to the cultural values associated with that language (Wong and Hong, 2005) and how users from the same culture, when processing information in different languages, obtain significantly different results in terms of perceived risk online (Alcántara-Pilar, Del Barrio-García and Porcu, 2013).The authors appreciate the financial help provided via a research project of group ADEMAR (University of Granada) under the auspices of the Andalusian Program for R&D, number P06-SEJ02170, and Research Program from the Faculty of Education and Humanities of Ceuta

Consumer searching information process and Culture Values

The use of Internet as a new market has increased interest in research on Consumer Behaviour Online. Due to its complexity, each investigation has been centred on different aspects. So to continue, a theoretical model will be offered developed from TAM and the State of Flow but adding some new elements related to social pressure and the intention to reduce cognitive effort of the navigator so that he can concentrate more on enjoying himself while navigating and shopping

Stabilization of Polymeric Nanofibers Layers for Use as Real-Time and In-Flow Photonic Sensors

In order to increase the sensitivity of a sensor, the relationship between its volume and the surface available to be functionalized is of great importance. Accordingly, porous materials are becoming very relevant, because they have a notable surface-to-volume ratio. Moreover, they offer the possibility to infiltrate the target substances on them. Among other porous structures, polymeric nanofibers (NFs) layers fabricated by electrospinning have emerged as a very promising alternative to low-cost and easy-to-produce high-performance photonic sensors. However, experimental results show a spectrum drift when performing sensing measurements in real-time. That drift is responsible for a significant error when trying to determine the refractive index variation for a target solution, and, because of that, for the detection of the presence of certain analytes. In order to avoid that problem, different chemical and thermal treatments were studied. The best results were obtained for thermal steps at 190 °C during times between 3 and 5 h. As a result, spectrum drifts lower than 5 pm/min and sensitivities of 518 nm/refractive index unit (RIU) in the visible range of the spectrum were achieved in different electrospun NFs sensors.This work was supported by the Spanish government through the project TEC2015-63838-C3-1-ROPTONANOSENS and from the Basque government through the project KK-2019/00101 -µ4INDUSTR

The effect of culture and the cultural framework of language on online information - processing

The present work examines the effect of the user’s language, as a vehicle for cultural values, on their processing of the information contained within a website. A sample of 491 internet users from two different cultures (British and Spanish) was created. Half the users were asked to browse the experimental website in their mother tongue, while the other half browsed in their second language (British participants browsing in Spanish and the Spanish browsing in English). The key findings of the research demonstrate that information-processing is moderated by the user’s culture and the language in which they process the information

Factores Asociados a Trastornos del Nivel y Contenido de la Conciencia en Pacientes del Pabellón E-1 del Hospital Nacional Hipólito Unanue durante el 2016

Objetivo: Identificar los factores asociados a trastornos del nivel y contenido de la conciencia en pacientes del pabellón E1 del HNHU durante el 2016. Métodos: Se realizó un estudio de tipo observacional, retrospectivo y analítico en el servicio de Medicina Pabellón E-1 del Hospital Nacional Hipólito Unanue. Resultados: La mayoría de la población en estudio resultaron ser adultos mayores (más de 60 años) además que dentro del grupo de adultos menores de 60 años sólo el 22.2% presento estado confusional con ideación delirante; el género en el que más predominó fue en el femenino, 74 de los 199 pacientes en estudio usaron ventilación mecánica en algún momento; 152 de los 199 pacientes usaron sonda nasogástrica en algún momento durante su hospitalización. Conclusiones: Se determinó que el principal factor asociado en este caso es la edad; para tal caso se vio está relacionada también con la menor presencia de estado confusional con ideación delirante. No se encontró relación significativa con el resto de variables estudiadas

Sensitivity comparison of a self-standing porous silicon membrane under flow-through and flow-over conditionshttps://aplicat.upv.es/senia-app/edicion/mantArticuloBib.faces?p_idioma=v

© 2019 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertisíng or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.[EN] An optical sensor based on a self-standing porous silicon (PS) membrane is presented. The sensor was created by electrochemically etching a heavily doped p-type silicon wafer with an organic electrolyte that contained dimethylformamide. After fabrication, a high-current density close to electropolishing was applied in order to allow the detachment from the substrate using a lift-off method. The PS membrane was integrated ina microfluidic cell for sensing purposes, and reflectance spectra were continuously obtained while the target substance was flowed. A comparison of the bulk sensitivity is achieved when flowing through and over the pores is reported. During the experiments,a maximum sensitivity of 770 nm/RIU measured at 1700 nm was achieved. Experimental sensitivity values are in good agreement with the theoretical calculations performed when flowing through the PS membrane, it means that the highest possible sensitivity of that sensor was achieved. In contrast, a drop in the sensi-tivity of around 25% was observed when flowing over the PS membrane.This work was supported by the Ministry of Economy and Competitiveness. The associate editor coordinating the review of this paper and approving it for publication was Prof. Aime Lay-Ekuakille.Martín-Sánchez, D.; Ponce-Alcántara, S.; García-Rupérez, J. (2019). Sensitivity comparison of a self-standing porous silicon membrane under flow-through and flow-over conditionshttps://aplicat.upv.es/senia-app/edicion/mantArticuloBib.faces?p_idioma=v. IEEE Sensors Journal. 19(9):3279-3281. https://doi.org/10.1109/JSEN.2019.2893885S3279328119

The effect of culture and language on perceived risk online

The present paper analyzes whether cultural values and language can influence the way in which information on a website is processed, in terms of perceived risk. An online experiment was conducted, using a sample comprising users from the United Kingdom and Spain. Participants were asked to browse a website relating to a fictitious tourist destination, with half the sample accessing the site in their mother tongue and the other half in their second language. The key findings show that Internet users’ perception of risk is moderated by the language used, with the degree of bilingualism being a key factor