The objective of the present work is to provide a better understanding of magnetron sputtered transparent conducting oxides based on ZnO in order to use them as electrodes in thin film silicon solar cells at the Grup d'Energia Solar of the Universitat de Barcelona. This thesis presents the properties of magnetron sputtered aluminium and gallium doped ZnO as well as the properties of multi-compound materials deposited by the co-sputtering of zinc oxide and indium tin oxide. The application of ZnO based transparent conducting oxides to the back reflector of pin amorphous solar cells is also discussed. A set of aluminium doped zinc oxide layers were deposited under different substrate temperature and discharge power. The structural, electrical and optical properties were characterised and discussed. The higher substrate temperatures and discharge powers used during deposition led to highly transparent layers in the visible range with lower resistivities. The polycrystalline layers were oriented with the c-axis perpendicular to the substrate surface and the crystalline quality of the layers improved at higher temperatures and powers. A remarkable increase in mobility was found for temperatures above 300°C and the carrier concentration also rose with temperature reaching 3.71x1020 cm-3 at 420°C. The most remarkable feature found at higher deposition power was the increase in deposition rate (from 0.9 to 9 nm/min). By means of a high temperature (650°C) annealing process under a capping layer of silicon or alumina, the mobility of aluminium doped zinc oxide layers was considerably raised achieving 68.5 cm2V-1s-1. This process led also to more transparent layers in the near infrared as well as in the ultraviolet part of the spectrum. Gallium doped zinc oxide films were deposited in order to investigate the suitability of gallium as a dopant in zinc oxide layers. Highly transparent layers with higher carrier concentrations but lower mobilities compared to aluminium doped zinc oxide were obtained. The dependence of the layer properties on the pressure, doping concentration, substrate temperature and oxygen volume concentration during deposition were studied in order to find the adequate layer to be applied as electrode in thin film solar cells. 4 wt.% Ga2O3 doping concentration was found to be optimal for the production of highly conductive ZnO:Ga layers with a high band gap energy. The incorporation of oxygen gas during the sputter deposition led to more transparent layers at wavelengths longer than 1100 nm, but was found to be detrimental for the electrical properties of the studied layers. By means of co-sputtering, a set of multi-compound layers formed by Zn-In-Sn-O were deposited and carefully characterised. The resulting layers were studied as a function of the Zn content ratio, which varied between 17.1 to 67.3%. The layers were amorphous in nature but presented embedded nanometric crystals. The incorporation of Zn cations into an indium tin oxide matrix favoured the transmittance but did not modify the mobility. The carrier concentration was found to decrease resulting in an increase in resistivity. The electronic band structure was investigated by means of photoelectron spectroscopy. The measurements showed that, with an increase in Zn concentration, the oxygen vacancy concentration of the surface increased resulting in a degenerately n-doped surface layer. The work function of the material was determined by low intensity X-ray photoelectron spectroscopy and the values varied between 4.7 and 4.3 eV with the variation of Zn content. The final experiments were focussed on the application of ZnO layers in the back reflectors of pin amorphous silicon solar cells. Trials were performed onto pin structures deposited at T-Solar Global SA and the Universitat de Barcelona. The cells deposited at T-Solar were long exposed to air before a back reflector could be deposited and evidence for the formation of a thin silicon oxide layer at the interface was obtained. The oxide layer was removed using acid etching in dilute HF, but an analysis by X-ray photoelectron spectroscopy showed that the cleaning step resulted in an important amount of carbon contamination on the surface. Both, the silicon oxide and the carbon layer led to devices with S-shaped J-V curves. Later, the n-type interface was protected by a thin ZnO:Al layer at T-Solar to avoid oxidation during transportation. However, the existence of this thin ZnO:Al protective layer determined the growth of the subsequently deposited layers. Thus, the deposition of ZnO layers under different conditions led to similar results. Finally, different back reflectors were tried over the solar cells fabricated at UB. Aluminium and gallium doped zinc oxide layers were deposited on amorphous silicon pin structures, and a clear improvement in performance with respect to devices with only a metal layer as back reflector was observed. Similar performances were observed when Ga doped ZnO or Al doped ZnO was used in the back reflector. It showed that both gallium and aluminium were suitable dopants for the ZnO to be applied in the back reflector. / L'objectiu d'aquest treball rau en l'estudi i optimització dels òxids conductors transparents basats en l'òxid de zinc. Aquests materials, que s'han dipositat mitjançant polvorització catòdica magnetró, es van estudiar amb la finalitat d'emprar-los com elèctrodes en cèl•lules solars de silici en capa prima al Grup d'Energia Solar de la Universitat de Barcelona. En aquesta tesi es presenten les propietats de l'òxid de zinc dopat amb alumini o amb gal•li, així com les propietats de multi-compostos dipositats a partir de la co-polvorització catòdica d'òxid de zinc i d'òxid d'indi dopat amb estany. També es discuteix l'aplicació d'òxids conductors transparents basats en l'òxid de zinc al reflector posterior de cèl•lules solars de silici amorf amb estructura tipus pin. S’ha trobat que l’òxid de zinc dopat amb alumini, a altes temperatures de substrat i altes potències, presenta una elevada transmitància òptica i una baixa resistivitat. La mobilitat de les capes augmentà considerablement fins assolir 68.5 cm2V-1s-1 mitjançant l'aplicació de tractaments tèrmics a alta temperatura previ dipòsit d'una capa protectora de silici amorf o d'alúmina. Pel cas de l'òxid de zinc dopat amb gal•li s'han obtingut una sèrie de capes altament transparents i amb concentracions de portadors superiors, però amb mobilitats inferiors que les de capes dopades amb alumini. Mitjançant co-polvorització d’òxid de zinc i òxid d’indi dopat amb estany s’han obtingut capes amorfes del multi-compost Zn-In-Sn-O amb un contingut de zinc que varia entre el 17.1 i el 67.3%. La incorporació del zinc a l'òxid d'indi dopat amb estany afavoreix l'increment de la transmitància, sense que la mobilitat de les capes es vegi afectada. En canvi, la concentració de portadors disminueix amb la incorporació de Zn. Comparant l'ús del gal•li i de l'alumini com a dopants de l'òxid de zinc del reflector posterior de cèl•lules de silici amorf tipus pin, s'ha observat una gran similitud en el comportament dels dispositius. Això ens ha portat a la conclusió que ambdós materials són adients per ser emprats com a reflectors posteriors.

This thesis is focused on the study of molecular interactions at the atomistic detail and is divided into one introductory chapter and four chapters referencing different problems and methodological approaches. All of them are focused on the development and improvement of computational Monte Carlo algorithms to study, in an efficient manner, the behavior of these systems at a classical molecular mechanics level. The four biophysical problems studied in this thesis are: induced fit docking between protein-ligand and between DNA-ligand to understand the binding mechanism, protein stretching response, and generation/ scoring of protein-protein docking poses. The thesis is organized as follows: First chapter corresponds to the state of the art in computational methods to study biophysical interactions, which is the starting point of this thesis. Our in-house PELE algorithm and the main standard methods such as molecular dynamics will be explained in detail. Chapter two is focused on the main PELE modifications to add new features, such as the addition of a new force field, implicit solvent and an anisotropic network specific for DNA simulation studies. We study, compare and validate the conformations generated by six representative DNA fragments with the new PELE features using molecular dynamics as a reference. Chapter three is devoted to applying the new methods implemented and tested in PELE to study protein-ligand interactions and DNA-ligand interactions using four systems. First, we study the porphyrin binding to Gun4 protein combining PELE and molecular dynamics simulations. Besides, we provide a docking pose that has been corroborated by a new crystal structure published during the revision process of the submitted study showing the accuracy of our predictions. In the second project, we use our improved version of PELE to generate the first structural model of an alpha glucose 1,6-bisphosphate substrate bound to the human Phosphomannomutase 2 demonstrating that this ligand can adopt two low-energy orientations. The third project is the study of DNA-ligand interactions for three cisplatin drugs where we evaluate the binding free energy using Markov state models. We show excellent results respect another free energy methods studied with molecular dynamics. The last project is the study of the daunomycin DNA intercalator where we simulate and study the binding process with PELE. Chapter four is focused on the computational study of force extension profiles during the protein unfolding. We added a dynamic harmonic constraint following a similar procedure applied in steered molecular dynamics to our Monte Carlo approach to fix or pull some selected atoms forcing the protein unfolding in a defined direction. We implement and compare with steered molecular dynamics this technique with Ubiquitin and Azurin proteins. Moreover, we add this feature to a well-known algorithm called MCPRO from William Jorgensen¿s group at YALE University to evaluate the free energy associated to the unfolding of the deca-alanine system. Chapter five corresponds to the introduction of a multiscale approach to study protein-protein docking. A coarse-grained model will be combined with a Monte Carlo exploration reducing the degrees of freedom to generate thousands of protein-protein poses in a quick way. Poses produced by this procedure will be refined and ranked through a protonation, hydrogen bond optimization, and minimization protocol at the all-atom representation to identify the best poses. I present two test cases where this procedure has been applied showing a good accuracy in the predictions: tryptogalinin and ferredoxin/flavodoxin systems. / Aquesta tesi es centra en l'estudi de les interaccions moleculars amb detall atomic i es divideix en un capítol d'introducció i quatre capítols que fan referència a diferents problemes i enfocaments metodològics. Tots ells se centren en el desenvolupament i millora dels algoritmes computacionals de Monte Carlo per estudiar, de manera eficient, el comportament d'aquests sistemes a un nivell mecànica molecular clàssica. Els quatre problemes biofísics estudiats en aquesta tesi són: acoblament induït entre la proteïna-lligand i entre DNA-lligant per comprendre el mecanisme d'unió, resposta de les proteïnes a l'estirament, i la generació/puntuació d'acoblament entre poses proteïna-proteïna. La tesi s'organitza de la següent manera: El primer capítol correspon a l'estat de l'art en mètodes computacionals per estudiar les interaccions biofísiques, que és el punt de partida d'aquesta tesi. El nostre PELE algoritme i els principals mètodes estàndard com ara la dinàmica molecular s'explicaran en detall. El capítol dos es centra en les principals modificacions PELE per afegir noves característiques, com ara l'addició d'un nou camp de força, solvent implícit i modes normals per aquests estudis de simulació d'ADN. Es fa un estudi, comparació i validació de les conformacions generades per sis fragments d'ADN representatius amb PELE utilitzant dinàmica molecular com a referència. El tercer capítol està dedicat a l'aplicació dels nous mètodes implementats i provats en PELE per estudiar les interaccions proteïna-lligand i la interacció lligand-DNA utilitzant quatre sistemes. En primer lloc, se estudia la unió a proteïnes GUN4 combinant PELE i simulacions de dinàmica molecular. A més, es proposa un acoblament que ha sigut corroborat per una nova estructura cristal·lina publicada durant el procés de revisió de l'estudi mostrant l'exactitud de les nostres prediccions. En el segon projecte, hem utilitzat la nostra versió millorada de PELE per generar el primer model estructural d'una glucosa alfa substrat 1,6-bisfosfat unit a la fosfomanomutasa humana 2, que demostra que aquest lligant pot adoptar dues orientacions de baiza energia. El tercer projecte és l'estudi de les interaccions d'ADN lligant per tres medicaments cisplatí on se avalua l'energia lliure d'unió utilitzant Markov States Models. Es mostren excel·lents resultats respecte d'altres mètodes d'energia lliure estudiats amb dinàmica molecular. L'últim projecte és l'estudi de l'intercalador d'ADN anomenat daunomicina on es simula i estudia el procés d'unió amb PELE. El capítol 4 es centra en l'estudi computacional dels perfils d'extensió de la força durant el desplegament de la proteïna. Hem afegit una restricció harmònica dinàmica seguint un procediment similar al aplicat en dinàmica molecular en el nostre algoritme Monte Carlo per fixar o moure alguns àtoms seleccionats obligant a desplegar la proteïna en una direcció definida. Aquesta tècnica s'ha implementat i comparat amb dinàmica molecular per les proteïnes ubiquitina i azurin. D'altra banda, hem afegit aquesta modificació a un algoritme ben conegut anomenat MCPRO del grup de William Jorgensen a la Universitat de Yale per avaluar l'energia lliure associada al desplegament del sistema deca alanina. El capítol cinc correspon a la introducció d'un enfocament multiescala per estudiar l'acoblament proteïna-proteïna. Un model de gra gruixut es combinat amb una exploració Monte Carlo per reduir els graus de llibertat i generar milers de poses proteïna-proteïna d'una manera ràpida. Les poses produides per aquest procediment es perfeccionan i evaluan a través d'una protonació, optimització d'enllaços d'hidrogen, i minimització a escala atòmica per identificar les millors poses. Es presenten dos casos de prova on s'ha aplicat aquest procediment que mostra una bona precisió en les prediccions: tryptogalinin i ferredoxina / flavodoxina systems.

During the last decades, silicon nanocrystals have focused great attention due to the size-dependent physical properties they present, attributed to the quantum confinement effect. This, added to the bulk silicon compatibility with the well-established microelectronics technology and the low mining and manipulation costs this material presents, makes silicon a potential candidate for the growing photonics and optoelectronics fields. In particular, the tunnability of the electronic properties of silicon nanocrystals can be reached by controlling the nanocrystal size. This has been recently achieved by means of the superlattice approach, consisting of the alternated deposition of ultra-thin (2-4 nm) stoichiometric and silicon-rich layers of a given silicon-rich material. After a high-temperature annealing treatment, the silicon excess precipitates and crystallizes in the final form of nanocrystals, whose properties strongly depend on the fabrication process. Consequently, an ordered arrange of size-controlled nanocrystals (the superlattice) is obtained. In this Thesis Project, the structural, optical, electrical and electro-optical properties of silicon nanocrystal superlattices have been studied, using two different silicon-based materials as host matrices: silicon oxide and silicon carbide. The fabrication of these material systems has been carried out at different European institutions, specialists in the controlled deposition of nm¬thick films. Aiming at the nanocrystal superlattices characterization, different experimental techniques have been employed, which yield structural (transmission and scanning electron microscopies, X-ray diffraction), optical (optical absorption, photoluminescence and Raman scattering spectroscopies) and electrical / electro-optical (current versus voltage analysis in dark and under illumination, and electroluminescence, electro-optical response and light-beam induced photocurrent spectroscopies) information. From the material's point of view, the optimum structural properties that allow an almost perfect nanocrystal arrangement, size control and crystalline degree have been determined, always aiming at an optimum light emission and/or light absorption. Within this frame, fundamental studies have been performed to assess the crystalline degree of the nanostructures (confirming an atomic-thin transition layer between the crystalline nanocrystal core and the surrounding matrix), and to carefully inspect the controversial origin of luminescence within the nanocrystals when embedded in a silicon oxide matrix; as well, the structural conditions under which size-confinement of nanocrystals is reached when embedded in silicon carbide are reported. Once the best structural and optical properties from silicon nanocrystal superlattices were found, these material systems have been employed as active layers for light emitting and light converter (i.e. photovoltaic) devices. In oxide-based systems, the mechanisms that govern charge transport through the superlattices have been studied, and impact ionization has been hypothesized as the main electroluminescence excitation mechanism according to the experimental observations. In addition, the structural conditions (sublayer thicknesses, silicon-rich layer stoichiometry) that yield a maximum electroluminescence efficiency have been determined. Regarding silicon nanocrystals embedded in silicon carbide, a correlation has been established between the charge photogeneration and extraction when acting as an absorber material, which allowed assessing the structural conditions that maximize charge transport while minimizing the non-desirable recombination. Finally, via spectral response measurements, quantum confinement of excitons within silicon nanocrystals has been reported in silicon carbide matrix for the first time. In conclusion, the study on silicon nanocrystal superlattices developed within the present Thesis Project reveals the potential of silicon oxide as host matrix for silicon nanostructures to be used as light-emitting devices; instead, silicon carbide has proved a more suitable host material for photovoltaic applications, which sheds light to the future application of silicon nanocrystals as the top cell of an all-Si tandem cell. / Els nanocristalls de silici han esdevingut objecte d'estudi durant l'últim quart de segle, degut a què presenten, a causa de l'efecte de confinament quàntic, unes propietats físiques dependents de la seva mida. A més, la compatibilitat del silici massiu amb la ben establerta tecnologia microelectrònica juga en favor de la seva utilització i el seu desenvolupament per a futures aplicacions en el camp de la fotònica i l'optoelectrónica. El control del creixement de nanocristalls de silici es pot dur a terme mitjançant el dipòsit de superxarxes d'entre 2 i 4 nm de gruix, on capes de material estequiomètric basat en silici s'alternen amb altres de material ric en silici. Un posterior procés de recuit a alta temperatura permet la precipitació de l'excés de silici i la seva cristal.lització, tot originant una xarxa ordenada de nanocristalls de silici de mida controlada. En aquesta Tesi, s'han estudiat les propietats estructurals, òptiques, elèctriques i electro-òptiques de superxarxes de nanocristalls de silici embeguts en dues matrius diferents: òxid de silici i carbur de silici. Amb tal objectiu, s'han emprat tot un seguit de tècniques experimentals, que comprenen la caracterització estructural (microscòpia electrònica de transmissió i d'escombrat, difracció de raigs X), òptica (espectroscòpies d'absorció òptica, de fotoluminescència i dispersió Raman) i elèctrica / electro-òptica (caracterització intensitat-voltatge en foscor o sota il.luminació, electroluminescència, resposta electro-òptica), entre d'altres. Des del punt de vista del material, s'han estudiat les propietats estructurals òptimes per tal d'obtenir un perfecte ordenament en la xarxa de nanocristalls, una major qualitat cristal.lina i unes propietats d'emissió òptimes. L'optimització del material s'ha dut a terme en vistes a la seva utilització com a capa activa dins de dispositius emissors de llum i fotovoltaics, l'eficiència dels quals ha estat monitoritzada segons els diferents paràmetres estructurals (gruix de les capes nanomètriques involucrades, estequiometria, temperatura de recuit). Finalment, els nanocristalls de silici embeguts en òxid de silici han demostrat un major rendiment com a emissors de llum, mentre que una matriu de carbur de silici beneficia les propietats d'absorció i extracció (fotovoltaiques) del sistema.

Gene expression is a complex and highly regulated process. Most of the regulation is controlled by short DNA sequences that can be bound by some proteins called transcription factors (TF). Binding to these sites, the transcription factors, can start the transcription of mRNA, stop it, or just control the amount of mRNA produced. The DNA binding sites of these transcription factors have some specific characteristics: (1) They are short sequences (2) They can be located anywhere in the genome and (3) they are degenerated, which means that some mutations in the binding site sequence do not alter its functionality. These characteristics made impossible to look for a specific sequences in a specific region and, create the need to model the binding sites in order to detect them. Due to the importance of gene expression in the study of cell differentiation and its implication in some genetic diseases, many computational models and experimental processes to model binding site motifs and then find them into a genome have appeared. The computational models can be divided into two main groups: motif discovery methods which try to find binding sites within a set of co-regulated sequences without previous knowledge and motif search methods which use previous known sites to create a model and then try to locate binding sequences fitting this model. Most of the algorithms for binding site detection (both discovery and search) are based on Position weight matrices (PWM), which are matrices of frequencies of each nucleotide in each position, and assume that positions are independent. Some others take into account interdependences, but they need many sequences to be trained and high computational times. The focus of this thesis is to use the conversion from symbolical to numerical DNA and the previous knowledge of binding site sequences in order to construct models for DNA motifs. In this context, known multivariate signal processing techniques can be the ideal tools to construct models which can take into account interdependences without needing a large number of sequences or a high computational time. To characterize the transcriptions factors, the relationships TF-protein were studied, showing that most transcription factors regulate the expression of 5-10 genes and at the same time most proteins are regulated by more than 1 TF. The study of interdependences between positions showed that more than 90% of the binding sites have significant interdependences, but that the percentage of interdependences is not enough to classify TF according to structure. The conversion of DNA motif matrices into numerical matrices allows the use ofl Component Analysis (PCA) to model the binding sites which captures the information of the interdependences into the covariance, a second order statistics. Using the hypothesis that the binding sites will fit better to the PCA model than genomic, sequences, the Q-residuals can be used to detect binding sites within the genome. When compared to PWM the Q-residuals detector performs as least as well, and the improvement of detection is significantly correlated to the percentage of positions with interdependences. The disadvantage of these PCa models is that they are difficult to interpret. Converting the DNA symbolical matrix into a DNA numerical cube allows the calculation PARAFAC models which are easier to interpret. Since PARAFAC models have unique solutions, their scores can be combined with the PARAFAC Q-residuals in order to construct a quadratic detector that also performs better than PSSM models. When the numerical detectors are compared to detectors that take into account interdependences, they perform better when there are not many sequences available, but there are more sensitive to the number of positions.

Tesi realitzada a l'Institut de Recerca en Energia de Catalunya (IREC) / Solar cells generate electrical power by direct conversion of solar radiation into electricity using semiconductors. Once produced, the solar cells do not require the use of water; operate in silence and can be easily installed almost everywhere, as solar panels with low technological risk. In this thesis new photovoltaic materials and solar cells are investigated. From the beginning of the semiconductor era, silicon has been present; the semiconductor theory improved with the silicon technology, almost taking the idealized models to reality in within silicon. In the recent years plenty of new natural and artificially produced materials have seen the light; some of them are still waiting to be understood and explained by a new theory that has to be experimentally proved right. The clue for a better and faster progress is to work in a multidisciplinary frame; as this thesis shows, all research and knowledge has to have future protections and possibilities of been used in the benefit of our society. Today, the photovoltaic technology (PV) based on silicon solar cells dominates the market. The thin film PV such as GaAs, Cu(In,Ga)Se2 (GIGS) and CdTe have reached power conversion efficiencies above 20% which makes them industrially interesting despite the use of scare and/or very toxic elements. Researchers and investors are expectant for a new stable, eco-friendly, inexpensive, fast and easy to produce material that could be used in a big scale and long term for photovoltaic terrestrial applications. Some years ago it was believed that this ideal material was near to be confirmed when the reflectors were on a new chalcogenide material: Cu2ZnSn(SxSe1-x)4 (CZTSSe) called kesterite after its crystal structure. This semiconductor is very attractive due to its constituent elements, semiconductor properties. Its similarity with GIGS and compatibility with the already existing industrial processes made possible its rapid power conversion efficiency rise as absorber material in thin film solar cells. Through the years kesterite has been found to be a challenging material due to the energetically feasible mixture of stannite and kesterite structures, the high probability of defects, and the narrowness of the optimum compositional region (compared with that of chalcopyrites) that eases the formation of secondary phases limiting the efficiency of the solar cells. Recently, CZTSSe thin film solar cells with certified efficiency of 12.6% were produced by IBM; synthesized by spin-coating using a hydrazine-based pure solution approach on a soda-lime glass (SLG) Mo coated substrate. The use of hydrazine is the key for the record as well its mayor drawback however it demonstrates the robustness of the solution-based techniques. In this thesis the use of a cool-wall vertical pneumatic spray pyrolysis system (SP) is demonstrated as a synthesis technique of CZTS kesterite thin films from water and alcohol-based precursor solutions containing metal salts and thiourea. In the course of this thesis, the possibilities and limitations of this synthesis technique and the resulting films are explored in the frame of system- and solution-related parameters. The SP system used in this thesis is sophisticate and advantageous; is able of reproduce the open-air conditions used in typical spray systems but also it is capable of grow films by spraying in an oxygen-free atmospheres such as Ar or Ar-H2 or any other. It was completely new spray approach by the year of the publication of our first repot (2013) with a 0.5% efficient working solar cell. A remarkable efficiency value by the time of publication if considered the combo challenge: material + deposition technique. In this thesis, air, Ar and Ar-H2 were used as carrier gas and atmosphere, where the so sprayed films were studied in combination with other system parameters (solution flux, time of spraying, substrate temperature, etc.) and some solution related parameters (solvent, metal precursors concentration, solution stability, etc.). To obtain device grade films, the sprayed kesterite ought to be annealed; this annealing process is also subject of study in this thesis. One step annealing at high temperature (580°C) at room pressure in S-containing reactive atmosphere was optimized for the CZTS-based thin films with efficiencies of 1.4%. To synthesize CZTSSe films, different annealing approaches were tried; one step room pressure annealing (at 550°C) in Se- containing reactive atmosphere probed to be the optimum for sprayed kesterite from methanol-based precursor solutions for solar cells with the highest conversion efficiency of 1.9% obtained in this thesis. The results showed here open many new possibilities for the use of spray systems for the synthesis of PV quality materials for solar cells applications. / En esta tesis se demuestra el uso de un sistema de spray pyrolysis utilizado para sintetizar kesterita de azufre puro (CZTS) un material que representa un reto tecnológico y científico en el campo de las celdas solares de películas delgadas. La síntesis de este material es llevada a cabo en un sistema de spray en atmosfera controlada en el marco de los parámetros del sistema y de la solución; evitando el uso de reactivos altamente peligrosos utilizando en su caso agua y alcoholes. Se demuestra la síntesis de materiales del tipo CZTSSe después de un proceso de selenización; las celdas solares resultantes muestran las posibilidades del material y del sistema.

Instead of a linear and smooth evolution, many physical system react to external stimuli in avalanche dynamics. When an out of equilibrium system governed by disorder is externally driven the evolution of internal variables is local and non-homogeneous. This process is a collective behaviour adiabatically quick known as avalanches. Avalanche dynamics are associated to the transformation of spatial domains in different scales: from microscopic, to large catastrophic events such as earthquakes or solar flares. Avalanche dynamics is also involved in interdisiplinar topics such as the return prices of stock markets, the signalling in neuron networks or the biological evolution. Many avalanche dynamics are characterised by scale invariance, trademark of criticality. The physics in a so-called critical point are the same in all observational scales. Some avalanche dynamics share empirical laws and can define Universality Classes, reducing the complexity of systems to simpler mathematical models. Scale invariance causes avalanche distributions to be power-laws, determined by critical exponents. It is difficult to predict the behaviour of critical avalanche dynamics. Maximum Likelihood techniques are the standard method to determine critical exponents. Whether by physical reasons or instrumental resolutions, scale invariance can only be found within a certain magnitude range. The Maximum Likelihood Exponent Maps (MLEM) is a methodology developed to determine both the critical exponent and the boundaries of the scale invariance regime. Hazard assessment related to avalanche dynamics rely on the event probabilities within temporal intervals. We adopted some analytical techniques to study the avalanches as events in a point process. The intensity of the point process can be defined by exogenous effects or the history of the process itself (endogenous effects). The distribution of waiting times had shown the existence of a new scale invariance in the case of earthquakes, the so called Unified Scaling Law (USL). We have found similar scaling behaviours in other experimental systems. We used the so-called Bi test to identify endogenous effects in a given point process. Such effects can sometimes be adjusted to the so-called Epidemic Type Aftershock Sequence (ETAS) model by the method of the Mean Aftershock Sequence (MAS). All these techniques have been used to analyse different systems exhibiting avalanche dynamics. The mechanical failure under uniaxial compression of heterogeneous materials is caused by a sequence of fractures and displacements that can be detected by Acoustic Emission techniques. We performed compression experiments over samples of porous materials while registering the Acoustic Emission. This work discusses the results obtained with a mesoporous silica glass (SiO_2), natural goethite (FeO(OH)) ore and artificially sintered alumina (Al2O3). Scale invariance and endogenous effects were identified in such samples. Furthermore, the silica glass rendered strong analogies with the statistical laws of earthquakes. Martensitic transformations are a sort of structural phase transitions found in several materials sometimes referred as Shape Memory Alloys. Such transformations take place in an avalanche process close to criticality that can be detected by high sensitivity calorimetry, acoustic emission or magnetic (Barkhausen) noise in the case of magneto-structural transitions. Our statistical analysis rendered scale invariance and endogenous effects. Finally, the same methodology was applied to the numerical results of metastable loops in the Random Field Ising Model (RFIM). A classification method of spanning avalanches was verified by means of MLEM. The RFIM doesn't manifest endogenous production of avalanches. Hence, criticality in avalanche dynamics may not be a sufficient condition to find this phenomenology. / En comptes de mostrar una evolució lineal i suau, molts sistemes físics reaccionen als estímuls externs en forma de dinàmica d'allaus. Al conduir externament un sistema dominat pel desordre fora de l'equilibri, l'evolució de les variables internes es produeix de forma local i no homogènia en processos col·lectius i instantanis que anomenem allaus. Les dinàmiques d'allaus presenten sovint invariància d'escala associada a un fenomen de criticalitat. Les distribucions d'allaus crítiques són del tipus lleis de potència i estan determinades per exponents crítics, avaluats amb tècniques de Màxima Versemblança. Per poder determinar els extrems de la invariància d'escala, hem desenvolupat els anomenats Mapes d'Exponent per Màxima Versemblança. L'estudi de les allaus com a esdeveniments en 'point processes' i l'avaluació d'efectes exògens i endògens és fonamental per entendre les dinàmiques d'allaus i estimar riscos. Hem corroborat la Llei d'Escala Unificada de temps d'espera en sistemes experimentals. El test de Bi ens permet determinar si un 'point process' conté efectes endògens i els podem ajustar un model de rèpliques si hi identifiquem certs patrons a través del mètode de la Seqüència de Repliques Mitjana. Amb l'ajut d'aquestes tècniques hem analitzat les propietats de les allaus generades en: - L'emissió acústica en processos de fallida mecànica sota compressió uniaxial de diversos materials porosos: vidre porós Vycor® (SiO2); mineral de goethita (FeO(OH)) i alúmina sinteritzada artificialment (Al2O3). - Les senyals calorimètriques l'emissió acústica i el soroll Barkhausen associat a les transformacions martensítiques de diferents aliatges (FePd, CuZnAl i NiMnGa). - El creixement de dominis en les simulacions numèriques de dinàmica metastable en el Random Field Ising Model (RFIM). Tots els processos experimentals exhibeixen estadístiques d'invariància d'escala en un cert rang de magnituds, i presenten, sovint, producció endògena d'allaus. En el cas de la compressió del Vycor®, la similitud amb les lleis estadístiques dels terratrèmols és notable. Els estudis sobre el RFIM han permès verificar un sistema de classificació d'allaus. No hem observat que el model sigui capaç de generar producció endògena d'allaus, posant en dubte que la criticalitat sigui condició suficient per trobar aquesta fenomenologia.

Introduction: The present thesis is devoted to the study of semiconductor lasers subject to delayed optical feedback and coupling. The complex spectral and dynamical properties of these systems have been investigated using state-of-the-art telecommunications detection technologies. With such tools, we have been able to experimentally characterize previously unknown features in our delay-coupled systems. Along this work, both fundamental and applied results are presented for the different experiments investigated. Results: The first part of the thesis is focusing on the system of the single delayed feedback laser. The problem of feedback characterization is approached from a time scale perspective, relating the dynamical regimes to the characteristic frequencies of the delayed feedback laser. We have empirically found that the ratios of these characteristic frequencies completely determine the dynamical behavior. This constitutes a model independent approach that can be used, for example, to test the validity of numerical models that aim at explaining the dynamical behavior of these lasers. Furthermore, the general extent of our approach is validated by measuring various laser diodes with distinct characteristics. Specific properties of the dynamics of the single laser with feedback system have also been characterized by means of the intensity autocorrelation function. For this purpose, the experimental autocorrelation is compared with the autocorrelation obtained from a model of a stochastic linear oscillator with delay. The relation between the model parameters and the experimental system parameters is analyzed and discussed together with the limits of validity of this approach. In the second part, systems with two delay-coupled lasers are studied. The phenomenon of chaos synchronization is explored in two different configurations: a unidirectional coupling configuration where the delayed feedback laser signal is optically coupled to a second laser, and a bidirectional scheme of two mutually coupled lasers with self-feedback. In the first configuration, the relation between the consistency of the dynamics and the synchronizability with the second laser is studied. In the latter scheme, the robustness of the synchronized state is characterized against detuning in parameters and noise. The knowledge gained in the synchronization experiments is used to implement a classical public-channel secure-key exchange protocol in the bidirectional coupling scheme. This protocol is demonstrated experimentally, and its advantages and weaknesses are analyzed. Finally, we present a practical photonic implementation of a dynamical system experiencing two different delay times depending on the state of the system. The stationary spectral characteristics of this experimental system are studied and the conditions for the dynamics to occur in separated states are highlighted. We have also investigated the real-time intensity and optical spectrum dynamics to demonstrate the existence and properties of state-dependent delay dynamics. Qualitatively similar properties can be found from a proper numerical model of this system. Conclusions: Altogether, we have presented fundamental and applied aspects of semiconductor lasers optically coupled with delay. The presented phenomenology is of immediate potential use for a variety of applications that range from photonics-based reservoir computing to chaos communications. In addition, the presented fundamental insights can potentially be extended to other classes of dynamical systems. Contents: Resum (iv) Abstract (vi) List of Publications (vii) 1 Introduction (1) 1.1 Motivation (1) 1.2 Semiconductor Laser Devices (2) 1.3 Nonlinear Dynamics of Semiconductor Lasers (5) 1.3.1 Delayed Optical Feedback Effects on the Emission of Semiconductor Lasers (6) 1.4 Chaos Synchronization in Optically-Coupled Semiconductor Lasers (11) 1.5 Outline of this Thesis (14) 2 Semiconductor Lasers Subject to Delayed Optical Feedback: Similarity Properties in the Dynamics (17) 2.1 Introduction (17) 2.1.1 Strong and Weak Chaos Regimes (18) 2.1.2 Chapter Outline (18) 2.1.3 Contributions to the Work in the Present Chapter (19) 2.2 Experimental Methods (19) 2.2.1 Semiconductor Lasers (19) 2.2.2 Feedback Experiments in Fiber-Based Setups (20) 2.2.3 Acquisition Conditions (21) 2.3 Characteristic Frequencies of Delayed Feedback Lasers (21) 2.3.1 Autocorrelation Function of the Intensity Dynamics (24) 2.4 Invariant Dynamics Signature (25) 2.4.1 Physical Mechanism for Weak and Strong Chaos (27) 2.5 Full Rescaling of the Dynamics (30) 2.6 Dynamical Regimes (32) 2.6.1 Low Feedback Strengths (32) 2.6.2 Intermediate Feedback Strengths (34) 2.6.3 High Feedback Strengths (34) 2.7 Comparison with Numerical Modelling (35) 2.8 Similarity Properties in Quantum Dot Lasers (38) 2.8.1 Brief Introduction to Quantum Dot Lasers Particularities (38) 2.8.2 Invariant Dynamics Signature in Quantum-Dot Lasers (40) 2.9 Discussion and Summary (42) 3 Properties of the Autocorrelation Function of a Laser with Feedback (45) 3.1 Introduction (45) 3.1.1 Chapter Outline (46) 3.1.2 Contributions to the Work in the Present Chapter (46) 3.2 Experimental Methods (46) 3.2.1 Experimental Technique to Determine the Delay Time (47) 3.3 Autocorrelation Function of a Linear Stochastic Delay Model (47) 3.4 Comparison of the Autocorrelation Functions of the Laser and the Linear Model (51) 3.5 Limits of Validity of the Linear Approximation (53) 3.6 Parameters Extraction from the Fit of the Autocorrelation Function (56) 3.6.1 Time Delay Extraction (58) 3.7 Summary and Discussion (59) 4 Chaos Synchronization in Delay-Coupled Semiconductor Lasers (61) 4.1 Introduction (61) 4.1.1 Chapter Outline (63) 4.1.2 Contributions to the Work in the Present Chapter (63) 4.2 Experimental Methods (64) 4.2.1 Experimental Setups for Synchronization Experiments (64) 4.2.2 Cross-Correlation Analysis (66) 4.3 Correlations and Synchronization of Unidirectionally Coupled Lasers in Open-Loop Configuration (66) 4.4 Synchronization of Two Mutually-Coupled Semiconductor Lasers with a Passive Relay (73) 4.4.1 Influence of Spectral Detuning (76) 4.4.2 Isochronous Synchronization Regime (78) 4.4.3 Noise-Induced Desynchronization Events: Bubbling (79) 4.5 Summary and Discussion (86) 5 Bidirectional Secure Key Exchange using Chaotic Semiconductor Lasers (89) 5.1 Introduction (89) 5.1.1 Chapter Outline (93) 5.1.2 Contributions to the Work in the Present Chapter (93) 5.2 Experimental Methods (94) 5.3 Encrypted-Key Distribution Scheme (95) 5.3.1 Simultaneous Bidirectional Key Exchange Protocol (96) 5.3.2 Particularities of the Experimental Setup (96) 5.3.3 Proof of Concept (99) 5.4 Security Analysis of Our Scheme (102) 5.5 Discussion and Summary (106) 6 State-Dependent Delay Dynamics in Semiconductor Lasers (109) 6.1 Introduction (109) 6.1.1 Chapter Outline (111) 6.1.2 Contributions to the Work in the Present Chapter (111) 6.2 Experimental Methods (111) 6.3 Experimental Results (114) 6.4 Numerical Modeling (124) 6.5 Switching Characteristics (127) 6.6 Summary and Discussion (129) 7 Concluding Remarks (131) A Appendix A (137) A.1 Laser Sources (137) A.2 Feedback Experiments in Fiber-Based Setups (140) A.3 Signal Detection (141) A.4 List of Instruments and Components (142) Abbreviations (145) Bibliography (147)

Aquesta tesi està centrada en l'estudi dels Keplerats, una família de polioxometalats amb simetria icosaèdrica. Els polioxometalats són clústers inorgànics aniònics formats per uniats MOn, on M és un metall de transició normalment en el seu estat d'oxidació més elevat. (Mo(VI), W(VI), V(V)...). Per una banda, l'estructura electrònica dels Keplerats s'ha estudiat des d'un punt de vista de la Teoría del Funcional de la Densitat (DFT). A més, s'ha analitzat la interacció entre la càpsula Mo132 i els seus corresponents lligands interns. Per altra banda, amb col·laboració amb altres grups, tant experimentals com teòrics, es proposa un mecanisme de formació de la càpsula Mo132 a partir de dades obtingudes mitjançant espectroscòpia Raman. Part d'aquesta informació obtinguda mitjançant DFT s'ha utilitzat per obtenir els paràmetres necessaris per portar a terme una sèrie de simulacions de Dinàmica Molecular amb la finalitat d'estudiar el comportament del macro-ió Mo132 en solució aquosa en presència de diferents cations (centrant-se en la importància de la hidrofobicitat del catió), així com els efectes de la temperatura en aquest comportament. / Esta Tesis está centrada en el estudio de Kepleratos, una familia de polioxometalatos con simetría icosaédrica. Los polioxometalatos son clusters inorgánicos anionicos compuestos por unidades MOn, donde M es un metal de transición normalmente en su estado de oxidación más alto (Mo(VI), W(VI), V(V)...). Por un lado, la estructura electrónica de los Kepleratos se ha estudiado desde un punto de vista de la Teoría del Funcional Densidad (DFT). Además, se ha analizado la interacción entre la cápsula Mo132 y sus correspondientes ligandos internos. Por otro lado, en colaboración con otros grupos, tanto experimental como teórico, se propone un mecanismo de formación de la cápsula Mo132 a partir de los datos obtenidos mediante espectroscopía Raman. Parte de la información obtenida mediante DFT se ha utilizado para obtener los parámetros necesarios para realizar una serie de simulaciones de Dinámica Molecular con el fin de estudiar el comportamiento del macro-ión Mo132 en solución acuosa en presencia de diferentes cationes (centrándose en la importancia de la hidrofobicidad del catión), así como los efectos de la temperatura en dicho comportamiento. / This Thesis is aimed at the study of a family of icosahedral symmetry polyoxometalates: the so-called Keplerates. Polyoxometalates are inorganic anionic clustters composed of MOn units, where M represents a transition metal atom usually at its highest state of oxidation Mo(VI), W(VI), V(V)...). On one hand, the electronic structure of Keplerates is studied from a Density Functional Theorey (DFT) point of view. Furthermore, the interaction between the Mo132 capsule and its inner ligands has been analyzed. On the other hand, in collaboration with both experimental and theoretical groups, a formation mechanism for the Mo132 capsule is proposed, based on Raman espectroscopy data. Part of the information achieved by DFT has been used to obtain the parameters required in order to perform Molcular Dynamics simulations regarding the behaviour of the Mo132 macro-ion in aqueous solution in the presence of different cations (focusing on the relevance of the hydrophobic character of teh cation), as well as the effects that temperature has on the system.

En base als reptes sorgits a conseqüència de l'escalat de la tecnologia, la present tesis desenvolupa i analitza un conjunt d'eines orientades a avaluar la sensibilitat a la propagació d'esdeveniments SET en circuits microelectrònics. S'han proposant varies mètriques de propagació de SETs considerant l'impacto dels emmascaraments lògic, elèctric i combinat lògic-elèctric. Aquestes mètriques proporcionen una via d'anàlisi per quantificar tant les regions més susceptibles a propagar SETs com les sortides més susceptibles de rebre'ls. S'ha desenvolupat un conjunt d'algorismes de cerca de camins sensibilitzables altament adaptables a múltiples aplicacions, un sistema lògic especific i diverses tècniques de simplificació de circuits. S'ha demostrat que el retard d'un camí donat depèn dels vectors de sensibilització aplicats a les portes que formen part del mateix, essent aquesta variació de retard comparable a la atribuïble a les variacions paramètriques del proces. / En base a los desafíos surgidos a consecuencia del escalado de la tecnología, la presente tesis desarrolla y analiza un conjunto de herramientas orientadas a evaluar la sensibilidad a la propagación de eventos SET en circuitos microelectrónicos. Se han propuesto varias métricas de propagación de SETs considerando el impacto de los enmascaramientos lógico, eléctrico y combinado lógico-eléctrico. Estas métricas proporcionan una vía de análisis para cuantificar tanto las regiones más susceptibles a propagar eventos SET como las salidas más susceptibles a recibirlos. Ha sido desarrollado un conjunto de algoritmos de búsqueda de caminos sensibilizables altamente adaptables a múltiples aplicaciones, un sistema lógico especifico y diversas técnicas de simplificación de circuitos. Se ha demostrado que el retardo de un camino dado depende de los vectores de sensibilización aplicados a las puertas que forman parte del mismo, siendo esta variación de retardo comparable a la atribuible a las variaciones paramétricas del proceso. / Based on the challenges arising as a result of technology scaling, this thesis develops and evaluates a complete framework for SET propagation sensitivity. The framework comprises a number of processing tools capable of handling circuits with high complexity in an efficient way. Various SET propagation metrics have been proposed considering the impact of logic, electric and combined logic-electric masking. Such metrics provide a valuable vehicle to grade either in-circuit regions being more susceptible of propagating SETs toward the circuit outputs or circuit outputs more susceptible to produce SET. A quite efficient and customizable true path finding algorithm with a specific logic system has been constructed and its efficacy demonstrated on large benchmark circuits. It has been shown that the delay of a path depends on the sensitization vectors applied to the gates within the path. In some cases, this variation is comparable to the one caused by process parameters variations.

A recent sensitivity analysis done for the new generation of fast reactors [1] has shown the importance of improved cross section data for several actinides. Among them, the neutron-induced fission cross section of 240,242Pu requires a level of accuracy of 1-3% and 3-5%, respectively, from the current status of 6% and 20%. Moreover, nearly all the measurements in the literature have been done relative to 235U(n,f). Therefore, using other references samples such as 237Np or 238U will provide the scientific community with more valuable data. The work was carried out at the Institute for Reference Materials and Measurements (JRC-IRMM). The Van de Graaff accelerator was used for producing a quasi-monoenergetic neutron flux in the energy range of 0.3MeV to 3MeV. Protons were accelerated thanks to a potential difference. A neutron producing target was placed at the end of the beam line: 7Li(p,n)7Be or T(p,n)3He. Then, a twin Frisch-grid ionization chamber (TFGIC) was used as detector. The setup of the detector consists in a common cathode, two anodes and two grids. In the cathode the sample under study and the reference sample are placed in a back-to-back configuration. Each electrode is connected to a preamplifier, and then to a 100MHz 12 bit waveform digitizer. All raw signals are stored for an offline analysis using C++ under the ROOT framework. All the samples used were produced by the target preparation group at JRC-IRMM. The enrichment of the plutonium samples was of 99.89% for 240Pu and of 99.97% for 242Pu. The plutonium masses were chosen to minimize their alpha activity (0.8MBq for 240Pu and 0.1MBq for 242Pu). Three different reference fission cross sections were employed: 235U(n,f), 238U(n,f) and 237Np(n,f). The mass of all the reference samples used was remeasured by means of low geometry alpha counting or/and by a single grid ionization chamber. The mass uncertainty of each sample was lower than 2%. Results were obtained not only for the neutron-induced fission cross section of 240,242Pu in the region from 0.3 MeV up to 3 MeV, but for the 238U(n,f) cross section and the 237Np(n,f) cross section. The neutron flux from the Van de Graaff was characterized by means of MCNP simulations. A clear influence of the different structures between the neutron producing targets and the deposits was found, specially when the ratios measured involved a fissile sample and a threshold sample. The spontaneous fission of 240,242Pu is, as well, an important correction. Thus, this property was measured independently in this work, reaching an uncertainty lower than 1.3% for both isotopes. More corrections were due to the high electronic threshold needed to not trigger on alpha particles, the fission fragment loss due to the sample thickness, neutron emission anisotropy, etc. On average the results of the 240,242Pu(n,f) cross section are in agreement with previous experimental data, even though the trend is slightly lower than present evaluations. In the case of 242Pu(n,f) cross section the resonance-peak structure at 1.1 MeV could not be reproduced in any case. The results of the 237Np(n,f) cross section show an increase at the plateau region with respect to the ENDF/B-VII.1 evaluation in the same way as the data from Paradela (2010) [2]. The results for the 238U(n,f) cross section show a higher cross section than the ENDF evaluation but in agreement with the present JEFF 3.2 evaluation. [1] Uncertainty and target accuracy assessment for innovative systems using recent covariance data evaluations, Volume 26, 2008, OECD-NEA [2] Paradela, C. et al., Neutron-induced fission cross section of U-234 and Np-237 measured at the CERN Neutron Time-of-Flight (n_TOF) facility.,Physical Review C. 82, 3, 034601 (2010) / Un anàlisi de sensitivitat [1] recent per la nova generació de reactors ràpids va mostrar la importància de millorar les seccions eficaç de varis actínids. Entre ells, la secció eficaç de fissió per neutró induït del 240,242Pu requereix una millora en la seva precisió des d'un 6% a un 1-3% pel 240Pu i des d'un 20% a un 3-5% pel 242Pu. A més, quasi bé totes les dades experimentals disponibles a la literatura han estat determinades relatives a la secció eficaç del 235U(n,f). Per tant, la utilització d'altres isòtops com a referències, tal com el 237Np(n,f) o el 238U(n,f), proveirà a la comunitat científica amb dades valuoses. Aquest treball ha estat realitzat a l'Institute for Reference Materials and Measurements (JRC-IRMM). L'accelerador Van de Graaff disponible al JRC-IRMM s'ha emprat per produir un flux de neutrons quasi mono-energètics en el rang de 0.3 MeV a 3 MeV. Els protons van ser accelerats de fer-los impactar amb una mostra de producció de neutrons: 7Li(p,n)7Be o T(p,n)3He. A continuació, una doble cambra d'ionització amb grid (TFGIC) es va emplaçar com a detector consistent en un càtode, dos ànodes i dos grids. En el càtode es situen la mostra a estudiar i la mostra de referència. Cada un dels elèctrodes és connectat a un preamplificador i, a continuació, a un digitilitzador amb una freqüència de 100 MHz i 12 bit. Les senyals originals són emmagatzemades sense cap tractament previ per a un posterior anàlisi. El tractament de dades es va realitzar mitjançant el codi de programació C++ sota el marc de ROOT. Totes les mostres emprades en aquest experiment s'han produït al grup de preparació de mostres del JRC-IRMM. L'enriquiment de les mostres de plutoni era de 99.89% pel 240Pu (0.8MBq) i del 99.97% pel 242Pu (0.1MBq). La massa de les tres mostres de referència (235U(n,f), 238U(n,f) i 237Np(n,f)) també va ser mesurada. La incertesa de cada massa és inferior al 2%. La principal correcció aplicaca als resultats obtinguts ha estat per la caracterització del flux de neutrons mitjançant el codi de simulació Monte Carlo MCNP. Els resultats de les simulacions han mostrat una clara influència de les diferents estructures emplaçades entre la mostra de producció de neutrons i les mostres de fissió. Altres correccions s¿han realitzat per la fissió espontània del 240,242Pu (mesurada independentment en aquest treball amb una incertesa inferior al 1,3%), la deficiència d'esdeveniments a causa del llindar de detecció, l'eficiència del detector, l'anisotropia en l'emissió dels neutrons, etc. Tot i que el principal objectiu va ser l'obtenció de la secció eficaç de fissió per neutró induït del 240,242Pu en la regió de 0.3 MeV a 3 MeV, resultats addicionals han estat obtinguts per la secció eficaç del 238U(n,f) i el 237Np(n,f). Els resultats obtinguts mostren un acord significatiu entre la secció eficaç del 240,242Pu(n,f) i resultats experimentals anteriors, tot i que la tendència és lleugerament inferior a les avaluacions (ENDF/B-VII.1, JEFF 3.1 i JENDL 4.0) disponibles. En el cas de la secció eficaç del 242Pu(n,f), a més, el pic de ressonància al voltant de 1.1 MeV predit per quasi totes les dades experimentals anteriors i les avaluacions actuals no s'ha reproduït en aquest experiment. Els resultats de la secció eficaç del 237Np(n,f) presenten un increment en la regió plana després del llindar de fissió d'un 5-7% respecte l'avaluació ENDF/B-VII.1, i en concordança amb els resultats obtinguts per Paradela (2010) [2]. Finalment, els resultats de la secció eficaç del 238U(n,f) mostren un increment al voltant d'un 7-9% a la zona plana després del llindar de fissió, aquesta predicció concorda amb l'avaluació JEFF 3.2. [1] Uncertainty and target accuracy assessment for innovative systems using recent covariance data evaluations, Volume 26, 2008, OECD-NEA [2] Paradela, C. et al., Neutron-induced fission cross section of U-234 and Np-237 measured at the CERN Neutron Time-of-Flight (n_TOF) facility.,Physical Review C. 82, 3, 034601 (2010)